Bump version to 0.6.4 (#13253 )

[red-knot] fix lookup of nonlocal names in deferred annotations (#13236 )
Initially I had deferred annotation name lookups reuse the "public symbol type", since that gives the correct "from end of scope" view of reaching definitions that we want. But there is a key difference; public symbol types are based only on definitions in the queried scope (or "name in the given namespace" in runtime terms), they don't ever look up a name in nonlocal/global/builtin scopes. Deferred annotation resolution should do this lookup. Add a test, and fix deferred name resolution to support nonlocal/global/builtin names. Fixes #13176
2024-09-05 21:05:15 +05:30 · 2024-09-04 10:10:54 -07:00 · 2024-09-04 14:24:58 +00:00 · 2024-09-04 14:19:11 +00:00 · 2024-09-04 10:19:50 +00:00 · 2024-09-04 09:35:58 +00:00
566 changed files with 22312 additions and 7994 deletions
--- a/.devcontainer/devcontainer.json
+++ b/.devcontainer/devcontainer.json
@@ -20,7 +20,7 @@
 			"extensions": [
 				"ms-python.python",
 				"rust-lang.rust-analyzer",
-				"serayuzgur.crates",
+				"fill-labs.dependi",
 				"tamasfe.even-better-toml",
 				"Swellaby.vscode-rust-test-adapter",
 				"charliermarsh.ruff"
--- a/.github/renovate.json5
+++ b/.github/renovate.json5
@@ -14,12 +14,26 @@
    rangeStrategy: "update-lockfile",
  },
  pep621: {
+    // The default for this package manager is to only search for `pyproject.toml` files
+    // found at the repository root: https://docs.renovatebot.com/modules/manager/pep621/#file-matching
    fileMatch: ["^(python|scripts)/.*pyproject\\.toml$"],
  },
  pip_requirements: {
-    fileMatch: ["^docs/requirements.*\\.txt$"],
+    // The default for this package manager is to run on all requirements.txt files:
+    // https://docs.renovatebot.com/modules/manager/pip_requirements/#file-matching
+    // `fileMatch` doesn't work for excluding files; to exclude `requirements.txt` files
+    // outside the `doc/` directory, we instead have to use `ignorePaths`. Unlike `fileMatch`,
+    // which takes a regex string, `ignorePaths` takes a glob string, so we have to use
+    // a "negative glob pattern".
+    // See:
+    // - https://docs.renovatebot.com/modules/manager/#ignoring-files-that-match-the-default-filematch
+    // - https://docs.renovatebot.com/configuration-options/#ignorepaths
+    // - https://docs.renovatebot.com/string-pattern-matching/#negative-matching
+    ignorePaths: ["!docs/requirements*.txt"]
  },
  npm: {
+    // The default for this package manager is to only search for `package.json` files
+    // found at the repository root: https://docs.renovatebot.com/modules/manager/npm/#file-matching
    fileMatch: ["^playground/.*package\\.json$"],
  },
  "pre-commit": {
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -37,7 +37,7 @@ jobs:
        with:
          fetch-depth: 0

-      - uses: tj-actions/changed-files@v44
+      - uses: tj-actions/changed-files@v45
        id: changed
        with:
          files_yaml: |
@@ -142,6 +142,13 @@ jobs:

      # Check for broken links in the documentation.
      - run: cargo doc --all --no-deps
+        env:
+          RUSTDOCFLAGS: "-D warnings"
+      # Use --document-private-items so that all our doc comments are kept in
+      # sync, not just public items. Eventually we should do this for all
+      # crates; for now add crates here as they are warning-clean to prevent
+      # regression.
+      - run: cargo doc --no-deps -p red_knot_python_semantic -p red_knot -p ruff_db --document-private-items
        env:
          # Setting RUSTDOCFLAGS because `cargo doc --check` isn't yet implemented (https://github.com/rust-lang/cargo/issues/10025).
          RUSTDOCFLAGS: "-D warnings"
--- a/.github/workflows/publish-docs.yml
+++ b/.github/workflows/publish-docs.yml
@@ -34,10 +34,10 @@ jobs:
      - name: "Set docs version"
        run: |
          version="${{ (inputs.plan != '' && fromJson(inputs.plan).announcement_tag) || inputs.ref }}"
-          # if version is missing, exit with error
-          if [[ -z "$version" ]]; then
-          echo "Can't build docs without a version."
-          exit 1
+          # if version is missing, use 'latest'
+          if [ -z "$version" ]; then
+            echo "Using 'latest' as version"
+            version="latest"
          fi

          # Use version as display name for now
@@ -145,6 +145,7 @@ jobs:
          GITHUB_TOKEN: ${{ secrets.ASTRAL_DOCS_PAT }}
        run: |
          branch_name="${{ env.branch_name }}"
+
          # auto-merge the PR if the build was triggered by a release. Manual builds should be reviewed by a human.
          # give the PR a few seconds to be created before trying to auto-merge it
          sleep 10
--- a/.markdownlint.yaml
+++ b/.markdownlint.yaml
@@ -14,6 +14,9 @@ MD041: false
 # MD013/line-length
 MD013: false

+# MD014/commands-show-output
+MD014: false
+
 # MD024/no-duplicate-heading
 MD024:
  # Allow when nested under different parents e.g. CHANGELOG.md
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -6,6 +6,8 @@ exclude: |
    crates/red_knot_workspace/resources/.*|
    crates/ruff_linter/resources/.*|
    crates/ruff_linter/src/rules/.*/snapshots/.*|
+    crates/ruff_notebook/resources/.*|
+    crates/ruff_server/resources/.*|
    crates/ruff/resources/.*|
    crates/ruff_python_formatter/resources/.*|
    crates/ruff_python_formatter/tests/snapshots/.*|
@@ -15,7 +17,7 @@ exclude: |

 repos:
  - repo: https://github.com/abravalheri/validate-pyproject
-    rev: v0.18
+    rev: v0.19
    hooks:
      - id: validate-pyproject

@@ -43,7 +45,7 @@ repos:
          )$

  - repo: https://github.com/crate-ci/typos
-    rev: v1.23.6
+    rev: v1.24.3
    hooks:
      - id: typos

@@ -57,7 +59,7 @@ repos:
        pass_filenames: false # This makes it a lot faster

  - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.5.6
+    rev: v0.6.3
    hooks:
      - id: ruff-format
      - id: ruff
--- a/BREAKING_CHANGES.md
+++ b/BREAKING_CHANGES.md
@@ -1,5 +1,43 @@
 # Breaking Changes

+## 0.6.0
+
+- Detect imports in `src` layouts by default for `isort` rules ([#12848](https://github.com/astral-sh/ruff/pull/12848))
+
+- The pytest rules `PT001` and `PT023` now default to omitting the decorator parentheses when there are no arguments ([#12838](https://github.com/astral-sh/ruff/pull/12838)).
+
+- Lint and format Jupyter Notebook by default ([#12878](https://github.com/astral-sh/ruff/pull/12878)).
+
+    You can disable specific rules for notebooks using [`per-file-ignores`](https://docs.astral.sh/ruff/settings/#lint_per-file-ignores):
+
+    ```toml
+    [tool.ruff.lint.per-file-ignores]
+    "*.ipynb" = ["E501"] # disable line-too-long in notebooks
+    ```
+
+    If you'd prefer to either only lint or only format Jupyter Notebook files, you can use the
+    section-specific `exclude` option to do so. For example, the following would only lint Jupyter
+    Notebook files and not format them:
+
+    ```toml
+    [tool.ruff.format]
+    exclude = ["*.ipynb"]
+    ```
+
+    And, conversely, the following would only format Jupyter Notebook files and not lint them:
+
+    ```toml
+    [tool.ruff.lint]
+    exclude = ["*.ipynb"]
+    ```
+
+    You can completely disable Jupyter Notebook support by updating the [`extend-exclude`](https://docs.astral.sh/ruff/settings/#extend-exclude) setting:
+
+    ```toml
+    [tool.ruff]
+    extend-exclude = ["*.ipynb"]
+    ```
+
 ## 0.5.0

 - Follow the XDG specification to discover user-level configurations on macOS (same as on other Unix platforms)
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,205 @@
 # Changelog

+## 0.6.4
+
+### Preview features
+
+- \[`flake8-builtins`\] Use dynamic builtins list based on Python version ([#13172](https://github.com/astral-sh/ruff/pull/13172))
+- \[`pydoclint`\] Permit yielding `None` in `DOC402` and `DOC403` ([#13148](https://github.com/astral-sh/ruff/pull/13148))
+- \[`pylint`\] Update diagnostic message for `PLW3201` ([#13194](https://github.com/astral-sh/ruff/pull/13194))
+- \[`ruff`\] Implement `post-init-default` (`RUF033`) ([#13192](https://github.com/astral-sh/ruff/pull/13192))
+- \[`ruff`\] Implement useless if-else (`RUF034`) ([#13218](https://github.com/astral-sh/ruff/pull/13218))
+
+### Rule changes
+
+- \[`flake8-pyi`\] Respect `pep8_naming.classmethod-decorators` settings when determining if a method is a classmethod in `custom-type-var-return-type` (`PYI019`) ([#13162](https://github.com/astral-sh/ruff/pull/13162))
+- \[`flake8-pyi`\] Teach various rules that annotations might be stringized ([#12951](https://github.com/astral-sh/ruff/pull/12951))
+- \[`pylint`\] Avoid `no-self-use` for `attrs`-style validators ([#13166](https://github.com/astral-sh/ruff/pull/13166))
+- \[`pylint`\] Recurse into subscript subexpressions when searching for list/dict lookups (`PLR1733`, `PLR1736`) ([#13186](https://github.com/astral-sh/ruff/pull/13186))
+- \[`pyupgrade`\] Detect `aiofiles.open` calls in `UP015` ([#13173](https://github.com/astral-sh/ruff/pull/13173))
+- \[`pyupgrade`\] Mark `sys.version_info[0] < 3` and similar comparisons as outdated (`UP036`) ([#13175](https://github.com/astral-sh/ruff/pull/13175))
+
+### CLI
+
+- Enrich messages of SARIF results ([#13180](https://github.com/astral-sh/ruff/pull/13180))
+- Handle singular case for incompatible rules warning in `ruff format` output ([#13212](https://github.com/astral-sh/ruff/pull/13212))
+
+### Bug fixes
+
+- \[`pydocstyle`\] Improve heuristics for detecting Google-style docstrings ([#13142](https://github.com/astral-sh/ruff/pull/13142))
+- \[`refurb`\] Treat `sep` arguments with effects as unsafe removals (`FURB105`) ([#13165](https://github.com/astral-sh/ruff/pull/13165))
+
+## 0.6.3
+
+### Preview features
+
+- \[`flake8-simplify`\] Extend `open-file-with-context-handler` to work with `dbm.sqlite3` (`SIM115`) ([#13104](https://github.com/astral-sh/ruff/pull/13104))
+- \[`pycodestyle`\] Disable `E741` in stub files (`.pyi`) ([#13119](https://github.com/astral-sh/ruff/pull/13119))
+- \[`pydoclint`\] Avoid `DOC201` on explicit returns in functions that only return `None` ([#13064](https://github.com/astral-sh/ruff/pull/13064))
+
+### Rule changes
+
+- \[`flake8-async`\] Disable check for `asyncio` before Python 3.11 (`ASYNC109`) ([#13023](https://github.com/astral-sh/ruff/pull/13023))
+
+### Bug fixes
+
+- \[`FastAPI`\] Avoid introducing invalid syntax in fix for `fast-api-non-annotated-dependency` (`FAST002`) ([#13133](https://github.com/astral-sh/ruff/pull/13133))
+- \[`flake8-implicit-str-concat`\] Normalize octals before merging concatenated strings in `single-line-implicit-string-concatenation` (`ISC001`) ([#13118](https://github.com/astral-sh/ruff/pull/13118))
+- \[`flake8-pytest-style`\] Improve help message for `pytest-incorrect-mark-parentheses-style` (`PT023`) ([#13092](https://github.com/astral-sh/ruff/pull/13092))
+- \[`pylint`\] Avoid autofix for calls that aren't `min` or `max` as starred expression (`PLW3301`) ([#13089](https://github.com/astral-sh/ruff/pull/13089))
+- \[`ruff`\] Add `datetime.time`, `datetime.tzinfo`, and `datetime.timezone` as immutable function calls (`RUF009`) ([#13109](https://github.com/astral-sh/ruff/pull/13109))
+- \[`ruff`\] Extend comment deletion for `RUF100` to include trailing text from `noqa` directives while preserving any following comments on the same line, if any ([#13105](https://github.com/astral-sh/ruff/pull/13105))
+- Fix dark theme on initial page load for the Ruff playground ([#13077](https://github.com/astral-sh/ruff/pull/13077))
+
+## 0.6.2
+
+### Preview features
+
+- \[`flake8-simplify`\] Extend `open-file-with-context-handler` to work with other standard-library IO modules (`SIM115`) ([#12959](https://github.com/astral-sh/ruff/pull/12959))
+- \[`ruff`\] Avoid `unused-async` for functions with FastAPI route decorator (`RUF029`) ([#12938](https://github.com/astral-sh/ruff/pull/12938))
+- \[`ruff`\] Ignore `fstring-missing-syntax` (`RUF027`) for `fastAPI` paths ([#12939](https://github.com/astral-sh/ruff/pull/12939))
+- \[`ruff`\] Implement check for Decimal called with a float literal (RUF032) ([#12909](https://github.com/astral-sh/ruff/pull/12909))
+
+### Rule changes
+
+- \[`flake8-bugbear`\] Update diagnostic message when expression is at the end of function (`B015`) ([#12944](https://github.com/astral-sh/ruff/pull/12944))
+- \[`flake8-pyi`\] Skip type annotations in `string-or-bytes-too-long` (`PYI053`) ([#13002](https://github.com/astral-sh/ruff/pull/13002))
+- \[`flake8-type-checking`\] Always recognise relative imports as first-party ([#12994](https://github.com/astral-sh/ruff/pull/12994))
+- \[`flake8-unused-arguments`\] Ignore unused arguments on stub functions (`ARG001`) ([#12966](https://github.com/astral-sh/ruff/pull/12966))
+- \[`pylint`\] Ignore augmented assignment for `self-cls-assignment` (`PLW0642`) ([#12957](https://github.com/astral-sh/ruff/pull/12957))
+
+### Server
+
+- Show full context in error log messages ([#13029](https://github.com/astral-sh/ruff/pull/13029))
+
+### Bug fixes
+
+- \[`pep8-naming`\] Don't flag `from` imports following conventional import names (`N817`) ([#12946](https://github.com/astral-sh/ruff/pull/12946))
+- \[`pylint`\] - Allow `__new__` methods to have `cls` as their first argument even if decorated with `@staticmethod` for `bad-staticmethod-argument` (`PLW0211`) ([#12958](https://github.com/astral-sh/ruff/pull/12958))
+
+### Documentation
+
+- Add `hyperfine` installation instructions; update `hyperfine` code samples ([#13034](https://github.com/astral-sh/ruff/pull/13034))
+- Expand note to use Ruff with other language server in Kate ([#12806](https://github.com/astral-sh/ruff/pull/12806))
+- Update example for `PT001` as per the new default behavior ([#13019](https://github.com/astral-sh/ruff/pull/13019))
+- \[`perflint`\] Improve docs for `try-except-in-loop` (`PERF203`) ([#12947](https://github.com/astral-sh/ruff/pull/12947))
+- \[`pydocstyle`\] Add reference to `lint.pydocstyle.ignore-decorators` setting to rule docs ([#12996](https://github.com/astral-sh/ruff/pull/12996))
+
+## 0.6.1
+
+This is a hotfix release to address an issue with `ruff-pre-commit`. In v0.6,
+Ruff changed its behavior to lint and format Jupyter notebooks by default;
+however, due to an oversight, these files were still excluded by default if
+Ruff was run via pre-commit, leading to inconsistent behavior.
+This has [now been fixed](https://github.com/astral-sh/ruff-pre-commit/pull/96).
+
+### Preview features
+
+- \[`fastapi`\] Implement `fast-api-unused-path-parameter` (`FAST003`) ([#12638](https://github.com/astral-sh/ruff/pull/12638))
+
+### Rule changes
+
+- \[`pylint`\] Rename `too-many-positional` to `too-many-positional-arguments` (`R0917`) ([#12905](https://github.com/astral-sh/ruff/pull/12905))
+
+### Server
+
+- Fix crash when applying "fix-all" code-action to notebook cells ([#12929](https://github.com/astral-sh/ruff/pull/12929))
+
+### Other changes
+
+- \[`flake8-naming`\]: Respect import conventions (`N817`) ([#12922](https://github.com/astral-sh/ruff/pull/12922))
+
+## 0.6.0
+
+Check out the [blog post](https://astral.sh/blog/ruff-v0.6.0) for a migration guide and overview of the changes!
+
+### Breaking changes
+
+See also, the "Remapped rules" section which may result in disabled rules.
+
+- Lint and format Jupyter Notebook by default ([#12878](https://github.com/astral-sh/ruff/pull/12878)).
+- Detect imports in `src` layouts by default for `isort` rules ([#12848](https://github.com/astral-sh/ruff/pull/12848))
+- The pytest rules `PT001` and `PT023` now default to omitting the decorator parentheses when there are no arguments ([#12838](https://github.com/astral-sh/ruff/pull/12838)).
+
+### Deprecations
+
+The following rules are now deprecated:
+
+- [`pytest-missing-fixture-name-underscore`](https://docs.astral.sh/ruff/rules/pytest-missing-fixture-name-underscore/) (`PT004`)
+- [`pytest-incorrect-fixture-name-underscore`](https://docs.astral.sh/ruff/rules/pytest-incorrect-fixture-name-underscore/) (`PT005`)
+- [`unpacked-list-comprehension`](https://docs.astral.sh/ruff/rules/unpacked-list-comprehension/) (`UP027`)
+
+### Remapped rules
+
+The following rules have been remapped to new rule codes:
+
+- [`unnecessary-dict-comprehension-for-iterable`](https://docs.astral.sh/ruff/rules/unnecessary-dict-comprehension-for-iterable/): `RUF025` to `C420`
+
+### Stabilization
+
+The following rules have been stabilized and are no longer in preview:
+
+- [`singledispatch-method`](https://docs.astral.sh/ruff/rules/singledispatch-method/) (`PLE1519`)
+- [`singledispatchmethod-function`](https://docs.astral.sh/ruff/rules/singledispatchmethod-function/) (`PLE1520`)
+- [`bad-staticmethod-argument`](https://docs.astral.sh/ruff/rules/bad-staticmethod-argument/) (`PLW0211`)
+- [`if-stmt-min-max`](https://docs.astral.sh/ruff/rules/if-stmt-min-max/) (`PLR1730`)
+- [`invalid-bytes-return-type`](https://docs.astral.sh/ruff/rules/invalid-bytes-return-type/) (`PLE0308`)
+- [`invalid-hash-return-type`](https://docs.astral.sh/ruff/rules/invalid-hash-return-type/) (`PLE0309`)
+- [`invalid-index-return-type`](https://docs.astral.sh/ruff/rules/invalid-index-return-type/) (`PLE0305`)
+- [`invalid-length-return-type`](https://docs.astral.sh/ruff/rules/invalid-length-return-type/) (`PLEE303`)
+- [`self-or-cls-assignment`](https://docs.astral.sh/ruff/rules/self-or-cls-assignment/) (`PLW0642`)
+- [`byte-string-usage`](https://docs.astral.sh/ruff/rules/byte-string-usage/) (`PYI057`)
+- [`duplicate-literal-member`](https://docs.astral.sh/ruff/rules/duplicate-literal-member/) (`PYI062`)
+- [`redirected-noqa`](https://docs.astral.sh/ruff/rules/redirected-noqa/) (`RUF101`)
+
+The following behaviors have been stabilized:
+
+- [`cancel-scope-no-checkpoint`](https://docs.astral.sh/ruff/rules/cancel-scope-no-checkpoint/) (`ASYNC100`): Support `asyncio` and `anyio` context mangers.
+- [`async-function-with-timeout`](https://docs.astral.sh/ruff/rules/async-function-with-timeout/) (`ASYNC109`): Support `asyncio` and `anyio` context mangers.
+- [`async-busy-wait`](https://docs.astral.sh/ruff/rules/async-busy-wait/) (`ASYNC110`): Support `asyncio` and `anyio` context mangers.
+- [`async-zero-sleep`](https://docs.astral.sh/ruff/rules/async-zero-sleep/) (`ASYNC115`): Support `anyio` context mangers.
+- [`long-sleep-not-forever`](https://docs.astral.sh/ruff/rules/long-sleep-not-forever/) (`ASYNC116`): Support `anyio` context mangers.
+
+The following fixes have been stabilized:
+
+- [`superfluous-else-return`](https://docs.astral.sh/ruff/rules/superfluous-else-return/) (`RET505`)
+- [`superfluous-else-raise`](https://docs.astral.sh/ruff/rules/superfluous-else-raise/) (`RET506`)
+- [`superfluous-else-continue`](https://docs.astral.sh/ruff/rules/superfluous-else-continue/) (`RET507`)
+- [`superfluous-else-break`](https://docs.astral.sh/ruff/rules/superfluous-else-break/) (`RET508`)
+
+### Preview features
+
+- \[`flake8-simplify`\] Further simplify to binary in preview for (`SIM108`) ([#12796](https://github.com/astral-sh/ruff/pull/12796))
+- \[`pyupgrade`\] Show violations without auto-fix (`UP031`) ([#11229](https://github.com/astral-sh/ruff/pull/11229))
+
+### Rule changes
+
+- \[`flake8-import-conventions`\] Add `xml.etree.ElementTree` to default conventions ([#12455](https://github.com/astral-sh/ruff/pull/12455))
+- \[`flake8-pytest-style`\] Add a space after comma in CSV output (`PT006`) ([#12853](https://github.com/astral-sh/ruff/pull/12853))
+
+### Server
+
+- Show a message for incorrect settings ([#12781](https://github.com/astral-sh/ruff/pull/12781))
+
+### Bug fixes
+
+- \[`flake8-async`\] Do not lint yield in context manager (`ASYNC100`) ([#12896](https://github.com/astral-sh/ruff/pull/12896))
+- \[`flake8-comprehensions`\] Do not lint `async for` comprehensions (`C419`) ([#12895](https://github.com/astral-sh/ruff/pull/12895))
+- \[`flake8-return`\] Only add return `None` at end of a function (`RET503`) ([#11074](https://github.com/astral-sh/ruff/pull/11074))
+- \[`flake8-type-checking`\] Avoid treating `dataclasses.KW_ONLY` as typing-only (`TCH003`) ([#12863](https://github.com/astral-sh/ruff/pull/12863))
+- \[`pep8-naming`\] Treat `type(Protocol)` et al as metaclass base (`N805`) ([#12770](https://github.com/astral-sh/ruff/pull/12770))
+- \[`pydoclint`\] Don't enforce returns and yields in abstract methods (`DOC201`, `DOC202`) ([#12771](https://github.com/astral-sh/ruff/pull/12771))
+- \[`ruff`\] Skip tuples with slice expressions in (`RUF031`) ([#12768](https://github.com/astral-sh/ruff/pull/12768))
+- \[`ruff`\] Ignore unparenthesized tuples in subscripts when the subscript is a type annotation or type alias (`RUF031`) ([#12762](https://github.com/astral-sh/ruff/pull/12762))
+- \[`ruff`\] Ignore template strings passed to logging and `builtins._()` calls (`RUF027`) ([#12889](https://github.com/astral-sh/ruff/pull/12889))
+- \[`ruff`\] Do not remove parens for tuples with starred expressions in Python \<=3.10 (`RUF031`) ([#12784](https://github.com/astral-sh/ruff/pull/12784))
+- Evaluate default parameter values for a function in that function's enclosing scope ([#12852](https://github.com/astral-sh/ruff/pull/12852))
+
+### Other changes
+
+- Respect VS Code cell metadata when detecting the language of Jupyter Notebook cells ([#12864](https://github.com/astral-sh/ruff/pull/12864))
+- Respect `kernelspec` notebook metadata when detecting the preferred language for a Jupyter Notebook ([#12875](https://github.com/astral-sh/ruff/pull/12875))
+
 ## 0.5.7

 ### Preview features
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -2,35 +2,6 @@

 Welcome! We're happy to have you here. Thank you in advance for your contribution to Ruff.

- [The Basics](#the-basics)
-    - [Prerequisites](#prerequisites)
-    - [Development](#development)
-    - [Project Structure](#project-structure)
-    - [Example: Adding a new lint rule](#example-adding-a-new-lint-rule)
-        - [Rule naming convention](#rule-naming-convention)
-        - [Rule testing: fixtures and snapshots](#rule-testing-fixtures-and-snapshots)
-    - [Example: Adding a new configuration option](#example-adding-a-new-configuration-option)
- [MkDocs](#mkdocs)
- [Release Process](#release-process)
-    - [Creating a new release](#creating-a-new-release)
- [Ecosystem CI](#ecosystem-ci)
- [Benchmarking and Profiling](#benchmarking-and-profiling)
-    - [CPython Benchmark](#cpython-benchmark)
-    - [Microbenchmarks](#microbenchmarks)
-        - [Benchmark-driven Development](#benchmark-driven-development)
-        - [PR Summary](#pr-summary)
-        - [Tips](#tips)
-    - [Profiling Projects](#profiling-projects)
-        - [Linux](#linux)
-        - [Mac](#mac)
- [`cargo dev`](#cargo-dev)
- [Subsystems](#subsystems)
-    - [Compilation Pipeline](#compilation-pipeline)
-    - [Import Categorization](#import-categorization)
-        - [Project root](#project-root)
-        - [Package root](#package-root)
-        - [Import categorization](#import-categorization-1)
-
 ## The Basics

 Ruff welcomes contributions in the form of pull requests.
@@ -333,22 +304,34 @@ even patch releases may contain [non-backwards-compatible changes](https://semve
 ### Creating a new release

 1. Install `uv`: `curl -LsSf https://astral.sh/uv/install.sh | sh`
+
 1. Run `./scripts/release.sh`; this command will:
+
    - Generate a temporary virtual environment with `rooster`
    - Generate a changelog entry in `CHANGELOG.md`
    - Update versions in `pyproject.toml` and `Cargo.toml`
    - Update references to versions in the `README.md` and documentation
    - Display contributors for the release
+
 1. The changelog should then be editorialized for consistency
+
    - Often labels will be missing from pull requests they will need to be manually organized into the proper section
    - Changes should be edited to be user-facing descriptions, avoiding internal details
+
 1. Highlight any breaking changes in `BREAKING_CHANGES.md`
+
 1. Run `cargo check`. This should update the lock file with new versions.
+
 1. Create a pull request with the changelog and version updates
+
 1. Merge the PR
+
 1. Run the [release workflow](https://github.com/astral-sh/ruff/actions/workflows/release.yml) with:
+
    - The new version number (without starting `v`)
+
 1. The release workflow will do the following:
+
    1. Build all the assets. If this fails (even though we tested in step 4), we haven't tagged or
        uploaded anything, you can restart after pushing a fix. If you just need to rerun the build,
        make sure you're [re-running all the failed
@@ -359,14 +342,25 @@ even patch releases may contain [non-backwards-compatible changes](https://semve
    1. Attach artifacts to draft GitHub release
    1. Trigger downstream repositories. This can fail non-catastrophically, as we can run any
        downstream jobs manually if needed.
+
 1. Verify the GitHub release:
+
    1. The Changelog should match the content of `CHANGELOG.md`
-    1. Append the contributors from the `bump.sh` script
+    1. Append the contributors from the `scripts/release.sh` script
+
 1. If needed, [update the schemastore](https://github.com/astral-sh/ruff/blob/main/scripts/update_schemastore.py).
+
    1. One can determine if an update is needed when
        `git diff old-version-tag new-version-tag -- ruff.schema.json` returns a non-empty diff.
    1. Once run successfully, you should follow the link in the output to create a PR.
-1. If needed, update the `ruff-lsp` and `ruff-vscode` repositories.
+
+1. If needed, update the [`ruff-lsp`](https://github.com/astral-sh/ruff-lsp) and
+    [`ruff-vscode`](https://github.com/astral-sh/ruff-vscode) repositories and follow
+    the release instructions in those repositories. `ruff-lsp` should always be updated
+    before `ruff-vscode`.
+
+    This step is generally not required for a patch release, but should always be done
+    for a minor release.

 ## Ecosystem CI

@@ -389,7 +383,7 @@ We have several ways of benchmarking and profiling Ruff:
 - Microbenchmarks which run the linter or the formatter on individual files. These run on pull requests.
 - Profiling the linter on either the microbenchmarks or entire projects

-> \[!NOTE\]
+> **Note**
 > When running benchmarks, ensure that your CPU is otherwise idle (e.g., close any background
 > applications, like web browsers). You may also want to switch your CPU to a "performance"
 > mode, if it exists, especially when benchmarking short-lived processes.
@@ -403,12 +397,18 @@ which makes it a good target for benchmarking.
 git clone --branch 3.10 https://github.com/python/cpython.git crates/ruff_linter/resources/test/cpython
 ```

+Install `hyperfine`:
+
+```shell
+cargo install hyperfine
+```
+
 To benchmark the release build:

 ```shell
 cargo build --release && hyperfine --warmup 10 \
-  "./target/release/ruff ./crates/ruff_linter/resources/test/cpython/ --no-cache -e" \
-  "./target/release/ruff ./crates/ruff_linter/resources/test/cpython/ -e"
+  "./target/release/ruff check ./crates/ruff_linter/resources/test/cpython/ --no-cache -e" \
+  "./target/release/ruff check ./crates/ruff_linter/resources/test/cpython/ -e"

 Benchmark 1: ./target/release/ruff ./crates/ruff_linter/resources/test/cpython/ --no-cache
  Time (mean ± σ):     293.8 ms ±   3.2 ms    [User: 2384.6 ms, System: 90.3 ms]
@@ -427,7 +427,7 @@ To benchmark against the ecosystem's existing tools:

 ```shell
 hyperfine --ignore-failure --warmup 5 \
-  "./target/release/ruff ./crates/ruff_linter/resources/test/cpython/ --no-cache" \
+  "./target/release/ruff check ./crates/ruff_linter/resources/test/cpython/ --no-cache" \
  "pyflakes crates/ruff_linter/resources/test/cpython" \
  "autoflake --recursive --expand-star-imports --remove-all-unused-imports --remove-unused-variables --remove-duplicate-keys resources/test/cpython" \
  "pycodestyle crates/ruff_linter/resources/test/cpython" \
@@ -473,7 +473,7 @@ To benchmark a subset of rules, e.g. `LineTooLong` and `DocLineTooLong`:

 ```shell
 cargo build --release && hyperfine --warmup 10 \
-  "./target/release/ruff ./crates/ruff_linter/resources/test/cpython/ --no-cache -e --select W505,E501"
+  "./target/release/ruff check ./crates/ruff_linter/resources/test/cpython/ --no-cache -e --select W505,E501"
 ```

 You can run `poetry install` from `./scripts/benchmarks` to create a working environment for the
@@ -530,6 +530,8 @@ You can run the benchmarks with
 cargo benchmark
 ```

+`cargo benchmark` is an alias for `cargo bench -p ruff_benchmark --bench linter --bench formatter --`
+
 #### Benchmark-driven Development

 Ruff uses [Criterion.rs](https://bheisler.github.io/criterion.rs/book/) for benchmarks. You can use
@@ -568,7 +570,7 @@ cargo install critcmp

 #### Tips

- Use `cargo bench -p ruff_benchmark <filter>` to only run specific benchmarks. For example: `cargo benchmark lexer`
+- Use `cargo bench -p ruff_benchmark <filter>` to only run specific benchmarks. For example: `cargo bench -p ruff_benchmark lexer`
    to only run the lexer benchmarks.
 - Use `cargo bench -p ruff_benchmark -- --quiet` for a more cleaned up output (without statistical relevance)
 - Use `cargo bench -p ruff_benchmark -- --quick` to get faster results (more prone to noise)
@@ -911,9 +913,5 @@ There are three ways in which an import can be categorized as "first-party":
    the `src` setting and, for each directory, check for the existence of a subdirectory `foo` or a
    file `foo.py`.

-By default, `src` is set to the project root. In the above example, we'd want to set
-`src = ["./src"]` to ensure that we locate `./my_project/src/foo` and thus categorize `import foo`
-as first-party in `baz.py`. In practice, for this limited example, setting `src = ["./src"]` is
-unnecessary, as all imports within `./my_project/src/foo` would be categorized as first-party via
-the same-package heuristic; but if your project contains multiple packages, you'll want to set `src`
-explicitly.
+By default, `src` is set to the project root, along with `"src"` subdirectory in the project root.
+This ensures that Ruff supports both flat and "src" layouts out of the box.
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -95,9 +95,9 @@ dependencies = [

 [[package]]
 name = "anstyle"
-version = "1.0.6"
+version = "1.0.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8901269c6307e8d93993578286ac0edf7f195079ffff5ebdeea6a59ffb7e36bc"
+checksum = "1bec1de6f59aedf83baf9ff929c98f2ad654b97c9510f4e70cf6f661d49fd5b1"

 [[package]]
 name = "anstyle-parse"
@@ -228,9 +228,9 @@ dependencies = [

 [[package]]
 name = "camino"
-version = "1.1.7"
+version = "1.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e0ec6b951b160caa93cc0c7b209e5a3bff7aae9062213451ac99493cd844c239"
+checksum = "8b96ec4966b5813e2c0507c1f86115c8c5abaadc3980879c3424042a02fd1ad3"

 [[package]]
 name = "cast"
@@ -270,6 +270,12 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fd16c4719339c4530435d38e511904438d07cce7950afa3718a84ac36c10e89e"

+[[package]]
+name = "cfg_aliases"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
+
 [[package]]
 name = "chic"
 version = "1.2.2"
@@ -288,7 +294,7 @@ dependencies = [
 "android-tzdata",
 "iana-time-zone",
 "num-traits",
- "windows-targets 0.52.5",
+ "windows-targets 0.52.6",
 ]

 [[package]]
@@ -320,9 +326,9 @@ dependencies = [

 [[package]]
 name = "clap"
-version = "4.5.13"
+version = "4.5.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0fbb260a053428790f3de475e304ff84cdbc4face759ea7a3e64c1edd938a7fc"
+checksum = "ed6719fffa43d0d87e5fd8caeab59be1554fb028cd30edc88fc4369b17971019"
 dependencies = [
 "clap_builder",
 "clap_derive",
@@ -330,9 +336,9 @@ dependencies = [

 [[package]]
 name = "clap_builder"
-version = "4.5.13"
+version = "4.5.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "64b17d7ea74e9f833c7dbf2cbe4fb12ff26783eda4782a8975b72f895c9b4d99"
+checksum = "216aec2b177652e3846684cbfe25c9964d18ec45234f0f5da5157b207ed1aab6"
 dependencies = [
 "anstream",
 "anstyle",
@@ -395,7 +401,7 @@ version = "3.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2f8c93eb5f77c9050c7750e14f13ef1033a40a0aac70c6371535b6763a01438c"
 dependencies = [
- "nix",
+ "nix 0.28.0",
 "terminfo",
 "thiserror",
 "which",
@@ -612,12 +618,12 @@ checksum = "7a81dae078cea95a014a339291cec439d2f232ebe854a9d672b796c6afafa9b7"

 [[package]]
 name = "ctrlc"
-version = "3.4.4"
+version = "3.4.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "672465ae37dc1bc6380a6547a8883d5dd397b0f1faaad4f265726cc7042a5345"
+checksum = "90eeab0aa92f3f9b4e87f258c72b139c207d251f9cbc1080a0086b86a8870dd3"
 dependencies = [
- "nix",
- "windows-sys 0.52.0",
+ "nix 0.29.0",
+ "windows-sys 0.59.0",
 ]

 [[package]]
@@ -820,14 +826,14 @@ dependencies = [

 [[package]]
 name = "filetime"
-version = "0.2.23"
+version = "0.2.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1ee447700ac8aa0b2f2bd7bc4462ad686ba06baa6727ac149a2d6277f0d240fd"
+checksum = "bf401df4a4e3872c4fe8151134cf483738e74b67fc934d6532c882b3d24a4550"
 dependencies = [
 "cfg-if",
 "libc",
- "redox_syscall",
- "windows-sys 0.52.0",
+ "libredox",
+ "windows-sys 0.59.0",
 ]

 [[package]]
@@ -1047,9 +1053,9 @@ dependencies = [

 [[package]]
 name = "indexmap"
-version = "2.3.0"
+version = "2.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "de3fc2e30ba82dd1b3911c8de1ffc143c74a914a14e99514d7637e3099df5ea0"
+checksum = "93ead53efc7ea8ed3cfb0c79fc8023fbb782a5432b52830b6518941cebe6505c"
 dependencies = [
 "equivalent",
 "hashbrown",
@@ -1143,9 +1149,9 @@ dependencies = [

 [[package]]
 name = "is-macro"
-version = "0.3.5"
+version = "0.3.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "59a85abdc13717906baccb5a1e435556ce0df215f242892f721dff62bf25288f"
+checksum = "2069faacbe981460232f880d26bf3c7634e322d49053aa48c27e3ae642f728f1"
 dependencies = [
 "Inflector",
 "proc-macro2",
@@ -1215,9 +1221,9 @@ checksum = "8b23360e99b8717f20aaa4598f5a6541efbe30630039fbc7706cf954a87947ae"

 [[package]]
 name = "js-sys"
-version = "0.3.69"
+version = "0.3.70"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "29c15563dc2726973df627357ce0c9ddddbea194836909d655df6a75d2cf296d"
+checksum = "1868808506b929d7b0cfa8f75951347aa71bb21144b7791bae35d9bccfcfe37a"
 dependencies = [
 "wasm-bindgen",
 ]
@@ -1250,9 +1256,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"

 [[package]]
 name = "libc"
-version = "0.2.155"
+version = "0.2.158"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "97b3888a4aecf77e811145cadf6eef5901f4782c53886191b2f693f24761847c"
+checksum = "d8adc4bb1803a324070e64a98ae98f38934d91957a99cfb3a43dcbc01bc56439"

 [[package]]
 name = "libcst"
@@ -1297,6 +1303,7 @@ checksum = "c0ff37bd590ca25063e35af745c343cb7a0271906fb7b37e4813e8f79f00268d"
 dependencies = [
 "bitflags 2.6.0",
 "libc",
+ "redox_syscall 0.5.3",
 ]

 [[package]]
@@ -1387,6 +1394,16 @@ dependencies = [
 "libmimalloc-sys",
 ]

+[[package]]
+name = "minicov"
+version = "0.3.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c71e683cd655513b99affab7d317deb690528255a0d5f717f1024093c12b169"
+dependencies = [
+ "cc",
+ "walkdir",
+]
+
 [[package]]
 name = "minimal-lexical"
 version = "0.2.1"
@@ -1437,7 +1454,19 @@ checksum = "ab2156c4fce2f8df6c499cc1c763e4394b7482525bf2a9701c9d79d215f519e4"
 dependencies = [
 "bitflags 2.6.0",
 "cfg-if",
- "cfg_aliases",
+ "cfg_aliases 0.1.1",
+ "libc",
+]
+
+[[package]]
+name = "nix"
+version = "0.29.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "71e2746dc3a24dd78b3cfcb7be93368c6de9963d30f43a6a73998a9cf4b17b46"
+dependencies = [
+ "bitflags 2.6.0",
+ "cfg-if",
+ "cfg_aliases 0.2.1",
 "libc",
 ]

@@ -1524,9 +1553,9 @@ checksum = "04744f49eae99ab78e0d5c0b603ab218f515ea8cfe5a456d7629ad883a3b6e7d"

 [[package]]
 name = "ordermap"
-version = "0.5.1"
+version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8c81974681ab4f0cc9fe49cad56f821d1cc67a08cd2caa9b5d58b0adaa5dd36d"
+checksum = "61d7d835be600a7ac71b24e39c92fe6fad9e818b3c71bfc379e3ba65e327d77f"
 dependencies = [
 "indexmap",
 ]
@@ -1564,7 +1593,7 @@ checksum = "4c42a9226546d68acdd9c0a280d17ce19bfe27a46bf68784e4066115788d008e"
 dependencies = [
 "cfg-if",
 "libc",
- "redox_syscall",
+ "redox_syscall 0.4.1",
 "smallvec",
 "windows-targets 0.48.5",
 ]
@@ -1774,9 +1803,9 @@ dependencies = [

 [[package]]
 name = "quick-junit"
-version = "0.4.0"
+version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cfc1a6a5406a114913df2df8507998c755311b55b78584bed5f6e88f6417c4d4"
+checksum = "62ffd2f9a162cfae131bed6d9d1ed60adced33be340a94f96952897d7cb0c240"
 dependencies = [
 "chrono",
 "indexmap",
@@ -1789,18 +1818,18 @@ dependencies = [

 [[package]]
 name = "quick-xml"
-version = "0.31.0"
+version = "0.36.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1004a344b30a54e2ee58d66a71b32d2db2feb0a31f9a2d302bf0536f15de2a33"
+checksum = "96a05e2e8efddfa51a84ca47cec303fac86c8541b686d37cac5efc0e094417bc"
 dependencies = [
 "memchr",
 ]

 [[package]]
 name = "quote"
-version = "1.0.36"
+version = "1.0.37"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0fa76aaf39101c457836aec0ce2316dbdc3ab723cdda1c6bd4e6ad4208acaca7"
+checksum = "b5b9d34b8991d19d98081b46eacdd8eb58c6f2b201139f7c5f643cc155a633af"
 dependencies = [
 "proc-macro2",
 ]
@@ -1897,12 +1926,17 @@ dependencies = [
 "ruff_db",
 "ruff_index",
 "ruff_python_ast",
+ "ruff_python_literal",
 "ruff_python_parser",
 "ruff_python_stdlib",
+ "ruff_source_file",
 "ruff_text_size",
 "rustc-hash 2.0.0",
 "salsa",
+ "smallvec",
+ "static_assertions",
 "tempfile",
+ "thiserror",
 "tracing",
 "walkdir",
 "zip",
@@ -1918,10 +1952,8 @@ dependencies = [
 "libc",
 "lsp-server",
 "lsp-types",
- "red_knot_python_semantic",
 "red_knot_workspace",
 "ruff_db",
- "ruff_linter",
 "ruff_notebook",
 "ruff_python_ast",
 "ruff_source_file",
@@ -1957,13 +1989,15 @@ dependencies = [
 "anyhow",
 "crossbeam",
 "notify",
+ "rayon",
 "red_knot_python_semantic",
 "ruff_cache",
 "ruff_db",
 "ruff_python_ast",
+ "ruff_text_size",
 "rustc-hash 2.0.0",
 "salsa",
- "thiserror",
+ "tempfile",
 "tracing",
 ]

@@ -1976,6 +2010,15 @@ dependencies = [
 "bitflags 1.3.2",
 ]

+[[package]]
+name = "redox_syscall"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2a908a6e00f1fdd0dfd9c0eb08ce85126f6d8bbda50017e74bc4a4b7d4a926a4"
+dependencies = [
+ "bitflags 2.6.0",
+]
+
 [[package]]
 name = "redox_users"
 version = "0.4.5"
@@ -2048,7 +2091,7 @@ dependencies = [

 [[package]]
 name = "ruff"
-version = "0.5.7"
+version = "0.6.4"
 dependencies = [
 "anyhow",
 "argfile",
@@ -2106,6 +2149,7 @@ dependencies = [
 "criterion",
 "mimalloc",
 "once_cell",
+ "rayon",
 "red_knot_python_semantic",
 "red_knot_workspace",
 "ruff_db",
@@ -2156,6 +2200,7 @@ dependencies = [
 "rustc-hash 2.0.0",
 "salsa",
 "tempfile",
+ "thiserror",
 "tracing",
 "tracing-subscriber",
 "tracing-tree",
@@ -2239,7 +2284,7 @@ dependencies = [

 [[package]]
 name = "ruff_linter"
-version = "0.5.7"
+version = "0.6.4"
 dependencies = [
 "aho-corasick",
 "annotate-snippets 0.9.2",
@@ -2559,7 +2604,7 @@ dependencies = [

 [[package]]
 name = "ruff_wasm"
-version = "0.5.7"
+version = "0.6.4"
 dependencies = [
 "console_error_panic_hook",
 "console_log",
@@ -2699,7 +2744,7 @@ checksum = "e86697c916019a8588c99b5fac3cead74ec0b4b819707a682fd4d23fa0ce1ba1"
 [[package]]
 name = "salsa"
 version = "0.18.0"
-source = "git+https://github.com/MichaReiser/salsa.git?tag=red-knot-0.0.1#ece083e15b79f155f9e4368ec1318cec9a08d88b"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=f608ff8b24f07706492027199f51132244034f29#f608ff8b24f07706492027199f51132244034f29"
 dependencies = [
 "append-only-vec",
 "arc-swap",
@@ -2719,12 +2764,12 @@ dependencies = [
 [[package]]
 name = "salsa-macro-rules"
 version = "0.1.0"
-source = "git+https://github.com/MichaReiser/salsa.git?tag=red-knot-0.0.1#ece083e15b79f155f9e4368ec1318cec9a08d88b"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=f608ff8b24f07706492027199f51132244034f29#f608ff8b24f07706492027199f51132244034f29"

 [[package]]
 name = "salsa-macros"
 version = "0.18.0"
-source = "git+https://github.com/MichaReiser/salsa.git?tag=red-knot-0.0.1#ece083e15b79f155f9e4368ec1318cec9a08d88b"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=f608ff8b24f07706492027199f51132244034f29#f608ff8b24f07706492027199f51132244034f29"
 dependencies = [
 "heck",
 "proc-macro2",
@@ -2786,9 +2831,9 @@ checksum = "1c107b6f4780854c8b126e228ea8869f4d7b71260f962fefb57b996b8959ba6b"

 [[package]]
 name = "serde"
-version = "1.0.204"
+version = "1.0.209"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bc76f558e0cbb2a839d37354c575f1dc3fdc6546b5be373ba43d95f231bf7c12"
+checksum = "99fce0ffe7310761ca6bf9faf5115afbc19688edd00171d81b1bb1b116c63e09"
 dependencies = [
 "serde_derive",
 ]
@@ -2806,9 +2851,9 @@ dependencies = [

 [[package]]
 name = "serde_derive"
-version = "1.0.204"
+version = "1.0.209"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e0cd7e117be63d3c3678776753929474f3b04a43a080c744d6b0ae2a8c28e222"
+checksum = "a5831b979fd7b5439637af1752d535ff49f4860c0f341d1baeb6faf0f4242170"
 dependencies = [
 "proc-macro2",
 "quote",
@@ -2828,9 +2873,9 @@ dependencies = [

 [[package]]
 name = "serde_json"
-version = "1.0.122"
+version = "1.0.127"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "784b6203951c57ff748476b126ccb5e8e2959a5c19e5c617ab1956be3dbc68da"
+checksum = "8043c06d9f82bd7271361ed64f415fe5e12a77fdb52e573e7f06a516dea329ad"
 dependencies = [
 "itoa",
 "memchr",
@@ -2860,9 +2905,9 @@ dependencies = [

 [[package]]
 name = "serde_test"
-version = "1.0.176"
+version = "1.0.177"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5a2f49ace1498612d14f7e0b8245519584db8299541dfe31a06374a828d620ab"
+checksum = "7f901ee573cab6b3060453d2d5f0bae4e6d628c23c0a962ff9b5f1d7c8d4f1ed"
 dependencies = [
 "serde",
 ]
@@ -2989,9 +3034,9 @@ checksum = "81cdd64d312baedb58e21336b31bc043b77e01cc99033ce76ef539f78e965ebc"

 [[package]]
 name = "syn"
-version = "2.0.72"
+version = "2.0.76"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dc4b9b9bf2add8093d3f2c0204471e951b2285580335de42f9d2534f3ae7a8af"
+checksum = "578e081a14e0cefc3279b0472138c513f37b41a08d5a3cca9b6e4e8ceb6cd525"
 dependencies = [
 "proc-macro2",
 "quote",
@@ -3011,15 +3056,15 @@ dependencies = [

 [[package]]
 name = "tempfile"
-version = "3.11.0"
+version = "3.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b8fcd239983515c23a32fb82099f97d0b11b8c72f654ed659363a95c3dad7a53"
+checksum = "04cbcdd0c794ebb0d4cf35e88edd2f7d2c4c3e9a5a6dab322839b321c6a87a64"
 dependencies = [
 "cfg-if",
 "fastrand",
 "once_cell",
 "rustix",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]

 [[package]]
@@ -3395,9 +3440,9 @@ checksum = "8ecb6da28b8a351d773b68d5825ac39017e680750f980f3a1a85cd8dd28a47c1"

 [[package]]
 name = "ureq"
-version = "2.10.0"
+version = "2.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "72139d247e5f97a3eff96229a7ae85ead5328a39efe76f8bf5a06313d505b6ea"
+checksum = "b74fc6b57825be3373f7054754755f03ac3a8f5d70015ccad699ba2029956f4a"
 dependencies = [
 "base64",
 "flate2",
@@ -3513,19 +3558,20 @@ checksum = "9c8d87e72b64a3b4db28d11ce29237c246188f4f51057d65a7eab63b7987e423"

 [[package]]
 name = "wasm-bindgen"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4be2531df63900aeb2bca0daaaddec08491ee64ceecbee5076636a3b026795a8"
+checksum = "a82edfc16a6c469f5f44dc7b571814045d60404b55a0ee849f9bcfa2e63dd9b5"
 dependencies = [
 "cfg-if",
+ "once_cell",
 "wasm-bindgen-macro",
 ]

 [[package]]
 name = "wasm-bindgen-backend"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "614d787b966d3989fa7bb98a654e369c762374fd3213d212cfc0251257e747da"
+checksum = "9de396da306523044d3302746f1208fa71d7532227f15e347e2d93e4145dd77b"
 dependencies = [
 "bumpalo",
 "log",
@@ -3538,9 +3584,9 @@ dependencies = [

 [[package]]
 name = "wasm-bindgen-futures"
-version = "0.4.42"
+version = "0.4.43"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "76bc14366121efc8dbb487ab05bcc9d346b3b5ec0eaa76e46594cabbe51762c0"
+checksum = "61e9300f63a621e96ed275155c108eb6f843b6a26d053f122ab69724559dc8ed"
 dependencies = [
 "cfg-if",
 "js-sys",
@@ -3550,9 +3596,9 @@ dependencies = [

 [[package]]
 name = "wasm-bindgen-macro"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a1f8823de937b71b9460c0c34e25f3da88250760bec0ebac694b49997550d726"
+checksum = "585c4c91a46b072c92e908d99cb1dcdf95c5218eeb6f3bf1efa991ee7a68cccf"
 dependencies = [
 "quote",
 "wasm-bindgen-macro-support",
@@ -3560,9 +3606,9 @@ dependencies = [

 [[package]]
 name = "wasm-bindgen-macro-support"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e94f17b526d0a461a191c78ea52bbce64071ed5c04c9ffe424dcb38f74171bb7"
+checksum = "afc340c74d9005395cf9dd098506f7f44e38f2b4a21c6aaacf9a105ea5e1e836"
 dependencies = [
 "proc-macro2",
 "quote",
@@ -3573,18 +3619,19 @@ dependencies = [

 [[package]]
 name = "wasm-bindgen-shared"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "af190c94f2773fdb3729c55b007a722abb5384da03bc0986df4c289bf5567e96"
+checksum = "c62a0a307cb4a311d3a07867860911ca130c3494e8c2719593806c08bc5d0484"

 [[package]]
 name = "wasm-bindgen-test"
-version = "0.3.42"
+version = "0.3.43"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d9bf62a58e0780af3e852044583deee40983e5886da43a271dd772379987667b"
+checksum = "68497a05fb21143a08a7d24fc81763384a3072ee43c44e86aad1744d6adef9d9"
 dependencies = [
 "console_error_panic_hook",
 "js-sys",
+ "minicov",
 "scoped-tls",
 "wasm-bindgen",
 "wasm-bindgen-futures",
@@ -3593,9 +3640,9 @@ dependencies = [

 [[package]]
 name = "wasm-bindgen-test-macro"
-version = "0.3.42"
+version = "0.3.43"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b7f89739351a2e03cb94beb799d47fb2cac01759b40ec441f7de39b00cbf7ef0"
+checksum = "4b8220be1fa9e4c889b30fd207d4906657e7e90b12e0e6b0c8b8d8709f5de021"
 dependencies = [
 "proc-macro2",
 "quote",
@@ -3689,7 +3736,7 @@ version = "0.52.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "33ab640c8d7e35bf8ba19b884ba838ceb4fba93a4e8c65a9059d08afcfc683d9"
 dependencies = [
- "windows-targets 0.52.5",
+ "windows-targets 0.52.6",
 ]

 [[package]]
@@ -3707,7 +3754,16 @@ version = "0.52.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "282be5f36a8ce781fad8c8ae18fa3f9beff57ec1b52cb3de0789201425d9a33d"
 dependencies = [
- "windows-targets 0.52.5",
+ "windows-targets 0.52.6",
+]
+
+[[package]]
+name = "windows-sys"
+version = "0.59.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e38bc4d79ed67fd075bcc251a1c39b32a1776bbe92e5bef1f0bf1f8c531853b"
+dependencies = [
+ "windows-targets 0.52.6",
 ]

 [[package]]
@@ -3727,18 +3783,18 @@ dependencies = [

 [[package]]
 name = "windows-targets"
-version = "0.52.5"
+version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6f0713a46559409d202e70e28227288446bf7841d3211583a4b53e3f6d96e7eb"
+checksum = "9b724f72796e036ab90c1021d4780d4d3d648aca59e491e6b98e725b84e99973"
 dependencies = [
- "windows_aarch64_gnullvm 0.52.5",
- "windows_aarch64_msvc 0.52.5",
- "windows_i686_gnu 0.52.5",
+ "windows_aarch64_gnullvm 0.52.6",
+ "windows_aarch64_msvc 0.52.6",
+ "windows_i686_gnu 0.52.6",
 "windows_i686_gnullvm",
- "windows_i686_msvc 0.52.5",
- "windows_x86_64_gnu 0.52.5",
- "windows_x86_64_gnullvm 0.52.5",
- "windows_x86_64_msvc 0.52.5",
+ "windows_i686_msvc 0.52.6",
+ "windows_x86_64_gnu 0.52.6",
+ "windows_x86_64_gnullvm 0.52.6",
+ "windows_x86_64_msvc 0.52.6",
 ]

 [[package]]
@@ -3749,9 +3805,9 @@ checksum = "2b38e32f0abccf9987a4e3079dfb67dcd799fb61361e53e2882c3cbaf0d905d8"

 [[package]]
 name = "windows_aarch64_gnullvm"
-version = "0.52.5"
+version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7088eed71e8b8dda258ecc8bac5fb1153c5cffaf2578fc8ff5d61e23578d3263"
+checksum = "32a4622180e7a0ec044bb555404c800bc9fd9ec262ec147edd5989ccd0c02cd3"

 [[package]]
 name = "windows_aarch64_msvc"
@@ -3761,9 +3817,9 @@ checksum = "dc35310971f3b2dbbf3f0690a219f40e2d9afcf64f9ab7cc1be722937c26b4bc"

 [[package]]
 name = "windows_aarch64_msvc"
-version = "0.52.5"
+version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9985fd1504e250c615ca5f281c3f7a6da76213ebd5ccc9561496568a2752afb6"
+checksum = "09ec2a7bb152e2252b53fa7803150007879548bc709c039df7627cabbd05d469"

 [[package]]
 name = "windows_i686_gnu"
@@ -3773,15 +3829,15 @@ checksum = "a75915e7def60c94dcef72200b9a8e58e5091744960da64ec734a6c6e9b3743e"

 [[package]]
 name = "windows_i686_gnu"
-version = "0.52.5"
+version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "88ba073cf16d5372720ec942a8ccbf61626074c6d4dd2e745299726ce8b89670"
+checksum = "8e9b5ad5ab802e97eb8e295ac6720e509ee4c243f69d781394014ebfe8bbfa0b"

 [[package]]
 name = "windows_i686_gnullvm"
-version = "0.52.5"
+version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "87f4261229030a858f36b459e748ae97545d6f1ec60e5e0d6a3d32e0dc232ee9"
+checksum = "0eee52d38c090b3caa76c563b86c3a4bd71ef1a819287c19d586d7334ae8ed66"

 [[package]]
 name = "windows_i686_msvc"
@@ -3791,9 +3847,9 @@ checksum = "8f55c233f70c4b27f66c523580f78f1004e8b5a8b659e05a4eb49d4166cca406"

 [[package]]
 name = "windows_i686_msvc"
-version = "0.52.5"
+version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "db3c2bf3d13d5b658be73463284eaf12830ac9a26a90c717b7f771dfe97487bf"
+checksum = "240948bc05c5e7c6dabba28bf89d89ffce3e303022809e73deaefe4f6ec56c66"

 [[package]]
 name = "windows_x86_64_gnu"
@@ -3803,9 +3859,9 @@ checksum = "53d40abd2583d23e4718fddf1ebec84dbff8381c07cae67ff7768bbf19c6718e"

 [[package]]
 name = "windows_x86_64_gnu"
-version = "0.52.5"
+version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4e4246f76bdeff09eb48875a0fd3e2af6aada79d409d33011886d3e1581517d9"
+checksum = "147a5c80aabfbf0c7d901cb5895d1de30ef2907eb21fbbab29ca94c5b08b1a78"

 [[package]]
 name = "windows_x86_64_gnullvm"
@@ -3815,9 +3871,9 @@ checksum = "0b7b52767868a23d5bab768e390dc5f5c55825b6d30b86c844ff2dc7414044cc"

 [[package]]
 name = "windows_x86_64_gnullvm"
-version = "0.52.5"
+version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "852298e482cd67c356ddd9570386e2862b5673c85bd5f88df9ab6802b334c596"
+checksum = "24d5b23dc417412679681396f2b49f3de8c1473deb516bd34410872eff51ed0d"

 [[package]]
 name = "windows_x86_64_msvc"
@@ -3827,9 +3883,9 @@ checksum = "ed94fce61571a4006852b7389a063ab983c02eb1bb37b47f8272ce92d06d9538"

 [[package]]
 name = "windows_x86_64_msvc"
-version = "0.52.5"
+version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bec47e5bfd1bff0eeaf6d8b485cc1074891a197ab4225d504cb7a1ab88b02bf0"
+checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"

 [[package]]
 name = "winnow"
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -102,13 +102,13 @@ pep440_rs = { version = "0.6.0", features = ["serde"] }
 pretty_assertions = "1.3.0"
 proc-macro2 = { version = "1.0.79" }
 pyproject-toml = { version = "0.9.0" }
-quick-junit = { version = "0.4.0" }
+quick-junit = { version = "0.5.0" }
 quote = { version = "1.0.23" }
 rand = { version = "0.8.5" }
 rayon = { version = "1.10.0" }
 regex = { version = "1.10.2" }
 rustc-hash = { version = "2.0.0" }
-salsa = { git = "https://github.com/MichaReiser/salsa.git", tag = "red-knot-0.0.1" }
+salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "f608ff8b24f07706492027199f51132244034f29" }
 schemars = { version = "0.8.16" }
 seahash = { version = "4.1.0" }
 serde = { version = "1.0.197", features = ["derive"] }
--- a/README.md
+++ b/README.md
@@ -110,7 +110,7 @@ For more, see the [documentation](https://docs.astral.sh/ruff/).
 1. [Who's Using Ruff?](#whos-using-ruff)
 1. [License](#license)

-## Getting Started
+## Getting Started<a id="getting-started"></a>

 For more, see the [documentation](https://docs.astral.sh/ruff/).

@@ -136,8 +136,8 @@ curl -LsSf https://astral.sh/ruff/install.sh | sh
 powershell -c "irm https://astral.sh/ruff/install.ps1 | iex"

 # For a specific version.
-curl -LsSf https://astral.sh/ruff/0.5.7/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.5.7/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.6.4/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.6.4/install.ps1 | iex"
 ```

 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -170,7 +170,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
  # Ruff version.
-  rev: v0.5.7
+  rev: v0.6.4
  hooks:
    # Run the linter.
    - id: ruff
@@ -195,7 +195,7 @@ jobs:
      - uses: chartboost/ruff-action@v1
 ```

-### Configuration
+### Configuration<a id="configuration"></a>

 Ruff can be configured through a `pyproject.toml`, `ruff.toml`, or `.ruff.toml` file (see:
 [_Configuration_](https://docs.astral.sh/ruff/configuration/), or [_Settings_](https://docs.astral.sh/ruff/settings/)
@@ -291,7 +291,7 @@ features that may change prior to stabilization.
 See `ruff help` for more on Ruff's top-level commands, or `ruff help check` and `ruff help format`
 for more on the linting and formatting commands, respectively.

-## Rules
+## Rules<a id="rules"></a>

 <!-- Begin section: Rules -->

@@ -367,21 +367,21 @@ quality tools, including:

 For a complete enumeration of the supported rules, see [_Rules_](https://docs.astral.sh/ruff/rules/).

-## Contributing
+## Contributing<a id="contributing"></a>

 Contributions are welcome and highly appreciated. To get started, check out the
 [**contributing guidelines**](https://docs.astral.sh/ruff/contributing/).

 You can also join us on [**Discord**](https://discord.com/invite/astral-sh).

-## Support
+## Support<a id="support"></a>

 Having trouble? Check out the existing issues on [**GitHub**](https://github.com/astral-sh/ruff/issues),
 or feel free to [**open a new one**](https://github.com/astral-sh/ruff/issues/new).

 You can also ask for help on [**Discord**](https://discord.com/invite/astral-sh).

-## Acknowledgements
+## Acknowledgements<a id="acknowledgements"></a>

 Ruff's linter draws on both the APIs and implementation details of many other
 tools in the Python ecosystem, especially [Flake8](https://github.com/PyCQA/flake8), [Pyflakes](https://github.com/PyCQA/pyflakes),
@@ -405,7 +405,7 @@ Ruff is the beneficiary of a large number of [contributors](https://github.com/a

 Ruff is released under the MIT license.

-## Who's Using Ruff?
+## Who's Using Ruff?<a id="whos-using-ruff"></a>

 Ruff is used by a number of major open-source projects and companies, including:

@@ -524,7 +524,7 @@ If you're using Ruff, consider adding the Ruff badge to your project's `README.m
 <a href="https://github.com/astral-sh/ruff"><img src="https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/astral-sh/ruff/main/assets/badge/v2.json" alt="Ruff" style="max-width:100%;"></a>
 ```

-## License
+## License<a id="license"></a>

 This repository is licensed under the [MIT License](https://github.com/astral-sh/ruff/blob/main/LICENSE)

--- a/crates/red_knot/docs/tracing.md
+++ b/crates/red_knot/docs/tracing.md
@@ -13,12 +13,17 @@ The CLI supports different verbosity levels.
 - `-vv` activates `debug!` and timestamps: This should be enough information to get to the bottom of bug reports. When you're processing many packages or files, you'll get pages and pages of output, but each line is link to a specific action or state change.
 - `-vvv` activates `trace!` (only in debug builds) and shows tracing-spans: At this level, you're logging everything. Most of this is wasted, it's really slow, we dump e.g. the entire resolution graph. Only useful to developers, and you almost certainly want to use `RED_KNOT_LOG` to filter it down to the area your investigating.

-## `RED_KNOT_LOG`
+## Better logging with `RED_KNOT_LOG` and `RAYON_NUM_THREADS`

 By default, the CLI shows messages from the `ruff` and `red_knot` crates. Tracing messages from other crates are not shown.
 The `RED_KNOT_LOG` environment variable allows you to customize which messages are shown by specifying one
 or more [filter directives](https://docs.rs/tracing-subscriber/latest/tracing_subscriber/filter/struct.EnvFilter.html#directives).

+The `RAYON_NUM_THREADS` environment variable, meanwhile, can be used to control the level of concurrency red-knot uses.
+By default, red-knot will attempt to parallelize its work so that multiple files are checked simultaneously,
+but this can result in a confused logging output where messages from different threads are intertwined.
+To switch off concurrency entirely and have more readable logs, use `RAYON_NUM_THREADS=1`.
+
 ### Examples

 #### Show all debug messages
--- a/crates/red_knot/src/logging.rs
+++ b/crates/red_knot/src/logging.rs
@@ -5,8 +5,8 @@ use colored::Colorize;
 use std::fmt;
 use std::fs::File;
 use std::io::BufWriter;
-use tracing::log::LevelFilter;
 use tracing::{Event, Subscriber};
+use tracing_subscriber::filter::LevelFilter;
 use tracing_subscriber::fmt::format::Writer;
 use tracing_subscriber::fmt::{FmtContext, FormatEvent, FormatFields};
 use tracing_subscriber::registry::LookupSpan;
@@ -60,10 +60,10 @@ pub(crate) enum VerbosityLevel {
 impl VerbosityLevel {
    const fn level_filter(self) -> LevelFilter {
        match self {
-            VerbosityLevel::Default => LevelFilter::Warn,
-            VerbosityLevel::Verbose => LevelFilter::Info,
-            VerbosityLevel::ExtraVerbose => LevelFilter::Debug,
-            VerbosityLevel::Trace => LevelFilter::Trace,
+            VerbosityLevel::Default => LevelFilter::WARN,
+            VerbosityLevel::Verbose => LevelFilter::INFO,
+            VerbosityLevel::ExtraVerbose => LevelFilter::DEBUG,
+            VerbosityLevel::Trace => LevelFilter::TRACE,
        }
    }

@@ -88,7 +88,7 @@ pub(crate) fn setup_tracing(level: VerbosityLevel) -> anyhow::Result<TracingGuar
        match level {
            VerbosityLevel::Default => {
                // Show warning traces
-                EnvFilter::default().add_directive(tracing::level_filters::LevelFilter::WARN.into())
+                EnvFilter::default().add_directive(LevelFilter::WARN.into())
            }
            level => {
                let level_filter = level.level_filter();
--- a/crates/red_knot/src/main.rs
+++ b/crates/red_knot/src/main.rs
@@ -7,12 +7,12 @@ use colored::Colorize;
 use crossbeam::channel as crossbeam_channel;
 use salsa::plumbing::ZalsaDatabase;

-use red_knot_python_semantic::{ProgramSettings, SearchPathSettings};
+use red_knot_python_semantic::SitePackages;
 use red_knot_server::run_server;
 use red_knot_workspace::db::RootDatabase;
-use red_knot_workspace::site_packages::VirtualEnvironment;
 use red_knot_workspace::watch;
 use red_knot_workspace::watch::WorkspaceWatcher;
+use red_knot_workspace::workspace::settings::Configuration;
 use red_knot_workspace::workspace::WorkspaceMetadata;
 use ruff_db::system::{OsSystem, System, SystemPath, SystemPathBuf};
 use target_version::TargetVersion;
@@ -65,15 +65,14 @@ to resolve type information for the project's third-party dependencies.",
        value_name = "PATH",
        help = "Additional path to use as a module-resolution source (can be passed multiple times)"
    )]
-    extra_search_path: Vec<SystemPathBuf>,
+    extra_search_path: Option<Vec<SystemPathBuf>>,

    #[arg(
        long,
        help = "Python version to assume when resolving types",
-        default_value_t = TargetVersion::default(),
-        value_name="VERSION")
-    ]
-    target_version: TargetVersion,
+        value_name = "VERSION"
+    )]
+    target_version: Option<TargetVersion>,

    #[clap(flatten)]
    verbosity: Verbosity,
@@ -86,6 +85,36 @@ to resolve type information for the project's third-party dependencies.",
    watch: bool,
 }

+impl Args {
+    fn to_configuration(&self, cli_cwd: &SystemPath) -> Configuration {
+        let mut configuration = Configuration::default();
+
+        if let Some(target_version) = self.target_version {
+            configuration.target_version = Some(target_version.into());
+        }
+
+        if let Some(venv_path) = &self.venv_path {
+            configuration.search_paths.site_packages = Some(SitePackages::Derived {
+                venv_path: SystemPath::absolute(venv_path, cli_cwd),
+            });
+        }
+
+        if let Some(custom_typeshed_dir) = &self.custom_typeshed_dir {
+            configuration.search_paths.custom_typeshed =
+                Some(SystemPath::absolute(custom_typeshed_dir, cli_cwd));
+        }
+
+        if let Some(extra_search_paths) = &self.extra_search_path {
+            configuration.search_paths.extra_paths = extra_search_paths
+                .iter()
+                .map(|path| Some(SystemPath::absolute(path, cli_cwd)))
+                .collect();
+        }
+
+        configuration
+    }
+}
+
 #[derive(Debug, clap::Subcommand)]
 pub enum Command {
    /// Start the language server
@@ -115,22 +144,13 @@ pub fn main() -> ExitStatus {
 }

 fn run() -> anyhow::Result<ExitStatus> {
-    let Args {
-        command,
-        current_directory,
-        custom_typeshed_dir,
-        extra_search_path: extra_paths,
-        venv_path,
-        target_version,
-        verbosity,
-        watch,
-    } = Args::parse_from(std::env::args().collect::<Vec<_>>());
+    let args = Args::parse_from(std::env::args().collect::<Vec<_>>());

-    if matches!(command, Some(Command::Server)) {
+    if matches!(args.command, Some(Command::Server)) {
        return run_server().map(|()| ExitStatus::Success);
    }

-    let verbosity = verbosity.level();
+    let verbosity = args.verbosity.level();
    countme::enable(verbosity.is_trace());
    let _guard = setup_tracing(verbosity)?;

@@ -146,10 +166,12 @@ fn run() -> anyhow::Result<ExitStatus> {
            })?
    };

-    let cwd = current_directory
+    let cwd = args
+        .current_directory
+        .as_ref()
        .map(|cwd| {
            if cwd.as_std_path().is_dir() {
-                Ok(SystemPath::absolute(&cwd, &cli_base_path))
+                Ok(SystemPath::absolute(cwd, &cli_base_path))
            } else {
                Err(anyhow!(
                    "Provided current-directory path '{cwd}' is not a directory."
@@ -160,33 +182,18 @@ fn run() -> anyhow::Result<ExitStatus> {
        .unwrap_or_else(|| cli_base_path.clone());

    let system = OsSystem::new(cwd.clone());
-    let workspace_metadata = WorkspaceMetadata::from_path(system.current_directory(), &system)?;
-
-    // TODO: Verify the remaining search path settings eagerly.
-    let site_packages = venv_path
-        .map(|path| {
-            VirtualEnvironment::new(path, &OsSystem::new(cli_base_path))
-                .and_then(|venv| venv.site_packages_directories(&system))
-        })
-        .transpose()?
-        .unwrap_or_default();
-
-    // TODO: Respect the settings from the workspace metadata. when resolving the program settings.
-    let program_settings = ProgramSettings {
-        target_version: target_version.into(),
-        search_paths: SearchPathSettings {
-            extra_paths,
-            src_root: workspace_metadata.root().to_path_buf(),
-            custom_typeshed: custom_typeshed_dir,
-            site_packages,
-        },
-    };
+    let cli_configuration = args.to_configuration(&cwd);
+    let workspace_metadata = WorkspaceMetadata::from_path(
+        system.current_directory(),
+        &system,
+        Some(cli_configuration.clone()),
+    )?;

    // TODO: Use the `program_settings` to compute the key for the database's persistent
    //   cache and load the cache if it exists.
-    let mut db = RootDatabase::new(workspace_metadata, program_settings, system);
+    let mut db = RootDatabase::new(workspace_metadata, system)?;

-    let (main_loop, main_loop_cancellation_token) = MainLoop::new();
+    let (main_loop, main_loop_cancellation_token) = MainLoop::new(cli_configuration);

    // Listen to Ctrl+C and abort the watch mode.
    let main_loop_cancellation_token = Mutex::new(Some(main_loop_cancellation_token));
@@ -198,7 +205,7 @@ fn run() -> anyhow::Result<ExitStatus> {
        }
    })?;

-    let exit_status = if watch {
+    let exit_status = if args.watch {
        main_loop.watch(&mut db)?
    } else {
        main_loop.run(&mut db)
@@ -238,10 +245,12 @@ struct MainLoop {

    /// The file system watcher, if running in watch mode.
    watcher: Option<WorkspaceWatcher>,
+
+    cli_configuration: Configuration,
 }

 impl MainLoop {
-    fn new() -> (Self, MainLoopCancellationToken) {
+    fn new(cli_configuration: Configuration) -> (Self, MainLoopCancellationToken) {
        let (sender, receiver) = crossbeam_channel::bounded(10);

        (
@@ -249,6 +258,7 @@ impl MainLoop {
                sender: sender.clone(),
                receiver,
                watcher: None,
+                cli_configuration,
            },
            MainLoopCancellationToken { sender },
        )
@@ -331,7 +341,7 @@ impl MainLoop {
                MainLoopMessage::ApplyChanges(changes) => {
                    revision += 1;
                    // Automatically cancels any pending queries and waits for them to complete.
-                    db.apply_changes(changes);
+                    db.apply_changes(changes, Some(&self.cli_configuration));
                    if let Some(watcher) = self.watcher.as_mut() {
                        watcher.update(db);
                    }
--- a/crates/red_knot/tests/file_watching.rs
+++ b/crates/red_knot/tests/file_watching.rs
@@ -4,14 +4,12 @@ use std::io::Write;
 use std::time::Duration;

 use anyhow::{anyhow, Context};
-use salsa::Setter;

-use red_knot_python_semantic::{
-    resolve_module, ModuleName, Program, ProgramSettings, PythonVersion, SearchPathSettings,
-};
+use red_knot_python_semantic::{resolve_module, ModuleName, Program, PythonVersion, SitePackages};
 use red_knot_workspace::db::RootDatabase;
 use red_knot_workspace::watch;
 use red_knot_workspace::watch::{directory_watcher, WorkspaceWatcher};
+use red_knot_workspace::workspace::settings::{Configuration, SearchPathConfiguration};
 use red_knot_workspace::workspace::WorkspaceMetadata;
 use ruff_db::files::{system_path_to_file, File, FileError};
 use ruff_db::source::source_text;
@@ -26,6 +24,7 @@ struct TestCase {
    /// We need to hold on to it in the test case or the temp files get deleted.
    _temp_dir: tempfile::TempDir,
    root_dir: SystemPathBuf,
+    configuration: Configuration,
 }

 impl TestCase {
@@ -41,10 +40,6 @@ impl TestCase {
        &self.db
    }

-    fn db_mut(&mut self) -> &mut RootDatabase {
-        &mut self.db
-    }
-
    fn stop_watch(&mut self) -> Vec<watch::ChangeEvent> {
        self.try_stop_watch(Duration::from_secs(10))
            .expect("Expected watch changes but observed none.")
@@ -105,27 +100,32 @@ impl TestCase {
        Some(all_events)
    }

+    fn apply_changes(&mut self, changes: Vec<watch::ChangeEvent>) {
+        self.db.apply_changes(changes, Some(&self.configuration));
+    }
+
    fn update_search_path_settings(
        &mut self,
-        f: impl FnOnce(&SearchPathSettings) -> SearchPathSettings,
-    ) {
+        configuration: SearchPathConfiguration,
+    ) -> anyhow::Result<()> {
        let program = Program::get(self.db());
-        let search_path_settings = program.search_paths(self.db());

-        let new_settings = f(search_path_settings);
+        self.configuration.search_paths = configuration.clone();
+        let new_settings = configuration.into_settings(self.db.workspace().root(&self.db));

-        program.set_search_paths(&mut self.db).to(new_settings);
+        program.update_search_paths(&mut self.db, &new_settings)?;

        if let Some(watcher) = &mut self.watcher {
            watcher.update(&self.db);
            assert!(!watcher.has_errored_paths());
        }
+
+        Ok(())
    }

    fn collect_package_files(&self, path: &SystemPath) -> Vec<File> {
        let package = self.db().workspace().package(self.db(), path).unwrap();
        let files = package.files(self.db());
-        let files = files.read();
        let mut collected: Vec<_> = files.into_iter().collect();
        collected.sort_unstable_by_key(|file| file.path(self.db()).as_system_path().unwrap());
        collected
@@ -178,17 +178,14 @@ fn setup<F>(setup_files: F) -> anyhow::Result<TestCase>
 where
    F: SetupFiles,
 {
-    setup_with_search_paths(setup_files, |_root, workspace_path| SearchPathSettings {
-        extra_paths: vec![],
-        src_root: workspace_path.to_path_buf(),
-        custom_typeshed: None,
-        site_packages: vec![],
+    setup_with_search_paths(setup_files, |_root, _workspace_path| {
+        SearchPathConfiguration::default()
    })
 }

 fn setup_with_search_paths<F>(
    setup_files: F,
-    create_search_paths: impl FnOnce(&SystemPath, &SystemPath) -> SearchPathSettings,
+    create_search_paths: impl FnOnce(&SystemPath, &SystemPath) -> SearchPathConfiguration,
 ) -> anyhow::Result<TestCase>
 where
    F: SetupFiles,
@@ -220,25 +217,34 @@ where

    let system = OsSystem::new(&workspace_path);

-    let workspace = WorkspaceMetadata::from_path(&workspace_path, &system)?;
-    let search_paths = create_search_paths(&root_path, workspace.root());
+    let search_paths = create_search_paths(&root_path, &workspace_path);

    for path in search_paths
        .extra_paths
        .iter()
-        .chain(search_paths.site_packages.iter())
+        .flatten()
        .chain(search_paths.custom_typeshed.iter())
+        .chain(search_paths.site_packages.iter().flat_map(|site_packages| {
+            if let SitePackages::Known(path) = site_packages {
+                path.as_slice()
+            } else {
+                &[]
+            }
+        }))
    {
        std::fs::create_dir_all(path.as_std_path())
            .with_context(|| format!("Failed to create search path '{path}'"))?;
    }

-    let settings = ProgramSettings {
-        target_version: PythonVersion::default(),
+    let configuration = Configuration {
+        target_version: Some(PythonVersion::PY312),
        search_paths,
    };

-    let db = RootDatabase::new(workspace, settings, system);
+    let workspace =
+        WorkspaceMetadata::from_path(&workspace_path, &system, Some(configuration.clone()))?;
+
+    let db = RootDatabase::new(workspace, system)?;

    let (sender, receiver) = crossbeam::channel::unbounded();
    let watcher = directory_watcher(move |events| sender.send(events).unwrap())
@@ -253,6 +259,7 @@ where
        watcher: Some(watcher),
        _temp_dir: temp_dir,
        root_dir: root_path,
+        configuration,
    };

    // Sometimes the file watcher reports changes for events that happened before the watcher was started.
@@ -305,7 +312,7 @@ fn new_file() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    let foo = case.system_file(&foo_path).expect("foo.py to exist.");

@@ -328,7 +335,7 @@ fn new_ignored_file() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    assert!(case.system_file(&foo_path).is_ok());
    assert_eq!(&case.collect_package_files(&bar_path), &[bar_file]);
@@ -352,7 +359,7 @@ fn changed_file() -> anyhow::Result<()> {

    assert!(!changes.is_empty());

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    assert_eq!(source_text(case.db(), foo).as_str(), "print('Version 2')");
    assert_eq!(&case.collect_package_files(&foo_path), &[foo]);
@@ -375,7 +382,7 @@ fn deleted_file() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    assert!(!foo.exists(case.db()));
    assert_eq!(&case.collect_package_files(&foo_path), &[] as &[File]);
@@ -407,7 +414,7 @@ fn move_file_to_trash() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    assert!(!foo.exists(case.db()));
    assert_eq!(&case.collect_package_files(&foo_path), &[] as &[File]);
@@ -439,7 +446,7 @@ fn move_file_to_workspace() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    let foo_in_workspace = case.system_file(&foo_in_workspace_path)?;

@@ -467,7 +474,7 @@ fn rename_file() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    assert!(!foo.exists(case.db()));

@@ -508,7 +515,7 @@ fn directory_moved_to_workspace() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    let init_file = case
        .system_file(sub_new_path.join("__init__.py"))
@@ -559,7 +566,7 @@ fn directory_moved_to_trash() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    // `import sub.a` should no longer resolve
    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_none());
@@ -613,7 +620,7 @@ fn directory_renamed() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    // `import sub.a` should no longer resolve
    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_none());
@@ -678,7 +685,7 @@ fn directory_deleted() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    // `import sub.a` should no longer resolve
    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_none());
@@ -692,15 +699,13 @@ fn directory_deleted() -> anyhow::Result<()> {

 #[test]
 fn search_path() -> anyhow::Result<()> {
-    let mut case =
-        setup_with_search_paths([("bar.py", "import sub.a")], |root_path, workspace_path| {
-            SearchPathSettings {
-                extra_paths: vec![],
-                src_root: workspace_path.to_path_buf(),
-                custom_typeshed: None,
-                site_packages: vec![root_path.join("site_packages")],
-            }
-        })?;
+    let mut case = setup_with_search_paths(
+        [("bar.py", "import sub.a")],
+        |root_path, _workspace_path| SearchPathConfiguration {
+            site_packages: Some(SitePackages::Known(vec![root_path.join("site_packages")])),
+            ..SearchPathConfiguration::default()
+        },
+    )?;

    let site_packages = case.root_path().join("site_packages");

@@ -713,7 +718,7 @@ fn search_path() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("a").unwrap()).is_some());
    assert_eq!(
@@ -734,16 +739,17 @@ fn add_search_path() -> anyhow::Result<()> {
    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("a").unwrap()).is_none());

    // Register site-packages as a search path.
-    case.update_search_path_settings(|settings| SearchPathSettings {
-        site_packages: vec![site_packages.clone()],
-        ..settings.clone()
-    });
+    case.update_search_path_settings(SearchPathConfiguration {
+        site_packages: Some(SitePackages::Known(vec![site_packages.clone()])),
+        ..SearchPathConfiguration::default()
+    })
+    .expect("Search path settings to be valid");

    std::fs::write(site_packages.join("a.py").as_std_path(), "class A: ...")?;

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("a").unwrap()).is_some());

@@ -752,22 +758,21 @@ fn add_search_path() -> anyhow::Result<()> {

 #[test]
 fn remove_search_path() -> anyhow::Result<()> {
-    let mut case =
-        setup_with_search_paths([("bar.py", "import sub.a")], |root_path, workspace_path| {
-            SearchPathSettings {
-                extra_paths: vec![],
-                src_root: workspace_path.to_path_buf(),
-                custom_typeshed: None,
-                site_packages: vec![root_path.join("site_packages")],
-            }
-        })?;
+    let mut case = setup_with_search_paths(
+        [("bar.py", "import sub.a")],
+        |root_path, _workspace_path| SearchPathConfiguration {
+            site_packages: Some(SitePackages::Known(vec![root_path.join("site_packages")])),
+            ..SearchPathConfiguration::default()
+        },
+    )?;

    // Remove site packages from the search path settings.
    let site_packages = case.root_path().join("site_packages");
-    case.update_search_path_settings(|settings| SearchPathSettings {
-        site_packages: vec![],
-        ..settings.clone()
-    });
+    case.update_search_path_settings(SearchPathConfiguration {
+        site_packages: None,
+        ..SearchPathConfiguration::default()
+    })
+    .expect("Search path settings to be valid");

    std::fs::write(site_packages.join("a.py").as_std_path(), "class A: ...")?;

@@ -778,6 +783,48 @@ fn remove_search_path() -> anyhow::Result<()> {
    Ok(())
 }

+#[test]
+fn changed_versions_file() -> anyhow::Result<()> {
+    let mut case = setup_with_search_paths(
+        |root_path: &SystemPath, workspace_path: &SystemPath| {
+            std::fs::write(workspace_path.join("bar.py").as_std_path(), "import sub.a")?;
+            std::fs::create_dir_all(root_path.join("typeshed/stdlib").as_std_path())?;
+            std::fs::write(root_path.join("typeshed/stdlib/VERSIONS").as_std_path(), "")?;
+            std::fs::write(
+                root_path.join("typeshed/stdlib/os.pyi").as_std_path(),
+                "# not important",
+            )?;
+
+            Ok(())
+        },
+        |root_path, _workspace_path| SearchPathConfiguration {
+            custom_typeshed: Some(root_path.join("typeshed")),
+            ..SearchPathConfiguration::default()
+        },
+    )?;
+
+    // Unset the custom typeshed directory.
+    assert_eq!(
+        resolve_module(case.db(), ModuleName::new("os").unwrap()),
+        None
+    );
+
+    std::fs::write(
+        case.root_path()
+            .join("typeshed/stdlib/VERSIONS")
+            .as_std_path(),
+        "os: 3.0-",
+    )?;
+
+    let changes = case.stop_watch();
+
+    case.apply_changes(changes);
+
+    assert!(resolve_module(case.db(), ModuleName::new("os").unwrap()).is_some());
+
+    Ok(())
+}
+
 /// Watch a workspace that contains two files where one file is a hardlink to another.
 ///
 /// Setup:
@@ -824,7 +871,7 @@ fn hard_links_in_workspace() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    assert_eq!(source_text(case.db(), foo).as_str(), "print('Version 2')");

@@ -895,7 +942,7 @@ fn hard_links_to_target_outside_workspace() -> anyhow::Result<()> {

    let changes = case.stop_watch();

-    case.db_mut().apply_changes(changes);
+    case.apply_changes(changes);

    assert_eq!(source_text(case.db(), bar).as_str(), "print('Version 2')");

@@ -934,7 +981,7 @@ mod unix {

        let changes = case.stop_watch();

-        case.db_mut().apply_changes(changes);
+        case.apply_changes(changes);

        assert_eq!(
            foo.permissions(case.db()),
@@ -1019,7 +1066,7 @@ mod unix {

        let changes = case.take_watch_changes();

-        case.db_mut().apply_changes(changes);
+        case.apply_changes(changes);

        assert_eq!(
            source_text(case.db(), baz.file()).as_str(),
@@ -1032,7 +1079,7 @@ mod unix {

        let changes = case.stop_watch();

-        case.db_mut().apply_changes(changes);
+        case.apply_changes(changes);

        assert_eq!(
            source_text(case.db(), baz.file()).as_str(),
@@ -1103,7 +1150,7 @@ mod unix {

        let changes = case.stop_watch();

-        case.db_mut().apply_changes(changes);
+        case.apply_changes(changes);

        // The file watcher is guaranteed to emit one event for the changed file, but it isn't specified
        // if the event is emitted for the "original" or linked path because both paths are watched.
@@ -1172,11 +1219,11 @@ mod unix {

                Ok(())
            },
-            |_root, workspace| SearchPathSettings {
-                extra_paths: vec![],
-                src_root: workspace.to_path_buf(),
-                custom_typeshed: None,
-                site_packages: vec![workspace.join(".venv/lib/python3.12/site-packages")],
+            |_root, workspace| SearchPathConfiguration {
+                site_packages: Some(SitePackages::Known(vec![
+                    workspace.join(".venv/lib/python3.12/site-packages")
+                ])),
+                ..SearchPathConfiguration::default()
            },
        )?;

@@ -1211,7 +1258,7 @@ mod unix {

        let changes = case.stop_watch();

-        case.db_mut().apply_changes(changes);
+        case.apply_changes(changes);

        assert_eq!(
            source_text(case.db(), baz_original_file).as_str(),
--- a/crates/red_knot_python_semantic/Cargo.toml
+++ b/crates/red_knot_python_semantic/Cargo.toml
@@ -15,8 +15,11 @@ ruff_db = { workspace = true }
 ruff_index = { workspace = true }
 ruff_python_ast = { workspace = true }
 ruff_python_stdlib = { workspace = true }
+ruff_source_file = { workspace = true }
 ruff_text_size = { workspace = true }
+ruff_python_literal = { workspace = true }

+anyhow = { workspace = true }
 bitflags = { workspace = true }
 camino = { workspace = true }
 compact_str = { workspace = true }
@@ -24,9 +27,12 @@ countme = { workspace = true }
 once_cell = { workspace = true }
 ordermap = { workspace = true }
 salsa = { workspace = true }
+thiserror = { workspace = true }
 tracing = { workspace = true }
 rustc-hash = { workspace = true }
 hashbrown = { workspace = true }
+smallvec = { workspace = true }
+static_assertions = { workspace = true }

 [build-dependencies]
 path-slash = { workspace = true }
@@ -34,7 +40,7 @@ walkdir = { workspace = true }
 zip = { workspace = true, features = ["zstd", "deflate"] }

 [dev-dependencies]
-ruff_db = { workspace = true, features = ["os", "testing"]}
+ruff_db = { workspace = true, features = ["os", "testing"] }
 ruff_python_parser = { workspace = true }

 anyhow = { workspace = true }
--- a/crates/red_knot_python_semantic/src/ast_node_ref.rs
+++ b/crates/red_knot_python_semantic/src/ast_node_ref.rs
@@ -31,10 +31,10 @@ impl<T> AstNodeRef<T> {
    /// which the `AstNodeRef` belongs.
    ///
    /// ## Safety
+    ///
    /// Dereferencing the `node` can result in undefined behavior if `parsed` isn't the
    /// [`ParsedModule`] to which `node` belongs. It's the caller's responsibility to ensure that
    /// the invariant `node belongs to parsed` is upheld.
-
    pub(super) unsafe fn new(parsed: ParsedModule, node: &T) -> Self {
        Self {
            _parsed: parsed,
--- a/crates/red_knot_python_semantic/src/builtins.rs
+++ b/crates/red_knot_python_semantic/src/builtins.rs
@@ -1,16 +0,0 @@
-use crate::module_name::ModuleName;
-use crate::module_resolver::resolve_module;
-use crate::semantic_index::global_scope;
-use crate::semantic_index::symbol::ScopeId;
-use crate::Db;
-
-/// Salsa query to get the builtins scope.
-///
-/// Can return None if a custom typeshed is used that is missing `builtins.pyi`.
-#[salsa::tracked]
-pub(crate) fn builtins_scope(db: &dyn Db) -> Option<ScopeId<'_>> {
-    let builtins_name =
-        ModuleName::new_static("builtins").expect("Expected 'builtins' to be a valid module name");
-    let builtins_file = resolve_module(db, builtins_name)?.file();
-    Some(global_scope(db, builtins_file))
-}
--- a/crates/red_knot_python_semantic/src/db.rs
+++ b/crates/red_knot_python_semantic/src/db.rs
@@ -1,15 +1,18 @@
+use ruff_db::files::File;
 use ruff_db::{Db as SourceDb, Upcast};

 /// Database giving access to semantic information about a Python program.
 #[salsa::db]
-pub trait Db: SourceDb + Upcast<dyn SourceDb> {}
+pub trait Db: SourceDb + Upcast<dyn SourceDb> {
+    fn is_file_open(&self, file: File) -> bool;
+}

 #[cfg(test)]
 pub(crate) mod tests {
    use std::sync::Arc;

    use crate::module_resolver::vendored_typeshed_stubs;
-    use ruff_db::files::Files;
+    use ruff_db::files::{File, Files};
    use ruff_db::system::{DbWithTestSystem, System, TestSystem};
    use ruff_db::vendored::VendoredFileSystem;
    use ruff_db::{Db as SourceDb, Upcast};
@@ -91,7 +94,11 @@ pub(crate) mod tests {
    }

    #[salsa::db]
-    impl Db for TestDb {}
+    impl Db for TestDb {
+        fn is_file_open(&self, file: File) -> bool {
+            !file.path(self).is_vendored_path()
+        }
+    }

    #[salsa::db]
    impl salsa::Database for TestDb {
--- a/crates/red_knot_python_semantic/src/lib.rs
+++ b/crates/red_knot_python_semantic/src/lib.rs
@@ -5,12 +5,11 @@ use rustc_hash::FxHasher;
 pub use db::Db;
 pub use module_name::ModuleName;
 pub use module_resolver::{resolve_module, system_module_search_paths, vendored_typeshed_stubs};
-pub use program::{Program, ProgramSettings, SearchPathSettings};
+pub use program::{Program, ProgramSettings, SearchPathSettings, SitePackages};
 pub use python_version::PythonVersion;
 pub use semantic_model::{HasTy, SemanticModel};

 pub mod ast_node_ref;
-mod builtins;
 mod db;
 mod module_name;
 mod module_resolver;
@@ -19,6 +18,9 @@ mod program;
 mod python_version;
 pub mod semantic_index;
 mod semantic_model;
+pub(crate) mod site_packages;
+mod stdlib;
 pub mod types;

 type FxOrderSet<V> = ordermap::set::OrderSet<V, BuildHasherDefault<FxHasher>>;
+type FxOrderMap<K, V> = ordermap::map::OrderMap<K, V, BuildHasherDefault<FxHasher>>;
--- a/crates/red_knot_python_semantic/src/module_name.rs
+++ b/crates/red_knot_python_semantic/src/module_name.rs
@@ -168,6 +168,24 @@ impl ModuleName {
        };
        Some(Self(name))
    }
+
+    /// Extend `self` with the components of `other`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use red_knot_python_semantic::ModuleName;
+    ///
+    /// let mut module_name = ModuleName::new_static("foo").unwrap();
+    /// module_name.extend(&ModuleName::new_static("bar").unwrap());
+    /// assert_eq!(&module_name, "foo.bar");
+    /// module_name.extend(&ModuleName::new_static("baz.eggs.ham").unwrap());
+    /// assert_eq!(&module_name, "foo.bar.baz.eggs.ham");
+    /// ```
+    pub fn extend(&mut self, other: &ModuleName) {
+        self.0.push('.');
+        self.0.push_str(other);
+    }
 }

 impl Deref for ModuleName {
--- a/crates/red_knot_python_semantic/src/module_resolver/mod.rs
+++ b/crates/red_knot_python_semantic/src/module_resolver/mod.rs
@@ -2,16 +2,17 @@ use std::iter::FusedIterator;

 pub(crate) use module::Module;
 pub use resolver::resolve_module;
+pub(crate) use resolver::{file_to_module, SearchPaths};
 use ruff_db::system::SystemPath;
 pub use typeshed::vendored_typeshed_stubs;

+use crate::module_resolver::resolver::search_paths;
 use crate::Db;
-use resolver::{module_resolution_settings, SearchPathIterator};
+use resolver::SearchPathIterator;

 mod module;
 mod path;
 mod resolver;
-mod state;
 mod typeshed;

 #[cfg(test)]
@@ -20,7 +21,7 @@ mod testing;
 /// Returns an iterator over all search paths pointing to a system path
 pub fn system_module_search_paths(db: &dyn Db) -> SystemModuleSearchPathsIter {
    SystemModuleSearchPathsIter {
-        inner: module_resolution_settings(db).search_paths(db),
+        inner: search_paths(db),
    }
 }

--- a/crates/red_knot_python_semantic/src/module_resolver/module.rs
+++ b/crates/red_knot_python_semantic/src/module_resolver/module.rs
@@ -77,3 +77,9 @@ pub enum ModuleKind {
    /// A python package (`foo/__init__.py` or `foo/__init__.pyi`)
    Package,
 }
+
+impl ModuleKind {
+    pub const fn is_package(self) -> bool {
+        matches!(self, ModuleKind::Package)
+    }
+}
--- a/crates/red_knot_python_semantic/src/module_resolver/path.rs
+++ b/crates/red_knot_python_semantic/src/module_resolver/path.rs
@@ -9,11 +9,11 @@ use ruff_db::files::{system_path_to_file, vendored_path_to_file, File, FileError
 use ruff_db::system::{System, SystemPath, SystemPathBuf};
 use ruff_db::vendored::{VendoredPath, VendoredPathBuf};

+use super::typeshed::{typeshed_versions, TypeshedVersionsParseError, TypeshedVersionsQueryResult};
 use crate::db::Db;
 use crate::module_name::ModuleName;
-
-use super::state::ResolverState;
-use super::typeshed::{TypeshedVersionsParseError, TypeshedVersionsQueryResult};
+use crate::module_resolver::resolver::ResolverContext;
+use crate::site_packages::SitePackagesDiscoveryError;

 /// A path that points to a Python module.
 ///
@@ -60,7 +60,7 @@ impl ModulePath {
    }

    #[must_use]
-    pub(crate) fn is_directory(&self, resolver: &ResolverState) -> bool {
+    pub(super) fn is_directory(&self, resolver: &ResolverContext) -> bool {
        let ModulePath {
            search_path,
            relative_path,
@@ -74,7 +74,7 @@ impl ModulePath {
                    == Err(FileError::IsADirectory)
            }
            SearchPathInner::StandardLibraryCustom(stdlib_root) => {
-                match query_stdlib_version(Some(stdlib_root), relative_path, resolver) {
+                match query_stdlib_version(relative_path, resolver) {
                    TypeshedVersionsQueryResult::DoesNotExist => false,
                    TypeshedVersionsQueryResult::Exists
                    | TypeshedVersionsQueryResult::MaybeExists => {
@@ -84,7 +84,7 @@ impl ModulePath {
                }
            }
            SearchPathInner::StandardLibraryVendored(stdlib_root) => {
-                match query_stdlib_version(None, relative_path, resolver) {
+                match query_stdlib_version(relative_path, resolver) {
                    TypeshedVersionsQueryResult::DoesNotExist => false,
                    TypeshedVersionsQueryResult::Exists
                    | TypeshedVersionsQueryResult::MaybeExists => resolver
@@ -96,7 +96,7 @@ impl ModulePath {
    }

    #[must_use]
-    pub(crate) fn is_regular_package(&self, resolver: &ResolverState) -> bool {
+    pub(super) fn is_regular_package(&self, resolver: &ResolverContext) -> bool {
        let ModulePath {
            search_path,
            relative_path,
@@ -113,7 +113,7 @@ impl ModulePath {
                        .is_ok()
            }
            SearchPathInner::StandardLibraryCustom(search_path) => {
-                match query_stdlib_version(Some(search_path), relative_path, resolver) {
+                match query_stdlib_version(relative_path, resolver) {
                    TypeshedVersionsQueryResult::DoesNotExist => false,
                    TypeshedVersionsQueryResult::Exists
                    | TypeshedVersionsQueryResult::MaybeExists => system_path_to_file(
@@ -124,7 +124,7 @@ impl ModulePath {
                }
            }
            SearchPathInner::StandardLibraryVendored(search_path) => {
-                match query_stdlib_version(None, relative_path, resolver) {
+                match query_stdlib_version(relative_path, resolver) {
                    TypeshedVersionsQueryResult::DoesNotExist => false,
                    TypeshedVersionsQueryResult::Exists
                    | TypeshedVersionsQueryResult::MaybeExists => resolver
@@ -136,7 +136,7 @@ impl ModulePath {
    }

    #[must_use]
-    pub(crate) fn to_file(&self, resolver: &ResolverState) -> Option<File> {
+    pub(super) fn to_file(&self, resolver: &ResolverContext) -> Option<File> {
        let db = resolver.db.upcast();
        let ModulePath {
            search_path,
@@ -150,7 +150,7 @@ impl ModulePath {
                system_path_to_file(db, search_path.join(relative_path)).ok()
            }
            SearchPathInner::StandardLibraryCustom(stdlib_root) => {
-                match query_stdlib_version(Some(stdlib_root), relative_path, resolver) {
+                match query_stdlib_version(relative_path, resolver) {
                    TypeshedVersionsQueryResult::DoesNotExist => None,
                    TypeshedVersionsQueryResult::Exists
                    | TypeshedVersionsQueryResult::MaybeExists => {
@@ -159,7 +159,7 @@ impl ModulePath {
                }
            }
            SearchPathInner::StandardLibraryVendored(stdlib_root) => {
-                match query_stdlib_version(None, relative_path, resolver) {
+                match query_stdlib_version(relative_path, resolver) {
                    TypeshedVersionsQueryResult::DoesNotExist => None,
                    TypeshedVersionsQueryResult::Exists
                    | TypeshedVersionsQueryResult::MaybeExists => {
@@ -273,19 +273,15 @@ fn stdlib_path_to_module_name(relative_path: &Utf8Path) -> Option<ModuleName> {

 #[must_use]
 fn query_stdlib_version(
-    custom_stdlib_root: Option<&SystemPath>,
    relative_path: &Utf8Path,
-    resolver: &ResolverState,
+    context: &ResolverContext,
 ) -> TypeshedVersionsQueryResult {
    let Some(module_name) = stdlib_path_to_module_name(relative_path) else {
        return TypeshedVersionsQueryResult::DoesNotExist;
    };
-    let ResolverState {
-        db,
-        typeshed_versions,
-        target_version,
-    } = resolver;
-    typeshed_versions.query_module(*db, &module_name, custom_stdlib_root, *target_version)
+    let ResolverContext { db, target_version } = context;
+
+    typeshed_versions(*db).query_module(&module_name, *target_version)
 }

 /// Enumeration describing the various ways in which validation of a search path might fail.
@@ -293,7 +289,7 @@ fn query_stdlib_version(
 /// If validation fails for a search path derived from the user settings,
 /// a message must be displayed to the user,
 /// as type checking cannot be done reliably in these circumstances.
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug)]
 pub(crate) enum SearchPathValidationError {
    /// The path provided by the user was not a directory
    NotADirectory(SystemPathBuf),
@@ -304,18 +300,20 @@ pub(crate) enum SearchPathValidationError {
    NoStdlibSubdirectory(SystemPathBuf),

    /// The typeshed path provided by the user is a directory,
-    /// but no `stdlib/VERSIONS` file exists.
+    /// but `stdlib/VERSIONS` could not be read.
    /// (This is only relevant for stdlib search paths.)
-    NoVersionsFile(SystemPathBuf),
-
-    /// `stdlib/VERSIONS` is a directory.
-    /// (This is only relevant for stdlib search paths.)
-    VersionsIsADirectory(SystemPathBuf),
+    FailedToReadVersionsFile {
+        path: SystemPathBuf,
+        error: std::io::Error,
+    },

    /// The path provided by the user is a directory,
    /// and a `stdlib/VERSIONS` file exists, but it fails to parse.
    /// (This is only relevant for stdlib search paths.)
    VersionsParseError(TypeshedVersionsParseError),
+
+    /// Failed to discover the site-packages for the configured virtual environment.
+    SitePackagesDiscovery(SitePackagesDiscoveryError),
 }

 impl fmt::Display for SearchPathValidationError {
@@ -325,9 +323,16 @@ impl fmt::Display for SearchPathValidationError {
            Self::NoStdlibSubdirectory(path) => {
                write!(f, "The directory at {path} has no `stdlib/` subdirectory")
            }
-            Self::NoVersionsFile(path) => write!(f, "Expected a file at {path}/stdlib/VERSIONS"),
-            Self::VersionsIsADirectory(path) => write!(f, "{path}/stdlib/VERSIONS is a directory."),
+            Self::FailedToReadVersionsFile { path, error } => {
+                write!(
+                    f,
+                    "Failed to read the custom typeshed versions file '{path}': {error}"
+                )
+            }
            Self::VersionsParseError(underlying_error) => underlying_error.fmt(f),
+            SearchPathValidationError::SitePackagesDiscovery(error) => {
+                write!(f, "Failed to discover the site-packages directory: {error}")
+            }
        }
    }
 }
@@ -342,6 +347,18 @@ impl std::error::Error for SearchPathValidationError {
    }
 }

+impl From<TypeshedVersionsParseError> for SearchPathValidationError {
+    fn from(value: TypeshedVersionsParseError) -> Self {
+        Self::VersionsParseError(value)
+    }
+}
+
+impl From<SitePackagesDiscoveryError> for SearchPathValidationError {
+    fn from(value: SitePackagesDiscoveryError) -> Self {
+        Self::SitePackagesDiscovery(value)
+    }
+}
+
 type SearchPathResult<T> = Result<T, SearchPathValidationError>;

 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -384,11 +401,10 @@ pub(crate) struct SearchPath(Arc<SearchPathInner>);

 impl SearchPath {
    fn directory_path(system: &dyn System, root: SystemPathBuf) -> SearchPathResult<SystemPathBuf> {
-        let canonicalized = system.canonicalize_path(&root).unwrap_or(root);
-        if system.is_directory(&canonicalized) {
-            Ok(canonicalized)
+        if system.is_directory(&root) {
+            Ok(root)
        } else {
-            Err(SearchPathValidationError::NotADirectory(canonicalized))
+            Err(SearchPathValidationError::NotADirectory(root))
        }
    }

@@ -407,32 +423,22 @@ impl SearchPath {
    }

    /// Create a new standard-library search path pointing to a custom directory on disk
-    pub(crate) fn custom_stdlib(db: &dyn Db, typeshed: SystemPathBuf) -> SearchPathResult<Self> {
+    pub(crate) fn custom_stdlib(db: &dyn Db, typeshed: &SystemPath) -> SearchPathResult<Self> {
        let system = db.system();
-        if !system.is_directory(&typeshed) {
+        if !system.is_directory(typeshed) {
            return Err(SearchPathValidationError::NotADirectory(
                typeshed.to_path_buf(),
            ));
        }
+
        let stdlib =
            Self::directory_path(system, typeshed.join("stdlib")).map_err(|err| match err {
-                SearchPathValidationError::NotADirectory(path) => {
-                    SearchPathValidationError::NoStdlibSubdirectory(path)
+                SearchPathValidationError::NotADirectory(_) => {
+                    SearchPathValidationError::NoStdlibSubdirectory(typeshed.to_path_buf())
                }
                err => err,
            })?;
-        let typeshed_versions =
-            system_path_to_file(db.upcast(), stdlib.join("VERSIONS")).map_err(|err| match err {
-                FileError::NotFound => SearchPathValidationError::NoVersionsFile(typeshed),
-                FileError::IsADirectory => {
-                    SearchPathValidationError::VersionsIsADirectory(typeshed)
-                }
-            })?;
-        super::typeshed::parse_typeshed_versions(db, typeshed_versions)
-            .as_ref()
-            .map_err(|validation_error| {
-                SearchPathValidationError::VersionsParseError(validation_error.clone())
-            })?;
+
        Ok(Self(Arc::new(SearchPathInner::StandardLibraryCustom(
            stdlib,
        ))))
@@ -623,11 +629,11 @@ mod tests {
    use ruff_db::Db;

    use crate::db::tests::TestDb;
-
-    use super::*;
    use crate::module_resolver::testing::{FileSpec, MockedTypeshed, TestCase, TestCaseBuilder};
    use crate::python_version::PythonVersion;

+    use super::*;
+
    impl ModulePath {
        #[must_use]
        fn join(&self, component: &str) -> ModulePath {
@@ -638,15 +644,6 @@ mod tests {
    }

    impl SearchPath {
-        #[must_use]
-        pub(crate) fn is_stdlib_search_path(&self) -> bool {
-            matches!(
-                &*self.0,
-                SearchPathInner::StandardLibraryCustom(_)
-                    | SearchPathInner::StandardLibraryVendored(_)
-            )
-        }
-
        fn join(&self, component: &str) -> ModulePath {
            self.to_module_path().join(component)
        }
@@ -661,7 +658,7 @@ mod tests {
            .build();

        assert_eq!(
-            SearchPath::custom_stdlib(&db, stdlib.parent().unwrap().to_path_buf())
+            SearchPath::custom_stdlib(&db, stdlib.parent().unwrap())
                .unwrap()
                .to_module_path()
                .with_py_extension(),
@@ -669,7 +666,7 @@ mod tests {
        );

        assert_eq!(
-            &SearchPath::custom_stdlib(&db, stdlib.parent().unwrap().to_path_buf())
+            &SearchPath::custom_stdlib(&db, stdlib.parent().unwrap())
                .unwrap()
                .join("foo")
                .with_pyi_extension(),
@@ -780,7 +777,7 @@ mod tests {
        let TestCase { db, stdlib, .. } = TestCaseBuilder::new()
            .with_custom_typeshed(MockedTypeshed::default())
            .build();
-        SearchPath::custom_stdlib(&db, stdlib.parent().unwrap().to_path_buf())
+        SearchPath::custom_stdlib(&db, stdlib.parent().unwrap())
            .unwrap()
            .to_module_path()
            .push("bar.py");
@@ -792,7 +789,7 @@ mod tests {
        let TestCase { db, stdlib, .. } = TestCaseBuilder::new()
            .with_custom_typeshed(MockedTypeshed::default())
            .build();
-        SearchPath::custom_stdlib(&db, stdlib.parent().unwrap().to_path_buf())
+        SearchPath::custom_stdlib(&db, stdlib.parent().unwrap())
            .unwrap()
            .to_module_path()
            .push("bar.rs");
@@ -824,7 +821,7 @@ mod tests {
            .with_custom_typeshed(MockedTypeshed::default())
            .build();

-        let root = SearchPath::custom_stdlib(&db, stdlib.parent().unwrap().to_path_buf()).unwrap();
+        let root = SearchPath::custom_stdlib(&db, stdlib.parent().unwrap()).unwrap();

        // Must have a `.pyi` extension or no extension:
        let bad_absolute_path = SystemPath::new("foo/stdlib/x.py");
@@ -872,8 +869,7 @@ mod tests {
            .with_custom_typeshed(typeshed)
            .with_target_version(target_version)
            .build();
-        let stdlib =
-            SearchPath::custom_stdlib(&db, stdlib.parent().unwrap().to_path_buf()).unwrap();
+        let stdlib = SearchPath::custom_stdlib(&db, stdlib.parent().unwrap()).unwrap();
        (db, stdlib)
    }

@@ -898,7 +894,7 @@ mod tests {
        };

        let (db, stdlib_path) = py38_typeshed_test_case(TYPESHED);
-        let resolver = ResolverState::new(&db, PythonVersion::PY38);
+        let resolver = ResolverContext::new(&db, PythonVersion::PY38);

        let asyncio_regular_package = stdlib_path.join("asyncio");
        assert!(asyncio_regular_package.is_directory(&resolver));
@@ -926,7 +922,7 @@ mod tests {
        };

        let (db, stdlib_path) = py38_typeshed_test_case(TYPESHED);
-        let resolver = ResolverState::new(&db, PythonVersion::PY38);
+        let resolver = ResolverContext::new(&db, PythonVersion::PY38);

        let xml_namespace_package = stdlib_path.join("xml");
        assert!(xml_namespace_package.is_directory(&resolver));
@@ -948,7 +944,7 @@ mod tests {
        };

        let (db, stdlib_path) = py38_typeshed_test_case(TYPESHED);
-        let resolver = ResolverState::new(&db, PythonVersion::PY38);
+        let resolver = ResolverContext::new(&db, PythonVersion::PY38);

        let functools_module = stdlib_path.join("functools.pyi");
        assert!(functools_module.to_file(&resolver).is_some());
@@ -964,7 +960,7 @@ mod tests {
        };

        let (db, stdlib_path) = py38_typeshed_test_case(TYPESHED);
-        let resolver = ResolverState::new(&db, PythonVersion::PY38);
+        let resolver = ResolverContext::new(&db, PythonVersion::PY38);

        let collections_regular_package = stdlib_path.join("collections");
        assert_eq!(collections_regular_package.to_file(&resolver), None);
@@ -980,7 +976,7 @@ mod tests {
        };

        let (db, stdlib_path) = py38_typeshed_test_case(TYPESHED);
-        let resolver = ResolverState::new(&db, PythonVersion::PY38);
+        let resolver = ResolverContext::new(&db, PythonVersion::PY38);

        let importlib_namespace_package = stdlib_path.join("importlib");
        assert_eq!(importlib_namespace_package.to_file(&resolver), None);
@@ -1001,7 +997,7 @@ mod tests {
        };

        let (db, stdlib_path) = py38_typeshed_test_case(TYPESHED);
-        let resolver = ResolverState::new(&db, PythonVersion::PY38);
+        let resolver = ResolverContext::new(&db, PythonVersion::PY38);

        let non_existent = stdlib_path.join("doesnt_even_exist");
        assert_eq!(non_existent.to_file(&resolver), None);
@@ -1029,7 +1025,7 @@ mod tests {
        };

        let (db, stdlib_path) = py39_typeshed_test_case(TYPESHED);
-        let resolver = ResolverState::new(&db, PythonVersion::PY39);
+        let resolver = ResolverContext::new(&db, PythonVersion::PY39);

        // Since we've set the target version to Py39,
        // `collections` should now exist as a directory, according to VERSIONS...
@@ -1058,7 +1054,7 @@ mod tests {
        };

        let (db, stdlib_path) = py39_typeshed_test_case(TYPESHED);
-        let resolver = ResolverState::new(&db, PythonVersion::PY39);
+        let resolver = ResolverContext::new(&db, PythonVersion::PY39);

        // The `importlib` directory now also exists
        let importlib_namespace_package = stdlib_path.join("importlib");
@@ -1082,7 +1078,7 @@ mod tests {
        };

        let (db, stdlib_path) = py39_typeshed_test_case(TYPESHED);
-        let resolver = ResolverState::new(&db, PythonVersion::PY39);
+        let resolver = ResolverContext::new(&db, PythonVersion::PY39);

        // The `xml` package no longer exists on py39:
        let xml_namespace_package = stdlib_path.join("xml");
--- a/crates/red_knot_python_semantic/src/module_resolver/resolver.rs
+++ b/crates/red_knot_python_semantic/src/module_resolver/resolver.rs
@@ -1,18 +1,19 @@
+use rustc_hash::{FxBuildHasher, FxHashSet};
 use std::borrow::Cow;
 use std::iter::FusedIterator;
-
-use rustc_hash::{FxBuildHasher, FxHashSet};
+use std::ops::Deref;

 use ruff_db::files::{File, FilePath, FileRootKind};
-use ruff_db::system::{DirectoryEntry, SystemPath, SystemPathBuf};
-use ruff_db::vendored::VendoredPath;
+use ruff_db::system::{DirectoryEntry, System, SystemPath, SystemPathBuf};
+use ruff_db::vendored::{VendoredFileSystem, VendoredPath};

 use super::module::{Module, ModuleKind};
 use super::path::{ModulePath, SearchPath, SearchPathValidationError};
-use super::state::ResolverState;
 use crate::db::Db;
 use crate::module_name::ModuleName;
-use crate::{Program, PythonVersion, SearchPathSettings};
+use crate::module_resolver::typeshed::{vendored_typeshed_versions, TypeshedVersions};
+use crate::site_packages::VirtualEnvironment;
+use crate::{Program, PythonVersion, SearchPathSettings, SitePackages};

 /// Resolves a module name to a module.
 pub fn resolve_module(db: &dyn Db, module_name: ModuleName) -> Option<Module> {
@@ -40,7 +41,7 @@ pub(crate) fn resolve_module_query<'db>(

    let module = Module::new(name.clone(), kind, search_path, module_file);

-    tracing::debug!(
+    tracing::trace!(
        "Resolved module '{name}' to '{path}'.",
        path = module_file.path(db)
    );
@@ -84,9 +85,7 @@ pub(crate) fn file_to_module(db: &dyn Db, file: File) -> Option<Module> {
        FilePath::SystemVirtual(_) => return None,
    };

-    let settings = module_resolution_settings(db);
-
-    let mut search_paths = settings.search_paths(db);
+    let mut search_paths = search_paths(db);

    let module_name = loop {
        let candidate = search_paths.next()?;
@@ -119,106 +118,182 @@ pub(crate) fn file_to_module(db: &dyn Db, file: File) -> Option<Module> {
    }
 }

-/// Validate and normalize the raw settings given by the user
-/// into settings we can use for module resolution
-///
-/// This method also implements the typing spec's [module resolution order].
-///
-/// [module resolution order]: https://typing.readthedocs.io/en/latest/spec/distributing.html#import-resolution-ordering
-fn try_resolve_module_resolution_settings(
-    db: &dyn Db,
-) -> Result<ModuleResolutionSettings, SearchPathValidationError> {
-    let program = Program::get(db.upcast());
-
-    let SearchPathSettings {
-        extra_paths,
-        src_root,
-        custom_typeshed,
-        site_packages,
-    } = program.search_paths(db.upcast());
-
-    if !extra_paths.is_empty() {
-        tracing::info!("Extra search paths: {extra_paths:?}");
-    }
-
-    if let Some(custom_typeshed) = custom_typeshed {
-        tracing::info!("Custom typeshed directory: {custom_typeshed}");
-    }
-
-    let system = db.system();
-    let files = db.files();
-
-    let mut static_search_paths = vec![];
-
-    for path in extra_paths {
-        let search_path = SearchPath::extra(system, path.clone())?;
-        files.try_add_root(
-            db.upcast(),
-            search_path.as_system_path().unwrap(),
-            FileRootKind::LibrarySearchPath,
-        );
-        static_search_paths.push(search_path);
-    }
-
-    static_search_paths.push(SearchPath::first_party(system, src_root.clone())?);
-
-    static_search_paths.push(if let Some(custom_typeshed) = custom_typeshed.as_ref() {
-        let search_path = SearchPath::custom_stdlib(db, custom_typeshed.clone())?;
-        files.try_add_root(
-            db.upcast(),
-            search_path.as_system_path().unwrap(),
-            FileRootKind::LibrarySearchPath,
-        );
-        search_path
-    } else {
-        SearchPath::vendored_stdlib()
-    });
-
-    let mut site_packages_paths: Vec<_> = Vec::with_capacity(site_packages.len());
-
-    for path in site_packages {
-        let search_path = SearchPath::site_packages(system, path.to_path_buf())?;
-        files.try_add_root(
-            db.upcast(),
-            search_path.as_system_path().unwrap(),
-            FileRootKind::LibrarySearchPath,
-        );
-        site_packages_paths.push(search_path);
-    }
-
-    // TODO vendor typeshed's third-party stubs as well as the stdlib and fallback to them as a final step
-
-    let target_version = program.target_version(db.upcast());
-    tracing::info!("Target version: {target_version}");
-
-    // Filter out module resolution paths that point to the same directory on disk (the same invariant maintained by [`sys.path` at runtime]).
-    // (Paths may, however, *overlap* -- e.g. you could have both `src/` and `src/foo`
-    // as module resolution paths simultaneously.)
-    //
-    // [`sys.path` at runtime]: https://docs.python.org/3/library/site.html#module-site
-    // This code doesn't use an `IndexSet` because the key is the system path and not the search root.
-    let mut seen_paths =
-        FxHashSet::with_capacity_and_hasher(static_search_paths.len(), FxBuildHasher);
-
-    static_search_paths.retain(|path| {
-        if let Some(path) = path.as_system_path() {
-            seen_paths.insert(path.to_path_buf())
-        } else {
-            true
-        }
-    });
-
-    Ok(ModuleResolutionSettings {
-        target_version,
-        static_search_paths,
-        site_packages_paths,
-    })
+pub(crate) fn search_paths(db: &dyn Db) -> SearchPathIterator {
+    Program::get(db).search_paths(db).iter(db)
 }

-#[salsa::tracked(return_ref)]
-pub(crate) fn module_resolution_settings(db: &dyn Db) -> ModuleResolutionSettings {
-    // TODO proper error handling if this returns an error:
-    try_resolve_module_resolution_settings(db).unwrap()
+#[derive(Debug, PartialEq, Eq)]
+pub(crate) struct SearchPaths {
+    /// Search paths that have been statically determined purely from reading Ruff's configuration settings.
+    /// These shouldn't ever change unless the config settings themselves change.
+    static_paths: Vec<SearchPath>,
+
+    /// site-packages paths are not included in the above field:
+    /// if there are multiple site-packages paths, editable installations can appear
+    /// *between* the site-packages paths on `sys.path` at runtime.
+    /// That means we can't know where a second or third `site-packages` path should sit
+    /// in terms of module-resolution priority until we've discovered the editable installs
+    /// for the first `site-packages` path
+    site_packages: Vec<SearchPath>,
+
+    typeshed_versions: ResolvedTypeshedVersions,
+}
+
+impl SearchPaths {
+    /// Validate and normalize the raw settings given by the user
+    /// into settings we can use for module resolution
+    ///
+    /// This method also implements the typing spec's [module resolution order].
+    ///
+    /// [module resolution order]: https://typing.readthedocs.io/en/latest/spec/distributing.html#import-resolution-ordering
+    pub(crate) fn from_settings(
+        db: &dyn Db,
+        settings: &SearchPathSettings,
+    ) -> Result<Self, SearchPathValidationError> {
+        fn canonicalize(path: &SystemPath, system: &dyn System) -> SystemPathBuf {
+            system
+                .canonicalize_path(path)
+                .unwrap_or_else(|_| path.to_path_buf())
+        }
+
+        let SearchPathSettings {
+            extra_paths,
+            src_root,
+            custom_typeshed,
+            site_packages: site_packages_paths,
+        } = settings;
+
+        let system = db.system();
+        let files = db.files();
+
+        let mut static_paths = vec![];
+
+        for path in extra_paths {
+            let path = canonicalize(path, system);
+            files.try_add_root(db.upcast(), &path, FileRootKind::LibrarySearchPath);
+            tracing::debug!("Adding extra search-path '{path}'");
+
+            static_paths.push(SearchPath::extra(system, path)?);
+        }
+
+        tracing::debug!("Adding first-party search path '{src_root}'");
+        static_paths.push(SearchPath::first_party(system, src_root.to_path_buf())?);
+
+        let (typeshed_versions, stdlib_path) = if let Some(custom_typeshed) = custom_typeshed {
+            let custom_typeshed = canonicalize(custom_typeshed, system);
+            tracing::debug!("Adding custom-stdlib search path '{custom_typeshed}'");
+
+            files.try_add_root(
+                db.upcast(),
+                &custom_typeshed,
+                FileRootKind::LibrarySearchPath,
+            );
+
+            let versions_path = custom_typeshed.join("stdlib/VERSIONS");
+
+            let versions_content = system.read_to_string(&versions_path).map_err(|error| {
+                SearchPathValidationError::FailedToReadVersionsFile {
+                    path: versions_path,
+                    error,
+                }
+            })?;
+
+            let parsed: TypeshedVersions = versions_content.parse()?;
+
+            let search_path = SearchPath::custom_stdlib(db, &custom_typeshed)?;
+
+            (ResolvedTypeshedVersions::Custom(parsed), search_path)
+        } else {
+            tracing::debug!("Using vendored stdlib");
+            (
+                ResolvedTypeshedVersions::Vendored(vendored_typeshed_versions()),
+                SearchPath::vendored_stdlib(),
+            )
+        };
+
+        static_paths.push(stdlib_path);
+
+        let site_packages_paths = match site_packages_paths {
+            SitePackages::Derived { venv_path } => VirtualEnvironment::new(venv_path, system)
+                .and_then(|venv| venv.site_packages_directories(system))?,
+            SitePackages::Known(paths) => paths
+                .iter()
+                .map(|path| canonicalize(path, system))
+                .collect(),
+        };
+
+        let mut site_packages: Vec<_> = Vec::with_capacity(site_packages_paths.len());
+
+        for path in site_packages_paths {
+            tracing::debug!("Adding site-packages search path '{path}'");
+            files.try_add_root(db.upcast(), &path, FileRootKind::LibrarySearchPath);
+            site_packages.push(SearchPath::site_packages(system, path)?);
+        }
+
+        // TODO vendor typeshed's third-party stubs as well as the stdlib and fallback to them as a final step
+
+        // Filter out module resolution paths that point to the same directory on disk (the same invariant maintained by [`sys.path` at runtime]).
+        // (Paths may, however, *overlap* -- e.g. you could have both `src/` and `src/foo`
+        // as module resolution paths simultaneously.)
+        //
+        // This code doesn't use an `IndexSet` because the key is the system path and not the search root.
+        //
+        // [`sys.path` at runtime]: https://docs.python.org/3/library/site.html#module-site
+        let mut seen_paths = FxHashSet::with_capacity_and_hasher(static_paths.len(), FxBuildHasher);
+
+        static_paths.retain(|path| {
+            if let Some(path) = path.as_system_path() {
+                seen_paths.insert(path.to_path_buf())
+            } else {
+                true
+            }
+        });
+
+        Ok(SearchPaths {
+            static_paths,
+            site_packages,
+            typeshed_versions,
+        })
+    }
+
+    pub(super) fn iter<'a>(&'a self, db: &'a dyn Db) -> SearchPathIterator<'a> {
+        SearchPathIterator {
+            db,
+            static_paths: self.static_paths.iter(),
+            dynamic_paths: None,
+        }
+    }
+
+    pub(crate) fn custom_stdlib(&self) -> Option<&SystemPath> {
+        self.static_paths.iter().find_map(|search_path| {
+            if search_path.is_standard_library() {
+                search_path.as_system_path()
+            } else {
+                None
+            }
+        })
+    }
+
+    pub(super) fn typeshed_versions(&self) -> &TypeshedVersions {
+        &self.typeshed_versions
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+enum ResolvedTypeshedVersions {
+    Vendored(&'static TypeshedVersions),
+    Custom(TypeshedVersions),
+}
+
+impl Deref for ResolvedTypeshedVersions {
+    type Target = TypeshedVersions;
+
+    fn deref(&self) -> &Self::Target {
+        match self {
+            ResolvedTypeshedVersions::Vendored(versions) => versions,
+            ResolvedTypeshedVersions::Custom(versions) => versions,
+        }
+    }
 }

 /// Collect all dynamic search paths. For each `site-packages` path:
@@ -231,19 +306,21 @@ pub(crate) fn module_resolution_settings(db: &dyn Db) -> ModuleResolutionSetting
 /// module-resolution priority.
 #[salsa::tracked(return_ref)]
 pub(crate) fn dynamic_resolution_paths(db: &dyn Db) -> Vec<SearchPath> {
-    let ModuleResolutionSettings {
-        target_version: _,
-        static_search_paths,
-        site_packages_paths,
-    } = module_resolution_settings(db);
+    tracing::debug!("Resolving dynamic module resolution paths");
+
+    let SearchPaths {
+        static_paths,
+        site_packages,
+        typeshed_versions: _,
+    } = Program::get(db).search_paths(db);

    let mut dynamic_paths = Vec::new();

-    if site_packages_paths.is_empty() {
+    if site_packages.is_empty() {
        return dynamic_paths;
    }

-    let mut existing_paths: FxHashSet<_> = static_search_paths
+    let mut existing_paths: FxHashSet<_> = static_paths
        .iter()
        .filter_map(|path| path.as_system_path())
        .map(Cow::Borrowed)
@@ -252,7 +329,7 @@ pub(crate) fn dynamic_resolution_paths(db: &dyn Db) -> Vec<SearchPath> {
    let files = db.files();
    let system = db.system();

-    for site_packages_search_path in site_packages_paths {
+    for site_packages_search_path in site_packages {
        let site_packages_dir = site_packages_search_path
            .as_system_path()
            .expect("Expected site package path to be a system path");
@@ -299,9 +376,17 @@ pub(crate) fn dynamic_resolution_paths(db: &dyn Db) -> Vec<SearchPath> {
        let installations = all_pth_files.iter().flat_map(PthFile::items);

        for installation in installations {
+            let installation = system
+                .canonicalize_path(&installation)
+                .unwrap_or(installation);
+
            if existing_paths.insert(Cow::Owned(installation.clone())) {
-                match SearchPath::editable(system, installation) {
+                match SearchPath::editable(system, installation.clone()) {
                    Ok(search_path) => {
+                        tracing::debug!(
+                            "Adding editable installation to module resolution path {path}",
+                            path = installation
+                        );
                        dynamic_paths.push(search_path);
                    }

@@ -448,38 +533,6 @@ impl<'db> Iterator for PthFileIterator<'db> {
    }
 }

-/// Validated and normalized module-resolution settings.
-#[derive(Clone, Debug, PartialEq, Eq)]
-pub(crate) struct ModuleResolutionSettings {
-    target_version: PythonVersion,
-
-    /// Search paths that have been statically determined purely from reading Ruff's configuration settings.
-    /// These shouldn't ever change unless the config settings themselves change.
-    static_search_paths: Vec<SearchPath>,
-
-    /// site-packages paths are not included in the above field:
-    /// if there are multiple site-packages paths, editable installations can appear
-    /// *between* the site-packages paths on `sys.path` at runtime.
-    /// That means we can't know where a second or third `site-packages` path should sit
-    /// in terms of module-resolution priority until we've discovered the editable installs
-    /// for the first `site-packages` path
-    site_packages_paths: Vec<SearchPath>,
-}
-
-impl ModuleResolutionSettings {
-    fn target_version(&self) -> PythonVersion {
-        self.target_version
-    }
-
-    pub(crate) fn search_paths<'db>(&'db self, db: &'db dyn Db) -> SearchPathIterator<'db> {
-        SearchPathIterator {
-            db,
-            static_paths: self.static_search_paths.iter(),
-            dynamic_paths: None,
-        }
-    }
-}
-
 /// A thin wrapper around `ModuleName` to make it a Salsa ingredient.
 ///
 /// This is needed because Salsa requires that all query arguments are salsa ingredients.
@@ -492,13 +545,13 @@ struct ModuleNameIngredient<'db> {
 /// Given a module name and a list of search paths in which to lookup modules,
 /// attempt to resolve the module name
 fn resolve_name(db: &dyn Db, name: &ModuleName) -> Option<(SearchPath, File, ModuleKind)> {
-    let resolver_settings = module_resolution_settings(db);
-    let target_version = resolver_settings.target_version();
-    let resolver_state = ResolverState::new(db, target_version);
+    let program = Program::get(db);
+    let target_version = program.target_version(db);
+    let resolver_state = ResolverContext::new(db, target_version);
    let is_builtin_module =
        ruff_python_stdlib::sys::is_builtin_module(target_version.minor, name.as_str());

-    for search_path in resolver_settings.search_paths(db) {
+    for search_path in search_paths(db) {
        // When a builtin module is imported, standard module resolution is bypassed:
        // the module name always resolves to the stdlib module,
        // even if there's a module of the same name in the first-party root
@@ -557,7 +610,7 @@ fn resolve_name(db: &dyn Db, name: &ModuleName) -> Option<(SearchPath, File, Mod
 fn resolve_package<'a, 'db, I>(
    module_search_path: &SearchPath,
    components: I,
-    resolver_state: &ResolverState<'db>,
+    resolver_state: &ResolverContext<'db>,
 ) -> Result<ResolvedPackage, PackageKind>
 where
    I: Iterator<Item = &'a str>,
@@ -639,6 +692,21 @@ impl PackageKind {
    }
 }

+pub(super) struct ResolverContext<'db> {
+    pub(super) db: &'db dyn Db,
+    pub(super) target_version: PythonVersion,
+}
+
+impl<'db> ResolverContext<'db> {
+    pub(super) fn new(db: &'db dyn Db, target_version: PythonVersion) -> Self {
+        Self { db, target_version }
+    }
+
+    pub(super) fn vendored(&self) -> &VendoredFileSystem {
+        self.db.vendored()
+    }
+}
+
 #[cfg(test)]
 mod tests {
    use ruff_db::files::{system_path_to_file, File, FilePath};
@@ -652,6 +720,8 @@ mod tests {
    use crate::module_name::ModuleName;
    use crate::module_resolver::module::ModuleKind;
    use crate::module_resolver::testing::{FileSpec, MockedTypeshed, TestCase, TestCaseBuilder};
+    use crate::ProgramSettings;
+    use crate::PythonVersion;

    use super::*;

@@ -791,7 +861,7 @@ mod tests {
                "Search path for {module_name} was unexpectedly {search_path:?}"
            );
            assert!(
-                search_path.is_stdlib_search_path(),
+                search_path.is_standard_library(),
                "Expected a stdlib search path, but got {search_path:?}"
            );
        }
@@ -887,7 +957,7 @@ mod tests {
                "Search path for {module_name} was unexpectedly {search_path:?}"
            );
            assert!(
-                search_path.is_stdlib_search_path(),
+                search_path.is_standard_library(),
                "Expected a stdlib search path, but got {search_path:?}"
            );
        }
@@ -1202,14 +1272,19 @@ mod tests {
        std::fs::write(foo.as_std_path(), "")?;
        std::os::unix::fs::symlink(foo.as_std_path(), bar.as_std_path())?;

-        let search_paths = SearchPathSettings {
-            extra_paths: vec![],
-            src_root: src.clone(),
-            custom_typeshed: Some(custom_typeshed.clone()),
-            site_packages: vec![site_packages],
-        };
-
-        Program::new(&db, PythonVersion::PY38, search_paths);
+        Program::from_settings(
+            &db,
+            &ProgramSettings {
+                target_version: PythonVersion::PY38,
+                search_paths: SearchPathSettings {
+                    extra_paths: vec![],
+                    src_root: src.clone(),
+                    custom_typeshed: Some(custom_typeshed.clone()),
+                    site_packages: SitePackages::Known(vec![site_packages]),
+                },
+            },
+        )
+        .context("Invalid program settings")?;

        let foo_module = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
        let bar_module = resolve_module(&db, ModuleName::new_static("bar").unwrap()).unwrap();
@@ -1673,8 +1748,7 @@ not_a_directory
            .with_site_packages_files(&[("_foo.pth", "/src")])
            .build();

-        let search_paths: Vec<&SearchPath> =
-            module_resolution_settings(&db).search_paths(&db).collect();
+        let search_paths: Vec<&SearchPath> = search_paths(&db).collect();

        assert!(search_paths.contains(
            &&SearchPath::first_party(db.system(), SystemPathBuf::from("/src")).unwrap()
@@ -1703,16 +1777,22 @@ not_a_directory
        ])
        .unwrap();

-        Program::new(
+        Program::from_settings(
            &db,
-            PythonVersion::default(),
-            SearchPathSettings {
-                extra_paths: vec![],
-                src_root: SystemPathBuf::from("/src"),
-                custom_typeshed: None,
-                site_packages: vec![venv_site_packages, system_site_packages],
+            &ProgramSettings {
+                target_version: PythonVersion::default(),
+                search_paths: SearchPathSettings {
+                    extra_paths: vec![],
+                    src_root: SystemPathBuf::from("/src"),
+                    custom_typeshed: None,
+                    site_packages: SitePackages::Known(vec![
+                        venv_site_packages,
+                        system_site_packages,
+                    ]),
+                },
            },
-        );
+        )
+        .expect("Valid program settings");

        // The editable installs discovered from the `.pth` file in the first `site-packages` directory
        // take precedence over the second `site-packages` directory...
--- a/crates/red_knot_python_semantic/src/module_resolver/state.rs
+++ b/crates/red_knot_python_semantic/src/module_resolver/state.rs
@@ -1,25 +0,0 @@
-use ruff_db::vendored::VendoredFileSystem;
-
-use super::typeshed::LazyTypeshedVersions;
-use crate::db::Db;
-use crate::python_version::PythonVersion;
-
-pub(crate) struct ResolverState<'db> {
-    pub(crate) db: &'db dyn Db,
-    pub(crate) typeshed_versions: LazyTypeshedVersions<'db>,
-    pub(crate) target_version: PythonVersion,
-}
-
-impl<'db> ResolverState<'db> {
-    pub(crate) fn new(db: &'db dyn Db, target_version: PythonVersion) -> Self {
-        Self {
-            db,
-            typeshed_versions: LazyTypeshedVersions::new(),
-            target_version,
-        }
-    }
-
-    pub(crate) fn vendored(&self) -> &VendoredFileSystem {
-        self.db.vendored()
-    }
-}
--- a/crates/red_knot_python_semantic/src/module_resolver/testing.rs
+++ b/crates/red_knot_python_semantic/src/module_resolver/testing.rs
@@ -4,6 +4,7 @@ use ruff_db::vendored::VendoredPathBuf;
 use crate::db::tests::TestDb;
 use crate::program::{Program, SearchPathSettings};
 use crate::python_version::PythonVersion;
+use crate::{ProgramSettings, SitePackages};

 /// A test case for the module resolver.
 ///
@@ -178,6 +179,7 @@ impl TestCaseBuilder<UnspecifiedTypeshed> {
            first_party_files,
            site_packages_files,
        } = self;
+
        TestCaseBuilder {
            typeshed_option: typeshed,
            target_version,
@@ -194,6 +196,7 @@ impl TestCaseBuilder<UnspecifiedTypeshed> {
            site_packages,
            target_version,
        } = self.with_custom_typeshed(MockedTypeshed::default()).build();
+
        TestCase {
            db,
            src,
@@ -220,16 +223,19 @@ impl TestCaseBuilder<MockedTypeshed> {
        let src = Self::write_mock_directory(&mut db, "/src", first_party_files);
        let typeshed = Self::build_typeshed_mock(&mut db, &typeshed_option);

-        Program::new(
+        Program::from_settings(
            &db,
-            target_version,
-            SearchPathSettings {
-                extra_paths: vec![],
-                src_root: src.clone(),
-                custom_typeshed: Some(typeshed.clone()),
-                site_packages: vec![site_packages.clone()],
+            &ProgramSettings {
+                target_version,
+                search_paths: SearchPathSettings {
+                    extra_paths: vec![],
+                    src_root: src.clone(),
+                    custom_typeshed: Some(typeshed.clone()),
+                    site_packages: SitePackages::Known(vec![site_packages.clone()]),
+                },
            },
-        );
+        )
+        .expect("Valid program settings");

        TestCase {
            db,
@@ -273,16 +279,17 @@ impl TestCaseBuilder<VendoredTypeshed> {
            Self::write_mock_directory(&mut db, "/site-packages", site_packages_files);
        let src = Self::write_mock_directory(&mut db, "/src", first_party_files);

-        Program::new(
+        Program::from_settings(
            &db,
-            target_version,
-            SearchPathSettings {
-                extra_paths: vec![],
-                src_root: src.clone(),
-                custom_typeshed: None,
-                site_packages: vec![site_packages.clone()],
+            &ProgramSettings {
+                target_version,
+                search_paths: SearchPathSettings {
+                    site_packages: SitePackages::Known(vec![site_packages.clone()]),
+                    ..SearchPathSettings::new(src.clone())
+                },
            },
-        );
+        )
+        .expect("Valid search path settings");

        TestCase {
            db,
--- a/crates/red_knot_python_semantic/src/module_resolver/typeshed/mod.rs
+++ b/crates/red_knot_python_semantic/src/module_resolver/typeshed/mod.rs
@@ -1,6 +1,6 @@
 pub use self::vendored::vendored_typeshed_stubs;
 pub(super) use self::versions::{
-    parse_typeshed_versions, LazyTypeshedVersions, TypeshedVersionsParseError,
+    typeshed_versions, vendored_typeshed_versions, TypeshedVersions, TypeshedVersionsParseError,
    TypeshedVersionsQueryResult,
 };

--- a/crates/red_knot_python_semantic/src/module_resolver/typeshed/versions.rs
+++ b/crates/red_knot_python_semantic/src/module_resolver/typeshed/versions.rs
@@ -1,4 +1,3 @@
-use std::cell::OnceCell;
 use std::collections::BTreeMap;
 use std::fmt;
 use std::num::{NonZeroU16, NonZeroUsize};
@@ -6,78 +5,12 @@ use std::ops::{RangeFrom, RangeInclusive};
 use std::str::FromStr;

 use once_cell::sync::Lazy;
-use ruff_db::system::SystemPath;
 use rustc_hash::FxHashMap;

-use ruff_db::files::{system_path_to_file, File};
-
 use super::vendored::vendored_typeshed_stubs;
 use crate::db::Db;
 use crate::module_name::ModuleName;
-use crate::python_version::PythonVersion;
-
-#[derive(Debug)]
-pub(crate) struct LazyTypeshedVersions<'db>(OnceCell<&'db TypeshedVersions>);
-
-impl<'db> LazyTypeshedVersions<'db> {
-    #[must_use]
-    pub(crate) fn new() -> Self {
-        Self(OnceCell::new())
-    }
-
-    /// Query whether a module exists at runtime in the stdlib on a certain Python version.
-    ///
-    /// Simply probing whether a file exists in typeshed is insufficient for this question,
-    /// as a module in the stdlib may have been added in Python 3.10, but the typeshed stub
-    /// will still be available (either in a custom typeshed dir or in our vendored copy)
-    /// even if the user specified Python 3.8 as the target version.
-    ///
-    /// For top-level modules and packages, the VERSIONS file can always provide an unambiguous answer
-    /// as to whether the module exists on the specified target version. However, VERSIONS does not
-    /// provide comprehensive information on all submodules, meaning that this method sometimes
-    /// returns [`TypeshedVersionsQueryResult::MaybeExists`].
-    /// See [`TypeshedVersionsQueryResult`] for more details.
-    #[must_use]
-    pub(crate) fn query_module(
-        &self,
-        db: &'db dyn Db,
-        module: &ModuleName,
-        stdlib_root: Option<&SystemPath>,
-        target_version: PythonVersion,
-    ) -> TypeshedVersionsQueryResult {
-        let versions = self.0.get_or_init(|| {
-            let versions_path = if let Some(system_path) = stdlib_root {
-                system_path.join("VERSIONS")
-            } else {
-                return &VENDORED_VERSIONS;
-            };
-            let Ok(versions_file) = system_path_to_file(db.upcast(), &versions_path) else {
-                todo!(
-                    "Still need to figure out how to handle VERSIONS files being deleted \
-                    from custom typeshed directories! Expected a file to exist at {versions_path}"
-                )
-            };
-            // TODO(Alex/Micha): If VERSIONS is invalid,
-            // this should invalidate not just the specific module resolution we're currently attempting,
-            // but all type inference that depends on any standard-library types.
-            // Unwrapping here is not correct...
-            parse_typeshed_versions(db, versions_file).as_ref().unwrap()
-        });
-        versions.query_module(module, target_version)
-    }
-}
-
-#[salsa::tracked(return_ref)]
-pub(crate) fn parse_typeshed_versions(
-    db: &dyn Db,
-    versions_file: File,
-) -> Result<TypeshedVersions, TypeshedVersionsParseError> {
-    // TODO: Handle IO errors
-    let file_content = versions_file
-        .read_to_string(db.upcast())
-        .unwrap_or_default();
-    file_content.parse()
-}
+use crate::{Program, PythonVersion};

 static VENDORED_VERSIONS: Lazy<TypeshedVersions> = Lazy::new(|| {
    TypeshedVersions::from_str(
@@ -88,6 +21,14 @@ static VENDORED_VERSIONS: Lazy<TypeshedVersions> = Lazy::new(|| {
    .unwrap()
 });

+pub(crate) fn vendored_typeshed_versions() -> &'static TypeshedVersions {
+    &VENDORED_VERSIONS
+}
+
+pub(crate) fn typeshed_versions(db: &dyn Db) -> &TypeshedVersions {
+    Program::get(db).search_paths(db).typeshed_versions()
+}
+
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub(crate) struct TypeshedVersionsParseError {
    line_number: Option<NonZeroU16>,
@@ -174,7 +115,7 @@ impl TypeshedVersions {
    }

    #[must_use]
-    fn query_module(
+    pub(in crate::module_resolver) fn query_module(
        &self,
        module: &ModuleName,
        target_version: PythonVersion,
@@ -204,7 +145,7 @@ impl TypeshedVersions {
    }
 }

-/// Possible answers [`LazyTypeshedVersions::query_module()`] could give to the question:
+/// Possible answers [`TypeshedVersions::query_module()`] could give to the question:
 /// "Does this module exist in the stdlib at runtime on a certain target version?"
 #[derive(Debug, Copy, PartialEq, Eq, Clone, Hash)]
 pub(crate) enum TypeshedVersionsQueryResult {
--- a/crates/red_knot_python_semantic/src/program.rs
+++ b/crates/red_knot_python_semantic/src/program.rs
@@ -1,32 +1,66 @@
 use crate::python_version::PythonVersion;
-use crate::Db;
-use ruff_db::system::SystemPathBuf;
+use anyhow::Context;
 use salsa::Durability;
+use salsa::Setter;
+
+use ruff_db::system::{SystemPath, SystemPathBuf};
+
+use crate::module_resolver::SearchPaths;
+use crate::Db;

 #[salsa::input(singleton)]
 pub struct Program {
    pub target_version: PythonVersion,

    #[return_ref]
-    pub search_paths: SearchPathSettings,
+    pub(crate) search_paths: SearchPaths,
 }

 impl Program {
-    pub fn from_settings(db: &dyn Db, settings: ProgramSettings) -> Self {
-        Program::builder(settings.target_version, settings.search_paths)
+    pub fn from_settings(db: &dyn Db, settings: &ProgramSettings) -> anyhow::Result<Self> {
+        let ProgramSettings {
+            target_version,
+            search_paths,
+        } = settings;
+
+        tracing::info!("Target version: Python {target_version}");
+
+        let search_paths = SearchPaths::from_settings(db, search_paths)
+            .with_context(|| "Invalid search path settings")?;
+
+        Ok(Program::builder(settings.target_version, search_paths)
            .durability(Durability::HIGH)
-            .new(db)
+            .new(db))
+    }
+
+    pub fn update_search_paths(
+        self,
+        db: &mut dyn Db,
+        search_path_settings: &SearchPathSettings,
+    ) -> anyhow::Result<()> {
+        let search_paths = SearchPaths::from_settings(db, search_path_settings)?;
+
+        if self.search_paths(db) != &search_paths {
+            tracing::debug!("Update search paths");
+            self.set_search_paths(db).to(search_paths);
+        }
+
+        Ok(())
+    }
+
+    pub fn custom_stdlib_search_path(self, db: &dyn Db) -> Option<&SystemPath> {
+        self.search_paths(db).custom_stdlib()
    }
 }

-#[derive(Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ProgramSettings {
    pub target_version: PythonVersion,
    pub search_paths: SearchPathSettings,
 }

 /// Configures the search paths for module resolution.
-#[derive(Eq, PartialEq, Debug, Clone, Default)]
+#[derive(Eq, PartialEq, Debug, Clone)]
 pub struct SearchPathSettings {
    /// List of user-provided paths that should take first priority in the module resolution.
    /// Examples in other type checkers are mypy's MYPYPATH environment variable,
@@ -42,5 +76,25 @@ pub struct SearchPathSettings {
    pub custom_typeshed: Option<SystemPathBuf>,

    /// The path to the user's `site-packages` directory, where third-party packages from ``PyPI`` are installed.
-    pub site_packages: Vec<SystemPathBuf>,
+    pub site_packages: SitePackages,
+}
+
+impl SearchPathSettings {
+    pub fn new(src_root: SystemPathBuf) -> Self {
+        Self {
+            src_root,
+            extra_paths: vec![],
+            custom_typeshed: None,
+            site_packages: SitePackages::Known(vec![]),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum SitePackages {
+    Derived {
+        venv_path: SystemPathBuf,
+    },
+    /// Resolved site packages paths
+    Known(Vec<SystemPathBuf>),
 }
--- a/crates/red_knot_python_semantic/src/semantic_index.rs
+++ b/crates/red_knot_python_semantic/src/semantic_index.rs
@@ -16,10 +16,9 @@ use crate::semantic_index::expression::Expression;
 use crate::semantic_index::symbol::{
    FileScopeId, NodeWithScopeKey, NodeWithScopeRef, Scope, ScopeId, ScopedSymbolId, SymbolTable,
 };
+use crate::semantic_index::use_def::UseDefMap;
 use crate::Db;

-pub(crate) use self::use_def::UseDefMap;
-
 pub mod ast_ids;
 mod builder;
 pub mod definition;
@@ -27,6 +26,8 @@ pub mod expression;
 pub mod symbol;
 mod use_def;

+pub(crate) use self::use_def::{DefinitionWithConstraints, DefinitionWithConstraintsIterator};
+
 type SymbolMap = hashbrown::HashMap<ScopedSymbolId, (), ()>;

 /// Returns the semantic index for `file`.
@@ -89,8 +90,6 @@ pub(crate) struct SemanticIndex<'db> {
    scopes: IndexVec<FileScopeId, Scope>,

    /// Map expressions to their corresponding scope.
-    /// We can't use [`ExpressionId`] here, because the challenge is how to get from
-    /// an [`ast::Expr`] to an [`ExpressionId`] (which requires knowing the scope).
    scopes_by_expression: FxHashMap<ExpressionNodeKey, FileScopeId>,

    /// Map from a node creating a definition to its definition.
@@ -118,7 +117,7 @@ pub(crate) struct SemanticIndex<'db> {
 impl<'db> SemanticIndex<'db> {
    /// Returns the symbol table for a specific scope.
    ///
-    /// Use the Salsa cached [`symbol_table`] query if you only need the
+    /// Use the Salsa cached [`symbol_table()`] query if you only need the
    /// symbol table for a single scope.
    pub(super) fn symbol_table(&self, scope_id: FileScopeId) -> Arc<SymbolTable> {
        self.symbol_tables[scope_id].clone()
@@ -126,7 +125,7 @@ impl<'db> SemanticIndex<'db> {

    /// Returns the use-def map for a specific scope.
    ///
-    /// Use the Salsa cached [`use_def_map`] query if you only need the
+    /// Use the Salsa cached [`use_def_map()`] query if you only need the
    /// use-def map for a single scope.
    pub(super) fn use_def_map(&self, scope_id: FileScopeId) -> Arc<UseDefMap> {
        self.use_def_maps[scope_id].clone()
@@ -155,6 +154,10 @@ impl<'db> SemanticIndex<'db> {
        &self.scopes[id]
    }

+    pub(crate) fn scope_ids(&self) -> impl Iterator<Item = ScopeId> {
+        self.scope_ids_by_scope.iter().copied()
+    }
+
    /// Returns the id of the parent scope.
    pub(crate) fn parent_scope_id(&self, scope_id: FileScopeId) -> Option<FileScopeId> {
        let scope = self.scope(scope_id);
@@ -309,14 +312,32 @@ mod tests {
    use ruff_db::parsed::parsed_module;
    use ruff_db::system::DbWithTestSystem;
    use ruff_python_ast as ast;
+    use ruff_text_size::{Ranged, TextRange};

    use crate::db::tests::TestDb;
-    use crate::semantic_index::ast_ids::HasScopedUseId;
-    use crate::semantic_index::definition::DefinitionKind;
-    use crate::semantic_index::symbol::{FileScopeId, Scope, ScopeKind, SymbolTable};
+    use crate::semantic_index::ast_ids::{HasScopedUseId, ScopedUseId};
+    use crate::semantic_index::definition::{Definition, DefinitionKind};
+    use crate::semantic_index::symbol::{
+        FileScopeId, Scope, ScopeKind, ScopedSymbolId, SymbolTable,
+    };
+    use crate::semantic_index::use_def::UseDefMap;
    use crate::semantic_index::{global_scope, semantic_index, symbol_table, use_def_map};
    use crate::Db;

+    impl UseDefMap<'_> {
+        fn first_public_definition(&self, symbol: ScopedSymbolId) -> Option<Definition<'_>> {
+            self.public_definitions(symbol)
+                .next()
+                .map(|constrained_definition| constrained_definition.definition)
+        }
+
+        fn first_use_definition(&self, use_id: ScopedUseId) -> Option<Definition<'_>> {
+            self.use_definitions(use_id)
+                .next()
+                .map(|constrained_definition| constrained_definition.definition)
+        }
+    }
+
    struct TestCase {
        db: TestDb,
        file: File,
@@ -375,9 +396,7 @@ mod tests {
        let foo = global_table.symbol_id_by_name("foo").unwrap();

        let use_def = use_def_map(&db, scope);
-        let [definition] = use_def.public_definitions(foo) else {
-            panic!("expected one definition");
-        };
+        let definition = use_def.first_public_definition(foo).unwrap();
        assert!(matches!(definition.node(&db), DefinitionKind::Import(_)));
    }

@@ -412,13 +431,13 @@ mod tests {
        );

        let use_def = use_def_map(&db, scope);
-        let [definition] = use_def.public_definitions(
-            global_table
-                .symbol_id_by_name("foo")
-                .expect("symbol to exist"),
-        ) else {
-            panic!("expected one definition");
-        };
+        let definition = use_def
+            .first_public_definition(
+                global_table
+                    .symbol_id_by_name("foo")
+                    .expect("symbol to exist"),
+            )
+            .unwrap();
        assert!(matches!(
            definition.node(&db),
            DefinitionKind::ImportFrom(_)
@@ -439,17 +458,34 @@ mod tests {
            "a symbol used but not defined in a scope should have only the used flag"
        );
        let use_def = use_def_map(&db, scope);
-        let [definition] =
-            use_def.public_definitions(global_table.symbol_id_by_name("x").expect("symbol exists"))
-        else {
-            panic!("expected one definition");
-        };
+        let definition = use_def
+            .first_public_definition(global_table.symbol_id_by_name("x").expect("symbol exists"))
+            .unwrap();
        assert!(matches!(
            definition.node(&db),
            DefinitionKind::Assignment(_)
        ));
    }

+    #[test]
+    fn augmented_assignment() {
+        let TestCase { db, file } = test_case("x += 1");
+        let scope = global_scope(&db, file);
+        let global_table = symbol_table(&db, scope);
+
+        assert_eq!(names(&global_table), vec!["x"]);
+
+        let use_def = use_def_map(&db, scope);
+        let definition = use_def
+            .first_public_definition(global_table.symbol_id_by_name("x").unwrap())
+            .unwrap();
+
+        assert!(matches!(
+            definition.node(&db),
+            DefinitionKind::AugmentedAssignment(_)
+        ));
+    }
+
    #[test]
    fn class_scope() {
        let TestCase { db, file } = test_case(
@@ -478,11 +514,9 @@ y = 2
        assert_eq!(names(&class_table), vec!["x"]);

        let use_def = index.use_def_map(class_scope_id);
-        let [definition] =
-            use_def.public_definitions(class_table.symbol_id_by_name("x").expect("symbol exists"))
-        else {
-            panic!("expected one definition");
-        };
+        let definition = use_def
+            .first_public_definition(class_table.symbol_id_by_name("x").expect("symbol exists"))
+            .unwrap();
        assert!(matches!(
            definition.node(&db),
            DefinitionKind::Assignment(_)
@@ -516,19 +550,311 @@ y = 2
        assert_eq!(names(&function_table), vec!["x"]);

        let use_def = index.use_def_map(function_scope_id);
-        let [definition] = use_def.public_definitions(
-            function_table
-                .symbol_id_by_name("x")
-                .expect("symbol exists"),
-        ) else {
-            panic!("expected one definition");
-        };
+        let definition = use_def
+            .first_public_definition(
+                function_table
+                    .symbol_id_by_name("x")
+                    .expect("symbol exists"),
+            )
+            .unwrap();
        assert!(matches!(
            definition.node(&db),
            DefinitionKind::Assignment(_)
        ));
    }

+    #[test]
+    fn function_parameter_symbols() {
+        let TestCase { db, file } = test_case(
+            "
+def f(a: str, /, b: str, c: int = 1, *args, d: int = 2, **kwargs):
+    pass
+",
+        );
+
+        let index = semantic_index(&db, file);
+        let global_table = symbol_table(&db, global_scope(&db, file));
+
+        assert_eq!(names(&global_table), vec!["str", "int", "f"]);
+
+        let [(function_scope_id, _function_scope)] = index
+            .child_scopes(FileScopeId::global())
+            .collect::<Vec<_>>()[..]
+        else {
+            panic!("Expected a function scope")
+        };
+
+        let function_table = index.symbol_table(function_scope_id);
+        assert_eq!(
+            names(&function_table),
+            vec!["a", "b", "c", "args", "d", "kwargs"],
+        );
+
+        let use_def = index.use_def_map(function_scope_id);
+        for name in ["a", "b", "c", "d"] {
+            let definition = use_def
+                .first_public_definition(
+                    function_table
+                        .symbol_id_by_name(name)
+                        .expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(
+                definition.node(&db),
+                DefinitionKind::ParameterWithDefault(_)
+            ));
+        }
+        for name in ["args", "kwargs"] {
+            let definition = use_def
+                .first_public_definition(
+                    function_table
+                        .symbol_id_by_name(name)
+                        .expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(definition.node(&db), DefinitionKind::Parameter(_)));
+        }
+    }
+
+    #[test]
+    fn lambda_parameter_symbols() {
+        let TestCase { db, file } = test_case("lambda a, b, c=1, *args, d=2, **kwargs: None");
+
+        let index = semantic_index(&db, file);
+        let global_table = symbol_table(&db, global_scope(&db, file));
+
+        assert!(names(&global_table).is_empty());
+
+        let [(lambda_scope_id, _lambda_scope)] = index
+            .child_scopes(FileScopeId::global())
+            .collect::<Vec<_>>()[..]
+        else {
+            panic!("Expected a lambda scope")
+        };
+
+        let lambda_table = index.symbol_table(lambda_scope_id);
+        assert_eq!(
+            names(&lambda_table),
+            vec!["a", "b", "c", "args", "d", "kwargs"],
+        );
+
+        let use_def = index.use_def_map(lambda_scope_id);
+        for name in ["a", "b", "c", "d"] {
+            let definition = use_def
+                .first_public_definition(
+                    lambda_table.symbol_id_by_name(name).expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(
+                definition.node(&db),
+                DefinitionKind::ParameterWithDefault(_)
+            ));
+        }
+        for name in ["args", "kwargs"] {
+            let definition = use_def
+                .first_public_definition(
+                    lambda_table.symbol_id_by_name(name).expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(definition.node(&db), DefinitionKind::Parameter(_)));
+        }
+    }
+
+    /// Test case to validate that the comprehension scope is correctly identified and that the target
+    /// variable is defined only in the comprehension scope and not in the global scope.
+    #[test]
+    fn comprehension_scope() {
+        let TestCase { db, file } = test_case(
+            "
+[x for x, y in iter1]
+",
+        );
+
+        let index = semantic_index(&db, file);
+        let global_table = index.symbol_table(FileScopeId::global());
+
+        assert_eq!(names(&global_table), vec!["iter1"]);
+
+        let [(comprehension_scope_id, comprehension_scope)] = index
+            .child_scopes(FileScopeId::global())
+            .collect::<Vec<_>>()[..]
+        else {
+            panic!("expected one child scope")
+        };
+
+        assert_eq!(comprehension_scope.kind(), ScopeKind::Comprehension);
+        assert_eq!(
+            comprehension_scope_id.to_scope_id(&db, file).name(&db),
+            "<listcomp>"
+        );
+
+        let comprehension_symbol_table = index.symbol_table(comprehension_scope_id);
+
+        assert_eq!(names(&comprehension_symbol_table), vec!["x", "y"]);
+
+        let use_def = index.use_def_map(comprehension_scope_id);
+        for name in ["x", "y"] {
+            let definition = use_def
+                .first_public_definition(
+                    comprehension_symbol_table
+                        .symbol_id_by_name(name)
+                        .expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(
+                definition.node(&db),
+                DefinitionKind::Comprehension(_)
+            ));
+        }
+    }
+
+    /// Test case to validate that the `x` variable used in the comprehension is referencing the
+    /// `x` variable defined by the inner generator (`for x in iter2`) and not the outer one.
+    #[test]
+    fn multiple_generators() {
+        let TestCase { db, file } = test_case(
+            "
+[x for x in iter1 for x in iter2]
+",
+        );
+
+        let index = semantic_index(&db, file);
+        let [(comprehension_scope_id, _)] = index
+            .child_scopes(FileScopeId::global())
+            .collect::<Vec<_>>()[..]
+        else {
+            panic!("expected one child scope")
+        };
+
+        let use_def = index.use_def_map(comprehension_scope_id);
+
+        let module = parsed_module(&db, file).syntax();
+        let element = module.body[0]
+            .as_expr_stmt()
+            .unwrap()
+            .value
+            .as_list_comp_expr()
+            .unwrap()
+            .elt
+            .as_name_expr()
+            .unwrap();
+        let element_use_id =
+            element.scoped_use_id(&db, comprehension_scope_id.to_scope_id(&db, file));
+
+        let definition = use_def.first_use_definition(element_use_id).unwrap();
+        let DefinitionKind::Comprehension(comprehension) = definition.node(&db) else {
+            panic!("expected generator definition")
+        };
+        let target = comprehension.target();
+        let name = target.id().as_str();
+
+        assert_eq!(name, "x");
+        assert_eq!(target.range(), TextRange::new(23.into(), 24.into()));
+    }
+
+    /// Test case to validate that the nested comprehension creates a new scope which is a child of
+    /// the outer comprehension scope and the variables are correctly defined in the respective
+    /// scopes.
+    #[test]
+    fn nested_generators() {
+        let TestCase { db, file } = test_case(
+            "
+[{x for x in iter2} for y in iter1]
+",
+        );
+
+        let index = semantic_index(&db, file);
+        let global_table = index.symbol_table(FileScopeId::global());
+
+        assert_eq!(names(&global_table), vec!["iter1"]);
+
+        let [(comprehension_scope_id, comprehension_scope)] = index
+            .child_scopes(FileScopeId::global())
+            .collect::<Vec<_>>()[..]
+        else {
+            panic!("expected one child scope")
+        };
+
+        assert_eq!(comprehension_scope.kind(), ScopeKind::Comprehension);
+        assert_eq!(
+            comprehension_scope_id.to_scope_id(&db, file).name(&db),
+            "<listcomp>"
+        );
+
+        let comprehension_symbol_table = index.symbol_table(comprehension_scope_id);
+
+        assert_eq!(names(&comprehension_symbol_table), vec!["y", "iter2"]);
+
+        let [(inner_comprehension_scope_id, inner_comprehension_scope)] = index
+            .child_scopes(comprehension_scope_id)
+            .collect::<Vec<_>>()[..]
+        else {
+            panic!("expected one inner generator scope")
+        };
+
+        assert_eq!(inner_comprehension_scope.kind(), ScopeKind::Comprehension);
+        assert_eq!(
+            inner_comprehension_scope_id
+                .to_scope_id(&db, file)
+                .name(&db),
+            "<setcomp>"
+        );
+
+        let inner_comprehension_symbol_table = index.symbol_table(inner_comprehension_scope_id);
+
+        assert_eq!(names(&inner_comprehension_symbol_table), vec!["x"]);
+    }
+
+    #[test]
+    fn with_item_definition() {
+        let TestCase { db, file } = test_case(
+            "
+with item1 as x, item2 as y:
+    pass
+",
+        );
+
+        let index = semantic_index(&db, file);
+        let global_table = index.symbol_table(FileScopeId::global());
+
+        assert_eq!(names(&global_table), vec!["item1", "x", "item2", "y"]);
+
+        let use_def = index.use_def_map(FileScopeId::global());
+        for name in ["x", "y"] {
+            let Some(definition) = use_def.first_public_definition(
+                global_table.symbol_id_by_name(name).expect("symbol exists"),
+            ) else {
+                panic!("Expected with item definition for {name}");
+            };
+            assert!(matches!(definition.node(&db), DefinitionKind::WithItem(_)));
+        }
+    }
+
+    #[test]
+    fn with_item_unpacked_definition() {
+        let TestCase { db, file } = test_case(
+            "
+with context() as (x, y):
+    pass
+",
+        );
+
+        let index = semantic_index(&db, file);
+        let global_table = index.symbol_table(FileScopeId::global());
+
+        assert_eq!(names(&global_table), vec!["context", "x", "y"]);
+
+        let use_def = index.use_def_map(FileScopeId::global());
+        for name in ["x", "y"] {
+            let Some(definition) = use_def.first_public_definition(
+                global_table.symbol_id_by_name(name).expect("symbol exists"),
+            ) else {
+                panic!("Expected with item definition for {name}");
+            };
+            assert!(matches!(definition.node(&db), DefinitionKind::WithItem(_)));
+        }
+    }
+
    #[test]
    fn dupes() {
        let TestCase { db, file } = test_case(
@@ -562,13 +888,13 @@ def func():
        assert_eq!(names(&func2_table), vec!["y"]);

        let use_def = index.use_def_map(FileScopeId::global());
-        let [definition] = use_def.public_definitions(
-            global_table
-                .symbol_id_by_name("func")
-                .expect("symbol exists"),
-        ) else {
-            panic!("expected one definition");
-        };
+        let definition = use_def
+            .first_public_definition(
+                global_table
+                    .symbol_id_by_name("func")
+                    .expect("symbol exists"),
+            )
+            .unwrap();
        assert!(matches!(definition.node(&db), DefinitionKind::Function(_)));
    }

@@ -669,9 +995,7 @@ class C[T]:
        };
        let x_use_id = x_use_expr_name.scoped_use_id(&db, scope);
        let use_def = use_def_map(&db, scope);
-        let [definition] = use_def.use_definitions(x_use_id) else {
-            panic!("expected one definition");
-        };
+        let definition = use_def.first_use_definition(x_use_id).unwrap();
        let DefinitionKind::Assignment(assignment) = definition.node(&db) else {
            panic!("should be an assignment definition")
        };
@@ -762,4 +1086,140 @@ def x():
            vec!["bar", "foo", "Test", "<module>"]
        );
    }
+
+    #[test]
+    fn match_stmt() {
+        let TestCase { db, file } = test_case(
+            "
+match subject:
+    case a: ...
+    case [b, c, *d]: ...
+    case e as f: ...
+    case {'x': g, **h}: ...
+    case Foo(i, z=j): ...
+    case k | l: ...
+    case _: ...
+",
+        );
+
+        let global_scope_id = global_scope(&db, file);
+        let global_table = symbol_table(&db, global_scope_id);
+
+        assert!(global_table.symbol_by_name("Foo").unwrap().is_used());
+        assert_eq!(
+            names(&global_table),
+            vec!["subject", "a", "b", "c", "d", "e", "f", "g", "h", "Foo", "i", "j", "k", "l"]
+        );
+
+        let use_def = use_def_map(&db, global_scope_id);
+        for (name, expected_index) in [
+            ("a", 0),
+            ("b", 0),
+            ("c", 1),
+            ("d", 2),
+            ("e", 0),
+            ("f", 1),
+            ("g", 0),
+            ("h", 1),
+            ("i", 0),
+            ("j", 1),
+            ("k", 0),
+            ("l", 1),
+        ] {
+            let definition = use_def
+                .first_public_definition(
+                    global_table.symbol_id_by_name(name).expect("symbol exists"),
+                )
+                .expect("Expected with item definition for {name}");
+            if let DefinitionKind::MatchPattern(pattern) = definition.node(&db) {
+                assert_eq!(pattern.index(), expected_index);
+            } else {
+                panic!("Expected match pattern definition for {name}");
+            }
+        }
+    }
+
+    #[test]
+    fn nested_match_case() {
+        let TestCase { db, file } = test_case(
+            "
+match 1:
+    case first:
+        match 2:
+            case second:
+                pass
+",
+        );
+
+        let global_scope_id = global_scope(&db, file);
+        let global_table = symbol_table(&db, global_scope_id);
+
+        assert_eq!(names(&global_table), vec!["first", "second"]);
+
+        let use_def = use_def_map(&db, global_scope_id);
+        for (name, expected_index) in [("first", 0), ("second", 0)] {
+            let definition = use_def
+                .first_public_definition(
+                    global_table.symbol_id_by_name(name).expect("symbol exists"),
+                )
+                .expect("Expected with item definition for {name}");
+            if let DefinitionKind::MatchPattern(pattern) = definition.node(&db) {
+                assert_eq!(pattern.index(), expected_index);
+            } else {
+                panic!("Expected match pattern definition for {name}");
+            }
+        }
+    }
+
+    #[test]
+    fn for_loops_single_assignment() {
+        let TestCase { db, file } = test_case("for x in a: pass");
+        let scope = global_scope(&db, file);
+        let global_table = symbol_table(&db, scope);
+
+        assert_eq!(&names(&global_table), &["a", "x"]);
+
+        let use_def = use_def_map(&db, scope);
+        let definition = use_def
+            .first_public_definition(global_table.symbol_id_by_name("x").unwrap())
+            .unwrap();
+
+        assert!(matches!(definition.node(&db), DefinitionKind::For(_)));
+    }
+
+    #[test]
+    fn for_loops_simple_unpacking() {
+        let TestCase { db, file } = test_case("for (x, y) in a: pass");
+        let scope = global_scope(&db, file);
+        let global_table = symbol_table(&db, scope);
+
+        assert_eq!(&names(&global_table), &["a", "x", "y"]);
+
+        let use_def = use_def_map(&db, scope);
+        let x_definition = use_def
+            .first_public_definition(global_table.symbol_id_by_name("x").unwrap())
+            .unwrap();
+        let y_definition = use_def
+            .first_public_definition(global_table.symbol_id_by_name("y").unwrap())
+            .unwrap();
+
+        assert!(matches!(x_definition.node(&db), DefinitionKind::For(_)));
+        assert!(matches!(y_definition.node(&db), DefinitionKind::For(_)));
+    }
+
+    #[test]
+    fn for_loops_complex_unpacking() {
+        let TestCase { db, file } = test_case("for [((a,) b), (c, d)] in e: pass");
+        let scope = global_scope(&db, file);
+        let global_table = symbol_table(&db, scope);
+
+        assert_eq!(&names(&global_table), &["e", "a", "b", "c", "d"]);
+
+        let use_def = use_def_map(&db, scope);
+        let definition = use_def
+            .first_public_definition(global_table.symbol_id_by_name("a").unwrap())
+            .unwrap();
+
+        assert!(matches!(definition.node(&db), DefinitionKind::For(_)));
+    }
 }
--- a/crates/red_knot_python_semantic/src/semantic_index/ast_ids.rs
+++ b/crates/red_knot_python_semantic/src/semantic_index/ast_ids.rs
@@ -26,9 +26,9 @@ use crate::Db;
 /// ```
 #[derive(Debug)]
 pub(crate) struct AstIds {
-    /// Maps expressions to their expression id. Uses `NodeKey` because it avoids cloning [`Parsed`].
+    /// Maps expressions to their expression id.
    expressions_map: FxHashMap<ExpressionNodeKey, ScopedExpressionId>,
-    /// Maps expressions which "use" a symbol (that is, [`ExprName`]) to a use id.
+    /// Maps expressions which "use" a symbol (that is, [`ast::ExprName`]) to a use id.
    uses_map: FxHashMap<ExpressionNodeKey, ScopedUseId>,
 }

--- a/crates/red_knot_python_semantic/src/semantic_index/builder.rs
+++ b/crates/red_knot_python_semantic/src/semantic_index/builder.rs
@@ -7,14 +7,15 @@ use ruff_db::parsed::ParsedModule;
 use ruff_index::IndexVec;
 use ruff_python_ast as ast;
 use ruff_python_ast::name::Name;
-use ruff_python_ast::visitor::{walk_expr, walk_stmt, Visitor};
+use ruff_python_ast::visitor::{walk_expr, walk_pattern, walk_stmt, Visitor};
+use ruff_python_ast::AnyParameterRef;

 use crate::ast_node_ref::AstNodeRef;
 use crate::semantic_index::ast_ids::node_key::ExpressionNodeKey;
 use crate::semantic_index::ast_ids::AstIdsBuilder;
 use crate::semantic_index::definition::{
-    AssignmentDefinitionNodeRef, Definition, DefinitionNodeKey, DefinitionNodeRef,
-    ImportFromDefinitionNodeRef,
+    AssignmentDefinitionNodeRef, ComprehensionDefinitionNodeRef, Definition, DefinitionNodeKey,
+    DefinitionNodeRef, ForStmtDefinitionNodeRef, ImportFromDefinitionNodeRef,
 };
 use crate::semantic_index::expression::Expression;
 use crate::semantic_index::symbol::{
@@ -25,6 +26,8 @@ use crate::semantic_index::use_def::{FlowSnapshot, UseDefMapBuilder};
 use crate::semantic_index::SemanticIndex;
 use crate::Db;

+use super::definition::{MatchPatternDefinitionNodeRef, WithItemDefinitionNodeRef};
+
 pub(super) struct SemanticIndexBuilder<'db> {
    // Builder state
    db: &'db dyn Db,
@@ -33,6 +36,8 @@ pub(super) struct SemanticIndexBuilder<'db> {
    scope_stack: Vec<FileScopeId>,
    /// The assignment we're currently visiting.
    current_assignment: Option<CurrentAssignment<'db>>,
+    /// The match case we're currently visiting.
+    current_match_case: Option<CurrentMatchCase<'db>>,
    /// Flow states at each `break` in the current loop.
    loop_break_states: Vec<FlowSnapshot>,

@@ -56,6 +61,7 @@ impl<'db> SemanticIndexBuilder<'db> {
            module: parsed,
            scope_stack: Vec::new(),
            current_assignment: None,
+            current_match_case: None,
            loop_break_states: vec![],

            scopes: IndexVec::new(),
@@ -155,7 +161,7 @@ impl<'db> SemanticIndexBuilder<'db> {
        self.current_use_def_map_mut().restore(state);
    }

-    fn flow_merge(&mut self, state: &FlowSnapshot) {
+    fn flow_merge(&mut self, state: FlowSnapshot) {
        self.current_use_def_map_mut().merge(state);
    }

@@ -174,7 +180,7 @@ impl<'db> SemanticIndexBuilder<'db> {
        symbol: ScopedSymbolId,
        definition_node: impl Into<DefinitionNodeRef<'a>>,
    ) -> Definition<'db> {
-        let definition_node = definition_node.into();
+        let definition_node: DefinitionNodeRef<'_> = definition_node.into();
        let definition = Definition::new(
            self.db,
            self.file,
@@ -187,17 +193,27 @@ impl<'db> SemanticIndexBuilder<'db> {
            countme::Count::default(),
        );

-        self.definitions_by_node
+        let existing_definition = self
+            .definitions_by_node
            .insert(definition_node.key(), definition);
+        debug_assert_eq!(existing_definition, None);
+
        self.current_use_def_map_mut()
            .record_definition(symbol, definition);

        definition
    }

+    fn add_constraint(&mut self, constraint_node: &ast::Expr) -> Expression<'db> {
+        let expression = self.add_standalone_expression(constraint_node);
+        self.current_use_def_map_mut().record_constraint(expression);
+
+        expression
+    }
+
    /// Record an expression that needs to be a Salsa ingredient, because we need to infer its type
    /// standalone (type narrowing tests, RHS of an assignment.)
-    fn add_standalone_expression(&mut self, expression_node: &ast::Expr) {
+    fn add_standalone_expression(&mut self, expression_node: &ast::Expr) -> Expression<'db> {
        let expression = Expression::new(
            self.db,
            self.file,
@@ -210,6 +226,7 @@ impl<'db> SemanticIndexBuilder<'db> {
        );
        self.expressions_by_node
            .insert(expression_node.into(), expression);
+        expression
    }

    fn with_type_params(
@@ -258,6 +275,69 @@ impl<'db> SemanticIndexBuilder<'db> {
        nested_scope
    }

+    /// Visit a list of [`Comprehension`] nodes, assumed to be the "generators" that compose a
+    /// comprehension (that is, the `for x in y` and `for y in z` parts of `x for x in y for y in z`.)
+    ///
+    /// [`Comprehension`]: ast::Comprehension
+    fn visit_generators(&mut self, scope: NodeWithScopeRef, generators: &'db [ast::Comprehension]) {
+        let mut generators_iter = generators.iter();
+
+        let Some(generator) = generators_iter.next() else {
+            unreachable!("Expression must contain at least one generator");
+        };
+
+        // The `iter` of the first generator is evaluated in the outer scope, while all subsequent
+        // nodes are evaluated in the inner scope.
+        self.add_standalone_expression(&generator.iter);
+        self.visit_expr(&generator.iter);
+        self.push_scope(scope);
+
+        self.current_assignment = Some(CurrentAssignment::Comprehension {
+            node: generator,
+            first: true,
+        });
+        self.visit_expr(&generator.target);
+        self.current_assignment = None;
+
+        for expr in &generator.ifs {
+            self.visit_expr(expr);
+        }
+
+        for generator in generators_iter {
+            self.add_standalone_expression(&generator.iter);
+            self.visit_expr(&generator.iter);
+
+            self.current_assignment = Some(CurrentAssignment::Comprehension {
+                node: generator,
+                first: false,
+            });
+            self.visit_expr(&generator.target);
+            self.current_assignment = None;
+
+            for expr in &generator.ifs {
+                self.visit_expr(expr);
+            }
+        }
+    }
+
+    fn declare_parameter(&mut self, parameter: AnyParameterRef) {
+        let symbol =
+            self.add_or_update_symbol(parameter.name().id().clone(), SymbolFlags::IS_DEFINED);
+
+        let definition = self.add_definition(symbol, parameter);
+
+        if let AnyParameterRef::NonVariadic(with_default) = parameter {
+            // Insert a mapping from the parameter to the same definition.
+            // This ensures that calling `HasTy::ty` on the inner parameter returns
+            // a valid type (and doesn't panic)
+            let existing_definition = self.definitions_by_node.insert(
+                DefinitionNodeRef::from(AnyParameterRef::Variadic(&with_default.parameter)).key(),
+                definition,
+            );
+            debug_assert_eq!(existing_definition, None);
+        }
+    }
+
    pub(super) fn build(mut self) -> SemanticIndex<'db> {
        let module = self.module;
        self.visit_body(module.suite());
@@ -321,10 +401,6 @@ where
                    self.visit_decorator(decorator);
                }

-                let symbol = self
-                    .add_or_update_symbol(function_def.name.id.clone(), SymbolFlags::IS_DEFINED);
-                self.add_definition(symbol, function_def);
-
                self.with_type_params(
                    NodeWithScopeRef::FunctionTypeParameters(function_def),
                    function_def.type_params.as_deref(),
@@ -335,10 +411,31 @@ where
                        }

                        builder.push_scope(NodeWithScopeRef::Function(function_def));
+
+                        // Add symbols and definitions for the parameters to the function scope.
+                        for parameter in &*function_def.parameters {
+                            builder.declare_parameter(parameter);
+                        }
+
                        builder.visit_body(&function_def.body);
                        builder.pop_scope()
                    },
                );
+                // The default value of the parameters needs to be evaluated in the
+                // enclosing scope.
+                for default in function_def
+                    .parameters
+                    .iter_non_variadic_params()
+                    .filter_map(|param| param.default.as_deref())
+                {
+                    self.visit_expr(default);
+                }
+                // The symbol for the function name itself has to be evaluated
+                // at the end to match the runtime evaluation of parameter defaults
+                // and return-type annotations.
+                let symbol = self
+                    .add_or_update_symbol(function_def.name.id.clone(), SymbolFlags::IS_DEFINED);
+                self.add_definition(symbol, function_def);
            }
            ast::Stmt::ClassDef(class) => {
                for decorator in &class.decorator_list {
@@ -410,9 +507,24 @@ where
                self.visit_expr(&node.target);
                self.current_assignment = None;
            }
+            ast::Stmt::AugAssign(
+                aug_assign @ ast::StmtAugAssign {
+                    range: _,
+                    target,
+                    op: _,
+                    value,
+                },
+            ) => {
+                debug_assert!(self.current_assignment.is_none());
+                self.visit_expr(value);
+                self.current_assignment = Some(aug_assign.into());
+                self.visit_expr(target);
+                self.current_assignment = None;
+            }
            ast::Stmt::If(node) => {
                self.visit_expr(&node.test);
                let pre_if = self.flow_snapshot();
+                self.add_constraint(&node.test);
                self.visit_body(&node.body);
                let mut post_clauses: Vec<FlowSnapshot> = vec![];
                for clause in &node.elif_else_clauses {
@@ -425,7 +537,7 @@ where
                    self.visit_elif_else_clause(clause);
                }
                for post_clause_state in post_clauses {
-                    self.flow_merge(&post_clause_state);
+                    self.flow_merge(post_clause_state);
                }
                let has_else = node
                    .elif_else_clauses
@@ -434,7 +546,7 @@ where
                if !has_else {
                    // if there's no else clause, then it's possible we took none of the branches,
                    // and the pre_if state can reach here
-                    self.flow_merge(&pre_if);
+                    self.flow_merge(pre_if);
                }
            }
            ast::Stmt::While(node) => {
@@ -452,18 +564,62 @@ where

                // We may execute the `else` clause without ever executing the body, so merge in
                // the pre-loop state before visiting `else`.
-                self.flow_merge(&pre_loop);
+                self.flow_merge(pre_loop);
                self.visit_body(&node.orelse);

                // Breaking out of a while loop bypasses the `else` clause, so merge in the break
                // states after visiting `else`.
                for break_state in break_states {
-                    self.flow_merge(&break_state);
+                    self.flow_merge(break_state);
                }
            }
+            ast::Stmt::With(ast::StmtWith { items, body, .. }) => {
+                for item in items {
+                    self.visit_expr(&item.context_expr);
+                    if let Some(optional_vars) = item.optional_vars.as_deref() {
+                        self.add_standalone_expression(&item.context_expr);
+                        self.current_assignment = Some(item.into());
+                        self.visit_expr(optional_vars);
+                        self.current_assignment = None;
+                    }
+                }
+                self.visit_body(body);
+            }
            ast::Stmt::Break(_) => {
                self.loop_break_states.push(self.flow_snapshot());
            }
+
+            ast::Stmt::For(
+                for_stmt @ ast::StmtFor {
+                    range: _,
+                    is_async: _,
+                    target,
+                    iter,
+                    body,
+                    orelse,
+                },
+            ) => {
+                // TODO add control flow similar to `ast::Stmt::While` above
+                self.add_standalone_expression(iter);
+                self.visit_expr(iter);
+                debug_assert!(self.current_assignment.is_none());
+                self.current_assignment = Some(for_stmt.into());
+                self.visit_expr(target);
+                self.current_assignment = None;
+                self.visit_body(body);
+                self.visit_body(orelse);
+            }
+            ast::Stmt::Match(ast::StmtMatch {
+                subject,
+                cases,
+                range: _,
+            }) => {
+                self.add_standalone_expression(subject);
+                self.visit_expr(subject);
+                for case in cases {
+                    self.visit_match_case(case);
+                }
+            }
            _ => {
                walk_stmt(self, stmt);
            }
@@ -476,14 +632,22 @@ where
        self.current_ast_ids().record_expression(expr);

        match expr {
-            ast::Expr::Name(name_node) => {
-                let ast::ExprName { id, ctx, .. } = name_node;
-                let flags = match ctx {
+            ast::Expr::Name(name_node @ ast::ExprName { id, ctx, .. }) => {
+                let mut flags = match ctx {
                    ast::ExprContext::Load => SymbolFlags::IS_USED,
                    ast::ExprContext::Store => SymbolFlags::IS_DEFINED,
                    ast::ExprContext::Del => SymbolFlags::IS_DEFINED,
                    ast::ExprContext::Invalid => SymbolFlags::empty(),
                };
+                if matches!(
+                    self.current_assignment,
+                    Some(CurrentAssignment::AugAssign(_))
+                ) && !ctx.is_invalid()
+                {
+                    // For augmented assignment, the target expression is also used, so we should
+                    // record that as a use.
+                    flags |= SymbolFlags::IS_USED;
+                }
                let symbol = self.add_or_update_symbol(id.clone(), flags);
                if flags.contains(SymbolFlags::IS_DEFINED) {
                    match self.current_assignment {
@@ -499,9 +663,44 @@ where
                        Some(CurrentAssignment::AnnAssign(ann_assign)) => {
                            self.add_definition(symbol, ann_assign);
                        }
+                        Some(CurrentAssignment::AugAssign(aug_assign)) => {
+                            self.add_definition(symbol, aug_assign);
+                        }
+                        Some(CurrentAssignment::For(node)) => {
+                            self.add_definition(
+                                symbol,
+                                ForStmtDefinitionNodeRef {
+                                    iterable: &node.iter,
+                                    target: name_node,
+                                    is_async: node.is_async,
+                                },
+                            );
+                        }
                        Some(CurrentAssignment::Named(named)) => {
+                            // TODO(dhruvmanila): If the current scope is a comprehension, then the
+                            // named expression is implicitly nonlocal. This is yet to be
+                            // implemented.
                            self.add_definition(symbol, named);
                        }
+                        Some(CurrentAssignment::Comprehension { node, first }) => {
+                            self.add_definition(
+                                symbol,
+                                ComprehensionDefinitionNodeRef {
+                                    iterable: &node.iter,
+                                    target: name_node,
+                                    first,
+                                },
+                            );
+                        }
+                        Some(CurrentAssignment::WithItem(with_item)) => {
+                            self.add_definition(
+                                symbol,
+                                WithItemDefinitionNodeRef {
+                                    node: with_item,
+                                    target: name_node,
+                                },
+                            );
+                        }
                        None => {}
                    }
                }
@@ -515,19 +714,34 @@ where
            }
            ast::Expr::Named(node) => {
                debug_assert!(self.current_assignment.is_none());
-                self.current_assignment = Some(node.into());
                // TODO walrus in comprehensions is implicitly nonlocal
+                self.visit_expr(&node.value);
+                self.current_assignment = Some(node.into());
                self.visit_expr(&node.target);
                self.current_assignment = None;
-                self.visit_expr(&node.value);
            }
            ast::Expr::Lambda(lambda) => {
                if let Some(parameters) = &lambda.parameters {
+                    // The default value of the parameters needs to be evaluated in the
+                    // enclosing scope.
+                    for default in parameters
+                        .iter_non_variadic_params()
+                        .filter_map(|param| param.default.as_deref())
+                    {
+                        self.visit_expr(default);
+                    }
                    self.visit_parameters(parameters);
                }
                self.push_scope(NodeWithScopeRef::Lambda(lambda));
+
+                // Add symbols and definitions for the parameters to the lambda scope.
+                if let Some(parameters) = &lambda.parameters {
+                    for parameter in &**parameters {
+                        self.declare_parameter(parameter);
+                    }
+                }
+
                self.visit_expr(lambda.body.as_ref());
-                self.pop_scope();
            }
            ast::Expr::If(ast::ExprIf {
                body, test, orelse, ..
@@ -541,12 +755,130 @@ where
                let post_body = self.flow_snapshot();
                self.flow_restore(pre_if);
                self.visit_expr(orelse);
-                self.flow_merge(&post_body);
+                self.flow_merge(post_body);
+            }
+            ast::Expr::ListComp(
+                list_comprehension @ ast::ExprListComp {
+                    elt, generators, ..
+                },
+            ) => {
+                self.visit_generators(
+                    NodeWithScopeRef::ListComprehension(list_comprehension),
+                    generators,
+                );
+                self.visit_expr(elt);
+            }
+            ast::Expr::SetComp(
+                set_comprehension @ ast::ExprSetComp {
+                    elt, generators, ..
+                },
+            ) => {
+                self.visit_generators(
+                    NodeWithScopeRef::SetComprehension(set_comprehension),
+                    generators,
+                );
+                self.visit_expr(elt);
+            }
+            ast::Expr::Generator(
+                generator @ ast::ExprGenerator {
+                    elt, generators, ..
+                },
+            ) => {
+                self.visit_generators(NodeWithScopeRef::GeneratorExpression(generator), generators);
+                self.visit_expr(elt);
+            }
+            ast::Expr::DictComp(
+                dict_comprehension @ ast::ExprDictComp {
+                    key,
+                    value,
+                    generators,
+                    ..
+                },
+            ) => {
+                self.visit_generators(
+                    NodeWithScopeRef::DictComprehension(dict_comprehension),
+                    generators,
+                );
+                self.visit_expr(key);
+                self.visit_expr(value);
            }
            _ => {
                walk_expr(self, expr);
            }
        }
+
+        if matches!(
+            expr,
+            ast::Expr::Lambda(_)
+                | ast::Expr::ListComp(_)
+                | ast::Expr::SetComp(_)
+                | ast::Expr::Generator(_)
+                | ast::Expr::DictComp(_)
+        ) {
+            self.pop_scope();
+        }
+    }
+
+    fn visit_parameters(&mut self, parameters: &'ast ast::Parameters) {
+        // Intentionally avoid walking default expressions, as we handle them in the enclosing
+        // scope.
+        for parameter in parameters.iter().map(ast::AnyParameterRef::as_parameter) {
+            self.visit_parameter(parameter);
+        }
+    }
+
+    fn visit_match_case(&mut self, match_case: &'ast ast::MatchCase) {
+        debug_assert!(self.current_match_case.is_none());
+        self.current_match_case = Some(CurrentMatchCase::new(&match_case.pattern));
+        self.visit_pattern(&match_case.pattern);
+        self.current_match_case = None;
+
+        if let Some(expr) = &match_case.guard {
+            self.visit_expr(expr);
+        }
+        self.visit_body(&match_case.body);
+    }
+
+    fn visit_pattern(&mut self, pattern: &'ast ast::Pattern) {
+        if let ast::Pattern::MatchStar(ast::PatternMatchStar {
+            name: Some(name),
+            range: _,
+        }) = pattern
+        {
+            let symbol = self.add_or_update_symbol(name.id().clone(), SymbolFlags::IS_DEFINED);
+            let state = self.current_match_case.as_ref().unwrap();
+            self.add_definition(
+                symbol,
+                MatchPatternDefinitionNodeRef {
+                    pattern: state.pattern,
+                    identifier: name,
+                    index: state.index,
+                },
+            );
+        }
+
+        walk_pattern(self, pattern);
+
+        if let ast::Pattern::MatchAs(ast::PatternMatchAs {
+            name: Some(name), ..
+        })
+        | ast::Pattern::MatchMapping(ast::PatternMatchMapping {
+            rest: Some(name), ..
+        }) = pattern
+        {
+            let symbol = self.add_or_update_symbol(name.id().clone(), SymbolFlags::IS_DEFINED);
+            let state = self.current_match_case.as_ref().unwrap();
+            self.add_definition(
+                symbol,
+                MatchPatternDefinitionNodeRef {
+                    pattern: state.pattern,
+                    identifier: name,
+                    index: state.index,
+                },
+            );
+        }
+
+        self.current_match_case.as_mut().unwrap().index += 1;
    }
 }

@@ -554,7 +886,14 @@ where
 enum CurrentAssignment<'a> {
    Assign(&'a ast::StmtAssign),
    AnnAssign(&'a ast::StmtAnnAssign),
+    AugAssign(&'a ast::StmtAugAssign),
+    For(&'a ast::StmtFor),
    Named(&'a ast::ExprNamed),
+    Comprehension {
+        node: &'a ast::Comprehension,
+        first: bool,
+    },
+    WithItem(&'a ast::WithItem),
 }

 impl<'a> From<&'a ast::StmtAssign> for CurrentAssignment<'a> {
@@ -569,8 +908,50 @@ impl<'a> From<&'a ast::StmtAnnAssign> for CurrentAssignment<'a> {
    }
 }

+impl<'a> From<&'a ast::StmtAugAssign> for CurrentAssignment<'a> {
+    fn from(value: &'a ast::StmtAugAssign) -> Self {
+        Self::AugAssign(value)
+    }
+}
+
+impl<'a> From<&'a ast::StmtFor> for CurrentAssignment<'a> {
+    fn from(value: &'a ast::StmtFor) -> Self {
+        Self::For(value)
+    }
+}
+
 impl<'a> From<&'a ast::ExprNamed> for CurrentAssignment<'a> {
    fn from(value: &'a ast::ExprNamed) -> Self {
        Self::Named(value)
    }
 }
+
+impl<'a> From<&'a ast::WithItem> for CurrentAssignment<'a> {
+    fn from(value: &'a ast::WithItem) -> Self {
+        Self::WithItem(value)
+    }
+}
+
+struct CurrentMatchCase<'a> {
+    /// The pattern that's part of the current match case.
+    pattern: &'a ast::Pattern,
+
+    /// The index of the sub-pattern that's being currently visited within the pattern.
+    ///
+    /// For example:
+    /// ```py
+    /// match subject:
+    ///     case a as b: ...
+    ///     case [a, b]: ...
+    ///     case a | b: ...
+    /// ```
+    ///
+    /// In all of the above cases, the index would be 0 for `a` and 1 for `b`.
+    index: u32,
+}
+
+impl<'a> CurrentMatchCase<'a> {
+    fn new(pattern: &'a ast::Pattern) -> Self {
+        Self { pattern, index: 0 }
+    }
+}
--- a/crates/red_knot_python_semantic/src/semantic_index/definition.rs
+++ b/crates/red_knot_python_semantic/src/semantic_index/definition.rs
@@ -39,11 +39,17 @@ impl<'db> Definition<'db> {
 pub(crate) enum DefinitionNodeRef<'a> {
    Import(&'a ast::Alias),
    ImportFrom(ImportFromDefinitionNodeRef<'a>),
+    For(ForStmtDefinitionNodeRef<'a>),
    Function(&'a ast::StmtFunctionDef),
    Class(&'a ast::StmtClassDef),
    NamedExpression(&'a ast::ExprNamed),
    Assignment(AssignmentDefinitionNodeRef<'a>),
    AnnotatedAssignment(&'a ast::StmtAnnAssign),
+    AugmentedAssignment(&'a ast::StmtAugAssign),
+    Comprehension(ComprehensionDefinitionNodeRef<'a>),
+    Parameter(ast::AnyParameterRef<'a>),
+    WithItem(WithItemDefinitionNodeRef<'a>),
+    MatchPattern(MatchPatternDefinitionNodeRef<'a>),
 }

 impl<'a> From<&'a ast::StmtFunctionDef> for DefinitionNodeRef<'a> {
@@ -70,6 +76,12 @@ impl<'a> From<&'a ast::StmtAnnAssign> for DefinitionNodeRef<'a> {
    }
 }

+impl<'a> From<&'a ast::StmtAugAssign> for DefinitionNodeRef<'a> {
+    fn from(node: &'a ast::StmtAugAssign) -> Self {
+        Self::AugmentedAssignment(node)
+    }
+}
+
 impl<'a> From<&'a ast::Alias> for DefinitionNodeRef<'a> {
    fn from(node_ref: &'a ast::Alias) -> Self {
        Self::Import(node_ref)
@@ -82,12 +94,42 @@ impl<'a> From<ImportFromDefinitionNodeRef<'a>> for DefinitionNodeRef<'a> {
    }
 }

+impl<'a> From<ForStmtDefinitionNodeRef<'a>> for DefinitionNodeRef<'a> {
+    fn from(value: ForStmtDefinitionNodeRef<'a>) -> Self {
+        Self::For(value)
+    }
+}
+
 impl<'a> From<AssignmentDefinitionNodeRef<'a>> for DefinitionNodeRef<'a> {
    fn from(node_ref: AssignmentDefinitionNodeRef<'a>) -> Self {
        Self::Assignment(node_ref)
    }
 }

+impl<'a> From<WithItemDefinitionNodeRef<'a>> for DefinitionNodeRef<'a> {
+    fn from(node_ref: WithItemDefinitionNodeRef<'a>) -> Self {
+        Self::WithItem(node_ref)
+    }
+}
+
+impl<'a> From<ComprehensionDefinitionNodeRef<'a>> for DefinitionNodeRef<'a> {
+    fn from(node: ComprehensionDefinitionNodeRef<'a>) -> Self {
+        Self::Comprehension(node)
+    }
+}
+
+impl<'a> From<ast::AnyParameterRef<'a>> for DefinitionNodeRef<'a> {
+    fn from(node: ast::AnyParameterRef<'a>) -> Self {
+        Self::Parameter(node)
+    }
+}
+
+impl<'a> From<MatchPatternDefinitionNodeRef<'a>> for DefinitionNodeRef<'a> {
+    fn from(node: MatchPatternDefinitionNodeRef<'a>) -> Self {
+        Self::MatchPattern(node)
+    }
+}
+
 #[derive(Copy, Clone, Debug)]
 pub(crate) struct ImportFromDefinitionNodeRef<'a> {
    pub(crate) node: &'a ast::StmtImportFrom,
@@ -100,6 +142,37 @@ pub(crate) struct AssignmentDefinitionNodeRef<'a> {
    pub(crate) target: &'a ast::ExprName,
 }

+#[derive(Copy, Clone, Debug)]
+pub(crate) struct WithItemDefinitionNodeRef<'a> {
+    pub(crate) node: &'a ast::WithItem,
+    pub(crate) target: &'a ast::ExprName,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) struct ForStmtDefinitionNodeRef<'a> {
+    pub(crate) iterable: &'a ast::Expr,
+    pub(crate) target: &'a ast::ExprName,
+    pub(crate) is_async: bool,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) struct ComprehensionDefinitionNodeRef<'a> {
+    pub(crate) iterable: &'a ast::Expr,
+    pub(crate) target: &'a ast::ExprName,
+    pub(crate) first: bool,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) struct MatchPatternDefinitionNodeRef<'a> {
+    /// The outermost pattern node in which the identifier being defined occurs.
+    pub(crate) pattern: &'a ast::Pattern,
+    /// The identifier being defined.
+    pub(crate) identifier: &'a ast::Identifier,
+    /// The index of the identifier in the pattern when visiting the `pattern` node in evaluation
+    /// order.
+    pub(crate) index: u32,
+}
+
 impl DefinitionNodeRef<'_> {
    #[allow(unsafe_code)]
    pub(super) unsafe fn into_owned(self, parsed: ParsedModule) -> DefinitionKind {
@@ -131,6 +204,50 @@ impl DefinitionNodeRef<'_> {
            DefinitionNodeRef::AnnotatedAssignment(assign) => {
                DefinitionKind::AnnotatedAssignment(AstNodeRef::new(parsed, assign))
            }
+            DefinitionNodeRef::AugmentedAssignment(augmented_assignment) => {
+                DefinitionKind::AugmentedAssignment(AstNodeRef::new(parsed, augmented_assignment))
+            }
+            DefinitionNodeRef::For(ForStmtDefinitionNodeRef {
+                iterable,
+                target,
+                is_async,
+            }) => DefinitionKind::For(ForStmtDefinitionKind {
+                iterable: AstNodeRef::new(parsed.clone(), iterable),
+                target: AstNodeRef::new(parsed, target),
+                is_async,
+            }),
+            DefinitionNodeRef::Comprehension(ComprehensionDefinitionNodeRef {
+                iterable,
+                target,
+                first,
+            }) => DefinitionKind::Comprehension(ComprehensionDefinitionKind {
+                iterable: AstNodeRef::new(parsed.clone(), iterable),
+                target: AstNodeRef::new(parsed, target),
+                first,
+            }),
+            DefinitionNodeRef::Parameter(parameter) => match parameter {
+                ast::AnyParameterRef::Variadic(parameter) => {
+                    DefinitionKind::Parameter(AstNodeRef::new(parsed, parameter))
+                }
+                ast::AnyParameterRef::NonVariadic(parameter) => {
+                    DefinitionKind::ParameterWithDefault(AstNodeRef::new(parsed, parameter))
+                }
+            },
+            DefinitionNodeRef::WithItem(WithItemDefinitionNodeRef { node, target }) => {
+                DefinitionKind::WithItem(WithItemDefinitionKind {
+                    node: AstNodeRef::new(parsed.clone(), node),
+                    target: AstNodeRef::new(parsed, target),
+                })
+            }
+            DefinitionNodeRef::MatchPattern(MatchPatternDefinitionNodeRef {
+                pattern,
+                identifier,
+                index,
+            }) => DefinitionKind::MatchPattern(MatchPatternDefinitionKind {
+                pattern: AstNodeRef::new(parsed.clone(), pattern),
+                identifier: AstNodeRef::new(parsed, identifier),
+                index,
+            }),
        }
    }

@@ -148,6 +265,21 @@ impl DefinitionNodeRef<'_> {
                target,
            }) => target.into(),
            Self::AnnotatedAssignment(node) => node.into(),
+            Self::AugmentedAssignment(node) => node.into(),
+            Self::For(ForStmtDefinitionNodeRef {
+                iterable: _,
+                target,
+                is_async: _,
+            }) => target.into(),
+            Self::Comprehension(ComprehensionDefinitionNodeRef { target, .. }) => target.into(),
+            Self::Parameter(node) => match node {
+                ast::AnyParameterRef::Variadic(parameter) => parameter.into(),
+                ast::AnyParameterRef::NonVariadic(parameter) => parameter.into(),
+            },
+            Self::WithItem(WithItemDefinitionNodeRef { node: _, target }) => target.into(),
+            Self::MatchPattern(MatchPatternDefinitionNodeRef { identifier, .. }) => {
+                identifier.into()
+            }
        }
    }
 }
@@ -161,6 +293,52 @@ pub enum DefinitionKind {
    NamedExpression(AstNodeRef<ast::ExprNamed>),
    Assignment(AssignmentDefinitionKind),
    AnnotatedAssignment(AstNodeRef<ast::StmtAnnAssign>),
+    AugmentedAssignment(AstNodeRef<ast::StmtAugAssign>),
+    For(ForStmtDefinitionKind),
+    Comprehension(ComprehensionDefinitionKind),
+    Parameter(AstNodeRef<ast::Parameter>),
+    ParameterWithDefault(AstNodeRef<ast::ParameterWithDefault>),
+    WithItem(WithItemDefinitionKind),
+    MatchPattern(MatchPatternDefinitionKind),
+}
+
+#[derive(Clone, Debug)]
+#[allow(dead_code)]
+pub struct MatchPatternDefinitionKind {
+    pattern: AstNodeRef<ast::Pattern>,
+    identifier: AstNodeRef<ast::Identifier>,
+    index: u32,
+}
+
+impl MatchPatternDefinitionKind {
+    pub(crate) fn pattern(&self) -> &ast::Pattern {
+        self.pattern.node()
+    }
+
+    pub(crate) fn index(&self) -> u32 {
+        self.index
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct ComprehensionDefinitionKind {
+    iterable: AstNodeRef<ast::Expr>,
+    target: AstNodeRef<ast::ExprName>,
+    first: bool,
+}
+
+impl ComprehensionDefinitionKind {
+    pub(crate) fn iterable(&self) -> &ast::Expr {
+        self.iterable.node()
+    }
+
+    pub(crate) fn target(&self) -> &ast::ExprName {
+        self.target.node()
+    }
+
+    pub(crate) fn is_first(&self) -> bool {
+        self.first
+    }
 }

 #[derive(Clone, Debug)]
@@ -180,7 +358,6 @@ impl ImportFromDefinitionKind {
 }

 #[derive(Clone, Debug)]
-#[allow(dead_code)]
 pub struct AssignmentDefinitionKind {
    assignment: AstNodeRef<ast::StmtAssign>,
    target: AstNodeRef<ast::ExprName>,
@@ -190,6 +367,47 @@ impl AssignmentDefinitionKind {
    pub(crate) fn assignment(&self) -> &ast::StmtAssign {
        self.assignment.node()
    }
+
+    pub(crate) fn target(&self) -> &ast::ExprName {
+        self.target.node()
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct WithItemDefinitionKind {
+    node: AstNodeRef<ast::WithItem>,
+    target: AstNodeRef<ast::ExprName>,
+}
+
+impl WithItemDefinitionKind {
+    pub(crate) fn node(&self) -> &ast::WithItem {
+        self.node.node()
+    }
+
+    pub(crate) fn target(&self) -> &ast::ExprName {
+        self.target.node()
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct ForStmtDefinitionKind {
+    iterable: AstNodeRef<ast::Expr>,
+    target: AstNodeRef<ast::ExprName>,
+    is_async: bool,
+}
+
+impl ForStmtDefinitionKind {
+    pub(crate) fn iterable(&self) -> &ast::Expr {
+        self.iterable.node()
+    }
+
+    pub(crate) fn target(&self) -> &ast::ExprName {
+        self.target.node()
+    }
+
+    pub(crate) fn is_async(&self) -> bool {
+        self.is_async
+    }
 }

 #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
@@ -230,3 +448,33 @@ impl From<&ast::StmtAnnAssign> for DefinitionNodeKey {
        Self(NodeKey::from_node(node))
    }
 }
+
+impl From<&ast::StmtAugAssign> for DefinitionNodeKey {
+    fn from(node: &ast::StmtAugAssign) -> Self {
+        Self(NodeKey::from_node(node))
+    }
+}
+
+impl From<&ast::StmtFor> for DefinitionNodeKey {
+    fn from(value: &ast::StmtFor) -> Self {
+        Self(NodeKey::from_node(value))
+    }
+}
+
+impl From<&ast::Parameter> for DefinitionNodeKey {
+    fn from(node: &ast::Parameter) -> Self {
+        Self(NodeKey::from_node(node))
+    }
+}
+
+impl From<&ast::ParameterWithDefault> for DefinitionNodeKey {
+    fn from(node: &ast::ParameterWithDefault) -> Self {
+        Self(NodeKey::from_node(node))
+    }
+}
+
+impl From<&ast::Identifier> for DefinitionNodeKey {
+    fn from(identifier: &ast::Identifier) -> Self {
+        Self(NodeKey::from_node(identifier))
+    }
+}
--- a/crates/red_knot_python_semantic/src/semantic_index/expression.rs
+++ b/crates/red_knot_python_semantic/src/semantic_index/expression.rs
@@ -21,7 +21,7 @@ pub(crate) struct Expression<'db> {
    /// The expression node.
    #[no_eq]
    #[return_ref]
-    pub(crate) node: AstNodeRef<ast::Expr>,
+    pub(crate) node_ref: AstNodeRef<ast::Expr>,

    #[no_eq]
    count: countme::Count<Expression<'static>>,
--- a/crates/red_knot_python_semantic/src/semantic_index/symbol.rs
+++ b/crates/red_knot_python_semantic/src/semantic_index/symbol.rs
@@ -114,6 +114,10 @@ impl<'db> ScopeId<'db> {
            NodeWithScopeKind::ClassTypeParameters(_)
                | NodeWithScopeKind::FunctionTypeParameters(_)
                | NodeWithScopeKind::Function(_)
+                | NodeWithScopeKind::ListComprehension(_)
+                | NodeWithScopeKind::SetComprehension(_)
+                | NodeWithScopeKind::DictComprehension(_)
+                | NodeWithScopeKind::GeneratorExpression(_)
        )
    }

@@ -127,6 +131,10 @@ impl<'db> ScopeId<'db> {
            NodeWithScopeKind::Function(function)
            | NodeWithScopeKind::FunctionTypeParameters(function) => function.name.as_str(),
            NodeWithScopeKind::Lambda(_) => "<lambda>",
+            NodeWithScopeKind::ListComprehension(_) => "<listcomp>",
+            NodeWithScopeKind::SetComprehension(_) => "<setcomp>",
+            NodeWithScopeKind::DictComprehension(_) => "<dictcomp>",
+            NodeWithScopeKind::GeneratorExpression(_) => "<generator>",
        }
    }
 }
@@ -141,6 +149,10 @@ impl FileScopeId {
        FileScopeId::from_u32(0)
    }

+    pub fn is_global(self) -> bool {
+        self == FileScopeId::global()
+    }
+
    pub fn to_scope_id(self, db: &dyn Db, file: File) -> ScopeId<'_> {
        let index = semantic_index(db, file);
        index.scope_ids_by_scope[self]
@@ -170,6 +182,13 @@ pub enum ScopeKind {
    Annotation,
    Class,
    Function,
+    Comprehension,
+}
+
+impl ScopeKind {
+    pub const fn is_comprehension(self) -> bool {
+        matches!(self, ScopeKind::Comprehension)
+    }
 }

 /// Symbol table for a specific [`Scope`].
@@ -300,6 +319,10 @@ pub(crate) enum NodeWithScopeRef<'a> {
    Lambda(&'a ast::ExprLambda),
    FunctionTypeParameters(&'a ast::StmtFunctionDef),
    ClassTypeParameters(&'a ast::StmtClassDef),
+    ListComprehension(&'a ast::ExprListComp),
+    SetComprehension(&'a ast::ExprSetComp),
+    DictComprehension(&'a ast::ExprDictComp),
+    GeneratorExpression(&'a ast::ExprGenerator),
 }

 impl NodeWithScopeRef<'_> {
@@ -326,6 +349,18 @@ impl NodeWithScopeRef<'_> {
            NodeWithScopeRef::ClassTypeParameters(class) => {
                NodeWithScopeKind::ClassTypeParameters(AstNodeRef::new(module, class))
            }
+            NodeWithScopeRef::ListComprehension(comprehension) => {
+                NodeWithScopeKind::ListComprehension(AstNodeRef::new(module, comprehension))
+            }
+            NodeWithScopeRef::SetComprehension(comprehension) => {
+                NodeWithScopeKind::SetComprehension(AstNodeRef::new(module, comprehension))
+            }
+            NodeWithScopeRef::DictComprehension(comprehension) => {
+                NodeWithScopeKind::DictComprehension(AstNodeRef::new(module, comprehension))
+            }
+            NodeWithScopeRef::GeneratorExpression(generator) => {
+                NodeWithScopeKind::GeneratorExpression(AstNodeRef::new(module, generator))
+            }
        }
    }

@@ -337,6 +372,10 @@ impl NodeWithScopeRef<'_> {
            NodeWithScopeRef::Lambda(_) => ScopeKind::Function,
            NodeWithScopeRef::FunctionTypeParameters(_)
            | NodeWithScopeRef::ClassTypeParameters(_) => ScopeKind::Annotation,
+            NodeWithScopeRef::ListComprehension(_)
+            | NodeWithScopeRef::SetComprehension(_)
+            | NodeWithScopeRef::DictComprehension(_)
+            | NodeWithScopeRef::GeneratorExpression(_) => ScopeKind::Comprehension,
        }
    }

@@ -356,6 +395,18 @@ impl NodeWithScopeRef<'_> {
            NodeWithScopeRef::ClassTypeParameters(class) => {
                NodeWithScopeKey::ClassTypeParameters(NodeKey::from_node(class))
            }
+            NodeWithScopeRef::ListComprehension(comprehension) => {
+                NodeWithScopeKey::ListComprehension(NodeKey::from_node(comprehension))
+            }
+            NodeWithScopeRef::SetComprehension(comprehension) => {
+                NodeWithScopeKey::SetComprehension(NodeKey::from_node(comprehension))
+            }
+            NodeWithScopeRef::DictComprehension(comprehension) => {
+                NodeWithScopeKey::DictComprehension(NodeKey::from_node(comprehension))
+            }
+            NodeWithScopeRef::GeneratorExpression(generator) => {
+                NodeWithScopeKey::GeneratorExpression(NodeKey::from_node(generator))
+            }
        }
    }
 }
@@ -369,6 +420,10 @@ pub enum NodeWithScopeKind {
    Function(AstNodeRef<ast::StmtFunctionDef>),
    FunctionTypeParameters(AstNodeRef<ast::StmtFunctionDef>),
    Lambda(AstNodeRef<ast::ExprLambda>),
+    ListComprehension(AstNodeRef<ast::ExprListComp>),
+    SetComprehension(AstNodeRef<ast::ExprSetComp>),
+    DictComprehension(AstNodeRef<ast::ExprDictComp>),
+    GeneratorExpression(AstNodeRef<ast::ExprGenerator>),
 }

 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
@@ -379,4 +434,8 @@ pub(crate) enum NodeWithScopeKey {
    Function(NodeKey),
    FunctionTypeParameters(NodeKey),
    Lambda(NodeKey),
+    ListComprehension(NodeKey),
+    SetComprehension(NodeKey),
+    DictComprehension(NodeKey),
+    GeneratorExpression(NodeKey),
 }
--- a/crates/red_knot_python_semantic/src/semantic_index/use_def.rs
+++ b/crates/red_knot_python_semantic/src/semantic_index/use_def.rs
@@ -1,4 +1,5 @@
-//! Build a map from each use of a symbol to the definitions visible from that use.
+//! Build a map from each use of a symbol to the definitions visible from that use, and the
+//! type-narrowing constraints that apply to each definition.
 //!
 //! Let's take this code sample:
 //!
@@ -6,7 +7,7 @@
 //! x = 1
 //! x = 2
 //! y = x
-//! if flag:
+//! if y is not None:
 //!     x = 3
 //! else:
 //!     x = 4
@@ -34,8 +35,8 @@
 //! [`AstIds`](crate::semantic_index::ast_ids::AstIds) we number all uses (that means a `Name` node
 //! with `Load` context) so we have a `ScopedUseId` to efficiently represent each use.
 //!
-//! The other case we need to handle is when a symbol is referenced from a different scope (the
-//! most obvious example of this is an import). We call this "public" use of a symbol. So the other
+//! Another case we need to handle is when a symbol is referenced from a different scope (the most
+//! obvious example of this is an import). We call this "public" use of a symbol. So the other
 //! question we need to be able to answer is, what are the publicly-visible definitions of each
 //! symbol?
 //!
@@ -53,42 +54,55 @@
 //! start.)
 //!
 //! So this means that the publicly-visible definitions of a symbol are the definitions still
-//! visible at the end of the scope.
+//! visible at the end of the scope; effectively we have an implicit "use" of every symbol at the
+//! end of the scope.
 //!
-//! The data structure we build to answer these two questions is the `UseDefMap`. It has a
+//! We also need to know, for a given definition of a symbol, what type-narrowing constraints apply
+//! to it. For instance, in this code sample:
+//!
+//! ```python
+//! x = 1 if flag else None
+//! if x is not None:
+//!     y = x
+//! ```
+//!
+//! At the use of `x` in `y = x`, the visible definition of `x` is `1 if flag else None`, which
+//! would infer as the type `Literal[1] | None`. But the constraint `x is not None` dominates this
+//! use, which means we can rule out the possibility that `x` is `None` here, which should give us
+//! the type `Literal[1]` for this use.
+//!
+//! The data structure we build to answer these questions is the `UseDefMap`. It has a
 //! `definitions_by_use` vector indexed by [`ScopedUseId`] and a `public_definitions` vector
 //! indexed by [`ScopedSymbolId`]. The values in each of these vectors are (in principle) a list of
-//! visible definitions at that use, or at the end of the scope for that symbol.
+//! visible definitions at that use, or at the end of the scope for that symbol, with a list of the
+//! dominating constraints for each of those definitions.
 //!
-//! In order to avoid vectors-of-vectors and all the allocations that would entail, we don't
-//! actually store these "list of visible definitions" as a vector of [`Definition`] IDs. Instead,
-//! the values in `definitions_by_use` and `public_definitions` are a [`Definitions`] struct that
-//! keeps a [`Range`] into a third vector of [`Definition`] IDs, `all_definitions`. The trick with
-//! this representation is that it requires that the definitions visible at any given use of a
-//! symbol are stored sequentially in `all_definitions`.
+//! In order to avoid vectors-of-vectors-of-vectors and all the allocations that would entail, we
+//! don't actually store these "list of visible definitions" as a vector of [`Definition`].
+//! Instead, the values in `definitions_by_use` and `public_definitions` are a [`SymbolState`]
+//! struct which uses bit-sets to track definitions and constraints in terms of
+//! [`ScopedDefinitionId`] and [`ScopedConstraintId`], which are indices into the `all_definitions`
+//! and `all_constraints` indexvecs in the [`UseDefMap`].
 //!
-//! There is another special kind of possible "definition" for a symbol: it might be unbound in the
-//! scope. (This isn't equivalent to "zero visible definitions", since we may go through an `if`
-//! that has a definition for the symbol, leaving us with one visible definition, but still also
-//! the "unbound" possibility, since we might not have taken the `if` branch.)
+//! There is another special kind of possible "definition" for a symbol: there might be a path from
+//! the scope entry to a given use in which the symbol is never bound.
 //!
 //! The simplest way to model "unbound" would be as an actual [`Definition`] itself: the initial
 //! visible [`Definition`] for each symbol in a scope. But actually modeling it this way would
-//! dramatically increase the number of [`Definition`] that Salsa must track. Since "unbound" is a
+//! unnecessarily increase the number of [`Definition`] that Salsa must track. Since "unbound" is a
 //! special definition in that all symbols share it, and it doesn't have any additional per-symbol
-//! state, we can represent it more efficiently: we use the `may_be_unbound` boolean on the
-//! [`Definitions`] struct. If this flag is `true`, it means the symbol/use really has one
-//! additional visible "definition", which is the unbound state. If this flag is `false`, it means
-//! we've eliminated the possibility of unbound: every path we've followed includes a definition
-//! for this symbol.
+//! state, and constraints are irrelevant to it, we can represent it more efficiently: we use the
+//! `may_be_unbound` boolean on the [`SymbolState`] struct. If this flag is `true`, it means the
+//! symbol/use really has one additional visible "definition", which is the unbound state. If this
+//! flag is `false`, it means we've eliminated the possibility of unbound: every path we've
+//! followed includes a definition for this symbol.
 //!
-//! To build a [`UseDefMap`], the [`UseDefMapBuilder`] is notified of each new use and definition
-//! as they are encountered by the
+//! To build a [`UseDefMap`], the [`UseDefMapBuilder`] is notified of each new use, definition, and
+//! constraint as they are encountered by the
 //! [`SemanticIndexBuilder`](crate::semantic_index::builder::SemanticIndexBuilder) AST visit. For
-//! each symbol, the builder tracks the currently-visible definitions for that symbol. When we hit
-//! a use of a symbol, it records the currently-visible definitions for that symbol as the visible
-//! definitions for that use. When we reach the end of the scope, it records the currently-visible
-//! definitions for each symbol as the public definitions of that symbol.
+//! each symbol, the builder tracks the `SymbolState` for that symbol. When we hit a use of a
+//! symbol, it records the current state for that symbol for that use. When we reach the end of the
+//! scope, it records the state for each symbol as the public definitions of that symbol.
 //!
 //! Let's walk through the above example. Initially we record for `x` that it has no visible
 //! definitions, and may be unbound. When we see `x = 1`, we record that as the sole visible
@@ -98,10 +112,11 @@
 //!
 //! Then we hit the `if` branch. We visit the `test` node (`flag` in this case), since that will
 //! happen regardless. Then we take a pre-branch snapshot of the currently visible definitions for
-//! all symbols, which we'll need later. Then we go ahead and visit the `if` body. When we see `x =
-//! 3`, it replaces `x = 2` as the sole visible definition of `x`. At the end of the `if` body, we
-//! take another snapshot of the currently-visible definitions; we'll call this the post-if-body
-//! snapshot.
+//! all symbols, which we'll need later. Then we record `flag` as a possible constraint on the
+//! currently visible definition (`x = 2`), and go ahead and visit the `if` body. When we see `x =
+//! 3`, it replaces `x = 2` (constrained by `flag`) as the sole visible definition of `x`. At the
+//! end of the `if` body, we take another snapshot of the currently-visible definitions; we'll call
+//! this the post-if-body snapshot.
 //!
 //! Now we need to visit the `else` clause. The conditions when entering the `else` clause should
 //! be the pre-if conditions; if we are entering the `else` clause, we know that the `if` test
@@ -125,98 +140,142 @@
 //! (In the future we may have some other questions we want to answer as well, such as "is this
 //! definition used?", which will require tracking a bit more info in our map, e.g. a "used" bit
 //! for each [`Definition`] which is flipped to true when we record that definition for a use.)
+use self::symbol_state::{
+    ConstraintIdIterator, DefinitionIdWithConstraintsIterator, ScopedConstraintId,
+    ScopedDefinitionId, SymbolState,
+};
 use crate::semantic_index::ast_ids::ScopedUseId;
 use crate::semantic_index::definition::Definition;
+use crate::semantic_index::expression::Expression;
 use crate::semantic_index::symbol::ScopedSymbolId;
 use ruff_index::IndexVec;
-use std::ops::Range;

-/// All definitions that can reach a given use of a name.
+mod bitset;
+mod symbol_state;
+
+/// Applicable definitions and constraints for every use of a name.
 #[derive(Debug, PartialEq, Eq)]
 pub(crate) struct UseDefMap<'db> {
-    // TODO store constraints with definitions for type narrowing
-    /// Definition IDs array for `definitions_by_use` and `public_definitions` to slice into.
-    all_definitions: Vec<Definition<'db>>,
+    /// Array of [`Definition`] in this scope.
+    all_definitions: IndexVec<ScopedDefinitionId, Definition<'db>>,

-    /// Definitions that can reach a [`ScopedUseId`].
-    definitions_by_use: IndexVec<ScopedUseId, Definitions>,
+    /// Array of constraints (as [`Expression`]) in this scope.
+    all_constraints: IndexVec<ScopedConstraintId, Expression<'db>>,

-    /// Definitions of each symbol visible at end of scope.
-    public_definitions: IndexVec<ScopedSymbolId, Definitions>,
+    /// [`SymbolState`] visible at a [`ScopedUseId`].
+    definitions_by_use: IndexVec<ScopedUseId, SymbolState>,
+
+    /// [`SymbolState`] visible at end of scope for each symbol.
+    public_definitions: IndexVec<ScopedSymbolId, SymbolState>,
 }

 impl<'db> UseDefMap<'db> {
-    pub(crate) fn use_definitions(&self, use_id: ScopedUseId) -> &[Definition<'db>] {
-        &self.all_definitions[self.definitions_by_use[use_id].definitions_range.clone()]
+    pub(crate) fn use_definitions(
+        &self,
+        use_id: ScopedUseId,
+    ) -> DefinitionWithConstraintsIterator<'_, 'db> {
+        DefinitionWithConstraintsIterator {
+            all_definitions: &self.all_definitions,
+            all_constraints: &self.all_constraints,
+            inner: self.definitions_by_use[use_id].visible_definitions(),
+        }
    }

    pub(crate) fn use_may_be_unbound(&self, use_id: ScopedUseId) -> bool {
-        self.definitions_by_use[use_id].may_be_unbound
+        self.definitions_by_use[use_id].may_be_unbound()
    }

-    pub(crate) fn public_definitions(&self, symbol: ScopedSymbolId) -> &[Definition<'db>] {
-        &self.all_definitions[self.public_definitions[symbol].definitions_range.clone()]
+    pub(crate) fn public_definitions(
+        &self,
+        symbol: ScopedSymbolId,
+    ) -> DefinitionWithConstraintsIterator<'_, 'db> {
+        DefinitionWithConstraintsIterator {
+            all_definitions: &self.all_definitions,
+            all_constraints: &self.all_constraints,
+            inner: self.public_definitions[symbol].visible_definitions(),
+        }
    }

    pub(crate) fn public_may_be_unbound(&self, symbol: ScopedSymbolId) -> bool {
-        self.public_definitions[symbol].may_be_unbound
+        self.public_definitions[symbol].may_be_unbound()
    }
 }

-/// Definitions visible for a symbol at a particular use (or end-of-scope).
-#[derive(Clone, Debug, PartialEq, Eq)]
-struct Definitions {
-    /// [`Range`] in `all_definitions` of the visible definition IDs.
-    definitions_range: Range<usize>,
-    /// Is the symbol possibly unbound at this point?
-    may_be_unbound: bool,
-}
-
-impl Definitions {
-    /// The default state of a symbol is "no definitions, may be unbound", aka definitely-unbound.
-    fn unbound() -> Self {
-        Self {
-            definitions_range: Range::default(),
-            may_be_unbound: true,
-        }
-    }
-}
-
-impl Default for Definitions {
-    fn default() -> Self {
-        Definitions::unbound()
-    }
-}
-
-/// A snapshot of the visible definitions for each symbol at a particular point in control flow.
-#[derive(Clone, Debug)]
-pub(super) struct FlowSnapshot {
-    definitions_by_symbol: IndexVec<ScopedSymbolId, Definitions>,
-}
-
 #[derive(Debug)]
+pub(crate) struct DefinitionWithConstraintsIterator<'map, 'db> {
+    all_definitions: &'map IndexVec<ScopedDefinitionId, Definition<'db>>,
+    all_constraints: &'map IndexVec<ScopedConstraintId, Expression<'db>>,
+    inner: DefinitionIdWithConstraintsIterator<'map>,
+}
+
+impl<'map, 'db> Iterator for DefinitionWithConstraintsIterator<'map, 'db> {
+    type Item = DefinitionWithConstraints<'map, 'db>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|def_id_with_constraints| DefinitionWithConstraints {
+                definition: self.all_definitions[def_id_with_constraints.definition],
+                constraints: ConstraintsIterator {
+                    all_constraints: self.all_constraints,
+                    constraint_ids: def_id_with_constraints.constraint_ids,
+                },
+            })
+    }
+}
+
+impl std::iter::FusedIterator for DefinitionWithConstraintsIterator<'_, '_> {}
+
+pub(crate) struct DefinitionWithConstraints<'map, 'db> {
+    pub(crate) definition: Definition<'db>,
+    pub(crate) constraints: ConstraintsIterator<'map, 'db>,
+}
+
+pub(crate) struct ConstraintsIterator<'map, 'db> {
+    all_constraints: &'map IndexVec<ScopedConstraintId, Expression<'db>>,
+    constraint_ids: ConstraintIdIterator<'map>,
+}
+
+impl<'map, 'db> Iterator for ConstraintsIterator<'map, 'db> {
+    type Item = Expression<'db>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.constraint_ids
+            .next()
+            .map(|constraint_id| self.all_constraints[constraint_id])
+    }
+}
+
+impl std::iter::FusedIterator for ConstraintsIterator<'_, '_> {}
+
+/// A snapshot of the definitions and constraints state at a particular point in control flow.
+#[derive(Clone, Debug)]
+pub(super) struct FlowSnapshot {
+    definitions_by_symbol: IndexVec<ScopedSymbolId, SymbolState>,
+}
+
+#[derive(Debug, Default)]
 pub(super) struct UseDefMapBuilder<'db> {
-    /// Definition IDs array for `definitions_by_use` and `definitions_by_symbol` to slice into.
-    all_definitions: Vec<Definition<'db>>,
+    /// Append-only array of [`Definition`]; None is unbound.
+    all_definitions: IndexVec<ScopedDefinitionId, Definition<'db>>,
+
+    /// Append-only array of constraints (as [`Expression`]).
+    all_constraints: IndexVec<ScopedConstraintId, Expression<'db>>,

    /// Visible definitions at each so-far-recorded use.
-    definitions_by_use: IndexVec<ScopedUseId, Definitions>,
+    definitions_by_use: IndexVec<ScopedUseId, SymbolState>,

    /// Currently visible definitions for each symbol.
-    definitions_by_symbol: IndexVec<ScopedSymbolId, Definitions>,
+    definitions_by_symbol: IndexVec<ScopedSymbolId, SymbolState>,
 }

 impl<'db> UseDefMapBuilder<'db> {
    pub(super) fn new() -> Self {
-        Self {
-            all_definitions: Vec::new(),
-            definitions_by_use: IndexVec::new(),
-            definitions_by_symbol: IndexVec::new(),
-        }
+        Self::default()
    }

    pub(super) fn add_symbol(&mut self, symbol: ScopedSymbolId) {
-        let new_symbol = self.definitions_by_symbol.push(Definitions::unbound());
+        let new_symbol = self.definitions_by_symbol.push(SymbolState::unbound());
        debug_assert_eq!(symbol, new_symbol);
    }

@@ -227,13 +286,15 @@ impl<'db> UseDefMapBuilder<'db> {
    ) {
        // We have a new definition of a symbol; this replaces any previous definitions in this
        // path.
-        let def_idx = self.all_definitions.len();
-        self.all_definitions.push(definition);
-        self.definitions_by_symbol[symbol] = Definitions {
-            #[allow(clippy::range_plus_one)]
-            definitions_range: def_idx..(def_idx + 1),
-            may_be_unbound: false,
-        };
+        let def_id = self.all_definitions.push(definition);
+        self.definitions_by_symbol[symbol] = SymbolState::with(def_id);
+    }
+
+    pub(super) fn record_constraint(&mut self, constraint: Expression<'db>) {
+        let constraint_id = self.all_constraints.push(constraint);
+        for definitions in &mut self.definitions_by_symbol {
+            definitions.add_constraint(constraint_id);
+        }
    }

    pub(super) fn record_use(&mut self, symbol: ScopedSymbolId, use_id: ScopedUseId) {
@@ -265,15 +326,15 @@ impl<'db> UseDefMapBuilder<'db> {

        // If the snapshot we are restoring is missing some symbols we've recorded since, we need
        // to fill them in so the symbol IDs continue to line up. Since they don't exist in the
-        // snapshot, the correct state to fill them in with is "unbound", the default.
+        // snapshot, the correct state to fill them in with is "unbound".
        self.definitions_by_symbol
-            .resize(num_symbols, Definitions::unbound());
+            .resize(num_symbols, SymbolState::unbound());
    }

    /// Merge the given snapshot into the current state, reflecting that we might have taken either
    /// path to get here. The new visible-definitions state for each symbol should include
    /// definitions from both the prior state and the snapshot.
-    pub(super) fn merge(&mut self, snapshot: &FlowSnapshot) {
+    pub(super) fn merge(&mut self, snapshot: FlowSnapshot) {
        // The tricky thing about merging two Ranges pointing into `all_definitions` is that if the
        // two Ranges aren't already adjacent in `all_definitions`, we will have to copy at least
        // one or the other of the ranges to the end of `all_definitions` so as to make them
@@ -287,66 +348,26 @@ impl<'db> UseDefMapBuilder<'db> {
        // greater than the number of known symbols in a previously-taken snapshot.
        debug_assert!(self.definitions_by_symbol.len() >= snapshot.definitions_by_symbol.len());

-        for (symbol_id, current) in self.definitions_by_symbol.iter_mut_enumerated() {
-            let Some(snapshot) = snapshot.definitions_by_symbol.get(symbol_id) else {
-                // Symbol not present in snapshot, so it's unbound from that path.
-                current.may_be_unbound = true;
-                continue;
-            };
-
-            // If the symbol can be unbound in either predecessor, it can be unbound post-merge.
-            current.may_be_unbound |= snapshot.may_be_unbound;
-
-            // Merge the definition ranges.
-            let current = &mut current.definitions_range;
-            let snapshot = &snapshot.definitions_range;
-
-            // We never create reversed ranges.
-            debug_assert!(current.end >= current.start);
-            debug_assert!(snapshot.end >= snapshot.start);
-
-            if current == snapshot {
-                // Ranges already identical, nothing to do.
-            } else if snapshot.is_empty() {
-                // Merging from an empty range; nothing to do.
-            } else if (*current).is_empty() {
-                // Merging to an empty range; just use the incoming range.
-                *current = snapshot.clone();
-            } else if snapshot.end >= current.start && snapshot.start <= current.end {
-                // Ranges are adjacent or overlapping, merge them in-place.
-                *current = current.start.min(snapshot.start)..current.end.max(snapshot.end);
-            } else if current.end == self.all_definitions.len() {
-                // Ranges are not adjacent or overlapping, `current` is at the end of
-                // `all_definitions`, we need to copy `snapshot` to the end so they are adjacent
-                // and can be merged into one range.
-                self.all_definitions.extend_from_within(snapshot.clone());
-                current.end = self.all_definitions.len();
-            } else if snapshot.end == self.all_definitions.len() {
-                // Ranges are not adjacent or overlapping, `snapshot` is at the end of
-                // `all_definitions`, we need to copy `current` to the end so they are adjacent and
-                // can be merged into one range.
-                self.all_definitions.extend_from_within(current.clone());
-                current.start = snapshot.start;
-                current.end = self.all_definitions.len();
+        let mut snapshot_definitions_iter = snapshot.definitions_by_symbol.into_iter();
+        for current in &mut self.definitions_by_symbol {
+            if let Some(snapshot) = snapshot_definitions_iter.next() {
+                current.merge(snapshot);
            } else {
-                // Ranges are not adjacent and neither one is at the end of `all_definitions`, we
-                // have to copy both to the end so they are adjacent and we can merge them.
-                let start = self.all_definitions.len();
-                self.all_definitions.extend_from_within(current.clone());
-                self.all_definitions.extend_from_within(snapshot.clone());
-                current.start = start;
-                current.end = self.all_definitions.len();
+                // Symbol not present in snapshot, so it's unbound from that path.
+                current.add_unbound();
            }
        }
    }

    pub(super) fn finish(mut self) -> UseDefMap<'db> {
        self.all_definitions.shrink_to_fit();
+        self.all_constraints.shrink_to_fit();
        self.definitions_by_symbol.shrink_to_fit();
        self.definitions_by_use.shrink_to_fit();

        UseDefMap {
            all_definitions: self.all_definitions,
+            all_constraints: self.all_constraints,
            definitions_by_use: self.definitions_by_use,
            public_definitions: self.definitions_by_symbol,
        }
--- a/crates/red_knot_python_semantic/src/semantic_index/use_def/bitset.rs
+++ b/crates/red_knot_python_semantic/src/semantic_index/use_def/bitset.rs
@@ -0,0 +1,228 @@
+/// Ordered set of `u32`.
+///
+/// Uses an inline bit-set for small values (up to 64 * B), falls back to heap allocated vector of
+/// blocks for larger values.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) enum BitSet<const B: usize> {
+    /// Bit-set (in 64-bit blocks) for the first 64 * B entries.
+    Inline([u64; B]),
+
+    /// Overflow beyond 64 * B.
+    Heap(Vec<u64>),
+}
+
+impl<const B: usize> Default for BitSet<B> {
+    fn default() -> Self {
+        // B * 64 must fit in a u32, or else we have unusable bits; this assertion makes the
+        // truncating casts to u32 below safe. This would be better as a const assertion, but
+        // that's not possible on stable with const generic params. (B should never really be
+        // anywhere close to this large.)
+        assert!(B * 64 < (u32::MAX as usize));
+        // This implementation requires usize >= 32 bits.
+        static_assertions::const_assert!(usize::BITS >= 32);
+        Self::Inline([0; B])
+    }
+}
+
+impl<const B: usize> BitSet<B> {
+    /// Create and return a new [`BitSet`] with a single `value` inserted.
+    pub(super) fn with(value: u32) -> Self {
+        let mut bitset = Self::default();
+        bitset.insert(value);
+        bitset
+    }
+
+    /// Convert from Inline to Heap, if needed, and resize the Heap vector, if needed.
+    fn resize(&mut self, value: u32) {
+        let num_blocks_needed = (value / 64) + 1;
+        match self {
+            Self::Inline(blocks) => {
+                let mut vec = blocks.to_vec();
+                vec.resize(num_blocks_needed as usize, 0);
+                *self = Self::Heap(vec);
+            }
+            Self::Heap(vec) => {
+                vec.resize(num_blocks_needed as usize, 0);
+            }
+        }
+    }
+
+    fn blocks_mut(&mut self) -> &mut [u64] {
+        match self {
+            Self::Inline(blocks) => blocks.as_mut_slice(),
+            Self::Heap(blocks) => blocks.as_mut_slice(),
+        }
+    }
+
+    fn blocks(&self) -> &[u64] {
+        match self {
+            Self::Inline(blocks) => blocks.as_slice(),
+            Self::Heap(blocks) => blocks.as_slice(),
+        }
+    }
+
+    /// Insert a value into the [`BitSet`].
+    ///
+    /// Return true if the value was newly inserted, false if already present.
+    pub(super) fn insert(&mut self, value: u32) -> bool {
+        let value_usize = value as usize;
+        let (block, index) = (value_usize / 64, value_usize % 64);
+        if block >= self.blocks().len() {
+            self.resize(value);
+        }
+        let blocks = self.blocks_mut();
+        let missing = blocks[block] & (1 << index) == 0;
+        blocks[block] |= 1 << index;
+        missing
+    }
+
+    /// Intersect in-place with another [`BitSet`].
+    pub(super) fn intersect(&mut self, other: &BitSet<B>) {
+        let my_blocks = self.blocks_mut();
+        let other_blocks = other.blocks();
+        let min_len = my_blocks.len().min(other_blocks.len());
+        for i in 0..min_len {
+            my_blocks[i] &= other_blocks[i];
+        }
+        for block in my_blocks.iter_mut().skip(min_len) {
+            *block = 0;
+        }
+    }
+
+    /// Return an iterator over the values (in ascending order) in this [`BitSet`].
+    pub(super) fn iter(&self) -> BitSetIterator<'_, B> {
+        let blocks = self.blocks();
+        BitSetIterator {
+            blocks,
+            current_block_index: 0,
+            current_block: blocks[0],
+        }
+    }
+}
+
+/// Iterator over values in a [`BitSet`].
+#[derive(Debug)]
+pub(super) struct BitSetIterator<'a, const B: usize> {
+    /// The blocks we are iterating over.
+    blocks: &'a [u64],
+
+    /// The index of the block we are currently iterating through.
+    current_block_index: usize,
+
+    /// The block we are currently iterating through (and zeroing as we go.)
+    current_block: u64,
+}
+
+impl<const B: usize> Iterator for BitSetIterator<'_, B> {
+    type Item = u32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while self.current_block == 0 {
+            if self.current_block_index + 1 >= self.blocks.len() {
+                return None;
+            }
+            self.current_block_index += 1;
+            self.current_block = self.blocks[self.current_block_index];
+        }
+        let lowest_bit_set = self.current_block.trailing_zeros();
+        // reset the lowest set bit, without a data dependency on `lowest_bit_set`
+        self.current_block &= self.current_block.wrapping_sub(1);
+        // SAFETY: `lowest_bit_set` cannot be more than 64, `current_block_index` cannot be more
+        // than `B - 1`, and we check above that `B * 64 < u32::MAX`. So both `64 *
+        // current_block_index` and the final value here must fit in u32.
+        #[allow(clippy::cast_possible_truncation)]
+        Some(lowest_bit_set + (64 * self.current_block_index) as u32)
+    }
+}
+
+impl<const B: usize> std::iter::FusedIterator for BitSetIterator<'_, B> {}
+
+#[cfg(test)]
+mod tests {
+    use super::BitSet;
+
+    fn assert_bitset<const B: usize>(bitset: &BitSet<B>, contents: &[u32]) {
+        assert_eq!(bitset.iter().collect::<Vec<_>>(), contents);
+    }
+
+    #[test]
+    fn iter() {
+        let mut b = BitSet::<1>::with(3);
+        b.insert(27);
+        b.insert(6);
+        assert!(matches!(b, BitSet::Inline(_)));
+        assert_bitset(&b, &[3, 6, 27]);
+    }
+
+    #[test]
+    fn iter_overflow() {
+        let mut b = BitSet::<1>::with(140);
+        b.insert(100);
+        b.insert(129);
+        assert!(matches!(b, BitSet::Heap(_)));
+        assert_bitset(&b, &[100, 129, 140]);
+    }
+
+    #[test]
+    fn intersect() {
+        let mut b1 = BitSet::<1>::with(4);
+        let mut b2 = BitSet::<1>::with(4);
+        b1.insert(23);
+        b2.insert(5);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[4]);
+    }
+
+    #[test]
+    fn intersect_mixed_1() {
+        let mut b1 = BitSet::<1>::with(4);
+        let mut b2 = BitSet::<1>::with(4);
+        b1.insert(89);
+        b2.insert(5);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[4]);
+    }
+
+    #[test]
+    fn intersect_mixed_2() {
+        let mut b1 = BitSet::<1>::with(4);
+        let mut b2 = BitSet::<1>::with(4);
+        b1.insert(23);
+        b2.insert(89);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[4]);
+    }
+
+    #[test]
+    fn intersect_heap() {
+        let mut b1 = BitSet::<1>::with(4);
+        let mut b2 = BitSet::<1>::with(4);
+        b1.insert(89);
+        b2.insert(90);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[4]);
+    }
+
+    #[test]
+    fn intersect_heap_2() {
+        let mut b1 = BitSet::<1>::with(89);
+        let mut b2 = BitSet::<1>::with(89);
+        b1.insert(91);
+        b2.insert(90);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[89]);
+    }
+
+    #[test]
+    fn multiple_blocks() {
+        let mut b = BitSet::<2>::with(120);
+        b.insert(45);
+        assert!(matches!(b, BitSet::Inline(_)));
+        assert_bitset(&b, &[45, 120]);
+    }
+}
--- a/crates/red_knot_python_semantic/src/semantic_index/use_def/symbol_state.rs
+++ b/crates/red_knot_python_semantic/src/semantic_index/use_def/symbol_state.rs
@@ -0,0 +1,374 @@
+//! Track visible definitions of a symbol, and applicable constraints per definition.
+//!
+//! These data structures operate entirely on scope-local newtype-indices for definitions and
+//! constraints, referring to their location in the `all_definitions` and `all_constraints`
+//! indexvecs in [`super::UseDefMapBuilder`].
+//!
+//! We need to track arbitrary associations between definitions and constraints, not just a single
+//! set of currently dominating constraints (where "dominating" means "control flow must have
+//! passed through it to reach this point"), because we can have dominating constraints that apply
+//! to some definitions but not others, as in this code:
+//!
+//! ```python
+//! x = 1 if flag else None
+//! if x is not None:
+//!     if flag2:
+//!         x = 2 if flag else None
+//!     x
+//! ```
+//!
+//! The `x is not None` constraint dominates the final use of `x`, but it applies only to the first
+//! definition of `x`, not the second, so `None` is a possible value for `x`.
+//!
+//! And we can't just track, for each definition, an index into a list of dominating constraints,
+//! either, because we can have definitions which are still visible, but subject to constraints
+//! that are no longer dominating, as in this code:
+//!
+//! ```python
+//! x = 0
+//! if flag1:
+//!     x = 1 if flag2 else None
+//!     assert x is not None
+//! x
+//! ```
+//!
+//! From the point of view of the final use of `x`, the `x is not None` constraint no longer
+//! dominates, but it does dominate the `x = 1 if flag2 else None` definition, so we have to keep
+//! track of that.
+//!
+//! The data structures used here ([`BitSet`] and [`smallvec::SmallVec`]) optimize for keeping all
+//! data inline (avoiding lots of scattered allocations) in small-to-medium cases, and falling back
+//! to heap allocation to be able to scale to arbitrary numbers of definitions and constraints when
+//! needed.
+use super::bitset::{BitSet, BitSetIterator};
+use ruff_index::newtype_index;
+use smallvec::SmallVec;
+
+/// A newtype-index for a definition in a particular scope.
+#[newtype_index]
+pub(super) struct ScopedDefinitionId;
+
+/// A newtype-index for a constraint expression in a particular scope.
+#[newtype_index]
+pub(super) struct ScopedConstraintId;
+
+/// Can reference this * 64 total definitions inline; more will fall back to the heap.
+const INLINE_DEFINITION_BLOCKS: usize = 3;
+
+/// A [`BitSet`] of [`ScopedDefinitionId`], representing visible definitions of a symbol in a scope.
+type Definitions = BitSet<INLINE_DEFINITION_BLOCKS>;
+type DefinitionsIterator<'a> = BitSetIterator<'a, INLINE_DEFINITION_BLOCKS>;
+
+/// Can reference this * 64 total constraints inline; more will fall back to the heap.
+const INLINE_CONSTRAINT_BLOCKS: usize = 2;
+
+/// Can keep inline this many visible definitions per symbol at a given time; more will go to heap.
+const INLINE_VISIBLE_DEFINITIONS_PER_SYMBOL: usize = 4;
+
+/// One [`BitSet`] of applicable [`ScopedConstraintId`] per visible definition.
+type InlineConstraintArray =
+    [BitSet<INLINE_CONSTRAINT_BLOCKS>; INLINE_VISIBLE_DEFINITIONS_PER_SYMBOL];
+type Constraints = SmallVec<InlineConstraintArray>;
+type ConstraintsIterator<'a> = std::slice::Iter<'a, BitSet<INLINE_CONSTRAINT_BLOCKS>>;
+type ConstraintsIntoIterator = smallvec::IntoIter<InlineConstraintArray>;
+
+/// Visible definitions and narrowing constraints for a single symbol at some point in control flow.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(super) struct SymbolState {
+    /// [`BitSet`]: which [`ScopedDefinitionId`] are visible for this symbol?
+    visible_definitions: Definitions,
+
+    /// For each definition, which [`ScopedConstraintId`] apply?
+    ///
+    /// This is a [`smallvec::SmallVec`] which should always have one [`BitSet`] of constraints per
+    /// definition in `visible_definitions`.
+    constraints: Constraints,
+
+    /// Could the symbol be unbound at this point?
+    may_be_unbound: bool,
+}
+
+/// A single [`ScopedDefinitionId`] with an iterator of its applicable [`ScopedConstraintId`].
+#[derive(Debug)]
+pub(super) struct DefinitionIdWithConstraints<'a> {
+    pub(super) definition: ScopedDefinitionId,
+    pub(super) constraint_ids: ConstraintIdIterator<'a>,
+}
+
+impl SymbolState {
+    /// Return a new [`SymbolState`] representing an unbound symbol.
+    pub(super) fn unbound() -> Self {
+        Self {
+            visible_definitions: Definitions::default(),
+            constraints: Constraints::default(),
+            may_be_unbound: true,
+        }
+    }
+
+    /// Return a new [`SymbolState`] representing a symbol with a single visible definition.
+    pub(super) fn with(definition_id: ScopedDefinitionId) -> Self {
+        let mut constraints = Constraints::with_capacity(1);
+        constraints.push(BitSet::default());
+        Self {
+            visible_definitions: Definitions::with(definition_id.into()),
+            constraints,
+            may_be_unbound: false,
+        }
+    }
+
+    /// Add Unbound as a possibility for this symbol.
+    pub(super) fn add_unbound(&mut self) {
+        self.may_be_unbound = true;
+    }
+
+    /// Add given constraint to all currently-visible definitions.
+    pub(super) fn add_constraint(&mut self, constraint_id: ScopedConstraintId) {
+        for bitset in &mut self.constraints {
+            bitset.insert(constraint_id.into());
+        }
+    }
+
+    /// Merge another [`SymbolState`] into this one.
+    pub(super) fn merge(&mut self, b: SymbolState) {
+        let mut a = Self {
+            visible_definitions: Definitions::default(),
+            constraints: Constraints::default(),
+            may_be_unbound: self.may_be_unbound || b.may_be_unbound,
+        };
+        std::mem::swap(&mut a, self);
+        let mut a_defs_iter = a.visible_definitions.iter();
+        let mut b_defs_iter = b.visible_definitions.iter();
+        let mut a_constraints_iter = a.constraints.into_iter();
+        let mut b_constraints_iter = b.constraints.into_iter();
+
+        let mut opt_a_def: Option<u32> = a_defs_iter.next();
+        let mut opt_b_def: Option<u32> = b_defs_iter.next();
+
+        // Iterate through the definitions from `a` and `b`, always processing the lower definition
+        // ID first, and pushing each definition onto the merged `SymbolState` with its
+        // constraints. If a definition is found in both `a` and `b`, push it with the intersection
+        // of the constraints from the two paths; a constraint that applies from only one possible
+        // path is irrelevant.
+
+        // Helper to push `def`, with constraints in `constraints_iter`, onto `self`.
+        let push = |def, constraints_iter: &mut ConstraintsIntoIterator, merged: &mut Self| {
+            merged.visible_definitions.insert(def);
+            // SAFETY: we only ever create SymbolState with either no definitions and no constraint
+            // bitsets (`::unbound`) or one definition and one constraint bitset (`::with`), and
+            // `::merge` always pushes one definition and one constraint bitset together (just
+            // below), so the number of definitions and the number of constraint bitsets can never
+            // get out of sync.
+            let constraints = constraints_iter
+                .next()
+                .expect("definitions and constraints length mismatch");
+            merged.constraints.push(constraints);
+        };
+
+        loop {
+            match (opt_a_def, opt_b_def) {
+                (Some(a_def), Some(b_def)) => match a_def.cmp(&b_def) {
+                    std::cmp::Ordering::Less => {
+                        // Next definition ID is only in `a`, push it to `self` and advance `a`.
+                        push(a_def, &mut a_constraints_iter, self);
+                        opt_a_def = a_defs_iter.next();
+                    }
+                    std::cmp::Ordering::Greater => {
+                        // Next definition ID is only in `b`, push it to `self` and advance `b`.
+                        push(b_def, &mut b_constraints_iter, self);
+                        opt_b_def = b_defs_iter.next();
+                    }
+                    std::cmp::Ordering::Equal => {
+                        // Next definition is in both; push to `self` and intersect constraints.
+                        push(a_def, &mut b_constraints_iter, self);
+                        // SAFETY: we only ever create SymbolState with either no definitions and
+                        // no constraint bitsets (`::unbound`) or one definition and one constraint
+                        // bitset (`::with`), and `::merge` always pushes one definition and one
+                        // constraint bitset together (just below), so the number of definitions
+                        // and the number of constraint bitsets can never get out of sync.
+                        let a_constraints = a_constraints_iter
+                            .next()
+                            .expect("definitions and constraints length mismatch");
+                        // If the same definition is visible through both paths, any constraint
+                        // that applies on only one path is irrelevant to the resulting type from
+                        // unioning the two paths, so we intersect the constraints.
+                        self.constraints
+                            .last_mut()
+                            .unwrap()
+                            .intersect(&a_constraints);
+                        opt_a_def = a_defs_iter.next();
+                        opt_b_def = b_defs_iter.next();
+                    }
+                },
+                (Some(a_def), None) => {
+                    // We've exhausted `b`, just push the def from `a` and move on to the next.
+                    push(a_def, &mut a_constraints_iter, self);
+                    opt_a_def = a_defs_iter.next();
+                }
+                (None, Some(b_def)) => {
+                    // We've exhausted `a`, just push the def from `b` and move on to the next.
+                    push(b_def, &mut b_constraints_iter, self);
+                    opt_b_def = b_defs_iter.next();
+                }
+                (None, None) => break,
+            }
+        }
+    }
+
+    /// Get iterator over visible definitions with constraints.
+    pub(super) fn visible_definitions(&self) -> DefinitionIdWithConstraintsIterator {
+        DefinitionIdWithConstraintsIterator {
+            definitions: self.visible_definitions.iter(),
+            constraints: self.constraints.iter(),
+        }
+    }
+
+    /// Could the symbol be unbound?
+    pub(super) fn may_be_unbound(&self) -> bool {
+        self.may_be_unbound
+    }
+}
+
+/// The default state of a symbol (if we've seen no definitions of it) is unbound.
+impl Default for SymbolState {
+    fn default() -> Self {
+        SymbolState::unbound()
+    }
+}
+
+#[derive(Debug)]
+pub(super) struct DefinitionIdWithConstraintsIterator<'a> {
+    definitions: DefinitionsIterator<'a>,
+    constraints: ConstraintsIterator<'a>,
+}
+
+impl<'a> Iterator for DefinitionIdWithConstraintsIterator<'a> {
+    type Item = DefinitionIdWithConstraints<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match (self.definitions.next(), self.constraints.next()) {
+            (None, None) => None,
+            (Some(def), Some(constraints)) => Some(DefinitionIdWithConstraints {
+                definition: ScopedDefinitionId::from_u32(def),
+                constraint_ids: ConstraintIdIterator {
+                    wrapped: constraints.iter(),
+                },
+            }),
+            // SAFETY: see above.
+            _ => unreachable!("definitions and constraints length mismatch"),
+        }
+    }
+}
+
+impl std::iter::FusedIterator for DefinitionIdWithConstraintsIterator<'_> {}
+
+#[derive(Debug)]
+pub(super) struct ConstraintIdIterator<'a> {
+    wrapped: BitSetIterator<'a, INLINE_CONSTRAINT_BLOCKS>,
+}
+
+impl Iterator for ConstraintIdIterator<'_> {
+    type Item = ScopedConstraintId;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.wrapped.next().map(ScopedConstraintId::from_u32)
+    }
+}
+
+impl std::iter::FusedIterator for ConstraintIdIterator<'_> {}
+
+#[cfg(test)]
+mod tests {
+    use super::{ScopedConstraintId, ScopedDefinitionId, SymbolState};
+
+    impl SymbolState {
+        pub(crate) fn assert(&self, may_be_unbound: bool, expected: &[&str]) {
+            assert_eq!(self.may_be_unbound(), may_be_unbound);
+            let actual = self
+                .visible_definitions()
+                .map(|def_id_with_constraints| {
+                    format!(
+                        "{}<{}>",
+                        def_id_with_constraints.definition.as_u32(),
+                        def_id_with_constraints
+                            .constraint_ids
+                            .map(ScopedConstraintId::as_u32)
+                            .map(|idx| idx.to_string())
+                            .collect::<Vec<_>>()
+                            .join(", ")
+                    )
+                })
+                .collect::<Vec<_>>();
+            assert_eq!(actual, expected);
+        }
+    }
+
+    #[test]
+    fn unbound() {
+        let cd = SymbolState::unbound();
+
+        cd.assert(true, &[]);
+    }
+
+    #[test]
+    fn with() {
+        let cd = SymbolState::with(ScopedDefinitionId::from_u32(0));
+
+        cd.assert(false, &["0<>"]);
+    }
+
+    #[test]
+    fn add_unbound() {
+        let mut cd = SymbolState::with(ScopedDefinitionId::from_u32(0));
+        cd.add_unbound();
+
+        cd.assert(true, &["0<>"]);
+    }
+
+    #[test]
+    fn add_constraint() {
+        let mut cd = SymbolState::with(ScopedDefinitionId::from_u32(0));
+        cd.add_constraint(ScopedConstraintId::from_u32(0));
+
+        cd.assert(false, &["0<0>"]);
+    }
+
+    #[test]
+    fn merge() {
+        // merging the same definition with the same constraint keeps the constraint
+        let mut cd0a = SymbolState::with(ScopedDefinitionId::from_u32(0));
+        cd0a.add_constraint(ScopedConstraintId::from_u32(0));
+
+        let mut cd0b = SymbolState::with(ScopedDefinitionId::from_u32(0));
+        cd0b.add_constraint(ScopedConstraintId::from_u32(0));
+
+        cd0a.merge(cd0b);
+        let mut cd0 = cd0a;
+        cd0.assert(false, &["0<0>"]);
+
+        // merging the same definition with differing constraints drops all constraints
+        let mut cd1a = SymbolState::with(ScopedDefinitionId::from_u32(1));
+        cd1a.add_constraint(ScopedConstraintId::from_u32(1));
+
+        let mut cd1b = SymbolState::with(ScopedDefinitionId::from_u32(1));
+        cd1b.add_constraint(ScopedConstraintId::from_u32(2));
+
+        cd1a.merge(cd1b);
+        let cd1 = cd1a;
+        cd1.assert(false, &["1<>"]);
+
+        // merging a constrained definition with unbound keeps both
+        let mut cd2a = SymbolState::with(ScopedDefinitionId::from_u32(2));
+        cd2a.add_constraint(ScopedConstraintId::from_u32(3));
+
+        let cd2b = SymbolState::unbound();
+
+        cd2a.merge(cd2b);
+        let cd2 = cd2a;
+        cd2.assert(true, &["2<3>"]);
+
+        // merging different definitions keeps them each with their existing constraints
+        cd0.merge(cd2);
+        let cd = cd0;
+        cd.assert(true, &["0<0>", "2<3>"]);
+    }
+}
--- a/crates/red_knot_python_semantic/src/semantic_model.rs
+++ b/crates/red_knot_python_semantic/src/semantic_model.rs
@@ -1,12 +1,14 @@
-use ruff_db::files::File;
+use ruff_db::files::{File, FilePath};
+use ruff_db::source::line_index;
 use ruff_python_ast as ast;
-use ruff_python_ast::{Expr, ExpressionRef, StmtClassDef};
+use ruff_python_ast::{Expr, ExpressionRef};
+use ruff_source_file::LineIndex;

 use crate::module_name::ModuleName;
 use crate::module_resolver::{resolve_module, Module};
 use crate::semantic_index::ast_ids::HasScopedAstId;
 use crate::semantic_index::semantic_index;
-use crate::types::{definition_ty, global_symbol_ty_by_name, infer_scope_types, Type};
+use crate::types::{definition_ty, global_symbol_ty, infer_scope_types, Type};
 use crate::Db;

 pub struct SemanticModel<'db> {
@@ -25,12 +27,20 @@ impl<'db> SemanticModel<'db> {
        self.db
    }

+    pub fn file_path(&self) -> &FilePath {
+        self.file.path(self.db)
+    }
+
+    pub fn line_index(&self) -> LineIndex {
+        line_index(self.db.upcast(), self.file)
+    }
+
    pub fn resolve_module(&self, module_name: ModuleName) -> Option<Module> {
        resolve_module(self.db, module_name)
    }

    pub fn global_symbol_ty(&self, module: &Module, symbol_name: &str) -> Type<'db> {
-        global_symbol_ty_by_name(self.db, module.file(), symbol_name)
+        global_symbol_ty(self.db, module.file(), symbol_name)
    }
 }

@@ -137,29 +147,24 @@ impl HasTy for ast::Expr {
    }
 }

-impl HasTy for ast::StmtFunctionDef {
-    fn ty<'db>(&self, model: &SemanticModel<'db>) -> Type<'db> {
-        let index = semantic_index(model.db, model.file);
-        let definition = index.definition(self);
-        definition_ty(model.db, definition)
-    }
+macro_rules! impl_definition_has_ty {
+    ($ty: ty) => {
+        impl HasTy for $ty {
+            #[inline]
+            fn ty<'db>(&self, model: &SemanticModel<'db>) -> Type<'db> {
+                let index = semantic_index(model.db, model.file);
+                let definition = index.definition(self);
+                definition_ty(model.db, definition)
+            }
+        }
+    };
 }

-impl HasTy for StmtClassDef {
-    fn ty<'db>(&self, model: &SemanticModel<'db>) -> Type<'db> {
-        let index = semantic_index(model.db, model.file);
-        let definition = index.definition(self);
-        definition_ty(model.db, definition)
-    }
-}
-
-impl HasTy for ast::Alias {
-    fn ty<'db>(&self, model: &SemanticModel<'db>) -> Type<'db> {
-        let index = semantic_index(model.db, model.file);
-        let definition = index.definition(self);
-        definition_ty(model.db, definition)
-    }
-}
+impl_definition_has_ty!(ast::StmtFunctionDef);
+impl_definition_has_ty!(ast::StmtClassDef);
+impl_definition_has_ty!(ast::Alias);
+impl_definition_has_ty!(ast::Parameter);
+impl_definition_has_ty!(ast::ParameterWithDefault);

 #[cfg(test)]
 mod tests {
@@ -171,29 +176,27 @@ mod tests {
    use crate::program::{Program, SearchPathSettings};
    use crate::python_version::PythonVersion;
    use crate::types::Type;
-    use crate::{HasTy, SemanticModel};
+    use crate::{HasTy, ProgramSettings, SemanticModel};

-    fn setup_db() -> TestDb {
-        let db = TestDb::new();
-        Program::new(
+    fn setup_db<'a>(files: impl IntoIterator<Item = (&'a str, &'a str)>) -> anyhow::Result<TestDb> {
+        let mut db = TestDb::new();
+        db.write_files(files)?;
+
+        Program::from_settings(
            &db,
-            PythonVersion::default(),
-            SearchPathSettings {
-                extra_paths: vec![],
-                src_root: SystemPathBuf::from("/src"),
-                site_packages: vec![],
-                custom_typeshed: None,
+            &ProgramSettings {
+                target_version: PythonVersion::default(),
+                search_paths: SearchPathSettings::new(SystemPathBuf::from("/src")),
            },
-        );
+        )?;

-        db
+        Ok(db)
    }

    #[test]
    fn function_ty() -> anyhow::Result<()> {
-        let mut db = setup_db();
+        let db = setup_db([("/src/foo.py", "def test(): pass")])?;

-        db.write_file("/src/foo.py", "def test(): pass")?;
        let foo = system_path_to_file(&db, "/src/foo.py").unwrap();

        let ast = parsed_module(&db, foo);
@@ -209,9 +212,8 @@ mod tests {

    #[test]
    fn class_ty() -> anyhow::Result<()> {
-        let mut db = setup_db();
+        let db = setup_db([("/src/foo.py", "class Test: pass")])?;

-        db.write_file("/src/foo.py", "class Test: pass")?;
        let foo = system_path_to_file(&db, "/src/foo.py").unwrap();

        let ast = parsed_module(&db, foo);
@@ -227,12 +229,11 @@ mod tests {

    #[test]
    fn alias_ty() -> anyhow::Result<()> {
-        let mut db = setup_db();
-
-        db.write_files([
+        let db = setup_db([
            ("/src/foo.py", "class Test: pass"),
            ("/src/bar.py", "from foo import Test"),
        ])?;
+
        let bar = system_path_to_file(&db, "/src/bar.py").unwrap();

        let ast = parsed_module(&db, bar);
--- a/crates/red_knot_python_semantic/src/site_packages.rs
+++ b/crates/red_knot_python_semantic/src/site_packages.rs
@@ -13,9 +13,10 @@ use std::io;
 use std::num::NonZeroUsize;
 use std::ops::Deref;

-use red_knot_python_semantic::PythonVersion;
 use ruff_db::system::{System, SystemPath, SystemPathBuf};

+use crate::PythonVersion;
+
 type SitePackagesDiscoveryResult<T> = Result<T, SitePackagesDiscoveryError>;

 /// Abstraction for a Python virtual environment.
@@ -24,7 +25,7 @@ type SitePackagesDiscoveryResult<T> = Result<T, SitePackagesDiscoveryError>;
 /// The format of this file is not defined anywhere, and exactly which keys are present
 /// depends on the tool that was used to create the virtual environment.
 #[derive(Debug)]
-pub struct VirtualEnvironment {
+pub(crate) struct VirtualEnvironment {
    venv_path: SysPrefixPath,
    base_executable_home_path: PythonHomePath,
    include_system_site_packages: bool,
@@ -41,7 +42,7 @@ pub struct VirtualEnvironment {
 }

 impl VirtualEnvironment {
-    pub fn new(
+    pub(crate) fn new(
        path: impl AsRef<SystemPath>,
        system: &dyn System,
    ) -> SitePackagesDiscoveryResult<Self> {
@@ -55,7 +56,7 @@ impl VirtualEnvironment {

        let venv_path = SysPrefixPath::new(path, system)?;
        let pyvenv_cfg_path = venv_path.join("pyvenv.cfg");
-        tracing::debug!("Attempting to parse virtual environment metadata at {pyvenv_cfg_path}");
+        tracing::debug!("Attempting to parse virtual environment metadata at '{pyvenv_cfg_path}'");

        let pyvenv_cfg = system
            .read_to_string(&pyvenv_cfg_path)
@@ -157,7 +158,7 @@ impl VirtualEnvironment {
    /// Return a list of `site-packages` directories that are available from this virtual environment
    ///
    /// See the documentation for `site_packages_dir_from_sys_prefix` for more details.
-    pub fn site_packages_directories(
+    pub(crate) fn site_packages_directories(
        &self,
        system: &dyn System,
    ) -> SitePackagesDiscoveryResult<Vec<SystemPathBuf>> {
@@ -191,7 +192,7 @@ impl VirtualEnvironment {
            } else {
                tracing::warn!(
                    "Failed to resolve `sys.prefix` of the system Python installation \
-from the `home` value in the `pyvenv.cfg` file at {}. \
+from the `home` value in the `pyvenv.cfg` file at '{}'. \
 System site-packages will not be used for module resolution.",
                    venv_path.join("pyvenv.cfg")
                );
@@ -204,7 +205,7 @@ System site-packages will not be used for module resolution.",
 }

 #[derive(Debug, thiserror::Error)]
-pub enum SitePackagesDiscoveryError {
+pub(crate) enum SitePackagesDiscoveryError {
    #[error("Invalid --venv-path argument: {0} could not be canonicalized")]
    VenvDirCanonicalizationError(SystemPathBuf, #[source] io::Error),
    #[error("Invalid --venv-path argument: {0} does not point to a directory on disk")]
@@ -221,7 +222,7 @@ pub enum SitePackagesDiscoveryError {

 /// The various ways in which parsing a `pyvenv.cfg` file could fail
 #[derive(Debug)]
-pub enum PyvenvCfgParseErrorKind {
+pub(crate) enum PyvenvCfgParseErrorKind {
    TooManyEquals { line_number: NonZeroUsize },
    MalformedKeyValuePair { line_number: NonZeroUsize },
    NoHomeKey,
@@ -370,7 +371,7 @@ fn site_packages_directory_from_sys_prefix(
 ///
 /// [`sys.prefix`]: https://docs.python.org/3/library/sys.html#sys.prefix
 #[derive(Debug, PartialEq, Eq, Clone)]
-pub struct SysPrefixPath(SystemPathBuf);
+pub(crate) struct SysPrefixPath(SystemPathBuf);

 impl SysPrefixPath {
    fn new(
@@ -425,7 +426,7 @@ impl Deref for SysPrefixPath {

 impl fmt::Display for SysPrefixPath {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "`sys.prefix` path {}", self.0)
+        write!(f, "`sys.prefix` path '{}'", self.0)
    }
 }

@@ -482,7 +483,7 @@ impl Deref for PythonHomePath {

 impl fmt::Display for PythonHomePath {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "`home` location {}", self.0)
+        write!(f, "`home` location '{}'", self.0)
    }
 }

--- a/crates/red_knot_python_semantic/src/stdlib.rs
+++ b/crates/red_knot_python_semantic/src/stdlib.rs
@@ -0,0 +1,77 @@
+use crate::module_name::ModuleName;
+use crate::module_resolver::resolve_module;
+use crate::semantic_index::global_scope;
+use crate::semantic_index::symbol::ScopeId;
+use crate::types::{global_symbol_ty, Type};
+use crate::Db;
+
+/// Enumeration of various core stdlib modules, for which we have dedicated Salsa queries.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum CoreStdlibModule {
+    Builtins,
+    Types,
+    Typeshed,
+}
+
+impl CoreStdlibModule {
+    fn name(self) -> ModuleName {
+        let module_name = match self {
+            Self::Builtins => "builtins",
+            Self::Types => "types",
+            Self::Typeshed => "_typeshed",
+        };
+        ModuleName::new_static(module_name)
+            .unwrap_or_else(|| panic!("{module_name} should be a valid module name!"))
+    }
+}
+
+/// Lookup the type of `symbol` in a given core module
+///
+/// Returns `Unbound` if the given core module cannot be resolved for some reason
+fn core_module_symbol_ty<'db>(
+    db: &'db dyn Db,
+    core_module: CoreStdlibModule,
+    symbol: &str,
+) -> Type<'db> {
+    resolve_module(db, core_module.name())
+        .map(|module| global_symbol_ty(db, module.file(), symbol))
+        .unwrap_or(Type::Unbound)
+}
+
+/// Lookup the type of `symbol` in the builtins namespace.
+///
+/// Returns `Unbound` if the `builtins` module isn't available for some reason.
+#[inline]
+pub(crate) fn builtins_symbol_ty<'db>(db: &'db dyn Db, symbol: &str) -> Type<'db> {
+    core_module_symbol_ty(db, CoreStdlibModule::Builtins, symbol)
+}
+
+/// Lookup the type of `symbol` in the `types` module namespace.
+///
+/// Returns `Unbound` if the `types` module isn't available for some reason.
+#[inline]
+pub(crate) fn types_symbol_ty<'db>(db: &'db dyn Db, symbol: &str) -> Type<'db> {
+    core_module_symbol_ty(db, CoreStdlibModule::Types, symbol)
+}
+
+/// Lookup the type of `symbol` in the `_typeshed` module namespace.
+///
+/// Returns `Unbound` if the `_typeshed` module isn't available for some reason.
+#[inline]
+pub(crate) fn typeshed_symbol_ty<'db>(db: &'db dyn Db, symbol: &str) -> Type<'db> {
+    core_module_symbol_ty(db, CoreStdlibModule::Typeshed, symbol)
+}
+
+/// Get the scope of a core stdlib module.
+///
+/// Can return `None` if a custom typeshed is used that is missing the core module in question.
+fn core_module_scope(db: &dyn Db, core_module: CoreStdlibModule) -> Option<ScopeId<'_>> {
+    resolve_module(db, core_module.name()).map(|module| global_scope(db, module.file()))
+}
+
+/// Get the `builtins` module scope.
+///
+/// Can return `None` if a custom typeshed is used that is missing `builtins.pyi`.
+pub(crate) fn builtins_module_scope(db: &dyn Db) -> Option<ScopeId<'_>> {
+    core_module_scope(db, CoreStdlibModule::Builtins)
+}
--- a/crates/red_knot_python_semantic/src/types.rs
+++ b/crates/red_knot_python_semantic/src/types.rs
@@ -1,19 +1,47 @@
+use infer::TypeInferenceBuilder;
 use ruff_db::files::File;
-use ruff_python_ast::name::Name;
+use ruff_python_ast as ast;

-use crate::builtins::builtins_scope;
-use crate::semantic_index::definition::Definition;
+use crate::semantic_index::ast_ids::HasScopedAstId;
+use crate::semantic_index::definition::{Definition, DefinitionKind};
 use crate::semantic_index::symbol::{ScopeId, ScopedSymbolId};
-use crate::semantic_index::{global_scope, symbol_table, use_def_map};
+use crate::semantic_index::{
+    global_scope, semantic_index, symbol_table, use_def_map, DefinitionWithConstraints,
+    DefinitionWithConstraintsIterator,
+};
+use crate::stdlib::{builtins_symbol_ty, types_symbol_ty, typeshed_symbol_ty};
+use crate::types::narrow::narrowing_constraint;
 use crate::{Db, FxOrderSet};

+pub(crate) use self::builder::{IntersectionBuilder, UnionBuilder};
+pub(crate) use self::diagnostic::TypeCheckDiagnostics;
+pub(crate) use self::infer::{
+    infer_deferred_types, infer_definition_types, infer_expression_types, infer_scope_types,
+    TypeInference,
+};
+
+mod builder;
+mod diagnostic;
 mod display;
 mod infer;
+mod narrow;

-pub(crate) use self::infer::{infer_definition_types, infer_scope_types};
+pub fn check_types(db: &dyn Db, file: File) -> TypeCheckDiagnostics {
+    let _span = tracing::trace_span!("check_types", file=?file.path(db)).entered();
+
+    let index = semantic_index(db, file);
+    let mut diagnostics = TypeCheckDiagnostics::new();
+
+    for scope_id in index.scope_ids() {
+        let result = infer_scope_types(db, scope_id);
+        diagnostics.extend(result.diagnostics());
+    }
+
+    diagnostics
+}

 /// Infer the public type of a symbol (its type as seen from outside its scope).
-pub(crate) fn symbol_ty<'db>(
+pub(crate) fn symbol_ty_by_id<'db>(
    db: &'db dyn Db,
    scope: ScopeId<'db>,
    symbol: ScopedSymbolId,
@@ -31,30 +59,17 @@ pub(crate) fn symbol_ty<'db>(
 }

 /// Shorthand for `symbol_ty` that takes a symbol name instead of an ID.
-pub(crate) fn symbol_ty_by_name<'db>(
-    db: &'db dyn Db,
-    scope: ScopeId<'db>,
-    name: &str,
-) -> Type<'db> {
+pub(crate) fn symbol_ty<'db>(db: &'db dyn Db, scope: ScopeId<'db>, name: &str) -> Type<'db> {
    let table = symbol_table(db, scope);
    table
        .symbol_id_by_name(name)
-        .map(|symbol| symbol_ty(db, scope, symbol))
+        .map(|symbol| symbol_ty_by_id(db, scope, symbol))
        .unwrap_or(Type::Unbound)
 }

 /// Shorthand for `symbol_ty` that looks up a module-global symbol by name in a file.
-pub(crate) fn global_symbol_ty_by_name<'db>(db: &'db dyn Db, file: File, name: &str) -> Type<'db> {
-    symbol_ty_by_name(db, global_scope(db, file), name)
-}
-
-/// Shorthand for `symbol_ty` that looks up a symbol in the builtins.
-///
-/// Returns `Unbound` if the builtins module isn't available for some reason.
-pub(crate) fn builtins_symbol_ty_by_name<'db>(db: &'db dyn Db, name: &str) -> Type<'db> {
-    builtins_scope(db)
-        .map(|builtins| symbol_ty_by_name(db, builtins, name))
-        .unwrap_or(Type::Unbound)
+pub(crate) fn global_symbol_ty<'db>(db: &'db dyn Db, file: File, name: &str) -> Type<'db> {
+    symbol_ty(db, global_scope(db, file), name)
 }

 /// Infer the type of a [`Definition`].
@@ -63,6 +78,24 @@ pub(crate) fn definition_ty<'db>(db: &'db dyn Db, definition: Definition<'db>) -
    inference.definition_ty(definition)
 }

+/// Infer the type of a (possibly deferred) sub-expression of a [`Definition`].
+///
+/// ## Panics
+/// If the given expression is not a sub-expression of the given [`Definition`].
+pub(crate) fn definition_expression_ty<'db>(
+    db: &'db dyn Db,
+    definition: Definition<'db>,
+    expression: &ast::Expr,
+) -> Type<'db> {
+    let expr_id = expression.scoped_ast_id(db, definition.scope(db));
+    let inference = infer_definition_types(db, definition);
+    if let Some(ty) = inference.try_expression_ty(expr_id) {
+        ty
+    } else {
+        infer_deferred_types(db, definition).expression_ty(expr_id)
+    }
+}
+
 /// Infer the combined type of an array of [`Definition`]s, plus one optional "unbound type".
 ///
 /// Will return a union if there is more than one definition, or at least one plus an unbound
@@ -80,44 +113,65 @@ pub(crate) fn definition_ty<'db>(db: &'db dyn Db, definition: Definition<'db>) -
 /// provide an `unbound_ty`.
 pub(crate) fn definitions_ty<'db>(
    db: &'db dyn Db,
-    definitions: &[Definition<'db>],
+    definitions_with_constraints: DefinitionWithConstraintsIterator<'_, 'db>,
    unbound_ty: Option<Type<'db>>,
 ) -> Type<'db> {
-    let def_types = definitions.iter().map(|def| definition_ty(db, *def));
+    let def_types = definitions_with_constraints.map(
+        |DefinitionWithConstraints {
+             definition,
+             constraints,
+         }| {
+            let mut constraint_tys =
+                constraints.filter_map(|test| narrowing_constraint(db, test, definition));
+            let definition_ty = definition_ty(db, definition);
+            if let Some(first_constraint_ty) = constraint_tys.next() {
+                let mut builder = IntersectionBuilder::new(db);
+                builder = builder
+                    .add_positive(definition_ty)
+                    .add_positive(first_constraint_ty);
+                for constraint_ty in constraint_tys {
+                    builder = builder.add_positive(constraint_ty);
+                }
+                builder.build()
+            } else {
+                definition_ty
+            }
+        },
+    );
    let mut all_types = unbound_ty.into_iter().chain(def_types);

-    let Some(first) = all_types.next() else {
-        panic!("definitions_ty should never be called with zero definitions and no unbound_ty.")
-    };
+    let first = all_types
+        .next()
+        .expect("definitions_ty should never be called with zero definitions and no unbound_ty.");

    if let Some(second) = all_types.next() {
-        let mut builder = UnionTypeBuilder::new(db);
+        let mut builder = UnionBuilder::new(db);
        builder = builder.add(first).add(second);

        for variant in all_types {
            builder = builder.add(variant);
        }

-        Type::Union(builder.build())
+        builder.build()
    } else {
        first
    }
 }

 /// Unique ID for a type.
-#[derive(Copy, Clone, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 pub enum Type<'db> {
    /// the dynamic type: a statically-unknown set of values
    Any,
    /// the empty set of values
    Never,
-    /// unknown type (no annotation)
+    /// unknown type (either no annotation, or some kind of type error)
    /// equivalent to Any, or possibly to object in strict mode
    Unknown,
    /// name does not exist or is not bound to any value (this represents an error, but with some
    /// leniency options it could be silently resolved to Unknown in some cases)
    Unbound,
-    /// the None object (TODO remove this in favor of Instance(types.NoneType)
+    /// the None object -- TODO remove this in favor of Instance(types.NoneType)
    None,
    /// a specific function object
    Function(FunctionType<'db>),
@@ -127,11 +181,21 @@ pub enum Type<'db> {
    Class(ClassType<'db>),
    /// the set of Python objects with the given class in their __class__'s method resolution order
    Instance(ClassType<'db>),
+    /// the set of objects in any of the types in the union
    Union(UnionType<'db>),
+    /// the set of objects in all of the types in the intersection
    Intersection(IntersectionType<'db>),
+    /// An integer literal
    IntLiteral(i64),
    /// A boolean literal, either `True` or `False`.
    BooleanLiteral(bool),
+    /// A string literal
+    StringLiteral(StringLiteralType<'db>),
+    /// A string known to originate only from literal values, but whose value is not known (unlike
+    /// `StringLiteral` above).
+    LiteralString,
+    /// A bytes literal
+    BytesLiteral(BytesLiteralType<'db>),
    // TODO protocols, callable types, overloads, generics, type vars
 }

@@ -140,49 +204,243 @@ impl<'db> Type<'db> {
        matches!(self, Type::Unbound)
    }

-    pub const fn is_unknown(&self) -> bool {
-        matches!(self, Type::Unknown)
+    pub const fn is_never(&self) -> bool {
+        matches!(self, Type::Never)
+    }
+
+    pub const fn into_class_type(self) -> Option<ClassType<'db>> {
+        match self {
+            Type::Class(class_type) => Some(class_type),
+            _ => None,
+        }
+    }
+
+    pub fn expect_class(self) -> ClassType<'db> {
+        self.into_class_type()
+            .expect("Expected a Type::Class variant")
+    }
+
+    pub const fn into_module_type(self) -> Option<File> {
+        match self {
+            Type::Module(file) => Some(file),
+            _ => None,
+        }
+    }
+
+    pub fn expect_module(self) -> File {
+        self.into_module_type()
+            .expect("Expected a Type::Module variant")
+    }
+
+    pub const fn into_union_type(self) -> Option<UnionType<'db>> {
+        match self {
+            Type::Union(union_type) => Some(union_type),
+            _ => None,
+        }
+    }
+
+    pub fn expect_union(self) -> UnionType<'db> {
+        self.into_union_type()
+            .expect("Expected a Type::Union variant")
+    }
+
+    pub const fn into_intersection_type(self) -> Option<IntersectionType<'db>> {
+        match self {
+            Type::Intersection(intersection_type) => Some(intersection_type),
+            _ => None,
+        }
+    }
+
+    pub fn expect_intersection(self) -> IntersectionType<'db> {
+        self.into_intersection_type()
+            .expect("Expected a Type::Intersection variant")
+    }
+
+    pub const fn into_function_type(self) -> Option<FunctionType<'db>> {
+        match self {
+            Type::Function(function_type) => Some(function_type),
+            _ => None,
+        }
+    }
+
+    pub fn expect_function(self) -> FunctionType<'db> {
+        self.into_function_type()
+            .expect("Expected a Type::Function variant")
+    }
+
+    pub const fn into_int_literal_type(self) -> Option<i64> {
+        match self {
+            Type::IntLiteral(value) => Some(value),
+            _ => None,
+        }
+    }
+
+    pub fn expect_int_literal(self) -> i64 {
+        self.into_int_literal_type()
+            .expect("Expected a Type::IntLiteral variant")
+    }
+
+    pub fn may_be_unbound(&self, db: &'db dyn Db) -> bool {
+        match self {
+            Type::Unbound => true,
+            Type::Union(union) => union.contains(db, Type::Unbound),
+            // Unbound can't appear in an intersection, because an intersection with Unbound
+            // simplifies to just Unbound.
+            _ => false,
+        }
    }

    #[must_use]
-    pub fn member(&self, db: &'db dyn Db, name: &Name) -> Type<'db> {
+    pub fn replace_unbound_with(&self, db: &'db dyn Db, replacement: Type<'db>) -> Type<'db> {
+        match self {
+            Type::Unbound => replacement,
+            Type::Union(union) => {
+                union.map(db, |element| element.replace_unbound_with(db, replacement))
+            }
+            ty => *ty,
+        }
+    }
+
+    /// Resolve a member access of a type.
+    ///
+    /// For example, if `foo` is `Type::Instance(<Bar>)`,
+    /// `foo.member(&db, "baz")` returns the type of `baz` attributes
+    /// as accessed from instances of the `Bar` class.
+    ///
+    /// TODO: use of this method currently requires manually checking
+    /// whether the returned type is `Unknown`/`Unbound`
+    /// (or a union with `Unknown`/`Unbound`) in many places.
+    /// Ideally we'd use a more type-safe pattern, such as returning
+    /// an `Option` or a `Result` from this method, which would force
+    /// us to explicitly consider whether to handle an error or propagate
+    /// it up the call stack.
+    #[must_use]
+    pub fn member(&self, db: &'db dyn Db, name: &str) -> Type<'db> {
        match self {
            Type::Any => Type::Any,
-            Type::Never => todo!("attribute lookup on Never type"),
+            Type::Never => {
+                // TODO: attribute lookup on Never type
+                Type::Unknown
+            }
            Type::Unknown => Type::Unknown,
            Type::Unbound => Type::Unbound,
-            Type::None => todo!("attribute lookup on None type"),
-            Type::Function(_) => todo!("attribute lookup on Function type"),
-            Type::Module(file) => global_symbol_ty_by_name(db, *file, name),
+            Type::None => {
+                // TODO: attribute lookup on None type
+                Type::Unknown
+            }
+            Type::Function(_) => {
+                // TODO: attribute lookup on function type
+                Type::Unknown
+            }
+            Type::Module(file) => global_symbol_ty(db, *file, name),
            Type::Class(class) => class.class_member(db, name),
            Type::Instance(_) => {
                // TODO MRO? get_own_instance_member, get_instance_member
-                todo!("attribute lookup on Instance type")
+                Type::Unknown
            }
-            Type::Union(union) => Type::Union(
-                union
-                    .elements(db)
-                    .iter()
-                    .fold(UnionTypeBuilder::new(db), |builder, element_ty| {
-                        builder.add(element_ty.member(db, name))
-                    })
-                    .build(),
-            ),
+            Type::Union(union) => union.map(db, |element| element.member(db, name)),
            Type::Intersection(_) => {
                // TODO perform the get_member on each type in the intersection
                // TODO return the intersection of those results
-                todo!("attribute lookup on Intersection type")
+                Type::Unknown
            }
            Type::IntLiteral(_) => {
                // TODO raise error
                Type::Unknown
            }
            Type::BooleanLiteral(_) => Type::Unknown,
+            Type::StringLiteral(_) => {
+                // TODO defer to `typing.LiteralString`/`builtins.str` methods
+                // from typeshed's stubs
+                Type::Unknown
+            }
+            Type::LiteralString => {
+                // TODO defer to `typing.LiteralString`/`builtins.str` methods
+                // from typeshed's stubs
+                Type::Unknown
+            }
+            Type::BytesLiteral(_) => {
+                // TODO defer to Type::Instance(<bytes from typeshed>).member
+                Type::Unknown
+            }
        }
    }

+    /// Return the type resulting from calling an object of this type.
+    ///
+    /// Returns `None` if `self` is not a callable type.
    #[must_use]
-    pub fn instance(&self) -> Type<'db> {
+    pub fn call(&self, db: &'db dyn Db) -> Option<Type<'db>> {
+        match self {
+            Type::Function(function_type) => Some(function_type.return_type(db)),
+
+            // TODO annotated return type on `__new__` or metaclass `__call__`
+            Type::Class(class) => Some(Type::Instance(*class)),
+
+            // TODO: handle classes which implement the Callable protocol
+            Type::Instance(_instance_ty) => Some(Type::Unknown),
+
+            // `Any` is callable, and its return type is also `Any`.
+            Type::Any => Some(Type::Any),
+
+            Type::Unknown => Some(Type::Unknown),
+
+            // TODO: union and intersection types, if they reduce to `Callable`
+            Type::Union(_) => Some(Type::Unknown),
+            Type::Intersection(_) => Some(Type::Unknown),
+
+            _ => None,
+        }
+    }
+
+    /// Given the type of an object that is iterated over in some way,
+    /// return the type of objects that are yielded by that iteration.
+    ///
+    /// E.g., for the following loop, given the type of `x`, infer the type of `y`:
+    /// ```python
+    /// for y in x:
+    ///     pass
+    /// ```
+    fn iterate(&self, db: &'db dyn Db) -> IterationOutcome<'db> {
+        // `self` represents the type of the iterable;
+        // `__iter__` and `__next__` are both looked up on the class of the iterable:
+        let iterable_meta_type = self.to_meta_type(db);
+
+        let dunder_iter_method = iterable_meta_type.member(db, "__iter__");
+        if !dunder_iter_method.is_unbound() {
+            let Some(iterator_ty) = dunder_iter_method.call(db) else {
+                return IterationOutcome::NotIterable {
+                    not_iterable_ty: *self,
+                };
+            };
+
+            let dunder_next_method = iterator_ty.to_meta_type(db).member(db, "__next__");
+            return dunder_next_method
+                .call(db)
+                .map(|element_ty| IterationOutcome::Iterable { element_ty })
+                .unwrap_or(IterationOutcome::NotIterable {
+                    not_iterable_ty: *self,
+                });
+        }
+
+        // Although it's not considered great practice,
+        // classes that define `__getitem__` are also iterable,
+        // even if they do not define `__iter__`.
+        //
+        // TODO(Alex) this is only valid if the `__getitem__` method is annotated as
+        // accepting `int` or `SupportsIndex`
+        let dunder_get_item_method = iterable_meta_type.member(db, "__getitem__");
+
+        dunder_get_item_method
+            .call(db)
+            .map(|element_ty| IterationOutcome::Iterable { element_ty })
+            .unwrap_or(IterationOutcome::NotIterable {
+                not_iterable_ty: *self,
+            })
+    }
+
+    #[must_use]
+    pub fn to_instance(&self) -> Type<'db> {
        match self {
            Type::Any => Type::Any,
            Type::Unknown => Type::Unknown,
@@ -190,12 +448,65 @@ impl<'db> Type<'db> {
            _ => Type::Unknown, // TODO type errors
        }
    }
+
+    /// Given a type that is assumed to represent an instance of a class,
+    /// return a type that represents that class itself.
+    #[must_use]
+    pub fn to_meta_type(&self, db: &'db dyn Db) -> Type<'db> {
+        match self {
+            Type::Unbound => Type::Unbound,
+            Type::Never => Type::Never,
+            Type::Instance(class) => Type::Class(*class),
+            Type::Union(union) => union.map(db, |ty| ty.to_meta_type(db)),
+            Type::BooleanLiteral(_) => builtins_symbol_ty(db, "bool"),
+            Type::BytesLiteral(_) => builtins_symbol_ty(db, "bytes"),
+            Type::IntLiteral(_) => builtins_symbol_ty(db, "int"),
+            Type::Function(_) => types_symbol_ty(db, "FunctionType"),
+            Type::Module(_) => types_symbol_ty(db, "ModuleType"),
+            Type::None => typeshed_symbol_ty(db, "NoneType"),
+            // TODO not accurate if there's a custom metaclass...
+            Type::Class(_) => builtins_symbol_ty(db, "type"),
+            // TODO can we do better here? `type[LiteralString]`?
+            Type::StringLiteral(_) | Type::LiteralString => builtins_symbol_ty(db, "str"),
+            // TODO: `type[Any]`?
+            Type::Any => Type::Any,
+            // TODO: `type[Unknown]`?
+            Type::Unknown => Type::Unknown,
+            // TODO intersections
+            Type::Intersection(_) => Type::Unknown,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum IterationOutcome<'db> {
+    Iterable { element_ty: Type<'db> },
+    NotIterable { not_iterable_ty: Type<'db> },
+}
+
+impl<'db> IterationOutcome<'db> {
+    fn unwrap_with_diagnostic(
+        self,
+        iterable_node: ast::AnyNodeRef,
+        inference_builder: &mut TypeInferenceBuilder<'db>,
+    ) -> Type<'db> {
+        match self {
+            Self::Iterable { element_ty } => element_ty,
+            Self::NotIterable { not_iterable_ty } => {
+                inference_builder.not_iterable_diagnostic(iterable_node, not_iterable_ty);
+                Type::Unknown
+            }
+        }
+    }
 }

 #[salsa::interned]
 pub struct FunctionType<'db> {
    /// name of the function at definition
-    pub name: Name,
+    #[return_ref]
+    pub name: ast::name::Name,
+
+    definition: Definition<'db>,

    /// types of all decorators on this function
    decorators: Vec<Type<'db>>,
@@ -205,24 +516,69 @@ impl<'db> FunctionType<'db> {
    pub fn has_decorator(self, db: &dyn Db, decorator: Type<'_>) -> bool {
        self.decorators(db).contains(&decorator)
    }
+
+    /// inferred return type for this function
+    pub fn return_type(&self, db: &'db dyn Db) -> Type<'db> {
+        let definition = self.definition(db);
+        let DefinitionKind::Function(function_stmt_node) = definition.node(db) else {
+            panic!("Function type definition must have `DefinitionKind::Function`")
+        };
+
+        // TODO if a function `bar` is decorated by `foo`,
+        // where `foo` is annotated as returning a type `X` that is a subtype of `Callable`,
+        // we need to infer the return type from `X`'s return annotation
+        // rather than from `bar`'s return annotation
+        // in order to determine the type that `bar` returns
+        if !function_stmt_node.decorator_list.is_empty() {
+            return Type::Unknown;
+        }
+
+        function_stmt_node
+            .returns
+            .as_ref()
+            .map(|returns| {
+                if function_stmt_node.is_async {
+                    // TODO: generic `types.CoroutineType`!
+                    Type::Unknown
+                } else {
+                    definition_expression_ty(db, definition, returns.as_ref())
+                }
+            })
+            .unwrap_or(Type::Unknown)
+    }
 }

 #[salsa::interned]
 pub struct ClassType<'db> {
    /// Name of the class at definition
-    pub name: Name,
+    #[return_ref]
+    pub name: ast::name::Name,

-    /// Types of all class bases
-    bases: Vec<Type<'db>>,
+    definition: Definition<'db>,

    body_scope: ScopeId<'db>,
 }

 impl<'db> ClassType<'db> {
+    /// Return an iterator over the types of this class's bases.
+    ///
+    /// # Panics:
+    /// If `definition` is not a `DefinitionKind::Class`.
+    pub fn bases(&self, db: &'db dyn Db) -> impl Iterator<Item = Type<'db>> {
+        let definition = self.definition(db);
+        let DefinitionKind::Class(class_stmt_node) = definition.node(db) else {
+            panic!("Class type definition must have DefinitionKind::Class");
+        };
+        class_stmt_node
+            .bases()
+            .iter()
+            .map(move |base_expr| definition_expression_ty(db, definition, base_expr))
+    }
+
    /// Returns the class member of this class named `name`.
    ///
    /// The member resolves to a member of the class itself or any of its bases.
-    pub fn class_member(self, db: &'db dyn Db, name: &Name) -> Type<'db> {
+    pub fn class_member(self, db: &'db dyn Db, name: &str) -> Type<'db> {
        let member = self.own_class_member(db, name);
        if !member.is_unbound() {
            return member;
@@ -232,12 +588,12 @@ impl<'db> ClassType<'db> {
    }

    /// Returns the inferred type of the class member named `name`.
-    pub fn own_class_member(self, db: &'db dyn Db, name: &Name) -> Type<'db> {
+    pub fn own_class_member(self, db: &'db dyn Db, name: &str) -> Type<'db> {
        let scope = self.body_scope(db);
-        symbol_ty_by_name(db, scope, name)
+        symbol_ty(db, scope, name)
    }

-    pub fn inherited_class_member(self, db: &'db dyn Db, name: &Name) -> Type<'db> {
+    pub fn inherited_class_member(self, db: &'db dyn Db, name: &str) -> Type<'db> {
        for base in self.bases(db) {
            let member = base.member(db, name);
            if !member.is_unbound() {
@@ -251,7 +607,8 @@ impl<'db> ClassType<'db> {

 #[salsa::interned]
 pub struct UnionType<'db> {
-    /// the union type includes values in any of these types
+    /// The union type includes values in any of these types.
+    #[return_ref]
    elements: FxOrderSet<Type<'db>>,
 }

@@ -259,50 +616,275 @@ impl<'db> UnionType<'db> {
    pub fn contains(&self, db: &'db dyn Db, ty: Type<'db>) -> bool {
        self.elements(db).contains(&ty)
    }
-}

-struct UnionTypeBuilder<'db> {
-    elements: FxOrderSet<Type<'db>>,
-    db: &'db dyn Db,
-}
-
-impl<'db> UnionTypeBuilder<'db> {
-    fn new(db: &'db dyn Db) -> Self {
-        Self {
-            db,
-            elements: FxOrderSet::default(),
-        }
-    }
-
-    /// Adds a type to this union.
-    fn add(mut self, ty: Type<'db>) -> Self {
-        match ty {
-            Type::Union(union) => {
-                self.elements.extend(&union.elements(self.db));
-            }
-            _ => {
-                self.elements.insert(ty);
-            }
-        }
-
-        self
-    }
-
-    fn build(self) -> UnionType<'db> {
-        UnionType::new(self.db, self.elements)
+    /// Apply a transformation function to all elements of the union,
+    /// and create a new union from the resulting set of types
+    pub fn map(
+        &self,
+        db: &'db dyn Db,
+        mut transform_fn: impl FnMut(&Type<'db>) -> Type<'db>,
+    ) -> Type<'db> {
+        self.elements(db)
+            .into_iter()
+            .fold(UnionBuilder::new(db), |builder, element| {
+                builder.add(transform_fn(element))
+            })
+            .build()
    }
 }

-// Negation types aren't expressible in annotations, and are most likely to arise from type
-// narrowing along with intersections (e.g. `if not isinstance(...)`), so we represent them
-// directly in intersections rather than as a separate type. This sacrifices some efficiency in the
-// case where a Not appears outside an intersection (unclear when that could even happen, but we'd
-// have to represent it as a single-element intersection if it did) in exchange for better
-// efficiency in the within-intersection case.
 #[salsa::interned]
 pub struct IntersectionType<'db> {
-    // the intersection type includes only values in all of these types
+    /// The intersection type includes only values in all of these types.
+    #[return_ref]
    positive: FxOrderSet<Type<'db>>,
-    // the intersection type does not include any value in any of these types
+
+    /// The intersection type does not include any value in any of these types.
+    ///
+    /// Negation types aren't expressible in annotations, and are most likely to arise from type
+    /// narrowing along with intersections (e.g. `if not isinstance(...)`), so we represent them
+    /// directly in intersections rather than as a separate type.
+    #[return_ref]
    negative: FxOrderSet<Type<'db>>,
 }
+
+#[salsa::interned]
+pub struct StringLiteralType<'db> {
+    #[return_ref]
+    value: Box<str>,
+}
+
+#[salsa::interned]
+pub struct BytesLiteralType<'db> {
+    #[return_ref]
+    value: Box<[u8]>,
+}
+
+#[cfg(test)]
+mod tests {
+    use anyhow::Context;
+
+    use ruff_db::files::system_path_to_file;
+    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+
+    use crate::db::tests::TestDb;
+    use crate::{Program, ProgramSettings, PythonVersion, SearchPathSettings};
+
+    use super::TypeCheckDiagnostics;
+
+    fn setup_db() -> TestDb {
+        let db = TestDb::new();
+        db.memory_file_system()
+            .create_directory_all("/src")
+            .unwrap();
+
+        Program::from_settings(
+            &db,
+            &ProgramSettings {
+                target_version: PythonVersion::default(),
+                search_paths: SearchPathSettings::new(SystemPathBuf::from("/src")),
+            },
+        )
+        .expect("Valid search path settings");
+
+        db
+    }
+
+    fn assert_diagnostic_messages(diagnostics: &TypeCheckDiagnostics, expected: &[&str]) {
+        let messages: Vec<&str> = diagnostics
+            .iter()
+            .map(|diagnostic| diagnostic.message())
+            .collect();
+        assert_eq!(&messages, expected);
+    }
+
+    #[test]
+    fn unresolved_import_statement() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_file("src/foo.py", "import bar\n")
+            .context("Failed to write foo.py")?;
+
+        let foo = system_path_to_file(&db, "src/foo.py").context("Failed to resolve foo.py")?;
+
+        let diagnostics = super::check_types(&db, foo);
+        assert_diagnostic_messages(&diagnostics, &["Cannot resolve import 'bar'."]);
+
+        Ok(())
+    }
+
+    #[test]
+    fn unresolved_import_from_statement() {
+        let mut db = setup_db();
+
+        db.write_file("src/foo.py", "from bar import baz\n")
+            .unwrap();
+        let foo = system_path_to_file(&db, "src/foo.py").unwrap();
+        let diagnostics = super::check_types(&db, foo);
+        assert_diagnostic_messages(&diagnostics, &["Cannot resolve import 'bar'."]);
+    }
+
+    #[test]
+    fn unresolved_import_from_resolved_module() {
+        let mut db = setup_db();
+
+        db.write_files([("/src/a.py", ""), ("/src/b.py", "from a import thing")])
+            .unwrap();
+
+        let b_file = system_path_to_file(&db, "/src/b.py").unwrap();
+        let b_file_diagnostics = super::check_types(&db, b_file);
+        assert_diagnostic_messages(&b_file_diagnostics, &["Module 'a' has no member 'thing'"]);
+    }
+
+    #[test]
+    fn resolved_import_of_symbol_from_unresolved_import() {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("/src/a.py", "import foo as foo"),
+            ("/src/b.py", "from a import foo"),
+        ])
+        .unwrap();
+
+        let a_file = system_path_to_file(&db, "/src/a.py").unwrap();
+        let a_file_diagnostics = super::check_types(&db, a_file);
+        assert_diagnostic_messages(&a_file_diagnostics, &["Cannot resolve import 'foo'."]);
+
+        // Importing the unresolved import into a second first-party file should not trigger
+        // an additional "unresolved import" violation
+        let b_file = system_path_to_file(&db, "/src/b.py").unwrap();
+        let b_file_diagnostics = super::check_types(&db, b_file);
+        assert_eq!(&*b_file_diagnostics, &[]);
+    }
+
+    #[test]
+    fn invalid_callable() {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "src/a.py",
+            "
+            nonsense = 123
+            x = nonsense()
+            ",
+        )
+        .unwrap();
+
+        let a_file = system_path_to_file(&db, "/src/a.py").unwrap();
+        let a_file_diagnostics = super::check_types(&db, a_file);
+        assert_diagnostic_messages(
+            &a_file_diagnostics,
+            &["Object of type 'Literal[123]' is not callable"],
+        );
+    }
+
+    #[test]
+    fn invalid_iterable() {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "src/a.py",
+            "
+            nonsense = 123
+            for x in nonsense:
+                pass
+            ",
+        )
+        .unwrap();
+
+        let a_file = system_path_to_file(&db, "/src/a.py").unwrap();
+        let a_file_diagnostics = super::check_types(&db, a_file);
+        assert_diagnostic_messages(
+            &a_file_diagnostics,
+            &["Object of type 'Literal[123]' is not iterable"],
+        );
+    }
+
+    #[test]
+    fn new_iteration_protocol_takes_precedence_over_old_style() {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "src/a.py",
+            "
+            class NotIterable:
+                def __getitem__(self, key: int) -> int:
+                    return 42
+
+                __iter__ = None
+
+            for x in NotIterable():
+                pass
+            ",
+        )
+        .unwrap();
+
+        let a_file = system_path_to_file(&db, "/src/a.py").unwrap();
+        let a_file_diagnostics = super::check_types(&db, a_file);
+        assert_diagnostic_messages(
+            &a_file_diagnostics,
+            &["Object of type 'NotIterable' is not iterable"],
+        );
+    }
+
+    #[test]
+    fn starred_expressions_must_be_iterable() {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "src/a.py",
+            "
+            class NotIterable: pass
+
+            class Iterator:
+                def __next__(self) -> int:
+                    return 42
+
+            class Iterable:
+                def __iter__(self) -> Iterator:
+
+            x = [*NotIterable()]
+            y = [*Iterable()]
+            ",
+        )
+        .unwrap();
+
+        let a_file = system_path_to_file(&db, "/src/a.py").unwrap();
+        let a_file_diagnostics = super::check_types(&db, a_file);
+        assert_diagnostic_messages(
+            &a_file_diagnostics,
+            &["Object of type 'NotIterable' is not iterable"],
+        );
+    }
+
+    #[test]
+    fn yield_from_expression_must_be_iterable() {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "src/a.py",
+            "
+            class NotIterable: pass
+
+            class Iterator:
+                def __next__(self) -> int:
+                    return 42
+
+            class Iterable:
+                def __iter__(self) -> Iterator:
+
+            def generator_function():
+                yield from Iterable()
+                yield from NotIterable()
+            ",
+        )
+        .unwrap();
+
+        let a_file = system_path_to_file(&db, "/src/a.py").unwrap();
+        let a_file_diagnostics = super::check_types(&db, a_file);
+        assert_diagnostic_messages(
+            &a_file_diagnostics,
+            &["Object of type 'NotIterable' is not iterable"],
+        );
+    }
+}
--- a/crates/red_knot_python_semantic/src/types/builder.rs
+++ b/crates/red_knot_python_semantic/src/types/builder.rs
@@ -0,0 +1,542 @@
+//! Smart builders for union and intersection types.
+//!
+//! Invariants we maintain here:
+//!   * No single-element union types (should just be the contained type instead.)
+//!   * No single-positive-element intersection types. Single-negative-element are OK, we don't
+//!     have a standalone negation type so there's no other representation for this.
+//!   * The same type should never appear more than once in a union or intersection. (This should
+//!     be expanded to cover subtyping -- see below -- but for now we only implement it for type
+//!     identity.)
+//!   * Disjunctive normal form (DNF): the tree of unions and intersections can never be deeper
+//!     than a union-of-intersections. Unions cannot contain other unions (the inner union just
+//!     flattens into the outer one), intersections cannot contain other intersections (also
+//!     flattens), and intersections cannot contain unions (the intersection distributes over the
+//!     union, inverting it into a union-of-intersections).
+//!
+//! The implication of these invariants is that a [`UnionBuilder`] does not necessarily build a
+//! [`Type::Union`]. For example, if only one type is added to the [`UnionBuilder`], `build()` will
+//! just return that type directly. The same is true for [`IntersectionBuilder`]; for example, if a
+//! union type is added to the intersection, it will distribute and [`IntersectionBuilder::build`]
+//! may end up returning a [`Type::Union`] of intersections.
+//!
+//! In the future we should have these additional invariants, but they aren't implemented yet:
+//!   * No type in a union can be a subtype of any other type in the union (just eliminate the
+//!     subtype from the union).
+//!   * No type in an intersection can be a supertype of any other type in the intersection (just
+//!     eliminate the supertype from the intersection).
+//!   * An intersection containing two non-overlapping types should simplify to [`Type::Never`].
+use crate::types::{builtins_symbol_ty, IntersectionType, Type, UnionType};
+use crate::{Db, FxOrderSet};
+use ordermap::set::MutableValues;
+
+pub(crate) struct UnionBuilder<'db> {
+    elements: FxOrderSet<Type<'db>>,
+    db: &'db dyn Db,
+}
+
+impl<'db> UnionBuilder<'db> {
+    pub(crate) fn new(db: &'db dyn Db) -> Self {
+        Self {
+            db,
+            elements: FxOrderSet::default(),
+        }
+    }
+
+    /// Adds a type to this union.
+    pub(crate) fn add(mut self, ty: Type<'db>) -> Self {
+        match ty {
+            Type::Union(union) => {
+                self.elements.extend(union.elements(self.db));
+            }
+            Type::Never => {}
+            _ => {
+                self.elements.insert(ty);
+            }
+        }
+
+        self
+    }
+
+    /// Performs the following normalizations:
+    ///     - Replaces `Literal[True,False]` with `bool`.
+    ///     - TODO For enums `E` with members `X1`,...,`Xn`, replaces
+    ///     `Literal[E.X1,...,E.Xn]` with `E`.
+    fn simplify(&mut self) {
+        if let Some(true_index) = self.elements.get_index_of(&Type::BooleanLiteral(true)) {
+            if self.elements.contains(&Type::BooleanLiteral(false)) {
+                *self.elements.get_index_mut2(true_index).unwrap() =
+                    builtins_symbol_ty(self.db, "bool");
+                self.elements.remove(&Type::BooleanLiteral(false));
+            }
+        }
+    }
+
+    pub(crate) fn build(mut self) -> Type<'db> {
+        match self.elements.len() {
+            0 => Type::Never,
+            1 => self.elements[0],
+            _ => {
+                self.simplify();
+
+                match self.elements.len() {
+                    0 => Type::Never,
+                    1 => self.elements[0],
+                    _ => {
+                        self.elements.shrink_to_fit();
+                        Type::Union(UnionType::new(self.db, self.elements))
+                    }
+                }
+            }
+        }
+    }
+}
+
+#[derive(Clone)]
+pub(crate) struct IntersectionBuilder<'db> {
+    // Really this builds a union-of-intersections, because we always keep our set-theoretic types
+    // in disjunctive normal form (DNF), a union of intersections. In the simplest case there's
+    // just a single intersection in this vector, and we are building a single intersection type,
+    // but if a union is added to the intersection, we'll distribute ourselves over that union and
+    // create a union of intersections.
+    intersections: Vec<InnerIntersectionBuilder<'db>>,
+    db: &'db dyn Db,
+}
+
+impl<'db> IntersectionBuilder<'db> {
+    pub(crate) fn new(db: &'db dyn Db) -> Self {
+        Self {
+            db,
+            intersections: vec![InnerIntersectionBuilder::new()],
+        }
+    }
+
+    fn empty(db: &'db dyn Db) -> Self {
+        Self {
+            db,
+            intersections: vec![],
+        }
+    }
+
+    pub(crate) fn add_positive(mut self, ty: Type<'db>) -> Self {
+        if let Type::Union(union) = ty {
+            // Distribute ourself over this union: for each union element, clone ourself and
+            // intersect with that union element, then create a new union-of-intersections with all
+            // of those sub-intersections in it. E.g. if `self` is a simple intersection `T1 & T2`
+            // and we add `T3 | T4` to the intersection, we don't get `T1 & T2 & (T3 | T4)` (that's
+            // not in DNF), we distribute the union and get `(T1 & T3) | (T2 & T3) | (T1 & T4) |
+            // (T2 & T4)`. If `self` is already a union-of-intersections `(T1 & T2) | (T3 & T4)`
+            // and we add `T5 | T6` to it, that flattens all the way out to `(T1 & T2 & T5) | (T1 &
+            // T2 & T6) | (T3 & T4 & T5) ...` -- you get the idea.
+            union
+                .elements(self.db)
+                .iter()
+                .map(|elem| self.clone().add_positive(*elem))
+                .fold(IntersectionBuilder::empty(self.db), |mut builder, sub| {
+                    builder.intersections.extend(sub.intersections);
+                    builder
+                })
+        } else {
+            // If we are already a union-of-intersections, distribute the new intersected element
+            // across all of those intersections.
+            for inner in &mut self.intersections {
+                inner.add_positive(self.db, ty);
+            }
+            self
+        }
+    }
+
+    pub(crate) fn add_negative(mut self, ty: Type<'db>) -> Self {
+        // See comments above in `add_positive`; this is just the negated version.
+        if let Type::Union(union) = ty {
+            union
+                .elements(self.db)
+                .iter()
+                .map(|elem| self.clone().add_negative(*elem))
+                .fold(IntersectionBuilder::empty(self.db), |mut builder, sub| {
+                    builder.intersections.extend(sub.intersections);
+                    builder
+                })
+        } else {
+            for inner in &mut self.intersections {
+                inner.add_negative(self.db, ty);
+            }
+            self
+        }
+    }
+
+    pub(crate) fn build(mut self) -> Type<'db> {
+        // Avoid allocating the UnionBuilder unnecessarily if we have just one intersection:
+        if self.intersections.len() == 1 {
+            self.intersections.pop().unwrap().build(self.db)
+        } else {
+            let mut builder = UnionBuilder::new(self.db);
+            for inner in self.intersections {
+                builder = builder.add(inner.build(self.db));
+            }
+            builder.build()
+        }
+    }
+}
+
+#[derive(Debug, Clone, Default)]
+struct InnerIntersectionBuilder<'db> {
+    positive: FxOrderSet<Type<'db>>,
+    negative: FxOrderSet<Type<'db>>,
+}
+
+impl<'db> InnerIntersectionBuilder<'db> {
+    fn new() -> Self {
+        Self::default()
+    }
+
+    /// Adds a positive type to this intersection.
+    fn add_positive(&mut self, db: &'db dyn Db, ty: Type<'db>) {
+        match ty {
+            Type::Intersection(inter) => {
+                let pos = inter.positive(db);
+                let neg = inter.negative(db);
+                self.positive.extend(pos.difference(&self.negative));
+                self.negative.extend(neg.difference(&self.positive));
+                self.positive.retain(|elem| !neg.contains(elem));
+                self.negative.retain(|elem| !pos.contains(elem));
+            }
+            _ => {
+                if !self.negative.remove(&ty) {
+                    self.positive.insert(ty);
+                };
+            }
+        }
+    }
+
+    /// Adds a negative type to this intersection.
+    fn add_negative(&mut self, db: &'db dyn Db, ty: Type<'db>) {
+        // TODO Any/Unknown actually should not self-cancel
+        match ty {
+            Type::Intersection(intersection) => {
+                let pos = intersection.negative(db);
+                let neg = intersection.positive(db);
+                self.positive.extend(pos.difference(&self.negative));
+                self.negative.extend(neg.difference(&self.positive));
+                self.positive.retain(|elem| !neg.contains(elem));
+                self.negative.retain(|elem| !pos.contains(elem));
+            }
+            Type::Never => {}
+            Type::Unbound => {}
+            _ => {
+                if !self.positive.remove(&ty) {
+                    self.negative.insert(ty);
+                };
+            }
+        }
+    }
+
+    fn simplify(&mut self) {
+        // TODO this should be generalized based on subtyping, for now we just handle a few cases
+
+        // Never is a subtype of all types
+        if self.positive.contains(&Type::Never) {
+            self.positive.retain(Type::is_never);
+            self.negative.clear();
+        }
+
+        if self.positive.contains(&Type::Unbound) {
+            self.positive.retain(Type::is_unbound);
+            self.negative.clear();
+        }
+
+        // None intersects only with object
+        for pos in &self.positive {
+            if let Type::Instance(_) = pos {
+                // could be `object` type
+            } else {
+                self.negative.remove(&Type::None);
+                break;
+            }
+        }
+    }
+
+    fn build(mut self, db: &'db dyn Db) -> Type<'db> {
+        self.simplify();
+        match (self.positive.len(), self.negative.len()) {
+            (0, 0) => Type::Never,
+            (1, 0) => self.positive[0],
+            _ => {
+                self.positive.shrink_to_fit();
+                self.negative.shrink_to_fit();
+                Type::Intersection(IntersectionType::new(db, self.positive, self.negative))
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{IntersectionBuilder, IntersectionType, Type, UnionBuilder, UnionType};
+    use crate::db::tests::TestDb;
+    use crate::program::{Program, SearchPathSettings};
+    use crate::python_version::PythonVersion;
+    use crate::types::builtins_symbol_ty;
+    use crate::ProgramSettings;
+    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+
+    impl<'db> UnionType<'db> {
+        fn elements_vec(self, db: &'db TestDb) -> Vec<Type<'db>> {
+            self.elements(db).into_iter().copied().collect()
+        }
+    }
+
+    fn setup_db() -> TestDb {
+        let db = TestDb::new();
+
+        let src_root = SystemPathBuf::from("/src");
+        db.memory_file_system()
+            .create_directory_all(&src_root)
+            .unwrap();
+
+        Program::from_settings(
+            &db,
+            &ProgramSettings {
+                target_version: PythonVersion::default(),
+                search_paths: SearchPathSettings::new(src_root),
+            },
+        )
+        .expect("Valid search path settings");
+
+        db
+    }
+
+    #[test]
+    fn build_union() {
+        let db = setup_db();
+        let t0 = Type::IntLiteral(0);
+        let t1 = Type::IntLiteral(1);
+        let union = UnionBuilder::new(&db)
+            .add(t0)
+            .add(t1)
+            .build()
+            .expect_union();
+
+        assert_eq!(union.elements_vec(&db), &[t0, t1]);
+    }
+
+    #[test]
+    fn build_union_single() {
+        let db = setup_db();
+        let t0 = Type::IntLiteral(0);
+        let ty = UnionBuilder::new(&db).add(t0).build();
+
+        assert_eq!(ty, t0);
+    }
+
+    #[test]
+    fn build_union_empty() {
+        let db = setup_db();
+        let ty = UnionBuilder::new(&db).build();
+
+        assert_eq!(ty, Type::Never);
+    }
+
+    #[test]
+    fn build_union_never() {
+        let db = setup_db();
+        let t0 = Type::IntLiteral(0);
+        let ty = UnionBuilder::new(&db).add(t0).add(Type::Never).build();
+
+        assert_eq!(ty, t0);
+    }
+
+    #[test]
+    fn build_union_bool() {
+        let db = setup_db();
+        let bool_ty = builtins_symbol_ty(&db, "bool");
+
+        let t0 = Type::BooleanLiteral(true);
+        let t1 = Type::BooleanLiteral(true);
+        let t2 = Type::BooleanLiteral(false);
+        let t3 = Type::IntLiteral(17);
+
+        let union = UnionBuilder::new(&db)
+            .add(t0)
+            .add(t1)
+            .add(t3)
+            .build()
+            .expect_union();
+        assert_eq!(union.elements_vec(&db), &[t0, t3]);
+        let union = UnionBuilder::new(&db)
+            .add(t0)
+            .add(t1)
+            .add(t2)
+            .add(t3)
+            .build()
+            .expect_union();
+
+        assert_eq!(union.elements_vec(&db), &[bool_ty, t3]);
+    }
+
+    #[test]
+    fn build_union_flatten() {
+        let db = setup_db();
+        let t0 = Type::IntLiteral(0);
+        let t1 = Type::IntLiteral(1);
+        let t2 = Type::IntLiteral(2);
+        let u1 = UnionBuilder::new(&db).add(t0).add(t1).build();
+        let union = UnionBuilder::new(&db)
+            .add(u1)
+            .add(t2)
+            .build()
+            .expect_union();
+
+        assert_eq!(union.elements_vec(&db), &[t0, t1, t2]);
+    }
+
+    impl<'db> IntersectionType<'db> {
+        fn pos_vec(self, db: &'db TestDb) -> Vec<Type<'db>> {
+            self.positive(db).into_iter().copied().collect()
+        }
+
+        fn neg_vec(self, db: &'db TestDb) -> Vec<Type<'db>> {
+            self.negative(db).into_iter().copied().collect()
+        }
+    }
+
+    #[test]
+    fn build_intersection() {
+        let db = setup_db();
+        let t0 = Type::IntLiteral(0);
+        let ta = Type::Any;
+        let intersection = IntersectionBuilder::new(&db)
+            .add_positive(ta)
+            .add_negative(t0)
+            .build()
+            .expect_intersection();
+
+        assert_eq!(intersection.pos_vec(&db), &[ta]);
+        assert_eq!(intersection.neg_vec(&db), &[t0]);
+    }
+
+    #[test]
+    fn build_intersection_flatten_positive() {
+        let db = setup_db();
+        let ta = Type::Any;
+        let t1 = Type::IntLiteral(1);
+        let t2 = Type::IntLiteral(2);
+        let i0 = IntersectionBuilder::new(&db)
+            .add_positive(ta)
+            .add_negative(t1)
+            .build();
+        let intersection = IntersectionBuilder::new(&db)
+            .add_positive(t2)
+            .add_positive(i0)
+            .build()
+            .expect_intersection();
+
+        assert_eq!(intersection.pos_vec(&db), &[t2, ta]);
+        assert_eq!(intersection.neg_vec(&db), &[t1]);
+    }
+
+    #[test]
+    fn build_intersection_flatten_negative() {
+        let db = setup_db();
+        let ta = Type::Any;
+        let t1 = Type::IntLiteral(1);
+        let t2 = Type::IntLiteral(2);
+        let i0 = IntersectionBuilder::new(&db)
+            .add_positive(ta)
+            .add_negative(t1)
+            .build();
+        let intersection = IntersectionBuilder::new(&db)
+            .add_positive(t2)
+            .add_negative(i0)
+            .build()
+            .expect_intersection();
+
+        assert_eq!(intersection.pos_vec(&db), &[t2, t1]);
+        assert_eq!(intersection.neg_vec(&db), &[ta]);
+    }
+
+    #[test]
+    fn intersection_distributes_over_union() {
+        let db = setup_db();
+        let t0 = Type::IntLiteral(0);
+        let t1 = Type::IntLiteral(1);
+        let ta = Type::Any;
+        let u0 = UnionBuilder::new(&db).add(t0).add(t1).build();
+
+        let union = IntersectionBuilder::new(&db)
+            .add_positive(ta)
+            .add_positive(u0)
+            .build()
+            .expect_union();
+        let [Type::Intersection(i0), Type::Intersection(i1)] = union.elements_vec(&db)[..] else {
+            panic!("expected a union of two intersections");
+        };
+        assert_eq!(i0.pos_vec(&db), &[ta, t0]);
+        assert_eq!(i1.pos_vec(&db), &[ta, t1]);
+    }
+
+    #[test]
+    fn build_intersection_self_negation() {
+        let db = setup_db();
+        let ty = IntersectionBuilder::new(&db)
+            .add_positive(Type::None)
+            .add_negative(Type::None)
+            .build();
+
+        assert_eq!(ty, Type::Never);
+    }
+
+    #[test]
+    fn build_intersection_simplify_negative_never() {
+        let db = setup_db();
+        let ty = IntersectionBuilder::new(&db)
+            .add_positive(Type::None)
+            .add_negative(Type::Never)
+            .build();
+
+        assert_eq!(ty, Type::None);
+    }
+
+    #[test]
+    fn build_intersection_simplify_positive_never() {
+        let db = setup_db();
+        let ty = IntersectionBuilder::new(&db)
+            .add_positive(Type::None)
+            .add_positive(Type::Never)
+            .build();
+
+        assert_eq!(ty, Type::Never);
+    }
+
+    #[test]
+    fn build_intersection_simplify_positive_unbound() {
+        let db = setup_db();
+        let ty = IntersectionBuilder::new(&db)
+            .add_positive(Type::Unbound)
+            .add_positive(Type::IntLiteral(1))
+            .build();
+
+        assert_eq!(ty, Type::Unbound);
+    }
+
+    #[test]
+    fn build_intersection_simplify_negative_unbound() {
+        let db = setup_db();
+        let ty = IntersectionBuilder::new(&db)
+            .add_negative(Type::Unbound)
+            .add_positive(Type::IntLiteral(1))
+            .build();
+
+        assert_eq!(ty, Type::IntLiteral(1));
+    }
+
+    #[test]
+    fn build_intersection_simplify_negative_none() {
+        let db = setup_db();
+        let ty = IntersectionBuilder::new(&db)
+            .add_negative(Type::None)
+            .add_positive(Type::IntLiteral(1))
+            .build();
+
+        assert_eq!(ty, Type::IntLiteral(1));
+    }
+}
--- a/crates/red_knot_python_semantic/src/types/diagnostic.rs
+++ b/crates/red_knot_python_semantic/src/types/diagnostic.rs
@@ -0,0 +1,111 @@
+use ruff_db::files::File;
+use ruff_text_size::{Ranged, TextRange};
+use std::fmt::Formatter;
+use std::ops::Deref;
+use std::sync::Arc;
+
+#[derive(Debug, Eq, PartialEq)]
+pub struct TypeCheckDiagnostic {
+    // TODO: Don't use string keys for rules
+    pub(super) rule: String,
+    pub(super) message: String,
+    pub(super) range: TextRange,
+    pub(super) file: File,
+}
+
+impl TypeCheckDiagnostic {
+    pub fn rule(&self) -> &str {
+        &self.rule
+    }
+
+    pub fn message(&self) -> &str {
+        &self.message
+    }
+
+    pub fn file(&self) -> File {
+        self.file
+    }
+}
+
+impl Ranged for TypeCheckDiagnostic {
+    fn range(&self) -> TextRange {
+        self.range
+    }
+}
+
+/// A collection of type check diagnostics.
+///
+/// The diagnostics are wrapped in an `Arc` because they need to be cloned multiple times
+/// when going from `infer_expression` to `check_file`. We could consider
+/// making [`TypeCheckDiagnostic`] a Salsa struct to have them Arena-allocated (once the Tables refactor is done).
+/// Using Salsa struct does have the downside that it leaks the Salsa dependency into diagnostics and
+/// each Salsa-struct comes with an overhead.
+#[derive(Default, Eq, PartialEq)]
+pub struct TypeCheckDiagnostics {
+    inner: Vec<std::sync::Arc<TypeCheckDiagnostic>>,
+}
+
+impl TypeCheckDiagnostics {
+    pub fn new() -> Self {
+        Self { inner: Vec::new() }
+    }
+
+    pub(super) fn push(&mut self, diagnostic: TypeCheckDiagnostic) {
+        self.inner.push(Arc::new(diagnostic));
+    }
+
+    pub(crate) fn shrink_to_fit(&mut self) {
+        self.inner.shrink_to_fit();
+    }
+}
+
+impl Extend<TypeCheckDiagnostic> for TypeCheckDiagnostics {
+    fn extend<T: IntoIterator<Item = TypeCheckDiagnostic>>(&mut self, iter: T) {
+        self.inner.extend(iter.into_iter().map(std::sync::Arc::new));
+    }
+}
+
+impl Extend<std::sync::Arc<TypeCheckDiagnostic>> for TypeCheckDiagnostics {
+    fn extend<T: IntoIterator<Item = Arc<TypeCheckDiagnostic>>>(&mut self, iter: T) {
+        self.inner.extend(iter);
+    }
+}
+
+impl<'a> Extend<&'a std::sync::Arc<TypeCheckDiagnostic>> for TypeCheckDiagnostics {
+    fn extend<T: IntoIterator<Item = &'a Arc<TypeCheckDiagnostic>>>(&mut self, iter: T) {
+        self.inner
+            .extend(iter.into_iter().map(std::sync::Arc::clone));
+    }
+}
+
+impl std::fmt::Debug for TypeCheckDiagnostics {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl Deref for TypeCheckDiagnostics {
+    type Target = [std::sync::Arc<TypeCheckDiagnostic>];
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl IntoIterator for TypeCheckDiagnostics {
+    type Item = Arc<TypeCheckDiagnostic>;
+    type IntoIter = std::vec::IntoIter<std::sync::Arc<TypeCheckDiagnostic>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.inner.into_iter()
+    }
+}
+
+impl<'a> IntoIterator for &'a TypeCheckDiagnostics {
+    type Item = &'a Arc<TypeCheckDiagnostic>;
+    type IntoIter = std::slice::Iter<'a, std::sync::Arc<TypeCheckDiagnostic>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.inner.iter()
+    }
+}
--- a/crates/red_knot_python_semantic/src/types/display.rs
+++ b/crates/red_knot_python_semantic/src/types/display.rs
@@ -2,13 +2,20 @@

 use std::fmt::{Display, Formatter};

+use ruff_python_ast::str::Quote;
+use ruff_python_literal::escape::AsciiEscape;
+
 use crate::types::{IntersectionType, Type, UnionType};
-use crate::Db;
+use crate::{Db, FxOrderMap};

 impl<'db> Type<'db> {
    pub fn display(&'db self, db: &'db dyn Db) -> DisplayType<'db> {
        DisplayType { ty: self, db }
    }
+
+    fn representation(&'db self, db: &'db dyn Db) -> DisplayRepresentation<'db> {
+        DisplayRepresentation { db, ty: self }
+    }
 }

 #[derive(Copy, Clone)]
@@ -18,6 +25,39 @@ pub struct DisplayType<'db> {
 }

 impl Display for DisplayType<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        let representation = self.ty.representation(self.db);
+        if matches!(
+            self.ty,
+            Type::IntLiteral(_)
+                | Type::BooleanLiteral(_)
+                | Type::StringLiteral(_)
+                | Type::BytesLiteral(_)
+                | Type::Class(_)
+                | Type::Function(_)
+        ) {
+            write!(f, "Literal[{representation}]",)
+        } else {
+            representation.fmt(f)
+        }
+    }
+}
+
+impl std::fmt::Debug for DisplayType<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        std::fmt::Display::fmt(self, f)
+    }
+}
+
+/// Writes the string representation of a type, which is the value displayed either as
+/// `Literal[<repr>]` or `Literal[<repr1>, <repr2>]` for literal types or as `<repr>` for
+/// non literals
+struct DisplayRepresentation<'db> {
+    ty: &'db Type<'db>,
+    db: &'db dyn Db,
+}
+
+impl std::fmt::Display for DisplayRepresentation<'_> {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        match self.ty {
            Type::Any => f.write_str("Any"),
@@ -29,25 +69,27 @@ impl Display for DisplayType<'_> {
                write!(f, "<module '{:?}'>", file.path(self.db))
            }
            // TODO functions and classes should display using a fully qualified name
-            Type::Class(class) => write!(f, "Literal[{}]", class.name(self.db)),
-            Type::Instance(class) => f.write_str(&class.name(self.db)),
-            Type::Function(function) => write!(f, "Literal[{}]", function.name(self.db)),
+            Type::Class(class) => f.write_str(class.name(self.db)),
+            Type::Instance(class) => f.write_str(class.name(self.db)),
+            Type::Function(function) => f.write_str(function.name(self.db)),
            Type::Union(union) => union.display(self.db).fmt(f),
            Type::Intersection(intersection) => intersection.display(self.db).fmt(f),
-            Type::IntLiteral(n) => write!(f, "Literal[{n}]"),
-            Type::BooleanLiteral(boolean) => {
-                write!(f, "Literal[{}]", if *boolean { "True" } else { "False" })
+            Type::IntLiteral(n) => write!(f, "{n}"),
+            Type::BooleanLiteral(boolean) => f.write_str(if *boolean { "True" } else { "False" }),
+            Type::StringLiteral(string) => {
+                write!(f, r#""{}""#, string.value(self.db).replace('"', r#"\""#))
+            }
+            Type::LiteralString => f.write_str("LiteralString"),
+            Type::BytesLiteral(bytes) => {
+                let escape =
+                    AsciiEscape::with_preferred_quote(bytes.value(self.db).as_ref(), Quote::Double);
+
+                escape.bytes_repr().write(f)
            }
        }
    }
 }

-impl std::fmt::Debug for DisplayType<'_> {
-    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
-        std::fmt::Display::fmt(self, f)
-    }
-}
-
 impl<'db> UnionType<'db> {
    fn display(&'db self, db: &'db dyn Db) -> DisplayUnionType<'db> {
        DisplayUnionType { db, ty: self }
@@ -61,45 +103,58 @@ struct DisplayUnionType<'db> {

 impl Display for DisplayUnionType<'_> {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
-        let union = self.ty;
+        let elements = self.ty.elements(self.db);

-        let (int_literals, other_types): (Vec<Type>, Vec<Type>) = union
-            .elements(self.db)
-            .iter()
-            .copied()
-            .partition(|ty| matches!(ty, Type::IntLiteral(_)));
+        // Group literal types by kind.
+        let mut grouped_literals = FxOrderMap::default();
+
+        for element in elements {
+            if let Ok(literal_kind) = LiteralTypeKind::try_from(*element) {
+                grouped_literals
+                    .entry(literal_kind)
+                    .or_insert_with(Vec::new)
+                    .push(*element);
+            }
+        }

        let mut first = true;
-        if !int_literals.is_empty() {
-            f.write_str("Literal[")?;
-            let mut nums: Vec<_> = int_literals
-                .into_iter()
-                .filter_map(|ty| {
-                    if let Type::IntLiteral(n) = ty {
-                        Some(n)
-                    } else {
-                        None
-                    }
-                })
-                .collect();
-            nums.sort_unstable();
-            for num in nums {
+
+        // Print all types, but write all literals together (while preserving their position).
+        for ty in elements {
+            if let Ok(literal_kind) = LiteralTypeKind::try_from(*ty) {
+                let Some(mut literals) = grouped_literals.remove(&literal_kind) else {
+                    continue;
+                };
+
                if !first {
-                    f.write_str(", ")?;
+                    f.write_str(" | ")?;
+                };
+
+                f.write_str("Literal[")?;
+
+                if literal_kind == LiteralTypeKind::IntLiteral {
+                    literals.sort_unstable_by_key(|ty| ty.expect_int_literal());
                }
-                write!(f, "{num}")?;
-                first = false;
+
+                for (i, literal_ty) in literals.iter().enumerate() {
+                    if i > 0 {
+                        f.write_str(", ")?;
+                    }
+                    literal_ty.representation(self.db).fmt(f)?;
+                }
+                f.write_str("]")?;
+            } else {
+                if !first {
+                    f.write_str(" | ")?;
+                };
+
+                ty.display(self.db).fmt(f)?;
            }
-            f.write_str("]")?;
+
+            first = false;
        }

-        for ty in other_types {
-            if !first {
-                f.write_str(" | ")?;
-            };
-            first = false;
-            write!(f, "{}", ty.display(self.db))?;
-        }
+        debug_assert!(grouped_literals.is_empty());

        Ok(())
    }
@@ -111,6 +166,30 @@ impl std::fmt::Debug for DisplayUnionType<'_> {
    }
 }

+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
+enum LiteralTypeKind {
+    Class,
+    Function,
+    IntLiteral,
+    StringLiteral,
+    BytesLiteral,
+}
+
+impl TryFrom<Type<'_>> for LiteralTypeKind {
+    type Error = ();
+
+    fn try_from(value: Type<'_>) -> Result<Self, Self::Error> {
+        match value {
+            Type::Class(_) => Ok(Self::Class),
+            Type::Function(_) => Ok(Self::Function),
+            Type::IntLiteral(_) => Ok(Self::IntLiteral),
+            Type::StringLiteral(_) => Ok(Self::StringLiteral),
+            Type::BytesLiteral(_) => Ok(Self::BytesLiteral),
+            _ => Err(()),
+        }
+    }
+}
+
 impl<'db> IntersectionType<'db> {
    fn display(&'db self, db: &'db dyn Db) -> DisplayIntersectionType<'db> {
        DisplayIntersectionType { db, ty: self }
@@ -150,3 +229,89 @@ impl std::fmt::Debug for DisplayIntersectionType<'_> {
        std::fmt::Display::fmt(self, f)
    }
 }
+
+#[cfg(test)]
+mod tests {
+    use ruff_db::files::system_path_to_file;
+    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+
+    use crate::db::tests::TestDb;
+    use crate::types::{global_symbol_ty, BytesLiteralType, StringLiteralType, Type, UnionBuilder};
+    use crate::{Program, ProgramSettings, PythonVersion, SearchPathSettings};
+
+    fn setup_db() -> TestDb {
+        let db = TestDb::new();
+
+        let src_root = SystemPathBuf::from("/src");
+        db.memory_file_system()
+            .create_directory_all(&src_root)
+            .unwrap();
+
+        Program::from_settings(
+            &db,
+            &ProgramSettings {
+                target_version: PythonVersion::default(),
+                search_paths: SearchPathSettings::new(src_root),
+            },
+        )
+        .expect("Valid search path settings");
+
+        db
+    }
+
+    #[test]
+    fn test_condense_literal_display_by_type() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "src/main.py",
+            "
+            def foo(x: int) -> int:
+                return x + 1
+
+            def bar(s: str) -> str:
+                return s
+
+            class A: ...
+            class B: ...
+            ",
+        )?;
+        let mod_file = system_path_to_file(&db, "src/main.py").expect("Expected file to exist.");
+
+        let vec: Vec<Type<'_>> = vec![
+            Type::Unknown,
+            Type::IntLiteral(-1),
+            global_symbol_ty(&db, mod_file, "A"),
+            Type::StringLiteral(StringLiteralType::new(&db, Box::from("A"))),
+            Type::BytesLiteral(BytesLiteralType::new(&db, Box::from([0]))),
+            Type::BytesLiteral(BytesLiteralType::new(&db, Box::from([7]))),
+            Type::IntLiteral(0),
+            Type::IntLiteral(1),
+            Type::StringLiteral(StringLiteralType::new(&db, Box::from("B"))),
+            global_symbol_ty(&db, mod_file, "foo"),
+            global_symbol_ty(&db, mod_file, "bar"),
+            global_symbol_ty(&db, mod_file, "B"),
+            Type::BooleanLiteral(true),
+            Type::None,
+        ];
+        let builder = vec.iter().fold(UnionBuilder::new(&db), |builder, literal| {
+            builder.add(*literal)
+        });
+        let union = builder.build().expect_union();
+        let display = format!("{}", union.display(&db));
+        assert_eq!(
+            display,
+            concat!(
+                "Unknown | ",
+                "Literal[-1, 0, 1] | ",
+                "Literal[A, B] | ",
+                "Literal[\"A\", \"B\"] | ",
+                "Literal[b\"\\x00\", b\"\\x07\"] | ",
+                "Literal[foo, bar] | ",
+                "Literal[True] | ",
+                "None"
+            )
+        );
+        Ok(())
+    }
+}
--- a/crates/red_knot_python_semantic/src/types/infer.rs
+++ b/crates/red_knot_python_semantic/src/types/infer.rs
--- a/crates/red_knot_python_semantic/src/types/narrow.rs
+++ b/crates/red_knot_python_semantic/src/types/narrow.rs
@@ -0,0 +1,115 @@
+use crate::semantic_index::ast_ids::HasScopedAstId;
+use crate::semantic_index::definition::Definition;
+use crate::semantic_index::expression::Expression;
+use crate::semantic_index::symbol::{ScopeId, ScopedSymbolId, SymbolTable};
+use crate::semantic_index::symbol_table;
+use crate::types::{infer_expression_types, IntersectionBuilder, Type, TypeInference};
+use crate::Db;
+use ruff_python_ast as ast;
+use rustc_hash::FxHashMap;
+use std::sync::Arc;
+
+/// Return the type constraint that `test` (if true) would place on `definition`, if any.
+///
+/// For example, if we have this code:
+///
+/// ```python
+/// y = 1 if flag else None
+/// x = 1 if flag else None
+/// if x is not None:
+///     ...
+/// ```
+///
+/// The `test` expression `x is not None` places the constraint "not None" on the definition of
+/// `x`, so in that case we'd return `Some(Type::Intersection(negative=[Type::None]))`.
+///
+/// But if we called this with the same `test` expression, but the `definition` of `y`, no
+/// constraint is applied to that definition, so we'd just return `None`.
+pub(crate) fn narrowing_constraint<'db>(
+    db: &'db dyn Db,
+    test: Expression<'db>,
+    definition: Definition<'db>,
+) -> Option<Type<'db>> {
+    all_narrowing_constraints(db, test)
+        .get(&definition.symbol(db))
+        .copied()
+}
+
+#[salsa::tracked(return_ref)]
+fn all_narrowing_constraints<'db>(
+    db: &'db dyn Db,
+    test: Expression<'db>,
+) -> NarrowingConstraints<'db> {
+    NarrowingConstraintsBuilder::new(db, test).finish()
+}
+
+type NarrowingConstraints<'db> = FxHashMap<ScopedSymbolId, Type<'db>>;
+
+struct NarrowingConstraintsBuilder<'db> {
+    db: &'db dyn Db,
+    expression: Expression<'db>,
+    constraints: NarrowingConstraints<'db>,
+}
+
+impl<'db> NarrowingConstraintsBuilder<'db> {
+    fn new(db: &'db dyn Db, expression: Expression<'db>) -> Self {
+        Self {
+            db,
+            expression,
+            constraints: NarrowingConstraints::default(),
+        }
+    }
+
+    fn finish(mut self) -> NarrowingConstraints<'db> {
+        if let ast::Expr::Compare(expr_compare) = self.expression.node_ref(self.db).node() {
+            self.add_expr_compare(expr_compare);
+        }
+        // TODO other test expression kinds
+
+        self.constraints.shrink_to_fit();
+        self.constraints
+    }
+
+    fn symbols(&self) -> Arc<SymbolTable> {
+        symbol_table(self.db, self.scope())
+    }
+
+    fn scope(&self) -> ScopeId<'db> {
+        self.expression.scope(self.db)
+    }
+
+    fn inference(&self) -> &'db TypeInference<'db> {
+        infer_expression_types(self.db, self.expression)
+    }
+
+    fn add_expr_compare(&mut self, expr_compare: &ast::ExprCompare) {
+        let ast::ExprCompare {
+            range: _,
+            left,
+            ops,
+            comparators,
+        } = expr_compare;
+
+        if let ast::Expr::Name(ast::ExprName {
+            range: _,
+            id,
+            ctx: _,
+        }) = left.as_ref()
+        {
+            // SAFETY: we should always have a symbol for every Name node.
+            let symbol = self.symbols().symbol_id_by_name(id).unwrap();
+            let scope = self.scope();
+            let inference = self.inference();
+            for (op, comparator) in std::iter::zip(&**ops, &**comparators) {
+                let comp_ty = inference.expression_ty(comparator.scoped_ast_id(self.db, scope));
+                if matches!(op, ast::CmpOp::IsNot) {
+                    let ty = IntersectionBuilder::new(self.db)
+                        .add_negative(comp_ty)
+                        .build();
+                    self.constraints.insert(symbol, ty);
+                };
+                // TODO other comparison types
+            }
+        }
+    }
+}
--- a/crates/red_knot_python_semantic/vendor/typeshed/source_commit.txt
+++ b/crates/red_knot_python_semantic/vendor/typeshed/source_commit.txt
@@ -1 +1 @@
-4ef2d66663fc080fefa379e6ae5fc45d4f8b54eb
+23d867efb2df6de5600f64656f1aa8a83e06109e
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_ast.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_ast.pyi
@@ -1,7 +1,7 @@
 import sys
 import typing_extensions
 from typing import Any, ClassVar, Generic, Literal, TypedDict, overload
-from typing_extensions import Unpack
+from typing_extensions import Self, Unpack

 PyCF_ONLY_AST: Literal[1024]
 PyCF_TYPE_COMMENTS: Literal[4096]
@@ -34,6 +34,9 @@ class AST:
    if sys.version_info >= (3, 13):
        _field_types: ClassVar[dict[str, Any]]

+    if sys.version_info >= (3, 14):
+        def __replace__(self) -> Self: ...
+
 class mod(AST): ...
 class type_ignore(AST): ...

@@ -44,6 +47,9 @@ class TypeIgnore(type_ignore):
    tag: str
    def __init__(self, lineno: int, tag: str) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, lineno: int = ..., tag: str = ...) -> Self: ...
+
 class FunctionType(mod):
    if sys.version_info >= (3, 10):
        __match_args__ = ("argtypes", "returns")
@@ -57,6 +63,9 @@ class FunctionType(mod):
    else:
        def __init__(self, argtypes: list[expr], returns: expr) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, argtypes: list[expr] = ..., returns: expr = ...) -> Self: ...
+
 class Module(mod):
    if sys.version_info >= (3, 10):
        __match_args__ = ("body", "type_ignores")
@@ -67,6 +76,9 @@ class Module(mod):
    else:
        def __init__(self, body: list[stmt], type_ignores: list[TypeIgnore]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, body: list[stmt] = ..., type_ignores: list[TypeIgnore] = ...) -> Self: ...
+
 class Interactive(mod):
    if sys.version_info >= (3, 10):
        __match_args__ = ("body",)
@@ -76,12 +88,18 @@ class Interactive(mod):
    else:
        def __init__(self, body: list[stmt]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, body: list[stmt] = ...) -> Self: ...
+
 class Expression(mod):
    if sys.version_info >= (3, 10):
        __match_args__ = ("body",)
    body: expr
    def __init__(self, body: expr) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, body: expr = ...) -> Self: ...
+
 class stmt(AST):
    lineno: int
    col_offset: int
@@ -89,6 +107,9 @@ class stmt(AST):
    end_col_offset: int | None
    def __init__(self, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class FunctionDef(stmt):
    if sys.version_info >= (3, 12):
        __match_args__ = ("name", "args", "body", "decorator_list", "returns", "type_comment", "type_params")
@@ -152,6 +173,19 @@ class FunctionDef(stmt):
            **kwargs: Unpack[_Attributes],
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            name: _Identifier = ...,
+            args: arguments = ...,
+            body: list[stmt] = ...,
+            decorator_list: list[expr] = ...,
+            returns: expr | None = ...,
+            type_comment: str | None = ...,
+            type_params: list[type_param] = ...,
+        ) -> Self: ...
+
 class AsyncFunctionDef(stmt):
    if sys.version_info >= (3, 12):
        __match_args__ = ("name", "args", "body", "decorator_list", "returns", "type_comment", "type_params")
@@ -215,6 +249,19 @@ class AsyncFunctionDef(stmt):
            **kwargs: Unpack[_Attributes],
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            name: _Identifier = ...,
+            args: arguments = ...,
+            body: list[stmt],
+            decorator_list: list[expr],
+            returns: expr | None,
+            type_comment: str | None,
+            type_params: list[type_param],
+        ) -> Self: ...
+
 class ClassDef(stmt):
    if sys.version_info >= (3, 12):
        __match_args__ = ("name", "bases", "keywords", "body", "decorator_list", "type_params")
@@ -260,12 +307,28 @@ class ClassDef(stmt):
            **kwargs: Unpack[_Attributes],
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            name: _Identifier,
+            bases: list[expr],
+            keywords: list[keyword],
+            body: list[stmt],
+            decorator_list: list[expr],
+            type_params: list[type_param],
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 class Return(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("value",)
    value: expr | None
    def __init__(self, value: expr | None = None, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, value: expr | None = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Delete(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("targets",)
@@ -275,6 +338,9 @@ class Delete(stmt):
    else:
        def __init__(self, targets: list[expr], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, targets: list[expr] = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Assign(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("targets", "value", "type_comment")
@@ -295,6 +361,11 @@ class Assign(stmt):
            self, targets: list[expr], value: expr, type_comment: str | None = None, **kwargs: Unpack[_Attributes]
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, targets: list[expr] = ..., value: expr = ..., type_comment: str | None = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class AugAssign(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("target", "op", "value")
@@ -305,6 +376,16 @@ class AugAssign(stmt):
        self, target: Name | Attribute | Subscript, op: operator, value: expr, **kwargs: Unpack[_Attributes]
    ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            target: Name | Attribute | Subscript = ...,
+            op: operator = ...,
+            value: expr = ...,
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 class AnnAssign(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("target", "annotation", "value", "simple")
@@ -332,6 +413,17 @@ class AnnAssign(stmt):
        **kwargs: Unpack[_Attributes],
    ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            target: Name | Attribute | Subscript = ...,
+            annotation: expr = ...,
+            value: expr | None = ...,
+            simple: int = ...,
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 class For(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("target", "iter", "body", "orelse", "type_comment")
@@ -361,6 +453,18 @@ class For(stmt):
            **kwargs: Unpack[_Attributes],
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            target: expr = ...,
+            iter: expr = ...,
+            body: list[stmt] = ...,
+            orelse: list[stmt] = ...,
+            type_comment: str | None = ...,
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 class AsyncFor(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("target", "iter", "body", "orelse", "type_comment")
@@ -390,6 +494,18 @@ class AsyncFor(stmt):
            **kwargs: Unpack[_Attributes],
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            target: expr = ...,
+            iter: expr = ...,
+            body: list[stmt] = ...,
+            orelse: list[stmt] = ...,
+            type_comment: str | None = ...,
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 class While(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("test", "body", "orelse")
@@ -403,6 +519,9 @@ class While(stmt):
    else:
        def __init__(self, test: expr, body: list[stmt], orelse: list[stmt], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, test: expr, body: list[stmt], orelse: list[stmt], **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class If(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("test", "body", "orelse")
@@ -416,6 +535,11 @@ class If(stmt):
    else:
        def __init__(self, test: expr, body: list[stmt], orelse: list[stmt], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, test: expr = ..., body: list[stmt] = ..., orelse: list[stmt] = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class With(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("items", "body", "type_comment")
@@ -435,6 +559,16 @@ class With(stmt):
            self, items: list[withitem], body: list[stmt], type_comment: str | None = None, **kwargs: Unpack[_Attributes]
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            items: list[withitem] = ...,
+            body: list[stmt] = ...,
+            type_comment: str | None = ...,
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 class AsyncWith(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("items", "body", "type_comment")
@@ -454,6 +588,16 @@ class AsyncWith(stmt):
            self, items: list[withitem], body: list[stmt], type_comment: str | None = None, **kwargs: Unpack[_Attributes]
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            items: list[withitem] = ...,
+            body: list[stmt] = ...,
+            type_comment: str | None = ...,
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 class Raise(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("exc", "cause")
@@ -461,6 +605,9 @@ class Raise(stmt):
    cause: expr | None
    def __init__(self, exc: expr | None = None, cause: expr | None = None, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, exc: expr | None = ..., cause: expr | None = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Try(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("body", "handlers", "orelse", "finalbody")
@@ -487,6 +634,17 @@ class Try(stmt):
            **kwargs: Unpack[_Attributes],
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            body: list[stmt] = ...,
+            handlers: list[ExceptHandler] = ...,
+            orelse: list[stmt] = ...,
+            finalbody: list[stmt] = ...,
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 if sys.version_info >= (3, 11):
    class TryStar(stmt):
        __match_args__ = ("body", "handlers", "orelse", "finalbody")
@@ -513,6 +671,17 @@ if sys.version_info >= (3, 11):
                **kwargs: Unpack[_Attributes],
            ) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self,
+                *,
+                body: list[stmt] = ...,
+                handlers: list[ExceptHandler] = ...,
+                orelse: list[stmt] = ...,
+                finalbody: list[stmt] = ...,
+                **kwargs: Unpack[_Attributes],
+            ) -> Self: ...
+
 class Assert(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("test", "msg")
@@ -520,6 +689,9 @@ class Assert(stmt):
    msg: expr | None
    def __init__(self, test: expr, msg: expr | None = None, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, test: expr, msg: expr | None, **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Import(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("names",)
@@ -529,6 +701,9 @@ class Import(stmt):
    else:
        def __init__(self, names: list[alias], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, names: list[alias] = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class ImportFrom(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("module", "names", "level")
@@ -550,6 +725,11 @@ class ImportFrom(stmt):
            self, module: str | None = None, *, names: list[alias], level: int, **kwargs: Unpack[_Attributes]
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, module: str | None = ..., names: list[alias] = ..., level: int = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class Global(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("names",)
@@ -559,6 +739,9 @@ class Global(stmt):
    else:
        def __init__(self, names: list[_Identifier], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, names: list[_Identifier], **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Nonlocal(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("names",)
@@ -568,12 +751,18 @@ class Nonlocal(stmt):
    else:
        def __init__(self, names: list[_Identifier], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, names: list[_Identifier] = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Expr(stmt):
    if sys.version_info >= (3, 10):
        __match_args__ = ("value",)
    value: expr
    def __init__(self, value: expr, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, value: expr = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Pass(stmt): ...
 class Break(stmt): ...
 class Continue(stmt): ...
@@ -585,6 +774,9 @@ class expr(AST):
    end_col_offset: int | None
    def __init__(self, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class BoolOp(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("op", "values")
@@ -595,6 +787,9 @@ class BoolOp(expr):
    else:
        def __init__(self, op: boolop, values: list[expr], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, op: boolop = ..., values: list[expr] = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class BinOp(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("left", "op", "right")
@@ -603,6 +798,11 @@ class BinOp(expr):
    right: expr
    def __init__(self, left: expr, op: operator, right: expr, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, left: expr = ..., op: operator = ..., right: expr = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class UnaryOp(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("op", "operand")
@@ -610,6 +810,9 @@ class UnaryOp(expr):
    operand: expr
    def __init__(self, op: unaryop, operand: expr, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, op: unaryop = ..., operand: expr = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Lambda(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("args", "body")
@@ -617,6 +820,9 @@ class Lambda(expr):
    body: expr
    def __init__(self, args: arguments, body: expr, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, args: arguments = ..., body: expr = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class IfExp(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("test", "body", "orelse")
@@ -625,6 +831,11 @@ class IfExp(expr):
    orelse: expr
    def __init__(self, test: expr, body: expr, orelse: expr, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, test: expr = ..., body: expr = ..., orelse: expr = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class Dict(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("keys", "values")
@@ -635,6 +846,11 @@ class Dict(expr):
    else:
        def __init__(self, keys: list[expr | None], values: list[expr], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, keys: list[expr | None] = ..., values: list[expr] = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class Set(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("elts",)
@@ -644,6 +860,9 @@ class Set(expr):
    else:
        def __init__(self, elts: list[expr], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, elts: list[expr] = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class ListComp(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("elt", "generators")
@@ -654,6 +873,11 @@ class ListComp(expr):
    else:
        def __init__(self, elt: expr, generators: list[comprehension], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, elt: expr = ..., generators: list[comprehension] = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class SetComp(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("elt", "generators")
@@ -664,6 +888,11 @@ class SetComp(expr):
    else:
        def __init__(self, elt: expr, generators: list[comprehension], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, elt: expr = ..., generators: list[comprehension] = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class DictComp(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("key", "value", "generators")
@@ -677,6 +906,11 @@ class DictComp(expr):
    else:
        def __init__(self, key: expr, value: expr, generators: list[comprehension], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, key: expr = ..., value: expr = ..., generators: list[comprehension] = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class GeneratorExp(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("elt", "generators")
@@ -687,24 +921,38 @@ class GeneratorExp(expr):
    else:
        def __init__(self, elt: expr, generators: list[comprehension], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, elt: expr = ..., generators: list[comprehension] = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class Await(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("value",)
    value: expr
    def __init__(self, value: expr, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, value: expr = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Yield(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("value",)
    value: expr | None
    def __init__(self, value: expr | None = None, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, value: expr | None = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class YieldFrom(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("value",)
    value: expr
    def __init__(self, value: expr, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, value: expr = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Compare(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("left", "ops", "comparators")
@@ -718,6 +966,11 @@ class Compare(expr):
    else:
        def __init__(self, left: expr, ops: list[cmpop], comparators: list[expr], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, left: expr = ..., ops: list[cmpop] = ..., comparators: list[expr] = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class Call(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("func", "args", "keywords")
@@ -731,6 +984,11 @@ class Call(expr):
    else:
        def __init__(self, func: expr, args: list[expr], keywords: list[keyword], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, func: expr = ..., args: list[expr] = ..., keywords: list[keyword] = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class FormattedValue(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("value", "conversion", "format_spec")
@@ -739,6 +997,11 @@ class FormattedValue(expr):
    format_spec: expr | None
    def __init__(self, value: expr, conversion: int, format_spec: expr | None = None, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, value: expr = ..., conversion: int = ..., format_spec: expr | None = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class JoinedStr(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("values",)
@@ -748,16 +1011,24 @@ class JoinedStr(expr):
    else:
        def __init__(self, values: list[expr], **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, values: list[expr] = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Constant(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("value", "kind")
    value: Any  # None, str, bytes, bool, int, float, complex, Ellipsis
    kind: str | None
-    # Aliases for value, for backwards compatibility
-    s: Any
-    n: int | float | complex
+    if sys.version_info < (3, 14):
+        # Aliases for value, for backwards compatibility
+        s: Any
+        n: int | float | complex
+
    def __init__(self, value: Any, kind: str | None = None, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, value: Any = ..., kind: str | None = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class NamedExpr(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("target", "value")
@@ -765,6 +1036,9 @@ class NamedExpr(expr):
    value: expr
    def __init__(self, target: Name, value: expr, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, target: Name = ..., value: expr = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Attribute(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("value", "attr", "ctx")
@@ -773,6 +1047,11 @@ class Attribute(expr):
    ctx: expr_context  # Not present in Python < 3.13 if not passed to `__init__`
    def __init__(self, value: expr, attr: _Identifier, ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, value: expr = ..., attr: _Identifier = ..., ctx: expr_context = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 if sys.version_info >= (3, 9):
    _Slice: typing_extensions.TypeAlias = expr
    _SliceAttributes: typing_extensions.TypeAlias = _Attributes
@@ -792,6 +1071,16 @@ class Slice(_Slice):
        self, lower: expr | None = None, upper: expr | None = None, step: expr | None = None, **kwargs: Unpack[_SliceAttributes]
    ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            lower: expr | None = ...,
+            upper: expr | None = ...,
+            step: expr | None = ...,
+            **kwargs: Unpack[_SliceAttributes],
+        ) -> Self: ...
+
 if sys.version_info < (3, 9):
    class ExtSlice(slice):
        dims: list[slice]
@@ -809,6 +1098,11 @@ class Subscript(expr):
    ctx: expr_context  # Not present in Python < 3.13 if not passed to `__init__`
    def __init__(self, value: expr, slice: _Slice, ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, value: expr = ..., slice: _Slice = ..., ctx: expr_context = ..., **kwargs: Unpack[_Attributes]
+        ) -> Self: ...
+
 class Starred(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("value", "ctx")
@@ -816,6 +1110,9 @@ class Starred(expr):
    ctx: expr_context  # Not present in Python < 3.13 if not passed to `__init__`
    def __init__(self, value: expr, ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, value: expr = ..., ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Name(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("id", "ctx")
@@ -823,6 +1120,9 @@ class Name(expr):
    ctx: expr_context  # Not present in Python < 3.13 if not passed to `__init__`
    def __init__(self, id: _Identifier, ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, id: _Identifier = ..., ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class List(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("elts", "ctx")
@@ -833,6 +1133,9 @@ class List(expr):
    else:
        def __init__(self, elts: list[expr], ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, elts: list[expr] = ..., ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class Tuple(expr):
    if sys.version_info >= (3, 10):
        __match_args__ = ("elts", "ctx")
@@ -845,6 +1148,9 @@ class Tuple(expr):
    else:
        def __init__(self, elts: list[expr], ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, elts: list[expr] = ..., ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class expr_context(AST): ...

 if sys.version_info < (3, 9):
@@ -908,6 +1214,9 @@ class comprehension(AST):
    else:
        def __init__(self, target: expr, iter: expr, ifs: list[expr], is_async: int) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, target: expr = ..., iter: expr = ..., ifs: list[expr] = ..., is_async: int = ...) -> Self: ...
+
 class excepthandler(AST):
    lineno: int
    col_offset: int
@@ -915,6 +1224,11 @@ class excepthandler(AST):
    end_col_offset: int | None
    def __init__(self, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self, *, lineno: int = ..., col_offset: int = ..., end_lineno: int | None = ..., end_col_offset: int | None = ...
+        ) -> Self: ...
+
 class ExceptHandler(excepthandler):
    if sys.version_info >= (3, 10):
        __match_args__ = ("type", "name", "body")
@@ -935,6 +1249,16 @@ class ExceptHandler(excepthandler):
            self, type: expr | None = None, name: _Identifier | None = None, *, body: list[stmt], **kwargs: Unpack[_Attributes]
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            type: expr | None = ...,
+            name: _Identifier | None = ...,
+            body: list[stmt] = ...,
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 class arguments(AST):
    if sys.version_info >= (3, 10):
        __match_args__ = ("posonlyargs", "args", "vararg", "kwonlyargs", "kw_defaults", "kwarg", "defaults")
@@ -993,6 +1317,19 @@ class arguments(AST):
            defaults: list[expr],
        ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            posonlyargs: list[arg] = ...,
+            args: list[arg] = ...,
+            vararg: arg | None = ...,
+            kwonlyargs: list[arg] = ...,
+            kw_defaults: list[expr | None] = ...,
+            kwarg: arg | None = ...,
+            defaults: list[expr] = ...,
+        ) -> Self: ...
+
 class arg(AST):
    lineno: int
    col_offset: int
@@ -1007,6 +1344,16 @@ class arg(AST):
        self, arg: _Identifier, annotation: expr | None = None, type_comment: str | None = None, **kwargs: Unpack[_Attributes]
    ) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(
+            self,
+            *,
+            arg: _Identifier = ...,
+            annotation: expr | None = ...,
+            type_comment: str | None = ...,
+            **kwargs: Unpack[_Attributes],
+        ) -> Self: ...
+
 class keyword(AST):
    lineno: int
    col_offset: int
@@ -1021,6 +1368,9 @@ class keyword(AST):
    @overload
    def __init__(self, arg: _Identifier | None = None, *, value: expr, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, arg: _Identifier | None = ..., value: expr = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class alias(AST):
    lineno: int
    col_offset: int
@@ -1032,6 +1382,9 @@ class alias(AST):
    asname: _Identifier | None
    def __init__(self, name: str, asname: _Identifier | None = None, **kwargs: Unpack[_Attributes]) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, name: str = ..., asname: _Identifier | None = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
+
 class withitem(AST):
    if sys.version_info >= (3, 10):
        __match_args__ = ("context_expr", "optional_vars")
@@ -1039,6 +1392,9 @@ class withitem(AST):
    optional_vars: expr | None
    def __init__(self, context_expr: expr, optional_vars: expr | None = None) -> None: ...

+    if sys.version_info >= (3, 14):
+        def __replace__(self, *, context_expr: expr = ..., optional_vars: expr | None = ...) -> Self: ...
+
 if sys.version_info >= (3, 10):
    class Match(stmt):
        __match_args__ = ("subject", "cases")
@@ -1049,6 +1405,11 @@ if sys.version_info >= (3, 10):
        else:
            def __init__(self, subject: expr, cases: list[match_case], **kwargs: Unpack[_Attributes]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self, *, subject: expr = ..., cases: list[match_case] = ..., **kwargs: Unpack[_Attributes]
+            ) -> Self: ...
+
    class pattern(AST):
        lineno: int
        col_offset: int
@@ -1056,6 +1417,11 @@ if sys.version_info >= (3, 10):
        end_col_offset: int
        def __init__(self, **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self, *, lineno: int = ..., col_offset: int = ..., end_lineno: int = ..., end_col_offset: int = ...
+            ) -> Self: ...
+
    # Without the alias, Pyright complains variables named pattern are recursively defined
    _Pattern: typing_extensions.TypeAlias = pattern

@@ -1072,16 +1438,25 @@ if sys.version_info >= (3, 10):
            @overload
            def __init__(self, pattern: _Pattern, guard: expr | None = None, *, body: list[stmt]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(self, *, pattern: _Pattern = ..., guard: expr | None = ..., body: list[stmt] = ...) -> Self: ...
+
    class MatchValue(pattern):
        __match_args__ = ("value",)
        value: expr
        def __init__(self, value: expr, **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(self, *, value: expr = ..., **kwargs: Unpack[_Attributes[int]]) -> Self: ...
+
    class MatchSingleton(pattern):
        __match_args__ = ("value",)
        value: Literal[True, False] | None
        def __init__(self, value: Literal[True, False] | None, **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(self, *, value: Literal[True, False] | None = ..., **kwargs: Unpack[_Attributes[int]]) -> Self: ...
+
    class MatchSequence(pattern):
        __match_args__ = ("patterns",)
        patterns: list[pattern]
@@ -1090,11 +1465,17 @@ if sys.version_info >= (3, 10):
        else:
            def __init__(self, patterns: list[pattern], **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(self, *, patterns: list[pattern] = ..., **kwargs: Unpack[_Attributes[int]]) -> Self: ...
+
    class MatchStar(pattern):
        __match_args__ = ("name",)
        name: _Identifier | None
        def __init__(self, name: _Identifier | None, **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(self, *, name: _Identifier | None = ..., **kwargs: Unpack[_Attributes[int]]) -> Self: ...
+
    class MatchMapping(pattern):
        __match_args__ = ("keys", "patterns", "rest")
        keys: list[expr]
@@ -1117,6 +1498,16 @@ if sys.version_info >= (3, 10):
                **kwargs: Unpack[_Attributes[int]],
            ) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self,
+                *,
+                keys: list[expr] = ...,
+                patterns: list[pattern] = ...,
+                rest: _Identifier | None = ...,
+                **kwargs: Unpack[_Attributes[int]],
+            ) -> Self: ...
+
    class MatchClass(pattern):
        __match_args__ = ("cls", "patterns", "kwd_attrs", "kwd_patterns")
        cls: expr
@@ -1142,6 +1533,17 @@ if sys.version_info >= (3, 10):
                **kwargs: Unpack[_Attributes[int]],
            ) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self,
+                *,
+                cls: expr = ...,
+                patterns: list[pattern] = ...,
+                kwd_attrs: list[_Identifier] = ...,
+                kwd_patterns: list[pattern] = ...,
+                **kwargs: Unpack[_Attributes[int]],
+            ) -> Self: ...
+
    class MatchAs(pattern):
        __match_args__ = ("pattern", "name")
        pattern: _Pattern | None
@@ -1150,6 +1552,11 @@ if sys.version_info >= (3, 10):
            self, pattern: _Pattern | None = None, name: _Identifier | None = None, **kwargs: Unpack[_Attributes[int]]
        ) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self, *, pattern: _Pattern | None = ..., name: _Identifier | None = ..., **kwargs: Unpack[_Attributes[int]]
+            ) -> Self: ...
+
    class MatchOr(pattern):
        __match_args__ = ("patterns",)
        patterns: list[pattern]
@@ -1158,6 +1565,9 @@ if sys.version_info >= (3, 10):
        else:
            def __init__(self, patterns: list[pattern], **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(self, *, patterns: list[pattern] = ..., **kwargs: Unpack[_Attributes[int]]) -> Self: ...
+
 if sys.version_info >= (3, 12):
    class type_param(AST):
        lineno: int
@@ -1166,6 +1576,9 @@ if sys.version_info >= (3, 12):
        end_col_offset: int
        def __init__(self, **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(self, **kwargs: Unpack[_Attributes[int]]) -> Self: ...
+
    class TypeVar(type_param):
        if sys.version_info >= (3, 13):
            __match_args__ = ("name", "bound", "default_value")
@@ -1185,6 +1598,16 @@ if sys.version_info >= (3, 12):
        else:
            def __init__(self, name: _Identifier, bound: expr | None = None, **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self,
+                *,
+                name: _Identifier = ...,
+                bound: expr | None = ...,
+                default_value: expr | None = ...,
+                **kwargs: Unpack[_Attributes[int]],
+            ) -> Self: ...
+
    class ParamSpec(type_param):
        if sys.version_info >= (3, 13):
            __match_args__ = ("name", "default_value")
@@ -1199,6 +1622,11 @@ if sys.version_info >= (3, 12):
        else:
            def __init__(self, name: _Identifier, **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self, *, name: _Identifier = ..., default_value: expr | None = ..., **kwargs: Unpack[_Attributes[int]]
+            ) -> Self: ...
+
    class TypeVarTuple(type_param):
        if sys.version_info >= (3, 13):
            __match_args__ = ("name", "default_value")
@@ -1213,6 +1641,11 @@ if sys.version_info >= (3, 12):
        else:
            def __init__(self, name: _Identifier, **kwargs: Unpack[_Attributes[int]]) -> None: ...

+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self, *, name: _Identifier = ..., default_value: expr | None = ..., **kwargs: Unpack[_Attributes[int]]
+            ) -> Self: ...
+
    class TypeAlias(stmt):
        __match_args__ = ("name", "type_params", "value")
        name: Name
@@ -1231,3 +1664,13 @@ if sys.version_info >= (3, 12):
            def __init__(
                self, name: Name, type_params: list[type_param], value: expr, **kwargs: Unpack[_Attributes[int]]
            ) -> None: ...
+
+        if sys.version_info >= (3, 14):
+            def __replace__(
+                self,
+                *,
+                name: Name = ...,
+                type_params: list[type_param] = ...,
+                value: expr = ...,
+                **kwargs: Unpack[_Attributes[int]],
+            ) -> Self: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_collections_abc.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_collections_abc.pyi
@@ -1,13 +1,12 @@
 import sys
 from abc import abstractmethod
 from types import MappingProxyType
-from typing import (  # noqa: Y022,Y038,Y057
+from typing import (  # noqa: Y022,Y038
    AbstractSet as Set,
    AsyncGenerator as AsyncGenerator,
    AsyncIterable as AsyncIterable,
    AsyncIterator as AsyncIterator,
    Awaitable as Awaitable,
-    ByteString as ByteString,
    Callable as Callable,
    Collection as Collection,
    Container as Container,
@@ -59,8 +58,12 @@ __all__ = [
    "ValuesView",
    "Sequence",
    "MutableSequence",
-    "ByteString",
 ]
+if sys.version_info < (3, 14):
+    from typing import ByteString as ByteString  # noqa: Y057
+
+    __all__ += ["ByteString"]
+
 if sys.version_info >= (3, 12):
    __all__ += ["Buffer"]

--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_ctypes.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_ctypes.pyi
@@ -51,8 +51,8 @@ class _CDataMeta(type):
    # By default mypy complains about the following two methods, because strictly speaking cls
    # might not be a Type[_CT]. However this can never actually happen, because the only class that
    # uses _CDataMeta as its metaclass is _CData. So it's safe to ignore the errors here.
-    def __mul__(cls: type[_CT], other: int) -> type[Array[_CT]]: ...  # type: ignore[misc]
-    def __rmul__(cls: type[_CT], other: int) -> type[Array[_CT]]: ...  # type: ignore[misc]
+    def __mul__(cls: type[_CT], other: int) -> type[Array[_CT]]: ...  # type: ignore[misc]  # pyright: ignore[reportGeneralTypeIssues]
+    def __rmul__(cls: type[_CT], other: int) -> type[Array[_CT]]: ...  # type: ignore[misc]  # pyright: ignore[reportGeneralTypeIssues]

 class _CData(metaclass=_CDataMeta):
    _b_base_: int
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_operator.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_operator.pyi
@@ -2,7 +2,7 @@ import sys
 from _typeshed import SupportsGetItem
 from collections.abc import Callable, Container, Iterable, MutableMapping, MutableSequence, Sequence
 from typing import Any, AnyStr, Generic, Protocol, SupportsAbs, SupportsIndex, TypeVar, final, overload
-from typing_extensions import ParamSpec, TypeAlias, TypeVarTuple, Unpack
+from typing_extensions import ParamSpec, TypeAlias, TypeIs, TypeVarTuple, Unpack

 _R = TypeVar("_R")
 _T = TypeVar("_T")
@@ -145,3 +145,7 @@ if sys.version_info >= (3, 11):
    def call(obj: Callable[_P, _R], /, *args: _P.args, **kwargs: _P.kwargs) -> _R: ...

 def _compare_digest(a: AnyStr, b: AnyStr, /) -> bool: ...
+
+if sys.version_info >= (3, 14):
+    def is_none(a: object, /) -> TypeIs[None]: ...
+    def is_not_none(a: _T | None, /) -> TypeIs[_T]: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_stat.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_stat.pyi
@@ -28,9 +28,9 @@ S_IFDIR: Final = 0o040000

 # These are 0 on systems that don't support the specific kind of file.
 # Example: Linux doesn't support door files, so S_IFDOOR is 0 on linux.
-S_IFDOOR: int
-S_IFPORT: int
-S_IFWHT: int
+S_IFDOOR: Final[int]
+S_IFPORT: Final[int]
+S_IFWHT: Final[int]

 S_ISUID: Final = 0o4000
 S_ISGID: Final = 0o2000
@@ -79,9 +79,9 @@ def S_ISWHT(mode: int, /) -> bool: ...
 def filemode(mode: int, /) -> str: ...

 if sys.platform == "win32":
-    IO_REPARSE_TAG_SYMLINK: int
-    IO_REPARSE_TAG_MOUNT_POINT: int
-    IO_REPARSE_TAG_APPEXECLINK: int
+    IO_REPARSE_TAG_SYMLINK: Final = 0xA000000C
+    IO_REPARSE_TAG_MOUNT_POINT: Final = 0xA0000003
+    IO_REPARSE_TAG_APPEXECLINK: Final = 0x8000001B

 if sys.platform == "win32":
    FILE_ATTRIBUTE_ARCHIVE: Final = 32
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_thread.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_thread.pyi
@@ -1,3 +1,4 @@
+import signal
 import sys
 from _typeshed import structseq
 from collections.abc import Callable
@@ -16,16 +17,39 @@ class LockType:
    def acquire(self, blocking: bool = True, timeout: float = -1) -> bool: ...
    def release(self) -> None: ...
    def locked(self) -> bool: ...
+    def acquire_lock(self, blocking: bool = True, timeout: float = -1) -> bool: ...
+    def release_lock(self) -> None: ...
+    def locked_lock(self) -> bool: ...
    def __enter__(self) -> bool: ...
    def __exit__(
        self, type: type[BaseException] | None, value: BaseException | None, traceback: TracebackType | None
    ) -> None: ...

+if sys.version_info >= (3, 13):
+    @final
+    class _ThreadHandle:
+        ident: int
+
+        def join(self, timeout: float | None = None, /) -> None: ...
+        def is_done(self) -> bool: ...
+        def _set_done(self) -> None: ...
+
+    def start_joinable_thread(
+        function: Callable[[], object], handle: _ThreadHandle | None = None, daemon: bool = True
+    ) -> _ThreadHandle: ...
+    lock = LockType
+
@overload
 def start_new_thread(function: Callable[[Unpack[_Ts]], object], args: tuple[Unpack[_Ts]], /) -> int: ...
@overload
 def start_new_thread(function: Callable[..., object], args: tuple[Any, ...], kwargs: dict[str, Any], /) -> int: ...
-def interrupt_main() -> None: ...
+
+if sys.version_info >= (3, 10):
+    def interrupt_main(signum: signal.Signals = ..., /) -> None: ...
+
+else:
+    def interrupt_main() -> None: ...
+
 def exit() -> NoReturn: ...
 def allocate_lock() -> LockType: ...
 def get_ident() -> int: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_tkinter.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/_tkinter.pyi
@@ -106,8 +106,8 @@ EXCEPTION: Final = 8
 READABLE: Final = 2
 WRITABLE: Final = 4

-TCL_VERSION: str
-TK_VERSION: str
+TCL_VERSION: Final[str]
+TK_VERSION: Final[str]

@final
 class TkttType:
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/argparse.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/argparse.pyi
@@ -357,7 +357,17 @@ class Action(_AttributeHolder):

 if sys.version_info >= (3, 12):
    class BooleanOptionalAction(Action):
-        if sys.version_info >= (3, 13):
+        if sys.version_info >= (3, 14):
+            def __init__(
+                self,
+                option_strings: Sequence[str],
+                dest: str,
+                default: bool | None = None,
+                required: bool = False,
+                help: str | None = None,
+                deprecated: bool = False,
+            ) -> None: ...
+        elif sys.version_info >= (3, 13):
            @overload
            def __init__(
                self,
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/ast.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/ast.pyi
@@ -10,27 +10,28 @@ class _ABC(type):
    if sys.version_info >= (3, 9):
        def __init__(cls, *args: Unused) -> None: ...

-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class Num(Constant, metaclass=_ABC):
-    value: int | float | complex
+if sys.version_info < (3, 14):
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class Num(Constant, metaclass=_ABC):
+        value: int | float | complex

-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class Str(Constant, metaclass=_ABC):
-    value: str
-    # Aliases for value, for backwards compatibility
-    s: str
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class Str(Constant, metaclass=_ABC):
+        value: str
+        # Aliases for value, for backwards compatibility
+        s: str

-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class Bytes(Constant, metaclass=_ABC):
-    value: bytes
-    # Aliases for value, for backwards compatibility
-    s: bytes
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class Bytes(Constant, metaclass=_ABC):
+        value: bytes
+        # Aliases for value, for backwards compatibility
+        s: bytes

-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class NameConstant(Constant, metaclass=_ABC): ...
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class NameConstant(Constant, metaclass=_ABC): ...

-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class Ellipsis(Constant, metaclass=_ABC): ...
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class Ellipsis(Constant, metaclass=_ABC): ...

 if sys.version_info >= (3, 9):
    class slice(AST): ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/asyncio/tasks.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/asyncio/tasks.pyi
@@ -151,13 +151,13 @@ if sys.version_info >= (3, 10):
    @overload
    def gather(*coros_or_futures: _FutureLike[_T], return_exceptions: Literal[False] = False) -> Future[list[_T]]: ...  # type: ignore[overload-overlap]
    @overload
-    def gather(coro_or_future1: _FutureLike[_T1], /, *, return_exceptions: bool) -> Future[tuple[_T1 | BaseException]]: ...  # type: ignore[overload-overlap]
+    def gather(coro_or_future1: _FutureLike[_T1], /, *, return_exceptions: bool) -> Future[tuple[_T1 | BaseException]]: ...
    @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
        coro_or_future1: _FutureLike[_T1], coro_or_future2: _FutureLike[_T2], /, *, return_exceptions: bool
    ) -> Future[tuple[_T1 | BaseException, _T2 | BaseException]]: ...
    @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
        coro_or_future1: _FutureLike[_T1],
        coro_or_future2: _FutureLike[_T2],
        coro_or_future3: _FutureLike[_T3],
@@ -166,7 +166,7 @@ if sys.version_info >= (3, 10):
        return_exceptions: bool,
    ) -> Future[tuple[_T1 | BaseException, _T2 | BaseException, _T3 | BaseException]]: ...
    @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
        coro_or_future1: _FutureLike[_T1],
        coro_or_future2: _FutureLike[_T2],
        coro_or_future3: _FutureLike[_T3],
@@ -176,7 +176,7 @@ if sys.version_info >= (3, 10):
        return_exceptions: bool,
    ) -> Future[tuple[_T1 | BaseException, _T2 | BaseException, _T3 | BaseException, _T4 | BaseException]]: ...
    @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
        coro_or_future1: _FutureLike[_T1],
        coro_or_future2: _FutureLike[_T2],
        coro_or_future3: _FutureLike[_T3],
@@ -189,7 +189,7 @@ if sys.version_info >= (3, 10):
        tuple[_T1 | BaseException, _T2 | BaseException, _T3 | BaseException, _T4 | BaseException, _T5 | BaseException]
    ]: ...
    @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
        coro_or_future1: _FutureLike[_T1],
        coro_or_future2: _FutureLike[_T2],
        coro_or_future3: _FutureLike[_T3],
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/asyncio/unix_events.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/asyncio/unix_events.pyi
@@ -159,7 +159,7 @@ if sys.platform != "win32":

    class _UnixSelectorEventLoop(BaseSelectorEventLoop):
        if sys.version_info >= (3, 13):
-            async def create_unix_server(  # type: ignore[override]
+            async def create_unix_server(
                self,
                protocol_factory: _ProtocolFactory,
                path: StrPath | None = None,
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/builtins.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/builtins.pyi
@@ -33,7 +33,8 @@ from collections.abc import Awaitable, Callable, Iterable, Iterator, MutableSet,
 from io import BufferedRandom, BufferedReader, BufferedWriter, FileIO, TextIOWrapper
 from types import CellType, CodeType, TracebackType

-# mypy crashes if any of {ByteString, Sequence, MutableSequence, Mapping, MutableMapping} are imported from collections.abc in builtins.pyi
+# mypy crashes if any of {ByteString, Sequence, MutableSequence, Mapping, MutableMapping}
+# are imported from collections.abc in builtins.pyi
 from typing import (  # noqa: Y022
    IO,
    Any,
@@ -967,7 +968,9 @@ class tuple(Sequence[_T_co]):
    if sys.version_info >= (3, 9):
        def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...

-# Doesn't exist at runtime, but deleting this breaks mypy. See #2999
+# Doesn't exist at runtime, but deleting this breaks mypy and pyright. See:
+# https://github.com/python/typeshed/issues/7580
+# https://github.com/python/mypy/issues/8240
@final
@type_check_only
 class function:
@@ -1084,7 +1087,8 @@ class dict(MutableMapping[_KT, _VT]):
    def keys(self) -> dict_keys[_KT, _VT]: ...
    def values(self) -> dict_values[_KT, _VT]: ...
    def items(self) -> dict_items[_KT, _VT]: ...
-    # Signature of `dict.fromkeys` should be kept identical to `fromkeys` methods of `OrderedDict`/`ChainMap`/`UserDict` in `collections`
+    # Signature of `dict.fromkeys` should be kept identical to
+    # `fromkeys` methods of `OrderedDict`/`ChainMap`/`UserDict` in `collections`
    # TODO: the true signature of `dict.fromkeys` is not expressible in the current type system.
    # See #3800 & https://github.com/python/typing/issues/548#issuecomment-683336963.
    @classmethod
@@ -1744,7 +1748,7 @@ _SupportsSumNoDefaultT = TypeVar("_SupportsSumNoDefaultT", bound=_SupportsSumWit
 # without creating many false-positive errors (see #7578).
 # Instead, we special-case the most common examples of this: bool and literal integers.
@overload
-def sum(iterable: Iterable[bool | _LiteralInteger], /, start: int = 0) -> int: ...  # type: ignore[overload-overlap]
+def sum(iterable: Iterable[bool | _LiteralInteger], /, start: int = 0) -> int: ...
@overload
 def sum(iterable: Iterable[_SupportsSumNoDefaultT], /) -> _SupportsSumNoDefaultT | Literal[0]: ...
@overload
@@ -1752,9 +1756,8 @@ def sum(iterable: Iterable[_AddableT1], /, start: _AddableT2) -> _AddableT1 | _A

 # The argument to `vars()` has to have a `__dict__` attribute, so the second overload can't be annotated with `object`
 # (A "SupportsDunderDict" protocol doesn't work)
-# Use a type: ignore to make complaints about overlapping overloads go away
@overload
-def vars(object: type, /) -> types.MappingProxyType[str, Any]: ...  # type: ignore[overload-overlap]
+def vars(object: type, /) -> types.MappingProxyType[str, Any]: ...
@overload
 def vars(object: Any = ..., /) -> dict[str, Any]: ...

--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/cmd.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/cmd.pyi
@@ -1,10 +1,11 @@
 from collections.abc import Callable
 from typing import IO, Any, Final
+from typing_extensions import LiteralString

 __all__ = ["Cmd"]

 PROMPT: Final = "(Cmd) "
-IDENTCHARS: str  # Too big to be `Literal`
+IDENTCHARS: Final[LiteralString]  # Too big to be `Literal`

 class Cmd:
    prompt: str
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/collections/init.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/collections/init.pyi
@@ -345,15 +345,15 @@ class _OrderedDictValuesView(ValuesView[_VT_co], Reversible[_VT_co]):
 # but they are not exposed anywhere)
 # pyright doesn't have a specific error code for subclassing error!
@final
-class _odict_keys(dict_keys[_KT_co, _VT_co], Reversible[_KT_co]):  # type: ignore[misc]  # pyright: ignore
+class _odict_keys(dict_keys[_KT_co, _VT_co], Reversible[_KT_co]):  # type: ignore[misc]  # pyright: ignore[reportGeneralTypeIssues]
    def __reversed__(self) -> Iterator[_KT_co]: ...

@final
-class _odict_items(dict_items[_KT_co, _VT_co], Reversible[tuple[_KT_co, _VT_co]]):  # type: ignore[misc]  # pyright: ignore
+class _odict_items(dict_items[_KT_co, _VT_co], Reversible[tuple[_KT_co, _VT_co]]):  # type: ignore[misc]  # pyright: ignore[reportGeneralTypeIssues]
    def __reversed__(self) -> Iterator[tuple[_KT_co, _VT_co]]: ...

@final
-class _odict_values(dict_values[_KT_co, _VT_co], Reversible[_VT_co], Generic[_KT_co, _VT_co]):  # type: ignore[misc]  # pyright: ignore
+class _odict_values(dict_values[_KT_co, _VT_co], Reversible[_VT_co], Generic[_KT_co, _VT_co]):  # type: ignore[misc]  # pyright: ignore[reportGeneralTypeIssues]
    def __reversed__(self) -> Iterator[_VT_co]: ...

 class OrderedDict(dict[_KT, _VT], Reversible[_KT], Generic[_KT, _VT]):
@@ -475,7 +475,8 @@ class ChainMap(MutableMapping[_KT, _VT]):
    def pop(self, key: _KT, default: _T) -> _VT | _T: ...
    def copy(self) -> Self: ...
    __copy__ = copy
-    # All arguments to `fromkeys` are passed to `dict.fromkeys` at runtime, so the signature should be kept in line with `dict.fromkeys`.
+    # All arguments to `fromkeys` are passed to `dict.fromkeys` at runtime,
+    # so the signature should be kept in line with `dict.fromkeys`.
    @classmethod
    @overload
    def fromkeys(cls, iterable: Iterable[_T]) -> ChainMap[_T, Any | None]: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/contextlib.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/contextlib.pyi
@@ -55,6 +55,7 @@ class AbstractAsyncContextManager(Protocol[_T_co, _ExitT_co]):
    ) -> _ExitT_co: ...

 class ContextDecorator:
+    def _recreate_cm(self) -> Self: ...
    def __call__(self, func: _F) -> _F: ...

 class _GeneratorContextManager(AbstractContextManager[_T_co, bool | None], ContextDecorator):
@@ -80,6 +81,7 @@ if sys.version_info >= (3, 10):
    _AF = TypeVar("_AF", bound=Callable[..., Awaitable[Any]])

    class AsyncContextDecorator:
+        def _recreate_cm(self) -> Self: ...
        def __call__(self, func: _AF) -> _AF: ...

    class _AsyncGeneratorContextManager(AbstractAsyncContextManager[_T_co, bool | None], AsyncContextDecorator):
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/crypt.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/crypt.pyi
@@ -1,12 +1,13 @@
 import sys
+from typing import Final

 if sys.platform != "win32":
    class _Method: ...
-    METHOD_CRYPT: _Method
-    METHOD_MD5: _Method
-    METHOD_SHA256: _Method
-    METHOD_SHA512: _Method
-    METHOD_BLOWFISH: _Method
+    METHOD_CRYPT: Final[_Method]
+    METHOD_MD5: Final[_Method]
+    METHOD_SHA256: Final[_Method]
+    METHOD_SHA512: Final[_Method]
+    METHOD_BLOWFISH: Final[_Method]
    methods: list[_Method]
    def mksalt(method: _Method | None = None, *, rounds: int | None = None) -> str: ...
    def crypt(word: str, salt: str | _Method | None = None) -> str: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/ctypes/init.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/ctypes/init.pyi
@@ -185,3 +185,8 @@ if sys.version_info >= (3, 12):
    c_time_t: type[c_int32 | c_int64]  # alias for one or the other at runtime

 class py_object(_CanCastTo, _SimpleCData[_T]): ...
+
+if sys.version_info >= (3, 14):
+    class c_float_complex(_SimpleCData[complex]): ...
+    class c_double_complex(_SimpleCData[complex]): ...
+    class c_longdouble_complex(_SimpleCData[complex]): ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/ctypes/_endian.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/ctypes/_endian.pyi
@@ -1,12 +1,5 @@
 import sys
-from _ctypes import RTLD_GLOBAL as RTLD_GLOBAL, RTLD_LOCAL as RTLD_LOCAL, Structure, Union
-from ctypes import DEFAULT_MODE as DEFAULT_MODE, cdll as cdll, pydll as pydll, pythonapi as pythonapi
-
-if sys.version_info >= (3, 12):
-    from _ctypes import SIZEOF_TIME_T as SIZEOF_TIME_T
-
-if sys.platform == "win32":
-    from ctypes import oledll as oledll, windll as windll
+from ctypes import Structure, Union

 # At runtime, the native endianness is an alias for Structure,
 # while the other is a subclass with a metaclass added in.
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/dataclasses.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/dataclasses.pyi
@@ -5,7 +5,7 @@ from _typeshed import DataclassInstance
 from builtins import type as Type  # alias to avoid name clashes with fields named "type"
 from collections.abc import Callable, Iterable, Mapping
 from typing import Any, Generic, Literal, Protocol, TypeVar, overload
-from typing_extensions import TypeAlias, TypeIs
+from typing_extensions import Never, TypeAlias, TypeIs

 if sys.version_info >= (3, 9):
    from types import GenericAlias
@@ -213,6 +213,10 @@ else:
    ) -> Any: ...

 def fields(class_or_instance: DataclassInstance | type[DataclassInstance]) -> tuple[Field[Any], ...]: ...
+
+# HACK: `obj: Never` typing matches if object argument is using `Any` type.
+@overload
+def is_dataclass(obj: Never) -> TypeIs[DataclassInstance | type[DataclassInstance]]: ...  # type: ignore[narrowed-type-not-subtype]  # pyright: ignore[reportGeneralTypeIssues]
@overload
 def is_dataclass(obj: type) -> TypeIs[type[DataclassInstance]]: ...
@overload
@@ -225,18 +229,17 @@ if sys.version_info >= (3, 9):
 else:
    class _InitVarMeta(type):
        # Not used, instead `InitVar.__class_getitem__` is called.
-        # pyright ignore is needed because pyright (not unreasonably) thinks this
-        # is an invalid use of InitVar.
-        def __getitem__(self, params: Any) -> InitVar[Any]: ...  # pyright: ignore
+        # pyright (not unreasonably) thinks this is an invalid use of InitVar.
+        def __getitem__(self, params: Any) -> InitVar[Any]: ...  # pyright: ignore[reportInvalidTypeForm]

 class InitVar(Generic[_T], metaclass=_InitVarMeta):
    type: Type[_T]
    def __init__(self, type: Type[_T]) -> None: ...
    if sys.version_info >= (3, 9):
        @overload
-        def __class_getitem__(cls, type: Type[_T]) -> InitVar[_T]: ...  # pyright: ignore
+        def __class_getitem__(cls, type: Type[_T]) -> InitVar[_T]: ...  # pyright: ignore[reportInvalidTypeForm]
        @overload
-        def __class_getitem__(cls, type: Any) -> InitVar[Any]: ...  # pyright: ignore
+        def __class_getitem__(cls, type: Any) -> InitVar[Any]: ...  # pyright: ignore[reportInvalidTypeForm]

 if sys.version_info >= (3, 12):
    def make_dataclass(
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/datetime.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/datetime.pyi
@@ -265,12 +265,12 @@ class datetime(date):
        def fromtimestamp(cls, timestamp: float, /, tz: _TzInfo | None = ...) -> Self: ...

    @classmethod
-    @deprecated("Use timezone-aware objects to represent datetimes in UTC; e.g. by calling .fromtimestamp(datetime.UTC)")
+    @deprecated("Use timezone-aware objects to represent datetimes in UTC; e.g. by calling .fromtimestamp(datetime.timezone.utc)")
    def utcfromtimestamp(cls, t: float, /) -> Self: ...
    @classmethod
    def now(cls, tz: _TzInfo | None = None) -> Self: ...
    @classmethod
-    @deprecated("Use timezone-aware objects to represent datetimes in UTC; e.g. by calling .now(datetime.UTC)")
+    @deprecated("Use timezone-aware objects to represent datetimes in UTC; e.g. by calling .now(datetime.timezone.utc)")
    def utcnow(cls) -> Self: ...
    @classmethod
    def combine(cls, date: _Date, time: _Time, tzinfo: _TzInfo | None = ...) -> Self: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/cmd.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/cmd.pyi
@@ -1,6 +1,26 @@
 from _typeshed import BytesPath, Incomplete, StrOrBytesPath, StrPath, Unused
 from abc import abstractmethod
 from collections.abc import Callable, Iterable
+from distutils.command.bdist import bdist
+from distutils.command.bdist_dumb import bdist_dumb
+from distutils.command.bdist_rpm import bdist_rpm
+from distutils.command.build import build
+from distutils.command.build_clib import build_clib
+from distutils.command.build_ext import build_ext
+from distutils.command.build_py import build_py
+from distutils.command.build_scripts import build_scripts
+from distutils.command.check import check
+from distutils.command.clean import clean
+from distutils.command.config import config
+from distutils.command.install import install
+from distutils.command.install_data import install_data
+from distutils.command.install_egg_info import install_egg_info
+from distutils.command.install_headers import install_headers
+from distutils.command.install_lib import install_lib
+from distutils.command.install_scripts import install_scripts
+from distutils.command.register import register
+from distutils.command.sdist import sdist
+from distutils.command.upload import upload
 from distutils.dist import Distribution
 from distutils.file_util import _BytesPathT, _StrPathT
 from typing import Any, ClassVar, Literal, TypeVar, overload
@@ -10,6 +30,7 @@ _CommandT = TypeVar("_CommandT", bound=Command)
 _Ts = TypeVarTuple("_Ts")

 class Command:
+    dry_run: Literal[0, 1]  # Exposed from __getattr_. Same as Distribution.dry_run
    distribution: Distribution
    # Any to work around variance issues
    sub_commands: ClassVar[list[tuple[str, Callable[[Any], bool] | None]]]
@@ -28,8 +49,108 @@ class Command:
    def ensure_dirname(self, option: str) -> None: ...
    def get_command_name(self) -> str: ...
    def set_undefined_options(self, src_cmd: str, *option_pairs: tuple[str, str]) -> None: ...
+    # NOTE: This list comes directly from the distutils/command folder. Minus bdist_msi and bdist_wininst.
+    @overload
+    def get_finalized_command(self, command: Literal["bdist"], create: bool | Literal[0, 1] = 1) -> bdist: ...
+    @overload
+    def get_finalized_command(self, command: Literal["bdist_dumb"], create: bool | Literal[0, 1] = 1) -> bdist_dumb: ...
+    @overload
+    def get_finalized_command(self, command: Literal["bdist_rpm"], create: bool | Literal[0, 1] = 1) -> bdist_rpm: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build"], create: bool | Literal[0, 1] = 1) -> build: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build_clib"], create: bool | Literal[0, 1] = 1) -> build_clib: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build_ext"], create: bool | Literal[0, 1] = 1) -> build_ext: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build_py"], create: bool | Literal[0, 1] = 1) -> build_py: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build_scripts"], create: bool | Literal[0, 1] = 1) -> build_scripts: ...
+    @overload
+    def get_finalized_command(self, command: Literal["check"], create: bool | Literal[0, 1] = 1) -> check: ...
+    @overload
+    def get_finalized_command(self, command: Literal["clean"], create: bool | Literal[0, 1] = 1) -> clean: ...
+    @overload
+    def get_finalized_command(self, command: Literal["config"], create: bool | Literal[0, 1] = 1) -> config: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install"], create: bool | Literal[0, 1] = 1) -> install: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install_data"], create: bool | Literal[0, 1] = 1) -> install_data: ...
+    @overload
+    def get_finalized_command(
+        self, command: Literal["install_egg_info"], create: bool | Literal[0, 1] = 1
+    ) -> install_egg_info: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install_headers"], create: bool | Literal[0, 1] = 1) -> install_headers: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install_lib"], create: bool | Literal[0, 1] = 1) -> install_lib: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install_scripts"], create: bool | Literal[0, 1] = 1) -> install_scripts: ...
+    @overload
+    def get_finalized_command(self, command: Literal["register"], create: bool | Literal[0, 1] = 1) -> register: ...
+    @overload
+    def get_finalized_command(self, command: Literal["sdist"], create: bool | Literal[0, 1] = 1) -> sdist: ...
+    @overload
+    def get_finalized_command(self, command: Literal["upload"], create: bool | Literal[0, 1] = 1) -> upload: ...
+    @overload
    def get_finalized_command(self, command: str, create: bool | Literal[0, 1] = 1) -> Command: ...
    @overload
+    def reinitialize_command(self, command: Literal["bdist"], reinit_subcommands: bool | Literal[0, 1] = 0) -> bdist: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["bdist_dumb"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> bdist_dumb: ...
+    @overload
+    def reinitialize_command(self, command: Literal["bdist_rpm"], reinit_subcommands: bool | Literal[0, 1] = 0) -> bdist_rpm: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build"], reinit_subcommands: bool | Literal[0, 1] = 0) -> build: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["build_clib"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> build_clib: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_ext"], reinit_subcommands: bool | Literal[0, 1] = 0) -> build_ext: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_py"], reinit_subcommands: bool | Literal[0, 1] = 0) -> build_py: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["build_scripts"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> build_scripts: ...
+    @overload
+    def reinitialize_command(self, command: Literal["check"], reinit_subcommands: bool | Literal[0, 1] = 0) -> check: ...
+    @overload
+    def reinitialize_command(self, command: Literal["clean"], reinit_subcommands: bool | Literal[0, 1] = 0) -> clean: ...
+    @overload
+    def reinitialize_command(self, command: Literal["config"], reinit_subcommands: bool | Literal[0, 1] = 0) -> config: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install"], reinit_subcommands: bool | Literal[0, 1] = 0) -> install: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_data"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_data: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_egg_info"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_egg_info: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_headers"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_headers: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_lib"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_lib: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_scripts"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_scripts: ...
+    @overload
+    def reinitialize_command(self, command: Literal["register"], reinit_subcommands: bool | Literal[0, 1] = 0) -> register: ...
+    @overload
+    def reinitialize_command(self, command: Literal["sdist"], reinit_subcommands: bool | Literal[0, 1] = 0) -> sdist: ...
+    @overload
+    def reinitialize_command(self, command: Literal["upload"], reinit_subcommands: bool | Literal[0, 1] = 0) -> upload: ...
+    @overload
    def reinitialize_command(self, command: str, reinit_subcommands: bool | Literal[0, 1] = 0) -> Command: ...
    @overload
    def reinitialize_command(self, command: _CommandT, reinit_subcommands: bool | Literal[0, 1] = 0) -> _CommandT: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/init.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/init.pyi
@@ -0,0 +1,48 @@
+import sys
+
+from . import (
+    bdist,
+    bdist_dumb,
+    bdist_rpm,
+    build,
+    build_clib,
+    build_ext,
+    build_py,
+    build_scripts,
+    check,
+    clean,
+    install,
+    install_data,
+    install_headers,
+    install_lib,
+    install_scripts,
+    register,
+    sdist,
+    upload,
+)
+
+__all__ = [
+    "build",
+    "build_py",
+    "build_ext",
+    "build_clib",
+    "build_scripts",
+    "clean",
+    "install",
+    "install_lib",
+    "install_headers",
+    "install_scripts",
+    "install_data",
+    "sdist",
+    "register",
+    "bdist",
+    "bdist_dumb",
+    "bdist_rpm",
+    "check",
+    "upload",
+]
+
+if sys.version_info < (3, 10):
+    from . import bdist_wininst
+
+    __all__ += ["bdist_wininst"]
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/check.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/check.pyi
@@ -1,4 +1,4 @@
-from typing import Any, ClassVar, Literal
+from typing import Any, ClassVar, Final, Literal
 from typing_extensions import TypeAlias

 from ..cmd import Command
@@ -22,7 +22,7 @@ class SilentReporter(_Reporter):
    ) -> None: ...
    def system_message(self, level, message, *children, **kwargs): ...

-HAS_DOCUTILS: bool
+HAS_DOCUTILS: Final[bool]

 class check(Command):
    description: str
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/config.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/config.pyi
@@ -1,12 +1,12 @@
 from _typeshed import StrOrBytesPath
 from collections.abc import Sequence
 from re import Pattern
-from typing import Any, ClassVar, Literal
+from typing import Any, ClassVar, Final, Literal

 from ..ccompiler import CCompiler
 from ..cmd import Command

-LANG_EXT: dict[str, str]
+LANG_EXT: Final[dict[str, str]]

 class config(Command):
    description: str
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/install.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/install.pyi
@@ -1,11 +1,16 @@
+import sys
 from collections.abc import Callable
-from typing import Any, ClassVar
+from typing import Any, ClassVar, Final, Literal

 from ..cmd import Command

-HAS_USER_SITE: bool
-SCHEME_KEYS: tuple[str, ...]
-INSTALL_SCHEMES: dict[str, dict[Any, Any]]
+HAS_USER_SITE: Final[bool]
+
+SCHEME_KEYS: Final[tuple[Literal["purelib"], Literal["platlib"], Literal["headers"], Literal["scripts"], Literal["data"]]]
+INSTALL_SCHEMES: Final[dict[str, dict[str, str]]]
+
+if sys.version_info < (3, 10):
+    WINDOWS_SCHEME: Final[dict[str, str]]

 class install(Command):
    description: str
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/install_lib.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/install_lib.pyi
@@ -1,8 +1,8 @@
-from typing import Any, ClassVar
+from typing import Any, ClassVar, Final

 from ..cmd import Command

-PYTHON_SOURCE_EXTENSION: str
+PYTHON_SOURCE_EXTENSION: Final = ".py"

 class install_lib(Command):
    description: str
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/core.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/core.pyi
@@ -3,9 +3,9 @@ from collections.abc import Mapping
 from distutils.cmd import Command as Command
 from distutils.dist import Distribution as Distribution
 from distutils.extension import Extension as Extension
-from typing import Any, Literal
+from typing import Any, Final, Literal

-USAGE: str
+USAGE: Final[str]

 def gen_usage(script_name: StrOrBytesPath) -> str: ...

--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/cygwinccompiler.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/cygwinccompiler.pyi
@@ -1,20 +1,20 @@
 from distutils.unixccompiler import UnixCCompiler
 from distutils.version import LooseVersion
 from re import Pattern
-from typing import Literal
+from typing import Final, Literal

 def get_msvcr() -> list[str] | None: ...

 class CygwinCCompiler(UnixCCompiler): ...
 class Mingw32CCompiler(CygwinCCompiler): ...

-CONFIG_H_OK: str
-CONFIG_H_NOTOK: str
-CONFIG_H_UNCERTAIN: str
+CONFIG_H_OK: Final = "ok"
+CONFIG_H_NOTOK: Final = "not ok"
+CONFIG_H_UNCERTAIN: Final = "uncertain"

 def check_config_h() -> tuple[Literal["ok", "not ok", "uncertain"], str]: ...

-RE_VERSION: Pattern[bytes]
+RE_VERSION: Final[Pattern[bytes]]

 def get_versions() -> tuple[LooseVersion | None, ...]: ...
 def is_cygwingcc() -> bool: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/debug.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/debug.pyi
@@ -1 +1,3 @@
-DEBUG: bool | None
+from typing import Final
+
+DEBUG: Final[str | None]
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/dist.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/dist.pyi
@@ -1,6 +1,26 @@
 from _typeshed import Incomplete, StrOrBytesPath, StrPath, SupportsWrite
 from collections.abc import Iterable, MutableMapping
 from distutils.cmd import Command
+from distutils.command.bdist import bdist
+from distutils.command.bdist_dumb import bdist_dumb
+from distutils.command.bdist_rpm import bdist_rpm
+from distutils.command.build import build
+from distutils.command.build_clib import build_clib
+from distutils.command.build_ext import build_ext
+from distutils.command.build_py import build_py
+from distutils.command.build_scripts import build_scripts
+from distutils.command.check import check
+from distutils.command.clean import clean
+from distutils.command.config import config
+from distutils.command.install import install
+from distutils.command.install_data import install_data
+from distutils.command.install_egg_info import install_egg_info
+from distutils.command.install_headers import install_headers
+from distutils.command.install_lib import install_lib
+from distutils.command.install_scripts import install_scripts
+from distutils.command.register import register
+from distutils.command.sdist import sdist
+from distutils.command.upload import upload
 from re import Pattern
 from typing import IO, ClassVar, Literal, TypeVar, overload
 from typing_extensions import TypeAlias
@@ -63,18 +83,14 @@ class Distribution:
    def __init__(self, attrs: MutableMapping[str, Incomplete] | None = None) -> None: ...
    def get_option_dict(self, command: str) -> dict[str, tuple[str, str]]: ...
    def parse_config_files(self, filenames: Iterable[str] | None = None) -> None: ...
-    @overload
-    def get_command_obj(self, command: str, create: Literal[1, True] = 1) -> Command: ...
-    @overload
-    def get_command_obj(self, command: str, create: Literal[0, False]) -> Command | None: ...
    global_options: ClassVar[_OptionsList]
    common_usage: ClassVar[str]
    display_options: ClassVar[_OptionsList]
    display_option_names: ClassVar[list[str]]
    negative_opt: ClassVar[dict[str, str]]
-    verbose: int
-    dry_run: int
-    help: int
+    verbose: Literal[0, 1]
+    dry_run: Literal[0, 1]
+    help: Literal[0, 1]
    command_packages: list[str] | None
    script_name: str | None
    script_args: list[str] | None
@@ -108,8 +124,137 @@ class Distribution:
    def print_commands(self) -> None: ...
    def get_command_list(self): ...
    def get_command_packages(self): ...
+    # NOTE: This list comes directly from the distutils/command folder. Minus bdist_msi and bdist_wininst.
+    @overload
+    def get_command_obj(self, command: Literal["bdist"], create: Literal[1, True] = 1) -> bdist: ...
+    @overload
+    def get_command_obj(self, command: Literal["bdist_dumb"], create: Literal[1, True] = 1) -> bdist_dumb: ...
+    @overload
+    def get_command_obj(self, command: Literal["bdist_rpm"], create: Literal[1, True] = 1) -> bdist_rpm: ...
+    @overload
+    def get_command_obj(self, command: Literal["build"], create: Literal[1, True] = 1) -> build: ...
+    @overload
+    def get_command_obj(self, command: Literal["build_clib"], create: Literal[1, True] = 1) -> build_clib: ...
+    @overload
+    def get_command_obj(self, command: Literal["build_ext"], create: Literal[1, True] = 1) -> build_ext: ...
+    @overload
+    def get_command_obj(self, command: Literal["build_py"], create: Literal[1, True] = 1) -> build_py: ...
+    @overload
+    def get_command_obj(self, command: Literal["build_scripts"], create: Literal[1, True] = 1) -> build_scripts: ...
+    @overload
+    def get_command_obj(self, command: Literal["check"], create: Literal[1, True] = 1) -> check: ...
+    @overload
+    def get_command_obj(self, command: Literal["clean"], create: Literal[1, True] = 1) -> clean: ...
+    @overload
+    def get_command_obj(self, command: Literal["config"], create: Literal[1, True] = 1) -> config: ...
+    @overload
+    def get_command_obj(self, command: Literal["install"], create: Literal[1, True] = 1) -> install: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_data"], create: Literal[1, True] = 1) -> install_data: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_egg_info"], create: Literal[1, True] = 1) -> install_egg_info: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_headers"], create: Literal[1, True] = 1) -> install_headers: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_lib"], create: Literal[1, True] = 1) -> install_lib: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_scripts"], create: Literal[1, True] = 1) -> install_scripts: ...
+    @overload
+    def get_command_obj(self, command: Literal["register"], create: Literal[1, True] = 1) -> register: ...
+    @overload
+    def get_command_obj(self, command: Literal["sdist"], create: Literal[1, True] = 1) -> sdist: ...
+    @overload
+    def get_command_obj(self, command: Literal["upload"], create: Literal[1, True] = 1) -> upload: ...
+    @overload
+    def get_command_obj(self, command: str, create: Literal[1, True] = 1) -> Command: ...
+    # Not replicating the overloads for "Command | None", user may use "isinstance"
+    @overload
+    def get_command_obj(self, command: str, create: Literal[0, False]) -> Command | None: ...
+    @overload
+    def get_command_class(self, command: Literal["bdist"]) -> type[bdist]: ...
+    @overload
+    def get_command_class(self, command: Literal["bdist_dumb"]) -> type[bdist_dumb]: ...
+    @overload
+    def get_command_class(self, command: Literal["bdist_rpm"]) -> type[bdist_rpm]: ...
+    @overload
+    def get_command_class(self, command: Literal["build"]) -> type[build]: ...
+    @overload
+    def get_command_class(self, command: Literal["build_clib"]) -> type[build_clib]: ...
+    @overload
+    def get_command_class(self, command: Literal["build_ext"]) -> type[build_ext]: ...
+    @overload
+    def get_command_class(self, command: Literal["build_py"]) -> type[build_py]: ...
+    @overload
+    def get_command_class(self, command: Literal["build_scripts"]) -> type[build_scripts]: ...
+    @overload
+    def get_command_class(self, command: Literal["check"]) -> type[check]: ...
+    @overload
+    def get_command_class(self, command: Literal["clean"]) -> type[clean]: ...
+    @overload
+    def get_command_class(self, command: Literal["config"]) -> type[config]: ...
+    @overload
+    def get_command_class(self, command: Literal["install"]) -> type[install]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_data"]) -> type[install_data]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_egg_info"]) -> type[install_egg_info]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_headers"]) -> type[install_headers]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_lib"]) -> type[install_lib]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_scripts"]) -> type[install_scripts]: ...
+    @overload
+    def get_command_class(self, command: Literal["register"]) -> type[register]: ...
+    @overload
+    def get_command_class(self, command: Literal["sdist"]) -> type[sdist]: ...
+    @overload
+    def get_command_class(self, command: Literal["upload"]) -> type[upload]: ...
+    @overload
    def get_command_class(self, command: str) -> type[Command]: ...
    @overload
+    def reinitialize_command(self, command: Literal["bdist"], reinit_subcommands: bool = False) -> bdist: ...
+    @overload
+    def reinitialize_command(self, command: Literal["bdist_dumb"], reinit_subcommands: bool = False) -> bdist_dumb: ...
+    @overload
+    def reinitialize_command(self, command: Literal["bdist_rpm"], reinit_subcommands: bool = False) -> bdist_rpm: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build"], reinit_subcommands: bool = False) -> build: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_clib"], reinit_subcommands: bool = False) -> build_clib: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_ext"], reinit_subcommands: bool = False) -> build_ext: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_py"], reinit_subcommands: bool = False) -> build_py: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_scripts"], reinit_subcommands: bool = False) -> build_scripts: ...
+    @overload
+    def reinitialize_command(self, command: Literal["check"], reinit_subcommands: bool = False) -> check: ...
+    @overload
+    def reinitialize_command(self, command: Literal["clean"], reinit_subcommands: bool = False) -> clean: ...
+    @overload
+    def reinitialize_command(self, command: Literal["config"], reinit_subcommands: bool = False) -> config: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install"], reinit_subcommands: bool = False) -> install: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install_data"], reinit_subcommands: bool = False) -> install_data: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_egg_info"], reinit_subcommands: bool = False
+    ) -> install_egg_info: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install_headers"], reinit_subcommands: bool = False) -> install_headers: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install_lib"], reinit_subcommands: bool = False) -> install_lib: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install_scripts"], reinit_subcommands: bool = False) -> install_scripts: ...
+    @overload
+    def reinitialize_command(self, command: Literal["register"], reinit_subcommands: bool = False) -> register: ...
+    @overload
+    def reinitialize_command(self, command: Literal["sdist"], reinit_subcommands: bool = False) -> sdist: ...
+    @overload
+    def reinitialize_command(self, command: Literal["upload"], reinit_subcommands: bool = False) -> upload: ...
+    @overload
    def reinitialize_command(self, command: str, reinit_subcommands: bool = False) -> Command: ...
    @overload
    def reinitialize_command(self, command: _CommandT, reinit_subcommands: bool = False) -> _CommandT: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/fancy_getopt.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/fancy_getopt.pyi
@@ -1,15 +1,15 @@
 from collections.abc import Iterable, Mapping
 from re import Pattern
-from typing import Any, overload
+from typing import Any, Final, overload
 from typing_extensions import TypeAlias

 _Option: TypeAlias = tuple[str, str | None, str]
 _GR: TypeAlias = tuple[list[str], OptionDummy]

-longopt_pat: str
-longopt_re: Pattern[str]
-neg_alias_re: Pattern[str]
-longopt_xlate: dict[int, int]
+longopt_pat: Final = r"[a-zA-Z](?:[a-zA-Z0-9-]*)"
+longopt_re: Final[Pattern[str]]
+neg_alias_re: Final[Pattern[str]]
+longopt_xlate: Final[dict[int, int]]

 class FancyGetopt:
    def __init__(self, option_table: list[_Option] | None = None) -> None: ...
@@ -25,7 +25,7 @@ def fancy_getopt(
    options: list[_Option], negative_opt: Mapping[_Option, _Option], object: Any, args: list[str] | None
 ) -> list[str] | _GR: ...

-WS_TRANS: dict[int, str]
+WS_TRANS: Final[dict[int, str]]

 def wrap_text(text: str, width: int) -> list[str]: ...
 def translate_longopt(opt: str) -> str: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/log.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/log.pyi
@@ -1,10 +1,10 @@
-from typing import Any
+from typing import Any, Final

-DEBUG: int
-INFO: int
-WARN: int
-ERROR: int
-FATAL: int
+DEBUG: Final = 1
+INFO: Final = 2
+WARN: Final = 3
+ERROR: Final = 4
+FATAL: Final = 5

 class Log:
    def __init__(self, threshold: int = 3) -> None: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/sysconfig.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/sysconfig.pyi
@@ -1,15 +1,15 @@
 import sys
 from collections.abc import Mapping
 from distutils.ccompiler import CCompiler
-from typing import Literal, overload
+from typing import Final, Literal, overload
 from typing_extensions import deprecated

-PREFIX: str
-EXEC_PREFIX: str
-BASE_PREFIX: str
-BASE_EXEC_PREFIX: str
-project_base: str
-python_build: bool
+PREFIX: Final[str]
+EXEC_PREFIX: Final[str]
+BASE_PREFIX: Final[str]
+BASE_EXEC_PREFIX: Final[str]
+project_base: Final[str]
+python_build: Final[bool]

 def expand_makefile_vars(s: str, vars: Mapping[str, str]) -> str: ...
@overload
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/email/message.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/email/message.pyi
@@ -50,7 +50,8 @@ class Message(Generic[_HeaderT, _HeaderParamT]):
    def get_payload(self, i: None = None, *, decode: Literal[True]) -> _EncodedPayloadType | Any: ...
    @overload  # not multipart, IDEM but w/o kwarg
    def get_payload(self, i: None, decode: Literal[True]) -> _EncodedPayloadType | Any: ...
-    # If `charset=None` and payload supports both `encode` AND `decode`, then an invalid payload could be passed, but this is unlikely
+    # If `charset=None` and payload supports both `encode` AND `decode`,
+    # then an invalid payload could be passed, but this is unlikely
    # Not[_SupportsEncodeToPayload]
    @overload
    def set_payload(
@@ -146,7 +147,11 @@ class Message(Generic[_HeaderT, _HeaderParamT]):
 class MIMEPart(Message[_HeaderRegistryT, _HeaderRegistryParamT]):
    def __init__(self, policy: Policy | None = None) -> None: ...
    def get_body(self, preferencelist: Sequence[str] = ("related", "html", "plain")) -> MIMEPart[_HeaderRegistryT] | None: ...
-    def iter_attachments(self) -> Iterator[MIMEPart[_HeaderRegistryT]]: ...
+    def attach(self, payload: Self) -> None: ...  # type: ignore[override]
+    # The attachments are created via type(self) in the attach method. It's theoretically
+    # possible to sneak other attachment types into a MIMEPart instance, but could cause
+    # cause unforseen consequences.
+    def iter_attachments(self) -> Iterator[Self]: ...
    def iter_parts(self) -> Iterator[MIMEPart[_HeaderRegistryT]]: ...
    def get_content(self, *args: Any, content_manager: ContentManager | None = None, **kw: Any) -> Any: ...
    def set_content(self, *args: Any, content_manager: ContentManager | None = None, **kw: Any) -> None: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/email/utils.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/email/utils.pyi
@@ -66,7 +66,10 @@ def mktime_tz(data: _PDTZ) -> int: ...
 def formatdate(timeval: float | None = None, localtime: bool = False, usegmt: bool = False) -> str: ...
 def format_datetime(dt: datetime.datetime, usegmt: bool = False) -> str: ...

-if sys.version_info >= (3, 12):
+if sys.version_info >= (3, 14):
+    def localtime(dt: datetime.datetime | None = None) -> datetime.datetime: ...
+
+elif sys.version_info >= (3, 12):
    @overload
    def localtime(dt: datetime.datetime | None = None) -> datetime.datetime: ...
    @overload
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/filecmp.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/filecmp.pyi
@@ -17,13 +17,24 @@ def cmpfiles(
 ) -> tuple[list[AnyStr], list[AnyStr], list[AnyStr]]: ...

 class dircmp(Generic[AnyStr]):
-    def __init__(
-        self,
-        a: GenericPath[AnyStr],
-        b: GenericPath[AnyStr],
-        ignore: Sequence[AnyStr] | None = None,
-        hide: Sequence[AnyStr] | None = None,
-    ) -> None: ...
+    if sys.version_info >= (3, 13):
+        def __init__(
+            self,
+            a: GenericPath[AnyStr],
+            b: GenericPath[AnyStr],
+            ignore: Sequence[AnyStr] | None = None,
+            hide: Sequence[AnyStr] | None = None,
+            *,
+            shallow: bool = True,
+        ) -> None: ...
+    else:
+        def __init__(
+            self,
+            a: GenericPath[AnyStr],
+            b: GenericPath[AnyStr],
+            ignore: Sequence[AnyStr] | None = None,
+            hide: Sequence[AnyStr] | None = None,
+        ) -> None: ...
    left: AnyStr
    right: AnyStr
    hide: Sequence[AnyStr]
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/ftplib.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/ftplib.pyi
@@ -86,7 +86,7 @@ class FTP:
    def makeport(self) -> socket: ...
    def makepasv(self) -> tuple[str, int]: ...
    def login(self, user: str = "", passwd: str = "", acct: str = "") -> str: ...
-    # In practice, `rest` rest can actually be anything whose str() is an integer sequence, so to make it simple we allow integers.
+    # In practice, `rest` can actually be anything whose str() is an integer sequence, so to make it simple we allow integers
    def ntransfercmd(self, cmd: str, rest: int | str | None = None) -> tuple[socket, int | None]: ...
    def transfercmd(self, cmd: str, rest: int | str | None = None) -> socket: ...
    def retrbinary(
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/importlib/metadata/init.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/importlib/metadata/init.pyi
@@ -155,7 +155,7 @@ if sys.version_info >= (3, 10) and sys.version_info < (3, 12):
        @property
        def names(self) -> set[str]: ...
        @overload
-        def select(self) -> Self: ...  # type: ignore[misc]
+        def select(self) -> Self: ...
        @overload
        def select(
            self,
@@ -277,7 +277,7 @@ if sys.version_info >= (3, 12):

 elif sys.version_info >= (3, 10):
    @overload
-    def entry_points() -> SelectableGroups: ...  # type: ignore[overload-overlap]
+    def entry_points() -> SelectableGroups: ...
    @overload
    def entry_points(
        *, name: str = ..., value: str = ..., group: str = ..., module: str = ..., attr: str = ..., extras: list[str] = ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/json/encoder.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/json/encoder.pyi
@@ -1,12 +1,12 @@
 from collections.abc import Callable, Iterator
 from re import Pattern
-from typing import Any
+from typing import Any, Final

-ESCAPE: Pattern[str]
-ESCAPE_ASCII: Pattern[str]
-HAS_UTF8: Pattern[bytes]
-ESCAPE_DCT: dict[str, str]
-INFINITY: float
+ESCAPE: Final[Pattern[str]]
+ESCAPE_ASCII: Final[Pattern[str]]
+HAS_UTF8: Final[Pattern[bytes]]
+ESCAPE_DCT: Final[dict[str, str]]
+INFINITY: Final[float]

 def py_encode_basestring(s: str) -> str: ...  # undocumented
 def py_encode_basestring_ascii(s: str) -> str: ...  # undocumented
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/lib2to3/fixes/fix_unicode.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/lib2to3/fixes/fix_unicode.pyi
@@ -6,7 +6,7 @@ from ..pytree import Node

 class FixUnicode(fixer_base.BaseFix):
    BM_compatible: ClassVar[Literal[True]]
-    PATTERN: ClassVar[Literal["STRING | 'unicode' | 'unichr'"]]  # type: ignore[name-defined]  # Name "STRING" is not defined
+    PATTERN: ClassVar[str]
    unicode_literals: bool
    def start_tree(self, tree: Node, filename: StrPath) -> None: ...
    def transform(self, node, results): ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/logging/init.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/logging/init.pyi
@@ -55,10 +55,9 @@ __all__ = [
    "setLogRecordFactory",
    "lastResort",
    "raiseExceptions",
+    "warn",
 ]

-if sys.version_info < (3, 13):
-    __all__ += ["warn"]
 if sys.version_info >= (3, 11):
    __all__ += ["getLevelNamesMapping"]
 if sys.version_info >= (3, 12):
@@ -157,17 +156,16 @@ class Logger(Filterer):
        stacklevel: int = 1,
        extra: Mapping[str, object] | None = None,
    ) -> None: ...
-    if sys.version_info < (3, 13):
-        def warn(
-            self,
-            msg: object,
-            *args: object,
-            exc_info: _ExcInfoType = None,
-            stack_info: bool = False,
-            stacklevel: int = 1,
-            extra: Mapping[str, object] | None = None,
-        ) -> None: ...
-
+    @deprecated("Deprecated; use warning() instead.")
+    def warn(
+        self,
+        msg: object,
+        *args: object,
+        exc_info: _ExcInfoType = None,
+        stack_info: bool = False,
+        stacklevel: int = 1,
+        extra: Mapping[str, object] | None = None,
+    ) -> None: ...
    def error(
        self,
        msg: object,
@@ -412,18 +410,17 @@ class LoggerAdapter(Generic[_L]):
        extra: Mapping[str, object] | None = None,
        **kwargs: object,
    ) -> None: ...
-    if sys.version_info < (3, 13):
-        def warn(
-            self,
-            msg: object,
-            *args: object,
-            exc_info: _ExcInfoType = None,
-            stack_info: bool = False,
-            stacklevel: int = 1,
-            extra: Mapping[str, object] | None = None,
-            **kwargs: object,
-        ) -> None: ...
-
+    @deprecated("Deprecated; use warning() instead.")
+    def warn(
+        self,
+        msg: object,
+        *args: object,
+        exc_info: _ExcInfoType = None,
+        stack_info: bool = False,
+        stacklevel: int = 1,
+        extra: Mapping[str, object] | None = None,
+        **kwargs: object,
+    ) -> None: ...
    def error(
        self,
        msg: object,
@@ -523,17 +520,15 @@ def warning(
    stacklevel: int = 1,
    extra: Mapping[str, object] | None = None,
 ) -> None: ...
-
-if sys.version_info < (3, 13):
-    def warn(
-        msg: object,
-        *args: object,
-        exc_info: _ExcInfoType = None,
-        stack_info: bool = False,
-        stacklevel: int = 1,
-        extra: Mapping[str, object] | None = None,
-    ) -> None: ...
-
+@deprecated("Deprecated; use warning() instead.")
+def warn(
+    msg: object,
+    *args: object,
+    exc_info: _ExcInfoType = None,
+    stack_info: bool = False,
+    stacklevel: int = 1,
+    extra: Mapping[str, object] | None = None,
+) -> None: ...
 def error(
    msg: object,
    *args: object,
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/multiprocessing/sharedctypes.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/multiprocessing/sharedctypes.pyi
@@ -73,7 +73,7 @@ def copy(obj: _CT) -> _CT: ...
@overload
 def synchronized(obj: _SimpleCData[_T], lock: _LockLike | None = None, ctx: Any | None = None) -> Synchronized[_T]: ...
@overload
-def synchronized(obj: ctypes.Array[c_char], lock: _LockLike | None = None, ctx: Any | None = None) -> SynchronizedString: ...  # type: ignore
+def synchronized(obj: ctypes.Array[c_char], lock: _LockLike | None = None, ctx: Any | None = None) -> SynchronizedString: ...
@overload
 def synchronized(
    obj: ctypes.Array[_SimpleCData[_T]], lock: _LockLike | None = None, ctx: Any | None = None
@@ -115,12 +115,12 @@ class SynchronizedArray(SynchronizedBase[ctypes.Array[_SimpleCData[_T]]], Generi
 class SynchronizedString(SynchronizedArray[bytes]):
    @overload  # type: ignore[override]
    def __getitem__(self, i: slice) -> bytes: ...
-    @overload  # type: ignore[override]
+    @overload
    def __getitem__(self, i: int) -> bytes: ...
    @overload  # type: ignore[override]
    def __setitem__(self, i: slice, value: bytes) -> None: ...
-    @overload  # type: ignore[override]
-    def __setitem__(self, i: int, value: bytes) -> None: ...  # type: ignore[override]
+    @overload
+    def __setitem__(self, i: int, value: bytes) -> None: ...
    def __getslice__(self, start: int, stop: int) -> bytes: ...  # type: ignore[override]
    def __setslice__(self, start: int, stop: int, values: bytes) -> None: ...  # type: ignore[override]

--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/operator.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/operator.pyi
@@ -61,6 +61,9 @@ __all__ = [
 if sys.version_info >= (3, 11):
    __all__ += ["call"]

+if sys.version_info >= (3, 14):
+    __all__ += ["is_none", "is_not_none"]
+
 __lt__ = lt
 __le__ = le
 __eq__ = eq
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/os/init.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/os/init.pyi
@@ -365,7 +365,9 @@ class stat_result(structseq[float], tuple[int, int, int, int, int, int, int, flo
    if sys.version_info >= (3, 12) and sys.platform == "win32":
        @property
        @deprecated(
-            "Use st_birthtime instead to retrieve the file creation time. In the future, this property will contain the last metadata change time."
+            """\
+Use st_birthtime instead to retrieve the file creation time. \
+In the future, this property will contain the last metadata change time."""
        )
        def st_ctime(self) -> float: ...
    else:
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pathlib.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pathlib.pyi
@@ -159,6 +159,20 @@ class Path(PurePath):
    def lchmod(self, mode: int) -> None: ...
    def lstat(self) -> stat_result: ...
    def mkdir(self, mode: int = 0o777, parents: bool = False, exist_ok: bool = False) -> None: ...
+
+    if sys.version_info >= (3, 14):
+        def copy(self, target: StrPath, *, follow_symlinks: bool = True, preserve_metadata: bool = False) -> None: ...
+        def copytree(
+            self,
+            target: StrPath,
+            *,
+            follow_symlinks: bool = True,
+            preserve_metadata: bool = False,
+            dirs_exist_ok: bool = False,
+            ignore: Callable[[Self], bool] | None = None,
+            on_error: Callable[[OSError], object] | None = None,
+        ) -> None: ...
+
    # Adapted from builtins.open
    # Text mode: always returns a TextIOWrapper
    # The Traversable .open in stdlib/importlib/abc.pyi should be kept in sync with this.
@@ -232,10 +246,18 @@ class Path(PurePath):
    if sys.version_info >= (3, 9):
        def readlink(self) -> Self: ...

-    def rename(self, target: str | PurePath) -> Self: ...
-    def replace(self, target: str | PurePath) -> Self: ...
+    if sys.version_info >= (3, 10):
+        def rename(self, target: StrPath) -> Self: ...
+        def replace(self, target: StrPath) -> Self: ...
+    else:
+        def rename(self, target: str | PurePath) -> Self: ...
+        def replace(self, target: str | PurePath) -> Self: ...
+
    def resolve(self, strict: bool = False) -> Self: ...
    def rmdir(self) -> None: ...
+    if sys.version_info >= (3, 14):
+        def delete(self, ignore_errors: bool = False, on_error: Callable[[OSError], object] | None = None) -> None: ...
+
    def symlink_to(self, target: StrOrBytesPath, target_is_directory: bool = False) -> None: ...
    if sys.version_info >= (3, 10):
        def hardlink_to(self, target: StrOrBytesPath) -> None: ...
@@ -266,6 +288,9 @@ class Path(PurePath):
            self, top_down: bool = ..., on_error: Callable[[OSError], object] | None = ..., follow_symlinks: bool = ...
        ) -> Iterator[tuple[Self, list[str], list[str]]]: ...

+    if sys.version_info >= (3, 14):
+        def rmtree(self, ignore_errors: bool = False, on_error: Callable[[OSError], object] | None = None) -> None: ...
+
 class PosixPath(Path, PurePosixPath): ...
 class WindowsPath(Path, PureWindowsPath): ...

--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pdb.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pdb.pyi
@@ -84,7 +84,7 @@ class Pdb(Bdb, Cmd):
        def _runscript(self, filename: str) -> None: ...

    if sys.version_info >= (3, 13):
-        def completedefault(self, text: str, line: str, begidx: int, endidx: int) -> list[str]: ...  # type: ignore[override]
+        def completedefault(self, text: str, line: str, begidx: int, endidx: int) -> list[str]: ...

    def do_commands(self, arg: str) -> bool | None: ...
    def do_break(self, arg: str, temporary: bool = ...) -> bool | None: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/poplib.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/poplib.pyi
@@ -67,5 +67,6 @@ class POP3_SSL(POP3):
            timeout: float = ...,
            context: ssl.SSLContext | None = None,
        ) -> None: ...
-        # "context" is actually the last argument, but that breaks LSP and it doesn't really matter because all the arguments are ignored
+        # "context" is actually the last argument,
+        # but that breaks LSP and it doesn't really matter because all the arguments are ignored
        def stls(self, context: Any = None, keyfile: Any = None, certfile: Any = None) -> NoReturn: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pty.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pty.pyi
@@ -1,7 +1,7 @@
 import sys
 from collections.abc import Callable, Iterable
 from typing import Final
-from typing_extensions import TypeAlias
+from typing_extensions import TypeAlias, deprecated

 if sys.platform != "win32":
    __all__ = ["openpty", "fork", "spawn"]
@@ -13,7 +13,12 @@ if sys.platform != "win32":

    CHILD: Final = 0
    def openpty() -> tuple[int, int]: ...
-    def master_open() -> tuple[int, str]: ...  # deprecated, use openpty()
-    def slave_open(tty_name: str) -> int: ...  # deprecated, use openpty()
+
+    if sys.version_info < (3, 14):
+        @deprecated("Deprecated in 3.12, to be removed in 3.14; use openpty() instead")
+        def master_open() -> tuple[int, str]: ...
+        @deprecated("Deprecated in 3.12, to be removed in 3.14; use openpty() instead")
+        def slave_open(tty_name: str) -> int: ...
+
    def fork() -> tuple[int, int]: ...
    def spawn(argv: str | Iterable[str], master_read: _Reader = ..., stdin_read: _Reader = ...) -> int: ...
--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pyexpat/init.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pyexpat/init.pyi
@@ -15,9 +15,9 @@ class ExpatError(Exception):
    offset: int

 error = ExpatError
-XML_PARAM_ENTITY_PARSING_NEVER: int
-XML_PARAM_ENTITY_PARSING_UNLESS_STANDALONE: int
-XML_PARAM_ENTITY_PARSING_ALWAYS: int
+XML_PARAM_ENTITY_PARSING_NEVER: Final = 0
+XML_PARAM_ENTITY_PARSING_UNLESS_STANDALONE: Final = 1
+XML_PARAM_ENTITY_PARSING_ALWAYS: Final = 2

 _Model: TypeAlias = tuple[int, int, str | None, tuple[Any, ...]]

--- a/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pyexpat/errors.pyi
+++ b/crates/red_knot_python_semantic/vendor/typeshed/stdlib/pyexpat/errors.pyi
@@ -1,49 +1,51 @@
 import sys
+from typing import Final
+from typing_extensions import LiteralString

 codes: dict[str, int]
 messages: dict[int, str]

-XML_ERROR_ABORTED: str
-XML_ERROR_ASYNC_ENTITY: str
-XML_ERROR_ATTRIBUTE_EXTERNAL_ENTITY_REF: str
-XML_ERROR_BAD_CHAR_REF: str
-XML_ERROR_BINARY_ENTITY_REF: str
-XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING: str
-XML_ERROR_DUPLICATE_ATTRIBUTE: str
-XML_ERROR_ENTITY_DECLARED_IN_PE: str
-XML_ERROR_EXTERNAL_ENTITY_HANDLING: str
-XML_ERROR_FEATURE_REQUIRES_XML_DTD: str
-XML_ERROR_FINISHED: str
-XML_ERROR_INCOMPLETE_PE: str
-XML_ERROR_INCORRECT_ENCODING: str
-XML_ERROR_INVALID_TOKEN: str
-XML_ERROR_JUNK_AFTER_DOC_ELEMENT: str
-XML_ERROR_MISPLACED_XML_PI: str
-XML_ERROR_NOT_STANDALONE: str
-XML_ERROR_NOT_SUSPENDED: str
-XML_ERROR_NO_ELEMENTS: str
-XML_ERROR_NO_MEMORY: str
-XML_ERROR_PARAM_ENTITY_REF: str
-XML_ERROR_PARTIAL_CHAR: str
-XML_ERROR_PUBLICID: str
-XML_ERROR_RECURSIVE_ENTITY_REF: str
-XML_ERROR_SUSPENDED: str
-XML_ERROR_SUSPEND_PE: str
-XML_ERROR_SYNTAX: str
-XML_ERROR_TAG_MISMATCH: str
-XML_ERROR_TEXT_DECL: str
-XML_ERROR_UNBOUND_PREFIX: str
-XML_ERROR_UNCLOSED_CDATA_SECTION: str
-XML_ERROR_UNCLOSED_TOKEN: str
-XML_ERROR_UNDECLARING_PREFIX: str
-XML_ERROR_UNDEFINED_ENTITY: str
-XML_ERROR_UNEXPECTED_STATE: str
-XML_ERROR_UNKNOWN_ENCODING: str
-XML_ERROR_XML_DECL: str
+XML_ERROR_ABORTED: Final[LiteralString]
+XML_ERROR_ASYNC_ENTITY: Final[LiteralString]
+XML_ERROR_ATTRIBUTE_EXTERNAL_ENTITY_REF: Final[LiteralString]
+XML_ERROR_BAD_CHAR_REF: Final[LiteralString]
+XML_ERROR_BINARY_ENTITY_REF: Final[LiteralString]
+XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING: Final[LiteralString]
+XML_ERROR_DUPLICATE_ATTRIBUTE: Final[LiteralString]
+XML_ERROR_ENTITY_DECLARED_IN_PE: Final[LiteralString]
+XML_ERROR_EXTERNAL_ENTITY_HANDLING: Final[LiteralString]
+XML_ERROR_FEATURE_REQUIRES_XML_DTD: Final[LiteralString]
+XML_ERROR_FINISHED: Final[LiteralString]
+XML_ERROR_INCOMPLETE_PE: Final[LiteralString]
+XML_ERROR_INCORRECT_ENCODING: Final[LiteralString]
+XML_ERROR_INVALID_TOKEN: Final[LiteralString]
+XML_ERROR_JUNK_AFTER_DOC_ELEMENT: Final[LiteralString]
+XML_ERROR_MISPLACED_XML_PI: Final[LiteralString]
+XML_ERROR_NOT_STANDALONE: Final[LiteralString]
+XML_ERROR_NOT_SUSPENDED: Final[LiteralString]
+XML_ERROR_NO_ELEMENTS: Final[LiteralString]
+XML_ERROR_NO_MEMORY: Final[LiteralString]
+XML_ERROR_PARAM_ENTITY_REF: Final[LiteralString]
+XML_ERROR_PARTIAL_CHAR: Final[LiteralString]
+XML_ERROR_PUBLICID: Final[LiteralString]
+XML_ERROR_RECURSIVE_ENTITY_REF: Final[LiteralString]
+XML_ERROR_SUSPENDED: Final[LiteralString]
+XML_ERROR_SUSPEND_PE: Final[LiteralString]
+XML_ERROR_SYNTAX: Final[LiteralString]
+XML_ERROR_TAG_MISMATCH: Final[LiteralString]
+XML_ERROR_TEXT_DECL: Final[LiteralString]
+XML_ERROR_UNBOUND_PREFIX: Final[LiteralString]
+XML_ERROR_UNCLOSED_CDATA_SECTION: Final[LiteralString]
+XML_ERROR_UNCLOSED_TOKEN: Final[LiteralString]
+XML_ERROR_UNDECLARING_PREFIX: Final[LiteralString]
+XML_ERROR_UNDEFINED_ENTITY: Final[LiteralString]
+XML_ERROR_UNEXPECTED_STATE: Final[LiteralString]
+XML_ERROR_UNKNOWN_ENCODING: Final[LiteralString]
+XML_ERROR_XML_DECL: Final[LiteralString]
 if sys.version_info >= (3, 11):
-    XML_ERROR_RESERVED_PREFIX_XML: str
-    XML_ERROR_RESERVED_PREFIX_XMLNS: str
-    XML_ERROR_RESERVED_NAMESPACE_URI: str
-    XML_ERROR_INVALID_ARGUMENT: str
-    XML_ERROR_NO_BUFFER: str
-    XML_ERROR_AMPLIFICATION_LIMIT_BREACH: str
+    XML_ERROR_RESERVED_PREFIX_XML: Final[LiteralString]
+    XML_ERROR_RESERVED_PREFIX_XMLNS: Final[LiteralString]
+    XML_ERROR_RESERVED_NAMESPACE_URI: Final[LiteralString]
+    XML_ERROR_INVALID_ARGUMENT: Final[LiteralString]
+    XML_ERROR_NO_BUFFER: Final[LiteralString]
+    XML_ERROR_AMPLIFICATION_LIMIT_BREACH: Final[LiteralString]
--- a/Show More
+++ b/Show More