[red-knot] Eliminate None in equality-comparison narrowing

Add a regression test for the cycle documented in
https://github.com/astral-sh/ruff/issues/14767, which no longer panics
(or even causes a cycle at all.)

Fixes https://github.com/astral-sh/ruff/issues/14767

.github/actionlint.yaml

@@ -6,5 +6,6 @@ self-hosted-runner:
   labels:
     - depot-ubuntu-latest-8
     - depot-ubuntu-22.04-16
+    - depot-ubuntu-22.04-32
     - github-windows-2025-x86_64-8
     - github-windows-2025-x86_64-16

.github/workflows/build-binaries.yml

@@ -377,7 +377,7 @@ jobs:
           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

.github/workflows/ci.yaml

@@ -237,13 +237,13 @@ jobs:
       - 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@be7c31b6745feec79dec5eb79178466c0670bb2d # v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-nextest
       - name: "Install cargo insta"
-        uses: taiki-e/install-action@be7c31b6745feec79dec5eb79178466c0670bb2d # v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-insta
       - name: Red-knot mdtests (GitHub annotations)
@@ -291,13 +291,13 @@ jobs:
       - 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@be7c31b6745feec79dec5eb79178466c0670bb2d # v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-nextest
       - name: "Install cargo insta"
-        uses: taiki-e/install-action@be7c31b6745feec79dec5eb79178466c0670bb2d # v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-insta
       - name: "Run tests"
@@ -320,7 +320,7 @@ jobs:
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install cargo nextest"
-        uses: taiki-e/install-action@be7c31b6745feec79dec5eb79178466c0670bb2d # v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-nextest
       - name: "Run tests"
@@ -346,7 +346,7 @@ jobs:
       - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
       - name: "Install Rust toolchain"
         run: rustup target add wasm32-unknown-unknown
-      - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
         with:
           node-version: 20
           cache: "npm"
@@ -376,7 +376,7 @@ jobs:
       - 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
 
@@ -401,13 +401,13 @@ jobs:
           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@be7c31b6745feec79dec5eb79178466c0670bb2d # v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-nextest
       - name: "Install cargo insta"
-        uses: taiki-e/install-action@be7c31b6745feec79dec5eb79178466c0670bb2d # v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-insta
       - name: "Run tests"
@@ -433,7 +433,7 @@ jobs:
       - 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"
@@ -455,7 +455,7 @@ jobs:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: astral-sh/setup-uv@0c5e2b8115b80b4c7c5ddf6ffdd634974642d182 # v5.4.1
+      - 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
@@ -641,7 +641,7 @@ jobs:
       - 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
 
@@ -681,7 +681,7 @@ jobs:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: astral-sh/setup-uv@0c5e2b8115b80b4c7c5ddf6ffdd634974642d182 # v5.4.1
+      - uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5.4.2
       - name: "Cache pre-commit"
         uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4.2.3
         with:
@@ -720,7 +720,7 @@ jobs:
       - name: "Install Rust toolchain"
         run: rustup show
       - name: Install uv
-        uses: astral-sh/setup-uv@0c5e2b8115b80b4c7c5ddf6ffdd634974642d182 # v5.4.1
+        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
@@ -821,7 +821,7 @@ jobs:
       - 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
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
         with:
           node-version: 22
           cache: "npm"
@@ -857,7 +857,7 @@ jobs:
         run: rustup show
 
       - name: "Install codspeed"
-        uses: taiki-e/install-action@be7c31b6745feec79dec5eb79178466c0670bb2d # v2
+        uses: taiki-e/install-action@09dc018eee06ae1c9e0409786563f534210ceb83 # v2
         with:
           tool: cargo-codspeed
 

.github/workflows/daily_fuzz.yaml

@@ -34,11 +34,11 @@ jobs:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           persist-credentials: false
-      - uses: astral-sh/setup-uv@0c5e2b8115b80b4c7c5ddf6ffdd634974642d182 # v5.4.1
+      - 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: 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,

.github/workflows/daily_property_tests.yaml

@@ -36,7 +36,7 @@ jobs:
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install mold"
-        uses: rui314/setup-mold@v1
+        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

.github/workflows/mypy_primer.yaml

@@ -21,11 +21,12 @@ env:
   CARGO_NET_RETRY: 10
   CARGO_TERM_COLOR: always
   RUSTUP_MAX_RETRIES: 10
+  RUST_BACKTRACE: 1
 
 jobs:
   mypy_primer:
     name: Run mypy_primer
-    runs-on: depot-ubuntu-22.04-16
+    runs-on: depot-ubuntu-22.04-32
     timeout-minutes: 20
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
@@ -35,7 +36,7 @@ jobs:
           persist-credentials: false
 
       - name: Install the latest version of uv
-        uses: astral-sh/setup-uv@0c5e2b8115b80b4c7c5ddf6ffdd634974642d182 # v5.4.1
+        uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5.4.2
 
       - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
         with:
@@ -45,13 +46,15 @@ jobs:
 
       - name: Install mypy_primer
         run: |
-          uv tool install "git+https://github.com/astral-sh/mypy_primer.git@add-red-knot-support-v5"
+          uv tool install "git+https://github.com/hauntsaninja/mypy_primer@ebaa9fd27b51a278873b63676fd25490cec6823b"
 
       - 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 +65,14 @@ 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|isort|itsdangerous|rich|packaging|pybind11|pyinstrument|typeshed-stats|scrapy|werkzeug|bidict|async-utils|python-chess|dacite|python-htmlgen|paroxython|porcupine|psycopg)$' \
+            --project-selector "/($PRIMER_SELECTOR)\$" \
             --output concise \
             --debug > mypy_primer.diff || [ $? -eq 1 ]
 

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

@@ -35,7 +35,7 @@ jobs:
           persist-credentials: false
       - name: "Install Rust toolchain"
         run: rustup target add wasm32-unknown-unknown
-      - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
         with:
           node-version: 22
       - uses: jetli/wasm-bindgen-action@20b33e20595891ab1a0ed73145d8a21fc96e7c29 # v0.2.0

.github/workflows/publish-playground.yml

@@ -29,7 +29,7 @@ jobs:
           persist-credentials: false
       - name: "Install Rust toolchain"
         run: rustup target add wasm32-unknown-unknown
-      - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
         with:
           node-version: 22
           cache: "npm"

.github/workflows/publish-pypi.yml

@@ -22,7 +22,7 @@ jobs:
       id-token: write
     steps:
       - name: "Install uv"
-        uses: astral-sh/setup-uv@0c5e2b8115b80b4c7c5ddf6ffdd634974642d182 # v5.4.1
+        uses: astral-sh/setup-uv@d4b2f3b6ecc6e67c4457f6d3e41ec42d3d0fcb86 # v5.4.2
       - uses: actions/download-artifact@95815c38cf2ff2164869cbab79da8d1f422bc89e # v4.2.1
         with:
           pattern: wheels-*

.github/workflows/publish-wasm.yml

@@ -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@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
         with:
           node-version: 20
           registry-url: "https://registry.npmjs.org"

.github/workflows/release.yml

@@ -40,6 +40,7 @@ permissions:
 # If there's a prerelease-style suffix to the version, then the release(s)
 # will be marked as a prerelease.
 on:
+  pull_request:
   workflow_dispatch:
     inputs:
       tag:
@@ -60,7 +61,7 @@ jobs:
     env:
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: actions/checkout@85e6279cec87321a52edac9c87bce653a07cf6c2
         with:
           persist-credentials: false
           submodules: recursive
@@ -68,9 +69,9 @@ jobs:
         # we specify bash to get pipefail; it guards against the `curl` command
         # failing. otherwise `sh` won't catch that `curl` returned non-0
         shell: bash
-        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/astral-sh/cargo-dist/releases/download/v0.28.4-prerelease.1/cargo-dist-installer.sh | sh"
+        run: "curl --proto '=https' --tlsv1.2 -LsSf https://github.com/astral-sh/cargo-dist/releases/download/v0.28.4/cargo-dist-installer.sh | sh"
       - name: Cache dist
-        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02
+        uses: actions/upload-artifact@6027e3dd177782cd8ab9af838c04fd81a07f1d47
         with:
           name: cargo-dist-cache
           path: ~/.cargo/bin/dist
@@ -86,7 +87,7 @@ jobs:
           cat plan-dist-manifest.json
           echo "manifest=$(jq -c "." plan-dist-manifest.json)" >> "$GITHUB_OUTPUT"
       - name: "Upload dist-manifest.json"
-        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02
+        uses: actions/upload-artifact@6027e3dd177782cd8ab9af838c04fd81a07f1d47
         with:
           name: artifacts-plan-dist-manifest
           path: plan-dist-manifest.json
@@ -123,7 +124,7 @@ jobs:
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       BUILD_MANIFEST_NAME: target/distrib/global-dist-manifest.json
     steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: actions/checkout@85e6279cec87321a52edac9c87bce653a07cf6c2
         with:
           persist-credentials: false
           submodules: recursive
@@ -153,7 +154,7 @@ jobs:
 
           cp dist-manifest.json "$BUILD_MANIFEST_NAME"
       - name: "Upload artifacts"
-        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02
+        uses: actions/upload-artifact@6027e3dd177782cd8ab9af838c04fd81a07f1d47
         with:
           name: artifacts-build-global
           path: |
@@ -174,7 +175,7 @@ jobs:
     outputs:
       val: ${{ steps.host.outputs.manifest }}
     steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: actions/checkout@85e6279cec87321a52edac9c87bce653a07cf6c2
         with:
           persist-credentials: false
           submodules: recursive
@@ -200,7 +201,7 @@ jobs:
           cat dist-manifest.json
           echo "manifest=$(jq -c "." dist-manifest.json)" >> "$GITHUB_OUTPUT"
       - name: "Upload dist-manifest.json"
-        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02
+        uses: actions/upload-artifact@6027e3dd177782cd8ab9af838c04fd81a07f1d47
         with:
           # Overwrite the previous copy
           name: artifacts-dist-manifest
@@ -250,7 +251,7 @@ jobs:
     env:
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      - uses: actions/checkout@85e6279cec87321a52edac9c87bce653a07cf6c2
         with:
           persist-credentials: false
           submodules: recursive

.pre-commit-config.yaml

@@ -79,7 +79,7 @@ repos:
         pass_filenames: false # This makes it a lot faster
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.11.5
+    rev: v0.11.6
     hooks:
       - id: ruff-format
       - id: ruff
@@ -97,7 +97,7 @@ 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: v1.5.2
+    rev: v1.6.0
     hooks:
       - id: zizmor
 

Cargo.lock

@@ -334,9 +334,9 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "4.5.36"
+version = "4.5.37"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2df961d8c8a0d08aa9945718ccf584145eee3f3aa06cddbeac12933781102e04"
+checksum = "eccb054f56cbd38340b380d4a8e69ef1f02f1af43db2f0cc817a4774d80ae071"
 dependencies = [
  "clap_builder",
  "clap_derive",
@@ -344,9 +344,9 @@ dependencies = [
 
 [[package]]
 name = "clap_builder"
-version = "4.5.36"
+version = "4.5.37"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "132dbda40fb6753878316a489d5a1242a8ef2f0d9e47ba01c951ea8aa7d013a5"
+checksum = "efd9466fac8543255d3b1fcad4762c5e116ffe808c8a3043d4263cd4fd4862a2"
 dependencies = [
  "anstream",
  "anstyle",
@@ -478,7 +478,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "117725a109d387c937a1533ce01b450cbde6b88abceea8473c4d7a85853cda3c"
 dependencies = [
  "lazy_static",
- "windows-sys 0.48.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -487,7 +487,7 @@ version = "3.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fde0e0ec90c9dfb3b4b1a0891a7dcd0e2bffde2f7efed5fe7c9bb00e5bfb915e"
 dependencies = [
- "windows-sys 0.48.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -918,7 +918,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "33d852cb9b869c2a9b3df2f71a3074817f01e1844f839a144f5fcef059a4eb5d"
 dependencies = [
  "libc",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -1499,7 +1499,7 @@ checksum = "e04d7f318608d35d4b61ddd75cbdaee86b023ebe2bd5a66ee0915f0bf93095a9"
 dependencies = [
  "hermit-abi 0.5.0",
  "libc",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -1553,9 +1553,9 @@ checksum = "4a5f13b858c8d314ee3e8f639011f7ccefe71f97f96e50151fb991f267928e2c"
 
 [[package]]
 name = "jiff"
-version = "0.2.4"
+version = "0.2.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d699bc6dfc879fb1bf9bdff0d4c56f0884fc6f0d0eb0fba397a6d00cd9a6b85e"
+checksum = "59ec30f7142be6fe14e1b021f50b85db8df2d4324ea6e91ec3e5dcde092021d0"
 dependencies = [
  "jiff-static",
  "jiff-tzdb-platform",
@@ -1563,14 +1563,14 @@ dependencies = [
  "portable-atomic",
  "portable-atomic-util",
  "serde",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
 name = "jiff-static"
-version = "0.2.4"
+version = "0.2.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8d16e75759ee0aa64c57a56acbf43916987b20c77373cb7e808979e02b93c9f9"
+checksum = "526b834d727fd59d37b076b0c3236d9adde1b1729a4361e20b2026f738cc1dbe"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1645,9 +1645,9 @@ checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
 
 [[package]]
 name = "libc"
-version = "0.2.171"
+version = "0.2.172"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c19937216e9d3aa9956d9bb8dfc0b0c8beb6058fc4f7a4dc4d850edf86a237d6"
+checksum = "d750af042f7ef4f724306de029d18836c26c1765a54a6a3f094cbd23a7267ffa"
 
 [[package]]
 name = "libcst"
@@ -2327,9 +2327,9 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.94"
+version = "1.0.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a31971752e70b8b2686d7e46ec17fb38dad4051d94024c88df49b667caea9c84"
+checksum = "02b3e5e68a3a1a02aad3ec490a98007cbc13c37cbe84a3cd7b8e406d76e7f778"
 dependencies = [
  "unicode-ident",
 ]
@@ -2420,13 +2420,12 @@ dependencies = [
 
 [[package]]
 name = "rand"
-version = "0.9.0"
+version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3779b94aeb87e8bd4e834cee3650289ee9e0d5677f976ecdb6d219e5f4f6cd94"
+checksum = "9fbfd9d094a40bf3ae768db9361049ace4c0e04a4fd6b359518bd7b73a73dd97"
 dependencies = [
  "rand_chacha 0.9.0",
  "rand_core 0.9.3",
- "zerocopy",
 ]
 
 [[package]]
@@ -3084,7 +3083,7 @@ version = "0.0.0"
 dependencies = [
  "anyhow",
  "itertools 0.14.0",
- "rand 0.9.0",
+ "rand 0.9.1",
  "ruff_diagnostics",
  "ruff_source_file",
  "ruff_text_size",
@@ -3428,7 +3427,7 @@ dependencies = [
  "errno",
  "libc",
  "linux-raw-sys 0.4.15",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -3441,7 +3440,7 @@ dependencies = [
  "errno",
  "libc",
  "linux-raw-sys 0.9.3",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -3675,9 +3674,9 @@ dependencies = [
 
 [[package]]
 name = "shellexpand"
-version = "3.1.0"
+version = "3.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "da03fa3b94cc19e3ebfc88c4229c49d8f08cdbd1228870a45f0ffdf84988e14b"
+checksum = "8b1fdf65dd6331831494dd616b30351c38e96e45921a27745cf98490458b90bb"
 dependencies = [
  "dirs",
 ]
@@ -3827,7 +3826,7 @@ dependencies = [
  "getrandom 0.3.2",
  "once_cell",
  "rustix 1.0.2",
- "windows-sys 0.59.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -4328,7 +4327,7 @@ checksum = "458f7a779bf54acc9f347480ac654f68407d3aab21269a6e3c9f922acd9e2da9"
 dependencies = [
  "getrandom 0.3.2",
  "js-sys",
- "rand 0.9.0",
+ "rand 0.9.1",
  "uuid-macro-internal",
  "wasm-bindgen",
 ]
@@ -4599,7 +4598,7 @@ version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf221c93e13a30d793f7645a0e7762c55d169dbb0a49671918a2319d289b10bb"
 dependencies = [
- "windows-sys 0.48.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]

Cargo.toml

@@ -231,6 +231,10 @@ unused_peekable = "warn"
 # Diagnostics are not actionable: Enable once https://github.com/rust-lang/rust-clippy/issues/13774 is resolved.
 large_stack_arrays = "allow"
 
+# Salsa generates functions with parameters for each field of a `salsa::interned` struct.
+# If we don't allow this, we get warnings for structs with too many fields.
+too_many_arguments = "allow"
+
 [profile.release]
 # Note that we set these explicitly, and these values
 # were chosen based on a trade-off between compile times
@@ -272,7 +276,9 @@ inherits = "release"
 # Config for 'dist'
 [workspace.metadata.dist]
 # The preferred dist version to use in CI (Cargo.toml SemVer syntax)
-cargo-dist-version = "0.28.4-prerelease.1"
+cargo-dist-version = "0.28.4"
+# Make distability of apps opt-in instead of opt-out
+dist = false
 # CI backends to support
 ci = "github"
 # The installers to generate for each app
@@ -306,7 +312,7 @@ auto-includes = false
 # Whether dist should create a Github Release or use an existing draft
 create-release = true
 # Which actions to run on pull requests
-pr-run-mode = "skip"
+pr-run-mode = "plan"
 # Whether CI should trigger releases with dispatches instead of tag pushes
 dispatch-releases = true
 # Which phase dist should use to create the GitHub release
@@ -334,7 +340,7 @@ install-path = ["$XDG_BIN_HOME/", "$XDG_DATA_HOME/../bin", "~/.local/bin"]
 global = "depot-ubuntu-latest-4"
 
 [workspace.metadata.dist.github-action-commits]
-"actions/checkout" = "11bd71901bbe5b1630ceea73d27597364c9af683" # v4
-"actions/upload-artifact" = "ea165f8d65b6e75b540449e92b4886f43607fa02" # v4.6.2
+"actions/checkout" = "85e6279cec87321a52edac9c87bce653a07cf6c2" # v4
+"actions/upload-artifact" = "6027e3dd177782cd8ab9af838c04fd81a07f1d47" # v4.6.2
 "actions/download-artifact" = "95815c38cf2ff2164869cbab79da8d1f422bc89e" # v4.2.1
 "actions/attest-build-provenance" = "c074443f1aee8d4aeeae555aebba3282517141b2" #v2.2.3

crates/red_knot/docs/mypy_primer.md

@@ -2,16 +2,16 @@
 
 ## Basics
 
-For now, we use our own [fork of mypy primer]. It can be run using `uvx --from "…" mypy_primer`. For example, to see the help message, run:
+`mypy_primer` can be run using `uvx --from "…" mypy_primer`. For example, to see the help message, run:
 
 ```sh
-uvx --from "git+https://github.com/astral-sh/mypy_primer.git@add-red-knot-support" mypy_primer -h
+uvx --from "git+https://github.com/hauntsaninja/mypy_primer" mypy_primer -h
 ```
 
 Alternatively, you can install the forked version of `mypy_primer` using:
 
 ```sh
-uv tool install "git+https://github.com/astral-sh/mypy_primer.git@add-red-knot-support"
+uv tool install "git+https://github.com/hauntsaninja/mypy_primer"
 ```
 
 and then run it using `uvx mypy_primer` or just `mypy_primer`, if your `PATH` is set up accordingly (see: [Tool executables]).
@@ -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.
@@ -56,6 +56,5 @@ mypy_primer --repo /path/to/ruff --old origin/main --new my/local-branch …
 
 Note that you might need to clean up `/tmp/mypy_primer` in order for this to work correctly.
 
-[fork of mypy primer]: https://github.com/astral-sh/mypy_primer/tree/add-red-knot-support
-[full list of ecosystem projects]: https://github.com/astral-sh/mypy_primer/blob/add-red-knot-support/mypy_primer/projects.py
+[full list of ecosystem projects]: https://github.com/hauntsaninja/mypy_primer/blob/master/mypy_primer/projects.py
 [tool executables]: https://docs.astral.sh/uv/concepts/tools/#tool-executables

crates/red_knot/tests/cli.rs

@@ -32,12 +32,12 @@ fn config_override_python_version() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    error: lint:unresolved-attribute
+    error: lint:unresolved-attribute: Type `<module 'sys'>` has no attribute `last_exc`
      --> <temp_dir>/test.py:5:7
       |
     4 | # Access `sys.last_exc` that was only added in Python 3.12
     5 | print(sys.last_exc)
-      |       ^^^^^^^^^^^^ Type `<module 'sys'>` has no attribute `last_exc`
+      |       ^^^^^^^^^^^^
       |
 
     Found 1 diagnostic
@@ -165,11 +165,11 @@ fn cli_arguments_are_relative_to_the_current_directory() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    error: lint:unresolved-import
+    error: lint:unresolved-import: Cannot resolve import `utils`
      --> <temp_dir>/child/test.py:2:6
       |
     2 | from utils import add
-      |      ^^^^^ Cannot resolve import `utils`
+      |      ^^^^^
     3 |
     4 | stat = add(10, 15)
       |
@@ -252,7 +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
@@ -265,22 +265,22 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    error: lint:division-by-zero
+    error: lint:division-by-zero: Cannot divide object of type `Literal[4]` by zero
      --> <temp_dir>/test.py:2:5
       |
     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
+    warning: lint:possibly-unresolved-reference: Name `x` used when possibly not defined
      --> <temp_dir>/test.py:7:7
       |
     5 |     x = a
     6 |
     7 | print(x)  # possibly-unresolved-reference
-      |       ^ Name `x` used when possibly not defined
+      |       ^
       |
 
     Found 2 diagnostics
@@ -301,13 +301,13 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
     success: true
     exit_code: 0
     ----- stdout -----
-    warning: lint:division-by-zero
+    warning: lint:division-by-zero: Cannot divide object of type `Literal[4]` by zero
      --> <temp_dir>/test.py:2:5
       |
     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)):
       |
 
     Found 1 diagnostic
@@ -328,7 +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
@@ -341,33 +341,33 @@ fn cli_rule_severity() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    error: lint:unresolved-import
+    error: lint:unresolved-import: Cannot resolve import `does_not_exit`
      --> <temp_dir>/test.py:2:8
       |
     2 | import does_not_exit
-      |        ^^^^^^^^^^^^^ Cannot resolve import `does_not_exit`
+      |        ^^^^^^^^^^^^^
     3 |
     4 | y = 4 / 0
       |
 
-    error: lint:division-by-zero
+    error: lint:division-by-zero: Cannot divide object of type `Literal[4]` by zero
      --> <temp_dir>/test.py:4:5
       |
     2 | import does_not_exit
     3 |
     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
+    warning: lint:possibly-unresolved-reference: Name `x` used when possibly not defined
      --> <temp_dir>/test.py:9:7
       |
     7 |     x = a
     8 |
     9 | print(x)  # possibly-unresolved-reference
-      |       ^ Name `x` used when possibly not defined
+      |       ^
       |
 
     Found 3 diagnostics
@@ -388,24 +388,24 @@ fn cli_rule_severity() -> anyhow::Result<()> {
     success: true
     exit_code: 0
     ----- stdout -----
-    warning: lint:unresolved-import
+    warning: lint:unresolved-import: Cannot resolve import `does_not_exit`
      --> <temp_dir>/test.py:2:8
       |
     2 | import does_not_exit
-      |        ^^^^^^^^^^^^^ Cannot resolve import `does_not_exit`
+      |        ^^^^^^^^^^^^^
     3 |
     4 | y = 4 / 0
       |
 
-    warning: lint:division-by-zero
+    warning: lint:division-by-zero: Cannot divide object of type `Literal[4]` by zero
      --> <temp_dir>/test.py:4:5
       |
     2 | import does_not_exit
     3 |
     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)):
       |
 
     Found 2 diagnostics
@@ -426,7 +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
@@ -439,22 +439,22 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    error: lint:division-by-zero
+    error: lint:division-by-zero: Cannot divide object of type `Literal[4]` by zero
      --> <temp_dir>/test.py:2:5
       |
     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
+    warning: lint:possibly-unresolved-reference: Name `x` used when possibly not defined
      --> <temp_dir>/test.py:7:7
       |
     5 |     x = a
     6 |
     7 | print(x)  # possibly-unresolved-reference
-      |       ^ Name `x` used when possibly not defined
+      |       ^
       |
 
     Found 2 diagnostics
@@ -476,13 +476,13 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
     success: true
     exit_code: 0
     ----- stdout -----
-    warning: lint:division-by-zero
+    warning: lint:division-by-zero: Cannot divide object of type `Literal[4]` by zero
      --> <temp_dir>/test.py:2:5
       |
     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)):
       |
 
     Found 1 diagnostic
@@ -555,11 +555,11 @@ fn exit_code_only_warnings() -> anyhow::Result<()> {
     success: true
     exit_code: 0
     ----- stdout -----
-    warning: lint:unresolved-reference
+    warning: lint:unresolved-reference: Name `x` used when not defined
      --> <temp_dir>/test.py:1:7
       |
     1 | print(x)  # [unresolved-reference]
-      |       ^ Name `x` used when not defined
+      |       ^
       |
 
     Found 1 diagnostic
@@ -638,11 +638,11 @@ fn exit_code_no_errors_but_error_on_warning_is_true() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    warning: lint:unresolved-reference
+    warning: lint:unresolved-reference: Name `x` used when not defined
      --> <temp_dir>/test.py:1:7
       |
     1 | print(x)  # [unresolved-reference]
-      |       ^ Name `x` used when not defined
+      |       ^
       |
 
     Found 1 diagnostic
@@ -670,11 +670,11 @@ fn exit_code_no_errors_but_error_on_warning_is_enabled_in_configuration() -> any
     success: false
     exit_code: 1
     ----- stdout -----
-    warning: lint:unresolved-reference
+    warning: lint:unresolved-reference: Name `x` used when not defined
      --> <temp_dir>/test.py:1:7
       |
     1 | print(x)  # [unresolved-reference]
-      |       ^ Name `x` used when not defined
+      |       ^
       |
 
     Found 1 diagnostic
@@ -699,20 +699,20 @@ fn exit_code_both_warnings_and_errors() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    warning: lint:unresolved-reference
+    warning: lint:unresolved-reference: Name `x` used when not defined
      --> <temp_dir>/test.py:2:7
       |
     2 | print(x)     # [unresolved-reference]
-      |       ^ Name `x` used when not defined
+      |       ^
     3 | print(4[1])  # [non-subscriptable]
       |
 
-    error: lint:non-subscriptable
+    error: lint:non-subscriptable: Cannot subscript object of type `Literal[4]` with no `__getitem__` method
      --> <temp_dir>/test.py:3:7
       |
     2 | print(x)     # [unresolved-reference]
     3 | print(4[1])  # [non-subscriptable]
-      |       ^ Cannot subscript object of type `Literal[4]` with no `__getitem__` method
+      |       ^
       |
 
     Found 2 diagnostics
@@ -737,20 +737,20 @@ fn exit_code_both_warnings_and_errors_and_error_on_warning_is_true() -> anyhow::
     success: false
     exit_code: 1
     ----- stdout -----
-    warning: lint:unresolved-reference
+    warning: lint:unresolved-reference: Name `x` used when not defined
      --> <temp_dir>/test.py:2:7
       |
     2 | print(x)     # [unresolved-reference]
-      |       ^ Name `x` used when not defined
+      |       ^
     3 | print(4[1])  # [non-subscriptable]
       |
 
-    error: lint:non-subscriptable
+    error: lint:non-subscriptable: Cannot subscript object of type `Literal[4]` with no `__getitem__` method
      --> <temp_dir>/test.py:3:7
       |
     2 | print(x)     # [unresolved-reference]
     3 | print(4[1])  # [non-subscriptable]
-      |       ^ Cannot subscript object of type `Literal[4]` with no `__getitem__` method
+      |       ^
       |
 
     Found 2 diagnostics
@@ -775,20 +775,20 @@ fn exit_code_exit_zero_is_true() -> anyhow::Result<()> {
     success: true
     exit_code: 0
     ----- stdout -----
-    warning: lint:unresolved-reference
+    warning: lint:unresolved-reference: Name `x` used when not defined
      --> <temp_dir>/test.py:2:7
       |
     2 | print(x)     # [unresolved-reference]
-      |       ^ Name `x` used when not defined
+      |       ^
     3 | print(4[1])  # [non-subscriptable]
       |
 
-    error: lint:non-subscriptable
+    error: lint:non-subscriptable: Cannot subscript object of type `Literal[4]` with no `__getitem__` method
      --> <temp_dir>/test.py:3:7
       |
     2 | print(x)     # [unresolved-reference]
     3 | print(4[1])  # [non-subscriptable]
-      |       ^ Cannot subscript object of type `Literal[4]` with no `__getitem__` method
+      |       ^
       |
 
     Found 2 diagnostics
@@ -814,7 +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)
@@ -835,22 +835,22 @@ fn user_configuration() -> anyhow::Result<()> {
     success: true
     exit_code: 0
     ----- stdout -----
-    warning: lint:division-by-zero
+    warning: lint:division-by-zero: Cannot divide object of type `Literal[4]` by zero
      --> <temp_dir>/project/main.py:2:5
       |
     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
+    warning: lint:possibly-unresolved-reference: Name `x` used when possibly not defined
      --> <temp_dir>/project/main.py:7:7
       |
     5 |     x = a
     6 |
     7 | print(x)
-      |       ^ Name `x` used when possibly not defined
+      |       ^
       |
 
     Found 2 diagnostics
@@ -877,22 +877,22 @@ fn user_configuration() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    warning: lint:division-by-zero
+    warning: lint:division-by-zero: Cannot divide object of type `Literal[4]` by zero
      --> <temp_dir>/project/main.py:2:5
       |
     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)):
       |
 
-    error: lint:possibly-unresolved-reference
+    error: lint:possibly-unresolved-reference: Name `x` used when possibly not defined
      --> <temp_dir>/project/main.py:7:7
       |
     5 |     x = a
     6 |
     7 | print(x)
-      |       ^ Name `x` used when possibly not defined
+      |       ^
       |
 
     Found 2 diagnostics
@@ -935,25 +935,25 @@ fn check_specific_paths() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    error: lint:unresolved-import
+    error: lint:unresolved-import: Cannot resolve import `does_not_exist`
      --> <temp_dir>/project/tests/test_main.py:2:8
       |
     2 | import does_not_exist  # error: unresolved-import
-      |        ^^^^^^^^^^^^^^ Cannot resolve import `does_not_exist`
+      |        ^^^^^^^^^^^^^^
       |
 
-    error: lint:division-by-zero
+    error: lint:division-by-zero: Cannot divide object of type `Literal[4]` by zero
      --> <temp_dir>/project/main.py:2:5
       |
     2 | y = 4 / 0  # error: division-by-zero
-      |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
+      |     ^^^^^
       |
 
-    error: lint:unresolved-import
+    error: lint:unresolved-import: Cannot resolve import `main2`
      --> <temp_dir>/project/other.py:2:6
       |
     2 | from main2 import z  # error: unresolved-import
-      |      ^^^^^ Cannot resolve import `main2`
+      |      ^^^^^
     3 |
     4 | print(z)
       |
@@ -972,18 +972,18 @@ fn check_specific_paths() -> anyhow::Result<()> {
     success: false
     exit_code: 1
     ----- stdout -----
-    error: lint:unresolved-import
+    error: lint:unresolved-import: Cannot resolve import `does_not_exist`
      --> <temp_dir>/project/tests/test_main.py:2:8
       |
     2 | import does_not_exist  # error: unresolved-import
-      |        ^^^^^^^^^^^^^^ Cannot resolve import `does_not_exist`
+      |        ^^^^^^^^^^^^^^
       |
 
-    error: lint:unresolved-import
+    error: lint:unresolved-import: Cannot resolve import `main2`
      --> <temp_dir>/project/other.py:2:6
       |
     2 | from main2 import z  # error: unresolved-import
-      |      ^^^^^ Cannot resolve import `main2`
+      |      ^^^^^
     3 |
     4 | print(z)
       |

crates/red_knot_ide/src/db.rs

@@ -10,7 +10,7 @@ pub(crate) mod tests {
 
     use super::Db;
     use red_knot_python_semantic::lint::{LintRegistry, RuleSelection};
-    use red_knot_python_semantic::{default_lint_registry, Db as SemanticDb};
+    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;
@@ -83,6 +83,10 @@ 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 SourceDb> for TestDb {

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

@@ -0,0 +1,4 @@
+from __future__ import annotations
+
+def foo(a: foo()):
+    pass

crates/red_knot_project/src/db.rs

@@ -149,6 +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]
@@ -207,7 +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;
@@ -281,6 +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/lib.rs

@@ -10,7 +10,8 @@ use red_knot_python_semantic::lint::{LintRegistry, LintRegistryBuilder, RuleSele
 use red_knot_python_semantic::register_lints;
 use red_knot_python_semantic::types::check_types;
 use ruff_db::diagnostic::{
-    create_parse_diagnostic, Annotation, Diagnostic, DiagnosticId, Severity, Span,
+    create_parse_diagnostic, create_unsupported_syntax_diagnostic, Annotation, Diagnostic,
+    DiagnosticId, Severity, Span,
 };
 use ruff_db::files::File;
 use ruff_db::parsed::parsed_module;
@@ -424,6 +425,13 @@ fn check_file_impl(db: &dyn Db, file: File) -> Vec<Diagnostic> {
             .map(|error| create_parse_diagnostic(file, error)),
     );
 
+    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| {
@@ -520,11 +528,13 @@ mod tests {
     use crate::db::tests::TestDb;
     use crate::{check_file_impl, ProjectMetadata};
     use red_knot_python_semantic::types::check_types;
+    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<()> {
@@ -532,6 +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();
 

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/resources/mdtest/annotations/callable.md

@@ -237,6 +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

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

@@ -48,6 +48,11 @@ 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
 
@@ -94,6 +99,11 @@ class Foo:
 
 ## Non-deferred self-reference annotations in a class definition
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 ```py
 class Foo:
     # error: [unresolved-reference]
@@ -146,3 +156,24 @@ def _():
         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/invalid.md

@@ -89,7 +89,7 @@ def _(
     reveal_type(k)  # revealed: Unknown
     reveal_type(p)  # revealed: Unknown
     reveal_type(q)  # revealed: int | Unknown
-    reveal_type(r)  # revealed: @Todo(generics)
+    reveal_type(r)  # revealed: @Todo(unknown type subscript)
 ```
 
 ## Invalid Collection based AST nodes

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

@@ -137,7 +137,7 @@ from other import Literal
 a1: Literal[26]
 
 def f():
-    reveal_type(a1)  # revealed: @Todo(generics)
+    reveal_type(a1)  # revealed: @Todo(unknown type subscript)
 ```
 
 ## Detecting typing_extensions.Literal

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 overloaded 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 overloaded function)
+reveal_type(template.format(foo, bar))  # revealed: LiteralString
 ```
 
 ### Assignability

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

@@ -67,21 +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): ...
 
-# revealed: tuple[Literal[SetSubclass], Literal[set], Literal[MutableSet], Literal[AbstractSet], Literal[Collection], Literal[Iterable], Literal[Container], @Todo(protocol), 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): ...
@@ -92,11 +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): ...
@@ -113,7 +117,8 @@ reveal_type(DefaultDictSubclass.__mro__)
 
 class DequeSubclass(typing.Deque): ...
 
-# revealed: tuple[Literal[DequeSubclass], Literal[deque], Literal[MutableSequence], Literal[Sequence], Literal[Reversible], Literal[Collection], Literal[Iterable], Literal[Container], @Todo(protocol), 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/unsupported_special_forms.md

@@ -41,7 +41,7 @@ class Foo:
 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
+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"
@@ -49,6 +49,7 @@ def _(
     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
@@ -65,7 +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]
@@ -73,12 +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/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
@@ -56,7 +61,7 @@ reveal_type(d)  # revealed: tuple[tuple[str, str], tuple[int, int]]
 reveal_type(e)  # revealed: @Todo(full tuple[...] support)
 reveal_type(f)  # revealed: @Todo(full tuple[...] support)
 reveal_type(g)  # revealed: @Todo(full tuple[...] support)
-reveal_type(h)  # revealed: tuple[@Todo(generics), @Todo(generics)]
+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/attributes.md

@@ -302,7 +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)
@@ -397,15 +397,27 @@ 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
@@ -1665,7 +1677,7 @@ 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:
@@ -1698,9 +1710,9 @@ Most attribute accesses on bool-literal types are delegated to `builtins.bool`,
 bools are instances of that class:
 
 ```py
-# revealed: bound method Literal[True].__and__(**kwargs: @Todo(todo signature **kwargs)) -> @Todo(return type of overloaded function)
+# revealed: Overload[(value: bool, /) -> bool, (value: int, /) -> int]
 reveal_type(True.__and__)
-# revealed: bound method Literal[False].__or__(**kwargs: @Todo(todo signature **kwargs)) -> @Todo(return type of overloaded function)
+# revealed: Overload[(value: bool, /) -> bool, (value: int, /) -> int]
 reveal_type(False.__or__)
 ```
 
@@ -1716,7 +1728,8 @@ 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 Literal[b"foo"].join(iterable_of_bytes: @Todo(generics), /) -> bytes
+# 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)
 ```
@@ -1819,6 +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

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

@@ -310,9 +310,7 @@ 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 overloaded 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 overloaded 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 overloaded function)
+reveal_type(literal_string_instance + A())  # revealed: A
 ```
 
 ## Operations involving instances of classes inheriting from `Any`

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

@@ -50,9 +50,11 @@ 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 overloaded function)
-    reveal_type(2**x)  # revealed: @Todo(return type of overloaded function)
-    reveal_type(x**x)  # revealed: @Todo(return type of overloaded 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

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/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

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

@@ -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
@@ -399,6 +399,11 @@ reveal_type(getattr_static(C, "f").__get__("dummy", C))  # revealed: bound metho
 
 ### 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:
 

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

@@ -162,6 +162,31 @@ def _(flag: bool):
     reveal_type(f("string"))  # revealed: Literal["string", "'string'"]
 ```
 
+## Unions with literals and negations
+
+```py
+from typing import Literal, Union
+from knot_extensions import Not, AlwaysFalsy, static_assert, is_subtype_of, is_assignable_to
+
+static_assert(is_subtype_of(Literal["a", ""], Union[Literal["a", ""], Not[AlwaysFalsy]]))
+static_assert(is_subtype_of(Not[AlwaysFalsy], Union[Literal["", "a"], Not[AlwaysFalsy]]))
+static_assert(is_subtype_of(Literal["a", ""], Union[Not[AlwaysFalsy], Literal["a", ""]]))
+static_assert(is_subtype_of(Not[AlwaysFalsy], Union[Not[AlwaysFalsy], Literal["a", ""]]))
+
+static_assert(is_subtype_of(Literal["a", ""], Union[Literal["a", ""], Not[Literal[""]]]))
+static_assert(is_subtype_of(Not[Literal[""]], Union[Literal["a", ""], Not[Literal[""]]]))
+static_assert(is_subtype_of(Literal["a", ""], Union[Not[Literal[""]], Literal["a", ""]]))
+static_assert(is_subtype_of(Not[Literal[""]], Union[Not[Literal[""]], Literal["a", ""]]))
+
+def _(
+    x: Union[Literal["a", ""], Not[AlwaysFalsy]],
+    y: Union[Literal["a", ""], Not[Literal[""]]],
+):
+    reveal_type(x)  # revealed: Literal[""] | ~AlwaysFalsy
+    # TODO should be `object`
+    reveal_type(y)  # revealed: Literal[""] | ~Literal[""]
+```
+
 ## Cannot use an argument as both a value and a type form
 
 ```py
@@ -201,3 +226,15 @@ def _(literals_2: Literal[0, 1], b: bool, flag: bool):
     # 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

@@ -265,6 +265,11 @@ def f(flag: bool):
 
 ## Supers with Generic Classes
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 ```py
 from knot_extensions import TypeOf, static_assert, is_subtype_of
 
@@ -316,6 +321,11 @@ class A:
 
 ### 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.

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

crates/red_knot_python_semantic/resources/mdtest/dataclass_transform.md

@@ -0,0 +1,293 @@
+# `typing.dataclass_transform`
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+`dataclass_transform` is a decorator that can be used to let type checkers know that a function,
+class, or metaclass is a `dataclass`-like construct.
+
+## Basic example
+
+```py
+from typing_extensions import dataclass_transform
+
+@dataclass_transform()
+def my_dataclass[T](cls: type[T]) -> type[T]:
+    # modify cls
+    return cls
+
+@my_dataclass
+class Person:
+    name: str
+    age: int | None = None
+
+Person("Alice", 20)
+Person("Bob", None)
+Person("Bob")
+
+# error: [missing-argument]
+Person()
+```
+
+## Decorating decorators that take parameters themselves
+
+If we want our `dataclass`-like decorator to also take parameters, that is also possible:
+
+```py
+from typing_extensions import dataclass_transform, Callable
+
+@dataclass_transform()
+def versioned_class[T](*, version: int = 1):
+    def decorator(cls):
+        # modify cls
+        return cls
+    return decorator
+
+@versioned_class(version=2)
+class Person:
+    name: str
+    age: int | None = None
+
+Person("Alice", 20)
+
+# error: [missing-argument]
+Person()
+```
+
+We properly type-check the arguments to the decorator:
+
+```py
+from typing_extensions import dataclass_transform, Callable
+
+# error: [invalid-argument-type]
+@versioned_class(version="a string")
+class C:
+    name: str
+```
+
+## Types of decorators
+
+The examples from this section are straight from the Python documentation on
+[`typing.dataclass_transform`].
+
+### Decorating a decorator function
+
+```py
+from typing_extensions import dataclass_transform
+
+@dataclass_transform()
+def create_model[T](cls: type[T]) -> type[T]:
+    ...
+    return cls
+
+@create_model
+class CustomerModel:
+    id: int
+    name: str
+
+CustomerModel(id=1, name="Test")
+```
+
+### Decorating a metaclass
+
+```py
+from typing_extensions import dataclass_transform
+
+@dataclass_transform()
+class ModelMeta(type): ...
+
+class ModelBase(metaclass=ModelMeta): ...
+
+class CustomerModel(ModelBase):
+    id: int
+    name: str
+
+CustomerModel(id=1, name="Test")
+
+# error: [missing-argument]
+CustomerModel()
+```
+
+### Decorating a base class
+
+```py
+from typing_extensions import dataclass_transform
+
+@dataclass_transform()
+class ModelBase: ...
+
+class CustomerModel(ModelBase):
+    id: int
+    name: str
+
+# TODO: this is not supported yet
+# error: [unknown-argument]
+# error: [unknown-argument]
+CustomerModel(id=1, name="Test")
+```
+
+## Arguments to `dataclass_transform`
+
+### `eq_default`
+
+`eq=True/False` does not have a observable effect (apart from a minor change regarding whether
+`other` is positional-only or not, which is not modelled at the moment).
+
+### `order_default`
+
+The `order_default` argument controls whether methods such as `__lt__` are generated by default.
+This can be overwritten using the `order` argument to the custom decorator:
+
+```py
+from typing_extensions import dataclass_transform
+
+@dataclass_transform()
+def normal(*, order: bool = False):
+    raise NotImplementedError
+
+@dataclass_transform(order_default=False)
+def order_default_false(*, order: bool = False):
+    raise NotImplementedError
+
+@dataclass_transform(order_default=True)
+def order_default_true(*, order: bool = True):
+    raise NotImplementedError
+
+@normal
+class Normal:
+    inner: int
+
+Normal(1) < Normal(2)  # error: [unsupported-operator]
+
+@normal(order=True)
+class NormalOverwritten:
+    inner: int
+
+NormalOverwritten(1) < NormalOverwritten(2)
+
+@order_default_false
+class OrderFalse:
+    inner: int
+
+OrderFalse(1) < OrderFalse(2)  # error: [unsupported-operator]
+
+@order_default_false(order=True)
+class OrderFalseOverwritten:
+    inner: int
+
+OrderFalseOverwritten(1) < OrderFalseOverwritten(2)
+
+@order_default_true
+class OrderTrue:
+    inner: int
+
+OrderTrue(1) < OrderTrue(2)
+
+@order_default_true(order=False)
+class OrderTrueOverwritten:
+    inner: int
+
+# error: [unsupported-operator]
+OrderTrueOverwritten(1) < OrderTrueOverwritten(2)
+```
+
+### `kw_only_default`
+
+To do
+
+### `field_specifiers`
+
+To do
+
+## Overloaded dataclass-like decorators
+
+In the case of an overloaded decorator, the `dataclass_transform` decorator can be applied to the
+implementation, or to *one* of the overloads.
+
+### Applying `dataclass_transform` to the implementation
+
+```py
+from typing_extensions import dataclass_transform, TypeVar, Callable, overload
+
+T = TypeVar("T", bound=type)
+
+@overload
+def versioned_class(
+    cls: T,
+    *,
+    version: int = 1,
+) -> T: ...
+@overload
+def versioned_class(
+    *,
+    version: int = 1,
+) -> Callable[[T], T]: ...
+@dataclass_transform()
+def versioned_class(
+    cls: T | None = None,
+    *,
+    version: int = 1,
+) -> T | Callable[[T], T]:
+    raise NotImplementedError
+
+@versioned_class
+class D1:
+    x: str
+
+@versioned_class(version=2)
+class D2:
+    x: str
+
+D1("a")
+D2("a")
+
+D1(1.2)  # error: [invalid-argument-type]
+D2(1.2)  # error: [invalid-argument-type]
+```
+
+### Applying `dataclass_transform` to an overload
+
+```py
+from typing_extensions import dataclass_transform, TypeVar, Callable, overload
+
+T = TypeVar("T", bound=type)
+
+@overload
+@dataclass_transform()
+def versioned_class(
+    cls: T,
+    *,
+    version: int = 1,
+) -> T: ...
+@overload
+def versioned_class(
+    *,
+    version: int = 1,
+) -> Callable[[T], T]: ...
+def versioned_class(
+    cls: T | None = None,
+    *,
+    version: int = 1,
+) -> T | Callable[[T], T]:
+    raise NotImplementedError
+
+@versioned_class
+class D1:
+    x: str
+
+@versioned_class(version=2)
+class D2:
+    x: str
+
+# TODO: these should not be errors
+D1("a")  # error: [too-many-positional-arguments]
+D2("a")  # error: [too-many-positional-arguments]
+
+# TODO: these should be invalid-argument-type errors
+D1(1.2)  # error: [too-many-positional-arguments]
+D2(1.2)  # error: [too-many-positional-arguments]
+```
+
+[`typing.dataclass_transform`]: https://docs.python.org/3/library/typing.html#typing.dataclass_transform

crates/red_knot_python_semantic/resources/mdtest/dataclasses.md

@@ -297,6 +297,11 @@ 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:
 
@@ -471,6 +476,11 @@ reveal_type(C.__init__)  # revealed: (x: int = Literal[15], y: int = Literal[0],
 
 ## Generic dataclasses
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 ```py
 from dataclasses import dataclass
 
@@ -537,14 +547,14 @@ the descriptor's `__get__` method as if it had been called on the class itself,
 for the `instance` argument.
 
 ```py
-from typing import overload
+from typing import Literal, overload
 from dataclasses import dataclass
 
 class ConvertToLength:
     _len: int = 0
 
     @overload
-    def __get__(self, instance: None, owner: type) -> str: ...
+    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:
@@ -560,12 +570,10 @@ class ConvertToLength:
 class C:
     converter: ConvertToLength = ConvertToLength()
 
-# TODO: Should be `(converter: str = Literal[""]) -> None` once we understand overloads
-reveal_type(C.__init__)  # revealed: (converter: str = str | int) -> None
+reveal_type(C.__init__)  # revealed: (converter: str = Literal[""]) -> None
 
 c = C("abc")
-# TODO: Should be `int` once we understand overloads
-reveal_type(c.converter)  # revealed: str | int
+reveal_type(c.converter)  # revealed: int
 
 # This is also okay:
 C()
@@ -601,8 +609,7 @@ class AcceptsStrAndInt:
 class C:
     field: AcceptsStrAndInt = AcceptsStrAndInt()
 
-# TODO: Should be `field: str | int = int` once we understand overloads
-reveal_type(C.__init__)  # revealed: (field: Unknown = int) -> None
+reveal_type(C.__init__)  # revealed: (field: str | int = int) -> None
 ```
 
 ## `dataclasses.field`
@@ -682,7 +689,7 @@ from dataclasses import dataclass
 
 dataclass_with_order = dataclass(order=True)
 
-reveal_type(dataclass_with_order)  # revealed: <decorator produced by dataclasses.dataclass>
+reveal_type(dataclass_with_order)  # revealed: <decorator produced by dataclass-like function>
 
 @dataclass_with_order
 class C:

crates/red_knot_python_semantic/resources/mdtest/decorators.md

@@ -145,10 +145,10 @@ def f(x: int) -> int:
     return x**2
 
 # TODO: Should be `_lru_cache_wrapper[int]`
-reveal_type(f)  # revealed: @Todo(generics)
+reveal_type(f)  # revealed: @Todo(specialized non-generic class)
 
 # TODO: Should be `int`
-reveal_type(f(1))  # revealed: @Todo(generics)
+reveal_type(f(1))  # revealed: @Todo(specialized non-generic class)
 ```
 
 ## Lambdas as decorators

crates/red_knot_python_semantic/resources/mdtest/descriptor_protocol.md

@@ -459,11 +459,9 @@ class Descriptor:
 class C:
     d: Descriptor = Descriptor()
 
-# TODO: should be `Literal["called on class object"]
-reveal_type(C.d)  # revealed: LiteralString
+reveal_type(C.d)  # revealed: Literal["called on class object"]
 
-# TODO: should be `Literal["called on instance"]
-reveal_type(C().d)  # revealed: LiteralString
+reveal_type(C().d)  # revealed: Literal["called on instance"]
 ```
 
 ## Descriptor protocol for dunder methods

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

@@ -0,0 +1,19 @@
+# Shadowing
+
+<!-- snapshot-diagnostics -->
+
+## Implicit class shadowing
+
+```py
+class C: ...
+
+C = 1  # error: [invalid-assignment]
+```
+
+## Implicit function shadowing
+
+```py
+def f(): ...
+
+f = 1  # error: [invalid-assignment]
+```

crates/red_knot_python_semantic/resources/mdtest/diagnostics/unpacking.md

@@ -8,14 +8,20 @@
 a, b = 1  # error: [not-iterable]
 ```
 
-## Too many values to unpack
+## Exactly too many values to unpack
 
 ```py
 a, b = (1, 2, 3)  # error: [invalid-assignment]
 ```
 
-## Too few values to unpack
+## Exactly too few values to unpack
 
 ```py
 a, b = (1,)  # error: [invalid-assignment]
 ```
+
+## Too few values to unpack
+
+```py
+[a, *b, c, d] = (1, 2)  # error: [invalid-assignment]
+```

crates/red_knot_python_semantic/resources/mdtest/diagnostics/version_related_syntax_errors.md

@@ -0,0 +1,37 @@
+# Version-related syntax error diagnostics
+
+## `match` statement
+
+The `match` statement was introduced in Python 3.10.
+
+### Before 3.10
+
+<!-- snapshot-diagnostics -->
+
+We should emit a syntax error before 3.10.
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+```py
+match 2:  # error: 1 [invalid-syntax] "Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)"
+    case 1:
+        print("it's one")
+```
+
+### After 3.10
+
+On or after 3.10, no error should be reported.
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+match 2:
+    case 1:
+        print("it's one")
+```

crates/red_knot_python_semantic/resources/mdtest/directives/assert_never.md

@@ -26,6 +26,11 @@ def _(never: Never, any_: Any, unknown: Unknown, flag: bool):
 
 ## Use case: Type narrowing and exhaustiveness checking
 
+```toml
+[environment]
+python-version = "3.10"
+```
+
 `assert_never` can be used in combination with type narrowing as a way to make sure that all cases
 are handled in a series of `isinstance` checks or other narrowing patterns that are supported.
 

crates/red_knot_python_semantic/resources/mdtest/directives/cast.md

@@ -61,7 +61,7 @@ from knot_extensions import Unknown
 
 def f(x: Any, y: Unknown, z: Any | str | int):
     a = cast(dict[str, Any], x)
-    reveal_type(a)  # revealed: @Todo(generics)
+    reveal_type(a)  # revealed: @Todo(specialized non-generic class)
 
     b = cast(Any, y)
     reveal_type(b)  # revealed: Any

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

@@ -76,6 +76,11 @@ def g(x: Any = "foo"):
 
 ## Stub functions
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 ### In Protocol
 
 ```py

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

@@ -56,6 +56,11 @@ def f() -> int:
 
 ### In Protocol
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 ```py
 from typing import Protocol, TypeVar
 
@@ -69,8 +74,6 @@ class Baz(Bar):
 T = TypeVar("T")
 
 class Qux(Protocol[T]):
-    # TODO: no error
-    # error: [invalid-return-type]
     def f(self) -> int: ...
 
 class Foo(Protocol):
@@ -85,6 +88,11 @@ class Lorem(t[0]):
 
 ### In abstract method
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 ```py
 from abc import ABC, abstractmethod
 

crates/red_knot_python_semantic/resources/mdtest/generics/classes.md

@@ -1,5 +1,10 @@
 # Generic classes
 
+```toml
+[environment]
+python-version = "3.13"
+```
+
 ## PEP 695 syntax
 
 TODO: Add a `red_knot_extension` function that asserts whether a function or class is generic.
@@ -40,8 +45,6 @@ from typing import Generic, TypeVar
 
 T = TypeVar("T")
 
-# TODO: no error
-# error: [invalid-base]
 class C(Generic[T]): ...
 ```
 
@@ -159,12 +162,12 @@ consistent with each other.
 
 ```py
 class C[T]:
-    def __new__(cls, x: T) -> "C"[T]:
+    def __new__(cls, x: T) -> "C[T]":
         return object.__new__(cls)
 
 reveal_type(C(1))  # revealed: C[Literal[1]]
 
-# TODO: error: [invalid-argument-type]
+# error: [invalid-assignment] "Object of type `C[Literal["five"]]` is not assignable to `C[int]`"
 wrong_innards: C[int] = C("five")
 ```
 
@@ -176,7 +179,7 @@ class C[T]:
 
 reveal_type(C(1))  # revealed: C[Literal[1]]
 
-# TODO: error: [invalid-argument-type]
+# error: [invalid-assignment] "Object of type `C[Literal["five"]]` is not assignable to `C[int]`"
 wrong_innards: C[int] = C("five")
 ```
 
@@ -184,14 +187,14 @@ wrong_innards: C[int] = C("five")
 
 ```py
 class C[T]:
-    def __new__(cls, x: T) -> "C"[T]:
+    def __new__(cls, x: T) -> "C[T]":
         return object.__new__(cls)
 
     def __init__(self, x: T) -> None: ...
 
 reveal_type(C(1))  # revealed: C[Literal[1]]
 
-# TODO: error: [invalid-argument-type]
+# error: [invalid-assignment] "Object of type `C[Literal["five"]]` is not assignable to `C[int]`"
 wrong_innards: C[int] = C("five")
 ```
 
@@ -199,25 +202,25 @@ wrong_innards: C[int] = C("five")
 
 ```py
 class C[T]:
-    def __new__(cls, *args, **kwargs) -> "C"[T]:
+    def __new__(cls, *args, **kwargs) -> "C[T]":
         return object.__new__(cls)
 
     def __init__(self, x: T) -> None: ...
 
 reveal_type(C(1))  # revealed: C[Literal[1]]
 
-# TODO: error: [invalid-argument-type]
+# error: [invalid-assignment] "Object of type `C[Literal["five"]]` is not assignable to `C[int]`"
 wrong_innards: C[int] = C("five")
 
 class D[T]:
-    def __new__(cls, x: T) -> "D"[T]:
+    def __new__(cls, x: T) -> "D[T]":
         return object.__new__(cls)
 
     def __init__(self, *args, **kwargs) -> None: ...
 
 reveal_type(D(1))  # revealed: D[Literal[1]]
 
-# TODO: error: [invalid-argument-type]
+# error: [invalid-assignment] "Object of type `D[Literal["five"]]` is not assignable to `D[int]`"
 wrong_innards: D[int] = D("five")
 ```
 
@@ -242,7 +245,7 @@ reveal_type(C(1, "string"))  # revealed: C[Unknown]
 # error: [invalid-argument-type]
 reveal_type(C(1, True))  # revealed: C[Unknown]
 
-# TODO: error for the correct reason
+# TODO: [invalid-assignment] "Object of type `C[Literal["five"]]` is not assignable to `C[int]`"
 # error: [invalid-argument-type] "Argument to this function is incorrect: Expected `S`, found `Literal[1]`"
 wrong_innards: C[int] = C("five", 1)
 ```

crates/red_knot_python_semantic/resources/mdtest/generics/functions.md

@@ -1,5 +1,10 @@
 # Generic functions
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 ## Typevar must be used at least twice
 
 If you're only using a typevar for a single parameter, you don't need the typevar — just use

crates/red_knot_python_semantic/resources/mdtest/generics/pep695.md

@@ -1,5 +1,10 @@
 # PEP 695 Generics
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 [PEP 695] and Python 3.12 introduced new, more ergonomic syntax for type variables.
 
 ## Type variables
@@ -59,19 +64,19 @@ is.)
 from knot_extensions import is_fully_static, static_assert
 from typing import Any
 
-def unbounded_unconstrained[T](t: list[T]) -> None:
+def unbounded_unconstrained[T](t: T) -> None:
     static_assert(is_fully_static(T))
 
-def bounded[T: int](t: list[T]) -> None:
+def bounded[T: int](t: T) -> None:
     static_assert(is_fully_static(T))
 
-def bounded_by_gradual[T: Any](t: list[T]) -> None:
+def bounded_by_gradual[T: Any](t: T) -> None:
     static_assert(not is_fully_static(T))
 
-def constrained[T: (int, str)](t: list[T]) -> None:
+def constrained[T: (int, str)](t: T) -> None:
     static_assert(is_fully_static(T))
 
-def constrained_by_gradual[T: (int, Any)](t: list[T]) -> None:
+def constrained_by_gradual[T: (int, Any)](t: T) -> None:
     static_assert(not is_fully_static(T))
 ```
 
@@ -94,7 +99,7 @@ class Base(Super): ...
 class Sub(Base): ...
 class Unrelated: ...
 
-def unbounded_unconstrained[T, U](t: list[T], u: list[U]) -> None:
+def unbounded_unconstrained[T, U](t: T, u: U) -> None:
     static_assert(is_assignable_to(T, T))
     static_assert(is_assignable_to(T, object))
     static_assert(not is_assignable_to(T, Super))
@@ -124,7 +129,7 @@ is a final class, since the typevar can still be specialized to `Never`.)
 from typing import Any
 from typing_extensions import final
 
-def bounded[T: Super](t: list[T]) -> None:
+def bounded[T: Super](t: T) -> None:
     static_assert(is_assignable_to(T, Super))
     static_assert(not is_assignable_to(T, Sub))
     static_assert(not is_assignable_to(Super, T))
@@ -135,7 +140,7 @@ def bounded[T: Super](t: list[T]) -> None:
     static_assert(not is_subtype_of(Super, T))
     static_assert(not is_subtype_of(Sub, T))
 
-def bounded_by_gradual[T: Any](t: list[T]) -> None:
+def bounded_by_gradual[T: Any](t: T) -> None:
     static_assert(is_assignable_to(T, Any))
     static_assert(is_assignable_to(Any, T))
     static_assert(is_assignable_to(T, Super))
@@ -153,7 +158,7 @@ def bounded_by_gradual[T: Any](t: list[T]) -> None:
 @final
 class FinalClass: ...
 
-def bounded_final[T: FinalClass](t: list[T]) -> None:
+def bounded_final[T: FinalClass](t: T) -> None:
     static_assert(is_assignable_to(T, FinalClass))
     static_assert(not is_assignable_to(FinalClass, T))
 
@@ -167,14 +172,14 @@ true even if both typevars are bounded by the same final class, since you can sp
 typevars to `Never` in addition to that final class.
 
 ```py
-def two_bounded[T: Super, U: Super](t: list[T], u: list[U]) -> None:
+def two_bounded[T: Super, U: Super](t: T, u: U) -> None:
     static_assert(not is_assignable_to(T, U))
     static_assert(not is_assignable_to(U, T))
 
     static_assert(not is_subtype_of(T, U))
     static_assert(not is_subtype_of(U, T))
 
-def two_final_bounded[T: FinalClass, U: FinalClass](t: list[T], u: list[U]) -> None:
+def two_final_bounded[T: FinalClass, U: FinalClass](t: T, u: U) -> None:
     static_assert(not is_assignable_to(T, U))
     static_assert(not is_assignable_to(U, T))
 
@@ -189,7 +194,7 @@ intersection of all of its constraints is a subtype of the typevar.
 ```py
 from knot_extensions import Intersection
 
-def constrained[T: (Base, Unrelated)](t: list[T]) -> None:
+def constrained[T: (Base, Unrelated)](t: T) -> None:
     static_assert(not is_assignable_to(T, Super))
     static_assert(not is_assignable_to(T, Base))
     static_assert(not is_assignable_to(T, Sub))
@@ -214,7 +219,7 @@ def constrained[T: (Base, Unrelated)](t: list[T]) -> None:
     static_assert(not is_subtype_of(Super | Unrelated, T))
     static_assert(is_subtype_of(Intersection[Base, Unrelated], T))
 
-def constrained_by_gradual[T: (Base, Any)](t: list[T]) -> None:
+def constrained_by_gradual[T: (Base, Any)](t: T) -> None:
     static_assert(is_assignable_to(T, Super))
     static_assert(is_assignable_to(T, Base))
     static_assert(not is_assignable_to(T, Sub))
@@ -256,7 +261,7 @@ distinct constraints, meaning that there is (still) no guarantee that they will
 the same type.
 
 ```py
-def two_constrained[T: (int, str), U: (int, str)](t: list[T], u: list[U]) -> None:
+def two_constrained[T: (int, str), U: (int, str)](t: T, u: U) -> None:
     static_assert(not is_assignable_to(T, U))
     static_assert(not is_assignable_to(U, T))
 
@@ -266,7 +271,7 @@ def two_constrained[T: (int, str), U: (int, str)](t: list[T], u: list[U]) -> Non
 @final
 class AnotherFinalClass: ...
 
-def two_final_constrained[T: (FinalClass, AnotherFinalClass), U: (FinalClass, AnotherFinalClass)](t: list[T], u: list[U]) -> None:
+def two_final_constrained[T: (FinalClass, AnotherFinalClass), U: (FinalClass, AnotherFinalClass)](t: T, u: U) -> None:
     static_assert(not is_assignable_to(T, U))
     static_assert(not is_assignable_to(U, T))
 
@@ -285,7 +290,7 @@ non-singleton type.
 ```py
 from knot_extensions import is_singleton, is_single_valued, static_assert
 
-def unbounded_unconstrained[T](t: list[T]) -> None:
+def unbounded_unconstrained[T](t: T) -> None:
     static_assert(not is_singleton(T))
     static_assert(not is_single_valued(T))
 ```
@@ -294,7 +299,7 @@ A bounded typevar is not a singleton, even if its bound is a singleton, since it
 specialized to `Never`.
 
 ```py
-def bounded[T: None](t: list[T]) -> None:
+def bounded[T: None](t: T) -> None:
     static_assert(not is_singleton(T))
     static_assert(not is_single_valued(T))
 ```
@@ -305,14 +310,14 @@ specialize a constrained typevar to a subtype of a constraint.)
 ```py
 from typing_extensions import Literal
 
-def constrained_non_singletons[T: (int, str)](t: list[T]) -> None:
+def constrained_non_singletons[T: (int, str)](t: T) -> None:
     static_assert(not is_singleton(T))
     static_assert(not is_single_valued(T))
 
-def constrained_singletons[T: (Literal[True], Literal[False])](t: list[T]) -> None:
+def constrained_singletons[T: (Literal[True], Literal[False])](t: T) -> None:
     static_assert(is_singleton(T))
 
-def constrained_single_valued[T: (Literal[True], tuple[()])](t: list[T]) -> None:
+def constrained_single_valued[T: (Literal[True], tuple[()])](t: T) -> None:
     static_assert(is_single_valued(T))
 ```
 

crates/red_knot_python_semantic/resources/mdtest/generics/scoping.md

@@ -1,5 +1,10 @@
 # Scoping rules for type variables
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 Most of these tests come from the [Scoping rules for type variables][scoping] section of the typing
 spec.
 
@@ -132,8 +137,6 @@ from typing import TypeVar, Generic
 T = TypeVar("T")
 S = TypeVar("S")
 
-# TODO: no error
-# error: [invalid-base]
 class Legacy(Generic[T]):
     def m(self, x: T, y: S) -> S:
         return y
@@ -169,13 +172,11 @@ S = TypeVar("S")
 
 def f(x: T) -> None:
     x: list[T] = []
-    # TODO: error
+    # TODO: invalid-assignment error
     y: list[S] = []
 
-# TODO: no error
-# error: [invalid-base]
 class C(Generic[T]):
-    # TODO: error
+    # TODO: error: cannot use S if it's not in the current generic context
     x: list[S] = []
 
     # This is not an error, as shown in the previous test
@@ -195,11 +196,11 @@ S = TypeVar("S")
 
 def f[T](x: T) -> None:
     x: list[T] = []
-    # TODO: error
+    # TODO: invalid assignment error
     y: list[S] = []
 
 class C[T]:
-    # TODO: error
+    # TODO: error: cannot use S if it's not in the current generic context
     x: list[S] = []
 
     def m1(self, x: S) -> S:
@@ -254,8 +255,7 @@ def f[T](x: T, y: T) -> None:
     class Ok[S]: ...
     # TODO: error for reuse of typevar
     class Bad1[T]: ...
-    # TODO: no non-subscriptable error, error for reuse of typevar
-    # error: [non-subscriptable]
+    # TODO: error for reuse of typevar
     class Bad2(Iterable[T]): ...
 ```
 
@@ -268,8 +268,7 @@ class C[T]:
     class Ok1[S]: ...
     # TODO: error for reuse of typevar
     class Bad1[T]: ...
-    # TODO: no non-subscriptable error, error for reuse of typevar
-    # error: [non-subscriptable]
+    # TODO: error for reuse of typevar
     class Bad2(Iterable[T]): ...
 ```
 
@@ -283,7 +282,7 @@ class C[T]:
     ok1: list[T] = []
 
     class Bad:
-        # TODO: error
+        # TODO: error: cannot refer to T in nested scope
         bad: list[T] = []
 
     class Inner[S]: ...

crates/red_knot_python_semantic/resources/mdtest/generics/variance.md

@@ -0,0 +1,277 @@
+# Variance
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+Type variables have a property called _variance_ that affects the subtyping and assignability
+relations. Much more detail can be found in the [spec]. To summarize, each typevar is either
+**covariant**, **contravariant**, **invariant**, or **bivariant**. (Note that bivariance is not
+currently mentioned in the typing spec, but is a fourth case that we must consider.)
+
+For all of the examples below, we will consider a typevar `T`, a generic class using that typevar
+`C[T]`, and two types `A` and `B`.
+
+## Covariance
+
+With a covariant typevar, subtyping is in "alignment": if `A <: B`, then `C[A] <: C[B]`.
+
+Types that "produce" data on demand are covariant in their typevar. If you expect a sequence of
+`int`s, someone can safely provide a sequence of `bool`s, since each `bool` element that you would
+get from the sequence is a valid `int`.
+
+```py
+from knot_extensions import is_assignable_to, is_equivalent_to, is_gradual_equivalent_to, is_subtype_of, static_assert, Unknown
+from typing import Any
+
+class A: ...
+class B(A): ...
+
+class C[T]:
+    def receive(self) -> T:
+        raise ValueError
+
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_assignable_to(C[B], C[A]))
+static_assert(not is_assignable_to(C[A], C[B]))
+static_assert(is_assignable_to(C[A], C[Any]))
+static_assert(is_assignable_to(C[B], C[Any]))
+static_assert(is_assignable_to(C[Any], C[A]))
+static_assert(is_assignable_to(C[Any], C[B]))
+
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_subtype_of(C[B], C[A]))
+static_assert(not is_subtype_of(C[A], C[B]))
+static_assert(not is_subtype_of(C[A], C[Any]))
+static_assert(not is_subtype_of(C[B], C[Any]))
+static_assert(not is_subtype_of(C[Any], C[A]))
+static_assert(not is_subtype_of(C[Any], C[B]))
+
+static_assert(is_equivalent_to(C[A], C[A]))
+static_assert(is_equivalent_to(C[B], C[B]))
+static_assert(not is_equivalent_to(C[B], C[A]))
+static_assert(not is_equivalent_to(C[A], C[B]))
+static_assert(not is_equivalent_to(C[A], C[Any]))
+static_assert(not is_equivalent_to(C[B], C[Any]))
+static_assert(not is_equivalent_to(C[Any], C[A]))
+static_assert(not is_equivalent_to(C[Any], C[B]))
+
+static_assert(is_gradual_equivalent_to(C[A], C[A]))
+static_assert(is_gradual_equivalent_to(C[B], C[B]))
+static_assert(is_gradual_equivalent_to(C[Any], C[Any]))
+static_assert(is_gradual_equivalent_to(C[Any], C[Unknown]))
+static_assert(not is_gradual_equivalent_to(C[B], C[A]))
+static_assert(not is_gradual_equivalent_to(C[A], C[B]))
+static_assert(not is_gradual_equivalent_to(C[A], C[Any]))
+static_assert(not is_gradual_equivalent_to(C[B], C[Any]))
+static_assert(not is_gradual_equivalent_to(C[Any], C[A]))
+static_assert(not is_gradual_equivalent_to(C[Any], C[B]))
+```
+
+## Contravariance
+
+With a contravariant typevar, subtyping is in "opposition": if `A <: B`, then `C[B] <: C[A]`.
+
+Types that "consume" data are contravariant in their typevar. If you expect a consumer that receives
+`bool`s, someone can safely provide a consumer that expects to receive `int`s, since each `bool`
+that you pass into the consumer is a valid `int`.
+
+```py
+from knot_extensions import is_assignable_to, is_equivalent_to, is_gradual_equivalent_to, is_subtype_of, static_assert, Unknown
+from typing import Any
+
+class A: ...
+class B(A): ...
+
+class C[T]:
+    def send(self, value: T): ...
+
+static_assert(not is_assignable_to(C[B], C[A]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_assignable_to(C[A], C[B]))
+static_assert(is_assignable_to(C[A], C[Any]))
+static_assert(is_assignable_to(C[B], C[Any]))
+static_assert(is_assignable_to(C[Any], C[A]))
+static_assert(is_assignable_to(C[Any], C[B]))
+
+static_assert(not is_subtype_of(C[B], C[A]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_subtype_of(C[A], C[B]))
+static_assert(not is_subtype_of(C[A], C[Any]))
+static_assert(not is_subtype_of(C[B], C[Any]))
+static_assert(not is_subtype_of(C[Any], C[A]))
+static_assert(not is_subtype_of(C[Any], C[B]))
+
+static_assert(is_equivalent_to(C[A], C[A]))
+static_assert(is_equivalent_to(C[B], C[B]))
+static_assert(not is_equivalent_to(C[B], C[A]))
+static_assert(not is_equivalent_to(C[A], C[B]))
+static_assert(not is_equivalent_to(C[A], C[Any]))
+static_assert(not is_equivalent_to(C[B], C[Any]))
+static_assert(not is_equivalent_to(C[Any], C[A]))
+static_assert(not is_equivalent_to(C[Any], C[B]))
+
+static_assert(is_gradual_equivalent_to(C[A], C[A]))
+static_assert(is_gradual_equivalent_to(C[B], C[B]))
+static_assert(is_gradual_equivalent_to(C[Any], C[Any]))
+static_assert(is_gradual_equivalent_to(C[Any], C[Unknown]))
+static_assert(not is_gradual_equivalent_to(C[B], C[A]))
+static_assert(not is_gradual_equivalent_to(C[A], C[B]))
+static_assert(not is_gradual_equivalent_to(C[A], C[Any]))
+static_assert(not is_gradual_equivalent_to(C[B], C[Any]))
+static_assert(not is_gradual_equivalent_to(C[Any], C[A]))
+static_assert(not is_gradual_equivalent_to(C[Any], C[B]))
+```
+
+## Invariance
+
+With an invariant typevar, _no_ specializations of the generic class are subtypes of each other.
+
+This often occurs for types that are both producers _and_ consumers, like a mutable `list`.
+Iterating over the elements in a list would work with a covariant typevar, just like with the
+"producer" type above. Appending elements to a list would work with a contravariant typevar, just
+like with the "consumer" type above. However, a typevar cannot be both covariant and contravariant
+at the same time!
+
+If you expect a mutable list of `int`s, it's not safe for someone to provide you with a mutable list
+of `bool`s, since you might try to add an element to the list: if you try to add an `int`, the list
+would no longer only contain elements that are subtypes of `bool`.
+
+Conversely, if you expect a mutable list of `bool`s, it's not safe for someone to provide you with a
+mutable list of `int`s, since you might try to extract elements from the list: you expect every
+element that you extract to be a subtype of `bool`, but the list can contain any `int`.
+
+In the end, if you expect a mutable list, you must always be given a list of exactly that type,
+since we can't know in advance which of the allowed methods you'll want to use.
+
+```py
+from knot_extensions import is_assignable_to, is_equivalent_to, is_gradual_equivalent_to, is_subtype_of, static_assert, Unknown
+from typing import Any
+
+class A: ...
+class B(A): ...
+
+class C[T]:
+    def send(self, value: T): ...
+    def receive(self) -> T:
+        raise ValueError
+
+static_assert(not is_assignable_to(C[B], C[A]))
+static_assert(not is_assignable_to(C[A], C[B]))
+static_assert(is_assignable_to(C[A], C[Any]))
+static_assert(is_assignable_to(C[B], C[Any]))
+static_assert(is_assignable_to(C[Any], C[A]))
+static_assert(is_assignable_to(C[Any], C[B]))
+
+static_assert(not is_subtype_of(C[B], C[A]))
+static_assert(not is_subtype_of(C[A], C[B]))
+static_assert(not is_subtype_of(C[A], C[Any]))
+static_assert(not is_subtype_of(C[B], C[Any]))
+static_assert(not is_subtype_of(C[Any], C[A]))
+static_assert(not is_subtype_of(C[Any], C[B]))
+
+static_assert(is_equivalent_to(C[A], C[A]))
+static_assert(is_equivalent_to(C[B], C[B]))
+static_assert(not is_equivalent_to(C[B], C[A]))
+static_assert(not is_equivalent_to(C[A], C[B]))
+static_assert(not is_equivalent_to(C[A], C[Any]))
+static_assert(not is_equivalent_to(C[B], C[Any]))
+static_assert(not is_equivalent_to(C[Any], C[A]))
+static_assert(not is_equivalent_to(C[Any], C[B]))
+
+static_assert(is_gradual_equivalent_to(C[A], C[A]))
+static_assert(is_gradual_equivalent_to(C[B], C[B]))
+static_assert(is_gradual_equivalent_to(C[Any], C[Any]))
+static_assert(is_gradual_equivalent_to(C[Any], C[Unknown]))
+static_assert(not is_gradual_equivalent_to(C[B], C[A]))
+static_assert(not is_gradual_equivalent_to(C[A], C[B]))
+static_assert(not is_gradual_equivalent_to(C[A], C[Any]))
+static_assert(not is_gradual_equivalent_to(C[B], C[Any]))
+static_assert(not is_gradual_equivalent_to(C[Any], C[A]))
+static_assert(not is_gradual_equivalent_to(C[Any], C[B]))
+```
+
+## Bivariance
+
+With a bivariant typevar, _all_ specializations of the generic class are subtypes of (and in fact,
+equivalent to) each other.
+
+This is a bit of pathological case, which really only happens when the class doesn't use the typevar
+at all. (If it did, it would have to be covariant, contravariant, or invariant, depending on _how_
+the typevar was used.)
+
+```py
+from knot_extensions import is_assignable_to, is_equivalent_to, is_gradual_equivalent_to, is_subtype_of, static_assert, Unknown
+from typing import Any
+
+class A: ...
+class B(A): ...
+
+class C[T]:
+    pass
+
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_assignable_to(C[B], C[A]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_assignable_to(C[A], C[B]))
+static_assert(is_assignable_to(C[A], C[Any]))
+static_assert(is_assignable_to(C[B], C[Any]))
+static_assert(is_assignable_to(C[Any], C[A]))
+static_assert(is_assignable_to(C[Any], C[B]))
+
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_subtype_of(C[B], C[A]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_subtype_of(C[A], C[B]))
+static_assert(not is_subtype_of(C[A], C[Any]))
+static_assert(not is_subtype_of(C[B], C[Any]))
+static_assert(not is_subtype_of(C[Any], C[A]))
+static_assert(not is_subtype_of(C[Any], C[B]))
+
+static_assert(is_equivalent_to(C[A], C[A]))
+static_assert(is_equivalent_to(C[B], C[B]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_equivalent_to(C[B], C[A]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_equivalent_to(C[A], C[B]))
+static_assert(not is_equivalent_to(C[A], C[Any]))
+static_assert(not is_equivalent_to(C[B], C[Any]))
+static_assert(not is_equivalent_to(C[Any], C[A]))
+static_assert(not is_equivalent_to(C[Any], C[B]))
+
+static_assert(is_gradual_equivalent_to(C[A], C[A]))
+static_assert(is_gradual_equivalent_to(C[B], C[B]))
+static_assert(is_gradual_equivalent_to(C[Any], C[Any]))
+static_assert(is_gradual_equivalent_to(C[Any], C[Unknown]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_gradual_equivalent_to(C[B], C[A]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_gradual_equivalent_to(C[A], C[B]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_gradual_equivalent_to(C[A], C[Any]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_gradual_equivalent_to(C[B], C[Any]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_gradual_equivalent_to(C[Any], C[A]))
+# TODO: no error
+# error: [static-assert-error]
+static_assert(is_gradual_equivalent_to(C[Any], C[B]))
+```
+
+[spec]: https://typing.python.org/en/latest/spec/generics.html#variance

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

@@ -122,6 +122,11 @@ from c import Y  # error: [unresolved-import]
 
 ## Esoteric definitions and redefinintions
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 We understand all public symbols defined in an external module as being imported by a `*` import,
 not just those that are defined in `StmtAssign` nodes and `StmtAnnAssign` nodes. This section
 provides tests for definitions, and redefinitions, that use more esoteric AST nodes.

crates/red_knot_python_semantic/resources/mdtest/intersection_types.md

@@ -842,7 +842,7 @@ def unknown(
 
 ### Mixed dynamic types
 
-We currently do not simplify mixed dynamic types, but might consider doing so in the future:
+Gradually-equivalent types can be simplified out of intersections:
 
 ```py
 from typing import Any
@@ -854,10 +854,10 @@ def mixed(
     i3: Intersection[Not[Any], Unknown],
     i4: Intersection[Not[Any], Not[Unknown]],
 ) -> None:
-    reveal_type(i1)  # revealed: Any & Unknown
-    reveal_type(i2)  # revealed: Any & Unknown
-    reveal_type(i3)  # revealed: Any & Unknown
-    reveal_type(i4)  # revealed: Any & Unknown
+    reveal_type(i1)  # revealed: Any
+    reveal_type(i2)  # revealed: Any
+    reveal_type(i3)  # revealed: Any
+    reveal_type(i4)  # revealed: Any
 ```
 
 ## Invalid

crates/red_knot_python_semantic/resources/mdtest/metaclass.md

@@ -216,6 +216,11 @@ reveal_type(A.__class__)  # revealed: type[Unknown]
 
 ## PEP 695 generic
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 ```py
 class M(type): ...
 class A[T: str](metaclass=M): ...

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

@@ -0,0 +1,53 @@
+# Narrowing with assert statements
+
+## `assert` a value `is None` or `is not None`
+
+```py
+def _(x: str | None, y: str | None):
+    assert x is not None
+    reveal_type(x)  # revealed: str
+    assert y is None
+    reveal_type(y)  # revealed: None
+```
+
+## `assert` a value is truthy or falsy
+
+```py
+def _(x: bool, y: bool):
+    assert x
+    reveal_type(x)  # revealed: Literal[True]
+    assert not y
+    reveal_type(y)  # revealed: Literal[False]
+```
+
+## `assert` with `is` and `==` for literals
+
+```py
+from typing import Literal
+
+def _(x: Literal[1, 2, 3], y: Literal[1, 2, 3]):
+    assert x is 2
+    reveal_type(x)  # revealed: Literal[2]
+    assert y == 2
+    reveal_type(y)  # revealed: Literal[1, 2, 3]
+```
+
+## `assert` with `isinstance`
+
+```py
+def _(x: int | str):
+    assert isinstance(x, int)
+    reveal_type(x)  # revealed: int
+```
+
+## `assert` a value `in` a tuple
+
+```py
+from typing import Literal
+
+def _(x: Literal[1, 2, 3], y: Literal[1, 2, 3]):
+    assert x in (1, 2)
+    reveal_type(x)  # revealed: Literal[1, 2]
+    assert y not in (1, 2)
+    reveal_type(y)  # revealed: Literal[3]
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals/boolean.md

@@ -223,3 +223,15 @@ def _(x: str | None, y: str | None):
     if y is not x:
         reveal_type(y)  # revealed: str | None
 ```
+
+## Assignment expressions
+
+```py
+def f() -> bool:
+    return True
+
+if x := f():
+    reveal_type(x)  # revealed: Literal[True]
+else:
+    reveal_type(x)  # revealed: Literal[False]
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals/elif_else.md

@@ -47,3 +47,16 @@ def _(flag1: bool, flag2: bool):
         # TODO should be Never
         reveal_type(x)  # revealed: Literal[1, 2]
 ```
+
+## Assignment expressions
+
+```py
+def f() -> int | str | None: ...
+
+if isinstance(x := f(), int):
+    reveal_type(x)  # revealed: int
+elif isinstance(x, str):
+    reveal_type(x)  # revealed: str & ~int
+else:
+    reveal_type(x)  # revealed: None
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals/in.md

@@ -78,3 +78,17 @@ def _(x: Literal[1, "a", "b", "c", "d"]):
     else:
         reveal_type(x)  # revealed: Literal[1, "d"]
 ```
+
+## Assignment expressions
+
+```py
+from typing import Literal
+
+def f() -> Literal[1, 2, 3]:
+    return 1
+
+if (x := f()) in (1,):
+    reveal_type(x)  # revealed: Literal[1]
+else:
+    reveal_type(x)  # revealed: Literal[2, 3]
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals/is.md

@@ -100,3 +100,16 @@ def _(flag: bool):
     else:
         reveal_type(x)  # revealed: Literal[42]
 ```
+
+## Assignment expressions
+
+```py
+from typing import Literal
+
+def f() -> Literal[1, 2] | None: ...
+
+if (x := f()) is None:
+    reveal_type(x)  # revealed: None
+else:
+    reveal_type(x)  # revealed: Literal[1, 2]
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals/is_not.md

@@ -82,3 +82,14 @@ def _(x_flag: bool, y_flag: bool):
         reveal_type(x)  # revealed: bool
         reveal_type(y)  # revealed: bool
 ```
+
+## Assignment expressions
+
+```py
+def f() -> int | str | None: ...
+
+if (x := f()) is not None:
+    reveal_type(x)  # revealed: int | str
+else:
+    reveal_type(x)  # revealed: None
+```

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals/not_eq.md

@@ -89,3 +89,18 @@ def _(flag1: bool, flag2: bool, a: int):
     else:
         reveal_type(x)  # revealed: Literal[1, 2]
 ```
+
+## Assignment expressions
+
+```py
+from typing import Literal
+
+def f() -> Literal[1, 2, 3]:
+    return 1
+
+if (x := f()) != 1:
+    reveal_type(x)  # revealed: Literal[2, 3]
+else:
+    # TODO should be Literal[1]
+    reveal_type(x)  # revealed: Literal[1, 2, 3]
+```

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

@@ -1,5 +1,10 @@
 # Narrowing for `match` statements
 
+```toml
+[environment]
+python-version = "3.10"
+```
+
 ## Single `match` pattern
 
 ```py
@@ -34,8 +39,7 @@ match x:
     case A():
         reveal_type(x)  # revealed: A
     case B():
-        # TODO could be `B & ~A`
-        reveal_type(x)  # revealed: B
+        reveal_type(x)  # revealed: B & ~A
 
 reveal_type(x)  # revealed: object
 ```
@@ -83,7 +87,7 @@ match x:
     case 6.0:
         reveal_type(x)  # revealed: float
     case 1j:
-        reveal_type(x)  # revealed: complex
+        reveal_type(x)  # revealed: complex & ~float
     case b"foo":
         reveal_type(x)  # revealed: Literal[b"foo"]
 
@@ -129,11 +133,11 @@ match x:
     case "foo" | 42 | None:
         reveal_type(x)  # revealed: Literal["foo", 42] | None
     case "foo" | tuple():
-        reveal_type(x)  # revealed: Literal["foo"] | tuple
+        reveal_type(x)  # revealed: tuple
     case True | False:
         reveal_type(x)  # revealed: bool
     case 3.14 | 2.718 | 1.414:
-        reveal_type(x)  # revealed: float
+        reveal_type(x)  # revealed: float & ~tuple
 
 reveal_type(x)  # revealed: object
 ```
@@ -160,3 +164,49 @@ match x:
 
 reveal_type(x)  # revealed: object
 ```
+
+## Narrowing due to guard
+
+```py
+def get_object() -> object:
+    return object()
+
+x = get_object()
+
+reveal_type(x)  # revealed: object
+
+match x:
+    case str() | float() if type(x) is str:
+        reveal_type(x)  #  revealed: str
+    case "foo" | 42 | None if isinstance(x, int):
+        reveal_type(x)  #  revealed: Literal[42]
+    case False if x:
+        reveal_type(x)  #  revealed: Never
+    case "foo" if x := "bar":
+        reveal_type(x)  # revealed: Literal["bar"]
+
+reveal_type(x)  # revealed: object
+```
+
+## Guard and reveal_type in guard
+
+```py
+def get_object() -> object:
+    return object()
+
+x = get_object()
+
+reveal_type(x)  # revealed: object
+
+match x:
+    case str() | float() if type(x) is str and reveal_type(x):  # revealed: str
+        pass
+    case "foo" | 42 | None if isinstance(x, int) and reveal_type(x):  #  revealed: Literal[42]
+        pass
+    case False if x and reveal_type(x):  #  revealed: Never
+        pass
+    case "foo" if (x := "bar") and reveal_type(x):  #  revealed: Literal["bar"]
+        pass
+
+reveal_type(x)  # revealed: object
+```

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

@@ -246,7 +246,7 @@ class MetaTruthy(type):
 
 class MetaDeferred(type):
     def __bool__(self) -> MetaAmbiguous:
-        return MetaAmbiguous()
+        raise NotImplementedError
 
 class AmbiguousClass(metaclass=MetaAmbiguous): ...
 class FalsyClass(metaclass=MetaFalsy): ...

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

@@ -111,6 +111,11 @@ def _(x: A | B):
 
 ## Narrowing for generic classes
 
+```toml
+[environment]
+python-version = "3.13"
+```
+
 Note that `type` returns the runtime class of an object, which does _not_ include specializations in
 the case of a generic class. (The typevars are erased.) That means we cannot narrow the type to the
 specialization that we compare with; we must narrow to an unknown specialization of the generic
@@ -139,3 +144,13 @@ def _(x: Base):
         # express a constraint like `Base & ~ProperSubtypeOf[Base]`.
         reveal_type(x)  # revealed: Base
 ```
+
+## Assignment expressions
+
+```py
+def _(x: object):
+    if (y := type(x)) is bool:
+        reveal_type(y)  # revealed: Literal[bool]
+    if (type(y := x)) is bool:
+        reveal_type(y)  # revealed: bool
+```

crates/red_knot_python_semantic/resources/mdtest/overloads.md

@@ -0,0 +1,638 @@
+# Overloads
+
+Reference: <https://typing.python.org/en/latest/spec/overload.html>
+
+## `typing.overload`
+
+The definition of `typing.overload` in typeshed is an identity function.
+
+```py
+from typing import overload
+
+def foo(x: int) -> int:
+    return x
+
+reveal_type(foo)  # revealed: def foo(x: int) -> int
+bar = overload(foo)
+reveal_type(bar)  # revealed: def foo(x: int) -> int
+```
+
+## Functions
+
+```py
+from typing import overload
+
+@overload
+def add() -> None: ...
+@overload
+def add(x: int) -> int: ...
+@overload
+def add(x: int, y: int) -> int: ...
+def add(x: int | None = None, y: int | None = None) -> int | None:
+    return (x or 0) + (y or 0)
+
+reveal_type(add)  # revealed: Overload[() -> None, (x: int) -> int, (x: int, y: int) -> int]
+reveal_type(add())  # revealed: None
+reveal_type(add(1))  # revealed: int
+reveal_type(add(1, 2))  # revealed: int
+```
+
+## Overriding
+
+These scenarios are to verify that the overloaded and non-overloaded definitions are correctly
+overridden by each other.
+
+An overloaded function is overriding another overloaded function:
+
+```py
+from typing import overload
+
+@overload
+def foo() -> None: ...
+@overload
+def foo(x: int) -> int: ...
+def foo(x: int | None = None) -> int | None:
+    return x
+
+reveal_type(foo)  # revealed: Overload[() -> None, (x: int) -> int]
+reveal_type(foo())  # revealed: None
+reveal_type(foo(1))  # revealed: int
+
+@overload
+def foo() -> None: ...
+@overload
+def foo(x: str) -> str: ...
+def foo(x: str | None = None) -> str | None:
+    return x
+
+reveal_type(foo)  # revealed: Overload[() -> None, (x: str) -> str]
+reveal_type(foo())  # revealed: None
+reveal_type(foo(""))  # revealed: str
+```
+
+A non-overloaded function is overriding an overloaded function:
+
+```py
+def foo(x: int) -> int:
+    return x
+
+reveal_type(foo)  # revealed: def foo(x: int) -> int
+```
+
+An overloaded function is overriding a non-overloaded function:
+
+```py
+reveal_type(foo)  # revealed: def foo(x: int) -> int
+
+@overload
+def foo() -> None: ...
+@overload
+def foo(x: bytes) -> bytes: ...
+def foo(x: bytes | None = None) -> bytes | None:
+    return x
+
+reveal_type(foo)  # revealed: Overload[() -> None, (x: bytes) -> bytes]
+reveal_type(foo())  # revealed: None
+reveal_type(foo(b""))  # revealed: bytes
+```
+
+## Methods
+
+```py
+from typing import overload
+
+class Foo1:
+    @overload
+    def method(self) -> None: ...
+    @overload
+    def method(self, x: int) -> int: ...
+    def method(self, x: int | None = None) -> int | None:
+        return x
+
+foo1 = Foo1()
+reveal_type(foo1.method)  # revealed: Overload[() -> None, (x: int) -> int]
+reveal_type(foo1.method())  # revealed: None
+reveal_type(foo1.method(1))  # revealed: int
+
+class Foo2:
+    @overload
+    def method(self) -> None: ...
+    @overload
+    def method(self, x: str) -> str: ...
+    def method(self, x: str | None = None) -> str | None:
+        return x
+
+foo2 = Foo2()
+reveal_type(foo2.method)  # revealed: Overload[() -> None, (x: str) -> str]
+reveal_type(foo2.method())  # revealed: None
+reveal_type(foo2.method(""))  # revealed: str
+```
+
+## Constructor
+
+```py
+from typing import overload
+
+class Foo:
+    @overload
+    def __init__(self) -> None: ...
+    @overload
+    def __init__(self, x: int) -> None: ...
+    def __init__(self, x: int | None = None) -> None:
+        self.x = x
+
+foo = Foo()
+reveal_type(foo)  # revealed: Foo
+reveal_type(foo.x)  # revealed: Unknown | int | None
+
+foo1 = Foo(1)
+reveal_type(foo1)  # revealed: Foo
+reveal_type(foo1.x)  # revealed: Unknown | int | None
+```
+
+## Version specific
+
+Function definitions can vary between multiple Python versions.
+
+### Overload and non-overload (3.9)
+
+Here, the same function is overloaded in one version and not in another.
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+```py
+import sys
+from typing import overload
+
+if sys.version_info < (3, 10):
+    def func(x: int) -> int:
+        return x
+
+elif sys.version_info <= (3, 12):
+    @overload
+    def func() -> None: ...
+    @overload
+    def func(x: int) -> int: ...
+    def func(x: int | None = None) -> int | None:
+        return x
+
+reveal_type(func)  # revealed: def func(x: int) -> int
+func()  # error: [missing-argument]
+```
+
+### Overload and non-overload (3.10)
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+import sys
+from typing import overload
+
+if sys.version_info < (3, 10):
+    def func(x: int) -> int:
+        return x
+
+elif sys.version_info <= (3, 12):
+    @overload
+    def func() -> None: ...
+    @overload
+    def func(x: int) -> int: ...
+    def func(x: int | None = None) -> int | None:
+        return x
+
+reveal_type(func)  # revealed: Overload[() -> None, (x: int) -> int]
+reveal_type(func())  # revealed: None
+reveal_type(func(1))  # revealed: int
+```
+
+### Some overloads are version specific (3.9)
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+`overloaded.pyi`:
+
+```pyi
+import sys
+from typing import overload
+
+if sys.version_info >= (3, 10):
+    @overload
+    def func() -> None: ...
+
+@overload
+def func(x: int) -> int: ...
+@overload
+def func(x: str) -> str: ...
+```
+
+`main.py`:
+
+```py
+from overloaded import func
+
+reveal_type(func)  # revealed: Overload[(x: int) -> int, (x: str) -> str]
+func()  # error: [no-matching-overload]
+reveal_type(func(1))  # revealed: int
+reveal_type(func(""))  # revealed: str
+```
+
+### Some overloads are version specific (3.10)
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+`overloaded.pyi`:
+
+```pyi
+import sys
+from typing import overload
+
+@overload
+def func() -> None: ...
+
+if sys.version_info >= (3, 10):
+    @overload
+    def func(x: int) -> int: ...
+
+@overload
+def func(x: str) -> str: ...
+```
+
+`main.py`:
+
+```py
+from overloaded import func
+
+reveal_type(func)  # revealed: Overload[() -> None, (x: int) -> int, (x: str) -> str]
+reveal_type(func())  # revealed: None
+reveal_type(func(1))  # revealed: int
+reveal_type(func(""))  # revealed: str
+```
+
+## Generic
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+For an overloaded generic function, it's not necessary for all overloads to be generic.
+
+```py
+from typing import overload
+
+@overload
+def func() -> None: ...
+@overload
+def func[T](x: T) -> T: ...
+def func[T](x: T | None = None) -> T | None:
+    return x
+
+reveal_type(func)  # revealed: Overload[() -> None, (x: T) -> T]
+reveal_type(func())  # revealed: None
+reveal_type(func(1))  # revealed: Literal[1]
+reveal_type(func(""))  # revealed: Literal[""]
+```
+
+## Invalid
+
+### At least two overloads
+
+At least two `@overload`-decorated definitions must be present.
+
+```py
+from typing import overload
+
+# TODO: error
+@overload
+def func(x: int) -> int: ...
+def func(x: int | str) -> int | str:
+    return x
+```
+
+### Overload without an implementation
+
+#### Regular modules
+
+In regular modules, a series of `@overload`-decorated definitions must be followed by exactly one
+non-`@overload`-decorated definition (for the same function/method).
+
+```py
+from typing import overload
+
+# TODO: error because implementation does not exists
+@overload
+def func(x: int) -> int: ...
+@overload
+def func(x: str) -> str: ...
+
+class Foo:
+    # TODO: error because implementation does not exists
+    @overload
+    def method(self, x: int) -> int: ...
+    @overload
+    def method(self, x: str) -> str: ...
+```
+
+#### Stub files
+
+Overload definitions within stub files are exempt from this check.
+
+```pyi
+from typing import overload
+
+@overload
+def func(x: int) -> int: ...
+@overload
+def func(x: str) -> str: ...
+```
+
+#### Protocols
+
+Overload definitions within protocols are exempt from this check.
+
+```py
+from typing import Protocol, overload
+
+class Foo(Protocol):
+    @overload
+    def f(self, x: int) -> int: ...
+    @overload
+    def f(self, x: str) -> str: ...
+```
+
+#### Abstract methods
+
+Overload definitions within abstract base classes are exempt from this check.
+
+```py
+from abc import ABC, abstractmethod
+from typing import overload
+
+class AbstractFoo(ABC):
+    @overload
+    @abstractmethod
+    def f(self, x: int) -> int: ...
+    @overload
+    @abstractmethod
+    def f(self, x: str) -> str: ...
+```
+
+Using the `@abstractmethod` decorator requires that the class's metaclass is `ABCMeta` or is derived
+from it.
+
+```py
+class Foo:
+    # TODO: Error because implementation does not exists
+    @overload
+    @abstractmethod
+    def f(self, x: int) -> int: ...
+    @overload
+    @abstractmethod
+    def f(self, x: str) -> str: ...
+```
+
+And, the `@abstractmethod` decorator must be present on all the `@overload`-ed methods.
+
+```py
+class PartialFoo1(ABC):
+    @overload
+    @abstractmethod
+    def f(self, x: int) -> int: ...
+    @overload
+    def f(self, x: str) -> str: ...
+
+class PartialFoo(ABC):
+    @overload
+    def f(self, x: int) -> int: ...
+    @overload
+    @abstractmethod
+    def f(self, x: str) -> str: ...
+```
+
+### Inconsistent decorators
+
+#### `@staticmethod` / `@classmethod`
+
+If one overload signature is decorated with `@staticmethod` or `@classmethod`, all overload
+signatures must be similarly decorated. The implementation, if present, must also have a consistent
+decorator.
+
+```py
+from __future__ import annotations
+
+from typing import overload
+
+class CheckStaticMethod:
+    # TODO: error because `@staticmethod` does not exist on all overloads
+    @overload
+    def method1(x: int) -> int: ...
+    @overload
+    def method1(x: str) -> str: ...
+    @staticmethod
+    def method1(x: int | str) -> int | str:
+        return x
+    # TODO: error because `@staticmethod` does not exist on all overloads
+    @overload
+    def method2(x: int) -> int: ...
+    @overload
+    @staticmethod
+    def method2(x: str) -> str: ...
+    @staticmethod
+    def method2(x: int | str) -> int | str:
+        return x
+    # TODO: error because `@staticmethod` does not exist on the implementation
+    @overload
+    @staticmethod
+    def method3(x: int) -> int: ...
+    @overload
+    @staticmethod
+    def method3(x: str) -> str: ...
+    def method3(x: int | str) -> int | str:
+        return x
+
+    @overload
+    @staticmethod
+    def method4(x: int) -> int: ...
+    @overload
+    @staticmethod
+    def method4(x: str) -> str: ...
+    @staticmethod
+    def method4(x: int | str) -> int | str:
+        return x
+
+class CheckClassMethod:
+    def __init__(self, x: int) -> None:
+        self.x = x
+    # TODO: error because `@classmethod` does not exist on all overloads
+    @overload
+    @classmethod
+    def try_from1(cls, x: int) -> CheckClassMethod: ...
+    @overload
+    def try_from1(cls, x: str) -> None: ...
+    @classmethod
+    def try_from1(cls, x: int | str) -> CheckClassMethod | None:
+        if isinstance(x, int):
+            return cls(x)
+        return None
+    # TODO: error because `@classmethod` does not exist on all overloads
+    @overload
+    def try_from2(cls, x: int) -> CheckClassMethod: ...
+    @overload
+    @classmethod
+    def try_from2(cls, x: str) -> None: ...
+    @classmethod
+    def try_from2(cls, x: int | str) -> CheckClassMethod | None:
+        if isinstance(x, int):
+            return cls(x)
+        return None
+    # TODO: error because `@classmethod` does not exist on the implementation
+    @overload
+    @classmethod
+    def try_from3(cls, x: int) -> CheckClassMethod: ...
+    @overload
+    @classmethod
+    def try_from3(cls, x: str) -> None: ...
+    def try_from3(cls, x: int | str) -> CheckClassMethod | None:
+        if isinstance(x, int):
+            return cls(x)
+        return None
+
+    @overload
+    @classmethod
+    def try_from4(cls, x: int) -> CheckClassMethod: ...
+    @overload
+    @classmethod
+    def try_from4(cls, x: str) -> None: ...
+    @classmethod
+    def try_from4(cls, x: int | str) -> CheckClassMethod | None:
+        if isinstance(x, int):
+            return cls(x)
+        return None
+```
+
+#### `@final` / `@override`
+
+If a `@final` or `@override` decorator is supplied for a function with overloads, the decorator
+should be applied only to the overload implementation if it is present.
+
+```py
+from typing_extensions import final, overload, override
+
+class Foo:
+    @overload
+    def method1(self, x: int) -> int: ...
+    @overload
+    def method1(self, x: str) -> str: ...
+    @final
+    def method1(self, x: int | str) -> int | str:
+        return x
+    # TODO: error because `@final` is not on the implementation
+    @overload
+    @final
+    def method2(self, x: int) -> int: ...
+    @overload
+    def method2(self, x: str) -> str: ...
+    def method2(self, x: int | str) -> int | str:
+        return x
+    # TODO: error because `@final` is not on the implementation
+    @overload
+    def method3(self, x: int) -> int: ...
+    @overload
+    @final
+    def method3(self, x: str) -> str: ...
+    def method3(self, x: int | str) -> int | str:
+        return x
+
+class Base:
+    @overload
+    def method(self, x: int) -> int: ...
+    @overload
+    def method(self, x: str) -> str: ...
+    def method(self, x: int | str) -> int | str:
+        return x
+
+class Sub1(Base):
+    @overload
+    def method(self, x: int) -> int: ...
+    @overload
+    def method(self, x: str) -> str: ...
+    @override
+    def method(self, x: int | str) -> int | str:
+        return x
+
+class Sub2(Base):
+    # TODO: error because `@override` is not on the implementation
+    @overload
+    def method(self, x: int) -> int: ...
+    @overload
+    @override
+    def method(self, x: str) -> str: ...
+    def method(self, x: int | str) -> int | str:
+        return x
+
+class Sub3(Base):
+    # TODO: error because `@override` is not on the implementation
+    @overload
+    @override
+    def method(self, x: int) -> int: ...
+    @overload
+    def method(self, x: str) -> str: ...
+    def method(self, x: int | str) -> int | str:
+        return x
+```
+
+#### `@final` / `@override` in stub files
+
+If an overload implementation isn’t present (for example, in a stub file), the `@final` or
+`@override` decorator should be applied only to the first overload.
+
+```pyi
+from typing_extensions import final, overload, override
+
+class Foo:
+    @overload
+    @final
+    def method1(self, x: int) -> int: ...
+    @overload
+    def method1(self, x: str) -> str: ...
+
+    # TODO: error because `@final` is not on the first overload
+    @overload
+    def method2(self, x: int) -> int: ...
+    @final
+    @overload
+    def method2(self, x: str) -> str: ...
+
+class Base:
+    @overload
+    def method(self, x: int) -> int: ...
+    @overload
+    def method(self, x: str) -> str: ...
+
+class Sub1(Base):
+    @overload
+    @override
+    def method(self, x: int) -> int: ...
+    @overload
+    def method(self, x: str) -> str: ...
+
+class Sub2(Base):
+    # TODO: error because `@override` is not on the first overload
+    @overload
+    def method(self, x: int) -> int: ...
+    @overload
+    @override
+    def method(self, x: str) -> str: ...
+```

crates/red_knot_python_semantic/resources/mdtest/protocols.md

@@ -15,6 +15,11 @@ types, on the other hand: a type which is defined by its properties and behaviou
 
 ## Defining a protocol
 
+```toml
+[environment]
+python-version = "3.12"
+```
+
 A protocol is defined by inheriting from the `Protocol` class, which is annotated as an instance of
 `_SpecialForm` in typeshed's stubs.
 
@@ -23,8 +28,7 @@ from typing import Protocol
 
 class MyProtocol(Protocol): ...
 
-# TODO: at runtime this is `(<class '__main__.MyProtocol'>, <class 'typing.Protocol'>, <class 'typing.Generic'>, <class 'object'>)`
-reveal_type(MyProtocol.__mro__)  # revealed: tuple[Literal[MyProtocol], @Todo(protocol), Literal[object]]
+reveal_type(MyProtocol.__mro__)  # revealed: tuple[Literal[MyProtocol], typing.Protocol, typing.Generic, Literal[object]]
 ```
 
 Just like for any other class base, it is an error for `Protocol` to appear multiple times in a
@@ -36,27 +40,63 @@ class Foo(Protocol, Protocol): ...  # error: [inconsistent-mro]
 reveal_type(Foo.__mro__)  # revealed: tuple[Literal[Foo], Unknown, Literal[object]]
 ```
 
+Protocols can also be generic, either by including `Generic[]` in the bases list, subscripting
+`Protocol` directly in the bases list, using PEP-695 type parameters, or some combination of the
+above:
+
+```py
+from typing import TypeVar, Generic
+
+T = TypeVar("T")
+
+class Bar0(Protocol[T]):
+    x: T
+
+class Bar1(Protocol[T], Generic[T]):
+    x: T
+
+class Bar2[T](Protocol):
+    x: T
+
+class Bar3[T](Protocol[T]):
+    x: T
+```
+
+It's an error to include both bare `Protocol` and subscripted `Protocol[]` in the bases list
+simultaneously:
+
+```py
+# TODO: should emit a `[duplicate-bases]` error here:
+class DuplicateBases(Protocol, Protocol[T]):
+    x: T
+
+# TODO: should not have `Generic` multiple times and `Protocol` multiple times
+# revealed: tuple[Literal[DuplicateBases], typing.Protocol, typing.Generic, @Todo(`Protocol[]` subscript), @Todo(`Generic[]` subscript), Literal[object]]
+reveal_type(DuplicateBases.__mro__)
+```
+
 The introspection helper `typing(_extensions).is_protocol` can be used to verify whether a class is
 a protocol class or not:
 
 ```py
 from typing_extensions import is_protocol
 
-# TODO: should be `Literal[True]`
-reveal_type(is_protocol(MyProtocol))  # revealed: bool
+reveal_type(is_protocol(MyProtocol))  # revealed: Literal[True]
+reveal_type(is_protocol(Bar0))  # revealed: Literal[True]
+reveal_type(is_protocol(Bar1))  # revealed: Literal[True]
+reveal_type(is_protocol(Bar2))  # revealed: Literal[True]
+reveal_type(is_protocol(Bar3))  # revealed: Literal[True]
 
 class NotAProtocol: ...
 
-# TODO: should be `Literal[False]`
-reveal_type(is_protocol(NotAProtocol))  # revealed: bool
+reveal_type(is_protocol(NotAProtocol))  # revealed: Literal[False]
 ```
 
 A type checker should follow the typeshed stubs if a non-class is passed in, and typeshed's stubs
-indicate that the argument passed in must be an instance of `type`. `Literal[False]` should be
-inferred as the return type, however.
+indicate that the argument passed in must be an instance of `type`.
 
 ```py
-# TODO: the diagnostic is correct, but should infer `Literal[False]`
+# We could also reasonably infer `Literal[False]` here, but it probably doesn't matter that much:
 # error: [invalid-argument-type]
 reveal_type(is_protocol("not a class"))  # revealed: bool
 ```
@@ -67,12 +107,10 @@ it is not sufficient for it to have `Protocol` in its MRO.
 ```py
 class SubclassOfMyProtocol(MyProtocol): ...
 
-# TODO
-# revealed: tuple[Literal[SubclassOfMyProtocol], Literal[MyProtocol], @Todo(protocol), Literal[object]]
+# revealed: tuple[Literal[SubclassOfMyProtocol], Literal[MyProtocol], typing.Protocol, typing.Generic, Literal[object]]
 reveal_type(SubclassOfMyProtocol.__mro__)
 
-# TODO: should be `Literal[False]`
-reveal_type(is_protocol(SubclassOfMyProtocol))  # revealed: bool
+reveal_type(is_protocol(SubclassOfMyProtocol))  # revealed: Literal[False]
 ```
 
 A protocol class may inherit from other protocols, however, as long as it re-inherits from
@@ -81,38 +119,33 @@ A protocol class may inherit from other protocols, however, as long as it re-inh
 ```py
 class SubProtocol(MyProtocol, Protocol): ...
 
-# TODO: should be `Literal[True]`
-reveal_type(is_protocol(SubProtocol))  # revealed: bool
+reveal_type(is_protocol(SubProtocol))  # revealed: Literal[True]
 
 class OtherProtocol(Protocol):
     some_attribute: str
 
 class ComplexInheritance(SubProtocol, OtherProtocol, Protocol): ...
 
-# TODO
-# revealed: tuple[Literal[ComplexInheritance], Literal[SubProtocol], Literal[MyProtocol], Literal[OtherProtocol], @Todo(protocol), Literal[object]]
+# revealed: tuple[Literal[ComplexInheritance], Literal[SubProtocol], Literal[MyProtocol], Literal[OtherProtocol], typing.Protocol, typing.Generic, Literal[object]]
 reveal_type(ComplexInheritance.__mro__)
 
-# TODO: should be `Literal[True]`
-reveal_type(is_protocol(ComplexInheritance))  # revealed: bool
+reveal_type(is_protocol(ComplexInheritance))  # revealed: Literal[True]
 ```
 
 If `Protocol` is present in the bases tuple, all other bases in the tuple must be protocol classes,
 or `TypeError` is raised at runtime when the class is created.
 
 ```py
-# TODO: should emit `[invalid-protocol]`
+# error: [invalid-protocol] "Protocol class `Invalid` cannot inherit from non-protocol class `NotAProtocol`"
 class Invalid(NotAProtocol, Protocol): ...
 
-# TODO
-# revealed: tuple[Literal[Invalid], Literal[NotAProtocol], @Todo(protocol), Literal[object]]
+# revealed: tuple[Literal[Invalid], Literal[NotAProtocol], typing.Protocol, typing.Generic, Literal[object]]
 reveal_type(Invalid.__mro__)
 
-# TODO: should emit an `[invalid-protocol`] error
+# error: [invalid-protocol] "Protocol class `AlsoInvalid` cannot inherit from non-protocol class `NotAProtocol`"
 class AlsoInvalid(MyProtocol, OtherProtocol, NotAProtocol, Protocol): ...
 
-# TODO
-# revealed: tuple[Literal[AlsoInvalid], Literal[MyProtocol], Literal[OtherProtocol], Literal[NotAProtocol], @Todo(protocol), Literal[object]]
+# revealed: tuple[Literal[AlsoInvalid], Literal[MyProtocol], Literal[OtherProtocol], Literal[NotAProtocol], typing.Protocol, typing.Generic, Literal[object]]
 reveal_type(AlsoInvalid.__mro__)
 ```
 
@@ -130,12 +163,12 @@ T = TypeVar("T")
 # type checkers.
 class Fine(Protocol, object): ...
 
-# TODO
-reveal_type(Fine.__mro__)  # revealed: tuple[Literal[Fine], @Todo(protocol), Literal[object]]
+reveal_type(Fine.__mro__)  # revealed: tuple[Literal[Fine], typing.Protocol, typing.Generic, Literal[object]]
 
-# TODO: should not error
-class StillFine(Protocol, Generic[T], object): ...  # error: [invalid-base]
+class StillFine(Protocol, Generic[T], object): ...
 class EvenThis[T](Protocol, object): ...
+class OrThis(Protocol[T], Generic[T]): ...
+class AndThis(Protocol[T], Generic[T], object): ...
 ```
 
 And multiple inheritance from a mix of protocol and non-protocol classes is fine as long as
@@ -144,8 +177,7 @@ And multiple inheritance from a mix of protocol and non-protocol classes is fine
 ```py
 class FineAndDandy(MyProtocol, OtherProtocol, NotAProtocol): ...
 
-# TODO
-# revealed: tuple[Literal[FineAndDandy], Literal[MyProtocol], Literal[OtherProtocol], @Todo(protocol), Literal[NotAProtocol], Literal[object]]
+# revealed: tuple[Literal[FineAndDandy], Literal[MyProtocol], Literal[OtherProtocol], typing.Protocol, typing.Generic, Literal[NotAProtocol], Literal[object]]
 reveal_type(FineAndDandy.__mro__)
 ```
 
@@ -153,8 +185,7 @@ But if `Protocol` is not present in the bases list, the resulting class doesn't
 class anymore:
 
 ```py
-# TODO: should reveal `Literal[False]`
-reveal_type(is_protocol(FineAndDandy))  # revealed: bool
+reveal_type(is_protocol(FineAndDandy))  # revealed: Literal[False]
 ```
 
 A class does not *have* to inherit from a protocol class in order for it to be considered a subtype
@@ -222,18 +253,21 @@ reveal_type(issubclass(MyProtocol, Protocol))  # revealed: bool
 ```py
 import typing
 import typing_extensions
-from knot_extensions import static_assert, is_equivalent_to
+from knot_extensions import static_assert, is_equivalent_to, TypeOf
+
+static_assert(is_equivalent_to(TypeOf[typing.Protocol], TypeOf[typing_extensions.Protocol]))
+static_assert(is_equivalent_to(int | str | TypeOf[typing.Protocol], TypeOf[typing_extensions.Protocol] | str | int))
 
 class Foo(typing.Protocol):
     x: int
 
-# TODO: should not error
-class Bar(typing_extensions.Protocol):  # error: [invalid-base]
+class Bar(typing_extensions.Protocol):
     x: int
 
-# TODO: these should pass
-static_assert(typing_extensions.is_protocol(Foo))  # error: [static-assert-error]
-static_assert(typing_extensions.is_protocol(Bar))  # error: [static-assert-error]
+static_assert(typing_extensions.is_protocol(Foo))
+static_assert(typing_extensions.is_protocol(Bar))
+
+# TODO: should pass
 static_assert(is_equivalent_to(Foo, Bar))  # error: [static-assert-error]
 ```
 
@@ -244,14 +278,14 @@ The same goes for `typing.runtime_checkable` and `typing_extensions.runtime_chec
 class RuntimeCheckableFoo(typing.Protocol):
     x: int
 
-# TODO: should not error
 @typing.runtime_checkable
-class RuntimeCheckableBar(typing_extensions.Protocol):  # error: [invalid-base]
+class RuntimeCheckableBar(typing_extensions.Protocol):
     x: int
 
-# TODO: these should pass
-static_assert(typing_extensions.is_protocol(RuntimeCheckableFoo))  # error: [static-assert-error]
-static_assert(typing_extensions.is_protocol(RuntimeCheckableBar))  # error: [static-assert-error]
+static_assert(typing_extensions.is_protocol(RuntimeCheckableFoo))
+static_assert(typing_extensions.is_protocol(RuntimeCheckableBar))
+
+# TODO: should pass
 static_assert(is_equivalent_to(RuntimeCheckableFoo, RuntimeCheckableBar))  # error: [static-assert-error]
 
 # These should not error because the protocols are decorated with `@runtime_checkable`
@@ -259,6 +293,15 @@ isinstance(object(), RuntimeCheckableFoo)
 isinstance(object(), RuntimeCheckableBar)
 ```
 
+However, we understand that they are not necessarily the same symbol at the same memory address at
+runtime -- these reveal `bool` rather than `Literal[True]` or `Literal[False]`, which would be
+incorrect:
+
+```py
+reveal_type(typing.Protocol is typing_extensions.Protocol)  # revealed: bool
+reveal_type(typing.Protocol is not typing_extensions.Protocol)  # revealed: bool
+```
+
 ## Calls to protocol classes
 
 Neither `Protocol`, nor any protocol class, can be directly instantiated:
@@ -304,8 +347,7 @@ via `typing_extensions`.
 ```py
 from typing_extensions import Protocol, get_protocol_members
 
-# TODO: should not error
-class Foo(Protocol):  # error: [invalid-base]
+class Foo(Protocol):
     x: int
 
     @property
@@ -330,7 +372,7 @@ class Foo(Protocol):  # error: [invalid-base]
 # `tuple[Literal["x"], Literal["y"], Literal["z"], Literal["method_member"]]`
 #
 # `frozenset[Literal["x", "y", "z", "method_member"]]`
-reveal_type(get_protocol_members(Foo))  # revealed: @Todo(generics)
+reveal_type(get_protocol_members(Foo))  # revealed: @Todo(specialized non-generic class)
 ```
 
 Calling `get_protocol_members` on a non-protocol class raises an error at runtime:
@@ -339,15 +381,14 @@ Calling `get_protocol_members` on a non-protocol class raises an error at runtim
 class NotAProtocol: ...
 
 # TODO: should emit `[invalid-protocol]` error, should reveal `Unknown`
-reveal_type(get_protocol_members(NotAProtocol))  # revealed: @Todo(generics)
+reveal_type(get_protocol_members(NotAProtocol))  # revealed: @Todo(specialized non-generic class)
 ```
 
 Certain special attributes and methods are not considered protocol members at runtime, and should
 not be considered protocol members by type checkers either:
 
 ```py
-# TODO: should not error
-class Lumberjack(Protocol):  # error: [invalid-base]
+class Lumberjack(Protocol):
     __slots__ = ()
     __match_args__ = ()
     x: int
@@ -359,7 +400,7 @@ class Lumberjack(Protocol):  # error: [invalid-base]
         self.x = x
 
 # TODO: `tuple[Literal["x"]]` or `frozenset[Literal["x"]]`
-reveal_type(get_protocol_members(Lumberjack))  # revealed: @Todo(generics)
+reveal_type(get_protocol_members(Lumberjack))  # revealed: @Todo(specialized non-generic class)
 ```
 
 ## Subtyping of protocols with attribute members

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

@@ -14,7 +14,7 @@ reveal_type(__package__)  # revealed: str | None
 reveal_type(__doc__)  # revealed: str | None
 reveal_type(__spec__)  # revealed: ModuleSpec | None
 
-reveal_type(__path__)  # revealed: @Todo(generics)
+reveal_type(__path__)  # revealed: @Todo(specialized non-generic class)
 
 class X:
     reveal_type(__name__)  # revealed: str
@@ -59,7 +59,7 @@ reveal_type(typing.__eq__)  # revealed: bound method ModuleType.__eq__(value: ob
 reveal_type(typing.__class__)  # revealed: Literal[ModuleType]
 
 # TODO: needs support generics; should be `dict[str, Any]`:
-reveal_type(typing.__dict__)  # revealed: @Todo(generics)
+reveal_type(typing.__dict__)  # revealed: @Todo(specialized non-generic class)
 ```
 
 Typeshed includes a fake `__getattr__` method in the stub for `types.ModuleType` to help out with
@@ -92,8 +92,8 @@ import foo
 from foo import __dict__ as foo_dict
 
 # TODO: needs support generics; should be `dict[str, Any]` for both of these:
-reveal_type(foo.__dict__)  # revealed: @Todo(generics)
-reveal_type(foo_dict)  # revealed: @Todo(generics)
+reveal_type(foo.__dict__)  # revealed: @Todo(specialized non-generic class)
+reveal_type(foo_dict)  # revealed: @Todo(specialized non-generic class)
 ```
 
 ## Conditionally global or `ModuleType` attribute

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

@@ -5,7 +5,7 @@
 ```py
 class C: ...
 
-C = 1  # error: "Implicit shadowing of class `C`; annotate to make it explicit if this is intentional"
+C = 1  # error: "Implicit shadowing of class `C`"
 ```
 
 ## Explicit

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

@@ -15,7 +15,7 @@ def f(x: str):
 ```py
 def f(): ...
 
-f = 1  # error: "Implicit shadowing of function `f`; annotate to make it explicit if this is intentional"
+f = 1  # error: "Implicit shadowing of function `f`"
 ```
 
 ## Explicit shadowing

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_Data_descriptors_-_Invalid_`__set__`_method_signature.snap

@@ -28,12 +28,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Invalid assignment to data descriptor attribute `attr` on type `C` with custom `__set__` method
   --> /src/mdtest_snippet.py:11:1
    |
 10 | # TODO: ideally, we would mention why this is an invalid assignment (wrong number of arguments for `__set__`)
 11 | instance.attr = 1  # error: [invalid-assignment]
-   | ^^^^^^^^^^^^^ Invalid assignment to data descriptor attribute `attr` on type `C` with custom `__set__` method
+   | ^^^^^^^^^^^^^
    |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_Data_descriptors_-_Invalid_argument_type.snap

@@ -29,12 +29,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Invalid assignment to data descriptor attribute `attr` on type `C` with custom `__set__` method
   --> /src/mdtest_snippet.py:12:1
    |
 11 | # TODO: ideally, we would mention why this is an invalid assignment (wrong argument type for `value` parameter)
 12 | instance.attr = "wrong"  # error: [invalid-assignment]
-   | ^^^^^^^^^^^^^ Invalid assignment to data descriptor attribute `attr` on type `C` with custom `__set__` method
+   | ^^^^^^^^^^^^^
    |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_Instance_attributes_with_class-level_defaults.snap

@@ -26,13 +26,13 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
  --> /src/mdtest_snippet.py:6:1
   |
 4 | instance = C()
 5 | instance.attr = 1  # fine
 6 | instance.attr = "wrong"  # error: [invalid-assignment]
-  | ^^^^^^^^^^^^^ Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
+  | ^^^^^^^^^^^^^
 7 |
 8 | C.attr = 1  # fine
   |
@@ -40,12 +40,12 @@ error: lint:invalid-assignment
 ```
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
  --> /src/mdtest_snippet.py:9:1
   |
 8 | C.attr = 1  # fine
 9 | C.attr = "wrong"  # error: [invalid-assignment]
-  | ^^^^^^ Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
+  | ^^^^^^
   |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_Possibly-unbound_attributes.snap

@@ -26,13 +26,13 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-warning: lint:possibly-unbound-attribute
+warning: lint:possibly-unbound-attribute: Attribute `attr` on type `Literal[C]` is possibly unbound
  --> /src/mdtest_snippet.py:6:5
   |
 4 |             attr: int = 0
 5 |
 6 |     C.attr = 1  # error: [possibly-unbound-attribute]
-  |     ^^^^^^ Attribute `attr` on type `Literal[C]` is possibly unbound
+  |     ^^^^^^
 7 |
 8 |     instance = C()
   |
@@ -40,12 +40,12 @@ warning: lint:possibly-unbound-attribute
 ```
 
 ```
-warning: lint:possibly-unbound-attribute
+warning: lint:possibly-unbound-attribute: Attribute `attr` on type `C` is possibly unbound
  --> /src/mdtest_snippet.py:9:5
   |
 8 |     instance = C()
 9 |     instance.attr = 1  # error: [possibly-unbound-attribute]
-  |     ^^^^^^^^^^^^^ Attribute `attr` on type `C` is possibly unbound
+  |     ^^^^^^^^^^^^^
   |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_Pure_instance_attributes.snap

@@ -26,13 +26,13 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
  --> /src/mdtest_snippet.py:7:1
   |
 5 | instance = C()
 6 | instance.attr = 1  # fine
 7 | instance.attr = "wrong"  # error: [invalid-assignment]
-  | ^^^^^^^^^^^^^ Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
+  | ^^^^^^^^^^^^^
 8 |
 9 | C.attr = 1  # error: [invalid-attribute-access]
   |
@@ -40,13 +40,13 @@ error: lint:invalid-assignment
 ```
 
 ```
-error: lint:invalid-attribute-access
+error: lint:invalid-attribute-access: Cannot assign to instance attribute `attr` from the class object `Literal[C]`
  --> /src/mdtest_snippet.py:9:1
   |
 7 | instance.attr = "wrong"  # error: [invalid-assignment]
 8 |
 9 | C.attr = 1  # error: [invalid-attribute-access]
-  | ^^^^^^ Cannot assign to instance attribute `attr` from the class object `Literal[C]`
+  | ^^^^^^
   |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_Setting_attributes_on_union_types.snap

@@ -37,12 +37,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Object of type `Literal[1]` is not assignable to attribute `attr` on type `Literal[C1, C1]`
   --> /src/mdtest_snippet.py:11:5
    |
 10 |     # TODO: The error message here could be improved to explain why the assignment fails.
 11 |     C1.attr = 1  # error: [invalid-assignment]
-   |     ^^^^^^^ Object of type `Literal[1]` is not assignable to attribute `attr` on type `Literal[C1, C1]`
+   |     ^^^^^^^
 12 |
 13 |     class C2:
    |

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_Unknown_attributes.snap

@@ -23,13 +23,13 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:unresolved-attribute
+error: lint:unresolved-attribute: Unresolved attribute `non_existent` on type `Literal[C]`.
  --> /src/mdtest_snippet.py:3:1
   |
 1 | class C: ...
 2 |
 3 | C.non_existent = 1  # error: [unresolved-attribute]
-  | ^^^^^^^^^^^^^^ Unresolved attribute `non_existent` on type `Literal[C]`.
+  | ^^^^^^^^^^^^^^
 4 |
 5 | instance = C()
   |
@@ -37,12 +37,12 @@ error: lint:unresolved-attribute
 ```
 
 ```
-error: lint:unresolved-attribute
+error: lint:unresolved-attribute: Unresolved attribute `non_existent` on type `C`.
  --> /src/mdtest_snippet.py:6:1
   |
 5 | instance = C()
 6 | instance.non_existent = 1  # error: [unresolved-attribute]
-  | ^^^^^^^^^^^^^^^^^^^^^ Unresolved attribute `non_existent` on type `C`.
+  | ^^^^^^^^^^^^^^^^^^^^^
   |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/attribute_assignment.md_-_Attribute_assignment_-_`ClassVar`s.snap

@@ -27,12 +27,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/diagnostics/attrib
 # Diagnostics
 
 ```
-error: lint:invalid-assignment
+error: lint:invalid-assignment: Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
  --> /src/mdtest_snippet.py:7:1
   |
 6 | C.attr = 1  # fine
 7 | C.attr = "wrong"  # error: [invalid-assignment]
-  | ^^^^^^ Object of type `Literal["wrong"]` is not assignable to attribute `attr` of type `int`
+  | ^^^^^^
 8 |
 9 | instance = C()
   |
@@ -40,12 +40,12 @@ error: lint:invalid-assignment
 ```
 
 ```
-error: lint:invalid-attribute-access
+error: lint:invalid-attribute-access: Cannot assign to ClassVar `attr` from an instance of type `C`
   --> /src/mdtest_snippet.py:10:1
    |
  9 | instance = C()
 10 | instance.attr = 1  # error: [invalid-attribute-access]
-   | ^^^^^^^^^^^^^ Cannot assign to ClassVar `attr` from an instance of type `C`
+   | ^^^^^^^^^^^^^
    |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/basic.md_-_Structures_-_Unresolvable_module_import.snap

@@ -18,11 +18,11 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/import/basic.md
 # Diagnostics
 
 ```
-error: lint:unresolved-import
+error: lint:unresolved-import: Cannot resolve import `zqzqzqzqzqzqzq`
  --> /src/mdtest_snippet.py:1:8
   |
 1 | import zqzqzqzqzqzqzq  # error: [unresolved-import] "Cannot resolve import `zqzqzqzqzqzqzq`"
-  |        ^^^^^^^^^^^^^^ Cannot resolve import `zqzqzqzqzqzqzq`
+  |        ^^^^^^^^^^^^^^
   |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/basic.md_-_Structures_-_Unresolvable_submodule_imports.snap

@@ -27,12 +27,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/import/basic.md
 # Diagnostics
 
 ```
-error: lint:unresolved-import
+error: lint:unresolved-import: Cannot resolve import `a.foo`
  --> /src/mdtest_snippet.py:2:8
   |
 1 | # Topmost component resolvable, submodule not resolvable:
 2 | import a.foo  # error: [unresolved-import] "Cannot resolve import `a.foo`"
-  |        ^^^^^ Cannot resolve import `a.foo`
+  |        ^^^^^
 3 |
 4 | # Topmost component unresolvable:
   |
@@ -40,12 +40,12 @@ error: lint:unresolved-import
 ```
 
 ```
-error: lint:unresolved-import
+error: lint:unresolved-import: Cannot resolve import `b.foo`
  --> /src/mdtest_snippet.py:5:8
   |
 4 | # Topmost component unresolvable:
 5 | import b.foo  # error: [unresolved-import] "Cannot resolve import `b.foo`"
-  |        ^^^^^ Cannot resolve import `b.foo`
+  |        ^^^^^
   |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Bad_`__getitem__`_method.snap

@@ -28,12 +28,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable` is not iterable because it has no `__iter__` method and its `__getitem__` method has an incorrect signature for the old-style iteration protocol (expected a signature at least as permissive as `def __getitem__(self, key: int): ...`)
   --> /src/mdtest_snippet.py:10:10
    |
  9 | # error: [not-iterable]
 10 | for x in Iterable():
-   |          ^^^^^^^^^^ Object of type `Iterable` is not iterable because it has no `__iter__` method and its `__getitem__` method has an incorrect signature for the old-style iteration protocol (expected a signature at least as permissive as `def __getitem__(self, key: int): ...`)
+   |          ^^^^^^^^^^
 11 |     reveal_type(x)  # revealed: int
    |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Invalid_iterable.snap

@@ -20,12 +20,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Literal[123]` is not iterable because it doesn't have an `__iter__` method or a `__getitem__` method
  --> /src/mdtest_snippet.py:2:10
   |
 1 | nonsense = 123
 2 | for x in nonsense:  # error: [not-iterable]
-  |          ^^^^^^^^ Object of type `Literal[123]` is not iterable because it doesn't have an `__iter__` method or a `__getitem__` method
+  |          ^^^^^^^^
 3 |     pass
   |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_New_over_old_style_iteration_protocol.snap

@@ -24,13 +24,13 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `NotIterable` is not iterable because its `__iter__` attribute has type `None`, which is not callable
  --> /src/mdtest_snippet.py:6:10
   |
 4 |     __iter__: None = None
 5 |
 6 | for x in NotIterable():  # error: [not-iterable]
-  |          ^^^^^^^^^^^^^ Object of type `NotIterable` is not iterable because its `__iter__` attribute has type `None`, which is not callable
+  |          ^^^^^^^^^^^^^
 7 |     pass
   |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_No_`__iter__`_method_and_`__getitem__`_is_not_callable.snap

@@ -25,12 +25,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Bad` is not iterable because it has no `__iter__` method and its `__getitem__` attribute has type `None`, which is not callable
  --> /src/mdtest_snippet.py:7:10
   |
 6 | # error: [not-iterable]
 7 | for x in Bad():
-  |          ^^^^^ Object of type `Bad` is not iterable because it has no `__iter__` method and its `__getitem__` attribute has type `None`, which is not callable
+  |          ^^^^^
 8 |     reveal_type(x)  # revealed: Unknown
   |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Possibly-not-callable_`__getitem__`_method.snap

@@ -46,12 +46,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable1` may not be iterable because it has no `__iter__` method and its `__getitem__` attribute (with type `CustomCallable`) may not be callable
   --> /src/mdtest_snippet.py:22:14
    |
 21 |     # error: [not-iterable]
 22 |     for x in Iterable1():
-   |              ^^^^^^^^^^^ Object of type `Iterable1` may not be iterable because it has no `__iter__` method and its `__getitem__` attribute (with type `CustomCallable`) may not be callable
+   |              ^^^^^^^^^^^
 23 |         # TODO... `int` might be ideal here?
 24 |         reveal_type(x)  # revealed: int | Unknown
    |
@@ -73,12 +73,12 @@ info: revealed-type: Revealed type
 ```
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable2` may not be iterable because it has no `__iter__` method and its `__getitem__` attribute (with type `(bound method Iterable2.__getitem__(key: int) -> int) | None`) may not be callable
   --> /src/mdtest_snippet.py:27:14
    |
 26 |     # error: [not-iterable]
 27 |     for y in Iterable2():
-   |              ^^^^^^^^^^^ Object of type `Iterable2` may not be iterable because it has no `__iter__` method and its `__getitem__` attribute (with type `(bound method Iterable2.__getitem__(key: int) -> int) | None`) may not be callable
+   |              ^^^^^^^^^^^
 28 |         # TODO... `int` might be ideal here?
 29 |         reveal_type(y)  # revealed: int | Unknown
    |

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Possibly_invalid_`__getitem__`_methods.snap

@@ -43,12 +43,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable1` may not be iterable because it has no `__iter__` method and its `__getitem__` attribute (with type `(bound method Iterable1.__getitem__(item: int) -> str) | None`) may not be callable
   --> /src/mdtest_snippet.py:20:14
    |
 19 |     # error: [not-iterable]
 20 |     for x in Iterable1():
-   |              ^^^^^^^^^^^ Object of type `Iterable1` may not be iterable because it has no `__iter__` method and its `__getitem__` attribute (with type `(bound method Iterable1.__getitem__(item: int) -> str) | None`) may not be callable
+   |              ^^^^^^^^^^^
 21 |         # TODO: `str` might be better
 22 |         reveal_type(x)  # revealed: str | Unknown
    |
@@ -70,12 +70,12 @@ info: revealed-type: Revealed type
 ```
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable2` may not be iterable because it has no `__iter__` method and its `__getitem__` method (with type `(bound method Iterable2.__getitem__(item: int) -> str) | (bound method Iterable2.__getitem__(item: str) -> int)`) may have an incorrect signature for the old-style iteration protocol (expected a signature at least as permissive as `def __getitem__(self, key: int): ...`)
   --> /src/mdtest_snippet.py:25:14
    |
 24 |     # error: [not-iterable]
 25 |     for y in Iterable2():
-   |              ^^^^^^^^^^^ Object of type `Iterable2` may not be iterable because it has no `__iter__` method and its `__getitem__` method (with type `(bound method Iterable2.__getitem__(item: int) -> str) | (bound method Iterable2.__getitem__(item: str) -> int)`) may have an incorrect signature for the old-style iteration protocol (expected a signature at least as permissive as `def __getitem__(self, key: int): ...`)
+   |              ^^^^^^^^^^^
 26 |         reveal_type(y)  # revealed: str | int
    |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Possibly_invalid_`__iter__`_methods.snap

@@ -47,12 +47,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable1` may not be iterable because its `__iter__` method (with type `(bound method Iterable1.__iter__() -> Iterator) | (bound method Iterable1.__iter__(invalid_extra_arg) -> Iterator)`) may have an invalid signature (expected `def __iter__(self): ...`)
   --> /src/mdtest_snippet.py:17:14
    |
 16 |     # error: [not-iterable]
 17 |     for x in Iterable1():
-   |              ^^^^^^^^^^^ Object of type `Iterable1` may not be iterable because its `__iter__` method (with type `(bound method Iterable1.__iter__() -> Iterator) | (bound method Iterable1.__iter__(invalid_extra_arg) -> Iterator)`) may have an invalid signature (expected `def __iter__(self): ...`)
+   |              ^^^^^^^^^^^
 18 |         reveal_type(x)  # revealed: int
    |
 
@@ -73,12 +73,12 @@ info: revealed-type: Revealed type
 ```
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable2` may not be iterable because its `__iter__` attribute (with type `(bound method Iterable2.__iter__() -> Iterator) | None`) may not be callable
   --> /src/mdtest_snippet.py:28:14
    |
 27 |     # error: [not-iterable]
 28 |     for x in Iterable2():
-   |              ^^^^^^^^^^^ Object of type `Iterable2` may not be iterable because its `__iter__` attribute (with type `(bound method Iterable2.__iter__() -> Iterator) | None`) may not be callable
+   |              ^^^^^^^^^^^
 29 |         # TODO: `int` would probably be better here:
 30 |         reveal_type(x)  # revealed: int | Unknown
    |

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Possibly_invalid_`__next__`_method.snap

@@ -51,12 +51,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable1` may not be iterable because its `__iter__` method returns an object of type `Iterator1`, which may have an invalid `__next__` method (expected `def __next__(self): ...`)
   --> /src/mdtest_snippet.py:28:14
    |
 27 |     # error: [not-iterable]
 28 |     for x in Iterable1():
-   |              ^^^^^^^^^^^ Object of type `Iterable1` may not be iterable because its `__iter__` method returns an object of type `Iterator1`, which may have an invalid `__next__` method (expected `def __next__(self): ...`)
+   |              ^^^^^^^^^^^
 29 |         reveal_type(x)  # revealed: int | str
    |
 
@@ -77,12 +77,12 @@ info: revealed-type: Revealed type
 ```
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable2` may not be iterable because its `__iter__` method returns an object of type `Iterator2`, which has a `__next__` attribute that may not be callable
   --> /src/mdtest_snippet.py:32:14
    |
 31 |     # error: [not-iterable]
 32 |     for y in Iterable2():
-   |              ^^^^^^^^^^^ Object of type `Iterable2` may not be iterable because its `__iter__` method returns an object of type `Iterator2`, which has a `__next__` attribute that may not be callable
+   |              ^^^^^^^^^^^
 33 |         # TODO: `int` would probably be better here:
 34 |         reveal_type(y)  # revealed: int | Unknown
    |

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Possibly_unbound_`__iter__`_and_bad_`__getitem__`_method.snap

@@ -36,12 +36,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable` may not be iterable because it may not have an `__iter__` method and its `__getitem__` method has an incorrect signature for the old-style iteration protocol (expected a signature at least as permissive as `def __getitem__(self, key: int): ...`)
   --> /src/mdtest_snippet.py:18:14
    |
 17 |     # error: [not-iterable]
 18 |     for x in Iterable():
-   |              ^^^^^^^^^^ Object of type `Iterable` may not be iterable because it may not have an `__iter__` method and its `__getitem__` method has an incorrect signature for the old-style iteration protocol (expected a signature at least as permissive as `def __getitem__(self, key: int): ...`)
+   |              ^^^^^^^^^^
 19 |         reveal_type(x)  # revealed: int | bytes
    |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Possibly_unbound_`__iter__`_and_possibly_invalid_`__getitem__`.snap

@@ -54,12 +54,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable1` may not be iterable because it may not have an `__iter__` method and its `__getitem__` attribute (with type `(bound method Iterable1.__getitem__(item: int) -> str) | None`) may not be callable
   --> /src/mdtest_snippet.py:31:14
    |
 30 |     # error: [not-iterable]
 31 |     for x in Iterable1():
-   |              ^^^^^^^^^^^ Object of type `Iterable1` may not be iterable because it may not have an `__iter__` method and its `__getitem__` attribute (with type `(bound method Iterable1.__getitem__(item: int) -> str) | None`) may not be callable
+   |              ^^^^^^^^^^^
 32 |         # TODO: `bytes | str` might be better
 33 |         reveal_type(x)  # revealed: bytes | str | Unknown
    |
@@ -81,12 +81,12 @@ info: revealed-type: Revealed type
 ```
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable2` may not be iterable because it may not have an `__iter__` method and its `__getitem__` method (with type `(bound method Iterable2.__getitem__(item: int) -> str) | (bound method Iterable2.__getitem__(item: str) -> int)`) may have an incorrect signature for the old-style iteration protocol (expected a signature at least as permissive as `def __getitem__(self, key: int): ...`)
   --> /src/mdtest_snippet.py:36:14
    |
 35 |     # error: [not-iterable]
 36 |     for y in Iterable2():
-   |              ^^^^^^^^^^^ Object of type `Iterable2` may not be iterable because it may not have an `__iter__` method and its `__getitem__` method (with type `(bound method Iterable2.__getitem__(item: int) -> str) | (bound method Iterable2.__getitem__(item: str) -> int)`) may have an incorrect signature for the old-style iteration protocol (expected a signature at least as permissive as `def __getitem__(self, key: int): ...`)
+   |              ^^^^^^^^^^^
 37 |         reveal_type(y)  # revealed: bytes | str | int
    |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Possibly_unbound_`__iter__`_and_possibly_unbound_`__getitem__`.snap

@@ -35,12 +35,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable` may not be iterable because it may not have an `__iter__` method or a `__getitem__` method
   --> /src/mdtest_snippet.py:17:14
    |
 16 |     # error: [not-iterable]
 17 |     for x in Iterable():
-   |              ^^^^^^^^^^ Object of type `Iterable` may not be iterable because it may not have an `__iter__` method or a `__getitem__` method
+   |              ^^^^^^^^^^
 18 |         reveal_type(x)  # revealed: int | bytes
    |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Union_type_as_iterable_where_one_union_element_has_invalid_`__iter__`_method.snap

@@ -36,13 +36,13 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Test | Test2` may not be iterable because its `__iter__` method returns an object of type `TestIter | int`, which may not have a `__next__` method
   --> /src/mdtest_snippet.py:18:14
    |
 16 |     # TODO: Improve error message to state which union variant isn't iterable (https://github.com/astral-sh/ruff/issues/13989)
 17 |     # error: [not-iterable]
 18 |     for x in Test() if flag else Test2():
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ Object of type `Test | Test2` may not be iterable because its `__iter__` method returns an object of type `TestIter | int`, which may not have a `__next__` method
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 19 |         reveal_type(x)  # revealed: int
    |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_Union_type_as_iterable_where_one_union_element_has_no_`__iter__`_method.snap

@@ -31,13 +31,13 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Test | Literal[42]` may not be iterable because it may not have an `__iter__` method and it doesn't have a `__getitem__` method
   --> /src/mdtest_snippet.py:13:14
    |
 11 | def _(flag: bool):
 12 |     # error: [not-iterable]
 13 |     for x in Test() if flag else 42:
-   |              ^^^^^^^^^^^^^^^^^^^^^^ Object of type `Test | Literal[42]` may not be iterable because it may not have an `__iter__` method and it doesn't have a `__getitem__` method
+   |              ^^^^^^^^^^^^^^^^^^^^^^
 14 |         reveal_type(x)  # revealed: int
    |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_With_non-callable_iterator.snap

@@ -33,25 +33,25 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `NotIterable` is not iterable because its `__iter__` attribute has type `int | None`, which is not callable
   --> /src/mdtest_snippet.py:11:14
    |
 10 |     # error: [not-iterable]
 11 |     for x in NotIterable():
-   |              ^^^^^^^^^^^^^ Object of type `NotIterable` is not iterable because its `__iter__` attribute has type `int | None`, which is not callable
+   |              ^^^^^^^^^^^^^
 12 |         pass
    |
 
 ```
 
 ```
-warning: lint:possibly-unresolved-reference
+warning: lint:possibly-unresolved-reference: Name `x` used when possibly not defined
   --> /src/mdtest_snippet.py:16:17
    |
 14 |     # revealed: Unknown
 15 |     # error: [possibly-unresolved-reference]
 16 |     reveal_type(x)
-   |                 ^ Name `x` used when possibly not defined
+   |                 ^
    |
 
 ```

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_`__iter__`_does_not_return_an_iterator.snap

@@ -26,12 +26,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Bad` is not iterable because its `__iter__` method returns an object of type `int`, which has no `__next__` method
  --> /src/mdtest_snippet.py:8:10
   |
 7 | # error: [not-iterable]
 8 | for x in Bad():
-  |          ^^^^^ Object of type `Bad` is not iterable because its `__iter__` method returns an object of type `int`, which has no `__next__` method
+  |          ^^^^^
 9 |     reveal_type(x)  # revealed: Unknown
   |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_`__iter__`_method_with_a_bad_signature.snap

@@ -30,12 +30,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable` is not iterable because its `__iter__` method has an invalid signature (expected `def __iter__(self): ...`)
   --> /src/mdtest_snippet.py:12:10
    |
 11 | # error: [not-iterable]
 12 | for x in Iterable():
-   |          ^^^^^^^^^^ Object of type `Iterable` is not iterable because its `__iter__` method has an invalid signature (expected `def __iter__(self): ...`)
+   |          ^^^^^^^^^^
 13 |     reveal_type(x)  # revealed: int
    |
 

crates/red_knot_python_semantic/resources/mdtest/snapshots/for.md_-_For_loops_-_`__iter__`_returns_an_iterator_with_an_invalid_`__next__`_method.snap

@@ -41,12 +41,12 @@ mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
 # Diagnostics
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable1` is not iterable because its `__iter__` method returns an object of type `Iterator1`, which has an invalid `__next__` method (expected `def __next__(self): ...`)
   --> /src/mdtest_snippet.py:19:10
    |
 18 | # error: [not-iterable]
 19 | for x in Iterable1():
-   |          ^^^^^^^^^^^ Object of type `Iterable1` is not iterable because its `__iter__` method returns an object of type `Iterator1`, which has an invalid `__next__` method (expected `def __next__(self): ...`)
+   |          ^^^^^^^^^^^
 20 |     reveal_type(x)  # revealed: int
    |
 
@@ -67,12 +67,12 @@ info: revealed-type: Revealed type
 ```
 
 ```
-error: lint:not-iterable
+error: lint:not-iterable: Object of type `Iterable2` is not iterable because its `__iter__` method returns an object of type `Iterator2`, which has a `__next__` attribute that is not callable
   --> /src/mdtest_snippet.py:23:10
    |
 22 | # error: [not-iterable]
 23 | for y in Iterable2():
-   |          ^^^^^^^^^^^ Object of type `Iterable2` is not iterable because its `__iter__` method returns an object of type `Iterator2`, which has a `__next__` attribute that is not callable
+   |          ^^^^^^^^^^^
 24 |     reveal_type(y)  # revealed: Unknown
    |