Update CHANGELOG.md with the new commits for 0.8.1 (#14664)

The 0.8.1 release was delayed, so this PR updates the CHANGELOG.md with
the latest commits on `main`.

.github/CODEOWNERS

@@ -13,9 +13,10 @@
 # flake8-pyi
 /crates/ruff_linter/src/rules/flake8_pyi/ @AlexWaygood
 
-# Script for fuzzing the parser
-/scripts/fuzz-parser/ @AlexWaygood
+# Script for fuzzing the parser/red-knot etc.
+/python/py-fuzzer/ @AlexWaygood
 
 # red-knot
 /crates/red_knot* @carljm @MichaReiser @AlexWaygood @sharkdp
 /crates/ruff_db/ @carljm @MichaReiser @AlexWaygood @sharkdp
+/scripts/knot_benchmark/ @carljm @MichaReiser @AlexWaygood @sharkdp

.github/workflows/ci.yaml

@@ -49,7 +49,7 @@ jobs:
               - crates/ruff_text_size/**
               - crates/ruff_python_ast/**
               - crates/ruff_python_parser/**
-              - scripts/fuzz-parser/**
+              - python/py-fuzzer/**
               - .github/workflows/ci.yaml
 
             linter:
@@ -82,6 +82,7 @@ jobs:
             code:
               - "**/*"
               - "!**/*.md"
+              - "crates/red_knot_python_semantic/resources/mdtest/**/*.md"
               - "!docs/**"
               - "!assets/**"
 
@@ -115,7 +116,7 @@ jobs:
 
   cargo-test-linux:
     name: "cargo test (linux)"
-    runs-on: ubuntu-latest
+    runs-on: depot-ubuntu-22.04-16
     needs: determine_changes
     if: ${{ needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main' }}
     timeout-minutes: 20
@@ -157,9 +158,36 @@ jobs:
           name: ruff
           path: target/debug/ruff
 
+  cargo-test-linux-release:
+    name: "cargo test (linux, release)"
+    runs-on: depot-ubuntu-22.04-16
+    needs: determine_changes
+    if: ${{ needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main' }}
+    timeout-minutes: 20
+    steps:
+      - uses: actions/checkout@v4
+      - name: "Install Rust toolchain"
+        run: rustup show
+      - name: "Install mold"
+        uses: rui314/setup-mold@v1
+      - name: "Install cargo nextest"
+        uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-nextest
+      - name: "Install cargo insta"
+        uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-insta
+      - uses: Swatinem/rust-cache@v2
+      - name: "Run tests"
+        shell: bash
+        env:
+          NEXTEST_PROFILE: "ci"
+        run: cargo insta test --release --all-features --unreferenced reject --test-runner nextest
+
   cargo-test-windows:
     name: "cargo test (windows)"
-    runs-on: windows-latest
+    runs-on: windows-latest-xlarge
     needs: determine_changes
     if: ${{ needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main' }}
     timeout-minutes: 20
@@ -197,6 +225,8 @@ jobs:
           cache: "npm"
           cache-dependency-path: playground/package-lock.json
       - uses: jetli/wasm-pack-action@v0.4.0
+        with:
+          version: v0.13.1
       - uses: Swatinem/rust-cache@v2
       - name: "Test ruff_wasm"
         run: |
@@ -210,8 +240,7 @@ jobs:
   cargo-build-release:
     name: "cargo build (release)"
     runs-on: macos-latest
-    needs: determine_changes
-    if: ${{ needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main' }}
+    if: ${{ github.ref == 'refs/heads/main' }}
     timeout-minutes: 20
     steps:
       - uses: actions/checkout@v4
@@ -255,11 +284,11 @@ jobs:
           NEXTEST_PROFILE: "ci"
         run: cargo +${{ steps.msrv.outputs.value }} insta test --all-features --unreferenced reject --test-runner nextest
 
-  cargo-fuzz:
-    name: "cargo fuzz"
+  cargo-fuzz-build:
+    name: "cargo fuzz build"
     runs-on: ubuntu-latest
     needs: determine_changes
-    if: ${{ needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main' }}
+    if: ${{ github.ref == 'refs/heads/main' }}
     timeout-minutes: 10
     steps:
       - uses: actions/checkout@v4
@@ -278,7 +307,7 @@ jobs:
       - run: cargo fuzz build -s none
 
   fuzz-parser:
-    name: "Fuzz the parser"
+    name: "fuzz parser"
     runs-on: ubuntu-latest
     needs:
       - cargo-test-linux
@@ -289,13 +318,7 @@ jobs:
       FORCE_COLOR: 1
     steps:
       - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
-        with:
-          python-version: ${{ env.PYTHON_VERSION }}
-      - name: Install uv
-        run: curl -LsSf https://astral.sh/uv/install.sh | sh
-      - name: Install Python requirements
-        run: uv pip install -r scripts/fuzz-parser/requirements.txt --system
+      - uses: astral-sh/setup-uv@v4
       - uses: actions/download-artifact@v4
         name: Download Ruff binary to test
         id: download-cached-binary
@@ -307,7 +330,15 @@ jobs:
           # Make executable, since artifact download doesn't preserve this
           chmod +x ${{ steps.download-cached-binary.outputs.download-path }}/ruff
 
-          python scripts/fuzz-parser/fuzz.py 0-500 --test-executable ${{ steps.download-cached-binary.outputs.download-path }}/ruff
+          (
+            uvx \
+            --python=${{ env.PYTHON_VERSION }} \
+            --from=./python/py-fuzzer \
+            fuzz \
+            --test-executable=${{ steps.download-cached-binary.outputs.download-path }}/ruff \
+            --bin=ruff \
+            0-500
+          )
 
   scripts:
     name: "test scripts"
@@ -331,7 +362,7 @@ jobs:
 
   ecosystem:
     name: "ecosystem"
-    runs-on: ubuntu-latest
+    runs-on: depot-ubuntu-latest-8
     needs:
       - cargo-test-linux
       - determine_changes
@@ -561,12 +592,12 @@ jobs:
         run: rustup show
       - name: "Cache rust"
         uses: Swatinem/rust-cache@v2
-      - name: "Formatter progress"
+      - name: "Run checks"
         run: scripts/formatter_ecosystem_checks.sh
       - name: "Github step summary"
-        run: cat target/progress_projects_stats.txt > $GITHUB_STEP_SUMMARY
+        run: cat target/formatter-ecosystem/stats.txt > $GITHUB_STEP_SUMMARY
       - name: "Remove checkouts from cache"
-        run: rm -r target/progress_projects
+        run: rm -r target/formatter-ecosystem
 
   check-ruff-lsp:
     name: "test ruff-lsp"

.github/workflows/daily_fuzz.yaml

@@ -32,13 +32,7 @@ jobs:
     if: ${{ github.repository == 'astral-sh/ruff' || github.event_name != 'schedule' }}
     steps:
       - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
-        with:
-          python-version: "3.12"
-      - name: Install uv
-        run: curl -LsSf https://astral.sh/uv/install.sh | sh
-      - name: Install Python requirements
-        run: uv pip install -r scripts/fuzz-parser/requirements.txt --system
+      - uses: astral-sh/setup-uv@v4
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install mold"
@@ -49,7 +43,16 @@ jobs:
         # but this is outweighed by the fact that a release build takes *much* longer to compile in CI
         run: cargo build --locked
       - name: Fuzz
-        run: python scripts/fuzz-parser/fuzz.py $(shuf -i 0-9999999999999999999 -n 1000) --test-executable target/debug/ruff
+        run: |
+          (
+            uvx \
+            --python=3.12 \
+            --from=./python/py-fuzzer \
+            fuzz \
+            --test-executable=target/debug/ruff \
+            --bin=ruff \
+            $(shuf -i 0-9999999999999999999 -n 1000)
+          )
 
   create-issue-on-failure:
     name: Create an issue if the daily fuzz surfaced any bugs

.github/workflows/release.yml

@@ -1,4 +1,4 @@
-# This file was autogenerated by cargo-dist: https://opensource.axo.dev/cargo-dist/
+# This file was autogenerated by dist: https://opensource.axo.dev/cargo-dist/
 #
 # Copyright 2022-2024, axodotdev
 # SPDX-License-Identifier: MIT or Apache-2.0
@@ -6,7 +6,7 @@
 # CI that:
 #
 # * checks for a Git Tag that looks like a release
-# * builds artifacts with cargo-dist (archives, installers, hashes)
+# * builds artifacts with dist (archives, installers, hashes)
 # * uploads those artifacts to temporary workflow zip
 # * on success, uploads the artifacts to a GitHub Release
 #
@@ -24,10 +24,10 @@ permissions:
 # must be a Cargo-style SemVer Version (must have at least major.minor.patch).
 #
 # If PACKAGE_NAME is specified, then the announcement will be for that
-# package (erroring out if it doesn't have the given version or isn't cargo-dist-able).
+# package (erroring out if it doesn't have the given version or isn't dist-able).
 #
 # If PACKAGE_NAME isn't specified, then the announcement will be for all
-# (cargo-dist-able) packages in the workspace with that version (this mode is
+# (dist-able) packages in the workspace with that version (this mode is
 # intended for workspaces with only one dist-able package, or with all dist-able
 # packages versioned/released in lockstep).
 #
@@ -48,7 +48,7 @@ on:
         type: string
 
 jobs:
-  # Run 'cargo dist plan' (or host) to determine what tasks we need to do
+  # Run 'dist plan' (or host) to determine what tasks we need to do
   plan:
     runs-on: "ubuntu-20.04"
     outputs:
@@ -62,16 +62,16 @@ jobs:
       - uses: actions/checkout@v4
         with:
           submodules: recursive
-      - name: Install cargo-dist
+      - name: Install dist
         # we specify bash to get pipefail; it guards against the `curl` command
         # failing. otherwise `sh` won't catch that `curl` returned non-0
         shell: bash
-        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/axodotdev/cargo-dist/releases/download/v0.22.1/cargo-dist-installer.sh | sh"
-      - name: Cache cargo-dist
+        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/axodotdev/cargo-dist/releases/download/v0.25.2-prerelease.3/cargo-dist-installer.sh | sh"
+      - name: Cache dist
         uses: actions/upload-artifact@v4
         with:
           name: cargo-dist-cache
-          path: ~/.cargo/bin/cargo-dist
+          path: ~/.cargo/bin/dist
       # sure would be cool if github gave us proper conditionals...
       # so here's a doubly-nested ternary-via-truthiness to try to provide the best possible
       # functionality based on whether this is a pull_request, and whether it's from a fork.
@@ -79,8 +79,8 @@ jobs:
       # but also really annoying to build CI around when it needs secrets to work right.)
       - id: plan
         run: |
-          cargo dist ${{ (inputs.tag && inputs.tag != 'dry-run' && format('host --steps=create --tag={0}', inputs.tag)) || 'plan' }} --output-format=json > plan-dist-manifest.json
-          echo "cargo dist ran successfully"
+          dist ${{ (inputs.tag && inputs.tag != 'dry-run' && format('host --steps=create --tag={0}', inputs.tag)) || 'plan' }} --output-format=json > plan-dist-manifest.json
+          echo "dist ran successfully"
           cat plan-dist-manifest.json
           echo "manifest=$(jq -c "." plan-dist-manifest.json)" >> "$GITHUB_OUTPUT"
       - name: "Upload dist-manifest.json"
@@ -124,12 +124,12 @@ jobs:
       - uses: actions/checkout@v4
         with:
           submodules: recursive
-      - name: Install cached cargo-dist
+      - name: Install cached dist
         uses: actions/download-artifact@v4
         with:
           name: cargo-dist-cache
           path: ~/.cargo/bin/
-      - run: chmod +x ~/.cargo/bin/cargo-dist
+      - run: chmod +x ~/.cargo/bin/dist
       # Get all the local artifacts for the global tasks to use (for e.g. checksums)
       - name: Fetch local artifacts
         uses: actions/download-artifact@v4
@@ -140,8 +140,8 @@ jobs:
       - id: cargo-dist
         shell: bash
         run: |
-          cargo dist build ${{ needs.plan.outputs.tag-flag }} --output-format=json "--artifacts=global" > dist-manifest.json
-          echo "cargo dist ran successfully"
+          dist build ${{ needs.plan.outputs.tag-flag }} --output-format=json "--artifacts=global" > dist-manifest.json
+          echo "dist ran successfully"
 
           # Parse out what we just built and upload it to scratch storage
           echo "paths<<EOF" >> "$GITHUB_OUTPUT"
@@ -174,12 +174,12 @@ jobs:
       - uses: actions/checkout@v4
         with:
           submodules: recursive
-      - name: Install cached cargo-dist
+      - name: Install cached dist
         uses: actions/download-artifact@v4
         with:
           name: cargo-dist-cache
           path: ~/.cargo/bin/
-      - run: chmod +x ~/.cargo/bin/cargo-dist
+      - run: chmod +x ~/.cargo/bin/dist
       # Fetch artifacts from scratch-storage
       - name: Fetch artifacts
         uses: actions/download-artifact@v4
@@ -191,7 +191,7 @@ jobs:
       - id: host
         shell: bash
         run: |
-          cargo dist host ${{ needs.plan.outputs.tag-flag }} --steps=upload --steps=release --output-format=json > dist-manifest.json
+          dist host ${{ needs.plan.outputs.tag-flag }} --steps=upload --steps=release --output-format=json > dist-manifest.json
           echo "artifacts uploaded and released successfully"
           cat dist-manifest.json
           echo "manifest=$(jq -c "." dist-manifest.json)" >> "$GITHUB_OUTPUT"

.pre-commit-config.yaml

@@ -17,7 +17,7 @@ exclude: |
 
 repos:
   - repo: https://github.com/abravalheri/validate-pyproject
-    rev: v0.22
+    rev: v0.23
     hooks:
       - id: validate-pyproject
 
@@ -73,7 +73,7 @@ repos:
         pass_filenames: false # This makes it a lot faster
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.7.3
+    rev: v0.7.4
     hooks:
       - id: ruff-format
       - id: ruff

BREAKING_CHANGES.md

@@ -1,5 +1,30 @@
 # Breaking Changes
 
+## 0.8.0
+
+- **Default to Python 3.9**
+
+    Ruff now defaults to Python 3.9 instead of 3.8 if no explicit Python version is configured using [`ruff.target-version`](https://docs.astral.sh/ruff/settings/#target-version) or [`project.requires-python`](https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#python-requires) ([#13896](https://github.com/astral-sh/ruff/pull/13896))
+
+- **Changed location of `pydoclint` diagnostics**
+
+    [`pydoclint`](https://docs.astral.sh/ruff/rules/#pydoclint-doc) diagnostics now point to the first-line of the problematic docstring. Previously, this was not the case.
+
+    If you've opted into these preview rules but have them suppressed using
+    [`noqa`](https://docs.astral.sh/ruff/linter/#error-suppression) comments in
+    some places, this change may mean that you need to move the `noqa` suppression
+    comments. Most users should be unaffected by this change.
+
+- **Use XDG (i.e. `~/.local/bin`) instead of the Cargo home directory in the standalone installer**
+
+    Previously, Ruff's installer used `$CARGO_HOME` or `~/.cargo/bin` for its target install directory. Now, Ruff will be installed into `$XDG_BIN_HOME`, `$XDG_DATA_HOME/../bin`, or `~/.local/bin` (in that order).
+
+    This change is only relevant to users of the standalone Ruff installer (using the shell or PowerShell script). If you installed Ruff using uv or pip, you should be unaffected.
+
+- **Changes to the line width calculation**
+
+    Ruff now uses a new version of the [unicode-width](https://github.com/unicode-rs/unicode-width) Rust crate to calculate the line width. In very rare cases, this may lead to lines containing Unicode characters being reformatted, or being considered too long when they were not before ([`E501`](https://docs.astral.sh/ruff/rules/line-too-long/)).
+
 ## 0.7.0
 
 - The pytest rules `PT001` and `PT023` now default to omitting the decorator parentheses when there are no arguments

CHANGELOG.md

@@ -1,5 +1,145 @@
 # Changelog
 
+## 0.8.1
+
+### Preview features
+
+- Formatter: Avoid invalid syntax for format-spec with quotes for all Python versions ([#14625](https://github.com/astral-sh/ruff/pull/14625))
+- Formatter: Consider quotes inside format-specs when choosing the quotes for an f-string ([#14493](https://github.com/astral-sh/ruff/pull/14493))
+- Formatter: Do not consider f-strings with escaped newlines as multiline ([#14624](https://github.com/astral-sh/ruff/pull/14624))
+- Formatter: Fix f-string formatting in assignment statement ([#14454](https://github.com/astral-sh/ruff/pull/14454))
+- Formatter: Fix unnecessary space around power operator (`**`) in overlong f-string expressions ([#14489](https://github.com/astral-sh/ruff/pull/14489))
+- \[`airflow`\] Avoid implicit `schedule` argument to `DAG` and `@dag` (`AIR301`) ([#14581](https://github.com/astral-sh/ruff/pull/14581))
+- \[`flake8-builtins`\] Exempt private built-in modules (`A005`) ([#14505](https://github.com/astral-sh/ruff/pull/14505))
+- \[`flake8-pytest-style`\] Fix `pytest.mark.parametrize` rules to check calls instead of decorators ([#14515](https://github.com/astral-sh/ruff/pull/14515))
+- \[`flake8-type-checking`\] Implement `runtime-cast-value` (`TC006`) ([#14511](https://github.com/astral-sh/ruff/pull/14511))
+- \[`flake8-type-checking`\] Implement `unquoted-type-alias` (`TC007`) and `quoted-type-alias` (`TC008`) ([#12927](https://github.com/astral-sh/ruff/pull/12927))
+- \[`flake8-use-pathlib`\] Recommend `Path.iterdir()` over `os.listdir()` (`PTH208`) ([#14509](https://github.com/astral-sh/ruff/pull/14509))
+- \[`pylint`\] Extend `invalid-envvar-default` to detect `os.environ.get` (`PLW1508`) ([#14512](https://github.com/astral-sh/ruff/pull/14512))
+- \[`pylint`\] Implement `len-test` (`PLC1802`) ([#14309](https://github.com/astral-sh/ruff/pull/14309))
+- \[`refurb`\] Fix bug where methods defined using lambdas were flagged by `FURB118` ([#14639](https://github.com/astral-sh/ruff/pull/14639))
+- \[`ruff`\] Auto-add `r` prefix when string has no backslashes for `unraw-re-pattern` (`RUF039`) ([#14536](https://github.com/astral-sh/ruff/pull/14536))
+- \[`ruff`\] Implement `invalid-assert-message-literal-argument` (`RUF040`) ([#14488](https://github.com/astral-sh/ruff/pull/14488))
+- \[`ruff`\] Implement `unnecessary-nested-literal` (`RUF041`) ([#14323](https://github.com/astral-sh/ruff/pull/14323))
+- \[`ruff`\] Implement `unnecessary-regular-expression` (`RUF055`) ([#14659](https://github.com/astral-sh/ruff/pull/14659))
+
+### Rule changes
+
+- Ignore more rules for stub files ([#14541](https://github.com/astral-sh/ruff/pull/14541))
+- \[`pep8-naming`\] Eliminate false positives for single-letter names (`N811`, `N814`) ([#14584](https://github.com/astral-sh/ruff/pull/14584))
+- \[`pyflakes`\] Avoid false positives in `@no_type_check` contexts (`F821`, `F722`) ([#14615](https://github.com/astral-sh/ruff/pull/14615))
+- \[`ruff`\] Detect redirected-noqa in file-level comments (`RUF101`) ([#14635](https://github.com/astral-sh/ruff/pull/14635))
+- \[`ruff`\] Mark fixes for `unsorted-dunder-all` and `unsorted-dunder-slots` as unsafe when there are complex comments in the sequence (`RUF022`, `RUF023`) ([#14560](https://github.com/astral-sh/ruff/pull/14560))
+
+### Bug fixes
+
+- Avoid fixing code to `None | None` for `redundant-none-literal` (`PYI061`) and `never-union` (`RUF020`) ([#14583](https://github.com/astral-sh/ruff/pull/14583), [#14589](https://github.com/astral-sh/ruff/pull/14589))
+- \[`flake8-bugbear`\] Fix `mutable-contextvar-default` to resolve annotated function calls properly (`B039`) ([#14532](https://github.com/astral-sh/ruff/pull/14532))
+- \[`flake8-pyi`, `ruff`\] Fix traversal of nested literals and unions (`PYI016`, `PYI051`, `PYI055`, `PYI062`, `RUF041`) ([#14641](https://github.com/astral-sh/ruff/pull/14641))
+- \[`flake8-pyi`\] Avoid rewriting invalid type expressions in `unnecessary-type-union` (`PYI055`) ([#14660](https://github.com/astral-sh/ruff/pull/14660))
+- \[`flake8-type-checking`\] Avoid syntax errors and type checking problem for quoted annotations autofix (`TC003`, `TC006`) ([#14634](https://github.com/astral-sh/ruff/pull/14634))
+- \[`pylint`\] Do not wrap function calls in parentheses in the fix for unnecessary-dunder-call (`PLC2801`) ([#14601](https://github.com/astral-sh/ruff/pull/14601))
+- \[`ruff`\] Handle `attrs`'s `auto_attribs` correctly (`RUF009`) ([#14520](https://github.com/astral-sh/ruff/pull/14520))
+
+## 0.8.0
+
+Check out the [blog post](https://astral.sh/blog/ruff-v0.8.0) for a migration guide and overview of the changes!
+
+### Breaking changes
+
+See also, the "Remapped rules" section which may result in disabled rules.
+
+- **Default to Python 3.9**
+
+    Ruff now defaults to Python 3.9 instead of 3.8 if no explicit Python version is configured using [`ruff.target-version`](https://docs.astral.sh/ruff/settings/#target-version) or [`project.requires-python`](https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#python-requires) ([#13896](https://github.com/astral-sh/ruff/pull/13896))
+
+- **Changed location of `pydoclint` diagnostics**
+
+    [`pydoclint`](https://docs.astral.sh/ruff/rules/#pydoclint-doc) diagnostics now point to the first-line of the problematic docstring. Previously, this was not the case.
+
+    If you've opted into these preview rules but have them suppressed using
+    [`noqa`](https://docs.astral.sh/ruff/linter/#error-suppression) comments in
+    some places, this change may mean that you need to move the `noqa` suppression
+    comments. Most users should be unaffected by this change.
+
+- **Use XDG (i.e. `~/.local/bin`) instead of the Cargo home directory in the standalone installer**
+
+    Previously, Ruff's installer used `$CARGO_HOME` or `~/.cargo/bin` for its target install directory. Now, Ruff will be installed into `$XDG_BIN_HOME`, `$XDG_DATA_HOME/../bin`, or `~/.local/bin` (in that order).
+
+    This change is only relevant to users of the standalone Ruff installer (using the shell or PowerShell script). If you installed Ruff using uv or pip, you should be unaffected.
+
+- **Changes to the line width calculation**
+
+    Ruff now uses a new version of the [unicode-width](https://github.com/unicode-rs/unicode-width) Rust crate to calculate the line width. In very rare cases, this may lead to lines containing Unicode characters being reformatted, or being considered too long when they were not before ([`E501`](https://docs.astral.sh/ruff/rules/line-too-long/)).
+
+### Removed Rules
+
+The following deprecated rules have been removed:
+
+- [`missing-type-self`](https://docs.astral.sh/ruff/rules/missing-type-self/) (`ANN101`)
+- [`missing-type-cls`](https://docs.astral.sh/ruff/rules/missing-type-cls/) (`ANN102`)
+- [`syntax-error`](https://docs.astral.sh/ruff/rules/syntax-error/) (`E999`)
+- [`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:
+
+- [`flake8-type-checking`](https://docs.astral.sh/ruff/rules/#flake8-type-checking-tc): `TCH` to `TC`
+
+### Stabilization
+
+The following rules have been stabilized and are no longer in preview:
+
+- [`builtin-import-shadowing`](https://docs.astral.sh/ruff/rules/builtin-import-shadowing/) (`A004`)
+- [`mutable-contextvar-default`](https://docs.astral.sh/ruff/rules/mutable-contextvar-default/) (`B039`)
+- [`fast-api-redundant-response-model`](https://docs.astral.sh/ruff/rules/fast-api-redundant-response-model/) (`FAST001`)
+- [`fast-api-non-annotated-dependency`](https://docs.astral.sh/ruff/rules/fast-api-non-annotated-dependency/) (`FAST002`)
+- [`dict-index-missing-items`](https://docs.astral.sh/ruff/rules/dict-index-missing-items/) (`PLC0206`)
+- [`pep484-style-positional-only-parameter`](https://docs.astral.sh/ruff/rules/pep484-style-positional-only-parameter/) (`PYI063`)
+- [`redundant-final-literal`](https://docs.astral.sh/ruff/rules/redundant-final-literal/) (`PYI064`)
+- [`bad-version-info-order`](https://docs.astral.sh/ruff/rules/bad-version-info-order/) (`PYI066`)
+- [`parenthesize-chained-operators`](https://docs.astral.sh/ruff/rules/parenthesize-chained-operators/) (`RUF021`)
+- [`unsorted-dunder-all`](https://docs.astral.sh/ruff/rules/unsorted-dunder-all/) (`RUF022`)
+- [`unsorted-dunder-slots`](https://docs.astral.sh/ruff/rules/unsorted-dunder-slots/) (`RUF023`)
+- [`assert-with-print-message`](https://docs.astral.sh/ruff/rules/assert-with-print-message/) (`RUF030`)
+- [`unnecessary-default-type-args`](https://docs.astral.sh/ruff/rules/unnecessary-default-type-args/) (`UP043`)
+
+The following behaviors have been stabilized:
+
+- [`ambiguous-variable-name`](https://docs.astral.sh/ruff/rules/ambiguous-variable-name/) (`E741`): Violations in stub files are now ignored. Stub authors typically don't control variable names.
+- [`printf-string-formatting`](https://docs.astral.sh/ruff/rules/printf-string-formatting/) (`UP031`): Report all `printf`-like usages even if no autofix is available
+
+The following fixes have been stabilized:
+
+- [`zip-instead-of-pairwise`](https://docs.astral.sh/ruff/rules/zip-instead-of-pairwise/) (`RUF007`)
+
+### Preview features
+
+- \[`flake8-datetimez`\] Exempt `min.time()` and `max.time()` (`DTZ901`) ([#14394](https://github.com/astral-sh/ruff/pull/14394))
+- \[`flake8-pie`\] Mark fix as unsafe if the following statement is a string literal (`PIE790`) ([#14393](https://github.com/astral-sh/ruff/pull/14393))
+- \[`flake8-pyi`\] New rule `redundant-none-literal` (`PYI061`) ([#14316](https://github.com/astral-sh/ruff/pull/14316))
+- \[`flake8-pyi`\] Add autofix for `redundant-numeric-union` (`PYI041`) ([#14273](https://github.com/astral-sh/ruff/pull/14273))
+- \[`ruff`\] New rule `map-int-version-parsing` (`RUF048`) ([#14373](https://github.com/astral-sh/ruff/pull/14373))
+- \[`ruff`\] New rule `redundant-bool-literal` (`RUF038`) ([#14319](https://github.com/astral-sh/ruff/pull/14319))
+- \[`ruff`\] New rule `unraw-re-pattern` (`RUF039`) ([#14446](https://github.com/astral-sh/ruff/pull/14446))
+- \[`pycodestyle`\] Exempt `pytest.importorskip()` calls (`E402`) ([#14474](https://github.com/astral-sh/ruff/pull/14474))
+- \[`pylint`\] Autofix suggests using sets when possible (`PLR1714`) ([#14372](https://github.com/astral-sh/ruff/pull/14372))
+
+### Rule changes
+
+- [`invalid-pyproject-toml`](https://docs.astral.sh/ruff/rules/invalid-pyproject-toml/) (`RUF200`): Updated to reflect the provisionally accepted [PEP 639](https://peps.python.org/pep-0639/).
+- \[`flake8-pyi`\] Avoid panic in unfixable case (`PYI041`) ([#14402](https://github.com/astral-sh/ruff/pull/14402))
+- \[`flake8-type-checking`\] Correctly handle quotes in subscript expression when generating an autofix ([#14371](https://github.com/astral-sh/ruff/pull/14371))
+- \[`pylint`\] Suggest correct autofix for `__contains__` (`PLC2801`) ([#14424](https://github.com/astral-sh/ruff/pull/14424))
+
+### Configuration
+
+- Ruff now emits a warning instead of an error when a configuration [`ignore`](https://docs.astral.sh/ruff/settings/#lint_ignore)s a rule that has been removed ([#14435](https://github.com/astral-sh/ruff/pull/14435))
+- Ruff now validates that `lint.flake8-import-conventions.aliases` only uses valid module names and aliases ([#14477](https://github.com/astral-sh/ruff/pull/14477))
+
 ## 0.7.4
 
 ### Preview features
@@ -978,7 +1118,7 @@ The following deprecated CLI commands have been removed:
 ### Preview features
 
 - \[`flake8-bugbear`\] Implement `return-in-generator` (`B901`) ([#11644](https://github.com/astral-sh/ruff/pull/11644))
-- \[`flake8-pyi`\] Implement `PYI063` ([#11699](https://github.com/astral-sh/ruff/pull/11699))
+- \[`flake8-pyi`\] Implement `pep484-style-positional-only-parameter` (`PYI063`) ([#11699](https://github.com/astral-sh/ruff/pull/11699))
 - \[`pygrep_hooks`\] Check blanket ignores via file-level pragmas (`PGH004`) ([#11540](https://github.com/astral-sh/ruff/pull/11540))
 
 ### Rule changes

CONTRIBUTING.md

@@ -139,7 +139,7 @@ At a high level, the steps involved in adding a new lint rule are as follows:
 1. Create a file for your rule (e.g., `crates/ruff_linter/src/rules/flake8_bugbear/rules/assert_false.rs`).
 
 1. In that file, define a violation struct (e.g., `pub struct AssertFalse`). You can grep for
-    `#[violation]` to see examples.
+    `#[derive(ViolationMetadata)]` to see examples.
 
 1. In that file, define a function that adds the violation to the diagnostic list as appropriate
     (e.g., `pub(crate) fn assert_false`) based on whatever inputs are required for the rule (e.g.,

Cargo.lock

@@ -213,10 +213,16 @@ dependencies = [
 ]
 
 [[package]]
-name = "bstr"
-version = "1.10.0"
+name = "boxcar"
+version = "0.2.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "40723b8fb387abc38f4f4a37c09073622e41dd12327033091ef8950659e6dc0c"
+checksum = "7f839cdf7e2d3198ac6ca003fd8ebc61715755f41c1cad15ff13df67531e00ed"
+
+[[package]]
+name = "bstr"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1a68f1f47cdf0ec8ee4b941b2eee2a80cb796db73118c0dd09ac63fbe405be22"
 dependencies = [
  "memchr",
  "regex-automata 0.4.8",
@@ -347,9 +353,9 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "4.5.20"
+version = "4.5.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b97f376d85a664d5837dbae44bf546e6477a679ff6610010f17276f686d867e8"
+checksum = "fb3b4b9e5a7c7514dfa52869339ee98b3156b0bfb4e8a77c4ff4babb64b1604f"
 dependencies = [
  "clap_builder",
  "clap_derive",
@@ -357,9 +363,9 @@ dependencies = [
 
 [[package]]
 name = "clap_builder"
-version = "4.5.20"
+version = "4.5.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "19bc80abd44e4bed93ca373a0704ccbd1b710dc5749406201bb018272808dc54"
+checksum = "b17a95aa67cc7b5ebd32aa5370189aa0d79069ef1c64ce893bd30fb24bff20ec"
 dependencies = [
  "anstream",
  "anstyle",
@@ -407,7 +413,7 @@ dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -687,7 +693,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "strsim 0.10.0",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -698,7 +704,7 @@ checksum = "a668eda54683121533a393014d8692171709ff57a7d61f187b6e782719f8933f"
 dependencies = [
  "darling_core",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -752,23 +758,23 @@ dependencies = [
 
 [[package]]
 name = "dir-test"
-version = "0.3.0"
+version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5c44bdf9319ad5223afb7eb15a7110452b0adf0373ea6756561b2c708eef0dd1"
+checksum = "b12781621d53fd9087021f5a338df5c57c04f84a6231c1f4726f45e2e333470b"
 dependencies = [
  "dir-test-macros",
 ]
 
 [[package]]
 name = "dir-test-macros"
-version = "0.3.0"
+version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "644f96047137dfaa7a09e34d4623f9e52a1926ecc25ba32ad2ba3fc422536b25"
+checksum = "1340852f50b2285d01a7f598cc5d08b572669c3e09e614925175cc3c26787b91"
 dependencies = [
  "glob",
  "proc-macro2",
  "quote",
- "syn 1.0.109",
+ "syn",
 ]
 
 [[package]]
@@ -820,7 +826,7 @@ checksum = "97369cbbc041bc366949bc74d34658d6cda5621039731c6310521892a3a20ae0"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -1062,9 +1068,9 @@ dependencies = [
 
 [[package]]
 name = "hashbrown"
-version = "0.15.1"
+version = "0.15.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3a9bfc1af68b1726ea47d3d5109de126281def866b33970e10fbab11b5dafab3"
+checksum = "bf151400ff0baff5465007dd2f3e717f3fe502074ca563069ce3a6629d07b289"
 
 [[package]]
 name = "hashlink"
@@ -1240,7 +1246,7 @@ checksum = "1ec89e9337638ecdc08744df490b221a7399bf8d164eb52a665454e60e075ad6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -1313,22 +1319,22 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "707907fe3c25f5424cce2cb7e1cbcafee6bdbe735ca90ef77c29e84591e5b9da"
 dependencies = [
  "equivalent",
- "hashbrown 0.15.1",
+ "hashbrown 0.15.2",
  "serde",
 ]
 
 [[package]]
 name = "indicatif"
-version = "0.17.8"
+version = "0.17.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "763a5a8f45087d6bcea4222e7b72c291a054edf80e4ef6efd2a4979878c7bea3"
+checksum = "cbf675b85ed934d3c67b5c5469701eec7db22689d0a2139d856e0925fa28b281"
 dependencies = [
  "console",
- "instant",
  "number_prefix",
  "portable-atomic",
- "unicode-width 0.1.13",
+ "unicode-width 0.2.0",
  "vt100",
+ "web-time",
 ]
 
 [[package]]
@@ -1414,7 +1420,7 @@ dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -1514,15 +1520,15 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.162"
+version = "0.2.164"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "18d287de67fe55fd7e1581fe933d965a5a9477b38e949cfa9f8574ef01506398"
+checksum = "433bfe06b8c75da9b2e3fbea6e5329ff87748f0b144ef75306e674c3f6f7c13f"
 
 [[package]]
 name = "libcst"
-version = "1.5.0"
+version = "1.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1586dd7a857d8a61a577afde1a24cc9573ff549eff092d5ce968b1ec93cc61b6"
+checksum = "fa3e60579a8cba3d86aa4a5f7fc98973cc0fd2ac270bf02f85a9bef09700b075"
 dependencies = [
  "chic",
  "libcst_derive",
@@ -1540,7 +1546,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a2ae40017ac09cd2c6a53504cb3c871c7f2b41466eac5bc66ba63f39073b467b"
 dependencies = [
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -1704,9 +1710,9 @@ checksum = "308d96db8debc727c3fd9744aac51751243420e46edf401010908da7f8d5e57c"
 
 [[package]]
 name = "newtype-uuid"
-version = "1.1.0"
+version = "1.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3526cb7c660872e401beaf3297f95f548ce3b4b4bdd8121b7c0713771d7c4a6e"
+checksum = "4c8781e2ef64806278a55ad223f0bc875772fd40e1fe6e73e8adbf027817229d"
 dependencies = [
  "uuid",
 ]
@@ -1935,18 +1941,6 @@ version = "0.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e3aeb8f54c078314c2065ee649a7241f46b9d8e418e1a9581ba0546657d7aa3a"
 
-[[package]]
-name = "pep440_rs"
-version = "0.4.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e0c29f9c43de378b4e4e0cd7dbcce0e5cfb80443de8c05620368b2948bc936a1"
-dependencies = [
- "once_cell",
- "regex",
- "serde",
- "unicode-width 0.1.13",
-]
-
 [[package]]
 name = "pep440_rs"
 version = "0.7.2"
@@ -1956,22 +1950,29 @@ dependencies = [
  "serde",
  "unicode-width 0.2.0",
  "unscanny",
+ "version-ranges",
 ]
 
 [[package]]
 name = "pep508_rs"
-version = "0.3.0"
+version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "910c513bea0f4f833122321c0f20e8c704e01de98692f6989c2ec21f43d88b1e"
+checksum = "8c2feee999fa547bacab06a4881bacc74688858b92fa8ef1e206c748b0a76048"
 dependencies = [
+ "boxcar",
+ "indexmap",
+ "itertools 0.13.0",
  "once_cell",
- "pep440_rs 0.4.0",
+ "pep440_rs",
  "regex",
+ "rustc-hash 2.0.0",
  "serde",
+ "smallvec",
  "thiserror 1.0.67",
- "tracing",
- "unicode-width 0.1.13",
+ "unicode-width 0.2.0",
  "url",
+ "urlencoding",
+ "version-ranges",
 ]
 
 [[package]]
@@ -2011,7 +2012,7 @@ dependencies = [
  "pest_meta",
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -2126,46 +2127,47 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.89"
+version = "1.0.92"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f139b0662de085916d1fb67d2b4169d1addddda1919e696f3252b740b629986e"
+checksum = "37d3544b3f2748c54e147655edb5025752e2303145b5aefb3c3ea2c78b973bb0"
 dependencies = [
  "unicode-ident",
 ]
 
 [[package]]
 name = "pyproject-toml"
-version = "0.9.0"
+version = "0.13.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "95c3dd745f99aa3c554b7bb00859f7d18c2f1d6afd749ccc86d60b61e702abd9"
+checksum = "643af57c3f36ba90a8b53e972727d8092f7408a9ebfbaf4c3d2c17b07c58d835"
 dependencies = [
  "indexmap",
- "pep440_rs 0.4.0",
+ "pep440_rs",
  "pep508_rs",
  "serde",
+ "thiserror 1.0.67",
  "toml",
 ]
 
 [[package]]
 name = "quick-junit"
-version = "0.5.0"
+version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "62ffd2f9a162cfae131bed6d9d1ed60adced33be340a94f96952897d7cb0c240"
+checksum = "3ed1a693391a16317257103ad06a88c6529ac640846021da7c435a06fffdacd7"
 dependencies = [
  "chrono",
  "indexmap",
  "newtype-uuid",
  "quick-xml",
  "strip-ansi-escapes",
- "thiserror 1.0.67",
+ "thiserror 2.0.3",
  "uuid",
 ]
 
 [[package]]
 name = "quick-xml"
-version = "0.36.1"
+version = "0.37.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "96a05e2e8efddfa51a84ca47cec303fac86c8541b686d37cac5efc0e094417bc"
+checksum = "f22f29bdff3987b4d8632ef95fd6424ec7e4e0a57e2f4fc63e489e75357f6a03"
 dependencies = [
  "memchr",
 ]
@@ -2264,7 +2266,7 @@ dependencies = [
  "compact_str",
  "countme",
  "dir-test",
- "hashbrown 0.15.1",
+ "hashbrown 0.15.2",
  "indexmap",
  "insta",
  "itertools 0.13.0",
@@ -2370,7 +2372,7 @@ dependencies = [
  "glob",
  "insta",
  "notify",
- "pep440_rs 0.7.2",
+ "pep440_rs",
  "rayon",
  "red_knot_python_semantic",
  "red_knot_vendored",
@@ -2487,7 +2489,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.7.4"
+version = "0.8.1"
 dependencies = [
  "anyhow",
  "argfile",
@@ -2674,7 +2676,7 @@ dependencies = [
  "serde",
  "static_assertions",
  "tracing",
- "unicode-width 0.1.13",
+ "unicode-width 0.2.0",
 ]
 
 [[package]]
@@ -2706,7 +2708,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_linter"
-version = "0.7.4"
+version = "0.8.1"
 dependencies = [
  "aho-corasick",
  "annotate-snippets 0.9.2",
@@ -2729,7 +2731,7 @@ dependencies = [
  "natord",
  "path-absolutize",
  "pathdiff",
- "pep440_rs 0.7.2",
+ "pep440_rs",
  "pyproject-toml",
  "quick-junit",
  "regex",
@@ -2760,7 +2762,7 @@ dependencies = [
  "toml",
  "typed-arena",
  "unicode-normalization",
- "unicode-width 0.1.13",
+ "unicode-width 0.2.0",
  "unicode_names2",
  "url",
 ]
@@ -2773,7 +2775,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "ruff_python_trivia",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3021,7 +3023,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_wasm"
-version = "0.7.4"
+version = "0.8.1"
 dependencies = [
  "console_error_panic_hook",
  "console_log",
@@ -3060,7 +3062,7 @@ dependencies = [
  "matchit",
  "path-absolutize",
  "path-slash",
- "pep440_rs 0.7.2",
+ "pep440_rs",
  "regex",
  "ruff_cache",
  "ruff_formatter",
@@ -3070,6 +3072,7 @@ dependencies = [
  "ruff_python_ast",
  "ruff_python_formatter",
  "ruff_python_semantic",
+ "ruff_python_stdlib",
  "ruff_source_file",
  "rustc-hash 2.0.0",
  "schemars",
@@ -3192,7 +3195,7 @@ dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
  "synstructure",
 ]
 
@@ -3226,7 +3229,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "serde_derive_internals",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3249,9 +3252,9 @@ checksum = "1c107b6f4780854c8b126e228ea8869f4d7b71260f962fefb57b996b8959ba6b"
 
 [[package]]
 name = "serde"
-version = "1.0.214"
+version = "1.0.215"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f55c3193aca71c12ad7890f1785d2b73e1b9f63a0bbc353c08ef26fe03fc56b5"
+checksum = "6513c1ad0b11a9376da888e3e0baa0077f1aed55c17f50e7b2397136129fb88f"
 dependencies = [
  "serde_derive",
 ]
@@ -3269,13 +3272,13 @@ dependencies = [
 
 [[package]]
 name = "serde_derive"
-version = "1.0.214"
+version = "1.0.215"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "de523f781f095e28fa605cdce0f8307e451cc0fd14e2eb4cd2e98a355b147766"
+checksum = "ad1e866f866923f252f05c889987993144fb74e722403468a4ebd70c3cd756c0"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3286,14 +3289,14 @@ checksum = "330f01ce65a3a5fe59a60c82f3c9a024b573b8a6e875bd233fe5f934e71d54e3"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
 name = "serde_json"
-version = "1.0.132"
+version = "1.0.133"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d726bfaff4b320266d395898905d0eba0345aae23b54aee3a737e260fd46db03"
+checksum = "c7fceb2473b9166b2294ef05efcb65a3db80803f0b03ef86a5fc88a2b85ee377"
 dependencies = [
  "itoa",
  "memchr",
@@ -3309,7 +3312,7 @@ checksum = "6c64451ba24fc7a6a2d60fc75dd9c83c90903b19028d4eff35e88fc1e86564e9"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3350,7 +3353,7 @@ dependencies = [
  "darling",
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3458,7 +3461,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "rustversion",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3469,20 +3472,9 @@ checksum = "81cdd64d312baedb58e21336b31bc043b77e01cc99033ce76ef539f78e965ebc"
 
 [[package]]
 name = "syn"
-version = "1.0.109"
+version = "2.0.89"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "72b64191b275b66ffe2469e8af2c1cfe3bafa67b529ead792a6d0160888b4237"
-dependencies = [
- "proc-macro2",
- "quote",
- "unicode-ident",
-]
-
-[[package]]
-name = "syn"
-version = "2.0.87"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "25aa4ce346d03a6dcd68dd8b4010bcb74e54e62c90c573f394c46eae99aba32d"
+checksum = "44d46482f1c1c87acd84dea20c1bf5ebff4c757009ed6bf19cfd36fb10e92c4e"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3497,7 +3489,7 @@ checksum = "c8af7666ab7b6390ab78131fb5b0fce11d6b7a6951602017c35fa82800708971"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3560,7 +3552,7 @@ dependencies = [
  "cfg-if",
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3571,7 +3563,7 @@ checksum = "5c89e72a01ed4c579669add59014b9a524d609c0c88c6a585ce37485879f6ffb"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
  "test-case-core",
 ]
 
@@ -3601,7 +3593,7 @@ checksum = "b607164372e89797d78b8e23a6d67d5d1038c1c65efd52e1389ef8b77caba2a6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3612,7 +3604,7 @@ checksum = "f077553d607adc1caf65430528a576c757a71ed73944b66ebb58ef2bbd243568"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3734,7 +3726,7 @@ checksum = "34704c8d6ebcbc939824180af020566b01a7c01f80641264eba0999f6c2b6be7"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -3873,9 +3865,9 @@ dependencies = [
 
 [[package]]
 name = "unicode-ident"
-version = "1.0.13"
+version = "1.0.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e91b56cd4cadaeb79bbf1a5645f6b4f8dc5bde8834ad5894a8db35fda9efa1fe"
+checksum = "adb9e6ca4f869e1180728b7950e35922a7fc6397f7b641499e8f3ef06e50dc83"
 
 [[package]]
 name = "unicode-normalization"
@@ -3950,9 +3942,9 @@ dependencies = [
 
 [[package]]
 name = "url"
-version = "2.5.3"
+version = "2.5.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8d157f1b96d14500ffdc1f10ba712e780825526c03d9a49b4d0324b0d9113ada"
+checksum = "32f8b686cadd1473f4bd0117a5d28d36b1ade384ea9b5069a1c40aefed7fda60"
 dependencies = [
  "form_urlencoded",
  "idna",
@@ -3960,6 +3952,12 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "urlencoding"
+version = "2.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "daf8dba3b7eb870caf1ddeed7bc9d2a049f3cfdfae7cb521b087cc33ae4c49da"
+
 [[package]]
 name = "utf16_iter"
 version = "1.0.5"
@@ -3998,7 +3996,7 @@ checksum = "6b91f57fe13a38d0ce9e28a03463d8d3c2468ed03d75375110ec71d93b449a08"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -4007,6 +4005,15 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "830b7e5d4d90034032940e4ace0d9a9a057e7a45cd94e6c007832e39edb82f6d"
 
+[[package]]
+name = "version-ranges"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8d079415ceb2be83fc355adbadafe401307d5c309c7e6ade6638e6f9f42f42d"
+dependencies = [
+ "smallvec",
+]
+
 [[package]]
 name = "version_check"
 version = "0.9.4"
@@ -4084,7 +4091,7 @@ dependencies = [
  "once_cell",
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
  "wasm-bindgen-shared",
 ]
 
@@ -4118,7 +4125,7 @@ checksum = "26c6ab57572f7a24a4985830b120de1594465e5d500f24afe89e16b4e833ef68"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
  "wasm-bindgen-backend",
  "wasm-bindgen-shared",
 ]
@@ -4152,7 +4159,7 @@ checksum = "c97b2ef2c8d627381e51c071c2ab328eac606d3f69dd82bcbca20a9e389d95f0"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -4455,7 +4462,7 @@ checksum = "28cc31741b18cb6f1d5ff12f5b7523e3d6eb0852bbbad19d73905511d9849b95"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
  "synstructure",
 ]
 
@@ -4476,7 +4483,7 @@ checksum = "9ce1b18ccd8e73a9321186f97e46f9f04b778851177567b1975109d26a08d2a6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]
@@ -4496,7 +4503,7 @@ checksum = "0ea7b4a3637ea8669cedf0f1fd5c286a17f3de97b8dd5a70a6c167a1730e63a5"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
  "synstructure",
 ]
 
@@ -4525,7 +4532,7 @@ checksum = "6eafa6dfb17584ea3e2bd6e76e0cc15ad7af12b09abdd1ca55961bed9b1063c6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.87",
+ "syn",
 ]
 
 [[package]]

Cargo.toml

@@ -65,7 +65,7 @@ compact_str = "0.8.0"
 criterion = { version = "0.5.1", default-features = false }
 crossbeam = { version = "0.8.4" }
 dashmap = { version = "6.0.1" }
-dir-test = { version = "0.3.0" }
+dir-test = { version = "0.4.0" }
 dunce = { version = "1.0.5" }
 drop_bomb = { version = "0.1.5" }
 env_logger = { version = "0.11.0" }
@@ -111,7 +111,7 @@ pathdiff = { version = "0.2.1" }
 pep440_rs = { version = "0.7.1" }
 pretty_assertions = "1.3.0"
 proc-macro2 = { version = "1.0.79" }
-pyproject-toml = { version = "0.9.0" }
+pyproject-toml = { version = "0.13.4" }
 quick-junit = { version = "0.5.0" }
 quote = { version = "1.0.23" }
 rand = { version = "0.8.5" }
@@ -151,7 +151,7 @@ tracing-tree = { version = "0.4.0" }
 typed-arena = { version = "2.0.2" }
 unic-ucd-category = { version = "0.9" }
 unicode-ident = { version = "1.0.12" }
-unicode-width = { version = "0.1.11" }
+unicode-width = { version = "0.2.0" }
 unicode_names2 = { version = "1.2.2" }
 unicode-normalization = { version = "0.1.23" }
 ureq = { version = "2.9.6" }
@@ -248,10 +248,10 @@ debug = 1
 [profile.dist]
 inherits = "release"
 
-# Config for 'cargo dist'
+# Config for 'dist'
 [workspace.metadata.dist]
-# The preferred cargo-dist version to use in CI (Cargo.toml SemVer syntax)
-cargo-dist-version = "0.22.1"
+# The preferred dist version to use in CI (Cargo.toml SemVer syntax)
+cargo-dist-version = "0.25.2-prerelease.3"
 # CI backends to support
 ci = "github"
 # The installers to generate for each app
@@ -282,13 +282,13 @@ targets = [
 ]
 # Whether to auto-include files like READMEs, LICENSEs, and CHANGELOGs (default true)
 auto-includes = false
-# Whether cargo-dist should create a GitHub Release or use an existing draft
+# Whether dist should create a Github Release or use an existing draft
 create-release = true
 # Which actions to run on pull requests
 pr-run-mode = "skip"
 # Whether CI should trigger releases with dispatches instead of tag pushes
 dispatch-releases = true
-# Which phase cargo-dist should use to create the GitHub release
+# Which phase dist should use to create the GitHub release
 github-release = "announce"
 # Whether CI should include auto-generated code to build local artifacts
 build-local-artifacts = false
@@ -297,14 +297,10 @@ local-artifacts-jobs = ["./build-binaries", "./build-docker"]
 # Publish jobs to run in CI
 publish-jobs = ["./publish-pypi", "./publish-wasm"]
 # Post-announce jobs to run in CI
-post-announce-jobs = [
-    "./notify-dependents",
-    "./publish-docs",
-    "./publish-playground",
-]
+post-announce-jobs = ["./notify-dependents", "./publish-docs", "./publish-playground"]
 # Custom permissions for GitHub Jobs
 github-custom-job-permissions = { "build-docker" = { packages = "write", contents = "read" }, "publish-wasm" = { contents = "read", id-token = "write", packages = "write" } }
 # Whether to install an updater program
 install-updater = false
 # Path that installers should place binaries in
-install-path = "CARGO_HOME"
+install-path = ["$XDG_BIN_HOME/", "$XDG_DATA_HOME/../bin", "~/.local/bin"]

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/0.7.4/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.7.4/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.8.1/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.8.1/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: v0.7.4
+  rev: v0.8.1
   hooks:
     # Run the linter.
     - id: ruff
@@ -238,8 +238,8 @@ exclude = [
 line-length = 88
 indent-width = 4
 
-# Assume Python 3.8
-target-version = "py38"
+# Assume Python 3.9
+target-version = "py39"
 
 [lint]
 # Enable Pyflakes (`F`) and a subset of the pycodestyle (`E`)  codes by default.

clippy.toml

@@ -1,21 +1,25 @@
 doc-valid-idents = [
-  "..",
-  "CodeQL",
-  "FastAPI",
-  "IPython",
-  "LangChain",
-  "LibCST",
-  "McCabe",
-  "NumPy",
-  "SCREAMING_SNAKE_CASE",
-  "SQLAlchemy",
-  "StackOverflow",
-  "PyCharm",
+    "..",
+    "CodeQL",
+    "FastAPI",
+    "IPython",
+    "LangChain",
+    "LibCST",
+    "McCabe",
+    "NumPy",
+    "SCREAMING_SNAKE_CASE",
+    "SQLAlchemy",
+    "StackOverflow",
+    "PyCharm",
+    "SNMPv1",
+    "SNMPv2",
+    "SNMPv3",
+    "PyFlakes"
 ]
 
 ignore-interior-mutability = [
-  # Interned is read-only. The wrapped `Rc` never gets updated.
-  "ruff_formatter::format_element::Interned",
-  # The expression is read-only.
-  "ruff_python_ast::hashable::HashableExpr",
+    # Interned is read-only. The wrapped `Rc` never gets updated.
+    "ruff_formatter::format_element::Interned",
+    # The expression is read-only.
+    "ruff_python_ast::hashable::HashableExpr",
 ]

crates/red_knot/src/target_version.rs

@@ -4,8 +4,8 @@
 #[derive(Copy, Clone, Hash, Debug, PartialEq, Eq, PartialOrd, Ord, Default, clap::ValueEnum)]
 pub enum TargetVersion {
     Py37,
-    #[default]
     Py38,
+    #[default]
     Py39,
     Py310,
     Py311,
@@ -46,3 +46,17 @@ impl From<TargetVersion> for red_knot_python_semantic::PythonVersion {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::target_version::TargetVersion;
+    use red_knot_python_semantic::PythonVersion;
+
+    #[test]
+    fn same_default_as_python_version() {
+        assert_eq!(
+            PythonVersion::from(TargetVersion::default()),
+            PythonVersion::default()
+        );
+    }
+}

crates/red_knot/tests/file_watching.rs

@@ -4,7 +4,6 @@ use std::io::Write;
 use std::time::Duration;
 
 use anyhow::{anyhow, Context};
-
 use red_knot_python_semantic::{resolve_module, ModuleName, Program, PythonVersion, SitePackages};
 use red_knot_workspace::db::{Db, RootDatabase};
 use red_knot_workspace::watch;
@@ -14,7 +13,7 @@ use red_knot_workspace::workspace::WorkspaceMetadata;
 use ruff_db::files::{system_path_to_file, File, FileError};
 use ruff_db::source::source_text;
 use ruff_db::system::{OsSystem, SystemPath, SystemPathBuf};
-use ruff_db::testing::setup_logging;
+use ruff_db::testing::{setup_logging, setup_logging_with_filter};
 use ruff_db::Upcast;
 
 struct TestCase {
@@ -47,6 +46,8 @@ impl TestCase {
     }
 
     fn try_stop_watch(&mut self, timeout: Duration) -> Option<Vec<watch::ChangeEvent>> {
+        tracing::debug!("Try stopping watch with timeout {:?}", timeout);
+
         let watcher = self
             .watcher
             .take()
@@ -56,8 +57,11 @@ impl TestCase {
             .changes_receiver
             .recv_timeout(timeout)
             .unwrap_or_default();
+
         watcher.flush();
+        tracing::debug!("Flushed file watcher");
         watcher.stop();
+        tracing::debug!("Stopping file watcher");
 
         for event in &self.changes_receiver {
             all_events.extend(event);
@@ -600,6 +604,8 @@ fn directory_moved_to_trash() -> anyhow::Result<()> {
 
 #[test]
 fn directory_renamed() -> anyhow::Result<()> {
+    let _tracing = setup_logging_with_filter("file_watching=TRACE,red_knot=TRACE");
+
     let mut case = setup([
         ("bar.py", "import sub.a"),
         ("sub/__init__.py", ""),
@@ -640,6 +646,10 @@ fn directory_renamed() -> anyhow::Result<()> {
 
     let changes = case.stop_watch();
 
+    for event in &changes {
+        tracing::debug!("Event: {:?}", event);
+    }
+
     case.apply_changes(changes);
 
     // `import sub.a` should no longer resolve

crates/red_knot_python_semantic/resources/mdtest/annotations/never.md

@@ -0,0 +1,62 @@
+# NoReturn & Never
+
+`NoReturn` is used to annotate the return type for functions that never return. `Never` is the
+bottom type, representing the empty set of Python objects. These two annotations can be used
+interchangeably.
+
+## Function Return Type Annotation
+
+```py
+from typing import NoReturn
+
+def stop() -> NoReturn:
+    raise RuntimeError("no way")
+
+# revealed: Never
+reveal_type(stop())
+```
+
+## Assignment
+
+```py
+from typing import NoReturn, Never, Any
+
+# error: [invalid-type-parameter] "Type `typing.Never` expected no type parameter"
+x: Never[int]
+a1: NoReturn
+# TODO: Test `Never` is only available in python >= 3.11
+a2: Never
+b1: Any
+b2: int
+
+def f():
+    # revealed: Never
+    reveal_type(a1)
+    # revealed: Never
+    reveal_type(a2)
+
+    # Never is assignable to all types.
+    v1: int = a1
+    v2: str = a1
+    # Other types are not assignable to Never except for Never (and Any).
+    v3: Never = b1
+    v4: Never = a2
+    v5: Any = b2
+    # error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to `Never`"
+    v6: Never = 1
+```
+
+## Typing Extensions
+
+```py
+from typing_extensions import NoReturn, Never
+
+x: NoReturn
+y: Never
+
+def f():
+    # revealed: Never
+    reveal_type(x)
+    # revealed: Never
+    reveal_type(y)
+```

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

@@ -0,0 +1,47 @@
+# Optional
+
+## Annotation
+
+`typing.Optional` is equivalent to using the type with a None in a Union.
+
+```py
+from typing import Optional
+
+a: Optional[int]
+a1: Optional[bool]
+a2: Optional[Optional[bool]]
+a3: Optional[None]
+
+def f():
+    # revealed: int | None
+    reveal_type(a)
+    # revealed: bool | None
+    reveal_type(a1)
+    # revealed: bool | None
+    reveal_type(a2)
+    # revealed: None
+    reveal_type(a3)
+```
+
+## Assignment
+
+```py
+from typing import Optional
+
+a: Optional[int] = 1
+a = None
+# error: [invalid-assignment] "Object of type `Literal[""]` is not assignable to `int | None`"
+a = ""
+```
+
+## Typing Extensions
+
+```py
+from typing_extensions import Optional
+
+a: Optional[int]
+
+def f():
+    # revealed: int | None
+    reveal_type(a)
+```

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

@@ -9,10 +9,10 @@ Ts = TypeVarTuple("Ts")
 
 def append_int(*args: *Ts) -> tuple[*Ts, int]:
     # TODO: should show some representation of the variadic generic type
-    reveal_type(args)  # revealed: @Todo
+    reveal_type(args)  # revealed: @Todo(function parameter type)
 
     return (*args, 1)
 
 # TODO should be tuple[Literal[True], Literal["a"], int]
-reveal_type(append_int(True, "a"))  # revealed: @Todo
+reveal_type(append_int(True, "a"))  # revealed: @Todo(full tuple[...] support)
 ```

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

@@ -189,3 +189,31 @@ reveal_type(d)  # revealed: Foo
 ## Parameter
 
 TODO: Add tests once parameter inference is supported
+
+## Invalid expressions
+
+The expressions in these string annotations aren't valid expressions in this context but we
+shouldn't panic.
+
+```py
+a: "1 or 2"
+b: "(x := 1)"
+c: "1 + 2"
+d: "lambda x: x"
+e: "x if True else y"
+f: "{'a': 1, 'b': 2}"
+g: "{1, 2}"
+h: "[i for i in range(5)]"
+i: "{i for i in range(5)}"
+j: "{i: i for i in range(5)}"
+k: "(i for i in range(5))"
+l: "await 1"
+# error: [forward-annotation-syntax-error]
+m: "yield 1"
+# error: [forward-annotation-syntax-error]
+n: "yield from 1"
+o: "1 < 2"
+p: "call()"
+r: "[1, 2]"
+s: "(1, 2)"
+```

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

@@ -0,0 +1,61 @@
+# Union
+
+## Annotation
+
+`typing.Union` can be used to construct union types same as `|` operator.
+
+```py
+from typing import Union
+
+a: Union[int, str]
+a1: Union[int, bool]
+a2: Union[int, Union[float, str]]
+a3: Union[int, None]
+a4: Union[Union[float, str]]
+a5: Union[int]
+a6: Union[()]
+
+def f():
+    # revealed: int | str
+    reveal_type(a)
+    # Since bool is a subtype of int we simplify to int here. But we do allow assigning boolean values (see below).
+    # revealed: int
+    reveal_type(a1)
+    # revealed: int | float | str
+    reveal_type(a2)
+    # revealed: int | None
+    reveal_type(a3)
+    # revealed: float | str
+    reveal_type(a4)
+    # revealed: int
+    reveal_type(a5)
+    # revealed: Never
+    reveal_type(a6)
+```
+
+## Assignment
+
+```py
+from typing import Union
+
+a: Union[int, str]
+a = 1
+a = ""
+a1: Union[int, bool]
+a1 = 1
+a1 = True
+# error: [invalid-assignment] "Object of type `Literal[b""]` is not assignable to `int | str`"
+a = b""
+```
+
+## Typing Extensions
+
+```py
+from typing_extensions import Union
+
+a: Union[int, str]
+
+def f():
+    # revealed: int | str
+    reveal_type(a)
+```

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

@@ -51,12 +51,12 @@ reveal_type(c)  # revealed: tuple[str, int]
 reveal_type(d)  # revealed: tuple[tuple[str, str], tuple[int, int]]
 
 # TODO: homogenous tuples, PEP-646 tuples
-reveal_type(e)  # revealed: @Todo
-reveal_type(f)  # revealed: @Todo
-reveal_type(g)  # revealed: @Todo
+reveal_type(e)  # revealed: @Todo(full tuple[...] support)
+reveal_type(f)  # revealed: @Todo(full tuple[...] support)
+reveal_type(g)  # revealed: @Todo(full tuple[...] support)
 
 # TODO: support more kinds of type expressions in annotations
-reveal_type(h)  # revealed: @Todo
+reveal_type(h)  # revealed: @Todo(full tuple[...] support)
 
 reveal_type(i)  # revealed: tuple[str | int, str | int]
 reveal_type(j)  # revealed: tuple[str | int]

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

@@ -317,7 +317,7 @@ reveal_type(1 + A())  # revealed: int
 reveal_type(A() + "foo")  # revealed: A
 # TODO should be `A` since `str.__add__` doesn't support `A` instances
 # TODO overloads
-reveal_type("foo" + A())  # revealed: @Todo
+reveal_type("foo" + A())  # revealed: @Todo(return type)
 
 reveal_type(A() + b"foo")  # revealed: A
 # TODO should be `A` since `bytes.__add__` doesn't support `A` instances
@@ -325,7 +325,7 @@ reveal_type(b"foo" + A())  # revealed: bytes
 
 reveal_type(A() + ())  # revealed: A
 # TODO this should be `A`, since `tuple.__add__` doesn't support `A` instances
-reveal_type(() + A())  # revealed: @Todo
+reveal_type(() + A())  # revealed: @Todo(return type)
 
 literal_string_instance = "foo" * 1_000_000_000
 # the test is not testing what it's meant to be testing if this isn't a `LiteralString`:
@@ -334,7 +334,7 @@ reveal_type(literal_string_instance)  # revealed: LiteralString
 reveal_type(A() + literal_string_instance)  # revealed: A
 # TODO should be `A` since `str.__add__` doesn't support `A` instances
 # TODO overloads
-reveal_type(literal_string_instance + A())  # revealed: @Todo
+reveal_type(literal_string_instance + A())  # revealed: @Todo(return type)
 ```
 
 ## Operations involving instances of classes inheriting from `Any`

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

@@ -16,7 +16,7 @@ async def get_int_async() -> int:
     return 42
 
 # TODO: we don't yet support `types.CoroutineType`, should be generic `Coroutine[Any, Any, int]`
-reveal_type(get_int_async())  # revealed: @Todo
+reveal_type(get_int_async())  # revealed: @Todo(generic types.CoroutineType)
 ```
 
 ## Generic
@@ -44,7 +44,7 @@ def bar() -> str:
     return "bar"
 
 # TODO: should reveal `int`, as the decorator replaces `bar` with `foo`
-reveal_type(bar())  # revealed: @Todo
+reveal_type(bar())  # revealed: @Todo(return type)
 ```
 
 ## Invalid callable

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

@@ -58,7 +58,9 @@ reveal_type(c >= d)  # revealed: Literal[True]
 #### Results with Ambiguity
 
 ```py
-def bool_instance() -> bool: ...
+def bool_instance() -> bool:
+    return True
+
 def int_instance() -> int:
     return 42
 
@@ -134,23 +136,158 @@ reveal_type(c >= c)  # revealed: Literal[True]
 
 #### Non Boolean Rich Comparisons
 
+Rich comparison methods defined in a class affect tuple comparisons as well. Proper type inference
+should be possible even in cases where these methods return non-boolean types.
+
+Note: Tuples use lexicographic comparisons. If the `==` result for all paired elements in the tuple
+is True, the comparison then considers the tuple’s length. Regardless of the return type of the
+dunder methods, the final result can still be a boolean value.
+
+(+cpython: For tuples, `==` and `!=` always produce boolean results, regardless of the return type
+of the dunder methods.)
+
 ```py
+from __future__ import annotations
+
 class A:
-    def __eq__(self, o) -> str: ...
-    def __ne__(self, o) -> int: ...
-    def __lt__(self, o) -> float: ...
-    def __le__(self, o) -> object: ...
-    def __gt__(self, o) -> tuple: ...
-    def __ge__(self, o) -> list: ...
+    def __eq__(self, o: object) -> str:
+        return "hello"
+
+    def __ne__(self, o: object) -> bytes:
+        return b"world"
+
+    def __lt__(self, o: A) -> float:
+        return 3.14
+
+    def __le__(self, o: A) -> complex:
+        return complex(0.5, -0.5)
+
+    def __gt__(self, o: A) -> tuple:
+        return (1, 2, 3)
+
+    def __ge__(self, o: A) -> list:
+        return [1, 2, 3]
 
 a = (A(), A())
 
+reveal_type(a == a)  # revealed: bool
+reveal_type(a != a)  # revealed: bool
+reveal_type(a < a)  # revealed: float | Literal[False]
+reveal_type(a <= a)  # revealed: complex | Literal[True]
+reveal_type(a > a)  # revealed: tuple | Literal[False]
+reveal_type(a >= a)  # revealed: list | Literal[True]
+
+# If lexicographic comparison is finished before comparing A()
+b = ("1_foo", A())
+c = ("2_bar", A())
+
+reveal_type(b == c)  # revealed: Literal[False]
+reveal_type(b != c)  # revealed: Literal[True]
+reveal_type(b < c)  # revealed: Literal[True]
+reveal_type(b <= c)  # revealed: Literal[True]
+reveal_type(b > c)  # revealed: Literal[False]
+reveal_type(b >= c)  # revealed: Literal[False]
+
+class B:
+    def __lt__(self, o: B) -> set:
+        return set()
+
+reveal_type((A(), B()) < (A(), B()))  # revealed: float | set | Literal[False]
+```
+
+#### Special Handling of Eq and NotEq in Lexicographic Comparisons
+
+> Example: `(int_instance(), "foo") == (int_instance(), "bar")`
+
+`Eq` and `NotEq` have unique behavior compared to other operators in lexicographic comparisons.
+Specifically, for `Eq`, if any non-equal pair exists within the tuples being compared, we can
+immediately conclude that the tuples are not equal. Conversely, for `NotEq`, if any non-equal pair
+exists, we can determine that the tuples are unequal.
+
+In contrast, with operators like `<` and `>`, the comparison must consider each pair of elements
+sequentially, and the final outcome might remain ambiguous until all pairs are compared.
+
+```py
+def str_instance() -> str:
+    return "hello"
+
+def int_instance() -> int:
+    return 42
+
+reveal_type("foo" == "bar")  # revealed: Literal[False]
+reveal_type(("foo",) == ("bar",))  # revealed: Literal[False]
+reveal_type((4, "foo") == (4, "bar"))  # revealed: Literal[False]
+reveal_type((int_instance(), "foo") == (int_instance(), "bar"))  # revealed: Literal[False]
+
+a = (str_instance(), int_instance(), "foo")
+
 reveal_type(a == a)  # revealed: bool
 reveal_type(a != a)  # revealed: bool
 reveal_type(a < a)  # revealed: bool
 reveal_type(a <= a)  # revealed: bool
 reveal_type(a > a)  # revealed: bool
 reveal_type(a >= a)  # revealed: bool
+
+b = (str_instance(), int_instance(), "bar")
+
+reveal_type(a == b)  # revealed: Literal[False]
+reveal_type(a != b)  # revealed: Literal[True]
+reveal_type(a < b)  # revealed: bool
+reveal_type(a <= b)  # revealed: bool
+reveal_type(a > b)  # revealed: bool
+reveal_type(a >= b)  # revealed: bool
+
+c = (str_instance(), int_instance(), "foo", "different_length")
+reveal_type(a == c)  # revealed: Literal[False]
+reveal_type(a != c)  # revealed: Literal[True]
+reveal_type(a < c)  # revealed: bool
+reveal_type(a <= c)  # revealed: bool
+reveal_type(a > c)  # revealed: bool
+reveal_type(a >= c)  # revealed: bool
+```
+
+#### Error Propagation
+
+Errors occurring within a tuple comparison should propagate outward. However, if the tuple
+comparison can clearly conclude before encountering an error, the error should not be raised.
+
+```py
+def int_instance() -> int:
+    return 42
+
+def str_instance() -> str:
+    return "hello"
+
+class A: ...
+
+# error: [unsupported-operator] "Operator `<` is not supported for types `A` and `A`"
+A() < A()
+# error: [unsupported-operator] "Operator `<=` is not supported for types `A` and `A`"
+A() <= A()
+# error: [unsupported-operator] "Operator `>` is not supported for types `A` and `A`"
+A() > A()
+# error: [unsupported-operator] "Operator `>=` is not supported for types `A` and `A`"
+A() >= A()
+
+a = (0, int_instance(), A())
+
+# error: [unsupported-operator] "Operator `<` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
+reveal_type(a < a)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `<=` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
+reveal_type(a <= a)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `>` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
+reveal_type(a > a)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `>=` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
+reveal_type(a >= a)  # revealed: Unknown
+
+# Comparison between `a` and `b` should only involve the first elements, `Literal[0]` and `Literal[99999]`,
+# and should terminate immediately.
+b = (99999, int_instance(), A())
+
+reveal_type(a < b)  # revealed: Literal[True]
+reveal_type(a <= b)  # revealed: Literal[True]
+reveal_type(a > b)  # revealed: Literal[False]
+reveal_type(a >= b)  # revealed: Literal[False]
 ```
 
 ### Membership Test Comparisons

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

@@ -4,6 +4,8 @@
 def bool_instance() -> bool:
     return True
 
+class A: ...
+
 a = 1 in 7  # error: "Operator `in` is not supported for types `Literal[1]` and `Literal[7]`"
 reveal_type(a)  # revealed: bool
 
@@ -33,4 +35,8 @@ reveal_type(e)  # revealed: bool
 f = (1, 2) < (1, "hello")
 # TODO: should be Unknown, once operand type check is implemented
 reveal_type(f)  # revealed: bool
+
+# error: [unsupported-operator] "Operator `<` is not supported for types `A` and `A`, in comparing `tuple[bool, A]` with `tuple[bool, A]`"
+g = (bool_instance(), A()) < (bool_instance(), A())
+reveal_type(g)  # revealed: Unknown
 ```

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

@@ -50,11 +50,11 @@ def foo(
         help()
     except x as e:
         # TODO: should be `AttributeError`
-        reveal_type(e)  # revealed: @Todo
+        reveal_type(e)  # revealed: @Todo(exception type)
     except y as f:
         # TODO: should be `OSError | RuntimeError`
-        reveal_type(f)  # revealed: @Todo
+        reveal_type(f)  # revealed: @Todo(exception type)
     except z as g:
         # TODO: should be `BaseException`
-        reveal_type(g)  # revealed: @Todo
+        reveal_type(g)  # revealed: @Todo(exception type)
 ```

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

@@ -22,3 +22,22 @@ reveal_type(1 if None else 2)  # revealed: Literal[2]
 reveal_type(1 if "" else 2)  # revealed: Literal[2]
 reveal_type(1 if 0 else 2)  # revealed: Literal[2]
 ```
+
+## Leaked Narrowing Constraint
+
+(issue #14588)
+
+The test inside an if expression should not affect code outside of the expression.
+
+```py
+def bool_instance() -> bool:
+    return True
+
+x: Literal[42, "hello"] = 42 if bool_instance() else "hello"
+
+reveal_type(x)  # revealed: Literal[42] | Literal["hello"]
+
+_ = ... if isinstance(x, str) else ...
+
+reveal_type(x)  # revealed: Literal[42] | Literal["hello"]
+```

crates/red_knot_python_semantic/resources/mdtest/generics.md

@@ -18,7 +18,7 @@ box: MyBox[int] = MyBox(5)
 wrong_innards: MyBox[int] = MyBox("five")
 
 # TODO reveal int
-reveal_type(box.data)  # revealed: @Todo
+reveal_type(box.data)  # revealed: @Todo(instance attributes)
 
 reveal_type(MyBox.box_model_number)  # revealed: Literal[695]
 ```
@@ -39,7 +39,7 @@ class MySecureBox[T](MyBox[T]): ...
 secure_box: MySecureBox[int] = MySecureBox(5)
 reveal_type(secure_box)  # revealed: MySecureBox
 # TODO reveal int
-reveal_type(secure_box.data)  # revealed: @Todo
+reveal_type(secure_box.data)  # revealed: @Todo(instance attributes)
 ```
 
 ## Cyclical class definition
@@ -60,52 +60,20 @@ reveal_type(S)  # revealed: Literal[S]
 
 ## Type params
 
-A PEP695 type variable defines a value of type `typing.TypeVar` with attributes `__name__`,
-`__bounds__`, `__constraints__`, and `__default__` (the latter three all lazily evaluated):
+A PEP695 type variable defines a value of type `typing.TypeVar`.
 
 ```py
-def f[T, U: A, V: (A, B), W = A, X: A = A1]():
+def f[T]():
     reveal_type(T)  # revealed: T
     reveal_type(T.__name__)  # revealed: Literal["T"]
-    reveal_type(T.__bound__)  # revealed: None
-    reveal_type(T.__constraints__)  # revealed: tuple[()]
-    reveal_type(T.__default__)  # revealed: NoDefault
-
-    reveal_type(U)  # revealed: U
-    reveal_type(U.__name__)  # revealed: Literal["U"]
-    reveal_type(U.__bound__)  # revealed: type[A]
-    reveal_type(U.__constraints__)  # revealed: tuple[()]
-    reveal_type(U.__default__)  # revealed: NoDefault
-
-    reveal_type(V)  # revealed: V
-    reveal_type(V.__name__)  # revealed: Literal["V"]
-    reveal_type(V.__bound__)  # revealed: None
-    reveal_type(V.__constraints__)  # revealed: tuple[type[A], type[B]]
-    reveal_type(V.__default__)  # revealed: NoDefault
-
-    reveal_type(W)  # revealed: W
-    reveal_type(W.__name__)  # revealed: Literal["W"]
-    reveal_type(W.__bound__)  # revealed: None
-    reveal_type(W.__constraints__)  # revealed: tuple[()]
-    reveal_type(W.__default__)  # revealed: type[A]
-
-    reveal_type(X)  # revealed: X
-    reveal_type(X.__name__)  # revealed: Literal["X"]
-    reveal_type(X.__bound__)  # revealed: type[A]
-    reveal_type(X.__constraints__)  # revealed: tuple[()]
-    reveal_type(X.__default__)  # revealed: type[A1]
-
-class A: ...
-class B: ...
-class A1(A): ...
 ```
 
 ## Minimum two constraints
 
-A typevar with less than two constraints emits a diagnostic and is treated as unconstrained:
+A typevar with less than two constraints emits a diagnostic:
 
 ```py
 # error: [invalid-typevar-constraints] "TypeVar must have at least two constrained types"
 def f[T: (int,)]():
-    reveal_type(T.__constraints__)  # revealed: tuple[()]
+    pass
 ```

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

@@ -51,6 +51,8 @@ invalid1: Literal[3 + 4]
 invalid2: Literal[4 + 3j]
 # error: [invalid-literal-parameter]
 invalid3: Literal[(3, 4)]
+
+hello = "hello"
 invalid4: Literal[
     1 + 2,  # error: [invalid-literal-parameter]
     "foo",
@@ -76,7 +78,7 @@ from other import Literal
 a1: Literal[26]
 
 def f():
-    reveal_type(a1)  # revealed: @Todo
+    reveal_type(a1)  # revealed: @Todo(generics)
 ```
 
 ## Detecting typing_extensions.Literal

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

@@ -18,7 +18,7 @@ async def foo():
         pass
 
     # TODO: should reveal `Unknown` because `__aiter__` is not defined
-    # revealed: @Todo
+    # revealed: @Todo(async iterables/iterators)
     # error: [possibly-unresolved-reference]
     reveal_type(x)
 ```
@@ -40,6 +40,6 @@ async def foo():
         pass
 
     # error: [possibly-unresolved-reference]
-    # revealed: @Todo
+    # revealed: @Todo(async iterables/iterators)
     reveal_type(x)
 ```

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

@@ -52,3 +52,29 @@ else:
 reveal_type(x)  # revealed: Literal[2, 3]
 reveal_type(y)  # revealed: Literal[1, 2, 4]
 ```
+
+## Nested while loops
+
+```py
+def flag() -> bool:
+    return True
+
+x = 1
+
+while flag():
+    x = 2
+
+    while flag():
+        x = 3
+        if flag():
+            break
+    else:
+        x = 4
+
+    if flag():
+        break
+else:
+    x = 5
+
+reveal_type(x)  # revealed: Literal[3, 4, 5]
+```

crates/red_knot_python_semantic/resources/mdtest/metaclass.md

@@ -171,7 +171,7 @@ def f(*args, **kwargs) -> int: ...
 class A(metaclass=f): ...
 
 # TODO should be `type[int]`
-reveal_type(A.__class__)  # revealed: @Todo
+reveal_type(A.__class__)  # revealed: @Todo(metaclass not a class)
 ```
 
 ## Cyclic

crates/red_knot_python_semantic/resources/mdtest/mro.md

@@ -256,7 +256,7 @@ class O: ...
 class X(O): ...
 class Y(O): ...
 
-if bool():
+if returns_bool():
     foo = Y
 else:
     foo = object

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

@@ -0,0 +1,64 @@
+# Consolidating narrowed types after if statement
+
+## After if-else statements, narrowing has no effect if the variable is not mutated in any branch
+
+```py
+def optional_int() -> int | None: ...
+
+x = optional_int()
+
+if x is None:
+    pass
+else:
+    pass
+
+reveal_type(x)  # revealed: int | None
+```
+
+## Narrowing can have a persistent effect if the variable is mutated in one branch
+
+```py
+def optional_int() -> int | None: ...
+
+x = optional_int()
+
+if x is None:
+    x = 10
+else:
+    pass
+
+reveal_type(x)  # revealed: int
+```
+
+## An if statement without an explicit `else` branch is equivalent to one with a no-op `else` branch
+
+```py
+def optional_int() -> int | None: ...
+
+x = optional_int()
+y = optional_int()
+
+if x is None:
+    x = 0
+
+if y is None:
+    pass
+
+reveal_type(x)  # revealed: int
+reveal_type(y)  # revealed: int | None
+```
+
+## An if-elif without an explicit else branch is equivalent to one with an empty else branch
+
+```py
+def optional_int() -> int | None: ...
+
+x = optional_int()
+
+if x is None:
+    x = 0
+elif x > 50:
+    x = 50
+
+reveal_type(x)  # revealed: int
+```

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

@@ -0,0 +1,152 @@
+# Narrowing for checks involving `type(x)`
+
+## `type(x) is C`
+
+```py
+class A: ...
+class B: ...
+
+def get_a_or_b() -> A | B:
+    return A()
+
+x = get_a_or_b()
+
+if type(x) is A:
+    reveal_type(x)  # revealed: A
+else:
+    # It would be wrong to infer `B` here. The type
+    # of `x` could be a subclass of `A`, so we need
+    # to infer the full union type:
+    reveal_type(x)  # revealed: A | B
+```
+
+## `type(x) is not C`
+
+```py
+class A: ...
+class B: ...
+
+def get_a_or_b() -> A | B:
+    return A()
+
+x = get_a_or_b()
+
+if type(x) is not A:
+    # Same reasoning as above: no narrowing should occur here.
+    reveal_type(x)  # revealed: A | B
+else:
+    reveal_type(x)  # revealed: A
+```
+
+## `type(x) == C`, `type(x) != C`
+
+No narrowing can occur for equality comparisons, since there might be a custom `__eq__`
+implementation on the metaclass.
+
+TODO: Narrowing might be possible in some cases where the classes themselves are `@final` or their
+metaclass is `@final`.
+
+```py
+class IsEqualToEverything(type):
+    def __eq__(cls, other):
+        return True
+
+class A(metaclass=IsEqualToEverything): ...
+class B(metaclass=IsEqualToEverything): ...
+
+def get_a_or_b() -> A | B:
+    return B()
+
+x = get_a_or_b()
+
+if type(x) == A:
+    reveal_type(x)  # revealed: A | B
+
+if type(x) != A:
+    reveal_type(x)  # revealed: A | B
+```
+
+## No narrowing for custom `type` callable
+
+```py
+class A: ...
+class B: ...
+
+def type(x):
+    return int
+
+def get_a_or_b() -> A | B:
+    return A()
+
+x = get_a_or_b()
+
+if type(x) is A:
+    reveal_type(x)  # revealed: A | B
+else:
+    reveal_type(x)  # revealed: A | B
+```
+
+## No narrowing for multiple arguments
+
+No narrowing should occur if `type` is used to dynamically create a class:
+
+```py
+def get_str_or_int() -> str | int:
+    return "test"
+
+x = get_str_or_int()
+
+if type(x, (), {}) is str:
+    reveal_type(x)  # revealed: str | int
+else:
+    reveal_type(x)  # revealed: str | int
+```
+
+## No narrowing for keyword arguments
+
+`type` can't be used with a keyword argument:
+
+```py
+def get_str_or_int() -> str | int:
+    return "test"
+
+x = get_str_or_int()
+
+# TODO: we could issue a diagnostic here
+if type(object=x) is str:
+    reveal_type(x)  # revealed: str | int
+```
+
+## Narrowing if `type` is aliased
+
+```py
+class A: ...
+class B: ...
+
+alias_for_type = type
+
+def get_a_or_b() -> A | B:
+    return A()
+
+x = get_a_or_b()
+
+if alias_for_type(x) is A:
+    reveal_type(x)  # revealed: A
+```
+
+## Limitations
+
+```py
+class Base: ...
+class Derived(Base): ...
+
+def get_base() -> Base:
+    return Base()
+
+x = get_base()
+
+if type(x) is Base:
+    # Ideally, this could be narrower, but there is now way to
+    # express a constraint like `Base & ~ProperSubtypeOf[Base]`.
+    reveal_type(x)  # revealed: Base
+```

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

@@ -17,8 +17,7 @@ reveal_type(__doc__)  # revealed: str | None
 # (needs support for `*` imports)
 reveal_type(__spec__)  # revealed: Unknown | None
 
-# TODO: generics
-reveal_type(__path__)  # revealed: @Todo
+reveal_type(__path__)  # revealed: @Todo(generics)
 
 class X:
     reveal_type(__name__)  # revealed: str
@@ -64,7 +63,7 @@ reveal_type(typing.__class__)  # revealed: Literal[type]
 
 # TODO: needs support for attribute access on instances, properties and generics;
 # should be `dict[str, Any]`
-reveal_type(typing.__dict__)  # revealed: @Todo
+reveal_type(typing.__dict__)  # revealed: @Todo(instance attributes)
 ```
 
 Typeshed includes a fake `__getattr__` method in the stub for `types.ModuleType` to help out with
@@ -96,8 +95,8 @@ from foo import __dict__ as foo_dict
 
 # TODO: needs support for attribute access on instances, properties, and generics;
 # should be `dict[str, Any]` for both of these:
-reveal_type(foo.__dict__)  # revealed: @Todo
-reveal_type(foo_dict)  # revealed: @Todo
+reveal_type(foo.__dict__)  # revealed: @Todo(instance attributes)
+reveal_type(foo_dict)  # revealed: @Todo(instance attributes)
 ```
 
 ## Conditionally global or `ModuleType` attribute

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

@@ -27,7 +27,7 @@ def int_instance() -> int:
 
 a = b"abcde"[int_instance()]
 # TODO: Support overloads... Should be `bytes`
-reveal_type(a)  # revealed: @Todo
+reveal_type(a)  # revealed: @Todo(return type)
 ```
 
 ## Slices
@@ -47,11 +47,11 @@ def int_instance() -> int: ...
 
 byte_slice1 = b[int_instance() : int_instance()]
 # TODO: Support overloads... Should be `bytes`
-reveal_type(byte_slice1)  # revealed: @Todo
+reveal_type(byte_slice1)  # revealed: @Todo(return type)
 
 def bytes_instance() -> bytes: ...
 
 byte_slice2 = bytes_instance()[0:5]
 # TODO: Support overloads... Should be `bytes`
-reveal_type(byte_slice2)  # revealed: @Todo
+reveal_type(byte_slice2)  # revealed: @Todo(return type)
 ```

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

@@ -21,10 +21,11 @@ reveal_type(Identity[0])  # revealed: str
 ## Class getitem union
 
 ```py
-flag = True
+def bool_instance() -> bool:
+    return True
 
 class UnionClassGetItem:
-    if flag:
+    if bool_instance():
 
         def __class_getitem__(cls, item: int) -> str:
             return item
@@ -59,9 +60,10 @@ reveal_type(x[0])  # revealed: str | int
 ## Class getitem with unbound method union
 
 ```py
-flag = True
+def bool_instance() -> bool:
+    return True
 
-if flag:
+if bool_instance():
     class Spam:
         def __class_getitem__(self, x: int) -> str:
             return "foo"
@@ -77,9 +79,10 @@ reveal_type(Spam[42])
 ## TODO: Class getitem non-class union
 
 ```py
-flag = True
+def bool_instance() -> bool:
+    return True
 
-if flag:
+if bool_instance():
     class Eggs:
         def __class_getitem__(self, x: int) -> str:
             return "foo"

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

@@ -30,10 +30,11 @@ reveal_type(Identity()[0])  # revealed: int
 ## Getitem union
 
 ```py
-flag = True
+def bool_instance() -> bool:
+    return True
 
 class Identity:
-    if flag:
+    if bool_instance():
 
         def __getitem__(self, index: int) -> int:
             return index

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

@@ -12,13 +12,13 @@ x = [1, 2, 3]
 reveal_type(x)  # revealed: list
 
 # TODO reveal int
-reveal_type(x[0])  # revealed: @Todo
+reveal_type(x[0])  # revealed: @Todo(return type)
 
 # TODO reveal list
-reveal_type(x[0:1])  # revealed: @Todo
+reveal_type(x[0:1])  # revealed: @Todo(return type)
 
 # TODO error
-reveal_type(x["a"])  # revealed: @Todo
+reveal_type(x["a"])  # revealed: @Todo(return type)
 ```
 
 ## Assignments within list assignment

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

@@ -23,7 +23,7 @@ def int_instance() -> int: ...
 
 a = "abcde"[int_instance()]
 # TODO: Support overloads... Should be `str`
-reveal_type(a)  # revealed: @Todo
+reveal_type(a)  # revealed: @Todo(return type)
 ```
 
 ## Slices
@@ -78,13 +78,13 @@ def int_instance() -> int: ...
 
 substring1 = s[int_instance() : int_instance()]
 # TODO: Support overloads... Should be `LiteralString`
-reveal_type(substring1)  # revealed: @Todo
+reveal_type(substring1)  # revealed: @Todo(return type)
 
 def str_instance() -> str: ...
 
 substring2 = str_instance()[0:5]
 # TODO: Support overloads... Should be `str`
-reveal_type(substring2)  # revealed: @Todo
+reveal_type(substring2)  # revealed: @Todo(return type)
 ```
 
 ## Unsupported slice types

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

@@ -71,5 +71,5 @@ def int_instance() -> int: ...
 
 tuple_slice = t[int_instance() : int_instance()]
 # TODO: Support overloads... Should be `tuple[Literal[1, 'a', b"b"] | None, ...]`
-reveal_type(tuple_slice)  # revealed: @Todo
+reveal_type(tuple_slice)  # revealed: @Todo(return type)
 ```

crates/red_knot_python_semantic/resources/mdtest/sys_version_info.md

@@ -22,23 +22,23 @@ type:
 ```py
 import sys
 
-reveal_type(sys.version_info >= (3, 8))  # revealed: Literal[True]
-reveal_type((3, 8) <= sys.version_info)  # revealed: Literal[True]
+reveal_type(sys.version_info >= (3, 9))  # revealed: Literal[True]
+reveal_type((3, 9) <= sys.version_info)  # revealed: Literal[True]
 
-reveal_type(sys.version_info > (3, 8))  # revealed: Literal[True]
-reveal_type((3, 8) < sys.version_info)  # revealed: Literal[True]
+reveal_type(sys.version_info > (3, 9))  # revealed: Literal[True]
+reveal_type((3, 9) < sys.version_info)  # revealed: Literal[True]
 
-reveal_type(sys.version_info < (3, 8))  # revealed: Literal[False]
-reveal_type((3, 8) > sys.version_info)  # revealed: Literal[False]
+reveal_type(sys.version_info < (3, 9))  # revealed: Literal[False]
+reveal_type((3, 9) > sys.version_info)  # revealed: Literal[False]
 
-reveal_type(sys.version_info <= (3, 8))  # revealed: Literal[False]
-reveal_type((3, 8) >= sys.version_info)  # revealed: Literal[False]
+reveal_type(sys.version_info <= (3, 9))  # revealed: Literal[False]
+reveal_type((3, 9) >= sys.version_info)  # revealed: Literal[False]
 
-reveal_type(sys.version_info == (3, 8))  # revealed: Literal[False]
-reveal_type((3, 8) == sys.version_info)  # revealed: Literal[False]
+reveal_type(sys.version_info == (3, 9))  # revealed: Literal[False]
+reveal_type((3, 9) == sys.version_info)  # revealed: Literal[False]
 
-reveal_type(sys.version_info != (3, 8))  # revealed: Literal[True]
-reveal_type((3, 8) != sys.version_info)  # revealed: Literal[True]
+reveal_type(sys.version_info != (3, 9))  # revealed: Literal[True]
+reveal_type((3, 9) != sys.version_info)  # revealed: Literal[True]
 ```
 
 ## Non-literal types from comparisons
@@ -49,17 +49,16 @@ sometimes not:
 ```py
 import sys
 
-reveal_type(sys.version_info >= (3, 8, 1))  # revealed: bool
-reveal_type(sys.version_info >= (3, 8, 1, "final", 0))  # revealed: bool
+reveal_type(sys.version_info >= (3, 9, 1))  # revealed: bool
+reveal_type(sys.version_info >= (3, 9, 1, "final", 0))  # revealed: bool
 
 # TODO: While this won't fail at runtime, the user has probably made a mistake
 # if they're comparing a tuple of length >5 with `sys.version_info`
 # (`sys.version_info` is a tuple of length 5). It might be worth
 # emitting a lint diagnostic of some kind warning them about the probable error?
-reveal_type(sys.version_info >= (3, 8, 1, "final", 0, 5))  # revealed: bool
+reveal_type(sys.version_info >= (3, 9, 1, "final", 0, 5))  # revealed: bool
 
-# TODO: this should be `Literal[False]`; see #14279
-reveal_type(sys.version_info == (3, 8, 1, "finallllll", 0))  # revealed: bool
+reveal_type(sys.version_info == (3, 8, 1, "finallllll", 0))  # revealed: Literal[False]
 ```
 
 ## Imports and aliases
@@ -71,11 +70,11 @@ another name:
 from sys import version_info
 from sys import version_info as foo
 
-reveal_type(version_info >= (3, 8))  # revealed: Literal[True]
-reveal_type(foo >= (3, 8))  # revealed: Literal[True]
+reveal_type(version_info >= (3, 9))  # revealed: Literal[True]
+reveal_type(foo >= (3, 9))  # revealed: Literal[True]
 
 bar = version_info
-reveal_type(bar >= (3, 8))  # revealed: Literal[True]
+reveal_type(bar >= (3, 9))  # revealed: Literal[True]
 ```
 
 ## Non-stdlib modules named `sys`
@@ -92,7 +91,7 @@ version_info: tuple[int, int] = (4, 2)
 ```py path=package/script.py
 from .sys import version_info
 
-reveal_type(version_info >= (3, 8))  # revealed: bool
+reveal_type(version_info >= (3, 9))  # revealed: bool
 ```
 
 ## Accessing fields by name
@@ -103,8 +102,8 @@ The fields of `sys.version_info` can be accessed by name:
 import sys
 
 reveal_type(sys.version_info.major >= 3)  # revealed: Literal[True]
-reveal_type(sys.version_info.minor >= 8)  # revealed: Literal[True]
-reveal_type(sys.version_info.minor >= 9)  # revealed: Literal[False]
+reveal_type(sys.version_info.minor >= 9)  # revealed: Literal[True]
+reveal_type(sys.version_info.minor >= 10)  # revealed: Literal[False]
 ```
 
 But the `micro`, `releaselevel` and `serial` fields are inferred as `@Todo` until we support
@@ -113,9 +112,9 @@ properties on instance types:
 ```py path=b.py
 import sys
 
-reveal_type(sys.version_info.micro)  # revealed: @Todo
-reveal_type(sys.version_info.releaselevel)  # revealed: @Todo
-reveal_type(sys.version_info.serial)  # revealed: @Todo
+reveal_type(sys.version_info.micro)  # revealed: @Todo(instance attributes)
+reveal_type(sys.version_info.releaselevel)  # revealed: @Todo(instance attributes)
+reveal_type(sys.version_info.serial)  # revealed: @Todo(instance attributes)
 ```
 
 ## Accessing fields by index/slice
@@ -126,14 +125,14 @@ The fields of `sys.version_info` can be accessed by index or by slice:
 import sys
 
 reveal_type(sys.version_info[0] < 3)  # revealed: Literal[False]
-reveal_type(sys.version_info[1] > 8)  # revealed: Literal[False]
+reveal_type(sys.version_info[1] > 9)  # revealed: Literal[False]
 
-# revealed: tuple[Literal[3], Literal[8], int, Literal["alpha", "beta", "candidate", "final"], int]
+# revealed: tuple[Literal[3], Literal[9], int, Literal["alpha", "beta", "candidate", "final"], int]
 reveal_type(sys.version_info[:5])
 
-reveal_type(sys.version_info[:2] >= (3, 8))  # revealed: Literal[True]
-reveal_type(sys.version_info[0:2] >= (3, 9))  # revealed: Literal[False]
-reveal_type(sys.version_info[:3] >= (3, 9, 1))  # revealed: Literal[False]
+reveal_type(sys.version_info[:2] >= (3, 9))  # revealed: Literal[True]
+reveal_type(sys.version_info[0:2] >= (3, 10))  # revealed: Literal[False]
+reveal_type(sys.version_info[:3] >= (3, 10, 1))  # revealed: Literal[False]
 reveal_type(sys.version_info[3] == "final")  # revealed: bool
 reveal_type(sys.version_info[3] == "finalllllll")  # revealed: Literal[False]
 ```

crates/red_knot_python_semantic/resources/mdtest/type_alias.md

@@ -0,0 +1,71 @@
+# Type aliases
+
+## Basic
+
+```py
+type IntOrStr = int | str
+
+reveal_type(IntOrStr)  # revealed: typing.TypeAliasType
+reveal_type(IntOrStr.__name__)  # revealed: Literal["IntOrStr"]
+
+x: IntOrStr = 1
+
+reveal_type(x)  # revealed: Literal[1]
+
+def f() -> None:
+    reveal_type(x)  # revealed: int | str
+```
+
+## `__value__` attribute
+
+```py
+type IntOrStr = int | str
+
+# TODO: This should either fall back to the specified type from typeshed,
+# which is `Any`, or be the actual type of the runtime value expression
+# `int | str`, i.e. `types.UnionType`.
+reveal_type(IntOrStr.__value__)  # revealed: @Todo(instance attributes)
+```
+
+## Invalid assignment
+
+```py
+type OptionalInt = int | None
+
+# error: [invalid-assignment]
+x: OptionalInt = "1"
+```
+
+## Type aliases in type aliases
+
+```py
+type IntOrStr = int | str
+type IntOrStrOrBytes = IntOrStr | bytes
+
+x: IntOrStrOrBytes = 1
+
+def f() -> None:
+    reveal_type(x)  # revealed: int | str | bytes
+```
+
+## Aliased type aliases
+
+```py
+type IntOrStr = int | str
+MyIntOrStr = IntOrStr
+
+x: MyIntOrStr = 1
+
+# error: [invalid-assignment]
+y: MyIntOrStr = None
+```
+
+## Generic type aliases
+
+```py
+type ListOrSet[T] = list[T] | set[T]
+
+# TODO: Should be `tuple[typing.TypeVar | typing.ParamSpec | typing.TypeVarTuple, ...]`,
+# as specified in the `typeshed` stubs.
+reveal_type(ListOrSet.__type_params__)  # revealed: @Todo(instance attributes)
+```

crates/red_knot_python_semantic/resources/mdtest/unpacking.md

@@ -84,7 +84,7 @@ reveal_type(b)  # revealed: Literal[2]
 [a, *b, c, d] = (1, 2)
 reveal_type(a)  # revealed: Literal[1]
 # TODO: Should be list[Any] once support for assigning to starred expression is added
-reveal_type(b)  # revealed: @Todo
+reveal_type(b)  # revealed: @Todo(starred unpacking)
 reveal_type(c)  # revealed: Literal[2]
 reveal_type(d)  # revealed: Unknown
 ```
@@ -95,7 +95,7 @@ reveal_type(d)  # revealed: Unknown
 [a, *b, c] = (1, 2)
 reveal_type(a)  # revealed: Literal[1]
 # TODO: Should be list[Any] once support for assigning to starred expression is added
-reveal_type(b)  # revealed: @Todo
+reveal_type(b)  # revealed: @Todo(starred unpacking)
 reveal_type(c)  # revealed: Literal[2]
 ```
 
@@ -105,7 +105,7 @@ reveal_type(c)  # revealed: Literal[2]
 [a, *b, c] = (1, 2, 3)
 reveal_type(a)  # revealed: Literal[1]
 # TODO: Should be list[int] once support for assigning to starred expression is added
-reveal_type(b)  # revealed: @Todo
+reveal_type(b)  # revealed: @Todo(starred unpacking)
 reveal_type(c)  # revealed: Literal[3]
 ```
 
@@ -115,7 +115,7 @@ reveal_type(c)  # revealed: Literal[3]
 [a, *b, c, d] = (1, 2, 3, 4, 5, 6)
 reveal_type(a)  # revealed: Literal[1]
 # TODO: Should be list[int] once support for assigning to starred expression is added
-reveal_type(b)  # revealed: @Todo
+reveal_type(b)  # revealed: @Todo(starred unpacking)
 reveal_type(c)  # revealed: Literal[5]
 reveal_type(d)  # revealed: Literal[6]
 ```
@@ -127,7 +127,7 @@ reveal_type(d)  # revealed: Literal[6]
 reveal_type(a)  # revealed: Literal[1]
 reveal_type(b)  # revealed: Literal[2]
 # TODO: Should be list[int] once support for assigning to starred expression is added
-reveal_type(c)  # revealed: @Todo
+reveal_type(c)  # revealed: @Todo(starred unpacking)
 ```
 
 ### Starred expression (6)
@@ -138,7 +138,7 @@ reveal_type(c)  # revealed: @Todo
 reveal_type(a)  # revealed: Literal[1]
 reveal_type(b)  # revealed: Unknown
 reveal_type(c)  # revealed: Unknown
-reveal_type(d)  # revealed: @Todo
+reveal_type(d)  # revealed: @Todo(starred unpacking)
 reveal_type(e)  # revealed: Unknown
 reveal_type(f)  # revealed: Unknown
 ```
@@ -222,7 +222,7 @@ reveal_type(b)  # revealed: LiteralString
 (a, *b, c, d) = "ab"
 reveal_type(a)  # revealed: LiteralString
 # TODO: Should be list[LiteralString] once support for assigning to starred expression is added
-reveal_type(b)  # revealed: @Todo
+reveal_type(b)  # revealed: @Todo(starred unpacking)
 reveal_type(c)  # revealed: LiteralString
 reveal_type(d)  # revealed: Unknown
 ```
@@ -233,7 +233,7 @@ reveal_type(d)  # revealed: Unknown
 (a, *b, c) = "ab"
 reveal_type(a)  # revealed: LiteralString
 # TODO: Should be list[Any] once support for assigning to starred expression is added
-reveal_type(b)  # revealed: @Todo
+reveal_type(b)  # revealed: @Todo(starred unpacking)
 reveal_type(c)  # revealed: LiteralString
 ```
 
@@ -243,7 +243,7 @@ reveal_type(c)  # revealed: LiteralString
 (a, *b, c) = "abc"
 reveal_type(a)  # revealed: LiteralString
 # TODO: Should be list[LiteralString] once support for assigning to starred expression is added
-reveal_type(b)  # revealed: @Todo
+reveal_type(b)  # revealed: @Todo(starred unpacking)
 reveal_type(c)  # revealed: LiteralString
 ```
 
@@ -253,7 +253,7 @@ reveal_type(c)  # revealed: LiteralString
 (a, *b, c, d) = "abcdef"
 reveal_type(a)  # revealed: LiteralString
 # TODO: Should be list[LiteralString] once support for assigning to starred expression is added
-reveal_type(b)  # revealed: @Todo
+reveal_type(b)  # revealed: @Todo(starred unpacking)
 reveal_type(c)  # revealed: LiteralString
 reveal_type(d)  # revealed: LiteralString
 ```
@@ -265,5 +265,5 @@ reveal_type(d)  # revealed: LiteralString
 reveal_type(a)  # revealed: LiteralString
 reveal_type(b)  # revealed: LiteralString
 # TODO: Should be list[int] once support for assigning to starred expression is added
-reveal_type(c)  # revealed: @Todo
+reveal_type(c)  # revealed: @Todo(starred unpacking)
 ```

crates/red_knot_python_semantic/resources/mdtest/with/async.md

@@ -17,5 +17,5 @@ class Manager:
 
 async def test():
     async with Manager() as f:
-        reveal_type(f)  # revealed: @Todo
+        reveal_type(f)  # revealed: @Todo(async with statement)
 ```

crates/red_knot_python_semantic/src/python_version.rs

@@ -39,7 +39,7 @@ impl PythonVersion {
 
 impl Default for PythonVersion {
     fn default() -> Self {
-        Self::PY38
+        Self::PY39
     }
 }
 

crates/red_knot_python_semantic/src/semantic_index/builder.rs

@@ -36,12 +36,25 @@ use super::definition::{
 
 mod except_handlers;
 
+/// Are we in a state where a `break` statement is allowed?
+#[derive(Clone, Copy, Debug)]
+enum LoopState {
+    InLoop,
+    NotInLoop,
+}
+
+impl LoopState {
+    fn is_inside(self) -> bool {
+        matches!(self, LoopState::InLoop)
+    }
+}
+
 pub(super) struct SemanticIndexBuilder<'db> {
     // Builder state
     db: &'db dyn Db,
     file: File,
     module: &'db ParsedModule,
-    scope_stack: Vec<FileScopeId>,
+    scope_stack: Vec<(FileScopeId, LoopState)>,
     /// The assignments we're currently visiting, with
     /// the most recent visit at the end of the Vec
     current_assignments: Vec<CurrentAssignment<'db>>,
@@ -103,9 +116,24 @@ impl<'db> SemanticIndexBuilder<'db> {
         *self
             .scope_stack
             .last()
+            .map(|(scope, _)| scope)
             .expect("Always to have a root scope")
     }
 
+    fn loop_state(&self) -> LoopState {
+        self.scope_stack
+            .last()
+            .expect("Always to have a root scope")
+            .1
+    }
+
+    fn set_inside_loop(&mut self, state: LoopState) {
+        self.scope_stack
+            .last_mut()
+            .expect("Always to have a root scope")
+            .1 = state;
+    }
+
     fn push_scope(&mut self, node: NodeWithScopeRef) {
         let parent = self.current_scope();
         self.push_scope_with_parent(node, Some(parent));
@@ -131,15 +159,16 @@ impl<'db> SemanticIndexBuilder<'db> {
         let scope_id = ScopeId::new(self.db, self.file, file_scope_id, countme::Count::default());
 
         self.scope_ids_by_scope.push(scope_id);
-        self.scopes_by_node.insert(node.node_key(), file_scope_id);
+        let previous = self.scopes_by_node.insert(node.node_key(), file_scope_id);
+        debug_assert_eq!(previous, None);
 
         debug_assert_eq!(ast_id_scope, file_scope_id);
 
-        self.scope_stack.push(file_scope_id);
+        self.scope_stack.push((file_scope_id, LoopState::NotInLoop));
     }
 
     fn pop_scope(&mut self) -> FileScopeId {
-        let id = self.scope_stack.pop().expect("Root scope to be present");
+        let (id, _) = self.scope_stack.pop().expect("Root scope to be present");
         let children_end = self.scopes.next_index();
         let scope = &mut self.scopes[id];
         scope.descendents = scope.descendents.start..children_end;
@@ -589,6 +618,27 @@ where
                     },
                 );
             }
+            ast::Stmt::TypeAlias(type_alias) => {
+                let symbol = self.add_symbol(
+                    type_alias
+                        .name
+                        .as_name_expr()
+                        .map(|name| name.id.clone())
+                        .unwrap_or("<unknown>".into()),
+                );
+                self.add_definition(symbol, type_alias);
+                self.visit_expr(&type_alias.name);
+
+                self.with_type_params(
+                    NodeWithScopeRef::TypeAliasTypeParameters(type_alias),
+                    type_alias.type_params.as_ref(),
+                    |builder| {
+                        builder.push_scope(NodeWithScopeRef::TypeAlias(type_alias));
+                        builder.visit_expr(&type_alias.value);
+                        builder.pop_scope()
+                    },
+                );
+            }
             ast::Stmt::Import(node) => {
                 for alias in &node.names {
                     let symbol_name = if let Some(asname) = &alias.asname {
@@ -719,7 +769,22 @@ where
                 let mut constraints = vec![constraint];
                 self.visit_body(&node.body);
                 let mut post_clauses: Vec<FlowSnapshot> = vec![];
-                for clause in &node.elif_else_clauses {
+                let elif_else_clauses = node
+                    .elif_else_clauses
+                    .iter()
+                    .map(|clause| (clause.test.as_ref(), clause.body.as_slice()));
+                let has_else = node
+                    .elif_else_clauses
+                    .last()
+                    .is_some_and(|clause| clause.test.is_none());
+                let elif_else_clauses = elif_else_clauses.chain(if has_else {
+                    // if there's an `else` clause already, we don't need to add another
+                    None
+                } else {
+                    // if there's no `else` branch, we should add a no-op `else` branch
+                    Some((None, Default::default()))
+                });
+                for (clause_test, clause_body) in 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.flow_snapshot());
@@ -729,24 +794,15 @@ where
                     for constraint in &constraints {
                         self.record_negated_constraint(*constraint);
                     }
-                    if let Some(elif_test) = &clause.test {
+                    if let Some(elif_test) = clause_test {
                         self.visit_expr(elif_test);
                         constraints.push(self.record_expression_constraint(elif_test));
                     }
-                    self.visit_body(&clause.body);
+                    self.visit_body(clause_body);
                 }
                 for post_clause_state in post_clauses {
                     self.flow_merge(post_clause_state);
                 }
-                let has_else = node
-                    .elif_else_clauses
-                    .last()
-                    .is_some_and(|clause| clause.test.is_none());
-                if !has_else {
-                    // if there's no else clause, then it's possible we took none of the branches,
-                    // and the pre_if state can reach here
-                    self.flow_merge(pre_if);
-                }
             }
             ast::Stmt::While(ast::StmtWhile {
                 test,
@@ -763,7 +819,10 @@ where
 
                 // TODO: definitions created inside the body should be fully visible
                 // to other statements/expressions inside the body --Alex/Carl
+                let outer_loop_state = self.loop_state();
+                self.set_inside_loop(LoopState::InLoop);
                 self.visit_body(body);
+                self.set_inside_loop(outer_loop_state);
 
                 // Get the break states from the body of this loop, and restore the saved outer
                 // ones.
@@ -802,7 +861,9 @@ where
                 self.visit_body(body);
             }
             ast::Stmt::Break(_) => {
-                self.loop_break_states.push(self.flow_snapshot());
+                if self.loop_state().is_inside() {
+                    self.loop_break_states.push(self.flow_snapshot());
+                }
             }
 
             ast::Stmt::For(
@@ -829,7 +890,10 @@ where
                 // TODO: Definitions created by loop variables
                 // (and definitions created inside the body)
                 // are fully visible to other statements/expressions inside the body --Alex/Carl
+                let outer_loop_state = self.loop_state();
+                self.set_inside_loop(LoopState::InLoop);
                 self.visit_body(body);
+                self.set_inside_loop(outer_loop_state);
 
                 let break_states =
                     std::mem::replace(&mut self.loop_break_states, saved_break_states);
@@ -1131,8 +1195,8 @@ where
                 // AST inspection, so we can't simplify here, need to record test expression for
                 // later checking)
                 self.visit_expr(test);
-                let constraint = self.record_expression_constraint(test);
                 let pre_if = self.flow_snapshot();
+                let constraint = self.record_expression_constraint(test);
                 self.visit_expr(body);
                 let post_body = self.flow_snapshot();
                 self.flow_restore(pre_if);

crates/red_knot_python_semantic/src/semantic_index/definition.rs

@@ -83,6 +83,7 @@ pub(crate) enum DefinitionNodeRef<'a> {
     For(ForStmtDefinitionNodeRef<'a>),
     Function(&'a ast::StmtFunctionDef),
     Class(&'a ast::StmtClassDef),
+    TypeAlias(&'a ast::StmtTypeAlias),
     NamedExpression(&'a ast::ExprNamed),
     Assignment(AssignmentDefinitionNodeRef<'a>),
     AnnotatedAssignment(&'a ast::StmtAnnAssign),
@@ -109,6 +110,12 @@ impl<'a> From<&'a ast::StmtClassDef> for DefinitionNodeRef<'a> {
     }
 }
 
+impl<'a> From<&'a ast::StmtTypeAlias> for DefinitionNodeRef<'a> {
+    fn from(node: &'a ast::StmtTypeAlias) -> Self {
+        Self::TypeAlias(node)
+    }
+}
+
 impl<'a> From<&'a ast::ExprNamed> for DefinitionNodeRef<'a> {
     fn from(node: &'a ast::ExprNamed) -> Self {
         Self::NamedExpression(node)
@@ -265,6 +272,9 @@ impl<'db> DefinitionNodeRef<'db> {
             DefinitionNodeRef::Class(class) => {
                 DefinitionKind::Class(AstNodeRef::new(parsed, class))
             }
+            DefinitionNodeRef::TypeAlias(type_alias) => {
+                DefinitionKind::TypeAlias(AstNodeRef::new(parsed, type_alias))
+            }
             DefinitionNodeRef::NamedExpression(named) => {
                 DefinitionKind::NamedExpression(AstNodeRef::new(parsed, named))
             }
@@ -358,6 +368,7 @@ impl<'db> DefinitionNodeRef<'db> {
             }
             Self::Function(node) => node.into(),
             Self::Class(node) => node.into(),
+            Self::TypeAlias(node) => node.into(),
             Self::NamedExpression(node) => node.into(),
             Self::Assignment(AssignmentDefinitionNodeRef {
                 value: _,
@@ -434,6 +445,7 @@ pub enum DefinitionKind<'db> {
     ImportFrom(ImportFromDefinitionKind),
     Function(AstNodeRef<ast::StmtFunctionDef>),
     Class(AstNodeRef<ast::StmtClassDef>),
+    TypeAlias(AstNodeRef<ast::StmtTypeAlias>),
     NamedExpression(AstNodeRef<ast::ExprNamed>),
     Assignment(AssignmentDefinitionKind<'db>),
     AnnotatedAssignment(AstNodeRef<ast::StmtAnnAssign>),
@@ -456,6 +468,7 @@ impl DefinitionKind<'_> {
             // functions, classes, and imports always bind, and we consider them declarations
             DefinitionKind::Function(_)
             | DefinitionKind::Class(_)
+            | DefinitionKind::TypeAlias(_)
             | DefinitionKind::Import(_)
             | DefinitionKind::ImportFrom(_)
             | DefinitionKind::TypeVar(_)
@@ -682,6 +695,12 @@ impl From<&ast::StmtClassDef> for DefinitionNodeKey {
     }
 }
 
+impl From<&ast::StmtTypeAlias> for DefinitionNodeKey {
+    fn from(node: &ast::StmtTypeAlias) -> Self {
+        Self(NodeKey::from_node(node))
+    }
+}
+
 impl From<&ast::ExprName> for DefinitionNodeKey {
     fn from(node: &ast::ExprName) -> Self {
         Self(NodeKey::from_node(node))

crates/red_knot_python_semantic/src/semantic_index/symbol.rs

@@ -116,14 +116,11 @@ impl<'db> ScopeId<'db> {
         // Type parameter scopes behave like function scopes in terms of name resolution; CPython
         // symbol table also uses the term "function-like" for these scopes.
         matches!(
-            self.node(db),
-            NodeWithScopeKind::ClassTypeParameters(_)
-                | NodeWithScopeKind::FunctionTypeParameters(_)
-                | NodeWithScopeKind::Function(_)
-                | NodeWithScopeKind::ListComprehension(_)
-                | NodeWithScopeKind::SetComprehension(_)
-                | NodeWithScopeKind::DictComprehension(_)
-                | NodeWithScopeKind::GeneratorExpression(_)
+            self.node(db).scope_kind(),
+            ScopeKind::Annotation
+                | ScopeKind::Function
+                | ScopeKind::TypeAlias
+                | ScopeKind::Comprehension
         )
     }
 
@@ -144,6 +141,12 @@ impl<'db> ScopeId<'db> {
             }
             NodeWithScopeKind::Function(function)
             | NodeWithScopeKind::FunctionTypeParameters(function) => function.name.as_str(),
+            NodeWithScopeKind::TypeAlias(type_alias)
+            | NodeWithScopeKind::TypeAliasTypeParameters(type_alias) => type_alias
+                .name
+                .as_name_expr()
+                .map(|name| name.id.as_str())
+                .unwrap_or("<type alias>"),
             NodeWithScopeKind::Lambda(_) => "<lambda>",
             NodeWithScopeKind::ListComprehension(_) => "<listcomp>",
             NodeWithScopeKind::SetComprehension(_) => "<setcomp>",
@@ -201,6 +204,7 @@ pub enum ScopeKind {
     Class,
     Function,
     Comprehension,
+    TypeAlias,
 }
 
 impl ScopeKind {
@@ -326,6 +330,8 @@ pub(crate) enum NodeWithScopeRef<'a> {
     Lambda(&'a ast::ExprLambda),
     FunctionTypeParameters(&'a ast::StmtFunctionDef),
     ClassTypeParameters(&'a ast::StmtClassDef),
+    TypeAlias(&'a ast::StmtTypeAlias),
+    TypeAliasTypeParameters(&'a ast::StmtTypeAlias),
     ListComprehension(&'a ast::ExprListComp),
     SetComprehension(&'a ast::ExprSetComp),
     DictComprehension(&'a ast::ExprDictComp),
@@ -347,6 +353,12 @@ impl NodeWithScopeRef<'_> {
             NodeWithScopeRef::Function(function) => {
                 NodeWithScopeKind::Function(AstNodeRef::new(module, function))
             }
+            NodeWithScopeRef::TypeAlias(type_alias) => {
+                NodeWithScopeKind::TypeAlias(AstNodeRef::new(module, type_alias))
+            }
+            NodeWithScopeRef::TypeAliasTypeParameters(type_alias) => {
+                NodeWithScopeKind::TypeAliasTypeParameters(AstNodeRef::new(module, type_alias))
+            }
             NodeWithScopeRef::Lambda(lambda) => {
                 NodeWithScopeKind::Lambda(AstNodeRef::new(module, lambda))
             }
@@ -387,6 +399,12 @@ impl NodeWithScopeRef<'_> {
             NodeWithScopeRef::ClassTypeParameters(class) => {
                 NodeWithScopeKey::ClassTypeParameters(NodeKey::from_node(class))
             }
+            NodeWithScopeRef::TypeAlias(type_alias) => {
+                NodeWithScopeKey::TypeAlias(NodeKey::from_node(type_alias))
+            }
+            NodeWithScopeRef::TypeAliasTypeParameters(type_alias) => {
+                NodeWithScopeKey::TypeAliasTypeParameters(NodeKey::from_node(type_alias))
+            }
             NodeWithScopeRef::ListComprehension(comprehension) => {
                 NodeWithScopeKey::ListComprehension(NodeKey::from_node(comprehension))
             }
@@ -411,6 +429,8 @@ pub enum NodeWithScopeKind {
     ClassTypeParameters(AstNodeRef<ast::StmtClassDef>),
     Function(AstNodeRef<ast::StmtFunctionDef>),
     FunctionTypeParameters(AstNodeRef<ast::StmtFunctionDef>),
+    TypeAliasTypeParameters(AstNodeRef<ast::StmtTypeAlias>),
+    TypeAlias(AstNodeRef<ast::StmtTypeAlias>),
     Lambda(AstNodeRef<ast::ExprLambda>),
     ListComprehension(AstNodeRef<ast::ExprListComp>),
     SetComprehension(AstNodeRef<ast::ExprSetComp>),
@@ -423,9 +443,11 @@ impl NodeWithScopeKind {
         match self {
             Self::Module => ScopeKind::Module,
             Self::Class(_) => ScopeKind::Class,
-            Self::Function(_) => ScopeKind::Function,
-            Self::Lambda(_) => ScopeKind::Function,
-            Self::FunctionTypeParameters(_) | Self::ClassTypeParameters(_) => ScopeKind::Annotation,
+            Self::Function(_) | Self::Lambda(_) => ScopeKind::Function,
+            Self::FunctionTypeParameters(_)
+            | Self::ClassTypeParameters(_)
+            | Self::TypeAliasTypeParameters(_) => ScopeKind::Annotation,
+            Self::TypeAlias(_) => ScopeKind::TypeAlias,
             Self::ListComprehension(_)
             | Self::SetComprehension(_)
             | Self::DictComprehension(_)
@@ -446,6 +468,13 @@ impl NodeWithScopeKind {
             _ => panic!("expected function"),
         }
     }
+
+    pub fn expect_type_alias(&self) -> &ast::StmtTypeAlias {
+        match self {
+            Self::TypeAlias(type_alias) => type_alias.node(),
+            _ => panic!("expected type alias"),
+        }
+    }
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
@@ -455,6 +484,8 @@ pub(crate) enum NodeWithScopeKey {
     ClassTypeParameters(NodeKey),
     Function(NodeKey),
     FunctionTypeParameters(NodeKey),
+    TypeAlias(NodeKey),
+    TypeAliasTypeParameters(NodeKey),
     Lambda(NodeKey),
     ListComprehension(NodeKey),
     SetComprehension(NodeKey),

crates/red_knot_python_semantic/src/types.rs

@@ -324,6 +324,61 @@ fn declarations_ty<'db>(
     }
 }
 
+/// Meta data for `Type::Todo`, which represents a known limitation in red-knot.
+#[cfg(debug_assertions)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum TodoType {
+    FileAndLine(&'static str, u32),
+    Message(&'static str),
+}
+
+#[cfg(debug_assertions)]
+impl std::fmt::Display for TodoType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            TodoType::FileAndLine(file, line) => write!(f, "[{file}:{line}]"),
+            TodoType::Message(msg) => write!(f, "({msg})"),
+        }
+    }
+}
+
+#[cfg(not(debug_assertions))]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub struct TodoType;
+
+#[cfg(not(debug_assertions))]
+impl std::fmt::Display for TodoType {
+    fn fmt(&self, _: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        Ok(())
+    }
+}
+
+/// Create a `Type::Todo` variant to represent a known limitation in the type system.
+///
+/// It can be used with a custom message (preferred): `todo_type!("PEP 604 not supported")`,
+/// or simply using `todo_type!()`, which will include information about the file and line.
+#[cfg(debug_assertions)]
+macro_rules! todo_type {
+    () => {
+        Type::Todo(crate::types::TodoType::FileAndLine(file!(), line!()))
+    };
+    ($message:literal) => {
+        Type::Todo(crate::types::TodoType::Message($message))
+    };
+}
+
+#[cfg(not(debug_assertions))]
+macro_rules! todo_type {
+    () => {
+        Type::Todo(crate::types::TodoType)
+    };
+    ($message:literal) => {
+        Type::Todo(crate::types::TodoType)
+    };
+}
+
+pub(crate) use todo_type;
+
 /// Representation of a type: a set of possible values at runtime.
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, salsa::Update)]
 pub enum Type<'db> {
@@ -340,7 +395,9 @@ pub enum Type<'db> {
     /// General rule: `Todo` should only propagate when the presence of the input `Todo` caused the
     /// output to be unknown. An output should only be `Todo` if fixing all `Todo` inputs to be not
     /// `Todo` would change the output type.
-    Todo,
+    ///
+    /// This variant should be created with the `todo_type!` macro.
+    Todo(TodoType),
     /// The empty set of values
     Never,
     /// A specific function object
@@ -384,7 +441,7 @@ impl<'db> Type<'db> {
     }
 
     pub const fn is_todo(&self) -> bool {
-        matches!(self, Type::Todo)
+        matches!(self, Type::Todo(_))
     }
 
     pub const fn class_literal(class: Class<'db>) -> Self {
@@ -480,6 +537,19 @@ impl<'db> Type<'db> {
             .expect("Expected a Type::IntLiteral variant")
     }
 
+    pub const fn into_known_instance(self) -> Option<KnownInstanceType<'db>> {
+        match self {
+            Type::KnownInstance(known_instance) => Some(known_instance),
+            _ => None,
+        }
+    }
+
+    #[track_caller]
+    pub fn expect_known_instance(self) -> KnownInstanceType<'db> {
+        self.into_known_instance()
+            .expect("Expected a Type::KnownInstance variant")
+    }
+
     pub const fn is_boolean_literal(&self) -> bool {
         matches!(self, Type::BooleanLiteral(..))
     }
@@ -530,8 +600,8 @@ impl<'db> Type<'db> {
             return true;
         }
         match (self, target) {
-            (Type::Unknown | Type::Any | Type::Todo, _) => false,
-            (_, Type::Unknown | Type::Any | Type::Todo) => false,
+            (Type::Unknown | Type::Any | Type::Todo(_), _) => false,
+            (_, Type::Unknown | Type::Any | Type::Todo(_)) => false,
             (Type::Never, _) => true,
             (_, Type::Never) => false,
             (_, Type::Instance(InstanceType { class }))
@@ -666,8 +736,8 @@ impl<'db> Type<'db> {
             return true;
         }
         match (self, target) {
-            (Type::Unknown | Type::Any | Type::Todo, _) => true,
-            (_, Type::Unknown | Type::Any | Type::Todo) => true,
+            (Type::Unknown | Type::Any | Type::Todo(_), _) => true,
+            (_, Type::Unknown | Type::Any | Type::Todo(_)) => true,
             (Type::Union(union), ty) => union
                 .elements(db)
                 .iter()
@@ -703,6 +773,7 @@ impl<'db> Type<'db> {
         // of `NoneType` and `NoDefaultType` in typeshed. This should not be required anymore once
         // we understand `sys.version_info` branches.
         self == other
+            || matches!((self, other), (Type::Todo(_), Type::Todo(_)))
             || matches!((self, other),
                 (
                     Type::Instance(InstanceType { class: self_class }),
@@ -726,7 +797,7 @@ impl<'db> Type<'db> {
 
             (Type::Any, _) | (_, Type::Any) => false,
             (Type::Unknown, _) | (_, Type::Unknown) => false,
-            (Type::Todo, _) | (_, Type::Todo) => false,
+            (Type::Todo(_), _) | (_, Type::Todo(_)) => false,
 
             (Type::Union(union), other) | (other, Type::Union(union)) => union
                 .elements(db)
@@ -931,7 +1002,7 @@ impl<'db> Type<'db> {
             Type::Any
             | Type::Never
             | Type::Unknown
-            | Type::Todo
+            | Type::Todo(_)
             | Type::IntLiteral(..)
             | Type::StringLiteral(..)
             | Type::BytesLiteral(..)
@@ -1007,7 +1078,10 @@ impl<'db> Type<'db> {
 
             Type::Instance(InstanceType { class }) => match class.known(db) {
                 Some(
-                    KnownClass::NoneType | KnownClass::NoDefaultType | KnownClass::VersionInfo,
+                    KnownClass::NoneType
+                    | KnownClass::NoDefaultType
+                    | KnownClass::VersionInfo
+                    | KnownClass::TypeAliasType,
                 ) => true,
                 Some(
                     KnownClass::Bool
@@ -1034,7 +1108,7 @@ impl<'db> Type<'db> {
             Type::Any
             | Type::Never
             | Type::Unknown
-            | Type::Todo
+            | Type::Todo(_)
             | Type::Union(..)
             | Type::Intersection(..)
             | Type::LiteralString => false,
@@ -1052,12 +1126,12 @@ impl<'db> Type<'db> {
             Type::Any => Type::Any.into(),
             Type::Never => {
                 // TODO: attribute lookup on Never type
-                Type::Todo.into()
+                todo_type!().into()
             }
             Type::Unknown => Type::Unknown.into(),
             Type::FunctionLiteral(_) => {
                 // TODO: attribute lookup on function type
-                Type::Todo.into()
+                todo_type!().into()
             }
             Type::ModuleLiteral(file) => {
                 // `__dict__` is a very special member that is never overridden by module globals;
@@ -1107,7 +1181,7 @@ impl<'db> Type<'db> {
                         Type::IntLiteral(Program::get(db).target_version(db).minor.into())
                     }
                     // TODO MRO? get_own_instance_member, get_instance_member
-                    _ => Type::Todo,
+                    _ => todo_type!("instance attributes"),
                 };
                 ty.into()
             }
@@ -1149,36 +1223,36 @@ impl<'db> Type<'db> {
             Type::Intersection(_) => {
                 // TODO perform the get_member on each type in the intersection
                 // TODO return the intersection of those results
-                Type::Todo.into()
+                todo_type!().into()
             }
             Type::IntLiteral(_) => {
                 // TODO raise error
-                Type::Todo.into()
+                todo_type!().into()
             }
-            Type::BooleanLiteral(_) => Type::Todo.into(),
+            Type::BooleanLiteral(_) => todo_type!().into(),
             Type::StringLiteral(_) => {
                 // TODO defer to `typing.LiteralString`/`builtins.str` methods
                 // from typeshed's stubs
-                Type::Todo.into()
+                todo_type!().into()
             }
             Type::LiteralString => {
                 // TODO defer to `typing.LiteralString`/`builtins.str` methods
                 // from typeshed's stubs
-                Type::Todo.into()
+                todo_type!().into()
             }
             Type::BytesLiteral(_) => {
                 // TODO defer to Type::Instance(<bytes from typeshed>).member
-                Type::Todo.into()
+                todo_type!().into()
             }
             Type::SliceLiteral(_) => {
                 // TODO defer to `builtins.slice` methods
-                Type::Todo.into()
+                todo_type!().into()
             }
             Type::Tuple(_) => {
                 // TODO: implement tuple methods
-                Type::Todo.into()
+                todo_type!().into()
             }
-            Type::Todo => Type::Todo.into(),
+            &todo @ Type::Todo(_) => todo.into(),
         }
     }
 
@@ -1188,7 +1262,7 @@ impl<'db> Type<'db> {
     /// when `bool(x)` is called on an object `x`.
     fn bool(&self, db: &'db dyn Db) -> Truthiness {
         match self {
-            Type::Any | Type::Todo | Type::Never | Type::Unknown => Truthiness::Ambiguous,
+            Type::Any | Type::Todo(_) | Type::Never | Type::Unknown => Truthiness::Ambiguous,
             Type::FunctionLiteral(_) => Truthiness::AlwaysTrue,
             Type::ModuleLiteral(_) => Truthiness::AlwaysTrue,
             Type::ClassLiteral(_) => {
@@ -1329,7 +1403,7 @@ impl<'db> Type<'db> {
             // `Any` is callable, and its return type is also `Any`.
             Type::Any => CallOutcome::callable(Type::Any),
 
-            Type::Todo => CallOutcome::callable(Type::Todo),
+            Type::Todo(_) => CallOutcome::callable(todo_type!()),
 
             Type::Unknown => CallOutcome::callable(Type::Unknown),
 
@@ -1342,7 +1416,7 @@ impl<'db> Type<'db> {
             ),
 
             // TODO: intersection types
-            Type::Intersection(_) => CallOutcome::callable(Type::Todo),
+            Type::Intersection(_) => CallOutcome::callable(todo_type!()),
 
             _ => CallOutcome::not_callable(self),
         }
@@ -1381,7 +1455,7 @@ impl<'db> Type<'db> {
             };
         }
 
-        if matches!(self, Type::Unknown | Type::Any | Type::Todo) {
+        if matches!(self, Type::Unknown | Type::Any | Type::Todo(_)) {
             // Explicit handling of `Unknown` and `Any` necessary until `type[Unknown]` and
             // `type[Any]` are not defined as `Todo` anymore.
             return IterationOutcome::Iterable { element_ty: self };
@@ -1440,14 +1514,14 @@ impl<'db> Type<'db> {
     pub fn to_instance(&self, db: &'db dyn Db) -> Type<'db> {
         match self {
             Type::Any => Type::Any,
-            Type::Todo => Type::Todo,
+            todo @ Type::Todo(_) => *todo,
             Type::Unknown => Type::Unknown,
             Type::Never => Type::Never,
             Type::ClassLiteral(ClassLiteralType { class }) => Type::instance(*class),
             Type::SubclassOf(SubclassOfType { class }) => Type::instance(*class),
             Type::Union(union) => union.map(db, |element| element.to_instance(db)),
             // TODO: we can probably do better here: --Alex
-            Type::Intersection(_) => Type::Todo,
+            Type::Intersection(_) => todo_type!(),
             // TODO: calling `.to_instance()` on any of these should result in a diagnostic,
             // since they already indicate that the object is an instance of some kind:
             Type::BooleanLiteral(_)
@@ -1478,7 +1552,11 @@ impl<'db> Type<'db> {
             Type::Unknown => Type::Unknown,
             // TODO map this to a new `Type::TypeVar` variant
             Type::KnownInstance(KnownInstanceType::TypeVar(_)) => *self,
-            _ => Type::Todo,
+            Type::KnownInstance(KnownInstanceType::TypeAliasType(alias)) => alias.value_ty(db),
+            Type::KnownInstance(KnownInstanceType::Never | KnownInstanceType::NoReturn) => {
+                Type::Never
+            }
+            _ => todo_type!(),
         }
     }
 
@@ -1553,8 +1631,8 @@ impl<'db> Type<'db> {
             // TODO: `type[Unknown]`?
             Type::Unknown => Type::Unknown,
             // TODO intersections
-            Type::Intersection(_) => Type::Todo,
-            Type::Todo => Type::Todo,
+            Type::Intersection(_) => todo_type!(),
+            todo @ Type::Todo(_) => *todo,
         }
     }
 
@@ -1642,6 +1720,7 @@ pub enum KnownClass {
     // Typing
     SpecialForm,
     TypeVar,
+    TypeAliasType,
     NoDefaultType,
     // sys
     VersionInfo,
@@ -1668,6 +1747,7 @@ impl<'db> KnownClass {
             Self::NoneType => "NoneType",
             Self::SpecialForm => "_SpecialForm",
             Self::TypeVar => "TypeVar",
+            Self::TypeAliasType => "TypeAliasType",
             Self::NoDefaultType => "_NoDefaultType",
             // This is the name the type of `sys.version_info` has in typeshed,
             // which is different to what `type(sys.version_info).__name__` is at runtime.
@@ -1706,7 +1786,7 @@ impl<'db> KnownClass {
             Self::VersionInfo => CoreStdlibModule::Sys,
             Self::GenericAlias | Self::ModuleType | Self::FunctionType => CoreStdlibModule::Types,
             Self::NoneType => CoreStdlibModule::Typeshed,
-            Self::SpecialForm | Self::TypeVar => CoreStdlibModule::Typing,
+            Self::SpecialForm | Self::TypeVar | Self::TypeAliasType => CoreStdlibModule::Typing,
             // TODO when we understand sys.version_info, we will need an explicit fallback here,
             // because typing_extensions has a 3.13+ re-export for the `typing.NoDefault`
             // singleton, but not for `typing._NoDefaultType`
@@ -1720,7 +1800,7 @@ impl<'db> KnownClass {
     const fn is_singleton(self) -> bool {
         // TODO there are other singleton types (EllipsisType, NotImplementedType)
         match self {
-            Self::NoneType | Self::NoDefaultType | Self::VersionInfo => true,
+            Self::NoneType | Self::NoDefaultType | Self::VersionInfo | Self::TypeAliasType => true,
             Self::Bool
             | Self::Object
             | Self::Bytes
@@ -1762,6 +1842,7 @@ impl<'db> KnownClass {
             "NoneType" => Self::NoneType,
             "ModuleType" => Self::ModuleType,
             "FunctionType" => Self::FunctionType,
+            "TypeAliasType" => Self::TypeAliasType,
             "_SpecialForm" => Self::SpecialForm,
             "_NoDefaultType" => Self::NoDefaultType,
             "_version_info" => Self::VersionInfo,
@@ -1795,7 +1876,7 @@ impl<'db> KnownClass {
             | Self::VersionInfo
             | Self::FunctionType => module.name() == self.canonical_module().as_str(),
             Self::NoneType => matches!(module.name().as_str(), "_typeshed" | "types"),
-            Self::SpecialForm | Self::TypeVar | Self::NoDefaultType => {
+            Self::SpecialForm | Self::TypeVar | Self::TypeAliasType | Self::NoDefaultType => {
                 matches!(module.name().as_str(), "typing" | "typing_extensions")
             }
         }
@@ -1807,24 +1888,44 @@ impl<'db> KnownClass {
 pub enum KnownInstanceType<'db> {
     /// The symbol `typing.Literal` (which can also be found as `typing_extensions.Literal`)
     Literal,
+    /// The symbol `typing.Optional` (which can also be found as `typing_extensions.Optional`)
+    Optional,
+    /// The symbol `typing.Union` (which can also be found as `typing_extensions.Union`)
+    Union,
+    /// The symbol `typing.NoReturn` (which can also be found as `typing_extensions.NoReturn`)
+    NoReturn,
+    /// The symbol `typing.Never` available since 3.11 (which can also be found as `typing_extensions.Never`)
+    Never,
     /// A single instance of `typing.TypeVar`
     TypeVar(TypeVarInstance<'db>),
+    /// A single instance of `typing.TypeAliasType` (PEP 695 type alias)
+    TypeAliasType(TypeAliasType<'db>),
     // TODO: fill this enum out with more special forms, etc.
 }
 
 impl<'db> KnownInstanceType<'db> {
     pub const fn as_str(self) -> &'static str {
         match self {
-            KnownInstanceType::Literal => "Literal",
-            KnownInstanceType::TypeVar(_) => "TypeVar",
+            Self::Literal => "Literal",
+            Self::Optional => "Optional",
+            Self::Union => "Union",
+            Self::TypeVar(_) => "TypeVar",
+            Self::NoReturn => "NoReturn",
+            Self::Never => "Never",
+            Self::TypeAliasType(_) => "TypeAliasType",
         }
     }
 
     /// Evaluate the known instance in boolean context
     pub const fn bool(self) -> Truthiness {
         match self {
-            Self::Literal => Truthiness::AlwaysTrue,
-            Self::TypeVar(_) => Truthiness::AlwaysTrue,
+            Self::Literal
+            | Self::Optional
+            | Self::TypeVar(_)
+            | Self::Union
+            | Self::NoReturn
+            | Self::Never
+            | Self::TypeAliasType(_) => Truthiness::AlwaysTrue,
         }
     }
 
@@ -1832,7 +1933,12 @@ impl<'db> KnownInstanceType<'db> {
     pub fn repr(self, db: &'db dyn Db) -> &'db str {
         match self {
             Self::Literal => "typing.Literal",
+            Self::Optional => "typing.Optional",
+            Self::Union => "typing.Union",
+            Self::NoReturn => "typing.NoReturn",
+            Self::Never => "typing.Never",
             Self::TypeVar(typevar) => typevar.name(db),
+            Self::TypeAliasType(_) => "typing.TypeAliasType",
         }
     }
 
@@ -1840,7 +1946,12 @@ impl<'db> KnownInstanceType<'db> {
     pub const fn class(self) -> KnownClass {
         match self {
             Self::Literal => KnownClass::SpecialForm,
+            Self::Optional => KnownClass::SpecialForm,
+            Self::Union => KnownClass::SpecialForm,
+            Self::NoReturn => KnownClass::SpecialForm,
+            Self::Never => KnownClass::SpecialForm,
             Self::TypeVar(_) => KnownClass::TypeVar,
+            Self::TypeAliasType(_) => KnownClass::TypeAliasType,
         }
     }
 
@@ -1859,6 +1970,10 @@ impl<'db> KnownInstanceType<'db> {
         }
         match (module.name().as_str(), instance_name) {
             ("typing" | "typing_extensions", "Literal") => Some(Self::Literal),
+            ("typing" | "typing_extensions", "Optional") => Some(Self::Optional),
+            ("typing" | "typing_extensions", "Union") => Some(Self::Union),
+            ("typing" | "typing_extensions", "NoReturn") => Some(Self::NoReturn),
+            ("typing" | "typing_extensions", "Never") => Some(Self::Never),
             _ => None,
         }
     }
@@ -1866,23 +1981,7 @@ impl<'db> KnownInstanceType<'db> {
     fn member(self, db: &'db dyn Db, name: &str) -> Symbol<'db> {
         let ty = match (self, name) {
             (Self::TypeVar(typevar), "__name__") => Type::string_literal(db, typevar.name(db)),
-            (Self::TypeVar(typevar), "__bound__") => typevar
-                .upper_bound(db)
-                .map(|ty| ty.to_meta_type(db))
-                .unwrap_or_else(|| KnownClass::NoneType.to_instance(db)),
-            (Self::TypeVar(typevar), "__constraints__") => {
-                let tuple_elements: Vec<Type<'db>> = typevar
-                    .constraints(db)
-                    .unwrap_or_default()
-                    .iter()
-                    .map(|ty| ty.to_meta_type(db))
-                    .collect();
-                Type::tuple(db, &tuple_elements)
-            }
-            (Self::TypeVar(typevar), "__default__") => typevar
-                .default_ty(db)
-                .map(|ty| ty.to_meta_type(db))
-                .unwrap_or_else(|| KnownClass::NoDefaultType.to_instance(db)),
+            (Self::TypeAliasType(alias), "__name__") => Type::string_literal(db, alias.name(db)),
             _ => return self.instance_fallback(db).member(db, name),
         };
         ty.into()
@@ -1914,6 +2013,7 @@ pub struct TypeVarInstance<'db> {
 }
 
 impl<'db> TypeVarInstance<'db> {
+    #[allow(unused)]
     pub(crate) fn upper_bound(self, db: &'db dyn Db) -> Option<Type<'db>> {
         if let Some(TypeVarBoundOrConstraints::UpperBound(ty)) = self.bound_or_constraints(db) {
             Some(ty)
@@ -1922,6 +2022,7 @@ impl<'db> TypeVarInstance<'db> {
         }
     }
 
+    #[allow(unused)]
     pub(crate) fn constraints(self, db: &'db dyn Db) -> Option<&[Type<'db>]> {
         if let Some(TypeVarBoundOrConstraints::Constraints(tuple)) = self.bound_or_constraints(db) {
             Some(tuple.elements(db))
@@ -2594,7 +2695,7 @@ impl<'db> Class<'db> {
             // TODO: If the metaclass is not a class, we should verify that it's a callable
             // which accepts the same arguments as `type.__new__` (otherwise error), and return
             // the meta-type of its return type. (And validate that is a class type?)
-            return Ok(Type::Todo);
+            return Ok(todo_type!("metaclass not a class"));
         };
 
         // Reconcile all base classes' metaclasses with the candidate metaclass.
@@ -2708,6 +2809,27 @@ impl<'db> Class<'db> {
     }
 }
 
+#[salsa::interned]
+pub struct TypeAliasType<'db> {
+    #[return_ref]
+    pub name: ast::name::Name,
+
+    rhs_scope: ScopeId<'db>,
+}
+
+#[salsa::tracked]
+impl<'db> TypeAliasType<'db> {
+    #[salsa::tracked]
+    pub fn value_ty(self, db: &'db dyn Db) -> Type<'db> {
+        let scope = self.rhs_scope(db);
+
+        let type_alias_stmt_node = scope.node(db).expect_type_alias();
+        let definition = semantic_index(db, scope.file(db)).definition(type_alias_stmt_node);
+
+        definition_expression_ty(db, definition, &type_alias_stmt_node.value)
+    }
+}
+
 /// Either the explicit `metaclass=` keyword of the class, or the inferred metaclass of one of its base classes.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub(super) struct MetaclassCandidate<'db> {
@@ -2894,6 +3016,11 @@ impl<'db> TupleType<'db> {
     }
 }
 
+// Make sure that the `Type` enum does not grow unexpectedly.
+#[cfg(not(debug_assertions))]
+#[cfg(target_pointer_width = "64")]
+static_assertions::assert_eq_size!(Type, [u8; 16]);
+
 #[cfg(test)]
 pub(crate) mod tests {
     use super::*;
@@ -2909,13 +3036,6 @@ pub(crate) mod tests {
     use ruff_python_ast as ast;
     use test_case::test_case;
 
-    #[cfg(target_pointer_width = "64")]
-    #[test]
-    fn no_bloat_enum_sizes() {
-        use std::mem::size_of;
-        assert_eq!(size_of::<Type>(), 16);
-    }
-
     pub(crate) fn setup_db() -> TestDb {
         let db = TestDb::new();
 
@@ -2969,7 +3089,7 @@ pub(crate) mod tests {
                 Ty::Unknown => Type::Unknown,
                 Ty::None => Type::none(db),
                 Ty::Any => Type::Any,
-                Ty::Todo => Type::Todo,
+                Ty::Todo => todo_type!("Ty::Todo"),
                 Ty::IntLiteral(n) => Type::IntLiteral(n),
                 Ty::StringLiteral(s) => Type::string_literal(db, s),
                 Ty::BooleanLiteral(b) => Type::BooleanLiteral(b),
@@ -3560,4 +3680,95 @@ pub(crate) mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn type_alias_types() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "src/mod.py",
+            r#"
+            type Alias1 = int
+            type Alias2 = int
+        "#,
+        )?;
+
+        let mod_py = system_path_to_file(&db, "src/mod.py")?;
+        let ty_alias1 = global_symbol(&db, mod_py, "Alias1").expect_type();
+        let ty_alias2 = global_symbol(&db, mod_py, "Alias2").expect_type();
+
+        let Type::KnownInstance(KnownInstanceType::TypeAliasType(alias1)) = ty_alias1 else {
+            panic!("Expected TypeAliasType, got {ty_alias1:?}");
+        };
+        assert_eq!(alias1.name(&db), "Alias1");
+        assert_eq!(alias1.value_ty(&db), KnownClass::Int.to_instance(&db));
+
+        // Two type aliases are distinct and disjoint, even if they refer to the same type
+        assert!(!ty_alias1.is_equivalent_to(&db, ty_alias2));
+        assert!(ty_alias1.is_disjoint_from(&db, ty_alias2));
+
+        Ok(())
+    }
+
+    /// All other tests also make sure that `Type::Todo` works as expected. This particular
+    /// test makes sure that we handle `Todo` types correctly, even if they originate from
+    /// different sources.
+    #[test]
+    fn todo_types() {
+        let db = setup_db();
+
+        let todo1 = todo_type!("1");
+        let todo2 = todo_type!("2");
+        let todo3 = todo_type!();
+        let todo4 = todo_type!();
+
+        assert!(todo1.is_equivalent_to(&db, todo2));
+        assert!(todo3.is_equivalent_to(&db, todo4));
+        assert!(todo1.is_equivalent_to(&db, todo3));
+
+        assert!(todo1.is_subtype_of(&db, todo2));
+        assert!(todo2.is_subtype_of(&db, todo1));
+
+        assert!(todo3.is_subtype_of(&db, todo4));
+        assert!(todo4.is_subtype_of(&db, todo3));
+
+        assert!(todo1.is_subtype_of(&db, todo3));
+        assert!(todo3.is_subtype_of(&db, todo1));
+
+        let int = KnownClass::Int.to_instance(&db);
+
+        assert!(int.is_assignable_to(&db, todo1));
+        assert!(int.is_assignable_to(&db, todo3));
+
+        assert!(todo1.is_assignable_to(&db, int));
+        assert!(todo3.is_assignable_to(&db, int));
+
+        // We lose information when combining several `Todo` types. This is an
+        // acknowledged limitation of the current implementation. We can not
+        // easily store the meta information of several `Todo`s in a single
+        // variant, as `TodoType` needs to implement `Copy`, meaning it can't
+        // contain `Vec`/`Box`/etc., and can't be boxed itself.
+        //
+        // Lifting this restriction would require us to intern `TodoType` in
+        // salsa, but that would mean we would have to pass in `db` everywhere.
+
+        // A union of several `Todo` types collapses to a single `Todo` type:
+        assert!(UnionType::from_elements(&db, vec![todo1, todo2, todo3, todo4]).is_todo());
+
+        // And similar for intersection types:
+        assert!(IntersectionBuilder::new(&db)
+            .add_positive(todo1)
+            .add_positive(todo2)
+            .add_positive(todo3)
+            .add_positive(todo4)
+            .build()
+            .is_todo());
+        assert!(IntersectionBuilder::new(&db)
+            .add_positive(todo1)
+            .add_negative(todo2)
+            .add_positive(todo3)
+            .add_negative(todo4)
+            .build()
+            .is_todo());
+    }
 }

crates/red_knot_python_semantic/src/types/builder.rs

@@ -309,7 +309,7 @@ impl<'db> InnerIntersectionBuilder<'db> {
                     self.add_positive(db, *neg);
                 }
             }
-            ty @ (Type::Any | Type::Unknown | Type::Todo) => {
+            ty @ (Type::Any | Type::Unknown | Type::Todo(_)) => {
                 // Adding any of these types to the negative side of an intersection
                 // is equivalent to adding it to the positive side. We do this to
                 // simplify the representation.
@@ -379,7 +379,7 @@ mod tests {
     use crate::program::{Program, SearchPathSettings};
     use crate::python_version::PythonVersion;
     use crate::stdlib::typing_symbol;
-    use crate::types::{global_symbol, KnownClass, UnionBuilder};
+    use crate::types::{global_symbol, todo_type, KnownClass, UnionBuilder};
     use crate::ProgramSettings;
     use ruff_db::files::system_path_to_file;
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
@@ -987,7 +987,7 @@ mod tests {
 
     #[test_case(Type::Any)]
     #[test_case(Type::Unknown)]
-    #[test_case(Type::Todo)]
+    #[test_case(todo_type!())]
     fn build_intersection_t_and_negative_t_does_not_simplify(ty: Type) {
         let db = setup_db();
 

crates/red_knot_python_semantic/src/types/display.rs

@@ -77,7 +77,7 @@ impl Display for DisplayRepresentation<'_> {
             }
             // `[Type::Todo]`'s display should be explicit that is not a valid display of
             // any other type
-            Type::Todo => f.write_str("@Todo"),
+            Type::Todo(todo) => write!(f, "@Todo{todo}"),
             Type::ModuleLiteral(file) => {
                 write!(f, "<module '{:?}'>", file.path(self.db))
             }

crates/red_knot_python_semantic/src/types/infer.rs

@@ -52,11 +52,12 @@ use crate::types::diagnostic::{TypeCheckDiagnostics, TypeCheckDiagnosticsBuilder
 use crate::types::mro::MroErrorKind;
 use crate::types::unpacker::{UnpackResult, Unpacker};
 use crate::types::{
-    bindings_ty, builtins_symbol, declarations_ty, global_symbol, symbol, typing_extensions_symbol,
-    Boundness, Class, ClassLiteralType, FunctionType, InstanceType, IntersectionBuilder,
-    IntersectionType, IterationOutcome, KnownClass, KnownFunction, KnownInstanceType,
-    MetaclassCandidate, MetaclassErrorKind, SliceLiteralType, Symbol, Truthiness, TupleType, Type,
-    TypeArrayDisplay, TypeVarBoundOrConstraints, TypeVarInstance, UnionBuilder, UnionType,
+    bindings_ty, builtins_symbol, declarations_ty, global_symbol, symbol, todo_type,
+    typing_extensions_symbol, Boundness, Class, ClassLiteralType, FunctionType, InstanceType,
+    IntersectionBuilder, IntersectionType, IterationOutcome, KnownClass, KnownFunction,
+    KnownInstanceType, MetaclassCandidate, MetaclassErrorKind, SliceLiteralType, Symbol,
+    Truthiness, TupleType, Type, TypeAliasType, TypeArrayDisplay, TypeVarBoundOrConstraints,
+    TypeVarInstance, UnionBuilder, UnionType,
 };
 use crate::unpack::Unpack;
 use crate::util::subscript::{PyIndex, PySlice};
@@ -438,6 +439,12 @@ impl<'db> TypeInferenceBuilder<'db> {
             NodeWithScopeKind::FunctionTypeParameters(function) => {
                 self.infer_function_type_params(function.node());
             }
+            NodeWithScopeKind::TypeAliasTypeParameters(type_alias) => {
+                self.infer_type_alias_type_params(type_alias.node());
+            }
+            NodeWithScopeKind::TypeAlias(type_alias) => {
+                self.infer_type_alias(type_alias.node());
+            }
             NodeWithScopeKind::ListComprehension(comprehension) => {
                 self.infer_list_comprehension_expression_scope(comprehension.node());
             }
@@ -605,6 +612,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                 self.infer_function_definition(function.node(), definition);
             }
             DefinitionKind::Class(class) => self.infer_class_definition(class.node(), definition),
+            DefinitionKind::TypeAlias(type_alias) => {
+                self.infer_type_alias_definition(type_alias.node(), definition);
+            }
             DefinitionKind::Import(import) => {
                 self.infer_import_definition(import.node(), definition);
             }
@@ -847,6 +857,19 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.infer_parameters(&function.parameters);
     }
 
+    fn infer_type_alias_type_params(&mut self, type_alias: &ast::StmtTypeAlias) {
+        let type_params = type_alias
+            .type_params
+            .as_ref()
+            .expect("type alias type params scope without type params");
+
+        self.infer_type_parameters(type_params);
+    }
+
+    fn infer_type_alias(&mut self, type_alias: &ast::StmtTypeAlias) {
+        self.infer_annotation_expression(&type_alias.value, DeferredExpressionState::Deferred);
+    }
+
     fn infer_function_body(&mut self, function: &ast::StmtFunctionDef) {
         self.infer_body(&function.body);
     }
@@ -1027,7 +1050,7 @@ impl<'db> TypeInferenceBuilder<'db> {
     ) {
         // TODO(dhruvmanila): Annotation expression is resolved at the enclosing scope, infer the
         // parameter type from there
-        let annotated_ty = Type::Todo;
+        let annotated_ty = todo_type!("function parameter type");
         if parameter.annotation.is_some() {
             self.add_declaration_with_binding(
                 parameter.into(),
@@ -1107,6 +1130,33 @@ impl<'db> TypeInferenceBuilder<'db> {
         }
     }
 
+    fn infer_type_alias_definition(
+        &mut self,
+        type_alias: &ast::StmtTypeAlias,
+        definition: Definition<'db>,
+    ) {
+        self.infer_expression(&type_alias.name);
+
+        let rhs_scope = self
+            .index
+            .node_scope(NodeWithScopeRef::TypeAlias(type_alias))
+            .to_scope_id(self.db, self.file);
+
+        let type_alias_ty =
+            Type::KnownInstance(KnownInstanceType::TypeAliasType(TypeAliasType::new(
+                self.db,
+                &type_alias.name.as_name_expr().unwrap().id,
+                rhs_scope,
+            )));
+
+        self.add_declaration_with_binding(
+            type_alias.into(),
+            definition,
+            type_alias_ty,
+            type_alias_ty,
+        );
+    }
+
     fn infer_if_statement(&mut self, if_statement: &ast::StmtIf) {
         let ast::StmtIf {
             range: _,
@@ -1236,7 +1286,7 @@ impl<'db> TypeInferenceBuilder<'db> {
     ) -> Type<'db> {
         // TODO: Handle async with statements (they use `aenter` and `aexit`)
         if is_async {
-            return Type::Todo;
+            return todo_type!("async with statement");
         }
 
         let context_manager_ty = context_expression_ty.to_meta_type(self.db);
@@ -1386,12 +1436,12 @@ impl<'db> TypeInferenceBuilder<'db> {
                     self.db,
                     tuple.elements(self.db).iter().map(|ty| {
                         ty.into_class_literal()
-                            .map_or(Type::Todo, |ClassLiteralType { class }| {
+                            .map_or(todo_type!(), |ClassLiteralType { class }| {
                                 Type::instance(class)
                             })
                     }),
                 ),
-                _ => Type::Todo,
+                _ => todo_type!("exception type"),
             }
         };
 
@@ -1461,7 +1511,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             default,
         } = node;
         self.infer_optional_expression(default.as_deref());
-        self.add_declaration_with_binding(node.into(), definition, Type::Todo, Type::Todo);
+        self.add_declaration_with_binding(node.into(), definition, todo_type!(), todo_type!());
     }
 
     fn infer_typevartuple_definition(
@@ -1475,7 +1525,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             default,
         } = node;
         self.infer_optional_expression(default.as_deref());
-        self.add_declaration_with_binding(node.into(), definition, Type::Todo, Type::Todo);
+        self.add_declaration_with_binding(node.into(), definition, todo_type!(), todo_type!());
     }
 
     fn infer_match_statement(&mut self, match_statement: &ast::StmtMatch) {
@@ -1510,7 +1560,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         // against the subject expression type (which we can query via `infer_expression_types`)
         // and extract the type at the `index` position if the pattern matches. This will be
         // similar to the logic in `self.infer_assignment_definition`.
-        self.add_binding(pattern.into(), definition, Type::Todo);
+        self.add_binding(pattern.into(), definition, todo_type!());
     }
 
     fn infer_match_pattern(&mut self, pattern: &ast::Pattern) {
@@ -1829,17 +1879,8 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.infer_augmented_op(assignment, target_type, value_type)
     }
 
-    fn infer_type_alias_statement(&mut self, type_alias_statement: &ast::StmtTypeAlias) {
-        let ast::StmtTypeAlias {
-            range: _,
-            name,
-            type_params: _,
-            value,
-        } = type_alias_statement;
-        self.infer_expression(value);
-        self.infer_expression(name);
-
-        // TODO: properly handle generic type aliases, which need their own annotation scope
+    fn infer_type_alias_statement(&mut self, node: &ast::StmtTypeAlias) {
+        self.infer_definition(node);
     }
 
     fn infer_for_statement(&mut self, for_statement: &ast::StmtFor) {
@@ -1874,8 +1915,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         let iterable_ty = self.infer_standalone_expression(iterable);
 
         let loop_var_value_ty = if is_async {
-            // TODO(Alex): async iterables/iterators!
-            Type::Todo
+            todo_type!("async iterables/iterators")
         } else {
             iterable_ty
                 .iterate(self.db)
@@ -2203,7 +2243,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             ast::Expr::Await(await_expression) => self.infer_await_expression(await_expression),
             ast::Expr::IpyEscapeCommand(_) => {
                 // TODO Implement Ipy escape command support
-                Type::Todo
+                todo_type!()
             }
         };
 
@@ -2285,6 +2325,12 @@ impl<'db> TypeInferenceBuilder<'db> {
                                 } = expression;
                                 let ty = self.infer_expression(expression);
 
+                                if let Some(ref format_spec) = format_spec {
+                                    for element in format_spec.elements.expressions() {
+                                        self.infer_expression(&element.expression);
+                                    }
+                                }
+
                                 // TODO: handle format specifiers by calling a method
                                 // (`Type::format`?) that handles the `__format__` method.
                                 // Conversion flags should be handled before calling `__format__`.
@@ -2391,7 +2437,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.infer_first_comprehension_iter(generators);
 
         // TODO generator type
-        Type::Todo
+        todo_type!()
     }
 
     fn infer_list_comprehension_expression(&mut self, listcomp: &ast::ExprListComp) -> Type<'db> {
@@ -2404,7 +2450,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.infer_first_comprehension_iter(generators);
 
         // TODO list type
-        Type::Todo
+        todo_type!()
     }
 
     fn infer_dict_comprehension_expression(&mut self, dictcomp: &ast::ExprDictComp) -> Type<'db> {
@@ -2418,7 +2464,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.infer_first_comprehension_iter(generators);
 
         // TODO dict type
-        Type::Todo
+        todo_type!()
     }
 
     fn infer_set_comprehension_expression(&mut self, setcomp: &ast::ExprSetComp) -> Type<'db> {
@@ -2431,7 +2477,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.infer_first_comprehension_iter(generators);
 
         // TODO set type
-        Type::Todo
+        todo_type!()
     }
 
     fn infer_generator_expression_scope(&mut self, generator: &ast::ExprGenerator) {
@@ -2546,7 +2592,7 @@ impl<'db> TypeInferenceBuilder<'db> {
 
         let target_ty = if is_async {
             // TODO: async iterables/iterators! -- Alex
-            Type::Todo
+            todo_type!("async iterables/iterators")
         } else {
             iterable_ty
                 .iterate(self.db)
@@ -2636,7 +2682,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         }
 
         // TODO function type
-        Type::Todo
+        todo_type!()
     }
 
     fn infer_call_expression(&mut self, call_expression: &ast::ExprCall) -> Type<'db> {
@@ -2667,7 +2713,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             .unwrap_with_diagnostic(value.as_ref().into(), &mut self.diagnostics);
 
         // TODO
-        Type::Todo
+        todo_type!()
     }
 
     fn infer_yield_expression(&mut self, yield_expression: &ast::ExprYield) -> Type<'db> {
@@ -2676,7 +2722,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.infer_optional_expression(value.as_deref());
 
         // TODO awaitable type
-        Type::Todo
+        todo_type!()
     }
 
     fn infer_yield_from_expression(&mut self, yield_from: &ast::ExprYieldFrom) -> Type<'db> {
@@ -2688,7 +2734,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             .unwrap_with_diagnostic(value.as_ref().into(), &mut self.diagnostics);
 
         // TODO get type from `ReturnType` of generator
-        Type::Todo
+        todo_type!()
     }
 
     fn infer_await_expression(&mut self, await_expression: &ast::ExprAwait) -> Type<'db> {
@@ -2697,7 +2743,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         self.infer_expression(value);
 
         // TODO awaitable type
-        Type::Todo
+        todo_type!()
     }
 
     /// Look up a name reference that isn't bound in the local scope.
@@ -2973,7 +3019,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                     Type::Unknown
                 }
             }
-            _ => Type::Todo, // TODO other unary op types
+            _ => todo_type!(), // TODO other unary op types
         }
     }
 
@@ -3221,7 +3267,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             (left, Type::BooleanLiteral(bool_value), op) => {
                 self.infer_binary_expression_type(left, Type::IntLiteral(i64::from(bool_value)), op)
             }
-            _ => Some(Type::Todo), // TODO
+            _ => Some(todo_type!()), // TODO
         }
     }
 
@@ -3637,16 +3683,16 @@ impl<'db> TypeInferenceBuilder<'db> {
                 let lhs_elements = lhs.elements(self.db);
                 let rhs_elements = rhs.elements(self.db);
 
-                let mut lexicographic_type_comparison =
-                    |op| self.infer_lexicographic_type_comparison(lhs_elements, op, rhs_elements);
+                let mut tuple_rich_comparison =
+                    |op| self.infer_tuple_rich_comparison(lhs_elements, op, rhs_elements);
 
                 match op {
-                    ast::CmpOp::Eq => lexicographic_type_comparison(RichCompareOperator::Eq),
-                    ast::CmpOp::NotEq => lexicographic_type_comparison(RichCompareOperator::Ne),
-                    ast::CmpOp::Lt => lexicographic_type_comparison(RichCompareOperator::Lt),
-                    ast::CmpOp::LtE => lexicographic_type_comparison(RichCompareOperator::Le),
-                    ast::CmpOp::Gt => lexicographic_type_comparison(RichCompareOperator::Gt),
-                    ast::CmpOp::GtE => lexicographic_type_comparison(RichCompareOperator::Ge),
+                    ast::CmpOp::Eq => tuple_rich_comparison(RichCompareOperator::Eq),
+                    ast::CmpOp::NotEq => tuple_rich_comparison(RichCompareOperator::Ne),
+                    ast::CmpOp::Lt => tuple_rich_comparison(RichCompareOperator::Lt),
+                    ast::CmpOp::LtE => tuple_rich_comparison(RichCompareOperator::Le),
+                    ast::CmpOp::Gt => tuple_rich_comparison(RichCompareOperator::Gt),
+                    ast::CmpOp::GtE => tuple_rich_comparison(RichCompareOperator::Ge),
                     ast::CmpOp::In | ast::CmpOp::NotIn => {
                         let mut eq_count = 0usize;
                         let mut not_eq_count = 0usize;
@@ -3659,7 +3705,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                             ).expect("infer_binary_type_comparison should never return None for `CmpOp::Eq`");
 
                             match eq_result {
-                                Type::Todo => return Ok(Type::Todo),
+                                todo @ Type::Todo(_) => return Ok(todo),
                                 ty => match ty.bool(self.db) {
                                     Truthiness::AlwaysTrue => eq_count += 1,
                                     Truthiness::AlwaysFalse => not_eq_count += 1,
@@ -3679,13 +3725,12 @@ impl<'db> TypeInferenceBuilder<'db> {
                     ast::CmpOp::Is | ast::CmpOp::IsNot => {
                         // - `[ast::CmpOp::Is]`: returns `false` if the elements are definitely unequal, otherwise `bool`
                         // - `[ast::CmpOp::IsNot]`: returns `true` if the elements are definitely unequal, otherwise `bool`
-                        let eq_result = lexicographic_type_comparison(RichCompareOperator::Eq)
-                            .expect(
+                        let eq_result = tuple_rich_comparison(RichCompareOperator::Eq).expect(
                             "infer_binary_type_comparison should never return None for `CmpOp::Eq`",
                         );
 
                         Ok(match eq_result {
-                            Type::Todo => Type::Todo,
+                            todo @ Type::Todo(_) => todo,
                             ty => match ty.bool(self.db) {
                                 Truthiness::AlwaysFalse => Type::BooleanLiteral(op.is_is_not()),
                                 _ => KnownClass::Bool.to_instance(self.db),
@@ -3740,58 +3785,85 @@ impl<'db> TypeInferenceBuilder<'db> {
             // TODO: handle more types
             _ => match op {
                 ast::CmpOp::Is | ast::CmpOp::IsNot => Ok(KnownClass::Bool.to_instance(self.db)),
-                _ => Ok(Type::Todo),
+                _ => Ok(todo_type!()),
             },
         }
     }
 
-    /// Performs lexicographic comparison between two slices of types.
+    /// Simulates rich comparison between tuples and returns the inferred result.
+    /// This performs a lexicographic comparison, returning a union of all possible return types that could result from the comparison.
     ///
-    /// For lexicographic comparison, elements from both slices are compared pairwise using
-    /// `infer_binary_type_comparison`. If a conclusive result cannot be determined as a `BooleanLiteral`,
-    /// it returns `bool`. Returns `None` if the comparison is not supported.
-    fn infer_lexicographic_type_comparison(
+    /// basically it's based on cpython's `tuple_richcompare`
+    /// see `<https://github.com/python/cpython/blob/9d6366b60d01305fc5e45100e0cd13e358aa397d/Objects/tupleobject.c#L637>`
+    fn infer_tuple_rich_comparison(
         &mut self,
         left: &[Type<'db>],
         op: RichCompareOperator,
         right: &[Type<'db>],
     ) -> Result<Type<'db>, CompareUnsupportedError<'db>> {
-        // Compare paired elements from left and right slices
-        for (l_ty, r_ty) in left.iter().copied().zip(right.iter().copied()) {
-            let eq_result = self
+        let left_iter = left.iter().copied();
+        let right_iter = right.iter().copied();
+
+        let mut builder = UnionBuilder::new(self.db);
+
+        for (l_ty, r_ty) in left_iter.zip(right_iter) {
+            let pairwise_eq_result = self
                 .infer_binary_type_comparison(l_ty, ast::CmpOp::Eq, r_ty)
                 .expect("infer_binary_type_comparison should never return None for `CmpOp::Eq`");
 
-            match eq_result {
+            match pairwise_eq_result {
                 // If propagation is required, return the result as is
-                Type::Todo => return Ok(Type::Todo),
+                todo @ Type::Todo(_) => return Ok(todo),
                 ty => match ty.bool(self.db) {
-                    // Types are equal, continue to the next pair
+                    // - AlwaysTrue : Continue to the next pair for lexicographic comparison
                     Truthiness::AlwaysTrue => continue,
-                    // Types are not equal, perform the specified comparison and return the result
-                    Truthiness::AlwaysFalse => {
-                        return self.infer_binary_type_comparison(l_ty, op.into(), r_ty)
+                    // - AlwaysFalse:
+                    // Lexicographic comparisons will always terminate with this pair.
+                    // Complete the comparison and return the result.
+                    // - Ambiguous:
+                    // Lexicographic comparisons might continue to the next pair (if eq_result is true),
+                    // or terminate here (if eq_result is false).
+                    // To account for cases where the comparison terminates here, add the pairwise comparison result to the union builder.
+                    eq_truthiness @ (Truthiness::AlwaysFalse | Truthiness::Ambiguous) => {
+                        let pairwise_compare_result = match op {
+                            RichCompareOperator::Lt
+                            | RichCompareOperator::Le
+                            | RichCompareOperator::Gt
+                            | RichCompareOperator::Ge => {
+                                self.infer_binary_type_comparison(l_ty, op.into(), r_ty)?
+                            }
+                            // For `==` and `!=`, we already figure out the result from `pairwise_eq_result`
+                            // NOTE: The CPython implementation does not account for non-boolean return types
+                            // or cases where `!=` is not the negation of `==`, we also do not consider these cases.
+                            RichCompareOperator::Eq => Type::BooleanLiteral(false),
+                            RichCompareOperator::Ne => Type::BooleanLiteral(true),
+                        };
+
+                        builder = builder.add(pairwise_compare_result);
+
+                        if eq_truthiness.is_ambiguous() {
+                            continue;
+                        }
+
+                        return Ok(builder.build());
                     }
-                    // If the intermediate result is ambiguous, we cannot determine the final result as BooleanLiteral.
-                    // In this case, we simply return a bool instance.
-                    Truthiness::Ambiguous => return Ok(KnownClass::Bool.to_instance(self.db)),
                 },
             }
         }
 
-        // At this point, the lengths of the two slices may be different, but the prefix of
-        // left and right slices is entirely identical.
-        // We return a comparison of the slice lengths based on the operator.
+        // if no more items to compare, we just compare sizes
         let (left_len, right_len) = (left.len(), right.len());
 
-        Ok(Type::BooleanLiteral(match op {
+        builder = builder.add(Type::BooleanLiteral(match op {
             RichCompareOperator::Eq => left_len == right_len,
             RichCompareOperator::Ne => left_len != right_len,
             RichCompareOperator::Lt => left_len < right_len,
             RichCompareOperator::Le => left_len <= right_len,
             RichCompareOperator::Gt => left_len > right_len,
             RichCompareOperator::Ge => left_len >= right_len,
-        }))
+        }));
+
+        Ok(builder.build())
     }
 
     fn infer_subscript_expression(&mut self, subscript: &ast::ExprSubscript) -> Type<'db> {
@@ -4157,6 +4229,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                     "annotation-f-string",
                     format_args!("Type expressions cannot use f-strings"),
                 );
+                self.infer_fstring_expression(fstring);
                 Type::Unknown
             }
 
@@ -4231,7 +4304,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                     self.infer_name_expression(name).in_type_expression(self.db)
                 }
                 ast::ExprContext::Invalid => Type::Unknown,
-                ast::ExprContext::Store | ast::ExprContext::Del => Type::Todo,
+                ast::ExprContext::Store | ast::ExprContext::Del => todo_type!(),
             },
 
             ast::Expr::Attribute(attribute_expression) => match attribute_expression.ctx {
@@ -4239,7 +4312,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                     .infer_attribute_expression(attribute_expression)
                     .in_type_expression(self.db),
                 ast::ExprContext::Invalid => Type::Unknown,
-                ast::ExprContext::Store | ast::ExprContext::Del => Type::Todo,
+                ast::ExprContext::Store | ast::ExprContext::Del => todo_type!(),
             },
 
             ast::Expr::NoneLiteral(_literal) => Type::none(self.db),
@@ -4249,14 +4322,14 @@ impl<'db> TypeInferenceBuilder<'db> {
 
             // TODO: an Ellipsis literal *on its own* does not have any meaning in annotation
             // expressions, but is meaningful in the context of a number of special forms.
-            ast::Expr::EllipsisLiteral(_literal) => Type::Todo,
+            ast::Expr::EllipsisLiteral(_literal) => todo_type!(),
 
             // Other literals do not have meaningful values in the annotation expression context.
             // However, we will we want to handle these differently when working with special forms,
             // since (e.g.) `123` is not valid in an annotation expression but `Literal[123]` is.
-            ast::Expr::BytesLiteral(_literal) => Type::Todo,
-            ast::Expr::NumberLiteral(_literal) => Type::Todo,
-            ast::Expr::BooleanLiteral(_literal) => Type::Todo,
+            ast::Expr::BytesLiteral(_literal) => todo_type!(),
+            ast::Expr::NumberLiteral(_literal) => todo_type!(),
+            ast::Expr::BooleanLiteral(_literal) => todo_type!(),
 
             ast::Expr::Subscript(subscript) => {
                 let ast::ExprSubscript {
@@ -4299,9 +4372,13 @@ impl<'db> TypeInferenceBuilder<'db> {
             // TODO PEP 646
             ast::Expr::Starred(starred) => {
                 self.infer_starred_expression(starred);
-                Type::Todo
+                todo_type!()
             }
 
+            // Avoid inferring the types of invalid type expressions that have been parsed from a
+            // string annotation, as they are not present in the semantic index.
+            _ if self.deferred_state.in_string_annotation() => Type::Unknown,
+
             // Forms which are invalid in the context of annotation expressions: we infer their
             // nested expressions as normal expressions, but the type of the top-level expression is
             // always `Type::Unknown` in these cases.
@@ -4385,7 +4462,6 @@ impl<'db> TypeInferenceBuilder<'db> {
                 self.infer_slice_expression(slice);
                 Type::Unknown
             }
-
             ast::Expr::IpyEscapeCommand(_) => todo!("Implement Ipy escape command support"),
         }
     }
@@ -4443,16 +4519,23 @@ impl<'db> TypeInferenceBuilder<'db> {
                     element_types.push(element_ty);
                 }
 
-                if return_todo {
-                    Type::Todo
+                let ty = if return_todo {
+                    todo_type!("full tuple[...] support")
                 } else {
                     Type::tuple(self.db, &element_types)
-                }
+                };
+
+                // Here, we store the type for the inner `int, str` tuple-expression,
+                // while the type for the outer `tuple[int, str]` slice-expression is
+                // stored in the surrounding `infer_type_expression` call:
+                self.store_expression_type(tuple_slice, ty);
+
+                ty
             }
             single_element => {
                 let single_element_ty = self.infer_type_expression(single_element);
                 if element_could_alter_type_of_whole_tuple(single_element, single_element_ty) {
-                    Type::Todo
+                    todo_type!()
                 } else {
                     Type::tuple(self.db, &[single_element_ty])
                 }
@@ -4463,18 +4546,18 @@ impl<'db> TypeInferenceBuilder<'db> {
     /// Given the slice of a `type[]` annotation, return the type that the annotation represents
     fn infer_subclass_of_type_expression(&mut self, slice: &ast::Expr) -> Type<'db> {
         match slice {
-            ast::Expr::Name(name) => {
-                let name_ty = self.infer_name_expression(name);
+            ast::Expr::Name(_) => {
+                let name_ty = self.infer_expression(slice);
                 if let Some(ClassLiteralType { class }) = name_ty.into_class_literal() {
                     Type::subclass_of(class)
                 } else {
-                    Type::Todo
+                    todo_type!()
                 }
             }
             // TODO: attributes, unions, subscripts, etc.
             _ => {
                 self.infer_type_expression(slice);
-                Type::Todo
+                todo_type!()
             }
         }
     }
@@ -4493,20 +4576,21 @@ impl<'db> TypeInferenceBuilder<'db> {
 
         match value_ty {
             Type::KnownInstance(known_instance) => {
-                self.infer_parameterized_known_instance_type_expression(known_instance, slice)
+                self.infer_parameterized_known_instance_type_expression(subscript, known_instance)
             }
             _ => {
                 self.infer_type_expression(slice);
-                Type::Todo // TODO: generics
+                todo_type!("generics")
             }
         }
     }
 
     fn infer_parameterized_known_instance_type_expression(
         &mut self,
+        subscript: &ast::ExprSubscript,
         known_instance: KnownInstanceType,
-        parameters: &ast::Expr,
     ) -> Type<'db> {
+        let parameters = &*subscript.slice;
         match known_instance {
             KnownInstanceType::Literal => match self.infer_literal_parameter_type(parameters) {
                 Ok(ty) => ty,
@@ -4524,7 +4608,40 @@ impl<'db> TypeInferenceBuilder<'db> {
                     Type::Unknown
                 }
             },
-            KnownInstanceType::TypeVar(_) => Type::Todo,
+            KnownInstanceType::Optional => {
+                let param_type = self.infer_type_expression(parameters);
+                UnionType::from_elements(self.db, [param_type, Type::none(self.db)])
+            }
+            KnownInstanceType::Union => match parameters {
+                ast::Expr::Tuple(t) => {
+                    let union_ty = UnionType::from_elements(
+                        self.db,
+                        t.iter().map(|elt| self.infer_type_expression(elt)),
+                    );
+                    self.store_expression_type(parameters, union_ty);
+                    union_ty
+                }
+                _ => self.infer_type_expression(parameters),
+            },
+            KnownInstanceType::TypeVar(_) => {
+                self.infer_type_expression(parameters);
+                todo_type!()
+            }
+            KnownInstanceType::TypeAliasType(_) => {
+                self.infer_type_expression(parameters);
+                todo_type!("generic type alias")
+            }
+            KnownInstanceType::NoReturn | KnownInstanceType::Never => {
+                self.diagnostics.add(
+                    subscript.into(),
+                    "invalid-type-parameter",
+                    format_args!(
+                        "Type `{}` expected no type parameter",
+                        known_instance.repr(self.db)
+                    ),
+                );
+                Type::Unknown
+            }
         }
     }
 
@@ -4537,8 +4654,15 @@ impl<'db> TypeInferenceBuilder<'db> {
             ast::Expr::Subscript(ast::ExprSubscript { value, slice, .. }) => {
                 let value_ty = self.infer_expression(value);
                 if matches!(value_ty, Type::KnownInstance(KnownInstanceType::Literal)) {
-                    self.infer_literal_parameter_type(slice)?
+                    let ty = self.infer_literal_parameter_type(slice)?;
+
+                    // This branch deals with annotations such as `Literal[Literal[1]]`.
+                    // Here, we store the type for the inner `Literal[1]` expression:
+                    self.store_expression_type(parameters, ty);
+                    ty
                 } else {
+                    self.store_expression_type(parameters, Type::Unknown);
+
                     return Err(vec![parameters]);
                 }
             }
@@ -4556,15 +4680,27 @@ impl<'db> TypeInferenceBuilder<'db> {
                     }
                 }
                 if errors.is_empty() {
-                    builder.build()
+                    let union_type = builder.build();
+
+                    // This branch deals with annotations such as `Literal[1, 2]`. Here, we
+                    // store the type for the inner `1, 2` tuple-expression:
+                    self.store_expression_type(parameters, union_type);
+
+                    union_type
                 } else {
+                    self.store_expression_type(parameters, Type::Unknown);
+
                     return Err(errors);
                 }
             }
 
-            ast::Expr::StringLiteral(literal) => self.infer_string_literal_expression(literal),
-            ast::Expr::BytesLiteral(literal) => self.infer_bytes_literal_expression(literal),
-            ast::Expr::BooleanLiteral(literal) => self.infer_boolean_literal_expression(literal),
+            literal @ (ast::Expr::StringLiteral(_)
+            | ast::Expr::BytesLiteral(_)
+            | ast::Expr::BooleanLiteral(_)
+            | ast::Expr::NoneLiteral(_)) => self.infer_expression(literal),
+            literal @ ast::Expr::NumberLiteral(ref number) if number.value.is_int() => {
+                self.infer_expression(literal)
+            }
             // For enum values
             ast::Expr::Attribute(ast::ExprAttribute { value, attr, .. }) => {
                 let value_ty = self.infer_expression(value);
@@ -4574,7 +4710,6 @@ impl<'db> TypeInferenceBuilder<'db> {
                     .ignore_possibly_unbound()
                     .unwrap_or(Type::Unknown)
             }
-            ast::Expr::NoneLiteral(_) => Type::none(self.db),
             // for negative and positive numbers
             ast::Expr::UnaryOp(ref u)
                 if matches!(u.op, UnaryOp::USub | UnaryOp::UAdd)
@@ -4582,10 +4717,8 @@ impl<'db> TypeInferenceBuilder<'db> {
             {
                 self.infer_unary_expression(u)
             }
-            ast::Expr::NumberLiteral(ref number) if number.value.is_int() => {
-                self.infer_number_literal_expression(number)
-            }
             _ => {
+                self.infer_expression(parameters);
                 return Err(vec![parameters]);
             }
         })
@@ -4876,8 +5009,8 @@ fn perform_membership_test_comparison<'db>(
 
     compare_result_opt
         .map(|ty| {
-            if matches!(ty, Type::Todo) {
-                return Type::Todo;
+            if matches!(ty, Type::Todo(_)) {
+                return ty;
             }
 
             match op {
@@ -5848,7 +5981,17 @@ mod tests {
 
         // We currently return `Todo` for all async comprehensions,
         // including comprehensions that have invalid syntax
-        assert_scope_ty(&db, "src/a.py", &["foo", "<listcomp>"], "x", "@Todo");
+        assert_scope_ty(
+            &db,
+            "src/a.py",
+            &["foo", "<listcomp>"],
+            "x",
+            if cfg!(debug_assertions) {
+                "@Todo(async iterables/iterators)"
+            } else {
+                "@Todo"
+            },
+        );
 
         Ok(())
     }
@@ -5872,7 +6015,17 @@ mod tests {
         )?;
 
         // TODO async iterables/iterators! --Alex
-        assert_scope_ty(&db, "src/a.py", &["foo", "<listcomp>"], "x", "@Todo");
+        assert_scope_ty(
+            &db,
+            "src/a.py",
+            &["foo", "<listcomp>"],
+            "x",
+            if cfg!(debug_assertions) {
+                "@Todo(async iterables/iterators)"
+            } else {
+                "@Todo"
+            },
+        );
 
         Ok(())
     }
@@ -5906,6 +6059,72 @@ mod tests {
         );
     }
 
+    #[test]
+    fn pep695_type_params() {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "src/a.py",
+            "
+            def f[T, U: A, V: (A, B), W = A, X: A = A1, Y: (int,)]():
+                pass
+
+            class A: ...
+            class B: ...
+            class A1(A): ...
+            ",
+        )
+        .unwrap();
+
+        let check_typevar = |var: &'static str,
+                             upper_bound: Option<&'static str>,
+                             constraints: Option<&[&'static str]>,
+                             default: Option<&'static str>| {
+            let var_ty = get_symbol(&db, "src/a.py", &["f"], var).expect_type();
+            assert_eq!(var_ty.display(&db).to_string(), var);
+
+            let expected_name_ty = format!(r#"Literal["{var}"]"#);
+            let name_ty = var_ty.member(&db, "__name__").expect_type();
+            assert_eq!(name_ty.display(&db).to_string(), expected_name_ty);
+
+            let KnownInstanceType::TypeVar(typevar) = var_ty.expect_known_instance() else {
+                panic!("expected TypeVar");
+            };
+
+            assert_eq!(
+                typevar
+                    .upper_bound(&db)
+                    .map(|ty| ty.display(&db).to_string()),
+                upper_bound.map(std::borrow::ToOwned::to_owned)
+            );
+            assert_eq!(
+                typevar.constraints(&db).map(|tys| tys
+                    .iter()
+                    .map(|ty| ty.display(&db).to_string())
+                    .collect::<Vec<_>>()),
+                constraints.map(|strings| strings
+                    .iter()
+                    .map(std::string::ToString::to_string)
+                    .collect::<Vec<_>>())
+            );
+            assert_eq!(
+                typevar
+                    .default_ty(&db)
+                    .map(|ty| ty.display(&db).to_string()),
+                default.map(std::borrow::ToOwned::to_owned)
+            );
+        };
+
+        check_typevar("T", None, None, None);
+        check_typevar("U", Some("A"), None, None);
+        check_typevar("V", None, Some(&["A", "B"]), None);
+        check_typevar("W", None, None, Some("A"));
+        check_typevar("X", Some("A"), None, Some("A1"));
+
+        // a typevar with less than two constraints is treated as unconstrained
+        check_typevar("Y", None, None, None);
+    }
+
     // Incremental inference tests
 
     fn first_public_binding<'db>(db: &'db TestDb, file: File, name: &str) -> Definition<'db> {

crates/red_knot_python_semantic/src/types/mro.rs

@@ -5,7 +5,7 @@ use itertools::Either;
 use rustc_hash::FxHashSet;
 
 use super::{Class, ClassLiteralType, KnownClass, KnownInstanceType, Type};
-use crate::Db;
+use crate::{types::todo_type, Db};
 
 /// The inferred method resolution order of a given class.
 ///
@@ -354,7 +354,7 @@ impl<'db> ClassBase<'db> {
         match ty {
             Type::Any => Some(Self::Any),
             Type::Unknown => Some(Self::Unknown),
-            Type::Todo => Some(Self::Todo),
+            Type::Todo(_) => Some(Self::Todo),
             Type::ClassLiteral(ClassLiteralType { class }) => Some(Self::Class(class)),
             Type::Union(_) => None, // TODO -- forces consideration of multiple possible MROs?
             Type::Intersection(_) => None, // TODO -- probably incorrect?
@@ -371,8 +371,13 @@ impl<'db> ClassBase<'db> {
             | Type::ModuleLiteral(_)
             | Type::SubclassOf(_) => None,
             Type::KnownInstance(known_instance) => match known_instance {
-                KnownInstanceType::Literal => None,
-                KnownInstanceType::TypeVar(_) => None,
+                KnownInstanceType::TypeVar(_)
+                | KnownInstanceType::TypeAliasType(_)
+                | KnownInstanceType::Literal
+                | KnownInstanceType::Union
+                | KnownInstanceType::NoReturn
+                | KnownInstanceType::Never
+                | KnownInstanceType::Optional => None,
             },
         }
     }
@@ -404,7 +409,7 @@ impl<'db> From<ClassBase<'db>> for Type<'db> {
     fn from(value: ClassBase<'db>) -> Self {
         match value {
             ClassBase::Any => Type::Any,
-            ClassBase::Todo => Type::Todo,
+            ClassBase::Todo => todo_type!(),
             ClassBase::Unknown => Type::Unknown,
             ClassBase::Class(class) => Type::class_literal(class),
         }

crates/red_knot_python_semantic/src/types/narrow.rs

@@ -257,17 +257,26 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
         expression: Expression<'db>,
         is_positive: bool,
     ) -> Option<NarrowingConstraints<'db>> {
+        fn is_narrowing_target_candidate(expr: &ast::Expr) -> bool {
+            matches!(expr, ast::Expr::Name(_) | ast::Expr::Call(_))
+        }
+
         let ast::ExprCompare {
             range: _,
             left,
             ops,
             comparators,
         } = expr_compare;
-        if !left.is_name_expr() && comparators.iter().all(|c| !c.is_name_expr()) {
-            // If none of the comparators are name expressions,
-            // we have no symbol to narrow down the type of.
+
+        // Performance optimization: early return if there are no potential narrowing targets.
+        if !is_narrowing_target_candidate(left)
+            && comparators
+                .iter()
+                .all(|c| !is_narrowing_target_candidate(c))
+        {
             return None;
         }
+
         if !is_positive && comparators.len() > 1 {
             // We can't negate a constraint made by a multi-comparator expression, since we can't
             // know which comparison part is the one being negated.
@@ -283,42 +292,85 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
             .tuple_windows::<(&ruff_python_ast::Expr, &ruff_python_ast::Expr)>();
         let mut constraints = NarrowingConstraints::default();
         for (op, (left, right)) in std::iter::zip(&**ops, comparator_tuples) {
-            if let ast::Expr::Name(ast::ExprName {
-                range: _,
-                id,
-                ctx: _,
-            }) = left
-            {
-                // SAFETY: we should always have a symbol for every Name node.
-                let symbol = self.symbols().symbol_id_by_name(id).unwrap();
-                let rhs_ty = inference.expression_ty(right.scoped_expression_id(self.db, scope));
+            let rhs_ty = inference.expression_ty(right.scoped_expression_id(self.db, scope));
 
-                match if is_positive { *op } else { op.negate() } {
-                    ast::CmpOp::IsNot => {
-                        if rhs_ty.is_singleton(self.db) {
-                            let ty = IntersectionBuilder::new(self.db)
-                                .add_negative(rhs_ty)
-                                .build();
-                            constraints.insert(symbol, ty);
-                        } else {
-                            // Non-singletons cannot be safely narrowed using `is not`
+            match left {
+                ast::Expr::Name(ast::ExprName {
+                    range: _,
+                    id,
+                    ctx: _,
+                }) => {
+                    let symbol = self
+                        .symbols()
+                        .symbol_id_by_name(id)
+                        .expect("Should always have a symbol for every Name node");
+
+                    match if is_positive { *op } else { op.negate() } {
+                        ast::CmpOp::IsNot => {
+                            if rhs_ty.is_singleton(self.db) {
+                                let ty = IntersectionBuilder::new(self.db)
+                                    .add_negative(rhs_ty)
+                                    .build();
+                                constraints.insert(symbol, ty);
+                            } else {
+                                // Non-singletons cannot be safely narrowed using `is not`
+                            }
                         }
-                    }
-                    ast::CmpOp::Is => {
-                        constraints.insert(symbol, rhs_ty);
-                    }
-                    ast::CmpOp::NotEq => {
-                        if rhs_ty.is_single_valued(self.db) {
-                            let ty = IntersectionBuilder::new(self.db)
-                                .add_negative(rhs_ty)
-                                .build();
-                            constraints.insert(symbol, ty);
+                        ast::CmpOp::Is => {
+                            constraints.insert(symbol, rhs_ty);
+                        }
+                        ast::CmpOp::NotEq => {
+                            if rhs_ty.is_single_valued(self.db) {
+                                let ty = IntersectionBuilder::new(self.db)
+                                    .add_negative(rhs_ty)
+                                    .build();
+                                constraints.insert(symbol, ty);
+                            }
+                        }
+                        _ => {
+                            // TODO other comparison types
                         }
-                    }
-                    _ => {
-                        // TODO other comparison types
                     }
                 }
+                ast::Expr::Call(ast::ExprCall {
+                    range: _,
+                    func: callable,
+                    arguments:
+                        ast::Arguments {
+                            args,
+                            keywords,
+                            range: _,
+                        },
+                }) if rhs_ty.is_class_literal() && keywords.is_empty() => {
+                    let [ast::Expr::Name(ast::ExprName { id, .. })] = &**args else {
+                        continue;
+                    };
+
+                    let is_valid_constraint = if is_positive {
+                        op == &ast::CmpOp::Is
+                    } else {
+                        op == &ast::CmpOp::IsNot
+                    };
+
+                    if !is_valid_constraint {
+                        continue;
+                    }
+
+                    let callable_ty =
+                        inference.expression_ty(callable.scoped_expression_id(self.db, scope));
+
+                    if callable_ty
+                        .into_class_literal()
+                        .is_some_and(|c| c.class.is_known(self.db, KnownClass::Type))
+                    {
+                        let symbol = self
+                            .symbols()
+                            .symbol_id_by_name(id)
+                            .expect("Should always have a symbol for every Name node");
+                        constraints.insert(symbol, rhs_ty.to_instance(self.db));
+                    }
+                }
+                _ => {}
             }
         }
         Some(constraints)

crates/red_knot_python_semantic/src/types/signatures.rs

@@ -1,7 +1,7 @@
 #![allow(dead_code)]
 use super::{definition_expression_ty, Type};
-use crate::semantic_index::definition::Definition;
 use crate::Db;
+use crate::{semantic_index::definition::Definition, types::todo_type};
 use ruff_python_ast::{self as ast, name::Name};
 
 /// A typed callable signature.
@@ -18,7 +18,7 @@ impl<'db> Signature<'db> {
     pub(crate) fn todo() -> Self {
         Self {
             parameters: Parameters::todo(),
-            return_ty: Type::Todo,
+            return_ty: todo_type!("return type"),
         }
     }
 
@@ -33,8 +33,7 @@ impl<'db> Signature<'db> {
             .as_ref()
             .map(|returns| {
                 if function_node.is_async {
-                    // TODO: generic `types.CoroutineType`!
-                    Type::Todo
+                    todo_type!("generic types.CoroutineType")
                 } else {
                     definition_expression_ty(db, definition, returns.as_ref())
                 }
@@ -81,11 +80,11 @@ impl<'db> Parameters<'db> {
         Self {
             variadic: Some(Parameter {
                 name: Some(Name::new_static("args")),
-                annotated_ty: Type::Todo,
+                annotated_ty: todo_type!(),
             }),
             keywords: Some(Parameter {
                 name: Some(Name::new_static("kwargs")),
-                annotated_ty: Type::Todo,
+                annotated_ty: todo_type!(),
             }),
             ..Default::default()
         }

crates/red_knot_python_semantic/src/types/unpacker.rs

@@ -6,7 +6,7 @@ use rustc_hash::FxHashMap;
 
 use crate::semantic_index::ast_ids::{HasScopedExpressionId, ScopedExpressionId};
 use crate::semantic_index::symbol::ScopeId;
-use crate::types::{Type, TypeCheckDiagnostics, TypeCheckDiagnosticsBuilder};
+use crate::types::{todo_type, Type, TypeCheckDiagnostics, TypeCheckDiagnosticsBuilder};
 use crate::Db;
 
 /// Unpacks the value expression type to their respective targets.
@@ -59,7 +59,7 @@ impl<'db> Unpacker<'db> {
                             // TODO: Combine the types into a list type. If the
                             // starred_element_types is empty, then it should be `List[Any]`.
                             // combine_types(starred_element_types);
-                            element_types.push(Type::Todo);
+                            element_types.push(todo_type!("starred unpacking"));
 
                             element_types.extend_from_slice(
                                 // SAFETY: Safe because of the length check above.
@@ -72,7 +72,7 @@ impl<'db> Unpacker<'db> {
                             // index.
                             element_types.resize(elts.len() - 1, Type::Unknown);
                             // TODO: This should be `list[Unknown]`
-                            element_types.insert(starred_index, Type::Todo);
+                            element_types.insert(starred_index, todo_type!("starred unpacking"));
                             Cow::Owned(element_types)
                         }
                     } else {

crates/red_knot_test/src/matcher.rs

@@ -180,6 +180,16 @@ where
     }
 }
 
+/// Discard `@Todo`-type metadata from expected types, which is not available
+/// when running in release mode.
+#[cfg(not(debug_assertions))]
+fn discard_todo_metadata(ty: &str) -> std::borrow::Cow<'_, str> {
+    static TODO_METADATA_REGEX: std::sync::LazyLock<regex::Regex> =
+        std::sync::LazyLock::new(|| regex::Regex::new(r"@Todo\([^)]*\)").unwrap());
+
+    TODO_METADATA_REGEX.replace_all(ty, "@Todo")
+}
+
 struct Matcher {
     line_index: LineIndex,
     source: SourceText,
@@ -276,6 +286,9 @@ impl Matcher {
                 }
             }
             Assertion::Revealed(expected_type) => {
+                #[cfg(not(debug_assertions))]
+                let expected_type = discard_todo_metadata(&expected_type);
+
                 let mut matched_revealed_type = None;
                 let mut matched_undefined_reveal = None;
                 let expected_reveal_type_message = format!("Revealed type is `{expected_type}`");

crates/red_knot_wasm/src/lib.rs

@@ -184,8 +184,8 @@ impl Settings {
 #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Default)]
 pub enum TargetVersion {
     Py37,
-    #[default]
     Py38,
+    #[default]
     Py39,
     Py310,
     Py311,
@@ -291,3 +291,17 @@ impl System for WasmSystem {
 fn not_found() -> std::io::Error {
     std::io::Error::new(std::io::ErrorKind::NotFound, "No such file or directory")
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::TargetVersion;
+    use red_knot_python_semantic::PythonVersion;
+
+    #[test]
+    fn same_default_as_python_version() {
+        assert_eq!(
+            PythonVersion::from(TargetVersion::default()),
+            PythonVersion::default()
+        );
+    }
+}

crates/red_knot_workspace/resources/test/corpus/15_while_break_invalid_in_class.py

@@ -0,0 +1,6 @@
+while True:
+
+    class A:
+        x: int
+
+        break

crates/red_knot_workspace/resources/test/corpus/15_while_break_invalid_in_func.py

@@ -0,0 +1,6 @@
+while True:
+
+    def b():
+        x: int
+
+        break

crates/red_knot_workspace/resources/test/corpus/16_for_break_invalid_in_class.py

@@ -0,0 +1,6 @@
+for _ in range(1):
+
+    class A:
+        x: int
+
+        break

crates/red_knot_workspace/resources/test/corpus/16_for_break_invalid_in_func.py

@@ -0,0 +1,6 @@
+for _ in range(1):
+
+    def b():
+        x: int
+
+        break

crates/red_knot_workspace/resources/test/corpus/89_type_alias_invalid_bound.py

@@ -0,0 +1 @@
+../../../../ruff_python_parser/resources/inline/err/type_param_invalid_bound_expr.py

crates/red_knot_workspace/resources/test/corpus/94_strformat_conversion.py

@@ -0,0 +1,3 @@
+msg = "hello"
+
+f"{msg!r:>{10+10}}"

crates/red_knot_workspace/resources/test/corpus/95_annotation_fstring_invalid.py

@@ -0,0 +1 @@
+x: f"Literal[{1 + 2}]" = 3

crates/red_knot_workspace/resources/test/corpus/95_annotation_union.py

@@ -0,0 +1,3 @@
+from typing import Union
+
+x: Union[int, str] = 1

crates/red_knot_workspace/src/workspace/snapshots/red_knot_workspace__workspace__metadata__tests__member_pattern_matching_file.snap

@@ -1,6 +1,7 @@
 ---
 source: crates/red_knot_workspace/src/workspace/metadata.rs
 expression: "&workspace"
+snapshot_kind: text
 ---
 WorkspaceMetadata(
   root: "/app",
@@ -23,7 +24,7 @@ WorkspaceMetadata(
     program: ProgramSettings(
       target_version: PythonVersion(
         major: 3,
-        minor: 8,
+        minor: 9,
       ),
       search_paths: SearchPathSettings(
         extra_paths: [],

crates/red_knot_workspace/src/workspace/snapshots/red_knot_workspace__workspace__metadata__tests__member_pattern_matching_hidden_folder.snap

@@ -1,6 +1,7 @@
 ---
 source: crates/red_knot_workspace/src/workspace/metadata.rs
 expression: workspace
+snapshot_kind: text
 ---
 WorkspaceMetadata(
   root: "/app",
@@ -23,7 +24,7 @@ WorkspaceMetadata(
     program: ProgramSettings(
       target_version: PythonVersion(
         major: 3,
-        minor: 8,
+        minor: 9,
       ),
       search_paths: SearchPathSettings(
         extra_paths: [],

crates/red_knot_workspace/src/workspace/snapshots/red_knot_workspace__workspace__metadata__tests__package_without_pyproject.snap

@@ -1,6 +1,7 @@
 ---
 source: crates/red_knot_workspace/src/workspace/metadata.rs
 expression: workspace
+snapshot_kind: text
 ---
 WorkspaceMetadata(
   root: "/app",
@@ -23,7 +24,7 @@ WorkspaceMetadata(
     program: ProgramSettings(
       target_version: PythonVersion(
         major: 3,
-        minor: 8,
+        minor: 9,
       ),
       search_paths: SearchPathSettings(
         extra_paths: [],

crates/red_knot_workspace/src/workspace/snapshots/red_knot_workspace__workspace__metadata__tests__single_package.snap

@@ -1,6 +1,7 @@
 ---
 source: crates/red_knot_workspace/src/workspace/metadata.rs
 expression: workspace
+snapshot_kind: text
 ---
 WorkspaceMetadata(
   root: "/app",
@@ -23,7 +24,7 @@ WorkspaceMetadata(
     program: ProgramSettings(
       target_version: PythonVersion(
         major: 3,
-        minor: 8,
+        minor: 9,
       ),
       search_paths: SearchPathSettings(
         extra_paths: [],

crates/red_knot_workspace/src/workspace/snapshots/red_knot_workspace__workspace__metadata__tests__workspace_excluded.snap

@@ -1,6 +1,7 @@
 ---
 source: crates/red_knot_workspace/src/workspace/metadata.rs
 expression: workspace
+snapshot_kind: text
 ---
 WorkspaceMetadata(
   root: "/app",
@@ -36,7 +37,7 @@ WorkspaceMetadata(
     program: ProgramSettings(
       target_version: PythonVersion(
         major: 3,
-        minor: 8,
+        minor: 9,
       ),
       search_paths: SearchPathSettings(
         extra_paths: [],

crates/red_knot_workspace/src/workspace/snapshots/red_knot_workspace__workspace__metadata__tests__workspace_members.snap

@@ -1,6 +1,7 @@
 ---
 source: crates/red_knot_workspace/src/workspace/metadata.rs
 expression: workspace
+snapshot_kind: text
 ---
 WorkspaceMetadata(
   root: "/app",
@@ -49,7 +50,7 @@ WorkspaceMetadata(
     program: ProgramSettings(
       target_version: PythonVersion(
         major: 3,
-        minor: 8,
+        minor: 9,
       ),
       search_paths: SearchPathSettings(
         extra_paths: [],

crates/red_knot_workspace/tests/check.rs

@@ -42,6 +42,7 @@ fn parser_no_panic() -> anyhow::Result<()> {
 }
 
 #[test]
+#[ignore = "Enable running once there are fewer failures"]
 fn linter_af_no_panic() -> anyhow::Result<()> {
     let workspace_root = get_workspace_root()?;
     run_corpus_tests(&format!(
@@ -50,6 +51,7 @@ fn linter_af_no_panic() -> anyhow::Result<()> {
 }
 
 #[test]
+#[ignore = "Enable running once there are fewer failures"]
 fn linter_gz_no_panic() -> anyhow::Result<()> {
     let workspace_root = get_workspace_root()?;
     run_corpus_tests(&format!(
@@ -259,39 +261,18 @@ impl SourceOrderVisitor<'_> for PullTypesVisitor<'_> {
 
         source_order::walk_alias(self, alias);
     }
-
-    fn visit_annotation(&mut self, annotation: &Expr) {
-        let _ty = annotation.ty(&self.model);
-
-        // Do not descend into annotation expressions, as we do not infer types
-        // for every *sub*expression of an annotation. For example: we can not
-        // infer a reasonable type for the ellipsis in `tuple[int, ...]`.
-    }
 }
 
 /// Whether or not the .py/.pyi version of this file is expected to fail
+#[rustfmt::skip]
 const KNOWN_FAILURES: &[(&str, bool, bool)] = &[
-    // Probably related to missing support for type aliases / type params:
-    ("crates/ruff_python_parser/resources/inline/err/type_param_invalid_bound_expr.py", true, true),
-    ("crates/ruff_python_parser/resources/inline/err/type_param_param_spec_invalid_default_expr.py", true, true),
-    ("crates/ruff_python_parser/resources/inline/err/type_param_type_var_invalid_default_expr.py", true, true),
-    ("crates/ruff_python_parser/resources/inline/err/type_param_type_var_missing_default.py", true, true),
-    ("crates/ruff_python_parser/resources/inline/err/type_param_type_var_tuple_invalid_default_expr.py", true, true),
-    ("crates/ruff_python_parser/resources/inline/ok/type_param_param_spec.py", true, true),
-    ("crates/ruff_python_parser/resources/inline/ok/type_param_type_var_tuple.py", true, true),
-    ("crates/ruff_python_parser/resources/inline/ok/type_param_type_var.py", true, true),
-    ("crates/ruff_python_parser/resources/valid/statement/type.py", true, true),
-    ("crates/ruff_linter/resources/test/fixtures/flake8_type_checking/TCH004_15.py", true, true),
-    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F401_19.py", true, true),
-    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_14.py", false, true),
-    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_17.py", true, true),
-    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_15.py", true, true),
-    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_20.py", true, true),
+    // related to circular references in class definitions
     ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_26.py", true, false),
-    // Fails for unknown reasons:
-    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F541.py", true, true),
-    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F632.py", true, true),
     ("crates/ruff_linter/resources/test/fixtures/pyflakes/F811_19.py", true, false),
     ("crates/ruff_linter/resources/test/fixtures/pyupgrade/UP039.py", true, false),
-    ("crates/ruff_python_parser/resources/valid/expressions/f_string.py", true, true),
+    // related to circular references in type aliases (salsa cycle panic):
+    ("crates/ruff_python_parser/resources/inline/err/type_alias_invalid_value_expr.py", true, true),
+    // related to circular references in f-string annotations (invalid syntax)
+    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_15.py", true, true),
+    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_14.py", false, true),
 ];

crates/ruff/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff"
-version = "0.7.4"
+version = "0.8.1"
 publish = true
 authors = { workspace = true }
 edition = { workspace = true }

crates/ruff/tests/integration_test.rs

@@ -840,7 +840,7 @@ fn stdin_multiple_parse_error() {
 
 #[test]
 fn parse_error_not_included() {
-    // Select any rule except for `E999`, syntax error should still be shown.
+    // Parse errors are always shown
     let mut cmd = RuffCheck::default().args(["--select=I"]).build();
     assert_cmd_snapshot!(cmd
         .pass_stdin("foo =\n"), @r"
@@ -859,27 +859,6 @@ fn parse_error_not_included() {
     ");
 }
 
-#[test]
-fn deprecated_parse_error_selection() {
-    let mut cmd = RuffCheck::default().args(["--select=E999"]).build();
-    assert_cmd_snapshot!(cmd
-        .pass_stdin("foo =\n"), @r"
-    success: false
-    exit_code: 1
-    ----- stdout -----
-    -:1:6: SyntaxError: Expected an expression
-      |
-    1 | foo =
-      |      ^
-      |
-
-    Found 1 error.
-
-    ----- stderr -----
-    warning: Rule `E999` is deprecated and will be removed in a future release. Syntax errors will always be shown regardless of whether this rule is selected or not.
-    ");
-}
-
 #[test]
 fn full_output_preview() {
     let mut cmd = RuffCheck::default().args(["--preview"]).build();
@@ -1250,6 +1229,68 @@ fn removed_indirect() {
     ");
 }
 
+#[test]
+fn removed_ignore_direct() {
+    let mut cmd = RuffCheck::default().args(["--ignore", "UP027"]).build();
+    assert_cmd_snapshot!(cmd, @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    All checks passed!
+
+    ----- stderr -----
+    warning: The following rules have been removed and ignoring them has no effect:
+        - UP027
+    ");
+}
+
+#[test]
+fn removed_ignore_multiple_direct() {
+    let mut cmd = RuffCheck::default()
+        .args(["--ignore", "UP027", "--ignore", "PLR1706"])
+        .build();
+    assert_cmd_snapshot!(cmd, @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    All checks passed!
+
+    ----- stderr -----
+    warning: The following rules have been removed and ignoring them has no effect:
+        - PLR1706
+        - UP027
+    ");
+}
+
+#[test]
+fn removed_ignore_remapped_direct() {
+    let mut cmd = RuffCheck::default().args(["--ignore", "PGH001"]).build();
+    assert_cmd_snapshot!(cmd, @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    All checks passed!
+
+    ----- stderr -----
+    warning: `PGH001` has been remapped to `S307`.
+    ");
+}
+
+#[test]
+fn removed_ignore_indirect() {
+    // `PLR170` includes removed rules but should not select or warn
+    // since it is not a "direct" selection
+    let mut cmd = RuffCheck::default().args(["--ignore", "PLR170"]).build();
+    assert_cmd_snapshot!(cmd, @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    All checks passed!
+
+    ----- stderr -----
+    ");
+}
+
 #[test]
 fn redirect_direct() {
     // Selection of a redirected rule directly should use the new rule and warn

crates/ruff/tests/lint.rs

@@ -1966,3 +1966,75 @@ fn nested_implicit_namespace_package() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn flake8_import_convention_invalid_aliases_config_alias_name() -> Result<()> {
+    let tempdir = TempDir::new()?;
+    let ruff_toml = tempdir.path().join("ruff.toml");
+    fs::write(
+        &ruff_toml,
+        r#"
+[lint.flake8-import-conventions.aliases]
+"module.name" = "invalid.alias"
+"#,
+    )?;
+
+    insta::with_settings!({
+        filters => vec![(tempdir_filter(&tempdir).as_str(), "[TMP]/")]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .args(STDIN_BASE_OPTIONS)
+            .arg("--config")
+            .arg(&ruff_toml)
+    , @r###"
+        success: false
+        exit_code: 2
+        ----- stdout -----
+
+        ----- stderr -----
+        ruff failed
+          Cause: Failed to parse [TMP]/ruff.toml
+          Cause: TOML parse error at line 2, column 2
+          |
+        2 | [lint.flake8-import-conventions.aliases]
+          |  ^^^^
+        invalid value: string "invalid.alias", expected a Python identifier
+        "###);});
+    Ok(())
+}
+
+#[test]
+fn flake8_import_convention_invalid_aliases_config_module_name() -> Result<()> {
+    let tempdir = TempDir::new()?;
+    let ruff_toml = tempdir.path().join("ruff.toml");
+    fs::write(
+        &ruff_toml,
+        r#"
+[lint.flake8-import-conventions.aliases]
+"module..invalid" = "alias"
+"#,
+    )?;
+
+    insta::with_settings!({
+        filters => vec![(tempdir_filter(&tempdir).as_str(), "[TMP]/")]
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .args(STDIN_BASE_OPTIONS)
+            .arg("--config")
+            .arg(&ruff_toml)
+    , @r###"
+        success: false
+        exit_code: 2
+        ----- stdout -----
+
+        ----- stderr -----
+        ruff failed
+          Cause: Failed to parse [TMP]/ruff.toml
+          Cause: TOML parse error at line 2, column 2
+          |
+        2 | [lint.flake8-import-conventions.aliases]
+          |  ^^^^
+        invalid value: string "module..invalid", expected a sequence of Python identifiers delimited by periods
+        "###);});
+    Ok(())
+}

crates/ruff/tests/snapshots/show_settings__display_default_settings.snap

@@ -88,7 +88,6 @@ linter.rules.enabled = [
 	ambiguous-class-name (E742),
 	ambiguous-function-name (E743),
 	io-error (E902),
-	syntax-error (E999),
 	unused-import (F401),
 	import-shadowed-by-loop-var (F402),
 	undefined-local-with-import-star (F403),
@@ -150,7 +149,6 @@ linter.rules.should_fix = [
 	ambiguous-class-name (E742),
 	ambiguous-function-name (E743),
 	io-error (E902),
-	syntax-error (E999),
 	unused-import (F401),
 	import-shadowed-by-loop-var (F402),
 	undefined-local-with-import-star (F403),

crates/ruff_benchmark/benches/red_knot.rs

@@ -123,15 +123,9 @@ fn benchmark_incremental(criterion: &mut Criterion) {
     fn setup() -> Case {
         let case = setup_case();
 
-        let result: Vec<_> = case
-            .db
-            .check()
-            .unwrap()
-            .into_iter()
-            .map(|diagnostic| diagnostic.display(&case.db).to_string())
-            .collect();
+        let result: Vec<_> = case.db.check().unwrap();
 
-        assert_eq!(result, EXPECTED_DIAGNOSTICS);
+        assert_diagnostics(&case.db, result);
 
         case.fs
             .write_file(
@@ -174,19 +168,29 @@ fn benchmark_cold(criterion: &mut Criterion) {
             setup_case,
             |case| {
                 let Case { db, .. } = case;
-                let result: Vec<_> = db
-                    .check()
-                    .unwrap()
-                    .into_iter()
-                    .map(|diagnostic| diagnostic.display(db).to_string())
-                    .collect();
+                let result: Vec<_> = db.check().unwrap();
 
-                assert_eq!(result, EXPECTED_DIAGNOSTICS);
+                assert_diagnostics(db, result);
             },
             BatchSize::SmallInput,
         );
     });
 }
 
+#[track_caller]
+fn assert_diagnostics(db: &dyn Db, diagnostics: Vec<Box<dyn Diagnostic>>) {
+    let normalized: Vec<_> = diagnostics
+        .into_iter()
+        .map(|diagnostic| {
+            diagnostic
+                .display(db.upcast())
+                .to_string()
+                .replace('\\', "/")
+        })
+        .collect();
+
+    assert_eq!(&normalized, EXPECTED_DIAGNOSTICS);
+}
+
 criterion_group!(check_file, benchmark_cold, benchmark_incremental);
 criterion_main!(check_file);

crates/ruff_diagnostics/src/lib.rs

@@ -2,7 +2,7 @@ pub use diagnostic::{Diagnostic, DiagnosticKind};
 pub use edit::Edit;
 pub use fix::{Applicability, Fix, IsolationLevel};
 pub use source_map::{SourceMap, SourceMarker};
-pub use violation::{AlwaysFixableViolation, FixAvailability, Violation};
+pub use violation::{AlwaysFixableViolation, FixAvailability, Violation, ViolationMetadata};
 
 mod diagnostic;
 mod edit;

crates/ruff_diagnostics/src/violation.rs

@@ -1,3 +1,4 @@
+use crate::DiagnosticKind;
 use std::fmt::{Debug, Display};
 
 #[derive(Debug, Copy, Clone)]
@@ -17,7 +18,16 @@ impl Display for FixAvailability {
     }
 }
 
-pub trait Violation: Debug + PartialEq + Eq {
+pub trait ViolationMetadata {
+    /// Returns the rule name of this violation
+    fn rule_name() -> &'static str;
+
+    /// Returns an explanation of what this violation catches,
+    /// why it's bad, and what users should do instead.
+    fn explain() -> Option<&'static str>;
+}
+
+pub trait Violation: ViolationMetadata {
     /// `None` in the case a fix is never available or otherwise Some
     /// [`FixAvailability`] describing the available fix.
     const FIX_AVAILABILITY: FixAvailability = FixAvailability::None;
@@ -41,7 +51,7 @@ pub trait Violation: Debug + PartialEq + Eq {
 
 /// This trait exists just to make implementing the [`Violation`] trait more
 /// convenient for violations that can always be fixed.
-pub trait AlwaysFixableViolation: Debug + PartialEq + Eq {
+pub trait AlwaysFixableViolation: ViolationMetadata {
     /// The message used to describe the violation.
     fn message(&self) -> String;
 
@@ -69,3 +79,16 @@ impl<V: AlwaysFixableViolation> Violation for V {
         <Self as AlwaysFixableViolation>::message_formats()
     }
 }
+
+impl<T> From<T> for DiagnosticKind
+where
+    T: Violation,
+{
+    fn from(value: T) -> Self {
+        Self {
+            body: Violation::message(&value),
+            suggestion: Violation::fix_title(&value),
+            name: T::rule_name().to_string(),
+        }
+    }
+}

crates/ruff_formatter/src/buffer.rs

@@ -1,10 +1,11 @@
 use super::{write, Arguments, FormatElement};
 use crate::format_element::Interned;
-use crate::prelude::LineMode;
+use crate::prelude::{LineMode, Tag};
 use crate::{FormatResult, FormatState};
 use rustc_hash::FxHashMap;
 use std::any::{Any, TypeId};
 use std::fmt::Debug;
+use std::num::NonZeroUsize;
 use std::ops::{Deref, DerefMut};
 
 /// A trait for writing or formatting into [`FormatElement`]-accepting buffers or streams.
@@ -294,10 +295,11 @@ where
     }
 }
 
-/// A Buffer that removes any soft line breaks.
+/// A Buffer that removes any soft line breaks or [`if_group_breaks`](crate::builders::if_group_breaks) elements.
 ///
 /// - Removes [`lines`](FormatElement::Line) with the mode [`Soft`](LineMode::Soft).
 /// - Replaces [`lines`](FormatElement::Line) with the mode [`Soft`](LineMode::SoftOrSpace) with a [`Space`](FormatElement::Space)
+/// - Removes [`if_group_breaks`](crate::builders::if_group_breaks) elements.
 ///
 /// # Examples
 ///
@@ -350,6 +352,8 @@ pub struct RemoveSoftLinesBuffer<'a, Context> {
     /// It's fine to not snapshot the cache. The worst that can happen is that it holds on interned elements
     /// that are now unused. But there's little harm in that and the cache is cleaned when dropping the buffer.
     interned_cache: FxHashMap<Interned, Interned>,
+
+    state: RemoveSoftLineBreaksState,
 }
 
 impl<'a, Context> RemoveSoftLinesBuffer<'a, Context> {
@@ -357,6 +361,7 @@ impl<'a, Context> RemoveSoftLinesBuffer<'a, Context> {
     pub fn new(inner: &'a mut dyn Buffer<Context = Context>) -> Self {
         Self {
             inner,
+            state: RemoveSoftLineBreaksState::default(),
             interned_cache: FxHashMap::default(),
         }
     }
@@ -375,6 +380,8 @@ fn clean_interned(
     if let Some(cleaned) = interned_cache.get(interned) {
         cleaned.clone()
     } else {
+        let mut state = RemoveSoftLineBreaksState::default();
+
         // Find the first soft line break element or interned element that must be changed
         let result = interned
             .iter()
@@ -382,8 +389,9 @@ fn clean_interned(
             .find_map(|(index, element)| match element {
                 FormatElement::Line(LineMode::Soft | LineMode::SoftOrSpace) => {
                     let mut cleaned = Vec::new();
-                    cleaned.extend_from_slice(&interned[..index]);
-                    Some((cleaned, &interned[index..]))
+                    let (before, after) = interned.split_at(index);
+                    cleaned.extend_from_slice(before);
+                    Some((cleaned, &after[1..]))
                 }
                 FormatElement::Interned(inner) => {
                     let cleaned_inner = clean_interned(inner, interned_cache);
@@ -398,19 +406,33 @@ fn clean_interned(
                     }
                 }
 
-                _ => None,
+                element => {
+                    if state.should_drop(element) {
+                        let mut cleaned = Vec::new();
+                        let (before, after) = interned.split_at(index);
+                        cleaned.extend_from_slice(before);
+                        Some((cleaned, &after[1..]))
+                    } else {
+                        None
+                    }
+                }
             });
 
         let result = match result {
             // Copy the whole interned buffer so that becomes possible to change the necessary elements.
             Some((mut cleaned, rest)) => {
                 for element in rest {
+                    if state.should_drop(element) {
+                        continue;
+                    }
+
                     let element = match element {
                         FormatElement::Line(LineMode::Soft) => continue,
                         FormatElement::Line(LineMode::SoftOrSpace) => FormatElement::Space,
                         FormatElement::Interned(interned) => {
                             FormatElement::Interned(clean_interned(interned, interned_cache))
                         }
+
                         element => element.clone(),
                     };
                     cleaned.push(element);
@@ -431,12 +453,17 @@ impl<Context> Buffer for RemoveSoftLinesBuffer<'_, Context> {
     type Context = Context;
 
     fn write_element(&mut self, element: FormatElement) {
+        if self.state.should_drop(&element) {
+            return;
+        }
+
         let element = match element {
             FormatElement::Line(LineMode::Soft) => return,
             FormatElement::Line(LineMode::SoftOrSpace) => FormatElement::Space,
             FormatElement::Interned(interned) => {
                 FormatElement::Interned(self.clean_interned(&interned))
             }
+
             element => element,
         };
 
@@ -456,14 +483,77 @@ impl<Context> Buffer for RemoveSoftLinesBuffer<'_, Context> {
     }
 
     fn snapshot(&self) -> BufferSnapshot {
-        self.inner.snapshot()
+        BufferSnapshot::Any(Box::new(RemoveSoftLinebreaksSnapshot {
+            inner: self.inner.snapshot(),
+            state: self.state,
+        }))
     }
 
     fn restore_snapshot(&mut self, snapshot: BufferSnapshot) {
-        self.inner.restore_snapshot(snapshot);
+        let RemoveSoftLinebreaksSnapshot { inner, state } = snapshot.unwrap_any();
+        self.inner.restore_snapshot(inner);
+        self.state = state;
     }
 }
 
+#[derive(Copy, Clone, Debug, Default)]
+enum RemoveSoftLineBreaksState {
+    #[default]
+    Default,
+    InIfGroupBreaks {
+        conditional_content_level: NonZeroUsize,
+    },
+}
+
+impl RemoveSoftLineBreaksState {
+    fn should_drop(&mut self, element: &FormatElement) -> bool {
+        match self {
+            Self::Default => {
+                // Entered the start of an `if_group_breaks`
+                if let FormatElement::Tag(Tag::StartConditionalContent(condition)) = element {
+                    if condition.mode.is_expanded() {
+                        *self = Self::InIfGroupBreaks {
+                            conditional_content_level: NonZeroUsize::new(1).unwrap(),
+                        };
+                        return true;
+                    }
+                }
+
+                false
+            }
+            Self::InIfGroupBreaks {
+                conditional_content_level,
+            } => {
+                match element {
+                    // A nested `if_group_breaks` or `if_group_fits`
+                    FormatElement::Tag(Tag::StartConditionalContent(_)) => {
+                        *conditional_content_level = conditional_content_level.saturating_add(1);
+                    }
+                    // The end of an `if_group_breaks` or `if_group_fits`.
+                    FormatElement::Tag(Tag::EndConditionalContent) => {
+                        if let Some(level) = NonZeroUsize::new(conditional_content_level.get() - 1)
+                        {
+                            *conditional_content_level = level;
+                        } else {
+                            // Found the end tag of the initial `if_group_breaks`. Skip this element but retain
+                            // the elements coming after
+                            *self = RemoveSoftLineBreaksState::Default;
+                        }
+                    }
+                    _ => {}
+                }
+
+                true
+            }
+        }
+    }
+}
+
+struct RemoveSoftLinebreaksSnapshot {
+    inner: BufferSnapshot,
+    state: RemoveSoftLineBreaksState,
+}
+
 pub trait BufferExtensions: Buffer + Sized {
     /// Returns a new buffer that calls the passed inspector for every element that gets written to the output
     #[must_use]

crates/ruff_linter/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff_linter"
-version = "0.7.4"
+version = "0.8.1"
 publish = false
 authors = { workspace = true }
 edition = { workspace = true }

crates/ruff_linter/resources/test/fixtures/airflow/AIR301.py

@@ -0,0 +1,15 @@
+from airflow import DAG, dag
+
+DAG(dag_id="class_default_schedule")
+
+DAG(dag_id="class_schedule", schedule="@hourly")
+
+
+@dag()
+def decorator_default_schedule():
+    pass
+
+
+@dag(schedule="0 * * * *")
+def decorator_schedule():
+    pass

crates/ruff_linter/resources/test/fixtures/flake8_annotations/annotation_presence.py

@@ -71,7 +71,7 @@ class Foo:
     def foo(self: "Foo", a: int, b: int) -> int:
         pass
 
-    # ANN101
+    # OK
     def foo(self, a: int, b: int) -> int:
         pass
 
@@ -125,12 +125,12 @@ class Foo:
     def foo(cls: Type["Foo"], a: int, b: int) -> int:
         pass
 
-    # ANN102
+    # OK
     @classmethod
     def foo(cls, a: int, b: int) -> int:
         pass
 
-    # ANN101
+    # OK
     def foo(self, /, a: int, b: int) -> int:
         pass
 

crates/ruff_linter/resources/test/fixtures/flake8_bugbear/B039.py

@@ -14,6 +14,8 @@ ContextVar("cv", default=frozenset())
 ContextVar("cv", default=MappingProxyType({}))
 ContextVar("cv", default=re.compile("foo"))
 ContextVar("cv", default=float(1))
+ContextVar("cv", default=frozenset[str]())
+ContextVar[frozenset[str]]("cv", default=frozenset[str]())
 
 # Bad
 ContextVar("cv", default=[])
@@ -25,6 +27,8 @@ ContextVar("cv", default=[char for char in "foo"])
 ContextVar("cv", default={char for char in "foo"})
 ContextVar("cv", default={char: idx for idx, char in enumerate("foo")})
 ContextVar("cv", default=collections.deque())
+ContextVar("cv", default=set[str]())
+ContextVar[set[str]]("cv", default=set[str]())
 
 def bar() -> list[int]:
     return [1, 2, 3]

crates/ruff_linter/resources/test/fixtures/flake8_datetimez/DTZ901.py

@@ -13,6 +13,12 @@ datetime.datetime.min.replace(hour=...)
 datetime.datetime.max.replace(tzinfo=...)
 datetime.datetime.min.replace(tzinfo=...)
 
+datetime.datetime.max.time()
+datetime.datetime.min.time()
+
+datetime.datetime.max.time(foo=...)
+datetime.datetime.min.time(foo=...)
+
 
 from datetime import datetime
 
@@ -28,3 +34,9 @@ datetime.min.replace(hour=...)
 # No error
 datetime.max.replace(tzinfo=...)
 datetime.min.replace(tzinfo=...)
+
+datetime.max.time()
+datetime.min.time()
+
+datetime.max.time(foo=...)
+datetime.min.time(foo=...)

crates/ruff_linter/resources/test/fixtures/flake8_pie/PIE790.py

@@ -235,3 +235,15 @@ if typing.TYPE_CHECKING:
     def contains_meaningful_ellipsis() -> list[int]:
         """Allow this in a TYPE_CHECKING block."""
         ...
+
+# https://github.com/astral-sh/ruff/issues/12616
+class PotentialDocstring1:
+    pass
+    """
+    Lorem ipsum dolor sit amet.
+    """
+
+
+class PotentialDocstring2:
+    ...
+    'Lorem ipsum dolor sit amet.'

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI016.py

@@ -84,3 +84,30 @@ field24: typing.Union[int, typing.Union[int, int]]  # PYI016: Duplicate union me
 # duplicates of the outer `int`), but not three times (which would indicate that
 # we incorrectly re-checked the nested union).
 field25: typing.Union[int, int | int]  # PYI016: Duplicate union member `int`
+
+# Should emit in cases with nested `typing.Union`
+field26: typing.Union[typing.Union[int, int]]  # PYI016: Duplicate union member `int`
+
+# Should emit in cases with nested `typing.Union`
+field27: typing.Union[typing.Union[typing.Union[int, int]]]  # PYI016: Duplicate union member `int`
+
+# Should emit in cases with mixed `typing.Union` and `|`
+field28: typing.Union[int | int]  # Error
+
+# Should emit twice in cases with multiple nested `typing.Union`
+field29: typing.Union[int, typing.Union[typing.Union[int, int]]]  # Error
+
+# Should emit once in cases with multiple nested `typing.Union`
+field30: typing.Union[int, typing.Union[typing.Union[int, str]]]  # Error
+
+# Should emit once, and fix to `typing.Union[float, int]`
+field31: typing.Union[float, typing.Union[int | int]]  # Error
+
+# Should emit once, and fix to `typing.Union[float, int]`
+field32: typing.Union[float, typing.Union[int | int | int]]  # Error
+
+# Test case for mixed union type fix
+field33: typing.Union[typing.Union[int | int] | typing.Union[int | int]] # Error
+
+# Test case for mixed union type
+field34: typing.Union[list[int], str] | typing.Union[bytes, list[int]]  # Error

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI016.pyi

@@ -84,3 +84,30 @@ field24: typing.Union[int, typing.Union[int, int]]  # PYI016: Duplicate union me
 # duplicates of the outer `int`), but not three times (which would indicate that
 # we incorrectly re-checked the nested union).
 field25: typing.Union[int, int | int]  # PYI016: Duplicate union member `int`
+
+# Should emit in cases with nested `typing.Union`
+field26: typing.Union[typing.Union[int, int]]  # PYI016: Duplicate union member `int`
+
+# Should emit in cases with nested `typing.Union`
+field27: typing.Union[typing.Union[typing.Union[int, int]]]  # PYI016: Duplicate union member `int`
+
+# Should emit in cases with mixed `typing.Union` and `|`
+field28: typing.Union[int | int]  # Error
+
+# Should emit twice in cases with multiple nested `typing.Union`
+field29: typing.Union[int, typing.Union[typing.Union[int, int]]]  # Error
+
+# Should emit once in cases with multiple nested `typing.Union`
+field30: typing.Union[int, typing.Union[typing.Union[int, str]]]  # Error
+
+# Should emit once, and fix to `typing.Union[float, int]`
+field31: typing.Union[float, typing.Union[int | int]]  # Error
+
+# Should emit once, and fix to `typing.Union[float, int]`
+field32: typing.Union[float, typing.Union[int | int | int]]  # Error
+
+# Test case for mixed union type fix
+field33: typing.Union[typing.Union[int | int] | typing.Union[int | int]] # Error
+
+# Test case for mixed union type
+field34: typing.Union[list[int], str] | typing.Union[bytes, list[int]]  # Error

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI041.py

@@ -39,14 +39,30 @@ async def f4(**kwargs: int | int | float) -> None:
     ...
 
 
-def f5(
+def f5(arg1: int, *args: Union[int, int, float]) -> None: 
+    ...
+
+
+def f6(arg1: int, *args: Union[Union[int, int, float]]) -> None: 
+    ...
+
+
+def f7(arg1: int, *args: Union[Union[Union[int, int, float]]]) -> None: 
+    ...
+
+
+def f8(arg1: int, *args: Union[Union[Union[int | int | float]]]) -> None: 
+    ...
+
+
+def f9(
     arg: Union[  # comment 
         float, # another
         complex, int]
     ) -> None: 
     ...
 
-def f6(
+def f10(
     arg: (
         int | # comment
         float |  # another

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI041.pyi

@@ -46,6 +46,18 @@ def f6(
     )    
     ) -> None: ... # PYI041
 
+def f5(arg1: int, *args: Union[int, int, float]) -> None: ...  # PYI041
+
+
+def f6(arg1: int, *args: Union[Union[int, int, float]]) -> None: ...  # PYI041
+
+
+def f7(arg1: int, *args: Union[Union[Union[int, int, float]]]) -> None: ...  # PYI041
+
+
+def f8(arg1: int, *args: Union[Union[Union[int | int | float]]]) -> None: ...  # PYI041
+
+
 class Foo:
     def good(self, arg: int) -> None: ...
 

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI051.py

@@ -5,6 +5,9 @@ A: str | Literal["foo"]
 B: TypeAlias = typing.Union[Literal[b"bar", b"foo"], bytes, str]
 C: TypeAlias = typing.Union[Literal[5], int, typing.Union[Literal["foo"], str]]
 D: TypeAlias = typing.Union[Literal[b"str_bytes", 42], bytes, int]
+E: TypeAlias = typing.Union[typing.Union[typing.Union[typing.Union[Literal["foo"], str]]]]
+F: TypeAlias = typing.Union[str, typing.Union[typing.Union[typing.Union[Literal["foo"], int]]]]
+G: typing.Union[str, typing.Union[typing.Union[typing.Union[Literal["foo"], int]]]]
 
 def func(x: complex | Literal[1J], y: Union[Literal[3.14], float]): ...
 

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI051.pyi

@@ -5,6 +5,9 @@ A: str | Literal["foo"]
 B: TypeAlias = typing.Union[Literal[b"bar", b"foo"], bytes, str]
 C: TypeAlias = typing.Union[Literal[5], int, typing.Union[Literal["foo"], str]]
 D: TypeAlias = typing.Union[Literal[b"str_bytes", 42], bytes, int]
+E: TypeAlias = typing.Union[typing.Union[typing.Union[typing.Union[Literal["foo"], str]]]]
+F: TypeAlias = typing.Union[str, typing.Union[typing.Union[typing.Union[Literal["foo"], int]]]]
+G: typing.Union[str, typing.Union[typing.Union[typing.Union[Literal["foo"], int]]]]
 
 def func(x: complex | Literal[1J], y: Union[Literal[3.14], float]): ...
 

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI055.py

@@ -1,11 +1,14 @@
 import builtins
 from typing import Union
 
-w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
-x: type[int] | type[str] | type[float]
-y: builtins.type[int] | type[str] | builtins.type[complex]
-z: Union[type[float], type[complex]]
-z: Union[type[float, int], type[complex]]
+s: builtins.type[int] | builtins.type[str] | builtins.type[complex]
+t: type[int] | type[str] | type[float]
+u: builtins.type[int] | type[str] | builtins.type[complex]
+v: Union[type[float], type[complex]]
+w: Union[type[float | int], type[complex]]
+x: Union[Union[type[Union[float, int]], type[complex]]]
+y: Union[Union[Union[type[float | int], type[complex]]]]
+z: Union[type[complex], Union[Union[type[Union[float, int]]]]]
 
 
 def func(arg: type[int] | str | type[float]) -> None:
@@ -13,8 +16,8 @@ def func(arg: type[int] | str | type[float]) -> None:
 
 
 # OK
-x: type[int, str, float]
-y: builtins.type[int, str, complex]
+x: type[int | str | float]
+y: builtins.type[int | str | complex]
 z: Union[float, complex]
 
 
@@ -65,3 +68,11 @@ def convert_union(union: UnionType) -> _T | None:
         Union[type[_T] | type[Converter[_T]] | str] | Converter[_T] | Callable[[str], _T], ...  # PYI055
     ] = union.__args__
     ...
+
+
+# `type[float, int]`` is not valid, use `type[float|int]` or `type[Union[float, int]]`
+# OK for PYI055, should be covered by another check.
+a: Union[type[float, int], type[complex]]  
+b: Union[Union[type[float, int], type[complex]]]
+c: Union[Union[Union[type[float, int], type[complex]]]]
+d: Union[type[complex], Union[Union[type[float, int]]]]

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI055.pyi

@@ -1,17 +1,20 @@
 import builtins
 from typing import Union
 
-w: builtins.type[int] | builtins.type[str] | builtins.type[complex]
-x: type[int] | type[str] | type[float]
-y: builtins.type[int] | type[str] | builtins.type[complex]
-z: Union[type[float], type[complex]]
-z: Union[type[float, int], type[complex]]
+s: builtins.type[int] | builtins.type[str] | builtins.type[complex]
+t: type[int] | type[str] | type[float]
+u: builtins.type[int] | type[str] | builtins.type[complex]
+v: Union[type[float], type[complex]]
+w: Union[type[Union[float, int]], type[complex]]
+x: Union[Union[type[Union[float, int]], type[complex]]]
+y: Union[Union[Union[type[Union[float, int]], type[complex]]]]
+z: Union[type[complex], Union[Union[type[Union[float, int]]]]]
 
 def func(arg: type[int] | str | type[float]) -> None: ...
 
 # OK
-x: type[int, str, float]
-y: builtins.type[int, str, complex]
+x: type[int | str | float]
+y: builtins.type[int | str | complex]
 z: Union[float, complex]
 
 def func(arg: type[int, float] | str) -> None: ...
@@ -26,3 +29,10 @@ def func():
     item3: Union[  # comment
         type[requests_mock.Mocker], # another comment
         type[httpretty], type[str]] = requests_mock.Mocker
+
+
+# OK
+w: Union[type[float, int], type[complex]]
+x: Union[Union[type[float, int], type[complex]]]
+y: Union[Union[Union[type[float, int], type[complex]]]]
+z: Union[type[complex], Union[Union[type[float, int]]]]

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI061.py

@@ -1,4 +1,4 @@
-from typing import Literal
+from typing import Literal, Union
 
 
 def func1(arg1: Literal[None]):
@@ -17,7 +17,7 @@ def func4(arg1: Literal[int, None, float]):
     ...
 
 
-def func5(arg1: Literal[None, None]): 
+def func5(arg1: Literal[None, None]):
     ...
 
 
@@ -25,13 +25,21 @@ def func6(arg1: Literal[
     "hello",
     None  # Comment 1
     , "world"
-    ]): 
+    ]):
     ...
 
 
 def func7(arg1: Literal[
     None  # Comment 1
-    ]): 
+    ]):
+    ...
+
+
+def func8(arg1: Literal[None] | None):
+    ...
+
+
+def func9(arg1: Union[Literal[None], None]):
     ...
 
 
@@ -58,3 +66,16 @@ Literal[1, None, "foo", None]  # Y061 None inside "Literal[]" expression. Replac
 # and there are no None members in the Literal[] slice,
 # only emit Y062:
 Literal[None, True, None, True]  # Y062 Duplicate "Literal[]" member "True"
+
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/14567
+x: Literal[None] | None
+y: None | Literal[None]
+z: Union[Literal[None], None]
+
+a: int | Literal[None] | None
+b: None | Literal[None] | None
+c: (None | Literal[None]) | None
+d: None | (Literal[None] | None)
+e: None | ((None | Literal[None]) | None) | None
+f: Literal[None] | Literal[None]

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI061.pyi

@@ -1,4 +1,4 @@
-from typing import Literal
+from typing import Literal, Union
 
 
 def func1(arg1: Literal[None]): ...
@@ -28,6 +28,12 @@ def func7(arg1: Literal[
 ]): ...
 
 
+def func8(arg1: Literal[None] | None):...
+
+
+def func9(arg1: Union[Literal[None], None]): ...
+
+
 # OK
 def good_func(arg1: Literal[int] | None): ...
 
@@ -35,3 +41,16 @@ def good_func(arg1: Literal[int] | None): ...
 # From flake8-pyi
 Literal[None]  # PYI061 None inside "Literal[]" expression. Replace with "None"
 Literal[True, None]  # PYI061 None inside "Literal[]" expression. Replace with "Literal[True] | None"
+
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/14567
+x: Literal[None] | None
+y: None | Literal[None]
+z: Union[Literal[None], None]
+
+a: int | Literal[None] | None
+b: None | Literal[None] | None
+c: (None | Literal[None]) | None
+d: None | (Literal[None] | None)
+e: None | ((None | Literal[None]) | None) | None
+f: Literal[None] | Literal[None]

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI062.py

@@ -25,3 +25,9 @@ Literal[
 MyType = Literal["foo", Literal[True, False, True], "bar"]  # PYI062
 
 n: Literal["No", "duplicates", "here", 1, "1"]
+
+
+# nested literals, all equivalent to `Literal[1]`
+Literal[Literal[1]]  # no duplicate
+Literal[Literal[Literal[1], Literal[1]]]  # once
+Literal[Literal[1], Literal[Literal[Literal[1]]]]  # once