Changelog for Ruff v0.7 (#13794)

Co-authored-by: Dhruv Manilawala <dhruvmanila@gmail.com>

.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"

.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: |
@@ -148,7 +148,7 @@ jobs:
       # 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
+      - run: cargo doc --no-deps -p red_knot_python_semantic -p red_knot -p red_knot_test -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"
@@ -518,6 +518,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
       - name: "Add SSH key"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
         uses: webfactory/ssh-agent@v0.9.0
@@ -525,13 +527,15 @@ jobs:
           ssh-private-key: ${{ secrets.MKDOCS_INSIDERS_SSH_KEY }}
       - name: "Install Rust toolchain"
         run: rustup show
+      - name: Install uv
+        uses: astral-sh/setup-uv@v3
       - uses: Swatinem/rust-cache@v2
       - name: "Install Insiders dependencies"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
-        run: pip install -r docs/requirements-insiders.txt
+        run: uv pip install -r docs/requirements-insiders.txt --system
       - name: "Install dependencies"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS != 'true' }}
-        run: pip install -r docs/requirements.txt
+        run: uv pip install -r docs/requirements.txt --system
       - name: "Update README File"
         run: python scripts/transform_readme.py --target mkdocs
       - name: "Generate docs"
@@ -608,7 +612,7 @@ jobs:
           just test
 
   benchmarks:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     needs: determine_changes
     if: ${{ github.repository == 'astral-sh/ruff' && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
     timeout-minutes: 20

.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

.github/workflows/release.yml

@@ -1,3 +1,5 @@
+# This file was autogenerated by cargo-dist: https://opensource.axo.dev/cargo-dist/
+#
 # Copyright 2022-2024, axodotdev
 # SPDX-License-Identifier: MIT or Apache-2.0
 #
@@ -64,7 +66,7 @@ jobs:
         # we specify bash to get pipefail; it guards against the `curl` command
         # failing. otherwise `sh` won't catch that `curl` returned non-0
         shell: bash
-        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/axodotdev/cargo-dist/releases/download/v0.18.0/cargo-dist-installer.sh | sh"
+        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/axodotdev/cargo-dist/releases/download/v0.22.1/cargo-dist-installer.sh | sh"
       - name: Cache cargo-dist
         uses: actions/upload-artifact@v4
         with:

.github/workflows/sync_typeshed.yaml

@@ -37,13 +37,13 @@ jobs:
       - name: Sync typeshed
         id: sync
         run: |
-          rm -rf ruff/crates/red_knot_python_semantic/vendor/typeshed
-          mkdir ruff/crates/red_knot_python_semantic/vendor/typeshed
-          cp typeshed/README.md ruff/crates/red_knot_python_semantic/vendor/typeshed
-          cp typeshed/LICENSE ruff/crates/red_knot_python_semantic/vendor/typeshed
-          cp -r typeshed/stdlib ruff/crates/red_knot_python_semantic/vendor/typeshed/stdlib
-          rm -rf ruff/crates/red_knot_python_semantic/vendor/typeshed/stdlib/@tests
-          git -C typeshed rev-parse HEAD > ruff/crates/red_knot_python_semantic/vendor/typeshed/source_commit.txt
+          rm -rf ruff/crates/red_knot_vendored/vendor/typeshed
+          mkdir ruff/crates/red_knot_vendored/vendor/typeshed
+          cp typeshed/README.md ruff/crates/red_knot_vendored/vendor/typeshed
+          cp typeshed/LICENSE ruff/crates/red_knot_vendored/vendor/typeshed
+          cp -r typeshed/stdlib ruff/crates/red_knot_vendored/vendor/typeshed/stdlib
+          rm -rf ruff/crates/red_knot_vendored/vendor/typeshed/stdlib/@tests
+          git -C typeshed rev-parse HEAD > ruff/crates/red_knot_vendored/vendor/typeshed/source_commit.txt
       - name: Commit the changes
         id: commit
         if: ${{ steps.sync.outcome == 'success' }}

.pre-commit-config.yaml

@@ -2,7 +2,7 @@ fail_fast: true
 
 exclude: |
   (?x)^(
-    crates/red_knot_python_semantic/vendor/.*|
+    crates/red_knot_vendored/vendor/.*|
     crates/red_knot_workspace/resources/.*|
     crates/ruff_linter/resources/.*|
     crates/ruff_linter/src/rules/.*/snapshots/.*|
@@ -17,7 +17,7 @@ exclude: |
 
 repos:
   - repo: https://github.com/abravalheri/validate-pyproject
-    rev: v0.19
+    rev: v0.20.2
     hooks:
       - id: validate-pyproject
 
@@ -28,6 +28,7 @@ repos:
         additional_dependencies:
           - mdformat-mkdocs
           - mdformat-admon
+          - mdformat-footnote
         exclude: |
           (?x)^(
             docs/formatter/black\.md
@@ -35,7 +36,7 @@ repos:
           )$
 
   - repo: https://github.com/igorshubovych/markdownlint-cli
-    rev: v0.41.0
+    rev: v0.42.0
     hooks:
       - id: markdownlint-fix
         exclude: |
@@ -45,7 +46,7 @@ repos:
           )$
 
   - repo: https://github.com/crate-ci/typos
-    rev: v1.23.6
+    rev: v1.25.0
     hooks:
       - id: typos
 
@@ -59,7 +60,7 @@ repos:
         pass_filenames: false # This makes it a lot faster
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.6.1
+    rev: v0.6.9
     hooks:
       - id: ruff-format
       - id: ruff
@@ -68,8 +69,8 @@ repos:
         require_serial: true
 
   # Prettier
-  - repo: https://github.com/pre-commit/mirrors-prettier
-    rev: v3.1.0
+  - repo: https://github.com/rbubley/mirrors-prettier
+    rev: v3.3.3
     hooks:
       - id: prettier
         types: [yaml]

CHANGELOG.md

@@ -1,5 +1,267 @@
 # Changelog
 
+## 0.7.0
+
+Check out the [blog post](https://astral.sh/blog/ruff-v0.7.0) for a migration guide and overview of the changes!
+
+### Breaking changes
+
+- 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), [#13292](https://github.com/astral-sh/ruff/pull/13292)).
+    This was a change that we attempted to make in Ruff v0.6.0, but only partially made due to an error on our part.
+    See the [blog post](https://astral.sh/blog/ruff-v0.7.0) for more details.
+- The `useless-try-except` rule (in our `tryceratops` category) has been recoded from `TRY302` to
+    `TRY203` ([#13502](https://github.com/astral-sh/ruff/pull/13502)). This ensures Ruff's code is consistent with
+    the same rule in the [`tryceratops`](https://github.com/guilatrova/tryceratops) linter.
+- The `lint.allow-unused-imports` setting has been removed ([#13677](https://github.com/astral-sh/ruff/pull/13677)). Use
+    [`lint.pyflakes.allow-unused-imports`](https://docs.astral.sh/ruff/settings/#lint_pyflakes_allowed-unused-imports)
+    instead.
+
+### Formatter preview style
+
+- Normalize implicit concatenated f-string quotes per part ([#13539](https://github.com/astral-sh/ruff/pull/13539))
+
+### Preview linter features
+
+- \[`refurb`\] implement `hardcoded-string-charset` (FURB156) ([#13530](https://github.com/astral-sh/ruff/pull/13530))
+- \[`refurb`\] Count codepoints not bytes for `slice-to-remove-prefix-or-suffix (FURB188)` ([#13631](https://github.com/astral-sh/ruff/pull/13631))
+
+### Rule changes
+
+- \[`pylint`\] Mark `PLE1141` fix as unsafe ([#13629](https://github.com/astral-sh/ruff/pull/13629))
+- \[`flake8-async`\] Consider async generators to be "checkpoints" for `cancel-scope-no-checkpoint` (`ASYNC100`) ([#13639](https://github.com/astral-sh/ruff/pull/13639))
+- \[`flake8-bugbear`\] Do not suggest setting parameter `strict=` to `False` in `B905` diagnostic message ([#13656](https://github.com/astral-sh/ruff/pull/13656))
+- \[`flake8-todos`\] Only flag the word "TODO", not words starting with "todo" (`TD006`) ([#13640](https://github.com/astral-sh/ruff/pull/13640))
+- \[`pycodestyle`\] Fix whitespace-related false positives and false negatives inside type-parameter lists (`E231`, `E251`) ([#13704](https://github.com/astral-sh/ruff/pull/13704))
+- \[`flake8-simplify`\] Stabilize preview behavior for `SIM115` so that the rule can detect files
+    being opened from a wider range of standard-library functions ([#12959](https://github.com/astral-sh/ruff/pull/12959)).
+
+### CLI
+
+- Add explanation of fixable in `--statistics` command ([#13774](https://github.com/astral-sh/ruff/pull/13774))
+
+### Bug fixes
+
+- \[`pyflakes`\] Allow `ipytest` cell magic (`F401`) ([#13745](https://github.com/astral-sh/ruff/pull/13745))
+- \[`flake8-use-pathlib`\] Fix `PTH123` false positive when `open` is passed a file descriptor ([#13616](https://github.com/astral-sh/ruff/pull/13616))
+- \[`flake8-bandit`\] Detect patterns from multi line SQL statements (`S608`) ([#13574](https://github.com/astral-sh/ruff/pull/13574))
+- \[`flake8-pyi`\] - Fix dropped expressions in `PYI030` autofix ([#13727](https://github.com/astral-sh/ruff/pull/13727))
+
+## 0.6.9
+
+### Preview features
+
+- Fix codeblock dynamic line length calculation for indented docstring examples ([#13523](https://github.com/astral-sh/ruff/pull/13523))
+- \[`refurb`\] Mark `FURB118` fix as unsafe ([#13613](https://github.com/astral-sh/ruff/pull/13613))
+
+### Rule changes
+
+- \[`pydocstyle`\] Don't raise `D208` when last line is non-empty ([#13372](https://github.com/astral-sh/ruff/pull/13372))
+- \[`pylint`\] Preserve trivia (i.e. comments) in `PLR5501` autofix ([#13573](https://github.com/astral-sh/ruff/pull/13573))
+
+### Configuration
+
+- \[`pyflakes`\] Add `allow-unused-imports` setting for `unused-import` rule (`F401`) ([#13601](https://github.com/astral-sh/ruff/pull/13601))
+
+### Bug fixes
+
+- Support ruff discovery in pip build environments ([#13591](https://github.com/astral-sh/ruff/pull/13591))
+- \[`flake8-bugbear`\] Avoid short circuiting `B017` for multiple context managers ([#13609](https://github.com/astral-sh/ruff/pull/13609))
+- \[`pylint`\] Do not offer an invalid fix for `PLR1716` when the comparisons contain parenthesis ([#13527](https://github.com/astral-sh/ruff/pull/13527))
+- \[`pyupgrade`\] Fix `UP043` to apply to `collections.abc.Generator` and `collections.abc.AsyncGenerator` ([#13611](https://github.com/astral-sh/ruff/pull/13611))
+- \[`refurb`\] Fix handling of slices in tuples for `FURB118`, e.g., `x[:, 1]` ([#13518](https://github.com/astral-sh/ruff/pull/13518))
+
+### Documentation
+
+- Update GitHub Action link to `astral-sh/ruff-action` ([#13551](https://github.com/astral-sh/ruff/pull/13551))
+
+## 0.6.8
+
+### Preview features
+
+- Remove unnecessary parentheses around `match case` clauses ([#13510](https://github.com/astral-sh/ruff/pull/13510))
+- Parenthesize overlong `if` guards in `match..case` clauses ([#13513](https://github.com/astral-sh/ruff/pull/13513))
+- Detect basic wildcard imports in `ruff analyze graph` ([#13486](https://github.com/astral-sh/ruff/pull/13486))
+- \[`pylint`\] Implement `boolean-chained-comparison` (`R1716`) ([#13435](https://github.com/astral-sh/ruff/pull/13435))
+
+### Rule changes
+
+- \[`lake8-simplify`\] Detect `SIM910` when using variadic keyword arguments, i.e., `**kwargs` ([#13503](https://github.com/astral-sh/ruff/pull/13503))
+- \[`pyupgrade`\] Avoid false negatives with non-reference shadowed bindings of loop variables (`UP028`) ([#13504](https://github.com/astral-sh/ruff/pull/13504))
+
+### Bug fixes
+
+- Detect tuples bound to variadic positional arguments i.e. `*args` ([#13512](https://github.com/astral-sh/ruff/pull/13512))
+- Exit gracefully on broken pipe errors ([#13485](https://github.com/astral-sh/ruff/pull/13485))
+- Avoid panic when analyze graph hits broken pipe ([#13484](https://github.com/astral-sh/ruff/pull/13484))
+
+### Performance
+
+- Reuse `BTreeSets` in module resolver ([#13440](https://github.com/astral-sh/ruff/pull/13440))
+- Skip traversal for non-compound statements ([#13441](https://github.com/astral-sh/ruff/pull/13441))
+
+## 0.6.7
+
+### Preview features
+
+- Add Python version support to ruff analyze CLI ([#13426](https://github.com/astral-sh/ruff/pull/13426))
+- Add `exclude` support to `ruff analyze` ([#13425](https://github.com/astral-sh/ruff/pull/13425))
+- Fix parentheses around return type annotations ([#13381](https://github.com/astral-sh/ruff/pull/13381))
+
+### Rule changes
+
+- \[`pycodestyle`\] Fix: Don't autofix if the first line ends in a question mark? (D400) ([#13399](https://github.com/astral-sh/ruff/pull/13399))
+
+### Bug fixes
+
+- Respect `lint.exclude` in ruff check `--add-noqa` ([#13427](https://github.com/astral-sh/ruff/pull/13427))
+
+### Performance
+
+- Avoid tracking module resolver files in Salsa ([#13437](https://github.com/astral-sh/ruff/pull/13437))
+- Use `forget` for module resolver database ([#13438](https://github.com/astral-sh/ruff/pull/13438))
+
+## 0.6.6
+
+### Preview features
+
+- \[`refurb`\] Skip `slice-to-remove-prefix-or-suffix` (`FURB188`) when non-trivial slice steps are present ([#13405](https://github.com/astral-sh/ruff/pull/13405))
+- Add a subcommand to generate dependency graphs ([#13402](https://github.com/astral-sh/ruff/pull/13402))
+
+### Formatter
+
+- Fix placement of inline parameter comments ([#13379](https://github.com/astral-sh/ruff/pull/13379))
+
+### Server
+
+- Fix off-by one error in the `LineIndex::offset` calculation ([#13407](https://github.com/astral-sh/ruff/pull/13407))
+
+### Bug fixes
+
+- \[`fastapi`\] Respect FastAPI aliases in route definitions ([#13394](https://github.com/astral-sh/ruff/pull/13394))
+- \[`pydocstyle`\] Respect word boundaries when detecting function signature in docs ([#13388](https://github.com/astral-sh/ruff/pull/13388))
+
+### Documentation
+
+- Add backlinks to rule overview linter ([#13368](https://github.com/astral-sh/ruff/pull/13368))
+- Fix documentation for editor vim plugin ALE ([#13348](https://github.com/astral-sh/ruff/pull/13348))
+- Fix rendering of `FURB188` docs ([#13406](https://github.com/astral-sh/ruff/pull/13406))
+
+## 0.6.5
+
+### Preview features
+
+- \[`pydoclint`\] Ignore `DOC201` when function name is "**new**" ([#13300](https://github.com/astral-sh/ruff/pull/13300))
+- \[`refurb`\] Implement `slice-to-remove-prefix-or-suffix` (`FURB188`) ([#13256](https://github.com/astral-sh/ruff/pull/13256))
+
+### Rule changes
+
+- \[`eradicate`\] Ignore script-comments with multiple end-tags (`ERA001`) ([#13283](https://github.com/astral-sh/ruff/pull/13283))
+- \[`pyflakes`\] Improve error message for `UndefinedName` when a builtin was added in a newer version than specified in Ruff config (`F821`) ([#13293](https://github.com/astral-sh/ruff/pull/13293))
+
+### Server
+
+- Add support for extensionless Python files for server ([#13326](https://github.com/astral-sh/ruff/pull/13326))
+- Fix configuration inheritance for configurations specified in the LSP settings ([#13285](https://github.com/astral-sh/ruff/pull/13285))
+
+### Bug fixes
+
+- \[`ruff`\] Handle unary operators in `decimal-from-float-literal` (`RUF032`) ([#13275](https://github.com/astral-sh/ruff/pull/13275))
+
+### CLI
+
+- Only include rules with diagnostics in SARIF metadata ([#13268](https://github.com/astral-sh/ruff/pull/13268))
+
+### Playground
+
+- Add "Copy as pyproject.toml/ruff.toml" and "Paste from TOML" ([#13328](https://github.com/astral-sh/ruff/pull/13328))
+- Fix errors not shown for restored snippet on page load ([#13262](https://github.com/astral-sh/ruff/pull/13262))
+
+## 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,

CONTRIBUTING.md

@@ -29,16 +29,14 @@ You'll also need [Insta](https://insta.rs/docs/) to update snapshot tests:
 cargo install cargo-insta
 ```
 
-And you'll need pre-commit to run some validation checks:
-
-```shell
-pipx install pre-commit  # or `pip install pre-commit` if you have a virtualenv
-```
+You'll need [uv](https://docs.astral.sh/uv/getting-started/installation/) (or `pipx` and `pip`) to
+run Python utility commands.
 
 You can optionally install pre-commit hooks to automatically run the validation checks
 when making a commit:
 
 ```shell
+uv tool install pre-commit
 pre-commit install
 ```
 
@@ -66,7 +64,7 @@ and that it passes both the lint and test validation checks:
 ```shell
 cargo clippy --workspace --all-targets --all-features -- -D warnings  # Rust linting
 RUFF_UPDATE_SCHEMA=1 cargo test  # Rust testing and updating ruff.schema.json
-pre-commit run --all-files --show-diff-on-failure  # Rust and Python formatting, Markdown and Python linting, etc.
+uvx pre-commit run --all-files --show-diff-on-failure  # Rust and Python formatting, Markdown and Python linting, etc.
 ```
 
 These checks will run on GitHub Actions when you open your pull request, but running them locally
@@ -267,26 +265,20 @@ To preview any changes to the documentation locally:
 
 1. Install the [Rust toolchain](https://www.rust-lang.org/tools/install).
 
-1. Install MkDocs and Material for MkDocs with:
-
-    ```shell
-    pip install -r docs/requirements.txt
-    ```
-
 1. Generate the MkDocs site with:
 
     ```shell
-    python scripts/generate_mkdocs.py
+    uv run --no-project --isolated --with-requirements docs/requirements.txt scripts/generate_mkdocs.py
     ```
 
 1. Run the development server with:
 
     ```shell
     # For contributors.
-    mkdocs serve -f mkdocs.public.yml
+    uvx --with-requirements docs/requirements.txt -- mkdocs serve -f mkdocs.public.yml
 
     # For members of the Astral org, which has access to MkDocs Insiders via sponsorship.
-    mkdocs serve -f mkdocs.insiders.yml
+    uvx --with-requirements docs/requirements-insiders.txt -- mkdocs serve -f mkdocs.insiders.yml
     ```
 
 The documentation should then be available locally at
@@ -368,9 +360,8 @@ GitHub Actions will run your changes against a number of real-world projects fro
 report on any linter or formatter differences. You can also run those checks locally via:
 
 ```shell
-pip install -e ./python/ruff-ecosystem
-ruff-ecosystem check ruff "./target/debug/ruff"
-ruff-ecosystem format ruff "./target/debug/ruff"
+uvx --from ./python/ruff-ecosystem ruff-ecosystem check ruff "./target/debug/ruff"
+uvx --from ./python/ruff-ecosystem ruff-ecosystem format ruff "./target/debug/ruff"
 ```
 
 See the [ruff-ecosystem package](https://github.com/astral-sh/ruff/tree/main/python/ruff-ecosystem) for more details.
@@ -397,12 +388,18 @@ 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]
@@ -421,7 +418,7 @@ 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" \
@@ -467,7 +464,7 @@ 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
@@ -524,6 +521,8 @@ 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
@@ -562,7 +561,7 @@ 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)

Cargo.toml

@@ -14,9 +14,10 @@ license = "MIT"
 [workspace.dependencies]
 ruff = { path = "crates/ruff" }
 ruff_cache = { path = "crates/ruff_cache" }
-ruff_db = { path = "crates/ruff_db" }
+ruff_db = { path = "crates/ruff_db", default-features = false }
 ruff_diagnostics = { path = "crates/ruff_diagnostics" }
 ruff_formatter = { path = "crates/ruff_formatter" }
+ruff_graph = { path = "crates/ruff_graph" }
 ruff_index = { path = "crates/ruff_index" }
 ruff_linter = { path = "crates/ruff_linter" }
 ruff_macros = { path = "crates/ruff_macros" }
@@ -33,15 +34,18 @@ ruff_python_trivia = { path = "crates/ruff_python_trivia" }
 ruff_server = { path = "crates/ruff_server" }
 ruff_source_file = { path = "crates/ruff_source_file" }
 ruff_text_size = { path = "crates/ruff_text_size" }
+red_knot_vendored = { path = "crates/red_knot_vendored" }
 ruff_workspace = { path = "crates/ruff_workspace" }
 
 red_knot_python_semantic = { path = "crates/red_knot_python_semantic" }
 red_knot_server = { path = "crates/red_knot_server" }
-red_knot_workspace = { path = "crates/red_knot_workspace" }
+red_knot_test = { path = "crates/red_knot_test" }
+red_knot_workspace = { path = "crates/red_knot_workspace", default-features = false }
 
 aho-corasick = { version = "1.1.3" }
 annotate-snippets = { version = "0.9.2", features = ["color"] }
 anyhow = { version = "1.0.80" }
+assert_fs = { version = "1.1.0" }
 argfile = { version = "0.2.0" }
 bincode = { version = "1.3.3" }
 bitflags = { version = "2.5.0" }
@@ -68,7 +72,11 @@ fern = { version = "0.6.1" }
 filetime = { version = "0.2.23" }
 glob = { version = "0.3.1" }
 globset = { version = "0.4.14" }
-hashbrown = "0.14.3"
+globwalk = { version = "0.9.1" }
+hashbrown = { version = "0.15.0", default-features = false, features = [
+    "raw-entry",
+    "inline-more",
+] }
 ignore = { version = "0.4.22" }
 imara-diff = { version = "0.1.5" }
 imperative = { version = "1.0.4" }
@@ -86,7 +94,7 @@ libcst = { version = "1.1.0", default-features = false }
 log = { version = "0.4.17" }
 lsp-server = { version = "0.7.6" }
 lsp-types = { git = "https://github.com/astral-sh/lsp-types.git", rev = "3512a9f", features = [
-  "proposed",
+    "proposed",
 ] }
 matchit = { version = "0.8.1" }
 memchr = { version = "2.7.1" }
@@ -102,13 +110,14 @@ 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" }
+rstest = { version = "0.22.0", default-features = false }
 rustc-hash = { version = "2.0.0" }
-salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "f608ff8b24f07706492027199f51132244034f29" }
+salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "b14be5c0392f4c55eca60b92e457a35549372382" }
 schemars = { version = "0.8.16" }
 seahash = { version = "4.1.0" }
 serde = { version = "1.0.197", features = ["derive"] }
@@ -116,7 +125,7 @@ serde-wasm-bindgen = { version = "0.6.4" }
 serde_json = { version = "1.0.113" }
 serde_test = { version = "1.0.152" }
 serde_with = { version = "3.6.0", default-features = false, features = [
-  "macros",
+    "macros",
 ] }
 shellexpand = { version = "3.0.0" }
 similar = { version = "2.4.0", features = ["inline"] }
@@ -133,7 +142,10 @@ toml = { version = "0.8.11" }
 tracing = { version = "0.1.40" }
 tracing-flame = { version = "0.2.0" }
 tracing-indicatif = { version = "0.3.6" }
-tracing-subscriber = { version = "0.3.18", default-features = false, features = ["env-filter", "fmt"] }
+tracing-subscriber = { version = "0.3.18", default-features = false, features = [
+    "env-filter",
+    "fmt",
+] }
 tracing-tree = { version = "0.4.0" }
 typed-arena = { version = "2.0.2" }
 unic-ucd-category = { version = "0.9" }
@@ -144,10 +156,10 @@ unicode-normalization = { version = "0.1.23" }
 ureq = { version = "2.9.6" }
 url = { version = "2.5.0" }
 uuid = { version = "1.6.1", features = [
-  "v4",
-  "fast-rng",
-  "macro-diagnostics",
-  "js",
+    "v4",
+    "fast-rng",
+    "macro-diagnostics",
+    "js",
 ] }
 walkdir = { version = "2.3.2" }
 wasm-bindgen = { version = "0.2.92" }
@@ -158,7 +170,10 @@ zip = { version = "0.6.6", default-features = false }
 [workspace.lints.rust]
 unsafe_code = "warn"
 unreachable_pub = "warn"
-unexpected_cfgs = { level = "warn", check-cfg = ["cfg(fuzzing)", "cfg(codspeed)"] }
+unexpected_cfgs = { level = "warn", check-cfg = [
+    "cfg(fuzzing)",
+    "cfg(codspeed)",
+] }
 
 [workspace.lints.clippy]
 pedantic = { level = "warn", priority = -2 }
@@ -230,9 +245,9 @@ inherits = "release"
 # Config for 'cargo dist'
 [workspace.metadata.dist]
 # The preferred cargo-dist version to use in CI (Cargo.toml SemVer syntax)
-cargo-dist-version = "0.18.0"
+cargo-dist-version = "0.22.1"
 # CI backends to support
-ci = ["github"]
+ci = "github"
 # The installers to generate for each app
 installers = ["shell", "powershell"]
 # The archive format to use for windows builds (defaults .zip)
@@ -241,33 +256,33 @@ windows-archive = ".zip"
 unix-archive = ".tar.gz"
 # Target platforms to build apps for (Rust target-triple syntax)
 targets = [
-  "aarch64-apple-darwin",
-  "aarch64-pc-windows-msvc",
-  "aarch64-unknown-linux-gnu",
-  "aarch64-unknown-linux-musl",
-  "arm-unknown-linux-musleabihf",
-  "armv7-unknown-linux-gnueabihf",
-  "armv7-unknown-linux-musleabihf",
-  "i686-pc-windows-msvc",
-  "i686-unknown-linux-gnu",
-  "i686-unknown-linux-musl",
-  "powerpc64-unknown-linux-gnu",
-  "powerpc64le-unknown-linux-gnu",
-  "s390x-unknown-linux-gnu",
-  "x86_64-apple-darwin",
-  "x86_64-pc-windows-msvc",
-  "x86_64-unknown-linux-gnu",
-  "x86_64-unknown-linux-musl",
+    "aarch64-apple-darwin",
+    "aarch64-pc-windows-msvc",
+    "aarch64-unknown-linux-gnu",
+    "aarch64-unknown-linux-musl",
+    "arm-unknown-linux-musleabihf",
+    "armv7-unknown-linux-gnueabihf",
+    "armv7-unknown-linux-musleabihf",
+    "i686-pc-windows-msvc",
+    "i686-unknown-linux-gnu",
+    "i686-unknown-linux-musl",
+    "powerpc64-unknown-linux-gnu",
+    "powerpc64le-unknown-linux-gnu",
+    "s390x-unknown-linux-gnu",
+    "x86_64-apple-darwin",
+    "x86_64-pc-windows-msvc",
+    "x86_64-unknown-linux-gnu",
+    "x86_64-unknown-linux-musl",
 ]
 # Whether to auto-include files like READMEs, LICENSEs, and CHANGELOGs (default true)
 auto-includes = false
 # Whether cargo-dist should create a GitHub Release or use an existing draft
 create-release = true
-# Publish jobs to run in CI
+# Which actions to run on pull requests
 pr-run-mode = "skip"
 # Whether CI should trigger releases with dispatches instead of tag pushes
 dispatch-releases = true
-# The stage during which the GitHub Release should be created
+# Which phase cargo-dist should use to create the GitHub release
 github-release = "announce"
 # Whether CI should include auto-generated code to build local artifacts
 build-local-artifacts = false
@@ -275,9 +290,15 @@ build-local-artifacts = false
 local-artifacts-jobs = ["./build-binaries", "./build-docker"]
 # Publish jobs to run in CI
 publish-jobs = ["./publish-pypi", "./publish-wasm"]
-# Announcement jobs to run in CI
-post-announce-jobs = ["./notify-dependents", "./publish-docs", "./publish-playground"]
+# Post-announce jobs to run in CI
+post-announce-jobs = [
+    "./notify-dependents",
+    "./publish-docs",
+    "./publish-playground",
+]
 # Custom permissions for GitHub Jobs
 github-custom-job-permissions = { "build-docker" = { packages = "write", contents = "read" }, "publish-wasm" = { contents = "read", id-token = "write", packages = "write" } }
 # Whether to install an updater program
 install-updater = false
+# Path that installers should place binaries in
+install-path = "CARGO_HOME"

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/0.6.1/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.6.1/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.7.0/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.7.0/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: v0.6.1
+  rev: v0.7.0
   hooks:
     # Run the linter.
     - id: ruff
@@ -182,7 +182,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 Ruff can also be used as a [VS Code extension](https://github.com/astral-sh/ruff-vscode) or with [various other editors](https://docs.astral.sh/ruff/editors/setup).
 
 Ruff can also be used as a [GitHub Action](https://github.com/features/actions) via
-[`ruff-action`](https://github.com/chartboost/ruff-action):
+[`ruff-action`](https://github.com/astral-sh/ruff-action):
 
 ```yaml
 name: Ruff
@@ -192,10 +192,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: chartboost/ruff-action@v1
+      - uses: astral-sh/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)
 

_typos.toml

@@ -1,6 +1,6 @@
 [files]
 # https://github.com/crate-ci/typos/issues/868
-extend-exclude = ["crates/red_knot_python_semantic/vendor/**/*", "**/resources/**/*", "**/snapshots/**/*"]
+extend-exclude = ["crates/red_knot_vendored/vendor/**/*", "**/resources/**/*", "**/snapshots/**/*"]
 
 [default.extend-words]
 "arange" = "arange"  # e.g. `numpy.arange`
@@ -8,7 +8,7 @@ hel = "hel"
 whos = "whos"
 spawnve = "spawnve"
 ned = "ned"
-pn = "pn"  # `import panel as pd` is a thing
+pn = "pn"  # `import panel as pn` is a thing
 poit = "poit"
 BA = "BA" # acronym for "Bad Allowed", used in testing.
 jod = "jod" # e.g., `jod-thread`

crates/red_knot/Cargo.toml

@@ -13,9 +13,8 @@ license.workspace = true
 
 [dependencies]
 red_knot_python_semantic = { workspace = true }
-red_knot_workspace = { workspace = true }
+red_knot_workspace = { workspace = true, features = ["zstd"] }
 red_knot_server = { workspace = true }
-
 ruff_db = { workspace = true, features = ["os", "cache"] }
 
 anyhow = { workspace = true }

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

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)?;
 
@@ -140,19 +160,21 @@ fn run() -> anyhow::Result<ExitStatus> {
         SystemPathBuf::from_path_buf(cwd)
             .map_err(|path| {
                 anyhow!(
-                    "The current working directory '{}' contains non-unicode characters. Red Knot only supports unicode paths.",
+                    "The current working directory `{}` contains non-Unicode characters. Red Knot only supports Unicode paths.",
                     path.display()
                 )
             })?
     };
 
-    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."
+                    "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);
                     }

crates/red_knot/tests/file_watching.rs

@@ -5,12 +5,11 @@ use std::time::Duration;
 
 use anyhow::{anyhow, Context};
 
-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;
@@ -25,7 +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,
-    search_path_settings: SearchPathSettings,
+    configuration: Configuration,
 }
 
 impl TestCase {
@@ -41,20 +40,16 @@ 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.")
+            .expect("Expected watch changes but observed none")
     }
 
     fn try_stop_watch(&mut self, timeout: Duration) -> Option<Vec<watch::ChangeEvent>> {
         let watcher = self
             .watcher
             .take()
-            .expect("Cannot call `stop_watch` more than once.");
+            .expect("Cannot call `stop_watch` more than once");
 
         let mut all_events = self
             .changes_receiver
@@ -77,7 +72,7 @@ impl TestCase {
     #[cfg(unix)]
     fn take_watch_changes(&self) -> Vec<watch::ChangeEvent> {
         self.try_take_watch_changes(Duration::from_secs(10))
-            .expect("Expected watch changes but observed none.")
+            .expect("Expected watch changes but observed none")
     }
 
     fn try_take_watch_changes(&self, timeout: Duration) -> Option<Vec<watch::ChangeEvent>> {
@@ -105,16 +100,20 @@ 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 new_settings = f(&self.search_path_settings);
+        self.configuration.search_paths = configuration.clone();
+        let new_settings = configuration.into_settings(self.db.workspace().root(&self.db));
 
-        program.update_search_paths(&mut self.db, new_settings.clone())?;
-        self.search_path_settings = new_settings;
+        program.update_search_paths(&mut self.db, &new_settings)?;
 
         if let Some(watcher) = &mut self.watcher {
             watcher.update(&self.db);
@@ -151,14 +150,14 @@ where
             let absolute_path = workspace_path.join(relative_path);
             if let Some(parent) = absolute_path.parent() {
                 std::fs::create_dir_all(parent).with_context(|| {
-                    format!("Failed to create parent directory for file '{relative_path}'.",)
+                    format!("Failed to create parent directory for file `{relative_path}`")
                 })?;
             }
 
             let mut file = std::fs::File::create(absolute_path.as_std_path())
-                .with_context(|| format!("Failed to open file '{relative_path}'"))?;
+                .with_context(|| format!("Failed to open file `{relative_path}`"))?;
             file.write_all(content.as_bytes())
-                .with_context(|| format!("Failed to write to file '{relative_path}'"))?;
+                .with_context(|| format!("Failed to write to file `{relative_path}`"))?;
             file.sync_data()?;
         }
 
@@ -179,17 +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,
@@ -198,7 +194,7 @@ where
 
     let root_path = SystemPath::from_std_path(temp_dir.path()).ok_or_else(|| {
         anyhow!(
-            "Temp directory '{}' is not a valid UTF-8 path.",
+            "Temporary directory `{}` is not a valid UTF-8 path.",
             temp_dir.path().display()
         )
     })?;
@@ -213,7 +209,7 @@ where
     let workspace_path = root_path.join("workspace");
 
     std::fs::create_dir_all(workspace_path.as_std_path())
-        .with_context(|| format!("Failed to create workspace directory '{workspace_path}'",))?;
+        .with_context(|| format!("Failed to create workspace directory `{workspace_path}`"))?;
 
     setup_files
         .setup(&root_path, &workspace_path)
@@ -221,25 +217,34 @@ where
 
     let system = OsSystem::new(&workspace_path);
 
-    let workspace = WorkspaceMetadata::from_path(&workspace_path, &system)?;
-    let search_path_settings = create_search_paths(&root_path, workspace.root());
+    let search_paths = create_search_paths(&root_path, &workspace_path);
 
-    for path in search_path_settings
+    for path in search_paths
         .extra_paths
         .iter()
-        .chain(search_path_settings.site_packages.iter())
-        .chain(search_path_settings.custom_typeshed.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}'"))?;
+            .with_context(|| format!("Failed to create search path `{path}`"))?;
     }
 
-    let settings = ProgramSettings {
-        target_version: PythonVersion::default(),
-        search_paths: search_path_settings.clone(),
+    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())
@@ -254,7 +259,7 @@ where
         watcher: Some(watcher),
         _temp_dir: temp_dir,
         root_dir: root_path,
-        search_path_settings,
+        configuration,
     };
 
     // Sometimes the file watcher reports changes for events that happened before the watcher was started.
@@ -307,7 +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.");
 
@@ -330,7 +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]);
@@ -354,7 +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]);
@@ -377,7 +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]);
@@ -409,7 +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]);
@@ -441,7 +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)?;
 
@@ -469,7 +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()));
 
@@ -496,7 +501,10 @@ fn directory_moved_to_workspace() -> anyhow::Result<()> {
         .with_context(|| "Failed to create __init__.py")?;
     std::fs::write(a_original_path.as_std_path(), "").with_context(|| "Failed to create a.py")?;
 
-    let sub_a_module = resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap());
+    let sub_a_module = resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap(),
+    );
 
     assert_eq!(sub_a_module, None);
     assert_eq!(
@@ -510,7 +518,7 @@ 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"))
@@ -520,7 +528,11 @@ fn directory_moved_to_workspace() -> anyhow::Result<()> {
         .expect("a.py to exist");
 
     // `import sub.a` should now resolve
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_some());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_some());
 
     assert_eq!(
         case.collect_package_files(&case.workspace_path("bar.py")),
@@ -539,7 +551,11 @@ fn directory_moved_to_trash() -> anyhow::Result<()> {
     ])?;
     let bar = case.system_file(case.workspace_path("bar.py")).unwrap();
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_some());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_some());
 
     let sub_path = case.workspace_path("sub");
     let init_file = case
@@ -561,10 +577,14 @@ 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());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_none());
 
     assert!(!init_file.exists(case.db()));
     assert!(!a_file.exists(case.db()));
@@ -587,10 +607,14 @@ fn directory_renamed() -> anyhow::Result<()> {
 
     let bar = case.system_file(case.workspace_path("bar.py")).unwrap();
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_some());
     assert!(resolve_module(
         case.db().upcast(),
-        ModuleName::new_static("foo.baz").unwrap()
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_some());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("foo.baz").unwrap()
     )
     .is_none());
 
@@ -615,14 +639,18 @@ 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());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_none());
     // `import foo.baz` should now resolve
     assert!(resolve_module(
         case.db().upcast(),
-        ModuleName::new_static("foo.baz").unwrap()
+        &ModuleName::new_static("foo.baz").unwrap()
     )
     .is_some());
 
@@ -660,7 +688,11 @@ fn directory_deleted() -> anyhow::Result<()> {
 
     let bar = case.system_file(case.workspace_path("bar.py")).unwrap();
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_some(),);
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_some());
 
     let sub_path = case.workspace_path("sub");
 
@@ -680,10 +712,14 @@ 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());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_none());
 
     assert!(!init_file.exists(case.db()));
     assert!(!a_file.exists(case.db()));
@@ -694,20 +730,18 @@ 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");
 
     assert_eq!(
-        resolve_module(case.db(), ModuleName::new("a").unwrap()),
+        resolve_module(case.db(), &ModuleName::new("a").unwrap()),
         None
     );
 
@@ -715,9 +749,9 @@ 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!(resolve_module(case.db().upcast(), &ModuleName::new_static("a").unwrap()).is_some());
     assert_eq!(
         case.collect_package_files(&case.workspace_path("bar.py")),
         &[case.system_file(case.workspace_path("bar.py")).unwrap()]
@@ -733,12 +767,12 @@ fn add_search_path() -> anyhow::Result<()> {
     let site_packages = case.workspace_path("site_packages");
     std::fs::create_dir_all(site_packages.as_std_path())?;
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("a").unwrap()).is_none());
+    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");
 
@@ -746,30 +780,28 @@ fn add_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!(resolve_module(case.db().upcast(), &ModuleName::new_static("a").unwrap()).is_some());
 
     Ok(())
 }
 
 #[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");
 
@@ -782,6 +814,48 @@ 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:
@@ -828,7 +902,7 @@ 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')");
 
@@ -899,7 +973,7 @@ 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')");
 
@@ -938,7 +1012,7 @@ mod unix {
 
         let changes = case.stop_watch();
 
-        case.db_mut().apply_changes(changes);
+        case.apply_changes(changes);
 
         assert_eq!(
             foo.permissions(case.db()),
@@ -1001,7 +1075,7 @@ mod unix {
 
         let baz = resolve_module(
             case.db().upcast(),
-            ModuleName::new_static("bar.baz").unwrap(),
+            &ModuleName::new_static("bar.baz").unwrap(),
         )
         .expect("Expected bar.baz to exist in site-packages.");
         let baz_workspace = case.workspace_path("bar/baz.py");
@@ -1023,7 +1097,7 @@ 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(),
@@ -1036,7 +1110,7 @@ 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(),
@@ -1082,7 +1156,7 @@ mod unix {
 
         let baz = resolve_module(
             case.db().upcast(),
-            ModuleName::new_static("bar.baz").unwrap(),
+            &ModuleName::new_static("bar.baz").unwrap(),
         )
         .expect("Expected bar.baz to exist in site-packages.");
         let bar_baz = case.workspace_path("bar/baz.py");
@@ -1107,7 +1181,7 @@ 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.
@@ -1176,17 +1250,17 @@ 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()
             },
         )?;
 
         let baz = resolve_module(
             case.db().upcast(),
-            ModuleName::new_static("bar.baz").unwrap(),
+            &ModuleName::new_static("bar.baz").unwrap(),
         )
         .expect("Expected bar.baz to exist in site-packages.");
         let baz_site_packages_path =
@@ -1215,7 +1289,7 @@ 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(),

crates/red_knot_python_semantic/Cargo.toml

@@ -17,35 +17,35 @@ 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 }
 countme = { workspace = true }
-once_cell = { workspace = true }
+itertools = { 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 }
-walkdir = { workspace = true }
-zip = { workspace = true, features = ["zstd", "deflate"] }
+test-case = { workspace = true }
+memchr = { workspace = true }
 
 [dev-dependencies]
 ruff_db = { workspace = true, features = ["os", "testing"] }
 ruff_python_parser = { workspace = true }
+red_knot_test = { workspace = true }
+red_knot_vendored = { workspace = true }
 
 anyhow = { workspace = true }
 insta = { workspace = true }
+rstest = { workspace = true }
 tempfile = { workspace = true }
-walkdir = { workspace = true }
-zip = { workspace = true }
 
 [lints]
 workspace = true

crates/red_knot_python_semantic/build.rs

@@ -1,87 +1,4 @@
-//! Build script to package our vendored typeshed files
-//! into a zip archive that can be included in the Ruff binary.
-//!
-//! This script should be automatically run at build time
-//! whenever the script itself changes, or whenever any files
-//! in `crates/red_knot_python_semantic/vendor/typeshed` change.
-
-use std::fs::File;
-use std::path::Path;
-
-use path_slash::PathExt;
-use zip::result::ZipResult;
-use zip::write::{FileOptions, ZipWriter};
-use zip::CompressionMethod;
-
-const TYPESHED_SOURCE_DIR: &str = "vendor/typeshed";
-const TYPESHED_ZIP_LOCATION: &str = "/zipped_typeshed.zip";
-
-/// Recursively zip the contents of an entire directory.
-///
-/// This routine is adapted from a recipe at
-/// <https://github.com/zip-rs/zip-old/blob/5d0f198124946b7be4e5969719a7f29f363118cd/examples/write_dir.rs>
-fn zip_dir(directory_path: &str, writer: File) -> ZipResult<File> {
-    let mut zip = ZipWriter::new(writer);
-
-    // Use deflated compression for WASM builds because compiling `zstd-sys` requires clang
-    // [source](https://github.com/gyscos/zstd-rs/wiki/Compile-for-WASM) which complicates the build
-    // by a lot. Deflated compression is slower but it shouldn't matter much for the WASM use case
-    // (WASM itself is already slower than a native build for a specific platform).
-    // We can't use `#[cfg(...)]` here because the target-arch in a build script is the
-    // architecture of the system running the build script and not the architecture of the build-target.
-    // That's why we use the `TARGET` environment variable here.
-    let method = if std::env::var("TARGET").unwrap().contains("wasm32") {
-        CompressionMethod::Deflated
-    } else {
-        CompressionMethod::Zstd
-    };
-
-    let options = FileOptions::default()
-        .compression_method(method)
-        .unix_permissions(0o644);
-
-    for entry in walkdir::WalkDir::new(directory_path) {
-        let dir_entry = entry.unwrap();
-        let absolute_path = dir_entry.path();
-        let normalized_relative_path = absolute_path
-            .strip_prefix(Path::new(directory_path))
-            .unwrap()
-            .to_slash()
-            .expect("Unexpected non-utf8 typeshed path!");
-
-        // Write file or directory explicitly
-        // Some unzip tools unzip files with directory paths correctly, some do not!
-        if absolute_path.is_file() {
-            println!("adding file {absolute_path:?} as {normalized_relative_path:?} ...");
-            zip.start_file(normalized_relative_path, options)?;
-            let mut f = File::open(absolute_path)?;
-            std::io::copy(&mut f, &mut zip).unwrap();
-        } else if !normalized_relative_path.is_empty() {
-            // Only if not root! Avoids path spec / warning
-            // and mapname conversion failed error on unzip
-            println!("adding dir {absolute_path:?} as {normalized_relative_path:?} ...");
-            zip.add_directory(normalized_relative_path, options)?;
-        }
-    }
-    zip.finish()
-}
-
-fn main() {
-    println!("cargo:rerun-if-changed={TYPESHED_SOURCE_DIR}");
-    assert!(
-        Path::new(TYPESHED_SOURCE_DIR).is_dir(),
-        "Where is typeshed?"
-    );
-    let out_dir = std::env::var("OUT_DIR").unwrap();
-
-    // N.B. Deliberately using `format!()` instead of `Path::join()` here,
-    // so that we use `/` as a path separator on all platforms.
-    // That enables us to load the typeshed zip at compile time in `module.rs`
-    // (otherwise we'd have to dynamically determine the exact path to the typeshed zip
-    // based on the default path separator for the specific platform we're on,
-    // which can't be done at compile time.)
-    let zipped_typeshed_location = format!("{out_dir}{TYPESHED_ZIP_LOCATION}");
-
-    let zipped_typeshed = File::create(zipped_typeshed_location).unwrap();
-    zip_dir(TYPESHED_SOURCE_DIR, zipped_typeshed).unwrap();
+/// Rebuild the crate if a test file is added or removed from
+pub fn main() {
+    println!("cargo:rerun-if-changed=resources/mdtest");
 }

crates/red_knot_python_semantic/resources/README.md

@@ -0,0 +1,4 @@
+Markdown files within the `mdtest/` subdirectory are tests of type inference and type checking;
+executed by the `tests/mdtest.rs` integration test.
+
+See `crates/red_knot_test/README.md` for documentation of this test format.

crates/red_knot_python_semantic/resources/mdtest/assignment/annotations.md

@@ -0,0 +1,25 @@
+# Assignment with annotations
+
+## Annotation only transparent to local inference
+
+```py
+x = 1
+x: int
+y = x
+
+reveal_type(y)  # revealed: Literal[1]
+```
+
+## Violates own annotation
+
+```py
+x: int = 'foo' # error: [invalid-assignment] "Object of type `Literal["foo"]` is not assignable to `int`"
+
+```
+
+## Violates previous annotation
+
+```py
+x: int
+x = 'foo'  # error: [invalid-assignment] "Object of type `Literal["foo"]` is not assignable to `int`"
+```

crates/red_knot_python_semantic/resources/mdtest/assignment/multi_target.md

@@ -0,0 +1,9 @@
+# Multi-target assignment
+
+## Basic
+
+```py
+x = y = 1
+reveal_type(x)  # revealed: Literal[1]
+reveal_type(y)  # revealed: Literal[1]
+```

crates/red_knot_python_semantic/resources/mdtest/assignment/unbound.md

@@ -0,0 +1,24 @@
+# Unbound
+
+## Unbound
+
+```py
+x = foo
+foo = 1
+reveal_type(x)  # revealed: Unbound
+```
+
+## Unbound class variable
+
+Name lookups within a class scope fall back to globals, but lookups of class attributes don't.
+
+```py
+x = 1
+class C:
+    y = x
+    if flag:
+        x = 2
+
+reveal_type(C.x) # revealed: Literal[2]
+reveal_type(C.y) # revealed: Literal[1]
+```

crates/red_knot_python_semantic/resources/mdtest/assignment/walrus.md

@@ -0,0 +1,17 @@
+# Walrus operator
+
+## Basic
+
+```py
+x = (y := 1) + 1
+reveal_type(x)  # revealed: Literal[2]
+reveal_type(y)  # revealed: Literal[1]
+```
+
+## Walrus self-addition
+
+```py
+x = 0
+(x := x + 1)
+reveal_type(x)  # revealed: Literal[1]
+```

crates/red_knot_python_semantic/resources/mdtest/attributes.md

@@ -0,0 +1,15 @@
+# Class attributes
+
+## Union of attributes
+
+```py
+if flag:
+    class C:
+        x = 1
+else:
+    class C:
+        x = 2
+
+y = C.x
+reveal_type(y)  # revealed: Literal[1, 2]
+```

crates/red_knot_python_semantic/resources/mdtest/binary/integers.md

@@ -0,0 +1,36 @@
+## Binary operations on integers
+
+## Basic Arithmetic
+
+```py
+a = 2 + 1
+b = a - 4
+c = a * b
+d = c // 3
+e = c / 3
+f = 5 % 3
+
+reveal_type(a)  # revealed: Literal[3]
+reveal_type(b)  # revealed: Literal[-1]
+reveal_type(c)  # revealed: Literal[-3]
+reveal_type(d)  # revealed: Literal[-1]
+reveal_type(e)  # revealed: float
+reveal_type(f)  # revealed: Literal[2]
+```
+
+## Division by Zero
+
+```py
+# TODO: `a` should be `int` and `e` should be `float` once we support inference.
+a = 1 / 0  # error: "Cannot divide object of type `Literal[1]` by zero"
+b = 2 // 0  # error: "Cannot floor divide object of type `Literal[2]` by zero"
+c = 3 % 0  # error: "Cannot reduce object of type `Literal[3]` modulo zero"
+d = int() / 0  # error: "Cannot divide object of type `int` by zero"
+e = 1.0 / 0  # error: "Cannot divide object of type `float` by zero"
+
+reveal_type(a)  # revealed: float
+reveal_type(b)  # revealed: int
+reveal_type(c)  # revealed: int
+reveal_type(d)  # revealed: @Todo
+reveal_type(e)  # revealed: @Todo
+```

crates/red_knot_python_semantic/resources/mdtest/call/callable_instance.md

@@ -0,0 +1,21 @@
+# Callable instance
+
+## Dunder call
+
+```py
+class Multiplier:
+    def __init__(self, factor: float):
+        self.factor = factor
+
+    def __call__(self, number: float) -> float:
+        return number * self.factor
+
+a = Multiplier(2.0)(3.0)
+
+class Unit: ...
+
+b = Unit()(3.0) # error: "Object of type `Unit` is not callable"
+
+reveal_type(a) # revealed: float
+reveal_type(b) # revealed: Unknown
+```

crates/red_knot_python_semantic/resources/mdtest/call/constructor.md

@@ -0,0 +1,8 @@
+# Constructor
+
+```py
+class Foo: ...
+
+x = Foo()
+reveal_type(x)  # revealed: Foo
+```

crates/red_knot_python_semantic/resources/mdtest/call/function.md

@@ -0,0 +1,51 @@
+# Call expression
+
+## Simple
+
+```py
+def get_int() -> int:
+    return 42
+
+x = get_int()
+reveal_type(x)  # revealed: int
+```
+
+## Async
+
+```py
+async def get_int_async() -> int:
+    return 42
+
+x = get_int_async()
+
+# TODO: we don't yet support `types.CoroutineType`, should be generic `Coroutine[Any, Any, int]`
+reveal_type(x)  # revealed: @Todo
+```
+
+## Decorated
+
+```py
+from typing import Callable
+
+def foo() -> int:
+    return 42
+
+def decorator(func) -> Callable[[], int]:
+    return foo
+
+@decorator
+def bar() -> str:
+    return 'bar'
+
+x = bar()
+
+# TODO: should reveal `int`, as the decorator replaces `bar` with `foo`
+reveal_type(x)  # revealed: @Todo
+```
+
+## Invalid callable
+
+```py
+nonsense = 123
+x = nonsense()  # error: "Object of type `Literal[123]` is not callable"
+```

crates/red_knot_python_semantic/resources/mdtest/call/union.md

@@ -0,0 +1,74 @@
+# Unions in calls
+
+## Union of return types
+
+```py
+if flag:
+    def f() -> int:
+        return 1
+else:
+    def f() -> str:
+        return 'foo'
+
+x = f()
+reveal_type(x)  # revealed: int | str
+```
+
+## Calling with an unknown union
+
+```py
+from nonexistent import f # error: [unresolved-import] "Cannot resolve import `nonexistent`"
+
+if flag:
+    def f() -> int:
+        return 1
+
+x = f()
+reveal_type(x)  # revealed: Unknown | int
+```
+
+## Non-callable elements in a union
+
+Calling a union with a non-callable element should emit a diagnostic.
+
+```py
+if flag:
+    f = 1
+else:
+    def f() -> int:
+        return 1
+
+x = f()  # error: "Object of type `Literal[1] | Literal[f]` is not callable (due to union element `Literal[1]`)"
+reveal_type(x)  # revealed: Unknown | int
+```
+
+## Multiple non-callable elements in a union
+
+Calling a union with multiple non-callable elements should mention all of them in the diagnostic.
+
+```py
+if flag:
+    f = 1
+elif flag2:
+    f = 'foo'
+else:
+    def f() -> int:
+        return 1
+
+x = f()  # error: "Object of type `Literal[1] | Literal["foo"] | Literal[f]` is not callable (due to union elements Literal[1], Literal["foo"])"
+reveal_type(x)  # revealed: Unknown | int
+```
+
+## All non-callable union elements
+
+Calling a union with no callable elements can emit a simpler diagnostic.
+
+```py
+if flag:
+    f = 1
+else:
+    f = 'foo'
+
+x = f()  # error: "Object of type `Literal[1] | Literal["foo"]` is not callable"
+reveal_type(x)  # revealed: Unknown
+```

crates/red_knot_python_semantic/resources/mdtest/comparison/byte_literals.md

@@ -0,0 +1,43 @@
+### Comparison: Byte literals
+
+These tests assert that we infer precise `Literal` types for comparisons between objects
+inferred as having `Literal` bytes types:
+
+```py
+reveal_type(b"abc" == b"abc")  # revealed: Literal[True]
+reveal_type(b"abc" == b"ab")   # revealed: Literal[False]
+
+reveal_type(b"abc" != b"abc")  # revealed: Literal[False]
+reveal_type(b"abc" != b"ab")   # revealed: Literal[True]
+
+reveal_type(b"abc" < b"abd")   # revealed: Literal[True]
+reveal_type(b"abc" < b"abb")   # revealed: Literal[False]
+
+reveal_type(b"abc" <= b"abc")  # revealed: Literal[True]
+reveal_type(b"abc" <= b"abb")  # revealed: Literal[False]
+
+reveal_type(b"abc" > b"abd")   # revealed: Literal[False]
+reveal_type(b"abc" > b"abb")   # revealed: Literal[True]
+
+reveal_type(b"abc" >= b"abc")  # revealed: Literal[True]
+reveal_type(b"abc" >= b"abd")  # revealed: Literal[False]
+
+reveal_type(b"" in b"")                      # revealed: Literal[True]
+reveal_type(b"" in b"abc")                   # revealed: Literal[True]
+reveal_type(b"abc" in b"")                   # revealed: Literal[False]
+reveal_type(b"ab" in b"abc")                 # revealed: Literal[True]
+reveal_type(b"abc" in b"abc")                # revealed: Literal[True]
+reveal_type(b"d" in b"abc")                  # revealed: Literal[False]
+reveal_type(b"ac" in b"abc")                 # revealed: Literal[False]
+reveal_type(b"\x81\x82" in b"\x80\x81\x82")  # revealed: Literal[True]
+reveal_type(b"\x82\x83" in b"\x80\x81\x82")  # revealed: Literal[False]
+
+reveal_type(b"ab" not in b"abc")             # revealed: Literal[False]
+reveal_type(b"ac" not in b"abc")             # revealed: Literal[True]
+
+reveal_type(b"abc" is b"abc")      # revealed: bool
+reveal_type(b"abc" is b"ab")       # revealed: Literal[False]
+
+reveal_type(b"abc" is not b"abc")  # revealed: bool
+reveal_type(b"abc" is not b"ab")   # revealed: Literal[True]
+```

crates/red_knot_python_semantic/resources/mdtest/comparison/integers.md

@@ -0,0 +1,41 @@
+# Comparing integers
+
+## Integer literals
+
+```py
+a = 1 == 1 == True
+b = 1 == 1 == 2 == 4
+c = False < True <= 2 < 3 != 6
+d = 1 < 1
+e = 1 > 1
+f = 1 is 1
+g = 1 is not 1
+h = 1 is 2
+i = 1 is not 7
+j = 1 <= "" and 0 < 1
+
+reveal_type(a)  # revealed: Literal[True]
+reveal_type(b)  # revealed: Literal[False]
+reveal_type(c)  # revealed: Literal[True]
+reveal_type(d)  # revealed: Literal[False]
+reveal_type(e)  # revealed: Literal[False]
+reveal_type(f)  # revealed: bool
+reveal_type(g)  # revealed: bool
+reveal_type(h)  # revealed: Literal[False]
+reveal_type(i)  # revealed: Literal[True]
+reveal_type(j)  # revealed: @Todo | Literal[True]
+```
+
+## Integer instance
+
+```py
+# TODO: implement lookup of `__eq__` on typeshed `int` stub.
+def int_instance() -> int: ...
+a = 1 == int_instance()
+b = 9 < int_instance()
+c = int_instance() < int_instance()
+
+reveal_type(a)  # revealed: @Todo
+reveal_type(b)  # revealed: bool
+reveal_type(c)  # revealed: bool
+```

crates/red_knot_python_semantic/resources/mdtest/comparison/non_boolean_returns.md

@@ -0,0 +1,37 @@
+# Non boolean returns
+
+Walking through examples:
+
+- `a = A() < B() < C()`
+
+    1. `A() < B() and B() < C()` - split in N comparison
+    1. `A()` and `B()`              - evaluate outcome types
+    1. `bool` and `bool`            - evaluate truthiness
+    1. `A | B`                    - union of "first true" types
+
+- `b = 0 < 1 < A() < 3`
+
+    1. `0 < 1 and 1 < A() and A() < 3` - split in N comparison
+    1. `True` and `bool` and `A` - evaluate outcome types
+    1. `True` and `bool` and `bool` - evaluate truthiness
+    1. `bool | A` - union of "true" types
+
+- `c = 10 < 0 < A() < B() < C()` short-circuit to False
+
+```py
+from __future__ import annotations
+class A:
+    def __lt__(self, other) -> A: ...
+class B:
+    def __lt__(self, other) -> B: ...
+class C:
+    def __lt__(self, other) -> C: ...
+
+a = A() < B() < C()
+b = 0 < 1 < A() < 3
+c = 10 < 0 < A() < B() < C()
+
+reveal_type(a)  # revealed: A | B
+reveal_type(b)  # revealed: bool | A
+reveal_type(c)  # revealed: Literal[False]
+```

crates/red_knot_python_semantic/resources/mdtest/comparison/strings.md

@@ -0,0 +1,29 @@
+# Comparing strings
+
+## String literals
+
+```py
+def str_instance() -> str: ...
+a = "abc" == "abc"
+b = "ab_cd" <= "ab_ce"
+c = "abc" in "ab cd"
+d = "" not in "hello"
+e = "--" is "--"
+f = "A" is "B"
+g = "--" is not "--"
+h = "A" is not "B"
+i = str_instance() < "..."
+# ensure we're not comparing the interned salsa symbols, which compare by order of declaration.
+j = "ab" < "ab_cd"
+
+reveal_type(a)  # revealed: Literal[True]
+reveal_type(b)  # revealed: Literal[True]
+reveal_type(c)  # revealed: Literal[False]
+reveal_type(d)  # revealed: Literal[False]
+reveal_type(e)  # revealed: bool
+reveal_type(f)  # revealed: Literal[False]
+reveal_type(g)  # revealed: bool
+reveal_type(h)  # revealed: Literal[True]
+reveal_type(i)  # revealed: bool
+reveal_type(j)  # revealed: Literal[True]
+```

crates/red_knot_python_semantic/resources/mdtest/comparison/tuples.md

@@ -0,0 +1,205 @@
+# Comparison - Tuples
+
+## Heterogeneous
+
+For tuples like `tuple[int, str, Literal[1]]`
+
+### Value Comparisons
+
+"Value Comparisons" refers to the operators: `==`, `!=`, `<`, `<=`, `>`, `>=`
+
+#### Results without Ambiguity
+
+Cases where the result can be definitively inferred as a `BooleanLiteral`.
+
+```py
+a = (1, "test", (3, 13), True)
+b = (1, "test", (3, 14), False)
+
+reveal_type(a == a)  # revealed: Literal[True]
+reveal_type(a != a)  # revealed: Literal[False]
+reveal_type(a < a)   # revealed: Literal[False]
+reveal_type(a <= a)  # revealed: Literal[True]
+reveal_type(a > a)   # revealed: Literal[False]
+reveal_type(a >= a)  # revealed: Literal[True]
+
+reveal_type(a == b)  # revealed: Literal[False]
+reveal_type(a != b)  # revealed: Literal[True]
+reveal_type(a < b)   # revealed: Literal[True]
+reveal_type(a <= b)  # revealed: Literal[True]
+reveal_type(a > b)   # revealed: Literal[False]
+reveal_type(a >= b)  # revealed: Literal[False]
+```
+
+Even when tuples have different lengths, comparisons should be handled appropriately.
+
+```py path=different_length.py
+a = (1, 2, 3)
+b = (1, 2, 3, 4)
+
+reveal_type(a == b)  # revealed: Literal[False]
+reveal_type(a != b)  # revealed: Literal[True]
+reveal_type(a < b)   # revealed: Literal[True]
+reveal_type(a <= b)  # revealed: Literal[True]
+reveal_type(a > b)   # revealed: Literal[False]
+reveal_type(a >= b)  # revealed: Literal[False]
+
+c = ("a", "b", "c", "d")
+d = ("a", "b", "c")
+
+reveal_type(c == d)  # revealed: Literal[False]
+reveal_type(c != d)  # revealed: Literal[True]
+reveal_type(c < d)   # revealed: Literal[False]
+reveal_type(c <= d)  # revealed: Literal[False]
+reveal_type(c > d)   # revealed: Literal[True]
+reveal_type(c >= d)  # revealed: Literal[True]
+```
+
+#### Results with Ambiguity
+
+```py
+def bool_instance() -> bool: ...
+def int_instance() -> int: ...
+
+a = (bool_instance(),)
+b = (int_instance(),)
+
+# TODO: All @Todo should be `bool`
+reveal_type(a == a)  # revealed: @Todo
+reveal_type(a != a)  # revealed: @Todo
+reveal_type(a < a)   # revealed: @Todo
+reveal_type(a <= a)  # revealed: @Todo
+reveal_type(a > a)   # revealed: @Todo
+reveal_type(a >= a)  # revealed: @Todo
+
+reveal_type(a == b)  # revealed: @Todo
+reveal_type(a != b)  # revealed: @Todo
+reveal_type(a < b)   # revealed: @Todo
+reveal_type(a <= b)  # revealed: @Todo
+reveal_type(a > b)   # revealed: @Todo
+reveal_type(a >= b)  # revealed: @Todo
+```
+
+#### Comparison Unsupported
+
+If two tuples contain types that do not support comparison, the result may be `Unknown`.
+However, `==` and `!=` are exceptions and can still provide definite results.
+
+```py
+a = (1, 2)
+b = (1, "hello")
+
+# TODO: should be Literal[False]
+reveal_type(a == b)  # revealed: @Todo
+
+# TODO: should be Literal[True]
+reveal_type(a != b)  # revealed: @Todo
+
+# TODO: should be Unknown and add more informative diagnostics
+reveal_type(a < b)   # revealed: @Todo
+reveal_type(a <= b)  # revealed: @Todo
+reveal_type(a > b)   # revealed: @Todo
+reveal_type(a >= b)  # revealed: @Todo
+```
+
+However, if the lexicographic comparison completes without reaching a point where str and int are compared,
+Python will still produce a result based on the prior elements.
+
+```py path=short_circuit.py
+a = (1, 2)
+b = (999999, "hello")
+
+reveal_type(a == b)  # revealed: Literal[False]
+reveal_type(a != b)  # revealed: Literal[True]
+reveal_type(a < b)   # revealed: Literal[True]
+reveal_type(a <= b)  # revealed: Literal[True]
+reveal_type(a > b)   # revealed: Literal[False]
+reveal_type(a >= b)  # revealed: Literal[False]
+```
+
+#### Matryoshka Tuples
+
+```py
+a = (1, True, "Hello")
+b = (a, a, a)
+c = (b, b, b)
+
+reveal_type(c == c)  # revealed: Literal[True]
+reveal_type(c != c)  # revealed: Literal[False]
+reveal_type(c < c)   # revealed: Literal[False]
+reveal_type(c <= c)  # revealed: Literal[True]
+reveal_type(c > c)   # revealed: Literal[False]
+reveal_type(c >= c)  # revealed: Literal[True]
+```
+
+#### Non Boolean Rich Comparisons
+
+```py
+class A():
+    def __eq__(self, o) -> str: ...
+    def __ne__(self, o) -> int: ...
+    def __lt__(self, o) -> float: ...
+    def __le__(self, o) -> object: ...
+    def __gt__(self, o) -> tuple: ...
+    def __ge__(self, o) -> list: ...
+
+a = (A(), A())
+
+# TODO: All @Todo should be bool
+reveal_type(a == a)  # revealed: @Todo
+reveal_type(a != a)  # revealed: @Todo
+reveal_type(a < a)   # revealed: @Todo
+reveal_type(a <= a)  # revealed: @Todo
+reveal_type(a > a)   # revealed: @Todo
+reveal_type(a >= a)  # revealed: @Todo
+```
+
+### Membership Test Comparisons
+
+"Membership Test Comparisons" refers to the operators `in` and `not in`.
+
+```py
+def int_instance() -> int: ...
+
+a = (1, 2)
+b = ((3, 4), (1, 2))
+c = ((1, 2, 3), (4, 5, 6))
+d = ((int_instance(), int_instance()), (int_instance(), int_instance()))
+
+reveal_type(a in b)  # revealed: Literal[True]
+reveal_type(a not in b)  # revealed: Literal[False]
+
+reveal_type(a in c)  # revealed: Literal[False]
+reveal_type(a not in c)  # revealed: Literal[True]
+
+# TODO: All @Todo should be bool
+reveal_type(a in d)  # revealed: @Todo
+reveal_type(a not in d)  # revealed: @Todo
+```
+
+### Identity Comparisons
+
+"Identity Comparisons" refers to `is` and `is not`.
+
+```py
+a = (1, 2)
+b = ("a", "b")
+c = (1, 2, 3)
+
+reveal_type(a is (1, 2))  # revealed: bool
+reveal_type(a is not (1, 2))  # revealed: bool
+
+# TODO: Update to Literal[False] once str == int comparison is implemented
+reveal_type(a is b)  # revealed: @Todo
+# TODO: Update to Literal[True] once str == int comparison is implemented
+reveal_type(a is not b)  # revealed: @Todo
+
+reveal_type(a is c)  # revealed: Literal[False]
+reveal_type(a is not c)  # revealed: Literal[True]
+```
+
+## Homogeneous
+
+For tuples like `tuple[int, ...]`, `tuple[Any, ...]`
+
+// TODO

crates/red_knot_python_semantic/resources/mdtest/comparison/unions.md

@@ -0,0 +1,76 @@
+# Comparison: Unions
+
+## Union on one side of the comparison
+
+Comparisons on union types need to consider all possible cases:
+
+```py
+one_or_two = 1 if flag else 2
+
+reveal_type(one_or_two <= 2)  # revealed: Literal[True]
+reveal_type(one_or_two <= 1)  # revealed: bool
+reveal_type(one_or_two <= 0)  # revealed: Literal[False]
+
+reveal_type(2 >= one_or_two)  # revealed: Literal[True]
+reveal_type(1 >= one_or_two)  # revealed: bool
+reveal_type(0 >= one_or_two)  # revealed: Literal[False]
+
+reveal_type(one_or_two < 1)  # revealed: Literal[False]
+reveal_type(one_or_two < 2)  # revealed: bool
+reveal_type(one_or_two < 3)  # revealed: Literal[True]
+
+reveal_type(one_or_two > 0)  # revealed: Literal[True]
+reveal_type(one_or_two > 1)  # revealed: bool
+reveal_type(one_or_two > 2)  # revealed: Literal[False]
+
+reveal_type(one_or_two == 3)  # revealed: Literal[False]
+reveal_type(one_or_two == 1)  # revealed: bool
+
+reveal_type(one_or_two != 3)  # revealed: Literal[True]
+reveal_type(one_or_two != 1)  # revealed: bool
+
+a_or_ab = "a" if flag else "ab"
+
+reveal_type(a_or_ab in "ab")  # revealed: Literal[True]
+reveal_type("a" in a_or_ab)  # revealed: Literal[True]
+
+reveal_type("c" not in a_or_ab)  # revealed: Literal[True]
+reveal_type("a" not in a_or_ab)  # revealed: Literal[False]
+
+reveal_type("b" in a_or_ab)  # revealed: bool
+reveal_type("b" not in a_or_ab)  # revealed: bool
+
+one_or_none = 1 if flag else None
+
+reveal_type(one_or_none is None)  # revealed: bool
+reveal_type(one_or_none is not None)  # revealed: bool
+```
+
+## Union on both sides of the comparison
+
+With unions on both sides, we need to consider the full cross product of
+options when building the resulting (union) type:
+
+```py
+small = 1 if flag_s else 2
+large = 2 if flag_l else 3
+
+reveal_type(small <= large)  # revealed: Literal[True]
+reveal_type(small >= large)  # revealed: bool
+
+reveal_type(small < large)   # revealed: bool
+reveal_type(small > large)   # revealed: Literal[False]
+```
+
+## Unsupported operations
+
+Make sure we emit a diagnostic if *any* of the possible comparisons is
+unsupported. For now, we fall back to `bool` for the result type instead of
+trying to infer something more precise from the other (supported) variants:
+
+```py
+x = [1, 2] if flag else 1
+
+result = 1 in x  # error: "Operator `in` is not supported"
+reveal_type(result)  # revealed: bool
+```

crates/red_knot_python_semantic/resources/mdtest/comparison/unsupported.md

@@ -0,0 +1,15 @@
+# Unsupported operators
+
+```py
+a = 1 in 7      # error: "Operator `in` is not supported for types `Literal[1]` and `Literal[7]`"
+b = 0 not in 10 # error: "Operator `not in` is not supported for types `Literal[0]` and `Literal[10]`"
+c = object() < 5 # error: "Operator `<` is not supported for types `object` and `Literal[5]`"
+# TODO should error, need to check if __lt__ signature is valid for right operand
+d = 5 < object()
+
+reveal_type(a)  # revealed: bool
+reveal_type(b)  # revealed: bool
+reveal_type(c)  # revealed: Unknown
+# TODO: should be `Unknown`
+reveal_type(d)  # revealed: bool
+```

crates/red_knot_python_semantic/resources/mdtest/conditional/if_expression.md

@@ -0,0 +1,35 @@
+# If expressions
+
+## Simple if-expression
+
+```py
+x = 1 if flag else 2
+reveal_type(x)  # revealed: Literal[1, 2]
+```
+
+## If-expression with walrus operator
+
+```py
+y = 0
+z = 0
+x = (y := 1) if flag else (z := 2)
+a = y
+b = z
+reveal_type(x)  # revealed: Literal[1, 2]
+reveal_type(a)  # revealed: Literal[0, 1]
+reveal_type(b)  # revealed: Literal[0, 2]
+```
+
+## Nested if-expression
+
+```py
+x = 1 if flag else 2 if flag2 else 3
+reveal_type(x)  # revealed: Literal[1, 2, 3]
+```
+
+## None
+
+```py
+x = 1 if flag else None
+reveal_type(x)  # revealed: Literal[1] | None
+```

crates/red_knot_python_semantic/resources/mdtest/conditional/if_statement.md

@@ -0,0 +1,98 @@
+# If statements
+
+## Simple if
+
+```py
+y = 1
+y = 2
+
+if flag:
+    y = 3
+
+x = y
+
+reveal_type(x)  # revealed: Literal[2, 3]
+```
+
+## Simple if-elif-else
+
+```py
+y = 1
+y = 2
+if flag:
+    y = 3
+elif flag2:
+    y = 4
+else:
+    r = y
+    y = 5
+    s = y
+x = y
+
+reveal_type(x)  # revealed: Literal[3, 4, 5]
+reveal_type(r)  # revealed: Unbound | Literal[2]
+reveal_type(s)  # revealed: Unbound | Literal[5]
+```
+
+## Single symbol across if-elif-else
+
+```py
+if flag:
+    y = 1
+elif flag2:
+    y = 2
+else:
+    y = 3
+reveal_type(y)  # revealed: Literal[1, 2, 3]
+```
+
+## if-elif-else without else assignment
+
+```py
+y = 0
+if flag:
+    y = 1
+elif flag2:
+    y = 2
+else:
+    pass
+reveal_type(y)  # revealed: Literal[0, 1, 2]
+```
+
+## if-elif-else with intervening assignment
+
+```py
+y = 0
+if flag:
+    y = 1
+    z = 3
+elif flag2:
+    y = 2
+else:
+    pass
+reveal_type(y)  # revealed: Literal[0, 1, 2]
+```
+
+## Nested if statement
+
+```py
+y = 0
+if flag:
+    if flag2:
+        y = 1
+reveal_type(y)  # revealed: Literal[0, 1]
+```
+
+## if-elif without else
+
+```py
+y = 1
+y = 2
+if flag:
+    y = 3
+elif flag2:
+    y = 4
+x = y
+
+reveal_type(x)  # revealed: Literal[2, 3, 4]
+```

crates/red_knot_python_semantic/resources/mdtest/conditional/match.md

@@ -0,0 +1,39 @@
+# Pattern matching
+
+## With wildcard
+
+```py
+match 0:
+    case 1:
+        y = 2
+    case _:
+        y = 3
+
+reveal_type(y)  # revealed: Literal[2, 3]
+```
+
+## Without wildcard
+
+```py
+match 0:
+    case 1:
+        y = 2
+    case 2:
+        y = 3
+
+reveal_type(y)  # revealed: Unbound | Literal[2, 3]
+```
+
+## Basic match
+
+```py
+y = 1
+y = 2
+match 0:
+    case 1:
+        y = 3
+    case 2:
+        y = 4
+
+reveal_type(y)  # revealed: Literal[2, 3, 4]
+```

crates/red_knot_python_semantic/resources/mdtest/declaration/error.md

@@ -0,0 +1,39 @@
+# Errors while declaring
+
+## Violates previous assignment
+
+```py
+x = 1
+x: str  # error: [invalid-declaration] "Cannot declare type `str` for inferred type `Literal[1]`"
+```
+
+## Incompatible declarations
+
+```py
+if flag:
+    x: str
+else:
+    x: int
+x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: str, int"
+```
+
+## Partial declarations
+
+```py
+if flag:
+    x: int
+x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: Unknown, int"
+```
+
+## Incompatible declarations with bad assignment
+
+```py
+if flag:
+    x: str
+else:
+    x: int
+
+# error: [conflicting-declarations]
+# error: [invalid-assignment]
+x = b'foo'
+```

crates/red_knot_python_semantic/resources/mdtest/exception/basic.md

@@ -0,0 +1,55 @@
+# Exception Handling
+
+## Single Exception
+
+```py
+import re
+try:
+    x
+except NameError as e:
+    reveal_type(e)  # revealed: NameError
+except re.error as f:
+    reveal_type(f)  # revealed: error
+```
+
+## Unknown type in except handler does not cause spurious diagnostic
+
+```py
+from nonexistent_module import foo # error: [unresolved-import]
+
+try:
+    x
+except foo as e:
+    reveal_type(foo)  # revealed: Unknown
+    reveal_type(e)  # revealed: Unknown
+```
+
+## Multiple Exceptions in a Tuple
+
+```py
+EXCEPTIONS = (AttributeError, TypeError)
+
+try:
+    x
+except (RuntimeError, OSError) as e:
+    reveal_type(e)  # revealed: RuntimeError | OSError
+except EXCEPTIONS as f:
+    reveal_type(f)  # revealed: AttributeError | TypeError
+```
+
+## Dynamic exception types
+
+```py
+def foo(x: type[AttributeError], y: tuple[type[OSError], type[RuntimeError]], z: tuple[type[BaseException], ...]):
+    try:
+        w
+    except x as e:
+        # TODO: should be `AttributeError`
+        reveal_type(e)  # revealed: @Todo
+    except y as f:
+        # TODO: should be `OSError | RuntimeError`
+        reveal_type(f)  # revealed: @Todo
+    except z as g:
+        # TODO: should be `BaseException`
+        reveal_type(g)  # revealed: @Todo
+```

crates/red_knot_python_semantic/resources/mdtest/exception/control_flow.md

@@ -0,0 +1,641 @@
+# Control flow for exception handlers
+
+These tests assert that we understand the possible "definition states" (which
+symbols might or might not be defined) in the various branches of a
+`try`/`except`/`else`/`finally` block.
+
+For a full writeup on the semantics of exception handlers,
+see [this document][1].
+
+The tests throughout this Markdown document use functions with names starting
+with `could_raise_*` to mark definitions that might or might not succeed
+(as the function could raise an exception). A type checker must assume that any
+arbitrary function call could raise an exception in Python; this is just a
+naming convention used in these tests for clarity, and to future-proof the
+tests against possible future improvements whereby certain statements or
+expressions could potentially be inferred as being incapable of causing an
+exception to be raised.
+
+## A single bare `except`
+
+Consider the following `try`/`except` block, with a single bare `except:`.
+There are different types for the variable `x` in the two branches of this
+block, and we can't determine which branch might have been taken from the
+perspective of code following this block. The inferred type after the block's
+conclusion is therefore the union of the type at the end of the `try` suite
+(`str`) and the type at the end of the `except` suite (`Literal[2]`).
+
+*Within* the `except` suite, we must infer a union of all possible "definition
+states" we could have been in at any point during the `try` suite. This is
+because control flow could have jumped to the `except` suite without any of the
+`try`-suite definitions successfully completing, with only *some* of the
+`try`-suite definitions successfully completing, or indeed with *all* of them
+successfully completing. The type of `x` at the beginning of the `except` suite
+in this example is therefore `Literal[1] | str`, taking into account that we
+might have jumped to the `except` suite before the
+`x = could_raise_returns_str()` redefinition, but we *also* could have jumped
+to the `except` suite *after* that redefinition.
+
+```py path=union_type_inferred.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = 2
+    reveal_type(x)  # revealed: Literal[2]
+
+reveal_type(x)  # revealed: str | Literal[2]
+```
+
+If `x` has the same type at the end of both branches, however, the branches
+unify and `x` is not inferred as having a union type following the
+`try`/`except` block:
+
+```py path=branches_unify_to_non_union_type.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+x = 1
+
+try:
+    x = could_raise_returns_str()
+except:
+    x = could_raise_returns_str()
+
+reveal_type(x)  # revealed: str
+```
+
+## A non-bare `except`
+
+For simple `try`/`except` blocks, an `except TypeError:` handler has the same
+control flow semantics as an `except:` handler. An `except TypeError:` handler
+will not catch *all* exceptions: if this is the only handler, it opens up the
+possibility that an exception might occur that would not be handled. However,
+as described in [the document on exception-handling semantics][1], that would
+lead to termination of the scope. It's therefore irrelevant to consider this
+possibility when it comes to control-flow analysis.
+
+```py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except TypeError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = 2
+    reveal_type(x)  # revealed: Literal[2]
+
+reveal_type(x)  # revealed: str | Literal[2]
+```
+
+## Multiple `except` branches
+
+If the scope reaches the final `reveal_type` call in this example,
+either the `try`-block suite of statements was executed in its entirety,
+or exactly one `except` suite was executed in its entirety.
+The inferred type of `x` at this point is the union of the types at the end of
+the three suites:
+
+- At the end of `try`, `type(x) == str`
+- At the end of `except TypeError`, `x == 2`
+- At the end of `except ValueError`, `x == 3`
+
+```py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except TypeError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = 2
+    reveal_type(x)  # revealed: Literal[2]
+except ValueError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = 3
+    reveal_type(x)  # revealed: Literal[3]
+
+reveal_type(x)  # revealed: str | Literal[2, 3]
+```
+
+## Exception handlers with `else` branches (but no `finally`)
+
+If we reach the `reveal_type` call at the end of this scope,
+either the `try` and `else` suites were both executed in their entireties,
+or the `except` suite was executed in its entirety. The type of `x` at this
+point is the union of the type at the end of the `else` suite and the type at
+the end of the `except` suite:
+
+- At the end of `else`, `x == 3`
+- At the end of `except`, `x == 2`
+
+```py path=single_except.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except TypeError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = 2
+    reveal_type(x)  # revealed: Literal[2]
+else:
+    reveal_type(x)  # revealed: str
+    x = 3
+    reveal_type(x)  # revealed: Literal[3]
+
+reveal_type(x)  # revealed: Literal[2, 3]
+```
+
+For a block that has multiple `except` branches and an `else` branch, the same
+principle applies. In order to reach the final `reveal_type` call,
+either exactly one of the `except` suites must have been executed in its
+entirety, or the `try` suite and the `else` suite must both have been executed
+in their entireties:
+
+```py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except TypeError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = 2
+    reveal_type(x)  # revealed: Literal[2]
+except ValueError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = 3
+    reveal_type(x)  # revealed: Literal[3]
+else:
+    reveal_type(x)  # revealed: str
+    x = 4
+    reveal_type(x)  # revealed: Literal[4]
+
+reveal_type(x)  # revealed: Literal[2, 3, 4]
+```
+
+## Exception handlers with `finally` branches (but no `except` branches)
+
+A `finally` suite is *always* executed. As such, if we reach the `reveal_type`
+call at the end of this example, we know that `x` *must* have been reassigned
+to `2` during the `finally` suite. The type of `x` at the end of the example is
+therefore `Literal[2]`:
+
+```py path=redef_in_finally.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+finally:
+    x = 2
+    reveal_type(x)  # revealed: Literal[2]
+
+reveal_type(x)  # revealed: Literal[2]
+```
+
+If `x` was *not* redefined in the `finally` suite, however, things are somewhat
+more complicated. If we reach the final `reveal_type` call,
+unlike the state when we're visiting the `finally` suite,
+we know that the `try`-block suite ran to completion.
+This means that there are fewer possible states at this point than there were
+when we were inside the `finally` block.
+
+(Our current model does *not* correctly infer the types *inside* `finally`
+suites, however; this is still a TODO item for us.)
+
+```py path=no_redef_in_finally.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+finally:
+    # TODO: should be Literal[1] | str
+    reveal_type(x)  # revealed: str
+
+reveal_type(x)  # revealed: str
+```
+
+## Combining an `except` branch with a `finally` branch
+
+As previously stated, we do not yet have accurate inference for types *inside*
+`finally` suites. When we do, however, we will have to take account of the
+following possibilities inside `finally` suites:
+
+- The `try` suite could have run to completion
+- Or we could have jumped from halfway through the `try` suite to an `except`
+    suite, and the `except` suite ran to completion
+- Or we could have jumped from halfway through the `try` suite straight to the
+    `finally` suite due to an unhandled exception
+- Or we could have jumped from halfway through the `try` suite to an
+    `except` suite, only for an exception raised in the `except` suite to cause
+    us to jump to the `finally` suite before the `except` suite ran to completion
+
+```py path=redef_in_finally.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+def could_raise_returns_bytes() -> bytes:
+    return b'foo'
+
+def could_raise_returns_bool() -> bool:
+    return True
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except TypeError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = could_raise_returns_bytes()
+    reveal_type(x)  # revealed: bytes
+    x = could_raise_returns_bool()
+    reveal_type(x)  # revealed: bool
+finally:
+    # TODO: should be `Literal[1] | str | bytes | bool`
+    reveal_type(x)  # revealed: str | bool
+    x = 2
+    reveal_type(x)  # revealed: Literal[2]
+
+reveal_type(x)  # revealed: Literal[2]
+```
+
+Now for an example without a redefinition in the `finally` suite.
+As before, there *should* be fewer possibilities after completion of the
+`finally` suite than there were during the `finally` suite itself.
+(In some control-flow possibilities, some exceptions were merely *suspended*
+during the `finally` suite; these lead to the scope's termination following the
+conclusion of the `finally` suite.)
+
+```py path=no_redef_in_finally.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+def could_raise_returns_bytes() -> bytes:
+    return b'foo'
+
+def could_raise_returns_bool() -> bool:
+    return True
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except TypeError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = could_raise_returns_bytes()
+    reveal_type(x)  # revealed: bytes
+    x = could_raise_returns_bool()
+    reveal_type(x)  # revealed: bool
+finally:
+    # TODO: should be `Literal[1] | str | bytes | bool`
+    reveal_type(x)  # revealed: str | bool
+
+reveal_type(x)  # revealed: str | bool
+```
+
+An example with multiple `except` branches and a `finally` branch:
+
+```py path=multiple_except_branches.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+def could_raise_returns_bytes() -> bytes:
+    return b'foo'
+
+def could_raise_returns_bool() -> bool:
+    return True
+
+def could_raise_returns_memoryview() -> memoryview:
+    return memoryview(b"")
+
+def could_raise_returns_float() -> float:
+    return 3.14
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except TypeError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = could_raise_returns_bytes()
+    reveal_type(x)  # revealed: bytes
+    x = could_raise_returns_bool()
+    reveal_type(x)  # revealed: bool
+except ValueError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = could_raise_returns_memoryview()
+    reveal_type(x)  # revealed: memoryview
+    x = could_raise_returns_float()
+    reveal_type(x)  # revealed: float
+finally:
+    # TODO: should be `Literal[1] | str | bytes | bool | memoryview | float`
+    reveal_type(x)  # revealed: str | bool | float
+
+reveal_type(x)  # revealed: str | bool | float
+```
+
+## Combining `except`, `else` and `finally` branches
+
+If the exception handler has an `else` branch, we must also take into account
+the possibility that control flow could have jumped to the `finally` suite from
+partway through the `else` suite due to an exception raised *there*.
+
+```py path=single_except_branch.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+def could_raise_returns_bytes() -> bytes:
+    return b'foo'
+
+def could_raise_returns_bool() -> bool:
+    return True
+
+def could_raise_returns_memoryview() -> memoryview:
+    return memoryview(b"")
+
+def could_raise_returns_float() -> float:
+    return 3.14
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except TypeError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = could_raise_returns_bytes()
+    reveal_type(x)  # revealed: bytes
+    x = could_raise_returns_bool()
+    reveal_type(x)  # revealed: bool
+else:
+    reveal_type(x)  # revealed: str
+    x = could_raise_returns_memoryview()
+    reveal_type(x)  # revealed: memoryview
+    x = could_raise_returns_float()
+    reveal_type(x)  # revealed: float
+finally:
+    # TODO: should be `Literal[1] | str | bytes | bool | memoryview | float`
+    reveal_type(x)  # revealed: bool | float
+
+reveal_type(x)  # revealed: bool | float
+```
+
+The same again, this time with multiple `except` branches:
+
+```py path=multiple_except_branches.py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+def could_raise_returns_bytes() -> bytes:
+    return b'foo'
+
+def could_raise_returns_bool() -> bool:
+    return True
+
+def could_raise_returns_memoryview() -> memoryview:
+    return memoryview(b"")
+
+def could_raise_returns_float() -> float:
+    return 3.14
+
+def could_raise_returns_range() -> range:
+    return range(42)
+
+def could_raise_returns_slice() -> slice:
+    return slice(None)
+
+x = 1
+
+try:
+    reveal_type(x)  # revealed: Literal[1]
+    x = could_raise_returns_str()
+    reveal_type(x)  # revealed: str
+except TypeError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = could_raise_returns_bytes()
+    reveal_type(x)  # revealed: bytes
+    x = could_raise_returns_bool()
+    reveal_type(x)  # revealed: bool
+except ValueError:
+    reveal_type(x)  # revealed: Literal[1] | str
+    x = could_raise_returns_memoryview()
+    reveal_type(x)  # revealed: memoryview
+    x = could_raise_returns_float()
+    reveal_type(x)  # revealed: float
+else:
+    reveal_type(x)  # revealed: str
+    x = could_raise_returns_range()
+    reveal_type(x)  # revealed: range
+    x = could_raise_returns_slice()
+    reveal_type(x)  # revealed: slice
+finally:
+    # TODO: should be `Literal[1] | str | bytes | bool | memoryview | float | range | slice`
+    reveal_type(x)  # revealed: bool | float | slice
+
+reveal_type(x)  # revealed: bool | float | slice
+```
+
+## Nested `try`/`except` blocks
+
+It would take advanced analysis, which we are not yet capable of, to be able
+to determine that an exception handler always suppresses all exceptions. This
+is partly because it is possible for statements in `except`, `else` and
+`finally` suites to raise exceptions as well as statements in `try` suites.
+This means that if an exception handler is nested inside the `try` statement of
+an enclosing exception handler, it should (at least for now) be treated the
+same as any other node: as a suite containing statements that could possibly
+raise exceptions, which would lead to control flow jumping out of that suite
+prior to the suite running to completion.
+
+```py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+def could_raise_returns_bytes() -> bytes:
+    return b'foo'
+
+def could_raise_returns_bool() -> bool:
+    return True
+
+def could_raise_returns_memoryview() -> memoryview:
+    return memoryview(b"")
+
+def could_raise_returns_float() -> float:
+    return 3.14
+
+def could_raise_returns_range() -> range:
+    return range(42)
+
+def could_raise_returns_slice() -> slice:
+    return slice(None)
+
+def could_raise_returns_complex() -> complex:
+    return 3j
+
+def could_raise_returns_bytearray() -> bytearray:
+    return bytearray()
+
+class Foo: ...
+class Bar: ...
+
+def could_raise_returns_Foo() -> Foo:
+    return Foo()
+
+def could_raise_returns_Bar() -> Bar:
+    return Bar()
+
+x = 1
+
+try:
+    try:
+        reveal_type(x)  # revealed: Literal[1]
+        x = could_raise_returns_str()
+        reveal_type(x)  # revealed: str
+    except TypeError:
+        reveal_type(x)  # revealed: Literal[1] | str
+        x = could_raise_returns_bytes()
+        reveal_type(x)  # revealed: bytes
+        x = could_raise_returns_bool()
+        reveal_type(x)  # revealed: bool
+    except ValueError:
+        reveal_type(x)  # revealed: Literal[1] | str
+        x = could_raise_returns_memoryview()
+        reveal_type(x)  # revealed: memoryview
+        x = could_raise_returns_float()
+        reveal_type(x)  # revealed: float
+    else:
+        reveal_type(x)  # revealed: str
+        x = could_raise_returns_range()
+        reveal_type(x)  # revealed: range
+        x = could_raise_returns_slice()
+        reveal_type(x)  # revealed: slice
+    finally:
+        # TODO: should be `Literal[1] | str | bytes | bool | memoryview | float | range | slice`
+        reveal_type(x)  # revealed: bool | float | slice
+        x = 2
+        reveal_type(x)  # revealed: Literal[2]
+    reveal_type(x)  # revealed: Literal[2]
+except:
+    reveal_type(x)  # revealed: Literal[1, 2] | str | bytes | bool | memoryview | float | range | slice
+    x = could_raise_returns_complex()
+    reveal_type(x)  # revealed: complex
+    x = could_raise_returns_bytearray()
+    reveal_type(x)  # revealed: bytearray
+else:
+    reveal_type(x)  # revealed: Literal[2]
+    x = could_raise_returns_Foo()
+    reveal_type(x)  # revealed: Foo
+    x = could_raise_returns_Bar()
+    reveal_type(x)  # revealed: Bar
+finally:
+    # TODO: should be `Literal[1, 2] | str | bytes | bool | memoryview | float | range | slice | complex | bytearray | Foo | Bar`
+    reveal_type(x)  # revealed: bytearray | Bar
+
+# Either one `except` branch or the `else`
+# must have been taken and completed to get here:
+reveal_type(x)  # revealed: bytearray | Bar
+```
+
+## Nested scopes inside `try` blocks
+
+Shadowing a variable in an inner scope has no effect on type inference of the
+variable by that name in the outer scope:
+
+```py
+def could_raise_returns_str() -> str:
+    return 'foo'
+
+def could_raise_returns_bytes() -> bytes:
+    return b'foo'
+
+def could_raise_returns_range() -> range:
+    return range(42)
+
+def could_raise_returns_bytearray() -> bytearray:
+    return bytearray()
+
+def could_raise_returns_float() -> float:
+    return 3.14
+
+x = 1
+
+try:
+    def foo(param=could_raise_returns_str()):
+        x = could_raise_returns_str()
+
+        try:
+            reveal_type(x)  # revealed: str
+            x = could_raise_returns_bytes()
+            reveal_type(x)  # revealed: bytes
+        except:
+            reveal_type(x)  # revealed: str | bytes
+            x = could_raise_returns_bytearray()
+            reveal_type(x)  # revealed: bytearray
+            x = could_raise_returns_float()
+            reveal_type(x)  # revealed: float
+        finally:
+            # TODO: should be `str | bytes | bytearray | float`
+            reveal_type(x)  # revealed: bytes | float
+        reveal_type(x)  # revealed: bytes | float
+
+    x = foo
+    reveal_type(x)  # revealed: Literal[foo]
+except:
+    reveal_type(x)  # revealed: Literal[1] | Literal[foo]
+
+    class Bar:
+        x = could_raise_returns_range()
+        reveal_type(x)  # revealed: range
+
+    x = Bar
+    reveal_type(x)  # revealed: Literal[Bar]
+finally:
+    # TODO: should be `Literal[1] | Literal[foo] | Literal[Bar]`
+    reveal_type(x)  # revealed: Literal[foo] | Literal[Bar]
+
+reveal_type(x)  # revealed: Literal[foo] | Literal[Bar]
+```
+
+[1]: https://astral-sh.notion.site/Exception-handler-control-flow-11348797e1ca80bb8ce1e9aedbbe439d

crates/red_knot_python_semantic/resources/mdtest/exception/except_star.md

@@ -0,0 +1,30 @@
+# Except star
+
+## Except\* with BaseException
+
+```py
+try:
+    x
+except* BaseException as e:
+    reveal_type(e)  # revealed: BaseExceptionGroup
+```
+
+## Except\* with specific exception
+
+```py
+try:
+    x
+except* OSError as e:
+    # TODO(Alex): more precise would be `ExceptionGroup[OSError]`
+    reveal_type(e)  # revealed: BaseExceptionGroup
+```
+
+## Except\* with multiple exceptions
+
+```py
+try:
+    x
+except* (TypeError, AttributeError) as e:
+    #TODO(Alex): more precise would be `ExceptionGroup[TypeError | AttributeError]`.
+    reveal_type(e)  # revealed: BaseExceptionGroup
+```

crates/red_knot_python_semantic/resources/mdtest/expression/boolean.md

@@ -0,0 +1,151 @@
+# Expressions
+
+## OR
+
+```py
+def foo() -> str:
+    pass
+
+a = True or False
+b = 'x' or 'y' or 'z'
+c = '' or 'y' or 'z'
+d = False or 'z'
+e = False or True
+f = False or False
+g = foo() or False
+h = foo() or True
+
+reveal_type(a)  # revealed: Literal[True]
+reveal_type(b)  # revealed: Literal["x"]
+reveal_type(c)  # revealed: Literal["y"]
+reveal_type(d)  # revealed: Literal["z"]
+reveal_type(e)  # revealed: Literal[True]
+reveal_type(f)  # revealed: Literal[False]
+reveal_type(g)  # revealed: str | Literal[False]
+reveal_type(h)  # revealed: str | Literal[True]
+```
+
+## AND
+
+```py
+def foo() -> str:
+    pass
+
+a = True and False
+b = False and True
+c = foo() and False
+d = foo() and True
+e = 'x' and 'y' and 'z'
+f = 'x' and 'y' and ''
+g = '' and 'y'
+
+reveal_type(a)  # revealed: Literal[False]
+reveal_type(b)  # revealed: Literal[False]
+reveal_type(c)  # revealed: str | Literal[False]
+reveal_type(d)  # revealed: str | Literal[True]
+reveal_type(e)  # revealed: Literal["z"]
+reveal_type(f)  # revealed: Literal[""]
+reveal_type(g)  # revealed: Literal[""]
+```
+
+## Simple function calls to bool
+
+```py
+def returns_bool() -> bool:
+    return True
+
+if returns_bool():
+    x = True
+else:
+    x = False
+
+reveal_type(x)  # revealed: bool
+```
+
+## Complex
+
+```py
+def foo() -> str:
+    pass
+
+a = "x" and "y" or "z"
+b = "x" or "y" and "z"
+c = "" and "y" or "z"
+d = "" or "y" and "z"
+e = "x" and "y" or ""
+f = "x" or "y" and ""
+
+reveal_type(a)  # revealed: Literal["y"]
+reveal_type(b)  # revealed: Literal["x"]
+reveal_type(c)  # revealed: Literal["z"]
+reveal_type(d)  # revealed: Literal["z"]
+reveal_type(e)  # revealed: Literal["y"]
+reveal_type(f)  # revealed: Literal["x"]
+```
+
+## `bool()` function
+
+## Evaluates to builtin
+
+```py path=a.py
+redefined_builtin_bool = bool
+
+def my_bool(x)-> bool: pass
+```
+
+```py
+from a import redefined_builtin_bool, my_bool
+a = redefined_builtin_bool(0)
+b = my_bool(0)
+
+reveal_type(a)  # revealed: Literal[False]
+reveal_type(b)  # revealed: bool
+```
+
+## Truthy values
+
+```py
+a = bool(1)
+b = bool((0,))
+c = bool("NON EMPTY")
+d = bool(True)
+
+def foo(): pass
+e = bool(foo)
+
+reveal_type(a)  # revealed: Literal[True]
+reveal_type(b)  # revealed: Literal[True]
+reveal_type(c)  # revealed: Literal[True]
+reveal_type(d)  # revealed: Literal[True]
+reveal_type(e)  # revealed: Literal[True]
+```
+
+## Falsy values
+
+```py
+a = bool(0)
+b = bool(())
+c = bool(None)
+d = bool("")
+e = bool(False)
+f = bool()
+
+reveal_type(a)  # revealed: Literal[False]
+reveal_type(b)  # revealed: Literal[False]
+reveal_type(c)  # revealed: Literal[False]
+reveal_type(d)  # revealed: Literal[False]
+reveal_type(e)  # revealed: Literal[False]
+reveal_type(f)  # revealed: Literal[False]
+```
+
+## Ambiguous values
+
+```py
+a = bool([])
+b = bool({})
+c = bool(set())
+
+reveal_type(a)  # revealed: bool
+reveal_type(b)  # revealed: bool
+reveal_type(c)  # revealed: bool
+```

crates/red_knot_python_semantic/resources/mdtest/import/basic.md

@@ -0,0 +1,23 @@
+# Structures
+
+## Class import following
+
+```py
+from b import C as D; E = D
+reveal_type(E) # revealed: Literal[C]
+```
+
+```py path=b.py
+class C: pass
+```
+
+## Module member resolution
+
+```py
+import b; D = b.C
+reveal_type(D) # revealed: Literal[C]
+```
+
+```py path=b.py
+class C: pass
+```

crates/red_knot_python_semantic/resources/mdtest/import/builtins.md

@@ -0,0 +1,6 @@
+# Importing builtin module
+
+```py
+import builtins; x = builtins.copyright
+reveal_type(x) # revealed: Literal[copyright]
+```

crates/red_knot_python_semantic/resources/mdtest/import/conditional.md

@@ -0,0 +1,75 @@
+# Conditional imports
+
+## Maybe unbound
+
+```py path=maybe_unbound.py
+if flag:
+    y = 3
+x = y
+reveal_type(x)  # revealed: Unbound | Literal[3]
+reveal_type(y)  # revealed: Unbound | Literal[3]
+```
+
+```py
+from maybe_unbound import x, y
+reveal_type(x)  # revealed: Literal[3]
+reveal_type(y)  # revealed: Literal[3]
+```
+
+## Maybe unbound annotated
+
+```py path=maybe_unbound_annotated.py
+if flag:
+    y: int = 3
+x = y
+reveal_type(x)  # revealed: Unbound | Literal[3]
+reveal_type(y)  # revealed: Unbound | Literal[3]
+```
+
+Importing an annotated name prefers the declared type over the inferred type:
+
+```py
+from maybe_unbound_annotated import x, y
+reveal_type(x)  # revealed: Literal[3]
+reveal_type(y)  # revealed: int
+```
+
+## Reimport
+
+```py path=c.py
+def f(): ...
+```
+
+```py path=b.py
+if flag:
+    from c import f
+else:
+    def f(): ...
+```
+
+```py
+from b import f
+# TODO: We should disambiguate in such cases, showing `Literal[b.f, c.f]`.
+reveal_type(f)  # revealed: Literal[f, f]
+```
+
+## Reimport with stub declaration
+
+When we have a declared type in one path and only an inferred-from-definition type in the other, we
+should still be able to unify those:
+
+```py path=c.pyi
+x: int
+```
+
+```py path=b.py
+if flag:
+    from c import x
+else:
+    x = 1
+```
+
+```py
+from b import x
+reveal_type(x)  # revealed: int
+```

crates/red_knot_python_semantic/resources/mdtest/import/errors.md

@@ -0,0 +1,52 @@
+# Unresolved Imports
+
+## Unresolved import statement
+
+```py
+import bar # error: "Cannot resolve import `bar`"
+reveal_type(bar)  # revealed: Unknown
+```
+
+## Unresolved import from statement
+
+```py
+from bar import baz # error: "Cannot resolve import `bar`"
+reveal_type(baz)  # revealed: Unknown
+```
+
+## Unresolved import from resolved module
+
+```py path=a.py
+```
+
+```py
+from a import thing # error: "Module `a` has no member `thing`"
+reveal_type(thing)  # revealed: Unknown
+```
+
+## Resolved import of symbol from unresolved import
+
+```py path=a.py
+import foo as foo # error: "Cannot resolve import `foo`"
+reveal_type(foo)  # revealed: Unknown
+```
+
+Importing the unresolved import into a second file should not trigger an additional "unresolved
+import" violation:
+
+```py
+from a import foo
+reveal_type(foo)  # revealed: Unknown
+```
+
+## No implicit shadowing
+
+```py path=b.py
+x: int
+```
+
+```py
+from b import x
+
+x = 'foo'  # error: [invalid-assignment] "Object of type `Literal["foo"]"
+```

crates/red_knot_python_semantic/resources/mdtest/import/relative.md

@@ -0,0 +1,133 @@
+# Relative
+
+## Non-existent
+
+```py path=package/__init__.py
+```
+
+```py path=package/bar.py
+from .foo import X # error: [unresolved-import]
+reveal_type(X)  # revealed: Unknown
+```
+
+## Simple
+
+```py path=package/__init__.py
+```
+
+```py path=package/foo.py
+X = 42
+```
+
+```py path=package/bar.py
+from .foo import X
+reveal_type(X)  # revealed: Literal[42]
+```
+
+## Dotted
+
+```py path=package/__init__.py
+```
+
+```py path=package/foo/bar/baz.py
+X = 42
+```
+
+```py path=package/bar.py
+from .foo.bar.baz import X
+reveal_type(X)  # revealed: Literal[42]
+```
+
+## Bare to package
+
+```py path=package/__init__.py
+X = 42
+```
+
+```py path=package/bar.py
+from . import X
+reveal_type(X)  # revealed: Literal[42]
+```
+
+## Non-existent + bare to package
+
+```py path=package/bar.py
+from . import X # error: [unresolved-import]
+reveal_type(X)  # revealed: Unknown
+```
+
+## Dunder init
+
+```py path=package/__init__.py
+from .foo import X
+reveal_type(X)  # revealed: Literal[42]
+```
+
+```py path=package/foo.py
+X = 42
+```
+
+## Non-existent + dunder init
+
+```py path=package/__init__.py
+from .foo import X # error: [unresolved-import]
+reveal_type(X)     # revealed: Unknown
+```
+
+## Long relative import
+
+```py path=package/__init__.py
+```
+
+```py path=package/foo.py
+X = 42
+```
+
+```py path=package/subpackage/subsubpackage/bar.py
+from ...foo import X
+reveal_type(X)  # revealed: Literal[42]
+```
+
+## Unbound symbol
+
+```py path=package/__init__.py
+```
+
+```py path=package/foo.py
+x
+```
+
+```py path=package/bar.py
+from .foo import x # error: [unresolved-import]
+reveal_type(x)     # revealed: Unknown
+```
+
+## Bare to module
+
+```py path=package/__init__.py
+```
+
+```py path=package/foo.py
+X = 42
+```
+
+```py path=package/bar.py
+# TODO: support submodule imports
+from . import foo  # error: [unresolved-import]
+y = foo.X
+
+# TODO: should be `Literal[42]`
+reveal_type(y)     # revealed: Unknown
+```
+
+## Non-existent + bare to module
+
+```py path=package/__init__.py
+```
+
+```py path=package/bar.py
+# TODO: support submodule imports
+from . import foo  # error: [unresolved-import]
+
+reveal_type(foo)   # revealed: Unknown
+```

crates/red_knot_python_semantic/resources/mdtest/import/stubs.md

@@ -0,0 +1,25 @@
+# Stubs
+
+## Import from stub declaration
+
+```py
+from b import x
+y = x
+reveal_type(y)  # revealed: int
+```
+
+```py path=b.pyi
+x: int
+```
+
+## Import from non-stub with declaration and definition
+
+```py
+from b import x
+y = x
+reveal_type(y)  # revealed: int
+```
+
+```py path=b.py
+x: int = 1
+```

crates/red_knot_python_semantic/resources/mdtest/literal/boolean.md

@@ -0,0 +1,8 @@
+# Boolean literals
+
+```py
+x = True
+y = False
+reveal_type(x)  # revealed: Literal[True]
+reveal_type(y)  # revealed: Literal[False]
+```

crates/red_knot_python_semantic/resources/mdtest/literal/collections/dictionary.md

@@ -0,0 +1,8 @@
+# Dictionaries
+
+## Empty dictionary
+
+```py
+x = {}
+reveal_type(x)  # revealed: dict
+```

crates/red_knot_python_semantic/resources/mdtest/literal/collections/list.md

@@ -0,0 +1,8 @@
+# Lists
+
+## Empty list
+
+```py
+x = []
+reveal_type(x)  # revealed: list
+```

crates/red_knot_python_semantic/resources/mdtest/literal/collections/set.md

@@ -0,0 +1,8 @@
+# Sets
+
+## Basic set
+
+```py
+x = {1, 2}
+reveal_type(x)  # revealed: set
+```

crates/red_knot_python_semantic/resources/mdtest/literal/collections/tuple.md

@@ -0,0 +1,20 @@
+# Tuples
+
+## Empty tuple
+
+```py
+x = ()
+reveal_type(x)  # revealed: tuple[()]
+```
+
+## Heterogeneous tuple
+
+```py
+x = (1, 'a')
+y = (1, (2, 3))
+z = (x, 2)
+
+reveal_type(x)  # revealed: tuple[Literal[1], Literal["a"]]
+reveal_type(y)  # revealed: tuple[Literal[1], tuple[Literal[2], Literal[3]]]
+reveal_type(z)  # revealed: tuple[tuple[Literal[1], Literal["a"]], Literal[2]]
+```

crates/red_knot_python_semantic/resources/mdtest/literal/complex.md

@@ -0,0 +1,7 @@
+# Complex literals
+
+## Complex numbers
+
+```py
+reveal_type(2j)  # revealed: complex
+```

crates/red_knot_python_semantic/resources/mdtest/literal/f_string.md

@@ -0,0 +1,44 @@
+# f-strings
+
+## Expression
+
+```py
+x = 0
+y = str()
+z = False
+
+a = f'hello'
+b = f'h {x}'
+c = 'one ' f'single ' f'literal'
+d = 'first ' f'second({b})' f' third'
+e = f'-{y}-'
+f = f'-{y}-' f'--' '--'
+g = f'{z} == {False} is {True}'
+
+reveal_type(a)  # revealed: Literal["hello"]
+reveal_type(b)  # revealed: Literal["h 0"]
+reveal_type(c)  # revealed: Literal["one single literal"]
+reveal_type(d)  # revealed: Literal["first second(h 0) third"]
+reveal_type(e)  # revealed: str
+reveal_type(f)  # revealed: str
+reveal_type(g)  # revealed: Literal["False == False is True"]
+```
+
+## Conversion Flags
+
+```py
+string = 'hello'
+a = f'{string!r}'
+
+# TODO: should be `Literal["'hello'"]`
+reveal_type(a)  # revealed: str
+```
+
+## Format Specifiers
+
+```py
+a = f'{1:02}'
+
+# TODO: should be `Literal["01"]`
+reveal_type(a)  # revealed: str
+```

crates/red_knot_python_semantic/resources/mdtest/literal/float.md

@@ -0,0 +1,7 @@
+# Float literals
+
+## Basic
+
+```py
+reveal_type(1.0)  # revealed: float
+```

crates/red_knot_python_semantic/resources/mdtest/literal/integer.md

@@ -0,0 +1,56 @@
+# Integer literals
+
+## Literals
+
+We can infer an integer literal type:
+
+```py
+reveal_type(1)  # revealed: Literal[1]
+```
+
+## Variable
+
+```py
+x = 1
+reveal_type(x)  # revealed: Literal[1]
+```
+
+## Overflow
+
+We only track integer literals within the range of an i64:
+
+```py
+reveal_type(9223372036854775808)  # revealed: int
+```
+
+## Big int
+
+We don't support big integer literals; we just infer `int` type instead:
+
+```py
+x = 10_000_000_000_000_000_000
+reveal_type(x)  # revealed: int
+```
+
+## Negated
+
+```py
+x = -1
+y = -1234567890987654321
+z = --987
+reveal_type(x)  # revealed: Literal[-1]
+reveal_type(y)  # revealed: Literal[-1234567890987654321]
+reveal_type(z)  # revealed: Literal[987]
+```
+
+## Floats
+
+```py
+reveal_type(1.0)  # revealed: float
+```
+
+## Complex
+
+```py
+reveal_type(2j)  # revealed: complex
+```

crates/red_knot_python_semantic/resources/mdtest/literal/string.md

@@ -0,0 +1,26 @@
+# String literals
+
+## Simple
+
+```py
+w = "Hello"
+x = 'world'
+y = "Guten " + 'tag'
+z = 'bon ' + "jour"
+
+reveal_type(w)  # revealed: Literal["Hello"]
+reveal_type(x)  # revealed: Literal["world"]
+reveal_type(y)  # revealed: Literal["Guten tag"]
+reveal_type(z)  # revealed: Literal["bon jour"]
+```
+
+## Nested Quotes
+
+```py
+x = 'I say "hello" to you'
+y = "You say \"hey\" back"
+z = 'No "closure here'
+reveal_type(x)  # revealed: Literal["I say \"hello\" to you"]
+reveal_type(y)  # revealed: Literal["You say \"hey\" back"]
+reveal_type(z)  # revealed: Literal["No \"closure here"]
+```

crates/red_knot_python_semantic/resources/mdtest/loops/async_for_loops.md

@@ -0,0 +1,41 @@
+# Async
+
+Async `for` loops do not work according to the synchronous iteration protocol.
+
+## Invalid async for loop
+
+```py
+async def foo():
+    class Iterator:
+        def __next__(self) -> int:
+            return 42
+
+    class Iterable:
+        def __iter__(self) -> Iterator:
+            return Iterator()
+
+    async for x in Iterator():
+        pass
+
+    # TODO
+    reveal_type(x)  # revealed: Unbound | @Todo
+```
+
+## Basic async for loop
+
+```py
+async def foo():
+    class IntAsyncIterator:
+        async def __anext__(self) -> int:
+            return 42
+
+    class IntAsyncIterable:
+        def __aiter__(self) -> IntAsyncIterator:
+            return IntAsyncIterator()
+
+    #TODO(Alex): async iterables/iterators!
+    async for x in IntAsyncIterable():
+        pass
+
+    reveal_type(x)  # revealed: Unbound | @Todo
+```

crates/red_knot_python_semantic/resources/mdtest/loops/for_loop.md

@@ -0,0 +1,134 @@
+# For loops
+
+## Basic `for` loop
+
+```py
+class IntIterator:
+    def __next__(self) -> int:
+        return 42
+
+class IntIterable:
+    def __iter__(self) -> IntIterator:
+        return IntIterator()
+
+for x in IntIterable():
+    pass
+
+reveal_type(x)  # revealed: Unbound | int
+```
+
+## With previous definition
+
+```py
+class IntIterator:
+    def __next__(self) -> int:
+        return 42
+
+class IntIterable:
+    def __iter__(self) -> IntIterator:
+        return IntIterator()
+
+x = 'foo'
+
+for x in IntIterable():
+    pass
+
+reveal_type(x)  # revealed: Literal["foo"] | int
+```
+
+## With `else` (no break)
+
+```py
+class IntIterator:
+    def __next__(self) -> int:
+        return 42
+
+class IntIterable:
+    def __iter__(self) -> IntIterator:
+        return IntIterator()
+
+for x in IntIterable():
+    pass
+else:
+    x = 'foo'
+
+reveal_type(x)  # revealed: Literal["foo"]
+```
+
+## May `break`
+
+```py
+class IntIterator:
+    def __next__(self) -> int:
+        return 42
+
+class IntIterable:
+    def __iter__(self) -> IntIterator:
+        return IntIterator()
+
+for x in IntIterable():
+    if x > 5:
+        break
+else:
+    x = 'foo'
+
+reveal_type(x)  # revealed: int | Literal["foo"]
+```
+
+## With old-style iteration protocol
+
+```py
+class OldStyleIterable:
+    def __getitem__(self, key: int) -> int:
+        return 42
+
+for x in OldStyleIterable():
+    pass
+
+reveal_type(x)  # revealed: Unbound | int
+```
+
+## With heterogeneous tuple
+
+```py
+for x in (1, 'a', b'foo'):
+    pass
+
+reveal_type(x)  # revealed: Unbound | Literal[1] | Literal["a"] | Literal[b"foo"]
+```
+
+## With non-callable iterator
+
+```py
+class NotIterable:
+    if flag:
+        __iter__ = 1
+    else:
+        __iter__ = None
+
+for x in NotIterable(): # error: "Object of type `NotIterable` is not iterable"
+    pass
+
+reveal_type(x)  # revealed: Unbound | Unknown
+```
+
+## Invalid iterable
+
+```py
+nonsense = 123
+for x in nonsense: # error: "Object of type `Literal[123]` is not iterable"
+    pass
+```
+
+## New over old style iteration protocol
+
+```py
+class NotIterable:
+    def __getitem__(self, key: int) -> int:
+        return 42
+
+    __iter__ = None
+
+for x in NotIterable(): # error: "Object of type `NotIterable` is not iterable"
+    pass
+```

crates/red_knot_python_semantic/resources/mdtest/loops/iterators.md

@@ -0,0 +1,18 @@
+# Iterators
+
+## Yield must be iterable
+
+```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() # error: "Object of type `NotIterable` is not iterable"
+```

crates/red_knot_python_semantic/resources/mdtest/loops/while_loop.md

@@ -0,0 +1,43 @@
+# While loops
+
+## Basic While Loop
+
+```py
+x = 1
+while flag:
+    x = 2
+
+reveal_type(x)  # revealed: Literal[1, 2]
+```
+
+## While with else (no break)
+
+```py
+x = 1
+while flag:
+    x = 2
+else:
+    y = x
+    x = 3
+
+reveal_type(x)  # revealed: Literal[3]
+reveal_type(y)  # revealed: Literal[1, 2]
+```
+
+## While with Else (may break)
+
+```py
+x = 1
+y = 0
+while flag:
+    x = 2
+    if flag2:
+        y = 4
+        break
+else:
+    y = x
+    x = 3
+
+reveal_type(x)  # revealed: Literal[2, 3]
+reveal_type(y)  # revealed: Literal[1, 2, 4]
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals_is.md

@@ -0,0 +1,29 @@
+# Narrowing for `is` conditionals
+
+## `is None`
+
+```py
+x = None if flag else 1
+
+if x is None:
+    # TODO the following should be simplified to 'None'
+    reveal_type(x)  # revealed: None | Literal[1] & None
+
+reveal_type(x)  # revealed: None | Literal[1]
+```
+
+## `is` for other types
+
+```py
+class A:
+    ...
+
+x = A()
+y = x if flag else None
+
+if y is x:
+    # TODO the following should be simplified to 'A'
+    reveal_type(y)  # revealed: A | None & A
+
+reveal_type(y)  # revealed: A | None
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals_is_not.md

@@ -0,0 +1,39 @@
+# Narrowing for `is not` conditionals
+
+## `is not None`
+
+The type guard removes `None` from the union type:
+
+```py
+x = None if flag else 1
+
+if x is not None:
+    reveal_type(x)  # revealed: Literal[1]
+
+reveal_type(x)  # revealed: None | Literal[1]
+```
+
+## `is not` for other singleton types
+
+```py
+x = True if flag else False
+reveal_type(x)  # revealed: bool
+
+if x is not False:
+    # TODO the following should be `Literal[True]`
+    reveal_type(x)  # revealed: bool & ~Literal[False]
+```
+
+## `is not` for non-singleton types
+
+Non-singleton types should *not* narrow the type: two instances of a
+non-singleton class may occupy different addresses in memory even if
+they compare equal.
+
+```py
+x = 345
+y = 345
+
+if x is not y:
+    reveal_type(x)  # revealed: Literal[345]
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/match.md

@@ -0,0 +1,17 @@
+# Narrowing for `match` statements
+
+## Single `match` pattern
+
+```py
+x = None if flag else 1
+reveal_type(x)  # revealed: None | Literal[1]
+
+y = 0
+
+match x:
+    case None:
+        y = x
+
+# TODO intersection simplification: should be just Literal[0] | None
+reveal_type(y)  # revealed: Literal[0] | None | Literal[1] & None
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/not_none.md

@@ -0,0 +1,9 @@
+# `is not None` narrowing
+
+```py
+x = None if flag else 1
+if x is not None:
+    reveal_type(x)  # revealed: Literal[1]
+
+reveal_type(x)  # revealed: None | Literal[1]
+```

crates/red_knot_python_semantic/resources/mdtest/scopes/builtin.md

@@ -0,0 +1,32 @@
+# Builtin scope
+
+## Conditionally global or builtin
+
+If a builtin name is conditionally defined as a global, a name lookup should union the builtin type
+with the conditionally-defined type:
+
+```py
+def returns_bool() -> bool:
+    return True
+
+if returns_bool():
+    copyright = 1
+
+def f():
+    reveal_type(copyright)  # revealed: Literal[copyright] | Literal[1]
+```
+
+## Conditionally global or builtin, with annotation
+
+Same is true if the name is annotated:
+
+```py
+def returns_bool() -> bool:
+    return True
+
+if returns_bool():
+    copyright: int = 1
+
+def f():
+    reveal_type(copyright)  # revealed: Literal[copyright] | int
+```

crates/red_knot_python_semantic/resources/mdtest/shadowing/class.md

@@ -0,0 +1,17 @@
+# Classes shadowing
+
+## Implicit error
+
+```py
+class C: pass
+C = 1 # error: "Implicit shadowing of class `C`; annotate to make it explicit if this is intentional"
+```
+
+## Explicit
+
+No diagnostic is raised in the case of explicit shadowing:
+
+```py
+class C: pass
+C: int = 1
+```

crates/red_knot_python_semantic/resources/mdtest/shadowing/function.md

@@ -0,0 +1,24 @@
+# Function shadowing
+
+## Parameter
+
+Parameter `x` of type `str` is shadowed and reassigned with a new `int` value inside the function. No diagnostics should be generated.
+
+```py path=a.py
+def f(x: str):
+    x: int = int(x)
+```
+
+## Implicit error
+
+```py path=a.py
+def f(): pass
+f = 1 # error: "Implicit shadowing of function `f`; annotate to make it explicit if this is intentional"
+```
+
+## Explicit shadowing
+
+```py path=a.py
+def f(): pass
+f: int = 1
+```

crates/red_knot_python_semantic/resources/mdtest/shadowing/variable_declaration.md

@@ -0,0 +1,11 @@
+# Shadwing declaration
+
+## Shadow after incompatible declarations is OK
+
+```py
+if flag:
+    x: str
+else:
+    x: int
+x: bytes = b'foo'
+```

crates/red_knot_python_semantic/resources/mdtest/stubs/class.md

@@ -0,0 +1,10 @@
+# Class defenitions in stubs
+
+## Cyclical class definition
+
+In type stubs, classes can reference themselves in their base class definitions. For example, in `typeshed`, we have `class str(Sequence[str]): ...`.
+
+```py path=a.pyi
+class C(C): ...
+reveal_type(C)  # revealed: Literal[C]
+```

crates/red_knot_python_semantic/resources/mdtest/subscript/bytes.md

@@ -0,0 +1,15 @@
+# Bytes subscript
+
+## Simple
+
+```py
+w = b'red' b'knot'
+x = b'hello'
+y = b'world' + b'!'
+z = b'\xff\x00'
+
+reveal_type(w)  # revealed: Literal[b"redknot"]
+reveal_type(x)  # revealed: Literal[b"hello"]
+reveal_type(y)  # revealed: Literal[b"world!"]
+reveal_type(z)  # revealed: Literal[b"\xff\x00"]
+```

crates/red_knot_python_semantic/resources/mdtest/subscript/class.md

@@ -0,0 +1,92 @@
+# Class subscript
+
+## Class getitem unbound
+
+```py
+class NotSubscriptable: pass
+a = NotSubscriptable[0]  # error: "Cannot subscript object of type `Literal[NotSubscriptable]` with no `__class_getitem__` method"
+```
+
+## Class getitem
+
+```py
+class Identity:
+    def __class_getitem__(cls, item: int) -> str:
+        return item
+
+a = Identity[0]  
+reveal_type(a) # revealed: str
+```
+
+## Class getitem union
+
+```py
+flag = True
+
+class Identity:
+    if flag:
+        def __class_getitem__(cls, item: int) -> str:
+            return item
+    else:
+        def __class_getitem__(cls, item: int) -> int:
+            return item
+
+a = Identity[0]  
+reveal_type(a) # revealed: str | int
+```
+
+## Class getitem with class union
+
+```py
+flag = True
+
+class Identity1:
+    def __class_getitem__(cls, item: int) -> str:
+        return item
+
+class Identity2:
+    def __class_getitem__(cls, item: int) -> int:
+        return item
+
+if flag:
+    a = Identity1
+else:
+    a = Identity2
+
+b = a[0]
+reveal_type(a) # revealed: Literal[Identity1, Identity2]
+reveal_type(b) # revealed: str | int
+```
+
+## Class getitem with unbound method union
+
+```py
+flag = True
+
+if flag:
+    class Identity:
+        def __class_getitem__(self, x: int) -> str:
+            pass
+else:
+    class Identity: pass
+
+a = Identity[42] # error: [call-non-callable] "Method `__class_getitem__` of type `Literal[__class_getitem__] | Unbound` is not callable on object of type `Literal[Identity, Identity]`" 
+reveal_type(a) # revealed: str | Unknown 
+```
+
+## TODO: Class getitem non-class union
+
+```py
+flag = True
+
+if flag:
+    class Identity:
+        def __class_getitem__(self, x: int) -> str:
+            pass
+else:
+    Identity = 1
+
+a = Identity[42] # error: "Cannot subscript object of type `Literal[Identity] | Literal[1]` with no `__getitem__` method"
+# TODO: should _probably_ emit `str | Unknown` 
+reveal_type(a) # revealed: Unknown 
+```

crates/red_knot_python_semantic/resources/mdtest/subscript/instance.md

@@ -0,0 +1,45 @@
+# Instance subscript
+
+## Getitem unbound
+
+```py
+class NotSubscriptable: pass
+a = NotSubscriptable()[0]  # error: "Cannot subscript object of type `NotSubscriptable` with no `__getitem__` method"
+```
+
+## Getitem not callable
+
+```py
+class NotSubscriptable:
+    __getitem__ = None
+
+a = NotSubscriptable()[0]  # error: "Method `__getitem__` of type `None` is not callable on object of type `NotSubscriptable`"
+```
+
+## Valid getitem
+
+```py
+class Identity:
+    def __getitem__(self, index: int) -> int:
+        return index
+
+a = Identity()[0]  
+reveal_type(a) # revealed: int
+```
+
+## Getitem union
+
+```py
+flag = True
+
+class Identity:
+    if flag:
+        def __getitem__(self, index: int) -> int:
+            return index
+    else:
+        def __getitem__(self, index: int) -> str:
+            return str(index)
+
+a = Identity()[0]  
+reveal_type(a) # revealed: int | str
+```

crates/red_knot_python_semantic/resources/mdtest/subscript/lists.md

@@ -0,0 +1,33 @@
+# List subscripts
+
+## Indexing into lists
+
+A list can be indexed into with:
+
+- numbers
+- slices
+
+```py
+x = [1, 2, 3]
+reveal_type(x)  # revealed: list
+# TODO reveal int
+reveal_type(x[0])  # revealed: @Todo
+# TODO reveal list
+reveal_type(x[0:1])  # revealed: @Todo
+# TODO error
+reveal_type(x["a"])  # revealed: @Todo
+```
+
+## Assignments within list assignment
+
+In assignment, we might also have a named assignment.
+This should also get type checked.
+
+```py
+x = [1, 2, 3]
+x[0 if (y := 2) else 1] = 5
+# TODO error? (indeterminite index type)
+x["a" if (y := 2) else 1] = 6
+# TODO error (can't index via string)
+x["a" if (y := 2) else "b"] = 6
+```

crates/red_knot_python_semantic/resources/mdtest/subscript/string.md

@@ -0,0 +1,32 @@
+# Subscript on strings
+
+## Simple
+
+```py
+s = 'abcde'
+
+a = s[0]
+b = s[1]
+c = s[-1]
+d = s[-2]
+e = s[8]        # error: [index-out-of-bounds] "Index 8 is out of bounds for string `Literal["abcde"]` with length 5"
+f = s[-8]       # error: [index-out-of-bounds] "Index -8 is out of bounds for string `Literal["abcde"]` with length 5"
+
+reveal_type(a)  # revealed: Literal["a"]
+reveal_type(b)  # revealed: Literal["b"]
+reveal_type(c)  # revealed: Literal["e"]
+reveal_type(d)  # revealed: Literal["d"]
+reveal_type(e)  # revealed: Unknown
+reveal_type(f)  # revealed: Unknown
+```
+
+## Function return
+
+```py
+def add(x: int, y: int) -> int:
+    return x + y
+
+a = 'abcde'[add(0, 1)]
+# TODO: Support overloads... Should be `str`
+reveal_type(a)  # revealed: @Todo
+```

crates/red_knot_python_semantic/resources/mdtest/subscript/tuple.md

@@ -0,0 +1,21 @@
+# Tuple subscripts
+
+## Basic
+
+```py
+t = (1, 'a', 'b')
+
+a = t[0]
+b = t[1]
+c = t[-1]
+d = t[-2]
+e = t[4]        # error: [index-out-of-bounds]
+f = t[-4]       # error: [index-out-of-bounds]
+
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal["a"]
+reveal_type(c)  # revealed: Literal["b"]
+reveal_type(d)  # revealed: Literal["a"]
+reveal_type(e)  # revealed: Unknown
+reveal_type(f)  # revealed: Unknown
+```

crates/red_knot_python_semantic/resources/mdtest/unary/integers.md

@@ -0,0 +1,37 @@
+# Unary Operations
+
+## Unary Addition
+
+```py
+a = +0
+b = +1
+c = +True
+
+reveal_type(a)  # revealed: Literal[0]
+reveal_type(b)  # revealed: Literal[1]
+reveal_type(c)  # revealed: Literal[1]
+```
+
+## Unary Subtraction
+
+```py
+a = -0
+b = -1
+c = -True
+
+reveal_type(a)  # revealed: Literal[0]
+reveal_type(b)  # revealed: Literal[-1]
+reveal_type(c)  # revealed: Literal[-1]
+```
+
+## Unary Bitwise Inversion
+
+```py
+a = ~0
+b = ~1
+c = ~True
+
+reveal_type(a) # revealed: Literal[-1] 
+reveal_type(b) # revealed: Literal[-2]
+reveal_type(c) # revealed: Literal[-2]
+```

crates/red_knot_python_semantic/resources/mdtest/unary/not.md

@@ -0,0 +1,149 @@
+# Unary not
+
+## None
+
+```py
+a = not None
+b = not not None
+reveal_type(a)  # revealed: Literal[True]
+reveal_type(b)  # revealed: Literal[False]
+```
+
+## Function
+
+```py
+from typing import reveal_type
+
+def f():
+    return 1
+
+a = not f
+b = not reveal_type
+
+reveal_type(a)  # revealed: Literal[False]
+# TODO Unknown should not be part of the type of typing.reveal_type
+# reveal_type(b)  revealed: Literal[False]
+```
+
+## Module
+
+```py
+import b; import warnings
+
+x = not b
+z = not warnings
+
+reveal_type(x)  # revealed: Literal[False]
+reveal_type(z)  # revealed: Literal[False]
+```
+
+```py path=b.py
+y = 1
+```
+
+## Union
+
+```py
+if flag:
+    p = 1
+    q = 3.3
+    r = "hello"
+    s = "world"
+    t = 0
+else:
+    p = "hello"
+    q = 4
+    r = ""
+    s = 0
+    t = ""
+
+a = not p
+b = not q
+c = not r
+d = not s
+e = not t
+
+reveal_type(a)  # revealed: Literal[False]
+reveal_type(b)  # revealed: bool
+reveal_type(c)  # revealed: bool
+reveal_type(d)  # revealed: bool
+reveal_type(e)  # revealed: Literal[True]
+```
+
+## Integer literal
+
+```py
+a = not 1
+b = not 1234567890987654321
+e = not 0
+x = not -1
+y = not -1234567890987654321
+z = not --987
+
+reveal_type(a)  # revealed: Literal[False]
+reveal_type(b)  # revealed: Literal[False]
+reveal_type(e)  # revealed: Literal[True]
+reveal_type(x)  # revealed: Literal[False]
+reveal_type(y)  # revealed: Literal[False]
+reveal_type(z)  # revealed: Literal[False]
+```
+
+## Boolean literal
+
+```py
+w = True
+x = False
+y = not w
+z = not x
+
+reveal_type(w)  # revealed: Literal[True]
+reveal_type(x)  # revealed: Literal[False]
+reveal_type(y)  # revealed: Literal[False]
+reveal_type(z)  # revealed: Literal[True]
+```
+
+## String literal
+
+```py
+a = not "hello"
+b = not ""
+c = not "0"
+d = not "hello" + "world"
+
+reveal_type(a)  # revealed: Literal[False]
+reveal_type(b)  # revealed: Literal[True]
+reveal_type(c)  # revealed: Literal[False]
+reveal_type(d)  # revealed: Literal[False]
+```
+
+## Bytes literal
+
+```py
+a = not b"hello"
+b = not b""
+c = not b"0"
+d = not b"hello" + b"world"
+
+reveal_type(a)  # revealed: Literal[False]
+reveal_type(b)  # revealed: Literal[True]
+reveal_type(c)  # revealed: Literal[False]
+reveal_type(d)  # revealed: Literal[False]
+```
+
+## Tuple
+
+```py
+a = not (1,)
+b = not (1, 2)
+c = not (1, 2, 3)
+d = not ()
+e = not ("hello",)
+f = not (1, "hello")
+
+reveal_type(a)  # revealed: Literal[False]
+reveal_type(b)  # revealed: Literal[False]
+reveal_type(c)  # revealed: Literal[False]
+reveal_type(d)  # revealed: Literal[True]
+reveal_type(e)  # revealed: Literal[False]
+reveal_type(f)  # revealed: Literal[False]
+```

crates/red_knot_python_semantic/resources/mdtest/unpacking.md

@@ -0,0 +1,273 @@
+# Unpacking
+
+## Tuple
+
+### Simple tuple
+
+```py
+(a, b, c) = (1, 2, 3)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Literal[3]
+```
+
+### Simple list
+
+```py
+[a, b, c] = (1, 2, 3)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Literal[3]
+```
+
+### Simple mixed
+
+```py
+[a, (b, c), d] = (1, (2, 3), 4)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Literal[3]
+reveal_type(d)  # revealed: Literal[4]
+```
+
+### Multiple assignment
+
+```py
+a, b = c = 1, 2
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: tuple[Literal[1], Literal[2]]
+```
+
+### Nested tuple with unpacking
+
+```py
+(a, (b, c), d) = (1, (2, 3), 4)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Literal[3]
+reveal_type(d)  # revealed: Literal[4]
+```
+
+### Nested tuple without unpacking
+
+```py
+(a, b, c) = (1, (2, 3), 4)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: tuple[Literal[2], Literal[3]]
+reveal_type(c)  # revealed: Literal[4]
+```
+
+### Uneven unpacking (1)
+
+```py
+# TODO: Add diagnostic (there aren't enough values to unpack)
+(a, b, c) = (1, 2)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Unknown
+```
+
+### Uneven unpacking (2)
+
+```py
+# TODO: Add diagnostic (too many values to unpack)
+(a, b) = (1, 2, 3)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+```
+
+### Starred expression (1)
+
+```py
+# TODO: Add diagnostic (need more values to unpack)
+# TODO: Remove 'not-iterable' diagnostic
+[a, *b, c, d] = (1, 2)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+# TODO: Should be list[Any] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: Literal[2]
+reveal_type(d)  # revealed: Unknown
+```
+
+### Starred expression (2)
+
+```py
+[a, *b, c] = (1, 2)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+# TODO: Should be list[Any] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: Literal[2]
+```
+
+### Starred expression (3)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+[a, *b, c] = (1, 2, 3)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+# TODO: Should be list[int] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: Literal[3]
+```
+
+### Starred expression (4)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+[a, *b, c, d] = (1, 2, 3, 4, 5, 6)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+# TODO: Should be list[int] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: Literal[5]
+reveal_type(d)  # revealed: Literal[6]
+```
+
+### Starred expression (5)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+[a, b, *c] = (1, 2, 3, 4)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+# TODO: Should be list[int] once support for assigning to starred expression is added
+reveal_type(c)  # revealed: @Todo
+```
+
+### Non-iterable unpacking
+
+TODO: Remove duplicate diagnostics. This is happening because for a sequence-like
+assignment target, multiple definitions are created and the inference engine runs
+on each of them which results in duplicate diagnostics.
+
+```py
+# error: "Object of type `Literal[1]` is not iterable"
+# error: "Object of type `Literal[1]` is not iterable"
+a, b = 1
+reveal_type(a)  # revealed: Unknown
+reveal_type(b)  # revealed: Unknown
+```
+
+### Custom iterator unpacking
+
+```py
+class Iterator:
+    def __next__(self) -> int:
+        return 42
+
+
+class Iterable:
+    def __iter__(self) -> Iterator:
+        return Iterator()
+
+
+(a, b) = Iterable()
+reveal_type(a)  # revealed: int
+reveal_type(b)  # revealed: int
+```
+
+### Custom iterator unpacking nested
+
+```py
+class Iterator:
+    def __next__(self) -> int:
+        return 42
+
+
+class Iterable:
+    def __iter__(self) -> Iterator:
+        return Iterator()
+
+
+(a, (b, c), d) = (1, Iterable(), 2)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: int
+reveal_type(c)  # revealed: int
+reveal_type(d)  # revealed: Literal[2]
+```
+
+## String
+
+### Simple unpacking
+
+```py
+a, b = 'ab'
+reveal_type(a)  # revealed: LiteralString
+reveal_type(b)  # revealed: LiteralString
+```
+
+### Uneven unpacking (1)
+
+```py
+# TODO: Add diagnostic (there aren't enough values to unpack)
+a, b, c = 'ab'
+reveal_type(a)  # revealed: LiteralString
+reveal_type(b)  # revealed: LiteralString
+reveal_type(c)  # revealed: Unknown
+```
+
+### Uneven unpacking (2)
+
+```py
+# TODO: Add diagnostic (too many values to unpack)
+a, b = 'abc'
+reveal_type(a)  # revealed: LiteralString
+reveal_type(b)  # revealed: LiteralString
+```
+
+### Starred expression (1)
+
+```py
+# TODO: Add diagnostic (need more values to unpack)
+# TODO: Remove 'not-iterable' diagnostic
+(a, *b, c, d) = "ab"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: LiteralString
+reveal_type(d)  # revealed: Unknown
+```
+
+### Starred expression (2)
+
+```py
+(a, *b, c) = "ab"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+# TODO: Should be list[Any] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: LiteralString
+```
+
+### Starred expression (3)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+(a, *b, c) = "abc"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: LiteralString
+```
+
+### Starred expression (4)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+(a, *b, c, d) = "abcdef"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: LiteralString
+reveal_type(d)  # revealed: LiteralString
+```
+
+### Starred expression (5)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+(a, b, *c) = "abcd"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+reveal_type(b)  # revealed: LiteralString
+# TODO: Should be list[int] once support for assigning to starred expression is added
+reveal_type(c)  # revealed: @Todo
+```

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,

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))
-}

crates/red_knot_python_semantic/src/db.rs

@@ -11,7 +11,6 @@ pub trait Db: SourceDb + Upcast<dyn SourceDb> {
 pub(crate) mod tests {
     use std::sync::Arc;
 
-    use crate::module_resolver::vendored_typeshed_stubs;
     use ruff_db::files::{File, Files};
     use ruff_db::system::{DbWithTestSystem, System, TestSystem};
     use ruff_db::vendored::VendoredFileSystem;
@@ -33,7 +32,7 @@ pub(crate) mod tests {
             Self {
                 storage: salsa::Storage::default(),
                 system: TestSystem::default(),
-                vendored: vendored_typeshed_stubs().clone(),
+                vendored: red_knot_vendored::file_system().clone(),
                 events: std::sync::Arc::default(),
                 files: Files::default(),
             }

crates/red_knot_python_semantic/src/lib.rs

@@ -4,13 +4,12 @@ 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 module_resolver::{resolve_module, system_module_search_paths, Module};
+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 +18,8 @@ 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>>;

crates/red_knot_python_semantic/src/module_resolver/mod.rs

@@ -1,10 +1,9 @@
 use std::iter::FusedIterator;
 
-pub(crate) use module::Module;
+pub 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;
@@ -13,7 +12,6 @@ use resolver::SearchPathIterator;
 mod module;
 mod path;
 mod resolver;
-mod state;
 mod typeshed;
 
 #[cfg(test)]

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.
 ///
@@ -59,8 +59,12 @@ impl ModulePath {
         self.relative_path.push(component);
     }
 
+    pub(crate) fn pop(&mut self) -> bool {
+        self.relative_path.pop()
+    }
+
     #[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 +78,7 @@ 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 +88,7 @@ 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 +100,7 @@ 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 +117,7 @@ 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 +128,7 @@ 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 +140,7 @@ 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 +154,7 @@ 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 +163,7 @@ 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 +277,15 @@ 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 +293,7 @@ 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 +304,20 @@ 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 +327,16 @@ 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 +351,18 @@ 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 +405,10 @@ 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 +427,22 @@ 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 +633,11 @@ 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 +648,6 @@ 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 +662,7 @@ 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 +670,7 @@ 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 +781,7 @@ 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 +793,7 @@ 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 +825,7 @@ 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 +873,7 @@ 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 +898,7 @@ 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 +926,7 @@ 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 +948,7 @@ 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 +964,7 @@ 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 +980,7 @@ 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 +1001,7 @@ 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 +1029,7 @@ 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 +1058,7 @@ 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 +1082,7 @@ 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");

crates/red_knot_python_semantic/src/module_resolver/resolver.rs

@@ -4,19 +4,20 @@ use std::iter::FusedIterator;
 use rustc_hash::{FxBuildHasher, FxHashSet};
 
 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 crate::db::Db;
 use crate::module_name::ModuleName;
-use crate::{Program, SearchPathSettings};
+use crate::module_resolver::typeshed::{vendored_typeshed_versions, TypeshedVersions};
+use crate::site_packages::VirtualEnvironment;
+use crate::{Program, PythonVersion, SearchPathSettings, SitePackages};
 
 use super::module::{Module, ModuleKind};
 use super::path::{ModulePath, SearchPath, SearchPathValidationError};
-use super::state::ResolverState;
 
 /// Resolves a module name to a module.
-pub fn resolve_module(db: &dyn Db, module_name: ModuleName) -> Option<Module> {
+pub fn resolve_module(db: &dyn Db, module_name: &ModuleName) -> Option<Module> {
     let interned_name = ModuleNameIngredient::new(db, module_name);
 
     resolve_module_query(db, interned_name)
@@ -35,14 +36,14 @@ pub(crate) fn resolve_module_query<'db>(
     let _span = tracing::trace_span!("resolve_module", %name).entered();
 
     let Some((search_path, module_file, kind)) = resolve_name(db, name) else {
-        tracing::debug!("Module '{name}' not found in the search paths.");
+        tracing::debug!("Module `{name}` not found in search paths");
         return None;
     };
 
     let module = Module::new(name.clone(), kind, search_path, module_file);
 
     tracing::trace!(
-        "Resolved module '{name}' to '{path}'.",
+        "Resolved module `{name}` to `{path}`",
         path = module_file.path(db)
     );
 
@@ -102,7 +103,7 @@ pub(crate) fn file_to_module(db: &dyn Db, file: File) -> Option<Module> {
     // If it doesn't, then that means that multiple modules have the same name in different
     // root paths, but that the module corresponding to `path` is in a lower priority search path,
     // in which case we ignore it.
-    let module = resolve_module(db, module_name)?;
+    let module = resolve_module(db, &module_name)?;
 
     if file == module.file() {
         Some(module)
@@ -122,7 +123,7 @@ pub(crate) fn search_paths(db: &dyn Db) -> SearchPathIterator {
     Program::get(db).search_paths(db).iter(db)
 }
 
-#[derive(Debug, PartialEq, Eq, Default)]
+#[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.
@@ -135,6 +136,8 @@ pub(crate) struct SearchPaths {
     /// 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: TypeshedVersions,
 }
 
 impl SearchPaths {
@@ -146,8 +149,14 @@ impl SearchPaths {
     /// [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,
+        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,
@@ -161,45 +170,65 @@ impl SearchPaths {
         let mut static_paths = vec![];
 
         for path in extra_paths {
-            tracing::debug!("Adding static extra search-path '{path}'");
+            let path = canonicalize(path, system);
+            files.try_add_root(db.upcast(), &path, FileRootKind::LibrarySearchPath);
+            tracing::debug!("Adding extra search-path '{path}'");
 
-            let search_path = SearchPath::extra(system, path)?;
-            files.try_add_root(
-                db.upcast(),
-                search_path.as_system_path().unwrap(),
-                FileRootKind::LibrarySearchPath,
-            );
-            static_paths.push(search_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)?);
+        static_paths.push(SearchPath::first_party(system, src_root.to_path_buf())?);
 
-        static_paths.push(if let Some(custom_typeshed) = custom_typeshed {
+        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}'");
 
-            let search_path = SearchPath::custom_stdlib(db, custom_typeshed)?;
             files.try_add_root(
                 db.upcast(),
-                search_path.as_system_path().unwrap(),
+                &custom_typeshed,
                 FileRootKind::LibrarySearchPath,
             );
-            search_path
+
+            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)?;
+
+            (parsed, search_path)
         } else {
-            SearchPath::vendored_stdlib()
-        });
+            tracing::debug!("Using vendored stdlib");
+            (
+                vendored_typeshed_versions(db),
+                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}'");
-            let search_path = SearchPath::site_packages(system, path)?;
-            files.try_add_root(
-                db.upcast(),
-                search_path.as_system_path().unwrap(),
-                FileRootKind::LibrarySearchPath,
-            );
-            site_packages.push(search_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
@@ -224,16 +253,31 @@ impl SearchPaths {
         Ok(SearchPaths {
             static_paths,
             site_packages,
+            typeshed_versions,
         })
     }
 
-    pub(crate) fn iter<'a>(&'a self, db: &'a dyn Db) -> SearchPathIterator<'a> {
+    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
+    }
 }
 
 /// Collect all dynamic search paths. For each `site-packages` path:
@@ -251,6 +295,7 @@ pub(crate) fn dynamic_resolution_paths(db: &dyn Db) -> Vec<SearchPath> {
     let SearchPaths {
         static_paths,
         site_packages,
+        typeshed_versions: _,
     } = Program::get(db).search_paths(db);
 
     let mut dynamic_paths = Vec::new();
@@ -279,7 +324,7 @@ pub(crate) fn dynamic_resolution_paths(db: &dyn Db) -> Vec<SearchPath> {
 
         let site_packages_root = files
             .root(db.upcast(), site_packages_dir)
-            .expect("Site-package root to have been created.");
+            .expect("Site-package root to have been created");
 
         // This query needs to be re-executed each time a `.pth` file
         // is added, modified or removed from the `site-packages` directory.
@@ -315,12 +360,16 @@ 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 = search_path.as_system_path().unwrap()
+                            path = installation
                         );
                         dynamic_paths.push(search_path);
                     }
@@ -482,7 +531,7 @@ struct ModuleNameIngredient<'db> {
 fn resolve_name(db: &dyn Db, name: &ModuleName) -> Option<(SearchPath, File, ModuleKind)> {
     let program = Program::get(db);
     let target_version = program.target_version(db);
-    let resolver_state = ResolverState::new(db, target_version);
+    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());
 
@@ -504,24 +553,16 @@ fn resolve_name(db: &dyn Db, name: &ModuleName) -> Option<(SearchPath, File, Mod
 
                 package_path.push(module_name);
 
-                // Must be a `__init__.pyi` or `__init__.py` or it isn't a package.
-                let kind = if package_path.is_directory(&resolver_state) {
-                    package_path.push("__init__");
-                    ModuleKind::Package
-                } else {
-                    ModuleKind::Module
-                };
-
-                // TODO Implement full https://peps.python.org/pep-0561/#type-checker-module-resolution-order resolution
-                if let Some(stub) = package_path.with_pyi_extension().to_file(&resolver_state) {
-                    return Some((search_path.clone(), stub, kind));
+                // Check for a regular package first (highest priority)
+                package_path.push("__init__");
+                if let Some(regular_package) = resolve_file_module(&package_path, &resolver_state) {
+                    return Some((search_path.clone(), regular_package, ModuleKind::Package));
                 }
 
-                if let Some(module) = package_path
-                    .with_py_extension()
-                    .and_then(|path| path.to_file(&resolver_state))
-                {
-                    return Some((search_path.clone(), module, kind));
+                // Check for a file module next
+                package_path.pop();
+                if let Some(file_module) = resolve_file_module(&package_path, &resolver_state) {
+                    return Some((search_path.clone(), file_module, ModuleKind::Module));
                 }
 
                 // For regular packages, don't search the next search path. All files of that
@@ -542,10 +583,27 @@ fn resolve_name(db: &dyn Db, name: &ModuleName) -> Option<(SearchPath, File, Mod
     None
 }
 
+/// If `module` exists on disk with either a `.pyi` or `.py` extension,
+/// return the [`File`] corresponding to that path.
+///
+/// `.pyi` files take priority, as they always have priority when
+/// resolving modules.
+fn resolve_file_module(module: &ModulePath, resolver_state: &ResolverContext) -> Option<File> {
+    // Stubs have precedence over source files
+    module
+        .with_pyi_extension()
+        .to_file(resolver_state)
+        .or_else(|| {
+            module
+                .with_py_extension()
+                .and_then(|path| path.to_file(resolver_state))
+        })
+}
+
 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>,
@@ -568,7 +626,10 @@ where
 
         if is_regular_package {
             in_namespace_package = false;
-        } else if package_path.is_directory(resolver_state) {
+        } else if package_path.is_directory(resolver_state)
+            // Pure modules hide namespace packages with the same name
+            && resolve_file_module(&package_path, resolver_state).is_none()
+        {
             // A directory without an `__init__.py` is a namespace package, continue with the next folder.
             in_namespace_package = true;
         } else if in_namespace_package {
@@ -627,6 +688,21 @@ 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};
@@ -652,11 +728,11 @@ mod tests {
             .build();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
 
         assert_eq!(
             Some(&foo_module),
-            resolve_module(&db, foo_module_name.clone()).as_ref()
+            resolve_module(&db, &foo_module_name).as_ref()
         );
 
         assert_eq!("foo", foo_module.name());
@@ -679,7 +755,7 @@ mod tests {
             .build();
 
         let builtins_module_name = ModuleName::new_static("builtins").unwrap();
-        let builtins = resolve_module(&db, builtins_module_name).expect("builtins to resolve");
+        let builtins = resolve_module(&db, &builtins_module_name).expect("builtins to resolve");
 
         assert_eq!(builtins.file().path(&db), &stdlib.join("builtins.pyi"));
     }
@@ -700,7 +776,7 @@ mod tests {
             .build();
 
         let builtins_module_name = ModuleName::new_static("builtins").unwrap();
-        let builtins = resolve_module(&db, builtins_module_name).expect("builtins to resolve");
+        let builtins = resolve_module(&db, &builtins_module_name).expect("builtins to resolve");
 
         assert_eq!(builtins.file().path(&db), &stdlib.join("builtins.pyi"));
     }
@@ -718,11 +794,11 @@ mod tests {
             .build();
 
         let functools_module_name = ModuleName::new_static("functools").unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
 
         assert_eq!(
             Some(&functools_module),
-            resolve_module(&db, functools_module_name).as_ref()
+            resolve_module(&db, &functools_module_name).as_ref()
         );
 
         assert_eq!(&stdlib, functools_module.search_path());
@@ -772,7 +848,7 @@ mod tests {
 
         let existing_modules = create_module_names(&["asyncio", "functools", "xml.etree"]);
         for module_name in existing_modules {
-            let resolved_module = resolve_module(&db, module_name.clone()).unwrap_or_else(|| {
+            let resolved_module = resolve_module(&db, &module_name).unwrap_or_else(|| {
                 panic!("Expected module {module_name} to exist in the mock stdlib")
             });
             let search_path = resolved_module.search_path();
@@ -781,7 +857,7 @@ 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:?}"
             );
         }
@@ -825,7 +901,7 @@ mod tests {
 
         for module_name in nonexisting_modules {
             assert!(
-                resolve_module(&db, module_name.clone()).is_none(),
+                resolve_module(&db, &module_name).is_none(),
                 "Unexpectedly resolved a module for {module_name}"
             );
         }
@@ -868,7 +944,7 @@ mod tests {
         ]);
 
         for module_name in existing_modules {
-            let resolved_module = resolve_module(&db, module_name.clone()).unwrap_or_else(|| {
+            let resolved_module = resolve_module(&db, &module_name).unwrap_or_else(|| {
                 panic!("Expected module {module_name} to exist in the mock stdlib")
             });
             let search_path = resolved_module.search_path();
@@ -877,7 +953,7 @@ 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:?}"
             );
         }
@@ -904,7 +980,7 @@ mod tests {
         let nonexisting_modules = create_module_names(&["importlib", "xml", "xml.etree"]);
         for module_name in nonexisting_modules {
             assert!(
-                resolve_module(&db, module_name.clone()).is_none(),
+                resolve_module(&db, &module_name).is_none(),
                 "Unexpectedly resolved a module for {module_name}"
             );
         }
@@ -926,11 +1002,11 @@ mod tests {
             .build();
 
         let functools_module_name = ModuleName::new_static("functools").unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
 
         assert_eq!(
             Some(&functools_module),
-            resolve_module(&db, functools_module_name).as_ref()
+            resolve_module(&db, &functools_module_name).as_ref()
         );
         assert_eq!(&src, functools_module.search_path());
         assert_eq!(ModuleKind::Module, functools_module.kind());
@@ -950,7 +1026,7 @@ mod tests {
             .build();
 
         let pydoc_data_topics_name = ModuleName::new_static("pydoc_data.topics").unwrap();
-        let pydoc_data_topics = resolve_module(&db, pydoc_data_topics_name).unwrap();
+        let pydoc_data_topics = resolve_module(&db, &pydoc_data_topics_name).unwrap();
 
         assert_eq!("pydoc_data.topics", pydoc_data_topics.name());
         assert_eq!(pydoc_data_topics.search_path(), &stdlib);
@@ -967,7 +1043,7 @@ mod tests {
             .build();
 
         let foo_path = src.join("foo/__init__.py");
-        let foo_module = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
+        let foo_module = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
 
         assert_eq!("foo", foo_module.name());
         assert_eq!(&src, foo_module.search_path());
@@ -994,7 +1070,7 @@ mod tests {
 
         let TestCase { db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
 
-        let foo_module = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
+        let foo_module = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
         let foo_init_path = src.join("foo/__init__.py");
 
         assert_eq!(&src, foo_module.search_path());
@@ -1011,13 +1087,32 @@ mod tests {
         );
     }
 
+    #[test]
+    fn single_file_takes_priority_over_namespace_package() {
+        //const SRC: &[FileSpec] = &[("foo.py", "x = 1")];
+        const SRC: &[FileSpec] = &[("foo.py", "x = 1"), ("foo/bar.py", "x = 2")];
+
+        let TestCase { db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
+
+        let foo_module_name = ModuleName::new_static("foo").unwrap();
+        let foo_bar_module_name = ModuleName::new_static("foo.bar").unwrap();
+
+        // `foo.py` takes priority over the `foo` namespace package
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
+        assert_eq!(foo_module.file().path(&db), &src.join("foo.py"));
+
+        // `foo.bar` isn't recognised as a module
+        let foo_bar_module = resolve_module(&db, &foo_bar_module_name);
+        assert_eq!(foo_bar_module, None);
+    }
+
     #[test]
     fn typing_stub_over_module() {
         const SRC: &[FileSpec] = &[("foo.py", "print('Hello, world!')"), ("foo.pyi", "x: int")];
 
         let TestCase { db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
 
-        let foo = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
+        let foo = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
         let foo_stub = src.join("foo.pyi");
 
         assert_eq!(&src, foo.search_path());
@@ -1041,7 +1136,7 @@ mod tests {
         let TestCase { db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
 
         let baz_module =
-            resolve_module(&db, ModuleName::new_static("foo.bar.baz").unwrap()).unwrap();
+            resolve_module(&db, &ModuleName::new_static("foo.bar.baz").unwrap()).unwrap();
         let baz_path = src.join("foo/bar/baz.py");
 
         assert_eq!(&src, baz_module.search_path());
@@ -1080,14 +1175,14 @@ mod tests {
         let one_module_name = ModuleName::new_static("parent.child.one").unwrap();
         let one_module_path = FilePath::System(src.join("parent/child/one.py"));
         assert_eq!(
-            resolve_module(&db, one_module_name),
+            resolve_module(&db, &one_module_name),
             path_to_module(&db, &one_module_path)
         );
 
         let two_module_name = ModuleName::new_static("parent.child.two").unwrap();
         let two_module_path = FilePath::System(site_packages.join("parent/child/two.py"));
         assert_eq!(
-            resolve_module(&db, two_module_name),
+            resolve_module(&db, &two_module_name),
             path_to_module(&db, &two_module_path)
         );
     }
@@ -1120,12 +1215,12 @@ mod tests {
 
         let one_module_path = FilePath::System(src.join("parent/child/one.py"));
         let one_module_name =
-            resolve_module(&db, ModuleName::new_static("parent.child.one").unwrap());
+            resolve_module(&db, &ModuleName::new_static("parent.child.one").unwrap());
         assert_eq!(one_module_name, path_to_module(&db, &one_module_path));
 
         assert_eq!(
             None,
-            resolve_module(&db, ModuleName::new_static("parent.child.two").unwrap())
+            resolve_module(&db, &ModuleName::new_static("parent.child.two").unwrap())
         );
     }
 
@@ -1141,7 +1236,7 @@ mod tests {
             .with_site_packages_files(&[("foo.py", "")])
             .build();
 
-        let foo_module = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
+        let foo_module = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
         let foo_src_path = src.join("foo.py");
 
         assert_eq!(&src, foo_module.search_path());
@@ -1194,20 +1289,20 @@ mod tests {
 
         Program::from_settings(
             &db,
-            ProgramSettings {
+            &ProgramSettings {
                 target_version: PythonVersion::PY38,
                 search_paths: SearchPathSettings {
                     extra_paths: vec![],
                     src_root: src.clone(),
                     custom_typeshed: Some(custom_typeshed.clone()),
-                    site_packages: vec![site_packages],
+                    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();
+        let foo_module = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
+        let bar_module = resolve_module(&db, &ModuleName::new_static("bar").unwrap()).unwrap();
 
         assert_ne!(foo_module, bar_module);
 
@@ -1242,7 +1337,7 @@ mod tests {
             .build();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
 
         let bar_path = src.join("bar.py");
         let bar = system_path_to_file(&db, &bar_path).expect("bar.py to exist");
@@ -1256,7 +1351,7 @@ mod tests {
         // Re-query the foo module. The foo module should still be cached because `bar.py` isn't relevant
         // for resolving `foo`.
 
-        let foo_module2 = resolve_module(&db, foo_module_name);
+        let foo_module2 = resolve_module(&db, &foo_module_name);
 
         assert!(!db
             .take_salsa_events()
@@ -1273,14 +1368,14 @@ mod tests {
         let foo_path = src.join("foo.py");
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        assert_eq!(resolve_module(&db, foo_module_name.clone()), None);
+        assert_eq!(resolve_module(&db, &foo_module_name), None);
 
         // Now write the foo file
         db.write_file(&foo_path, "x = 1")?;
 
         let foo_file = system_path_to_file(&db, &foo_path).expect("foo.py to exist");
 
-        let foo_module = resolve_module(&db, foo_module_name).expect("Foo module to resolve");
+        let foo_module = resolve_module(&db, &foo_module_name).expect("Foo module to resolve");
         assert_eq!(foo_file, foo_module.file());
 
         Ok(())
@@ -1294,7 +1389,7 @@ mod tests {
         let TestCase { mut db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).expect("foo module to exist");
+        let foo_module = resolve_module(&db, &foo_module_name).expect("foo module to exist");
         let foo_init_path = src.join("foo/__init__.py");
 
         assert_eq!(&foo_init_path, foo_module.file().path(&db));
@@ -1306,7 +1401,7 @@ mod tests {
         File::sync_path(&mut db, &foo_init_path);
         File::sync_path(&mut db, foo_init_path.parent().unwrap());
 
-        let foo_module = resolve_module(&db, foo_module_name).expect("Foo module to resolve");
+        let foo_module = resolve_module(&db, &foo_module_name).expect("Foo module to resolve");
         assert_eq!(&src.join("foo.py"), foo_module.file().path(&db));
 
         Ok(())
@@ -1332,7 +1427,7 @@ mod tests {
         let functools_module_name = ModuleName::new_static("functools").unwrap();
         let stdlib_functools_path = stdlib.join("functools.pyi");
 
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &stdlib);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1345,7 +1440,7 @@ mod tests {
         let site_packages_functools_path = site_packages.join("functools.py");
         db.write_file(&site_packages_functools_path, "f: int")
             .unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         let events = db.take_salsa_events();
         assert_function_query_was_not_run(
             &db,
@@ -1378,7 +1473,7 @@ mod tests {
             .build();
 
         let functools_module_name = ModuleName::new_static("functools").unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &stdlib);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1389,7 +1484,7 @@ mod tests {
         // since first-party files take higher priority in module resolution:
         let src_functools_path = src.join("functools.py");
         db.write_file(&src_functools_path, "FOO: int").unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &src);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1420,7 +1515,7 @@ mod tests {
         let functools_module_name = ModuleName::new_static("functools").unwrap();
         let src_functools_path = src.join("functools.py");
 
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &src);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1433,7 +1528,7 @@ mod tests {
             .remove_file(&src_functools_path)
             .unwrap();
         File::sync_path(&mut db, &src_functools_path);
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &stdlib);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1455,8 +1550,8 @@ mod tests {
         let foo_module_name = ModuleName::new_static("foo").unwrap();
         let foo_bar_module_name = ModuleName::new_static("foo.bar").unwrap();
 
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
-        let foo_bar_module = resolve_module(&db, foo_bar_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
+        let foo_bar_module = resolve_module(&db, &foo_bar_module_name).unwrap();
 
         assert_eq!(
             foo_module.file().path(&db),
@@ -1484,11 +1579,11 @@ mod tests {
 
         // Lines with leading whitespace in `.pth` files do not parse:
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        assert_eq!(resolve_module(&db, foo_module_name), None);
+        assert_eq!(resolve_module(&db, &foo_module_name), None);
 
         // Lines with trailing whitespace in `.pth` files do:
         let bar_module_name = ModuleName::new_static("bar").unwrap();
-        let bar_module = resolve_module(&db, bar_module_name.clone()).unwrap();
+        let bar_module = resolve_module(&db, &bar_module_name).unwrap();
         assert_eq!(
             bar_module.file().path(&db),
             &FilePath::system("/y/src/bar.py")
@@ -1507,7 +1602,7 @@ mod tests {
             .build();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
 
         assert_eq!(
             foo_module.file().path(&db),
@@ -1555,10 +1650,10 @@ not_a_directory
         let b_module_name = ModuleName::new_static("b").unwrap();
         let spam_module_name = ModuleName::new_static("spam").unwrap();
 
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
-        let a_module = resolve_module(&db, a_module_name.clone()).unwrap();
-        let b_module = resolve_module(&db, b_module_name.clone()).unwrap();
-        let spam_module = resolve_module(&db, spam_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
+        let a_module = resolve_module(&db, &a_module_name).unwrap();
+        let b_module = resolve_module(&db, &b_module_name).unwrap();
+        let spam_module = resolve_module(&db, &spam_module_name).unwrap();
 
         assert_eq!(
             foo_module.file().path(&db),
@@ -1586,14 +1681,14 @@ not_a_directory
         let foo_module_name = ModuleName::new_static("foo").unwrap();
         let bar_module_name = ModuleName::new_static("bar").unwrap();
 
-        let foo_module = resolve_module(&db, foo_module_name).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
         assert_eq!(
             foo_module.file().path(&db),
             &FilePath::system("/x/src/foo.py")
         );
 
         db.clear_salsa_events();
-        let bar_module = resolve_module(&db, bar_module_name).unwrap();
+        let bar_module = resolve_module(&db, &bar_module_name).unwrap();
         assert_eq!(
             bar_module.file().path(&db),
             &FilePath::system("/y/src/bar.py")
@@ -1618,7 +1713,7 @@ not_a_directory
         db.write_files(x_directory).unwrap();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
         assert_eq!(
             foo_module.file().path(&db),
             &FilePath::system("/x/src/foo.py")
@@ -1630,7 +1725,7 @@ not_a_directory
 
         File::sync_path(&mut db, &site_packages.join("_foo.pth"));
 
-        assert_eq!(resolve_module(&db, foo_module_name.clone()), None);
+        assert_eq!(resolve_module(&db, &foo_module_name), None);
     }
 
     #[test]
@@ -1645,7 +1740,7 @@ not_a_directory
         db.write_files(x_directory).unwrap();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
         let src_path = SystemPathBuf::from("/x/src");
         assert_eq!(
             foo_module.file().path(&db),
@@ -1658,7 +1753,7 @@ not_a_directory
         db.memory_file_system().remove_directory(&src_path).unwrap();
         File::sync_path(&mut db, &src_path.join("foo.py"));
         File::sync_path(&mut db, &src_path);
-        assert_eq!(resolve_module(&db, foo_module_name.clone()), None);
+        assert_eq!(resolve_module(&db, &foo_module_name), None);
     }
 
     #[test]
@@ -1699,13 +1794,16 @@ not_a_directory
 
         Program::from_settings(
             &db,
-            ProgramSettings {
+            &ProgramSettings {
                 target_version: PythonVersion::default(),
                 search_paths: SearchPathSettings {
                     extra_paths: vec![],
                     src_root: SystemPathBuf::from("/src"),
                     custom_typeshed: None,
-                    site_packages: vec![venv_site_packages, system_site_packages],
+                    site_packages: SitePackages::Known(vec![
+                        venv_site_packages,
+                        system_site_packages,
+                    ]),
                 },
             },
         )
@@ -1714,7 +1812,7 @@ not_a_directory
         // The editable installs discovered from the `.pth` file in the first `site-packages` directory
         // take precedence over the second `site-packages` directory...
         let a_module_name = ModuleName::new_static("a").unwrap();
-        let a_module = resolve_module(&db, a_module_name.clone()).unwrap();
+        let a_module = resolve_module(&db, &a_module_name).unwrap();
         assert_eq!(a_module.file().path(&db), &editable_install_location);
 
         db.memory_file_system()
@@ -1725,7 +1823,7 @@ not_a_directory
         // ...But now that the `.pth` file in the first `site-packages` directory has been deleted,
         // the editable install no longer exists, so the module now resolves to the file in the
         // second `site-packages` directory
-        let a_module = resolve_module(&db, a_module_name).unwrap();
+        let a_module = resolve_module(&db, &a_module_name).unwrap();
         assert_eq!(a_module.file().path(&db), &system_site_packages_location);
     }
 }

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()
-    }
-}

crates/red_knot_python_semantic/src/module_resolver/testing.rs

@@ -4,7 +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;
+use crate::{ProgramSettings, SitePackages};
 
 /// A test case for the module resolver.
 ///
@@ -179,6 +179,7 @@ impl TestCaseBuilder<UnspecifiedTypeshed> {
             first_party_files,
             site_packages_files,
         } = self;
+
         TestCaseBuilder {
             typeshed_option: typeshed,
             target_version,
@@ -195,6 +196,7 @@ impl TestCaseBuilder<UnspecifiedTypeshed> {
             site_packages,
             target_version,
         } = self.with_custom_typeshed(MockedTypeshed::default()).build();
+
         TestCase {
             db,
             src,
@@ -223,13 +225,13 @@ impl TestCaseBuilder<MockedTypeshed> {
 
         Program::from_settings(
             &db,
-            ProgramSettings {
+            &ProgramSettings {
                 target_version,
                 search_paths: SearchPathSettings {
                     extra_paths: vec![],
                     src_root: src.clone(),
                     custom_typeshed: Some(typeshed.clone()),
-                    site_packages: vec![site_packages.clone()],
+                    site_packages: SitePackages::Known(vec![site_packages.clone()]),
                 },
             },
         )
@@ -279,13 +281,11 @@ impl TestCaseBuilder<VendoredTypeshed> {
 
         Program::from_settings(
             &db,
-            ProgramSettings {
+            &ProgramSettings {
                 target_version,
                 search_paths: SearchPathSettings {
-                    extra_paths: vec![],
-                    src_root: src.clone(),
-                    custom_typeshed: None,
-                    site_packages: vec![site_packages.clone()],
+                    site_packages: SitePackages::Known(vec![site_packages.clone()]),
+                    ..SearchPathSettings::new(src.clone())
                 },
             },
         )

crates/red_knot_python_semantic/src/module_resolver/typeshed.rs

@@ -1,92 +1,27 @@
-use std::cell::OnceCell;
 use std::collections::BTreeMap;
 use std::fmt;
 use std::num::{NonZeroU16, NonZeroUsize};
 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;
+use crate::{Program, 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()
-}
-
-static VENDORED_VERSIONS: Lazy<TypeshedVersions> = Lazy::new(|| {
+pub(in crate::module_resolver) fn vendored_typeshed_versions(db: &dyn Db) -> TypeshedVersions {
     TypeshedVersions::from_str(
-        &vendored_typeshed_stubs()
+        &db.vendored()
             .read_to_string("stdlib/VERSIONS")
-            .unwrap(),
+            .expect("The vendored typeshed stubs should contain a VERSIONS file"),
     )
-    .unwrap()
-});
+    .expect("The VERSIONS file in the vendored typeshed stubs should be well-formed")
+}
+
+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 {
@@ -174,7 +109,7 @@ impl TypeshedVersions {
     }
 
     #[must_use]
-    fn query_module(
+    pub(in crate::module_resolver) fn query_module(
         &self,
         module: &ModuleName,
         target_version: PythonVersion,
@@ -204,7 +139,7 @@ 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 {
@@ -391,6 +326,8 @@ mod tests {
 
     use insta::assert_snapshot;
 
+    use crate::db::tests::TestDb;
+
     use super::*;
 
     const TYPESHED_STDLIB_DIR: &str = "stdlib";
@@ -412,12 +349,9 @@ mod tests {
 
     #[test]
     fn can_parse_vendored_versions_file() {
-        let versions_data = include_str!(concat!(
-            env!("CARGO_MANIFEST_DIR"),
-            "/vendor/typeshed/stdlib/VERSIONS"
-        ));
+        let db = TestDb::new();
 
-        let versions = TypeshedVersions::from_str(versions_data).unwrap();
+        let versions = vendored_typeshed_versions(&db);
         assert!(versions.len() > 100);
         assert!(versions.len() < 1000);
 
@@ -454,9 +388,10 @@ mod tests {
 
     #[test]
     fn typeshed_versions_consistent_with_vendored_stubs() {
-        const VERSIONS_DATA: &str = include_str!("../../../vendor/typeshed/stdlib/VERSIONS");
-        let vendored_typeshed_dir = Path::new("vendor/typeshed").canonicalize().unwrap();
-        let vendored_typeshed_versions = TypeshedVersions::from_str(VERSIONS_DATA).unwrap();
+        let db = TestDb::new();
+        let vendored_typeshed_versions = vendored_typeshed_versions(&db);
+        let vendored_typeshed_dir =
+            Path::new(env!("CARGO_MANIFEST_DIR")).join("../red_knot_vendored/vendor/typeshed");
 
         let mut empty_iterator = true;
 

crates/red_knot_python_semantic/src/module_resolver/typeshed/mod.rs

@@ -1,8 +0,0 @@
-pub use self::vendored::vendored_typeshed_stubs;
-pub(super) use self::versions::{
-    parse_typeshed_versions, LazyTypeshedVersions, TypeshedVersionsParseError,
-    TypeshedVersionsQueryResult,
-};
-
-mod vendored;
-mod versions;

crates/red_knot_python_semantic/src/program.rs

@@ -3,7 +3,7 @@ use anyhow::Context;
 use salsa::Durability;
 use salsa::Setter;
 
-use ruff_db::system::SystemPathBuf;
+use ruff_db::system::{SystemPath, SystemPathBuf};
 
 use crate::module_resolver::SearchPaths;
 use crate::Db;
@@ -12,13 +12,12 @@ use crate::Db;
 pub struct Program {
     pub target_version: PythonVersion,
 
-    #[default]
     #[return_ref]
     pub(crate) search_paths: SearchPaths,
 }
 
 impl Program {
-    pub fn from_settings(db: &dyn Db, settings: ProgramSettings) -> anyhow::Result<Self> {
+    pub fn from_settings(db: &dyn Db, settings: &ProgramSettings) -> anyhow::Result<Self> {
         let ProgramSettings {
             target_version,
             search_paths,
@@ -29,16 +28,15 @@ impl Program {
         let search_paths = SearchPaths::from_settings(db, search_paths)
             .with_context(|| "Invalid search path settings")?;
 
-        Ok(Program::builder(settings.target_version)
+        Ok(Program::builder(settings.target_version, search_paths)
             .durability(Durability::HIGH)
-            .search_paths(search_paths)
             .new(db))
     }
 
     pub fn update_search_paths(
-        &self,
+        self,
         db: &mut dyn Db,
-        search_path_settings: SearchPathSettings,
+        search_path_settings: &SearchPathSettings,
     ) -> anyhow::Result<()> {
         let search_paths = SearchPaths::from_settings(db, search_path_settings)?;
 
@@ -49,16 +47,20 @@ impl Program {
 
         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,
@@ -74,5 +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>),
 }

crates/red_knot_python_semantic/src/python_version.rs

@@ -54,6 +54,13 @@ impl TryFrom<(&str, &str)> for PythonVersion {
     }
 }
 
+impl From<(u8, u8)> for PythonVersion {
+    fn from(value: (u8, u8)) -> Self {
+        let (major, minor) = value;
+        Self { major, minor }
+    }
+}
+
 impl fmt::Display for PythonVersion {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let PythonVersion { major, minor } = self;

crates/red_knot_python_semantic/src/semantic_index.rs

@@ -1,7 +1,7 @@
 use std::iter::FusedIterator;
 use std::sync::Arc;
 
-use rustc_hash::FxHashMap;
+use rustc_hash::{FxBuildHasher, FxHashMap};
 use salsa::plumbing::AsId;
 
 use ruff_db::files::File;
@@ -21,14 +21,17 @@ use crate::Db;
 
 pub mod ast_ids;
 mod builder;
+pub(crate) mod constraint;
 pub mod definition;
 pub mod expression;
 pub mod symbol;
 mod use_def;
 
-pub(crate) use self::use_def::{DefinitionWithConstraints, DefinitionWithConstraintsIterator};
+pub(crate) use self::use_def::{
+    BindingWithConstraints, BindingWithConstraintsIterator, DeclarationsIterator,
+};
 
-type SymbolMap = hashbrown::HashMap<ScopedSymbolId, (), ()>;
+type SymbolMap = hashbrown::HashMap<ScopedSymbolId, (), FxBuildHasher>;
 
 /// Returns the semantic index for `file`.
 ///
@@ -112,6 +115,9 @@ pub(crate) struct SemanticIndex<'db> {
     /// Note: We should not depend on this map when analysing other files or
     /// changing a file invalidates all dependents.
     ast_ids: IndexVec<FileScopeId, AstIds>,
+
+    /// Flags about the global scope (code usage impacting inference)
+    has_future_annotations: bool,
 }
 
 impl<'db> SemanticIndex<'db> {
@@ -212,6 +218,12 @@ impl<'db> SemanticIndex<'db> {
     pub(crate) fn node_scope(&self, node: NodeWithScopeRef) -> FileScopeId {
         self.scopes_by_node[&node.node_key()]
     }
+
+    /// Checks if there is an import of `__future__.annotations` in the global scope, which affects
+    /// the logic for type inference.
+    pub(super) fn has_future_annotations(&self) -> bool {
+        self.has_future_annotations
+    }
 }
 
 pub struct AncestorsIter<'a> {
@@ -325,16 +337,16 @@ mod tests {
     use crate::Db;
 
     impl UseDefMap<'_> {
-        fn first_public_definition(&self, symbol: ScopedSymbolId) -> Option<Definition<'_>> {
-            self.public_definitions(symbol)
+        fn first_public_binding(&self, symbol: ScopedSymbolId) -> Option<Definition<'_>> {
+            self.public_bindings(symbol)
                 .next()
-                .map(|constrained_definition| constrained_definition.definition)
+                .map(|constrained_binding| constrained_binding.binding)
         }
 
-        fn first_use_definition(&self, use_id: ScopedUseId) -> Option<Definition<'_>> {
-            self.use_definitions(use_id)
+        fn first_binding_at_use(&self, use_id: ScopedUseId) -> Option<Definition<'_>> {
+            self.bindings_at_use(use_id)
                 .next()
-                .map(|constrained_definition| constrained_definition.definition)
+                .map(|constrained_binding| constrained_binding.binding)
         }
     }
 
@@ -396,8 +408,8 @@ mod tests {
         let foo = global_table.symbol_id_by_name("foo").unwrap();
 
         let use_def = use_def_map(&db, scope);
-        let definition = use_def.first_public_definition(foo).unwrap();
-        assert!(matches!(definition.node(&db), DefinitionKind::Import(_)));
+        let binding = use_def.first_public_binding(foo).unwrap();
+        assert!(matches!(binding.kind(&db), DefinitionKind::Import(_)));
     }
 
     #[test]
@@ -426,22 +438,19 @@ mod tests {
         assert!(
             global_table
                 .symbol_by_name("foo")
-                .is_some_and(|symbol| { symbol.is_defined() && !symbol.is_used() }),
+                .is_some_and(|symbol| { symbol.is_bound() && !symbol.is_used() }),
             "symbols that are defined get the defined flag"
         );
 
         let use_def = use_def_map(&db, scope);
-        let definition = use_def
-            .first_public_definition(
+        let binding = use_def
+            .first_public_binding(
                 global_table
                     .symbol_id_by_name("foo")
                     .expect("symbol to exist"),
             )
             .unwrap();
-        assert!(matches!(
-            definition.node(&db),
-            DefinitionKind::ImportFrom(_)
-        ));
+        assert!(matches!(binding.kind(&db), DefinitionKind::ImportFrom(_)));
     }
 
     #[test]
@@ -454,17 +463,14 @@ mod tests {
         assert!(
             global_table
                 .symbol_by_name("foo")
-                .is_some_and(|symbol| { !symbol.is_defined() && symbol.is_used() }),
-            "a symbol used but not defined in a scope should have only the used flag"
+                .is_some_and(|symbol| { !symbol.is_bound() && symbol.is_used() }),
+            "a symbol used but not bound in a scope should have only the used flag"
         );
         let use_def = use_def_map(&db, scope);
-        let definition = use_def
-            .first_public_definition(global_table.symbol_id_by_name("x").expect("symbol exists"))
+        let binding = use_def
+            .first_public_binding(global_table.symbol_id_by_name("x").expect("symbol exists"))
             .unwrap();
-        assert!(matches!(
-            definition.node(&db),
-            DefinitionKind::Assignment(_)
-        ));
+        assert!(matches!(binding.kind(&db), DefinitionKind::Assignment(_)));
     }
 
     #[test]
@@ -476,12 +482,12 @@ mod tests {
         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())
+        let binding = use_def
+            .first_public_binding(global_table.symbol_id_by_name("x").unwrap())
             .unwrap();
 
         assert!(matches!(
-            definition.node(&db),
+            binding.kind(&db),
             DefinitionKind::AugmentedAssignment(_)
         ));
     }
@@ -514,13 +520,10 @@ y = 2
         assert_eq!(names(&class_table), vec!["x"]);
 
         let use_def = index.use_def_map(class_scope_id);
-        let definition = use_def
-            .first_public_definition(class_table.symbol_id_by_name("x").expect("symbol exists"))
+        let binding = use_def
+            .first_public_binding(class_table.symbol_id_by_name("x").expect("symbol exists"))
             .unwrap();
-        assert!(matches!(
-            definition.node(&db),
-            DefinitionKind::Assignment(_)
-        ));
+        assert!(matches!(binding.kind(&db), DefinitionKind::Assignment(_)));
     }
 
     #[test]
@@ -550,17 +553,14 @@ y = 2
         assert_eq!(names(&function_table), vec!["x"]);
 
         let use_def = index.use_def_map(function_scope_id);
-        let definition = use_def
-            .first_public_definition(
+        let binding = use_def
+            .first_public_binding(
                 function_table
                     .symbol_id_by_name("x")
                     .expect("symbol exists"),
             )
             .unwrap();
-        assert!(matches!(
-            definition.node(&db),
-            DefinitionKind::Assignment(_)
-        ));
+        assert!(matches!(binding.kind(&db), DefinitionKind::Assignment(_)));
     }
 
     #[test]
@@ -575,7 +575,7 @@ def f(a: str, /, b: str, c: int = 1, *args, d: int = 2, **kwargs):
         let index = semantic_index(&db, file);
         let global_table = symbol_table(&db, global_scope(&db, file));
 
-        assert_eq!(names(&global_table), vec!["f", "str", "int"]);
+        assert_eq!(names(&global_table), vec!["str", "int", "f"]);
 
         let [(function_scope_id, _function_scope)] = index
             .child_scopes(FileScopeId::global())
@@ -592,27 +592,27 @@ def f(a: str, /, b: str, c: int = 1, *args, d: int = 2, **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(
+            let binding = use_def
+                .first_public_binding(
                     function_table
                         .symbol_id_by_name(name)
                         .expect("symbol exists"),
                 )
                 .unwrap();
             assert!(matches!(
-                definition.node(&db),
+                binding.kind(&db),
                 DefinitionKind::ParameterWithDefault(_)
             ));
         }
         for name in ["args", "kwargs"] {
-            let definition = use_def
-                .first_public_definition(
+            let binding = use_def
+                .first_public_binding(
                     function_table
                         .symbol_id_by_name(name)
                         .expect("symbol exists"),
                 )
                 .unwrap();
-            assert!(matches!(definition.node(&db), DefinitionKind::Parameter(_)));
+            assert!(matches!(binding.kind(&db), DefinitionKind::Parameter(_)));
         }
     }
 
@@ -640,23 +640,19 @@ def f(a: str, /, b: str, c: int = 1, *args, d: int = 2, **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"),
-                )
+            let binding = use_def
+                .first_public_binding(lambda_table.symbol_id_by_name(name).expect("symbol exists"))
                 .unwrap();
             assert!(matches!(
-                definition.node(&db),
+                binding.kind(&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"),
-                )
+            let binding = use_def
+                .first_public_binding(lambda_table.symbol_id_by_name(name).expect("symbol exists"))
                 .unwrap();
-            assert!(matches!(definition.node(&db), DefinitionKind::Parameter(_)));
+            assert!(matches!(binding.kind(&db), DefinitionKind::Parameter(_)));
         }
     }
 
@@ -666,7 +662,7 @@ def f(a: str, /, b: str, c: int = 1, *args, d: int = 2, **kwargs):
     fn comprehension_scope() {
         let TestCase { db, file } = test_case(
             "
-[x for x in iter1]
+[x for x, y in iter1]
 ",
         );
 
@@ -690,7 +686,22 @@ def f(a: str, /, b: str, c: int = 1, *args, d: int = 2, **kwargs):
 
         let comprehension_symbol_table = index.symbol_table(comprehension_scope_id);
 
-        assert_eq!(names(&comprehension_symbol_table), vec!["x"]);
+        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 binding = use_def
+                .first_public_binding(
+                    comprehension_symbol_table
+                        .symbol_id_by_name(name)
+                        .expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(
+                binding.kind(&db),
+                DefinitionKind::Comprehension(_)
+            ));
+        }
     }
 
     /// Test case to validate that the `x` variable used in the comprehension is referencing the
@@ -726,12 +737,12 @@ def f(a: str, /, b: str, c: int = 1, *args, d: int = 2, **kwargs):
         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 {
+        let binding = use_def.first_binding_at_use(element_use_id).unwrap();
+        let DefinitionKind::Comprehension(comprehension) = binding.kind(&db) else {
             panic!("expected generator definition")
         };
-        let ast::Comprehension { target, .. } = comprehension.node();
-        let name = target.as_name_expr().unwrap().id().as_str();
+        let target = comprehension.target();
+        let name = target.id().as_str();
 
         assert_eq!(name, "x");
         assert_eq!(target.range(), TextRange::new(23.into(), 24.into()));
@@ -790,6 +801,52 @@ def f(a: str, /, b: str, c: int = 1, *args, d: int = 2, **kwargs):
         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 binding = use_def
+                .first_public_binding(global_table.symbol_id_by_name(name).expect("symbol exists"))
+                .expect("Expected with item definition for {name}");
+            assert!(matches!(binding.kind(&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 binding = use_def
+                .first_public_binding(global_table.symbol_id_by_name(name).expect("symbol exists"))
+                .expect("Expected with item definition for {name}");
+            assert!(matches!(binding.kind(&db), DefinitionKind::WithItem(_)));
+        }
+    }
+
     #[test]
     fn dupes() {
         let TestCase { db, file } = test_case(
@@ -823,14 +880,14 @@ def func():
         assert_eq!(names(&func2_table), vec!["y"]);
 
         let use_def = index.use_def_map(FileScopeId::global());
-        let definition = use_def
-            .first_public_definition(
+        let binding = use_def
+            .first_public_binding(
                 global_table
                     .symbol_id_by_name("func")
                     .expect("symbol exists"),
             )
             .unwrap();
-        assert!(matches!(definition.node(&db), DefinitionKind::Function(_)));
+        assert!(matches!(binding.kind(&db), DefinitionKind::Function(_)));
     }
 
     #[test]
@@ -898,7 +955,7 @@ class C[T]:
         assert!(
             ann_table
                 .symbol_by_name("T")
-                .is_some_and(|s| s.is_defined() && !s.is_used()),
+                .is_some_and(|s| s.is_bound() && !s.is_used()),
             "type parameters are defined by the scope that introduces them"
         );
 
@@ -930,14 +987,14 @@ 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.first_use_definition(x_use_id).unwrap();
-        let DefinitionKind::Assignment(assignment) = definition.node(&db) else {
+        let binding = use_def.first_binding_at_use(x_use_id).unwrap();
+        let DefinitionKind::Assignment(assignment) = binding.kind(&db) else {
             panic!("should be an assignment definition")
         };
         let ast::Expr::NumberLiteral(ast::ExprNumberLiteral {
             value: ast::Number::Int(num),
             ..
-        }) = &*assignment.assignment().value
+        }) = assignment.value()
         else {
             panic!("should be a number literal")
         };
@@ -979,7 +1036,7 @@ class C[T]:
         }
 
         let TestCase { db, file } = test_case(
-            r#"
+            r"
 class Test:
     def foo():
         def bar():
@@ -988,7 +1045,7 @@ class Test:
         pass
 
 def x():
-    pass"#,
+    pass",
         );
 
         let index = semantic_index(&db, file);
@@ -1023,7 +1080,7 @@ def x():
     }
 
     #[test]
-    fn match_stmt_symbols() {
+    fn match_stmt() {
         let TestCase { db, file } = test_case(
             "
 match subject:
@@ -1037,12 +1094,120 @@ match subject:
 ",
         );
 
-        let global_table = symbol_table(&db, global_scope(&db, file));
+        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", "f", "e", "h", "g", "Foo", "i", "j", "k", "l"]
+            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 binding = use_def
+                .first_public_binding(global_table.symbol_id_by_name(name).expect("symbol exists"))
+                .expect("Expected with item definition for {name}");
+            if let DefinitionKind::MatchPattern(pattern) = binding.kind(&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 binding = use_def
+                .first_public_binding(global_table.symbol_id_by_name(name).expect("symbol exists"))
+                .expect("Expected with item definition for {name}");
+            if let DefinitionKind::MatchPattern(pattern) = binding.kind(&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 binding = use_def
+            .first_public_binding(global_table.symbol_id_by_name("x").unwrap())
+            .unwrap();
+
+        assert!(matches!(binding.kind(&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_binding = use_def
+            .first_public_binding(global_table.symbol_id_by_name("x").unwrap())
+            .unwrap();
+        let y_binding = use_def
+            .first_public_binding(global_table.symbol_id_by_name("y").unwrap())
+            .unwrap();
+
+        assert!(matches!(x_binding.kind(&db), DefinitionKind::For(_)));
+        assert!(matches!(y_binding.kind(&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 binding = use_def
+            .first_public_binding(global_table.symbol_id_by_name("a").unwrap())
+            .unwrap();
+
+        assert!(matches!(binding.kind(&db), DefinitionKind::For(_)));
     }
 }

crates/red_knot_python_semantic/src/semantic_index/builder/except_handlers.rs

@@ -0,0 +1,102 @@
+use crate::semantic_index::use_def::FlowSnapshot;
+
+use super::SemanticIndexBuilder;
+
+/// An abstraction over the fact that each scope should have its own [`TryNodeContextStack`]
+#[derive(Debug, Default)]
+pub(super) struct TryNodeContextStackManager(Vec<TryNodeContextStack>);
+
+impl TryNodeContextStackManager {
+    /// Push a new [`TryNodeContextStack`] onto the stack of stacks.
+    ///
+    /// Each [`TryNodeContextStack`] is only valid for a single scope
+    pub(super) fn enter_nested_scope(&mut self) {
+        self.0.push(TryNodeContextStack::default());
+    }
+
+    /// Pop a new [`TryNodeContextStack`] off the stack of stacks.
+    ///
+    /// Each [`TryNodeContextStack`] is only valid for a single scope
+    pub(super) fn exit_scope(&mut self) {
+        let popped_context = self.0.pop();
+        debug_assert!(
+            popped_context.is_some(),
+            "exit_scope() should never be called on an empty stack \
+(this indicates an unbalanced `enter_nested_scope()`/`exit_scope()` pair of calls)"
+        );
+    }
+
+    /// Push a [`TryNodeContext`] onto the [`TryNodeContextStack`]
+    /// at the top of our stack of stacks
+    pub(super) fn push_context(&mut self) {
+        self.current_try_context_stack().push_context();
+    }
+
+    /// Pop a [`TryNodeContext`] off the [`TryNodeContextStack`]
+    /// at the top of our stack of stacks. Return the Vec of [`FlowSnapshot`]s
+    /// recorded while we were visiting the `try` suite.
+    pub(super) fn pop_context(&mut self) -> Vec<FlowSnapshot> {
+        self.current_try_context_stack().pop_context()
+    }
+
+    /// Retrieve the stack that is at the top of our stack of stacks.
+    /// For each `try` block on that stack, push the snapshot onto the `try` block
+    pub(super) fn record_definition(&mut self, builder: &SemanticIndexBuilder) {
+        self.current_try_context_stack().record_definition(builder);
+    }
+
+    /// Retrieve the [`TryNodeContextStack`] that is relevant for the current scope.
+    fn current_try_context_stack(&mut self) -> &mut TryNodeContextStack {
+        self.0
+            .last_mut()
+            .expect("There should always be at least one `TryBlockContexts` on the stack")
+    }
+}
+
+/// The contexts of nested `try`/`except` blocks for a single scope
+#[derive(Debug, Default)]
+struct TryNodeContextStack(Vec<TryNodeContext>);
+
+impl TryNodeContextStack {
+    /// Push a new [`TryNodeContext`] for recording intermediate states
+    /// while visiting a [`ruff_python_ast::StmtTry`] node that has a `finally` branch.
+    fn push_context(&mut self) {
+        self.0.push(TryNodeContext::default());
+    }
+
+    /// Pop a [`TryNodeContext`] off the stack. Return the Vec of [`FlowSnapshot`]s
+    /// recorded while we were visiting the `try` suite.
+    fn pop_context(&mut self) -> Vec<FlowSnapshot> {
+        let TryNodeContext {
+            try_suite_snapshots,
+        } = self
+            .0
+            .pop()
+            .expect("Cannot pop a `try` block off an empty `TryBlockContexts` stack");
+        try_suite_snapshots
+    }
+
+    /// For each `try` block on the stack, push the snapshot onto the `try` block
+    fn record_definition(&mut self, builder: &SemanticIndexBuilder) {
+        for context in &mut self.0 {
+            context.record_definition(builder.flow_snapshot());
+        }
+    }
+}
+
+/// Context for tracking definitions over the course of a single
+/// [`ruff_python_ast::StmtTry`] node
+///
+/// It will likely be necessary to add more fields to this struct in the future
+/// when we add more advanced handling of `finally` branches.
+#[derive(Debug, Default)]
+struct TryNodeContext {
+    try_suite_snapshots: Vec<FlowSnapshot>,
+}
+
+impl TryNodeContext {
+    /// Take a record of what the internal state looked like after a definition
+    fn record_definition(&mut self, snapshot: FlowSnapshot) {
+        self.try_suite_snapshots.push(snapshot);
+    }
+}

crates/red_knot_python_semantic/src/semantic_index/constraint.rs

@@ -0,0 +1,39 @@
+use ruff_db::files::File;
+use ruff_python_ast as ast;
+
+use crate::ast_node_ref::AstNodeRef;
+use crate::db::Db;
+use crate::semantic_index::expression::Expression;
+use crate::semantic_index::symbol::{FileScopeId, ScopeId};
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) enum Constraint<'db> {
+    Expression(Expression<'db>),
+    Pattern(PatternConstraint<'db>),
+}
+
+#[salsa::tracked]
+pub(crate) struct PatternConstraint<'db> {
+    #[id]
+    pub(crate) file: File,
+
+    #[id]
+    pub(crate) file_scope: FileScopeId,
+
+    #[no_eq]
+    #[return_ref]
+    pub(crate) subject: AstNodeRef<ast::Expr>,
+
+    #[no_eq]
+    #[return_ref]
+    pub(crate) pattern: AstNodeRef<ast::Pattern>,
+
+    #[no_eq]
+    count: countme::Count<PatternConstraint<'static>>,
+}
+
+impl<'db> PatternConstraint<'db> {
+    pub(crate) fn scope(self, db: &'db dyn Db) -> ScopeId<'db> {
+        self.file_scope(db).to_scope_id(db, self.file(db))
+    }
+}

crates/red_knot_python_semantic/src/semantic_index/definition.rs

@@ -3,6 +3,7 @@ use ruff_db::parsed::ParsedModule;
 use ruff_python_ast as ast;
 
 use crate::ast_node_ref::AstNodeRef;
+use crate::module_resolver::file_to_module;
 use crate::node_key::NodeKey;
 use crate::semantic_index::symbol::{FileScopeId, ScopeId, ScopedSymbolId};
 use crate::Db;
@@ -23,7 +24,7 @@ pub struct Definition<'db> {
 
     #[no_eq]
     #[return_ref]
-    pub(crate) node: DefinitionKind,
+    pub(crate) kind: DefinitionKind,
 
     #[no_eq]
     count: countme::Count<Definition<'static>>,
@@ -33,12 +34,33 @@ impl<'db> Definition<'db> {
     pub(crate) fn scope(self, db: &'db dyn Db) -> ScopeId<'db> {
         self.file_scope(db).to_scope_id(db, self.file(db))
     }
+
+    pub(crate) fn category(self, db: &'db dyn Db) -> DefinitionCategory {
+        self.kind(db).category()
+    }
+
+    pub(crate) fn is_declaration(self, db: &'db dyn Db) -> bool {
+        self.kind(db).category().is_declaration()
+    }
+
+    pub(crate) fn is_binding(self, db: &'db dyn Db) -> bool {
+        self.kind(db).category().is_binding()
+    }
+
+    /// Return true if this is a symbol was defined in the `typing` or `typing_extensions` modules
+    pub(crate) fn is_typing_definition(self, db: &'db dyn Db) -> bool {
+        file_to_module(db, self.file(db)).is_some_and(|module| {
+            module.search_path().is_standard_library()
+                && matches!(&**module.name(), "typing" | "typing_extensions")
+        })
+    }
 }
 
 #[derive(Copy, Clone, Debug)]
 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),
@@ -47,6 +69,9 @@ pub(crate) enum DefinitionNodeRef<'a> {
     AugmentedAssignment(&'a ast::StmtAugAssign),
     Comprehension(ComprehensionDefinitionNodeRef<'a>),
     Parameter(ast::AnyParameterRef<'a>),
+    WithItem(WithItemDefinitionNodeRef<'a>),
+    MatchPattern(MatchPatternDefinitionNodeRef<'a>),
+    ExceptHandler(ExceptHandlerDefinitionNodeRef<'a>),
 }
 
 impl<'a> From<&'a ast::StmtFunctionDef> for DefinitionNodeRef<'a> {
@@ -91,12 +116,24 @@ 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)
@@ -109,6 +146,12 @@ impl<'a> From<ast::AnyParameterRef<'a>> for DefinitionNodeRef<'a> {
     }
 }
 
+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,
@@ -118,13 +161,47 @@ pub(crate) struct ImportFromDefinitionNodeRef<'a> {
 #[derive(Copy, Clone, Debug)]
 pub(crate) struct AssignmentDefinitionNodeRef<'a> {
     pub(crate) assignment: &'a ast::StmtAssign,
+    pub(crate) target_index: usize,
+    pub(crate) name: &'a ast::ExprName,
+    pub(crate) kind: AssignmentKind,
+}
+
+#[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 ExceptHandlerDefinitionNodeRef<'a> {
+    pub(crate) handler: &'a ast::ExceptHandlerExceptHandler,
+    pub(crate) is_star: bool,
+}
+
 #[derive(Copy, Clone, Debug)]
 pub(crate) struct ComprehensionDefinitionNodeRef<'a> {
-    pub(crate) node: &'a ast::Comprehension,
+    pub(crate) iterable: &'a ast::Expr,
+    pub(crate) target: &'a ast::ExprName,
     pub(crate) first: bool,
+    pub(crate) is_async: 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<'_> {
@@ -149,24 +226,43 @@ impl DefinitionNodeRef<'_> {
             DefinitionNodeRef::NamedExpression(named) => {
                 DefinitionKind::NamedExpression(AstNodeRef::new(parsed, named))
             }
-            DefinitionNodeRef::Assignment(AssignmentDefinitionNodeRef { assignment, target }) => {
-                DefinitionKind::Assignment(AssignmentDefinitionKind {
-                    assignment: AstNodeRef::new(parsed.clone(), assignment),
-                    target: AstNodeRef::new(parsed, target),
-                })
-            }
+            DefinitionNodeRef::Assignment(AssignmentDefinitionNodeRef {
+                assignment,
+                target_index,
+                name,
+                kind,
+            }) => DefinitionKind::Assignment(AssignmentDefinitionKind {
+                assignment: AstNodeRef::new(parsed.clone(), assignment),
+                target_index,
+                name: AstNodeRef::new(parsed, name),
+                kind,
+            }),
             DefinitionNodeRef::AnnotatedAssignment(assign) => {
                 DefinitionKind::AnnotatedAssignment(AstNodeRef::new(parsed, assign))
             }
             DefinitionNodeRef::AugmentedAssignment(augmented_assignment) => {
                 DefinitionKind::AugmentedAssignment(AstNodeRef::new(parsed, augmented_assignment))
             }
-            DefinitionNodeRef::Comprehension(ComprehensionDefinitionNodeRef { node, first }) => {
-                DefinitionKind::Comprehension(ComprehensionDefinitionKind {
-                    node: AstNodeRef::new(parsed, node),
-                    first,
-                })
-            }
+            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,
+                is_async,
+            }) => DefinitionKind::Comprehension(ComprehensionDefinitionKind {
+                iterable: AstNodeRef::new(parsed.clone(), iterable),
+                target: AstNodeRef::new(parsed, target),
+                first,
+                is_async,
+            }),
             DefinitionNodeRef::Parameter(parameter) => match parameter {
                 ast::AnyParameterRef::Variadic(parameter) => {
                     DefinitionKind::Parameter(AstNodeRef::new(parsed, parameter))
@@ -175,6 +271,28 @@ impl DefinitionNodeRef<'_> {
                     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,
+            }),
+            DefinitionNodeRef::ExceptHandler(ExceptHandlerDefinitionNodeRef {
+                handler,
+                is_star,
+            }) => DefinitionKind::ExceptHandler(ExceptHandlerDefinitionKind {
+                handler: AstNodeRef::new(parsed.clone(), handler),
+                is_star,
+            }),
         }
     }
 
@@ -189,19 +307,66 @@ impl DefinitionNodeRef<'_> {
             Self::NamedExpression(node) => node.into(),
             Self::Assignment(AssignmentDefinitionNodeRef {
                 assignment: _,
-                target,
-            }) => target.into(),
+                target_index: _,
+                name,
+                kind: _,
+            }) => name.into(),
             Self::AnnotatedAssignment(node) => node.into(),
             Self::AugmentedAssignment(node) => node.into(),
-            Self::Comprehension(ComprehensionDefinitionNodeRef { node, first: _ }) => 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()
+            }
+            Self::ExceptHandler(ExceptHandlerDefinitionNodeRef { handler, .. }) => handler.into(),
         }
     }
 }
 
+#[derive(Clone, Copy, Debug)]
+pub(crate) enum DefinitionCategory {
+    /// A Definition which binds a value to a name (e.g. `x = 1`).
+    Binding,
+    /// A Definition which declares the upper-bound of acceptable types for this name (`x: int`).
+    Declaration,
+    /// A Definition which both declares a type and binds a value (e.g. `x: int = 1`).
+    DeclarationAndBinding,
+}
+
+impl DefinitionCategory {
+    /// True if this definition establishes a "declared type" for the symbol.
+    ///
+    /// If so, any assignments reached by this definition are in error if they assign a value of a
+    /// type not assignable to the declared type.
+    ///
+    /// Annotations establish a declared type. So do function and class definitions, and imports.
+    pub(crate) fn is_declaration(self) -> bool {
+        matches!(
+            self,
+            DefinitionCategory::Declaration | DefinitionCategory::DeclarationAndBinding
+        )
+    }
+
+    /// True if this definition assigns a value to the symbol.
+    ///
+    /// False only for annotated assignments without a RHS.
+    pub(crate) fn is_binding(self) -> bool {
+        matches!(
+            self,
+            DefinitionCategory::Binding | DefinitionCategory::DeclarationAndBinding
+        )
+    }
+}
+
 #[derive(Clone, Debug)]
 pub enum DefinitionKind {
     Import(AstNodeRef<ast::Alias>),
@@ -212,25 +377,102 @@ pub enum DefinitionKind {
     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),
+    ExceptHandler(ExceptHandlerDefinitionKind),
+}
+
+impl DefinitionKind {
+    pub(crate) fn category(&self) -> DefinitionCategory {
+        match self {
+            // functions, classes, and imports always bind, and we consider them declarations
+            DefinitionKind::Function(_)
+            | DefinitionKind::Class(_)
+            | DefinitionKind::Import(_)
+            | DefinitionKind::ImportFrom(_) => DefinitionCategory::DeclarationAndBinding,
+            // a parameter always binds a value, but is only a declaration if annotated
+            DefinitionKind::Parameter(parameter) => {
+                if parameter.annotation.is_some() {
+                    DefinitionCategory::DeclarationAndBinding
+                } else {
+                    DefinitionCategory::Binding
+                }
+            }
+            // presence of a default is irrelevant, same logic as for a no-default parameter
+            DefinitionKind::ParameterWithDefault(parameter_with_default) => {
+                if parameter_with_default.parameter.annotation.is_some() {
+                    DefinitionCategory::DeclarationAndBinding
+                } else {
+                    DefinitionCategory::Binding
+                }
+            }
+            // annotated assignment is always a declaration, only a binding if there is a RHS
+            DefinitionKind::AnnotatedAssignment(ann_assign) => {
+                if ann_assign.value.is_some() {
+                    DefinitionCategory::DeclarationAndBinding
+                } else {
+                    DefinitionCategory::Declaration
+                }
+            }
+            // all of these bind values without declaring a type
+            DefinitionKind::NamedExpression(_)
+            | DefinitionKind::Assignment(_)
+            | DefinitionKind::AugmentedAssignment(_)
+            | DefinitionKind::For(_)
+            | DefinitionKind::Comprehension(_)
+            | DefinitionKind::WithItem(_)
+            | DefinitionKind::MatchPattern(_)
+            | DefinitionKind::ExceptHandler(_) => DefinitionCategory::Binding,
+        }
+    }
+}
+
+#[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 {
-    node: AstNodeRef<ast::Comprehension>,
+    iterable: AstNodeRef<ast::Expr>,
+    target: AstNodeRef<ast::ExprName>,
     first: bool,
+    is_async: bool,
 }
 
 impl ComprehensionDefinitionKind {
-    pub(crate) fn node(&self) -> &ast::Comprehension {
-        self.node.node()
+    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
     }
+
+    pub(crate) fn is_async(&self) -> bool {
+        self.is_async
+    }
 }
 
 #[derive(Clone, Debug)]
@@ -250,15 +492,47 @@ impl ImportFromDefinitionKind {
 }
 
 #[derive(Clone, Debug)]
-#[allow(dead_code)]
 pub struct AssignmentDefinitionKind {
     assignment: AstNodeRef<ast::StmtAssign>,
-    target: AstNodeRef<ast::ExprName>,
+    target_index: usize,
+    name: AstNodeRef<ast::ExprName>,
+    kind: AssignmentKind,
 }
 
 impl AssignmentDefinitionKind {
-    pub(crate) fn assignment(&self) -> &ast::StmtAssign {
-        self.assignment.node()
+    pub(crate) fn value(&self) -> &ast::Expr {
+        &self.assignment.node().value
+    }
+
+    pub(crate) fn target(&self) -> &ast::Expr {
+        &self.assignment.node().targets[self.target_index]
+    }
+
+    pub(crate) fn name(&self) -> &ast::ExprName {
+        self.name.node()
+    }
+
+    pub(crate) fn kind(&self) -> AssignmentKind {
+        self.kind
+    }
+}
+
+/// The kind of assignment target expression.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum AssignmentKind {
+    Sequence,
+    Name,
+}
+
+#[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 {
@@ -266,6 +540,47 @@ impl AssignmentDefinitionKind {
     }
 }
 
+#[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(Clone, Debug)]
+pub struct ExceptHandlerDefinitionKind {
+    handler: AstNodeRef<ast::ExceptHandlerExceptHandler>,
+    is_star: bool,
+}
+
+impl ExceptHandlerDefinitionKind {
+    pub(crate) fn node(&self) -> &ast::ExceptHandlerExceptHandler {
+        self.handler.node()
+    }
+
+    pub(crate) fn handled_exceptions(&self) -> Option<&ast::Expr> {
+        self.node().type_.as_deref()
+    }
+
+    pub(crate) fn is_star(&self) -> bool {
+        self.is_star
+    }
+}
+
 #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
 pub(crate) struct DefinitionNodeKey(NodeKey);
 
@@ -311,9 +626,9 @@ impl From<&ast::StmtAugAssign> for DefinitionNodeKey {
     }
 }
 
-impl From<&ast::Comprehension> for DefinitionNodeKey {
-    fn from(node: &ast::Comprehension) -> Self {
-        Self(NodeKey::from_node(node))
+impl From<&ast::StmtFor> for DefinitionNodeKey {
+    fn from(value: &ast::StmtFor) -> Self {
+        Self(NodeKey::from_node(value))
     }
 }
 
@@ -328,3 +643,15 @@ impl From<&ast::ParameterWithDefault> for DefinitionNodeKey {
         Self(NodeKey::from_node(node))
     }
 }
+
+impl From<&ast::Identifier> for DefinitionNodeKey {
+    fn from(identifier: &ast::Identifier) -> Self {
+        Self(NodeKey::from_node(identifier))
+    }
+}
+
+impl From<&ast::ExceptHandlerExceptHandler> for DefinitionNodeKey {
+    fn from(handler: &ast::ExceptHandlerExceptHandler) -> Self {
+        Self(NodeKey::from_node(handler))
+    }
+}