Merge branch 'main' into dcreager/function-enum

* main:
  Update pre-commit dependencies (#17506)
  [red-knot] Simplify visibility constraint handling for `*`-import definitions (#17486)
  [red-knot] Detect (some) invalid protocols (#17488)
  [red-knot] Correctly identify protocol classes (#17487)
  Update dependency ruff to v0.11.6 (#17516)
  Update Rust crate shellexpand to v3.1.1 (#17512)
  Update Rust crate proc-macro2 to v1.0.95 (#17510)
  Update Rust crate rand to v0.9.1 (#17511)
  Update Rust crate libc to v0.2.172 (#17509)
  Update Rust crate jiff to v0.2.9 (#17508)
  Update Rust crate clap to v4.5.37 (#17507)
  Update astral-sh/setup-uv action to v5.4.2 (#17504)
  Update taiki-e/install-action digest to 09dc018 (#17503)
  [red-knot] infer attribute assignments bound in comprehensions (#17396)
  [red-knot] simplify gradually-equivalent types out of unions and intersections (#17467)
  [red-knot] pull primer projects to run from file (#17473)

.github/CODEOWNERS

@@ -18,6 +18,7 @@
 /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
+/crates/red_knot* @carljm @MichaReiser @AlexWaygood @sharkdp @dcreager
+/crates/ruff_db/ @carljm @MichaReiser @AlexWaygood @sharkdp @dcreager
+/scripts/knot_benchmark/ @carljm @MichaReiser @AlexWaygood @sharkdp @dcreager
+/crates/red_knot_python_semantic @carljm @AlexWaygood @sharkdp @dcreager

.github/renovate.json5

@@ -40,6 +40,17 @@
     enabled: true,
   },
   packageRules: [
+    // Pin GitHub Actions to immutable SHAs.
+    {
+      matchDepTypes: ["action"],
+      pinDigests: true,
+    },
+    // Annotate GitHub Actions SHAs with a SemVer version.
+    {
+      extends: ["helpers:pinGitHubActionDigests"],
+      extractVersion: "^(?<version>v?\\d+\\.\\d+\\.\\d+)$",
+      versioning: "regex:^v?(?<major>\\d+)(\\.(?<minor>\\d+)\\.(?<patch>\\d+))?$",
+    },
     {
       // Group upload/download artifact updates, the versions are dependent
       groupName: "Artifact GitHub Actions dependencies",

.github/workflows/build-binaries.yml

@@ -28,7 +28,7 @@ permissions: {}
 env:
   PACKAGE_NAME: ruff
   MODULE_NAME: ruff
-  PYTHON_VERSION: "3.11"
+  PYTHON_VERSION: "3.13"
   CARGO_INCREMENTAL: 0
   CARGO_NET_RETRY: 10
   CARGO_TERM_COLOR: always
@@ -39,17 +39,17 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-build') }}
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           submodules: recursive
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
       - name: "Prep README.md"
         run: python scripts/transform_readme.py --target pypi
       - name: "Build sdist"
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@aef21716ff3dcae8a1c301d23ec3e4446972a6e3 # v1.49.1
         with:
           command: sdist
           args: --out dist
@@ -59,7 +59,7 @@ jobs:
           "${MODULE_NAME}" --help
           python -m "${MODULE_NAME}" --help
       - name: "Upload sdist"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: wheels-sdist
           path: dist
@@ -68,23 +68,23 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-build') }}
     runs-on: macos-14
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           submodules: recursive
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
           architecture: x64
       - name: "Prep README.md"
         run: python scripts/transform_readme.py --target pypi
       - name: "Build wheels - x86_64"
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@aef21716ff3dcae8a1c301d23ec3e4446972a6e3 # v1.49.1
         with:
           target: x86_64
           args: --release --locked --out dist
       - name: "Upload wheels"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: wheels-macos-x86_64
           path: dist
@@ -99,7 +99,7 @@ jobs:
           tar czvf $ARCHIVE_FILE $ARCHIVE_NAME
           shasum -a 256 $ARCHIVE_FILE > $ARCHIVE_FILE.sha256
       - name: "Upload binary"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: artifacts-macos-x86_64
           path: |
@@ -110,18 +110,18 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-build') }}
     runs-on: macos-14
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           submodules: recursive
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
           architecture: arm64
       - name: "Prep README.md"
         run: python scripts/transform_readme.py --target pypi
       - name: "Build wheels - aarch64"
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@aef21716ff3dcae8a1c301d23ec3e4446972a6e3 # v1.49.1
         with:
           target: aarch64
           args: --release --locked --out dist
@@ -131,7 +131,7 @@ jobs:
           ruff --help
           python -m ruff --help
       - name: "Upload wheels"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: wheels-aarch64-apple-darwin
           path: dist
@@ -146,7 +146,7 @@ jobs:
           tar czvf $ARCHIVE_FILE $ARCHIVE_NAME
           shasum -a 256 $ARCHIVE_FILE > $ARCHIVE_FILE.sha256
       - name: "Upload binary"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: artifacts-aarch64-apple-darwin
           path: |
@@ -166,18 +166,18 @@ jobs:
           - target: aarch64-pc-windows-msvc
             arch: x64
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           submodules: recursive
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
           architecture: ${{ matrix.platform.arch }}
       - name: "Prep README.md"
         run: python scripts/transform_readme.py --target pypi
       - name: "Build wheels"
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@aef21716ff3dcae8a1c301d23ec3e4446972a6e3 # v1.49.1
         with:
           target: ${{ matrix.platform.target }}
           args: --release --locked --out dist
@@ -192,7 +192,7 @@ jobs:
           "${MODULE_NAME}" --help
           python -m "${MODULE_NAME}" --help
       - name: "Upload wheels"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: wheels-${{ matrix.platform.target }}
           path: dist
@@ -203,7 +203,7 @@ jobs:
           7z a $ARCHIVE_FILE ./target/${{ matrix.platform.target }}/release/ruff.exe
           sha256sum $ARCHIVE_FILE > $ARCHIVE_FILE.sha256
       - name: "Upload binary"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: artifacts-${{ matrix.platform.target }}
           path: |
@@ -219,18 +219,18 @@ jobs:
           - x86_64-unknown-linux-gnu
           - i686-unknown-linux-gnu
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           submodules: recursive
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
           architecture: x64
       - name: "Prep README.md"
         run: python scripts/transform_readme.py --target pypi
       - name: "Build wheels"
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@aef21716ff3dcae8a1c301d23ec3e4446972a6e3 # v1.49.1
         with:
           target: ${{ matrix.target }}
           manylinux: auto
@@ -242,7 +242,7 @@ jobs:
           "${MODULE_NAME}" --help
           python -m "${MODULE_NAME}" --help
       - name: "Upload wheels"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: wheels-${{ matrix.target }}
           path: dist
@@ -260,7 +260,7 @@ jobs:
           tar czvf $ARCHIVE_FILE $ARCHIVE_NAME
           shasum -a 256 $ARCHIVE_FILE > $ARCHIVE_FILE.sha256
       - name: "Upload binary"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: artifacts-${{ matrix.target }}
           path: |
@@ -294,24 +294,24 @@ jobs:
             arch: arm
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           submodules: recursive
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
       - name: "Prep README.md"
         run: python scripts/transform_readme.py --target pypi
       - name: "Build wheels"
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@aef21716ff3dcae8a1c301d23ec3e4446972a6e3 # v1.49.1
         with:
           target: ${{ matrix.platform.target }}
           manylinux: auto
           docker-options: ${{ matrix.platform.maturin_docker_options }}
           args: --release --locked --out dist
-      - uses: uraimo/run-on-arch-action@v2
-        if: matrix.platform.arch != 'ppc64'
+      - uses: uraimo/run-on-arch-action@ac33288c3728ca72563c97b8b88dda5a65a84448 # v2
+        if: ${{ matrix.platform.arch != 'ppc64' && matrix.platform.arch != 'ppc64le'}}
         name: Test wheel
         with:
           arch: ${{ matrix.platform.arch == 'arm' && 'armv6' || matrix.platform.arch }}
@@ -325,7 +325,7 @@ jobs:
             pip3 install ${{ env.PACKAGE_NAME }} --no-index --find-links dist/ --force-reinstall
             ruff --help
       - name: "Upload wheels"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: wheels-${{ matrix.platform.target }}
           path: dist
@@ -343,7 +343,7 @@ jobs:
           tar czvf $ARCHIVE_FILE $ARCHIVE_NAME
           shasum -a 256 $ARCHIVE_FILE > $ARCHIVE_FILE.sha256
       - name: "Upload binary"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: artifacts-${{ matrix.platform.target }}
           path: |
@@ -359,25 +359,25 @@ jobs:
           - x86_64-unknown-linux-musl
           - i686-unknown-linux-musl
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           submodules: recursive
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
           architecture: x64
       - name: "Prep README.md"
         run: python scripts/transform_readme.py --target pypi
       - name: "Build wheels"
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@aef21716ff3dcae8a1c301d23ec3e4446972a6e3 # v1.49.1
         with:
           target: ${{ matrix.target }}
           manylinux: musllinux_1_2
           args: --release --locked --out dist
       - name: "Test wheel"
         if: matrix.target == 'x86_64-unknown-linux-musl'
-        uses: addnab/docker-run-action@v3
+        uses: addnab/docker-run-action@4f65fabd2431ebc8d299f8e5a018d79a769ae185 # v3
         with:
           image: alpine:latest
           options: -v ${{ github.workspace }}:/io -w /io
@@ -387,7 +387,7 @@ jobs:
             .venv/bin/pip3 install ${{ env.PACKAGE_NAME }} --no-index --find-links dist/ --force-reinstall
             .venv/bin/${{ env.MODULE_NAME }} --help
       - name: "Upload wheels"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: wheels-${{ matrix.target }}
           path: dist
@@ -405,7 +405,7 @@ jobs:
           tar czvf $ARCHIVE_FILE $ARCHIVE_NAME
           shasum -a 256 $ARCHIVE_FILE > $ARCHIVE_FILE.sha256
       - name: "Upload binary"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: artifacts-${{ matrix.target }}
           path: |
@@ -425,23 +425,23 @@ jobs:
             arch: armv7
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           submodules: recursive
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
       - name: "Prep README.md"
         run: python scripts/transform_readme.py --target pypi
       - name: "Build wheels"
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@aef21716ff3dcae8a1c301d23ec3e4446972a6e3 # v1.49.1
         with:
           target: ${{ matrix.platform.target }}
           manylinux: musllinux_1_2
           args: --release --locked --out dist
           docker-options: ${{ matrix.platform.maturin_docker_options }}
-      - uses: uraimo/run-on-arch-action@v2
+      - uses: uraimo/run-on-arch-action@ac33288c3728ca72563c97b8b88dda5a65a84448 # v2
         name: Test wheel
         with:
           arch: ${{ matrix.platform.arch }}
@@ -454,7 +454,7 @@ jobs:
             .venv/bin/pip3 install ${{ env.PACKAGE_NAME }} --no-index --find-links dist/ --force-reinstall
             .venv/bin/${{ env.MODULE_NAME }} --help
       - name: "Upload wheels"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: wheels-${{ matrix.platform.target }}
           path: dist
@@ -472,7 +472,7 @@ jobs:
           tar czvf $ARCHIVE_FILE $ARCHIVE_NAME
           shasum -a 256 $ARCHIVE_FILE > $ARCHIVE_FILE.sha256
       - name: "Upload binary"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: artifacts-${{ matrix.platform.target }}
           path: |

.github/workflows/build-docker.yml

@@ -33,14 +33,14 @@ jobs:
           - linux/amd64
           - linux/arm64
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           submodules: recursive
           persist-credentials: false
 
-      - uses: docker/setup-buildx-action@v3
+      - uses: docker/setup-buildx-action@b5ca514318bd6ebac0fb2aedd5d36ec1b5c232a2 # v3
 
-      - uses: docker/login-action@v3
+      - uses: docker/login-action@74a5d142397b4f367a81961eba4e8cd7edddf772 # v3
         with:
           registry: ghcr.io
           username: ${{ github.repository_owner }}
@@ -63,7 +63,7 @@ jobs:
 
       - name: Extract metadata (tags, labels) for Docker
         id: meta
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@902fa8ec7d6ecbf8d84d538b9b233a880e428804 # v5
         with:
           images: ${{ env.RUFF_BASE_IMG }}
           # Defining this makes sure the org.opencontainers.image.version OCI label becomes the actual release version and not the branch name
@@ -79,7 +79,7 @@ jobs:
       # Adapted from https://docs.docker.com/build/ci/github-actions/multi-platform/
       - name: Build and push by digest
         id: build
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@471d1dc4e07e5cdedd4c2171150001c434f0b7a4 # v6
         with:
           context: .
           platforms: ${{ matrix.platform }}
@@ -96,7 +96,7 @@ jobs:
           touch "/tmp/digests/${digest#sha256:}"
 
       - name: Upload digests
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: digests-${{ env.PLATFORM_TUPLE }}
           path: /tmp/digests/*
@@ -113,17 +113,17 @@ jobs:
     if: ${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
     steps:
       - name: Download digests
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e # v4.2.1
         with:
           path: /tmp/digests
           pattern: digests-*
           merge-multiple: true
 
-      - uses: docker/setup-buildx-action@v3
+      - uses: docker/setup-buildx-action@b5ca514318bd6ebac0fb2aedd5d36ec1b5c232a2 # v3
 
       - name: Extract metadata (tags, labels) for Docker
         id: meta
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@902fa8ec7d6ecbf8d84d538b9b233a880e428804 # v5
         with:
           images: ${{ env.RUFF_BASE_IMG }}
           # Order is on purpose such that the label org.opencontainers.image.version has the first pattern with the full version
@@ -131,7 +131,7 @@ jobs:
             type=pep440,pattern={{ version }},value=${{ fromJson(inputs.plan).announcement_tag }}
             type=pep440,pattern={{ major }}.{{ minor }},value=${{ fromJson(inputs.plan).announcement_tag }}
 
-      - uses: docker/login-action@v3
+      - uses: docker/login-action@74a5d142397b4f367a81961eba4e8cd7edddf772 # v3
         with:
           registry: ghcr.io
           username: ${{ github.repository_owner }}
@@ -167,9 +167,9 @@ jobs:
           - debian:bookworm-slim,bookworm-slim,debian-slim
           - buildpack-deps:bookworm,bookworm,debian
     steps:
-      - uses: docker/setup-buildx-action@v3
+      - uses: docker/setup-buildx-action@b5ca514318bd6ebac0fb2aedd5d36ec1b5c232a2 # v3
 
-      - uses: docker/login-action@v3
+      - uses: docker/login-action@74a5d142397b4f367a81961eba4e8cd7edddf772 # v3
         with:
           registry: ghcr.io
           username: ${{ github.repository_owner }}
@@ -219,7 +219,7 @@ jobs:
 
       - name: Extract metadata (tags, labels) for Docker
         id: meta
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@902fa8ec7d6ecbf8d84d538b9b233a880e428804 # v5
         # ghcr.io prefers index level annotations
         env:
           DOCKER_METADATA_ANNOTATIONS_LEVELS: index
@@ -231,7 +231,7 @@ jobs:
             ${{ env.TAG_PATTERNS }}
 
       - name: Build and push
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@471d1dc4e07e5cdedd4c2171150001c434f0b7a4 # v6
         with:
           context: .
           platforms: linux/amd64,linux/arm64
@@ -256,17 +256,17 @@ jobs:
     if: ${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
     steps:
       - name: Download digests
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e # v4.2.1
         with:
           path: /tmp/digests
           pattern: digests-*
           merge-multiple: true
 
-      - uses: docker/setup-buildx-action@v3
+      - uses: docker/setup-buildx-action@b5ca514318bd6ebac0fb2aedd5d36ec1b5c232a2 # v3
 
       - name: Extract metadata (tags, labels) for Docker
         id: meta
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@902fa8ec7d6ecbf8d84d538b9b233a880e428804 # v5
         env:
           DOCKER_METADATA_ANNOTATIONS_LEVELS: index
         with:
@@ -276,7 +276,7 @@ jobs:
             type=pep440,pattern={{ version }},value=${{ fromJson(inputs.plan).announcement_tag }}
             type=pep440,pattern={{ major }}.{{ minor }},value=${{ fromJson(inputs.plan).announcement_tag }}
 
-      - uses: docker/login-action@v3
+      - uses: docker/login-action@74a5d142397b4f367a81961eba4e8cd7edddf772 # v3
         with:
           registry: ghcr.io
           username: ${{ github.repository_owner }}

.github/workflows/ci.yaml

@@ -18,7 +18,7 @@ env:
   CARGO_TERM_COLOR: always
   RUSTUP_MAX_RETRIES: 10
   PACKAGE_NAME: ruff
-  PYTHON_VERSION: "3.12"
+  PYTHON_VERSION: "3.13"
 
 jobs:
   determine_changes:
@@ -26,83 +26,177 @@ jobs:
     runs-on: ubuntu-latest
     outputs:
       # Flag that is raised when any code that affects parser is changed
-      parser: ${{ steps.changed.outputs.parser_any_changed }}
+      parser: ${{ steps.check_parser.outputs.changed }}
       # Flag that is raised when any code that affects linter is changed
-      linter: ${{ steps.changed.outputs.linter_any_changed }}
+      linter: ${{ steps.check_linter.outputs.changed }}
       # Flag that is raised when any code that affects formatter is changed
-      formatter: ${{ steps.changed.outputs.formatter_any_changed }}
+      formatter: ${{ steps.check_formatter.outputs.changed }}
       # Flag that is raised when any code is changed
       # This is superset of the linter and formatter
-      code: ${{ steps.changed.outputs.code_any_changed }}
+      code: ${{ steps.check_code.outputs.changed }}
       # Flag that is raised when any code that affects the fuzzer is changed
-      fuzz: ${{ steps.changed.outputs.fuzz_any_changed }}
+      fuzz: ${{ steps.check_fuzzer.outputs.changed }}
+      # Flag that is set to "true" when code related to red-knot changes.
+      red_knot: ${{ steps.check_red_knot.outputs.changed }}
+
+      # Flag that is set to "true" when code related to the playground changes.
+      playground: ${{ steps.check_playground.outputs.changed }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           fetch-depth: 0
           persist-credentials: false
 
-      - uses: tj-actions/changed-files@v45
-        id: changed
-        with:
-          files_yaml: |
-            parser:
-              - Cargo.toml
-              - Cargo.lock
-              - crates/ruff_python_trivia/**
-              - crates/ruff_source_file/**
-              - crates/ruff_text_size/**
-              - crates/ruff_python_ast/**
-              - crates/ruff_python_parser/**
-              - python/py-fuzzer/**
-              - .github/workflows/ci.yaml
+      - name: Determine merge base
+        id: merge_base
+        env:
+          BASE_REF: ${{ github.event.pull_request.base.ref || 'main' }}
+        run: |
+          sha=$(git merge-base HEAD "origin/${BASE_REF}")
+          echo "sha=${sha}" >> "$GITHUB_OUTPUT"
 
-            linter:
-              - Cargo.toml
-              - Cargo.lock
-              - crates/**
-              - "!crates/red_knot*/**"
-              - "!crates/ruff_python_formatter/**"
-              - "!crates/ruff_formatter/**"
-              - "!crates/ruff_dev/**"
-              - scripts/*
-              - python/**
-              - .github/workflows/ci.yaml
+      - name: Check if the parser code changed
+        id: check_parser
+        env:
+          MERGE_BASE: ${{ steps.merge_base.outputs.sha }}
+        run: |
+          if git diff --quiet "${MERGE_BASE}...HEAD" -- \
+            ':Cargo.toml' \
+            ':Cargo.lock' \
+            ':crates/ruff_python_trivia/**' \
+            ':crates/ruff_source_file/**' \
+            ':crates/ruff_text_size/**' \
+            ':crates/ruff_python_ast/**' \
+            ':crates/ruff_python_parser/**' \
+            ':python/py-fuzzer/**' \
+            ':.github/workflows/ci.yaml' \
+          ; then
+              echo "changed=false" >> "$GITHUB_OUTPUT"
+          else
+              echo "changed=true" >> "$GITHUB_OUTPUT"
+          fi
 
-            formatter:
-              - Cargo.toml
-              - Cargo.lock
-              - crates/ruff_python_formatter/**
-              - crates/ruff_formatter/**
-              - crates/ruff_python_trivia/**
-              - crates/ruff_python_ast/**
-              - crates/ruff_source_file/**
-              - crates/ruff_python_index/**
-              - crates/ruff_text_size/**
-              - crates/ruff_python_parser/**
-              - crates/ruff_dev/**
-              - scripts/*
-              - python/**
-              - .github/workflows/ci.yaml
+      - name: Check if the linter code changed
+        id: check_linter
+        env:
+          MERGE_BASE: ${{ steps.merge_base.outputs.sha }}
+        run: |
+          if git diff --quiet "${MERGE_BASE}...HEAD" -- ':Cargo.toml' \
+            ':Cargo.lock' \
+            ':crates/**' \
+            ':!crates/red_knot*/**' \
+            ':!crates/ruff_python_formatter/**' \
+            ':!crates/ruff_formatter/**' \
+            ':!crates/ruff_dev/**' \
+            ':!crates/ruff_db/**' \
+            ':scripts/*' \
+            ':python/**' \
+            ':.github/workflows/ci.yaml' \
+          ; then
+              echo "changed=false" >> "$GITHUB_OUTPUT"
+          else
+              echo "changed=true" >> "$GITHUB_OUTPUT"
+          fi
 
-            fuzz:
-              - fuzz/Cargo.toml
-              - fuzz/Cargo.lock
-              - fuzz/fuzz_targets/**
+      - name: Check if the formatter code changed
+        id: check_formatter
+        env:
+          MERGE_BASE: ${{ steps.merge_base.outputs.sha }}
+        run: |
+          if git diff --quiet "${MERGE_BASE}...HEAD" -- ':Cargo.toml' \
+            ':Cargo.lock' \
+            ':crates/ruff_python_formatter/**' \
+            ':crates/ruff_formatter/**' \
+            ':crates/ruff_python_trivia/**' \
+            ':crates/ruff_python_ast/**' \
+            ':crates/ruff_source_file/**' \
+            ':crates/ruff_python_index/**' \
+            ':crates/ruff_python_index/**' \
+            ':crates/ruff_text_size/**' \
+            ':crates/ruff_python_parser/**' \
+            ':scripts/*' \
+            ':python/**' \
+            ':.github/workflows/ci.yaml' \
+          ; then
+              echo "changed=false" >> "$GITHUB_OUTPUT"
+          else
+              echo "changed=true" >> "$GITHUB_OUTPUT"
+          fi
 
-            code:
-              - "**/*"
-              - "!**/*.md"
-              - "crates/red_knot_python_semantic/resources/mdtest/**/*.md"
-              - "!docs/**"
-              - "!assets/**"
+      - name: Check if the fuzzer code changed
+        id: check_fuzzer
+        env:
+          MERGE_BASE: ${{ steps.merge_base.outputs.sha }}
+        run: |
+          if git diff --quiet "${MERGE_BASE}...HEAD" -- ':Cargo.toml' \
+            ':Cargo.lock' \
+            ':fuzz/fuzz_targets/**' \
+            ':.github/workflows/ci.yaml' \
+          ; then
+              echo "changed=false" >> "$GITHUB_OUTPUT"
+          else
+              echo "changed=true" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Check if there was any code related change
+        id: check_code
+        env:
+          MERGE_BASE: ${{ steps.merge_base.outputs.sha }}
+        run: |
+          if git diff --quiet "${MERGE_BASE}...HEAD" -- ':**' \
+            ':!**/*.md' \
+            ':crates/red_knot_python_semantic/resources/mdtest/**/*.md' \
+            ':!docs/**' \
+            ':!assets/**' \
+            ':.github/workflows/ci.yaml' \
+          ; then
+              echo "changed=false" >> "$GITHUB_OUTPUT"
+          else
+              echo "changed=true" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Check if there was any playground related change
+        id: check_playground
+        env:
+          MERGE_BASE: ${{ steps.merge_base.outputs.sha }}
+        run: |
+          if git diff --quiet "${MERGE_BASE}...HEAD" -- \
+            ':playground/**' \
+          ; then
+              echo "changed=false" >> "$GITHUB_OUTPUT"
+          else
+              echo "changed=true" >> "$GITHUB_OUTPUT"
+          fi
+
+      - name: Check if the red-knot code changed
+        id: check_red_knot
+        env:
+          MERGE_BASE: ${{ steps.merge_base.outputs.sha }}
+        run: |
+          if git diff --quiet "${MERGE_BASE}...HEAD" -- \
+            ':Cargo.toml' \
+            ':Cargo.lock' \
+            ':crates/red_knot*/**' \
+            ':crates/ruff_db/**' \
+            ':crates/ruff_annotate_snippets/**' \
+            ':crates/ruff_python_ast/**' \
+            ':crates/ruff_python_parser/**' \
+            ':crates/ruff_python_trivia/**' \
+            ':crates/ruff_source_file/**' \
+            ':crates/ruff_text_size/**' \
+            ':.github/workflows/ci.yaml' \
+          ; then
+              echo "changed=false" >> "$GITHUB_OUTPUT"
+          else
+              echo "changed=true" >> "$GITHUB_OUTPUT"
+          fi
 
   cargo-fmt:
     name: "cargo fmt"
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
       - name: "Install Rust toolchain"
@@ -116,10 +210,10 @@ jobs:
     if: ${{ needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main' }}
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         run: |
           rustup component add clippy
@@ -136,22 +230,30 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install mold"
-        uses: rui314/setup-mold@v1
+        uses: rui314/setup-mold@e16410e7f8d9e167b74ad5697a9089a35126eb50 # v1
       - name: "Install cargo nextest"
-        uses: taiki-e/install-action@v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-nextest
       - name: "Install cargo insta"
-        uses: taiki-e/install-action@v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-insta
+      - name: Red-knot mdtests (GitHub annotations)
+        if: ${{ needs.determine_changes.outputs.red_knot == 'true' }}
+        env:
+          NO_COLOR: 1
+          MDTEST_GITHUB_ANNOTATIONS_FORMAT: 1
+        # Ignore errors if this step fails; we want to continue to later steps in the workflow anyway.
+        # This step is just to get nice GitHub annotations on the PR diff in the files-changed tab.
+        run: cargo test -p red_knot_python_semantic --test mdtest || true
       - name: "Run tests"
         shell: bash
         env:
@@ -170,7 +272,7 @@ jobs:
         env:
           # Setting RUSTDOCFLAGS because `cargo doc --check` isn't yet implemented (https://github.com/rust-lang/cargo/issues/10025).
           RUSTDOCFLAGS: "-D warnings"
-      - uses: actions/upload-artifact@v4
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: ruff
           path: target/debug/ruff
@@ -182,20 +284,20 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install mold"
-        uses: rui314/setup-mold@v1
+        uses: rui314/setup-mold@e16410e7f8d9e167b74ad5697a9089a35126eb50 # v1
       - name: "Install cargo nextest"
-        uses: taiki-e/install-action@v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-nextest
       - name: "Install cargo insta"
-        uses: taiki-e/install-action@v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-insta
       - name: "Run tests"
@@ -211,14 +313,14 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install cargo nextest"
-        uses: taiki-e/install-action@v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-nextest
       - name: "Run tests"
@@ -238,18 +340,18 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         run: rustup target add wasm32-unknown-unknown
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
         with:
           node-version: 20
           cache: "npm"
           cache-dependency-path: playground/package-lock.json
-      - uses: jetli/wasm-pack-action@v0.4.0
+      - uses: jetli/wasm-pack-action@0d096b08b4e5a7de8c28de67e11e945404e9eefa # v0.4.0
         with:
           version: v0.13.1
       - name: "Test ruff_wasm"
@@ -267,14 +369,14 @@ jobs:
     if: ${{ github.ref == 'refs/heads/main' }}
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install mold"
-        uses: rui314/setup-mold@v1
+        uses: rui314/setup-mold@e16410e7f8d9e167b74ad5697a9089a35126eb50 # v1
       - name: "Build"
         run: cargo build --release --locked
 
@@ -285,27 +387,27 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: SebRollen/toml-action@v1.2.0
+      - uses: SebRollen/toml-action@b1b3628f55fc3a28208d4203ada8b737e9687876 # v1.2.0
         id: msrv
         with:
           file: "Cargo.toml"
           field: "workspace.package.rust-version"
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         env:
           MSRV: ${{ steps.msrv.outputs.value }}
         run: rustup default "${MSRV}"
       - name: "Install mold"
-        uses: rui314/setup-mold@v1
+        uses: rui314/setup-mold@e16410e7f8d9e167b74ad5697a9089a35126eb50 # v1
       - name: "Install cargo nextest"
-        uses: taiki-e/install-action@v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-nextest
       - name: "Install cargo insta"
-        uses: taiki-e/install-action@v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-insta
       - name: "Run tests"
@@ -322,16 +424,16 @@ jobs:
     if: ${{ github.ref == 'refs/heads/main' || needs.determine_changes.outputs.fuzz == 'true' || needs.determine_changes.outputs.code == 'true' }}
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
         with:
           workspaces: "fuzz -> target"
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install cargo-binstall"
-        uses: cargo-bins/cargo-binstall@main
+        uses: cargo-bins/cargo-binstall@63aaa5c1932cebabc34eceda9d92a70215dcead6 # v1.12.3
         with:
           tool: cargo-fuzz@0.11.2
       - name: "Install cargo-fuzz"
@@ -350,11 +452,11 @@ jobs:
     env:
       FORCE_COLOR: 1
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: astral-sh/setup-uv@v5
-      - uses: actions/download-artifact@v4
+      - uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5.4.2
+      - uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e # v4.2.1
         name: Download Ruff binary to test
         id: download-cached-binary
         with:
@@ -384,10 +486,10 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
     timeout-minutes: 5
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         run: rustup component add rustfmt
       # Run all code generation scripts, and verify that the current output is
@@ -416,21 +518,21 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && github.event_name == 'pull_request' && needs.determine_changes.outputs.code == 'true' }}
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
 
-      - uses: actions/download-artifact@v4
+      - uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e # v4.2.1
         name: Download comparison Ruff binary
         id: ruff-target
         with:
           name: ruff
           path: target/debug
 
-      - uses: dawidd6/action-download-artifact@v8
+      - uses: dawidd6/action-download-artifact@20319c5641d495c8a52e688b7dc5fada6c3a9fbc # v8
         name: Download baseline Ruff binary
         with:
           name: ruff
@@ -518,13 +620,13 @@ jobs:
         run: |
           echo ${{ github.event.number }} > pr-number
 
-      - uses: actions/upload-artifact@v4
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         name: Upload PR Number
         with:
           name: pr-number
           path: pr-number
 
-      - uses: actions/upload-artifact@v4
+      - uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         name: Upload Results
         with:
           name: ecosystem-result
@@ -536,10 +638,10 @@ jobs:
     needs: determine_changes
     if: ${{ needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main' }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: cargo-bins/cargo-binstall@main
+      - uses: cargo-bins/cargo-binstall@63aaa5c1932cebabc34eceda9d92a70215dcead6 # v1.12.3
       - run: cargo binstall --no-confirm cargo-shear
       - run: cargo shear
 
@@ -549,18 +651,18 @@ jobs:
     timeout-minutes: 20
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ env.PYTHON_VERSION }}
           architecture: x64
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Prep README.md"
         run: python scripts/transform_readme.py --target pypi
       - name: "Build wheels"
-        uses: PyO3/maturin-action@v1
+        uses: PyO3/maturin-action@aef21716ff3dcae8a1c301d23ec3e4446972a6e3 # v1.49.1
         with:
           args: --out dist
       - name: "Test wheel"
@@ -573,22 +675,15 @@ jobs:
 
   pre-commit:
     name: "pre-commit"
-    runs-on: ubuntu-latest
+    runs-on: depot-ubuntu-22.04-16
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: actions/setup-python@v5
-        with:
-          python-version: ${{ env.PYTHON_VERSION }}
-      - uses: Swatinem/rust-cache@v2
-      - name: "Install Rust toolchain"
-        run: rustup show
-      - name: "Install pre-commit"
-        run: pip install pre-commit
+      - uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5.4.2
       - name: "Cache pre-commit"
-        uses: actions/cache@v4
+        uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
         with:
           path: ~/.cache/pre-commit
           key: pre-commit-${{ hashFiles('.pre-commit-config.yaml') }}
@@ -597,7 +692,7 @@ jobs:
           echo '```console' > "$GITHUB_STEP_SUMMARY"
           # Enable color output for pre-commit and remove it for the summary
           # Use --hook-stage=manual to enable slower pre-commit hooks that are skipped by default
-          SKIP=cargo-fmt,clippy,dev-generate-all pre-commit run --all-files --show-diff-on-failure --color=always --hook-stage=manual | \
+          SKIP=cargo-fmt,clippy,dev-generate-all uvx --python="${PYTHON_VERSION}" pre-commit run --all-files --show-diff-on-failure --color=always --hook-stage=manual | \
             tee >(sed -E 's/\x1B\[([0-9]{1,2}(;[0-9]{1,2})*)?[mGK]//g' >> "$GITHUB_STEP_SUMMARY") >&1
           exit_code="${PIPESTATUS[0]}"
           echo '```' >> "$GITHUB_STEP_SUMMARY"
@@ -610,22 +705,22 @@ jobs:
     env:
       MKDOCS_INSIDERS_SSH_KEY_EXISTS: ${{ secrets.MKDOCS_INSIDERS_SSH_KEY != '' }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: "3.13"
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Add SSH key"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
-        uses: webfactory/ssh-agent@v0.9.0
+        uses: webfactory/ssh-agent@a6f90b1f127823b31d4d4a8d96047790581349bd # v0.9.1
         with:
           ssh-private-key: ${{ secrets.MKDOCS_INSIDERS_SSH_KEY }}
       - name: "Install Rust toolchain"
         run: rustup show
       - name: Install uv
-        uses: astral-sh/setup-uv@v5
+        uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5.4.2
       - name: "Install Insiders dependencies"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
         run: uv pip install -r docs/requirements-insiders.txt --system
@@ -652,10 +747,10 @@ jobs:
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && (needs.determine_changes.outputs.formatter == 'true' || github.ref == 'refs/heads/main') }}
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Run checks"
@@ -674,21 +769,22 @@ jobs:
       - determine_changes
     if: ${{ !contains(github.event.pull_request.labels.*.name, 'no-test') && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
     steps:
-      - uses: extractions/setup-just@v2
+      - uses: extractions/setup-just@dd310ad5a97d8e7b41793f8ef055398d51ad4de6 # v2
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         name: "Download ruff-lsp source"
         with:
           persist-credentials: false
           repository: "astral-sh/ruff-lsp"
 
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
-          python-version: ${{ env.PYTHON_VERSION }}
+          # installation fails on 3.13 and newer
+          python-version: "3.12"
 
-      - uses: actions/download-artifact@v4
+      - uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e # v4.2.1
         name: Download development ruff binary
         id: ruff-target
         with:
@@ -711,6 +807,39 @@ jobs:
 
           just test
 
+  check-playground:
+    name: "check playground"
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    needs:
+      - determine_changes
+    if: ${{ (needs.determine_changes.outputs.playground == 'true') }}
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          persist-credentials: false
+      - name: "Install Rust toolchain"
+        run: rustup target add wasm32-unknown-unknown
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
+      - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
+        with:
+          node-version: 22
+          cache: "npm"
+          cache-dependency-path: playground/package-lock.json
+      - uses: jetli/wasm-bindgen-action@20b33e20595891ab1a0ed73145d8a21fc96e7c29 # v0.2.0
+      - name: "Install Node dependencies"
+        run: npm ci
+        working-directory: playground
+      - name: "Build playgrounds"
+        run: npm run dev:wasm
+        working-directory: playground
+      - name: "Run TypeScript checks"
+        run: npm run check
+        working-directory: playground
+      - name: "Check formatting"
+        run: npm run fmt:check
+        working-directory: playground
+
   benchmarks:
     runs-on: ubuntu-24.04
     needs: determine_changes
@@ -718,17 +847,17 @@ jobs:
     timeout-minutes: 20
     steps:
       - name: "Checkout Branch"
-        uses: actions/checkout@v4
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
 
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
 
       - name: "Install Rust toolchain"
         run: rustup show
 
       - name: "Install codspeed"
-        uses: taiki-e/install-action@v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-codspeed
 
@@ -736,7 +865,7 @@ jobs:
         run: cargo codspeed build --features codspeed -p ruff_benchmark
 
       - name: "Run benchmarks"
-        uses: CodSpeedHQ/action@v3
+        uses: CodSpeedHQ/action@0010eb0ca6e89b80c88e8edaaa07cfe5f3e6664d # v3.5.0
         with:
           run: cargo codspeed run
           token: ${{ secrets.CODSPEED_TOKEN }}

.github/workflows/daily_fuzz.yaml

@@ -31,15 +31,15 @@ jobs:
     # Don't run the cron job on forks:
     if: ${{ github.repository == 'astral-sh/ruff' || github.event_name != 'schedule' }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: astral-sh/setup-uv@v5
+      - uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5.4.2
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install mold"
-        uses: rui314/setup-mold@v1
-      - uses: Swatinem/rust-cache@v2
+        uses: rui314/setup-mold@e16410e7f8d9e167b74ad5697a9089a35126eb50 # v1
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: Build ruff
         # A debug build means the script runs slower once it gets started,
         # but this is outweighed by the fact that a release build takes *much* longer to compile in CI
@@ -65,7 +65,7 @@ jobs:
     permissions:
       issues: write
     steps:
-      - uses: actions/github-script@v7
+      - uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           script: |

.github/workflows/daily_property_tests.yaml

@@ -30,14 +30,14 @@ jobs:
     # Don't run the cron job on forks:
     if: ${{ github.repository == 'astral-sh/ruff' || github.event_name != 'schedule' }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install mold"
-        uses: rui314/setup-mold@v1
-      - uses: Swatinem/rust-cache@v2
+        uses: rui314/setup-mold@e16410e7f8d9e167b74ad5697a9089a35126eb50 # v1
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: Build Red Knot
         # A release build takes longer (2 min vs 1 min), but the property tests run much faster in release
         # mode (1.5 min vs 14 min), so the overall time is shorter with a release build.
@@ -59,7 +59,7 @@ jobs:
     permissions:
       issues: write
     steps:
-      - uses: actions/github-script@v7
+      - uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           script: |

.github/workflows/mypy_primer.yaml

@@ -25,19 +25,19 @@ env:
 jobs:
   mypy_primer:
     name: Run mypy_primer
-    runs-on: ubuntu-24.04
+    runs-on: depot-ubuntu-22.04-16
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           path: ruff
           fetch-depth: 0
           persist-credentials: false
 
       - name: Install the latest version of uv
-        uses: astral-sh/setup-uv@v5
+        uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5.4.2
 
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
         with:
           workspaces: "ruff"
       - name: Install Rust toolchain
@@ -45,13 +45,15 @@ jobs:
 
       - name: Install mypy_primer
         run: |
-          uv tool install "git+https://github.com/astral-sh/mypy_primer.git@add-red-knot-support"
+          uv tool install "git+https://github.com/astral-sh/mypy_primer.git@add-red-knot-support-v5"
 
       - name: Run mypy_primer
         shell: bash
         run: |
           cd ruff
 
+          PRIMER_SELECTOR="$(paste -s -d'|' crates/red_knot_python_semantic/resources/primer/good.txt)"
+
           echo "new commit"
           git rev-list --format=%s --max-count=1 "$GITHUB_SHA"
 
@@ -62,13 +64,14 @@ jobs:
 
           cd ..
 
+          echo "Project selector: $PRIMER_SELECTOR"
           # Allow the exit code to be 0 or 1, only fail for actual mypy_primer crashes/bugs
           uvx mypy_primer \
             --repo ruff \
             --type-checker knot \
             --old base_commit \
             --new "$GITHUB_SHA" \
-            --project-selector '/(mypy_primer|black|pyp|git-revise|zipp|arrow)$' \
+            --project-selector "/($PRIMER_SELECTOR)\$" \
             --output concise \
             --debug > mypy_primer.diff || [ $? -eq 1 ]
 
@@ -81,13 +84,13 @@ jobs:
           echo ${{ github.event.number }} > pr-number
 
       - name: Upload diff
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: mypy_primer_diff
           path: mypy_primer.diff
 
       - name: Upload pr-number
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
         with:
           name: pr-number
           path: pr-number

.github/workflows/mypy_primer_comment.yaml

@@ -16,7 +16,7 @@ jobs:
     permissions:
       pull-requests: write
     steps:
-      - uses: dawidd6/action-download-artifact@v8
+      - uses: dawidd6/action-download-artifact@20319c5641d495c8a52e688b7dc5fada6c3a9fbc # v8
         name: Download PR number
         with:
           name: pr-number
@@ -32,7 +32,7 @@ jobs:
             echo "pr-number=$(<pr-number)" >> "$GITHUB_OUTPUT"
           fi
 
-      - uses: dawidd6/action-download-artifact@v8
+      - uses: dawidd6/action-download-artifact@20319c5641d495c8a52e688b7dc5fada6c3a9fbc # v8
         name: "Download mypy_primer results"
         id: download-mypy_primer_diff
         if: steps.pr-number.outputs.pr-number
@@ -79,7 +79,7 @@ jobs:
           echo 'EOF' >> "$GITHUB_OUTPUT"
 
       - name: Find existing comment
-        uses: peter-evans/find-comment@v3
+        uses: peter-evans/find-comment@3eae4d37986fb5a8592848f6a574fdf654e61f9e # v3
         if: steps.generate-comment.outcome == 'success'
         id: find-comment
         with:
@@ -89,7 +89,7 @@ jobs:
 
       - name: Create or update comment
         if: steps.find-comment.outcome == 'success'
-        uses: peter-evans/create-or-update-comment@v4
+        uses: peter-evans/create-or-update-comment@71345be0265236311c031f5c7866368bd1eff043 # v4
         with:
           comment-id: ${{ steps.find-comment.outputs.comment-id }}
           issue-number: ${{ steps.pr-number.outputs.pr-number }}

.github/workflows/notify-dependents.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: "Update pre-commit mirror"
-        uses: actions/github-script@v7
+        uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
         with:
           github-token: ${{ secrets.RUFF_PRE_COMMIT_PAT }}
           script: |

.github/workflows/pr-comment.yaml

@@ -16,7 +16,7 @@ jobs:
     permissions:
       pull-requests: write
     steps:
-      - uses: dawidd6/action-download-artifact@v8
+      - uses: dawidd6/action-download-artifact@20319c5641d495c8a52e688b7dc5fada6c3a9fbc # v8
         name: Download pull request number
         with:
           name: pr-number
@@ -32,7 +32,7 @@ jobs:
             echo "pr-number=$(<pr-number)" >> "$GITHUB_OUTPUT"
           fi
 
-      - uses: dawidd6/action-download-artifact@v8
+      - uses: dawidd6/action-download-artifact@20319c5641d495c8a52e688b7dc5fada6c3a9fbc # v8
         name: "Download ecosystem results"
         id: download-ecosystem-result
         if: steps.pr-number.outputs.pr-number
@@ -70,7 +70,7 @@ jobs:
           echo 'EOF' >> "$GITHUB_OUTPUT"
 
       - name: Find existing comment
-        uses: peter-evans/find-comment@v3
+        uses: peter-evans/find-comment@3eae4d37986fb5a8592848f6a574fdf654e61f9e # v3
         if: steps.generate-comment.outcome == 'success'
         id: find-comment
         with:
@@ -80,7 +80,7 @@ jobs:
 
       - name: Create or update comment
         if: steps.find-comment.outcome == 'success'
-        uses: peter-evans/create-or-update-comment@v4
+        uses: peter-evans/create-or-update-comment@71345be0265236311c031f5c7866368bd1eff043 # v4
         with:
           comment-id: ${{ steps.find-comment.outputs.comment-id }}
           issue-number: ${{ steps.pr-number.outputs.pr-number }}

.github/workflows/publish-docs.yml

@@ -23,12 +23,12 @@ jobs:
     env:
       MKDOCS_INSIDERS_SSH_KEY_EXISTS: ${{ secrets.MKDOCS_INSIDERS_SSH_KEY != '' }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           ref: ${{ inputs.ref }}
           persist-credentials: true
 
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: 3.12
 
@@ -61,14 +61,14 @@ jobs:
 
       - name: "Add SSH key"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
-        uses: webfactory/ssh-agent@v0.9.0
+        uses: webfactory/ssh-agent@a6f90b1f127823b31d4d4a8d96047790581349bd # v0.9.1
         with:
           ssh-private-key: ${{ secrets.MKDOCS_INSIDERS_SSH_KEY }}
 
       - name: "Install Rust toolchain"
         run: rustup show
 
-      - uses: Swatinem/rust-cache@v2
+      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
 
       - name: "Install Insiders dependencies"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}

.github/workflows/publish-knot-playground.yml

@@ -0,0 +1,58 @@
+# Publish the Red Knot playground.
+name: "[Knot Playground] Release"
+
+permissions: {}
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "crates/red_knot*/**"
+      - "crates/ruff_db/**"
+      - "crates/ruff_python_ast/**"
+      - "crates/ruff_python_parser/**"
+      - "playground/**"
+      - ".github/workflows/publish-knot-playground.yml"
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref_name }}
+  cancel-in-progress: true
+
+env:
+  CARGO_INCREMENTAL: 0
+  CARGO_NET_RETRY: 10
+  CARGO_TERM_COLOR: always
+  RUSTUP_MAX_RETRIES: 10
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    env:
+      CF_API_TOKEN_EXISTS: ${{ secrets.CF_API_TOKEN != '' }}
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          persist-credentials: false
+      - name: "Install Rust toolchain"
+        run: rustup target add wasm32-unknown-unknown
+      - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
+        with:
+          node-version: 22
+      - uses: jetli/wasm-bindgen-action@20b33e20595891ab1a0ed73145d8a21fc96e7c29 # v0.2.0
+      - name: "Install Node dependencies"
+        run: npm ci
+        working-directory: playground
+      - name: "Run TypeScript checks"
+        run: npm run check
+        working-directory: playground
+      - name: "Build Knot playground"
+        run: npm run build --workspace knot-playground
+        working-directory: playground
+      - name: "Deploy to Cloudflare Pages"
+        if: ${{ env.CF_API_TOKEN_EXISTS == 'true' }}
+        uses: cloudflare/wrangler-action@da0e0dfe58b7a431659754fdf3f186c529afbe65 # v3.14.1
+        with:
+          apiToken: ${{ secrets.CF_API_TOKEN }}
+          accountId: ${{ secrets.CF_ACCOUNT_ID }}
+          # `github.head_ref` is only set during pull requests and for manual runs or tags we use `main` to deploy to production
+          command: pages deploy playground/knot/dist --project-name=knot-playground --branch ${{ github.head_ref || 'main' }} --commit-hash ${GITHUB_SHA}

.github/workflows/publish-playground.yml

@@ -24,36 +24,31 @@ jobs:
     env:
       CF_API_TOKEN_EXISTS: ${{ secrets.CF_API_TOKEN != '' }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
       - name: "Install Rust toolchain"
         run: rustup target add wasm32-unknown-unknown
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
         with:
-          node-version: 20
+          node-version: 22
           cache: "npm"
           cache-dependency-path: playground/package-lock.json
-      - uses: jetli/wasm-pack-action@v0.4.0
-        with:
-          version: v0.13.1
-      - uses: jetli/wasm-bindgen-action@v0.2.0
-      - name: "Run wasm-pack"
-        run: wasm-pack build --target web --out-dir ../../playground/src/pkg crates/ruff_wasm
+      - uses: jetli/wasm-bindgen-action@20b33e20595891ab1a0ed73145d8a21fc96e7c29 # v0.2.0
       - name: "Install Node dependencies"
         run: npm ci
         working-directory: playground
       - name: "Run TypeScript checks"
         run: npm run check
         working-directory: playground
-      - name: "Build JavaScript bundle"
-        run: npm run build
+      - name: "Build Ruff playground"
+        run: npm run build --workspace ruff-playground
         working-directory: playground
       - name: "Deploy to Cloudflare Pages"
         if: ${{ env.CF_API_TOKEN_EXISTS == 'true' }}
-        uses: cloudflare/wrangler-action@v3.14.0
+        uses: cloudflare/wrangler-action@da0e0dfe58b7a431659754fdf3f186c529afbe65 # v3.14.1
         with:
           apiToken: ${{ secrets.CF_API_TOKEN }}
           accountId: ${{ secrets.CF_ACCOUNT_ID }}
           # `github.head_ref` is only set during pull requests and for manual runs or tags we use `main` to deploy to production
-          command: pages deploy playground/dist --project-name=ruff-playground --branch ${{ github.head_ref || 'main' }} --commit-hash ${GITHUB_SHA}
+          command: pages deploy playground/ruff/dist --project-name=ruff-playground --branch ${{ github.head_ref || 'main' }} --commit-hash ${GITHUB_SHA}

.github/workflows/publish-pypi.yml

@@ -22,8 +22,8 @@ jobs:
       id-token: write
     steps:
       - name: "Install uv"
-        uses: astral-sh/setup-uv@v5
-      - uses: actions/download-artifact@v4
+        uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5.4.2
+      - uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e # v4.2.1
         with:
           pattern: wheels-*
           path: wheels

.github/workflows/publish-wasm.yml

@@ -29,15 +29,15 @@ jobs:
         target: [web, bundler, nodejs]
       fail-fast: false
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
       - name: "Install Rust toolchain"
         run: rustup target add wasm32-unknown-unknown
-      - uses: jetli/wasm-pack-action@v0.4.0
+      - uses: jetli/wasm-pack-action@0d096b08b4e5a7de8c28de67e11e945404e9eefa # v0.4.0
         with:
           version: v0.13.1
-      - uses: jetli/wasm-bindgen-action@v0.2.0
+      - uses: jetli/wasm-bindgen-action@20b33e20595891ab1a0ed73145d8a21fc96e7c29 # v0.2.0
       - name: "Run wasm-pack build"
         run: wasm-pack build --target ${{ matrix.target }} crates/ruff_wasm
       - name: "Rename generated package"
@@ -45,7 +45,7 @@ jobs:
           jq '.name="@astral-sh/ruff-wasm-${{ matrix.target }}"' crates/ruff_wasm/pkg/package.json > /tmp/package.json
           mv /tmp/package.json crates/ruff_wasm/pkg
       - run: cp LICENSE crates/ruff_wasm/pkg # wasm-pack does not put the LICENSE file in the pkg
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
         with:
           node-version: 20
           registry-url: "https://registry.npmjs.org"

.github/workflows/release.yml

@@ -1,6 +1,7 @@
-# This file was autogenerated by dist: https://opensource.axo.dev/cargo-dist/
+# This file was autogenerated by dist: https://github.com/astral-sh/cargo-dist
 #
 # Copyright 2022-2024, axodotdev
+# Copyright 2025 Astral Software Inc.
 # SPDX-License-Identifier: MIT or Apache-2.0
 #
 # CI that:
@@ -50,7 +51,7 @@ on:
 jobs:
   # Run 'dist plan' (or host) to determine what tasks we need to do
   plan:
-    runs-on: "ubuntu-20.04"
+    runs-on: "depot-ubuntu-latest-4"
     outputs:
       val: ${{ steps.plan.outputs.manifest }}
       tag: ${{ (inputs.tag != 'dry-run' && inputs.tag) || '' }}
@@ -59,16 +60,17 @@ jobs:
     env:
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
         with:
+          persist-credentials: false
           submodules: recursive
       - name: Install dist
         # we specify bash to get pipefail; it guards against the `curl` command
         # failing. otherwise `sh` won't catch that `curl` returned non-0
         shell: bash
-        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/axodotdev/cargo-dist/releases/download/v0.25.2-prerelease.3/cargo-dist-installer.sh | sh"
+        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/astral-sh/cargo-dist/releases/download/v0.28.4-prerelease.1/cargo-dist-installer.sh | sh"
       - name: Cache dist
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02
         with:
           name: cargo-dist-cache
           path: ~/.cargo/bin/dist
@@ -84,7 +86,7 @@ jobs:
           cat plan-dist-manifest.json
           echo "manifest=$(jq -c "." plan-dist-manifest.json)" >> "$GITHUB_OUTPUT"
       - name: "Upload dist-manifest.json"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02
         with:
           name: artifacts-plan-dist-manifest
           path: plan-dist-manifest.json
@@ -116,23 +118,24 @@ jobs:
       - plan
       - custom-build-binaries
       - custom-build-docker
-    runs-on: "ubuntu-20.04"
+    runs-on: "depot-ubuntu-latest-4"
     env:
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       BUILD_MANIFEST_NAME: target/distrib/global-dist-manifest.json
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
         with:
+          persist-credentials: false
           submodules: recursive
       - name: Install cached dist
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e
         with:
           name: cargo-dist-cache
           path: ~/.cargo/bin/
       - 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
+        uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e
         with:
           pattern: artifacts-*
           path: target/distrib/
@@ -150,7 +153,7 @@ jobs:
 
           cp dist-manifest.json "$BUILD_MANIFEST_NAME"
       - name: "Upload artifacts"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02
         with:
           name: artifacts-build-global
           path: |
@@ -167,22 +170,23 @@ jobs:
     if: ${{ always() && needs.plan.outputs.publishing == 'true' && (needs.build-global-artifacts.result == 'skipped' || needs.build-global-artifacts.result == 'success') && (needs.custom-build-binaries.result == 'skipped' || needs.custom-build-binaries.result == 'success') && (needs.custom-build-docker.result == 'skipped' || needs.custom-build-docker.result == 'success') }}
     env:
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-    runs-on: "ubuntu-20.04"
+    runs-on: "depot-ubuntu-latest-4"
     outputs:
       val: ${{ steps.host.outputs.manifest }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
         with:
+          persist-credentials: false
           submodules: recursive
       - name: Install cached dist
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e
         with:
           name: cargo-dist-cache
           path: ~/.cargo/bin/
       - run: chmod +x ~/.cargo/bin/dist
       # Fetch artifacts from scratch-storage
       - name: Fetch artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e
         with:
           pattern: artifacts-*
           path: target/distrib/
@@ -196,7 +200,7 @@ jobs:
           cat dist-manifest.json
           echo "manifest=$(jq -c "." dist-manifest.json)" >> "$GITHUB_OUTPUT"
       - name: "Upload dist-manifest.json"
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02
         with:
           # Overwrite the previous copy
           name: artifacts-dist-manifest
@@ -242,16 +246,17 @@ jobs:
     # still allowing individual publish jobs to skip themselves (for prereleases).
     # "host" however must run to completion, no skipping allowed!
     if: ${{ always() && needs.host.result == 'success' && (needs.custom-publish-pypi.result == 'skipped' || needs.custom-publish-pypi.result == 'success') && (needs.custom-publish-wasm.result == 'skipped' || needs.custom-publish-wasm.result == 'success') }}
-    runs-on: "ubuntu-20.04"
+    runs-on: "depot-ubuntu-latest-4"
     env:
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
         with:
+          persist-credentials: false
           submodules: recursive
       # Create a GitHub Release while uploading all files to it
       - name: "Download GitHub Artifacts"
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e
         with:
           pattern: artifacts-*
           path: artifacts

.github/workflows/sync_typeshed.yaml

@@ -21,12 +21,12 @@ jobs:
       contents: write
       pull-requests: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         name: Checkout Ruff
         with:
           path: ruff
           persist-credentials: true
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         name: Checkout typeshed
         with:
           repository: python/typeshed
@@ -70,7 +70,7 @@ jobs:
     permissions:
       issues: write
     steps:
-      - uses: actions/github-script@v7
+      - uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           script: |

.ignore

@@ -0,0 +1 @@
+!/.github/

.pre-commit-config.yaml

@@ -18,8 +18,13 @@ exclude: |
   )$
 
 repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v5.0.0
+    hooks:
+      - id: check-merge-conflict
+
   - repo: https://github.com/abravalheri/validate-pyproject
-    rev: v0.23
+    rev: v0.24.1
     hooks:
       - id: validate-pyproject
 
@@ -60,7 +65,7 @@ repos:
           - black==25.1.0
 
   - repo: https://github.com/crate-ci/typos
-    rev: v1.30.0
+    rev: v1.31.1
     hooks:
       - id: typos
 
@@ -74,7 +79,7 @@ repos:
         pass_filenames: false # This makes it a lot faster
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.9.9
+    rev: v0.11.6
     hooks:
       - id: ruff-format
       - id: ruff
@@ -84,7 +89,7 @@ repos:
 
   # Prettier
   - repo: https://github.com/rbubley/mirrors-prettier
-    rev: v3.5.2
+    rev: v3.5.3
     hooks:
       - id: prettier
         types: [yaml]
@@ -92,12 +97,12 @@ repos:
   # zizmor detects security vulnerabilities in GitHub Actions workflows.
   # Additional configuration for the tool is found in `.github/zizmor.yml`
   - repo: https://github.com/woodruffw/zizmor-pre-commit
-    rev: v1.4.1
+    rev: v1.6.0
     hooks:
       - id: zizmor
 
   - repo: https://github.com/python-jsonschema/check-jsonschema
-    rev: 0.31.2
+    rev: 0.33.0
     hooks:
       - id: check-github-workflows
 

BREAKING_CHANGES.md

@@ -1,6 +1,8 @@
 # Breaking Changes
 
-## 0.10.0
+## 0.11.0
+
+This is a follow-up to release 0.10.0. Because of a mistake in the release process, the `requires-python` inference changes were not included in that release. Ruff 0.11.0 now includes this change as well as the stabilization of the preview behavior for `PGH004`.
 
 - **Changes to how the Python version is inferred when a `target-version` is not specified** ([#16319](https://github.com/astral-sh/ruff/pull/16319))
 
@@ -23,6 +25,13 @@
         search for the closest `pyproject.toml` in the parent directories and use its
         `requires-python` setting.
 
+## 0.10.0
+
+- **Changes to how the Python version is inferred when a `target-version` is not specified** ([#16319](https://github.com/astral-sh/ruff/pull/16319))
+
+    Because of a mistake in the release process, the `requires-python` inference changes are not included in this release and instead shipped as part of 0.11.0.
+    You can find a description of this change in the 0.11.0 section.
+
 - **Updated `TYPE_CHECKING` behavior** ([#16669](https://github.com/astral-sh/ruff/pull/16669))
 
     Previously, Ruff only recognized typechecking blocks that tested the `typing.TYPE_CHECKING` symbol. Now, Ruff recognizes any local variable named `TYPE_CHECKING`. This release also removes support for the legacy `if 0:` and `if False:` typechecking checks. Use a local `TYPE_CHECKING` variable instead.

CHANGELOG.md

@@ -1,13 +1,134 @@
 # Changelog
 
-## 0.10.0
+## 0.11.6
 
-Check out the [blog post](https://astral.sh/blog/ruff-v0.10.0) for a migration guide and overview of the changes!
+### Preview features
+
+- Avoid adding whitespace to the end of a docstring after an escaped quote ([#17216](https://github.com/astral-sh/ruff/pull/17216))
+- \[`airflow`\] Extract `AIR311` from `AIR301` rules (`AIR301`, `AIR311`) ([#17310](https://github.com/astral-sh/ruff/pull/17310), [#17422](https://github.com/astral-sh/ruff/pull/17422))
+
+### Bug fixes
+
+- Raise syntax error when `\` is at end of file ([#17409](https://github.com/astral-sh/ruff/pull/17409))
+
+## 0.11.5
+
+### Preview features
+
+- \[`airflow`\] Add missing `AIR302` attribute check ([#17115](https://github.com/astral-sh/ruff/pull/17115))
+- \[`airflow`\] Expand module path check to individual symbols (`AIR302`) ([#17278](https://github.com/astral-sh/ruff/pull/17278))
+- \[`airflow`\] Extract `AIR312` from `AIR302` rules (`AIR302`, `AIR312`) ([#17152](https://github.com/astral-sh/ruff/pull/17152))
+- \[`airflow`\] Update oudated `AIR301`, `AIR302` rules ([#17123](https://github.com/astral-sh/ruff/pull/17123))
+- [syntax-errors] Async comprehension in sync comprehension ([#17177](https://github.com/astral-sh/ruff/pull/17177))
+- [syntax-errors] Check annotations in annotated assignments ([#17283](https://github.com/astral-sh/ruff/pull/17283))
+- [syntax-errors] Extend annotation checks to `await` ([#17282](https://github.com/astral-sh/ruff/pull/17282))
+
+### Bug fixes
+
+- \[`flake8-pie`\] Avoid false positive for multiple assignment with `auto()` (`PIE796`) ([#17274](https://github.com/astral-sh/ruff/pull/17274))
+
+### Rule changes
+
+- \[`ruff`\] Fix `RUF100` to detect unused file-level `noqa` directives with specific codes (#17042) ([#17061](https://github.com/astral-sh/ruff/pull/17061))
+- \[`flake8-pytest-style`\] Avoid false positive for legacy form of `pytest.raises` (`PT011`) ([#17231](https://github.com/astral-sh/ruff/pull/17231))
+
+### Documentation
+
+- Fix formatting of "See Style Guide" link ([#17272](https://github.com/astral-sh/ruff/pull/17272))
+
+## 0.11.4
+
+### Preview features
+
+- \[`ruff`\] Implement `invalid-rule-code` as `RUF102` ([#17138](https://github.com/astral-sh/ruff/pull/17138))
+- [syntax-errors] Detect duplicate keys in `match` mapping patterns ([#17129](https://github.com/astral-sh/ruff/pull/17129))
+- [syntax-errors] Detect duplicate attributes in `match` class patterns ([#17186](https://github.com/astral-sh/ruff/pull/17186))
+- [syntax-errors] Detect invalid syntax in annotations ([#17101](https://github.com/astral-sh/ruff/pull/17101))
+
+### Bug fixes
+
+- [syntax-errors] Fix multiple assignment error for class fields in `match` patterns ([#17184](https://github.com/astral-sh/ruff/pull/17184))
+- Don't skip visiting non-tuple slice in `typing.Annotated` subscripts ([#17201](https://github.com/astral-sh/ruff/pull/17201))
+
+## 0.11.3
+
+### Preview features
+
+- \[`airflow`\] Add more autofixes for `AIR302` ([#16876](https://github.com/astral-sh/ruff/pull/16876), [#16977](https://github.com/astral-sh/ruff/pull/16977), [#16976](https://github.com/astral-sh/ruff/pull/16976), [#16965](https://github.com/astral-sh/ruff/pull/16965))
+- \[`airflow`\] Move `AIR301` to `AIR002` ([#16978](https://github.com/astral-sh/ruff/pull/16978))
+- \[`airflow`\] Move `AIR302` to `AIR301` and `AIR303` to `AIR302` ([#17151](https://github.com/astral-sh/ruff/pull/17151))
+- \[`flake8-bandit`\] Mark `str` and `list[str]` literals as trusted input (`S603`) ([#17136](https://github.com/astral-sh/ruff/pull/17136))
+- \[`ruff`\] Support slices in `RUF005` ([#17078](https://github.com/astral-sh/ruff/pull/17078))
+- [syntax-errors] Start detecting compile-time syntax errors ([#16106](https://github.com/astral-sh/ruff/pull/16106))
+- [syntax-errors] Duplicate type parameter names ([#16858](https://github.com/astral-sh/ruff/pull/16858))
+- [syntax-errors] Irrefutable `case` pattern before final case ([#16905](https://github.com/astral-sh/ruff/pull/16905))
+- [syntax-errors] Multiple assignments in `case` pattern ([#16957](https://github.com/astral-sh/ruff/pull/16957))
+- [syntax-errors] Single starred assignment target ([#17024](https://github.com/astral-sh/ruff/pull/17024))
+- [syntax-errors] Starred expressions in `return`, `yield`, and `for` ([#17134](https://github.com/astral-sh/ruff/pull/17134))
+- [syntax-errors] Store to or delete `__debug__` ([#16984](https://github.com/astral-sh/ruff/pull/16984))
+
+### Bug fixes
+
+- Error instead of `panic!` when running Ruff from a deleted directory (#16903) ([#17054](https://github.com/astral-sh/ruff/pull/17054))
+- [syntax-errors] Fix false positive for parenthesized tuple index ([#16948](https://github.com/astral-sh/ruff/pull/16948))
+
+### CLI
+
+- Check `pyproject.toml` correctly when it is passed via stdin ([#16971](https://github.com/astral-sh/ruff/pull/16971))
+
+### Configuration
+
+- \[`flake8-import-conventions`\] Add import `numpy.typing as npt` to default `flake8-import-conventions.aliases` ([#17133](https://github.com/astral-sh/ruff/pull/17133))
+
+### Documentation
+
+- \[`refurb`\] Document why `UserDict`, `UserList`, and `UserString` are preferred over `dict`, `list`, and `str` (`FURB189`) ([#16927](https://github.com/astral-sh/ruff/pull/16927))
+
+## 0.11.2
+
+### Preview features
+
+- [syntax-errors] Fix false-positive syntax errors emitted for annotations on variadic parameters before Python 3.11 ([#16878](https://github.com/astral-sh/ruff/pull/16878))
+
+## 0.11.1
+
+### Preview features
+
+- \[`airflow`\] Add `chain`, `chain_linear` and `cross_downstream` for `AIR302` ([#16647](https://github.com/astral-sh/ruff/pull/16647))
+- [syntax-errors] Improve error message and range for pre-PEP-614 decorator syntax errors ([#16581](https://github.com/astral-sh/ruff/pull/16581))
+- [syntax-errors] PEP 701 f-strings before Python 3.12 ([#16543](https://github.com/astral-sh/ruff/pull/16543))
+- [syntax-errors] Parenthesized context managers before Python 3.9 ([#16523](https://github.com/astral-sh/ruff/pull/16523))
+- [syntax-errors] Star annotations before Python 3.11 ([#16545](https://github.com/astral-sh/ruff/pull/16545))
+- [syntax-errors] Star expression in index before Python 3.11 ([#16544](https://github.com/astral-sh/ruff/pull/16544))
+- [syntax-errors] Unparenthesized assignment expressions in sets and indexes ([#16404](https://github.com/astral-sh/ruff/pull/16404))
+
+### Bug fixes
+
+- Server: Allow `FixAll` action in presence of version-specific syntax errors ([#16848](https://github.com/astral-sh/ruff/pull/16848))
+- \[`flake8-bandit`\] Allow raw strings in `suspicious-mark-safe-usage` (`S308`) #16702 ([#16770](https://github.com/astral-sh/ruff/pull/16770))
+- \[`refurb`\] Avoid panicking `unwrap` in `verbose-decimal-constructor` (`FURB157`) ([#16777](https://github.com/astral-sh/ruff/pull/16777))
+- \[`refurb`\] Fix starred expressions fix (`FURB161`) ([#16550](https://github.com/astral-sh/ruff/pull/16550))
+- Fix `--statistics` reporting for unsafe fixes ([#16756](https://github.com/astral-sh/ruff/pull/16756))
+
+### Rule changes
+
+- \[`flake8-executables`\] Allow `uv run` in shebang line for `shebang-missing-python` (`EXE003`) ([#16849](https://github.com/astral-sh/ruff/pull/16849),[#16855](https://github.com/astral-sh/ruff/pull/16855))
+
+### CLI
+
+- Add `--exit-non-zero-on-format` ([#16009](https://github.com/astral-sh/ruff/pull/16009))
+
+### Documentation
+
+- Update Ruff tutorial to avoid non-existent fix in `__init__.py` ([#16818](https://github.com/astral-sh/ruff/pull/16818))
+- \[`flake8-gettext`\] Swap `format-` and `printf-in-get-text-func-call` examples (`INT002`, `INT003`) ([#16769](https://github.com/astral-sh/ruff/pull/16769))
+
+## 0.11.0
+
+This is a follow-up to release 0.10.0. Because of a mistake in the release process, the `requires-python` inference changes were not included in that release. Ruff 0.11.0 now includes this change as well as the stabilization of the preview behavior for `PGH004`.
 
 ### Breaking changes
 
-See also, the "Remapped rules" section which may result in disabled rules.
-
 - **Changes to how the Python version is inferred when a `target-version` is not specified** ([#16319](https://github.com/astral-sh/ruff/pull/16319))
 
     In previous versions of Ruff, you could specify your Python version with:
@@ -29,13 +150,36 @@ See also, the "Remapped rules" section which may result in disabled rules.
         search for the closest `pyproject.toml` in the parent directories and use its
         `requires-python` setting.
 
+### Stabilization
+
+The following behaviors have been stabilized:
+
+- [`blanket-noqa`](https://docs.astral.sh/ruff/rules/blanket-noqa/) (`PGH004`): Also detect blanked file-level noqa comments (and not just line level comments).
+
+### Preview features
+
+- [syntax-errors] Tuple unpacking in `for` statement iterator clause before Python 3.9 ([#16558](https://github.com/astral-sh/ruff/pull/16558))
+
+## 0.10.0
+
+Check out the [blog post](https://astral.sh/blog/ruff-v0.10.0) for a migration guide and overview of the changes!
+
+### Breaking changes
+
+See also, the "Remapped rules" section which may result in disabled rules.
+
+- **Changes to how the Python version is inferred when a `target-version` is not specified** ([#16319](https://github.com/astral-sh/ruff/pull/16319))
+
+    Because of a mistake in the release process, the `requires-python` inference changes are not included in this release and instead shipped as part of 0.11.0.
+    You can find a description of this change in the 0.11.0 section.
+
 - **Updated `TYPE_CHECKING` behavior** ([#16669](https://github.com/astral-sh/ruff/pull/16669))
 
     Previously, Ruff only recognized typechecking blocks that tested the `typing.TYPE_CHECKING` symbol. Now, Ruff recognizes any local variable named `TYPE_CHECKING`. This release also removes support for the legacy `if 0:` and `if False:` typechecking checks. Use a local `TYPE_CHECKING` variable instead.
 
 - **More robust noqa parsing** ([#16483](https://github.com/astral-sh/ruff/pull/16483))
 
-    The syntax for both file-level and in-line suppression comments has been unified and made more robust to certain errors. In most cases, this will result in more suppression comments being read by Ruff, but there are a few instances where previously read comments will now log an error to the user instead. Please refer to the documentation on [_Error suppression_](https://docs.astral.sh/ruff/linter/#error-suppression) for the full specification.
+    The syntax for both file-level and in-line suppression comments has been unified and made more robust to certain errors. In most cases, this will result in more suppression comments being read by Ruff, but there are a few instances where previously read comments will now log an error to the user instead. Please refer to the documentation on [*Error suppression*](https://docs.astral.sh/ruff/linter/#error-suppression) for the full specification.
 
 - **Avoid unnecessary parentheses around with statements with a single context manager and a trailing comment** ([#14005](https://github.com/astral-sh/ruff/pull/14005))
 
@@ -86,7 +230,6 @@ The following behaviors have been stabilized:
 
 - [`bad-staticmethod-argument`](https://docs.astral.sh/ruff/rules/bad-staticmethod-argument/) (`PLW0211`) [`invalid-first-argument-name-for-class-method`](https://docs.astral.sh/ruff/rules/invalid-first-argument-name-for-class-method/) (`N804`): `__new__` methods are now no longer flagged by `invalid-first-argument-name-for-class-method` (`N804`) but instead by `bad-staticmethod-argument` (`PLW0211`)
 - [`bad-str-strip-call`](https://docs.astral.sh/ruff/rules/bad-str-strip-call/) (`PLE1310`): The rule now applies to objects which are known to have type `str` or `bytes`.
-- [`blanket-noqa`](https://docs.astral.sh/ruff/rules/blanket-noqa/) (`PGH004`): Also detect blanked file-level noqa comments (and not just line level comments).
 - [`custom-type-var-for-self`](https://docs.astral.sh/ruff/rules/custom-type-var-for-self/) (`PYI019`): More accurate detection of custom `TypeVars` replaceable by `Self`. The range of the diagnostic is now the full function header rather than just the return annotation.
 - [`invalid-argument-name`](https://docs.astral.sh/ruff/rules/invalid-argument-name/) (`N803`): Ignore argument names of functions decorated with `typing.override`
 - [`invalid-envvar-default`](https://docs.astral.sh/ruff/rules/invalid-envvar-default/) (`PLW1508`): Detect default value arguments to `os.environ.get` with invalid type.
@@ -1362,11 +1505,11 @@ The following rules have been stabilized and are no longer in preview:
 
 The following behaviors have been stabilized:
 
-- [`cancel-scope-no-checkpoint`](https://docs.astral.sh/ruff/rules/cancel-scope-no-checkpoint/) (`ASYNC100`): Support `asyncio` and `anyio` context mangers.
-- [`async-function-with-timeout`](https://docs.astral.sh/ruff/rules/async-function-with-timeout/) (`ASYNC109`): Support `asyncio` and `anyio` context mangers.
-- [`async-busy-wait`](https://docs.astral.sh/ruff/rules/async-busy-wait/) (`ASYNC110`): Support `asyncio` and `anyio` context mangers.
-- [`async-zero-sleep`](https://docs.astral.sh/ruff/rules/async-zero-sleep/) (`ASYNC115`): Support `anyio` context mangers.
-- [`long-sleep-not-forever`](https://docs.astral.sh/ruff/rules/long-sleep-not-forever/) (`ASYNC116`): Support `anyio` context mangers.
+- [`cancel-scope-no-checkpoint`](https://docs.astral.sh/ruff/rules/cancel-scope-no-checkpoint/) (`ASYNC100`): Support `asyncio` and `anyio` context managers.
+- [`async-function-with-timeout`](https://docs.astral.sh/ruff/rules/async-function-with-timeout/) (`ASYNC109`): Support `asyncio` and `anyio` context managers.
+- [`async-busy-wait`](https://docs.astral.sh/ruff/rules/async-busy-wait/) (`ASYNC110`): Support `asyncio` and `anyio` context managers.
+- [`async-zero-sleep`](https://docs.astral.sh/ruff/rules/async-zero-sleep/) (`ASYNC115`): Support `anyio` context managers.
+- [`long-sleep-not-forever`](https://docs.astral.sh/ruff/rules/long-sleep-not-forever/) (`ASYNC116`): Support `anyio` context managers.
 
 The following fixes have been stabilized:
 
@@ -1448,7 +1591,7 @@ The following fixes have been stabilized:
 
 ## 0.5.6
 
-Ruff 0.5.6 automatically enables linting and formatting of notebooks in _preview mode_.
+Ruff 0.5.6 automatically enables linting and formatting of notebooks in *preview mode*.
 You can opt-out of this behavior by adding `*.ipynb` to the `extend-exclude` setting.
 
 ```toml
@@ -2201,7 +2344,7 @@ To setup `ruff server` with your editor, refer to the [README.md](https://github
 
 ### Server
 
-_This section is devoted to updates for our new language server, written in Rust._
+*This section is devoted to updates for our new language server, written in Rust.*
 
 - Enable ruff-specific source actions ([#10916](https://github.com/astral-sh/ruff/pull/10916))
 - Refreshes diagnostics for open files when file configuration is changed ([#10988](https://github.com/astral-sh/ruff/pull/10988))
@@ -3608,7 +3751,7 @@ Read Ruff's new [versioning policy](https://docs.astral.sh/ruff/versioning/).
 - \[`refurb`\] Add `single-item-membership-test` (`FURB171`) ([#7815](https://github.com/astral-sh/ruff/pull/7815))
 - \[`pylint`\] Add `and-or-ternary` (`R1706`) ([#7811](https://github.com/astral-sh/ruff/pull/7811))
 
-_New rules are added in [preview](https://docs.astral.sh/ruff/preview/)._
+*New rules are added in [preview](https://docs.astral.sh/ruff/preview/).*
 
 ### Configuration
 

Cargo.toml

@@ -4,7 +4,7 @@ resolver = "2"
 
 [workspace.package]
 edition = "2021"
-rust-version = "1.83"
+rust-version = "1.84"
 homepage = "https://docs.astral.sh/ruff"
 documentation = "https://docs.astral.sh/ruff"
 repository = "https://github.com/astral-sh/ruff"
@@ -38,10 +38,11 @@ ruff_text_size = { path = "crates/ruff_text_size" }
 red_knot_vendored = { path = "crates/red_knot_vendored" }
 ruff_workspace = { path = "crates/ruff_workspace" }
 
+red_knot_ide = { path = "crates/red_knot_ide" }
+red_knot_project = { path = "crates/red_knot_project", default-features = false }
 red_knot_python_semantic = { path = "crates/red_knot_python_semantic" }
 red_knot_server = { path = "crates/red_knot_server" }
 red_knot_test = { path = "crates/red_knot_test" }
-red_knot_project = { path = "crates/red_knot_project", default-features = false }
 
 aho-corasick = { version = "1.1.3" }
 anstream = { version = "0.6.18" }
@@ -54,7 +55,6 @@ bitflags = { version = "2.5.0" }
 bstr = { version = "1.9.1" }
 cachedir = { version = "0.3.1" }
 camino = { version = "1.1.7" }
-chrono = { version = "0.4.35", default-features = false, features = ["clock"] }
 clap = { version = "4.5.3", features = ["derive"] }
 clap_complete_command = { version = "0.6.0" }
 clearscreen = { version = "4.0.0" }
@@ -63,7 +63,7 @@ colored = { version = "3.0.0" }
 console_error_panic_hook = { version = "0.1.7" }
 console_log = { version = "1.0.0" }
 countme = { version = "3.0.1" }
-compact_str = "0.8.0"
+compact_str = "0.9.0"
 criterion = { version = "0.5.1", default-features = false }
 crossbeam = { version = "0.8.4" }
 dashmap = { version = "6.0.1" }
@@ -71,7 +71,7 @@ dir-test = { version = "0.4.0" }
 dunce = { version = "1.0.5" }
 drop_bomb = { version = "0.1.5" }
 env_logger = { version = "0.11.0" }
-etcetera = { version = "0.8.0" }
+etcetera = { version = "0.10.0" }
 fern = { version = "0.7.0" }
 filetime = { version = "0.2.23" }
 getrandom = { version = "0.3.1" }
@@ -94,6 +94,7 @@ insta-cmd = { version = "0.6.0" }
 is-macro = { version = "0.3.5" }
 is-wsl = { version = "0.4.0" }
 itertools = { version = "0.14.0" }
+jiff = { version = "0.2.0" }
 js-sys = { version = "0.3.69" }
 jod-thread = { version = "0.1.2" }
 libc = { version = "0.2.153" }
@@ -123,7 +124,7 @@ rayon = { version = "1.10.0" }
 regex = { version = "1.10.2" }
 rustc-hash = { version = "2.0.0" }
 # When updating salsa, make sure to also update the revision in `fuzz/Cargo.toml`
-salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "095d8b2b8115c3cf8bf31914dd9ea74648bb7cf9" }
+salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "87bf6b6c2d5f6479741271da73bd9d30c2580c26" }
 schemars = { version = "0.8.16" }
 seahash = { version = "4.1.0" }
 serde = { version = "1.0.197", features = ["derive"] }
@@ -154,6 +155,7 @@ toml = { version = "0.8.11" }
 tracing = { version = "0.1.40" }
 tracing-flame = { version = "0.2.0" }
 tracing-indicatif = { version = "0.3.6" }
+tracing-log = { version = "0.2.0" }
 tracing-subscriber = { version = "0.3.18", default-features = false, features = [
     "env-filter",
     "fmt",
@@ -207,6 +209,7 @@ must_use_candidate = "allow"
 similar_names = "allow"
 single_match_else = "allow"
 too_many_lines = "allow"
+needless_continue = "allow"       # An explicit continue can be more readable, especially if the alternative is an empty block.
 # Without the hashes we run into a `rustfmt` bug in some snapshot tests, see #13250
 needless_raw_string_hashes = "allow"
 # Disallowed restriction lints
@@ -269,7 +272,7 @@ inherits = "release"
 # Config for 'dist'
 [workspace.metadata.dist]
 # The preferred dist version to use in CI (Cargo.toml SemVer syntax)
-cargo-dist-version = "0.25.2-prerelease.3"
+cargo-dist-version = "0.28.4-prerelease.1"
 # CI backends to support
 ci = "github"
 # The installers to generate for each app
@@ -326,3 +329,12 @@ github-custom-job-permissions = { "build-docker" = { packages = "write", content
 install-updater = false
 # Path that installers should place binaries in
 install-path = ["$XDG_BIN_HOME/", "$XDG_DATA_HOME/../bin", "~/.local/bin"]
+
+[workspace.metadata.dist.github-custom-runners]
+global = "depot-ubuntu-latest-4"
+
+[workspace.metadata.dist.github-action-commits]
+"actions/checkout" = "11bd71901bbe5b1630ceea73d27597364c9af683" # v4
+"actions/upload-artifact" = "ea165f8d65b6e75b540449e92b4886f43607fa02" # v4.6.2
+"actions/download-artifact" = "95815c38cf2ff2164869cbab79da8d1f422bc89e" # v4.2.1
+"actions/attest-build-provenance" = "c074443f1aee8d4aeeae555aebba3282517141b2" #v2.2.3

README.md

@@ -149,8 +149,8 @@ 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/0.10.0/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.10.0/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.11.6/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.11.6/install.ps1 | iex"
 ```
 
 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -183,7 +183,7 @@ 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: v0.10.0
+  rev: v0.11.6
   hooks:
     # Run the linter.
     - id: ruff

crates/red_knot/Cargo.toml

@@ -20,12 +20,12 @@ ruff_python_ast = { workspace = true }
 
 anyhow = { workspace = true }
 argfile = { workspace = true }
-chrono = { workspace = true }
 clap = { workspace = true, features = ["wrap_help"] }
 colored = { workspace = true }
 countme = { workspace = true, features = ["enable"] }
 crossbeam = { workspace = true }
 ctrlc = { version = "3.4.4" }
+jiff = { workspace = true }
 rayon = { workspace = true }
 salsa = { workspace = true }
 tracing = { workspace = true, features = ["release_max_level_debug"] }

crates/red_knot/docs/mypy_primer.md

@@ -31,7 +31,7 @@ mypy_primer \
 ```
 
 This will show the diagnostics diff for the `black` project between the `main` branch and your `my/feature` branch. To run the
-diff for all projects, you currently need to copy the project-selector regex from the CI pipeline in `.github/workflows/mypy_primer.yaml`.
+diff for all projects we currently enable in CI, use `--project-selector "/($(paste -s -d'|' crates/red_knot_python_semantic/resources/primer/good.txt))\$"`.
 
 You can also take a look at the [full list of ecosystem projects]. Note that some of them might still need a `knot_paths` configuration
 option to work correctly.

crates/red_knot/src/args.rs

@@ -50,6 +50,8 @@ pub(crate) struct CheckCommand {
 
     /// Path to the Python installation from which Red Knot resolves type information and third-party dependencies.
     ///
+    /// If not specified, Red Knot will look at the `VIRTUAL_ENV` environment variable.
+    ///
     /// Red Knot will search in the path's `site-packages` directories for type information and
     /// third-party imports.
     ///
@@ -69,12 +71,29 @@ pub(crate) struct CheckCommand {
     #[arg(long, value_name = "VERSION", alias = "target-version")]
     pub(crate) python_version: Option<PythonVersion>,
 
+    /// Target platform to assume when resolving types.
+    ///
+    /// This is used to specialize the type of `sys.platform` and will affect the visibility
+    /// of platform-specific functions and attributes. If the value is set to `all`, no
+    /// assumptions are made about the target platform. If unspecified, the current system's
+    /// platform will be used.
+    #[arg(long, value_name = "PLATFORM", alias = "platform")]
+    pub(crate) python_platform: Option<String>,
+
     #[clap(flatten)]
     pub(crate) verbosity: Verbosity,
 
     #[clap(flatten)]
     pub(crate) rules: RulesArg,
 
+    /// The format to use for printing diagnostic messages.
+    #[arg(long)]
+    pub(crate) output_format: Option<OutputFormat>,
+
+    /// Control when colored output is used.
+    #[arg(long, value_name = "WHEN")]
+    pub(crate) color: Option<TerminalColor>,
+
     /// Use exit code 1 if there are any warning-level diagnostics.
     #[arg(long, conflicts_with = "exit_zero", default_missing_value = "true", num_args=0..1)]
     pub(crate) error_on_warning: Option<bool>,
@@ -106,6 +125,9 @@ impl CheckCommand {
                 python_version: self
                     .python_version
                     .map(|version| RangedValue::cli(version.into())),
+                python_platform: self
+                    .python_platform
+                    .map(|platform| RangedValue::cli(platform.into())),
                 python: self.python.map(RelativePathBuf::cli),
                 typeshed: self.typeshed.map(RelativePathBuf::cli),
                 extra_paths: self.extra_search_path.map(|extra_search_paths| {
@@ -114,9 +136,11 @@ impl CheckCommand {
                         .map(RelativePathBuf::cli)
                         .collect()
                 }),
-                ..EnvironmentOptions::default()
             }),
             terminal: Some(TerminalOptions {
+                output_format: self
+                    .output_format
+                    .map(|output_format| RangedValue::cli(output_format.into())),
                 error_on_warning: self.error_on_warning,
             }),
             rules,
@@ -211,3 +235,46 @@ impl clap::Args for RulesArg {
         Self::augment_args(cmd)
     }
 }
+
+/// The diagnostic output format.
+#[derive(Copy, Clone, Hash, Debug, PartialEq, Eq, PartialOrd, Ord, Default, clap::ValueEnum)]
+pub enum OutputFormat {
+    /// Print diagnostics verbosely, with context and helpful hints.
+    ///
+    /// Diagnostic messages may include additional context and
+    /// annotations on the input to help understand the message.
+    #[default]
+    #[value(name = "full")]
+    Full,
+    /// Print diagnostics concisely, one per line.
+    ///
+    /// This will guarantee that each diagnostic is printed on
+    /// a single line. Only the most important or primary aspects
+    /// of the diagnostic are included. Contextual information is
+    /// dropped.
+    #[value(name = "concise")]
+    Concise,
+}
+
+impl From<OutputFormat> for ruff_db::diagnostic::DiagnosticFormat {
+    fn from(format: OutputFormat) -> ruff_db::diagnostic::DiagnosticFormat {
+        match format {
+            OutputFormat::Full => Self::Full,
+            OutputFormat::Concise => Self::Concise,
+        }
+    }
+}
+
+/// Control when colored output is used.
+#[derive(Copy, Clone, Hash, Debug, PartialEq, Eq, PartialOrd, Ord, Default, clap::ValueEnum)]
+pub(crate) enum TerminalColor {
+    /// Display colors if the output goes to an interactive terminal.
+    #[default]
+    Auto,
+
+    /// Always display colors.
+    Always,
+
+    /// Never display colors.
+    Never,
+}

crates/red_knot/src/logging.rs

@@ -190,8 +190,8 @@ where
         let ansi = writer.has_ansi_escapes();
 
         if self.display_timestamp {
-            let timestamp = chrono::Local::now()
-                .format("%Y-%m-%d %H:%M:%S.%f")
+            let timestamp = jiff::Zoned::now()
+                .strftime("%Y-%m-%d %H:%M:%S.%f")
                 .to_string();
             if ansi {
                 write!(writer, "{} ", timestamp.dimmed())?;
@@ -199,7 +199,7 @@ where
                 write!(
                     writer,
                     "{} ",
-                    chrono::Local::now().format("%Y-%m-%d %H:%M:%S.%f")
+                    jiff::Zoned::now().strftime("%Y-%m-%d %H:%M:%S.%f")
                 )?;
             }
         }

crates/red_knot/src/main.rs

@@ -4,7 +4,7 @@ use std::process::{ExitCode, Termination};
 use anyhow::Result;
 use std::sync::Mutex;
 
-use crate::args::{Args, CheckCommand, Command};
+use crate::args::{Args, CheckCommand, Command, TerminalColor};
 use crate::logging::setup_tracing;
 use anyhow::{anyhow, Context};
 use clap::Parser;
@@ -15,7 +15,7 @@ use red_knot_project::watch::ProjectWatcher;
 use red_knot_project::{watch, Db};
 use red_knot_project::{ProjectDatabase, ProjectMetadata};
 use red_knot_server::run_server;
-use ruff_db::diagnostic::{DisplayDiagnosticConfig, OldDiagnosticTrait, Severity};
+use ruff_db::diagnostic::{Diagnostic, DisplayDiagnosticConfig, Severity};
 use ruff_db::system::{OsSystem, SystemPath, SystemPathBuf};
 use salsa::plumbing::ZalsaDatabase;
 
@@ -76,10 +76,14 @@ pub(crate) fn version() -> Result<()> {
 }
 
 fn run_check(args: CheckCommand) -> anyhow::Result<ExitStatus> {
+    set_colored_override(args.color);
+
     let verbosity = args.verbosity.level();
     countme::enable(verbosity.is_trace());
     let _guard = setup_tracing(verbosity)?;
 
+    tracing::debug!("Version: {}", version::version());
+
     // The base path to which all CLI arguments are relative to.
     let cwd = {
         let cwd = std::env::current_dir().context("Failed to get the current working directory")?;
@@ -255,15 +259,16 @@ impl MainLoop {
                     result,
                     revision: check_revision,
                 } => {
+                    let terminal_settings = db.project().settings(db).terminal();
                     let display_config = DisplayDiagnosticConfig::default()
+                        .format(terminal_settings.output_format)
                         .color(colored::control::SHOULD_COLORIZE.should_colorize());
 
-                    let min_error_severity =
-                        if db.project().settings(db).terminal().error_on_warning {
-                            Severity::Warning
-                        } else {
-                            Severity::Error
-                        };
+                    let min_error_severity = if terminal_settings.error_on_warning {
+                        Severity::Warning
+                    } else {
+                        Severity::Error
+                    };
 
                     if check_revision == revision {
                         if db.project().files(db).is_empty() {
@@ -283,7 +288,7 @@ impl MainLoop {
                             let diagnostics_count = result.len();
 
                             for diagnostic in result {
-                                writeln!(stdout, "{}", diagnostic.display(db, &display_config))?;
+                                write!(stdout, "{}", diagnostic.display(db, &display_config))?;
 
                                 failed |= diagnostic.severity() >= min_error_severity;
                             }
@@ -354,9 +359,27 @@ enum MainLoopMessage {
     CheckWorkspace,
     CheckCompleted {
         /// The diagnostics that were found during the check.
-        result: Vec<Box<dyn OldDiagnosticTrait>>,
+        result: Vec<Diagnostic>,
         revision: u64,
     },
     ApplyChanges(Vec<watch::ChangeEvent>),
     Exit,
 }
+
+fn set_colored_override(color: Option<TerminalColor>) {
+    let Some(color) = color else {
+        return;
+    };
+
+    match color {
+        TerminalColor::Auto => {
+            colored::control::unset_override();
+        }
+        TerminalColor::Always => {
+            colored::control::set_override(true);
+        }
+        TerminalColor::Never => {
+            colored::control::set_override(false);
+        }
+    }
+}

crates/red_knot/tests/cli.rs

@@ -6,9 +6,9 @@ use std::process::Command;
 use tempfile::TempDir;
 
 /// Specifying an option on the CLI should take precedence over the same setting in the
-/// project's configuration.
+/// project's configuration. Here, this is tested for the Python version.
 #[test]
-fn config_override() -> anyhow::Result<()> {
+fn config_override_python_version() -> anyhow::Result<()> {
     let case = TestCase::with_files([
         (
             "pyproject.toml",
@@ -57,6 +57,67 @@ fn config_override() -> anyhow::Result<()> {
     Ok(())
 }
 
+/// Same as above, but for the Python platform.
+#[test]
+fn config_override_python_platform() -> anyhow::Result<()> {
+    let case = TestCase::with_files([
+        (
+            "pyproject.toml",
+            r#"
+            [tool.knot.environment]
+            python-platform = "linux"
+            "#,
+        ),
+        (
+            "test.py",
+            r#"
+            import sys
+            from typing_extensions import reveal_type
+
+            reveal_type(sys.platform)
+            "#,
+        ),
+    ])?;
+
+    assert_cmd_snapshot!(case.command(), @r#"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    info: revealed-type: Revealed type
+     --> <temp_dir>/test.py:5:1
+      |
+    3 | from typing_extensions import reveal_type
+    4 |
+    5 | reveal_type(sys.platform)
+      | ^^^^^^^^^^^^^^^^^^^^^^^^^ `Literal["linux"]`
+      |
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    "#);
+
+    assert_cmd_snapshot!(case.command().arg("--python-platform").arg("all"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    info: revealed-type: Revealed type
+     --> <temp_dir>/test.py:5:1
+      |
+    3 | from typing_extensions import reveal_type
+    4 |
+    5 | reveal_type(sys.platform)
+      | ^^^^^^^^^^^^^^^^^^^^^^^^^ `LiteralString`
+      |
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    ");
+
+    Ok(())
+}
+
 /// Paths specified on the CLI are relative to the current working directory and not the project root.
 ///
 /// We test this by adding an extra search path from the CLI to the libs directory when
@@ -191,7 +252,7 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
         r#"
             y = 4 / 0
 
-            for a in range(0, y):
+            for a in range(0, int(y)):
                 x = a
 
             print(x)  # possibly-unresolved-reference
@@ -210,7 +271,7 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
     2 | y = 4 / 0
       |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
     3 |
-    4 | for a in range(0, y):
+    4 | for a in range(0, int(y)):
       |
 
     warning: lint:possibly-unresolved-reference
@@ -219,7 +280,7 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
     5 |     x = a
     6 |
     7 | print(x)  # possibly-unresolved-reference
-      |       - Name `x` used when possibly not defined
+      |       ^ Name `x` used when possibly not defined
       |
 
     Found 2 diagnostics
@@ -244,9 +305,9 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
      --> <temp_dir>/test.py:2:5
       |
     2 | y = 4 / 0
-      |     ----- Cannot divide object of type `Literal[4]` by zero
+      |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
     3 |
-    4 | for a in range(0, y):
+    4 | for a in range(0, int(y)):
       |
 
     Found 1 diagnostic
@@ -267,7 +328,7 @@ fn cli_rule_severity() -> anyhow::Result<()> {
 
         y = 4 / 0
 
-        for a in range(0, y):
+        for a in range(0, int(y)):
             x = a
 
         print(x)  # possibly-unresolved-reference
@@ -297,7 +358,7 @@ fn cli_rule_severity() -> anyhow::Result<()> {
     4 | y = 4 / 0
       |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
     5 |
-    6 | for a in range(0, y):
+    6 | for a in range(0, int(y)):
       |
 
     warning: lint:possibly-unresolved-reference
@@ -306,7 +367,7 @@ fn cli_rule_severity() -> anyhow::Result<()> {
     7 |     x = a
     8 |
     9 | print(x)  # possibly-unresolved-reference
-      |       - Name `x` used when possibly not defined
+      |       ^ Name `x` used when possibly not defined
       |
 
     Found 3 diagnostics
@@ -331,7 +392,7 @@ fn cli_rule_severity() -> anyhow::Result<()> {
      --> <temp_dir>/test.py:2:8
       |
     2 | import does_not_exit
-      |        ------------- Cannot resolve import `does_not_exit`
+      |        ^^^^^^^^^^^^^ Cannot resolve import `does_not_exit`
     3 |
     4 | y = 4 / 0
       |
@@ -342,9 +403,9 @@ fn cli_rule_severity() -> anyhow::Result<()> {
     2 | import does_not_exit
     3 |
     4 | y = 4 / 0
-      |     ----- Cannot divide object of type `Literal[4]` by zero
+      |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
     5 |
-    6 | for a in range(0, y):
+    6 | for a in range(0, int(y)):
       |
 
     Found 2 diagnostics
@@ -365,7 +426,7 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
         r#"
         y = 4 / 0
 
-        for a in range(0, y):
+        for a in range(0, int(y)):
             x = a
 
         print(x)  # possibly-unresolved-reference
@@ -384,7 +445,7 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
     2 | y = 4 / 0
       |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
     3 |
-    4 | for a in range(0, y):
+    4 | for a in range(0, int(y)):
       |
 
     warning: lint:possibly-unresolved-reference
@@ -393,7 +454,7 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
     5 |     x = a
     6 |
     7 | print(x)  # possibly-unresolved-reference
-      |       - Name `x` used when possibly not defined
+      |       ^ Name `x` used when possibly not defined
       |
 
     Found 2 diagnostics
@@ -419,9 +480,9 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
      --> <temp_dir>/test.py:2:5
       |
     2 | y = 4 / 0
-      |     ----- Cannot divide object of type `Literal[4]` by zero
+      |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
     3 |
-    4 | for a in range(0, y):
+    4 | for a in range(0, int(y)):
       |
 
     Found 1 diagnostic
@@ -456,7 +517,7 @@ fn configuration_unknown_rules() -> anyhow::Result<()> {
       |
     2 | [tool.knot.rules]
     3 | division-by-zer = "warn" # incorrect rule name
-      | --------------- Unknown lint rule `division-by-zer`
+      | ^^^^^^^^^^^^^^^ Unknown lint rule `division-by-zer`
       |
 
     Found 1 diagnostic
@@ -498,7 +559,7 @@ fn exit_code_only_warnings() -> anyhow::Result<()> {
      --> <temp_dir>/test.py:1:7
       |
     1 | print(x)  # [unresolved-reference]
-      |       - Name `x` used when not defined
+      |       ^ Name `x` used when not defined
       |
 
     Found 1 diagnostic
@@ -523,12 +584,12 @@ fn exit_code_only_info() -> anyhow::Result<()> {
     success: true
     exit_code: 0
     ----- stdout -----
-    info: revealed-type
+    info: revealed-type: Revealed type
      --> <temp_dir>/test.py:3:1
       |
     2 | from typing_extensions import reveal_type
     3 | reveal_type(1)
-      | -------------- info: Revealed type is `Literal[1]`
+      | ^^^^^^^^^^^^^^ `Literal[1]`
       |
 
     Found 1 diagnostic
@@ -553,12 +614,12 @@ fn exit_code_only_info_and_error_on_warning_is_true() -> anyhow::Result<()> {
     success: true
     exit_code: 0
     ----- stdout -----
-    info: revealed-type
+    info: revealed-type: Revealed type
      --> <temp_dir>/test.py:3:1
       |
     2 | from typing_extensions import reveal_type
     3 | reveal_type(1)
-      | -------------- info: Revealed type is `Literal[1]`
+      | ^^^^^^^^^^^^^^ `Literal[1]`
       |
 
     Found 1 diagnostic
@@ -581,7 +642,7 @@ fn exit_code_no_errors_but_error_on_warning_is_true() -> anyhow::Result<()> {
      --> <temp_dir>/test.py:1:7
       |
     1 | print(x)  # [unresolved-reference]
-      |       - Name `x` used when not defined
+      |       ^ Name `x` used when not defined
       |
 
     Found 1 diagnostic
@@ -613,7 +674,7 @@ fn exit_code_no_errors_but_error_on_warning_is_enabled_in_configuration() -> any
      --> <temp_dir>/test.py:1:7
       |
     1 | print(x)  # [unresolved-reference]
-      |       - Name `x` used when not defined
+      |       ^ Name `x` used when not defined
       |
 
     Found 1 diagnostic
@@ -642,7 +703,7 @@ fn exit_code_both_warnings_and_errors() -> anyhow::Result<()> {
      --> <temp_dir>/test.py:2:7
       |
     2 | print(x)     # [unresolved-reference]
-      |       - Name `x` used when not defined
+      |       ^ Name `x` used when not defined
     3 | print(4[1])  # [non-subscriptable]
       |
 
@@ -680,7 +741,7 @@ fn exit_code_both_warnings_and_errors_and_error_on_warning_is_true() -> anyhow::
      --> <temp_dir>/test.py:2:7
       |
     2 | print(x)     # [unresolved-reference]
-      |       - Name `x` used when not defined
+      |       ^ Name `x` used when not defined
     3 | print(4[1])  # [non-subscriptable]
       |
 
@@ -718,7 +779,7 @@ fn exit_code_exit_zero_is_true() -> anyhow::Result<()> {
      --> <temp_dir>/test.py:2:7
       |
     2 | print(x)     # [unresolved-reference]
-      |       - Name `x` used when not defined
+      |       ^ Name `x` used when not defined
     3 | print(4[1])  # [non-subscriptable]
       |
 
@@ -753,7 +814,7 @@ fn user_configuration() -> anyhow::Result<()> {
             r#"
             y = 4 / 0
 
-            for a in range(0, y):
+            for a in range(0, int(y)):
                 x = a
 
             print(x)
@@ -778,9 +839,9 @@ fn user_configuration() -> anyhow::Result<()> {
      --> <temp_dir>/project/main.py:2:5
       |
     2 | y = 4 / 0
-      |     ----- Cannot divide object of type `Literal[4]` by zero
+      |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
     3 |
-    4 | for a in range(0, y):
+    4 | for a in range(0, int(y)):
       |
 
     warning: lint:possibly-unresolved-reference
@@ -789,7 +850,7 @@ fn user_configuration() -> anyhow::Result<()> {
     5 |     x = a
     6 |
     7 | print(x)
-      |       - Name `x` used when possibly not defined
+      |       ^ Name `x` used when possibly not defined
       |
 
     Found 2 diagnostics
@@ -820,9 +881,9 @@ fn user_configuration() -> anyhow::Result<()> {
      --> <temp_dir>/project/main.py:2:5
       |
     2 | y = 4 / 0
-      |     ----- Cannot divide object of type `Literal[4]` by zero
+      |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
     3 |
-    4 | for a in range(0, y):
+    4 | for a in range(0, int(y)):
       |
 
     error: lint:possibly-unresolved-reference
@@ -967,6 +1028,63 @@ fn check_non_existing_path() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[test]
+fn concise_diagnostics() -> anyhow::Result<()> {
+    let case = TestCase::with_file(
+        "test.py",
+        r#"
+        print(x)     # [unresolved-reference]
+        print(4[1])  # [non-subscriptable]
+        "#,
+    )?;
+
+    assert_cmd_snapshot!(case.command().arg("--output-format=concise"), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    warning[lint:unresolved-reference] <temp_dir>/test.py:2:7: Name `x` used when not defined
+    error[lint:non-subscriptable] <temp_dir>/test.py:3:7: Cannot subscript object of type `Literal[4]` with no `__getitem__` method
+    Found 2 diagnostics
+
+    ----- stderr -----
+    ");
+
+    Ok(())
+}
+
+/// This tests the diagnostic format for revealed type.
+///
+/// This test was introduced because changes were made to
+/// how the revealed type diagnostic was constructed and
+/// formatted in "verbose" mode. But it required extra
+/// logic to ensure the concise version didn't regress on
+/// information content. So this test was introduced to
+/// capture that.
+#[test]
+fn concise_revealed_type() -> anyhow::Result<()> {
+    let case = TestCase::with_file(
+        "test.py",
+        r#"
+        from typing_extensions import reveal_type
+
+        x = "hello"
+        reveal_type(x)
+        "#,
+    )?;
+
+    assert_cmd_snapshot!(case.command().arg("--output-format=concise"), @r#"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    info[revealed-type] <temp_dir>/test.py:5:1: Revealed type: `Literal["hello"]`
+    Found 1 diagnostic
+
+    ----- stderr -----
+    "#);
+
+    Ok(())
+}
+
 struct TestCase {
     _temp_dir: TempDir,
     _settings_scope: SettingsBindDropGuard,

crates/red_knot/tests/file_watching.rs

@@ -1,5 +1,3 @@
-#![allow(clippy::disallowed_names)]
-
 use std::collections::HashSet;
 use std::io::Write;
 use std::time::{Duration, Instant};
@@ -14,9 +12,9 @@ use red_knot_python_semantic::{resolve_module, ModuleName, PythonPlatform};
 use ruff_db::files::{system_path_to_file, File, FileError};
 use ruff_db::source::source_text;
 use ruff_db::system::{
-    OsSystem, System, SystemPath, SystemPathBuf, UserConfigDirectoryOverrideGuard,
+    file_time_now, OsSystem, System, SystemPath, SystemPathBuf, UserConfigDirectoryOverrideGuard,
 };
-use ruff_db::Upcast;
+use ruff_db::{Db as _, Upcast};
 use ruff_python_ast::PythonVersion;
 
 struct TestCase {
@@ -464,7 +462,7 @@ fn update_file(path: impl AsRef<SystemPath>, content: &str) -> anyhow::Result<()
 
         std::thread::sleep(Duration::from_nanos(10));
 
-        filetime::set_file_handle_times(&file, None, Some(filetime::FileTime::now()))?;
+        filetime::set_file_handle_times(&file, None, Some(file_time_now()))?;
     }
 }
 
@@ -1127,11 +1125,11 @@ print(sys.last_exc, os.getegid())
 
     assert_eq!(diagnostics.len(), 2);
     assert_eq!(
-        diagnostics[0].message(),
+        diagnostics[0].primary_message(),
         "Type `<module 'sys'>` has no attribute `last_exc`"
     );
     assert_eq!(
-        diagnostics[1].message(),
+        diagnostics[1].primary_message(),
         "Type `<module 'os'>` has no attribute `getegid`"
     );
 
@@ -1790,3 +1788,82 @@ fn changes_to_user_configuration() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+/// Tests that renaming a file from `lib.py` to `Lib.py` is correctly reflected.
+///
+/// This test currently fails on case-insensitive systems because `Files` is case-sensitive
+/// but the `System::metadata` call isn't. This means that
+/// Red Knot considers both `Lib.py` and `lib.py` to exist when only `lib.py` does
+///
+/// The incoming change events then are no-ops because they don't change either file's
+/// status nor does it update their last modified time (renaming a file doesn't bump it's
+/// last modified timestamp).
+///
+/// Fixing this requires to either make `Files` case-insensitive and store the
+/// real-case path (if it differs) on `File` or make `Files` use a
+/// case-sensitive `System::metadata` call. This does open the question if all
+/// `System` calls should be case sensitive. This would be the most consistent
+/// but might be hard to pull off.
+///
+/// What the right solution is also depends on if Red Knot itself should be case
+/// sensitive or not. E.g. should `include="src"` be case sensitive on all systems
+/// or only on case-sensitive systems?
+///
+/// Lastly, whatever solution we pick must also work well with VS Code which,
+/// unfortunately ,doesn't propagate casing-only renames.
+/// <https://github.com/rust-lang/rust-analyzer/issues/9581>
+#[ignore]
+#[test]
+fn rename_files_casing_only() -> anyhow::Result<()> {
+    let mut case = setup([("lib.py", "class Foo: ...")])?;
+
+    assert!(
+        resolve_module(case.db(), &ModuleName::new("lib").unwrap()).is_some(),
+        "Expected `lib` module to exist."
+    );
+    assert_eq!(
+        resolve_module(case.db(), &ModuleName::new("Lib").unwrap()),
+        None,
+        "Expected `Lib` module not to exist"
+    );
+
+    // Now rename `lib.py` to `Lib.py`
+    if case.db().system().case_sensitivity().is_case_sensitive() {
+        std::fs::rename(
+            case.project_path("lib.py").as_std_path(),
+            case.project_path("Lib.py").as_std_path(),
+        )
+        .context("Failed to rename `lib.py` to `Lib.py`")?;
+    } else {
+        // On case-insensitive file systems, renaming a file to a different casing is a no-op.
+        // Rename to a different name first
+        std::fs::rename(
+            case.project_path("lib.py").as_std_path(),
+            case.project_path("temp.py").as_std_path(),
+        )
+        .context("Failed to rename `lib.py` to `temp.py`")?;
+
+        std::fs::rename(
+            case.project_path("temp.py").as_std_path(),
+            case.project_path("Lib.py").as_std_path(),
+        )
+        .context("Failed to rename `temp.py` to `Lib.py`")?;
+    }
+
+    let changes = case.stop_watch(event_for_file("Lib.py"));
+    case.apply_changes(changes);
+
+    // Resolving `lib` should now fail but `Lib` should now succeed
+    assert_eq!(
+        resolve_module(case.db(), &ModuleName::new("lib").unwrap()),
+        None,
+        "Expected `lib` module to no longer exist."
+    );
+
+    assert!(
+        resolve_module(case.db(), &ModuleName::new("Lib").unwrap()).is_some(),
+        "Expected `Lib` module to exist"
+    );
+
+    Ok(())
+}

crates/red_knot_ide/Cargo.toml

@@ -0,0 +1,31 @@
+[package]
+name = "red_knot_ide"
+version = "0.0.0"
+publish = false
+authors = { workspace = true }
+edition = { workspace = true }
+rust-version = { workspace = true }
+homepage = { workspace = true }
+documentation = { workspace = true }
+repository = { workspace = true }
+license = { workspace = true }
+
+[dependencies]
+ruff_db = { workspace = true }
+ruff_python_ast = { workspace = true }
+ruff_python_parser = { workspace = true }
+ruff_text_size = { workspace = true }
+red_knot_python_semantic = { workspace = true }
+
+rustc-hash = { workspace = true }
+salsa = { workspace = true }
+smallvec = { workspace = true }
+tracing = { workspace = true }
+
+[dev-dependencies]
+red_knot_vendored = { workspace = true }
+
+insta = { workspace = true, features = ["filters"] }
+
+[lints]
+workspace = true

crates/red_knot_ide/src/db.rs

@@ -0,0 +1,138 @@
+use red_knot_python_semantic::Db as SemanticDb;
+use ruff_db::{Db as SourceDb, Upcast};
+
+#[salsa::db]
+pub trait Db: SemanticDb + Upcast<dyn SemanticDb> + Upcast<dyn SourceDb> {}
+
+#[cfg(test)]
+pub(crate) mod tests {
+    use std::sync::Arc;
+
+    use super::Db;
+    use red_knot_python_semantic::lint::{LintRegistry, RuleSelection};
+    use red_knot_python_semantic::{default_lint_registry, Db as SemanticDb, Program};
+    use ruff_db::files::{File, Files};
+    use ruff_db::system::{DbWithTestSystem, System, TestSystem};
+    use ruff_db::vendored::VendoredFileSystem;
+    use ruff_db::{Db as SourceDb, Upcast};
+
+    #[salsa::db]
+    #[derive(Clone)]
+    pub(crate) struct TestDb {
+        storage: salsa::Storage<Self>,
+        files: Files,
+        system: TestSystem,
+        vendored: VendoredFileSystem,
+        events: Arc<std::sync::Mutex<Vec<salsa::Event>>>,
+        rule_selection: Arc<RuleSelection>,
+    }
+
+    #[allow(dead_code)]
+    impl TestDb {
+        pub(crate) fn new() -> Self {
+            Self {
+                storage: salsa::Storage::default(),
+                system: TestSystem::default(),
+                vendored: red_knot_vendored::file_system().clone(),
+                events: Arc::default(),
+                files: Files::default(),
+                rule_selection: Arc::new(RuleSelection::from_registry(default_lint_registry())),
+            }
+        }
+
+        /// Takes the salsa events.
+        ///
+        /// ## Panics
+        /// If there are any pending salsa snapshots.
+        pub(crate) fn take_salsa_events(&mut self) -> Vec<salsa::Event> {
+            let inner = Arc::get_mut(&mut self.events).expect("no pending salsa snapshots");
+
+            let events = inner.get_mut().unwrap();
+            std::mem::take(&mut *events)
+        }
+
+        /// Clears the salsa events.
+        ///
+        /// ## Panics
+        /// If there are any pending salsa snapshots.
+        pub(crate) fn clear_salsa_events(&mut self) {
+            self.take_salsa_events();
+        }
+    }
+
+    impl DbWithTestSystem for TestDb {
+        fn test_system(&self) -> &TestSystem {
+            &self.system
+        }
+
+        fn test_system_mut(&mut self) -> &mut TestSystem {
+            &mut self.system
+        }
+    }
+
+    #[salsa::db]
+    impl SourceDb for TestDb {
+        fn vendored(&self) -> &VendoredFileSystem {
+            &self.vendored
+        }
+
+        fn system(&self) -> &dyn System {
+            &self.system
+        }
+
+        fn files(&self) -> &Files {
+            &self.files
+        }
+
+        fn python_version(&self) -> ruff_python_ast::PythonVersion {
+            Program::get(self).python_version(self)
+        }
+    }
+
+    impl Upcast<dyn SourceDb> for TestDb {
+        fn upcast(&self) -> &(dyn SourceDb + 'static) {
+            self
+        }
+        fn upcast_mut(&mut self) -> &mut (dyn SourceDb + 'static) {
+            self
+        }
+    }
+
+    impl Upcast<dyn SemanticDb> for TestDb {
+        fn upcast(&self) -> &(dyn SemanticDb + 'static) {
+            self
+        }
+
+        fn upcast_mut(&mut self) -> &mut dyn SemanticDb {
+            self
+        }
+    }
+
+    #[salsa::db]
+    impl SemanticDb for TestDb {
+        fn is_file_open(&self, file: File) -> bool {
+            !file.path(self).is_vendored_path()
+        }
+
+        fn rule_selection(&self) -> Arc<RuleSelection> {
+            self.rule_selection.clone()
+        }
+
+        fn lint_registry(&self) -> &LintRegistry {
+            default_lint_registry()
+        }
+    }
+
+    #[salsa::db]
+    impl Db for TestDb {}
+
+    #[salsa::db]
+    impl salsa::Database for TestDb {
+        fn salsa_event(&self, event: &dyn Fn() -> salsa::Event) {
+            let event = event();
+            tracing::trace!("event: {event:?}");
+            let mut events = self.events.lock().unwrap();
+            events.push(event);
+        }
+    }
+}

crates/red_knot_ide/src/find_node.rs

@@ -0,0 +1,106 @@
+use ruff_python_ast::visitor::source_order::{SourceOrderVisitor, TraversalSignal};
+use ruff_python_ast::AnyNodeRef;
+use ruff_text_size::{Ranged, TextRange};
+use std::fmt;
+use std::fmt::Formatter;
+
+/// Returns the node with a minimal range that fully contains `range`.
+///
+/// If `range` is empty and falls within a parser *synthesized* node generated during error recovery,
+/// then the first node with the given range is returned.
+///
+/// ## Panics
+/// Panics if `range` is not contained within `root`.
+pub(crate) fn covering_node(root: AnyNodeRef, range: TextRange) -> CoveringNode {
+    struct Visitor<'a> {
+        range: TextRange,
+        found: bool,
+        ancestors: Vec<AnyNodeRef<'a>>,
+    }
+
+    impl<'a> SourceOrderVisitor<'a> for Visitor<'a> {
+        fn enter_node(&mut self, node: AnyNodeRef<'a>) -> TraversalSignal {
+            // If the node fully contains the range, than it is a possible match but traverse into its children
+            // to see if there's a node with a narrower range.
+            if !self.found && node.range().contains_range(self.range) {
+                self.ancestors.push(node);
+                TraversalSignal::Traverse
+            } else {
+                TraversalSignal::Skip
+            }
+        }
+
+        fn leave_node(&mut self, node: AnyNodeRef<'a>) {
+            if !self.found && self.ancestors.last() == Some(&node) {
+                self.found = true;
+            }
+        }
+    }
+
+    assert!(
+        root.range().contains_range(range),
+        "Range is not contained within root"
+    );
+
+    let mut visitor = Visitor {
+        range,
+        found: false,
+        ancestors: Vec::new(),
+    };
+
+    root.visit_source_order(&mut visitor);
+
+    let minimal = visitor.ancestors.pop().unwrap_or(root);
+    CoveringNode {
+        node: minimal,
+        ancestors: visitor.ancestors,
+    }
+}
+
+/// The node with a minimal range that fully contains the search range.
+pub(crate) struct CoveringNode<'a> {
+    /// The node with a minimal range that fully contains the search range.
+    node: AnyNodeRef<'a>,
+
+    /// The node's ancestor (the spine up to the root).
+    ancestors: Vec<AnyNodeRef<'a>>,
+}
+
+impl<'a> CoveringNode<'a> {
+    pub(crate) fn node(&self) -> AnyNodeRef<'a> {
+        self.node
+    }
+
+    /// Returns the node's parent.
+    pub(crate) fn parent(&self) -> Option<AnyNodeRef<'a>> {
+        self.ancestors.last().copied()
+    }
+
+    /// Finds the minimal node that fully covers the range and fulfills the given predicate.
+    pub(crate) fn find(mut self, f: impl Fn(AnyNodeRef<'a>) -> bool) -> Result<Self, Self> {
+        if f(self.node) {
+            return Ok(self);
+        }
+
+        match self.ancestors.iter().rposition(|node| f(*node)) {
+            Some(index) => {
+                let node = self.ancestors[index];
+                self.ancestors.truncate(index);
+
+                Ok(Self {
+                    node,
+                    ancestors: self.ancestors,
+                })
+            }
+            None => Err(self),
+        }
+    }
+}
+
+impl fmt::Debug for CoveringNode<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("NodeWithAncestors")
+            .field(&self.node)
+            .finish()
+    }
+}

crates/red_knot_ide/src/goto.rs

@@ -0,0 +1,851 @@
+use crate::find_node::covering_node;
+use crate::{Db, HasNavigationTargets, NavigationTargets, RangedValue};
+use red_knot_python_semantic::types::Type;
+use red_knot_python_semantic::{HasType, SemanticModel};
+use ruff_db::files::{File, FileRange};
+use ruff_db::parsed::{parsed_module, ParsedModule};
+use ruff_python_ast::{self as ast, AnyNodeRef};
+use ruff_python_parser::TokenKind;
+use ruff_text_size::{Ranged, TextRange, TextSize};
+
+pub fn goto_type_definition(
+    db: &dyn Db,
+    file: File,
+    offset: TextSize,
+) -> Option<RangedValue<NavigationTargets>> {
+    let parsed = parsed_module(db.upcast(), file);
+    let goto_target = find_goto_target(parsed, offset)?;
+
+    let model = SemanticModel::new(db.upcast(), file);
+    let ty = goto_target.inferred_type(&model)?;
+
+    tracing::debug!(
+        "Inferred type of covering node is {}",
+        ty.display(db.upcast())
+    );
+
+    let navigation_targets = ty.navigation_targets(db);
+
+    Some(RangedValue {
+        range: FileRange::new(file, goto_target.range()),
+        value: navigation_targets,
+    })
+}
+
+#[derive(Clone, Copy, Debug)]
+pub(crate) enum GotoTarget<'a> {
+    Expression(ast::ExprRef<'a>),
+    FunctionDef(&'a ast::StmtFunctionDef),
+    ClassDef(&'a ast::StmtClassDef),
+    Parameter(&'a ast::Parameter),
+    Alias(&'a ast::Alias),
+
+    /// Go to on the module name of an import from
+    /// ```py
+    /// from foo import bar
+    ///      ^^^
+    /// ```
+    ImportedModule(&'a ast::StmtImportFrom),
+
+    /// Go to on the exception handler variable
+    /// ```py
+    /// try: ...
+    /// except Exception as e: ...
+    ///                     ^
+    /// ```
+    ExceptVariable(&'a ast::ExceptHandlerExceptHandler),
+
+    /// Go to on a keyword argument
+    /// ```py
+    /// test(a = 1)
+    ///      ^
+    /// ```
+    KeywordArgument(&'a ast::Keyword),
+
+    /// Go to on the rest parameter of a pattern match
+    ///
+    /// ```py
+    /// match x:
+    ///     case {"a": a, "b": b, **rest}: ...
+    ///                             ^^^^
+    /// ```
+    PatternMatchRest(&'a ast::PatternMatchMapping),
+
+    /// Go to on a keyword argument of a class pattern
+    ///
+    /// ```py
+    /// match Point3D(0, 0, 0):
+    ///     case Point3D(x=0, y=0, z=0): ...
+    ///                  ^    ^    ^
+    /// ```
+    PatternKeywordArgument(&'a ast::PatternKeyword),
+
+    /// Go to on a pattern star argument
+    ///
+    /// ```py
+    /// match array:
+    ///     case [*args]: ...
+    ///            ^^^^
+    PatternMatchStarName(&'a ast::PatternMatchStar),
+
+    /// Go to on the name of a pattern match as pattern
+    ///
+    /// ```py
+    /// match x:
+    ///     case [x] as y: ...
+    ///                 ^
+    PatternMatchAsName(&'a ast::PatternMatchAs),
+
+    /// Go to on the name of a type variable
+    ///
+    /// ```py
+    /// type Alias[T: int = bool] = list[T]
+    ///            ^
+    /// ```
+    TypeParamTypeVarName(&'a ast::TypeParamTypeVar),
+
+    /// Go to on the name of a type param spec
+    ///
+    /// ```py
+    /// type Alias[**P = [int, str]] = Callable[P, int]
+    ///              ^
+    /// ```
+    TypeParamParamSpecName(&'a ast::TypeParamParamSpec),
+
+    /// Go to on the name of a type var tuple
+    ///
+    /// ```py
+    /// type Alias[*Ts = ()] = tuple[*Ts]
+    ///             ^^
+    /// ```
+    TypeParamTypeVarTupleName(&'a ast::TypeParamTypeVarTuple),
+
+    NonLocal {
+        identifier: &'a ast::Identifier,
+    },
+    Globals {
+        identifier: &'a ast::Identifier,
+    },
+}
+
+impl<'db> GotoTarget<'db> {
+    pub(crate) fn inferred_type(self, model: &SemanticModel<'db>) -> Option<Type<'db>> {
+        let ty = match self {
+            GotoTarget::Expression(expression) => expression.inferred_type(model),
+            GotoTarget::FunctionDef(function) => function.inferred_type(model),
+            GotoTarget::ClassDef(class) => class.inferred_type(model),
+            GotoTarget::Parameter(parameter) => parameter.inferred_type(model),
+            GotoTarget::Alias(alias) => alias.inferred_type(model),
+            GotoTarget::ExceptVariable(except) => except.inferred_type(model),
+            GotoTarget::KeywordArgument(argument) => {
+                // TODO: Pyright resolves the declared type of the matching parameter. This seems more accurate
+                // than using the inferred value.
+                argument.value.inferred_type(model)
+            }
+            // TODO: Support identifier targets
+            GotoTarget::PatternMatchRest(_)
+            | GotoTarget::PatternKeywordArgument(_)
+            | GotoTarget::PatternMatchStarName(_)
+            | GotoTarget::PatternMatchAsName(_)
+            | GotoTarget::ImportedModule(_)
+            | GotoTarget::TypeParamTypeVarName(_)
+            | GotoTarget::TypeParamParamSpecName(_)
+            | GotoTarget::TypeParamTypeVarTupleName(_)
+            | GotoTarget::NonLocal { .. }
+            | GotoTarget::Globals { .. } => return None,
+        };
+
+        Some(ty)
+    }
+}
+
+impl Ranged for GotoTarget<'_> {
+    fn range(&self) -> TextRange {
+        match self {
+            GotoTarget::Expression(expression) => expression.range(),
+            GotoTarget::FunctionDef(function) => function.name.range,
+            GotoTarget::ClassDef(class) => class.name.range,
+            GotoTarget::Parameter(parameter) => parameter.name.range,
+            GotoTarget::Alias(alias) => alias.name.range,
+            GotoTarget::ImportedModule(module) => module.module.as_ref().unwrap().range,
+            GotoTarget::ExceptVariable(except) => except.name.as_ref().unwrap().range,
+            GotoTarget::KeywordArgument(keyword) => keyword.arg.as_ref().unwrap().range,
+            GotoTarget::PatternMatchRest(rest) => rest.rest.as_ref().unwrap().range,
+            GotoTarget::PatternKeywordArgument(keyword) => keyword.attr.range,
+            GotoTarget::PatternMatchStarName(star) => star.name.as_ref().unwrap().range,
+            GotoTarget::PatternMatchAsName(as_name) => as_name.name.as_ref().unwrap().range,
+            GotoTarget::TypeParamTypeVarName(type_var) => type_var.name.range,
+            GotoTarget::TypeParamParamSpecName(spec) => spec.name.range,
+            GotoTarget::TypeParamTypeVarTupleName(tuple) => tuple.name.range,
+            GotoTarget::NonLocal { identifier, .. } => identifier.range,
+            GotoTarget::Globals { identifier, .. } => identifier.range,
+        }
+    }
+}
+
+pub(crate) fn find_goto_target(parsed: &ParsedModule, offset: TextSize) -> Option<GotoTarget> {
+    let token = parsed
+        .tokens()
+        .at_offset(offset)
+        .max_by_key(|token| match token.kind() {
+            TokenKind::Name
+            | TokenKind::String
+            | TokenKind::Complex
+            | TokenKind::Float
+            | TokenKind::Int => 1,
+            _ => 0,
+        })?;
+
+    let covering_node = covering_node(parsed.syntax().into(), token.range())
+        .find(|node| node.is_identifier() || node.is_expression())
+        .ok()?;
+
+    tracing::trace!("Covering node is of kind {:?}", covering_node.node().kind());
+
+    match covering_node.node() {
+        AnyNodeRef::Identifier(identifier) => match covering_node.parent() {
+            Some(AnyNodeRef::StmtFunctionDef(function)) => Some(GotoTarget::FunctionDef(function)),
+            Some(AnyNodeRef::StmtClassDef(class)) => Some(GotoTarget::ClassDef(class)),
+            Some(AnyNodeRef::Parameter(parameter)) => Some(GotoTarget::Parameter(parameter)),
+            Some(AnyNodeRef::Alias(alias)) => Some(GotoTarget::Alias(alias)),
+            Some(AnyNodeRef::StmtImportFrom(from)) => Some(GotoTarget::ImportedModule(from)),
+            Some(AnyNodeRef::ExceptHandlerExceptHandler(handler)) => {
+                Some(GotoTarget::ExceptVariable(handler))
+            }
+            Some(AnyNodeRef::Keyword(keyword)) => Some(GotoTarget::KeywordArgument(keyword)),
+            Some(AnyNodeRef::PatternMatchMapping(mapping)) => {
+                Some(GotoTarget::PatternMatchRest(mapping))
+            }
+            Some(AnyNodeRef::PatternKeyword(keyword)) => {
+                Some(GotoTarget::PatternKeywordArgument(keyword))
+            }
+            Some(AnyNodeRef::PatternMatchStar(star)) => {
+                Some(GotoTarget::PatternMatchStarName(star))
+            }
+            Some(AnyNodeRef::PatternMatchAs(as_pattern)) => {
+                Some(GotoTarget::PatternMatchAsName(as_pattern))
+            }
+            Some(AnyNodeRef::TypeParamTypeVar(var)) => Some(GotoTarget::TypeParamTypeVarName(var)),
+            Some(AnyNodeRef::TypeParamParamSpec(bound)) => {
+                Some(GotoTarget::TypeParamParamSpecName(bound))
+            }
+            Some(AnyNodeRef::TypeParamTypeVarTuple(var_tuple)) => {
+                Some(GotoTarget::TypeParamTypeVarTupleName(var_tuple))
+            }
+            Some(AnyNodeRef::ExprAttribute(attribute)) => {
+                Some(GotoTarget::Expression(attribute.into()))
+            }
+            Some(AnyNodeRef::StmtNonlocal(_)) => Some(GotoTarget::NonLocal { identifier }),
+            Some(AnyNodeRef::StmtGlobal(_)) => Some(GotoTarget::Globals { identifier }),
+            None => None,
+            Some(parent) => {
+                tracing::debug!(
+                    "Missing `GoToTarget` for identifier with parent {:?}",
+                    parent.kind()
+                );
+                None
+            }
+        },
+
+        node => node.as_expr_ref().map(GotoTarget::Expression),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{cursor_test, CursorTest, IntoDiagnostic};
+    use crate::{goto_type_definition, NavigationTarget};
+    use insta::assert_snapshot;
+    use ruff_db::diagnostic::{
+        Annotation, Diagnostic, DiagnosticId, LintName, Severity, Span, SubDiagnostic,
+    };
+    use ruff_db::files::FileRange;
+    use ruff_text_size::Ranged;
+
+    #[test]
+    fn goto_type_of_expression_with_class_type() {
+        let test = cursor_test(
+            r#"
+            class Test: ...
+
+            a<CURSOR>b = Test()
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r###"
+        info: lint:goto-type-definition: Type definition
+         --> /main.py:2:19
+          |
+        2 |             class Test: ...
+          |                   ^^^^
+        3 |
+        4 |             ab = Test()
+          |
+        info: Source
+         --> /main.py:4:13
+          |
+        2 |             class Test: ...
+        3 |
+        4 |             ab = Test()
+          |             ^^
+          |
+        "###);
+    }
+
+    #[test]
+    fn goto_type_of_expression_with_function_type() {
+        let test = cursor_test(
+            r#"
+            def foo(a, b): ...
+
+            ab = foo
+
+            a<CURSOR>b
+        "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r###"
+        info: lint:goto-type-definition: Type definition
+         --> /main.py:2:17
+          |
+        2 |             def foo(a, b): ...
+          |                 ^^^
+        3 |
+        4 |             ab = foo
+          |
+        info: Source
+         --> /main.py:6:13
+          |
+        4 |             ab = foo
+        5 |
+        6 |             ab
+          |             ^^
+          |
+        "###);
+    }
+
+    #[test]
+    fn goto_type_of_expression_with_union_type() {
+        let test = cursor_test(
+            r#"
+
+            def foo(a, b): ...
+
+            def bar(a, b): ...
+
+            if random.choice():
+                a = foo
+            else:
+                a = bar
+
+            a<CURSOR>
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info: lint:goto-type-definition: Type definition
+         --> /main.py:3:17
+          |
+        3 |             def foo(a, b): ...
+          |                 ^^^
+        4 |
+        5 |             def bar(a, b): ...
+          |
+        info: Source
+          --> /main.py:12:13
+           |
+        10 |                 a = bar
+        11 |
+        12 |             a
+           |             ^
+           |
+
+        info: lint:goto-type-definition: Type definition
+         --> /main.py:5:17
+          |
+        3 |             def foo(a, b): ...
+        4 |
+        5 |             def bar(a, b): ...
+          |                 ^^^
+        6 |
+        7 |             if random.choice():
+          |
+        info: Source
+          --> /main.py:12:13
+           |
+        10 |                 a = bar
+        11 |
+        12 |             a
+           |             ^
+           |
+        ");
+    }
+
+    #[test]
+    fn goto_type_of_expression_with_module() {
+        let mut test = cursor_test(
+            r#"
+            import lib
+
+            lib<CURSOR>
+            "#,
+        );
+
+        test.write_file("lib.py", "a = 10").unwrap();
+
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info: lint:goto-type-definition: Type definition
+         --> /lib.py:1:1
+          |
+        1 | a = 10
+          | ^^^^^^
+          |
+        info: Source
+         --> /main.py:4:13
+          |
+        2 |             import lib
+        3 |
+        4 |             lib
+          |             ^^^
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_type_of_expression_with_literal_type() {
+        let test = cursor_test(
+            r#"
+            a: str = "test"
+
+            a<CURSOR>
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r#"
+        info: lint:goto-type-definition: Type definition
+           --> stdlib/builtins.pyi:438:7
+            |
+        436 |     def __getitem__(self, key: int, /) -> str | int | None: ...
+        437 |
+        438 | class str(Sequence[str]):
+            |       ^^^
+        439 |     @overload
+        440 |     def __new__(cls, object: object = ...) -> Self: ...
+            |
+        info: Source
+         --> /main.py:4:13
+          |
+        2 |             a: str = "test"
+        3 |
+        4 |             a
+          |             ^
+          |
+        "#);
+    }
+    #[test]
+    fn goto_type_of_expression_with_literal_node() {
+        let test = cursor_test(
+            r#"
+            a: str = "te<CURSOR>st"
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r#"
+        info: lint:goto-type-definition: Type definition
+           --> stdlib/builtins.pyi:438:7
+            |
+        436 |     def __getitem__(self, key: int, /) -> str | int | None: ...
+        437 |
+        438 | class str(Sequence[str]):
+            |       ^^^
+        439 |     @overload
+        440 |     def __new__(cls, object: object = ...) -> Self: ...
+            |
+        info: Source
+         --> /main.py:2:22
+          |
+        2 |             a: str = "test"
+          |                      ^^^^^^
+          |
+        "#);
+    }
+
+    #[test]
+    fn goto_type_of_expression_with_type_var_type() {
+        let test = cursor_test(
+            r#"
+            type Alias[T: int = bool] = list[T<CURSOR>]
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r###"
+        info: lint:goto-type-definition: Type definition
+         --> /main.py:2:24
+          |
+        2 |             type Alias[T: int = bool] = list[T]
+          |                        ^
+          |
+        info: Source
+         --> /main.py:2:46
+          |
+        2 |             type Alias[T: int = bool] = list[T]
+          |                                              ^
+          |
+        "###);
+    }
+
+    #[test]
+    fn goto_type_of_expression_with_type_param_spec() {
+        let test = cursor_test(
+            r#"
+            type Alias[**P = [int, str]] = Callable[P<CURSOR>, int]
+            "#,
+        );
+
+        // TODO: Goto type definition currently doesn't work for type param specs
+        // because the inference doesn't support them yet.
+        // This snapshot should show a single target pointing to `T`
+        assert_snapshot!(test.goto_type_definition(), @"No type definitions found");
+    }
+
+    #[test]
+    fn goto_type_of_expression_with_type_var_tuple() {
+        let test = cursor_test(
+            r#"
+            type Alias[*Ts = ()] = tuple[*Ts<CURSOR>]
+            "#,
+        );
+
+        // TODO: Goto type definition currently doesn't work for type var tuples
+        // because the inference doesn't support them yet.
+        // This snapshot should show a single target pointing to `T`
+        assert_snapshot!(test.goto_type_definition(), @"No type definitions found");
+    }
+
+    #[test]
+    fn goto_type_on_keyword_argument() {
+        let test = cursor_test(
+            r#"
+            def test(a: str): ...
+
+            test(a<CURSOR>= "123")
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r#"
+        info: lint:goto-type-definition: Type definition
+           --> stdlib/builtins.pyi:438:7
+            |
+        436 |     def __getitem__(self, key: int, /) -> str | int | None: ...
+        437 |
+        438 | class str(Sequence[str]):
+            |       ^^^
+        439 |     @overload
+        440 |     def __new__(cls, object: object = ...) -> Self: ...
+            |
+        info: Source
+         --> /main.py:4:18
+          |
+        2 |             def test(a: str): ...
+        3 |
+        4 |             test(a= "123")
+          |                  ^
+          |
+        "#);
+    }
+
+    #[test]
+    fn goto_type_on_incorrectly_typed_keyword_argument() {
+        let test = cursor_test(
+            r#"
+            def test(a: str): ...
+
+            test(a<CURSOR>= 123)
+            "#,
+        );
+
+        // TODO: This should jump to `str` and not `int` because
+        //   the keyword is typed as a string. It's only the passed argument that
+        //   is an int. Navigating to `str` would match pyright's behavior.
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info: lint:goto-type-definition: Type definition
+           --> stdlib/builtins.pyi:231:7
+            |
+        229 | _LiteralInteger = _PositiveInteger | _NegativeInteger | Literal[0]  # noqa: Y026  # TODO: Use TypeAlias once mypy bugs are fixed
+        230 |
+        231 | class int:
+            |       ^^^
+        232 |     @overload
+        233 |     def __new__(cls, x: ConvertibleToInt = ..., /) -> Self: ...
+            |
+        info: Source
+         --> /main.py:4:18
+          |
+        2 |             def test(a: str): ...
+        3 |
+        4 |             test(a= 123)
+          |                  ^
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_type_on_kwargs() {
+        let test = cursor_test(
+            r#"
+            def f(name: str): ...
+
+kwargs = { "name": "test"}
+
+f(**kwargs<CURSOR>)
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r#"
+        info: lint:goto-type-definition: Type definition
+            --> stdlib/builtins.pyi:1086:7
+             |
+        1084 |     def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
+        1085 |
+        1086 | class dict(MutableMapping[_KT, _VT]):
+             |       ^^^^
+        1087 |     # __init__ should be kept roughly in line with `collections.UserDict.__init__`, which has similar semantics
+        1088 |     # Also multiprocessing.managers.SyncManager.dict()
+             |
+        info: Source
+         --> /main.py:6:5
+          |
+        4 | kwargs = { "name": "test"}
+        5 |
+        6 | f(**kwargs)
+          |     ^^^^^^
+          |
+        "#);
+    }
+
+    #[test]
+    fn goto_type_of_expression_with_builtin() {
+        let test = cursor_test(
+            r#"
+            def foo(a: str):
+                a<CURSOR>
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info: lint:goto-type-definition: Type definition
+           --> stdlib/builtins.pyi:438:7
+            |
+        436 |     def __getitem__(self, key: int, /) -> str | int | None: ...
+        437 |
+        438 | class str(Sequence[str]):
+            |       ^^^
+        439 |     @overload
+        440 |     def __new__(cls, object: object = ...) -> Self: ...
+            |
+        info: Source
+         --> /main.py:3:17
+          |
+        2 |             def foo(a: str):
+        3 |                 a
+          |                 ^
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_type_definition_cursor_between_object_and_attribute() {
+        let test = cursor_test(
+            r#"
+            class X:
+                def foo(a, b): ...
+
+            x = X()
+
+            x<CURSOR>.foo()
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r###"
+        info: lint:goto-type-definition: Type definition
+         --> /main.py:2:19
+          |
+        2 |             class X:
+          |                   ^
+        3 |                 def foo(a, b): ...
+          |
+        info: Source
+         --> /main.py:7:13
+          |
+        5 |             x = X()
+        6 |
+        7 |             x.foo()
+          |             ^
+          |
+        "###);
+    }
+
+    #[test]
+    fn goto_between_call_arguments() {
+        let test = cursor_test(
+            r#"
+            def foo(a, b): ...
+
+            foo<CURSOR>()
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r###"
+        info: lint:goto-type-definition: Type definition
+         --> /main.py:2:17
+          |
+        2 |             def foo(a, b): ...
+          |                 ^^^
+        3 |
+        4 |             foo()
+          |
+        info: Source
+         --> /main.py:4:13
+          |
+        2 |             def foo(a, b): ...
+        3 |
+        4 |             foo()
+          |             ^^^
+          |
+        "###);
+    }
+
+    #[test]
+    fn goto_type_narrowing() {
+        let test = cursor_test(
+            r#"
+            def foo(a: str | None, b):
+                if a is not None:
+                    print(a<CURSOR>)
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info: lint:goto-type-definition: Type definition
+           --> stdlib/builtins.pyi:438:7
+            |
+        436 |     def __getitem__(self, key: int, /) -> str | int | None: ...
+        437 |
+        438 | class str(Sequence[str]):
+            |       ^^^
+        439 |     @overload
+        440 |     def __new__(cls, object: object = ...) -> Self: ...
+            |
+        info: Source
+         --> /main.py:4:27
+          |
+        2 |             def foo(a: str | None, b):
+        3 |                 if a is not None:
+        4 |                     print(a)
+          |                           ^
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_type_none() {
+        let test = cursor_test(
+            r#"
+            def foo(a: str | None, b):
+                a<CURSOR>
+            "#,
+        );
+
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info: lint:goto-type-definition: Type definition
+           --> stdlib/types.pyi:671:11
+            |
+        669 | if sys.version_info >= (3, 10):
+        670 |     @final
+        671 |     class NoneType:
+            |           ^^^^^^^^
+        672 |         def __bool__(self) -> Literal[False]: ...
+            |
+        info: Source
+         --> /main.py:3:17
+          |
+        2 |             def foo(a: str | None, b):
+        3 |                 a
+          |                 ^
+          |
+
+        info: lint:goto-type-definition: Type definition
+           --> stdlib/builtins.pyi:438:7
+            |
+        436 |     def __getitem__(self, key: int, /) -> str | int | None: ...
+        437 |
+        438 | class str(Sequence[str]):
+            |       ^^^
+        439 |     @overload
+        440 |     def __new__(cls, object: object = ...) -> Self: ...
+            |
+        info: Source
+         --> /main.py:3:17
+          |
+        2 |             def foo(a: str | None, b):
+        3 |                 a
+          |                 ^
+          |
+        ");
+    }
+
+    impl CursorTest {
+        fn goto_type_definition(&self) -> String {
+            let Some(targets) = goto_type_definition(&self.db, self.file, self.cursor_offset)
+            else {
+                return "No goto target found".to_string();
+            };
+
+            if targets.is_empty() {
+                return "No type definitions found".to_string();
+            }
+
+            let source = targets.range;
+            self.render_diagnostics(
+                targets
+                    .into_iter()
+                    .map(|target| GotoTypeDefinitionDiagnostic::new(source, &target)),
+            )
+        }
+    }
+
+    struct GotoTypeDefinitionDiagnostic {
+        source: FileRange,
+        target: FileRange,
+    }
+
+    impl GotoTypeDefinitionDiagnostic {
+        fn new(source: FileRange, target: &NavigationTarget) -> Self {
+            Self {
+                source,
+                target: FileRange::new(target.file(), target.focus_range()),
+            }
+        }
+    }
+
+    impl IntoDiagnostic for GotoTypeDefinitionDiagnostic {
+        fn into_diagnostic(self) -> Diagnostic {
+            let mut source = SubDiagnostic::new(Severity::Info, "Source");
+            source.annotate(Annotation::primary(
+                Span::from(self.source.file()).with_range(self.source.range()),
+            ));
+
+            let mut main = Diagnostic::new(
+                DiagnosticId::Lint(LintName::of("goto-type-definition")),
+                Severity::Info,
+                "Type definition".to_string(),
+            );
+            main.annotate(Annotation::primary(
+                Span::from(self.target.file()).with_range(self.target.range()),
+            ));
+            main.sub(source);
+
+            main
+        }
+    }
+}

crates/red_knot_ide/src/hover.rs

@@ -0,0 +1,602 @@
+use crate::goto::{find_goto_target, GotoTarget};
+use crate::{Db, MarkupKind, RangedValue};
+use red_knot_python_semantic::types::Type;
+use red_knot_python_semantic::SemanticModel;
+use ruff_db::files::{File, FileRange};
+use ruff_db::parsed::parsed_module;
+use ruff_text_size::{Ranged, TextSize};
+use std::fmt;
+use std::fmt::Formatter;
+
+pub fn hover(db: &dyn Db, file: File, offset: TextSize) -> Option<RangedValue<Hover>> {
+    let parsed = parsed_module(db.upcast(), file);
+    let goto_target = find_goto_target(parsed, offset)?;
+
+    if let GotoTarget::Expression(expr) = goto_target {
+        if expr.is_literal_expr() {
+            return None;
+        }
+    }
+
+    let model = SemanticModel::new(db.upcast(), file);
+    let ty = goto_target.inferred_type(&model)?;
+
+    tracing::debug!(
+        "Inferred type of covering node is {}",
+        ty.display(db.upcast())
+    );
+
+    // TODO: Add documentation of the symbol (not the type's definition).
+    // TODO: Render the symbol's signature instead of just its type.
+    let contents = vec![HoverContent::Type(ty)];
+
+    Some(RangedValue {
+        range: FileRange::new(file, goto_target.range()),
+        value: Hover { contents },
+    })
+}
+
+pub struct Hover<'db> {
+    contents: Vec<HoverContent<'db>>,
+}
+
+impl<'db> Hover<'db> {
+    /// Renders the hover to a string using the specified markup kind.
+    pub const fn display<'a>(&'a self, db: &'a dyn Db, kind: MarkupKind) -> DisplayHover<'a> {
+        DisplayHover {
+            db,
+            hover: self,
+            kind,
+        }
+    }
+
+    fn iter(&self) -> std::slice::Iter<'_, HoverContent<'db>> {
+        self.contents.iter()
+    }
+}
+
+impl<'db> IntoIterator for Hover<'db> {
+    type Item = HoverContent<'db>;
+    type IntoIter = std::vec::IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.contents.into_iter()
+    }
+}
+
+impl<'a, 'db> IntoIterator for &'a Hover<'db> {
+    type Item = &'a HoverContent<'db>;
+    type IntoIter = std::slice::Iter<'a, HoverContent<'db>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+pub struct DisplayHover<'a> {
+    db: &'a dyn Db,
+    hover: &'a Hover<'a>,
+    kind: MarkupKind,
+}
+
+impl fmt::Display for DisplayHover<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        let mut first = true;
+        for content in &self.hover.contents {
+            if !first {
+                self.kind.horizontal_line().fmt(f)?;
+            }
+
+            content.display(self.db, self.kind).fmt(f)?;
+            first = false;
+        }
+
+        Ok(())
+    }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum HoverContent<'db> {
+    Type(Type<'db>),
+}
+
+impl<'db> HoverContent<'db> {
+    fn display(&self, db: &'db dyn Db, kind: MarkupKind) -> DisplayHoverContent<'_, 'db> {
+        DisplayHoverContent {
+            db,
+            content: self,
+            kind,
+        }
+    }
+}
+
+pub(crate) struct DisplayHoverContent<'a, 'db> {
+    db: &'db dyn Db,
+    content: &'a HoverContent<'db>,
+    kind: MarkupKind,
+}
+
+impl fmt::Display for DisplayHoverContent<'_, '_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.content {
+            HoverContent::Type(ty) => self
+                .kind
+                .fenced_code_block(ty.display(self.db.upcast()), "text")
+                .fmt(f),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{cursor_test, CursorTest};
+    use crate::{hover, MarkupKind};
+    use insta::assert_snapshot;
+    use ruff_db::diagnostic::{
+        Annotation, Diagnostic, DiagnosticFormat, DiagnosticId, DisplayDiagnosticConfig, LintName,
+        Severity, Span,
+    };
+    use ruff_text_size::{Ranged, TextRange};
+
+    #[test]
+    fn hover_basic() {
+        let test = cursor_test(
+            r#"
+        a = 10
+
+        a<CURSOR>
+        "#,
+        );
+
+        assert_snapshot!(test.hover(), @r"
+        Literal[10]
+        ---------------------------------------------
+        ```text
+        Literal[10]
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:4:9
+          |
+        2 |         a = 10
+        3 |
+        4 |         a
+          |         ^- Cursor offset
+          |         |
+          |         source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_member() {
+        let test = cursor_test(
+            r#"
+        class Foo:
+            a: int = 10
+
+            def __init__(a: int, b: str):
+                self.a = a
+                self.b: str = b
+
+        foo = Foo()
+        foo.<CURSOR>a
+        "#,
+        );
+
+        assert_snapshot!(test.hover(), @r"
+        int
+        ---------------------------------------------
+        ```text
+        int
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+          --> /main.py:10:9
+           |
+         9 |         foo = Foo()
+        10 |         foo.a
+           |         ^^^^-
+           |         |   |
+           |         |   Cursor offset
+           |         source
+           |
+        ");
+    }
+
+    #[test]
+    fn hover_function_typed_variable() {
+        let test = cursor_test(
+            r#"
+            def foo(a, b): ...
+
+            foo<CURSOR>
+        "#,
+        );
+
+        assert_snapshot!(test.hover(), @r###"
+        def foo(a, b) -> Unknown
+        ---------------------------------------------
+        ```text
+        def foo(a, b) -> Unknown
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:4:13
+          |
+        2 |             def foo(a, b): ...
+        3 |
+        4 |             foo
+          |             ^^^- Cursor offset
+          |             |
+          |             source
+          |
+        "###);
+    }
+
+    #[test]
+    fn hover_binary_expression() {
+        let test = cursor_test(
+            r#"
+            def foo(a: int, b: int, c: int):
+                a + b ==<CURSOR> c
+        "#,
+        );
+
+        assert_snapshot!(test.hover(), @r"
+        bool
+        ---------------------------------------------
+        ```text
+        bool
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:3:17
+          |
+        2 |             def foo(a: int, b: int, c: int):
+        3 |                 a + b == c
+          |                 ^^^^^^^^-^
+          |                 |       |
+          |                 |       Cursor offset
+          |                 source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_keyword_parameter() {
+        let test = cursor_test(
+            r#"
+            def test(a: int): ...
+
+            test(a<CURSOR>= 123)
+            "#,
+        );
+
+        // TODO: This should reveal `int` because the user hovers over the parameter and not the value.
+        assert_snapshot!(test.hover(), @r"
+        Literal[123]
+        ---------------------------------------------
+        ```text
+        Literal[123]
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:4:18
+          |
+        2 |             def test(a: int): ...
+        3 |
+        4 |             test(a= 123)
+          |                  ^- Cursor offset
+          |                  |
+          |                  source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_union() {
+        let test = cursor_test(
+            r#"
+
+            def foo(a, b): ...
+
+            def bar(a, b): ...
+
+            if random.choice([True, False]):
+                a = foo
+            else:
+                a = bar
+
+            a<CURSOR>
+            "#,
+        );
+
+        assert_snapshot!(test.hover(), @r###"
+        (def foo(a, b) -> Unknown) | (def bar(a, b) -> Unknown)
+        ---------------------------------------------
+        ```text
+        (def foo(a, b) -> Unknown) | (def bar(a, b) -> Unknown)
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+          --> /main.py:12:13
+           |
+        10 |                 a = bar
+        11 |
+        12 |             a
+           |             ^- Cursor offset
+           |             |
+           |             source
+           |
+        "###);
+    }
+
+    #[test]
+    fn hover_module() {
+        let mut test = cursor_test(
+            r#"
+            import lib
+
+            li<CURSOR>b
+            "#,
+        );
+
+        test.write_file("lib.py", "a = 10").unwrap();
+
+        assert_snapshot!(test.hover(), @r"
+        <module 'lib'>
+        ---------------------------------------------
+        ```text
+        <module 'lib'>
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:4:13
+          |
+        2 |             import lib
+        3 |
+        4 |             lib
+          |             ^^-
+          |             | |
+          |             | Cursor offset
+          |             source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_type_of_expression_with_type_var_type() {
+        let test = cursor_test(
+            r#"
+            type Alias[T: int = bool] = list[T<CURSOR>]
+            "#,
+        );
+
+        assert_snapshot!(test.hover(), @r"
+        T
+        ---------------------------------------------
+        ```text
+        T
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:2:46
+          |
+        2 |             type Alias[T: int = bool] = list[T]
+          |                                              ^- Cursor offset
+          |                                              |
+          |                                              source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_type_of_expression_with_type_param_spec() {
+        let test = cursor_test(
+            r#"
+            type Alias[**P = [int, str]] = Callable[P<CURSOR>, int]
+            "#,
+        );
+
+        assert_snapshot!(test.hover(), @r"
+        @Todo
+        ---------------------------------------------
+        ```text
+        @Todo
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:2:53
+          |
+        2 |             type Alias[**P = [int, str]] = Callable[P, int]
+          |                                                     ^- Cursor offset
+          |                                                     |
+          |                                                     source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_type_of_expression_with_type_var_tuple() {
+        let test = cursor_test(
+            r#"
+            type Alias[*Ts = ()] = tuple[*Ts<CURSOR>]
+            "#,
+        );
+
+        assert_snapshot!(test.hover(), @r"
+        @Todo
+        ---------------------------------------------
+        ```text
+        @Todo
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:2:43
+          |
+        2 |             type Alias[*Ts = ()] = tuple[*Ts]
+          |                                           ^^- Cursor offset
+          |                                           |
+          |                                           source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_class_member_declaration() {
+        let test = cursor_test(
+            r#"
+        class Foo:
+            a<CURSOR>: int
+        "#,
+        );
+
+        // TODO: This should be int and not `Never`, https://github.com/astral-sh/ruff/issues/17122
+        assert_snapshot!(test.hover(), @r"
+        Never
+        ---------------------------------------------
+        ```text
+        Never
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:3:13
+          |
+        2 |         class Foo:
+        3 |             a: int
+          |             ^- Cursor offset
+          |             |
+          |             source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_type_narrowing() {
+        let test = cursor_test(
+            r#"
+            def foo(a: str | None, b):
+                if a is not None:
+                    print(a<CURSOR>)
+            "#,
+        );
+
+        assert_snapshot!(test.hover(), @r"
+        str
+        ---------------------------------------------
+        ```text
+        str
+        ```
+        ---------------------------------------------
+        info: lint:hover: Hovered content is
+         --> /main.py:4:27
+          |
+        2 |             def foo(a: str | None, b):
+        3 |                 if a is not None:
+        4 |                     print(a)
+          |                           ^- Cursor offset
+          |                           |
+          |                           source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_whitespace() {
+        let test = cursor_test(
+            r#"
+        class C:
+            <CURSOR>
+            foo: str = 'bar'
+        "#,
+        );
+
+        assert_snapshot!(test.hover(), @"Hover provided no content");
+    }
+
+    #[test]
+    fn hover_literal_int() {
+        let test = cursor_test(
+            r#"
+        print(
+            0 + 1<CURSOR>
+        )
+        "#,
+        );
+
+        assert_snapshot!(test.hover(), @"Hover provided no content");
+    }
+
+    #[test]
+    fn hover_literal_ellipsis() {
+        let test = cursor_test(
+            r#"
+        print(
+            .<CURSOR>..
+        )
+        "#,
+        );
+
+        assert_snapshot!(test.hover(), @"Hover provided no content");
+    }
+
+    #[test]
+    fn hover_docstring() {
+        let test = cursor_test(
+            r#"
+        def f():
+            """Lorem ipsum dolor sit amet.<CURSOR>"""
+        "#,
+        );
+
+        assert_snapshot!(test.hover(), @"Hover provided no content");
+    }
+
+    impl CursorTest {
+        fn hover(&self) -> String {
+            use std::fmt::Write;
+
+            let Some(hover) = hover(&self.db, self.file, self.cursor_offset) else {
+                return "Hover provided no content".to_string();
+            };
+
+            let source = hover.range;
+
+            let mut buf = String::new();
+
+            write!(
+                &mut buf,
+                "{plaintext}{line}{markdown}{line}",
+                plaintext = hover.display(&self.db, MarkupKind::PlainText),
+                line = MarkupKind::PlainText.horizontal_line(),
+                markdown = hover.display(&self.db, MarkupKind::Markdown),
+            )
+            .unwrap();
+
+            let config = DisplayDiagnosticConfig::default()
+                .color(false)
+                .format(DiagnosticFormat::Full);
+
+            let mut diagnostic = Diagnostic::new(
+                DiagnosticId::Lint(LintName::of("hover")),
+                Severity::Info,
+                "Hovered content is",
+            );
+            diagnostic.annotate(
+                Annotation::primary(Span::from(source.file()).with_range(source.range()))
+                    .message("source"),
+            );
+            diagnostic.annotate(
+                Annotation::secondary(
+                    Span::from(source.file()).with_range(TextRange::empty(self.cursor_offset)),
+                )
+                .message("Cursor offset"),
+            );
+
+            write!(buf, "{}", diagnostic.display(&self.db, &config)).unwrap();
+
+            buf
+        }
+    }
+}

crates/red_knot_ide/src/inlay_hints.rs

@@ -0,0 +1,279 @@
+use crate::Db;
+use red_knot_python_semantic::types::Type;
+use red_knot_python_semantic::{HasType, SemanticModel};
+use ruff_db::files::File;
+use ruff_db::parsed::parsed_module;
+use ruff_python_ast::visitor::source_order::{self, SourceOrderVisitor, TraversalSignal};
+use ruff_python_ast::{AnyNodeRef, Expr, Stmt};
+use ruff_text_size::{Ranged, TextRange, TextSize};
+use std::fmt;
+use std::fmt::Formatter;
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct InlayHint<'db> {
+    pub position: TextSize,
+    pub content: InlayHintContent<'db>,
+}
+
+impl<'db> InlayHint<'db> {
+    pub const fn display(&self, db: &'db dyn Db) -> DisplayInlayHint<'_, 'db> {
+        self.content.display(db)
+    }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum InlayHintContent<'db> {
+    Type(Type<'db>),
+    ReturnType(Type<'db>),
+}
+
+impl<'db> InlayHintContent<'db> {
+    pub const fn display(&self, db: &'db dyn Db) -> DisplayInlayHint<'_, 'db> {
+        DisplayInlayHint { db, hint: self }
+    }
+}
+
+pub struct DisplayInlayHint<'a, 'db> {
+    db: &'db dyn Db,
+    hint: &'a InlayHintContent<'db>,
+}
+
+impl fmt::Display for DisplayInlayHint<'_, '_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self.hint {
+            InlayHintContent::Type(ty) => {
+                write!(f, ": {}", ty.display(self.db.upcast()))
+            }
+            InlayHintContent::ReturnType(ty) => {
+                write!(f, " -> {}", ty.display(self.db.upcast()))
+            }
+        }
+    }
+}
+
+pub fn inlay_hints(db: &dyn Db, file: File, range: TextRange) -> Vec<InlayHint<'_>> {
+    let mut visitor = InlayHintVisitor::new(db, file, range);
+
+    let ast = parsed_module(db.upcast(), file);
+
+    visitor.visit_body(ast.suite());
+
+    visitor.hints
+}
+
+struct InlayHintVisitor<'db> {
+    model: SemanticModel<'db>,
+    hints: Vec<InlayHint<'db>>,
+    in_assignment: bool,
+    range: TextRange,
+}
+
+impl<'db> InlayHintVisitor<'db> {
+    fn new(db: &'db dyn Db, file: File, range: TextRange) -> Self {
+        Self {
+            model: SemanticModel::new(db.upcast(), file),
+            hints: Vec::new(),
+            in_assignment: false,
+            range,
+        }
+    }
+
+    fn add_type_hint(&mut self, position: TextSize, ty: Type<'db>) {
+        self.hints.push(InlayHint {
+            position,
+            content: InlayHintContent::Type(ty),
+        });
+    }
+}
+
+impl SourceOrderVisitor<'_> for InlayHintVisitor<'_> {
+    fn enter_node(&mut self, node: AnyNodeRef<'_>) -> TraversalSignal {
+        if self.range.intersect(node.range()).is_some() {
+            TraversalSignal::Traverse
+        } else {
+            TraversalSignal::Skip
+        }
+    }
+
+    fn visit_stmt(&mut self, stmt: &Stmt) {
+        let node = AnyNodeRef::from(stmt);
+
+        if !self.enter_node(node).is_traverse() {
+            return;
+        }
+
+        match stmt {
+            Stmt::Assign(assign) => {
+                self.in_assignment = true;
+                for target in &assign.targets {
+                    self.visit_expr(target);
+                }
+                self.in_assignment = false;
+
+                return;
+            }
+            // TODO
+            Stmt::FunctionDef(_) => {}
+            Stmt::For(_) => {}
+            Stmt::Expr(_) => {
+                // Don't traverse into expression statements because we don't show any hints.
+                return;
+            }
+            _ => {}
+        }
+
+        source_order::walk_stmt(self, stmt);
+    }
+
+    fn visit_expr(&mut self, expr: &'_ Expr) {
+        if !self.in_assignment {
+            return;
+        }
+
+        match expr {
+            Expr::Name(name) => {
+                if name.ctx.is_store() {
+                    let ty = expr.inferred_type(&self.model);
+                    self.add_type_hint(expr.range().end(), ty);
+                }
+            }
+            _ => {
+                source_order::walk_expr(self, expr);
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use insta::assert_snapshot;
+    use ruff_db::{
+        files::{system_path_to_file, File},
+        source::source_text,
+    };
+    use ruff_text_size::TextSize;
+
+    use crate::db::tests::TestDb;
+
+    use red_knot_python_semantic::{
+        Program, ProgramSettings, PythonPath, PythonPlatform, SearchPathSettings,
+    };
+    use ruff_db::system::{DbWithWritableSystem, SystemPathBuf};
+    use ruff_python_ast::PythonVersion;
+
+    pub(super) fn inlay_hint_test(source: &str) -> InlayHintTest {
+        const START: &str = "<START>";
+        const END: &str = "<END>";
+
+        let mut db = TestDb::new();
+
+        let start = source.find(START);
+        let end = source
+            .find(END)
+            .map(|x| if start.is_some() { x - START.len() } else { x })
+            .unwrap_or(source.len());
+
+        let range = TextRange::new(
+            TextSize::try_from(start.unwrap_or_default()).unwrap(),
+            TextSize::try_from(end).unwrap(),
+        );
+
+        let source = source.replace(START, "");
+        let source = source.replace(END, "");
+
+        db.write_file("main.py", source)
+            .expect("write to memory file system to be successful");
+
+        let file = system_path_to_file(&db, "main.py").expect("newly written file to existing");
+
+        Program::from_settings(
+            &db,
+            ProgramSettings {
+                python_version: PythonVersion::latest(),
+                python_platform: PythonPlatform::default(),
+                search_paths: SearchPathSettings {
+                    extra_paths: vec![],
+                    src_roots: vec![SystemPathBuf::from("/")],
+                    custom_typeshed: None,
+                    python_path: PythonPath::KnownSitePackages(vec![]),
+                },
+            },
+        )
+        .expect("Default settings to be valid");
+
+        InlayHintTest { db, file, range }
+    }
+
+    pub(super) struct InlayHintTest {
+        pub(super) db: TestDb,
+        pub(super) file: File,
+        pub(super) range: TextRange,
+    }
+
+    impl InlayHintTest {
+        fn inlay_hints(&self) -> String {
+            let hints = inlay_hints(&self.db, self.file, self.range);
+
+            let mut buf = source_text(&self.db, self.file).as_str().to_string();
+
+            let mut offset = 0;
+
+            for hint in hints {
+                let end_position = (hint.position.to_u32() as usize) + offset;
+                let hint_str = format!("[{}]", hint.display(&self.db));
+                buf.insert_str(end_position, &hint_str);
+                offset += hint_str.len();
+            }
+
+            buf
+        }
+    }
+
+    #[test]
+    fn test_assign_statement() {
+        let test = inlay_hint_test("x = 1");
+
+        assert_snapshot!(test.inlay_hints(), @r"
+        x[: Literal[1]] = 1
+        ");
+    }
+
+    #[test]
+    fn test_tuple_assignment() {
+        let test = inlay_hint_test("x, y = (1, 'abc')");
+
+        assert_snapshot!(test.inlay_hints(), @r#"
+        x[: Literal[1]], y[: Literal["abc"]] = (1, 'abc')
+        "#);
+    }
+
+    #[test]
+    fn test_nested_tuple_assignment() {
+        let test = inlay_hint_test("x, (y, z) = (1, ('abc', 2))");
+
+        assert_snapshot!(test.inlay_hints(), @r#"
+        x[: Literal[1]], (y[: Literal["abc"]], z[: Literal[2]]) = (1, ('abc', 2))
+        "#);
+    }
+
+    #[test]
+    fn test_assign_statement_with_type_annotation() {
+        let test = inlay_hint_test("x: int = 1");
+
+        assert_snapshot!(test.inlay_hints(), @r"
+        x: int = 1
+        ");
+    }
+
+    #[test]
+    fn test_assign_statement_out_of_range() {
+        let test = inlay_hint_test("<START>x = 1<END>\ny = 2");
+
+        assert_snapshot!(test.inlay_hints(), @r"
+        x[: Literal[1]] = 1
+        y = 2
+        ");
+    }
+}

crates/red_knot_ide/src/lib.rs

@@ -0,0 +1,296 @@
+mod db;
+mod find_node;
+mod goto;
+mod hover;
+mod inlay_hints;
+mod markup;
+
+pub use db::Db;
+pub use goto::goto_type_definition;
+pub use hover::hover;
+pub use inlay_hints::inlay_hints;
+pub use markup::MarkupKind;
+
+use rustc_hash::FxHashSet;
+use std::ops::{Deref, DerefMut};
+
+use red_knot_python_semantic::types::{Type, TypeDefinition};
+use ruff_db::files::{File, FileRange};
+use ruff_text_size::{Ranged, TextRange};
+
+/// Information associated with a text range.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
+pub struct RangedValue<T> {
+    pub range: FileRange,
+    pub value: T,
+}
+
+impl<T> RangedValue<T> {
+    pub fn file_range(&self) -> FileRange {
+        self.range
+    }
+}
+
+impl<T> Deref for RangedValue<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.value
+    }
+}
+
+impl<T> DerefMut for RangedValue<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.value
+    }
+}
+
+impl<T> IntoIterator for RangedValue<T>
+where
+    T: IntoIterator,
+{
+    type Item = T::Item;
+    type IntoIter = T::IntoIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.value.into_iter()
+    }
+}
+
+/// Target to which the editor can navigate to.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct NavigationTarget {
+    file: File,
+
+    /// The range that should be focused when navigating to the target.
+    ///
+    /// This is typically not the full range of the node. For example, it's the range of the class's name in a class definition.
+    ///
+    /// The `focus_range` must be fully covered by `full_range`.
+    focus_range: TextRange,
+
+    /// The range covering the entire target.
+    full_range: TextRange,
+}
+
+impl NavigationTarget {
+    pub fn file(&self) -> File {
+        self.file
+    }
+
+    pub fn focus_range(&self) -> TextRange {
+        self.focus_range
+    }
+
+    pub fn full_range(&self) -> TextRange {
+        self.full_range
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct NavigationTargets(smallvec::SmallVec<[NavigationTarget; 1]>);
+
+impl NavigationTargets {
+    fn single(target: NavigationTarget) -> Self {
+        Self(smallvec::smallvec![target])
+    }
+
+    fn empty() -> Self {
+        Self(smallvec::SmallVec::new())
+    }
+
+    fn unique(targets: impl IntoIterator<Item = NavigationTarget>) -> Self {
+        let unique: FxHashSet<_> = targets.into_iter().collect();
+        if unique.is_empty() {
+            Self::empty()
+        } else {
+            let mut targets = unique.into_iter().collect::<Vec<_>>();
+            targets.sort_by_key(|target| (target.file, target.focus_range.start()));
+            Self(targets.into())
+        }
+    }
+
+    fn iter(&self) -> std::slice::Iter<'_, NavigationTarget> {
+        self.0.iter()
+    }
+
+    #[cfg(test)]
+    fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+}
+
+impl IntoIterator for NavigationTargets {
+    type Item = NavigationTarget;
+    type IntoIter = smallvec::IntoIter<[NavigationTarget; 1]>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.into_iter()
+    }
+}
+
+impl<'a> IntoIterator for &'a NavigationTargets {
+    type Item = &'a NavigationTarget;
+    type IntoIter = std::slice::Iter<'a, NavigationTarget>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl FromIterator<NavigationTarget> for NavigationTargets {
+    fn from_iter<T: IntoIterator<Item = NavigationTarget>>(iter: T) -> Self {
+        Self::unique(iter)
+    }
+}
+
+pub trait HasNavigationTargets {
+    fn navigation_targets(&self, db: &dyn Db) -> NavigationTargets;
+}
+
+impl HasNavigationTargets for Type<'_> {
+    fn navigation_targets(&self, db: &dyn Db) -> NavigationTargets {
+        match self {
+            Type::Union(union) => union
+                .iter(db.upcast())
+                .flat_map(|target| target.navigation_targets(db))
+                .collect(),
+
+            Type::Intersection(intersection) => {
+                // Only consider the positive elements because the negative elements are mainly from narrowing constraints.
+                let mut targets = intersection
+                    .iter_positive(db.upcast())
+                    .filter(|ty| !ty.is_unknown());
+
+                let Some(first) = targets.next() else {
+                    return NavigationTargets::empty();
+                };
+
+                match targets.next() {
+                    Some(_) => {
+                        // If there are multiple types in the intersection, we can't navigate to a single one
+                        // because the type is the intersection of all those types.
+                        NavigationTargets::empty()
+                    }
+                    None => first.navigation_targets(db),
+                }
+            }
+
+            ty => ty
+                .definition(db.upcast())
+                .map(|definition| definition.navigation_targets(db))
+                .unwrap_or_else(NavigationTargets::empty),
+        }
+    }
+}
+
+impl HasNavigationTargets for TypeDefinition<'_> {
+    fn navigation_targets(&self, db: &dyn Db) -> NavigationTargets {
+        let full_range = self.full_range(db.upcast());
+        NavigationTargets::single(NavigationTarget {
+            file: full_range.file(),
+            focus_range: self.focus_range(db.upcast()).unwrap_or(full_range).range(),
+            full_range: full_range.range(),
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::db::tests::TestDb;
+    use insta::internals::SettingsBindDropGuard;
+    use red_knot_python_semantic::{
+        Program, ProgramSettings, PythonPath, PythonPlatform, SearchPathSettings,
+    };
+    use ruff_db::diagnostic::{Diagnostic, DiagnosticFormat, DisplayDiagnosticConfig};
+    use ruff_db::files::{system_path_to_file, File};
+    use ruff_db::system::{DbWithWritableSystem, SystemPath, SystemPathBuf};
+    use ruff_python_ast::PythonVersion;
+    use ruff_text_size::TextSize;
+
+    pub(super) fn cursor_test(source: &str) -> CursorTest {
+        let mut db = TestDb::new();
+        let cursor_offset = source.find("<CURSOR>").expect(
+            "`source`` should contain a `<CURSOR>` marker, indicating the position of the cursor.",
+        );
+
+        let mut content = source[..cursor_offset].to_string();
+        content.push_str(&source[cursor_offset + "<CURSOR>".len()..]);
+
+        db.write_file("main.py", &content)
+            .expect("write to memory file system to be successful");
+
+        let file = system_path_to_file(&db, "main.py").expect("newly written file to existing");
+
+        Program::from_settings(
+            &db,
+            ProgramSettings {
+                python_version: PythonVersion::latest(),
+                python_platform: PythonPlatform::default(),
+                search_paths: SearchPathSettings {
+                    extra_paths: vec![],
+                    src_roots: vec![SystemPathBuf::from("/")],
+                    custom_typeshed: None,
+                    python_path: PythonPath::KnownSitePackages(vec![]),
+                },
+            },
+        )
+        .expect("Default settings to be valid");
+
+        let mut insta_settings = insta::Settings::clone_current();
+        insta_settings.add_filter(r#"\\(\w\w|\s|\.|")"#, "/$1");
+        // Filter out TODO types because they are different between debug and release builds.
+        insta_settings.add_filter(r"@Todo\(.+\)", "@Todo");
+
+        let insta_settings_guard = insta_settings.bind_to_scope();
+
+        CursorTest {
+            db,
+            cursor_offset: TextSize::try_from(cursor_offset)
+                .expect("source to be smaller than 4GB"),
+            file,
+            _insta_settings_guard: insta_settings_guard,
+        }
+    }
+
+    pub(super) struct CursorTest {
+        pub(super) db: TestDb,
+        pub(super) cursor_offset: TextSize,
+        pub(super) file: File,
+        _insta_settings_guard: SettingsBindDropGuard,
+    }
+
+    impl CursorTest {
+        pub(super) fn write_file(
+            &mut self,
+            path: impl AsRef<SystemPath>,
+            content: &str,
+        ) -> std::io::Result<()> {
+            self.db.write_file(path, content)
+        }
+
+        pub(super) fn render_diagnostics<I, D>(&self, diagnostics: I) -> String
+        where
+            I: IntoIterator<Item = D>,
+            D: IntoDiagnostic,
+        {
+            use std::fmt::Write;
+
+            let mut buf = String::new();
+
+            let config = DisplayDiagnosticConfig::default()
+                .color(false)
+                .format(DiagnosticFormat::Full);
+            for diagnostic in diagnostics {
+                let diag = diagnostic.into_diagnostic();
+                write!(buf, "{}", diag.display(&self.db, &config)).unwrap();
+            }
+
+            buf
+        }
+    }
+
+    pub(super) trait IntoDiagnostic {
+        fn into_diagnostic(self) -> Diagnostic;
+    }
+}

crates/red_knot_ide/src/markup.rs

@@ -0,0 +1,66 @@
+use std::fmt;
+use std::fmt::Formatter;
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum MarkupKind {
+    PlainText,
+    Markdown,
+}
+
+impl MarkupKind {
+    pub(crate) const fn fenced_code_block<T>(self, code: T, language: &str) -> FencedCodeBlock<T>
+    where
+        T: fmt::Display,
+    {
+        FencedCodeBlock {
+            language,
+            code,
+            kind: self,
+        }
+    }
+
+    pub(crate) const fn horizontal_line(self) -> HorizontalLine {
+        HorizontalLine { kind: self }
+    }
+}
+
+pub(crate) struct FencedCodeBlock<'a, T> {
+    language: &'a str,
+    code: T,
+    kind: MarkupKind,
+}
+
+impl<T> fmt::Display for FencedCodeBlock<'_, T>
+where
+    T: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.kind {
+            MarkupKind::PlainText => self.code.fmt(f),
+            MarkupKind::Markdown => write!(
+                f,
+                "```{language}\n{code}\n```",
+                language = self.language,
+                code = self.code
+            ),
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub(crate) struct HorizontalLine {
+    kind: MarkupKind,
+}
+
+impl fmt::Display for HorizontalLine {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self.kind {
+            MarkupKind::PlainText => {
+                f.write_str("\n---------------------------------------------\n")
+            }
+            MarkupKind::Markdown => {
+                write!(f, "\n---\n")
+            }
+        }
+    }
+}

crates/red_knot_project/Cargo.toml

@@ -16,7 +16,9 @@ ruff_cache = { workspace = true }
 ruff_db = { workspace = true, features = ["cache", "serde"] }
 ruff_macros = { workspace = true }
 ruff_python_ast = { workspace = true, features = ["serde"] }
+ruff_python_formatter = { workspace = true, optional = true }
 ruff_text_size = { workspace = true }
+red_knot_ide = { workspace = true }
 red_knot_python_semantic = { workspace = true, features = ["serde"] }
 red_knot_vendored = { workspace = true }
 
@@ -42,8 +44,13 @@ insta = { workspace = true, features = ["redactions", "ron"] }
 [features]
 default = ["zstd"]
 deflate = ["red_knot_vendored/deflate"]
-schemars = ["dep:schemars", "ruff_db/schemars", "red_knot_python_semantic/schemars"]
+schemars = [
+    "dep:schemars",
+    "ruff_db/schemars",
+    "red_knot_python_semantic/schemars",
+]
 zstd = ["red_knot_vendored/zstd"]
+format = ["ruff_python_formatter"]
 
 [lints]
 workspace = true

crates/red_knot_project/resources/test/corpus/cycle_narrowing_constraints.py

@@ -0,0 +1,15 @@
+# Regression test for https://github.com/astral-sh/ruff/issues/17215
+# panicked in commit 1a6a10b30
+# error message:
+# dependency graph cycle querying all_narrowing_constraints_for_expression(Id(8591))
+
+def f(a: A, b: B, c: C):
+    unknown_a: UA = make_unknown()
+    unknown_b: UB = make_unknown()
+    unknown_c: UC = make_unknown()
+    unknown_d: UD = make_unknown()
+
+    if unknown_a and unknown_b:
+        if unknown_c:
+            if unknown_d:
+                return a, b, c

crates/red_knot_project/resources/test/corpus/cycle_negative_narrowing_constraints.py

@@ -0,0 +1,22 @@
+# Regression test for https://github.com/astral-sh/ruff/issues/17215
+# panicked in commit 1a6a10b30
+# error message:
+# dependency graph cycle querying all_negative_narrowing_constraints_for_expression(Id(859f))
+
+def f(f1: bool, f2: bool, f3: bool, f4: bool):
+    o1: UnknownClass = make_o()
+    o2: UnknownClass = make_o()
+    o3: UnknownClass = make_o()
+    o4: UnknownClass = make_o()
+
+    if f1 and f2 and f3 and f4:
+        if o1 == o2:
+            return None
+        if o2 == o3:
+            return None
+        if o3 == o4:
+            return None
+        if o4 == o1:
+            return None
+
+    return o1, o2, o3, o4

crates/red_knot_project/src/combine.rs

@@ -43,7 +43,7 @@ use ruff_python_ast::PythonVersion;
 /// resolved extra search path of `["b", "c", "a"]`, which means `a` will be tried last.
 ///
 /// There's an argument here that the user should be able to specify the order of the paths,
-/// because only then is the user in full control of where to insert the path when specyifing `extra-paths`
+/// because only then is the user in full control of where to insert the path when specifying `extra-paths`
 /// in multiple sources.
 ///
 /// ## Macro

crates/red_knot_project/src/db.rs

@@ -3,9 +3,10 @@ use std::sync::Arc;
 
 use crate::DEFAULT_LINT_REGISTRY;
 use crate::{Project, ProjectMetadata};
+use red_knot_ide::Db as IdeDb;
 use red_knot_python_semantic::lint::{LintRegistry, RuleSelection};
 use red_knot_python_semantic::{Db as SemanticDb, Program};
-use ruff_db::diagnostic::OldDiagnosticTrait;
+use ruff_db::diagnostic::Diagnostic;
 use ruff_db::files::{File, Files};
 use ruff_db::system::System;
 use ruff_db::vendored::VendoredFileSystem;
@@ -55,13 +56,12 @@ impl ProjectDatabase {
     }
 
     /// Checks all open files in the project and its dependencies.
-    pub fn check(&self) -> Result<Vec<Box<dyn OldDiagnosticTrait>>, Cancelled> {
+    pub fn check(&self) -> Result<Vec<Diagnostic>, Cancelled> {
         self.with_db(|db| db.project().check(db))
     }
 
-    pub fn check_file(&self, file: File) -> Result<Vec<Box<dyn OldDiagnosticTrait>>, Cancelled> {
-        let _span = tracing::debug_span!("check_file", file=%file.path(self)).entered();
-
+    #[tracing::instrument(level = "debug", skip(self))]
+    pub fn check_file(&self, file: File) -> Result<Vec<Diagnostic>, Cancelled> {
         self.with_db(|db| self.project().check_file(db, file))
     }
 
@@ -104,6 +104,19 @@ impl Upcast<dyn SourceDb> for ProjectDatabase {
     }
 }
 
+impl Upcast<dyn IdeDb> for ProjectDatabase {
+    fn upcast(&self) -> &(dyn IdeDb + 'static) {
+        self
+    }
+
+    fn upcast_mut(&mut self) -> &mut (dyn IdeDb + 'static) {
+        self
+    }
+}
+
+#[salsa::db]
+impl IdeDb for ProjectDatabase {}
+
 #[salsa::db]
 impl SemanticDb for ProjectDatabase {
     fn is_file_open(&self, file: File) -> bool {
@@ -136,6 +149,10 @@ impl SourceDb for ProjectDatabase {
     fn files(&self) -> &Files {
         &self.files
     }
+
+    fn python_version(&self) -> ruff_python_ast::PythonVersion {
+        Program::get(self).python_version(self)
+    }
 }
 
 #[salsa::db]
@@ -146,7 +163,7 @@ impl salsa::Database for ProjectDatabase {
         }
 
         let event = event();
-        if matches!(event.kind, salsa::EventKind::WillCheckCancellation { .. }) {
+        if matches!(event.kind, salsa::EventKind::WillCheckCancellation) {
             return;
         }
 
@@ -161,6 +178,32 @@ impl Db for ProjectDatabase {
     }
 }
 
+#[cfg(feature = "format")]
+mod format {
+    use crate::ProjectDatabase;
+    use ruff_db::files::File;
+    use ruff_db::Upcast;
+    use ruff_python_formatter::{Db as FormatDb, PyFormatOptions};
+
+    #[salsa::db]
+    impl FormatDb for ProjectDatabase {
+        fn format_options(&self, file: File) -> PyFormatOptions {
+            let source_ty = file.source_type(self);
+            PyFormatOptions::from_source_type(source_ty)
+        }
+    }
+
+    impl Upcast<dyn FormatDb> for ProjectDatabase {
+        fn upcast(&self) -> &(dyn FormatDb + 'static) {
+            self
+        }
+
+        fn upcast_mut(&mut self) -> &mut (dyn FormatDb + 'static) {
+            self
+        }
+    }
+}
+
 #[cfg(test)]
 pub(crate) mod tests {
     use std::sync::Arc;
@@ -168,7 +211,7 @@ pub(crate) mod tests {
     use salsa::Event;
 
     use red_knot_python_semantic::lint::{LintRegistry, RuleSelection};
-    use red_knot_python_semantic::Db as SemanticDb;
+    use red_knot_python_semantic::{Db as SemanticDb, Program};
     use ruff_db::files::Files;
     use ruff_db::system::{DbWithTestSystem, System, TestSystem};
     use ruff_db::vendored::VendoredFileSystem;
@@ -242,6 +285,10 @@ pub(crate) mod tests {
         fn files(&self) -> &Files {
             &self.files
         }
+
+        fn python_version(&self) -> ruff_python_ast::PythonVersion {
+            Program::get(self).python_version(self)
+        }
     }
 
     impl Upcast<dyn SemanticDb> for TestDb {

crates/red_knot_project/src/db/changes.rs

@@ -187,7 +187,7 @@ impl ProjectDatabase {
                     let program = Program::get(self);
                     if let Err(error) = program.update_from_settings(self, program_settings) {
                         tracing::error!("Failed to update the program settings, keeping the old program settings: {error}");
-                    };
+                    }
 
                     if metadata.root() == project.root(self) {
                         tracing::debug!("Reloading project after structural change");

crates/red_knot_project/src/lib.rs

@@ -9,7 +9,10 @@ pub use metadata::{ProjectDiscoveryError, ProjectMetadata};
 use red_knot_python_semantic::lint::{LintRegistry, LintRegistryBuilder, RuleSelection};
 use red_knot_python_semantic::register_lints;
 use red_knot_python_semantic::types::check_types;
-use ruff_db::diagnostic::{DiagnosticId, OldDiagnosticTrait, OldParseDiagnostic, Severity, Span};
+use ruff_db::diagnostic::{
+    create_parse_diagnostic, create_unsupported_syntax_diagnostic, Annotation, Diagnostic,
+    DiagnosticId, Severity, Span,
+};
 use ruff_db::files::File;
 use ruff_db::parsed::parsed_module;
 use ruff_db::source::{source_text, SourceTextError};
@@ -17,7 +20,6 @@ use ruff_db::system::{SystemPath, SystemPathBuf};
 use rustc_hash::FxHashSet;
 use salsa::Durability;
 use salsa::Setter;
-use std::borrow::Cow;
 use std::sync::Arc;
 use thiserror::Error;
 
@@ -163,24 +165,27 @@ impl Project {
     }
 
     /// Checks all open files in the project and its dependencies.
-    pub(crate) fn check(self, db: &ProjectDatabase) -> Vec<Box<dyn OldDiagnosticTrait>> {
+    pub(crate) fn check(self, db: &ProjectDatabase) -> Vec<Diagnostic> {
         let project_span = tracing::debug_span!("Project::check");
         let _span = project_span.enter();
 
         tracing::debug!("Checking project '{name}'", name = self.name(db));
 
-        let mut diagnostics: Vec<Box<dyn OldDiagnosticTrait>> = Vec::new();
-        diagnostics.extend(self.settings_diagnostics(db).iter().map(|diagnostic| {
-            let diagnostic: Box<dyn OldDiagnosticTrait> = Box::new(diagnostic.clone());
-            diagnostic
-        }));
+        let mut diagnostics: Vec<Diagnostic> = Vec::new();
+        diagnostics.extend(
+            self.settings_diagnostics(db)
+                .iter()
+                .map(OptionDiagnostic::to_diagnostic),
+        );
 
         let files = ProjectFiles::new(db, self);
 
-        diagnostics.extend(files.diagnostics().iter().cloned().map(|diagnostic| {
-            let diagnostic: Box<dyn OldDiagnosticTrait> = Box::new(diagnostic);
-            diagnostic
-        }));
+        diagnostics.extend(
+            files
+                .diagnostics()
+                .iter()
+                .map(IOErrorDiagnostic::to_diagnostic),
+        );
 
         let result = Arc::new(std::sync::Mutex::new(diagnostics));
         let inner_result = Arc::clone(&result);
@@ -195,7 +200,8 @@ impl Project {
                 let project_span = project_span.clone();
 
                 scope.spawn(move |_| {
-                    let check_file_span = tracing::debug_span!(parent: &project_span, "check_file", file=%file.path(&db));
+                    let check_file_span =
+                        tracing::debug_span!(parent: &project_span, "check_file", ?file);
                     let _entered = check_file_span.entered();
 
                     let file_diagnostics = check_file_impl(&db, file);
@@ -207,14 +213,11 @@ impl Project {
         Arc::into_inner(result).unwrap().into_inner().unwrap()
     }
 
-    pub(crate) fn check_file(self, db: &dyn Db, file: File) -> Vec<Box<dyn OldDiagnosticTrait>> {
+    pub(crate) fn check_file(self, db: &dyn Db, file: File) -> Vec<Diagnostic> {
         let mut file_diagnostics: Vec<_> = self
             .settings_diagnostics(db)
             .iter()
-            .map(|diagnostic| {
-                let diagnostic: Box<dyn OldDiagnosticTrait> = Box::new(diagnostic.clone());
-                diagnostic
-            })
+            .map(OptionDiagnostic::to_diagnostic)
             .collect();
 
         let check_diagnostics = check_file_impl(db, file);
@@ -325,7 +328,7 @@ impl Project {
         self.files(db).contains(&file)
     }
 
-    #[tracing::instrument(level = "debug", skip(db))]
+    #[tracing::instrument(level = "debug", skip(self, db))]
     pub fn remove_file(self, db: &mut dyn Db, file: File) {
         tracing::debug!(
             "Removing file `{}` from project `{}`",
@@ -397,35 +400,43 @@ impl Project {
     }
 }
 
-fn check_file_impl(db: &dyn Db, file: File) -> Vec<Box<dyn OldDiagnosticTrait>> {
-    let mut diagnostics: Vec<Box<dyn OldDiagnosticTrait>> = Vec::new();
+fn check_file_impl(db: &dyn Db, file: File) -> Vec<Diagnostic> {
+    let mut diagnostics: Vec<Diagnostic> = Vec::new();
 
     // Abort checking if there are IO errors.
     let source = source_text(db.upcast(), file);
 
     if let Some(read_error) = source.read_error() {
-        diagnostics.push(Box::new(IOErrorDiagnostic {
-            file: Some(file),
-            error: read_error.clone().into(),
-        }));
+        diagnostics.push(
+            IOErrorDiagnostic {
+                file: Some(file),
+                error: read_error.clone().into(),
+            }
+            .to_diagnostic(),
+        );
         return diagnostics;
     }
 
     let parsed = parsed_module(db.upcast(), file);
-    diagnostics.extend(parsed.errors().iter().map(|error| {
-        let diagnostic: Box<dyn OldDiagnosticTrait> =
-            Box::new(OldParseDiagnostic::new(file, error.clone()));
-        diagnostic
-    }));
+    diagnostics.extend(
+        parsed
+            .errors()
+            .iter()
+            .map(|error| create_parse_diagnostic(file, error)),
+    );
 
-    diagnostics.extend(check_types(db.upcast(), file).iter().map(|diagnostic| {
-        let boxed: Box<dyn OldDiagnosticTrait> = Box::new(diagnostic.clone());
-        boxed
-    }));
+    diagnostics.extend(
+        parsed
+            .unsupported_syntax_errors()
+            .iter()
+            .map(|error| create_unsupported_syntax_diagnostic(file, error)),
+    );
+
+    diagnostics.extend(check_types(db.upcast(), file).into_iter().cloned());
 
     diagnostics.sort_unstable_by_key(|diagnostic| {
         diagnostic
-            .span()
+            .primary_span()
             .and_then(|span| span.range())
             .unwrap_or_default()
             .start()
@@ -493,21 +504,13 @@ pub struct IOErrorDiagnostic {
     error: IOErrorKind,
 }
 
-impl OldDiagnosticTrait for IOErrorDiagnostic {
-    fn id(&self) -> DiagnosticId {
-        DiagnosticId::Io
-    }
-
-    fn message(&self) -> Cow<str> {
-        self.error.to_string().into()
-    }
-
-    fn span(&self) -> Option<Span> {
-        self.file.map(Span::from)
-    }
-
-    fn severity(&self) -> Severity {
-        Severity::Error
+impl IOErrorDiagnostic {
+    fn to_diagnostic(&self) -> Diagnostic {
+        let mut diag = Diagnostic::new(DiagnosticId::Io, Severity::Error, &self.error);
+        if let Some(file) = self.file {
+            diag.annotate(Annotation::primary(Span::from(file)));
+        }
+        diag
     }
 }
 
@@ -525,12 +528,13 @@ mod tests {
     use crate::db::tests::TestDb;
     use crate::{check_file_impl, ProjectMetadata};
     use red_knot_python_semantic::types::check_types;
-    use ruff_db::diagnostic::OldDiagnosticTrait;
+    use red_knot_python_semantic::{Program, ProgramSettings, PythonPlatform, SearchPathSettings};
     use ruff_db::files::system_path_to_file;
     use ruff_db::source::source_text;
     use ruff_db::system::{DbWithTestSystem, DbWithWritableSystem as _, SystemPath, SystemPathBuf};
     use ruff_db::testing::assert_function_query_was_not_run;
     use ruff_python_ast::name::Name;
+    use ruff_python_ast::PythonVersion;
 
     #[test]
     fn check_file_skips_type_checking_when_file_cant_be_read() -> ruff_db::system::Result<()> {
@@ -538,6 +542,16 @@ mod tests {
         let mut db = TestDb::new(project);
         let path = SystemPath::new("test.py");
 
+        Program::from_settings(
+            &db,
+            ProgramSettings {
+                python_version: PythonVersion::default(),
+                python_platform: PythonPlatform::default(),
+                search_paths: SearchPathSettings::new(vec![SystemPathBuf::from(".")]),
+            },
+        )
+        .expect("Failed to configure program settings");
+
         db.write_file(path, "x = 10")?;
         let file = system_path_to_file(&db, path).unwrap();
 
@@ -549,7 +563,7 @@ mod tests {
         assert_eq!(
             check_file_impl(&db, file)
                 .into_iter()
-                .map(|diagnostic| diagnostic.message().into_owned())
+                .map(|diagnostic| diagnostic.primary_message().to_string())
                 .collect::<Vec<_>>(),
             vec!["Failed to read file: No such file or directory".to_string()]
         );
@@ -565,7 +579,7 @@ mod tests {
         assert_eq!(
             check_file_impl(&db, file)
                 .into_iter()
-                .map(|diagnostic| diagnostic.message().into_owned())
+                .map(|diagnostic| diagnostic.primary_message().to_string())
                 .collect::<Vec<_>>(),
             vec![] as Vec<String>
         );

crates/red_knot_project/src/metadata.rs

@@ -64,7 +64,7 @@ impl ProjectMetadata {
     }
 
     /// Loads a project from a set of options with an optional pyproject-project table.
-    pub(crate) fn from_options(
+    pub fn from_options(
         mut options: Options,
         root: SystemPathBuf,
         project: Option<&Project>,

crates/red_knot_project/src/metadata/options.rs

@@ -2,14 +2,13 @@ use crate::metadata::value::{RangedValue, RelativePathBuf, ValueSource, ValueSou
 use crate::Db;
 use red_knot_python_semantic::lint::{GetLintError, Level, LintSource, RuleSelection};
 use red_knot_python_semantic::{ProgramSettings, PythonPath, PythonPlatform, SearchPathSettings};
-use ruff_db::diagnostic::{DiagnosticId, OldDiagnosticTrait, Severity, Span};
+use ruff_db::diagnostic::{Annotation, Diagnostic, DiagnosticFormat, DiagnosticId, Severity, Span};
 use ruff_db::files::system_path_to_file;
 use ruff_db::system::{System, SystemPath};
 use ruff_macros::Combine;
 use ruff_python_ast::PythonVersion;
 use rustc_hash::FxHashMap;
 use serde::{Deserialize, Serialize};
-use std::borrow::Cow;
 use std::fmt::Debug;
 use thiserror::Error;
 
@@ -37,30 +36,43 @@ pub struct Options {
 
 impl Options {
     pub(crate) fn from_toml_str(content: &str, source: ValueSource) -> Result<Self, KnotTomlError> {
-        let _guard = ValueSourceGuard::new(source);
+        let _guard = ValueSourceGuard::new(source, true);
         let options = toml::from_str(content)?;
         Ok(options)
     }
 
+    pub fn deserialize_with<'de, D>(source: ValueSource, deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let _guard = ValueSourceGuard::new(source, false);
+        Self::deserialize(deserializer)
+    }
+
     pub(crate) fn to_program_settings(
         &self,
         project_root: &SystemPath,
         system: &dyn System,
     ) -> ProgramSettings {
-        let (python_version, python_platform) = self
+        let python_version = self
             .environment
             .as_ref()
-            .map(|env| {
-                (
-                    env.python_version.as_deref().copied(),
-                    env.python_platform.as_deref(),
-                )
-            })
+            .and_then(|env| env.python_version.as_deref().copied())
             .unwrap_or_default();
-
+        let python_platform = self
+            .environment
+            .as_ref()
+            .and_then(|env| env.python_platform.as_deref().cloned())
+            .unwrap_or_else(|| {
+                let default = PythonPlatform::default();
+                tracing::info!(
+                    "Defaulting to default python version for this platform: '{default}'",
+                );
+                default
+            });
         ProgramSettings {
-            python_version: python_version.unwrap_or_default(),
-            python_platform: python_platform.cloned().unwrap_or_default(),
+            python_version,
+            python_platform,
             search_paths: self.to_search_path_settings(project_root, system),
         }
     }
@@ -106,9 +118,14 @@ impl Options {
             custom_typeshed: typeshed.map(|path| path.absolute(project_root, system)),
             python_path: python
                 .map(|python_path| {
-                    PythonPath::SysPrefix(python_path.absolute(project_root, system))
+                    PythonPath::from_cli_flag(python_path.absolute(project_root, system))
                 })
-                .unwrap_or(PythonPath::KnownSitePackages(vec![])),
+                .or_else(|| {
+                    std::env::var("VIRTUAL_ENV")
+                        .ok()
+                        .map(PythonPath::from_virtual_env_var)
+                })
+                .unwrap_or_else(|| PythonPath::Discover(project_root.to_path_buf())),
         }
     }
 
@@ -120,6 +137,11 @@ impl Options {
 
         if let Some(terminal) = self.terminal.as_ref() {
             settings.set_terminal(TerminalSettings {
+                output_format: terminal
+                    .output_format
+                    .as_deref()
+                    .copied()
+                    .unwrap_or_default(),
                 error_on_warning: terminal.error_on_warning.unwrap_or_default(),
             });
         }
@@ -207,7 +229,7 @@ impl Options {
 #[serde(rename_all = "kebab-case", deny_unknown_fields)]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct EnvironmentOptions {
-    /// Specifies the version of Python that will be used to execute the source code.
+    /// Specifies the version of Python that will be used to analyze the source code.
     /// The version should be specified as a string in the format `M.m` where `M` is the major version
     /// and `m` is the minor (e.g. "3.0" or "3.6").
     /// If a version is provided, knot will generate errors if the source code makes use of language features
@@ -216,11 +238,16 @@ pub struct EnvironmentOptions {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub python_version: Option<RangedValue<PythonVersion>>,
 
-    /// Specifies the target platform that will be used to execute the source code.
+    /// Specifies the target platform that will be used to analyze the source code.
     /// If specified, Red Knot will tailor its use of type stub files,
     /// which conditionalize type definitions based on the platform.
     ///
-    /// If no platform is specified, knot will use `all` or the current platform in the LSP use case.
+    /// If no platform is specified, knot will use the current platform:
+    /// - `win32` for Windows
+    /// - `darwin` for macOS
+    /// - `android` for Android
+    /// - `ios` for iOS
+    /// - `linux` for everything else
     #[serde(skip_serializing_if = "Option::is_none")]
     pub python_platform: Option<RangedValue<PythonPlatform>>,
 
@@ -277,6 +304,11 @@ impl FromIterator<(RangedValue<String>, RangedValue<Level>)> for Rules {
 #[serde(rename_all = "kebab-case", deny_unknown_fields)]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct TerminalOptions {
+    /// The format to use for printing diagnostic messages.
+    ///
+    /// Defaults to `full`.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub output_format: Option<RangedValue<DiagnosticFormat>>,
     /// Use exit code 1 if there are any warning-level diagnostics.
     ///
     /// Defaults to `false`.
@@ -374,22 +406,14 @@ impl OptionDiagnostic {
     fn with_span(self, span: Option<Span>) -> Self {
         OptionDiagnostic { span, ..self }
     }
-}
 
-impl OldDiagnosticTrait for OptionDiagnostic {
-    fn id(&self) -> DiagnosticId {
-        self.id
-    }
-
-    fn message(&self) -> Cow<str> {
-        Cow::Borrowed(&self.message)
-    }
-
-    fn span(&self) -> Option<Span> {
-        self.span.clone()
-    }
-
-    fn severity(&self) -> Severity {
-        self.severity
+    pub(crate) fn to_diagnostic(&self) -> Diagnostic {
+        if let Some(ref span) = self.span {
+            let mut diag = Diagnostic::new(self.id, self.severity, "");
+            diag.annotate(Annotation::primary(span.clone()).message(&self.message));
+            diag
+        } else {
+            Diagnostic::new(self.id, self.severity, &self.message)
+        }
     }
 }

crates/red_knot_project/src/metadata/pyproject.rs

@@ -34,7 +34,7 @@ impl PyProject {
         content: &str,
         source: ValueSource,
     ) -> Result<Self, PyProjectError> {
-        let _guard = ValueSourceGuard::new(source);
+        let _guard = ValueSourceGuard::new(source, true);
         toml::from_str(content).map_err(PyProjectError::TomlSyntax)
     }
 }

crates/red_knot_project/src/metadata/settings.rs

@@ -1,6 +1,7 @@
 use std::sync::Arc;
 
 use red_knot_python_semantic::lint::RuleSelection;
+use ruff_db::diagnostic::DiagnosticFormat;
 
 /// The resolved [`super::Options`] for the project.
 ///
@@ -49,5 +50,6 @@ impl Settings {
 
 #[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub struct TerminalSettings {
+    pub output_format: DiagnosticFormat,
     pub error_on_warning: bool,
 }

crates/red_knot_project/src/metadata/value.rs

@@ -19,6 +19,7 @@ pub enum ValueSource {
     /// Ideally, we'd use [`ruff_db::files::File`] but we can't because the database hasn't been
     /// created when loading the configuration.
     File(Arc<SystemPathBuf>),
+
     /// The value comes from a CLI argument, while it's left open if specified using a short argument,
     /// long argument (`--extra-paths`) or `--config key=value`.
     Cli,
@@ -41,18 +42,18 @@ thread_local! {
     /// Use the [`ValueSourceGuard`] to initialize the thread local before calling into any
     /// deserialization code. It ensures that the thread local variable gets cleaned up
     /// once deserialization is done (once the guard gets dropped).
-    static VALUE_SOURCE: RefCell<Option<ValueSource>> = const { RefCell::new(None) };
+    static VALUE_SOURCE: RefCell<Option<(ValueSource, bool)>> = const { RefCell::new(None) };
 }
 
 /// Guard to safely change the [`VALUE_SOURCE`] for the current thread.
 #[must_use]
 pub(super) struct ValueSourceGuard {
-    prev_value: Option<ValueSource>,
+    prev_value: Option<(ValueSource, bool)>,
 }
 
 impl ValueSourceGuard {
-    pub(super) fn new(source: ValueSource) -> Self {
-        let prev = VALUE_SOURCE.replace(Some(source));
+    pub(super) fn new(source: ValueSource, is_toml: bool) -> Self {
+        let prev = VALUE_SOURCE.replace(Some((source, is_toml)));
         Self { prev_value: prev }
     }
 }
@@ -265,18 +266,24 @@ where
     where
         D: Deserializer<'de>,
     {
-        let spanned: Spanned<T> = Spanned::deserialize(deserializer)?;
-        let span = spanned.span();
-        let range = TextRange::new(
-            TextSize::try_from(span.start).expect("Configuration file to be smaller than 4GB"),
-            TextSize::try_from(span.end).expect("Configuration file to be smaller than 4GB"),
-        );
+        VALUE_SOURCE.with_borrow(|source| {
+            let (source, has_span) = source.clone().unwrap();
 
-        Ok(VALUE_SOURCE.with_borrow(|source| {
-            let source = source.clone().unwrap();
+            if has_span {
+                let spanned: Spanned<T> = Spanned::deserialize(deserializer)?;
+                let span = spanned.span();
+                let range = TextRange::new(
+                    TextSize::try_from(span.start)
+                        .expect("Configuration file to be smaller than 4GB"),
+                    TextSize::try_from(span.end)
+                        .expect("Configuration file to be smaller than 4GB"),
+                );
 
-            Self::with_range(spanned.into_inner(), source, range)
-        }))
+                Ok(Self::with_range(spanned.into_inner(), source, range))
+            } else {
+                Ok(Self::new(T::deserialize(deserializer)?, source))
+            }
+        })
     }
 }
 

crates/red_knot_project/tests/check.rs

@@ -6,7 +6,9 @@ use ruff_db::parsed::parsed_module;
 use ruff_db::system::{SystemPath, SystemPathBuf, TestSystem};
 use ruff_python_ast::visitor::source_order;
 use ruff_python_ast::visitor::source_order::SourceOrderVisitor;
-use ruff_python_ast::{self as ast, Alias, Expr, Parameter, ParameterWithDefault, Stmt};
+use ruff_python_ast::{
+    self as ast, Alias, Comprehension, Expr, Parameter, ParameterWithDefault, Stmt,
+};
 
 fn setup_db(project_root: &SystemPath, system: TestSystem) -> anyhow::Result<ProjectDatabase> {
     let project = ProjectMetadata::discover(project_root, &system)?;
@@ -258,6 +260,14 @@ impl SourceOrderVisitor<'_> for PullTypesVisitor<'_> {
         source_order::walk_expr(self, expr);
     }
 
+    fn visit_comprehension(&mut self, comprehension: &Comprehension) {
+        self.visit_expr(&comprehension.iter);
+        self.visit_target(&comprehension.target);
+        for if_expr in &comprehension.ifs {
+            self.visit_expr(if_expr);
+        }
+    }
+
     fn visit_parameter(&mut self, parameter: &Parameter) {
         let _ty = parameter.inferred_type(&self.model);
 

crates/red_knot_python_semantic/mdtest.py

@@ -155,6 +155,7 @@ class MDTestRunner:
 
     def watch(self) -> Never:
         self._recompile_tests("Compiling tests...", message_on_success=False)
+        self._run_mdtest()
         self.console.print("[dim]Ready to watch for changes...[/dim]")
 
         for changes in watch(CRATE_ROOT):

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

@@ -29,7 +29,7 @@ It is invalid to parameterize `Annotated` with less than two arguments.
 ```py
 from typing_extensions import Annotated
 
-# error: [invalid-type-form] "`Annotated` requires at least two arguments when used in an annotation or type expression"
+# error: [invalid-type-form] "`typing.Annotated` requires at least two arguments when used in a type expression"
 def _(x: Annotated):
     reveal_type(x)  # revealed: Unknown
 
@@ -39,11 +39,11 @@ def _(flag: bool):
     else:
         X = bool
 
-    # error: [invalid-type-form] "`Annotated` requires at least two arguments when used in an annotation or type expression"
+    # error: [invalid-type-form] "`typing.Annotated` requires at least two arguments when used in a type expression"
     def f(y: X):
         reveal_type(y)  # revealed: Unknown | bool
 
-# error: [invalid-type-form] "`Annotated` requires at least two arguments when used in an annotation or type expression"
+# error: [invalid-type-form] "`typing.Annotated` requires at least two arguments when used in a type expression"
 def _(x: Annotated | bool):
     reveal_type(x)  # revealed: Unknown | bool
 
@@ -73,12 +73,10 @@ Inheriting from `Annotated[T, ...]` is equivalent to inheriting from `T` itself.
 ```py
 from typing_extensions import Annotated
 
-# TODO: False positive
-# error: [invalid-base]
 class C(Annotated[int, "foo"]): ...
 
 # TODO: Should be `tuple[Literal[C], Literal[int], Literal[object]]`
-reveal_type(C.__mro__)  # revealed: tuple[Literal[C], Unknown, Literal[object]]
+reveal_type(C.__mro__)  # revealed: tuple[Literal[C], @Todo(Inference of subscript on special form), Literal[object]]
 ```
 
 ### Not parameterized

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

@@ -2,10 +2,12 @@
 
 References:
 
-- <https://typing.readthedocs.io/en/latest/spec/callables.html#callable>
+- <https://typing.python.org/en/latest/spec/callables.html#callable>
 
-TODO: Use `collections.abc` as importing from `typing` is deprecated but this requires support for
-`*` imports. See: <https://docs.python.org/3/library/typing.html#deprecated-aliases>.
+Note that `typing.Callable` is deprecated at runtime, in favour of `collections.abc.Callable` (see:
+<https://docs.python.org/3/library/typing.html#deprecated-aliases>). However, removal of
+`typing.Callable` is not currently planned, and the canonical location of the stub for the symbol in
+typeshed is still `typing.pyi`.
 
 ## Invalid forms
 
@@ -47,8 +49,10 @@ def _(c: Callable[42, str]):
 Or, when one of the parameter type is invalid in the list:
 
 ```py
+# error: [invalid-type-form] "Int literals are not allowed in this context in a type expression"
+# error: [invalid-type-form] "Boolean literals are not allowed in this context in a type expression"
 def _(c: Callable[[int, 42, str, False], None]):
-    # revealed: (int, @Todo(number literal in type expression), str, @Todo(boolean literal in type expression), /) -> None
+    # revealed: (int, Unknown, str, Unknown, /) -> None
     reveal_type(c)
 ```
 
@@ -61,7 +65,7 @@ from typing import Callable
 
 # error: [invalid-type-form] "Special form `typing.Callable` expected exactly two arguments (parameter types and return type)"
 def _(c: Callable[[int, str]]):
-    reveal_type(c)  # revealed: (int, str, /) -> Unknown
+    reveal_type(c)  # revealed: (...) -> Unknown
 ```
 
 Or, an ellipsis:
@@ -72,6 +76,18 @@ def _(c: Callable[...]):
     reveal_type(c)  # revealed: (...) -> Unknown
 ```
 
+Or something else that's invalid in a type expression generally:
+
+```py
+# fmt: off
+
+def _(c: Callable[  # error: [invalid-type-form] "Special form `typing.Callable` expected exactly two arguments (parameter types and return type)"
+            {1, 2}  # error: [invalid-type-form] "The first argument to `Callable` must be either a list of types, ParamSpec, Concatenate, or `...`"
+        ]
+    ):
+    reveal_type(c)  # revealed: (...) -> Unknown
+```
+
 ### More than two arguments
 
 We can't reliably infer the callable type if there are more then 2 arguments because we don't know
@@ -85,6 +101,48 @@ def _(c: Callable[[int], str, str]):
     reveal_type(c)  # revealed: (...) -> Unknown
 ```
 
+### List as the second argument
+
+```py
+from typing import Callable
+
+# fmt: off
+
+def _(c: Callable[
+            int,  # error: [invalid-type-form] "The first argument to `Callable` must be either a list of types, ParamSpec, Concatenate, or `...`"
+            [str]  # error: [invalid-type-form] "List literals are not allowed in this context in a type expression"
+        ]
+    ):
+    reveal_type(c)  # revealed: (...) -> Unknown
+```
+
+### List as both arguments
+
+```py
+from typing import Callable
+
+# error: [invalid-type-form] "List literals are not allowed in this context in a type expression"
+def _(c: Callable[[int], [str]]):
+    reveal_type(c)  # revealed: (int, /) -> Unknown
+```
+
+### Three list arguments
+
+```py
+from typing import Callable
+
+# fmt: off
+
+
+def _(c: Callable[  # error: [invalid-type-form] "Special form `typing.Callable` expected exactly two arguments (parameter types and return type)"
+            [int],
+            [str],  # error: [invalid-type-form] "List literals are not allowed in this context in a type expression"
+            [bytes]  # error: [invalid-type-form] "List literals are not allowed in this context in a type expression"
+        ]
+    ):
+    reveal_type(c)  # revealed: (...) -> Unknown
+```
+
 ## Simple
 
 A simple `Callable` with multiple parameters and a return type:
@@ -96,6 +154,39 @@ def _(c: Callable[[int, str], int]):
     reveal_type(c)  # revealed: (int, str, /) -> int
 ```
 
+## Union
+
+```py
+from typing import Callable, Union
+
+def _(
+    c: Callable[[Union[int, str]], int] | None,
+    d: None | Callable[[Union[int, str]], int],
+    e: None | Callable[[Union[int, str]], int] | int,
+):
+    reveal_type(c)  # revealed: ((int | str, /) -> int) | None
+    reveal_type(d)  # revealed: None | ((int | str, /) -> int)
+    reveal_type(e)  # revealed: None | ((int | str, /) -> int) | int
+```
+
+## Intersection
+
+```py
+from typing import Callable, Union
+from knot_extensions import Intersection, Not
+
+def _(
+    c: Intersection[Callable[[Union[int, str]], int], int],
+    d: Intersection[int, Callable[[Union[int, str]], int]],
+    e: Intersection[int, Callable[[Union[int, str]], int], str],
+    f: Intersection[Not[Callable[[int, str], Intersection[int, str]]]],
+):
+    reveal_type(c)  # revealed: ((int | str, /) -> int) & int
+    reveal_type(d)  # revealed: int & ((int | str, /) -> int)
+    reveal_type(e)  # revealed: int & ((int | str, /) -> int) & str
+    reveal_type(f)  # revealed: ~((int, str, /) -> int & str)
+```
+
 ## Nested
 
 A nested `Callable` as one of the parameter types:
@@ -146,6 +237,11 @@ def _(c: Callable[[Concatenate[int, str, ...], int], int]):
 
 ## Using `typing.ParamSpec`
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 Using a `ParamSpec` in a `Callable` annotation:
 
 ```py
@@ -198,7 +294,7 @@ def _(c: Callable[[int, Unpack[Ts]], int]):
 from typing import Callable
 
 def _(c: Callable[[int], int]):
-    reveal_type(c.__init__)  # revealed: Literal[__init__]
+    reveal_type(c.__init__)  # revealed: def __init__(self) -> None
     reveal_type(c.__class__)  # revealed: type
 
     # TODO: The member lookup for `Callable` uses `object` which does not have a `__call__`
@@ -208,4 +304,4 @@ def _(c: Callable[[int], int]):
     reveal_type(c.__call__)  # revealed: Unknown
 ```
 
-[gradual form]: https://typing.readthedocs.io/en/latest/spec/glossary.html#term-gradual-form
+[gradual form]: https://typing.python.org/en/latest/spec/glossary.html#term-gradual-form

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

@@ -45,3 +45,135 @@ class Foo: ...
 
 reveal_type(get_foo())  # revealed: Foo
 ```
+
+## Deferred self-reference annotations in a class definition
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+from __future__ import annotations
+
+class Foo:
+    this: Foo
+    # error: [unresolved-reference]
+    _ = Foo()
+    # error: [unresolved-reference]
+    [Foo for _ in range(1)]
+    a = int
+
+    def f(self, x: Foo):
+        reveal_type(x)  # revealed: Foo
+
+    def g(self) -> Foo:
+        _: Foo = self
+        return self
+
+    class Bar:
+        foo: Foo
+        b = int
+
+        def f(self, x: Foo):
+            return self
+        # error: [unresolved-reference]
+        def g(self) -> Bar:
+            return self
+        # error: [unresolved-reference]
+        def h[T: Bar](self):
+            pass
+
+        class Baz[T: Foo]:
+            pass
+
+        # error: [unresolved-reference]
+        type S = a
+        type T = b
+
+    def h[T: Bar]():
+        # error: [unresolved-reference]
+        return Bar()
+    type Baz = Foo
+```
+
+## Non-deferred self-reference annotations in a class definition
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+class Foo:
+    # error: [unresolved-reference]
+    this: Foo
+    ok: "Foo"
+    # error: [unresolved-reference]
+    _ = Foo()
+    # error: [unresolved-reference]
+    [Foo for _ in range(1)]
+    a = int
+
+    # error: [unresolved-reference]
+    def f(self, x: Foo):
+        reveal_type(x)  # revealed: Unknown
+    # error: [unresolved-reference]
+    def g(self) -> Foo:
+        _: Foo = self
+        return self
+
+    class Bar:
+        # error: [unresolved-reference]
+        foo: Foo
+        b = int
+
+        # error: [unresolved-reference]
+        def f(self, x: Foo):
+            return self
+        # error: [unresolved-reference]
+        def g(self) -> Bar:
+            return self
+        # error: [unresolved-reference]
+        def h[T: Bar](self):
+            pass
+
+        class Baz[T: Foo]:
+            pass
+
+        # error: [unresolved-reference]
+        type S = a
+        type T = b
+
+    def h[T: Bar]():
+        # error: [unresolved-reference]
+        return Bar()
+    type Qux = Foo
+
+def _():
+    class C:
+        # error: [unresolved-reference]
+        def f(self) -> C:
+            return self
+```
+
+## Base class references
+
+### Not deferred by __future__.annotations
+
+```py
+from __future__ import annotations
+
+class A(B):  # error: [unresolved-reference]
+    pass
+
+class B:
+    pass
+```
+
+### Deferred in stub files
+
+```pyi
+class A(B): ...
+class B: ...
+```

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

@@ -2,7 +2,7 @@
 
 In order to support common use cases, an annotation of `float` actually means `int | float`, and an
 annotation of `complex` actually means `int | float | complex`. See
-[the specification](https://typing.readthedocs.io/en/latest/spec/special-types.html#special-cases-for-float-and-complex)
+[the specification](https://typing.python.org/en/latest/spec/special-types.html#special-cases-for-float-and-complex)
 
 ## float
 

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

@@ -9,6 +9,8 @@ import typing
 from knot_extensions import AlwaysTruthy, AlwaysFalsy
 from typing_extensions import Literal, Never
 
+class A: ...
+
 def _(
     a: type[int],
     b: AlwaysTruthy,
@@ -18,28 +20,95 @@ def _(
     f: Literal[b"foo"],
     g: tuple[int, str],
     h: Never,
+    i: int,
+    j: A,
 ):
     def foo(): ...
     def invalid(
-        i: a,  # error: [invalid-type-form] "Variable of type `type[int]` is not allowed in a type expression"
-        j: b,  # error: [invalid-type-form]
-        k: c,  # error: [invalid-type-form]
-        l: d,  # error: [invalid-type-form]
-        m: e,  # error: [invalid-type-form]
-        n: f,  # error: [invalid-type-form]
-        o: g,  # error: [invalid-type-form]
-        p: h,  # error: [invalid-type-form]
-        q: typing,  # error: [invalid-type-form]
-        r: foo,  # error: [invalid-type-form]
+        a_: a,  # error: [invalid-type-form] "Variable of type `type[int]` is not allowed in a type expression"
+        b_: b,  # error: [invalid-type-form]
+        c_: c,  # error: [invalid-type-form]
+        d_: d,  # error: [invalid-type-form]
+        e_: e,  # error: [invalid-type-form]
+        f_: f,  # error: [invalid-type-form]
+        g_: g,  # error: [invalid-type-form]
+        h_: h,  # error: [invalid-type-form]
+        i_: typing,  # error: [invalid-type-form]
+        j_: foo,  # error: [invalid-type-form]
+        k_: i,  # error: [invalid-type-form] "Variable of type `int` is not allowed in a type expression"
+        l_: j,  # error: [invalid-type-form] "Variable of type `A` is not allowed in a type expression"
     ):
-        reveal_type(i)  # revealed: Unknown
-        reveal_type(j)  # revealed: Unknown
-        reveal_type(k)  # revealed: Unknown
-        reveal_type(l)  # revealed: Unknown
-        reveal_type(m)  # revealed: Unknown
-        reveal_type(n)  # revealed: Unknown
-        reveal_type(o)  # revealed: Unknown
-        reveal_type(p)  # revealed: Unknown
-        reveal_type(q)  # revealed: Unknown
-        reveal_type(r)  # revealed: Unknown
+        reveal_type(a_)  # revealed: Unknown
+        reveal_type(b_)  # revealed: Unknown
+        reveal_type(c_)  # revealed: Unknown
+        reveal_type(d_)  # revealed: Unknown
+        reveal_type(e_)  # revealed: Unknown
+        reveal_type(f_)  # revealed: Unknown
+        reveal_type(g_)  # revealed: Unknown
+        reveal_type(h_)  # revealed: Unknown
+        reveal_type(i_)  # revealed: Unknown
+        reveal_type(j_)  # revealed: Unknown
+```
+
+## Invalid AST nodes
+
+```py
+def bar() -> None:
+    return None
+
+def _(
+    a: 1,  # error: [invalid-type-form] "Int literals are not allowed in this context in a type expression"
+    b: 2.3,  # error: [invalid-type-form] "Float literals are not allowed in type expressions"
+    c: 4j,  # error: [invalid-type-form] "Complex literals are not allowed in type expressions"
+    d: True,  # error: [invalid-type-form] "Boolean literals are not allowed in this context in a type expression"
+    e: int | b"foo",  # error: [invalid-type-form] "Bytes literals are not allowed in this context in a type expression"
+    f: 1 and 2,  # error: [invalid-type-form] "Boolean operations are not allowed in type expressions"
+    g: 1 or 2,  # error: [invalid-type-form] "Boolean operations are not allowed in type expressions"
+    h: (foo := 1),  # error: [invalid-type-form] "Named expressions are not allowed in type expressions"
+    i: not 1,  # error: [invalid-type-form] "Unary operations are not allowed in type expressions"
+    j: lambda: 1,  # error: [invalid-type-form] "`lambda` expressions are not allowed in type expressions"
+    k: 1 if True else 2,  # error: [invalid-type-form] "`if` expressions are not allowed in type expressions"
+    l: await 1,  # error: [invalid-type-form] "`await` expressions are not allowed in type expressions"
+    m: (yield 1),  # error: [invalid-type-form] "`yield` expressions are not allowed in type expressions"
+    n: (yield from [1]),  # error: [invalid-type-form] "`yield from` expressions are not allowed in type expressions"
+    o: 1 < 2,  # error: [invalid-type-form] "Comparison expressions are not allowed in type expressions"
+    p: bar(),  # error: [invalid-type-form] "Function calls are not allowed in type expressions"
+    q: int | f"foo",  # error: [invalid-type-form] "F-strings are not allowed in type expressions"
+    r: [1, 2, 3][1:2],  # error: [invalid-type-form] "Slices are not allowed in type expressions"
+):
+    reveal_type(a)  # revealed: Unknown
+    reveal_type(b)  # revealed: Unknown
+    reveal_type(c)  # revealed: Unknown
+    reveal_type(d)  # revealed: Unknown
+    reveal_type(e)  # revealed: int | Unknown
+    reveal_type(f)  # revealed: Unknown
+    reveal_type(g)  # revealed: Unknown
+    reveal_type(h)  # revealed: Unknown
+    reveal_type(i)  # revealed: Unknown
+    reveal_type(j)  # revealed: Unknown
+    reveal_type(k)  # revealed: Unknown
+    reveal_type(p)  # revealed: Unknown
+    reveal_type(q)  # revealed: int | Unknown
+    reveal_type(r)  # revealed: @Todo(unknown type subscript)
+```
+
+## Invalid Collection based AST nodes
+
+```py
+def _(
+    a: {1: 2},  # error: [invalid-type-form] "Dict literals are not allowed in type expressions"
+    b: {1, 2},  # error: [invalid-type-form] "Set literals are not allowed in type expressions"
+    c: {k: v for k, v in [(1, 2)]},  # error: [invalid-type-form] "Dict comprehensions are not allowed in type expressions"
+    d: [k for k in [1, 2]],  # error: [invalid-type-form] "List comprehensions are not allowed in type expressions"
+    e: {k for k in [1, 2]},  # error: [invalid-type-form] "Set comprehensions are not allowed in type expressions"
+    f: (k for k in [1, 2]),  # error: [invalid-type-form] "Generator expressions are not allowed in type expressions"
+    g: [int, str],  # error: [invalid-type-form] "List literals are not allowed in this context in a type expression"
+):
+    reveal_type(a)  # revealed: Unknown
+    reveal_type(b)  # revealed: Unknown
+    reveal_type(c)  # revealed: Unknown
+    reveal_type(d)  # revealed: Unknown
+    reveal_type(e)  # revealed: Unknown
+    reveal_type(f)  # revealed: Unknown
+    reveal_type(g)  # revealed: Unknown
 ```

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

@@ -1,6 +1,6 @@
 # Literal
 
-<https://typing.readthedocs.io/en/latest/spec/literal.html#literals>
+<https://typing.python.org/en/latest/spec/literal.html#literals>
 
 ## Parameterization
 
@@ -36,7 +36,7 @@ def f():
     reveal_type(a7)  # revealed: None
     reveal_type(a8)  # revealed: Literal[1]
     # TODO: This should be Color.RED
-    reveal_type(b1)  # revealed: Unknown | Literal[0]
+    reveal_type(b1)  # revealed: @Todo(Attribute access on enum classes)
 
 # error: [invalid-type-form]
 invalid1: Literal[3 + 4]
@@ -68,7 +68,7 @@ def x(
     a3: Literal[Literal["w"], Literal["r"], Literal[Literal["w+"]]],
     a4: Literal[True] | Literal[1, 2] | Literal["foo"],
 ):
-    reveal_type(a1)  # revealed: Literal[1, 2, 3, "foo", 5] | None
+    reveal_type(a1)  # revealed: Literal[1, 2, 3, 5, "foo"] | None
     reveal_type(a2)  # revealed: Literal["w", "r"]
     reveal_type(a3)  # revealed: Literal["w", "r", "w+"]
     reveal_type(a4)  # revealed: Literal[True, 1, 2, "foo"]
@@ -108,7 +108,7 @@ def union_example(
         None,
     ],
 ):
-    reveal_type(x)  # revealed: Unknown | Literal[-1, "A", b"A", b"\x00", b"\x07", 0, 1, "B", "foo", "bar", True] | None
+    reveal_type(x)  # revealed: Unknown | Literal[-1, 0, 1, "A", "B", "foo", "bar", b"A", b"\x00", b"\x07", True] | None
 ```
 
 ## Detecting Literal outside typing and typing_extensions
@@ -127,10 +127,17 @@ Literal: _SpecialForm
 ```py
 from other import Literal
 
+# TODO: can we add a subdiagnostic here saying something like:
+#
+#     `other.Literal` and `typing.Literal` have similar names, but are different symbols and don't have the same semantics
+#
+# ?
+#
+# error: [invalid-type-form] "Int literals are not allowed in this context in a type expression"
 a1: Literal[26]
 
 def f():
-    reveal_type(a1)  # revealed: @Todo(generics)
+    reveal_type(a1)  # revealed: @Todo(unknown type subscript)
 ```
 
 ## Detecting typing_extensions.Literal
@@ -149,7 +156,7 @@ def f():
 ```py
 from typing import Literal
 
-# error: [invalid-type-form] "`Literal` requires at least one argument when used in a type expression"
+# error: [invalid-type-form] "`typing.Literal` requires at least one argument when used in a type expression"
 def _(x: Literal):
     reveal_type(x)  # revealed: Unknown
 ```

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

@@ -72,13 +72,11 @@ reveal_type(baz)  # revealed: Literal["bazfoo"]
 qux = (foo, bar)
 reveal_type(qux)  # revealed: tuple[Literal["foo"], Literal["bar"]]
 
-# TODO: Infer "LiteralString"
-reveal_type(foo.join(qux))  # revealed: @Todo(return type of decorated function)
+reveal_type(foo.join(qux))  # revealed: LiteralString
 
 template: LiteralString = "{}, {}"
 reveal_type(template)  # revealed: Literal["{}, {}"]
-# TODO: Infer `LiteralString`
-reveal_type(template.format(foo, bar))  # revealed: @Todo(return type of decorated function)
+reveal_type(template.format(foo, bar))  # revealed: LiteralString
 ```
 
 ### Assignability
@@ -147,4 +145,4 @@ def f():
     reveal_type(x)  # revealed: LiteralString
 ```
 
-[1]: https://typing.readthedocs.io/en/latest/spec/literal.html#literalstring
+[1]: https://typing.python.org/en/latest/spec/literal.html#literalstring

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

@@ -0,0 +1,24 @@
+# NewType
+
+Currently, red-knot doesn't support `typing.NewType` in type annotations.
+
+## Valid forms
+
+```py
+from typing_extensions import NewType
+from types import GenericAlias
+
+X = GenericAlias(type, ())
+A = NewType("A", int)
+# TODO: typeshed for `typing.GenericAlias` uses `type` for the first argument. `NewType` should be special-cased
+# to be compatible with `type`
+# error: [invalid-argument-type] "Argument to this function is incorrect: Expected `type`, found `NewType`"
+B = GenericAlias(A, ())
+
+def _(
+    a: A,
+    b: B,
+):
+    reveal_type(a)  # revealed: @Todo(Support for `typing.NewType` instances in type expressions)
+    reveal_type(b)  # revealed: @Todo(Support for `typing.GenericAlias` instances in type expressions)
+```

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

@@ -45,3 +45,13 @@ def f():
     # revealed: int | None
     reveal_type(a)
 ```
+
+## Invalid
+
+```py
+from typing import Optional
+
+# error: [invalid-type-form] "`typing.Optional` requires exactly one argument when used in a type expression"
+def f(x: Optional) -> None:
+    reveal_type(x)  # revealed: Unknown
+```

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

@@ -1,5 +1,10 @@
 # Starred expression annotations
 
+```toml
+[environment]
+python-version = "3.11"
+```
+
 Type annotations for `*args` can be starred expressions themselves:
 
 ```py

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

@@ -67,22 +67,24 @@ import typing
 
 ####################
 ### Built-ins
+####################
 
 class ListSubclass(typing.List): ...
 
-# revealed: tuple[Literal[ListSubclass], Literal[list], Literal[MutableSequence], Literal[Sequence], Literal[Reversible], Literal[Collection], Literal[Iterable], Literal[Container], @Todo(protocol), Literal[object]]
+# TODO: generic protocols
+# revealed: tuple[Literal[ListSubclass], Literal[list], Literal[MutableSequence], Literal[Sequence], Literal[Reversible], Literal[Collection], Literal[Iterable], Literal[Container], @Todo(`Protocol[]` subscript), @Todo(`Generic[]` subscript), Literal[object]]
 reveal_type(ListSubclass.__mro__)
 
 class DictSubclass(typing.Dict): ...
 
-# TODO: should have `Generic`, should not have `Unknown`
-# revealed: tuple[Literal[DictSubclass], Literal[dict], Unknown, Literal[object]]
+# TODO: generic protocols
+# revealed: tuple[Literal[DictSubclass], Literal[dict], Literal[MutableMapping], Literal[Mapping], Literal[Collection], Literal[Iterable], Literal[Container], @Todo(`Protocol[]` subscript), @Todo(`Generic[]` subscript), Literal[object]]
 reveal_type(DictSubclass.__mro__)
 
 class SetSubclass(typing.Set): ...
 
-# TODO: should have `Generic`, should not have `Unknown`
-# revealed: tuple[Literal[SetSubclass], Literal[set], Unknown, Literal[object]]
+# TODO: generic protocols
+# revealed: tuple[Literal[SetSubclass], Literal[set], Literal[MutableSet], Literal[AbstractSet], Literal[Collection], Literal[Iterable], Literal[Container], @Todo(`Protocol[]` subscript), @Todo(`Generic[]` subscript), Literal[object]]
 reveal_type(SetSubclass.__mro__)
 
 class FrozenSetSubclass(typing.FrozenSet): ...
@@ -93,11 +95,12 @@ reveal_type(FrozenSetSubclass.__mro__)
 
 ####################
 ### `collections`
+####################
 
 class ChainMapSubclass(typing.ChainMap): ...
 
-# TODO: Should be (ChainMapSubclass, ChainMap, MutableMapping, Mapping, Collection, Sized, Iterable, Container, Generic, object)
-# revealed: tuple[Literal[ChainMapSubclass], Literal[ChainMap], Unknown, Literal[object]]
+# TODO: generic protocols
+# revealed: tuple[Literal[ChainMapSubclass], Literal[ChainMap], Literal[MutableMapping], Literal[Mapping], Literal[Collection], Literal[Iterable], Literal[Container], @Todo(`Protocol[]` subscript), @Todo(`Generic[]` subscript), Literal[object]]
 reveal_type(ChainMapSubclass.__mro__)
 
 class CounterSubclass(typing.Counter): ...
@@ -114,8 +117,8 @@ reveal_type(DefaultDictSubclass.__mro__)
 
 class DequeSubclass(typing.Deque): ...
 
-# TODO: Should be (DequeSubclass, deque, MutableSequence, Sequence, Reversible, Collection, Sized, Iterable, Container, Generic, object)
-# revealed: tuple[Literal[DequeSubclass], Literal[deque], Unknown, Literal[object]]
+# TODO: generic protocols
+# revealed: tuple[Literal[DequeSubclass], Literal[deque], Literal[MutableSequence], Literal[Sequence], Literal[Reversible], Literal[Collection], Literal[Iterable], Literal[Container], @Todo(`Protocol[]` subscript), @Todo(`Generic[]` subscript), Literal[object]]
 reveal_type(DequeSubclass.__mro__)
 
 class OrderedDictSubclass(typing.OrderedDict): ...

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

@@ -105,7 +105,7 @@ def f1(
 from typing import Literal
 
 def f(v: Literal["a", r"b", b"c", "d" "e", "\N{LATIN SMALL LETTER F}", "\x67", """h"""]):
-    reveal_type(v)  # revealed: Literal["a", "b", b"c", "de", "f", "g", "h"]
+    reveal_type(v)  # revealed: Literal["a", "b", "de", "f", "g", "h", b"c"]
 ```
 
 ## Class variables

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

@@ -2,7 +2,7 @@
 
 ## Annotation
 
-`typing.Union` can be used to construct union types same as `|` operator.
+`typing.Union` can be used to construct union types in the same way as the `|` operator.
 
 ```py
 from typing import Union
@@ -59,3 +59,30 @@ def f():
     # revealed: int | str
     reveal_type(a)
 ```
+
+## Invalid
+
+```py
+from typing import Union
+
+# error: [invalid-type-form] "`typing.Union` requires at least one argument when used in a type expression"
+def f(x: Union) -> None:
+    reveal_type(x)  # revealed: Unknown
+```
+
+## Implicit type aliases using new-style unions
+
+We don't recognise these as type aliases yet, but we also don't emit false-positive diagnostics if
+you use them in type expressions:
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+X = int | str
+
+def f(y: X):
+    reveal_type(y)  # revealed: @Todo(Support for `types.UnionType` instances in type expressions)
+```

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

@@ -18,7 +18,7 @@ def f(*args: Unpack[Ts]) -> tuple[Unpack[Ts]]:
     # TODO: should understand the annotation
     reveal_type(args)  # revealed: tuple
 
-    reveal_type(Alias)  # revealed: @Todo(Invalid or unsupported `KnownInstanceType` in `Type::to_type_expression`)
+    reveal_type(Alias)  # revealed: @Todo(Support for `typing.TypeAlias`)
 
 def g() -> TypeGuard[int]: ...
 def h() -> TypeIs[int]: ...
@@ -29,13 +29,35 @@ def i(callback: Callable[Concatenate[int, P], R_co], *args: P.args, **kwargs: P.
     # TODO: should understand the annotation
     reveal_type(kwargs)  # revealed: dict
 
-    # TODO: not an error; remove once `call` is implemented for `Callable`
-    # error: [call-non-callable]
     return callback(42, *args, **kwargs)
 
 class Foo:
     def method(self, x: Self):
-        reveal_type(x)  # revealed: @Todo(Invalid or unsupported `KnownInstanceType` in `Type::to_type_expression`)
+        reveal_type(x)  # revealed: @Todo(Support for `typing.Self`)
+```
+
+## Type expressions
+
+One thing that is supported is error messages for using special forms in type expressions.
+
+```py
+from typing_extensions import Unpack, TypeGuard, TypeIs, Concatenate, ParamSpec, Generic
+
+def _(
+    a: Unpack,  # error: [invalid-type-form] "`typing.Unpack` requires exactly one argument when used in a type expression"
+    b: TypeGuard,  # error: [invalid-type-form] "`typing.TypeGuard` requires exactly one argument when used in a type expression"
+    c: TypeIs,  # error: [invalid-type-form] "`typing.TypeIs` requires exactly one argument when used in a type expression"
+    d: Concatenate,  # error: [invalid-type-form] "`typing.Concatenate` requires at least two arguments when used in a type expression"
+    e: ParamSpec,
+    f: Generic,  # error: [invalid-type-form] "`typing.Generic` is not allowed in type expressions"
+) -> None:
+    reveal_type(a)  # revealed: Unknown
+    reveal_type(b)  # revealed: Unknown
+    reveal_type(c)  # revealed: Unknown
+    reveal_type(d)  # revealed: Unknown
+
+    def foo(a_: e) -> None:
+        reveal_type(a_)  # revealed: @Todo(Support for `typing.ParamSpec`)
 ```
 
 ## Inheritance
@@ -44,7 +66,7 @@ You can't inherit from most of these. `typing.Callable` is an exception.
 
 ```py
 from typing import Callable
-from typing_extensions import Self, Unpack, TypeGuard, TypeIs, Concatenate
+from typing_extensions import Self, Unpack, TypeGuard, TypeIs, Concatenate, Generic
 
 class A(Self): ...  # error: [invalid-base]
 class B(Unpack): ...  # error: [invalid-base]
@@ -52,12 +74,18 @@ class C(TypeGuard): ...  # error: [invalid-base]
 class D(TypeIs): ...  # error: [invalid-base]
 class E(Concatenate): ...  # error: [invalid-base]
 class F(Callable): ...
+class G(Generic): ...  # error: [invalid-base] "Cannot inherit from plain `Generic`"
 
 reveal_type(F.__mro__)  # revealed: tuple[Literal[F], @Todo(Support for Callable as a base class), Literal[object]]
 ```
 
 ## Subscriptability
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 Some of these are not subscriptable:
 
 ```py

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

@@ -1,6 +1,6 @@
 # Unsupported type qualifiers
 
-## Not yet supported
+## Not yet fully supported
 
 Several type qualifiers are unsupported by red-knot currently. However, we also don't emit
 false-positive errors if you use one in an annotation:
@@ -19,6 +19,33 @@ class Bar(TypedDict):
     z: ReadOnly[bytes]
 ```
 
+## Type expressions
+
+One thing that is supported is error messages for using type qualifiers in type expressions.
+
+```py
+from typing_extensions import Final, ClassVar, Required, NotRequired, ReadOnly
+
+def _(
+    a: (
+        Final  # error: [invalid-type-form] "Type qualifier `typing.Final` is not allowed in type expressions (only in annotation expressions)"
+        | int
+    ),
+    b: (
+        ClassVar  # error: [invalid-type-form] "Type qualifier `typing.ClassVar` is not allowed in type expressions (only in annotation expressions)"
+        | int
+    ),
+    c: Required,  # error: [invalid-type-form] "Type qualifier `typing.Required` is not allowed in type expressions (only in annotation expressions, and only with exactly one argument)"
+    d: NotRequired,  # error: [invalid-type-form] "Type qualifier `typing.NotRequired` is not allowed in type expressions (only in annotation expressions, and only with exactly one argument)"
+    e: ReadOnly,  # error: [invalid-type-form] "Type qualifier `typing.ReadOnly` is not allowed in type expressions (only in annotation expressions, and only with exactly one argument)"
+) -> None:
+    reveal_type(a)  # revealed: Unknown | int
+    reveal_type(b)  # revealed: Unknown | int
+    reveal_type(c)  # revealed: Unknown
+    reveal_type(d)  # revealed: Unknown
+    reveal_type(e)  # revealed: Unknown
+```
+
 ## Inheritance
 
 You can't inherit from a type qualifier.

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

@@ -25,6 +25,11 @@ x = "foo"  # error: [invalid-assignment] "Object of type `Literal["foo"]` is not
 
 ## Tuple annotations are understood
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 `module.py`:
 
 ```py
@@ -52,13 +57,11 @@ reveal_type(b)  # revealed: tuple[int]
 reveal_type(c)  # revealed: tuple[str, int]
 reveal_type(d)  # revealed: tuple[tuple[str, str], tuple[int, int]]
 
-# TODO: homogeneous tuples, PEP-646 tuples
+# TODO: homogeneous tuples, PEP-646 tuples, generics
 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(full tuple[...] support)
+reveal_type(h)  # revealed: tuple[@Todo(specialized non-generic class), @Todo(specialized non-generic class)]
 
 reveal_type(i)  # revealed: tuple[str | int, str | int]
 reveal_type(j)  # revealed: tuple[str | int]

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

@@ -10,6 +10,10 @@ reveal_type(x)  # revealed: Literal[2]
 x = 1.0
 x /= 2
 reveal_type(x)  # revealed: int | float
+
+x = (1, 2)
+x += (3, 4)
+reveal_type(x)  # revealed: tuple[Literal[1], Literal[2], Literal[3], Literal[4]]
 ```
 
 ## Dunder methods
@@ -161,3 +165,18 @@ def f(flag: bool, flag2: bool):
 
     reveal_type(f)  # revealed: int | str | float
 ```
+
+## Implicit dunder calls on class objects
+
+```py
+class Meta(type):
+    def __iadd__(cls, other: int) -> str:
+        return ""
+
+class C(metaclass=Meta): ...
+
+cls = C
+cls += 1
+
+reveal_type(cls)  # revealed: str
+```

crates/red_knot_python_semantic/resources/mdtest/attributes.md

@@ -41,8 +41,7 @@ reveal_type(c_instance.declared_only)  # revealed: bytes
 
 reveal_type(c_instance.declared_and_bound)  # revealed: bool
 
-# We probably don't want to emit a diagnostic for this being possibly undeclared/unbound.
-# mypy and pyright do not show an error here.
+# error: [possibly-unbound-attribute]
 reveal_type(c_instance.possibly_undeclared_unbound)  # revealed: str
 
 # This assignment is fine, as we infer `Unknown | Literal[1, "a"]` for `inferred_from_value`.
@@ -303,7 +302,7 @@ class C:
 
 c_instance = C()
 reveal_type(c_instance.a)  # revealed: Unknown | Literal[1]
-reveal_type(c_instance.b)  # revealed: Unknown | @Todo(starred unpacking)
+reveal_type(c_instance.b)  # revealed: Unknown
 ```
 
 #### Attributes defined in for-loop (unpacking)
@@ -339,8 +338,10 @@ class C:
         for self.z in NonIterable():
             pass
 
+# Iterable might be empty
+# error: [possibly-unbound-attribute]
 reveal_type(C().x)  # revealed: Unknown | int
-
+# error: [possibly-unbound-attribute]
 reveal_type(C().y)  # revealed: Unknown | str
 ```
 
@@ -396,21 +397,33 @@ class IntIterable:
     def __iter__(self) -> IntIterator:
         return IntIterator()
 
+class TupleIterator:
+    def __next__(self) -> tuple[int, str]:
+        return (1, "a")
+
+class TupleIterable:
+    def __iter__(self) -> TupleIterator:
+        return TupleIterator()
+
 class C:
     def __init__(self) -> None:
         [... for self.a in IntIterable()]
+        [... for (self.b, self.c) in TupleIterable()]
+        [... for self.d in IntIterable() for self.e in IntIterable()]
 
 c_instance = C()
 
-# TODO: Should be `Unknown | int`
-# error: [unresolved-attribute]
-reveal_type(c_instance.a)  # revealed: Unknown
+reveal_type(c_instance.a)  # revealed: Unknown | int
+reveal_type(c_instance.b)  # revealed: Unknown | int
+reveal_type(c_instance.c)  # revealed: Unknown | str
+reveal_type(c_instance.d)  # revealed: Unknown | int
+reveal_type(c_instance.e)  # revealed: Unknown | int
 ```
 
 #### Conditionally declared / bound attributes
 
-We currently do not raise a diagnostic or change behavior if an attribute is only conditionally
-defined. This is consistent with what mypy and pyright do.
+Attributes are possibly unbound if they, or the method to which they are added are conditionally
+declared / bound.
 
 ```py
 def flag() -> bool:
@@ -428,9 +441,13 @@ class C:
 
 c_instance = C()
 
+# error: [possibly-unbound-attribute]
 reveal_type(c_instance.a1)  # revealed: str | None
+# error: [possibly-unbound-attribute]
 reveal_type(c_instance.a2)  # revealed: str | None
+# error: [possibly-unbound-attribute]
 reveal_type(c_instance.b1)  # revealed: Unknown | Literal[1]
+# error: [possibly-unbound-attribute]
 reveal_type(c_instance.b2)  # revealed: Unknown | Literal[1]
 ```
 
@@ -539,10 +556,88 @@ class C:
         if (2 + 3) < 4:
             self.x: str = "a"
 
-# TODO: Ideally, this would result in a `unresolved-attribute` error. But mypy and pyright
-# do not support this either (for conditions that can only be resolved to `False` in type
-# inference), so it does not seem to be particularly important.
-reveal_type(C().x)  # revealed: str
+# error: [unresolved-attribute]
+reveal_type(C().x)  # revealed: Unknown
+```
+
+```py
+class C:
+    def __init__(self, cond: bool) -> None:
+        if True:
+            self.a = 1
+        else:
+            self.a = "a"
+
+        if False:
+            self.b = 2
+
+        if cond:
+            return
+
+        self.c = 3
+
+        self.d = 4
+        self.d = 5
+
+    def set_c(self, c: str) -> None:
+        self.c = c
+    if False:
+        def set_e(self, e: str) -> None:
+            self.e = e
+
+reveal_type(C(True).a)  # revealed: Unknown | Literal[1]
+# error: [unresolved-attribute]
+reveal_type(C(True).b)  # revealed: Unknown
+reveal_type(C(True).c)  # revealed: Unknown | Literal[3] | str
+# TODO: this attribute is possibly unbound
+reveal_type(C(True).d)  # revealed: Unknown | Literal[5]
+# error: [unresolved-attribute]
+reveal_type(C(True).e)  # revealed: Unknown
+```
+
+#### Attributes considered always bound
+
+```py
+class C:
+    def __init__(self, cond: bool):
+        self.x = 1
+        if cond:
+            raise ValueError("Something went wrong")
+
+        # We consider this attribute is always bound.
+        # This is because, it is not possible to access a partially-initialized object by normal means.
+        self.y = 2
+
+reveal_type(C(False).x)  # revealed: Unknown | Literal[1]
+reveal_type(C(False).y)  # revealed: Unknown | Literal[2]
+
+class C:
+    def __init__(self, b: bytes) -> None:
+        self.b = b
+
+        try:
+            s = b.decode()
+        except UnicodeDecodeError:
+            raise ValueError("Invalid UTF-8 sequence")
+
+        self.s = s
+
+reveal_type(C(b"abc").b)  # revealed: Unknown | bytes
+reveal_type(C(b"abc").s)  # revealed: Unknown | str
+
+class C:
+    def __init__(self, iter) -> None:
+        self.x = 1
+
+        for _ in iter:
+            pass
+
+        # The for-loop may not stop,
+        # but we consider the subsequent attributes to be definitely-bound.
+        self.y = 2
+
+reveal_type(C([]).x)  # revealed: Unknown | Literal[1]
+reveal_type(C([]).y)  # revealed: Unknown | Literal[2]
 ```
 
 #### Diagnostics are reported for the right-hand side of attribute assignments
@@ -551,6 +646,7 @@ reveal_type(C().x)  # revealed: str
 class C:
     def __init__(self) -> None:
         # error: [too-many-positional-arguments]
+        # error: [invalid-argument-type]
         self.x: int = len(1, 2, 3)
 ```
 
@@ -697,10 +793,10 @@ class Base:
         self.defined_in_init: str | None = "value in base"
 
 class Intermediate(Base):
-    # Re-declaring base class attributes with the *same *type is fine:
+    # Redeclaring base class attributes with the *same *type is fine:
     base_class_attribute_1: str | None = None
 
-    # Re-declaring them with a *narrower type* is unsound, because modifications
+    # Redeclaring them with a *narrower type* is unsound, because modifications
     # through a `Base` reference could violate that constraint.
     #
     # Mypy does not report an error here, but pyright does: "… overrides symbol
@@ -712,7 +808,7 @@ class Intermediate(Base):
     # TODO: This should be an error
     base_class_attribute_2: str
 
-    # Re-declaring attributes with a *wider type* directly violates LSP.
+    # Redeclaring attributes with a *wider type* directly violates LSP.
     #
     # In this case, both mypy and pyright report an error.
     #
@@ -818,40 +914,74 @@ def _(flag: bool):
     if flag:
         class C1:
             x = 1
+            y: int = 1
 
     else:
         class C1:
             x = 2
+            y: int | str = "b"
 
     reveal_type(C1.x)  # revealed: Unknown | Literal[1, 2]
+    reveal_type(C1.y)  # revealed: int | str
+
+    C1.y = 100
+    # error: [invalid-assignment] "Object of type `Literal["problematic"]` is not assignable to attribute `y` on type `Literal[C1, C1]`"
+    C1.y = "problematic"
 
     class C2:
         if flag:
             x = 3
+            y: int = 3
         else:
             x = 4
+            y: int | str = "d"
 
     reveal_type(C2.x)  # revealed: Unknown | Literal[3, 4]
+    reveal_type(C2.y)  # revealed: int | str
+
+    C2.y = 100
+    # error: [invalid-assignment] "Object of type `None` is not assignable to attribute `y` of type `int | str`"
+    C2.y = None
+    # TODO: should be an error, needs more sophisticated union handling in `validate_attribute_assignment`
+    C2.y = "problematic"
 
     if flag:
         class Meta3(type):
             x = 5
+            y: int = 5
 
     else:
         class Meta3(type):
             x = 6
+            y: int | str = "f"
 
     class C3(metaclass=Meta3): ...
     reveal_type(C3.x)  # revealed: Unknown | Literal[5, 6]
+    reveal_type(C3.y)  # revealed: int | str
+
+    C3.y = 100
+    # error: [invalid-assignment] "Object of type `None` is not assignable to attribute `y` of type `int | str`"
+    C3.y = None
+    # TODO: should be an error, needs more sophisticated union handling in `validate_attribute_assignment`
+    C3.y = "problematic"
 
     class Meta4(type):
         if flag:
             x = 7
+            y: int = 7
         else:
             x = 8
+            y: int | str = "h"
 
     class C4(metaclass=Meta4): ...
     reveal_type(C4.x)  # revealed: Unknown | Literal[7, 8]
+    reveal_type(C4.y)  # revealed: int | str
+
+    C4.y = 100
+    # error: [invalid-assignment] "Object of type `None` is not assignable to attribute `y` of type `int | str`"
+    C4.y = None
+    # TODO: should be an error, needs more sophisticated union handling in `validate_attribute_assignment`
+    C4.y = "problematic"
 ```
 
 ## Unions with possibly unbound paths
@@ -875,8 +1005,14 @@ def _(flag1: bool, flag2: bool):
     # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
     reveal_type(C.x)  # revealed: Unknown | Literal[1, 3]
 
+    # error: [invalid-assignment] "Object of type `Literal[100]` is not assignable to attribute `x` on type `Literal[C1, C2, C3]`"
+    C.x = 100
+
     # error: [possibly-unbound-attribute] "Attribute `x` on type `C1 | C2 | C3` is possibly unbound"
     reveal_type(C().x)  # revealed: Unknown | Literal[1, 3]
+
+    # error: [invalid-assignment] "Object of type `Literal[100]` is not assignable to attribute `x` on type `C1 | C2 | C3`"
+    C().x = 100
 ```
 
 ### Possibly-unbound within a class
@@ -901,10 +1037,16 @@ def _(flag: bool, flag1: bool, flag2: bool):
     # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
     reveal_type(C.x)  # revealed: Unknown | Literal[1, 2, 3]
 
+    # error: [possibly-unbound-attribute]
+    C.x = 100
+
     # Note: we might want to consider ignoring possibly-unbound diagnostics for instance attributes eventually,
     # see the "Possibly unbound/undeclared instance attribute" section below.
     # error: [possibly-unbound-attribute] "Attribute `x` on type `C1 | C2 | C3` is possibly unbound"
     reveal_type(C().x)  # revealed: Unknown | Literal[1, 2, 3]
+
+    # error: [possibly-unbound-attribute]
+    C().x = 100
 ```
 
 ### Possibly-unbound within gradual types
@@ -922,6 +1064,9 @@ def _(flag: bool):
             x: int
 
     reveal_type(Derived().x)  # revealed: int | Any
+
+    Derived().x = 1
+    Derived().x = "a"
 ```
 
 ### Attribute possibly unbound on a subclass but not on a superclass
@@ -936,8 +1081,10 @@ def _(flag: bool):
             x = 2
 
     reveal_type(Bar.x)  # revealed: Unknown | Literal[2, 1]
+    Bar.x = 3
 
     reveal_type(Bar().x)  # revealed: Unknown | Literal[2, 1]
+    Bar().x = 3
 ```
 
 ### Attribute possibly unbound on a subclass and on a superclass
@@ -955,8 +1102,14 @@ def _(flag: bool):
     # error: [possibly-unbound-attribute]
     reveal_type(Bar.x)  # revealed: Unknown | Literal[2, 1]
 
+    # error: [possibly-unbound-attribute]
+    Bar.x = 3
+
     # error: [possibly-unbound-attribute]
     reveal_type(Bar().x)  # revealed: Unknown | Literal[2, 1]
+
+    # error: [possibly-unbound-attribute]
+    Bar().x = 3
 ```
 
 ### Possibly unbound/undeclared instance attribute
@@ -975,6 +1128,9 @@ def _(flag: bool):
 
     # error: [possibly-unbound-attribute]
     reveal_type(Foo().x)  # revealed: int | Unknown
+
+    # error: [possibly-unbound-attribute]
+    Foo().x = 1
 ```
 
 #### Possibly unbound
@@ -985,10 +1141,18 @@ def _(flag: bool):
         def __init(self):
             if flag:
                 self.x = 1
+                self.y = "a"
+            else:
+                self.y = "b"
 
-    # Emitting a diagnostic in a case like this is not something we support, and it's unclear
-    # if we ever will (or want to)
+    # error: [possibly-unbound-attribute]
     reveal_type(Foo().x)  # revealed: Unknown | Literal[1]
+
+    # error: [possibly-unbound-attribute]
+    Foo().x = 2
+
+    reveal_type(Foo().y)  # revealed: Unknown | Literal["a", "b"]
+    Foo().y = "c"
 ```
 
 ### Unions with all paths unbound
@@ -1003,6 +1167,11 @@ def _(flag: bool):
 
     # error: [unresolved-attribute] "Type `Literal[C1, C2]` has no attribute `x`"
     reveal_type(C.x)  # revealed: Unknown
+
+    # TODO: This should ideally be a `unresolved-attribute` error. We need better union
+    # handling in `validate_attribute_assignment` for this.
+    # error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to attribute `x` on type `Literal[C1, C2]`"
+    C.x = 1
 ```
 
 ## Inherited class attributes
@@ -1017,6 +1186,8 @@ class B(A): ...
 class C(B): ...
 
 reveal_type(C.X)  # revealed: Unknown | Literal["foo"]
+
+C.X = "bar"
 ```
 
 ### Multiple inheritance
@@ -1040,6 +1211,8 @@ reveal_type(A.__mro__)
 
 # `E` is earlier in the MRO than `F`, so we should use the type of `E.X`
 reveal_type(A.X)  # revealed: Unknown | Literal[42]
+
+A.X = 100
 ```
 
 ## Intersections of attributes
@@ -1057,9 +1230,13 @@ class B: ...
 def _(a_and_b: Intersection[A, B]):
     reveal_type(a_and_b.x)  # revealed: int
 
+    a_and_b.x = 2
+
 # Same for class objects
 def _(a_and_b: Intersection[type[A], type[B]]):
     reveal_type(a_and_b.x)  # revealed: int
+
+    a_and_b.x = 2
 ```
 
 ### Attribute available on both elements
@@ -1069,6 +1246,7 @@ from knot_extensions import Intersection
 
 class P: ...
 class Q: ...
+class R(P, Q): ...
 
 class A:
     x: P = P()
@@ -1078,10 +1256,12 @@ class B:
 
 def _(a_and_b: Intersection[A, B]):
     reveal_type(a_and_b.x)  # revealed: P & Q
+    a_and_b.x = R()
 
 # Same for class objects
 def _(a_and_b: Intersection[type[A], type[B]]):
     reveal_type(a_and_b.x)  # revealed: P & Q
+    a_and_b.x = R()
 ```
 
 ### Possible unboundness
@@ -1091,6 +1271,7 @@ from knot_extensions import Intersection
 
 class P: ...
 class Q: ...
+class R(P, Q): ...
 
 def _(flag: bool):
     class A1:
@@ -1102,11 +1283,17 @@ def _(flag: bool):
     def inner1(a_and_b: Intersection[A1, B1]):
         # error: [possibly-unbound-attribute]
         reveal_type(a_and_b.x)  # revealed: P
+
+        # error: [possibly-unbound-attribute]
+        a_and_b.x = R()
     # Same for class objects
     def inner1_class(a_and_b: Intersection[type[A1], type[B1]]):
         # error: [possibly-unbound-attribute]
         reveal_type(a_and_b.x)  # revealed: P
 
+        # error: [possibly-unbound-attribute]
+        a_and_b.x = R()
+
     class A2:
         if flag:
             x: P = P()
@@ -1116,6 +1303,11 @@ def _(flag: bool):
 
     def inner2(a_and_b: Intersection[A2, B1]):
         reveal_type(a_and_b.x)  # revealed: P & Q
+
+        # TODO: this should not be an error, we need better intersection
+        # handling in `validate_attribute_assignment` for this
+        # error: [possibly-unbound-attribute]
+        a_and_b.x = R()
     # Same for class objects
     def inner2_class(a_and_b: Intersection[type[A2], type[B1]]):
         reveal_type(a_and_b.x)  # revealed: P & Q
@@ -1131,21 +1323,33 @@ def _(flag: bool):
     def inner3(a_and_b: Intersection[A3, B3]):
         # error: [possibly-unbound-attribute]
         reveal_type(a_and_b.x)  # revealed: P & Q
+
+        # error: [possibly-unbound-attribute]
+        a_and_b.x = R()
     # Same for class objects
     def inner3_class(a_and_b: Intersection[type[A3], type[B3]]):
         # error: [possibly-unbound-attribute]
         reveal_type(a_and_b.x)  # revealed: P & Q
 
+        # error: [possibly-unbound-attribute]
+        a_and_b.x = R()
+
     class A4: ...
     class B4: ...
 
     def inner4(a_and_b: Intersection[A4, B4]):
         # error: [unresolved-attribute]
         reveal_type(a_and_b.x)  # revealed: Unknown
+
+        # error: [invalid-assignment]
+        a_and_b.x = R()
     # Same for class objects
     def inner4_class(a_and_b: Intersection[type[A4], type[B4]]):
         # error: [unresolved-attribute]
         reveal_type(a_and_b.x)  # revealed: Unknown
+
+        # error: [invalid-assignment]
+        a_and_b.x = R()
 ```
 
 ### Intersection of implicit instance attributes
@@ -1181,7 +1385,7 @@ from typing import Any
 class Foo(Any): ...
 
 reveal_type(Foo.bar)  # revealed: Any
-reveal_type(Foo.__repr__)  # revealed: Literal[__repr__] & Any
+reveal_type(Foo.__repr__)  # revealed: (def __repr__(self) -> str) & Any
 ```
 
 Similar principles apply if `Any` appears in the middle of an inheritance hierarchy:
@@ -1291,6 +1495,59 @@ def _(ns: argparse.Namespace):
     reveal_type(ns.whatever)  # revealed: Any
 ```
 
+## Classes with custom `__setattr__` methods
+
+### Basic
+
+If a type provides a custom `__setattr__` method, we use the parameter type of that method as the
+type to validate attribute assignments. Consider the following `CustomSetAttr` class:
+
+```py
+class CustomSetAttr:
+    def __setattr__(self, name: str, value: int) -> None:
+        pass
+```
+
+We can set arbitrary attributes on instances of this class:
+
+```py
+c = CustomSetAttr()
+
+c.whatever = 42
+```
+
+### Type of the `name` parameter
+
+If the `name` parameter of the `__setattr__` method is annotated with a (union of) literal type(s),
+we only consider the attribute assignment to be valid if the assigned attribute is one of them:
+
+```py
+from typing import Literal
+
+class Date:
+    def __setattr__(self, name: Literal["day", "month", "year"], value: int) -> None:
+        pass
+
+date = Date()
+date.day = 8
+date.month = 4
+date.year = 2025
+
+# error: [unresolved-attribute] "Can not assign object of `Literal["UTC"]` to attribute `tz` on type `Date` with custom `__setattr__` method."
+date.tz = "UTC"
+```
+
+### `argparse.Namespace`
+
+A standard library example of a class with a custom `__setattr__` method is `argparse.Namespace`:
+
+```py
+import argparse
+
+def _(ns: argparse.Namespace):
+    ns.whatever = 42
+```
+
 ## Objects of all types have a `__class__` method
 
 The type of `x.__class__` is the same as `x`'s meta-type. `x.__class__` is always the same value as
@@ -1420,14 +1677,14 @@ functions are instances of that class:
 def f(): ...
 
 reveal_type(f.__defaults__)  # revealed: @Todo(full tuple[...] support) | None
-reveal_type(f.__kwdefaults__)  # revealed: @Todo(generics) | None
+reveal_type(f.__kwdefaults__)  # revealed: @Todo(specialized non-generic class) | None
 ```
 
 Some attributes are special-cased, however:
 
 ```py
 reveal_type(f.__get__)  # revealed: <method-wrapper `__get__` of `f`>
-reveal_type(f.__call__)  # revealed: <bound method `__call__` of `Literal[f]`>
+reveal_type(f.__call__)  # revealed: <method-wrapper `__call__` of `f`>
 ```
 
 ### Int-literal attributes
@@ -1436,8 +1693,8 @@ Most attribute accesses on int-literal types are delegated to `builtins.int`, si
 integers are instances of that class:
 
 ```py
-reveal_type((2).bit_length)  # revealed: <bound method `bit_length` of `Literal[2]`>
-reveal_type((2).denominator)  # revealed: @Todo(@property)
+reveal_type((2).bit_length)  # revealed: bound method Literal[2].bit_length() -> int
+reveal_type((2).denominator)  # revealed: Literal[1]
 ```
 
 Some attributes are special-cased, however:
@@ -1453,8 +1710,10 @@ Most attribute accesses on bool-literal types are delegated to `builtins.bool`,
 bools are instances of that class:
 
 ```py
-reveal_type(True.__and__)  # revealed: <bound method `__and__` of `Literal[True]`>
-reveal_type(False.__or__)  # revealed: <bound method `__or__` of `Literal[False]`>
+# revealed: Overload[(value: bool, /) -> bool, (value: int, /) -> int]
+reveal_type(True.__and__)
+# revealed: Overload[(value: bool, /) -> bool, (value: int, /) -> int]
+reveal_type(False.__or__)
 ```
 
 Some attributes are special-cased, however:
@@ -1469,8 +1728,10 @@ reveal_type(False.real)  # revealed: Literal[0]
 All attribute access on literal `bytes` types is currently delegated to `builtins.bytes`:
 
 ```py
-reveal_type(b"foo".join)  # revealed: <bound method `join` of `Literal[b"foo"]`>
-reveal_type(b"foo".endswith)  # revealed: <bound method `endswith` of `Literal[b"foo"]`>
+# revealed: bound method Literal[b"foo"].join(iterable_of_bytes: @Todo(specialized non-generic class), /) -> bytes
+reveal_type(b"foo".join)
+# revealed: bound method Literal[b"foo"].endswith(suffix: @Todo(Support for `typing.TypeAlias`), start: SupportsIndex | None = ellipsis, end: SupportsIndex | None = ellipsis, /) -> bool
+reveal_type(b"foo".endswith)
 ```
 
 ## Instance attribute edge cases
@@ -1571,6 +1832,89 @@ def f(never: Never):
     never.another_attribute = never
 ```
 
+### Cyclic implicit attributes
+
+Inferring types for undeclared implicit attributes can be cyclic:
+
+```py
+class C:
+    def __init__(self):
+        self.x = 1
+
+    def copy(self, other: "C"):
+        self.x = other.x
+
+reveal_type(C().x)  # revealed: Unknown | Literal[1]
+```
+
+If the only assignment to a name is cyclic, we just infer `Unknown` for that attribute:
+
+```py
+class D:
+    def copy(self, other: "D"):
+        self.x = other.x
+
+reveal_type(D().x)  # revealed: Unknown
+```
+
+If there is an annotation for a name, we don't try to infer any type from the RHS of assignments to
+that name, so these cases don't trigger any cycle:
+
+```py
+class E:
+    def __init__(self):
+        self.x: int = 1
+
+    def copy(self, other: "E"):
+        self.x = other.x
+
+reveal_type(E().x)  # revealed: int
+
+class F:
+    def __init__(self):
+        self.x = 1
+
+    def copy(self, other: "F"):
+        self.x: int = other.x
+
+reveal_type(F().x)  # revealed: int
+
+class G:
+    def copy(self, other: "G"):
+        self.x: int = other.x
+
+reveal_type(G().x)  # revealed: int
+```
+
+We can even handle cycles involving multiple classes:
+
+```py
+class A:
+    def __init__(self):
+        self.x = 1
+
+    def copy(self, other: "B"):
+        self.x = other.x
+
+class B:
+    def copy(self, other: "A"):
+        self.x = other.x
+
+reveal_type(B().x)  # revealed: Unknown | Literal[1]
+reveal_type(A().x)  # revealed: Unknown | Literal[1]
+```
+
+This case additionally tests our union/intersection simplification logic:
+
+```py
+class H:
+    def __init__(self):
+        self.x = 1
+
+    def copy(self, other: "H"):
+        self.x = other.x or self.x
+```
+
 ### Builtin types attributes
 
 This test can probably be removed eventually, but we currently include it because we do not yet
@@ -1605,6 +1949,23 @@ reveal_type(C.a_type)  # revealed: type
 reveal_type(C.a_none)  # revealed: None
 ```
 
+## Enum classes
+
+Enums are not supported yet; attribute access on an enum class is inferred as `Todo`.
+
+```py
+import enum
+
+reveal_type(enum.Enum.__members__)  # revealed: @Todo(Attribute access on enum classes)
+
+class Foo(enum.Enum):
+    BAR = 1
+
+reveal_type(Foo.BAR)  # revealed: @Todo(Attribute access on enum classes)
+reveal_type(Foo.BAR.value)  # revealed: @Todo(Attribute access on enum classes)
+reveal_type(Foo.__members__)  # revealed: @Todo(Attribute access on enum classes)
+```
+
 ## References
 
 Some of the tests in the *Class and instance variables* section draw inspiration from
@@ -1612,5 +1973,5 @@ Some of the tests in the *Class and instance variables* section draw inspiration
 
 [descriptor protocol tests]: descriptor_protocol.md
 [pyright's documentation]: https://microsoft.github.io/pyright/#/type-concepts-advanced?id=class-and-instance-variables
-[typing spec on `classvar`]: https://typing.readthedocs.io/en/latest/spec/class-compat.html#classvar
+[typing spec on `classvar`]: https://typing.python.org/en/latest/spec/class-compat.html#classvar
 [`typing.classvar`]: https://docs.python.org/3/library/typing.html#typing.ClassVar

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

@@ -350,30 +350,30 @@ reveal_type(no() + no())  # revealed: Unknown
 def f():
     pass
 
-# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f + f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `-` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `-` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f - f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `*` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `*` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f * f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `@` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `@` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f @ f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `/` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `/` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f / f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `%` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `%` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f % f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `**` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `**` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f**f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `<<` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `<<` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f << f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `>>` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `>>` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f >> f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `|` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `|` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f | f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `^` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `^` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f ^ f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `&` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `&` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f & f)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `//` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+# error: [unsupported-operator] "Operator `//` is unsupported between objects of type `def f() -> Unknown` and `def f() -> Unknown`"
 reveal_type(f // f)  # revealed: Unknown
 ```

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

@@ -14,43 +14,43 @@ We support inference for all Python's binary operators: `+`, `-`, `*`, `@`, `/`,
 
 ```py
 class A:
-    def __add__(self, other) -> A:
+    def __add__(self, other) -> "A":
         return self
 
-    def __sub__(self, other) -> A:
+    def __sub__(self, other) -> "A":
         return self
 
-    def __mul__(self, other) -> A:
+    def __mul__(self, other) -> "A":
         return self
 
-    def __matmul__(self, other) -> A:
+    def __matmul__(self, other) -> "A":
         return self
 
-    def __truediv__(self, other) -> A:
+    def __truediv__(self, other) -> "A":
         return self
 
-    def __floordiv__(self, other) -> A:
+    def __floordiv__(self, other) -> "A":
         return self
 
-    def __mod__(self, other) -> A:
+    def __mod__(self, other) -> "A":
         return self
 
-    def __pow__(self, other) -> A:
+    def __pow__(self, other) -> "A":
         return self
 
-    def __lshift__(self, other) -> A:
+    def __lshift__(self, other) -> "A":
         return self
 
-    def __rshift__(self, other) -> A:
+    def __rshift__(self, other) -> "A":
         return self
 
-    def __and__(self, other) -> A:
+    def __and__(self, other) -> "A":
         return self
 
-    def __xor__(self, other) -> A:
+    def __xor__(self, other) -> "A":
         return self
 
-    def __or__(self, other) -> A:
+    def __or__(self, other) -> "A":
         return self
 
 class B: ...
@@ -76,43 +76,43 @@ We also support inference for reflected operations:
 
 ```py
 class A:
-    def __radd__(self, other) -> A:
+    def __radd__(self, other) -> "A":
         return self
 
-    def __rsub__(self, other) -> A:
+    def __rsub__(self, other) -> "A":
         return self
 
-    def __rmul__(self, other) -> A:
+    def __rmul__(self, other) -> "A":
         return self
 
-    def __rmatmul__(self, other) -> A:
+    def __rmatmul__(self, other) -> "A":
         return self
 
-    def __rtruediv__(self, other) -> A:
+    def __rtruediv__(self, other) -> "A":
         return self
 
-    def __rfloordiv__(self, other) -> A:
+    def __rfloordiv__(self, other) -> "A":
         return self
 
-    def __rmod__(self, other) -> A:
+    def __rmod__(self, other) -> "A":
         return self
 
-    def __rpow__(self, other) -> A:
+    def __rpow__(self, other) -> "A":
         return self
 
-    def __rlshift__(self, other) -> A:
+    def __rlshift__(self, other) -> "A":
         return self
 
-    def __rrshift__(self, other) -> A:
+    def __rrshift__(self, other) -> "A":
         return self
 
-    def __rand__(self, other) -> A:
+    def __rand__(self, other) -> "A":
         return self
 
-    def __rxor__(self, other) -> A:
+    def __rxor__(self, other) -> "A":
         return self
 
-    def __ror__(self, other) -> A:
+    def __ror__(self, other) -> "A":
         return self
 
 class B: ...
@@ -157,11 +157,11 @@ the right-hand side is not a subtype of the left-hand side, `lhs.__add__` will t
 
 ```py
 class A:
-    def __add__(self, other: B) -> int:
+    def __add__(self, other: "B") -> int:
         return 42
 
 class B:
-    def __radd__(self, other: A) -> str:
+    def __radd__(self, other: "A") -> str:
         return "foo"
 
 reveal_type(A() + B())  # revealed:  int
@@ -169,10 +169,10 @@ reveal_type(A() + B())  # revealed:  int
 # Edge case: C is a subtype of C, *but* if the two sides are of *equal* types,
 # the lhs *still* takes precedence
 class C:
-    def __add__(self, other: C) -> int:
+    def __add__(self, other: "C") -> int:
         return 42
 
-    def __radd__(self, other: C) -> str:
+    def __radd__(self, other: "C") -> str:
         return "foo"
 
 reveal_type(C() + C())  # revealed: int
@@ -237,11 +237,11 @@ well.
 
 ```py
 class A:
-    def __sub__(self, other: A) -> A:
+    def __sub__(self, other: "A") -> "A":
         return A()
 
 class B:
-    def __rsub__(self, other: A) -> B:
+    def __rsub__(self, other: A) -> "B":
         return B()
 
 reveal_type(A() - B())  # revealed: B
@@ -300,19 +300,17 @@ its instance super-type.
 
 ```py
 class A:
-    def __add__(self, other) -> A:
+    def __add__(self, other) -> "A":
         return self
 
-    def __radd__(self, other) -> A:
+    def __radd__(self, other) -> "A":
         return self
 
 reveal_type(A() + 1)  # revealed: A
 reveal_type(1 + A())  # revealed: A
 
 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(return type of decorated function)
+reveal_type("foo" + A())  # revealed: A
 
 reveal_type(A() + b"foo")  # revealed: A
 # TODO should be `A` since `bytes.__add__` doesn't support `A` instances
@@ -320,16 +318,14 @@ 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(return type of decorated function)
+reveal_type(() + A())  # revealed: @Todo(full tuple[...] support)
 
 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`:
 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(return type of decorated function)
+reveal_type(literal_string_instance + A())  # revealed: A
 ```
 
 ## Operations involving instances of classes inheriting from `Any`
@@ -363,7 +359,7 @@ reveal_type(X() + Y())  # revealed: int
 
 ```py
 class NotBoolable:
-    __bool__ = 3
+    __bool__: int = 3
 
 a = NotBoolable()
 
@@ -371,6 +367,39 @@ a = NotBoolable()
 10 and a and True
 ```
 
+## Operations on class objects
+
+When operating on class objects, the corresponding dunder methods are looked up on the metaclass.
+
+```py
+from __future__ import annotations
+
+class Meta(type):
+    def __add__(self, other: Meta) -> int:
+        return 1
+
+    def __lt__(self, other: Meta) -> bool:
+        return True
+
+    def __getitem__(self, key: int) -> str:
+        return "a"
+
+class A(metaclass=Meta): ...
+class B(metaclass=Meta): ...
+
+reveal_type(A + B)  # revealed: int
+# error: [unsupported-operator] "Operator `-` is unsupported between objects of type `Literal[A]` and `Literal[B]`"
+reveal_type(A - B)  # revealed: Unknown
+
+reveal_type(A < B)  # revealed: bool
+reveal_type(A > B)  # revealed: bool
+
+# error: [unsupported-operator] "Operator `<=` is not supported for types `Literal[A]` and `Literal[B]`"
+reveal_type(A <= B)  # revealed: Unknown
+
+reveal_type(A[0])  # revealed: str
+```
+
 ## Unsupported
 
 ### Dunder as instance attribute
@@ -433,7 +462,7 @@ the unreflected dunder of the left-hand operand. For context, see
 
 ```py
 class Foo:
-    def __radd__(self, other: Foo) -> Foo:
+    def __radd__(self, other: "Foo") -> "Foo":
         return self
 
 # error: [unsupported-operator]

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

@@ -50,9 +50,23 @@ reveal_type(1 ** (largest_u32 + 1))  # revealed: int
 reveal_type(2**largest_u32)  # revealed: int
 
 def variable(x: int):
-    reveal_type(x**2)  # revealed: @Todo(return type of decorated function)
-    reveal_type(2**x)  # revealed: @Todo(return type of decorated function)
-    reveal_type(x**x)  # revealed: @Todo(return type of decorated function)
+    reveal_type(x**2)  # revealed: int
+    # TODO: should be `Any` (overload 5 on `__pow__`), requires correct overload matching
+    reveal_type(2**x)  # revealed: int
+    # TODO: should be `Any` (overload 5 on `__pow__`), requires correct overload matching
+    reveal_type(x**x)  # revealed: int
+```
+
+If the second argument is \<0, a `float` is returned at runtime. If the first argument is \<0 but
+the second argument is >=0, an `int` is still returned:
+
+```py
+reveal_type(1**0)  # revealed: Literal[1]
+reveal_type(0**1)  # revealed: Literal[0]
+reveal_type(0**0)  # revealed: Literal[1]
+reveal_type((-1) ** 2)  # revealed: Literal[1]
+reveal_type(2 ** (-1))  # revealed: float
+reveal_type((-1) ** (-1))  # revealed: float
 ```
 
 ## Division by Zero

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

@@ -0,0 +1,22 @@
+# Binary operations on tuples
+
+## Concatenation for heterogeneous tuples
+
+```py
+reveal_type((1, 2) + (3, 4))  # revealed: tuple[Literal[1], Literal[2], Literal[3], Literal[4]]
+reveal_type(() + (1, 2))  # revealed: tuple[Literal[1], Literal[2]]
+reveal_type((1, 2) + ())  # revealed: tuple[Literal[1], Literal[2]]
+reveal_type(() + ())  # revealed: tuple[()]
+
+def _(x: tuple[int, str], y: tuple[None, tuple[int]]):
+    reveal_type(x + y)  # revealed: tuple[int, str, None, tuple[int]]
+    reveal_type(y + x)  # revealed: tuple[None, tuple[int], int, str]
+```
+
+## Concatenation for homogeneous tuples
+
+```py
+def _(x: tuple[int, ...], y: tuple[str, ...]):
+    reveal_type(x + y)  # revealed: @Todo(full tuple[...] support)
+    reveal_type(x + (1, 2))  # revealed: @Todo(full tuple[...] support)
+```

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

@@ -49,3 +49,11 @@ def f4(x: float, y: float):
     reveal_type(x // y)  # revealed: int | float
     reveal_type(x % y)  # revealed: int | float
 ```
+
+If any of the union elements leads to a division by zero, we will report an error:
+
+```py
+def f5(m: int, n: Literal[-1, 0, 1]):
+    # error: [division-by-zero] "Cannot divide object of type `int` by zero"
+    return m / n
+```

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

@@ -43,7 +43,7 @@ if True and (x := 1):
 
 ```py
 def _(flag: bool):
-    flag or (x := 1) or reveal_type(x)  # revealed: Literal[1]
+    flag or (x := 1) or reveal_type(x)  # revealed: Never
 
     # error: [unresolved-reference]
     flag or reveal_type(y) or (y := 1)  # revealed: Unknown

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

@@ -0,0 +1,43 @@
+# `typing.Callable`
+
+```py
+from typing import Callable
+
+def _(c: Callable[[], int]):
+    reveal_type(c())  # revealed: int
+
+def _(c: Callable[[int, str], int]):
+    reveal_type(c(1, "a"))  # revealed: int
+
+    # error: [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["a"]`"
+    # error: [invalid-argument-type] "Argument to this function is incorrect: Expected `str`, found `Literal[1]`"
+    reveal_type(c("a", 1))  # revealed: int
+```
+
+The `Callable` annotation can only be used to describe positional-only parameters.
+
+```py
+def _(c: Callable[[int, str], None]):
+    # error: [unknown-argument] "Argument `a` does not match any known parameter"
+    # error: [unknown-argument] "Argument `b` does not match any known parameter"
+    # error: [missing-argument] "No arguments provided for required parameters 1, 2"
+    reveal_type(c(a=1, b="b"))  # revealed: None
+```
+
+If the annotation uses a gradual form (`...`) for the parameter list, then it can accept any kind of
+parameter with any type.
+
+```py
+def _(c: Callable[..., int]):
+    reveal_type(c())  # revealed: int
+    reveal_type(c(1))  # revealed: int
+    reveal_type(c(1, "str", False, a=[1, 2], b=(3, 4)))  # revealed: int
+```
+
+An invalid `Callable` form can accept any parameters and will return `Unknown`.
+
+```py
+# error: [invalid-type-form]
+def _(c: Callable[42, str]):
+    reveal_type(c())  # revealed: Unknown
+```

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

@@ -26,7 +26,11 @@ reveal_type(type(1))  # revealed: Literal[int]
 But a three-argument call to type creates a dynamic instance of the `type` class:
 
 ```py
+class Base: ...
+
 reveal_type(type("Foo", (), {}))  # revealed: type
+
+reveal_type(type("Foo", (Base,), {"attr": 1}))  # revealed: type
 ```
 
 Other numbers of arguments are invalid
@@ -38,3 +42,60 @@ type("Foo", ())
 # error: [no-matching-overload] "No overload of class `type` matches arguments"
 type("Foo", (), {}, weird_other_arg=42)
 ```
+
+The following calls are also invalid, due to incorrect argument types:
+
+```py
+class Base: ...
+
+# error: [no-matching-overload] "No overload of class `type` matches arguments"
+type(b"Foo", (), {})
+
+# error: [no-matching-overload] "No overload of class `type` matches arguments"
+type("Foo", Base, {})
+
+# TODO: this should be an error
+type("Foo", (1, 2), {})
+
+# TODO: this should be an error
+type("Foo", (Base,), {b"attr": 1})
+```
+
+## Calls to `str()`
+
+### Valid calls
+
+```py
+str()
+str("")
+str(b"")
+str(1)
+str(object=1)
+
+str(b"M\xc3\xbcsli", "utf-8")
+str(b"M\xc3\xbcsli", "utf-8", "replace")
+
+str(b"M\x00\xfc\x00s\x00l\x00i\x00", encoding="utf-16")
+str(b"M\x00\xfc\x00s\x00l\x00i\x00", encoding="utf-16", errors="ignore")
+
+str(bytearray.fromhex("4d c3 bc 73 6c 69"), "utf-8")
+str(bytearray(), "utf-8")
+
+str(encoding="utf-8", object=b"M\xc3\xbcsli")
+str(b"", errors="replace")
+str(encoding="utf-8")
+str(errors="replace")
+```
+
+### Invalid calls
+
+```py
+str(1, 2)  # error: [no-matching-overload]
+str(o=1)  # error: [no-matching-overload]
+
+# First argument is not a bytes-like object:
+str("Müsli", "utf-8")  # error: [no-matching-overload]
+
+# Second argument is not a valid encoding:
+str(b"M\xc3\xbcsli", b"utf-8")  # error: [no-matching-overload]
+```

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

@@ -71,7 +71,7 @@ def _(flag: bool):
 
     a = NonCallable()
     # error: [call-non-callable] "Object of type `Literal[1]` is not callable"
-    reveal_type(a())  # revealed: int | Unknown
+    reveal_type(a())  # revealed: Unknown | int
 ```
 
 ## Call binding errors
@@ -85,7 +85,7 @@ class C:
 
 c = C()
 
-# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 2 (`x`) of bound method `__call__`; expected type `int`"
+# error: 15 [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["foo"]`"
 reveal_type(c("foo"))  # revealed: int
 ```
 
@@ -99,7 +99,7 @@ class C:
 
 c = C()
 
-# error: 13 [invalid-argument-type] "Object of type `C` cannot be assigned to parameter 1 (`self`) of bound method `__call__`; expected type `int`"
+# error: 13 [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `C`"
 reveal_type(c())  # revealed: int
 ```
 

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

@@ -1,7 +1,325 @@
 # Constructor
 
+When classes are instantiated, Python calls the meta-class `__call__` method, which can either be
+customized by the user or `type.__call__` is used.
+
+The latter calls the `__new__` method of the class, which is responsible for creating the instance
+and then calls the `__init__` method on the resulting instance to initialize it with the same
+arguments.
+
+Both `__new__` and `__init__` are looked up using full descriptor protocol, but `__new__` is then
+called as an implicit static, rather than bound method with `cls` passed as the first argument.
+`__init__` has no special handling, it is fetched as bound method and is called just like any other
+dunder method.
+
+`type.__call__` does other things too, but this is not yet handled by us.
+
+Since every class has `object` in it's MRO, the default implementations are `object.__new__` and
+`object.__init__`. They have some special behavior, namely:
+
+- If neither `__new__` nor `__init__` are defined anywhere in the MRO of class (except for `object`)
+    \- no arguments are accepted and `TypeError` is raised if any are passed.
+- If `__new__` is defined, but `__init__` is not - `object.__init__` will allow arbitrary arguments!
+
+As of today there are a number of behaviors that we do not support:
+
+- `__new__` is assumed to return an instance of the class on which it is called
+- User defined `__call__` on metaclass is ignored
+
+## Creating an instance of the `object` class itself
+
+Test the behavior of the `object` class itself. As implementation has to ignore `object` own methods
+as defined in typeshed due to behavior not expressible in typeshed (see above how `__init__` behaves
+differently depending on whether `__new__` is defined or not), we have to test the behavior of
+`object` itself.
+
+```py
+reveal_type(object())  # revealed: object
+
+# error: [too-many-positional-arguments] "Too many positional arguments to class `object`: expected 0, got 1"
+reveal_type(object(1))  # revealed: object
+```
+
+## No init or new
+
 ```py
 class Foo: ...
 
 reveal_type(Foo())  # revealed: Foo
+
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 0, got 1"
+reveal_type(Foo(1))  # revealed: Foo
+```
+
+## `__new__` present on the class itself
+
+```py
+class Foo:
+    def __new__(cls, x: int) -> "Foo":
+        return object.__new__(cls)
+
+reveal_type(Foo(1))  # revealed: Foo
+
+# error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
+reveal_type(Foo())  # revealed: Foo
+# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 1, got 2"
+reveal_type(Foo(1, 2))  # revealed: Foo
+```
+
+## `__new__` present on a superclass
+
+If the `__new__` method is defined on a superclass, we can still infer the signature of the
+constructor from it.
+
+```py
+from typing_extensions import Self
+
+class Base:
+    def __new__(cls, x: int) -> Self: ...
+
+class Foo(Base): ...
+
+reveal_type(Foo(1))  # revealed: Foo
+
+# error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
+reveal_type(Foo())  # revealed: Foo
+# error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 1, got 2"
+reveal_type(Foo(1, 2))  # revealed: Foo
+```
+
+## Conditional `__new__`
+
+```py
+def _(flag: bool) -> None:
+    class Foo:
+        if flag:
+            def __new__(cls, x: int): ...
+        else:
+            def __new__(cls, x: int, y: int = 1): ...
+
+    reveal_type(Foo(1))  # revealed: Foo
+    # error: [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["1"]`"
+    reveal_type(Foo("1"))  # revealed: Foo
+    # error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
+    reveal_type(Foo())  # revealed: Foo
+    # error: [too-many-positional-arguments] "Too many positional arguments to function `__new__`: expected 1, got 2"
+    reveal_type(Foo(1, 2))  # revealed: Foo
+```
+
+## A descriptor in place of `__new__`
+
+```py
+class SomeCallable:
+    def __call__(self, cls, x: int) -> "Foo":
+        obj = object.__new__(cls)
+        obj.x = x
+        return obj
+
+class Descriptor:
+    def __get__(self, instance, owner) -> SomeCallable:
+        return SomeCallable()
+
+class Foo:
+    __new__: Descriptor = Descriptor()
+
+reveal_type(Foo(1))  # revealed: Foo
+# error: [missing-argument] "No argument provided for required parameter `x` of bound method `__call__`"
+reveal_type(Foo())  # revealed: Foo
+```
+
+## A callable instance in place of `__new__`
+
+### Bound
+
+```py
+class Callable:
+    def __call__(self, cls, x: int) -> "Foo":
+        return object.__new__(cls)
+
+class Foo:
+    __new__ = Callable()
+
+reveal_type(Foo(1))  # revealed: Foo
+# error: [missing-argument] "No argument provided for required parameter `x` of bound method `__call__`"
+reveal_type(Foo())  # revealed: Foo
+```
+
+### Possibly Unbound
+
+```py
+def _(flag: bool) -> None:
+    class Callable:
+        if flag:
+            def __call__(self, cls, x: int) -> "Foo":
+                return object.__new__(cls)
+
+    class Foo:
+        __new__ = Callable()
+
+    # error: [call-non-callable] "Object of type `Callable` is not callable (possibly unbound `__call__` method)"
+    reveal_type(Foo(1))  # revealed: Foo
+    # TODO should be - error: [missing-argument] "No argument provided for required parameter `x` of bound method `__call__`"
+    # but we currently infer the signature of `__call__` as unknown, so it accepts any arguments
+    # error: [call-non-callable] "Object of type `Callable` is not callable (possibly unbound `__call__` method)"
+    reveal_type(Foo())  # revealed: Foo
+```
+
+## `__init__` present on the class itself
+
+If the class has an `__init__` method, we can infer the signature of the constructor from it.
+
+```py
+class Foo:
+    def __init__(self, x: int): ...
+
+reveal_type(Foo(1))  # revealed: Foo
+
+# error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
+reveal_type(Foo())  # revealed: Foo
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
+reveal_type(Foo(1, 2))  # revealed: Foo
+```
+
+## `__init__` present on a superclass
+
+If the `__init__` method is defined on a superclass, we can still infer the signature of the
+constructor from it.
+
+```py
+class Base:
+    def __init__(self, x: int): ...
+
+class Foo(Base): ...
+
+reveal_type(Foo(1))  # revealed: Foo
+
+# error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
+reveal_type(Foo())  # revealed: Foo
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
+reveal_type(Foo(1, 2))  # revealed: Foo
+```
+
+## Conditional `__init__`
+
+```py
+def _(flag: bool) -> None:
+    class Foo:
+        if flag:
+            def __init__(self, x: int): ...
+        else:
+            def __init__(self, x: int, y: int = 1): ...
+
+    reveal_type(Foo(1))  # revealed: Foo
+    # error: [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["1"]`"
+    reveal_type(Foo("1"))  # revealed: Foo
+    # error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
+    reveal_type(Foo())  # revealed: Foo
+    # error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
+    reveal_type(Foo(1, 2))  # revealed: Foo
+```
+
+## A descriptor in place of `__init__`
+
+```py
+class SomeCallable:
+    # TODO: at runtime `__init__` is checked to return `None` and
+    # a `TypeError` is raised if it doesn't. However, apparently
+    # this is not true when the descriptor is used as `__init__`.
+    # However, we may still want to check this.
+    def __call__(self, x: int) -> str:
+        return "a"
+
+class Descriptor:
+    def __get__(self, instance, owner) -> SomeCallable:
+        return SomeCallable()
+
+class Foo:
+    __init__: Descriptor = Descriptor()
+
+reveal_type(Foo(1))  # revealed: Foo
+# error: [missing-argument] "No argument provided for required parameter `x` of bound method `__call__`"
+reveal_type(Foo())  # revealed: Foo
+```
+
+## A callable instance in place of `__init__`
+
+### Bound
+
+```py
+class Callable:
+    def __call__(self, x: int) -> None:
+        pass
+
+class Foo:
+    __init__ = Callable()
+
+reveal_type(Foo(1))  # revealed: Foo
+# error: [missing-argument] "No argument provided for required parameter `x` of bound method `__call__`"
+reveal_type(Foo())  # revealed: Foo
+```
+
+### Possibly Unbound
+
+```py
+def _(flag: bool) -> None:
+    class Callable:
+        if flag:
+            def __call__(self, x: int) -> None:
+                pass
+
+    class Foo:
+        __init__ = Callable()
+
+    # error: [call-non-callable] "Object of type `Callable` is not callable (possibly unbound `__call__` method)"
+    reveal_type(Foo(1))  # revealed: Foo
+    # TODO should be - error: [missing-argument] "No argument provided for required parameter `x` of bound method `__call__`"
+    # but we currently infer the signature of `__call__` as unknown, so it accepts any arguments
+    # error: [call-non-callable] "Object of type `Callable` is not callable (possibly unbound `__call__` method)"
+    reveal_type(Foo())  # revealed: Foo
+```
+
+## `__new__` and `__init__` both present
+
+### Identical signatures
+
+A common case is to have `__new__` and `__init__` with identical signatures (except for the first
+argument). We report errors for both `__new__` and `__init__` if the arguments are incorrect.
+
+At runtime `__new__` is called first and will fail without executing `__init__` if the arguments are
+incorrect. However, we decided that it is better to report errors for both methods, since after
+fixing the `__new__` method, the user may forget to fix the `__init__` method.
+
+```py
+class Foo:
+    def __new__(cls, x: int) -> "Foo":
+        return object.__new__(cls)
+
+    def __init__(self, x: int): ...
+
+# error: [missing-argument] "No argument provided for required parameter `x` of function `__new__`"
+# error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
+reveal_type(Foo())  # revealed: Foo
+
+reveal_type(Foo(1))  # revealed: Foo
+```
+
+### Compatible signatures
+
+But they can also be compatible, but not identical. We should correctly report errors only for the
+mthod that would fail.
+
+```py
+class Foo:
+    def __new__(cls, *args, **kwargs):
+        return object.__new__(cls)
+
+    def __init__(self, x: int) -> None:
+        self.x = x
+
+# error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
+reveal_type(Foo())  # revealed: Foo
+reveal_type(Foo(1))  # revealed: Foo
+
+# error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
+reveal_type(Foo(1, 2))  # revealed: Foo
 ```

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

@@ -204,6 +204,28 @@ def _(flag: bool):
     reveal_type(d[0])  # revealed: str | bytes
 ```
 
+## Calling a union of types without dunder methods
+
+We add instance attributes here to make sure that we don't treat the implicit dunder calls here like
+regular method calls.
+
+```py
+def external_getitem(instance, key: int) -> str:
+    return str(key)
+
+class NotSubscriptable1:
+    def __init__(self, value: int):
+        self.__getitem__ = external_getitem
+
+class NotSubscriptable2:
+    def __init__(self, value: int):
+        self.__getitem__ = external_getitem
+
+def _(union: NotSubscriptable1 | NotSubscriptable2):
+    # error: [non-subscriptable]
+    union[0]
+```
+
 ## Calling a possibly-unbound dunder method
 
 ```py

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

@@ -21,6 +21,11 @@ reveal_type(get_int_async())  # revealed: @Todo(generic types.CoroutineType)
 
 ## Generic
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 ```py
 def get_int[T]() -> int:
     return 42
@@ -37,16 +42,13 @@ def foo() -> int:
     return 42
 
 def decorator(func) -> Callable[[], int]:
-    # TODO: no error
-    # error: [invalid-return-type]
     return foo
 
 @decorator
 def bar() -> str:
     return "bar"
 
-# TODO: should reveal `int`, as the decorator replaces `bar` with `foo`
-reveal_type(bar())  # revealed: @Todo(return type of decorated function)
+reveal_type(bar())  # revealed: int
 ```
 
 ## Invalid callable
@@ -75,7 +77,7 @@ def _(flag: bool):
 def f(x: int) -> int:
     return 1
 
-# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 1 (`x`) of function `f`; expected type `int`"
+# error: 15 [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["foo"]`"
 reveal_type(f("foo"))  # revealed: int
 ```
 
@@ -85,7 +87,7 @@ reveal_type(f("foo"))  # revealed: int
 def f(x: int, /) -> int:
     return 1
 
-# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 1 (`x`) of function `f`; expected type `int`"
+# error: 15 [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["foo"]`"
 reveal_type(f("foo"))  # revealed: int
 ```
 
@@ -95,7 +97,7 @@ reveal_type(f("foo"))  # revealed: int
 def f(*args: int) -> int:
     return 1
 
-# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter `*args` of function `f`; expected type `int`"
+# error: 15 [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["foo"]`"
 reveal_type(f("foo"))  # revealed: int
 ```
 
@@ -105,7 +107,7 @@ reveal_type(f("foo"))  # revealed: int
 def f(x: int) -> int:
     return 1
 
-# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter `x` of function `f`; expected type `int`"
+# error: 15 [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["foo"]`"
 reveal_type(f(x="foo"))  # revealed: int
 ```
 
@@ -115,7 +117,7 @@ reveal_type(f(x="foo"))  # revealed: int
 def f(*, x: int) -> int:
     return 1
 
-# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter `x` of function `f`; expected type `int`"
+# error: 15 [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["foo"]`"
 reveal_type(f(x="foo"))  # revealed: int
 ```
 
@@ -125,7 +127,7 @@ reveal_type(f(x="foo"))  # revealed: int
 def f(**kwargs: int) -> int:
     return 1
 
-# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter `**kwargs` of function `f`; expected type `int`"
+# error: 15 [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["foo"]`"
 reveal_type(f(x="foo"))  # revealed: int
 ```
 
@@ -135,8 +137,8 @@ reveal_type(f(x="foo"))  # revealed: int
 def f(x: int = 1, y: str = "foo") -> int:
     return 1
 
-# error: 15 [invalid-argument-type] "Object of type `Literal[2]` cannot be assigned to parameter `y` of function `f`; expected type `str`"
-# error: 20 [invalid-argument-type] "Object of type `Literal["bar"]` cannot be assigned to parameter `x` of function `f`; expected type `int`"
+# error: 15 [invalid-argument-type] "Argument to this function is incorrect: Expected `str`, found `Literal[2]`"
+# error: 20 [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["bar"]`"
 reveal_type(f(y=2, x="bar"))  # revealed: int
 ```
 

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

@@ -56,10 +56,11 @@ We can access attributes on objects of all kinds:
 ```py
 import sys
 
-reveal_type(inspect.getattr_static(sys, "platform"))  # revealed: LiteralString
-reveal_type(inspect.getattr_static(inspect, "getattr_static"))  # revealed: Literal[getattr_static]
+reveal_type(inspect.getattr_static(sys, "dont_write_bytecode"))  # revealed: bool
+# revealed: def getattr_static(obj: object, attr: str, default: Any | None = ellipsis) -> Any
+reveal_type(inspect.getattr_static(inspect, "getattr_static"))
 
-reveal_type(inspect.getattr_static(1, "real"))  # revealed: Literal[real]
+reveal_type(inspect.getattr_static(1, "real"))  # revealed: property
 ```
 
 (Implicit) instance attributes can also be accessed through `inspect.getattr_static`:
@@ -114,7 +115,7 @@ inspect.getattr_static()
 # error: [missing-argument] "No argument provided for required parameter `attr`"
 inspect.getattr_static(C())
 
-# error: [invalid-argument-type] "Object of type `Literal[1]` cannot be assigned to parameter 2 (`attr`) of function `getattr_static`; expected type `str`"
+# error: [invalid-argument-type] "Argument to this function is incorrect: Expected `str`, found `Literal[1]`"
 inspect.getattr_static(C(), 1)
 
 # error: [too-many-positional-arguments] "Too many positional arguments to function `getattr_static`: expected 3, got 4"
@@ -143,8 +144,9 @@ from typing import Any
 def _(a: Any, tuple_of_any: tuple[Any]):
     reveal_type(inspect.getattr_static(a, "x", "default"))  # revealed: Any | Literal["default"]
 
-    # TODO: Ideally, this would just be `Literal[index]`
-    reveal_type(inspect.getattr_static(tuple_of_any, "index", "default"))  # revealed: Literal[index] | Literal["default"]
+    # TODO: Ideally, this would just be `def index(self, value: Any, start: SupportsIndex = Literal[0], stop: SupportsIndex = int, /) -> int`
+    # revealed: (def index(self, value: Any, start: SupportsIndex = Literal[0], stop: SupportsIndex = int, /) -> int) | Literal["default"]
+    reveal_type(inspect.getattr_static(tuple_of_any, "index", "default"))
 ```
 
 [official documentation]: https://docs.python.org/3/library/inspect.html#inspect.getattr_static

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

@@ -24,7 +24,7 @@ to the valid order:
 def f(**kw: int, x: str) -> int:
     return 1
 
-# error: 15 [invalid-argument-type] "Object of type `Literal[1]` cannot be assigned to parameter 1 (`x`) of function `f`; expected type `str`"
+# error: 15 [invalid-argument-type] "Argument to this function is incorrect: Expected `str`, found `Literal[1]`"
 reveal_type(f(1))  # revealed: int
 ```
 
@@ -38,7 +38,7 @@ def f(x: int = 1, y: str) -> int:
     return 1
 
 reveal_type(f(y="foo"))  # revealed: int
-# error: [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 1 (`x`) of function `f`; expected type `int`"
+# error: [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["foo"]`"
 # error: [missing-argument] "No argument provided for required parameter `y` of function `f`"
 reveal_type(f("foo"))  # revealed: int
 ```

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

@@ -32,20 +32,20 @@ the latter case, it returns a *bound method* object:
 ```py
 from inspect import getattr_static
 
-reveal_type(getattr_static(C, "f"))  # revealed: Literal[f]
+reveal_type(getattr_static(C, "f"))  # revealed: def f(self, x: int) -> str
 
 reveal_type(getattr_static(C, "f").__get__)  # revealed: <method-wrapper `__get__` of `f`>
 
-reveal_type(getattr_static(C, "f").__get__(None, C))  # revealed: Literal[f]
-reveal_type(getattr_static(C, "f").__get__(C(), C))  # revealed: <bound method `f` of `C`>
+reveal_type(getattr_static(C, "f").__get__(None, C))  # revealed: def f(self, x: int) -> str
+reveal_type(getattr_static(C, "f").__get__(C(), C))  # revealed: bound method C.f(x: int) -> str
 ```
 
 In conclusion, this is why we see the following two types when accessing the `f` attribute on the
 class object `C` and on an instance `C()`:
 
 ```py
-reveal_type(C.f)  # revealed: Literal[f]
-reveal_type(C().f)  # revealed: <bound method `f` of `C`>
+reveal_type(C.f)  # revealed: def f(self, x: int) -> str
+reveal_type(C().f)  # revealed: bound method C.f(x: int) -> str
 ```
 
 A bound method is a callable object that contains a reference to the `instance` that it was called
@@ -56,7 +56,7 @@ via `__func__`):
 bound_method = C().f
 
 reveal_type(bound_method.__self__)  # revealed: C
-reveal_type(bound_method.__func__)  # revealed: Literal[f]
+reveal_type(bound_method.__func__)  # revealed: def f(self, x: int) -> str
 ```
 
 When we call the bound method, the `instance` is implicitly passed as the first argument (`self`):
@@ -80,13 +80,13 @@ When we access methods from derived classes, they will be bound to instances of
 class D(C):
     pass
 
-reveal_type(D().f)  # revealed: <bound method `f` of `D`>
+reveal_type(D().f)  # revealed: bound method D.f(x: int) -> str
 ```
 
 If we access an attribute on a bound method object itself, it will defer to `types.MethodType`:
 
 ```py
-reveal_type(bound_method.__hash__)  # revealed: <bound method `__hash__` of `MethodType`>
+reveal_type(bound_method.__hash__)  # revealed: bound method MethodType.__hash__() -> int
 ```
 
 If an attribute is not available on the bound method object, it will be looked up on the underlying
@@ -94,7 +94,7 @@ function object. We model this explicitly, which means that we can access `__kwd
 methods, even though it is not available on `types.MethodType`:
 
 ```py
-reveal_type(bound_method.__kwdefaults__)  # revealed: @Todo(generics) | None
+reveal_type(bound_method.__kwdefaults__)  # revealed: @Todo(specialized non-generic class) | None
 ```
 
 ## Basic method calls on class objects and instances
@@ -181,10 +181,10 @@ class B:
         return "a"
 
 def f(a_or_b: A | B, any_or_a: Any | A):
-    reveal_type(a_or_b.f)  # revealed: <bound method `f` of `A`> | <bound method `f` of `B`>
+    reveal_type(a_or_b.f)  # revealed: (bound method A.f() -> int) | (bound method B.f() -> str)
     reveal_type(a_or_b.f())  # revealed: int | str
 
-    reveal_type(any_or_a.f)  # revealed: Any | <bound method `f` of `A`>
+    reveal_type(any_or_a.f)  # revealed: Any | (bound method A.f() -> int)
     reveal_type(any_or_a.f())  # revealed: Any | int
 ```
 
@@ -198,7 +198,7 @@ python-version = "3.12"
 ```py
 type IntOrStr = int | str
 
-reveal_type(IntOrStr.__or__)  # revealed: <bound method `__or__` of `typing.TypeAliasType`>
+reveal_type(IntOrStr.__or__)  # revealed: bound method typing.TypeAliasType.__or__(right: Any) -> _SpecialForm
 ```
 
 ## Error cases: Calling `__get__` for methods
@@ -270,7 +270,7 @@ class Meta(type):
 class C(metaclass=Meta):
     pass
 
-reveal_type(C.f)  # revealed: <bound method `f` of `Literal[C]`>
+reveal_type(C.f)  # revealed: bound method Literal[C].f(arg: int) -> str
 reveal_type(C.f(1))  # revealed: str
 ```
 
@@ -322,8 +322,8 @@ class C:
     def f(cls: type[C], x: int) -> str:
         return "a"
 
-reveal_type(C.f)  # revealed: <bound method `f` of `Literal[C]`>
-reveal_type(C().f)  # revealed: <bound method `f` of `type[C]`>
+reveal_type(C.f)  # revealed: bound method Literal[C].f(x: int) -> str
+reveal_type(C().f)  # revealed: bound method type[C].f(x: int) -> str
 ```
 
 The `cls` method argument is then implicitly passed as the first argument when calling the method:
@@ -350,7 +350,7 @@ class D:
         # This function is wrongly annotated, it should be `type[D]` instead of `D`
         pass
 
-# error: [invalid-argument-type] "Object of type `Literal[D]` cannot be assigned to parameter 1 (`cls`) of bound method `f`; expected type `D`"
+# error: [invalid-argument-type] "Argument to this function is incorrect: Expected `D`, found `Literal[D]`"
 D.f()
 ```
 
@@ -360,8 +360,8 @@ When a class method is accessed on a derived class, it is bound to that derived
 class Derived(C):
     pass
 
-reveal_type(Derived.f)  # revealed: <bound method `f` of `Literal[Derived]`>
-reveal_type(Derived().f)  # revealed: <bound method `f` of `type[Derived]`>
+reveal_type(Derived.f)  # revealed: bound method Literal[Derived].f(x: int) -> str
+reveal_type(Derived().f)  # revealed: bound method type[Derived].f(x: int) -> str
 
 reveal_type(Derived.f(1))  # revealed: str
 reveal_type(Derived().f(1))  # revealed: str
@@ -379,26 +379,31 @@ class C:
     @classmethod
     def f(cls): ...
 
-reveal_type(getattr_static(C, "f"))  # revealed: Literal[f]
+reveal_type(getattr_static(C, "f"))  # revealed: def f(cls) -> Unknown
 reveal_type(getattr_static(C, "f").__get__)  # revealed: <method-wrapper `__get__` of `f`>
 ```
 
 But we correctly model how the `classmethod` descriptor works:
 
 ```py
-reveal_type(getattr_static(C, "f").__get__(None, C))  # revealed: <bound method `f` of `Literal[C]`>
-reveal_type(getattr_static(C, "f").__get__(C(), C))  # revealed: <bound method `f` of `Literal[C]`>
-reveal_type(getattr_static(C, "f").__get__(C()))  # revealed: <bound method `f` of `type[C]`>
+reveal_type(getattr_static(C, "f").__get__(None, C))  # revealed: bound method Literal[C].f() -> Unknown
+reveal_type(getattr_static(C, "f").__get__(C(), C))  # revealed: bound method Literal[C].f() -> Unknown
+reveal_type(getattr_static(C, "f").__get__(C()))  # revealed: bound method type[C].f() -> Unknown
 ```
 
 The `owner` argument takes precedence over the `instance` argument:
 
 ```py
-reveal_type(getattr_static(C, "f").__get__("dummy", C))  # revealed: <bound method `f` of `Literal[C]`>
+reveal_type(getattr_static(C, "f").__get__("dummy", C))  # revealed: bound method Literal[C].f() -> Unknown
 ```
 
 ### Classmethods mixed with other decorators
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 When a `@classmethod` is additionally decorated with another decorator, it is still treated as a
 class method:
 
@@ -419,14 +424,10 @@ class C:
     def f2(cls: type[C], x: int) -> str:
         return "a"
 
-# TODO: We do not support decorators yet (only limited special cases). Eventually,
-# these should all return `str`:
-
-reveal_type(C.f1(1))  # revealed: @Todo(return type of decorated function)
-reveal_type(C().f1(1))  # revealed: @Todo(return type of decorated function)
-
-reveal_type(C.f2(1))  # revealed: @Todo(return type of decorated function)
-reveal_type(C().f2(1))  # revealed: @Todo(return type of decorated function)
+reveal_type(C.f1(1))  # revealed: str
+reveal_type(C().f1(1))  # revealed: str
+reveal_type(C.f2(1))  # revealed: str
+reveal_type(C().f2(1))  # revealed: str
 ```
 
 [functions and methods]: https://docs.python.org/3/howto/descriptor.html#functions-and-methods

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

@@ -0,0 +1,50 @@
+# `str.startswith`
+
+We special-case `str.startswith` to allow inference of precise Boolean literal types, because those
+are used in [`sys.platform` checks].
+
+```py
+reveal_type("abc".startswith(""))  # revealed: Literal[True]
+reveal_type("abc".startswith("a"))  # revealed: Literal[True]
+reveal_type("abc".startswith("ab"))  # revealed: Literal[True]
+reveal_type("abc".startswith("abc"))  # revealed: Literal[True]
+
+reveal_type("abc".startswith("abcd"))  # revealed: Literal[False]
+reveal_type("abc".startswith("bc"))  # revealed: Literal[False]
+
+reveal_type("AbC".startswith(""))  # revealed: Literal[True]
+reveal_type("AbC".startswith("A"))  # revealed: Literal[True]
+reveal_type("AbC".startswith("Ab"))  # revealed: Literal[True]
+reveal_type("AbC".startswith("AbC"))  # revealed: Literal[True]
+
+reveal_type("AbC".startswith("a"))  # revealed: Literal[False]
+reveal_type("AbC".startswith("aB"))  # revealed: Literal[False]
+
+reveal_type("".startswith(""))  # revealed: Literal[True]
+
+reveal_type("".startswith(" "))  # revealed: Literal[False]
+```
+
+Make sure that we fall back to `bool` for more complex cases:
+
+```py
+reveal_type("abc".startswith("b", 1))  # revealed: bool
+reveal_type("abc".startswith("bc", 1, 3))  # revealed: bool
+
+reveal_type("abc".startswith(("a", "x")))  # revealed: bool
+```
+
+And similiarly, we should still infer `bool` if the instance or the prefix are not string literals:
+
+```py
+from typing_extensions import LiteralString
+
+def _(string_instance: str, literalstring: LiteralString):
+    reveal_type(string_instance.startswith("a"))  # revealed: bool
+    reveal_type(literalstring.startswith("a"))  # revealed: bool
+
+    reveal_type("a".startswith(string_instance))  # revealed: bool
+    reveal_type("a".startswith(literalstring))  # revealed: bool
+```
+
+[`sys.platform` checks]: https://docs.python.org/3/library/sys.html#sys.platform

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

@@ -20,9 +20,11 @@ class C:
 def _(subclass_of_c: type[C]):
     reveal_type(subclass_of_c(1))  # revealed: C
 
-    # TODO: Those should all be errors
+    # error: [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `Literal["a"]`"
     reveal_type(subclass_of_c("a"))  # revealed: C
+    # error: [missing-argument] "No argument provided for required parameter `x` of bound method `__init__`"
     reveal_type(subclass_of_c())  # revealed: C
+    # error: [too-many-positional-arguments] "Too many positional arguments to bound method `__init__`: expected 1, got 2"
     reveal_type(subclass_of_c(1, 2))  # revealed: C
 ```
 

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

@@ -40,7 +40,7 @@ def _(flag: bool):
         def f() -> int:
             return 1
     x = f()  # error: [call-non-callable] "Object of type `Literal[1]` is not callable"
-    reveal_type(x)  # revealed: int | Unknown
+    reveal_type(x)  # revealed: Unknown | int
 ```
 
 ## Multiple non-callable elements in a union
@@ -58,7 +58,7 @@ def _(flag: bool, flag2: bool):
             return 1
     # TODO we should mention all non-callable elements of the union
     # error: [call-non-callable] "Object of type `Literal[1]` is not callable"
-    # revealed: int | Unknown
+    # revealed: Unknown | int
     reveal_type(f())
 ```
 
@@ -94,7 +94,7 @@ def _(flag: bool):
     else:
         f = f2
 
-    # error: [invalid-argument-type] "Object of type `Literal[3]` cannot be assigned to parameter 1 (`a`) of function `f2`; expected type `str`"
+    # error: [invalid-argument-type] "Argument to this function is incorrect: Expected `str`, found `Literal[3]`"
     x = f(3)
     reveal_type(x)  # revealed: int | str
 ```
@@ -148,3 +148,68 @@ def _(flag: bool):
     x = f(3)
     reveal_type(x)  # revealed: Unknown
 ```
+
+## Union including a special-cased function
+
+```py
+def _(flag: bool):
+    if flag:
+        f = str
+    else:
+        f = repr
+    reveal_type(str("string"))  # revealed: Literal["string"]
+    reveal_type(repr("string"))  # revealed: Literal["'string'"]
+    reveal_type(f("string"))  # revealed: Literal["string", "'string'"]
+```
+
+## Cannot use an argument as both a value and a type form
+
+```py
+from knot_extensions import is_fully_static
+
+def _(flag: bool):
+    if flag:
+        f = repr
+    else:
+        f = is_fully_static
+    # error: [conflicting-argument-forms] "Argument is used as both a value and a type form in call"
+    reveal_type(f(int))  # revealed: str | Literal[True]
+```
+
+## Size limit on unions of literals
+
+Beyond a certain size, large unions of literal types collapse to their nearest super-type (`int`,
+`bytes`, `str`).
+
+```py
+from typing import Literal
+
+def _(literals_2: Literal[0, 1], b: bool, flag: bool):
+    literals_4 = 2 * literals_2 + literals_2  # Literal[0, 1, 2, 3]
+    literals_16 = 4 * literals_4 + literals_4  # Literal[0, 1, .., 15]
+    literals_64 = 4 * literals_16 + literals_4  # Literal[0, 1, .., 63]
+    literals_128 = 2 * literals_64 + literals_2  # Literal[0, 1, .., 127]
+
+    # Going beyond the MAX_UNION_LITERALS limit (currently 200):
+    literals_256 = 16 * literals_16 + literals_16
+    reveal_type(literals_256)  # revealed: int
+
+    # Going beyond the limit when another type is already part of the union
+    bool_and_literals_128 = b if flag else literals_128  # bool | Literal[0, 1, ..., 127]
+    literals_128_shifted = literals_128 + 128  # Literal[128, 129, ..., 255]
+
+    # Now union the two:
+    reveal_type(bool_and_literals_128 if flag else literals_128_shifted)  # revealed: int
+```
+
+## Simplifying gradually-equivalent types
+
+If two types are gradually equivalent, we can keep just one of them in a union:
+
+```py
+from typing import Any, Union
+from knot_extensions import Intersection, Not
+
+def _(x: Union[Intersection[Any, Not[int]], Intersection[Any, Not[int]]]):
+    reveal_type(x)  # revealed: Any & ~int
+```

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

@@ -0,0 +1,410 @@
+# Super
+
+Python defines the terms *bound super object* and *unbound super object*.
+
+An **unbound super object** is created when `super` is called with only one argument. (e.g.
+`super(A)`). This object may later be bound using the `super.__get__` method. However, this form is
+rarely used in practice.
+
+A **bound super object** is created either by calling `super(pivot_class, owner)` or by using the
+implicit form `super()`, where both the pivot class and the owner are inferred. This is the most
+common usage.
+
+## Basic Usage
+
+### Explicit Super Object
+
+`super(pivot_class, owner)` performs attribute lookup along the MRO, starting immediately after the
+specified pivot class.
+
+```py
+class A:
+    def a(self): ...
+    aa: int = 1
+
+class B(A):
+    def b(self): ...
+    bb: int = 2
+
+class C(B):
+    def c(self): ...
+    cc: int = 3
+
+reveal_type(C.__mro__)  # revealed: tuple[Literal[C], Literal[B], Literal[A], Literal[object]]
+
+super(C, C()).a
+super(C, C()).b
+# error: [unresolved-attribute] "Type `<super: Literal[C], C>` has no attribute `c`"
+super(C, C()).c
+
+super(B, C()).a
+# error: [unresolved-attribute] "Type `<super: Literal[B], C>` has no attribute `b`"
+super(B, C()).b
+# error: [unresolved-attribute] "Type `<super: Literal[B], C>` has no attribute `c`"
+super(B, C()).c
+
+# error: [unresolved-attribute] "Type `<super: Literal[A], C>` has no attribute `a`"
+super(A, C()).a
+# error: [unresolved-attribute] "Type `<super: Literal[A], C>` has no attribute `b`"
+super(A, C()).b
+# error: [unresolved-attribute] "Type `<super: Literal[A], C>` has no attribute `c`"
+super(A, C()).c
+
+reveal_type(super(C, C()).a)  # revealed: bound method C.a() -> Unknown
+reveal_type(super(C, C()).b)  # revealed: bound method C.b() -> Unknown
+reveal_type(super(C, C()).aa)  # revealed: int
+reveal_type(super(C, C()).bb)  # revealed: int
+```
+
+### Implicit Super Object
+
+The implicit form `super()` is same as `super(__class__, <first argument>)`. The `__class__` refers
+to the class that contains the function where `super()` is used. The first argument refers to the
+current method’s first parameter (typically `self` or `cls`).
+
+```py
+from __future__ import annotations
+
+class A:
+    def __init__(self, a: int): ...
+    @classmethod
+    def f(cls): ...
+
+class B(A):
+    def __init__(self, a: int):
+        # TODO: Once `Self` is supported, this should be `<super: Literal[B], B>`
+        reveal_type(super())  # revealed: <super: Literal[B], Unknown>
+        super().__init__(a)
+
+    @classmethod
+    def f(cls):
+        # TODO: Once `Self` is supported, this should be `<super: Literal[B], Literal[B]>`
+        reveal_type(super())  # revealed: <super: Literal[B], Unknown>
+        super().f()
+
+super(B, B(42)).__init__(42)
+super(B, B).f()
+```
+
+### Unbound Super Object
+
+Calling `super(cls)` without a second argument returns an *unbound super object*. This is treated as
+a plain `super` instance and does not support name lookup via the MRO.
+
+```py
+class A:
+    a: int = 42
+
+class B(A): ...
+
+reveal_type(super(B))  # revealed: super
+
+# error: [unresolved-attribute] "Type `super` has no attribute `a`"
+super(B).a
+```
+
+## Attribute Assignment
+
+`super()` objects do not allow attribute assignment — even if the attribute is resolved
+successfully.
+
+```py
+class A:
+    a: int = 3
+
+class B(A): ...
+
+reveal_type(super(B, B()).a)  # revealed: int
+# error: [invalid-assignment] "Cannot assign to attribute `a` on type `<super: Literal[B], B>`"
+super(B, B()).a = 3
+# error: [invalid-assignment] "Cannot assign to attribute `a` on type `super`"
+super(B).a = 5
+```
+
+## Dynamic Types
+
+If any of the arguments is dynamic, we cannot determine the MRO to traverse. When accessing a
+member, it should effectively behave like a dynamic type.
+
+```py
+class A:
+    a: int = 1
+
+def f(x):
+    reveal_type(x)  # revealed: Unknown
+
+    reveal_type(super(x, x))  # revealed: <super: Unknown, Unknown>
+    reveal_type(super(A, x))  # revealed: <super: Literal[A], Unknown>
+    reveal_type(super(x, A()))  # revealed: <super: Unknown, A>
+
+    reveal_type(super(x, x).a)  # revealed: Unknown
+    reveal_type(super(A, x).a)  # revealed: Unknown
+    reveal_type(super(x, A()).a)  # revealed: Unknown
+```
+
+## Implicit `super()` in Complex Structure
+
+```py
+from __future__ import annotations
+
+class A:
+    def test(self):
+        reveal_type(super())  # revealed: <super: Literal[A], Unknown>
+
+    class B:
+        def test(self):
+            reveal_type(super())  # revealed: <super: Literal[B], Unknown>
+
+            class C(A.B):
+                def test(self):
+                    reveal_type(super())  # revealed: <super: Literal[C], Unknown>
+
+            def inner(t: C):
+                reveal_type(super())  # revealed: <super: Literal[B], C>
+            lambda x: reveal_type(super())  # revealed: <super: Literal[B], Unknown>
+```
+
+## Built-ins and Literals
+
+```py
+reveal_type(super(bool, True))  # revealed: <super: Literal[bool], bool>
+reveal_type(super(bool, bool()))  # revealed: <super: Literal[bool], bool>
+reveal_type(super(int, bool()))  # revealed: <super: Literal[int], bool>
+reveal_type(super(int, 3))  # revealed: <super: Literal[int], int>
+reveal_type(super(str, ""))  # revealed: <super: Literal[str], str>
+```
+
+## Descriptor Behavior with Super
+
+Accessing attributes through `super` still invokes descriptor protocol. However, the behavior can
+differ depending on whether the second argument to `super` is a class or an instance.
+
+```py
+class A:
+    def a1(self): ...
+    @classmethod
+    def a2(cls): ...
+
+class B(A): ...
+
+# A.__dict__["a1"].__get__(B(), B)
+reveal_type(super(B, B()).a1)  # revealed: bound method B.a1() -> Unknown
+# A.__dict__["a2"].__get__(B(), B)
+reveal_type(super(B, B()).a2)  # revealed: bound method type[B].a2() -> Unknown
+
+# A.__dict__["a1"].__get__(None, B)
+reveal_type(super(B, B).a1)  # revealed: def a1(self) -> Unknown
+# A.__dict__["a2"].__get__(None, B)
+reveal_type(super(B, B).a2)  # revealed: bound method Literal[B].a2() -> Unknown
+```
+
+## Union of Supers
+
+When the owner is a union type, `super()` is built separately for each branch, and the resulting
+super objects are combined into a union.
+
+```py
+class A: ...
+
+class B:
+    b: int = 42
+
+class C(A, B): ...
+class D(B, A): ...
+
+def f(x: C | D):
+    reveal_type(C.__mro__)  # revealed: tuple[Literal[C], Literal[A], Literal[B], Literal[object]]
+    reveal_type(D.__mro__)  # revealed: tuple[Literal[D], Literal[B], Literal[A], Literal[object]]
+
+    s = super(A, x)
+    reveal_type(s)  # revealed: <super: Literal[A], C> | <super: Literal[A], D>
+
+    # error: [possibly-unbound-attribute] "Attribute `b` on type `<super: Literal[A], C> | <super: Literal[A], D>` is possibly unbound"
+    s.b
+
+def f(flag: bool):
+    x = str() if flag else str("hello")
+    reveal_type(x)  # revealed: Literal["", "hello"]
+    reveal_type(super(str, x))  # revealed: <super: Literal[str], str>
+
+def f(x: int | str):
+    # error: [invalid-super-argument] "`str` is not an instance or subclass of `Literal[int]` in `super(Literal[int], str)` call"
+    super(int, x)
+```
+
+Even when `super()` is constructed separately for each branch of a union, it should behave correctly
+in all cases.
+
+```py
+def f(flag: bool):
+    if flag:
+        class A:
+            x = 1
+            y: int = 1
+
+            a: str = "hello"
+
+        class B(A): ...
+        s = super(B, B())
+    else:
+        class C:
+            x = 2
+            y: int | str = "test"
+
+        class D(C): ...
+        s = super(D, D())
+
+    reveal_type(s)  # revealed: <super: Literal[B], B> | <super: Literal[D], D>
+
+    reveal_type(s.x)  # revealed: Unknown | Literal[1, 2]
+    reveal_type(s.y)  # revealed: int | str
+
+    # error: [possibly-unbound-attribute] "Attribute `a` on type `<super: Literal[B], B> | <super: Literal[D], D>` is possibly unbound"
+    reveal_type(s.a)  # revealed: str
+```
+
+## Supers with Generic Classes
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+from knot_extensions import TypeOf, static_assert, is_subtype_of
+
+class A[T]:
+    def f(self, a: T) -> T:
+        return a
+
+class B[T](A[T]):
+    def f(self, b: T) -> T:
+        return super().f(b)
+```
+
+## Invalid Usages
+
+### Unresolvable `super()` Calls
+
+If an appropriate class and argument cannot be found, a runtime error will occur.
+
+```py
+from __future__ import annotations
+
+# error: [unavailable-implicit-super-arguments] "Cannot determine implicit arguments for 'super()' in this context"
+reveal_type(super())  # revealed: Unknown
+
+def f():
+    # error: [unavailable-implicit-super-arguments] "Cannot determine implicit arguments for 'super()' in this context"
+    super()
+
+# No first argument in its scope
+class A:
+    # error: [unavailable-implicit-super-arguments] "Cannot determine implicit arguments for 'super()' in this context"
+    s = super()
+
+    def f(self):
+        def g():
+            # error: [unavailable-implicit-super-arguments] "Cannot determine implicit arguments for 'super()' in this context"
+            super()
+        # error: [unavailable-implicit-super-arguments] "Cannot determine implicit arguments for 'super()' in this context"
+        lambda: super()
+
+        # error: [unavailable-implicit-super-arguments] "Cannot determine implicit arguments for 'super()' in this context"
+        (super() for _ in range(10))
+
+    @staticmethod
+    def h():
+        # error: [unavailable-implicit-super-arguments] "Cannot determine implicit arguments for 'super()' in this context"
+        super()
+```
+
+### Failing Condition Checks
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+`super()` requires its first argument to be a valid class, and its second argument to be either an
+instance or a subclass of the first. If either condition is violated, a `TypeError` is raised at
+runtime.
+
+```py
+def f(x: int):
+    # error: [invalid-super-argument] "`int` is not a valid class"
+    super(x, x)
+
+    type IntAlias = int
+    # error: [invalid-super-argument] "`typing.TypeAliasType` is not a valid class"
+    super(IntAlias, 0)
+
+# error: [invalid-super-argument] "`Literal[""]` is not an instance or subclass of `Literal[int]` in `super(Literal[int], Literal[""])` call"
+# revealed: Unknown
+reveal_type(super(int, str()))
+
+# error: [invalid-super-argument] "`Literal[str]` is not an instance or subclass of `Literal[int]` in `super(Literal[int], Literal[str])` call"
+# revealed: Unknown
+reveal_type(super(int, str))
+
+class A: ...
+class B(A): ...
+
+# error: [invalid-super-argument] "`A` is not an instance or subclass of `Literal[B]` in `super(Literal[B], A)` call"
+# revealed: Unknown
+reveal_type(super(B, A()))
+
+# error: [invalid-super-argument] "`object` is not an instance or subclass of `Literal[B]` in `super(Literal[B], object)` call"
+# revealed: Unknown
+reveal_type(super(B, object()))
+
+# error: [invalid-super-argument] "`Literal[A]` is not an instance or subclass of `Literal[B]` in `super(Literal[B], Literal[A])` call"
+# revealed: Unknown
+reveal_type(super(B, A))
+
+# error: [invalid-super-argument] "`Literal[object]` is not an instance or subclass of `Literal[B]` in `super(Literal[B], Literal[object])` call"
+# revealed: Unknown
+reveal_type(super(B, object))
+
+super(object, object()).__class__
+```
+
+### Instance Member Access via `super`
+
+Accessing instance members through `super()` is not allowed.
+
+```py
+from __future__ import annotations
+
+class A:
+    def __init__(self, a: int):
+        self.a = a
+
+class B(A):
+    def __init__(self, a: int):
+        super().__init__(a)
+        # TODO: Once `Self` is supported, this should raise `unresolved-attribute` error
+        super().a
+
+# error: [unresolved-attribute] "Type `<super: Literal[B], B>` has no attribute `a`"
+super(B, B(42)).a
+```
+
+### Dunder Method Resolution
+
+Dunder methods defined in the `owner` (from `super(pivot_class, owner)`) should not affect the super
+object itself. In other words, `super` should not be treated as if it inherits attributes of the
+`owner`.
+
+```py
+class A:
+    def __getitem__(self, key: int) -> int:
+        return 42
+
+class B(A): ...
+
+reveal_type(A()[0])  # revealed: int
+reveal_type(super(B, B()).__getitem__)  # revealed: bound method B.__getitem__(key: int) -> int
+# error: [non-subscriptable] "Cannot subscript object of type `<super: Literal[B], B>` with no `__getitem__` method"
+super(B, B())[0]
+```

crates/red_knot_python_semantic/resources/mdtest/comparison/instances/membership_test.md

@@ -191,7 +191,7 @@ It may also be more appropriate to use `unsupported-operator` as the error code.
 
 ```py
 class NotBoolable:
-    __bool__ = 3
+    __bool__: int = 3
 
 class WithContains:
     def __contains__(self, item) -> NotBoolable:

crates/red_knot_python_semantic/resources/mdtest/comparison/instances/rich_comparison.md

@@ -355,7 +355,7 @@ element) of a chained comparison.
 
 ```py
 class NotBoolable:
-    __bool__ = 3
+    __bool__: int = 3
 
 class Comparable:
     def __lt__(self, item) -> NotBoolable:

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

@@ -50,13 +50,17 @@ reveal_type(x)  # revealed: LiteralString
 if x != "abc":
     reveal_type(x)  # revealed: LiteralString & ~Literal["abc"]
 
-    reveal_type(x == "abc")  # revealed: Literal[False]
-    reveal_type("abc" == x)  # revealed: Literal[False]
+    # TODO: This should be `Literal[False]`
+    reveal_type(x == "abc")  # revealed: bool
+    # TODO: This should be `Literal[False]`
+    reveal_type("abc" == x)  # revealed: bool
     reveal_type(x == "something else")  # revealed: bool
     reveal_type("something else" == x)  # revealed: bool
 
-    reveal_type(x != "abc")  # revealed: Literal[True]
-    reveal_type("abc" != x)  # revealed: Literal[True]
+    # TODO: This should be `Literal[True]`
+    reveal_type(x != "abc")  # revealed: bool
+    # TODO: This should be `Literal[True]`
+    reveal_type("abc" != x)  # revealed: bool
     reveal_type(x != "something else")  # revealed: bool
     reveal_type("something else" != x)  # revealed: bool
 
@@ -79,10 +83,10 @@ def _(x: int):
     if x != 1:
         reveal_type(x)  # revealed: int & ~Literal[1]
 
-        reveal_type(x != 1)  # revealed: Literal[True]
+        reveal_type(x != 1)  # revealed: bool
         reveal_type(x != 2)  # revealed: bool
 
-        reveal_type(x == 1)  # revealed: Literal[False]
+        reveal_type(x == 1)  # revealed: bool
         reveal_type(x == 2)  # revealed: bool
 ```
 

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

@@ -355,7 +355,7 @@ def compute_chained_comparison():
 
 ```py
 class NotBoolable:
-    __bool__ = 5
+    __bool__: int = 5
 
 class Comparable:
     def __lt__(self, other) -> NotBoolable:
@@ -382,13 +382,13 @@ arbitrary objects to a `bool`, but a comparison of tuples will fail if the resul
 pair of elements at equivalent positions cannot be converted to a `bool`:
 
 ```py
+class NotBoolable:
+    __bool__: None = None
+
 class A:
     def __eq__(self, other) -> NotBoolable:
         return NotBoolable()
 
-class NotBoolable:
-    __bool__ = None
-
 # error: [unsupported-bool-conversion]
 (A(),) == (A(),)
 ```

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

@@ -40,7 +40,7 @@ def _(flag: bool):
 
 ```py
 class NotBoolable:
-    __bool__ = 3
+    __bool__: int = 3
 
 # error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable"
 3 if NotBoolable() else 4

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

@@ -152,7 +152,7 @@ def _(flag: bool):
 
 ```py
 class NotBoolable:
-    __bool__ = 3
+    __bool__: int = 3
 
 # error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable"
 if NotBoolable():

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

@@ -1,5 +1,10 @@
 # Pattern matching
 
+```toml
+[environment]
+python-version = "3.10"
+```
+
 ## With wildcard
 
 ```py
@@ -44,11 +49,245 @@ def _(target: int):
     reveal_type(y)  # revealed: Literal[2, 3, 4]
 ```
 
+## Value match
+
+A value pattern matches based on equality: the first `case` branch here will be taken if `subject`
+is equal to `2`, even if `subject` is not an instance of `int`. We can't know whether `C` here has a
+custom `__eq__` implementation that might cause it to compare equal to `2`, so we have to consider
+the possibility that the `case` branch might be taken even though the type `C` is disjoint from the
+type `Literal[2]`.
+
+This leads us to infer `Literal[1, 3]` as the type of `y` after the `match` statement, rather than
+`Literal[1]`:
+
+```py
+from typing import final
+
+@final
+class C:
+    pass
+
+def _(subject: C):
+    y = 1
+    match subject:
+        case 2:
+            y = 3
+    reveal_type(y)  # revealed: Literal[1, 3]
+```
+
+## Class match
+
+A `case` branch with a class pattern is taken if the subject is an instance of the given class, and
+all subpatterns in the class pattern match.
+
+```py
+from typing import final
+
+class Foo:
+    pass
+
+class FooSub(Foo):
+    pass
+
+class Bar:
+    pass
+
+@final
+class Baz:
+    pass
+
+def _(target: FooSub):
+    y = 1
+
+    match target:
+        case Baz():
+            y = 2
+        case Foo():
+            y = 3
+        case Bar():
+            y = 4
+
+    reveal_type(y)  # revealed: Literal[3]
+
+def _(target: FooSub):
+    y = 1
+
+    match target:
+        case Baz():
+            y = 2
+        case Bar():
+            y = 3
+        case Foo():
+            y = 4
+
+    reveal_type(y)  # revealed: Literal[3, 4]
+
+def _(target: FooSub | str):
+    y = 1
+
+    match target:
+        case Baz():
+            y = 2
+        case Foo():
+            y = 3
+        case Bar():
+            y = 4
+
+    reveal_type(y)  # revealed: Literal[1, 3, 4]
+```
+
+## Singleton match
+
+Singleton patterns are matched based on identity, not equality comparisons or `isinstance()` checks.
+
+```py
+from typing import Literal
+
+def _(target: Literal[True, False]):
+    y = 1
+
+    match target:
+        case True:
+            y = 2
+        case False:
+            y = 3
+        case None:
+            y = 4
+
+    # TODO: with exhaustiveness checking, this should be Literal[2, 3]
+    reveal_type(y)  # revealed: Literal[1, 2, 3]
+
+def _(target: bool):
+    y = 1
+
+    match target:
+        case True:
+            y = 2
+        case False:
+            y = 3
+        case None:
+            y = 4
+
+    # TODO: with exhaustiveness checking, this should be Literal[2, 3]
+    reveal_type(y)  # revealed: Literal[1, 2, 3]
+
+def _(target: None):
+    y = 1
+
+    match target:
+        case True:
+            y = 2
+        case False:
+            y = 3
+        case None:
+            y = 4
+
+    reveal_type(y)  # revealed: Literal[4]
+
+def _(target: None | Literal[True]):
+    y = 1
+
+    match target:
+        case True:
+            y = 2
+        case False:
+            y = 3
+        case None:
+            y = 4
+
+    # TODO: with exhaustiveness checking, this should be Literal[2, 4]
+    reveal_type(y)  # revealed: Literal[1, 2, 4]
+
+# bool is an int subclass
+def _(target: int):
+    y = 1
+
+    match target:
+        case True:
+            y = 2
+        case False:
+            y = 3
+        case None:
+            y = 4
+
+    reveal_type(y)  # revealed: Literal[1, 2, 3]
+
+def _(target: str):
+    y = 1
+
+    match target:
+        case True:
+            y = 2
+        case False:
+            y = 3
+        case None:
+            y = 4
+
+    reveal_type(y)  # revealed: Literal[1]
+```
+
+## Or match
+
+A `|` pattern matches if any of the subpatterns match.
+
+```py
+from typing import Literal, final
+
+def _(target: Literal["foo", "baz"]):
+    y = 1
+
+    match target:
+        case "foo" | "bar":
+            y = 2
+        case "baz":
+            y = 3
+
+    # TODO: with exhaustiveness, this should be Literal[2, 3]
+    reveal_type(y)  # revealed: Literal[1, 2, 3]
+
+def _(target: None):
+    y = 1
+
+    match target:
+        case None | 3:
+            y = 2
+        case "foo" | 4 | True:
+            y = 3
+
+    reveal_type(y)  # revealed: Literal[2]
+
+@final
+class Baz:
+    pass
+
+def _(target: int | None | float):
+    y = 1
+
+    match target:
+        case None | 3:
+            y = 2
+        case Baz():
+            y = 3
+
+    reveal_type(y)  # revealed: Literal[1, 2]
+
+def _(target: None | str):
+    y = 1
+
+    match target:
+        case Baz() | True | False:
+            y = 2
+        case int():
+            y = 3
+
+    reveal_type(y)  # revealed: Literal[1, 3]
+```
+
 ## Guard with object that implements `__bool__` incorrectly
 
 ```py
 class NotBoolable:
-    __bool__ = 3
+    __bool__: int = 3
 
 def _(target: int, flag: NotBoolable):
     y = 1

crates/red_knot_python_semantic/resources/mdtest/dataclasses.md

@@ -0,0 +1,731 @@
+# Dataclasses
+
+## Basic
+
+Decorating a class with `@dataclass` is a convenient way to add special methods such as `__init__`,
+`__repr__`, and `__eq__` to a class. The following example shows the basic usage of the `@dataclass`
+decorator. By default, only the three mentioned methods are generated.
+
+```py
+from dataclasses import dataclass
+
+@dataclass
+class Person:
+    name: str
+    age: int | None = None
+
+alice1 = Person("Alice", 30)
+alice2 = Person(name="Alice", age=30)
+alice3 = Person(age=30, name="Alice")
+alice4 = Person("Alice", age=30)
+
+reveal_type(alice1)  # revealed: Person
+reveal_type(type(alice1))  # revealed: type[Person]
+
+reveal_type(alice1.name)  # revealed: str
+reveal_type(alice1.age)  # revealed: int | None
+
+reveal_type(repr(alice1))  # revealed: str
+
+reveal_type(alice1 == alice2)  # revealed: bool
+reveal_type(alice1 == "Alice")  # revealed: bool
+
+bob = Person("Bob")
+bob2 = Person("Bob", None)
+bob3 = Person(name="Bob")
+bob4 = Person(name="Bob", age=None)
+```
+
+The signature of the `__init__` method is generated based on the classes attributes. The following
+calls are not valid:
+
+```py
+# error: [missing-argument]
+Person()
+
+# error: [too-many-positional-arguments]
+Person("Eve", 20, "too many arguments")
+
+# error: [invalid-argument-type]
+Person("Eve", "string instead of int")
+
+# error: [invalid-argument-type]
+# error: [invalid-argument-type]
+Person(20, "Eve")
+```
+
+## Signature of `__init__`
+
+TODO: All of the following tests are missing the `self` argument in the `__init__` signature.
+
+Declarations in the class body are used to generate the signature of the `__init__` method. If the
+attributes are not just declarations, but also bindings, the type inferred from bindings is used as
+the default value.
+
+```py
+from dataclasses import dataclass
+
+@dataclass
+class D:
+    x: int
+    y: str = "default"
+    z: int | None = 1 + 2
+
+reveal_type(D.__init__)  # revealed: (x: int, y: str = Literal["default"], z: int | None = Literal[3]) -> None
+```
+
+This also works if the declaration and binding are split:
+
+```py
+@dataclass
+class D:
+    x: int | None
+    x = None
+
+reveal_type(D.__init__)  # revealed: (x: int | None = None) -> None
+```
+
+Non-fully static types are handled correctly:
+
+```py
+from typing import Any
+
+@dataclass
+class C:
+    x: Any
+    y: int | Any
+    z: tuple[int, Any]
+
+reveal_type(C.__init__)  # revealed: (x: Any, y: int | Any, z: tuple[int, Any]) -> None
+```
+
+Variables without annotations are ignored:
+
+```py
+@dataclass
+class D:
+    x: int
+    y = 1
+
+reveal_type(D.__init__)  # revealed: (x: int) -> None
+```
+
+If attributes without default values are declared after attributes with default values, a
+`TypeError` will be raised at runtime. Ideally, we would emit a diagnostic in that case:
+
+```py
+@dataclass
+class D:
+    x: int = 1
+    # TODO: this should be an error: field without default defined after field with default
+    y: str
+```
+
+Pure class attributes (`ClassVar`) are not included in the signature of `__init__`:
+
+```py
+from typing import ClassVar
+
+@dataclass
+class D:
+    x: int
+    y: ClassVar[str] = "default"
+    z: bool
+
+reveal_type(D.__init__)  # revealed: (x: int, z: bool) -> None
+
+d = D(1, True)
+reveal_type(d.x)  # revealed: int
+reveal_type(d.y)  # revealed: str
+reveal_type(d.z)  # revealed: bool
+```
+
+Function declarations do not affect the signature of `__init__`:
+
+```py
+@dataclass
+class D:
+    x: int
+
+    def y(self) -> str:
+        return ""
+
+reveal_type(D.__init__)  # revealed: (x: int) -> None
+```
+
+And neither do nested class declarations:
+
+```py
+@dataclass
+class D:
+    x: int
+
+    class Nested:
+        y: str
+
+reveal_type(D.__init__)  # revealed: (x: int) -> None
+```
+
+But if there is a variable annotation with a function or class literal type, the signature of
+`__init__` will include this field:
+
+```py
+from knot_extensions import TypeOf
+
+class SomeClass: ...
+
+def some_function() -> None: ...
+@dataclass
+class D:
+    function_literal: TypeOf[some_function]
+    class_literal: TypeOf[SomeClass]
+    class_subtype_of: type[SomeClass]
+
+# revealed: (function_literal: def some_function() -> None, class_literal: Literal[SomeClass], class_subtype_of: type[SomeClass]) -> None
+reveal_type(D.__init__)
+```
+
+More realistically, dataclasses can have `Callable` attributes:
+
+```py
+from typing import Callable
+
+@dataclass
+class D:
+    c: Callable[[int], str]
+
+reveal_type(D.__init__)  # revealed: (c: (int, /) -> str) -> None
+```
+
+Implicit instance attributes do not affect the signature of `__init__`:
+
+```py
+@dataclass
+class D:
+    x: int
+
+    def f(self, y: str) -> None:
+        self.y: str = y
+
+reveal_type(D(1).y)  # revealed: str
+
+reveal_type(D.__init__)  # revealed: (x: int) -> None
+```
+
+Annotating expressions does not lead to an entry in `__annotations__` at runtime, and so it wouldn't
+be included in the signature of `__init__`. This is a case that we currently don't detect:
+
+```py
+@dataclass
+class D:
+    # (x) is an expression, not a "simple name"
+    (x): int = 1
+
+# TODO: should ideally not include a `x` parameter
+reveal_type(D.__init__)  # revealed: (x: int = Literal[1]) -> None
+```
+
+## `@dataclass` calls with arguments
+
+The `@dataclass` decorator can take several arguments to customize the existence of the generated
+methods. The following test makes sure that we still treat the class as a dataclass if (the default)
+arguments are passed in:
+
+```py
+from dataclasses import dataclass
+
+@dataclass(init=True, repr=True, eq=True)
+class Person:
+    name: str
+    age: int | None = None
+
+alice = Person("Alice", 30)
+reveal_type(repr(alice))  # revealed: str
+reveal_type(alice == alice)  # revealed: bool
+```
+
+If `init` is set to `False`, no `__init__` method is generated:
+
+```py
+from dataclasses import dataclass
+
+@dataclass(init=False)
+class C:
+    x: int
+
+C()  # Okay
+
+# error: [too-many-positional-arguments]
+C(1)
+
+repr(C())
+
+C() == C()
+```
+
+## Other dataclass parameters
+
+### `repr`
+
+A custom `__repr__` method is generated by default. It can be disabled by passing `repr=False`, but
+in that case `__repr__` is still available via `object.__repr__`:
+
+```py
+from dataclasses import dataclass
+
+@dataclass(repr=False)
+class WithoutRepr:
+    x: int
+
+reveal_type(WithoutRepr(1).__repr__)  # revealed: bound method WithoutRepr.__repr__() -> str
+```
+
+### `eq`
+
+The same is true for `__eq__`. Setting `eq=False` disables the generated `__eq__` method, but
+`__eq__` is still available via `object.__eq__`:
+
+```py
+from dataclasses import dataclass
+
+@dataclass(eq=False)
+class WithoutEq:
+    x: int
+
+reveal_type(WithoutEq(1) == WithoutEq(2))  # revealed: bool
+```
+
+### `order`
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+`order` is set to `False` by default. If `order=True`, `__lt__`, `__le__`, `__gt__`, and `__ge__`
+methods will be generated:
+
+```py
+from dataclasses import dataclass
+
+@dataclass
+class WithoutOrder:
+    x: int
+
+WithoutOrder(1) < WithoutOrder(2)  # error: [unsupported-operator]
+WithoutOrder(1) <= WithoutOrder(2)  # error: [unsupported-operator]
+WithoutOrder(1) > WithoutOrder(2)  # error: [unsupported-operator]
+WithoutOrder(1) >= WithoutOrder(2)  # error: [unsupported-operator]
+
+@dataclass(order=True)
+class WithOrder:
+    x: int
+
+WithOrder(1) < WithOrder(2)
+WithOrder(1) <= WithOrder(2)
+WithOrder(1) > WithOrder(2)
+WithOrder(1) >= WithOrder(2)
+```
+
+Comparisons are only allowed for `WithOrder` instances:
+
+```py
+WithOrder(1) < 2  # error: [unsupported-operator]
+WithOrder(1) <= 2  # error: [unsupported-operator]
+WithOrder(1) > 2  # error: [unsupported-operator]
+WithOrder(1) >= 2  # error: [unsupported-operator]
+```
+
+This also works for generic dataclasses:
+
+```py
+from dataclasses import dataclass
+
+@dataclass(order=True)
+class GenericWithOrder[T]:
+    x: T
+
+GenericWithOrder[int](1) < GenericWithOrder[int](1)
+
+GenericWithOrder[int](1) < GenericWithOrder[str]("a")  # error: [unsupported-operator]
+```
+
+If a class already defines one of the comparison methods, a `TypeError` is raised at runtime.
+Ideally, we would emit a diagnostic in that case:
+
+```py
+@dataclass(order=True)
+class AlreadyHasCustomDunderLt:
+    x: int
+
+    # TODO: Ideally, we would emit a diagnostic here
+    def __lt__(self, other: object) -> bool:
+        return False
+```
+
+### `unsafe_hash`
+
+To do
+
+### `frozen`
+
+To do
+
+### `match_args`
+
+To do
+
+### `kw_only`
+
+To do
+
+### `slots`
+
+To do
+
+### `weakref_slot`
+
+To do
+
+## Inheritance
+
+### Normal class inheriting from a dataclass
+
+```py
+from dataclasses import dataclass
+
+@dataclass
+class Base:
+    x: int
+
+class Derived(Base): ...
+
+d = Derived(1)  # OK
+reveal_type(d.x)  # revealed: int
+```
+
+### Dataclass inheriting from normal class
+
+```py
+from dataclasses import dataclass
+
+class Base:
+    x: int = 1
+
+@dataclass
+class Derived(Base):
+    y: str
+
+d = Derived("a")
+
+# error: [too-many-positional-arguments]
+# error: [invalid-argument-type]
+Derived(1, "a")
+```
+
+### Dataclass inheriting from another dataclass
+
+```py
+from dataclasses import dataclass
+
+@dataclass
+class Base:
+    x: int
+    y: str
+
+@dataclass
+class Derived(Base):
+    z: bool
+
+d = Derived(1, "a", True)  # OK
+
+reveal_type(d.x)  # revealed: int
+reveal_type(d.y)  # revealed: str
+reveal_type(d.z)  # revealed: bool
+
+# error: [missing-argument]
+Derived(1, "a")
+
+# error: [missing-argument]
+Derived(True)
+```
+
+### Overwriting attributes from base class
+
+The following example comes from the
+[Python documentation](https://docs.python.org/3/library/dataclasses.html#inheritance). The `x`
+attribute appears just once in the `__init__` signature, and the default value is taken from the
+derived class
+
+```py
+from dataclasses import dataclass
+from typing import Any
+
+@dataclass
+class Base:
+    x: Any = 15.0
+    y: int = 0
+
+@dataclass
+class C(Base):
+    z: int = 10
+    x: int = 15
+
+reveal_type(C.__init__)  # revealed: (x: int = Literal[15], y: int = Literal[0], z: int = Literal[10]) -> None
+```
+
+## Generic dataclasses
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+from dataclasses import dataclass
+
+@dataclass
+class DataWithDescription[T]:
+    data: T
+    description: str
+
+reveal_type(DataWithDescription[int])  # revealed: Literal[DataWithDescription[int]]
+
+d_int = DataWithDescription[int](1, "description")  # OK
+reveal_type(d_int.data)  # revealed: int
+reveal_type(d_int.description)  # revealed: str
+
+# error: [invalid-argument-type]
+DataWithDescription[int](None, "description")
+```
+
+## Descriptor-typed fields
+
+### Same type in `__get__` and `__set__`
+
+For the following descriptor, the return type of `__get__` and the type of the `value` parameter in
+`__set__` are the same. The generated `__init__` method takes an argument of this type (instead of
+the type of the descriptor), and the default value is also of this type:
+
+```py
+from typing import overload
+from dataclasses import dataclass
+
+class UppercaseString:
+    _value: str = ""
+
+    def __get__(self, instance: object, owner: None | type) -> str:
+        return self._value
+
+    def __set__(self, instance: object, value: str) -> None:
+        self._value = value.upper()
+
+@dataclass
+class C:
+    upper: UppercaseString = UppercaseString()
+
+reveal_type(C.__init__)  # revealed: (upper: str = str) -> None
+
+c = C("abc")
+reveal_type(c.upper)  # revealed: str
+
+# This is also okay:
+C()
+
+# error: [invalid-argument-type]
+C(1)
+
+# error: [too-many-positional-arguments]
+C("a", "b")
+```
+
+### Different types in `__get__` and `__set__`
+
+In general, the type of the `__init__` parameter is determined by the `value` parameter type of the
+`__set__` method (`str` in the example below). However, the default value is generated by calling
+the descriptor's `__get__` method as if it had been called on the class itself, i.e. passing `None`
+for the `instance` argument.
+
+```py
+from typing import Literal, overload
+from dataclasses import dataclass
+
+class ConvertToLength:
+    _len: int = 0
+
+    @overload
+    def __get__(self, instance: None, owner: type) -> Literal[""]: ...
+    @overload
+    def __get__(self, instance: object, owner: type | None) -> int: ...
+    def __get__(self, instance: object | None, owner: type | None) -> str | int:
+        if instance is None:
+            return ""
+
+        return self._len
+
+    def __set__(self, instance, value: str) -> None:
+        self._len = len(value)
+
+@dataclass
+class C:
+    converter: ConvertToLength = ConvertToLength()
+
+reveal_type(C.__init__)  # revealed: (converter: str = Literal[""]) -> None
+
+c = C("abc")
+reveal_type(c.converter)  # revealed: int
+
+# This is also okay:
+C()
+
+# error: [invalid-argument-type]
+C(1)
+
+# error: [too-many-positional-arguments]
+C("a", "b")
+```
+
+### With overloaded `__set__` method
+
+If the `__set__` method is overloaded, we determine the type for the `__init__` parameter as the
+union of all possible `value` parameter types:
+
+```py
+from typing import overload
+from dataclasses import dataclass
+
+class AcceptsStrAndInt:
+    def __get__(self, instance, owner) -> int:
+        return 0
+
+    @overload
+    def __set__(self, instance: object, value: str) -> None: ...
+    @overload
+    def __set__(self, instance: object, value: int) -> None: ...
+    def __set__(self, instance: object, value) -> None:
+        pass
+
+@dataclass
+class C:
+    field: AcceptsStrAndInt = AcceptsStrAndInt()
+
+reveal_type(C.__init__)  # revealed: (field: str | int = int) -> None
+```
+
+## `dataclasses.field`
+
+To do
+
+## Other special cases
+
+### `dataclasses.dataclass`
+
+We also understand dataclasses if they are decorated with the fully qualified name:
+
+```py
+import dataclasses
+
+@dataclasses.dataclass
+class C:
+    x: str
+
+reveal_type(C.__init__)  # revealed: (x: str) -> None
+```
+
+### Dataclass with custom `__init__` method
+
+If a class already defines `__init__`, it is not replaced by the `dataclass` decorator.
+
+```py
+from dataclasses import dataclass
+
+@dataclass(init=True)
+class C:
+    x: str
+
+    def __init__(self, x: int) -> None:
+        self.x = str(x)
+
+C(1)  # OK
+
+# error: [invalid-argument-type]
+C("a")
+```
+
+Similarly, if we set `init=False`, we still recognize the custom `__init__` method:
+
+```py
+@dataclass(init=False)
+class D:
+    def __init__(self, x: int) -> None:
+        self.x = str(x)
+
+D(1)  # OK
+D()  # error: [missing-argument]
+```
+
+### Accessing instance attributes on the class itself
+
+Just like for normal classes, accessing instance attributes on the class itself is not allowed:
+
+```py
+from dataclasses import dataclass
+
+@dataclass
+class C:
+    x: int
+
+# error: [unresolved-attribute] "Attribute `x` can only be accessed on instances, not on the class object `Literal[C]` itself."
+C.x
+```
+
+### Return type of `dataclass(...)`
+
+A call like `dataclass(order=True)` returns a callable itself, which is then used as the decorator.
+We can store the callable in a variable and later use it as a decorator:
+
+```py
+from dataclasses import dataclass
+
+dataclass_with_order = dataclass(order=True)
+
+reveal_type(dataclass_with_order)  # revealed: <decorator produced by dataclasses.dataclass>
+
+@dataclass_with_order
+class C:
+    x: int
+
+C(1) < C(2)  # ok
+```
+
+### Using `dataclass` as a function
+
+To do
+
+## Internals
+
+The `dataclass` decorator returns the class itself. This means that the type of `Person` is `type`,
+and attributes like the MRO are unchanged:
+
+```py
+from dataclasses import dataclass
+
+@dataclass
+class Person:
+    name: str
+    age: int | None = None
+
+reveal_type(type(Person))  # revealed: Literal[type]
+reveal_type(Person.__mro__)  # revealed: tuple[Literal[Person], Literal[object]]
+```
+
+The generated methods have the following signatures:
+
+```py
+# TODO: `self` is missing here
+reveal_type(Person.__init__)  # revealed: (name: str, age: int | None = None) -> None
+
+reveal_type(Person.__repr__)  # revealed: def __repr__(self) -> str
+
+reveal_type(Person.__eq__)  # revealed: def __eq__(self, value: object, /) -> bool
+```

crates/red_knot_python_semantic/resources/mdtest/decorators.md

@@ -0,0 +1,237 @@
+# Decorators
+
+Decorators are a way to modify function and class behavior. A decorator is a callable that takes the
+function or class as an argument and returns a modified version of it.
+
+## Basic example
+
+A decorated function definition is conceptually similar to `def f(x): ...` followed by
+`f = decorator(f)`. This means that the type of a decorated function is the same as the return type
+of the decorator (which does not necessarily need to be a callable type):
+
+```py
+def custom_decorator(f) -> int:
+    return 1
+
+@custom_decorator
+def f(x): ...
+
+reveal_type(f)  # revealed: int
+```
+
+## Type-annotated decorator
+
+More commonly, a decorator returns a modified callable type:
+
+```py
+from typing import Callable
+
+def ensure_positive(wrapped: Callable[[int], bool]) -> Callable[[int], bool]:
+    return lambda x: wrapped(x) and x > 0
+
+@ensure_positive
+def even(x: int) -> bool:
+    return x % 2 == 0
+
+reveal_type(even)  # revealed: (int, /) -> bool
+reveal_type(even(4))  # revealed: bool
+```
+
+## Decorators which take arguments
+
+Decorators can be arbitrary expressions. This is often useful when the decorator itself takes
+arguments:
+
+```py
+from typing import Callable
+
+def ensure_larger_than(lower_bound: int) -> Callable[[Callable[[int], bool]], Callable[[int], bool]]:
+    def decorator(wrapped: Callable[[int], bool]) -> Callable[[int], bool]:
+        return lambda x: wrapped(x) and x >= lower_bound
+    return decorator
+
+@ensure_larger_than(10)
+def even(x: int) -> bool:
+    return x % 2 == 0
+
+reveal_type(even)  # revealed: (int, /) -> bool
+reveal_type(even(14))  # revealed: bool
+```
+
+## Multiple decorators
+
+Multiple decorators can be applied to a single function. They are applied in "bottom-up" order,
+meaning that the decorator closest to the function definition is applied first:
+
+```py
+def maps_to_str(f) -> str:
+    return "a"
+
+def maps_to_int(f) -> int:
+    return 1
+
+def maps_to_bytes(f) -> bytes:
+    return b"a"
+
+@maps_to_str
+@maps_to_int
+@maps_to_bytes
+def f(x): ...
+
+reveal_type(f)  # revealed: str
+```
+
+## Decorating with a class
+
+When a function is decorated with a class-based decorator, the decorated function turns into an
+instance of the class (see also: [properties](properties.md)). Attributes of the class can be
+accessed on the decorated function.
+
+```py
+class accept_strings:
+    custom_attribute: str = "a"
+
+    def __init__(self, f):
+        self.f = f
+
+    def __call__(self, x: str | int) -> bool:
+        return self.f(int(x))
+
+@accept_strings
+def even(x: int) -> bool:
+    return x > 0
+
+reveal_type(even)  # revealed: accept_strings
+reveal_type(even.custom_attribute)  # revealed: str
+reveal_type(even("1"))  # revealed: bool
+reveal_type(even(1))  # revealed: bool
+
+# error: [invalid-argument-type]
+even(None)
+```
+
+## Common decorator patterns
+
+### `functools.wraps`
+
+This test mainly makes sure that we do not emit any diagnostics in a case where the decorator is
+implemented using `functools.wraps`.
+
+```py
+from typing import Callable
+from functools import wraps
+
+def custom_decorator(f) -> Callable[[int], str]:
+    @wraps(f)
+    def wrapper(*args, **kwargs):
+        print("Calling decorated function")
+        return f(*args, **kwargs)
+    return wrapper
+
+@custom_decorator
+def f(x: int) -> str:
+    return str(x)
+
+reveal_type(f)  # revealed: (int, /) -> str
+```
+
+### `functools.cache`
+
+```py
+from functools import cache
+
+@cache
+def f(x: int) -> int:
+    return x**2
+
+# TODO: Should be `_lru_cache_wrapper[int]`
+reveal_type(f)  # revealed: @Todo(specialized non-generic class)
+
+# TODO: Should be `int`
+reveal_type(f(1))  # revealed: @Todo(specialized non-generic class)
+```
+
+## Lambdas as decorators
+
+```py
+@lambda f: f
+def g(x: int) -> str:
+    return "a"
+
+# TODO: This should be `Literal[g]` or `(int, /) -> str`
+reveal_type(g)  # revealed: Unknown
+```
+
+## Error cases
+
+### Unknown decorator
+
+```py
+# error: [unresolved-reference] "Name `unknown_decorator` used when not defined"
+@unknown_decorator
+def f(x): ...
+
+reveal_type(f)  # revealed: Unknown
+```
+
+### Error in the decorator expression
+
+```py
+# error: [unsupported-operator]
+@(1 + "a")
+def f(x): ...
+
+reveal_type(f)  # revealed: Unknown
+```
+
+### Non-callable decorator
+
+```py
+non_callable = 1
+
+# error: [call-non-callable] "Object of type `Literal[1]` is not callable"
+@non_callable
+def f(x): ...
+
+reveal_type(f)  # revealed: Unknown
+```
+
+### Wrong signature
+
+#### Wrong argument type
+
+Here, we emit a diagnostic since `wrong_signature` takes an `int` instead of a callable type as the
+first argument:
+
+```py
+def wrong_signature(f: int) -> str:
+    return "a"
+
+# error: [invalid-argument-type] "Argument to this function is incorrect: Expected `int`, found `def f(x) -> Unknown`"
+@wrong_signature
+def f(x): ...
+
+reveal_type(f)  # revealed: str
+```
+
+#### Wrong number of arguments
+
+Decorators need to be callable with a single argument. If they are not, we emit a diagnostic:
+
+```py
+def takes_two_arguments(f, g) -> str:
+    return "a"
+
+# error: [missing-argument] "No argument provided for required parameter `g` of function `takes_two_arguments`"
+@takes_two_arguments
+def f(x): ...
+
+reveal_type(f)  # revealed: str
+
+def takes_no_argument() -> str:
+    return "a"
+
+# error: [too-many-positional-arguments] "Too many positional arguments to function `takes_no_argument`: expected 0, got 1"
+@takes_no_argument
+def g(x): ...
+```