Use mike for versioned documentation

## Summary

We already enforce this logic for the other `ARG` rules. I'm guessing
this was an oversight.

Closes https://github.com/astral-sh/ruff/issues/12963.

.github/workflows/publish-docs.yml

@@ -36,28 +36,30 @@ jobs:
           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
+            echo "Can't build docs without a version."
+            exit 1
           fi
 
           # Use version as display name for now
           display_name="$version"
 
-          echo "version=$version" >> $GITHUB_ENV
-          echo "display_name=$display_name" >> $GITHUB_ENV
+          # Extract the major and minor part of the version for the docs
+          docs_version="$(echo -n "$version" | cut -d "." -f 1-2)"
+
+          echo "version=$version" >> "$GITHUB_ENV"
+          echo "docs_version=$docs_version" >> "$GITHUB_ENV"
+          echo "display_name=$display_name" >> "$GITHUB_ENV"
 
       - name: "Set branch name"
         run: |
-          version="${{ env.version }}"
-          display_name="${{ env.display_name }}"
           timestamp="$(date +%s)"
 
-          # create branch_display_name from display_name by replacing all
+          # Create `branch_display_name` from `display_name` by replacing all
           # characters disallowed in git branch names with hyphens
-          branch_display_name="$(echo "$display_name" | tr -c '[:alnum:]._' '-' | tr -s '-')"
+          branch_display_name="$(echo -n "$display_name" | tr -c '[:alnum:]._' '-' | tr -s '-')"
 
-          echo "branch_name=update-docs-$branch_display_name-$timestamp" >> $GITHUB_ENV
-          echo "timestamp=$timestamp" >> $GITHUB_ENV
+          echo "branch_name=update-docs-$branch_display_name-$timestamp" >> "$GITHUB_ENV"
+          echo "timestamp=$timestamp" >> "$GITHUB_ENV"
 
       - name: "Add SSH key"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
@@ -70,7 +72,7 @@ jobs:
 
       - uses: Swatinem/rust-cache@v2
 
-      - name: "Install Insiders dependencies"
+      - name: "Install insiders dependencies"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
         run: pip install -r docs/requirements-insiders.txt
 
@@ -78,74 +80,86 @@ jobs:
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS != 'true' }}
         run: pip install -r docs/requirements.txt
 
-      - name: "Copy README File"
+      - name: "Fetch docs repo"
+        run: |
+          remote_name="astral-docs"
+
+          git remote add "$remote_name" https://${{ secrets.ASTRAL_DOCS_PAT }}@github.com/astral-sh/docs.git
+          git fetch astral-docs "main:$branch_name"
+
+          echo "remote_name=$remote_name" >> "$GITHUB_ENV"
+
+      - name: "Configure git"
+        run: |
+          git config user.name "astral-docs-bot"
+          git config user.email "176161322+astral-docs-bot@users.noreply.github.com"
+
+      - name: "Transform README and generate docs"
         run: |
           python scripts/transform_readme.py --target mkdocs
           python scripts/generate_mkdocs.py
 
       - name: "Build Insiders docs"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
-        run: mkdocs build --strict -f mkdocs.insiders.yml
+        run: |
+          mike deploy \
+            --remote "$remote_name" \
+            --branch "$branch_name" \
+            --message "Update ruff documentation for $version" \
+            --config-file mkdocs.insiders.yml \
+            --update-aliases \
+            --push \
+            "$docs_version" latest
 
       - name: "Build docs"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS != 'true' }}
-        run: mkdocs build --strict -f mkdocs.public.yml
-
-      - name: "Clone docs repo"
         run: |
-          version="${{ env.version }}"
-          git clone https://${{ secrets.ASTRAL_DOCS_PAT }}@github.com/astral-sh/docs.git astral-docs
-
-      - name: "Copy docs"
-        run: rm -rf astral-docs/site/ruff && mkdir -p astral-docs/site && cp -r site/ruff astral-docs/site/
-
-      - name: "Commit docs"
-        working-directory: astral-docs
-        run: |
-          branch_name="${{ env.branch_name }}"
-
-          git config user.name "astral-docs-bot"
-          git config user.email "176161322+astral-docs-bot@users.noreply.github.com"
-
-          git checkout -b $branch_name
-          git add site/ruff
-          git commit -m "Update ruff documentation for $version"
+          mike deploy \
+            --remote "$remote_name" \
+            --branch "$branch_name" \
+            --message "Update ruff documentation for $version" \
+            --config-file mkdocs.public.yml \
+            --update-aliases \
+            --push \
+            "$docs_version" latest
 
       - name: "Create Pull Request"
-        working-directory: astral-docs
         env:
           GITHUB_TOKEN: ${{ secrets.ASTRAL_DOCS_PAT }}
         run: |
-          version="${{ env.version }}"
-          display_name="${{ env.display_name }}"
-          branch_name="${{ env.branch_name }}"
+          # Set the docs repository
+          astral_docs_repo="astral-sh/docs"
 
-          # set the PR title
+          # Set the PR title
           pull_request_title="Update ruff documentation for $display_name"
 
           # Delete any existing pull requests that are open for this version
-          # by checking against pull_request_title because the new PR will
+          # by checking against `pull_request_title` because the new PR will
           # supersede the old one.
-          gh pr list --state open --json title --jq '.[] | select(.title == "$pull_request_title") | .number' | \
-            xargs -I {} gh pr close {}
+          gh pr list \
+            --state open \
+            --json title,number \
+            --jq '.[] | select(.title == "$pull_request_title") | .number' \
+            --repo "$astral_docs_repo" | \
+              xargs -I {} gh pr close {}
 
-          # push the branch to GitHub
-          git push origin $branch_name
-
-          # create the PR
-          gh pr create --base main --head $branch_name \
+          # Create the PR, the branch has already been pushed by `mike`
+          gh pr create --base main --head "$branch_name" \
             --title "$pull_request_title" \
             --body "Automated documentation update for $display_name" \
-            --label "documentation"
+            --label "documentation" \
+            --repo "$astral_docs_repo"
 
-      - name: "Merge Pull Request"
-        if: ${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
-        working-directory: astral-docs
-        env:
-          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
-          gh pr merge --squash $branch_name
+      # TODO(dhruvmanila): Uncomment once a patch and minor release are done, thus
+      # confirming that it works as intended
+      #
+      # - name: "Merge Pull Request"
+      #   if: ${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
+      #   env:
+      #     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
+      #     gh pr merge --squash $branch_name --repo "astral-sh/docs"

BREAKING_CHANGES.md

@@ -1,5 +1,43 @@
 # Breaking Changes
 
+## 0.6.0
+
+- Detect imports in `src` layouts by default for `isort` rules ([#12848](https://github.com/astral-sh/ruff/pull/12848))
+
+- The pytest rules `PT001` and `PT023` now default to omitting the decorator parentheses when there are no arguments ([#12838](https://github.com/astral-sh/ruff/pull/12838)).
+
+- Lint and format Jupyter Notebook by default ([#12878](https://github.com/astral-sh/ruff/pull/12878)).
+
+    You can disable specific rules for notebooks using [`per-file-ignores`](https://docs.astral.sh/ruff/settings/#lint_per-file-ignores):
+
+    ```toml
+    [tool.ruff.lint.per-file-ignores]
+    "*.ipynb" = ["E501"] # disable line-too-long in notebooks
+    ```
+
+    If you'd prefer to either only lint or only format Jupyter Notebook files, you can use the
+    section-specific `exclude` option to do so. For example, the following would only lint Jupyter
+    Notebook files and not format them:
+
+    ```toml
+    [tool.ruff.format]
+    exclude = ["*.ipynb"]
+    ```
+
+    And, conversely, the following would only format Jupyter Notebook files and not lint them:
+
+    ```toml
+    [tool.ruff.lint]
+    exclude = ["*.ipynb"]
+    ```
+
+    You can completely disable Jupyter Notebook support by updating the [`extend-exclude`](https://docs.astral.sh/ruff/settings/#extend-exclude) setting:
+
+    ```toml
+    [tool.ruff]
+    extend-exclude = ["*.ipynb"]
+    ```
+
 ## 0.5.0
 
 - Follow the XDG specification to discover user-level configurations on macOS (same as on other Unix platforms)

CHANGELOG.md

@@ -1,5 +1,120 @@
 # Changelog
 
+## 0.6.1
+
+This is a hotfix release to address an issue with `ruff-pre-commit`. In v0.6,
+Ruff changed its behavior to lint and format Jupyter notebooks by default;
+however, due to an oversight, these files were still excluded by default if
+Ruff was run via pre-commit, leading to inconsistent behavior.
+This has [now been fixed](https://github.com/astral-sh/ruff-pre-commit/pull/96).
+
+### Preview features
+
+- \[`fastapi`\] Implement `fast-api-unused-path-parameter` (`FAST003`) ([#12638](https://github.com/astral-sh/ruff/pull/12638))
+
+### Rule changes
+
+- \[`pylint`\] Rename `too-many-positional` to `too-many-positional-arguments` (`R0917`) ([#12905](https://github.com/astral-sh/ruff/pull/12905))
+
+### Server
+
+- Fix crash when applying "fix-all" code-action to notebook cells ([#12929](https://github.com/astral-sh/ruff/pull/12929))
+
+### Other changes
+
+- \[`flake8-naming`\]: Respect import conventions (`N817`) ([#12922](https://github.com/astral-sh/ruff/pull/12922))
+
+## 0.6.0
+
+Check out the [blog post](https://astral.sh/blog/ruff-v0.6.0) for a migration guide and overview of the changes!
+
+### Breaking changes
+
+See also, the "Remapped rules" section which may result in disabled rules.
+
+- Lint and format Jupyter Notebook by default ([#12878](https://github.com/astral-sh/ruff/pull/12878)).
+- Detect imports in `src` layouts by default for `isort` rules ([#12848](https://github.com/astral-sh/ruff/pull/12848))
+- The pytest rules `PT001` and `PT023` now default to omitting the decorator parentheses when there are no arguments ([#12838](https://github.com/astral-sh/ruff/pull/12838)).
+
+### Deprecations
+
+The following rules are now deprecated:
+
+- [`pytest-missing-fixture-name-underscore`](https://docs.astral.sh/ruff/rules/pytest-missing-fixture-name-underscore/) (`PT004`)
+- [`pytest-incorrect-fixture-name-underscore`](https://docs.astral.sh/ruff/rules/pytest-incorrect-fixture-name-underscore/) (`PT005`)
+- [`unpacked-list-comprehension`](https://docs.astral.sh/ruff/rules/unpacked-list-comprehension/) (`UP027`)
+
+### Remapped rules
+
+The following rules have been remapped to new rule codes:
+
+- [`unnecessary-dict-comprehension-for-iterable`](https://docs.astral.sh/ruff/rules/unnecessary-dict-comprehension-for-iterable/): `RUF025` to `C420`
+
+### Stabilization
+
+The following rules have been stabilized and are no longer in preview:
+
+- [`singledispatch-method`](https://docs.astral.sh/ruff/rules/singledispatch-method/) (`PLE1519`)
+- [`singledispatchmethod-function`](https://docs.astral.sh/ruff/rules/singledispatchmethod-function/) (`PLE1520`)
+- [`bad-staticmethod-argument`](https://docs.astral.sh/ruff/rules/bad-staticmethod-argument/) (`PLW0211`)
+- [`if-stmt-min-max`](https://docs.astral.sh/ruff/rules/if-stmt-min-max/) (`PLR1730`)
+- [`invalid-bytes-return-type`](https://docs.astral.sh/ruff/rules/invalid-bytes-return-type/) (`PLE0308`)
+- [`invalid-hash-return-type`](https://docs.astral.sh/ruff/rules/invalid-hash-return-type/) (`PLE0309`)
+- [`invalid-index-return-type`](https://docs.astral.sh/ruff/rules/invalid-index-return-type/) (`PLE0305`)
+- [`invalid-length-return-type`](https://docs.astral.sh/ruff/rules/invalid-length-return-type/) (`PLEE303`)
+- [`self-or-cls-assignment`](https://docs.astral.sh/ruff/rules/self-or-cls-assignment/) (`PLW0642`)
+- [`byte-string-usage`](https://docs.astral.sh/ruff/rules/byte-string-usage/) (`PYI057`)
+- [`duplicate-literal-member`](https://docs.astral.sh/ruff/rules/duplicate-literal-member/) (`PYI062`)
+- [`redirected-noqa`](https://docs.astral.sh/ruff/rules/redirected-noqa/) (`RUF101`)
+
+The following behaviors have been stabilized:
+
+- [`cancel-scope-no-checkpoint`](https://docs.astral.sh/ruff/rules/cancel-scope-no-checkpoint/) (`ASYNC100`): Support `asyncio` and `anyio` context mangers.
+- [`async-function-with-timeout`](https://docs.astral.sh/ruff/rules/async-function-with-timeout/) (`ASYNC109`): Support `asyncio` and `anyio` context mangers.
+- [`async-busy-wait`](https://docs.astral.sh/ruff/rules/async-busy-wait/) (`ASYNC110`): Support `asyncio` and `anyio` context mangers.
+- [`async-zero-sleep`](https://docs.astral.sh/ruff/rules/async-zero-sleep/) (`ASYNC115`): Support `anyio` context mangers.
+- [`long-sleep-not-forever`](https://docs.astral.sh/ruff/rules/long-sleep-not-forever/) (`ASYNC116`): Support `anyio` context mangers.
+
+The following fixes have been stabilized:
+
+- [`superfluous-else-return`](https://docs.astral.sh/ruff/rules/superfluous-else-return/) (`RET505`)
+- [`superfluous-else-raise`](https://docs.astral.sh/ruff/rules/superfluous-else-raise/) (`RET506`)
+- [`superfluous-else-continue`](https://docs.astral.sh/ruff/rules/superfluous-else-continue/) (`RET507`)
+- [`superfluous-else-break`](https://docs.astral.sh/ruff/rules/superfluous-else-break/) (`RET508`)
+
+### Preview features
+
+- \[`flake8-simplify`\] Further simplify to binary in preview for (`SIM108`) ([#12796](https://github.com/astral-sh/ruff/pull/12796))
+- \[`pyupgrade`\] Show violations without auto-fix (`UP031`) ([#11229](https://github.com/astral-sh/ruff/pull/11229))
+
+### Rule changes
+
+- \[`flake8-import-conventions`\] Add `xml.etree.ElementTree` to default conventions ([#12455](https://github.com/astral-sh/ruff/pull/12455))
+- \[`flake8-pytest-style`\] Add a space after comma in CSV output (`PT006`) ([#12853](https://github.com/astral-sh/ruff/pull/12853))
+
+### Server
+
+- Show a message for incorrect settings ([#12781](https://github.com/astral-sh/ruff/pull/12781))
+
+### Bug fixes
+
+- \[`flake8-async`\] Do not lint yield in context manager (`ASYNC100`) ([#12896](https://github.com/astral-sh/ruff/pull/12896))
+- \[`flake8-comprehensions`\] Do not lint `async for` comprehensions (`C419`) ([#12895](https://github.com/astral-sh/ruff/pull/12895))
+- \[`flake8-return`\] Only add return `None` at end of a function (`RET503`) ([#11074](https://github.com/astral-sh/ruff/pull/11074))
+- \[`flake8-type-checking`\] Avoid treating `dataclasses.KW_ONLY` as typing-only (`TCH003`) ([#12863](https://github.com/astral-sh/ruff/pull/12863))
+- \[`pep8-naming`\] Treat `type(Protocol)` et al as metaclass base (`N805`) ([#12770](https://github.com/astral-sh/ruff/pull/12770))
+- \[`pydoclint`\] Don't enforce returns and yields in abstract methods (`DOC201`, `DOC202`) ([#12771](https://github.com/astral-sh/ruff/pull/12771))
+- \[`ruff`\] Skip tuples with slice expressions in (`RUF031`) ([#12768](https://github.com/astral-sh/ruff/pull/12768))
+- \[`ruff`\] Ignore unparenthesized tuples in subscripts when the subscript is a type annotation or type alias (`RUF031`) ([#12762](https://github.com/astral-sh/ruff/pull/12762))
+- \[`ruff`\] Ignore template strings passed to logging and `builtins._()` calls (`RUF027`) ([#12889](https://github.com/astral-sh/ruff/pull/12889))
+- \[`ruff`\] Do not remove parens for tuples with starred expressions in Python \<=3.10 (`RUF031`) ([#12784](https://github.com/astral-sh/ruff/pull/12784))
+- Evaluate default parameter values for a function in that function's enclosing scope ([#12852](https://github.com/astral-sh/ruff/pull/12852))
+
+### Other changes
+
+- Respect VS Code cell metadata when detecting the language of Jupyter Notebook cells ([#12864](https://github.com/astral-sh/ruff/pull/12864))
+- Respect `kernelspec` notebook metadata when detecting the preferred language for a Jupyter Notebook ([#12875](https://github.com/astral-sh/ruff/pull/12875))
+
 ## 0.5.7
 
 ### Preview features

CONTRIBUTING.md

@@ -361,7 +361,7 @@ even patch releases may contain [non-backwards-compatible changes](https://semve
         downstream jobs manually if needed.
 1. Verify the GitHub release:
     1. The Changelog should match the content of `CHANGELOG.md`
-    1. Append the contributors from the `bump.sh` script
+    1. Append the contributors from the `scripts/release.sh` script
 1. If needed, [update the schemastore](https://github.com/astral-sh/ruff/blob/main/scripts/update_schemastore.py).
     1. One can determine if an update is needed when
         `git diff old-version-tag new-version-tag -- ruff.schema.json` returns a non-empty diff.

Cargo.lock

@@ -228,9 +228,9 @@ dependencies = [
 
 [[package]]
 name = "camino"
-version = "1.1.7"
+version = "1.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e0ec6b951b160caa93cc0c7b209e5a3bff7aae9062213451ac99493cd844c239"
+checksum = "8b96ec4966b5813e2c0507c1f86115c8c5abaadc3980879c3424042a02fd1ad3"
 
 [[package]]
 name = "cast"
@@ -270,6 +270,12 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fd16c4719339c4530435d38e511904438d07cce7950afa3718a84ac36c10e89e"
 
+[[package]]
+name = "cfg_aliases"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
+
 [[package]]
 name = "chic"
 version = "1.2.2"
@@ -320,9 +326,9 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "4.5.15"
+version = "4.5.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "11d8838454fda655dafd3accb2b6e2bea645b9e4078abe84a22ceb947235c5cc"
+checksum = "ed6719fffa43d0d87e5fd8caeab59be1554fb028cd30edc88fc4369b17971019"
 dependencies = [
  "clap_builder",
  "clap_derive",
@@ -395,7 +401,7 @@ version = "3.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2f8c93eb5f77c9050c7750e14f13ef1033a40a0aac70c6371535b6763a01438c"
 dependencies = [
- "nix",
+ "nix 0.28.0",
  "terminfo",
  "thiserror",
  "which",
@@ -612,12 +618,12 @@ checksum = "7a81dae078cea95a014a339291cec439d2f232ebe854a9d672b796c6afafa9b7"
 
 [[package]]
 name = "ctrlc"
-version = "3.4.4"
+version = "3.4.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "672465ae37dc1bc6380a6547a8883d5dd397b0f1faaad4f265726cc7042a5345"
+checksum = "90eeab0aa92f3f9b4e87f258c72b139c207d251f9cbc1080a0086b86a8870dd3"
 dependencies = [
- "nix",
- "windows-sys 0.52.0",
+ "nix 0.29.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -1047,9 +1053,9 @@ dependencies = [
 
 [[package]]
 name = "indexmap"
-version = "2.3.0"
+version = "2.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "de3fc2e30ba82dd1b3911c8de1ffc143c74a914a14e99514d7637e3099df5ea0"
+checksum = "93ead53efc7ea8ed3cfb0c79fc8023fbb782a5432b52830b6518941cebe6505c"
 dependencies = [
  "equivalent",
  "hashbrown",
@@ -1215,9 +1221,9 @@ checksum = "8b23360e99b8717f20aaa4598f5a6541efbe30630039fbc7706cf954a87947ae"
 
 [[package]]
 name = "js-sys"
-version = "0.3.69"
+version = "0.3.70"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "29c15563dc2726973df627357ce0c9ddddbea194836909d655df6a75d2cf296d"
+checksum = "1868808506b929d7b0cfa8f75951347aa71bb21144b7791bae35d9bccfcfe37a"
 dependencies = [
  "wasm-bindgen",
 ]
@@ -1250,9 +1256,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.155"
+version = "0.2.157"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "97b3888a4aecf77e811145cadf6eef5901f4782c53886191b2f693f24761847c"
+checksum = "374af5f94e54fa97cf75e945cce8a6b201e88a1a07e688b47dfd2a59c66dbd86"
 
 [[package]]
 name = "libcst"
@@ -1388,6 +1394,16 @@ dependencies = [
  "libmimalloc-sys",
 ]
 
+[[package]]
+name = "minicov"
+version = "0.3.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c71e683cd655513b99affab7d317deb690528255a0d5f717f1024093c12b169"
+dependencies = [
+ "cc",
+ "walkdir",
+]
+
 [[package]]
 name = "minimal-lexical"
 version = "0.2.1"
@@ -1438,7 +1454,19 @@ checksum = "ab2156c4fce2f8df6c499cc1c763e4394b7482525bf2a9701c9d79d215f519e4"
 dependencies = [
  "bitflags 2.6.0",
  "cfg-if",
- "cfg_aliases",
+ "cfg_aliases 0.1.1",
+ "libc",
+]
+
+[[package]]
+name = "nix"
+version = "0.29.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "71e2746dc3a24dd78b3cfcb7be93368c6de9963d30f43a6a73998a9cf4b17b46"
+dependencies = [
+ "bitflags 2.6.0",
+ "cfg-if",
+ "cfg_aliases 0.2.1",
  "libc",
 ]
 
@@ -1525,9 +1553,9 @@ checksum = "04744f49eae99ab78e0d5c0b603ab218f515ea8cfe5a456d7629ad883a3b6e7d"
 
 [[package]]
 name = "ordermap"
-version = "0.5.1"
+version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8c81974681ab4f0cc9fe49cad56f821d1cc67a08cd2caa9b5d58b0adaa5dd36d"
+checksum = "61d7d835be600a7ac71b24e39c92fe6fad9e818b3c71bfc379e3ba65e327d77f"
 dependencies = [
  "indexmap",
 ]
@@ -1905,6 +1933,7 @@ dependencies = [
  "rustc-hash 2.0.0",
  "salsa",
  "smallvec",
+ "static_assertions",
  "tempfile",
  "tracing",
  "walkdir",
@@ -2061,7 +2090,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.5.7"
+version = "0.6.1"
 dependencies = [
  "anyhow",
  "argfile",
@@ -2253,7 +2282,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_linter"
-version = "0.5.7"
+version = "0.6.1"
 dependencies = [
  "aho-corasick",
  "annotate-snippets 0.9.2",
@@ -2573,7 +2602,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_wasm"
-version = "0.5.7"
+version = "0.6.1"
 dependencies = [
  "console_error_panic_hook",
  "console_log",
@@ -2800,9 +2829,9 @@ checksum = "1c107b6f4780854c8b126e228ea8869f4d7b71260f962fefb57b996b8959ba6b"
 
 [[package]]
 name = "serde"
-version = "1.0.206"
+version = "1.0.208"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5b3e4cd94123dd520a128bcd11e34d9e9e423e7e3e50425cb1b4b1e3549d0284"
+checksum = "cff085d2cb684faa248efb494c39b68e522822ac0de72ccf08109abde717cfb2"
 dependencies = [
  "serde_derive",
 ]
@@ -2820,9 +2849,9 @@ dependencies = [
 
 [[package]]
 name = "serde_derive"
-version = "1.0.206"
+version = "1.0.208"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fabfb6138d2383ea8208cf98ccf69cdfb1aff4088460681d84189aa259762f97"
+checksum = "24008e81ff7613ed8e5ba0cfaf24e2c2f1e5b8a0495711e44fcd4882fca62bcf"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -2842,9 +2871,9 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.124"
+version = "1.0.125"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "66ad62847a56b3dba58cc891acd13884b9c61138d330c0d7b6181713d4fce38d"
+checksum = "83c8e735a073ccf5be70aa8066aa984eaf2fa000db6c8d0100ae605b366d31ed"
 dependencies = [
  "itoa",
  "memchr",
@@ -3003,9 +3032,9 @@ checksum = "81cdd64d312baedb58e21336b31bc043b77e01cc99033ce76ef539f78e965ebc"
 
 [[package]]
 name = "syn"
-version = "2.0.74"
+version = "2.0.75"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1fceb41e3d546d0bd83421d3409b1460cc7444cd389341a4c880fe7a042cb3d7"
+checksum = "f6af063034fc1935ede7be0122941bafa9bacb949334d090b77ca98b5817c7d9"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3527,19 +3556,20 @@ checksum = "9c8d87e72b64a3b4db28d11ce29237c246188f4f51057d65a7eab63b7987e423"
 
 [[package]]
 name = "wasm-bindgen"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4be2531df63900aeb2bca0daaaddec08491ee64ceecbee5076636a3b026795a8"
+checksum = "a82edfc16a6c469f5f44dc7b571814045d60404b55a0ee849f9bcfa2e63dd9b5"
 dependencies = [
  "cfg-if",
+ "once_cell",
  "wasm-bindgen-macro",
 ]
 
 [[package]]
 name = "wasm-bindgen-backend"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "614d787b966d3989fa7bb98a654e369c762374fd3213d212cfc0251257e747da"
+checksum = "9de396da306523044d3302746f1208fa71d7532227f15e347e2d93e4145dd77b"
 dependencies = [
  "bumpalo",
  "log",
@@ -3552,9 +3582,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-futures"
-version = "0.4.42"
+version = "0.4.43"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "76bc14366121efc8dbb487ab05bcc9d346b3b5ec0eaa76e46594cabbe51762c0"
+checksum = "61e9300f63a621e96ed275155c108eb6f843b6a26d053f122ab69724559dc8ed"
 dependencies = [
  "cfg-if",
  "js-sys",
@@ -3564,9 +3594,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-macro"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a1f8823de937b71b9460c0c34e25f3da88250760bec0ebac694b49997550d726"
+checksum = "585c4c91a46b072c92e908d99cb1dcdf95c5218eeb6f3bf1efa991ee7a68cccf"
 dependencies = [
  "quote",
  "wasm-bindgen-macro-support",
@@ -3574,9 +3604,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-macro-support"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e94f17b526d0a461a191c78ea52bbce64071ed5c04c9ffe424dcb38f74171bb7"
+checksum = "afc340c74d9005395cf9dd098506f7f44e38f2b4a21c6aaacf9a105ea5e1e836"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3587,18 +3617,19 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-shared"
-version = "0.2.92"
+version = "0.2.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "af190c94f2773fdb3729c55b007a722abb5384da03bc0986df4c289bf5567e96"
+checksum = "c62a0a307cb4a311d3a07867860911ca130c3494e8c2719593806c08bc5d0484"
 
 [[package]]
 name = "wasm-bindgen-test"
-version = "0.3.42"
+version = "0.3.43"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d9bf62a58e0780af3e852044583deee40983e5886da43a271dd772379987667b"
+checksum = "68497a05fb21143a08a7d24fc81763384a3072ee43c44e86aad1744d6adef9d9"
 dependencies = [
  "console_error_panic_hook",
  "js-sys",
+ "minicov",
  "scoped-tls",
  "wasm-bindgen",
  "wasm-bindgen-futures",
@@ -3607,9 +3638,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-test-macro"
-version = "0.3.42"
+version = "0.3.43"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b7f89739351a2e03cb94beb799d47fb2cac01759b40ec441f7de39b00cbf7ef0"
+checksum = "4b8220be1fa9e4c889b30fd207d4906657e7e90b12e0e6b0c8b8d8709f5de021"
 dependencies = [
  "proc-macro2",
  "quote",

README.md

@@ -136,8 +136,8 @@ curl -LsSf https://astral.sh/ruff/install.sh | sh
 powershell -c "irm https://astral.sh/ruff/install.ps1 | iex"
 
 # For a specific version.
-curl -LsSf https://astral.sh/ruff/0.5.7/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.5.7/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.6.1/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.6.1/install.ps1 | iex"
 ```
 
 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -170,7 +170,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.5.7
+  rev: v0.6.1
   hooks:
     # Run the linter.
     - id: ruff

crates/red_knot_python_semantic/Cargo.toml

@@ -26,10 +26,11 @@ countme = { workspace = true }
 once_cell = { workspace = true }
 ordermap = { workspace = true }
 salsa = { workspace = true }
-smallvec = { 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 }

crates/red_knot_python_semantic/src/module_name.rs

@@ -168,6 +168,24 @@ impl ModuleName {
         };
         Some(Self(name))
     }
+
+    /// Extend `self` with the components of `other`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use red_knot_python_semantic::ModuleName;
+    ///
+    /// let mut module_name = ModuleName::new_static("foo").unwrap();
+    /// module_name.extend(&ModuleName::new_static("bar").unwrap());
+    /// assert_eq!(&module_name, "foo.bar");
+    /// module_name.extend(&ModuleName::new_static("baz.eggs.ham").unwrap());
+    /// assert_eq!(&module_name, "foo.bar.baz.eggs.ham");
+    /// ```
+    pub fn extend(&mut self, other: &ModuleName) {
+        self.0.push('.');
+        self.0.push_str(other);
+    }
 }
 
 impl Deref for ModuleName {

crates/red_knot_python_semantic/src/module_resolver/mod.rs

@@ -2,7 +2,7 @@ use std::iter::FusedIterator;
 
 pub(crate) use module::Module;
 pub use resolver::resolve_module;
-pub(crate) use resolver::SearchPaths;
+pub(crate) use resolver::{file_to_module, SearchPaths};
 use ruff_db::system::SystemPath;
 pub use typeshed::vendored_typeshed_stubs;
 

crates/red_knot_python_semantic/src/module_resolver/module.rs

@@ -77,3 +77,9 @@ pub enum ModuleKind {
     /// A python package (`foo/__init__.py` or `foo/__init__.pyi`)
     Package,
 }
+
+impl ModuleKind {
+    pub const fn is_package(self) -> bool {
+        matches!(self, ModuleKind::Package)
+    }
+}

crates/red_knot_python_semantic/src/semantic_index.rs

@@ -16,10 +16,9 @@ use crate::semantic_index::expression::Expression;
 use crate::semantic_index::symbol::{
     FileScopeId, NodeWithScopeKey, NodeWithScopeRef, Scope, ScopeId, ScopedSymbolId, SymbolTable,
 };
+use crate::semantic_index::use_def::UseDefMap;
 use crate::Db;
 
-pub(crate) use self::use_def::UseDefMap;
-
 pub mod ast_ids;
 mod builder;
 pub mod definition;
@@ -27,6 +26,8 @@ pub mod expression;
 pub mod symbol;
 mod use_def;
 
+pub(crate) use self::use_def::{DefinitionWithConstraints, DefinitionWithConstraintsIterator};
+
 type SymbolMap = hashbrown::HashMap<ScopedSymbolId, (), ()>;
 
 /// Returns the semantic index for `file`.
@@ -126,7 +127,7 @@ impl<'db> SemanticIndex<'db> {
     ///
     /// Use the Salsa cached [`use_def_map()`] query if you only need the
     /// use-def map for a single scope.
-    pub(super) fn use_def_map(&self, scope_id: FileScopeId) -> Arc<UseDefMap<'db>> {
+    pub(super) fn use_def_map(&self, scope_id: FileScopeId) -> Arc<UseDefMap> {
         self.use_def_maps[scope_id].clone()
     }
 
@@ -310,12 +311,29 @@ mod tests {
     use ruff_text_size::{Ranged, TextRange};
 
     use crate::db::tests::TestDb;
-    use crate::semantic_index::ast_ids::HasScopedUseId;
-    use crate::semantic_index::definition::{DefinitionKind, DefinitionNode};
-    use crate::semantic_index::symbol::{FileScopeId, Scope, ScopeKind, SymbolTable};
+    use crate::semantic_index::ast_ids::{HasScopedUseId, ScopedUseId};
+    use crate::semantic_index::definition::{Definition, DefinitionKind};
+    use crate::semantic_index::symbol::{
+        FileScopeId, Scope, ScopeKind, ScopedSymbolId, SymbolTable,
+    };
+    use crate::semantic_index::use_def::UseDefMap;
     use crate::semantic_index::{global_scope, semantic_index, symbol_table, use_def_map};
     use crate::Db;
 
+    impl UseDefMap<'_> {
+        fn first_public_definition(&self, symbol: ScopedSymbolId) -> Option<Definition<'_>> {
+            self.public_definitions(symbol)
+                .next()
+                .map(|constrained_definition| constrained_definition.definition)
+        }
+
+        fn first_use_definition(&self, use_id: ScopedUseId) -> Option<Definition<'_>> {
+            self.use_definitions(use_id)
+                .next()
+                .map(|constrained_definition| constrained_definition.definition)
+        }
+    }
+
     struct TestCase {
         db: TestDb,
         file: File,
@@ -374,11 +392,8 @@ mod tests {
         let foo = global_table.symbol_id_by_name("foo").unwrap();
 
         let use_def = use_def_map(&db, scope);
-        let definition = use_def.public_definition(foo).unwrap();
-        assert!(matches!(
-            definition.kind(&db),
-            DefinitionKind::Node(DefinitionNode::Import(_))
-        ));
+        let definition = use_def.first_public_definition(foo).unwrap();
+        assert!(matches!(definition.node(&db), DefinitionKind::Import(_)));
     }
 
     #[test]
@@ -413,15 +428,15 @@ mod tests {
 
         let use_def = use_def_map(&db, scope);
         let definition = use_def
-            .public_definition(
+            .first_public_definition(
                 global_table
                     .symbol_id_by_name("foo")
                     .expect("symbol to exist"),
             )
             .unwrap();
         assert!(matches!(
-            definition.kind(&db),
-            DefinitionKind::Node(DefinitionNode::ImportFrom(_))
+            definition.node(&db),
+            DefinitionKind::ImportFrom(_)
         ));
     }
 
@@ -440,11 +455,11 @@ mod tests {
         );
         let use_def = use_def_map(&db, scope);
         let definition = use_def
-            .public_definition(global_table.symbol_id_by_name("x").expect("symbol exists"))
+            .first_public_definition(global_table.symbol_id_by_name("x").expect("symbol exists"))
             .unwrap();
         assert!(matches!(
-            definition.kind(&db),
-            DefinitionKind::Node(DefinitionNode::Assignment(_))
+            definition.node(&db),
+            DefinitionKind::Assignment(_)
         ));
     }
 
@@ -477,11 +492,11 @@ y = 2
 
         let use_def = index.use_def_map(class_scope_id);
         let definition = use_def
-            .public_definition(class_table.symbol_id_by_name("x").expect("symbol exists"))
+            .first_public_definition(class_table.symbol_id_by_name("x").expect("symbol exists"))
             .unwrap();
         assert!(matches!(
-            definition.kind(&db),
-            DefinitionKind::Node(DefinitionNode::Assignment(_))
+            definition.node(&db),
+            DefinitionKind::Assignment(_)
         ));
     }
 
@@ -513,18 +528,115 @@ y = 2
 
         let use_def = index.use_def_map(function_scope_id);
         let definition = use_def
-            .public_definition(
+            .first_public_definition(
                 function_table
                     .symbol_id_by_name("x")
                     .expect("symbol exists"),
             )
             .unwrap();
         assert!(matches!(
-            definition.kind(&db),
-            DefinitionKind::Node(DefinitionNode::Assignment(_))
+            definition.node(&db),
+            DefinitionKind::Assignment(_)
         ));
     }
 
+    #[test]
+    fn function_parameter_symbols() {
+        let TestCase { db, file } = test_case(
+            "
+def f(a: str, /, b: str, c: int = 1, *args, d: int = 2, **kwargs):
+    pass
+",
+        );
+
+        let index = semantic_index(&db, file);
+        let global_table = symbol_table(&db, global_scope(&db, file));
+
+        assert_eq!(names(&global_table), vec!["f", "str", "int"]);
+
+        let [(function_scope_id, _function_scope)] = index
+            .child_scopes(FileScopeId::global())
+            .collect::<Vec<_>>()[..]
+        else {
+            panic!("Expected a function scope")
+        };
+
+        let function_table = index.symbol_table(function_scope_id);
+        assert_eq!(
+            names(&function_table),
+            vec!["a", "b", "c", "args", "d", "kwargs"],
+        );
+
+        let use_def = index.use_def_map(function_scope_id);
+        for name in ["a", "b", "c", "d"] {
+            let definition = use_def
+                .first_public_definition(
+                    function_table
+                        .symbol_id_by_name(name)
+                        .expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(
+                definition.node(&db),
+                DefinitionKind::ParameterWithDefault(_)
+            ));
+        }
+        for name in ["args", "kwargs"] {
+            let definition = use_def
+                .first_public_definition(
+                    function_table
+                        .symbol_id_by_name(name)
+                        .expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(definition.node(&db), DefinitionKind::Parameter(_)));
+        }
+    }
+
+    #[test]
+    fn lambda_parameter_symbols() {
+        let TestCase { db, file } = test_case("lambda a, b, c=1, *args, d=2, **kwargs: None");
+
+        let index = semantic_index(&db, file);
+        let global_table = symbol_table(&db, global_scope(&db, file));
+
+        assert!(names(&global_table).is_empty());
+
+        let [(lambda_scope_id, _lambda_scope)] = index
+            .child_scopes(FileScopeId::global())
+            .collect::<Vec<_>>()[..]
+        else {
+            panic!("Expected a lambda scope")
+        };
+
+        let lambda_table = index.symbol_table(lambda_scope_id);
+        assert_eq!(
+            names(&lambda_table),
+            vec!["a", "b", "c", "args", "d", "kwargs"],
+        );
+
+        let use_def = index.use_def_map(lambda_scope_id);
+        for name in ["a", "b", "c", "d"] {
+            let definition = use_def
+                .first_public_definition(
+                    lambda_table.symbol_id_by_name(name).expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(
+                definition.node(&db),
+                DefinitionKind::ParameterWithDefault(_)
+            ));
+        }
+        for name in ["args", "kwargs"] {
+            let definition = use_def
+                .first_public_definition(
+                    lambda_table.symbol_id_by_name(name).expect("symbol exists"),
+                )
+                .unwrap();
+            assert!(matches!(definition.node(&db), DefinitionKind::Parameter(_)));
+        }
+    }
+
     /// Test case to validate that the comprehension scope is correctly identified and that the target
     /// variable is defined only in the comprehension scope and not in the global scope.
     #[test]
@@ -591,10 +703,8 @@ y = 2
         let element_use_id =
             element.scoped_use_id(&db, comprehension_scope_id.to_scope_id(&db, file));
 
-        let definition = use_def.definition_for_use(element_use_id).unwrap();
-        let DefinitionKind::Node(DefinitionNode::Comprehension(comprehension)) =
-            definition.kind(&db)
-        else {
+        let definition = use_def.first_use_definition(element_use_id).unwrap();
+        let DefinitionKind::Comprehension(comprehension) = definition.node(&db) else {
             panic!("expected generator definition")
         };
         let ast::Comprehension { target, .. } = comprehension.node();
@@ -608,7 +718,7 @@ y = 2
     /// the outer comprehension scope and the variables are correctly defined in the respective
     /// scopes.
     #[test]
-    fn nested_comprehensions() {
+    fn nested_generators() {
         let TestCase { db, file } = test_case(
             "
 [{x for x in iter2} for y in iter1]
@@ -641,7 +751,7 @@ y = 2
             .child_scopes(comprehension_scope_id)
             .collect::<Vec<_>>()[..]
         else {
-            panic!("expected one inner comprehension scope")
+            panic!("expected one inner generator scope")
         };
 
         assert_eq!(inner_comprehension_scope.kind(), ScopeKind::Comprehension);
@@ -691,16 +801,13 @@ def func():
 
         let use_def = index.use_def_map(FileScopeId::global());
         let definition = use_def
-            .public_definition(
+            .first_public_definition(
                 global_table
                     .symbol_id_by_name("func")
                     .expect("symbol exists"),
             )
             .unwrap();
-        assert!(matches!(
-            definition.kind(&db),
-            DefinitionKind::Node(DefinitionNode::Function(_))
-        ));
+        assert!(matches!(definition.node(&db), DefinitionKind::Function(_)));
     }
 
     #[test]
@@ -800,9 +907,8 @@ 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.definition_for_use(x_use_id).unwrap();
-        let DefinitionKind::Node(DefinitionNode::Assignment(assignment)) = definition.kind(&db)
-        else {
+        let definition = use_def.first_use_definition(x_use_id).unwrap();
+        let DefinitionKind::Assignment(assignment) = definition.node(&db) else {
             panic!("should be an assignment definition")
         };
         let ast::Expr::NumberLiteral(ast::ExprNumberLiteral {

crates/red_knot_python_semantic/src/semantic_index/builder.rs

@@ -8,20 +8,21 @@ use ruff_index::IndexVec;
 use ruff_python_ast as ast;
 use ruff_python_ast::name::Name;
 use ruff_python_ast::visitor::{walk_expr, walk_stmt, Visitor};
+use ruff_python_ast::AnyParameterRef;
 
 use crate::ast_node_ref::AstNodeRef;
 use crate::semantic_index::ast_ids::node_key::ExpressionNodeKey;
 use crate::semantic_index::ast_ids::AstIdsBuilder;
 use crate::semantic_index::definition::{
-    AssignmentDefinitionNodeRef, ComprehensionDefinitionNodeRef, Definition, DefinitionKind,
-    DefinitionNodeKey, DefinitionNodeRef, ImportFromDefinitionNodeRef,
+    AssignmentDefinitionNodeRef, ComprehensionDefinitionNodeRef, Definition, DefinitionNodeKey,
+    DefinitionNodeRef, ImportFromDefinitionNodeRef,
 };
 use crate::semantic_index::expression::Expression;
 use crate::semantic_index::symbol::{
     FileScopeId, NodeWithScopeKey, NodeWithScopeRef, Scope, ScopeId, ScopedSymbolId, SymbolFlags,
     SymbolTableBuilder,
 };
-use crate::semantic_index::use_def::{BasicBlockId, UseDefMapBuilder};
+use crate::semantic_index::use_def::{FlowSnapshot, UseDefMapBuilder};
 use crate::semantic_index::SemanticIndex;
 use crate::Db;
 
@@ -33,8 +34,8 @@ pub(super) struct SemanticIndexBuilder<'db> {
     scope_stack: Vec<FileScopeId>,
     /// The assignment we're currently visiting.
     current_assignment: Option<CurrentAssignment<'db>>,
-    /// Basic block ending at each `break` in the current loop.
-    loop_breaks: Vec<BasicBlockId>,
+    /// Flow states at each `break` in the current loop.
+    loop_break_states: Vec<FlowSnapshot>,
 
     // Semantic Index fields
     scopes: IndexVec<FileScopeId, Scope>,
@@ -56,7 +57,7 @@ impl<'db> SemanticIndexBuilder<'db> {
             module: parsed,
             scope_stack: Vec::new(),
             current_assignment: None,
-            loop_breaks: vec![],
+            loop_break_states: vec![],
 
             scopes: IndexVec::new(),
             symbol_tables: IndexVec::new(),
@@ -98,8 +99,7 @@ impl<'db> SemanticIndexBuilder<'db> {
 
         let file_scope_id = self.scopes.push(scope);
         self.symbol_tables.push(SymbolTableBuilder::new());
-        self.use_def_maps
-            .push(UseDefMapBuilder::new(self.db, self.file, file_scope_id));
+        self.use_def_maps.push(UseDefMapBuilder::new());
         let ast_id_scope = self.ast_ids.push(AstIdsBuilder::new());
 
         #[allow(unsafe_code)]
@@ -133,50 +133,41 @@ impl<'db> SemanticIndexBuilder<'db> {
         &mut self.symbol_tables[scope_id]
     }
 
-    fn current_use_def_map(&mut self) -> &mut UseDefMapBuilder<'db> {
+    fn current_use_def_map_mut(&mut self) -> &mut UseDefMapBuilder<'db> {
         let scope_id = self.current_scope();
         &mut self.use_def_maps[scope_id]
     }
 
+    fn current_use_def_map(&self) -> &UseDefMapBuilder<'db> {
+        let scope_id = self.current_scope();
+        &self.use_def_maps[scope_id]
+    }
+
     fn current_ast_ids(&mut self) -> &mut AstIdsBuilder {
         let scope_id = self.current_scope();
         &mut self.ast_ids[scope_id]
     }
 
-    /// Start a new basic block and return the previous block's ID.
-    fn next_block(&mut self) -> BasicBlockId {
-        self.current_use_def_map().next_block(/* sealed */ true)
+    fn flow_snapshot(&self) -> FlowSnapshot {
+        self.current_use_def_map().snapshot()
     }
 
-    /// Start a new unsealed basic block and return the previous block's ID.
-    fn next_block_unsealed(&mut self) -> BasicBlockId {
-        self.current_use_def_map().next_block(/* sealed */ false)
+    fn flow_restore(&mut self, state: FlowSnapshot) {
+        self.current_use_def_map_mut().restore(state);
     }
 
-    /// Seal an unsealed basic block.
-    fn seal_block(&mut self) {
-        self.current_use_def_map().seal_current_block();
-    }
-
-    /// Start a new basic block with the given block as predecessor.
-    fn new_block_from(&mut self, predecessor: BasicBlockId) {
-        self.current_use_def_map()
-            .new_block_from(predecessor, /* sealed */ true);
-    }
-
-    /// Add a predecessor to the current block.
-    fn merge_block(&mut self, predecessor: BasicBlockId) {
-        self.current_use_def_map().merge_block(predecessor);
-    }
-
-    /// Add predecessors to the current block.
-    fn merge_blocks(&mut self, predecessors: Vec<BasicBlockId>) {
-        self.current_use_def_map().merge_blocks(predecessors);
+    fn flow_merge(&mut self, state: FlowSnapshot) {
+        self.current_use_def_map_mut().merge(state);
     }
 
     fn add_or_update_symbol(&mut self, name: Name, flags: SymbolFlags) -> ScopedSymbolId {
         let symbol_table = self.current_symbol_table();
-        symbol_table.add_or_update_symbol(name, flags)
+        let (symbol_id, added) = symbol_table.add_or_update_symbol(name, flags);
+        if added {
+            let use_def_map = self.current_use_def_map_mut();
+            use_def_map.add_symbol(symbol_id);
+        }
+        symbol_id
     }
 
     fn add_definition<'a>(
@@ -191,21 +182,30 @@ impl<'db> SemanticIndexBuilder<'db> {
             self.current_scope(),
             symbol,
             #[allow(unsafe_code)]
-            DefinitionKind::Node(unsafe { definition_node.into_owned(self.module.clone()) }),
+            unsafe {
+                definition_node.into_owned(self.module.clone())
+            },
             countme::Count::default(),
         );
 
         self.definitions_by_node
             .insert(definition_node.key(), definition);
-        self.current_use_def_map()
+        self.current_use_def_map_mut()
             .record_definition(symbol, definition);
 
         definition
     }
 
+    fn add_constraint(&mut self, constraint_node: &ast::Expr) -> Expression<'db> {
+        let expression = self.add_standalone_expression(constraint_node);
+        self.current_use_def_map_mut().record_constraint(expression);
+
+        expression
+    }
+
     /// Record an expression that needs to be a Salsa ingredient, because we need to infer its type
     /// standalone (type narrowing tests, RHS of an assignment.)
-    fn add_standalone_expression(&mut self, expression_node: &ast::Expr) {
+    fn add_standalone_expression(&mut self, expression_node: &ast::Expr) -> Expression<'db> {
         let expression = Expression::new(
             self.db,
             self.file,
@@ -218,6 +218,7 @@ impl<'db> SemanticIndexBuilder<'db> {
         );
         self.expressions_by_node
             .insert(expression_node.into(), expression);
+        expression
     }
 
     fn with_type_params(
@@ -309,6 +310,23 @@ impl<'db> SemanticIndexBuilder<'db> {
         }
     }
 
+    fn declare_parameter(&mut self, parameter: AnyParameterRef) {
+        let symbol =
+            self.add_or_update_symbol(parameter.name().id().clone(), SymbolFlags::IS_DEFINED);
+
+        let definition = self.add_definition(symbol, parameter);
+
+        if let AnyParameterRef::NonVariadic(with_default) = parameter {
+            // Insert a mapping from the parameter to the same definition.
+            // This ensures that calling `HasTy::ty` on the inner parameter returns
+            // a valid type (and doesn't panic)
+            self.definitions_by_node.insert(
+                DefinitionNodeRef::from(AnyParameterRef::Variadic(&with_default.parameter)).key(),
+                definition,
+            );
+        }
+    }
+
     pub(super) fn build(mut self) -> SemanticIndex<'db> {
         let module = self.module;
         self.visit_body(module.suite());
@@ -376,6 +394,16 @@ where
                     .add_or_update_symbol(function_def.name.id.clone(), SymbolFlags::IS_DEFINED);
                 self.add_definition(symbol, function_def);
 
+                // The default value of the parameters needs to be evaluated in the
+                // enclosing scope.
+                for default in function_def
+                    .parameters
+                    .iter_non_variadic_params()
+                    .filter_map(|param| param.default.as_deref())
+                {
+                    self.visit_expr(default);
+                }
+
                 self.with_type_params(
                     NodeWithScopeRef::FunctionTypeParameters(function_def),
                     function_def.type_params.as_deref(),
@@ -386,6 +414,12 @@ where
                         }
 
                         builder.push_scope(NodeWithScopeRef::Function(function_def));
+
+                        // Add symbols and definitions for the parameters to the function scope.
+                        for parameter in &*function_def.parameters {
+                            builder.declare_parameter(parameter);
+                        }
+
                         builder.visit_body(&function_def.body);
                         builder.pop_scope()
                     },
@@ -463,19 +497,22 @@ where
             }
             ast::Stmt::If(node) => {
                 self.visit_expr(&node.test);
-                let pre_if = self.next_block();
+                let pre_if = self.flow_snapshot();
+                self.add_constraint(&node.test);
                 self.visit_body(&node.body);
-                let mut post_clauses: Vec<BasicBlockId> = vec![];
+                let mut post_clauses: Vec<FlowSnapshot> = vec![];
                 for clause in &node.elif_else_clauses {
                     // snapshot after every block except the last; the last one will just become
                     // the state that we merge the other snapshots into
-                    post_clauses.push(self.next_block());
+                    post_clauses.push(self.flow_snapshot());
                     // we can only take an elif/else branch if none of the previous ones were
                     // taken, so the block entry state is always `pre_if`
-                    self.new_block_from(pre_if);
+                    self.flow_restore(pre_if.clone());
                     self.visit_elif_else_clause(clause);
                 }
-                self.next_block_unsealed();
+                for post_clause_state in post_clauses {
+                    self.flow_merge(post_clause_state);
+                }
                 let has_else = node
                     .elif_else_clauses
                     .last()
@@ -483,39 +520,35 @@ where
                 if !has_else {
                     // if there's no else clause, then it's possible we took none of the branches,
                     // and the pre_if state can reach here
-                    self.merge_block(pre_if);
+                    self.flow_merge(pre_if);
                 }
-                self.merge_blocks(post_clauses);
-                self.seal_block();
             }
             ast::Stmt::While(node) => {
                 self.visit_expr(&node.test);
 
-                let pre_loop = self.next_block();
+                let pre_loop = self.flow_snapshot();
 
                 // Save aside any break states from an outer loop
-                let saved_break_states = std::mem::take(&mut self.loop_breaks);
+                let saved_break_states = std::mem::take(&mut self.loop_break_states);
                 self.visit_body(&node.body);
                 // Get the break states from the body of this loop, and restore the saved outer
                 // ones.
-                let break_states = std::mem::replace(&mut self.loop_breaks, saved_break_states);
+                let break_states =
+                    std::mem::replace(&mut self.loop_break_states, saved_break_states);
 
                 // We may execute the `else` clause without ever executing the body, so merge in
                 // the pre-loop state before visiting `else`.
-                self.next_block_unsealed();
-                self.merge_block(pre_loop);
-                self.seal_block();
+                self.flow_merge(pre_loop);
                 self.visit_body(&node.orelse);
 
                 // Breaking out of a while loop bypasses the `else` clause, so merge in the break
                 // states after visiting `else`.
-                self.next_block_unsealed();
-                self.merge_blocks(break_states);
-                self.seal_block();
+                for break_state in break_states {
+                    self.flow_merge(break_state);
+                }
             }
             ast::Stmt::Break(_) => {
-                let block_id = self.next_block();
-                self.loop_breaks.push(block_id);
+                self.loop_break_states.push(self.flow_snapshot());
             }
             _ => {
                 walk_stmt(self, stmt);
@@ -569,7 +602,7 @@ where
 
                 if flags.contains(SymbolFlags::IS_USED) {
                     let use_id = self.current_ast_ids().record_use(expr);
-                    self.current_use_def_map().record_use(symbol, use_id);
+                    self.current_use_def_map_mut().record_use(symbol, use_id);
                 }
 
                 walk_expr(self, expr);
@@ -584,9 +617,25 @@ where
             }
             ast::Expr::Lambda(lambda) => {
                 if let Some(parameters) = &lambda.parameters {
+                    // The default value of the parameters needs to be evaluated in the
+                    // enclosing scope.
+                    for default in parameters
+                        .iter_non_variadic_params()
+                        .filter_map(|param| param.default.as_deref())
+                    {
+                        self.visit_expr(default);
+                    }
                     self.visit_parameters(parameters);
                 }
                 self.push_scope(NodeWithScopeRef::Lambda(lambda));
+
+                // Add symbols and definitions for the parameters to the lambda scope.
+                if let Some(parameters) = &lambda.parameters {
+                    for parameter in &**parameters {
+                        self.declare_parameter(parameter);
+                    }
+                }
+
                 self.visit_expr(lambda.body.as_ref());
             }
             ast::Expr::If(ast::ExprIf {
@@ -596,14 +645,12 @@ where
                 // AST inspection, so we can't simplify here, need to record test expression for
                 // later checking)
                 self.visit_expr(test);
-                let pre_if = self.next_block();
+                let pre_if = self.flow_snapshot();
                 self.visit_expr(body);
-                let post_body = self.next_block();
-                self.new_block_from(pre_if);
+                let post_body = self.flow_snapshot();
+                self.flow_restore(pre_if);
                 self.visit_expr(orelse);
-                self.next_block_unsealed();
-                self.merge_block(post_body);
-                self.seal_block();
+                self.flow_merge(post_body);
             }
             ast::Expr::ListComp(
                 list_comprehension @ ast::ExprListComp {
@@ -666,6 +713,14 @@ where
             self.pop_scope();
         }
     }
+
+    fn visit_parameters(&mut self, parameters: &'ast ruff_python_ast::Parameters) {
+        // Intentionally avoid walking default expressions, as we handle them in the enclosing
+        // scope.
+        for parameter in parameters.iter().map(ast::AnyParameterRef::as_parameter) {
+            self.visit_parameter(parameter);
+        }
+    }
 }
 
 #[derive(Copy, Clone, Debug)]

crates/red_knot_python_semantic/src/semantic_index/definition.rs

@@ -1,6 +1,5 @@
 use ruff_db::files::File;
 use ruff_db::parsed::ParsedModule;
-use ruff_index::newtype_index;
 use ruff_python_ast as ast;
 
 use crate::ast_node_ref::AstNodeRef;
@@ -9,7 +8,7 @@ use crate::semantic_index::symbol::{FileScopeId, ScopeId, ScopedSymbolId};
 use crate::Db;
 
 #[salsa::tracked]
-pub(crate) struct Definition<'db> {
+pub struct Definition<'db> {
     /// The file in which the definition occurs.
     #[id]
     pub(crate) file: File,
@@ -24,7 +23,7 @@ pub(crate) struct Definition<'db> {
 
     #[no_eq]
     #[return_ref]
-    pub(crate) kind: DefinitionKind,
+    pub(crate) node: DefinitionKind,
 
     #[no_eq]
     count: countme::Count<Definition<'static>>,
@@ -36,22 +35,6 @@ impl<'db> Definition<'db> {
     }
 }
 
-#[derive(Clone, Debug)]
-pub(crate) enum DefinitionKind {
-    /// Inserted at control-flow merge points, if multiple definitions can reach the merge point.
-    ///
-    /// Operands are not kept inline, since it's not possible to construct cyclically-referential
-    /// Salsa tracked structs; they are kept instead in the
-    /// [`UseDefMap`](super::use_def::UseDefMap).
-    Phi(ScopedPhiId),
-
-    /// An assignment to the symbol.
-    Node(DefinitionNode),
-}
-
-#[newtype_index]
-pub(crate) struct ScopedPhiId;
-
 #[derive(Copy, Clone, Debug)]
 pub(crate) enum DefinitionNodeRef<'a> {
     Import(&'a ast::Alias),
@@ -62,6 +45,7 @@ pub(crate) enum DefinitionNodeRef<'a> {
     Assignment(AssignmentDefinitionNodeRef<'a>),
     AnnotatedAssignment(&'a ast::StmtAnnAssign),
     Comprehension(ComprehensionDefinitionNodeRef<'a>),
+    Parameter(ast::AnyParameterRef<'a>),
 }
 
 impl<'a> From<&'a ast::StmtFunctionDef> for DefinitionNodeRef<'a> {
@@ -112,6 +96,12 @@ impl<'a> From<ComprehensionDefinitionNodeRef<'a>> for DefinitionNodeRef<'a> {
     }
 }
 
+impl<'a> From<ast::AnyParameterRef<'a>> for DefinitionNodeRef<'a> {
+    fn from(node: ast::AnyParameterRef<'a>) -> Self {
+        Self::Parameter(node)
+    }
+}
+
 #[derive(Copy, Clone, Debug)]
 pub(crate) struct ImportFromDefinitionNodeRef<'a> {
     pub(crate) node: &'a ast::StmtImportFrom,
@@ -132,41 +122,49 @@ pub(crate) struct ComprehensionDefinitionNodeRef<'a> {
 
 impl DefinitionNodeRef<'_> {
     #[allow(unsafe_code)]
-    pub(super) unsafe fn into_owned(self, parsed: ParsedModule) -> DefinitionNode {
+    pub(super) unsafe fn into_owned(self, parsed: ParsedModule) -> DefinitionKind {
         match self {
             DefinitionNodeRef::Import(alias) => {
-                DefinitionNode::Import(AstNodeRef::new(parsed, alias))
+                DefinitionKind::Import(AstNodeRef::new(parsed, alias))
             }
             DefinitionNodeRef::ImportFrom(ImportFromDefinitionNodeRef { node, alias_index }) => {
-                DefinitionNode::ImportFrom(ImportFromDefinitionNode {
+                DefinitionKind::ImportFrom(ImportFromDefinitionKind {
                     node: AstNodeRef::new(parsed, node),
                     alias_index,
                 })
             }
             DefinitionNodeRef::Function(function) => {
-                DefinitionNode::Function(AstNodeRef::new(parsed, function))
+                DefinitionKind::Function(AstNodeRef::new(parsed, function))
             }
             DefinitionNodeRef::Class(class) => {
-                DefinitionNode::Class(AstNodeRef::new(parsed, class))
+                DefinitionKind::Class(AstNodeRef::new(parsed, class))
             }
             DefinitionNodeRef::NamedExpression(named) => {
-                DefinitionNode::NamedExpression(AstNodeRef::new(parsed, named))
+                DefinitionKind::NamedExpression(AstNodeRef::new(parsed, named))
             }
             DefinitionNodeRef::Assignment(AssignmentDefinitionNodeRef { assignment, target }) => {
-                DefinitionNode::Assignment(AssignmentDefinitionNode {
+                DefinitionKind::Assignment(AssignmentDefinitionKind {
                     assignment: AstNodeRef::new(parsed.clone(), assignment),
                     target: AstNodeRef::new(parsed, target),
                 })
             }
             DefinitionNodeRef::AnnotatedAssignment(assign) => {
-                DefinitionNode::AnnotatedAssignment(AstNodeRef::new(parsed, assign))
+                DefinitionKind::AnnotatedAssignment(AstNodeRef::new(parsed, assign))
             }
             DefinitionNodeRef::Comprehension(ComprehensionDefinitionNodeRef { node, first }) => {
-                DefinitionNode::Comprehension(ComprehensionDefinitionNode {
+                DefinitionKind::Comprehension(ComprehensionDefinitionKind {
                     node: AstNodeRef::new(parsed, node),
                     first,
                 })
             }
+            DefinitionNodeRef::Parameter(parameter) => match parameter {
+                ast::AnyParameterRef::Variadic(parameter) => {
+                    DefinitionKind::Parameter(AstNodeRef::new(parsed, parameter))
+                }
+                ast::AnyParameterRef::NonVariadic(parameter) => {
+                    DefinitionKind::ParameterWithDefault(AstNodeRef::new(parsed, parameter))
+                }
+            },
         }
     }
 
@@ -185,29 +183,35 @@ impl DefinitionNodeRef<'_> {
             }) => target.into(),
             Self::AnnotatedAssignment(node) => node.into(),
             Self::Comprehension(ComprehensionDefinitionNodeRef { node, first: _ }) => node.into(),
+            Self::Parameter(node) => match node {
+                ast::AnyParameterRef::Variadic(parameter) => parameter.into(),
+                ast::AnyParameterRef::NonVariadic(parameter) => parameter.into(),
+            },
         }
     }
 }
 
 #[derive(Clone, Debug)]
-pub enum DefinitionNode {
+pub enum DefinitionKind {
     Import(AstNodeRef<ast::Alias>),
-    ImportFrom(ImportFromDefinitionNode),
+    ImportFrom(ImportFromDefinitionKind),
     Function(AstNodeRef<ast::StmtFunctionDef>),
     Class(AstNodeRef<ast::StmtClassDef>),
     NamedExpression(AstNodeRef<ast::ExprNamed>),
-    Assignment(AssignmentDefinitionNode),
+    Assignment(AssignmentDefinitionKind),
     AnnotatedAssignment(AstNodeRef<ast::StmtAnnAssign>),
-    Comprehension(ComprehensionDefinitionNode),
+    Comprehension(ComprehensionDefinitionKind),
+    Parameter(AstNodeRef<ast::Parameter>),
+    ParameterWithDefault(AstNodeRef<ast::ParameterWithDefault>),
 }
 
 #[derive(Clone, Debug)]
-pub struct ComprehensionDefinitionNode {
+pub struct ComprehensionDefinitionKind {
     node: AstNodeRef<ast::Comprehension>,
     first: bool,
 }
 
-impl ComprehensionDefinitionNode {
+impl ComprehensionDefinitionKind {
     pub(crate) fn node(&self) -> &ast::Comprehension {
         self.node.node()
     }
@@ -218,12 +222,12 @@ impl ComprehensionDefinitionNode {
 }
 
 #[derive(Clone, Debug)]
-pub struct ImportFromDefinitionNode {
+pub struct ImportFromDefinitionKind {
     node: AstNodeRef<ast::StmtImportFrom>,
     alias_index: usize,
 }
 
-impl ImportFromDefinitionNode {
+impl ImportFromDefinitionKind {
     pub(crate) fn import(&self) -> &ast::StmtImportFrom {
         self.node.node()
     }
@@ -235,15 +239,19 @@ impl ImportFromDefinitionNode {
 
 #[derive(Clone, Debug)]
 #[allow(dead_code)]
-pub struct AssignmentDefinitionNode {
+pub struct AssignmentDefinitionKind {
     assignment: AstNodeRef<ast::StmtAssign>,
     target: AstNodeRef<ast::ExprName>,
 }
 
-impl AssignmentDefinitionNode {
+impl AssignmentDefinitionKind {
     pub(crate) fn assignment(&self) -> &ast::StmtAssign {
         self.assignment.node()
     }
+
+    pub(crate) fn target(&self) -> &ast::ExprName {
+        self.target.node()
+    }
 }
 
 #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
@@ -290,3 +298,15 @@ impl From<&ast::Comprehension> for DefinitionNodeKey {
         Self(NodeKey::from_node(node))
     }
 }
+
+impl From<&ast::Parameter> for DefinitionNodeKey {
+    fn from(node: &ast::Parameter) -> Self {
+        Self(NodeKey::from_node(node))
+    }
+}
+
+impl From<&ast::ParameterWithDefault> for DefinitionNodeKey {
+    fn from(node: &ast::ParameterWithDefault) -> Self {
+        Self(NodeKey::from_node(node))
+    }
+}

crates/red_knot_python_semantic/src/semantic_index/expression.rs

@@ -21,7 +21,7 @@ pub(crate) struct Expression<'db> {
     /// The expression node.
     #[no_eq]
     #[return_ref]
-    pub(crate) node: AstNodeRef<ast::Expr>,
+    pub(crate) node_ref: AstNodeRef<ast::Expr>,
 
     #[no_eq]
     count: countme::Count<Expression<'static>>,

crates/red_knot_python_semantic/src/semantic_index/symbol.rs

@@ -272,7 +272,7 @@ impl SymbolTableBuilder {
         &mut self,
         name: Name,
         flags: SymbolFlags,
-    ) -> ScopedSymbolId {
+    ) -> (ScopedSymbolId, bool) {
         let hash = SymbolTable::hash_name(&name);
         let entry = self
             .table
@@ -285,7 +285,7 @@ impl SymbolTableBuilder {
                 let symbol = &mut self.table.symbols[*entry.key()];
                 symbol.insert_flags(flags);
 
-                *entry.key()
+                (*entry.key(), false)
             }
             RawEntryMut::Vacant(entry) => {
                 let mut symbol = Symbol::new(name);
@@ -295,7 +295,7 @@ impl SymbolTableBuilder {
                 entry.insert_with_hasher(hash, id, (), |id| {
                     SymbolTable::hash_name(self.table.symbols[*id].name().as_str())
                 });
-                id
+                (id, true)
             }
         }
     }

crates/red_knot_python_semantic/src/semantic_index/use_def.rs

@@ -1,4 +1,5 @@
-//! Build a map from each use of a symbol to the definitions visible from that use.
+//! Build a map from each use of a symbol to the definitions visible from that use, and the
+//! type-narrowing constraints that apply to each definition.
 //!
 //! Let's take this code sample:
 //!
@@ -6,7 +7,7 @@
 //! x = 1
 //! x = 2
 //! y = x
-//! if flag:
+//! if y is not None:
 //!     x = 3
 //! else:
 //!     x = 4
@@ -34,8 +35,8 @@
 //! [`AstIds`](crate::semantic_index::ast_ids::AstIds) we number all uses (that means a `Name` node
 //! with `Load` context) so we have a `ScopedUseId` to efficiently represent each use.
 //!
-//! The other case we need to handle is when a symbol is referenced from a different scope (the
-//! most obvious example of this is an import). We call this "public" use of a symbol. So the other
+//! Another case we need to handle is when a symbol is referenced from a different scope (the most
+//! obvious example of this is an import). We call this "public" use of a symbol. So the other
 //! question we need to be able to answer is, what are the publicly-visible definitions of each
 //! symbol?
 //!
@@ -53,326 +54,322 @@
 //! start.)
 //!
 //! So this means that the publicly-visible definitions of a symbol are the definitions still
-//! visible at the end of the scope.
+//! visible at the end of the scope; effectively we have an implicit "use" of every symbol at the
+//! end of the scope.
 //!
-//! The data structure we build to answer these two questions is the `UseDefMap`. It has a
-//! `definitions_by_use` vector indexed by [`ScopedUseId`] and a `public_definitions` map
-//! indexed by [`ScopedSymbolId`]. The values in each are the visible definition of a symbol at
-//! that use, or at the end of the scope.
+//! We also need to know, for a given definition of a symbol, what type-narrowing constraints apply
+//! to it. For instance, in this code sample:
 //!
-//! Rather than have multiple definitions, we use a Phi definition at control flow join points to
-//! merge the visible definition in each path. This means at any given point we always have exactly
-//! one definition for a symbol. (This is analogous to static-single-assignment, or SSA, form, and
-//! in fact we use the algorithm from [Simple and efficient construction of static single
-//! assignment form](https://dl.acm.org/doi/10.1007/978-3-642-37051-9_6) here.)
+//! ```python
+//! x = 1 if flag else None
+//! if x is not None:
+//!     y = x
+//! ```
+//!
+//! At the use of `x` in `y = x`, the visible definition of `x` is `1 if flag else None`, which
+//! would infer as the type `Literal[1] | None`. But the constraint `x is not None` dominates this
+//! use, which means we can rule out the possibility that `x` is `None` here, which should give us
+//! the type `Literal[1]` for this use.
+//!
+//! The data structure we build to answer these questions is the `UseDefMap`. It has a
+//! `definitions_by_use` vector indexed by [`ScopedUseId`] and a `public_definitions` vector
+//! indexed by [`ScopedSymbolId`]. The values in each of these vectors are (in principle) a list of
+//! visible definitions at that use, or at the end of the scope for that symbol, with a list of the
+//! dominating constraints for each of those definitions.
+//!
+//! In order to avoid vectors-of-vectors-of-vectors and all the allocations that would entail, we
+//! don't actually store these "list of visible definitions" as a vector of [`Definition`].
+//! Instead, the values in `definitions_by_use` and `public_definitions` are a [`SymbolState`]
+//! struct which uses bit-sets to track definitions and constraints in terms of
+//! [`ScopedDefinitionId`] and [`ScopedConstraintId`], which are indices into the `all_definitions`
+//! and `all_constraints` indexvecs in the [`UseDefMap`].
+//!
+//! There is another special kind of possible "definition" for a symbol: there might be a path from
+//! the scope entry to a given use in which the symbol is never bound.
+//!
+//! The simplest way to model "unbound" would be as an actual [`Definition`] itself: the initial
+//! visible [`Definition`] for each symbol in a scope. But actually modeling it this way would
+//! unnecessarily increase the number of [`Definition`] that Salsa must track. Since "unbound" is a
+//! special definition in that all symbols share it, and it doesn't have any additional per-symbol
+//! state, and constraints are irrelevant to it, we can represent it more efficiently: we use the
+//! `may_be_unbound` boolean on the [`SymbolState`] struct. If this flag is `true`, it means the
+//! symbol/use really has one additional visible "definition", which is the unbound state. If this
+//! flag is `false`, it means we've eliminated the possibility of unbound: every path we've
+//! followed includes a definition for this symbol.
+//!
+//! To build a [`UseDefMap`], the [`UseDefMapBuilder`] is notified of each new use, definition, and
+//! constraint as they are encountered by the
+//! [`SemanticIndexBuilder`](crate::semantic_index::builder::SemanticIndexBuilder) AST visit. For
+//! each symbol, the builder tracks the `SymbolState` for that symbol. When we hit a use of a
+//! symbol, it records the current state for that symbol for that use. When we reach the end of the
+//! scope, it records the state for each symbol as the public definitions of that symbol.
+//!
+//! Let's walk through the above example. Initially we record for `x` that it has no visible
+//! definitions, and may be unbound. When we see `x = 1`, we record that as the sole visible
+//! definition of `x`, and flip `may_be_unbound` to `false`. Then we see `x = 2`, and it replaces
+//! `x = 1` as the sole visible definition of `x`. When we get to `y = x`, we record that the
+//! visible definitions for that use of `x` are just the `x = 2` definition.
+//!
+//! Then we hit the `if` branch. We visit the `test` node (`flag` in this case), since that will
+//! happen regardless. Then we take a pre-branch snapshot of the currently visible definitions for
+//! all symbols, which we'll need later. Then we record `flag` as a possible constraint on the
+//! currently visible definition (`x = 2`), and go ahead and visit the `if` body. When we see `x =
+//! 3`, it replaces `x = 2` (constrained by `flag`) as the sole visible definition of `x`. At the
+//! end of the `if` body, we take another snapshot of the currently-visible definitions; we'll call
+//! this the post-if-body snapshot.
+//!
+//! Now we need to visit the `else` clause. The conditions when entering the `else` clause should
+//! be the pre-if conditions; if we are entering the `else` clause, we know that the `if` test
+//! failed and we didn't execute the `if` body. So we first reset the builder to the pre-if state,
+//! using the snapshot we took previously (meaning we now have `x = 2` as the sole visible
+//! definition for `x` again), then visit the `else` clause, where `x = 4` replaces `x = 2` as the
+//! sole visible definition of `x`.
+//!
+//! Now we reach the end of the if/else, and want to visit the following code. The state here needs
+//! to reflect that we might have gone through the `if` branch, or we might have gone through the
+//! `else` branch, and we don't know which. So we need to "merge" our current builder state
+//! (reflecting the end-of-else state, with `x = 4` as the only visible definition) with our
+//! post-if-body snapshot (which has `x = 3` as the only visible definition). The result of this
+//! merge is that we now have two visible definitions of `x`: `x = 3` and `x = 4`.
+//!
+//! The [`UseDefMapBuilder`] itself just exposes methods for taking a snapshot, resetting to a
+//! snapshot, and merging a snapshot into the current state. The logic using these methods lives in
+//! [`SemanticIndexBuilder`](crate::semantic_index::builder::SemanticIndexBuilder), e.g. where it
+//! visits a `StmtIf` node.
+//!
+//! (In the future we may have some other questions we want to answer as well, such as "is this
+//! definition used?", which will require tracking a bit more info in our map, e.g. a "used" bit
+//! for each [`Definition`] which is flipped to true when we record that definition for a use.)
+use self::symbol_state::{
+    ConstraintIdIterator, DefinitionIdWithConstraintsIterator, ScopedConstraintId,
+    ScopedDefinitionId, SymbolState,
+};
 use crate::semantic_index::ast_ids::ScopedUseId;
-use crate::semantic_index::definition::{Definition, DefinitionKind, ScopedPhiId};
-use crate::semantic_index::symbol::{FileScopeId, ScopedSymbolId};
-use crate::Db;
-use ruff_db::files::File;
-use ruff_index::{newtype_index, IndexVec};
-use rustc_hash::{FxHashMap, FxHashSet};
-use smallvec::{smallvec, SmallVec};
+use crate::semantic_index::definition::Definition;
+use crate::semantic_index::expression::Expression;
+use crate::semantic_index::symbol::ScopedSymbolId;
+use ruff_index::IndexVec;
 
-/// Number of basic block predecessors we store inline.
-const PREDECESSORS: usize = 2;
+mod bitset;
+mod symbol_state;
 
-/// Input operands (definitions) for a Phi definition. None means not defined.
-// TODO would like to use SmallVec here but can't due to lifetime invariance issue.
-type PhiOperands<'db> = Vec<Option<Definition<'db>>>;
-
-/// Definition for each use of a name.
+/// Applicable definitions and constraints for every use of a name.
 #[derive(Debug, PartialEq, Eq)]
 pub(crate) struct UseDefMap<'db> {
-    // TODO store constraints with definitions for type narrowing
-    /// Definition that reaches each [`ScopedUseId`].
-    definitions_by_use: IndexVec<ScopedUseId, Option<Definition<'db>>>,
+    /// Array of [`Definition`] in this scope.
+    all_definitions: IndexVec<ScopedDefinitionId, Definition<'db>>,
 
-    /// Definition of each symbol visible at end of scope.
-    ///
-    /// Sparse, because it only includes symbols defined in the scope.
-    public_definitions: FxHashMap<ScopedSymbolId, Definition<'db>>,
+    /// Array of constraints (as [`Expression`]) in this scope.
+    all_constraints: IndexVec<ScopedConstraintId, Expression<'db>>,
 
-    /// Operands for each Phi definition in this scope.
-    phi_operands: IndexVec<ScopedPhiId, PhiOperands<'db>>,
+    /// [`SymbolState`] visible at a [`ScopedUseId`].
+    definitions_by_use: IndexVec<ScopedUseId, SymbolState>,
+
+    /// [`SymbolState`] visible at end of scope for each symbol.
+    public_definitions: IndexVec<ScopedSymbolId, SymbolState>,
 }
 
 impl<'db> UseDefMap<'db> {
-    /// Return the dominating definition for a given use of a name; None means not-defined.
-    pub(crate) fn definition_for_use(&self, use_id: ScopedUseId) -> Option<Definition<'db>> {
-        self.definitions_by_use[use_id]
+    pub(crate) fn use_definitions(
+        &self,
+        use_id: ScopedUseId,
+    ) -> DefinitionWithConstraintsIterator<'_, 'db> {
+        DefinitionWithConstraintsIterator {
+            all_definitions: &self.all_definitions,
+            all_constraints: &self.all_constraints,
+            inner: self.definitions_by_use[use_id].visible_definitions(),
+        }
     }
 
-    /// Return the definition visible at end of scope for a symbol.
-    ///
-    /// Return None if the symbol is never defined in the scope.
-    pub(crate) fn public_definition(&self, symbol_id: ScopedSymbolId) -> Option<Definition<'db>> {
-        self.public_definitions.get(&symbol_id).copied()
+    pub(crate) fn use_may_be_unbound(&self, use_id: ScopedUseId) -> bool {
+        self.definitions_by_use[use_id].may_be_unbound()
     }
 
-    /// Return the operands for a Phi in this scope; a None means not-defined.
-    pub(crate) fn phi_operands<'s>(&'s self, phi_id: ScopedPhiId) -> &'s [Option<Definition<'db>>] {
-        self.phi_operands[phi_id].as_slice()
+    pub(crate) fn public_definitions(
+        &self,
+        symbol: ScopedSymbolId,
+    ) -> DefinitionWithConstraintsIterator<'_, 'db> {
+        DefinitionWithConstraintsIterator {
+            all_definitions: &self.all_definitions,
+            all_constraints: &self.all_constraints,
+            inner: self.public_definitions[symbol].visible_definitions(),
+        }
+    }
+
+    pub(crate) fn public_may_be_unbound(&self, symbol: ScopedSymbolId) -> bool {
+        self.public_definitions[symbol].may_be_unbound()
     }
 }
 
-type PredecessorBlocks = SmallVec<[BasicBlockId; PREDECESSORS]>;
+#[derive(Debug)]
+pub(crate) struct DefinitionWithConstraintsIterator<'map, 'db> {
+    all_definitions: &'map IndexVec<ScopedDefinitionId, Definition<'db>>,
+    all_constraints: &'map IndexVec<ScopedConstraintId, Expression<'db>>,
+    inner: DefinitionIdWithConstraintsIterator<'map>,
+}
 
-/// A basic block is a linear region of code (no branches.)
-#[newtype_index]
-pub(super) struct BasicBlockId;
+impl<'map, 'db> Iterator for DefinitionWithConstraintsIterator<'map, 'db> {
+    type Item = DefinitionWithConstraints<'map, 'db>;
 
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|def_id_with_constraints| DefinitionWithConstraints {
+                definition: self.all_definitions[def_id_with_constraints.definition],
+                constraints: ConstraintsIterator {
+                    all_constraints: self.all_constraints,
+                    constraint_ids: def_id_with_constraints.constraint_ids,
+                },
+            })
+    }
+}
+
+impl std::iter::FusedIterator for DefinitionWithConstraintsIterator<'_, '_> {}
+
+pub(crate) struct DefinitionWithConstraints<'map, 'db> {
+    pub(crate) definition: Definition<'db>,
+    pub(crate) constraints: ConstraintsIterator<'map, 'db>,
+}
+
+pub(crate) struct ConstraintsIterator<'map, 'db> {
+    all_constraints: &'map IndexVec<ScopedConstraintId, Expression<'db>>,
+    constraint_ids: ConstraintIdIterator<'map>,
+}
+
+impl<'map, 'db> Iterator for ConstraintsIterator<'map, 'db> {
+    type Item = Expression<'db>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.constraint_ids
+            .next()
+            .map(|constraint_id| self.all_constraints[constraint_id])
+    }
+}
+
+impl std::iter::FusedIterator for ConstraintsIterator<'_, '_> {}
+
+/// A snapshot of the definitions and constraints state at a particular point in control flow.
+#[derive(Clone, Debug)]
+pub(super) struct FlowSnapshot {
+    definitions_by_symbol: IndexVec<ScopedSymbolId, SymbolState>,
+}
+
+#[derive(Debug, Default)]
 pub(super) struct UseDefMapBuilder<'db> {
-    db: &'db dyn Db,
-    file: File,
-    file_scope: FileScopeId,
+    /// Append-only array of [`Definition`]; None is unbound.
+    all_definitions: IndexVec<ScopedDefinitionId, Definition<'db>>,
 
-    /// Predecessor blocks for each basic block.
-    ///
-    /// Entry block has none, all other blocks have at least one, blocks that join control flow can
-    /// have two or more.
-    predecessors: IndexVec<BasicBlockId, PredecessorBlocks>,
+    /// Append-only array of constraints (as [`Expression`]).
+    all_constraints: IndexVec<ScopedConstraintId, Expression<'db>>,
 
-    /// The definition of each symbol which dominates each basic block.
-    ///
-    /// No entry means "lazily unfilled"; we haven't had to query for it yet, and we may never have
-    /// to, if the symbol isn't used in this block or any successor block.
-    ///
-    /// Each block has an [`FxHashMap`] of symbols instead of an [`IndexVec`] because it is lazy
-    /// and potentially sparse; it will only include a definition for a symbol that is actually
-    /// used in that block or a successor. An [`IndexVec`] would have to be eagerly filled with
-    /// placeholders.
-    definitions_per_block:
-        IndexVec<BasicBlockId, FxHashMap<ScopedSymbolId, Option<Definition<'db>>>>,
+    /// Visible definitions at each so-far-recorded use.
+    definitions_by_use: IndexVec<ScopedUseId, SymbolState>,
 
-    /// Incomplete Phi definitions in each block.
-    ///
-    /// An incomplete Phi is used when we don't know, while processing a block's body, what new
-    /// predecessors it may later gain (that is, backward jumps.)
-    ///
-    /// Sparse, because relative few blocks (just loop headers) will have any incomplete Phis.
-    incomplete_phis: FxHashMap<BasicBlockId, Vec<Definition<'db>>>,
-
-    /// Operands for each Phi definition in this scope.
-    phi_operands: IndexVec<ScopedPhiId, PhiOperands<'db>>,
-
-    /// Are this block's predecessors fully populated?
-    ///
-    /// If not, it isn't safe to recurse to predecessors yet; we might miss a predecessor block.
-    sealed_blocks: IndexVec<BasicBlockId, bool>,
-
-    /// Definition for each so-far-recorded use.
-    definitions_by_use: IndexVec<ScopedUseId, Option<Definition<'db>>>,
-
-    /// All symbols defined in this scope.
-    defined_symbols: FxHashSet<ScopedSymbolId>,
+    /// Currently visible definitions for each symbol.
+    definitions_by_symbol: IndexVec<ScopedSymbolId, SymbolState>,
 }
 
 impl<'db> UseDefMapBuilder<'db> {
-    pub(super) fn new(db: &'db dyn Db, file: File, file_scope: FileScopeId) -> Self {
-        let mut new = Self {
-            db,
-            file,
-            file_scope,
-            predecessors: IndexVec::new(),
-            definitions_per_block: IndexVec::new(),
-            incomplete_phis: FxHashMap::default(),
-            sealed_blocks: IndexVec::new(),
-            definitions_by_use: IndexVec::new(),
-            phi_operands: IndexVec::new(),
-            defined_symbols: FxHashSet::default(),
-        };
-
-        // create the entry basic block
-        new.predecessors.push(PredecessorBlocks::default());
-        new.definitions_per_block.push(FxHashMap::default());
-        new.sealed_blocks.push(true);
-
-        new
+    pub(super) fn new() -> Self {
+        Self::default()
+    }
+
+    pub(super) fn add_symbol(&mut self, symbol: ScopedSymbolId) {
+        let new_symbol = self.definitions_by_symbol.push(SymbolState::unbound());
+        debug_assert_eq!(symbol, new_symbol);
     }
 
-    /// Record a definition for a symbol.
     pub(super) fn record_definition(
         &mut self,
-        symbol_id: ScopedSymbolId,
+        symbol: ScopedSymbolId,
         definition: Definition<'db>,
     ) {
-        self.memoize(self.current_block_id(), symbol_id, Some(definition));
-        self.defined_symbols.insert(symbol_id);
+        // We have a new definition of a symbol; this replaces any previous definitions in this
+        // path.
+        let def_id = self.all_definitions.push(definition);
+        self.definitions_by_symbol[symbol] = SymbolState::with(def_id);
     }
 
-    /// Record a use of a symbol.
-    pub(super) fn record_use(&mut self, symbol_id: ScopedSymbolId, use_id: ScopedUseId) {
-        let definition_id = self.lookup(symbol_id);
-        let new_use = self.definitions_by_use.push(definition_id);
+    pub(super) fn record_constraint(&mut self, constraint: Expression<'db>) {
+        let constraint_id = self.all_constraints.push(constraint);
+        for definitions in &mut self.definitions_by_symbol {
+            definitions.add_constraint(constraint_id);
+        }
+    }
+
+    pub(super) fn record_use(&mut self, symbol: ScopedSymbolId, use_id: ScopedUseId) {
+        // We have a use of a symbol; clone the currently visible definitions for that symbol, and
+        // record them as the visible definitions for this use.
+        let new_use = self
+            .definitions_by_use
+            .push(self.definitions_by_symbol[symbol].clone());
         debug_assert_eq!(use_id, new_use);
     }
 
-    /// Get the id of the current basic block.
-    pub(super) fn current_block_id(&self) -> BasicBlockId {
-        BasicBlockId::from(self.definitions_per_block.len() - 1)
-    }
-
-    /// Push a new basic block, with given block as predecessor.
-    pub(super) fn new_block_from(&mut self, block_id: BasicBlockId, sealed: bool) {
-        self.new_block_with_predecessors(smallvec![block_id], sealed);
-    }
-
-    /// Push a new basic block, with current block as predecessor; return the current block's ID.
-    pub(super) fn next_block(&mut self, sealed: bool) -> BasicBlockId {
-        let current_block_id = self.current_block_id();
-        self.new_block_from(current_block_id, sealed);
-        current_block_id
-    }
-
-    /// Add a predecessor to the current block.
-    pub(super) fn merge_block(&mut self, new_predecessor: BasicBlockId) {
-        let block_id = self.current_block_id();
-        debug_assert!(!self.sealed_blocks[block_id]);
-        self.predecessors[block_id].push(new_predecessor);
-    }
-
-    /// Add predecessors to the current block.
-    pub(super) fn merge_blocks(&mut self, new_predecessors: Vec<BasicBlockId>) {
-        let block_id = self.current_block_id();
-        debug_assert!(!self.sealed_blocks[block_id]);
-        self.predecessors[block_id].extend(new_predecessors);
-    }
-
-    /// Mark the current block as sealed; it cannot have any more predecessors added.
-    pub(super) fn seal_current_block(&mut self) {
-        self.seal_block(self.current_block_id());
-    }
-
-    /// Mark a block as sealed; it cannot have any more predecessors added.
-    pub(super) fn seal_block(&mut self, block_id: BasicBlockId) {
-        debug_assert!(!self.sealed_blocks[block_id]);
-        if let Some(phis) = self.incomplete_phis.get(&block_id) {
-            for phi in phis.clone() {
-                self.add_phi_operands(block_id, phi);
-            }
-            self.incomplete_phis.remove(&block_id);
+    /// Take a snapshot of the current visible-symbols state.
+    pub(super) fn snapshot(&self) -> FlowSnapshot {
+        FlowSnapshot {
+            definitions_by_symbol: self.definitions_by_symbol.clone(),
+        }
+    }
+
+    /// Restore the current builder visible-definitions state to the given snapshot.
+    pub(super) fn restore(&mut self, snapshot: FlowSnapshot) {
+        // We never remove symbols from `definitions_by_symbol` (it's an IndexVec, and the symbol
+        // IDs must line up), so the current number of known symbols must always be equal to or
+        // greater than the number of known symbols in a previously-taken snapshot.
+        let num_symbols = self.definitions_by_symbol.len();
+        debug_assert!(num_symbols >= snapshot.definitions_by_symbol.len());
+
+        // Restore the current visible-definitions state to the given snapshot.
+        self.definitions_by_symbol = snapshot.definitions_by_symbol;
+
+        // If the snapshot we are restoring is missing some symbols we've recorded since, we need
+        // to fill them in so the symbol IDs continue to line up. Since they don't exist in the
+        // snapshot, the correct state to fill them in with is "unbound".
+        self.definitions_by_symbol
+            .resize(num_symbols, SymbolState::unbound());
+    }
+
+    /// Merge the given snapshot into the current state, reflecting that we might have taken either
+    /// path to get here. The new visible-definitions state for each symbol should include
+    /// definitions from both the prior state and the snapshot.
+    pub(super) fn merge(&mut self, snapshot: FlowSnapshot) {
+        // The tricky thing about merging two Ranges pointing into `all_definitions` is that if the
+        // two Ranges aren't already adjacent in `all_definitions`, we will have to copy at least
+        // one or the other of the ranges to the end of `all_definitions` so as to make them
+        // adjacent. We can't ever move things around in `all_definitions` because previously
+        // recorded uses may still have ranges pointing to any part of it; all we can do is append.
+        // It's possible we may end up with some old entries in `all_definitions` that nobody is
+        // pointing to, but that's OK.
+
+        // We never remove symbols from `definitions_by_symbol` (it's an IndexVec, and the symbol
+        // IDs must line up), so the current number of known symbols must always be equal to or
+        // greater than the number of known symbols in a previously-taken snapshot.
+        debug_assert!(self.definitions_by_symbol.len() >= snapshot.definitions_by_symbol.len());
+
+        let mut snapshot_definitions_iter = snapshot.definitions_by_symbol.into_iter();
+        for current in &mut self.definitions_by_symbol {
+            if let Some(snapshot) = snapshot_definitions_iter.next() {
+                current.merge(snapshot);
+            } else {
+                // Symbol not present in snapshot, so it's unbound from that path.
+                current.add_unbound();
+            }
         }
-        self.sealed_blocks[block_id] = true;
     }
 
     pub(super) fn finish(mut self) -> UseDefMap<'db> {
-        debug_assert!(self.incomplete_phis.is_empty());
-        debug_assert!(self.sealed_blocks.iter().all(|&b| b));
+        self.all_definitions.shrink_to_fit();
+        self.all_constraints.shrink_to_fit();
+        self.definitions_by_symbol.shrink_to_fit();
         self.definitions_by_use.shrink_to_fit();
-        self.phi_operands.shrink_to_fit();
-
-        let mut public_definitions: FxHashMap<ScopedSymbolId, Definition<'db>> =
-            FxHashMap::default();
-
-        for symbol_id in self.defined_symbols.clone() {
-            // SAFETY: We are only looking up defined symbols here, can't get None.
-            public_definitions.insert(symbol_id, self.lookup(symbol_id).unwrap());
-        }
 
         UseDefMap {
+            all_definitions: self.all_definitions,
+            all_constraints: self.all_constraints,
             definitions_by_use: self.definitions_by_use,
-            public_definitions,
-            phi_operands: self.phi_operands,
+            public_definitions: self.definitions_by_symbol,
         }
     }
-
-    /// Push a new basic block (with given predecessors) and return its ID.
-    fn new_block_with_predecessors(
-        &mut self,
-        predecessors: PredecessorBlocks,
-        sealed: bool,
-    ) -> BasicBlockId {
-        let new_block_id = self.predecessors.push(predecessors);
-        self.definitions_per_block.push(FxHashMap::default());
-        self.sealed_blocks.push(sealed);
-
-        new_block_id
-    }
-
-    /// Look up the dominating definition for a symbol in the current block.
-    ///
-    /// If there isn't a local definition, recursively look up the symbol in predecessor blocks,
-    /// memoizing the found symbol in each block.
-    fn lookup(&mut self, symbol_id: ScopedSymbolId) -> Option<Definition<'db>> {
-        self.lookup_impl(self.current_block_id(), symbol_id)
-    }
-
-    fn lookup_impl(
-        &mut self,
-        block_id: BasicBlockId,
-        symbol_id: ScopedSymbolId,
-    ) -> Option<Definition<'db>> {
-        if let Some(local) = self.definitions_per_block[block_id].get(&symbol_id) {
-            return *local;
-        }
-        if !self.sealed_blocks[block_id] {
-            // we may still be missing predecessors; insert an incomplete Phi.
-            let definition = self.create_incomplete_phi(block_id, symbol_id);
-            self.incomplete_phis
-                .entry(block_id)
-                .or_default()
-                .push(definition);
-            return Some(definition);
-        }
-        match self.predecessors[block_id].as_slice() {
-            // entry block, no definition found: return None
-            [] => None,
-            // single predecessor, recurse
-            &[single_predecessor_id] => {
-                let definition = self.lookup_impl(single_predecessor_id, symbol_id);
-                self.memoize(block_id, symbol_id, definition);
-                definition
-            }
-            // multiple predecessors: create and memoize an incomplete Phi to break cycles, then
-            // recurse into predecessors and fill the Phi operands.
-            _ => {
-                let phi = self.create_incomplete_phi(block_id, symbol_id);
-                self.add_phi_operands(block_id, phi);
-                Some(phi)
-            }
-        }
-    }
-
-    /// Recurse into predecessors to add operands for an incomplete Phi.
-    fn add_phi_operands(&mut self, block_id: BasicBlockId, phi: Definition<'db>) {
-        let predecessors: PredecessorBlocks = self.predecessors[block_id].clone();
-        let operands: PhiOperands = predecessors
-            .iter()
-            .map(|pred_id| self.lookup_impl(*pred_id, phi.symbol(self.db)))
-            .collect();
-        let DefinitionKind::Phi(phi_id) = phi.kind(self.db) else {
-            unreachable!("add_phi_operands called with non-Phi");
-        };
-        self.phi_operands[*phi_id] = operands;
-    }
-
-    /// Remember a given definition for a given symbol in the given block.
-    fn memoize(
-        &mut self,
-        block_id: BasicBlockId,
-        symbol_id: ScopedSymbolId,
-        definition_id: Option<Definition<'db>>,
-    ) {
-        self.definitions_per_block[block_id].insert(symbol_id, definition_id);
-    }
-
-    /// Create an incomplete Phi for the given block and symbol, memoize it, and return its ID.
-    fn create_incomplete_phi(
-        &mut self,
-        block_id: BasicBlockId,
-        symbol_id: ScopedSymbolId,
-    ) -> Definition<'db> {
-        let phi_id = self.phi_operands.push(vec![]);
-        let definition = Definition::new(
-            self.db,
-            self.file,
-            self.file_scope,
-            symbol_id,
-            DefinitionKind::Phi(phi_id),
-            countme::Count::default(),
-        );
-        self.memoize(block_id, symbol_id, Some(definition));
-        definition
-    }
 }

crates/red_knot_python_semantic/src/semantic_index/use_def/bitset.rs

@@ -0,0 +1,228 @@
+/// Ordered set of `u32`.
+///
+/// Uses an inline bit-set for small values (up to 64 * B), falls back to heap allocated vector of
+/// blocks for larger values.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) enum BitSet<const B: usize> {
+    /// Bit-set (in 64-bit blocks) for the first 64 * B entries.
+    Inline([u64; B]),
+
+    /// Overflow beyond 64 * B.
+    Heap(Vec<u64>),
+}
+
+impl<const B: usize> Default for BitSet<B> {
+    fn default() -> Self {
+        // B * 64 must fit in a u32, or else we have unusable bits; this assertion makes the
+        // truncating casts to u32 below safe. This would be better as a const assertion, but
+        // that's not possible on stable with const generic params. (B should never really be
+        // anywhere close to this large.)
+        assert!(B * 64 < (u32::MAX as usize));
+        // This implementation requires usize >= 32 bits.
+        static_assertions::const_assert!(usize::BITS >= 32);
+        Self::Inline([0; B])
+    }
+}
+
+impl<const B: usize> BitSet<B> {
+    /// Create and return a new [`BitSet`] with a single `value` inserted.
+    pub(super) fn with(value: u32) -> Self {
+        let mut bitset = Self::default();
+        bitset.insert(value);
+        bitset
+    }
+
+    /// Convert from Inline to Heap, if needed, and resize the Heap vector, if needed.
+    fn resize(&mut self, value: u32) {
+        let num_blocks_needed = (value / 64) + 1;
+        match self {
+            Self::Inline(blocks) => {
+                let mut vec = blocks.to_vec();
+                vec.resize(num_blocks_needed as usize, 0);
+                *self = Self::Heap(vec);
+            }
+            Self::Heap(vec) => {
+                vec.resize(num_blocks_needed as usize, 0);
+            }
+        }
+    }
+
+    fn blocks_mut(&mut self) -> &mut [u64] {
+        match self {
+            Self::Inline(blocks) => blocks.as_mut_slice(),
+            Self::Heap(blocks) => blocks.as_mut_slice(),
+        }
+    }
+
+    fn blocks(&self) -> &[u64] {
+        match self {
+            Self::Inline(blocks) => blocks.as_slice(),
+            Self::Heap(blocks) => blocks.as_slice(),
+        }
+    }
+
+    /// Insert a value into the [`BitSet`].
+    ///
+    /// Return true if the value was newly inserted, false if already present.
+    pub(super) fn insert(&mut self, value: u32) -> bool {
+        let value_usize = value as usize;
+        let (block, index) = (value_usize / 64, value_usize % 64);
+        if block >= self.blocks().len() {
+            self.resize(value);
+        }
+        let blocks = self.blocks_mut();
+        let missing = blocks[block] & (1 << index) == 0;
+        blocks[block] |= 1 << index;
+        missing
+    }
+
+    /// Intersect in-place with another [`BitSet`].
+    pub(super) fn intersect(&mut self, other: &BitSet<B>) {
+        let my_blocks = self.blocks_mut();
+        let other_blocks = other.blocks();
+        let min_len = my_blocks.len().min(other_blocks.len());
+        for i in 0..min_len {
+            my_blocks[i] &= other_blocks[i];
+        }
+        for block in my_blocks.iter_mut().skip(min_len) {
+            *block = 0;
+        }
+    }
+
+    /// Return an iterator over the values (in ascending order) in this [`BitSet`].
+    pub(super) fn iter(&self) -> BitSetIterator<'_, B> {
+        let blocks = self.blocks();
+        BitSetIterator {
+            blocks,
+            current_block_index: 0,
+            current_block: blocks[0],
+        }
+    }
+}
+
+/// Iterator over values in a [`BitSet`].
+#[derive(Debug)]
+pub(super) struct BitSetIterator<'a, const B: usize> {
+    /// The blocks we are iterating over.
+    blocks: &'a [u64],
+
+    /// The index of the block we are currently iterating through.
+    current_block_index: usize,
+
+    /// The block we are currently iterating through (and zeroing as we go.)
+    current_block: u64,
+}
+
+impl<const B: usize> Iterator for BitSetIterator<'_, B> {
+    type Item = u32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while self.current_block == 0 {
+            if self.current_block_index + 1 >= self.blocks.len() {
+                return None;
+            }
+            self.current_block_index += 1;
+            self.current_block = self.blocks[self.current_block_index];
+        }
+        let lowest_bit_set = self.current_block.trailing_zeros();
+        // reset the lowest set bit, without a data dependency on `lowest_bit_set`
+        self.current_block &= self.current_block.wrapping_sub(1);
+        // SAFETY: `lowest_bit_set` cannot be more than 64, `current_block_index` cannot be more
+        // than `B - 1`, and we check above that `B * 64 < u32::MAX`. So both `64 *
+        // current_block_index` and the final value here must fit in u32.
+        #[allow(clippy::cast_possible_truncation)]
+        Some(lowest_bit_set + (64 * self.current_block_index) as u32)
+    }
+}
+
+impl<const B: usize> std::iter::FusedIterator for BitSetIterator<'_, B> {}
+
+#[cfg(test)]
+mod tests {
+    use super::BitSet;
+
+    fn assert_bitset<const B: usize>(bitset: &BitSet<B>, contents: &[u32]) {
+        assert_eq!(bitset.iter().collect::<Vec<_>>(), contents);
+    }
+
+    #[test]
+    fn iter() {
+        let mut b = BitSet::<1>::with(3);
+        b.insert(27);
+        b.insert(6);
+        assert!(matches!(b, BitSet::Inline(_)));
+        assert_bitset(&b, &[3, 6, 27]);
+    }
+
+    #[test]
+    fn iter_overflow() {
+        let mut b = BitSet::<1>::with(140);
+        b.insert(100);
+        b.insert(129);
+        assert!(matches!(b, BitSet::Heap(_)));
+        assert_bitset(&b, &[100, 129, 140]);
+    }
+
+    #[test]
+    fn intersect() {
+        let mut b1 = BitSet::<1>::with(4);
+        let mut b2 = BitSet::<1>::with(4);
+        b1.insert(23);
+        b2.insert(5);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[4]);
+    }
+
+    #[test]
+    fn intersect_mixed_1() {
+        let mut b1 = BitSet::<1>::with(4);
+        let mut b2 = BitSet::<1>::with(4);
+        b1.insert(89);
+        b2.insert(5);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[4]);
+    }
+
+    #[test]
+    fn intersect_mixed_2() {
+        let mut b1 = BitSet::<1>::with(4);
+        let mut b2 = BitSet::<1>::with(4);
+        b1.insert(23);
+        b2.insert(89);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[4]);
+    }
+
+    #[test]
+    fn intersect_heap() {
+        let mut b1 = BitSet::<1>::with(4);
+        let mut b2 = BitSet::<1>::with(4);
+        b1.insert(89);
+        b2.insert(90);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[4]);
+    }
+
+    #[test]
+    fn intersect_heap_2() {
+        let mut b1 = BitSet::<1>::with(89);
+        let mut b2 = BitSet::<1>::with(89);
+        b1.insert(91);
+        b2.insert(90);
+
+        b1.intersect(&b2);
+        assert_bitset(&b1, &[89]);
+    }
+
+    #[test]
+    fn multiple_blocks() {
+        let mut b = BitSet::<2>::with(120);
+        b.insert(45);
+        assert!(matches!(b, BitSet::Inline(_)));
+        assert_bitset(&b, &[45, 120]);
+    }
+}

crates/red_knot_python_semantic/src/semantic_index/use_def/symbol_state.rs

@@ -0,0 +1,374 @@
+//! Track visible definitions of a symbol, and applicable constraints per definition.
+//!
+//! These data structures operate entirely on scope-local newtype-indices for definitions and
+//! constraints, referring to their location in the `all_definitions` and `all_constraints`
+//! indexvecs in [`super::UseDefMapBuilder`].
+//!
+//! We need to track arbitrary associations between definitions and constraints, not just a single
+//! set of currently dominating constraints (where "dominating" means "control flow must have
+//! passed through it to reach this point"), because we can have dominating constraints that apply
+//! to some definitions but not others, as in this code:
+//!
+//! ```python
+//! x = 1 if flag else None
+//! if x is not None:
+//!     if flag2:
+//!         x = 2 if flag else None
+//!     x
+//! ```
+//!
+//! The `x is not None` constraint dominates the final use of `x`, but it applies only to the first
+//! definition of `x`, not the second, so `None` is a possible value for `x`.
+//!
+//! And we can't just track, for each definition, an index into a list of dominating constraints,
+//! either, because we can have definitions which are still visible, but subject to constraints
+//! that are no longer dominating, as in this code:
+//!
+//! ```python
+//! x = 0
+//! if flag1:
+//!     x = 1 if flag2 else None
+//!     assert x is not None
+//! x
+//! ```
+//!
+//! From the point of view of the final use of `x`, the `x is not None` constraint no longer
+//! dominates, but it does dominate the `x = 1 if flag2 else None` definition, so we have to keep
+//! track of that.
+//!
+//! The data structures used here ([`BitSet`] and [`smallvec::SmallVec`]) optimize for keeping all
+//! data inline (avoiding lots of scattered allocations) in small-to-medium cases, and falling back
+//! to heap allocation to be able to scale to arbitrary numbers of definitions and constraints when
+//! needed.
+use super::bitset::{BitSet, BitSetIterator};
+use ruff_index::newtype_index;
+use smallvec::SmallVec;
+
+/// A newtype-index for a definition in a particular scope.
+#[newtype_index]
+pub(super) struct ScopedDefinitionId;
+
+/// A newtype-index for a constraint expression in a particular scope.
+#[newtype_index]
+pub(super) struct ScopedConstraintId;
+
+/// Can reference this * 64 total definitions inline; more will fall back to the heap.
+const INLINE_DEFINITION_BLOCKS: usize = 3;
+
+/// A [`BitSet`] of [`ScopedDefinitionId`], representing visible definitions of a symbol in a scope.
+type Definitions = BitSet<INLINE_DEFINITION_BLOCKS>;
+type DefinitionsIterator<'a> = BitSetIterator<'a, INLINE_DEFINITION_BLOCKS>;
+
+/// Can reference this * 64 total constraints inline; more will fall back to the heap.
+const INLINE_CONSTRAINT_BLOCKS: usize = 2;
+
+/// Can keep inline this many visible definitions per symbol at a given time; more will go to heap.
+const INLINE_VISIBLE_DEFINITIONS_PER_SYMBOL: usize = 4;
+
+/// One [`BitSet`] of applicable [`ScopedConstraintId`] per visible definition.
+type InlineConstraintArray =
+    [BitSet<INLINE_CONSTRAINT_BLOCKS>; INLINE_VISIBLE_DEFINITIONS_PER_SYMBOL];
+type Constraints = SmallVec<InlineConstraintArray>;
+type ConstraintsIterator<'a> = std::slice::Iter<'a, BitSet<INLINE_CONSTRAINT_BLOCKS>>;
+type ConstraintsIntoIterator = smallvec::IntoIter<InlineConstraintArray>;
+
+/// Visible definitions and narrowing constraints for a single symbol at some point in control flow.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(super) struct SymbolState {
+    /// [`BitSet`]: which [`ScopedDefinitionId`] are visible for this symbol?
+    visible_definitions: Definitions,
+
+    /// For each definition, which [`ScopedConstraintId`] apply?
+    ///
+    /// This is a [`smallvec::SmallVec`] which should always have one [`BitSet`] of constraints per
+    /// definition in `visible_definitions`.
+    constraints: Constraints,
+
+    /// Could the symbol be unbound at this point?
+    may_be_unbound: bool,
+}
+
+/// A single [`ScopedDefinitionId`] with an iterator of its applicable [`ScopedConstraintId`].
+#[derive(Debug)]
+pub(super) struct DefinitionIdWithConstraints<'a> {
+    pub(super) definition: ScopedDefinitionId,
+    pub(super) constraint_ids: ConstraintIdIterator<'a>,
+}
+
+impl SymbolState {
+    /// Return a new [`SymbolState`] representing an unbound symbol.
+    pub(super) fn unbound() -> Self {
+        Self {
+            visible_definitions: Definitions::default(),
+            constraints: Constraints::default(),
+            may_be_unbound: true,
+        }
+    }
+
+    /// Return a new [`SymbolState`] representing a symbol with a single visible definition.
+    pub(super) fn with(definition_id: ScopedDefinitionId) -> Self {
+        let mut constraints = Constraints::with_capacity(1);
+        constraints.push(BitSet::default());
+        Self {
+            visible_definitions: Definitions::with(definition_id.into()),
+            constraints,
+            may_be_unbound: false,
+        }
+    }
+
+    /// Add Unbound as a possibility for this symbol.
+    pub(super) fn add_unbound(&mut self) {
+        self.may_be_unbound = true;
+    }
+
+    /// Add given constraint to all currently-visible definitions.
+    pub(super) fn add_constraint(&mut self, constraint_id: ScopedConstraintId) {
+        for bitset in &mut self.constraints {
+            bitset.insert(constraint_id.into());
+        }
+    }
+
+    /// Merge another [`SymbolState`] into this one.
+    pub(super) fn merge(&mut self, b: SymbolState) {
+        let mut a = Self {
+            visible_definitions: Definitions::default(),
+            constraints: Constraints::default(),
+            may_be_unbound: self.may_be_unbound || b.may_be_unbound,
+        };
+        std::mem::swap(&mut a, self);
+        let mut a_defs_iter = a.visible_definitions.iter();
+        let mut b_defs_iter = b.visible_definitions.iter();
+        let mut a_constraints_iter = a.constraints.into_iter();
+        let mut b_constraints_iter = b.constraints.into_iter();
+
+        let mut opt_a_def: Option<u32> = a_defs_iter.next();
+        let mut opt_b_def: Option<u32> = b_defs_iter.next();
+
+        // Iterate through the definitions from `a` and `b`, always processing the lower definition
+        // ID first, and pushing each definition onto the merged `SymbolState` with its
+        // constraints. If a definition is found in both `a` and `b`, push it with the intersection
+        // of the constraints from the two paths; a constraint that applies from only one possible
+        // path is irrelevant.
+
+        // Helper to push `def`, with constraints in `constraints_iter`, onto `self`.
+        let push = |def, constraints_iter: &mut ConstraintsIntoIterator, merged: &mut Self| {
+            merged.visible_definitions.insert(def);
+            // SAFETY: we only ever create SymbolState with either no definitions and no constraint
+            // bitsets (`::unbound`) or one definition and one constraint bitset (`::with`), and
+            // `::merge` always pushes one definition and one constraint bitset together (just
+            // below), so the number of definitions and the number of constraint bitsets can never
+            // get out of sync.
+            let constraints = constraints_iter
+                .next()
+                .expect("definitions and constraints length mismatch");
+            merged.constraints.push(constraints);
+        };
+
+        loop {
+            match (opt_a_def, opt_b_def) {
+                (Some(a_def), Some(b_def)) => match a_def.cmp(&b_def) {
+                    std::cmp::Ordering::Less => {
+                        // Next definition ID is only in `a`, push it to `self` and advance `a`.
+                        push(a_def, &mut a_constraints_iter, self);
+                        opt_a_def = a_defs_iter.next();
+                    }
+                    std::cmp::Ordering::Greater => {
+                        // Next definition ID is only in `b`, push it to `self` and advance `b`.
+                        push(b_def, &mut b_constraints_iter, self);
+                        opt_b_def = b_defs_iter.next();
+                    }
+                    std::cmp::Ordering::Equal => {
+                        // Next definition is in both; push to `self` and intersect constraints.
+                        push(a_def, &mut b_constraints_iter, self);
+                        // SAFETY: we only ever create SymbolState with either no definitions and
+                        // no constraint bitsets (`::unbound`) or one definition and one constraint
+                        // bitset (`::with`), and `::merge` always pushes one definition and one
+                        // constraint bitset together (just below), so the number of definitions
+                        // and the number of constraint bitsets can never get out of sync.
+                        let a_constraints = a_constraints_iter
+                            .next()
+                            .expect("definitions and constraints length mismatch");
+                        // If the same definition is visible through both paths, any constraint
+                        // that applies on only one path is irrelevant to the resulting type from
+                        // unioning the two paths, so we intersect the constraints.
+                        self.constraints
+                            .last_mut()
+                            .unwrap()
+                            .intersect(&a_constraints);
+                        opt_a_def = a_defs_iter.next();
+                        opt_b_def = b_defs_iter.next();
+                    }
+                },
+                (Some(a_def), None) => {
+                    // We've exhausted `b`, just push the def from `a` and move on to the next.
+                    push(a_def, &mut a_constraints_iter, self);
+                    opt_a_def = a_defs_iter.next();
+                }
+                (None, Some(b_def)) => {
+                    // We've exhausted `a`, just push the def from `b` and move on to the next.
+                    push(b_def, &mut b_constraints_iter, self);
+                    opt_b_def = b_defs_iter.next();
+                }
+                (None, None) => break,
+            }
+        }
+    }
+
+    /// Get iterator over visible definitions with constraints.
+    pub(super) fn visible_definitions(&self) -> DefinitionIdWithConstraintsIterator {
+        DefinitionIdWithConstraintsIterator {
+            definitions: self.visible_definitions.iter(),
+            constraints: self.constraints.iter(),
+        }
+    }
+
+    /// Could the symbol be unbound?
+    pub(super) fn may_be_unbound(&self) -> bool {
+        self.may_be_unbound
+    }
+}
+
+/// The default state of a symbol (if we've seen no definitions of it) is unbound.
+impl Default for SymbolState {
+    fn default() -> Self {
+        SymbolState::unbound()
+    }
+}
+
+#[derive(Debug)]
+pub(super) struct DefinitionIdWithConstraintsIterator<'a> {
+    definitions: DefinitionsIterator<'a>,
+    constraints: ConstraintsIterator<'a>,
+}
+
+impl<'a> Iterator for DefinitionIdWithConstraintsIterator<'a> {
+    type Item = DefinitionIdWithConstraints<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match (self.definitions.next(), self.constraints.next()) {
+            (None, None) => None,
+            (Some(def), Some(constraints)) => Some(DefinitionIdWithConstraints {
+                definition: ScopedDefinitionId::from_u32(def),
+                constraint_ids: ConstraintIdIterator {
+                    wrapped: constraints.iter(),
+                },
+            }),
+            // SAFETY: see above.
+            _ => unreachable!("definitions and constraints length mismatch"),
+        }
+    }
+}
+
+impl std::iter::FusedIterator for DefinitionIdWithConstraintsIterator<'_> {}
+
+#[derive(Debug)]
+pub(super) struct ConstraintIdIterator<'a> {
+    wrapped: BitSetIterator<'a, INLINE_CONSTRAINT_BLOCKS>,
+}
+
+impl Iterator for ConstraintIdIterator<'_> {
+    type Item = ScopedConstraintId;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.wrapped.next().map(ScopedConstraintId::from_u32)
+    }
+}
+
+impl std::iter::FusedIterator for ConstraintIdIterator<'_> {}
+
+#[cfg(test)]
+mod tests {
+    use super::{ScopedConstraintId, ScopedDefinitionId, SymbolState};
+
+    impl SymbolState {
+        pub(crate) fn assert(&self, may_be_unbound: bool, expected: &[&str]) {
+            assert_eq!(self.may_be_unbound(), may_be_unbound);
+            let actual = self
+                .visible_definitions()
+                .map(|def_id_with_constraints| {
+                    format!(
+                        "{}<{}>",
+                        def_id_with_constraints.definition.as_u32(),
+                        def_id_with_constraints
+                            .constraint_ids
+                            .map(ScopedConstraintId::as_u32)
+                            .map(|idx| idx.to_string())
+                            .collect::<Vec<_>>()
+                            .join(", ")
+                    )
+                })
+                .collect::<Vec<_>>();
+            assert_eq!(actual, expected);
+        }
+    }
+
+    #[test]
+    fn unbound() {
+        let cd = SymbolState::unbound();
+
+        cd.assert(true, &[]);
+    }
+
+    #[test]
+    fn with() {
+        let cd = SymbolState::with(ScopedDefinitionId::from_u32(0));
+
+        cd.assert(false, &["0<>"]);
+    }
+
+    #[test]
+    fn add_unbound() {
+        let mut cd = SymbolState::with(ScopedDefinitionId::from_u32(0));
+        cd.add_unbound();
+
+        cd.assert(true, &["0<>"]);
+    }
+
+    #[test]
+    fn add_constraint() {
+        let mut cd = SymbolState::with(ScopedDefinitionId::from_u32(0));
+        cd.add_constraint(ScopedConstraintId::from_u32(0));
+
+        cd.assert(false, &["0<0>"]);
+    }
+
+    #[test]
+    fn merge() {
+        // merging the same definition with the same constraint keeps the constraint
+        let mut cd0a = SymbolState::with(ScopedDefinitionId::from_u32(0));
+        cd0a.add_constraint(ScopedConstraintId::from_u32(0));
+
+        let mut cd0b = SymbolState::with(ScopedDefinitionId::from_u32(0));
+        cd0b.add_constraint(ScopedConstraintId::from_u32(0));
+
+        cd0a.merge(cd0b);
+        let mut cd0 = cd0a;
+        cd0.assert(false, &["0<0>"]);
+
+        // merging the same definition with differing constraints drops all constraints
+        let mut cd1a = SymbolState::with(ScopedDefinitionId::from_u32(1));
+        cd1a.add_constraint(ScopedConstraintId::from_u32(1));
+
+        let mut cd1b = SymbolState::with(ScopedDefinitionId::from_u32(1));
+        cd1b.add_constraint(ScopedConstraintId::from_u32(2));
+
+        cd1a.merge(cd1b);
+        let cd1 = cd1a;
+        cd1.assert(false, &["1<>"]);
+
+        // merging a constrained definition with unbound keeps both
+        let mut cd2a = SymbolState::with(ScopedDefinitionId::from_u32(2));
+        cd2a.add_constraint(ScopedConstraintId::from_u32(3));
+
+        let cd2b = SymbolState::unbound();
+
+        cd2a.merge(cd2b);
+        let cd2 = cd2a;
+        cd2.assert(true, &["2<3>"]);
+
+        // merging different definitions keeps them each with their existing constraints
+        cd0.merge(cd2);
+        let cd = cd0;
+        cd.assert(true, &["0<0>", "2<3>"]);
+    }
+}

crates/red_knot_python_semantic/src/semantic_model.rs

@@ -1,7 +1,7 @@
 use ruff_db::files::{File, FilePath};
 use ruff_db::source::line_index;
 use ruff_python_ast as ast;
-use ruff_python_ast::{Expr, ExpressionRef, StmtClassDef};
+use ruff_python_ast::{Expr, ExpressionRef};
 use ruff_source_file::LineIndex;
 
 use crate::module_name::ModuleName;
@@ -147,29 +147,24 @@ impl HasTy for ast::Expr {
     }
 }
 
-impl HasTy for ast::StmtFunctionDef {
-    fn ty<'db>(&self, model: &SemanticModel<'db>) -> Type<'db> {
-        let index = semantic_index(model.db, model.file);
-        let definition = index.definition(self);
-        definition_ty(model.db, Some(definition))
-    }
+macro_rules! impl_definition_has_ty {
+    ($ty: ty) => {
+        impl HasTy for $ty {
+            #[inline]
+            fn ty<'db>(&self, model: &SemanticModel<'db>) -> Type<'db> {
+                let index = semantic_index(model.db, model.file);
+                let definition = index.definition(self);
+                definition_ty(model.db, definition)
+            }
+        }
+    };
 }
 
-impl HasTy for StmtClassDef {
-    fn ty<'db>(&self, model: &SemanticModel<'db>) -> Type<'db> {
-        let index = semantic_index(model.db, model.file);
-        let definition = index.definition(self);
-        definition_ty(model.db, Some(definition))
-    }
-}
-
-impl HasTy for ast::Alias {
-    fn ty<'db>(&self, model: &SemanticModel<'db>) -> Type<'db> {
-        let index = semantic_index(model.db, model.file);
-        let definition = index.definition(self);
-        definition_ty(model.db, Some(definition))
-    }
-}
+impl_definition_has_ty!(ast::StmtFunctionDef);
+impl_definition_has_ty!(ast::StmtClassDef);
+impl_definition_has_ty!(ast::Alias);
+impl_definition_has_ty!(ast::Parameter);
+impl_definition_has_ty!(ast::ParameterWithDefault);
 
 #[cfg(test)]
 mod tests {

crates/red_knot_python_semantic/src/types.rs

@@ -4,15 +4,22 @@ use ruff_python_ast::name::Name;
 use crate::builtins::builtins_scope;
 use crate::semantic_index::definition::Definition;
 use crate::semantic_index::symbol::{ScopeId, ScopedSymbolId};
-use crate::semantic_index::{global_scope, symbol_table, use_def_map};
+use crate::semantic_index::{
+    global_scope, symbol_table, use_def_map, DefinitionWithConstraints,
+    DefinitionWithConstraintsIterator,
+};
+use crate::types::narrow::narrowing_constraint;
 use crate::{Db, FxOrderSet};
 
 mod builder;
 mod display;
 mod infer;
+mod narrow;
 
-pub(crate) use self::builder::UnionBuilder;
-pub(crate) use self::infer::{infer_definition_types, infer_scope_types};
+pub(crate) use self::builder::{IntersectionBuilder, UnionBuilder};
+pub(crate) use self::infer::{
+    infer_definition_types, infer_expression_types, infer_scope_types, TypeInference,
+};
 
 /// Infer the public type of a symbol (its type as seen from outside its scope).
 pub(crate) fn symbol_ty<'db>(
@@ -23,7 +30,13 @@ pub(crate) fn symbol_ty<'db>(
     let _span = tracing::trace_span!("symbol_ty", ?symbol).entered();
 
     let use_def = use_def_map(db, scope);
-    definition_ty(db, use_def.public_definition(symbol))
+    definitions_ty(
+        db,
+        use_def.public_definitions(symbol),
+        use_def
+            .public_may_be_unbound(symbol)
+            .then_some(Type::Unbound),
+    )
 }
 
 /// Shorthand for `symbol_ty` that takes a symbol name instead of an ID.
@@ -54,16 +67,70 @@ pub(crate) fn builtins_symbol_ty_by_name<'db>(db: &'db dyn Db, name: &str) -> Ty
 }
 
 /// Infer the type of a [`Definition`].
-pub(crate) fn definition_ty<'db>(
+pub(crate) fn definition_ty<'db>(db: &'db dyn Db, definition: Definition<'db>) -> Type<'db> {
+    let inference = infer_definition_types(db, definition);
+    inference.definition_ty(definition)
+}
+
+/// Infer the combined type of an array of [`Definition`]s, plus one optional "unbound type".
+///
+/// Will return a union if there is more than one definition, or at least one plus an unbound
+/// type.
+///
+/// The "unbound type" represents the type in case control flow may not have passed through any
+/// definitions in this scope. If this isn't possible, then it will be `None`. If it is possible,
+/// and the result in that case should be Unbound (e.g. an unbound function local), then it will be
+/// `Some(Type::Unbound)`. If it is possible and the result should be something else (e.g. an
+/// implicit global lookup), then `unbound_type` will be `Some(the_global_symbol_type)`.
+///
+/// # Panics
+/// Will panic if called with zero definitions and no `unbound_ty`. This is a logic error,
+/// as any symbol with zero visible definitions clearly may be unbound, and the caller should
+/// provide an `unbound_ty`.
+pub(crate) fn definitions_ty<'db>(
     db: &'db dyn Db,
-    definition: Option<Definition<'db>>,
+    definitions_with_constraints: DefinitionWithConstraintsIterator<'_, 'db>,
+    unbound_ty: Option<Type<'db>>,
 ) -> Type<'db> {
-    match definition {
-        Some(definition) => {
-            let inference = infer_definition_types(db, definition);
-            inference.definition_ty(definition)
+    let def_types = definitions_with_constraints.map(
+        |DefinitionWithConstraints {
+             definition,
+             constraints,
+         }| {
+            let mut constraint_tys =
+                constraints.filter_map(|test| narrowing_constraint(db, test, definition));
+            let definition_ty = definition_ty(db, definition);
+            if let Some(first_constraint_ty) = constraint_tys.next() {
+                let mut builder = IntersectionBuilder::new(db);
+                builder = builder
+                    .add_positive(definition_ty)
+                    .add_positive(first_constraint_ty);
+                for constraint_ty in constraint_tys {
+                    builder = builder.add_positive(constraint_ty);
+                }
+                builder.build()
+            } else {
+                definition_ty
+            }
+        },
+    );
+    let mut all_types = unbound_ty.into_iter().chain(def_types);
+
+    let Some(first) = all_types.next() else {
+        panic!("definitions_ty should never be called with zero definitions and no unbound_ty.")
+    };
+
+    if let Some(second) = all_types.next() {
+        let mut builder = UnionBuilder::new(db);
+        builder = builder.add(first).add(second);
+
+        for variant in all_types {
+            builder = builder.add(variant);
         }
-        None => Type::Unbound,
+
+        builder.build()
+    } else {
+        first
     }
 }
 
@@ -74,7 +141,7 @@ pub enum Type<'db> {
     Any,
     /// the empty set of values
     Never,
-    /// unknown type (no annotation)
+    /// unknown type (either no annotation, or some kind of type error)
     /// equivalent to Any, or possibly to object in strict mode
     Unknown,
     /// name does not exist or is not bound to any value (this represents an error, but with some
@@ -106,10 +173,20 @@ impl<'db> Type<'db> {
         matches!(self, Type::Unbound)
     }
 
+    pub const fn is_unknown(&self) -> bool {
+        matches!(self, Type::Unknown)
+    }
+
+    pub const fn is_never(&self) -> bool {
+        matches!(self, Type::Never)
+    }
+
     pub fn may_be_unbound(&self, db: &'db dyn Db) -> bool {
         match self {
             Type::Unbound => true,
             Type::Union(union) => union.contains(db, Type::Unbound),
+            // Unbound can't appear in an intersection, because an intersection with Unbound
+            // simplifies to just Unbound.
             _ => false,
         }
     }

crates/red_knot_python_semantic/src/types/builder.rs

@@ -65,7 +65,6 @@ impl<'db> UnionBuilder<'db> {
     }
 }
 
-#[allow(unused)]
 #[derive(Clone)]
 pub(crate) struct IntersectionBuilder<'db> {
     // Really this builds a union-of-intersections, because we always keep our set-theoretic types
@@ -78,8 +77,7 @@ pub(crate) struct IntersectionBuilder<'db> {
 }
 
 impl<'db> IntersectionBuilder<'db> {
-    #[allow(dead_code)]
-    fn new(db: &'db dyn Db) -> Self {
+    pub(crate) fn new(db: &'db dyn Db) -> Self {
         Self {
             db,
             intersections: vec![InnerIntersectionBuilder::new()],
@@ -93,8 +91,7 @@ impl<'db> IntersectionBuilder<'db> {
         }
     }
 
-    #[allow(dead_code)]
-    fn add_positive(mut self, ty: Type<'db>) -> Self {
+    pub(crate) fn add_positive(mut self, ty: Type<'db>) -> Self {
         if let Type::Union(union) = ty {
             // Distribute ourself over this union: for each union element, clone ourself and
             // intersect with that union element, then create a new union-of-intersections with all
@@ -122,8 +119,7 @@ impl<'db> IntersectionBuilder<'db> {
         }
     }
 
-    #[allow(dead_code)]
-    fn add_negative(mut self, ty: Type<'db>) -> Self {
+    pub(crate) fn add_negative(mut self, ty: Type<'db>) -> Self {
         // See comments above in `add_positive`; this is just the negated version.
         if let Type::Union(union) = ty {
             union
@@ -142,8 +138,7 @@ impl<'db> IntersectionBuilder<'db> {
         }
     }
 
-    #[allow(dead_code)]
-    fn build(mut self) -> Type<'db> {
+    pub(crate) fn build(mut self) -> Type<'db> {
         // Avoid allocating the UnionBuilder unnecessarily if we have just one intersection:
         if self.intersections.len() == 1 {
             self.intersections.pop().unwrap().build(self.db)
@@ -157,7 +152,6 @@ impl<'db> IntersectionBuilder<'db> {
     }
 }
 
-#[allow(unused)]
 #[derive(Debug, Clone, Default)]
 struct InnerIntersectionBuilder<'db> {
     positive: FxOrderSet<Type<'db>>,
@@ -201,6 +195,7 @@ impl<'db> InnerIntersectionBuilder<'db> {
                 self.negative.retain(|elem| !pos.contains(elem));
             }
             Type::Never => {}
+            Type::Unbound => {}
             _ => {
                 if !self.positive.remove(&ty) {
                     self.negative.insert(ty);
@@ -214,9 +209,23 @@ impl<'db> InnerIntersectionBuilder<'db> {
 
         // Never is a subtype of all types
         if self.positive.contains(&Type::Never) {
-            self.positive.clear();
+            self.positive.retain(Type::is_never);
             self.negative.clear();
-            self.positive.insert(Type::Never);
+        }
+
+        if self.positive.contains(&Type::Unbound) {
+            self.positive.retain(Type::is_unbound);
+            self.negative.clear();
+        }
+
+        // None intersects only with object
+        for pos in &self.positive {
+            if let Type::Instance(_) = pos {
+                // could be `object` type
+            } else {
+                self.negative.remove(&Type::None);
+                break;
+            }
         }
     }
 
@@ -426,4 +435,37 @@ mod tests {
 
         assert_eq!(ty, Type::Never);
     }
+
+    #[test]
+    fn build_intersection_simplify_positive_unbound() {
+        let db = setup_db();
+        let ty = IntersectionBuilder::new(&db)
+            .add_positive(Type::Unbound)
+            .add_positive(Type::IntLiteral(1))
+            .build();
+
+        assert_eq!(ty, Type::Unbound);
+    }
+
+    #[test]
+    fn build_intersection_simplify_negative_unbound() {
+        let db = setup_db();
+        let ty = IntersectionBuilder::new(&db)
+            .add_negative(Type::Unbound)
+            .add_positive(Type::IntLiteral(1))
+            .build();
+
+        assert_eq!(ty, Type::IntLiteral(1));
+    }
+
+    #[test]
+    fn build_intersection_simplify_negative_none() {
+        let db = setup_db();
+        let ty = IntersectionBuilder::new(&db)
+            .add_negative(Type::None)
+            .add_positive(Type::IntLiteral(1))
+            .build();
+
+        assert_eq!(ty, Type::IntLiteral(1));
+    }
 }

crates/red_knot_python_semantic/src/types/infer.rs

@@ -20,6 +20,8 @@
 //!
 //! Inferring types at any of the three region granularities returns a [`TypeInference`], which
 //! holds types for every [`Definition`] and expression within the inferred region.
+use std::num::NonZeroU32;
+
 use rustc_hash::FxHashMap;
 use salsa;
 use salsa::plumbing::AsId;
@@ -27,23 +29,19 @@ use salsa::plumbing::AsId;
 use ruff_db::files::File;
 use ruff_db::parsed::parsed_module;
 use ruff_python_ast as ast;
-use ruff_python_ast::{ExprContext, TypeParams};
+use ruff_python_ast::{Expr, ExprContext};
 
 use crate::builtins::builtins_scope;
 use crate::module_name::ModuleName;
-use crate::module_resolver::resolve_module;
+use crate::module_resolver::{file_to_module, resolve_module};
 use crate::semantic_index::ast_ids::{HasScopedAstId, HasScopedUseId, ScopedExpressionId};
-use crate::semantic_index::definition::{
-    Definition, DefinitionKind, DefinitionNode, DefinitionNodeKey, ScopedPhiId,
-};
+use crate::semantic_index::definition::{Definition, DefinitionKind, DefinitionNodeKey};
 use crate::semantic_index::expression::Expression;
 use crate::semantic_index::semantic_index;
-use crate::semantic_index::symbol::{
-    FileScopeId, NodeWithScopeKind, NodeWithScopeRef, ScopeId, Symbol,
-};
+use crate::semantic_index::symbol::{FileScopeId, NodeWithScopeKind, NodeWithScopeRef, ScopeId};
 use crate::semantic_index::SemanticIndex;
 use crate::types::{
-    builtins_symbol_ty_by_name, definition_ty, global_symbol_ty_by_name, ClassType, FunctionType,
+    builtins_symbol_ty_by_name, definitions_ty, global_symbol_ty_by_name, ClassType, FunctionType,
     Name, Type, UnionBuilder,
 };
 use crate::Db;
@@ -280,50 +278,52 @@ impl<'db> TypeInferenceBuilder<'db> {
     }
 
     fn infer_region_definition(&mut self, definition: Definition<'db>) {
-        match definition.kind(self.db) {
-            DefinitionKind::Phi(phi_id) => self.infer_phi_definition(*phi_id, definition),
-            DefinitionKind::Node(node) => match node {
-                DefinitionNode::Function(function) => {
-                    self.infer_function_definition(function.node(), definition);
-                }
-                DefinitionNode::Class(class) => {
-                    self.infer_class_definition(class.node(), definition);
-                }
-                DefinitionNode::Import(import) => {
-                    self.infer_import_definition(import.node(), definition);
-                }
-                DefinitionNode::ImportFrom(import_from) => {
-                    self.infer_import_from_definition(
-                        import_from.import(),
-                        import_from.alias(),
-                        definition,
-                    );
-                }
-                DefinitionNode::Assignment(assignment) => {
-                    self.infer_assignment_definition(assignment.assignment(), definition);
-                }
-                DefinitionNode::AnnotatedAssignment(annotated_assignment) => {
-                    self.infer_annotated_assignment_definition(
-                        annotated_assignment.node(),
-                        definition,
-                    );
-                }
-                DefinitionNode::NamedExpression(named_expression) => {
-                    self.infer_named_expression_definition(named_expression.node(), definition);
-                }
-                DefinitionNode::Comprehension(comprehension) => {
-                    self.infer_comprehension_definition(
-                        comprehension.node(),
-                        comprehension.is_first(),
-                        definition,
-                    );
-                }
-            },
+        match definition.node(self.db) {
+            DefinitionKind::Function(function) => {
+                self.infer_function_definition(function.node(), definition);
+            }
+            DefinitionKind::Class(class) => self.infer_class_definition(class.node(), definition),
+            DefinitionKind::Import(import) => {
+                self.infer_import_definition(import.node(), definition);
+            }
+            DefinitionKind::ImportFrom(import_from) => {
+                self.infer_import_from_definition(
+                    import_from.import(),
+                    import_from.alias(),
+                    definition,
+                );
+            }
+            DefinitionKind::Assignment(assignment) => {
+                self.infer_assignment_definition(
+                    assignment.target(),
+                    assignment.assignment(),
+                    definition,
+                );
+            }
+            DefinitionKind::AnnotatedAssignment(annotated_assignment) => {
+                self.infer_annotated_assignment_definition(annotated_assignment.node(), definition);
+            }
+            DefinitionKind::NamedExpression(named_expression) => {
+                self.infer_named_expression_definition(named_expression.node(), definition);
+            }
+            DefinitionKind::Comprehension(comprehension) => {
+                self.infer_comprehension_definition(
+                    comprehension.node(),
+                    comprehension.is_first(),
+                    definition,
+                );
+            }
+            DefinitionKind::Parameter(parameter) => {
+                self.infer_parameter_definition(parameter, definition);
+            }
+            DefinitionKind::ParameterWithDefault(parameter_with_default) => {
+                self.infer_parameter_with_default_definition(parameter_with_default, definition);
+            }
         }
     }
 
     fn infer_region_expression(&mut self, expression: Expression<'db>) {
-        self.infer_expression(expression.node(self.db));
+        self.infer_expression(expression.node_ref(self.db));
     }
 
     fn infer_module(&mut self, module: &ast::ModModule) {
@@ -408,18 +408,6 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.extend(result);
     }
 
-    fn infer_phi_definition(&mut self, phi_id: ScopedPhiId, definition: Definition<'db>) {
-        let file_scope_id = self.scope.file_scope_id(self.db);
-        let use_def = self.index.use_def_map(file_scope_id);
-        let ty = use_def
-            .phi_operands(phi_id)
-            .iter()
-            .map(|&definition| definition_ty(self.db, definition))
-            .fold(UnionBuilder::new(self.db), UnionBuilder::add)
-            .build();
-        self.types.definitions.insert(definition, ty);
-    }
-
     fn infer_function_definition_statement(&mut self, function: &ast::StmtFunctionDef) {
         self.infer_definition(function);
     }
@@ -445,6 +433,13 @@ impl<'db> TypeInferenceBuilder<'db> {
             .map(|decorator| self.infer_decorator(decorator))
             .collect();
 
+        for default in parameters
+            .iter_non_variadic_params()
+            .filter_map(|param| param.default.as_deref())
+        {
+            self.infer_expression(default);
+        }
+
         // If there are type params, parameters and returns are evaluated in that scope.
         if type_params.is_none() {
             self.infer_parameters(parameters);
@@ -482,10 +477,12 @@ impl<'db> TypeInferenceBuilder<'db> {
         let ast::ParameterWithDefault {
             range: _,
             parameter,
-            default,
+            default: _,
         } = parameter_with_default;
-        self.infer_parameter(parameter);
-        self.infer_optional_expression(default.as_deref());
+
+        self.infer_optional_expression(parameter.annotation.as_deref());
+
+        self.infer_definition(parameter_with_default);
     }
 
     fn infer_parameter(&mut self, parameter: &ast::Parameter) {
@@ -494,7 +491,29 @@ impl<'db> TypeInferenceBuilder<'db> {
             name: _,
             annotation,
         } = parameter;
+
         self.infer_optional_expression(annotation.as_deref());
+
+        self.infer_definition(parameter);
+    }
+
+    fn infer_parameter_with_default_definition(
+        &mut self,
+        _parameter_with_default: &ast::ParameterWithDefault,
+        definition: Definition<'db>,
+    ) {
+        // TODO(dhruvmanila): Infer types from annotation or default expression
+        self.types.definitions.insert(definition, Type::Unknown);
+    }
+
+    fn infer_parameter_definition(
+        &mut self,
+        _parameter: &ast::Parameter,
+        definition: Definition<'db>,
+    ) {
+        // TODO(dhruvmanila): Annotation expression is resolved at the enclosing scope, infer the
+        // parameter type from there
+        self.types.definitions.insert(definition, Type::Unknown);
     }
 
     fn infer_class_definition_statement(&mut self, class: &ast::StmtClassDef) {
@@ -691,6 +710,7 @@ impl<'db> TypeInferenceBuilder<'db> {
 
     fn infer_assignment_definition(
         &mut self,
+        target: &ast::ExprName,
         assignment: &ast::StmtAssign,
         definition: Definition<'db>,
     ) {
@@ -700,6 +720,9 @@ impl<'db> TypeInferenceBuilder<'db> {
         let value_ty = self
             .types
             .expression_ty(assignment.value.scoped_ast_id(self.db, self.scope));
+        self.types
+            .expressions
+            .insert(target.scoped_ast_id(self.db, self.scope), value_ty);
         self.types.definitions.insert(definition, value_ty);
     }
 
@@ -809,7 +832,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             asname: _,
         } = alias;
 
-        let module_ty = self.module_ty_from_name(name);
+        let module_ty = self.module_ty_from_name(ModuleName::new(name));
         self.types.definitions.insert(definition, module_ty);
     }
 
@@ -847,27 +870,82 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.infer_optional_expression(cause.as_deref());
     }
 
+    /// Given a `from .foo import bar` relative import, resolve the relative module
+    /// we're importing `bar` from into an absolute [`ModuleName`]
+    /// using the name of the module we're currently analyzing.
+    ///
+    /// - `level` is the number of dots at the beginning of the relative module name:
+    ///   - `from .foo.bar import baz` => `level == 1`
+    ///   - `from ...foo.bar import baz` => `level == 3`
+    /// - `tail` is the relative module name stripped of all leading dots:
+    ///   - `from .foo import bar` => `tail == "foo"`
+    ///   - `from ..foo.bar import baz` => `tail == "foo.bar"`
+    fn relative_module_name(&self, tail: Option<&str>, level: NonZeroU32) -> Option<ModuleName> {
+        let Some(module) = file_to_module(self.db, self.file) else {
+            tracing::debug!("Failed to resolve file {:?} to a module", self.file);
+            return None;
+        };
+        let mut level = level.get();
+        if module.kind().is_package() {
+            level -= 1;
+        }
+        let mut module_name = module.name().to_owned();
+        for _ in 0..level {
+            module_name = module_name.parent()?;
+        }
+        if let Some(tail) = tail {
+            if let Some(valid_tail) = ModuleName::new(tail) {
+                module_name.extend(&valid_tail);
+            } else {
+                tracing::debug!("Failed to resolve relative import due to invalid syntax");
+                return None;
+            }
+        }
+        Some(module_name)
+    }
+
     fn infer_import_from_definition(
         &mut self,
         import_from: &ast::StmtImportFrom,
         alias: &ast::Alias,
         definition: Definition<'db>,
     ) {
-        let ast::StmtImportFrom { module, .. } = import_from;
-        let module_ty = if let Some(module) = module {
-            self.module_ty_from_name(module)
+        // TODO:
+        // - Absolute `*` imports (`from collections import *`)
+        // - Relative `*` imports (`from ...foo import *`)
+        // - Submodule imports (`from collections import abc`,
+        //   where `abc` is a submodule of the `collections` package)
+        //
+        // For the last item, see the currently skipped tests
+        // `follow_relative_import_bare_to_module()` and
+        // `follow_nonexistent_import_bare_to_module()`.
+        let ast::StmtImportFrom { module, level, .. } = import_from;
+        tracing::trace!("Resolving imported object {alias:?} from statement {import_from:?}");
+        let module_name = if let Some(level) = NonZeroU32::new(*level) {
+            self.relative_module_name(module.as_deref(), level)
         } else {
-            // TODO support relative imports
-            Type::Unknown
+            let module_name = module
+                .as_ref()
+                .expect("Non-relative import should always have a non-None `module`!");
+            ModuleName::new(module_name)
         };
 
+        let module_ty = self.module_ty_from_name(module_name);
+
         let ast::Alias {
             range: _,
             name,
             asname: _,
         } = alias;
 
-        let ty = module_ty.member(self.db, &Name::new(&name.id));
+        // If a symbol is unbound in the module the symbol was originally defined in,
+        // when we're trying to import the symbol from that module into "our" module,
+        // the runtime error will occur immediately (rather than when the symbol is *used*,
+        // as would be the case for a symbol with type `Unbound`), so it's appropriate to
+        // think of the type of the imported symbol as `Unknown` rather than `Unbound`
+        let ty = module_ty
+            .member(self.db, &Name::new(&name.id))
+            .replace_unbound_with(self.db, Type::Unknown);
 
         self.types.definitions.insert(definition, ty);
     }
@@ -883,11 +961,10 @@ impl<'db> TypeInferenceBuilder<'db> {
         }
     }
 
-    fn module_ty_from_name(&self, name: &ast::Identifier) -> Type<'db> {
-        let module = ModuleName::new(&name.id).and_then(|name| resolve_module(self.db, name));
-        module
-            .map(|module| Type::Module(module.file()))
-            .unwrap_or(Type::Unbound)
+    fn module_ty_from_name(&self, module_name: Option<ModuleName>) -> Type<'db> {
+        module_name
+            .and_then(|module_name| resolve_module(self.db, module_name))
+            .map_or(Type::Unknown, |module| Type::Module(module.file()))
     }
 
     fn infer_decorator(&mut self, decorator: &ast::Decorator) -> Type<'db> {
@@ -930,6 +1007,9 @@ impl<'db> TypeInferenceBuilder<'db> {
             ast::Expr::NumberLiteral(literal) => self.infer_number_literal_expression(literal),
             ast::Expr::BooleanLiteral(literal) => self.infer_boolean_literal_expression(literal),
             ast::Expr::StringLiteral(literal) => self.infer_string_literal_expression(literal),
+            ast::Expr::BytesLiteral(bytes_literal) => {
+                self.infer_bytes_literal_expression(bytes_literal)
+            }
             ast::Expr::FString(fstring) => self.infer_fstring_expression(fstring),
             ast::Expr::EllipsisLiteral(literal) => self.infer_ellipsis_literal_expression(literal),
             ast::Expr::Tuple(tuple) => self.infer_tuple_expression(tuple),
@@ -956,8 +1036,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             ast::Expr::Yield(yield_expression) => self.infer_yield_expression(yield_expression),
             ast::Expr::YieldFrom(yield_from) => self.infer_yield_from_expression(yield_from),
             ast::Expr::Await(await_expression) => self.infer_await_expression(await_expression),
-
-            _ => todo!("expression type resolution for {:?}", expression),
+            Expr::IpyEscapeCommand(_) => todo!("Implement Ipy escape command support"),
         };
 
         let expr_id = expression.scoped_ast_id(self.db, self.scope);
@@ -994,6 +1073,12 @@ impl<'db> TypeInferenceBuilder<'db> {
         Type::Unknown
     }
 
+    #[allow(clippy::unused_self)]
+    fn infer_bytes_literal_expression(&mut self, _literal: &ast::ExprBytesLiteral) -> Type<'db> {
+        // TODO
+        Type::Unknown
+    }
+
     fn infer_fstring_expression(&mut self, fstring: &ast::ExprFString) -> Type<'db> {
         let ast::ExprFString { range: _, value } = fstring;
 
@@ -1301,6 +1386,13 @@ impl<'db> TypeInferenceBuilder<'db> {
         } = lambda_expression;
 
         if let Some(parameters) = parameters {
+            for default in parameters
+                .iter_non_variadic_params()
+                .filter_map(|param| param.default.as_deref())
+            {
+                self.infer_expression(default);
+            }
+
             self.infer_parameters(parameters);
         }
 
@@ -1362,22 +1454,6 @@ impl<'db> TypeInferenceBuilder<'db> {
         Type::Unknown
     }
 
-    fn infer_global_name_reference(&self, symbol: &Symbol) -> Type<'db> {
-        let file_scope_id = self.scope.file_scope_id(self.db);
-        // implicit global
-        let mut ty = if file_scope_id == FileScopeId::global() {
-            Type::Unbound
-        } else {
-            global_symbol_ty_by_name(self.db, self.file, symbol.name())
-        };
-        // fallback to builtins
-        if ty.may_be_unbound(self.db) && Some(self.scope) != builtins_scope(self.db) {
-            ty = ty
-                .replace_unbound_with(self.db, builtins_symbol_ty_by_name(self.db, symbol.name()));
-        }
-        ty
-    }
-
     fn infer_name_expression(&mut self, name: &ast::ExprName) -> Type<'db> {
         let ast::ExprName { range: _, id, ctx } = name;
 
@@ -1386,18 +1462,38 @@ impl<'db> TypeInferenceBuilder<'db> {
                 let file_scope_id = self.scope.file_scope_id(self.db);
                 let use_def = self.index.use_def_map(file_scope_id);
                 let use_id = name.scoped_use_id(self.db, self.scope);
-                let mut ty = definition_ty(self.db, use_def.definition_for_use(use_id));
-                if ty.may_be_unbound(self.db) {
+                let may_be_unbound = use_def.use_may_be_unbound(use_id);
+
+                let unbound_ty = if may_be_unbound {
                     let symbols = self.index.symbol_table(file_scope_id);
+                    // SAFETY: the symbol table always creates a symbol for every Name node.
                     let symbol = symbols.symbol_by_name(id).unwrap();
                     if !symbol.is_defined() || !self.scope.is_function_like(self.db) {
-                        ty = ty.replace_unbound_with(
-                            self.db,
-                            self.infer_global_name_reference(symbol),
-                        );
+                        // implicit global
+                        let unbound_ty = if file_scope_id == FileScopeId::global() {
+                            Type::Unbound
+                        } else {
+                            global_symbol_ty_by_name(self.db, self.file, id)
+                        };
+                        // fallback to builtins
+                        if unbound_ty.may_be_unbound(self.db)
+                            && Some(self.scope) != builtins_scope(self.db)
+                        {
+                            Some(unbound_ty.replace_unbound_with(
+                                self.db,
+                                builtins_symbol_ty_by_name(self.db, id),
+                            ))
+                        } else {
+                            Some(unbound_ty)
+                        }
+                    } else {
+                        Some(Type::Unbound)
                     }
-                }
-                ty
+                } else {
+                    None
+                };
+
+                definitions_ty(self.db, use_def.use_definitions(use_id), unbound_ty)
             }
             ExprContext::Store | ExprContext::Del => Type::None,
             ExprContext::Invalid => Type::Unknown,
@@ -1550,7 +1646,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         Type::Unknown
     }
 
-    fn infer_type_parameters(&mut self, type_parameters: &TypeParams) {
+    fn infer_type_parameters(&mut self, type_parameters: &ast::TypeParams) {
         let ast::TypeParams {
             range: _,
             type_params,
@@ -1597,6 +1693,7 @@ impl<'db> TypeInferenceBuilder<'db> {
 #[cfg(test)]
 mod tests {
     use anyhow::Context;
+
     use ruff_db::files::{system_path_to_file, File};
     use ruff_db::parsed::parsed_module;
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
@@ -1686,6 +1783,166 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn follow_relative_import_simple() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("src/package/__init__.py", ""),
+            ("src/package/foo.py", "X = 42"),
+            ("src/package/bar.py", "from .foo import X"),
+        ])?;
+
+        assert_public_ty(&db, "src/package/bar.py", "X", "Literal[42]");
+
+        Ok(())
+    }
+
+    #[test]
+    fn follow_nonexistent_relative_import_simple() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("src/package/__init__.py", ""),
+            ("src/package/bar.py", "from .foo import X"),
+        ])?;
+
+        assert_public_ty(&db, "src/package/bar.py", "X", "Unknown");
+
+        Ok(())
+    }
+
+    #[test]
+    fn follow_relative_import_dotted() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("src/package/__init__.py", ""),
+            ("src/package/foo/bar/baz.py", "X = 42"),
+            ("src/package/bar.py", "from .foo.bar.baz import X"),
+        ])?;
+
+        assert_public_ty(&db, "src/package/bar.py", "X", "Literal[42]");
+
+        Ok(())
+    }
+
+    #[test]
+    fn follow_relative_import_bare_to_package() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("src/package/__init__.py", "X = 42"),
+            ("src/package/bar.py", "from . import X"),
+        ])?;
+
+        assert_public_ty(&db, "src/package/bar.py", "X", "Literal[42]");
+
+        Ok(())
+    }
+
+    #[test]
+    fn follow_nonexistent_relative_import_bare_to_package() -> anyhow::Result<()> {
+        let mut db = setup_db();
+        db.write_files([("src/package/bar.py", "from . import X")])?;
+        assert_public_ty(&db, "src/package/bar.py", "X", "Unknown");
+        Ok(())
+    }
+
+    #[ignore = "TODO: Submodule imports possibly not supported right now?"]
+    #[test]
+    fn follow_relative_import_bare_to_module() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("src/package/__init__.py", ""),
+            ("src/package/foo.py", "X = 42"),
+            ("src/package/bar.py", "from . import foo; y = foo.X"),
+        ])?;
+
+        assert_public_ty(&db, "src/package/bar.py", "y", "Literal[42]");
+
+        Ok(())
+    }
+
+    #[ignore = "TODO: Submodule imports possibly not supported right now?"]
+    #[test]
+    fn follow_nonexistent_import_bare_to_module() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("src/package/__init__.py", ""),
+            ("src/package/bar.py", "from . import foo"),
+        ])?;
+
+        assert_public_ty(&db, "src/package/bar.py", "foo", "Unknown");
+
+        Ok(())
+    }
+
+    #[test]
+    fn follow_relative_import_from_dunder_init() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("src/package/__init__.py", "from .foo import X"),
+            ("src/package/foo.py", "X = 42"),
+        ])?;
+
+        assert_public_ty(&db, "src/package/__init__.py", "X", "Literal[42]");
+
+        Ok(())
+    }
+
+    #[test]
+    fn follow_nonexistent_relative_import_from_dunder_init() -> anyhow::Result<()> {
+        let mut db = setup_db();
+        db.write_files([("src/package/__init__.py", "from .foo import X")])?;
+        assert_public_ty(&db, "src/package/__init__.py", "X", "Unknown");
+        Ok(())
+    }
+
+    #[test]
+    fn follow_very_relative_import() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("src/package/__init__.py", ""),
+            ("src/package/foo.py", "X = 42"),
+            (
+                "src/package/subpackage/subsubpackage/bar.py",
+                "from ...foo import X",
+            ),
+        ])?;
+
+        assert_public_ty(
+            &db,
+            "src/package/subpackage/subsubpackage/bar.py",
+            "X",
+            "Literal[42]",
+        );
+
+        Ok(())
+    }
+
+    #[test]
+    fn imported_unbound_symbol_is_unknown() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_files([
+            ("src/package/__init__.py", ""),
+            ("src/package/foo.py", "x"),
+            ("src/package/bar.py", "from package.foo import x"),
+        ])?;
+
+        // the type as seen from external modules (`Unknown`)
+        // is different from the type inside the module itself (`Unbound`):
+        assert_public_ty(&db, "src/package/foo.py", "x", "Unbound");
+        assert_public_ty(&db, "src/package/bar.py", "x", "Unknown");
+
+        Ok(())
+    }
+
     #[test]
     fn resolve_base_class_by_name() -> anyhow::Result<()> {
         let mut db = setup_db();
@@ -2347,6 +2604,26 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn narrow_not_none() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "/src/a.py",
+            "
+            x = None if flag else 1
+            y = 0
+            if x is not None:
+                y = x
+            ",
+        )?;
+
+        assert_public_ty(&db, "/src/a.py", "x", "Literal[1] | None");
+        assert_public_ty(&db, "/src/a.py", "y", "Literal[0, 1]");
+
+        Ok(())
+    }
+
     #[test]
     fn while_loop() -> anyhow::Result<()> {
         let mut db = setup_db();
@@ -2442,11 +2719,13 @@ mod tests {
         Ok(())
     }
 
-    fn public_def<'db>(db: &'db TestDb, file: File, name: &str) -> Definition<'db> {
+    fn first_public_def<'db>(db: &'db TestDb, file: File, name: &str) -> Definition<'db> {
         let scope = global_scope(db, file);
         use_def_map(db, scope)
-            .public_definition(symbol_table(db, scope).symbol_id_by_name(name).unwrap())
+            .public_definitions(symbol_table(db, scope).symbol_id_by_name(name).unwrap())
+            .next()
             .unwrap()
+            .definition
     }
 
     #[test]
@@ -2588,7 +2867,7 @@ mod tests {
         assert_function_query_was_not_run(
             &db,
             infer_definition_types,
-            public_def(&db, a, "x"),
+            first_public_def(&db, a, "x"),
             &events,
         );
 
@@ -2624,7 +2903,7 @@ mod tests {
         assert_function_query_was_not_run(
             &db,
             infer_definition_types,
-            public_def(&db, a, "x"),
+            first_public_def(&db, a, "x"),
             &events,
         );
         Ok(())

crates/red_knot_python_semantic/src/types/narrow.rs

@@ -0,0 +1,115 @@
+use crate::semantic_index::ast_ids::HasScopedAstId;
+use crate::semantic_index::definition::Definition;
+use crate::semantic_index::expression::Expression;
+use crate::semantic_index::symbol::{ScopeId, ScopedSymbolId, SymbolTable};
+use crate::semantic_index::symbol_table;
+use crate::types::{infer_expression_types, IntersectionBuilder, Type, TypeInference};
+use crate::Db;
+use ruff_python_ast as ast;
+use rustc_hash::FxHashMap;
+use std::sync::Arc;
+
+/// Return the type constraint that `test` (if true) would place on `definition`, if any.
+///
+/// For example, if we have this code:
+///
+/// ```python
+/// y = 1 if flag else None
+/// x = 1 if flag else None
+/// if x is not None:
+///     ...
+/// ```
+///
+/// The `test` expression `x is not None` places the constraint "not None" on the definition of
+/// `x`, so in that case we'd return `Some(Type::Intersection(negative=[Type::None]))`.
+///
+/// But if we called this with the same `test` expression, but the `definition` of `y`, no
+/// constraint is applied to that definition, so we'd just return `None`.
+pub(crate) fn narrowing_constraint<'db>(
+    db: &'db dyn Db,
+    test: Expression<'db>,
+    definition: Definition<'db>,
+) -> Option<Type<'db>> {
+    all_narrowing_constraints(db, test)
+        .get(&definition.symbol(db))
+        .copied()
+}
+
+#[salsa::tracked(return_ref)]
+fn all_narrowing_constraints<'db>(
+    db: &'db dyn Db,
+    test: Expression<'db>,
+) -> NarrowingConstraints<'db> {
+    NarrowingConstraintsBuilder::new(db, test).finish()
+}
+
+type NarrowingConstraints<'db> = FxHashMap<ScopedSymbolId, Type<'db>>;
+
+struct NarrowingConstraintsBuilder<'db> {
+    db: &'db dyn Db,
+    expression: Expression<'db>,
+    constraints: NarrowingConstraints<'db>,
+}
+
+impl<'db> NarrowingConstraintsBuilder<'db> {
+    fn new(db: &'db dyn Db, expression: Expression<'db>) -> Self {
+        Self {
+            db,
+            expression,
+            constraints: NarrowingConstraints::default(),
+        }
+    }
+
+    fn finish(mut self) -> NarrowingConstraints<'db> {
+        if let ast::Expr::Compare(expr_compare) = self.expression.node_ref(self.db).node() {
+            self.add_expr_compare(expr_compare);
+        }
+        // TODO other test expression kinds
+
+        self.constraints.shrink_to_fit();
+        self.constraints
+    }
+
+    fn symbols(&self) -> Arc<SymbolTable> {
+        symbol_table(self.db, self.scope())
+    }
+
+    fn scope(&self) -> ScopeId<'db> {
+        self.expression.scope(self.db)
+    }
+
+    fn inference(&self) -> &'db TypeInference<'db> {
+        infer_expression_types(self.db, self.expression)
+    }
+
+    fn add_expr_compare(&mut self, expr_compare: &ast::ExprCompare) {
+        let ast::ExprCompare {
+            range: _,
+            left,
+            ops,
+            comparators,
+        } = expr_compare;
+
+        if let ast::Expr::Name(ast::ExprName {
+            range: _,
+            id,
+            ctx: _,
+        }) = left.as_ref()
+        {
+            // SAFETY: we should always have a symbol for every Name node.
+            let symbol = self.symbols().symbol_id_by_name(id).unwrap();
+            let scope = self.scope();
+            let inference = self.inference();
+            for (op, comparator) in std::iter::zip(&**ops, &**comparators) {
+                let comp_ty = inference.expression_ty(comparator.scoped_ast_id(self.db, scope));
+                if matches!(op, ast::CmpOp::IsNot) {
+                    let ty = IntersectionBuilder::new(self.db)
+                        .add_negative(comp_ty)
+                        .build();
+                    self.constraints.insert(symbol, ty);
+                };
+                // TODO other comparison types
+            }
+        }
+    }
+}

crates/red_knot_python_semantic/vendor/typeshed/source_commit.txt

@@ -1 +1 @@
-4ef2d66663fc080fefa379e6ae5fc45d4f8b54eb
+1ace5718deaf3041f8e3d1dc9c9e8a8e830e517f

crates/red_knot_python_semantic/vendor/typeshed/stdlib/_ast.pyi

@@ -753,9 +753,11 @@ class Constant(expr):
         __match_args__ = ("value", "kind")
     value: Any  # None, str, bytes, bool, int, float, complex, Ellipsis
     kind: str | None
-    # Aliases for value, for backwards compatibility
-    s: Any
-    n: int | float | complex
+    if sys.version_info < (3, 14):
+        # Aliases for value, for backwards compatibility
+        s: Any
+        n: int | float | complex
+
     def __init__(self, value: Any, kind: str | None = None, **kwargs: Unpack[_Attributes]) -> None: ...
 
 class NamedExpr(expr):

crates/red_knot_python_semantic/vendor/typeshed/stdlib/_collections_abc.pyi

@@ -1,13 +1,12 @@
 import sys
 from abc import abstractmethod
 from types import MappingProxyType
-from typing import (  # noqa: Y022,Y038,Y057
+from typing import (  # noqa: Y022,Y038
     AbstractSet as Set,
     AsyncGenerator as AsyncGenerator,
     AsyncIterable as AsyncIterable,
     AsyncIterator as AsyncIterator,
     Awaitable as Awaitable,
-    ByteString as ByteString,
     Callable as Callable,
     Collection as Collection,
     Container as Container,
@@ -59,8 +58,12 @@ __all__ = [
     "ValuesView",
     "Sequence",
     "MutableSequence",
-    "ByteString",
 ]
+if sys.version_info < (3, 14):
+    from typing import ByteString as ByteString  # noqa: Y057
+
+    __all__ += ["ByteString"]
+
 if sys.version_info >= (3, 12):
     __all__ += ["Buffer"]
 

crates/red_knot_python_semantic/vendor/typeshed/stdlib/_ctypes.pyi

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

crates/red_knot_python_semantic/vendor/typeshed/stdlib/argparse.pyi

@@ -357,7 +357,17 @@ class Action(_AttributeHolder):
 
 if sys.version_info >= (3, 12):
     class BooleanOptionalAction(Action):
-        if sys.version_info >= (3, 13):
+        if sys.version_info >= (3, 14):
+            def __init__(
+                self,
+                option_strings: Sequence[str],
+                dest: str,
+                default: bool | None = None,
+                required: bool = False,
+                help: str | None = None,
+                deprecated: bool = False,
+            ) -> None: ...
+        elif sys.version_info >= (3, 13):
             @overload
             def __init__(
                 self,

crates/red_knot_python_semantic/vendor/typeshed/stdlib/ast.pyi

@@ -10,27 +10,28 @@ class _ABC(type):
     if sys.version_info >= (3, 9):
         def __init__(cls, *args: Unused) -> None: ...
 
-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class Num(Constant, metaclass=_ABC):
-    value: int | float | complex
+if sys.version_info < (3, 14):
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class Num(Constant, metaclass=_ABC):
+        value: int | float | complex
 
-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class Str(Constant, metaclass=_ABC):
-    value: str
-    # Aliases for value, for backwards compatibility
-    s: str
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class Str(Constant, metaclass=_ABC):
+        value: str
+        # Aliases for value, for backwards compatibility
+        s: str
 
-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class Bytes(Constant, metaclass=_ABC):
-    value: bytes
-    # Aliases for value, for backwards compatibility
-    s: bytes
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class Bytes(Constant, metaclass=_ABC):
+        value: bytes
+        # Aliases for value, for backwards compatibility
+        s: bytes
 
-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class NameConstant(Constant, metaclass=_ABC): ...
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class NameConstant(Constant, metaclass=_ABC): ...
 
-@deprecated("Replaced by ast.Constant; removal scheduled for Python 3.14")
-class Ellipsis(Constant, metaclass=_ABC): ...
+    @deprecated("Replaced by ast.Constant; removed in Python 3.14")
+    class Ellipsis(Constant, metaclass=_ABC): ...
 
 if sys.version_info >= (3, 9):
     class slice(AST): ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/asyncio/tasks.pyi

@@ -151,13 +151,13 @@ if sys.version_info >= (3, 10):
     @overload
     def gather(*coros_or_futures: _FutureLike[_T], return_exceptions: Literal[False] = False) -> Future[list[_T]]: ...  # type: ignore[overload-overlap]
     @overload
-    def gather(coro_or_future1: _FutureLike[_T1], /, *, return_exceptions: bool) -> Future[tuple[_T1 | BaseException]]: ...  # type: ignore[overload-overlap]
+    def gather(coro_or_future1: _FutureLike[_T1], /, *, return_exceptions: bool) -> Future[tuple[_T1 | BaseException]]: ...
     @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
         coro_or_future1: _FutureLike[_T1], coro_or_future2: _FutureLike[_T2], /, *, return_exceptions: bool
     ) -> Future[tuple[_T1 | BaseException, _T2 | BaseException]]: ...
     @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
         coro_or_future1: _FutureLike[_T1],
         coro_or_future2: _FutureLike[_T2],
         coro_or_future3: _FutureLike[_T3],
@@ -166,7 +166,7 @@ if sys.version_info >= (3, 10):
         return_exceptions: bool,
     ) -> Future[tuple[_T1 | BaseException, _T2 | BaseException, _T3 | BaseException]]: ...
     @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
         coro_or_future1: _FutureLike[_T1],
         coro_or_future2: _FutureLike[_T2],
         coro_or_future3: _FutureLike[_T3],
@@ -176,7 +176,7 @@ if sys.version_info >= (3, 10):
         return_exceptions: bool,
     ) -> Future[tuple[_T1 | BaseException, _T2 | BaseException, _T3 | BaseException, _T4 | BaseException]]: ...
     @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
         coro_or_future1: _FutureLike[_T1],
         coro_or_future2: _FutureLike[_T2],
         coro_or_future3: _FutureLike[_T3],
@@ -189,7 +189,7 @@ if sys.version_info >= (3, 10):
         tuple[_T1 | BaseException, _T2 | BaseException, _T3 | BaseException, _T4 | BaseException, _T5 | BaseException]
     ]: ...
     @overload
-    def gather(  # type: ignore[overload-overlap]
+    def gather(
         coro_or_future1: _FutureLike[_T1],
         coro_or_future2: _FutureLike[_T2],
         coro_or_future3: _FutureLike[_T3],

crates/red_knot_python_semantic/vendor/typeshed/stdlib/asyncio/unix_events.pyi

@@ -159,7 +159,7 @@ if sys.platform != "win32":
 
     class _UnixSelectorEventLoop(BaseSelectorEventLoop):
         if sys.version_info >= (3, 13):
-            async def create_unix_server(  # type: ignore[override]
+            async def create_unix_server(
                 self,
                 protocol_factory: _ProtocolFactory,
                 path: StrPath | None = None,

crates/red_knot_python_semantic/vendor/typeshed/stdlib/builtins.pyi

@@ -1744,7 +1744,7 @@ _SupportsSumNoDefaultT = TypeVar("_SupportsSumNoDefaultT", bound=_SupportsSumWit
 # without creating many false-positive errors (see #7578).
 # Instead, we special-case the most common examples of this: bool and literal integers.
 @overload
-def sum(iterable: Iterable[bool | _LiteralInteger], /, start: int = 0) -> int: ...  # type: ignore[overload-overlap]
+def sum(iterable: Iterable[bool | _LiteralInteger], /, start: int = 0) -> int: ...
 @overload
 def sum(iterable: Iterable[_SupportsSumNoDefaultT], /) -> _SupportsSumNoDefaultT | Literal[0]: ...
 @overload
@@ -1752,9 +1752,8 @@ def sum(iterable: Iterable[_AddableT1], /, start: _AddableT2) -> _AddableT1 | _A
 
 # The argument to `vars()` has to have a `__dict__` attribute, so the second overload can't be annotated with `object`
 # (A "SupportsDunderDict" protocol doesn't work)
-# Use a type: ignore to make complaints about overlapping overloads go away
 @overload
-def vars(object: type, /) -> types.MappingProxyType[str, Any]: ...  # type: ignore[overload-overlap]
+def vars(object: type, /) -> types.MappingProxyType[str, Any]: ...
 @overload
 def vars(object: Any = ..., /) -> dict[str, Any]: ...
 

crates/red_knot_python_semantic/vendor/typeshed/stdlib/contextlib.pyi

@@ -55,6 +55,7 @@ class AbstractAsyncContextManager(Protocol[_T_co, _ExitT_co]):
     ) -> _ExitT_co: ...
 
 class ContextDecorator:
+    def _recreate_cm(self) -> Self: ...
     def __call__(self, func: _F) -> _F: ...
 
 class _GeneratorContextManager(AbstractContextManager[_T_co, bool | None], ContextDecorator):
@@ -80,6 +81,7 @@ if sys.version_info >= (3, 10):
     _AF = TypeVar("_AF", bound=Callable[..., Awaitable[Any]])
 
     class AsyncContextDecorator:
+        def _recreate_cm(self) -> Self: ...
         def __call__(self, func: _AF) -> _AF: ...
 
     class _AsyncGeneratorContextManager(AbstractAsyncContextManager[_T_co, bool | None], AsyncContextDecorator):

crates/red_knot_python_semantic/vendor/typeshed/stdlib/ctypes/_endian.pyi

@@ -1,12 +1,5 @@
 import sys
-from _ctypes import RTLD_GLOBAL as RTLD_GLOBAL, RTLD_LOCAL as RTLD_LOCAL, Structure, Union
-from ctypes import DEFAULT_MODE as DEFAULT_MODE, cdll as cdll, pydll as pydll, pythonapi as pythonapi
-
-if sys.version_info >= (3, 12):
-    from _ctypes import SIZEOF_TIME_T as SIZEOF_TIME_T
-
-if sys.platform == "win32":
-    from ctypes import oledll as oledll, windll as windll
+from ctypes import Structure, Union
 
 # At runtime, the native endianness is an alias for Structure,
 # while the other is a subclass with a metaclass added in.

crates/red_knot_python_semantic/vendor/typeshed/stdlib/dataclasses.pyi

@@ -5,7 +5,7 @@ from _typeshed import DataclassInstance
 from builtins import type as Type  # alias to avoid name clashes with fields named "type"
 from collections.abc import Callable, Iterable, Mapping
 from typing import Any, Generic, Literal, Protocol, TypeVar, overload
-from typing_extensions import TypeAlias, TypeIs
+from typing_extensions import Never, TypeAlias, TypeIs
 
 if sys.version_info >= (3, 9):
     from types import GenericAlias
@@ -213,6 +213,10 @@ else:
     ) -> Any: ...
 
 def fields(class_or_instance: DataclassInstance | type[DataclassInstance]) -> tuple[Field[Any], ...]: ...
+
+# HACK: `obj: Never` typing matches if object argument is using `Any` type.
+@overload
+def is_dataclass(obj: Never) -> TypeIs[DataclassInstance | type[DataclassInstance]]: ...  # type: ignore[narrowed-type-not-subtype]  # pyright: ignore[reportGeneralTypeIssues]
 @overload
 def is_dataclass(obj: type) -> TypeIs[type[DataclassInstance]]: ...
 @overload

crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/cmd.pyi

@@ -1,6 +1,26 @@
 from _typeshed import BytesPath, Incomplete, StrOrBytesPath, StrPath, Unused
 from abc import abstractmethod
 from collections.abc import Callable, Iterable
+from distutils.command.bdist import bdist
+from distutils.command.bdist_dumb import bdist_dumb
+from distutils.command.bdist_rpm import bdist_rpm
+from distutils.command.build import build
+from distutils.command.build_clib import build_clib
+from distutils.command.build_ext import build_ext
+from distutils.command.build_py import build_py
+from distutils.command.build_scripts import build_scripts
+from distutils.command.check import check
+from distutils.command.clean import clean
+from distutils.command.config import config
+from distutils.command.install import install
+from distutils.command.install_data import install_data
+from distutils.command.install_egg_info import install_egg_info
+from distutils.command.install_headers import install_headers
+from distutils.command.install_lib import install_lib
+from distutils.command.install_scripts import install_scripts
+from distutils.command.register import register
+from distutils.command.sdist import sdist
+from distutils.command.upload import upload
 from distutils.dist import Distribution
 from distutils.file_util import _BytesPathT, _StrPathT
 from typing import Any, ClassVar, Literal, TypeVar, overload
@@ -28,8 +48,108 @@ class Command:
     def ensure_dirname(self, option: str) -> None: ...
     def get_command_name(self) -> str: ...
     def set_undefined_options(self, src_cmd: str, *option_pairs: tuple[str, str]) -> None: ...
+    # NOTE: This list comes directly from the distutils/command folder. Minus bdist_msi and bdist_wininst.
+    @overload
+    def get_finalized_command(self, command: Literal["bdist"], create: bool | Literal[0, 1] = 1) -> bdist: ...
+    @overload
+    def get_finalized_command(self, command: Literal["bdist_dumb"], create: bool | Literal[0, 1] = 1) -> bdist_dumb: ...
+    @overload
+    def get_finalized_command(self, command: Literal["bdist_rpm"], create: bool | Literal[0, 1] = 1) -> bdist_rpm: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build"], create: bool | Literal[0, 1] = 1) -> build: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build_clib"], create: bool | Literal[0, 1] = 1) -> build_clib: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build_ext"], create: bool | Literal[0, 1] = 1) -> build_ext: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build_py"], create: bool | Literal[0, 1] = 1) -> build_py: ...
+    @overload
+    def get_finalized_command(self, command: Literal["build_scripts"], create: bool | Literal[0, 1] = 1) -> build_scripts: ...
+    @overload
+    def get_finalized_command(self, command: Literal["check"], create: bool | Literal[0, 1] = 1) -> check: ...
+    @overload
+    def get_finalized_command(self, command: Literal["clean"], create: bool | Literal[0, 1] = 1) -> clean: ...
+    @overload
+    def get_finalized_command(self, command: Literal["config"], create: bool | Literal[0, 1] = 1) -> config: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install"], create: bool | Literal[0, 1] = 1) -> install: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install_data"], create: bool | Literal[0, 1] = 1) -> install_data: ...
+    @overload
+    def get_finalized_command(
+        self, command: Literal["install_egg_info"], create: bool | Literal[0, 1] = 1
+    ) -> install_egg_info: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install_headers"], create: bool | Literal[0, 1] = 1) -> install_headers: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install_lib"], create: bool | Literal[0, 1] = 1) -> install_lib: ...
+    @overload
+    def get_finalized_command(self, command: Literal["install_scripts"], create: bool | Literal[0, 1] = 1) -> install_scripts: ...
+    @overload
+    def get_finalized_command(self, command: Literal["register"], create: bool | Literal[0, 1] = 1) -> register: ...
+    @overload
+    def get_finalized_command(self, command: Literal["sdist"], create: bool | Literal[0, 1] = 1) -> sdist: ...
+    @overload
+    def get_finalized_command(self, command: Literal["upload"], create: bool | Literal[0, 1] = 1) -> upload: ...
+    @overload
     def get_finalized_command(self, command: str, create: bool | Literal[0, 1] = 1) -> Command: ...
     @overload
+    def reinitialize_command(self, command: Literal["bdist"], reinit_subcommands: bool | Literal[0, 1] = 0) -> bdist: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["bdist_dumb"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> bdist_dumb: ...
+    @overload
+    def reinitialize_command(self, command: Literal["bdist_rpm"], reinit_subcommands: bool | Literal[0, 1] = 0) -> bdist_rpm: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build"], reinit_subcommands: bool | Literal[0, 1] = 0) -> build: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["build_clib"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> build_clib: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_ext"], reinit_subcommands: bool | Literal[0, 1] = 0) -> build_ext: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_py"], reinit_subcommands: bool | Literal[0, 1] = 0) -> build_py: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["build_scripts"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> build_scripts: ...
+    @overload
+    def reinitialize_command(self, command: Literal["check"], reinit_subcommands: bool | Literal[0, 1] = 0) -> check: ...
+    @overload
+    def reinitialize_command(self, command: Literal["clean"], reinit_subcommands: bool | Literal[0, 1] = 0) -> clean: ...
+    @overload
+    def reinitialize_command(self, command: Literal["config"], reinit_subcommands: bool | Literal[0, 1] = 0) -> config: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install"], reinit_subcommands: bool | Literal[0, 1] = 0) -> install: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_data"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_data: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_egg_info"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_egg_info: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_headers"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_headers: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_lib"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_lib: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_scripts"], reinit_subcommands: bool | Literal[0, 1] = 0
+    ) -> install_scripts: ...
+    @overload
+    def reinitialize_command(self, command: Literal["register"], reinit_subcommands: bool | Literal[0, 1] = 0) -> register: ...
+    @overload
+    def reinitialize_command(self, command: Literal["sdist"], reinit_subcommands: bool | Literal[0, 1] = 0) -> sdist: ...
+    @overload
+    def reinitialize_command(self, command: Literal["upload"], reinit_subcommands: bool | Literal[0, 1] = 0) -> upload: ...
+    @overload
     def reinitialize_command(self, command: str, reinit_subcommands: bool | Literal[0, 1] = 0) -> Command: ...
     @overload
     def reinitialize_command(self, command: _CommandT, reinit_subcommands: bool | Literal[0, 1] = 0) -> _CommandT: ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/command/__init__.pyi

@@ -0,0 +1,48 @@
+import sys
+
+from . import (
+    bdist,
+    bdist_dumb,
+    bdist_rpm,
+    build,
+    build_clib,
+    build_ext,
+    build_py,
+    build_scripts,
+    check,
+    clean,
+    install,
+    install_data,
+    install_headers,
+    install_lib,
+    install_scripts,
+    register,
+    sdist,
+    upload,
+)
+
+__all__ = [
+    "build",
+    "build_py",
+    "build_ext",
+    "build_clib",
+    "build_scripts",
+    "clean",
+    "install",
+    "install_lib",
+    "install_headers",
+    "install_scripts",
+    "install_data",
+    "sdist",
+    "register",
+    "bdist",
+    "bdist_dumb",
+    "bdist_rpm",
+    "check",
+    "upload",
+]
+
+if sys.version_info < (3, 10):
+    from . import bdist_wininst
+
+    __all__ += ["bdist_wininst"]

crates/red_knot_python_semantic/vendor/typeshed/stdlib/distutils/dist.pyi

@@ -1,6 +1,26 @@
 from _typeshed import Incomplete, StrOrBytesPath, StrPath, SupportsWrite
 from collections.abc import Iterable, MutableMapping
 from distutils.cmd import Command
+from distutils.command.bdist import bdist
+from distutils.command.bdist_dumb import bdist_dumb
+from distutils.command.bdist_rpm import bdist_rpm
+from distutils.command.build import build
+from distutils.command.build_clib import build_clib
+from distutils.command.build_ext import build_ext
+from distutils.command.build_py import build_py
+from distutils.command.build_scripts import build_scripts
+from distutils.command.check import check
+from distutils.command.clean import clean
+from distutils.command.config import config
+from distutils.command.install import install
+from distutils.command.install_data import install_data
+from distutils.command.install_egg_info import install_egg_info
+from distutils.command.install_headers import install_headers
+from distutils.command.install_lib import install_lib
+from distutils.command.install_scripts import install_scripts
+from distutils.command.register import register
+from distutils.command.sdist import sdist
+from distutils.command.upload import upload
 from re import Pattern
 from typing import IO, ClassVar, Literal, TypeVar, overload
 from typing_extensions import TypeAlias
@@ -63,10 +83,6 @@ class Distribution:
     def __init__(self, attrs: MutableMapping[str, Incomplete] | None = None) -> None: ...
     def get_option_dict(self, command: str) -> dict[str, tuple[str, str]]: ...
     def parse_config_files(self, filenames: Iterable[str] | None = None) -> None: ...
-    @overload
-    def get_command_obj(self, command: str, create: Literal[1, True] = 1) -> Command: ...
-    @overload
-    def get_command_obj(self, command: str, create: Literal[0, False]) -> Command | None: ...
     global_options: ClassVar[_OptionsList]
     common_usage: ClassVar[str]
     display_options: ClassVar[_OptionsList]
@@ -108,8 +124,137 @@ class Distribution:
     def print_commands(self) -> None: ...
     def get_command_list(self): ...
     def get_command_packages(self): ...
+    # NOTE: This list comes directly from the distutils/command folder. Minus bdist_msi and bdist_wininst.
+    @overload
+    def get_command_obj(self, command: Literal["bdist"], create: Literal[1, True] = 1) -> bdist: ...
+    @overload
+    def get_command_obj(self, command: Literal["bdist_dumb"], create: Literal[1, True] = 1) -> bdist_dumb: ...
+    @overload
+    def get_command_obj(self, command: Literal["bdist_rpm"], create: Literal[1, True] = 1) -> bdist_rpm: ...
+    @overload
+    def get_command_obj(self, command: Literal["build"], create: Literal[1, True] = 1) -> build: ...
+    @overload
+    def get_command_obj(self, command: Literal["build_clib"], create: Literal[1, True] = 1) -> build_clib: ...
+    @overload
+    def get_command_obj(self, command: Literal["build_ext"], create: Literal[1, True] = 1) -> build_ext: ...
+    @overload
+    def get_command_obj(self, command: Literal["build_py"], create: Literal[1, True] = 1) -> build_py: ...
+    @overload
+    def get_command_obj(self, command: Literal["build_scripts"], create: Literal[1, True] = 1) -> build_scripts: ...
+    @overload
+    def get_command_obj(self, command: Literal["check"], create: Literal[1, True] = 1) -> check: ...
+    @overload
+    def get_command_obj(self, command: Literal["clean"], create: Literal[1, True] = 1) -> clean: ...
+    @overload
+    def get_command_obj(self, command: Literal["config"], create: Literal[1, True] = 1) -> config: ...
+    @overload
+    def get_command_obj(self, command: Literal["install"], create: Literal[1, True] = 1) -> install: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_data"], create: Literal[1, True] = 1) -> install_data: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_egg_info"], create: Literal[1, True] = 1) -> install_egg_info: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_headers"], create: Literal[1, True] = 1) -> install_headers: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_lib"], create: Literal[1, True] = 1) -> install_lib: ...
+    @overload
+    def get_command_obj(self, command: Literal["install_scripts"], create: Literal[1, True] = 1) -> install_scripts: ...
+    @overload
+    def get_command_obj(self, command: Literal["register"], create: Literal[1, True] = 1) -> register: ...
+    @overload
+    def get_command_obj(self, command: Literal["sdist"], create: Literal[1, True] = 1) -> sdist: ...
+    @overload
+    def get_command_obj(self, command: Literal["upload"], create: Literal[1, True] = 1) -> upload: ...
+    @overload
+    def get_command_obj(self, command: str, create: Literal[1, True] = 1) -> Command: ...
+    # Not replicating the overloads for "Command | None", user may use "isinstance"
+    @overload
+    def get_command_obj(self, command: str, create: Literal[0, False]) -> Command | None: ...
+    @overload
+    def get_command_class(self, command: Literal["bdist"]) -> type[bdist]: ...
+    @overload
+    def get_command_class(self, command: Literal["bdist_dumb"]) -> type[bdist_dumb]: ...
+    @overload
+    def get_command_class(self, command: Literal["bdist_rpm"]) -> type[bdist_rpm]: ...
+    @overload
+    def get_command_class(self, command: Literal["build"]) -> type[build]: ...
+    @overload
+    def get_command_class(self, command: Literal["build_clib"]) -> type[build_clib]: ...
+    @overload
+    def get_command_class(self, command: Literal["build_ext"]) -> type[build_ext]: ...
+    @overload
+    def get_command_class(self, command: Literal["build_py"]) -> type[build_py]: ...
+    @overload
+    def get_command_class(self, command: Literal["build_scripts"]) -> type[build_scripts]: ...
+    @overload
+    def get_command_class(self, command: Literal["check"]) -> type[check]: ...
+    @overload
+    def get_command_class(self, command: Literal["clean"]) -> type[clean]: ...
+    @overload
+    def get_command_class(self, command: Literal["config"]) -> type[config]: ...
+    @overload
+    def get_command_class(self, command: Literal["install"]) -> type[install]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_data"]) -> type[install_data]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_egg_info"]) -> type[install_egg_info]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_headers"]) -> type[install_headers]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_lib"]) -> type[install_lib]: ...
+    @overload
+    def get_command_class(self, command: Literal["install_scripts"]) -> type[install_scripts]: ...
+    @overload
+    def get_command_class(self, command: Literal["register"]) -> type[register]: ...
+    @overload
+    def get_command_class(self, command: Literal["sdist"]) -> type[sdist]: ...
+    @overload
+    def get_command_class(self, command: Literal["upload"]) -> type[upload]: ...
+    @overload
     def get_command_class(self, command: str) -> type[Command]: ...
     @overload
+    def reinitialize_command(self, command: Literal["bdist"], reinit_subcommands: bool = False) -> bdist: ...
+    @overload
+    def reinitialize_command(self, command: Literal["bdist_dumb"], reinit_subcommands: bool = False) -> bdist_dumb: ...
+    @overload
+    def reinitialize_command(self, command: Literal["bdist_rpm"], reinit_subcommands: bool = False) -> bdist_rpm: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build"], reinit_subcommands: bool = False) -> build: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_clib"], reinit_subcommands: bool = False) -> build_clib: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_ext"], reinit_subcommands: bool = False) -> build_ext: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_py"], reinit_subcommands: bool = False) -> build_py: ...
+    @overload
+    def reinitialize_command(self, command: Literal["build_scripts"], reinit_subcommands: bool = False) -> build_scripts: ...
+    @overload
+    def reinitialize_command(self, command: Literal["check"], reinit_subcommands: bool = False) -> check: ...
+    @overload
+    def reinitialize_command(self, command: Literal["clean"], reinit_subcommands: bool = False) -> clean: ...
+    @overload
+    def reinitialize_command(self, command: Literal["config"], reinit_subcommands: bool = False) -> config: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install"], reinit_subcommands: bool = False) -> install: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install_data"], reinit_subcommands: bool = False) -> install_data: ...
+    @overload
+    def reinitialize_command(
+        self, command: Literal["install_egg_info"], reinit_subcommands: bool = False
+    ) -> install_egg_info: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install_headers"], reinit_subcommands: bool = False) -> install_headers: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install_lib"], reinit_subcommands: bool = False) -> install_lib: ...
+    @overload
+    def reinitialize_command(self, command: Literal["install_scripts"], reinit_subcommands: bool = False) -> install_scripts: ...
+    @overload
+    def reinitialize_command(self, command: Literal["register"], reinit_subcommands: bool = False) -> register: ...
+    @overload
+    def reinitialize_command(self, command: Literal["sdist"], reinit_subcommands: bool = False) -> sdist: ...
+    @overload
+    def reinitialize_command(self, command: Literal["upload"], reinit_subcommands: bool = False) -> upload: ...
+    @overload
     def reinitialize_command(self, command: str, reinit_subcommands: bool = False) -> Command: ...
     @overload
     def reinitialize_command(self, command: _CommandT, reinit_subcommands: bool = False) -> _CommandT: ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/email/utils.pyi

@@ -66,7 +66,10 @@ def mktime_tz(data: _PDTZ) -> int: ...
 def formatdate(timeval: float | None = None, localtime: bool = False, usegmt: bool = False) -> str: ...
 def format_datetime(dt: datetime.datetime, usegmt: bool = False) -> str: ...
 
-if sys.version_info >= (3, 12):
+if sys.version_info >= (3, 14):
+    def localtime(dt: datetime.datetime | None = None) -> datetime.datetime: ...
+
+elif sys.version_info >= (3, 12):
     @overload
     def localtime(dt: datetime.datetime | None = None) -> datetime.datetime: ...
     @overload

crates/red_knot_python_semantic/vendor/typeshed/stdlib/filecmp.pyi

@@ -17,13 +17,24 @@ def cmpfiles(
 ) -> tuple[list[AnyStr], list[AnyStr], list[AnyStr]]: ...
 
 class dircmp(Generic[AnyStr]):
-    def __init__(
-        self,
-        a: GenericPath[AnyStr],
-        b: GenericPath[AnyStr],
-        ignore: Sequence[AnyStr] | None = None,
-        hide: Sequence[AnyStr] | None = None,
-    ) -> None: ...
+    if sys.version_info >= (3, 13):
+        def __init__(
+            self,
+            a: GenericPath[AnyStr],
+            b: GenericPath[AnyStr],
+            ignore: Sequence[AnyStr] | None = None,
+            hide: Sequence[AnyStr] | None = None,
+            *,
+            shallow: bool = True,
+        ) -> None: ...
+    else:
+        def __init__(
+            self,
+            a: GenericPath[AnyStr],
+            b: GenericPath[AnyStr],
+            ignore: Sequence[AnyStr] | None = None,
+            hide: Sequence[AnyStr] | None = None,
+        ) -> None: ...
     left: AnyStr
     right: AnyStr
     hide: Sequence[AnyStr]

crates/red_knot_python_semantic/vendor/typeshed/stdlib/importlib/metadata/__init__.pyi

@@ -155,7 +155,7 @@ if sys.version_info >= (3, 10) and sys.version_info < (3, 12):
         @property
         def names(self) -> set[str]: ...
         @overload
-        def select(self) -> Self: ...  # type: ignore[misc]
+        def select(self) -> Self: ...
         @overload
         def select(
             self,
@@ -277,7 +277,7 @@ if sys.version_info >= (3, 12):
 
 elif sys.version_info >= (3, 10):
     @overload
-    def entry_points() -> SelectableGroups: ...  # type: ignore[overload-overlap]
+    def entry_points() -> SelectableGroups: ...
     @overload
     def entry_points(
         *, name: str = ..., value: str = ..., group: str = ..., module: str = ..., attr: str = ..., extras: list[str] = ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/lib2to3/fixes/fix_unicode.pyi

@@ -6,7 +6,7 @@ from ..pytree import Node
 
 class FixUnicode(fixer_base.BaseFix):
     BM_compatible: ClassVar[Literal[True]]
-    PATTERN: ClassVar[Literal["STRING | 'unicode' | 'unichr'"]]  # type: ignore[name-defined]  # Name "STRING" is not defined
+    PATTERN: ClassVar[str]
     unicode_literals: bool
     def start_tree(self, tree: Node, filename: StrPath) -> None: ...
     def transform(self, node, results): ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/logging/__init__.pyi

@@ -55,10 +55,9 @@ __all__ = [
     "setLogRecordFactory",
     "lastResort",
     "raiseExceptions",
+    "warn",
 ]
 
-if sys.version_info < (3, 13):
-    __all__ += ["warn"]
 if sys.version_info >= (3, 11):
     __all__ += ["getLevelNamesMapping"]
 if sys.version_info >= (3, 12):
@@ -157,17 +156,16 @@ class Logger(Filterer):
         stacklevel: int = 1,
         extra: Mapping[str, object] | None = None,
     ) -> None: ...
-    if sys.version_info < (3, 13):
-        def warn(
-            self,
-            msg: object,
-            *args: object,
-            exc_info: _ExcInfoType = None,
-            stack_info: bool = False,
-            stacklevel: int = 1,
-            extra: Mapping[str, object] | None = None,
-        ) -> None: ...
-
+    @deprecated("Deprecated; use warning() instead.")
+    def warn(
+        self,
+        msg: object,
+        *args: object,
+        exc_info: _ExcInfoType = None,
+        stack_info: bool = False,
+        stacklevel: int = 1,
+        extra: Mapping[str, object] | None = None,
+    ) -> None: ...
     def error(
         self,
         msg: object,
@@ -412,18 +410,17 @@ class LoggerAdapter(Generic[_L]):
         extra: Mapping[str, object] | None = None,
         **kwargs: object,
     ) -> None: ...
-    if sys.version_info < (3, 13):
-        def warn(
-            self,
-            msg: object,
-            *args: object,
-            exc_info: _ExcInfoType = None,
-            stack_info: bool = False,
-            stacklevel: int = 1,
-            extra: Mapping[str, object] | None = None,
-            **kwargs: object,
-        ) -> None: ...
-
+    @deprecated("Deprecated; use warning() instead.")
+    def warn(
+        self,
+        msg: object,
+        *args: object,
+        exc_info: _ExcInfoType = None,
+        stack_info: bool = False,
+        stacklevel: int = 1,
+        extra: Mapping[str, object] | None = None,
+        **kwargs: object,
+    ) -> None: ...
     def error(
         self,
         msg: object,
@@ -523,17 +520,15 @@ def warning(
     stacklevel: int = 1,
     extra: Mapping[str, object] | None = None,
 ) -> None: ...
-
-if sys.version_info < (3, 13):
-    def warn(
-        msg: object,
-        *args: object,
-        exc_info: _ExcInfoType = None,
-        stack_info: bool = False,
-        stacklevel: int = 1,
-        extra: Mapping[str, object] | None = None,
-    ) -> None: ...
-
+@deprecated("Deprecated; use warning() instead.")
+def warn(
+    msg: object,
+    *args: object,
+    exc_info: _ExcInfoType = None,
+    stack_info: bool = False,
+    stacklevel: int = 1,
+    extra: Mapping[str, object] | None = None,
+) -> None: ...
 def error(
     msg: object,
     *args: object,

crates/red_knot_python_semantic/vendor/typeshed/stdlib/multiprocessing/sharedctypes.pyi

@@ -73,7 +73,7 @@ def copy(obj: _CT) -> _CT: ...
 @overload
 def synchronized(obj: _SimpleCData[_T], lock: _LockLike | None = None, ctx: Any | None = None) -> Synchronized[_T]: ...
 @overload
-def synchronized(obj: ctypes.Array[c_char], lock: _LockLike | None = None, ctx: Any | None = None) -> SynchronizedString: ...  # type: ignore
+def synchronized(obj: ctypes.Array[c_char], lock: _LockLike | None = None, ctx: Any | None = None) -> SynchronizedString: ...
 @overload
 def synchronized(
     obj: ctypes.Array[_SimpleCData[_T]], lock: _LockLike | None = None, ctx: Any | None = None
@@ -115,12 +115,12 @@ class SynchronizedArray(SynchronizedBase[ctypes.Array[_SimpleCData[_T]]], Generi
 class SynchronizedString(SynchronizedArray[bytes]):
     @overload  # type: ignore[override]
     def __getitem__(self, i: slice) -> bytes: ...
-    @overload  # type: ignore[override]
+    @overload
     def __getitem__(self, i: int) -> bytes: ...
     @overload  # type: ignore[override]
     def __setitem__(self, i: slice, value: bytes) -> None: ...
-    @overload  # type: ignore[override]
-    def __setitem__(self, i: int, value: bytes) -> None: ...  # type: ignore[override]
+    @overload
+    def __setitem__(self, i: int, value: bytes) -> None: ...
     def __getslice__(self, start: int, stop: int) -> bytes: ...  # type: ignore[override]
     def __setslice__(self, start: int, stop: int, values: bytes) -> None: ...  # type: ignore[override]
 

crates/red_knot_python_semantic/vendor/typeshed/stdlib/pathlib.pyi

@@ -159,6 +159,20 @@ class Path(PurePath):
     def lchmod(self, mode: int) -> None: ...
     def lstat(self) -> stat_result: ...
     def mkdir(self, mode: int = 0o777, parents: bool = False, exist_ok: bool = False) -> None: ...
+
+    if sys.version_info >= (3, 14):
+        def copy(self, target: StrPath, *, follow_symlinks: bool = True, preserve_metadata: bool = False) -> None: ...
+        def copytree(
+            self,
+            target: StrPath,
+            *,
+            follow_symlinks: bool = True,
+            preserve_metadata: bool = False,
+            dirs_exist_ok: bool = False,
+            ignore: Callable[[Self], bool] | None = None,
+            on_error: Callable[[OSError], object] | None = None,
+        ) -> None: ...
+
     # Adapted from builtins.open
     # Text mode: always returns a TextIOWrapper
     # The Traversable .open in stdlib/importlib/abc.pyi should be kept in sync with this.
@@ -232,10 +246,18 @@ class Path(PurePath):
     if sys.version_info >= (3, 9):
         def readlink(self) -> Self: ...
 
-    def rename(self, target: str | PurePath) -> Self: ...
-    def replace(self, target: str | PurePath) -> Self: ...
+    if sys.version_info >= (3, 10):
+        def rename(self, target: StrPath) -> Self: ...
+        def replace(self, target: StrPath) -> Self: ...
+    else:
+        def rename(self, target: str | PurePath) -> Self: ...
+        def replace(self, target: str | PurePath) -> Self: ...
+
     def resolve(self, strict: bool = False) -> Self: ...
     def rmdir(self) -> None: ...
+    if sys.version_info >= (3, 14):
+        def delete(self, ignore_errors: bool = False, on_error: Callable[[OSError], object] | None = None) -> None: ...
+
     def symlink_to(self, target: StrOrBytesPath, target_is_directory: bool = False) -> None: ...
     if sys.version_info >= (3, 10):
         def hardlink_to(self, target: StrOrBytesPath) -> None: ...
@@ -266,6 +288,9 @@ class Path(PurePath):
             self, top_down: bool = ..., on_error: Callable[[OSError], object] | None = ..., follow_symlinks: bool = ...
         ) -> Iterator[tuple[Self, list[str], list[str]]]: ...
 
+    if sys.version_info >= (3, 14):
+        def rmtree(self, ignore_errors: bool = False, on_error: Callable[[OSError], object] | None = None) -> None: ...
+
 class PosixPath(Path, PurePosixPath): ...
 class WindowsPath(Path, PureWindowsPath): ...
 

crates/red_knot_python_semantic/vendor/typeshed/stdlib/pdb.pyi

@@ -84,7 +84,7 @@ class Pdb(Bdb, Cmd):
         def _runscript(self, filename: str) -> None: ...
 
     if sys.version_info >= (3, 13):
-        def completedefault(self, text: str, line: str, begidx: int, endidx: int) -> list[str]: ...  # type: ignore[override]
+        def completedefault(self, text: str, line: str, begidx: int, endidx: int) -> list[str]: ...
 
     def do_commands(self, arg: str) -> bool | None: ...
     def do_break(self, arg: str, temporary: bool = ...) -> bool | None: ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/pty.pyi

@@ -1,7 +1,7 @@
 import sys
 from collections.abc import Callable, Iterable
 from typing import Final
-from typing_extensions import TypeAlias
+from typing_extensions import TypeAlias, deprecated
 
 if sys.platform != "win32":
     __all__ = ["openpty", "fork", "spawn"]
@@ -13,7 +13,12 @@ if sys.platform != "win32":
 
     CHILD: Final = 0
     def openpty() -> tuple[int, int]: ...
-    def master_open() -> tuple[int, str]: ...  # deprecated, use openpty()
-    def slave_open(tty_name: str) -> int: ...  # deprecated, use openpty()
+
+    if sys.version_info < (3, 14):
+        @deprecated("Deprecated in 3.12, to be removed in 3.14; use openpty() instead")
+        def master_open() -> tuple[int, str]: ...
+        @deprecated("Deprecated in 3.12, to be removed in 3.14; use openpty() instead")
+        def slave_open(tty_name: str) -> int: ...
+
     def fork() -> tuple[int, int]: ...
     def spawn(argv: str | Iterable[str], master_read: _Reader = ..., stdin_read: _Reader = ...) -> int: ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/re.pyi

@@ -74,7 +74,7 @@ class Match(Generic[AnyStr]):
     @overload
     def expand(self: Match[str], template: str) -> str: ...
     @overload
-    def expand(self: Match[bytes], template: ReadableBuffer) -> bytes: ...  # type: ignore[overload-overlap]
+    def expand(self: Match[bytes], template: ReadableBuffer) -> bytes: ...
     @overload
     def expand(self, template: AnyStr) -> AnyStr: ...
     # group() returns "AnyStr" or "AnyStr | None", depending on the pattern.
@@ -124,19 +124,21 @@ class Pattern(Generic[AnyStr]):
     @overload
     def search(self: Pattern[str], string: str, pos: int = 0, endpos: int = sys.maxsize) -> Match[str] | None: ...
     @overload
-    def search(self: Pattern[bytes], string: ReadableBuffer, pos: int = 0, endpos: int = sys.maxsize) -> Match[bytes] | None: ...  # type: ignore[overload-overlap]
+    def search(self: Pattern[bytes], string: ReadableBuffer, pos: int = 0, endpos: int = sys.maxsize) -> Match[bytes] | None: ...
     @overload
     def search(self, string: AnyStr, pos: int = 0, endpos: int = sys.maxsize) -> Match[AnyStr] | None: ...
     @overload
     def match(self: Pattern[str], string: str, pos: int = 0, endpos: int = sys.maxsize) -> Match[str] | None: ...
     @overload
-    def match(self: Pattern[bytes], string: ReadableBuffer, pos: int = 0, endpos: int = sys.maxsize) -> Match[bytes] | None: ...  # type: ignore[overload-overlap]
+    def match(self: Pattern[bytes], string: ReadableBuffer, pos: int = 0, endpos: int = sys.maxsize) -> Match[bytes] | None: ...
     @overload
     def match(self, string: AnyStr, pos: int = 0, endpos: int = sys.maxsize) -> Match[AnyStr] | None: ...
     @overload
     def fullmatch(self: Pattern[str], string: str, pos: int = 0, endpos: int = sys.maxsize) -> Match[str] | None: ...
     @overload
-    def fullmatch(self: Pattern[bytes], string: ReadableBuffer, pos: int = 0, endpos: int = sys.maxsize) -> Match[bytes] | None: ...  # type: ignore[overload-overlap]
+    def fullmatch(
+        self: Pattern[bytes], string: ReadableBuffer, pos: int = 0, endpos: int = sys.maxsize
+    ) -> Match[bytes] | None: ...
     @overload
     def fullmatch(self, string: AnyStr, pos: int = 0, endpos: int = sys.maxsize) -> Match[AnyStr] | None: ...
     @overload
@@ -155,13 +157,15 @@ class Pattern(Generic[AnyStr]):
     @overload
     def finditer(self: Pattern[str], string: str, pos: int = 0, endpos: int = sys.maxsize) -> Iterator[Match[str]]: ...
     @overload
-    def finditer(self: Pattern[bytes], string: ReadableBuffer, pos: int = 0, endpos: int = sys.maxsize) -> Iterator[Match[bytes]]: ...  # type: ignore[overload-overlap]
+    def finditer(
+        self: Pattern[bytes], string: ReadableBuffer, pos: int = 0, endpos: int = sys.maxsize
+    ) -> Iterator[Match[bytes]]: ...
     @overload
     def finditer(self, string: AnyStr, pos: int = 0, endpos: int = sys.maxsize) -> Iterator[Match[AnyStr]]: ...
     @overload
     def sub(self: Pattern[str], repl: str | Callable[[Match[str]], str], string: str, count: int = 0) -> str: ...
     @overload
-    def sub(  # type: ignore[overload-overlap]
+    def sub(
         self: Pattern[bytes],
         repl: ReadableBuffer | Callable[[Match[bytes]], ReadableBuffer],
         string: ReadableBuffer,
@@ -172,7 +176,7 @@ class Pattern(Generic[AnyStr]):
     @overload
     def subn(self: Pattern[str], repl: str | Callable[[Match[str]], str], string: str, count: int = 0) -> tuple[str, int]: ...
     @overload
-    def subn(  # type: ignore[overload-overlap]
+    def subn(
         self: Pattern[bytes],
         repl: ReadableBuffer | Callable[[Match[bytes]], ReadableBuffer],
         string: ReadableBuffer,

crates/red_knot_python_semantic/vendor/typeshed/stdlib/sqlite3/dbapi2.pyi

@@ -29,7 +29,10 @@ def DateFromTicks(ticks: float) -> Date: ...
 def TimeFromTicks(ticks: float) -> Time: ...
 def TimestampFromTicks(ticks: float) -> Timestamp: ...
 
-version_info: tuple[int, int, int]
+if sys.version_info < (3, 14):
+    # Deprecated in 3.12, removed in 3.14.
+    version_info: tuple[int, int, int]
+
 sqlite_version_info: tuple[int, int, int]
 Binary = memoryview
 
@@ -90,7 +93,10 @@ SQLITE_UPDATE: Final[int]
 adapters: dict[tuple[type[Any], type[Any]], _Adapter[Any]]
 converters: dict[str, _Converter]
 sqlite_version: str
-version: str
+
+if sys.version_info < (3, 14):
+    # Deprecated in 3.12, removed in 3.14.
+    version: str
 
 if sys.version_info >= (3, 11):
     SQLITE_ABORT: Final[int]

crates/red_knot_python_semantic/vendor/typeshed/stdlib/symtable.pyi

@@ -2,6 +2,7 @@ import sys
 from _collections_abc import dict_keys
 from collections.abc import Sequence
 from typing import Any
+from typing_extensions import deprecated
 
 __all__ = ["symtable", "SymbolTable", "Class", "Function", "Symbol"]
 
@@ -51,7 +52,9 @@ class Function(SymbolTable):
     def get_nonlocals(self) -> tuple[str, ...]: ...
 
 class Class(SymbolTable):
-    def get_methods(self) -> tuple[str, ...]: ...
+    if sys.version_info < (3, 16):
+        @deprecated("deprecated in Python 3.14, will be removed in Python 3.16")
+        def get_methods(self) -> tuple[str, ...]: ...
 
 class Symbol:
     def __init__(

crates/red_knot_python_semantic/vendor/typeshed/stdlib/tarfile.pyi

@@ -423,7 +423,7 @@ class TarInfo:
     name: str
     path: str
     size: int
-    mtime: int
+    mtime: int | float
     chksum: int
     devmajor: int
     devminor: int

crates/red_knot_python_semantic/vendor/typeshed/stdlib/tempfile.pyi

@@ -463,7 +463,7 @@ class TemporaryDirectory(Generic[AnyStr]):
 
 # The overloads overlap, but they should still work fine.
 @overload
-def mkstemp(  # type: ignore[overload-overlap]
+def mkstemp(
     suffix: str | None = None, prefix: str | None = None, dir: StrPath | None = None, text: bool = False
 ) -> tuple[int, str]: ...
 @overload
@@ -473,7 +473,7 @@ def mkstemp(
 
 # The overloads overlap, but they should still work fine.
 @overload
-def mkdtemp(suffix: str | None = None, prefix: str | None = None, dir: StrPath | None = None) -> str: ...  # type: ignore[overload-overlap]
+def mkdtemp(suffix: str | None = None, prefix: str | None = None, dir: StrPath | None = None) -> str: ...
 @overload
 def mkdtemp(suffix: bytes | None = None, prefix: bytes | None = None, dir: BytesPath | None = None) -> bytes: ...
 def mktemp(suffix: str = "", prefix: str = "tmp", dir: StrPath | None = None) -> str: ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/tkinter/__init__.pyi

@@ -2148,11 +2148,12 @@ class Listbox(Widget, XView, YView):
         selectborderwidth: _ScreenUnits = 0,
         selectforeground: str = ...,
         # from listbox man page: "The value of the [selectmode] option may be
-        # arbitrary, but the default bindings expect it to be ..."
+        # arbitrary, but the default bindings expect it to be either single,
+        # browse, multiple, or extended"
         #
         # I have never seen anyone setting this to something else than what
         # "the default bindings expect", but let's support it anyway.
-        selectmode: str = "browse",
+        selectmode: str | Literal["single", "browse", "multiple", "extended"] = "browse",  # noqa: Y051
         setgrid: bool = False,
         state: Literal["normal", "disabled"] = "normal",
         takefocus: _TakeFocusValue = "",
@@ -2187,7 +2188,7 @@ class Listbox(Widget, XView, YView):
         selectbackground: str = ...,
         selectborderwidth: _ScreenUnits = ...,
         selectforeground: str = ...,
-        selectmode: str = ...,
+        selectmode: str | Literal["single", "browse", "multiple", "extended"] = ...,  # noqa: Y051
         setgrid: bool = ...,
         state: Literal["normal", "disabled"] = ...,
         takefocus: _TakeFocusValue = ...,
@@ -2907,6 +2908,9 @@ class Scrollbar(Widget):
     def set(self, first: float | str, last: float | str) -> None: ...
 
 _TextIndex: TypeAlias = _tkinter.Tcl_Obj | str | float | Misc
+_WhatToCount: TypeAlias = Literal[
+    "chars", "displaychars", "displayindices", "displaylines", "indices", "lines", "xpixels", "ypixels"
+]
 
 class Text(Widget, XView, YView):
     def __init__(
@@ -3021,7 +3025,27 @@ class Text(Widget, XView, YView):
     config = configure
     def bbox(self, index: _TextIndex) -> tuple[int, int, int, int] | None: ...  # type: ignore[override]
     def compare(self, index1: _TextIndex, op: Literal["<", "<=", "==", ">=", ">", "!="], index2: _TextIndex) -> bool: ...
-    def count(self, index1, index2, *args): ...  # TODO
+    @overload
+    def count(self, index1: _TextIndex, index2: _TextIndex) -> tuple[int] | None: ...
+    @overload
+    def count(self, index1: _TextIndex, index2: _TextIndex, arg: _WhatToCount | Literal["update"], /) -> tuple[int] | None: ...
+    @overload
+    def count(self, index1: _TextIndex, index2: _TextIndex, arg1: Literal["update"], arg2: _WhatToCount, /) -> int | None: ...
+    @overload
+    def count(self, index1: _TextIndex, index2: _TextIndex, arg1: _WhatToCount, arg2: Literal["update"], /) -> int | None: ...
+    @overload
+    def count(self, index1: _TextIndex, index2: _TextIndex, arg1: _WhatToCount, arg2: _WhatToCount, /) -> tuple[int, int]: ...
+    @overload
+    def count(
+        self,
+        index1: _TextIndex,
+        index2: _TextIndex,
+        arg1: _WhatToCount | Literal["update"],
+        arg2: _WhatToCount | Literal["update"],
+        arg3: _WhatToCount | Literal["update"],
+        /,
+        *args: _WhatToCount | Literal["update"],
+    ) -> tuple[int, ...]: ...
     @overload
     def debug(self, boolean: None = None) -> bool: ...
     @overload
@@ -3564,7 +3588,7 @@ class Spinbox(Widget, XView):
     def scan_dragto(self, x): ...
     def selection(self, *args) -> tuple[int, ...]: ...
     def selection_adjust(self, index): ...
-    def selection_clear(self): ...
+    def selection_clear(self): ...  # type: ignore[override]
     def selection_element(self, element: Incomplete | None = None): ...
     def selection_from(self, index: int) -> None: ...
     def selection_present(self) -> None: ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/tkinter/ttk.pyi

@@ -1040,7 +1040,7 @@ class Treeview(Widget, tkinter.XView, tkinter.YView):
     @overload
     def heading(self, column: str | int, option: str) -> Any: ...
     @overload
-    def heading(self, column: str | int, option: None = None) -> _TreeviewHeaderDict: ...  # type: ignore[overload-overlap]
+    def heading(self, column: str | int, option: None = None) -> _TreeviewHeaderDict: ...
     @overload
     def heading(
         self,
@@ -1052,7 +1052,8 @@ class Treeview(Widget, tkinter.XView, tkinter.YView):
         anchor: tkinter._Anchor = ...,
         command: str | Callable[[], object] = ...,
     ) -> None: ...
-    def identify(self, component, x, y): ...  # Internal Method. Leave untyped
+    # Internal Method. Leave untyped:
+    def identify(self, component, x, y): ...  # type: ignore[override]
     def identify_row(self, y: int) -> str: ...
     def identify_column(self, x: int) -> str: ...
     def identify_region(self, x: int, y: int) -> Literal["heading", "separator", "tree", "cell", "nothing"]: ...
@@ -1084,7 +1085,7 @@ class Treeview(Widget, tkinter.XView, tkinter.YView):
     @overload
     def item(self, item: str | int, option: str) -> Any: ...
     @overload
-    def item(self, item: str | int, option: None = None) -> _TreeviewItemDict: ...  # type: ignore[overload-overlap]
+    def item(self, item: str | int, option: None = None) -> _TreeviewItemDict: ...
     @overload
     def item(
         self,

crates/red_knot_python_semantic/vendor/typeshed/stdlib/turtle.pyi

@@ -338,7 +338,7 @@ class TPen:
     def isvisible(self) -> bool: ...
     # Note: signatures 1 and 2 overlap unsafely when no arguments are provided
     @overload
-    def pen(self) -> _PenState: ...  # type: ignore[overload-overlap]
+    def pen(self) -> _PenState: ...
     @overload
     def pen(
         self,
@@ -384,7 +384,7 @@ class RawTurtle(TPen, TNavigator):
     def shape(self, name: str) -> None: ...
     # Unsafely overlaps when no arguments are provided
     @overload
-    def shapesize(self) -> tuple[float, float, float]: ...  # type: ignore[overload-overlap]
+    def shapesize(self) -> tuple[float, float, float]: ...
     @overload
     def shapesize(
         self, stretch_wid: float | None = None, stretch_len: float | None = None, outline: float | None = None
@@ -395,7 +395,7 @@ class RawTurtle(TPen, TNavigator):
     def shearfactor(self, shear: float) -> None: ...
     # Unsafely overlaps when no arguments are provided
     @overload
-    def shapetransform(self) -> tuple[float, float, float, float]: ...  # type: ignore[overload-overlap]
+    def shapetransform(self) -> tuple[float, float, float, float]: ...
     @overload
     def shapetransform(
         self, t11: float | None = None, t12: float | None = None, t21: float | None = None, t22: float | None = None
@@ -622,7 +622,7 @@ def isvisible() -> bool: ...
 
 # Note: signatures 1 and 2 overlap unsafely when no arguments are provided
 @overload
-def pen() -> _PenState: ...  # type: ignore[overload-overlap]
+def pen() -> _PenState: ...
 @overload
 def pen(
     pen: _PenState | None = None,
@@ -661,7 +661,7 @@ if sys.version_info >= (3, 12):
 
 # Unsafely overlaps when no arguments are provided
 @overload
-def shapesize() -> tuple[float, float, float]: ...  # type: ignore[overload-overlap]
+def shapesize() -> tuple[float, float, float]: ...
 @overload
 def shapesize(stretch_wid: float | None = None, stretch_len: float | None = None, outline: float | None = None) -> None: ...
 @overload
@@ -671,7 +671,7 @@ def shearfactor(shear: float) -> None: ...
 
 # Unsafely overlaps when no arguments are provided
 @overload
-def shapetransform() -> tuple[float, float, float, float]: ...  # type: ignore[overload-overlap]
+def shapetransform() -> tuple[float, float, float, float]: ...
 @overload
 def shapetransform(
     t11: float | None = None, t12: float | None = None, t21: float | None = None, t22: float | None = None

crates/red_knot_python_semantic/vendor/typeshed/stdlib/types.pyi

@@ -305,9 +305,9 @@ class MappingProxyType(Mapping[_KT, _VT_co]):
     def values(self) -> ValuesView[_VT_co]: ...
     def items(self) -> ItemsView[_KT, _VT_co]: ...
     @overload
-    def get(self, key: _KT, /) -> _VT_co | None: ...  # type: ignore[override]
+    def get(self, key: _KT, /) -> _VT_co | None: ...
     @overload
-    def get(self, key: _KT, default: _VT_co | _T2, /) -> _VT_co | _T2: ...  # type: ignore[override]
+    def get(self, key: _KT, default: _VT_co | _T2, /) -> _VT_co | _T2: ...
     if sys.version_info >= (3, 9):
         def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
         def __reversed__(self) -> Iterator[_KT]: ...
@@ -583,7 +583,7 @@ _P = ParamSpec("_P")
 
 # it's not really an Awaitable, but can be used in an await expression. Real type: Generator & Awaitable
 @overload
-def coroutine(func: Callable[_P, Generator[Any, Any, _R]]) -> Callable[_P, Awaitable[_R]]: ...  # type: ignore[overload-overlap]
+def coroutine(func: Callable[_P, Generator[Any, Any, _R]]) -> Callable[_P, Awaitable[_R]]: ...
 @overload
 def coroutine(func: _Fn) -> _Fn: ...
 

crates/red_knot_python_semantic/vendor/typeshed/stdlib/typing.pyi

@@ -846,7 +846,8 @@ class TextIO(IO[str]):
     @abstractmethod
     def __enter__(self) -> TextIO: ...
 
-ByteString: typing_extensions.TypeAlias = bytes | bytearray | memoryview
+if sys.version_info < (3, 14):
+    ByteString: typing_extensions.TypeAlias = bytes | bytearray | memoryview
 
 # Functions
 

crates/red_knot_python_semantic/vendor/typeshed/stdlib/unittest/mock.pyi

@@ -299,7 +299,7 @@ class _patcher:
     # Ideally we'd be able to add an overload for it so that the return type is _patch[MagicMock],
     # but that's impossible with the current type system.
     @overload
-    def __call__(  # type: ignore[overload-overlap]
+    def __call__(
         self,
         target: str,
         new: _T,

crates/red_knot_python_semantic/vendor/typeshed/stdlib/urllib/parse.pyi

@@ -198,13 +198,13 @@ else:
 
 # Requires an iterable of length 6
 @overload
-def urlunparse(components: Iterable[None]) -> Literal[b""]: ...
+def urlunparse(components: Iterable[None]) -> Literal[b""]: ...  # type: ignore[overload-overlap]
 @overload
 def urlunparse(components: Iterable[AnyStr | None]) -> AnyStr: ...
 
 # Requires an iterable of length 5
 @overload
-def urlunsplit(components: Iterable[None]) -> Literal[b""]: ...
+def urlunsplit(components: Iterable[None]) -> Literal[b""]: ...  # type: ignore[overload-overlap]
 @overload
 def urlunsplit(components: Iterable[AnyStr | None]) -> AnyStr: ...
 def unwrap(url: str) -> str: ...

crates/red_knot_python_semantic/vendor/typeshed/stdlib/urllib/request.pyi

@@ -79,6 +79,7 @@ else:
     def pathname2url(pathname: str) -> str: ...
 
 def getproxies() -> dict[str, str]: ...
+def getproxies_environment() -> dict[str, str]: ...
 def parse_http_list(s: str) -> list[str]: ...
 def parse_keqv_list(l: list[str]) -> dict[str, str]: ...
 

crates/red_knot_python_semantic/vendor/typeshed/stdlib/xml/dom/__init__.pyi

@@ -1,4 +1,4 @@
-from typing import Any
+from typing import Any, Final
 
 from .domreg import getDOMImplementation as getDOMImplementation, registerDOMImplementation as registerDOMImplementation
 
@@ -17,22 +17,22 @@ class Node:
     NOTATION_NODE: int
 
 # ExceptionCode
-INDEX_SIZE_ERR: int
-DOMSTRING_SIZE_ERR: int
-HIERARCHY_REQUEST_ERR: int
-WRONG_DOCUMENT_ERR: int
-INVALID_CHARACTER_ERR: int
-NO_DATA_ALLOWED_ERR: int
-NO_MODIFICATION_ALLOWED_ERR: int
-NOT_FOUND_ERR: int
-NOT_SUPPORTED_ERR: int
-INUSE_ATTRIBUTE_ERR: int
-INVALID_STATE_ERR: int
-SYNTAX_ERR: int
-INVALID_MODIFICATION_ERR: int
-NAMESPACE_ERR: int
-INVALID_ACCESS_ERR: int
-VALIDATION_ERR: int
+INDEX_SIZE_ERR: Final[int]
+DOMSTRING_SIZE_ERR: Final[int]
+HIERARCHY_REQUEST_ERR: Final[int]
+WRONG_DOCUMENT_ERR: Final[int]
+INVALID_CHARACTER_ERR: Final[int]
+NO_DATA_ALLOWED_ERR: Final[int]
+NO_MODIFICATION_ALLOWED_ERR: Final[int]
+NOT_FOUND_ERR: Final[int]
+NOT_SUPPORTED_ERR: Final[int]
+INUSE_ATTRIBUTE_ERR: Final[int]
+INVALID_STATE_ERR: Final[int]
+SYNTAX_ERR: Final[int]
+INVALID_MODIFICATION_ERR: Final[int]
+NAMESPACE_ERR: Final[int]
+INVALID_ACCESS_ERR: Final[int]
+VALIDATION_ERR: Final[int]
 
 class DOMException(Exception):
     code: int
@@ -62,8 +62,8 @@ class UserDataHandler:
     NODE_DELETED: int
     NODE_RENAMED: int
 
-XML_NAMESPACE: str
-XMLNS_NAMESPACE: str
-XHTML_NAMESPACE: str
-EMPTY_NAMESPACE: None
-EMPTY_PREFIX: None
+XML_NAMESPACE: Final[str]
+XMLNS_NAMESPACE: Final[str]
+XHTML_NAMESPACE: Final[str]
+EMPTY_NAMESPACE: Final[None]
+EMPTY_PREFIX: Final[None]

crates/red_knot_python_semantic/vendor/typeshed/stdlib/xml/etree/ElementInclude.pyi

@@ -1,14 +1,15 @@
 import sys
 from _typeshed import FileDescriptorOrPath
 from collections.abc import Callable
+from typing import Final
 from xml.etree.ElementTree import Element
 
-XINCLUDE: str
-XINCLUDE_INCLUDE: str
-XINCLUDE_FALLBACK: str
+XINCLUDE: Final[str]
+XINCLUDE_INCLUDE: Final[str]
+XINCLUDE_FALLBACK: Final[str]
 
 if sys.version_info >= (3, 9):
-    DEFAULT_MAX_INCLUSION_DEPTH: int
+    DEFAULT_MAX_INCLUSION_DEPTH: Final = 6
 
 class FatalIncludeError(SyntaxError): ...
 

crates/red_knot_python_semantic/vendor/typeshed/stdlib/xml/etree/ElementTree.pyi

@@ -2,7 +2,7 @@ import sys
 from _collections_abc import dict_keys
 from _typeshed import FileDescriptorOrPath, ReadableBuffer, SupportsRead, SupportsWrite
 from collections.abc import Callable, Generator, ItemsView, Iterable, Iterator, Mapping, Sequence
-from typing import Any, Literal, SupportsIndex, TypeVar, overload
+from typing import Any, Final, Literal, SupportsIndex, TypeVar, overload
 from typing_extensions import TypeAlias, TypeGuard, deprecated
 
 __all__ = [
@@ -41,7 +41,7 @@ _FileRead: TypeAlias = FileDescriptorOrPath | SupportsRead[bytes] | SupportsRead
 _FileWriteC14N: TypeAlias = FileDescriptorOrPath | SupportsWrite[bytes]
 _FileWrite: TypeAlias = _FileWriteC14N | SupportsWrite[str]
 
-VERSION: str
+VERSION: Final[str]
 
 class ParseError(SyntaxError):
     code: int

crates/red_knot_python_semantic/vendor/typeshed/stdlib/zipfile/__init__.pyi

@@ -94,6 +94,20 @@ class ZipExtFile(io.BufferedIOBase):
 class _Writer(Protocol):
     def write(self, s: str, /) -> object: ...
 
+class _ZipReadable(Protocol):
+    def seek(self, offset: int, whence: int = 0, /) -> int: ...
+    def read(self, n: int = -1, /) -> bytes: ...
+
+class _ZipTellable(Protocol):
+    def tell(self) -> int: ...
+
+class _ZipReadableTellable(_ZipReadable, _ZipTellable, Protocol): ...
+
+class _ZipWritable(Protocol):
+    def flush(self) -> None: ...
+    def close(self) -> None: ...
+    def write(self, b: bytes, /) -> int: ...
+
 class ZipFile:
     filename: str | None
     debug: int
@@ -106,24 +120,50 @@ class ZipFile:
     compresslevel: int | None  # undocumented
     mode: _ZipFileMode  # undocumented
     pwd: bytes | None  # undocumented
+    # metadata_encoding is new in 3.11
     if sys.version_info >= (3, 11):
         @overload
         def __init__(
             self,
             file: StrPath | IO[bytes],
+            mode: _ZipFileMode = "r",
+            compression: int = 0,
+            allowZip64: bool = True,
+            compresslevel: int | None = None,
+            *,
+            strict_timestamps: bool = True,
+            metadata_encoding: str | None = None,
+        ) -> None: ...
+        # metadata_encoding is only allowed for read mode
+        @overload
+        def __init__(
+            self,
+            file: StrPath | _ZipReadable,
             mode: Literal["r"] = "r",
             compression: int = 0,
             allowZip64: bool = True,
             compresslevel: int | None = None,
             *,
             strict_timestamps: bool = True,
-            metadata_encoding: str | None,
+            metadata_encoding: str | None = None,
         ) -> None: ...
         @overload
         def __init__(
             self,
-            file: StrPath | IO[bytes],
-            mode: _ZipFileMode = "r",
+            file: StrPath | _ZipWritable,
+            mode: Literal["w", "x"] = ...,
+            compression: int = 0,
+            allowZip64: bool = True,
+            compresslevel: int | None = None,
+            *,
+            strict_timestamps: bool = True,
+            metadata_encoding: None = None,
+        ) -> None: ...
+        @overload
+        def __init__(
+            self,
+            file: StrPath | _ZipReadableTellable,
+            mode: Literal["a"] = ...,
             compression: int = 0,
             allowZip64: bool = True,
             compresslevel: int | None = None,
@@ -132,6 +172,7 @@ class ZipFile:
             metadata_encoding: None = None,
         ) -> None: ...
     else:
+        @overload
         def __init__(
             self,
             file: StrPath | IO[bytes],
@@ -142,6 +183,39 @@ class ZipFile:
             *,
             strict_timestamps: bool = True,
         ) -> None: ...
+        @overload
+        def __init__(
+            self,
+            file: StrPath | _ZipReadable,
+            mode: Literal["r"] = "r",
+            compression: int = 0,
+            allowZip64: bool = True,
+            compresslevel: int | None = None,
+            *,
+            strict_timestamps: bool = True,
+        ) -> None: ...
+        @overload
+        def __init__(
+            self,
+            file: StrPath | _ZipWritable,
+            mode: Literal["w", "x"] = ...,
+            compression: int = 0,
+            allowZip64: bool = True,
+            compresslevel: int | None = None,
+            *,
+            strict_timestamps: bool = True,
+        ) -> None: ...
+        @overload
+        def __init__(
+            self,
+            file: StrPath | _ZipReadableTellable,
+            mode: Literal["a"] = ...,
+            compression: int = 0,
+            allowZip64: bool = True,
+            compresslevel: int | None = None,
+            *,
+            strict_timestamps: bool = True,
+        ) -> None: ...
 
     def __enter__(self) -> Self: ...
     def __exit__(

crates/red_knot_workspace/src/lint.rs

@@ -124,12 +124,16 @@ fn format_diagnostic(context: &SemanticLintContext, message: &str, start: TextSi
 }
 
 fn lint_unresolved_imports(context: &SemanticLintContext, import: AnyImportRef) {
+    // TODO: this treats any symbol with `Type::Unknown` as an unresolved import,
+    // which isn't really correct: if it exists but has `Type::Unknown` in the
+    // module we're importing it from, we shouldn't really emit a diagnostic here,
+    // but currently do.
     match import {
         AnyImportRef::Import(import) => {
             for alias in &import.names {
                 let ty = alias.ty(&context.semantic);
 
-                if ty.is_unbound() {
+                if ty.is_unknown() {
                     context.push_diagnostic(format_diagnostic(
                         context,
                         &format!("Unresolved import '{}'", &alias.name),
@@ -142,7 +146,7 @@ fn lint_unresolved_imports(context: &SemanticLintContext, import: AnyImportRef)
             for alias in &import.names {
                 let ty = alias.ty(&context.semantic);
 
-                if ty.is_unbound() {
+                if ty.is_unknown() {
                     context.push_diagnostic(format_diagnostic(
                         context,
                         &format!("Unresolved import '{}'", &alias.name),

crates/red_knot_workspace/tests/check.rs

@@ -1,9 +1,14 @@
-use red_knot_python_semantic::{ProgramSettings, PythonVersion, SearchPathSettings};
+use red_knot_python_semantic::{
+    HasTy, ProgramSettings, PythonVersion, SearchPathSettings, SemanticModel,
+};
 use red_knot_workspace::db::RootDatabase;
-use red_knot_workspace::lint::lint_semantic;
 use red_knot_workspace::workspace::WorkspaceMetadata;
-use ruff_db::files::system_path_to_file;
-use ruff_db::system::{OsSystem, SystemPathBuf};
+use ruff_db::files::{system_path_to_file, File};
+use ruff_db::parsed::parsed_module;
+use ruff_db::system::{OsSystem, SystemPath, SystemPathBuf};
+use ruff_python_ast::visitor::source_order;
+use ruff_python_ast::visitor::source_order::SourceOrderVisitor;
+use ruff_python_ast::{Alias, Expr, Parameter, ParameterWithDefault, Stmt};
 use std::fs;
 use std::path::PathBuf;
 
@@ -28,17 +33,100 @@ fn setup_db(workspace_root: SystemPathBuf) -> anyhow::Result<RootDatabase> {
 #[allow(clippy::print_stdout)]
 fn corpus_no_panic() -> anyhow::Result<()> {
     let corpus = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("resources/test/corpus");
-    let system_corpus =
-        SystemPathBuf::from_path_buf(corpus.clone()).expect("corpus path to be UTF8");
-    let db = setup_db(system_corpus.clone())?;
+    let system_corpus = SystemPath::from_std_path(&corpus).expect("corpus path to be UTF8");
+    let db = setup_db(system_corpus.to_path_buf())?;
 
     for path in fs::read_dir(&corpus).expect("corpus to be a directory") {
         let path = path.expect("path to not be an error").path();
         println!("checking {path:?}");
         let path = SystemPathBuf::from_path_buf(path.clone()).expect("path to be UTF-8");
-        // this test is only asserting that we can run the lint without a panic
+        // this test is only asserting that we can pull every expression type without a panic
+        // (and some non-expressions that clearly define a single type)
         let file = system_path_to_file(&db, path).expect("file to exist");
-        lint_semantic(&db, file);
+
+        pull_types(&db, file);
     }
     Ok(())
 }
+
+fn pull_types(db: &RootDatabase, file: File) {
+    let mut visitor = PullTypesVisitor::new(db, file);
+
+    let ast = parsed_module(db, file);
+
+    visitor.visit_body(ast.suite());
+}
+
+struct PullTypesVisitor<'db> {
+    model: SemanticModel<'db>,
+}
+
+impl<'db> PullTypesVisitor<'db> {
+    fn new(db: &'db RootDatabase, file: File) -> Self {
+        Self {
+            model: SemanticModel::new(db, file),
+        }
+    }
+}
+
+impl SourceOrderVisitor<'_> for PullTypesVisitor<'_> {
+    fn visit_stmt(&mut self, stmt: &Stmt) {
+        match stmt {
+            Stmt::FunctionDef(function) => {
+                let _ty = function.ty(&self.model);
+            }
+            Stmt::ClassDef(class) => {
+                let _ty = class.ty(&self.model);
+            }
+            Stmt::AnnAssign(_)
+            | Stmt::Return(_)
+            | Stmt::Delete(_)
+            | Stmt::Assign(_)
+            | Stmt::AugAssign(_)
+            | Stmt::TypeAlias(_)
+            | Stmt::For(_)
+            | Stmt::While(_)
+            | Stmt::If(_)
+            | Stmt::With(_)
+            | Stmt::Match(_)
+            | Stmt::Raise(_)
+            | Stmt::Try(_)
+            | Stmt::Assert(_)
+            | Stmt::Import(_)
+            | Stmt::ImportFrom(_)
+            | Stmt::Global(_)
+            | Stmt::Nonlocal(_)
+            | Stmt::Expr(_)
+            | Stmt::Pass(_)
+            | Stmt::Break(_)
+            | Stmt::Continue(_)
+            | Stmt::IpyEscapeCommand(_) => {}
+        }
+
+        source_order::walk_stmt(self, stmt);
+    }
+
+    fn visit_expr(&mut self, expr: &Expr) {
+        let _ty = expr.ty(&self.model);
+
+        source_order::walk_expr(self, expr);
+    }
+
+    fn visit_parameter(&mut self, parameter: &Parameter) {
+        let _ty = parameter.ty(&self.model);
+
+        source_order::walk_parameter(self, parameter);
+    }
+
+    fn visit_parameter_with_default(&mut self, parameter_with_default: &ParameterWithDefault) {
+        let _ty = parameter_with_default.ty(&self.model);
+
+        source_order::walk_parameter_with_default(self, parameter_with_default);
+    }
+
+    fn visit_alias(&mut self, alias: &Alias) {
+        let _ty = alias.ty(&self.model);
+
+        source_order::walk_alias(self, alias);
+    }
+}

crates/ruff/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff"
-version = "0.5.7"
+version = "0.6.1"
 publish = true
 authors = { workspace = true }
 edition = { workspace = true }

crates/ruff/tests/lint.rs

@@ -1434,7 +1434,7 @@ def unused(x):
 
     insta::assert_snapshot!(test_code, @r###"
 
-    def unused(x):  # noqa: ANN001, ANN201, ARG001, D103
+    def unused(x):  # noqa: ANN001, ANN201, D103
         pass
     "###);
 

crates/ruff_benchmark/benches/red_knot.rs

@@ -89,7 +89,7 @@ fn benchmark_incremental(criterion: &mut Criterion) {
                 let Case { db, parser, .. } = case;
                 let result = db.check_file(*parser).unwrap();
 
-                assert_eq!(result.len(), 402);
+                assert_eq!(result.len(), 34);
             },
             BatchSize::SmallInput,
         );
@@ -104,7 +104,7 @@ fn benchmark_cold(criterion: &mut Criterion) {
                 let Case { db, parser, .. } = case;
                 let result = db.check_file(*parser).unwrap();
 
-                assert_eq!(result.len(), 402);
+                assert_eq!(result.len(), 34);
             },
             BatchSize::SmallInput,
         );

crates/ruff_linter/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff_linter"
-version = "0.5.7"
+version = "0.6.1"
 publish = false
 authors = { workspace = true }
 edition = { workspace = true }

crates/ruff_linter/resources/test/fixtures/fastapi/FAST003.py

@@ -0,0 +1,134 @@
+from fastapi import FastAPI
+
+app = FastAPI()
+
+
+# Errors
+@app.get("/things/{thing_id}")
+async def read_thing(query: str):
+    return {"query": query}
+
+
+@app.get("/books/isbn-{isbn}")
+async def read_thing():
+    ...
+
+
+@app.get("/things/{thing_id:path}")
+async def read_thing(query: str):
+    return {"query": query}
+
+
+@app.get("/things/{thing_id : path}")
+async def read_thing(query: str):
+    return {"query": query}
+
+
+@app.get("/books/{author}/{title}")
+async def read_thing(author: str):
+    return {"author": author}
+
+
+@app.get("/books/{author_name}/{title}")
+async def read_thing():
+    ...
+
+
+@app.get("/books/{author}/{title}")
+async def read_thing(author: str, title: str, /):
+    return {"author": author, "title": title}
+
+
+@app.get("/books/{author}/{title}/{page}")
+async def read_thing(
+    author: str,
+    query: str,
+): ...
+
+
+@app.get("/books/{author}/{title}")
+async def read_thing():
+    ...
+
+
+@app.get("/books/{author}/{title}")
+async def read_thing(*, author: str):
+    ...
+
+
+@app.get("/books/{author}/{title}")
+async def read_thing(hello, /, *, author: str):
+    ...
+
+
+@app.get("/things/{thing_id}")
+async def read_thing(
+        query: str,
+):
+    return {"query": query}
+
+
+@app.get("/things/{thing_id}")
+async def read_thing(
+        query: str = "default",
+):
+    return {"query": query}
+
+
+@app.get("/things/{thing_id}")
+async def read_thing(
+        *, query: str = "default",
+):
+    return {"query": query}
+
+
+# OK
+@app.get("/things/{thing_id}")
+async def read_thing(thing_id: int, query: str):
+    return {"thing_id": thing_id, "query": query}
+
+
+@app.get("/books/isbn-{isbn}")
+async def read_thing(isbn: str):
+    return {"isbn": isbn}
+
+
+@app.get("/things/{thing_id:path}")
+async def read_thing(thing_id: str, query: str):
+    return {"thing_id": thing_id, "query": query}
+
+
+@app.get("/things/{thing_id : path}")
+async def read_thing(thing_id: str, query: str):
+    return {"thing_id": thing_id, "query": query}
+
+
+@app.get("/books/{author}/{title}")
+async def read_thing(author: str, title: str):
+    return {"author": author, "title": title}
+
+
+@app.get("/books/{author}/{title}")
+async def read_thing(*, author: str, title: str):
+    return {"author": author, "title": title}
+
+
+@app.get("/books/{author}/{title:path}")
+async def read_thing(*, author: str, title: str):
+    return {"author": author, "title": title}
+
+
+# Ignored
+@app.get("/things/{thing-id}")
+async def read_thing(query: str):
+    return {"query": query}
+
+
+@app.get("/things/{thing_id!r}")
+async def read_thing(query: str):
+    return {"query": query}
+
+
+@app.get("/things/{thing_id=}")
+async def read_thing(query: str):
+    return {"query": query}

crates/ruff_linter/resources/test/fixtures/flake8_async/ASYNC100.py

@@ -89,3 +89,26 @@ async def func():
 async def func():
     async with asyncio.timeout(delay=0.2), asyncio.timeout(delay=0.2):
         ...
+
+
+# Don't trigger for blocks with a yield statement
+async def foo():
+    with trio.fail_after(1):
+        yield
+
+
+async def foo(): # even if only one branch contains a yield, we skip the lint
+    with trio.fail_after(1):
+        if something:
+            ...
+        else:
+            yield
+
+
+# https://github.com/astral-sh/ruff/issues/12873
+@asynccontextmanager
+async def good_code():
+    with anyio.fail_after(10):
+        # There's no await keyword here, but we presume that there
+        # will be in the caller we yield to, so this is safe.
+        yield

crates/ruff_linter/resources/test/fixtures/flake8_bugbear/B015.py

@@ -17,6 +17,11 @@ def test():
     1 in (1, 2)
 
 
+def test2():
+    1 in (1, 2)
+    return
+
+
 data = [x for x in [1, 2, 3] if x in (1, 2)]
 
 

crates/ruff_linter/resources/test/fixtures/flake8_comprehensions/C419.py

@@ -55,3 +55,14 @@ max({x.id for x in bar})
 
 # should not be linted...
 sum({x.id for x in bar})
+
+
+# https://github.com/astral-sh/ruff/issues/12891
+from collections.abc import AsyncGenerator
+
+
+async def test() -> None:
+    async def async_gen() -> AsyncGenerator[bool, None]:
+        yield True
+
+    assert all([v async for v in async_gen()])  # OK

crates/ruff_linter/resources/test/fixtures/pep8_naming/N817.py

@@ -1,2 +1,10 @@
 import mod.CaMel as CM
 from mod import CamelCase as CC
+
+
+# OK depending on configured import convention
+import xml.etree.ElementTree as ET
+from xml.etree import ElementTree as ET
+
+# Always an error (relative import)
+from ..xml.eltree import ElementTree as ET

crates/ruff_linter/resources/test/fixtures/pylint/bad_staticmethod_argument.py

@@ -42,3 +42,9 @@ class Foo:
     @classmethod
     def graze(cls, x, y, z):
         pass
+
+
+class Foo:
+    @staticmethod
+    def __new__(cls, x, y, z):  # OK, see https://docs.python.org/3/reference/datamodel.html#basic-customization
+        pass

crates/ruff_linter/resources/test/fixtures/pylint/self_or_cls_assignment.py

@@ -3,7 +3,7 @@ class Fruit:
     def list_fruits(cls) -> None:
         cls = "apple"  # PLW0642
         cls: Fruit = "apple"  # PLW0642
-        cls += "orange"  # PLW0642
+        cls += "orange"  # OK, augmented assignments are ignored
         *cls = "banana"  # PLW0642
         cls, blah = "apple", "orange"  # PLW0642
         blah, (cls, blah2) = "apple", ("orange", "banana")  # PLW0642
@@ -16,7 +16,7 @@ class Fruit:
     def print_color(self) -> None:
         self = "red"  # PLW0642
         self: Self = "red"  # PLW0642
-        self += "blue"  # PLW0642
+        self += "blue"  # OK, augmented assignments are ignored
         *self = "blue"  # PLW0642
         self, blah = "red", "blue"  # PLW0642
         blah, (self, blah2) = "apple", ("orange", "banana")  # PLW0642

crates/ruff_linter/resources/test/fixtures/ruff/RUF027_1.py

@@ -59,3 +59,12 @@ def negative_cases():
     # See https://docs.python.org/3/howto/logging-cookbook.html#formatting-styles
     import logging
     logging.info("yet {another} non-f-string")
+
+    # See https://fastapi.tiangolo.com/tutorial/path-params/
+    from fastapi import FastAPI
+    app = FastAPI()
+    item_id = 42
+
+    @app.get("/items/{item_id}")
+    async def read_item(item_id):
+        return {"item_id": item_id}

crates/ruff_linter/resources/test/fixtures/ruff/RUF029.py

@@ -78,3 +78,13 @@ async def test():
 async def test() -> str:
     vals = [str(val) for val in await async_func(1)]
     return ",".join(vals)
+
+
+from fastapi import FastAPI
+
+app = FastAPI()
+
+
+@app.post("/count")
+async def fastapi_route(): # Ok: FastApi routes can be async without actually using await
+    return 1

crates/ruff_linter/src/checkers/ast/analyze/statement.rs

@@ -94,6 +94,9 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::FastApiNonAnnotatedDependency) {
                 fastapi::rules::fastapi_non_annotated_dependency(checker, function_def);
             }
+            if checker.enabled(Rule::FastApiUnusedPathParameter) {
+                fastapi::rules::fastapi_unused_path_parameter(checker, function_def);
+            }
             if checker.enabled(Rule::AmbiguousFunctionName) {
                 if let Some(diagnostic) = pycodestyle::rules::ambiguous_function_name(name) {
                     checker.diagnostics.push(diagnostic);
@@ -263,8 +266,8 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             if checker.enabled(Rule::TooManyArguments) {
                 pylint::rules::too_many_arguments(checker, function_def);
             }
-            if checker.enabled(Rule::TooManyPositional) {
-                pylint::rules::too_many_positional(checker, function_def);
+            if checker.enabled(Rule::TooManyPositionalArguments) {
+                pylint::rules::too_many_positional_arguments(checker, function_def);
             }
             if checker.enabled(Rule::TooManyReturnStatements) {
                 if let Some(diagnostic) = pylint::rules::too_many_return_statements(
@@ -704,11 +707,7 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                     }
                     if checker.enabled(Rule::CamelcaseImportedAsAcronym) {
                         if let Some(diagnostic) = pep8_naming::rules::camelcase_imported_as_acronym(
-                            name,
-                            asname,
-                            alias,
-                            stmt,
-                            &checker.settings.pep8_naming.ignore_names,
+                            name, asname, alias, stmt, checker,
                         ) {
                             checker.diagnostics.push(diagnostic);
                         }
@@ -1023,7 +1022,7 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                             asname,
                             alias,
                             stmt,
-                            &checker.settings.pep8_naming.ignore_names,
+                            checker,
                         ) {
                             checker.diagnostics.push(diagnostic);
                         }
@@ -1113,9 +1112,6 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
             }
         }
         Stmt::AugAssign(aug_assign @ ast::StmtAugAssign { target, .. }) => {
-            if checker.enabled(Rule::SelfOrClsAssignment) {
-                pylint::rules::self_or_cls_assignment(checker, target);
-            }
             if checker.enabled(Rule::GlobalStatement) {
                 if let Expr::Name(ast::ExprName { id, .. }) = target.as_ref() {
                     pylint::rules::global_statement(checker, id);

crates/ruff_linter/src/codes.rs

@@ -248,7 +248,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Pylint, "R0914") => (RuleGroup::Preview, rules::pylint::rules::TooManyLocals),
         (Pylint, "R0915") => (RuleGroup::Stable, rules::pylint::rules::TooManyStatements),
         (Pylint, "R0916") => (RuleGroup::Preview, rules::pylint::rules::TooManyBooleanExpressions),
-        (Pylint, "R0917") => (RuleGroup::Preview, rules::pylint::rules::TooManyPositional),
+        (Pylint, "R0917") => (RuleGroup::Preview, rules::pylint::rules::TooManyPositionalArguments),
         (Pylint, "R1701") => (RuleGroup::Removed, rules::pylint::rules::RepeatedIsinstanceCalls),
         (Pylint, "R1702") => (RuleGroup::Preview, rules::pylint::rules::TooManyNestedBlocks),
         (Pylint, "R1704") => (RuleGroup::Stable, rules::pylint::rules::RedefinedArgumentFromLocal),
@@ -920,6 +920,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         // fastapi
         (FastApi, "001") => (RuleGroup::Preview, rules::fastapi::rules::FastApiRedundantResponseModel),
         (FastApi, "002") => (RuleGroup::Preview, rules::fastapi::rules::FastApiNonAnnotatedDependency),
+        (FastApi, "003") => (RuleGroup::Preview, rules::fastapi::rules::FastApiUnusedPathParameter),
 
         // pydoclint
         (Pydoclint, "201") => (RuleGroup::Preview, rules::pydoclint::rules::DocstringMissingReturns),

crates/ruff_linter/src/fix/edits.rs

@@ -4,7 +4,7 @@ use anyhow::{Context, Result};
 
 use ruff_diagnostics::Edit;
 use ruff_python_ast::parenthesize::parenthesized_range;
-use ruff_python_ast::{self as ast, Arguments, ExceptHandler, Expr, ExprList, Stmt};
+use ruff_python_ast::{self as ast, Arguments, ExceptHandler, Expr, ExprList, Parameters, Stmt};
 use ruff_python_ast::{AnyNodeRef, ArgOrKeyword};
 use ruff_python_codegen::Stylist;
 use ruff_python_index::Indexer;
@@ -282,6 +282,59 @@ pub(crate) fn add_argument(
     }
 }
 
+/// Generic function to add a (regular) parameter to a function definition.
+pub(crate) fn add_parameter(parameter: &str, parameters: &Parameters, source: &str) -> Edit {
+    if let Some(last) = parameters
+        .args
+        .iter()
+        .filter(|arg| arg.default.is_none())
+        .last()
+    {
+        // Case 1: at least one regular parameter, so append after the last one.
+        Edit::insertion(format!(", {parameter}"), last.end())
+    } else if parameters.args.first().is_some() {
+        // Case 2: no regular parameters, but at least one keyword parameter, so add before the
+        // first.
+        let pos = parameters.start();
+        let mut tokenizer = SimpleTokenizer::starts_at(pos, source);
+        let name = tokenizer
+            .find(|token| token.kind == SimpleTokenKind::Name)
+            .expect("Unable to find name token");
+        Edit::insertion(format!("{parameter}, "), name.start())
+    } else if let Some(last) = parameters.posonlyargs.last() {
+        // Case 2: no regular parameter, but a positional-only parameter exists, so add after that.
+        // We take care to add it *after* the `/` separator.
+        let pos = last.end();
+        let mut tokenizer = SimpleTokenizer::starts_at(pos, source);
+        let slash = tokenizer
+            .find(|token| token.kind == SimpleTokenKind::Slash)
+            .expect("Unable to find `/` token");
+        // Try to find a comma after the slash.
+        let comma = tokenizer.find(|token| token.kind == SimpleTokenKind::Comma);
+        if let Some(comma) = comma {
+            Edit::insertion(format!(" {parameter},"), comma.start() + TextSize::from(1))
+        } else {
+            Edit::insertion(format!(", {parameter}"), slash.start())
+        }
+    } else if parameters.kwonlyargs.first().is_some() {
+        // Case 3: no regular parameter, but a keyword-only parameter exist, so add parameter before that.
+        // We need to backtrack to before the `*` separator.
+        // We know there is no non-keyword-only params, so we can safely assume that the `*` separator is the first
+        let pos = parameters.start();
+        let mut tokenizer = SimpleTokenizer::starts_at(pos, source);
+        let star = tokenizer
+            .find(|token| token.kind == SimpleTokenKind::Star)
+            .expect("Unable to find `*` token");
+        Edit::insertion(format!("{parameter}, "), star.start())
+    } else {
+        // Case 4: no parameters at all, so add parameter after the opening parenthesis.
+        Edit::insertion(
+            parameter.to_string(),
+            parameters.start() + TextSize::from(1),
+        )
+    }
+}
+
 /// Safely adjust the indentation of the indented block at [`TextRange`].
 ///
 /// The [`TextRange`] is assumed to represent an entire indented block, including the leading

crates/ruff_linter/src/rules/fastapi/mod.rs

@@ -15,6 +15,7 @@ mod tests {
 
     #[test_case(Rule::FastApiRedundantResponseModel, Path::new("FAST001.py"))]
     #[test_case(Rule::FastApiNonAnnotatedDependency, Path::new("FAST002.py"))]
+    #[test_case(Rule::FastApiUnusedPathParameter, Path::new("FAST003.py"))]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.as_ref(), path.to_string_lossy());
         let diagnostics = test_path(

crates/ruff_linter/src/rules/fastapi/rules/fastapi_unused_path_parameter.rs

@@ -0,0 +1,232 @@
+use std::iter::Peekable;
+use std::ops::Range;
+use std::str::CharIndices;
+
+use ruff_diagnostics::Fix;
+use ruff_diagnostics::{Diagnostic, FixAvailability, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast as ast;
+use ruff_python_semantic::Modules;
+use ruff_python_stdlib::identifiers::is_identifier;
+use ruff_text_size::{Ranged, TextSize};
+
+use crate::checkers::ast::Checker;
+use crate::fix::edits::add_parameter;
+use crate::rules::fastapi::rules::is_fastapi_route_decorator;
+
+/// ## What it does
+/// Identifies FastAPI routes that declare path parameters in the route path
+/// that are not included in the function signature.
+///
+/// ## Why is this bad?
+/// Path parameters are used to extract values from the URL path.
+///
+/// If a path parameter is declared in the route path but not in the function
+/// signature, it will not be accessible in the function body, which is likely
+/// a mistake.
+///
+/// If a path parameter is declared in the route path, but as a positional-only
+/// argument in the function signature, it will also not be accessible in the
+/// function body, as FastAPI will not inject the parameter.
+///
+/// ## Known problems
+/// If the path parameter is _not_ a valid Python identifier (e.g., `user-id`, as
+/// opposed to `user_id`), FastAPI will normalize it. However, this rule simply
+/// ignores such path parameters, as FastAPI's normalization behavior is undocumented.
+///
+/// ## Example
+///
+/// ```python
+/// from fastapi import FastAPI
+///
+/// app = FastAPI()
+///
+///
+/// @app.get("/things/{thing_id}")
+/// async def read_thing(query: str): ...
+/// ```
+///
+/// Use instead:
+///
+/// ```python
+/// from fastapi import FastAPI
+///
+/// app = FastAPI()
+///
+///
+/// @app.get("/things/{thing_id}")
+/// async def read_thing(thing_id: int, query: str): ...
+/// ```
+///
+/// ## Fix safety
+/// This rule's fix is marked as unsafe, as modifying a function signature can
+/// change the behavior of the code.
+#[violation]
+pub struct FastApiUnusedPathParameter {
+    arg_name: String,
+    function_name: String,
+    is_positional: bool,
+}
+
+impl Violation for FastApiUnusedPathParameter {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        let Self {
+            arg_name,
+            function_name,
+            is_positional,
+        } = self;
+        #[allow(clippy::if_not_else)]
+        if !is_positional {
+            format!("Parameter `{arg_name}` appears in route path, but not in `{function_name}` signature")
+        } else {
+            format!(
+                "Parameter `{arg_name}` appears in route path, but only as a positional-only argument in `{function_name}` signature"
+            )
+        }
+    }
+
+    fn fix_title(&self) -> Option<String> {
+        let Self {
+            arg_name,
+            is_positional,
+            ..
+        } = self;
+        if *is_positional {
+            None
+        } else {
+            Some(format!("Add `{arg_name}` to function signature"))
+        }
+    }
+}
+
+/// FAST003
+pub(crate) fn fastapi_unused_path_parameter(
+    checker: &mut Checker,
+    function_def: &ast::StmtFunctionDef,
+) {
+    if !checker.semantic().seen_module(Modules::FASTAPI) {
+        return;
+    }
+
+    // Get the route path from the decorator.
+    let route_decorator = function_def
+        .decorator_list
+        .iter()
+        .find_map(|decorator| is_fastapi_route_decorator(decorator, checker.semantic()));
+
+    let Some(route_decorator) = route_decorator else {
+        return;
+    };
+
+    let Some(path_arg) = route_decorator.arguments.args.first() else {
+        return;
+    };
+    let diagnostic_range = path_arg.range();
+
+    // We can't really handle anything other than string literals.
+    let path = match path_arg.as_string_literal_expr() {
+        Some(path_arg) => &path_arg.value,
+        None => return,
+    };
+
+    // Extract the path parameters from the route path.
+    let path_params = PathParamIterator::new(path.to_str());
+
+    // Extract the arguments from the function signature
+    let named_args: Vec<_> = function_def
+        .parameters
+        .args
+        .iter()
+        .chain(function_def.parameters.kwonlyargs.iter())
+        .map(|arg| arg.parameter.name.as_str())
+        .collect();
+
+    // Check if any of the path parameters are not in the function signature.
+    let mut diagnostics = vec![];
+    for (path_param, range) in path_params {
+        // Ignore invalid identifiers (e.g., `user-id`, as opposed to `user_id`)
+        if !is_identifier(path_param) {
+            continue;
+        }
+
+        // If the path parameter is already in the function signature, we don't need to do anything.
+        if named_args.contains(&path_param) {
+            continue;
+        }
+
+        // Determine whether the path parameter is used as a positional-only argument. In this case,
+        // the path parameter injection won't work, but we also can't fix it (yet), since we'd need
+        // to make the parameter non-positional-only.
+        let is_positional = function_def
+            .parameters
+            .posonlyargs
+            .iter()
+            .any(|arg| arg.parameter.name.as_str() == path_param);
+
+        let mut diagnostic = Diagnostic::new(
+            FastApiUnusedPathParameter {
+                arg_name: path_param.to_string(),
+                function_name: function_def.name.to_string(),
+                is_positional,
+            },
+            #[allow(clippy::cast_possible_truncation)]
+            diagnostic_range
+                .add_start(TextSize::from(range.start as u32 + 1))
+                .sub_end(TextSize::from((path.len() - range.end + 1) as u32)),
+        );
+        if !is_positional {
+            diagnostic.set_fix(Fix::unsafe_edit(add_parameter(
+                path_param,
+                &function_def.parameters,
+                checker.locator().contents(),
+            )));
+        }
+        diagnostics.push(diagnostic);
+    }
+
+    checker.diagnostics.extend(diagnostics);
+}
+
+/// An iterator to extract parameters from FastAPI route paths.
+///
+/// The iterator yields tuples of the parameter name and the range of the parameter in the input,
+/// inclusive of curly braces.
+#[derive(Debug)]
+struct PathParamIterator<'a> {
+    input: &'a str,
+    chars: Peekable<CharIndices<'a>>,
+}
+
+impl<'a> PathParamIterator<'a> {
+    fn new(input: &'a str) -> Self {
+        PathParamIterator {
+            input,
+            chars: input.char_indices().peekable(),
+        }
+    }
+}
+
+impl<'a> Iterator for PathParamIterator<'a> {
+    type Item = (&'a str, Range<usize>);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        while let Some((start, c)) = self.chars.next() {
+            if c == '{' {
+                if let Some((end, _)) = self.chars.by_ref().find(|&(_, ch)| ch == '}') {
+                    let param_content = &self.input[start + 1..end];
+                    // We ignore text after a colon, since those are path convertors
+                    // See also: https://fastapi.tiangolo.com/tutorial/path-params/?h=path#path-convertor
+                    let param_name_end = param_content.find(':').unwrap_or(param_content.len());
+                    let param_name = &param_content[..param_name_end].trim();
+
+                    #[allow(clippy::range_plus_one)]
+                    return Some((param_name, start..end + 1));
+                }
+            }
+        }
+        None
+    }
+}

crates/ruff_linter/src/rules/fastapi/rules/mod.rs

@@ -1,15 +1,20 @@
 pub(crate) use fastapi_non_annotated_dependency::*;
 pub(crate) use fastapi_redundant_response_model::*;
+pub(crate) use fastapi_unused_path_parameter::*;
 
 mod fastapi_non_annotated_dependency;
 mod fastapi_redundant_response_model;
+mod fastapi_unused_path_parameter;
 
-use ruff_python_ast::{Decorator, ExprCall, StmtFunctionDef};
+use ruff_python_ast as ast;
 use ruff_python_semantic::analyze::typing::resolve_assignment;
 use ruff_python_semantic::SemanticModel;
 
 /// Returns `true` if the function is a FastAPI route.
-pub(crate) fn is_fastapi_route(function_def: &StmtFunctionDef, semantic: &SemanticModel) -> bool {
+pub(crate) fn is_fastapi_route(
+    function_def: &ast::StmtFunctionDef,
+    semantic: &SemanticModel,
+) -> bool {
     return function_def
         .decorator_list
         .iter()
@@ -18,27 +23,29 @@ pub(crate) fn is_fastapi_route(function_def: &StmtFunctionDef, semantic: &Semant
 
 /// Returns `true` if the decorator is indicative of a FastAPI route.
 pub(crate) fn is_fastapi_route_decorator<'a>(
-    decorator: &'a Decorator,
+    decorator: &'a ast::Decorator,
     semantic: &'a SemanticModel,
-) -> Option<&'a ExprCall> {
+) -> Option<&'a ast::ExprCall> {
     let call = decorator.expression.as_call_expr()?;
-    let decorator_method = call.func.as_attribute_expr()?;
-    let method_name = &decorator_method.attr;
+    is_fastapi_route_call(call, semantic).then_some(call)
+}
+
+pub(crate) fn is_fastapi_route_call(call_expr: &ast::ExprCall, semantic: &SemanticModel) -> bool {
+    let ast::Expr::Attribute(ast::ExprAttribute { attr, value, .. }) = &*call_expr.func else {
+        return false;
+    };
 
     if !matches!(
-        method_name.as_str(),
+        attr.as_str(),
         "get" | "post" | "put" | "delete" | "patch" | "options" | "head" | "trace"
     ) {
-        return None;
+        return false;
     }
 
-    let qualified_name = resolve_assignment(&decorator_method.value, semantic)?;
-    if matches!(
-        qualified_name.segments(),
-        ["fastapi", "FastAPI" | "APIRouter"]
-    ) {
-        Some(call)
-    } else {
-        None
-    }
+    resolve_assignment(value, semantic).is_some_and(|qualified_name| {
+        matches!(
+            qualified_name.segments(),
+            ["fastapi", "FastAPI" | "APIRouter"]
+        )
+    })
 }

crates/ruff_linter/src/rules/fastapi/snapshots/ruff_linter__rules__fastapi__tests__fast-api-unused-path-parameter_FAST003.py.snap

@@ -0,0 +1,323 @@
+---
+source: crates/ruff_linter/src/rules/fastapi/mod.rs
+---
+FAST003.py:7:19: FAST003 [*] Parameter `thing_id` appears in route path, but not in `read_thing` signature
+  |
+6 | # Errors
+7 | @app.get("/things/{thing_id}")
+  |                   ^^^^^^^^^^ FAST003
+8 | async def read_thing(query: str):
+9 |     return {"query": query}
+  |
+  = help: Add `thing_id` to function signature
+
+ℹ Unsafe fix
+5 5 | 
+6 6 | # Errors
+7 7 | @app.get("/things/{thing_id}")
+8   |-async def read_thing(query: str):
+  8 |+async def read_thing(query: str, thing_id):
+9 9 |     return {"query": query}
+10 10 | 
+11 11 | 
+
+FAST003.py:12:23: FAST003 [*] Parameter `isbn` appears in route path, but not in `read_thing` signature
+   |
+12 | @app.get("/books/isbn-{isbn}")
+   |                       ^^^^^^ FAST003
+13 | async def read_thing():
+14 |     ...
+   |
+   = help: Add `isbn` to function signature
+
+ℹ Unsafe fix
+10 10 | 
+11 11 | 
+12 12 | @app.get("/books/isbn-{isbn}")
+13    |-async def read_thing():
+   13 |+async def read_thing(isbn):
+14 14 |     ...
+15 15 | 
+16 16 | 
+
+FAST003.py:17:19: FAST003 [*] Parameter `thing_id` appears in route path, but not in `read_thing` signature
+   |
+17 | @app.get("/things/{thing_id:path}")
+   |                   ^^^^^^^^^^^^^^^ FAST003
+18 | async def read_thing(query: str):
+19 |     return {"query": query}
+   |
+   = help: Add `thing_id` to function signature
+
+ℹ Unsafe fix
+15 15 | 
+16 16 | 
+17 17 | @app.get("/things/{thing_id:path}")
+18    |-async def read_thing(query: str):
+   18 |+async def read_thing(query: str, thing_id):
+19 19 |     return {"query": query}
+20 20 | 
+21 21 | 
+
+FAST003.py:22:19: FAST003 [*] Parameter `thing_id` appears in route path, but not in `read_thing` signature
+   |
+22 | @app.get("/things/{thing_id : path}")
+   |                   ^^^^^^^^^^^^^^^^^ FAST003
+23 | async def read_thing(query: str):
+24 |     return {"query": query}
+   |
+   = help: Add `thing_id` to function signature
+
+ℹ Unsafe fix
+20 20 | 
+21 21 | 
+22 22 | @app.get("/things/{thing_id : path}")
+23    |-async def read_thing(query: str):
+   23 |+async def read_thing(query: str, thing_id):
+24 24 |     return {"query": query}
+25 25 | 
+26 26 | 
+
+FAST003.py:27:27: FAST003 [*] Parameter `title` appears in route path, but not in `read_thing` signature
+   |
+27 | @app.get("/books/{author}/{title}")
+   |                           ^^^^^^^ FAST003
+28 | async def read_thing(author: str):
+29 |     return {"author": author}
+   |
+   = help: Add `title` to function signature
+
+ℹ Unsafe fix
+25 25 | 
+26 26 | 
+27 27 | @app.get("/books/{author}/{title}")
+28    |-async def read_thing(author: str):
+   28 |+async def read_thing(author: str, title):
+29 29 |     return {"author": author}
+30 30 | 
+31 31 | 
+
+FAST003.py:32:18: FAST003 [*] Parameter `author_name` appears in route path, but not in `read_thing` signature
+   |
+32 | @app.get("/books/{author_name}/{title}")
+   |                  ^^^^^^^^^^^^^ FAST003
+33 | async def read_thing():
+34 |     ...
+   |
+   = help: Add `author_name` to function signature
+
+ℹ Unsafe fix
+30 30 | 
+31 31 | 
+32 32 | @app.get("/books/{author_name}/{title}")
+33    |-async def read_thing():
+   33 |+async def read_thing(author_name):
+34 34 |     ...
+35 35 | 
+36 36 | 
+
+FAST003.py:32:32: FAST003 [*] Parameter `title` appears in route path, but not in `read_thing` signature
+   |
+32 | @app.get("/books/{author_name}/{title}")
+   |                                ^^^^^^^ FAST003
+33 | async def read_thing():
+34 |     ...
+   |
+   = help: Add `title` to function signature
+
+ℹ Unsafe fix
+30 30 | 
+31 31 | 
+32 32 | @app.get("/books/{author_name}/{title}")
+33    |-async def read_thing():
+   33 |+async def read_thing(title):
+34 34 |     ...
+35 35 | 
+36 36 | 
+
+FAST003.py:37:18: FAST003 Parameter `author` appears in route path, but only as a positional-only argument in `read_thing` signature
+   |
+37 | @app.get("/books/{author}/{title}")
+   |                  ^^^^^^^^ FAST003
+38 | async def read_thing(author: str, title: str, /):
+39 |     return {"author": author, "title": title}
+   |
+
+FAST003.py:37:27: FAST003 Parameter `title` appears in route path, but only as a positional-only argument in `read_thing` signature
+   |
+37 | @app.get("/books/{author}/{title}")
+   |                           ^^^^^^^ FAST003
+38 | async def read_thing(author: str, title: str, /):
+39 |     return {"author": author, "title": title}
+   |
+
+FAST003.py:42:27: FAST003 [*] Parameter `title` appears in route path, but not in `read_thing` signature
+   |
+42 | @app.get("/books/{author}/{title}/{page}")
+   |                           ^^^^^^^ FAST003
+43 | async def read_thing(
+44 |     author: str,
+   |
+   = help: Add `title` to function signature
+
+ℹ Unsafe fix
+42 42 | @app.get("/books/{author}/{title}/{page}")
+43 43 | async def read_thing(
+44 44 |     author: str,
+45    |-    query: str,
+   45 |+    query: str, title,
+46 46 | ): ...
+47 47 | 
+48 48 | 
+
+FAST003.py:42:35: FAST003 [*] Parameter `page` appears in route path, but not in `read_thing` signature
+   |
+42 | @app.get("/books/{author}/{title}/{page}")
+   |                                   ^^^^^^ FAST003
+43 | async def read_thing(
+44 |     author: str,
+   |
+   = help: Add `page` to function signature
+
+ℹ Unsafe fix
+42 42 | @app.get("/books/{author}/{title}/{page}")
+43 43 | async def read_thing(
+44 44 |     author: str,
+45    |-    query: str,
+   45 |+    query: str, page,
+46 46 | ): ...
+47 47 | 
+48 48 | 
+
+FAST003.py:49:18: FAST003 [*] Parameter `author` appears in route path, but not in `read_thing` signature
+   |
+49 | @app.get("/books/{author}/{title}")
+   |                  ^^^^^^^^ FAST003
+50 | async def read_thing():
+51 |     ...
+   |
+   = help: Add `author` to function signature
+
+ℹ Unsafe fix
+47 47 | 
+48 48 | 
+49 49 | @app.get("/books/{author}/{title}")
+50    |-async def read_thing():
+   50 |+async def read_thing(author):
+51 51 |     ...
+52 52 | 
+53 53 | 
+
+FAST003.py:49:27: FAST003 [*] Parameter `title` appears in route path, but not in `read_thing` signature
+   |
+49 | @app.get("/books/{author}/{title}")
+   |                           ^^^^^^^ FAST003
+50 | async def read_thing():
+51 |     ...
+   |
+   = help: Add `title` to function signature
+
+ℹ Unsafe fix
+47 47 | 
+48 48 | 
+49 49 | @app.get("/books/{author}/{title}")
+50    |-async def read_thing():
+   50 |+async def read_thing(title):
+51 51 |     ...
+52 52 | 
+53 53 | 
+
+FAST003.py:54:27: FAST003 [*] Parameter `title` appears in route path, but not in `read_thing` signature
+   |
+54 | @app.get("/books/{author}/{title}")
+   |                           ^^^^^^^ FAST003
+55 | async def read_thing(*, author: str):
+56 |     ...
+   |
+   = help: Add `title` to function signature
+
+ℹ Unsafe fix
+52 52 | 
+53 53 | 
+54 54 | @app.get("/books/{author}/{title}")
+55    |-async def read_thing(*, author: str):
+   55 |+async def read_thing(title, *, author: str):
+56 56 |     ...
+57 57 | 
+58 58 | 
+
+FAST003.py:59:27: FAST003 [*] Parameter `title` appears in route path, but not in `read_thing` signature
+   |
+59 | @app.get("/books/{author}/{title}")
+   |                           ^^^^^^^ FAST003
+60 | async def read_thing(hello, /, *, author: str):
+61 |     ...
+   |
+   = help: Add `title` to function signature
+
+ℹ Unsafe fix
+57 57 | 
+58 58 | 
+59 59 | @app.get("/books/{author}/{title}")
+60    |-async def read_thing(hello, /, *, author: str):
+   60 |+async def read_thing(hello, /, title, *, author: str):
+61 61 |     ...
+62 62 | 
+63 63 | 
+
+FAST003.py:64:19: FAST003 [*] Parameter `thing_id` appears in route path, but not in `read_thing` signature
+   |
+64 | @app.get("/things/{thing_id}")
+   |                   ^^^^^^^^^^ FAST003
+65 | async def read_thing(
+66 |         query: str,
+   |
+   = help: Add `thing_id` to function signature
+
+ℹ Unsafe fix
+63 63 | 
+64 64 | @app.get("/things/{thing_id}")
+65 65 | async def read_thing(
+66    |-        query: str,
+   66 |+        query: str, thing_id,
+67 67 | ):
+68 68 |     return {"query": query}
+69 69 | 
+
+FAST003.py:71:19: FAST003 [*] Parameter `thing_id` appears in route path, but not in `read_thing` signature
+   |
+71 | @app.get("/things/{thing_id}")
+   |                   ^^^^^^^^^^ FAST003
+72 | async def read_thing(
+73 |         query: str = "default",
+   |
+   = help: Add `thing_id` to function signature
+
+ℹ Unsafe fix
+70 70 | 
+71 71 | @app.get("/things/{thing_id}")
+72 72 | async def read_thing(
+73    |-        query: str = "default",
+   73 |+        thing_id, query: str = "default",
+74 74 | ):
+75 75 |     return {"query": query}
+76 76 | 
+
+FAST003.py:78:19: FAST003 [*] Parameter `thing_id` appears in route path, but not in `read_thing` signature
+   |
+78 | @app.get("/things/{thing_id}")
+   |                   ^^^^^^^^^^ FAST003
+79 | async def read_thing(
+80 |         *, query: str = "default",
+   |
+   = help: Add `thing_id` to function signature
+
+ℹ Unsafe fix
+77 77 | 
+78 78 | @app.get("/things/{thing_id}")
+79 79 | async def read_thing(
+80    |-        *, query: str = "default",
+   80 |+        thing_id, *, query: str = "default",
+81 81 | ):
+82 82 |     return {"query": query}
+83 83 |

crates/ruff_linter/src/rules/flake8_async/rules/async_function_with_timeout.rs

@@ -32,7 +32,7 @@ use crate::rules::flake8_async::helpers::AsyncModule;
 ///
 ///
 /// async def main():
-///     with asyncio.timeout(2):
+///     async with asyncio.timeout(2):
 ///         await long_running_task()
 /// ```
 ///

crates/ruff_linter/src/rules/flake8_async/rules/cancel_scope_no_checkpoint.rs

@@ -1,8 +1,8 @@
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
-use ruff_python_ast::helpers::AwaitVisitor;
+use ruff_python_ast::helpers::{any_over_body, AwaitVisitor};
 use ruff_python_ast::visitor::Visitor;
-use ruff_python_ast::{StmtWith, WithItem};
+use ruff_python_ast::{Expr, StmtWith, WithItem};
 
 use crate::checkers::ast::Checker;
 use crate::rules::flake8_async::helpers::MethodName;
@@ -10,6 +10,9 @@ use crate::rules::flake8_async::helpers::MethodName;
 /// ## What it does
 /// Checks for timeout context managers which do not contain a checkpoint.
 ///
+/// For the purposes of this check, `yield` is considered a checkpoint,
+/// since checkpoints may occur in the caller to which we yield.
+///
 /// ## Why is this bad?
 /// Some asynchronous context managers, such as `asyncio.timeout` and
 /// `trio.move_on_after`, have no effect unless they contain a checkpoint.
@@ -19,14 +22,14 @@ use crate::rules::flake8_async::helpers::MethodName;
 /// ## Example
 /// ```python
 /// async def func():
-///     with asyncio.timeout(2):
+///     async with asyncio.timeout(2):
 ///         do_something()
 /// ```
 ///
 /// Use instead:
 /// ```python
 /// async def func():
-///     with asyncio.timeout(2):
+///     async with asyncio.timeout(2):
 ///         do_something()
 ///         await awaitable()
 /// ```
@@ -80,6 +83,14 @@ pub(crate) fn cancel_scope_no_checkpoint(
         return;
     }
 
+    // Treat yields as checkpoints, since checkpoints can happen
+    // in the caller yielded to.
+    // See: https://flake8-async.readthedocs.io/en/latest/rules.html#async100
+    // See: https://github.com/astral-sh/ruff/issues/12873
+    if any_over_body(&with_stmt.body, &Expr::is_yield_expr) {
+        return;
+    }
+
     // If the body contains an `await` statement, the context manager is used correctly.
     let mut visitor = AwaitVisitor::default();
     visitor.visit_body(&with_stmt.body);

crates/ruff_linter/src/rules/flake8_bugbear/rules/useless_comparison.rs

@@ -1,6 +1,7 @@
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
-use ruff_python_ast::Expr;
+use ruff_python_ast::{Expr, Stmt};
+use ruff_python_semantic::ScopeKind;
 use ruff_text_size::Ranged;
 
 use crate::checkers::ast::Checker;
@@ -33,24 +34,34 @@ use super::super::helpers::at_last_top_level_expression_in_cell;
 /// ## References
 /// - [Python documentation: `assert` statement](https://docs.python.org/3/reference/simple_stmts.html#the-assert-statement)
 #[violation]
-pub struct UselessComparison;
+pub struct UselessComparison {
+    at: ComparisonLocationAt,
+}
 
 impl Violation for UselessComparison {
     #[derive_message_formats]
     fn message(&self) -> String {
-        format!(
-            "Pointless comparison. Did you mean to assign a value? \
-             Otherwise, prepend `assert` or remove it."
-        )
+        match self.at {
+            ComparisonLocationAt::MiddleBody => format!(
+                "Pointless comparison. Did you mean to assign a value? \
+                Otherwise, prepend `assert` or remove it."
+            ),
+            ComparisonLocationAt::EndOfFunction => format!(
+                "Pointless comparison at end of function scope. Did you mean \
+                to return the expression result?"
+            ),
+        }
     }
 }
 
 /// B015
 pub(crate) fn useless_comparison(checker: &mut Checker, expr: &Expr) {
     if expr.is_compare_expr() {
+        let semantic = checker.semantic();
+
         if checker.source_type.is_ipynb()
             && at_last_top_level_expression_in_cell(
-                checker.semantic(),
+                semantic,
                 checker.locator(),
                 checker.cell_offsets(),
             )
@@ -58,8 +69,34 @@ pub(crate) fn useless_comparison(checker: &mut Checker, expr: &Expr) {
             return;
         }
 
-        checker
-            .diagnostics
-            .push(Diagnostic::new(UselessComparison, expr.range()));
+        if let ScopeKind::Function(func_def) = semantic.current_scope().kind {
+            if func_def
+                .body
+                .last()
+                .and_then(Stmt::as_expr_stmt)
+                .is_some_and(|last_stmt| &*last_stmt.value == expr)
+            {
+                checker.diagnostics.push(Diagnostic::new(
+                    UselessComparison {
+                        at: ComparisonLocationAt::EndOfFunction,
+                    },
+                    expr.range(),
+                ));
+                return;
+            }
+        }
+
+        checker.diagnostics.push(Diagnostic::new(
+            UselessComparison {
+                at: ComparisonLocationAt::MiddleBody,
+            },
+            expr.range(),
+        ));
     }
 }
+
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+enum ComparisonLocationAt {
+    MiddleBody,
+    EndOfFunction,
+}

crates/ruff_linter/src/rules/flake8_bugbear/snapshots/ruff_linter__rules__flake8_bugbear__tests__B015_B015.py.snap

@@ -1,5 +1,6 @@
 ---
 source: crates/ruff_linter/src/rules/flake8_bugbear/mod.rs
+assertion_line: 74
 ---
 B015.py:3:1: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
   |
@@ -19,7 +20,7 @@ B015.py:7:1: B015 Pointless comparison. Did you mean to assign a value? Otherwis
   | ^^^^^^^^^^^ B015
   |
 
-B015.py:17:5: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
+B015.py:17:5: B015 Pointless comparison at end of function scope. Did you mean to return the expression result?
    |
 15 |     assert 1 in (1, 2)
 16 | 
@@ -27,11 +28,17 @@ B015.py:17:5: B015 Pointless comparison. Did you mean to assign a value? Otherwi
    |     ^^^^^^^^^^^ B015
    |
 
-B015.py:24:5: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
+B015.py:21:5: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
    |
-23 | class TestClass:
-24 |     1 == 1
+20 | def test2():
+21 |     1 in (1, 2)
+   |     ^^^^^^^^^^^ B015
+22 |     return
+   |
+
+B015.py:29:5: B015 Pointless comparison. Did you mean to assign a value? Otherwise, prepend `assert` or remove it.
+   |
+28 | class TestClass:
+29 |     1 == 1
    |     ^^^^^^ B015
    |
-
-

crates/ruff_linter/src/rules/flake8_comprehensions/rules/unnecessary_comprehension_in_call.rs

@@ -100,14 +100,21 @@ pub(crate) fn unnecessary_comprehension_in_call(
     let Some(arg) = args.first() else {
         return;
     };
-    let (Expr::ListComp(ast::ExprListComp { elt, .. })
-    | Expr::SetComp(ast::ExprSetComp { elt, .. })) = arg
+    let (Expr::ListComp(ast::ExprListComp {
+        elt, generators, ..
+    })
+    | Expr::SetComp(ast::ExprSetComp {
+        elt, generators, ..
+    })) = arg
     else {
         return;
     };
     if contains_await(elt) {
         return;
     }
+    if generators.iter().any(|generator| generator.is_async) {
+        return;
+    }
     let Some(Ok(builtin_function)) = checker
         .semantic()
         .resolve_builtin_symbol(func)

crates/ruff_linter/src/rules/flake8_unused_arguments/rules/unused_arguments.rs

@@ -344,6 +344,7 @@ pub(crate) fn unused_arguments(
             ) {
                 function_type::FunctionType::Function => {
                     if checker.enabled(Argumentable::Function.rule_code())
+                        && !function_type::is_stub(function_def, checker.semantic())
                         && !visibility::is_overload(decorator_list, checker.semantic())
                     {
                         function(

crates/ruff_linter/src/rules/flake8_unused_arguments/snapshots/ruff_linter__rules__flake8_unused_arguments__tests__ARG001_ARG.py.snap

@@ -32,33 +32,3 @@ ARG.py:13:12: ARG001 Unused function argument: `x`
    |            ^ ARG001
 14 |     print("Hello, world!")
    |
-
-ARG.py:17:7: ARG001 Unused function argument: `self`
-   |
-17 | def f(self, x):
-   |       ^^^^ ARG001
-18 |     ...
-   |
-
-ARG.py:17:13: ARG001 Unused function argument: `x`
-   |
-17 | def f(self, x):
-   |             ^ ARG001
-18 |     ...
-   |
-
-ARG.py:21:7: ARG001 Unused function argument: `cls`
-   |
-21 | def f(cls, x):
-   |       ^^^ ARG001
-22 |     ...
-   |
-
-ARG.py:21:12: ARG001 Unused function argument: `x`
-   |
-21 | def f(cls, x):
-   |            ^ ARG001
-22 |     ...
-   |
-
-

crates/ruff_linter/src/rules/pep8_naming/mod.rs

@@ -8,11 +8,12 @@ mod tests {
     use std::path::{Path, PathBuf};
 
     use anyhow::Result;
+    use rustc_hash::FxHashMap;
     use test_case::test_case;
 
     use crate::registry::Rule;
-    use crate::rules::pep8_naming;
     use crate::rules::pep8_naming::settings::IgnoreNames;
+    use crate::rules::{flake8_import_conventions, pep8_naming};
     use crate::test::test_path;
     use crate::{assert_messages, settings};
 
@@ -87,6 +88,25 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn camelcase_imported_as_incorrect_convention() -> Result<()> {
+        let diagnostics = test_path(
+            Path::new("pep8_naming").join("N817.py").as_path(),
+            &settings::LinterSettings {
+                flake8_import_conventions: flake8_import_conventions::settings::Settings {
+                    aliases: FxHashMap::from_iter([(
+                        "xml.etree.ElementTree".to_string(),
+                        "XET".to_string(),
+                    )]),
+                    ..Default::default()
+                },
+                ..settings::LinterSettings::for_rule(Rule::CamelcaseImportedAsAcronym)
+            },
+        )?;
+        assert_messages!(diagnostics);
+        Ok(())
+    }
+
     #[test]
     fn classmethod_decorators() -> Result<()> {
         let diagnostics = test_path(

crates/ruff_linter/src/rules/pep8_naming/rules/camelcase_imported_as_acronym.rs

@@ -1,12 +1,11 @@
-use ruff_python_ast::{Alias, Stmt};
-
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
+use ruff_python_ast::{Alias, Stmt};
 use ruff_python_stdlib::str::{self};
 use ruff_text_size::Ranged;
 
+use crate::checkers::ast::Checker;
 use crate::rules::pep8_naming::helpers;
-use crate::rules::pep8_naming::settings::IgnoreNames;
 
 /// ## What it does
 /// Checks for `CamelCase` imports that are aliased as acronyms.
@@ -23,6 +22,9 @@ use crate::rules::pep8_naming::settings::IgnoreNames;
 /// Note that this rule is distinct from `camelcase-imported-as-constant`
 /// to accommodate selective enforcement.
 ///
+/// Also note that import aliases following an import convention according to the
+/// [`lint.flake8-import-conventions.aliases`] option are allowed.
+///
 /// ## Example
 /// ```python
 /// from example import MyClassName as MCN
@@ -34,6 +36,9 @@ use crate::rules::pep8_naming::settings::IgnoreNames;
 /// ```
 ///
 /// [PEP 8]: https://peps.python.org/pep-0008/
+///
+/// ## Options
+/// - `lint.flake8-import-conventions.aliases`
 #[violation]
 pub struct CamelcaseImportedAsAcronym {
     name: String,
@@ -54,17 +59,25 @@ pub(crate) fn camelcase_imported_as_acronym(
     asname: &str,
     alias: &Alias,
     stmt: &Stmt,
-    ignore_names: &IgnoreNames,
+    checker: &Checker,
 ) -> Option<Diagnostic> {
     if helpers::is_camelcase(name)
         && !str::is_cased_lowercase(asname)
         && str::is_cased_uppercase(asname)
         && helpers::is_acronym(name, asname)
     {
+        let ignore_names = &checker.settings.pep8_naming.ignore_names;
+
         // Ignore any explicitly-allowed names.
         if ignore_names.matches(name) || ignore_names.matches(asname) {
             return None;
         }
+
+        // Ignore names that follow a community-agreed import convention.
+        if is_ignored_because_of_import_convention(asname, stmt, alias, checker) {
+            return None;
+        }
+
         let mut diagnostic = Diagnostic::new(
             CamelcaseImportedAsAcronym {
                 name: name.to_string(),
@@ -77,3 +90,34 @@ pub(crate) fn camelcase_imported_as_acronym(
     }
     None
 }
+
+fn is_ignored_because_of_import_convention(
+    asname: &str,
+    stmt: &Stmt,
+    alias: &Alias,
+    checker: &Checker,
+) -> bool {
+    let full_name = if let Some(import_from) = stmt.as_import_from_stmt() {
+        // Never test relative imports for exclusion because we can't resolve the full-module name.
+        let Some(module) = import_from.module.as_ref() else {
+            return false;
+        };
+
+        if import_from.level != 0 {
+            return false;
+        }
+
+        std::borrow::Cow::Owned(format!("{module}.{}", alias.name))
+    } else {
+        std::borrow::Cow::Borrowed(&*alias.name)
+    };
+
+    // Ignore names that follow a community-agreed import convention.
+    checker
+        .settings
+        .flake8_import_conventions
+        .aliases
+        .get(&*full_name)
+        .map(String::as_str)
+        == Some(asname)
+}

crates/ruff_linter/src/rules/pep8_naming/snapshots/ruff_linter__rules__pep8_naming__tests__N817_N817.py.snap

@@ -15,4 +15,9 @@ N817.py:2:17: N817 CamelCase `CamelCase` imported as acronym `CC`
   |                 ^^^^^^^^^^^^^^^ N817
   |
 
-
+N817.py:10:26: N817 CamelCase `ElementTree` imported as acronym `ET`
+   |
+ 9 | # Always an error (relative import)
+10 | from ..xml.eltree import ElementTree as ET
+   |                          ^^^^^^^^^^^^^^^^^ N817
+   |

crates/ruff_linter/src/rules/pep8_naming/snapshots/ruff_linter__rules__pep8_naming__tests__camelcase_imported_as_incorrect_convention.snap

@@ -0,0 +1,41 @@
+---
+source: crates/ruff_linter/src/rules/pep8_naming/mod.rs
+---
+N817.py:1:8: N817 CamelCase `CaMel` imported as acronym `CM`
+  |
+1 | import mod.CaMel as CM
+  |        ^^^^^^^^^^^^^^^ N817
+2 | from mod import CamelCase as CC
+  |
+
+N817.py:2:17: N817 CamelCase `CamelCase` imported as acronym `CC`
+  |
+1 | import mod.CaMel as CM
+2 | from mod import CamelCase as CC
+  |                 ^^^^^^^^^^^^^^^ N817
+  |
+
+N817.py:6:8: N817 CamelCase `ElementTree` imported as acronym `ET`
+  |
+5 | # OK depending on configured import convention
+6 | import xml.etree.ElementTree as ET
+  |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ N817
+7 | from xml.etree import ElementTree as ET
+  |
+
+N817.py:7:23: N817 CamelCase `ElementTree` imported as acronym `ET`
+  |
+5 | # OK depending on configured import convention
+6 | import xml.etree.ElementTree as ET
+7 | from xml.etree import ElementTree as ET
+  |                       ^^^^^^^^^^^^^^^^^ N817
+8 | 
+9 | # Always an error (relative import)
+  |
+
+N817.py:10:26: N817 CamelCase `ElementTree` imported as acronym `ET`
+   |
+ 9 | # Always an error (relative import)
+10 | from ..xml.eltree import ElementTree as ET
+   |                          ^^^^^^^^^^^^^^^^^ N817
+   |

crates/ruff_linter/src/rules/perflint/rules/try_except_in_loop.rs

@@ -15,21 +15,29 @@ use crate::settings::types::PythonVersion;
 /// Exception handling via `try`-`except` blocks incurs some performance
 /// overhead, regardless of whether an exception is raised.
 ///
-/// When possible, refactor your code to put the entire loop into the
-/// `try`-`except` block, rather than wrapping each iteration in a separate
-/// `try`-`except` block.
+/// To optimize your code, two techniques are possible:
+/// 1. Refactor your code to put the entire loop into the `try`-`except` block,
+///    rather than wrapping each iteration in a separate `try`-`except` block.
+/// 2. Use "Look Before You Leap" idioms that attempt to avoid exceptions
+///    being raised in the first place, avoiding the need to use `try`-`except`
+///    blocks in the first place.
 ///
 /// This rule is only enforced for Python versions prior to 3.11, which
-/// introduced "zero cost" exception handling.
+/// introduced "zero-cost" exception handling. However, note that even on
+/// Python 3.11 and newer, refactoring your code to avoid exception handling in
+/// tight loops can provide a significant speedup in some cases, as zero-cost
+/// exception handling is only zero-cost in the "happy path" where no exception
+/// is raised in the `try`-`except` block.
 ///
-/// Note that, as with all `perflint` rules, this is only intended as a
-/// micro-optimization, and will have a negligible impact on performance in
-/// most cases.
+/// As with all `perflint` rules, this is only intended as a
+/// micro-optimization. In many cases, it will have a negligible impact on
+/// performance.
 ///
 /// ## Example
 /// ```python
 /// string_numbers: list[str] = ["1", "2", "three", "4", "5"]
 ///
+/// # `try`/`except` that could be moved out of the loop:
 /// int_numbers: list[int] = []
 /// for num in string_numbers:
 ///     try:
@@ -37,6 +45,16 @@ use crate::settings::types::PythonVersion;
 ///     except ValueError as e:
 ///         print(f"Couldn't convert to integer: {e}")
 ///         break
+///
+/// # `try`/`except` used when "look before you leap" idioms could be used:
+/// number_names: dict[int, str] = {1: "one", 3: "three", 4: "four"}
+/// for number in range(5):
+///     try:
+///         name = number_names[number]
+///     except KeyError:
+///         continue
+///     else:
+///         print(f"The name of {number} is {name}")
 /// ```
 ///
 /// Use instead:
@@ -49,6 +67,12 @@ use crate::settings::types::PythonVersion;
 ///         int_numbers.append(int(num))
 /// except ValueError as e:
 ///     print(f"Couldn't convert to integer: {e}")
+///
+/// number_names: dict[int, str] = {1: "one", 3: "three", 4: "four"}
+/// for number in range(5):
+///     name = number_names.get(number)
+///     if name is not None:
+///         print(f"The name of {number} is {name}")
 /// ```
 ///
 /// ## Options

crates/ruff_linter/src/rules/pydocstyle/rules/blank_before_after_class.rs

@@ -34,6 +34,7 @@ use crate::registry::Rule;
 ///
 /// ```python
 /// class PhotoMetadata:
+///
 ///     """Metadata about a photo."""
 /// ```
 ///
@@ -125,6 +126,7 @@ impl AlwaysFixableViolation for OneBlankLineAfterClass {
 ///
 /// ```python
 /// class PhotoMetadata:
+///
 ///     """Metadata about a photo."""
 /// ```
 ///