macos 14 runner, no deployment target

Co-authored-by: Micha Reiser <micha@reiser.io>

.github/workflows/ci.yaml

@@ -148,7 +148,7 @@ jobs:
       # sync, not just public items. Eventually we should do this for all
       # crates; for now add crates here as they are warning-clean to prevent
       # regression.
-      - run: cargo doc --no-deps -p red_knot_python_semantic -p red_knot -p ruff_db --document-private-items
+      - run: cargo doc --no-deps -p red_knot_python_semantic -p red_knot -p red_knot_test -p ruff_db --document-private-items
         env:
           # Setting RUSTDOCFLAGS because `cargo doc --check` isn't yet implemented (https://github.com/rust-lang/cargo/issues/10025).
           RUSTDOCFLAGS: "-D warnings"
@@ -518,6 +518,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
       - name: "Add SSH key"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
         uses: webfactory/ssh-agent@v0.9.0
@@ -525,13 +527,15 @@ jobs:
           ssh-private-key: ${{ secrets.MKDOCS_INSIDERS_SSH_KEY }}
       - name: "Install Rust toolchain"
         run: rustup show
+      - name: Install uv
+        uses: astral-sh/setup-uv@v3
       - uses: Swatinem/rust-cache@v2
       - name: "Install Insiders dependencies"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
-        run: pip install -r docs/requirements-insiders.txt
+        run: uv pip install -r docs/requirements-insiders.txt --system
       - name: "Install dependencies"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS != 'true' }}
-        run: pip install -r docs/requirements.txt
+        run: uv pip install -r docs/requirements.txt --system
       - name: "Update README File"
         run: python scripts/transform_readme.py --target mkdocs
       - name: "Generate docs"
@@ -608,7 +612,7 @@ jobs:
           just test
 
   benchmarks:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     needs: determine_changes
     if: ${{ github.repository == 'astral-sh/ruff' && (needs.determine_changes.outputs.code == 'true' || github.ref == 'refs/heads/main') }}
     timeout-minutes: 20

.github/workflows/macos-12.yml

@@ -0,0 +1,76 @@
+name: "Test macOS 12 (x86_64)"
+
+on:
+  pull_request
+
+env:
+  PACKAGE_NAME: ruff
+  MODULE_NAME: ruff
+  PYTHON_VERSION: "3.11"
+  CARGO_INCREMENTAL: 0
+  CARGO_NET_RETRY: 10
+  CARGO_TERM_COLOR: always
+  RUSTUP_MAX_RETRIES: 10
+
+jobs:
+  macos-x86_64:
+    runs-on: macos-14
+#    env:
+#      MACOSX_DEPLOYMENT_TARGET: 13.7
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ env.PYTHON_VERSION }}
+          architecture: x64
+      - name: "Prep README.md"
+        run: python scripts/transform_readme.py --target pypi
+      - name: "Build wheels - x86_64"
+        uses: PyO3/maturin-action@v1
+        with:
+          target: x86_64
+          args: --release --locked --out dist
+      - name: "Upload wheels"
+        uses: actions/upload-artifact@v4
+        with:
+          name: wheels-macos-x86_64
+          path: dist
+      - name: "Archive binary"
+        run: |
+          TARGET=x86_64-apple-darwin
+          ARCHIVE_NAME=ruff-$TARGET
+          ARCHIVE_FILE=$ARCHIVE_NAME.tar.gz
+
+          mkdir -p $ARCHIVE_NAME
+          cp target/$TARGET/release/ruff $ARCHIVE_NAME/ruff
+          tar czvf $ARCHIVE_FILE $ARCHIVE_NAME
+          shasum -a 256 $ARCHIVE_FILE > $ARCHIVE_FILE.sha256
+      - name: "Upload binary"
+        uses: actions/upload-artifact@v4
+        with:
+          name: artifacts-macos-x86_64
+          path: |
+            *.tar.gz
+            *.sha256
+
+  test:
+    needs: macos-x86_64
+    runs-on: macos-12
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ env.PYTHON_VERSION }}
+          architecture: x64
+      - name: "Download binaries"
+        uses: actions/download-artifact@v4
+        with:
+          name: artifacts-macos-x86_64
+      - name: "Extract"
+        run: tar xzvf ruff-x86_64-apple-darwin.tar.gz
+      - name: "Run Ruff"
+        run: ./ruff-x86_64-apple-darwin/ruff --help

.github/workflows/sync_typeshed.yaml

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

.pre-commit-config.yaml

@@ -2,7 +2,7 @@ fail_fast: true
 
 exclude: |
   (?x)^(
-    crates/ruff_vendored/vendor/.*|
+    crates/red_knot_vendored/vendor/.*|
     crates/red_knot_workspace/resources/.*|
     crates/ruff_linter/resources/.*|
     crates/ruff_linter/src/rules/.*/snapshots/.*|
@@ -17,7 +17,7 @@ exclude: |
 
 repos:
   - repo: https://github.com/abravalheri/validate-pyproject
-    rev: v0.19
+    rev: v0.20.2
     hooks:
       - id: validate-pyproject
 
@@ -28,6 +28,7 @@ repos:
         additional_dependencies:
           - mdformat-mkdocs
           - mdformat-admon
+          - mdformat-footnote
         exclude: |
           (?x)^(
             docs/formatter/black\.md
@@ -35,7 +36,7 @@ repos:
           )$
 
   - repo: https://github.com/igorshubovych/markdownlint-cli
-    rev: v0.41.0
+    rev: v0.42.0
     hooks:
       - id: markdownlint-fix
         exclude: |
@@ -45,7 +46,7 @@ repos:
           )$
 
   - repo: https://github.com/crate-ci/typos
-    rev: v1.24.5
+    rev: v1.25.0
     hooks:
       - id: typos
 
@@ -59,7 +60,7 @@ repos:
         pass_filenames: false # This makes it a lot faster
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.6.5
+    rev: v0.6.9
     hooks:
       - id: ruff-format
       - id: ruff
@@ -68,8 +69,8 @@ repos:
         require_serial: true
 
   # Prettier
-  - repo: https://github.com/pre-commit/mirrors-prettier
-    rev: v3.1.0
+  - repo: https://github.com/rbubley/mirrors-prettier
+    rev: v3.3.3
     hooks:
       - id: prettier
         types: [yaml]

CHANGELOG.md

@@ -1,5 +1,58 @@
 # Changelog
 
+## 0.6.9
+
+### Preview features
+
+- Fix codeblock dynamic line length calculation for indented docstring examples ([#13523](https://github.com/astral-sh/ruff/pull/13523))
+- \[`refurb`\] Mark `FURB118` fix as unsafe ([#13613](https://github.com/astral-sh/ruff/pull/13613))
+
+### Rule changes
+
+- \[`pydocstyle`\] Don't raise `D208` when last line is non-empty ([#13372](https://github.com/astral-sh/ruff/pull/13372))
+- \[`pylint`\] Preserve trivia (i.e. comments) in `PLR5501` autofix ([#13573](https://github.com/astral-sh/ruff/pull/13573))
+
+### Configuration
+
+- \[`pyflakes`\] Add `allow-unused-imports` setting for `unused-import` rule (`F401`) ([#13601](https://github.com/astral-sh/ruff/pull/13601))
+
+### Bug fixes
+
+- Support ruff discovery in pip build environments ([#13591](https://github.com/astral-sh/ruff/pull/13591))
+- \[`flake8-bugbear`\] Avoid short circuiting `B017` for multiple context managers ([#13609](https://github.com/astral-sh/ruff/pull/13609))
+- \[`pylint`\] Do not offer an invalid fix for `PLR1716` when the comparisons contain parenthesis ([#13527](https://github.com/astral-sh/ruff/pull/13527))
+- \[`pyupgrade`\] Fix `UP043` to apply to `collections.abc.Generator` and `collections.abc.AsyncGenerator` ([#13611](https://github.com/astral-sh/ruff/pull/13611))
+- \[`refurb`\] Fix handling of slices in tuples for `FURB118`, e.g., `x[:, 1]` ([#13518](https://github.com/astral-sh/ruff/pull/13518))
+
+### Documentation
+
+- Update GitHub Action link to `astral-sh/ruff-action` ([#13551](https://github.com/astral-sh/ruff/pull/13551))
+
+## 0.6.8
+
+### Preview features
+
+- Remove unnecessary parentheses around `match case` clauses ([#13510](https://github.com/astral-sh/ruff/pull/13510))
+- Parenthesize overlong `if` guards in `match..case` clauses ([#13513](https://github.com/astral-sh/ruff/pull/13513))
+- Detect basic wildcard imports in `ruff analyze graph` ([#13486](https://github.com/astral-sh/ruff/pull/13486))
+- \[`pylint`\] Implement `boolean-chained-comparison` (`R1716`) ([#13435](https://github.com/astral-sh/ruff/pull/13435))
+
+### Rule changes
+
+- \[`lake8-simplify`\] Detect `SIM910` when using variadic keyword arguments, i.e., `**kwargs` ([#13503](https://github.com/astral-sh/ruff/pull/13503))
+- \[`pyupgrade`\] Avoid false negatives with non-reference shadowed bindings of loop variables (`UP028`) ([#13504](https://github.com/astral-sh/ruff/pull/13504))
+
+### Bug fixes
+
+- Detect tuples bound to variadic positional arguments i.e. `*args` ([#13512](https://github.com/astral-sh/ruff/pull/13512))
+- Exit gracefully on broken pipe errors ([#13485](https://github.com/astral-sh/ruff/pull/13485))
+- Avoid panic when analyze graph hits broken pipe ([#13484](https://github.com/astral-sh/ruff/pull/13484))
+
+### Performance
+
+- Reuse `BTreeSets` in module resolver ([#13440](https://github.com/astral-sh/ruff/pull/13440))
+- Skip traversal for non-compound statements ([#13441](https://github.com/astral-sh/ruff/pull/13441))
+
 ## 0.6.7
 
 ### Preview features

CONTRIBUTING.md

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

Cargo.lock

@@ -36,12 +36,6 @@ dependencies = [
  "memchr",
 ]
 
-[[package]]
-name = "allocator-api2"
-version = "0.2.16"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0942ffc6dcaadf03badf6e6a2d0228460359d5e34b57ccdc720b7382dfbd5ec5"
-
 [[package]]
 name = "android-tzdata"
 version = "0.1.1"
@@ -129,9 +123,9 @@ dependencies = [
 
 [[package]]
 name = "anyhow"
-version = "1.0.86"
+version = "1.0.89"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b3d1d046238990b9cf5bcde22a3fb3584ee5cf65fb2765f454ed428c7a0063da"
+checksum = "86fdf8605db99b54d3cd748a44c6d04df638eb5dafb219b135d0149bd0db01f6"
 
 [[package]]
 name = "append-only-vec"
@@ -225,7 +219,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "40723b8fb387abc38f4f4a37c09073622e41dd12327033091ef8950659e6dc0c"
 dependencies = [
  "memchr",
- "regex-automata 0.4.6",
+ "regex-automata 0.4.8",
  "serde",
 ]
 
@@ -353,9 +347,9 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "4.5.16"
+version = "4.5.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ed6719fffa43d0d87e5fd8caeab59be1554fb028cd30edc88fc4369b17971019"
+checksum = "b97f376d85a664d5837dbae44bf546e6477a679ff6610010f17276f686d867e8"
 dependencies = [
  "clap_builder",
  "clap_derive",
@@ -363,9 +357,9 @@ dependencies = [
 
 [[package]]
 name = "clap_builder"
-version = "4.5.15"
+version = "4.5.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "216aec2b177652e3846684cbfe25c9964d18ec45234f0f5da5157b207ed1aab6"
+checksum = "19bc80abd44e4bed93ca373a0704ccbd1b710dc5749406201bb018272808dc54"
 dependencies = [
  "anstream",
  "anstyle",
@@ -406,9 +400,9 @@ dependencies = [
 
 [[package]]
 name = "clap_derive"
-version = "4.5.13"
+version = "4.5.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "501d359d5f3dcaf6ecdeee48833ae73ec6e42723a1e52419c79abf9507eec0a0"
+checksum = "4ac6a0c7b1a9e9a5186361f67dfa1b88213572f427fb9ab038efb2bd8c582dab"
 dependencies = [
  "heck",
  "proc-macro2",
@@ -437,9 +431,9 @@ dependencies = [
 
 [[package]]
 name = "codspeed"
-version = "2.6.0"
+version = "2.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3a104ac948e0188b921eb3fcbdd55dcf62e542df4c7ab7e660623f6288302089"
+checksum = "450a0e9df9df1c154156f4344f99d8f6f6e69d0fc4de96ef6e2e68b2ec3bce97"
 dependencies = [
  "colored",
  "libc",
@@ -448,9 +442,9 @@ dependencies = [
 
 [[package]]
 name = "codspeed-criterion-compat"
-version = "2.6.0"
+version = "2.7.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "722c36bdc62d9436d027256ce2627af81ac7a596dfc7d13d849d0d212448d7fe"
+checksum = "8eb1a6cb9c20e177fde58cdef97c1c7c9264eb1424fe45c4fccedc2fb078a569"
 dependencies = [
  "codspeed",
  "colored",
@@ -714,7 +708,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "978747c1d849a7d2ee5e8adc0159961c48fb7e5db2f06af6723b80123bb53856"
 dependencies = [
  "cfg-if",
- "hashbrown",
+ "hashbrown 0.14.5",
  "lock_api",
  "once_cell",
  "parking_lot_core",
@@ -722,13 +716,13 @@ dependencies = [
 
 [[package]]
 name = "dashmap"
-version = "6.0.1"
+version = "6.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "804c8821570c3f8b70230c2ba75ffa5c0f9a4189b9a432b6656c536712acae28"
+checksum = "5041cc499144891f3790297212f32a74fb938e5136a14943f338ef9e0ae276cf"
 dependencies = [
  "cfg-if",
  "crossbeam-utils",
- "hashbrown",
+ "hashbrown 0.14.5",
  "lock_api",
  "once_cell",
  "parking_lot_core",
@@ -879,9 +873,9 @@ dependencies = [
 
 [[package]]
 name = "fastrand"
-version = "2.0.2"
+version = "2.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "658bd65b1cf4c852a3cc96f18a8ce7b5640f6b703f905c7d74532294c2a63984"
+checksum = "e8c02a5121d4ea3eb16a80748c74f5549a5665e4c21333c6098f283870fbdea6"
 
 [[package]]
 name = "fern"
@@ -894,9 +888,9 @@ dependencies = [
 
 [[package]]
 name = "filetime"
-version = "0.2.24"
+version = "0.2.25"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bf401df4a4e3872c4fe8151134cf483738e74b67fc934d6532c882b3d24a4550"
+checksum = "35c0522e981e68cbfa8c3f978441a5f34b30b96e146b33cd3359176b50fe8586"
 dependencies = [
  "cfg-if",
  "libc",
@@ -987,15 +981,15 @@ checksum = "d2fabcfbdc87f4758337ca535fb41a6d701b65693ce38287d856d1674551ec9b"
 
 [[package]]
 name = "globset"
-version = "0.4.14"
+version = "0.4.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "57da3b9b5b85bd66f31093f8c408b90a74431672542466497dcbdfdc02034be1"
+checksum = "15f1ce686646e7f1e19bf7d5533fe443a45dbfb990e00629110797578b42fb19"
 dependencies = [
  "aho-corasick",
  "bstr",
  "log",
- "regex-automata 0.4.6",
- "regex-syntax 0.8.3",
+ "regex-automata 0.4.8",
+ "regex-syntax 0.8.5",
 ]
 
 [[package]]
@@ -1026,16 +1020,21 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e5274423e17b7c9fc20b6e7e208532f9b19825d82dfd615708b70edd83df41f1"
 dependencies = [
  "ahash",
- "allocator-api2",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e087f84d4f86bf4b218b927129862374b72199ae7d8657835f1e89000eea4fb"
+
 [[package]]
 name = "hashlink"
 version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6ba4ff7128dee98c7dc9794b6a411377e1404dba1c97deb8d1a55297bd25d8af"
 dependencies = [
- "hashbrown",
+ "hashbrown 0.14.5",
 ]
 
 [[package]]
@@ -1106,15 +1105,15 @@ dependencies = [
 
 [[package]]
 name = "ignore"
-version = "0.4.22"
+version = "0.4.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b46810df39e66e925525d6e38ce1e7f6e1d208f72dc39757880fcb66e2c58af1"
+checksum = "6d89fd380afde86567dfba715db065673989d6253f42b88179abd3eae47bda4b"
 dependencies = [
  "crossbeam-deque",
  "globset",
  "log",
  "memchr",
- "regex-automata 0.4.6",
+ "regex-automata 0.4.8",
  "same-file",
  "walkdir",
  "winapi-util",
@@ -1127,7 +1126,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fc9da1a252bd44cd341657203722352efc9bc0c847d06ea6d2dc1cd1135e0a01"
 dependencies = [
  "ahash",
- "hashbrown",
+ "hashbrown 0.14.5",
 ]
 
 [[package]]
@@ -1142,12 +1141,12 @@ dependencies = [
 
 [[package]]
 name = "indexmap"
-version = "2.4.0"
+version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "93ead53efc7ea8ed3cfb0c79fc8023fbb782a5432b52830b6518941cebe6505c"
+checksum = "68b900aa2f7301e21c36462b170ee99994de34dff39a4a6a528e80e7376d07e5"
 dependencies = [
  "equivalent",
- "hashbrown",
+ "hashbrown 0.14.5",
  "serde",
 ]
 
@@ -1193,9 +1192,9 @@ dependencies = [
 
 [[package]]
 name = "insta"
-version = "1.39.0"
+version = "1.40.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "810ae6042d48e2c9e9215043563a58a80b877bc863228a74cf10c49d4620a6f5"
+checksum = "6593a41c7a73841868772495db7dc1e8ecab43bb5c0b6da2059246c4b506ab60"
 dependencies = [
  "console",
  "globset",
@@ -1312,9 +1311,9 @@ checksum = "8b23360e99b8717f20aaa4598f5a6541efbe30630039fbc7706cf954a87947ae"
 
 [[package]]
 name = "js-sys"
-version = "0.3.70"
+version = "0.3.72"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1868808506b929d7b0cfa8f75951347aa71bb21144b7791bae35d9bccfcfe37a"
+checksum = "6a88f1bda2bd75b0452a14784937d796722fdebfe50df998aeb3f0b7603019a9"
 dependencies = [
  "wasm-bindgen",
 ]
@@ -1347,15 +1346,15 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.158"
+version = "0.2.159"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d8adc4bb1803a324070e64a98ae98f38934d91957a99cfb3a43dcbc01bc56439"
+checksum = "561d97a539a36e26a9a5fad1ea11a3039a67714694aaa379433e580854bc3dc5"
 
 [[package]]
 name = "libcst"
-version = "1.4.0"
+version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "10293a04a48e8b0cb2cc825a93b83090e527bffd3c897a0255ad7bc96079e920"
+checksum = "1586dd7a857d8a61a577afde1a24cc9573ff549eff092d5ce968b1ec93cc61b6"
 dependencies = [
  "chic",
  "libcst_derive",
@@ -1405,9 +1404,9 @@ checksum = "0717cef1bc8b636c6e1c1bbdefc09e6322da8a9321966e8928ef80d20f7f770f"
 
 [[package]]
 name = "linux-raw-sys"
-version = "0.4.13"
+version = "0.4.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "01cda141df6706de531b6c46c3a33ecca755538219bd484262fa09410c13539c"
+checksum = "78b3ae25bc7c8c38cec158d1f2757ee79e9b3740fbc7ccf0e59e4b08d793fa89"
 
 [[package]]
 name = "lock_api"
@@ -1427,9 +1426,9 @@ checksum = "a7a70ba024b9dc04c27ea2f0c0548feb474ec5c54bba33a7f72f873a39d07b24"
 
 [[package]]
 name = "lsp-server"
-version = "0.7.6"
+version = "0.7.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "248f65b78f6db5d8e1b1604b4098a28b43d21a8eb1deeca22b1c421b276c7095"
+checksum = "550446e84739dcaf6d48a4a093973850669e13e8a34d8f8d64851041be267cd9"
 dependencies = [
  "crossbeam-channel",
  "log",
@@ -1626,9 +1625,9 @@ checksum = "830b246a0e5f20af87141b25c173cd1b609bd7779a4617d6ec582abaf90870f3"
 
 [[package]]
 name = "once_cell"
-version = "1.19.0"
+version = "1.20.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3fdb12b2476b595f9358c5161aa467c2438859caa136dec86c26fdd2efe17b92"
+checksum = "1261fe7e33c73b354eab43b1273a57c8f967d0391e80353e51f764ac02cf6775"
 
 [[package]]
 name = "oorandom"
@@ -1644,9 +1643,9 @@ checksum = "04744f49eae99ab78e0d5c0b603ab218f515ea8cfe5a456d7629ad883a3b6e7d"
 
 [[package]]
 name = "ordermap"
-version = "0.5.2"
+version = "0.5.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "61d7d835be600a7ac71b24e39c92fe6fad9e818b3c71bfc379e3ba65e327d77f"
+checksum = "31f2bd7b03bf2c767e1bb7b91505dbe022833776e60480275e6f2fb0db0c7503"
 dependencies = [
  "indexmap",
 ]
@@ -1691,9 +1690,9 @@ dependencies = [
 
 [[package]]
 name = "paste"
-version = "1.0.14"
+version = "1.0.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "de3145af08024dea9fa9914f381a17b8fc6034dfb00f3a84013f7ff43f29ed4c"
+checksum = "57c0d7b74b563b49d38dae00a0c37d4d6de9b432382b2892f0574ddcae73fd0a"
 
 [[package]]
 name = "path-absolutize"
@@ -1721,15 +1720,15 @@ checksum = "1e91099d4268b0e11973f036e885d652fb0b21fedcf69738c627f94db6a44f42"
 
 [[package]]
 name = "pathdiff"
-version = "0.2.1"
+version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8835116a5c179084a830efb3adc117ab007512b535bc1a21c991d3b32a6b44dd"
+checksum = "d61c5ce1153ab5b689d0c074c4e7fc613e942dfb7dd9eea5ab202d2ad91fe361"
 
 [[package]]
 name = "peg"
-version = "0.8.2"
+version = "0.8.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "400bcab7d219c38abf8bd7cc2054eb9bbbd4312d66f6a5557d572a203f646f61"
+checksum = "295283b02df346d1ef66052a757869b2876ac29a6bb0ac3f5f7cd44aebe40e8f"
 dependencies = [
  "peg-macros",
  "peg-runtime",
@@ -1737,9 +1736,9 @@ dependencies = [
 
 [[package]]
 name = "peg-macros"
-version = "0.8.2"
+version = "0.8.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "46e61cce859b76d19090f62da50a9fe92bab7c2a5f09e183763559a2ac392c90"
+checksum = "bdad6a1d9cf116a059582ce415d5f5566aabcd4008646779dab7fdc2a9a9d426"
 dependencies = [
  "peg-runtime",
  "proc-macro2",
@@ -1748,9 +1747,9 @@ dependencies = [
 
 [[package]]
 name = "peg-runtime"
-version = "0.8.2"
+version = "0.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "36bae92c60fa2398ce4678b98b2c4b5a7c61099961ca1fa305aec04a9ad28922"
+checksum = "e3aeb8f54c078314c2065ee649a7241f46b9d8e418e1a9581ba0546657d7aa3a"
 
 [[package]]
 name = "pep440_rs"
@@ -1934,9 +1933,9 @@ dependencies = [
 
 [[package]]
 name = "pretty_assertions"
-version = "1.4.0"
+version = "1.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "af7cee1a6c8a5b9208b3cb1061f10c0cb689087b3d8ce85fb9d2dd7a29b6ba66"
+checksum = "3ae130e2f271fbc2ac3a40fb1d07180839cdbbe443c7a27e1e3c13c5cac0116d"
 dependencies = [
  "diff",
  "yansi",
@@ -1944,9 +1943,9 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.86"
+version = "1.0.87"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5e719e8df665df0d1c8fbfd238015744736151d4445ec0836b8e628aae103b77"
+checksum = "b3e4daa0dcf6feba26f985457cdf104d4b4256fc5a09547140f3631bb076b19a"
 dependencies = [
  "unicode-ident",
 ]
@@ -2081,9 +2080,14 @@ dependencies = [
  "camino",
  "compact_str",
  "countme",
- "hashbrown",
+ "hashbrown 0.15.0",
  "insta",
+ "itertools 0.13.0",
+ "memchr",
  "ordermap",
+ "red_knot_test",
+ "red_knot_vendored",
+ "rstest",
  "ruff_db",
  "ruff_index",
  "ruff_python_ast",
@@ -2092,7 +2096,6 @@ dependencies = [
  "ruff_python_stdlib",
  "ruff_source_file",
  "ruff_text_size",
- "ruff_vendored",
  "rustc-hash 2.0.0",
  "salsa",
  "smallvec",
@@ -2127,6 +2130,37 @@ dependencies = [
  "tracing-subscriber",
 ]
 
+[[package]]
+name = "red_knot_test"
+version = "0.0.0"
+dependencies = [
+ "anyhow",
+ "colored",
+ "once_cell",
+ "red_knot_python_semantic",
+ "red_knot_vendored",
+ "regex",
+ "ruff_db",
+ "ruff_index",
+ "ruff_python_trivia",
+ "ruff_source_file",
+ "ruff_text_size",
+ "rustc-hash 2.0.0",
+ "salsa",
+ "smallvec",
+]
+
+[[package]]
+name = "red_knot_vendored"
+version = "0.0.0"
+dependencies = [
+ "once_cell",
+ "path-slash",
+ "ruff_db",
+ "walkdir",
+ "zip",
+]
+
 [[package]]
 name = "red_knot_wasm"
 version = "0.0.0"
@@ -2152,11 +2186,11 @@ dependencies = [
  "notify",
  "rayon",
  "red_knot_python_semantic",
+ "red_knot_vendored",
  "ruff_cache",
  "ruff_db",
  "ruff_python_ast",
  "ruff_text_size",
- "ruff_vendored",
  "rustc-hash 2.0.0",
  "salsa",
  "tempfile",
@@ -2194,14 +2228,14 @@ dependencies = [
 
 [[package]]
 name = "regex"
-version = "1.10.6"
+version = "1.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4219d74c6b67a3654a9fbebc4b419e22126d13d2f3c4a07ee0cb61ff79a79619"
+checksum = "38200e5ee88914975b69f657f0801b6f6dccafd44fd9326302a4aaeecfacb1d8"
 dependencies = [
  "aho-corasick",
  "memchr",
- "regex-automata 0.4.6",
- "regex-syntax 0.8.3",
+ "regex-automata 0.4.8",
+ "regex-syntax 0.8.5",
 ]
 
 [[package]]
@@ -2215,13 +2249,13 @@ dependencies = [
 
 [[package]]
 name = "regex-automata"
-version = "0.4.6"
+version = "0.4.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "86b83b8b9847f9bf95ef68afb0b8e6cdb80f498442f5179a29fad448fcc1eaea"
+checksum = "368758f23274712b504848e9d5a6f010445cc8b87a7cdb4d7cbee666c1288da3"
 dependencies = [
  "aho-corasick",
  "memchr",
- "regex-syntax 0.8.3",
+ "regex-syntax 0.8.5",
 ]
 
 [[package]]
@@ -2232,9 +2266,15 @@ checksum = "f162c6dd7b008981e4d40210aca20b4bd0f9b60ca9271061b07f78537722f2e1"
 
 [[package]]
 name = "regex-syntax"
-version = "0.8.3"
+version = "0.8.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "adad44e29e4c806119491a7f06f03de4d1af22c3a680dd47f1e6e179439d1f56"
+checksum = "2b15c43186be67a4fd63bee50d0303afffcef381492ebe2c5d87f324e1b8815c"
+
+[[package]]
+name = "relative-path"
+version = "1.9.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba39f3699c378cd8970968dcbff9c43159ea4cfbd88d43c00b22f2ef10a435d2"
 
 [[package]]
 name = "ring"
@@ -2251,9 +2291,36 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "rstest"
+version = "0.22.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7b423f0e62bdd61734b67cd21ff50871dfaeb9cc74f869dcd6af974fbcb19936"
+dependencies = [
+ "rstest_macros",
+ "rustc_version",
+]
+
+[[package]]
+name = "rstest_macros"
+version = "0.22.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c5e1711e7d14f74b12a58411c542185ef7fb7f2e7f8ee6e2940a883628522b42"
+dependencies = [
+ "cfg-if",
+ "glob",
+ "proc-macro2",
+ "quote",
+ "regex",
+ "relative-path",
+ "rustc_version",
+ "syn",
+ "unicode-ident",
+]
+
 [[package]]
 name = "ruff"
-version = "0.6.7"
+version = "0.6.9"
 dependencies = [
  "anyhow",
  "argfile",
@@ -2325,6 +2392,7 @@ dependencies = [
  "ruff_python_formatter",
  "ruff_python_parser",
  "ruff_python_trivia",
+ "rustc-hash 2.0.0",
  "serde",
  "serde_json",
  "tikv-jemallocator",
@@ -2351,7 +2419,7 @@ version = "0.0.0"
 dependencies = [
  "camino",
  "countme",
- "dashmap 6.0.1",
+ "dashmap 6.1.0",
  "filetime",
  "ignore",
  "insta",
@@ -2400,7 +2468,6 @@ dependencies = [
  "ruff_python_codegen",
  "ruff_python_formatter",
  "ruff_python_parser",
- "ruff_python_stdlib",
  "ruff_python_trivia",
  "ruff_workspace",
  "schemars",
@@ -2472,7 +2539,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_linter"
-version = "0.6.7"
+version = "0.6.9"
 dependencies = [
  "aho-corasick",
  "annotate-snippets 0.9.2",
@@ -2790,20 +2857,9 @@ dependencies = [
  "static_assertions",
 ]
 
-[[package]]
-name = "ruff_vendored"
-version = "0.0.0"
-dependencies = [
- "once_cell",
- "path-slash",
- "ruff_db",
- "walkdir",
- "zip",
-]
-
 [[package]]
 name = "ruff_wasm"
-version = "0.6.7"
+version = "0.6.9"
 dependencies = [
  "console_error_panic_hook",
  "console_log",
@@ -2885,10 +2941,19 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "583034fd73374156e66797ed8e5b0d5690409c9226b22d87cb7f19821c05d152"
 
 [[package]]
-name = "rustix"
-version = "0.38.34"
+name = "rustc_version"
+version = "0.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "70dc5ec042f7a43c4a73241207cecc9873a06d45debb38b329f8541d85c2730f"
+checksum = "cfcb3a22ef46e85b45de6ee7e79d063319ebb6594faafcf1c225ea92ab6e9b92"
+dependencies = [
+ "semver",
+]
+
+[[package]]
+name = "rustix"
+version = "0.38.37"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8acb788b847c24f28525660c4d7758620a7210875711f79e7f663cc152726811"
 dependencies = [
  "bitflags 2.6.0",
  "errno",
@@ -2944,12 +3009,12 @@ checksum = "e86697c916019a8588c99b5fac3cead74ec0b4b819707a682fd4d23fa0ce1ba1"
 [[package]]
 name = "salsa"
 version = "0.18.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=f608ff8b24f07706492027199f51132244034f29#f608ff8b24f07706492027199f51132244034f29"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=b14be5c0392f4c55eca60b92e457a35549372382#b14be5c0392f4c55eca60b92e457a35549372382"
 dependencies = [
  "append-only-vec",
  "arc-swap",
  "crossbeam",
- "dashmap 6.0.1",
+ "dashmap 6.1.0",
  "hashlink",
  "indexmap",
  "lazy_static",
@@ -2964,12 +3029,12 @@ dependencies = [
 [[package]]
 name = "salsa-macro-rules"
 version = "0.1.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=f608ff8b24f07706492027199f51132244034f29#f608ff8b24f07706492027199f51132244034f29"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=b14be5c0392f4c55eca60b92e457a35549372382#b14be5c0392f4c55eca60b92e457a35549372382"
 
 [[package]]
 name = "salsa-macros"
 version = "0.18.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=f608ff8b24f07706492027199f51132244034f29#f608ff8b24f07706492027199f51132244034f29"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=b14be5c0392f4c55eca60b92e457a35549372382#b14be5c0392f4c55eca60b92e457a35549372382"
 dependencies = [
  "heck",
  "proc-macro2",
@@ -3030,10 +3095,16 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1c107b6f4780854c8b126e228ea8869f4d7b71260f962fefb57b996b8959ba6b"
 
 [[package]]
-name = "serde"
-version = "1.0.209"
+name = "semver"
+version = "1.0.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "99fce0ffe7310761ca6bf9faf5115afbc19688edd00171d81b1bb1b116c63e09"
+checksum = "61697e0a1c7e512e84a621326239844a24d8207b4669b41bc18b32ea5cbf988b"
+
+[[package]]
+name = "serde"
+version = "1.0.210"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c8e3592472072e6e22e0a54d5904d9febf8508f65fb8552499a1abc7d1078c3a"
 dependencies = [
  "serde_derive",
 ]
@@ -3051,9 +3122,9 @@ dependencies = [
 
 [[package]]
 name = "serde_derive"
-version = "1.0.209"
+version = "1.0.210"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a5831b979fd7b5439637af1752d535ff49f4860c0f341d1baeb6faf0f4242170"
+checksum = "243902eda00fad750862fc144cea25caca5e20d615af0a81bee94ca738f1df1f"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3073,9 +3144,9 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.127"
+version = "1.0.128"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8043c06d9f82bd7271361ed64f415fe5e12a77fdb52e573e7f06a516dea329ad"
+checksum = "6ff5456707a1de34e7e37f2a6fd3d3f808c318259cbd01ab6377795054b483d8"
 dependencies = [
  "itoa",
  "memchr",
@@ -3114,9 +3185,9 @@ dependencies = [
 
 [[package]]
 name = "serde_with"
-version = "3.9.0"
+version = "3.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "69cecfa94848272156ea67b2b1a53f20fc7bc638c4a46d2f8abde08f05f4b857"
+checksum = "8e28bdad6db2b8340e449f7108f020b3b092e8583a9e3fb82713e1d4e71fe817"
 dependencies = [
  "serde",
  "serde_derive",
@@ -3125,9 +3196,9 @@ dependencies = [
 
 [[package]]
 name = "serde_with_macros"
-version = "3.9.0"
+version = "3.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a8fee4991ef4f274617a51ad4af30519438dacb2f56ac773b08a1922ff743350"
+checksum = "9d846214a9854ef724f3da161b426242d8de7c1fc7de2f89bb1efcb154dca79d"
 dependencies = [
  "darling",
  "proc-macro2",
@@ -3245,9 +3316,9 @@ checksum = "81cdd64d312baedb58e21336b31bc043b77e01cc99033ce76ef539f78e965ebc"
 
 [[package]]
 name = "syn"
-version = "2.0.76"
+version = "2.0.79"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "578e081a14e0cefc3279b0472138c513f37b41a08d5a3cca9b6e4e8ceb6cd525"
+checksum = "89132cd0bf050864e1d38dc3bbc07a0eb8e7530af26344d3d2bbbef83499f590"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3267,9 +3338,9 @@ dependencies = [
 
 [[package]]
 name = "tempfile"
-version = "3.12.0"
+version = "3.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "04cbcdd0c794ebb0d4cf35e88edd2f7d2c4c3e9a5a6dab322839b321c6a87a64"
+checksum = "f0f2c9fc62d0beef6951ccffd757e241266a2c833136efbe35af6cd2567dca5b"
 dependencies = [
  "cfg-if",
  "fastrand",
@@ -3280,12 +3351,12 @@ dependencies = [
 
 [[package]]
 name = "terminal_size"
-version = "0.3.0"
+version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "21bebf2b7c9e0a515f6e0f8c51dc0f8e4696391e6f1ff30379559f8365fb0df7"
+checksum = "4f599bd7ca042cfdf8f4512b277c02ba102247820f9d9d4a9f521f496751a6ef"
 dependencies = [
  "rustix",
- "windows-sys 0.48.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -3342,18 +3413,18 @@ dependencies = [
 
 [[package]]
 name = "thiserror"
-version = "1.0.63"
+version = "1.0.64"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c0342370b38b6a11b6cc11d6a805569958d54cfa061a29969c3b5ce2ea405724"
+checksum = "d50af8abc119fb8bb6dbabcfa89656f46f84aa0ac7688088608076ad2b459a84"
 dependencies = [
  "thiserror-impl",
 ]
 
 [[package]]
 name = "thiserror-impl"
-version = "1.0.63"
+version = "1.0.64"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a4558b58466b9ad7ca0f102865eccc95938dca1a74a856f2b57b6629050da261"
+checksum = "08904e7672f5eb876eaaf87e0ce17857500934f4981c4a0ab2b4aa98baac7fc3"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3614,15 +3685,15 @@ checksum = "08f95100a766bf4f8f28f90d77e0a5461bbdb219042e7679bebe79004fed8d75"
 
 [[package]]
 name = "unicode-ident"
-version = "1.0.12"
+version = "1.0.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b"
+checksum = "e91b56cd4cadaeb79bbf1a5645f6b4f8dc5bde8834ad5894a8db35fda9efa1fe"
 
 [[package]]
 name = "unicode-normalization"
-version = "0.1.23"
+version = "0.1.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a56d1686db2308d901306f92a263857ef59ea39678a5458e7cb17f01415101f5"
+checksum = "5033c97c4262335cded6d6fc3e5c18ab755e1a3dc96376350f3d8e9f009ad956"
 dependencies = [
  "tinyvec",
 ]
@@ -3635,9 +3706,9 @@ checksum = "0336d538f7abc86d282a4189614dfaa90810dfc2c6f6427eaf88e16311dd225d"
 
 [[package]]
 name = "unicode_names2"
-version = "1.2.2"
+version = "1.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "addeebf294df7922a1164f729fb27ebbbcea99cc32b3bf08afab62757f707677"
+checksum = "d1673eca9782c84de5f81b82e4109dcfb3611c8ba0d52930ec4a9478f547b2dd"
 dependencies = [
  "phf",
  "unicode_names2_generator",
@@ -3645,9 +3716,9 @@ dependencies = [
 
 [[package]]
 name = "unicode_names2_generator"
-version = "1.2.2"
+version = "1.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f444b8bba042fe3c1251ffaca35c603f2dc2ccc08d595c65a8c4f76f3e8426c0"
+checksum = "b91e5b84611016120197efd7dc93ef76774f4e084cd73c9fb3ea4a86c570c56e"
 dependencies = [
  "getopts",
  "log",
@@ -3787,9 +3858,9 @@ checksum = "9c8d87e72b64a3b4db28d11ce29237c246188f4f51057d65a7eab63b7987e423"
 
 [[package]]
 name = "wasm-bindgen"
-version = "0.2.93"
+version = "0.2.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a82edfc16a6c469f5f44dc7b571814045d60404b55a0ee849f9bcfa2e63dd9b5"
+checksum = "128d1e363af62632b8eb57219c8fd7877144af57558fb2ef0368d0087bddeb2e"
 dependencies = [
  "cfg-if",
  "once_cell",
@@ -3798,9 +3869,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-backend"
-version = "0.2.93"
+version = "0.2.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9de396da306523044d3302746f1208fa71d7532227f15e347e2d93e4145dd77b"
+checksum = "cb6dd4d3ca0ddffd1dd1c9c04f94b868c37ff5fac97c30b97cff2d74fce3a358"
 dependencies = [
  "bumpalo",
  "log",
@@ -3813,9 +3884,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-futures"
-version = "0.4.43"
+version = "0.4.45"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "61e9300f63a621e96ed275155c108eb6f843b6a26d053f122ab69724559dc8ed"
+checksum = "cc7ec4f8827a71586374db3e87abdb5a2bb3a15afed140221307c3ec06b1f63b"
 dependencies = [
  "cfg-if",
  "js-sys",
@@ -3825,9 +3896,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-macro"
-version = "0.2.93"
+version = "0.2.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "585c4c91a46b072c92e908d99cb1dcdf95c5218eeb6f3bf1efa991ee7a68cccf"
+checksum = "e79384be7f8f5a9dd5d7167216f022090cf1f9ec128e6e6a482a2cb5c5422c56"
 dependencies = [
  "quote",
  "wasm-bindgen-macro-support",
@@ -3835,9 +3906,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-macro-support"
-version = "0.2.93"
+version = "0.2.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "afc340c74d9005395cf9dd098506f7f44e38f2b4a21c6aaacf9a105ea5e1e836"
+checksum = "26c6ab57572f7a24a4985830b120de1594465e5d500f24afe89e16b4e833ef68"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3848,15 +3919,15 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-shared"
-version = "0.2.93"
+version = "0.2.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c62a0a307cb4a311d3a07867860911ca130c3494e8c2719593806c08bc5d0484"
+checksum = "65fc09f10666a9f147042251e0dda9c18f166ff7de300607007e96bdebc1068d"
 
 [[package]]
 name = "wasm-bindgen-test"
-version = "0.3.43"
+version = "0.3.45"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "68497a05fb21143a08a7d24fc81763384a3072ee43c44e86aad1744d6adef9d9"
+checksum = "d381749acb0943d357dcbd8f0b100640679883fcdeeef04def49daf8d33a5426"
 dependencies = [
  "console_error_panic_hook",
  "js-sys",
@@ -3869,9 +3940,9 @@ dependencies = [
 
 [[package]]
 name = "wasm-bindgen-test-macro"
-version = "0.3.43"
+version = "0.3.45"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4b8220be1fa9e4c889b30fd207d4906657e7e90b12e0e6b0c8b8d8709f5de021"
+checksum = "c97b2ef2c8d627381e51c071c2ab328eac606d3f69dd82bcbca20a9e389d95f0"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -4133,9 +4204,9 @@ checksum = "d135d17ab770252ad95e9a872d365cf3090e3be864a34ab46f48555993efc904"
 
 [[package]]
 name = "yansi"
-version = "0.5.1"
+version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "09041cd90cf85f7f8b2df60c646f853b7f535ce68f85244eb6731cf89fa498ec"
+checksum = "cfe53a6657fd280eaa890a3bc59152892ffa3e30101319d168b781ed6529b049"
 
 [[package]]
 name = "yansi-term"

Cargo.toml

@@ -34,11 +34,12 @@ ruff_python_trivia = { path = "crates/ruff_python_trivia" }
 ruff_server = { path = "crates/ruff_server" }
 ruff_source_file = { path = "crates/ruff_source_file" }
 ruff_text_size = { path = "crates/ruff_text_size" }
-ruff_vendored = { path = "crates/ruff_vendored" }
+red_knot_vendored = { path = "crates/red_knot_vendored" }
 ruff_workspace = { path = "crates/ruff_workspace" }
 
 red_knot_python_semantic = { path = "crates/red_knot_python_semantic" }
 red_knot_server = { path = "crates/red_knot_server" }
+red_knot_test = { path = "crates/red_knot_test" }
 red_knot_workspace = { path = "crates/red_knot_workspace", default-features = false }
 
 aho-corasick = { version = "1.1.3" }
@@ -72,7 +73,10 @@ filetime = { version = "0.2.23" }
 glob = { version = "0.3.1" }
 globset = { version = "0.4.14" }
 globwalk = { version = "0.9.1" }
-hashbrown = "0.14.3"
+hashbrown = { version = "0.15.0", default-features = false, features = [
+    "raw-entry",
+    "inline-more",
+] }
 ignore = { version = "0.4.22" }
 imara-diff = { version = "0.1.5" }
 imperative = { version = "1.0.4" }
@@ -90,7 +94,7 @@ libcst = { version = "1.1.0", default-features = false }
 log = { version = "0.4.17" }
 lsp-server = { version = "0.7.6" }
 lsp-types = { git = "https://github.com/astral-sh/lsp-types.git", rev = "3512a9f", features = [
-  "proposed",
+    "proposed",
 ] }
 matchit = { version = "0.8.1" }
 memchr = { version = "2.7.1" }
@@ -111,8 +115,9 @@ quote = { version = "1.0.23" }
 rand = { version = "0.8.5" }
 rayon = { version = "1.10.0" }
 regex = { version = "1.10.2" }
+rstest = { version = "0.22.0", default-features = false }
 rustc-hash = { version = "2.0.0" }
-salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "f608ff8b24f07706492027199f51132244034f29" }
+salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "b14be5c0392f4c55eca60b92e457a35549372382" }
 schemars = { version = "0.8.16" }
 seahash = { version = "4.1.0" }
 serde = { version = "1.0.197", features = ["derive"] }
@@ -120,7 +125,7 @@ serde-wasm-bindgen = { version = "0.6.4" }
 serde_json = { version = "1.0.113" }
 serde_test = { version = "1.0.152" }
 serde_with = { version = "3.6.0", default-features = false, features = [
-  "macros",
+    "macros",
 ] }
 shellexpand = { version = "3.0.0" }
 similar = { version = "2.4.0", features = ["inline"] }
@@ -137,7 +142,10 @@ toml = { version = "0.8.11" }
 tracing = { version = "0.1.40" }
 tracing-flame = { version = "0.2.0" }
 tracing-indicatif = { version = "0.3.6" }
-tracing-subscriber = { version = "0.3.18", default-features = false, features = ["env-filter", "fmt"] }
+tracing-subscriber = { version = "0.3.18", default-features = false, features = [
+    "env-filter",
+    "fmt",
+] }
 tracing-tree = { version = "0.4.0" }
 typed-arena = { version = "2.0.2" }
 unic-ucd-category = { version = "0.9" }
@@ -148,10 +156,10 @@ unicode-normalization = { version = "0.1.23" }
 ureq = { version = "2.9.6" }
 url = { version = "2.5.0" }
 uuid = { version = "1.6.1", features = [
-  "v4",
-  "fast-rng",
-  "macro-diagnostics",
-  "js",
+    "v4",
+    "fast-rng",
+    "macro-diagnostics",
+    "js",
 ] }
 walkdir = { version = "2.3.2" }
 wasm-bindgen = { version = "0.2.92" }
@@ -162,7 +170,10 @@ zip = { version = "0.6.6", default-features = false }
 [workspace.lints.rust]
 unsafe_code = "warn"
 unreachable_pub = "warn"
-unexpected_cfgs = { level = "warn", check-cfg = ["cfg(fuzzing)", "cfg(codspeed)"] }
+unexpected_cfgs = { level = "warn", check-cfg = [
+    "cfg(fuzzing)",
+    "cfg(codspeed)",
+] }
 
 [workspace.lints.clippy]
 pedantic = { level = "warn", priority = -2 }
@@ -245,23 +256,23 @@ windows-archive = ".zip"
 unix-archive = ".tar.gz"
 # Target platforms to build apps for (Rust target-triple syntax)
 targets = [
-  "aarch64-apple-darwin",
-  "aarch64-pc-windows-msvc",
-  "aarch64-unknown-linux-gnu",
-  "aarch64-unknown-linux-musl",
-  "arm-unknown-linux-musleabihf",
-  "armv7-unknown-linux-gnueabihf",
-  "armv7-unknown-linux-musleabihf",
-  "i686-pc-windows-msvc",
-  "i686-unknown-linux-gnu",
-  "i686-unknown-linux-musl",
-  "powerpc64-unknown-linux-gnu",
-  "powerpc64le-unknown-linux-gnu",
-  "s390x-unknown-linux-gnu",
-  "x86_64-apple-darwin",
-  "x86_64-pc-windows-msvc",
-  "x86_64-unknown-linux-gnu",
-  "x86_64-unknown-linux-musl",
+    "aarch64-apple-darwin",
+    "aarch64-pc-windows-msvc",
+    "aarch64-unknown-linux-gnu",
+    "aarch64-unknown-linux-musl",
+    "arm-unknown-linux-musleabihf",
+    "armv7-unknown-linux-gnueabihf",
+    "armv7-unknown-linux-musleabihf",
+    "i686-pc-windows-msvc",
+    "i686-unknown-linux-gnu",
+    "i686-unknown-linux-musl",
+    "powerpc64-unknown-linux-gnu",
+    "powerpc64le-unknown-linux-gnu",
+    "s390x-unknown-linux-gnu",
+    "x86_64-apple-darwin",
+    "x86_64-pc-windows-msvc",
+    "x86_64-unknown-linux-gnu",
+    "x86_64-unknown-linux-musl",
 ]
 # Whether to auto-include files like READMEs, LICENSEs, and CHANGELOGs (default true)
 auto-includes = false
@@ -280,7 +291,11 @@ local-artifacts-jobs = ["./build-binaries", "./build-docker"]
 # Publish jobs to run in CI
 publish-jobs = ["./publish-pypi", "./publish-wasm"]
 # Post-announce jobs to run in CI
-post-announce-jobs = ["./notify-dependents", "./publish-docs", "./publish-playground"]
+post-announce-jobs = [
+    "./notify-dependents",
+    "./publish-docs",
+    "./publish-playground",
+]
 # Custom permissions for GitHub Jobs
 github-custom-job-permissions = { "build-docker" = { packages = "write", contents = "read" }, "publish-wasm" = { contents = "read", id-token = "write", packages = "write" } }
 # Whether to install an updater program

README.md

@@ -136,8 +136,8 @@ curl -LsSf https://astral.sh/ruff/install.sh | sh
 powershell -c "irm https://astral.sh/ruff/install.ps1 | iex"
 
 # For a specific version.
-curl -LsSf https://astral.sh/ruff/0.6.7/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.6.7/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.6.9/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.6.9/install.ps1 | iex"
 ```
 
 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -170,7 +170,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.6.7
+  rev: v0.6.9
   hooks:
     # Run the linter.
     - id: ruff
@@ -182,7 +182,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 Ruff can also be used as a [VS Code extension](https://github.com/astral-sh/ruff-vscode) or with [various other editors](https://docs.astral.sh/ruff/editors/setup).
 
 Ruff can also be used as a [GitHub Action](https://github.com/features/actions) via
-[`ruff-action`](https://github.com/chartboost/ruff-action):
+[`ruff-action`](https://github.com/astral-sh/ruff-action):
 
 ```yaml
 name: Ruff
@@ -192,7 +192,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: chartboost/ruff-action@v1
+      - uses: astral-sh/ruff-action@v1
 ```
 
 ### Configuration<a id="configuration"></a>

_typos.toml

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

crates/red_knot/src/main.rs

@@ -160,7 +160,7 @@ fn run() -> anyhow::Result<ExitStatus> {
         SystemPathBuf::from_path_buf(cwd)
             .map_err(|path| {
                 anyhow!(
-                    "The current working directory '{}' contains non-unicode characters. Red Knot only supports unicode paths.",
+                    "The current working directory `{}` contains non-Unicode characters. Red Knot only supports Unicode paths.",
                     path.display()
                 )
             })?
@@ -174,7 +174,7 @@ fn run() -> anyhow::Result<ExitStatus> {
                 Ok(SystemPath::absolute(cwd, &cli_base_path))
             } else {
                 Err(anyhow!(
-                    "Provided current-directory path '{cwd}' is not a directory."
+                    "Provided current-directory path `{cwd}` is not a directory"
                 ))
             }
         })

crates/red_knot/tests/file_watching.rs

@@ -42,14 +42,14 @@ impl TestCase {
 
     fn stop_watch(&mut self) -> Vec<watch::ChangeEvent> {
         self.try_stop_watch(Duration::from_secs(10))
-            .expect("Expected watch changes but observed none.")
+            .expect("Expected watch changes but observed none")
     }
 
     fn try_stop_watch(&mut self, timeout: Duration) -> Option<Vec<watch::ChangeEvent>> {
         let watcher = self
             .watcher
             .take()
-            .expect("Cannot call `stop_watch` more than once.");
+            .expect("Cannot call `stop_watch` more than once");
 
         let mut all_events = self
             .changes_receiver
@@ -72,7 +72,7 @@ impl TestCase {
     #[cfg(unix)]
     fn take_watch_changes(&self) -> Vec<watch::ChangeEvent> {
         self.try_take_watch_changes(Duration::from_secs(10))
-            .expect("Expected watch changes but observed none.")
+            .expect("Expected watch changes but observed none")
     }
 
     fn try_take_watch_changes(&self, timeout: Duration) -> Option<Vec<watch::ChangeEvent>> {
@@ -150,14 +150,14 @@ where
             let absolute_path = workspace_path.join(relative_path);
             if let Some(parent) = absolute_path.parent() {
                 std::fs::create_dir_all(parent).with_context(|| {
-                    format!("Failed to create parent directory for file '{relative_path}'.",)
+                    format!("Failed to create parent directory for file `{relative_path}`")
                 })?;
             }
 
             let mut file = std::fs::File::create(absolute_path.as_std_path())
-                .with_context(|| format!("Failed to open file '{relative_path}'"))?;
+                .with_context(|| format!("Failed to open file `{relative_path}`"))?;
             file.write_all(content.as_bytes())
-                .with_context(|| format!("Failed to write to file '{relative_path}'"))?;
+                .with_context(|| format!("Failed to write to file `{relative_path}`"))?;
             file.sync_data()?;
         }
 
@@ -194,7 +194,7 @@ where
 
     let root_path = SystemPath::from_std_path(temp_dir.path()).ok_or_else(|| {
         anyhow!(
-            "Temp directory '{}' is not a valid UTF-8 path.",
+            "Temporary directory `{}` is not a valid UTF-8 path.",
             temp_dir.path().display()
         )
     })?;
@@ -209,7 +209,7 @@ where
     let workspace_path = root_path.join("workspace");
 
     std::fs::create_dir_all(workspace_path.as_std_path())
-        .with_context(|| format!("Failed to create workspace directory '{workspace_path}'",))?;
+        .with_context(|| format!("Failed to create workspace directory `{workspace_path}`"))?;
 
     setup_files
         .setup(&root_path, &workspace_path)
@@ -233,7 +233,7 @@ where
         }))
     {
         std::fs::create_dir_all(path.as_std_path())
-            .with_context(|| format!("Failed to create search path '{path}'"))?;
+            .with_context(|| format!("Failed to create search path `{path}`"))?;
     }
 
     let configuration = Configuration {
@@ -501,7 +501,10 @@ fn directory_moved_to_workspace() -> anyhow::Result<()> {
         .with_context(|| "Failed to create __init__.py")?;
     std::fs::write(a_original_path.as_std_path(), "").with_context(|| "Failed to create a.py")?;
 
-    let sub_a_module = resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap());
+    let sub_a_module = resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap(),
+    );
 
     assert_eq!(sub_a_module, None);
     assert_eq!(
@@ -525,7 +528,11 @@ fn directory_moved_to_workspace() -> anyhow::Result<()> {
         .expect("a.py to exist");
 
     // `import sub.a` should now resolve
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_some());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_some());
 
     assert_eq!(
         case.collect_package_files(&case.workspace_path("bar.py")),
@@ -544,7 +551,11 @@ fn directory_moved_to_trash() -> anyhow::Result<()> {
     ])?;
     let bar = case.system_file(case.workspace_path("bar.py")).unwrap();
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_some());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_some());
 
     let sub_path = case.workspace_path("sub");
     let init_file = case
@@ -569,7 +580,11 @@ fn directory_moved_to_trash() -> anyhow::Result<()> {
     case.apply_changes(changes);
 
     // `import sub.a` should no longer resolve
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_none());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_none());
 
     assert!(!init_file.exists(case.db()));
     assert!(!a_file.exists(case.db()));
@@ -592,10 +607,14 @@ fn directory_renamed() -> anyhow::Result<()> {
 
     let bar = case.system_file(case.workspace_path("bar.py")).unwrap();
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_some());
     assert!(resolve_module(
         case.db().upcast(),
-        ModuleName::new_static("foo.baz").unwrap()
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_some());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("foo.baz").unwrap()
     )
     .is_none());
 
@@ -623,11 +642,15 @@ fn directory_renamed() -> anyhow::Result<()> {
     case.apply_changes(changes);
 
     // `import sub.a` should no longer resolve
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_none());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_none());
     // `import foo.baz` should now resolve
     assert!(resolve_module(
         case.db().upcast(),
-        ModuleName::new_static("foo.baz").unwrap()
+        &ModuleName::new_static("foo.baz").unwrap()
     )
     .is_some());
 
@@ -665,7 +688,11 @@ fn directory_deleted() -> anyhow::Result<()> {
 
     let bar = case.system_file(case.workspace_path("bar.py")).unwrap();
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_some(),);
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_some());
 
     let sub_path = case.workspace_path("sub");
 
@@ -688,7 +715,11 @@ fn directory_deleted() -> anyhow::Result<()> {
     case.apply_changes(changes);
 
     // `import sub.a` should no longer resolve
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("sub.a").unwrap()).is_none());
+    assert!(resolve_module(
+        case.db().upcast(),
+        &ModuleName::new_static("sub.a").unwrap()
+    )
+    .is_none());
 
     assert!(!init_file.exists(case.db()));
     assert!(!a_file.exists(case.db()));
@@ -710,7 +741,7 @@ fn search_path() -> anyhow::Result<()> {
     let site_packages = case.root_path().join("site_packages");
 
     assert_eq!(
-        resolve_module(case.db(), ModuleName::new("a").unwrap()),
+        resolve_module(case.db(), &ModuleName::new("a").unwrap()),
         None
     );
 
@@ -720,7 +751,7 @@ fn search_path() -> anyhow::Result<()> {
 
     case.apply_changes(changes);
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("a").unwrap()).is_some());
+    assert!(resolve_module(case.db().upcast(), &ModuleName::new_static("a").unwrap()).is_some());
     assert_eq!(
         case.collect_package_files(&case.workspace_path("bar.py")),
         &[case.system_file(case.workspace_path("bar.py")).unwrap()]
@@ -736,7 +767,7 @@ fn add_search_path() -> anyhow::Result<()> {
     let site_packages = case.workspace_path("site_packages");
     std::fs::create_dir_all(site_packages.as_std_path())?;
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("a").unwrap()).is_none());
+    assert!(resolve_module(case.db().upcast(), &ModuleName::new_static("a").unwrap()).is_none());
 
     // Register site-packages as a search path.
     case.update_search_path_settings(SearchPathConfiguration {
@@ -751,7 +782,7 @@ fn add_search_path() -> anyhow::Result<()> {
 
     case.apply_changes(changes);
 
-    assert!(resolve_module(case.db().upcast(), ModuleName::new_static("a").unwrap()).is_some());
+    assert!(resolve_module(case.db().upcast(), &ModuleName::new_static("a").unwrap()).is_some());
 
     Ok(())
 }
@@ -805,7 +836,7 @@ fn changed_versions_file() -> anyhow::Result<()> {
 
     // Unset the custom typeshed directory.
     assert_eq!(
-        resolve_module(case.db(), ModuleName::new("os").unwrap()),
+        resolve_module(case.db(), &ModuleName::new("os").unwrap()),
         None
     );
 
@@ -820,7 +851,7 @@ fn changed_versions_file() -> anyhow::Result<()> {
 
     case.apply_changes(changes);
 
-    assert!(resolve_module(case.db(), ModuleName::new("os").unwrap()).is_some());
+    assert!(resolve_module(case.db(), &ModuleName::new("os").unwrap()).is_some());
 
     Ok(())
 }
@@ -1044,7 +1075,7 @@ mod unix {
 
         let baz = resolve_module(
             case.db().upcast(),
-            ModuleName::new_static("bar.baz").unwrap(),
+            &ModuleName::new_static("bar.baz").unwrap(),
         )
         .expect("Expected bar.baz to exist in site-packages.");
         let baz_workspace = case.workspace_path("bar/baz.py");
@@ -1125,7 +1156,7 @@ mod unix {
 
         let baz = resolve_module(
             case.db().upcast(),
-            ModuleName::new_static("bar.baz").unwrap(),
+            &ModuleName::new_static("bar.baz").unwrap(),
         )
         .expect("Expected bar.baz to exist in site-packages.");
         let bar_baz = case.workspace_path("bar/baz.py");
@@ -1229,7 +1260,7 @@ mod unix {
 
         let baz = resolve_module(
             case.db().upcast(),
-            ModuleName::new_static("bar.baz").unwrap(),
+            &ModuleName::new_static("bar.baz").unwrap(),
         )
         .expect("Expected bar.baz to exist in site-packages.");
         let baz_site_packages_path =

crates/red_knot_python_semantic/Cargo.toml

@@ -24,6 +24,7 @@ bitflags = { workspace = true }
 camino = { workspace = true }
 compact_str = { workspace = true }
 countme = { workspace = true }
+itertools = { workspace = true}
 ordermap = { workspace = true }
 salsa = { workspace = true }
 thiserror = { workspace = true }
@@ -33,14 +34,17 @@ hashbrown = { workspace = true }
 smallvec = { workspace = true }
 static_assertions = { workspace = true }
 test-case = { workspace = true }
+memchr = { workspace = true }
 
 [dev-dependencies]
 ruff_db = { workspace = true, features = ["os", "testing"] }
 ruff_python_parser = { workspace = true }
-ruff_vendored = { workspace = true }
+red_knot_test = { workspace = true }
+red_knot_vendored = { workspace = true }
 
 anyhow = { workspace = true }
 insta = { workspace = true }
+rstest = { workspace = true }
 tempfile = { workspace = true }
 
 [lints]

crates/red_knot_python_semantic/build.rs

@@ -0,0 +1,4 @@
+/// Rebuild the crate if a test file is added or removed from
+pub fn main() {
+    println!("cargo:rerun-if-changed=resources/mdtest");
+}

crates/red_knot_python_semantic/resources/README.md

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

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

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

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

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

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

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

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

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

crates/red_knot_python_semantic/resources/mdtest/attributes.md

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

@@ -0,0 +1,18 @@
+# Iterators
+
+## Yield must be iterable
+
+```py
+class NotIterable: pass
+
+class Iterator:
+    def __next__(self) -> int:
+        return 42
+
+class Iterable:
+    def __iter__(self) -> Iterator: ...
+
+def generator_function():
+    yield from Iterable()
+    yield from NotIterable() # error: "Object of type `NotIterable` is not iterable"
+```

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

crates/red_knot_python_semantic/resources/mdtest/unpacking.md

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

crates/red_knot_python_semantic/src/db.rs

@@ -32,7 +32,7 @@ pub(crate) mod tests {
             Self {
                 storage: salsa::Storage::default(),
                 system: TestSystem::default(),
-                vendored: ruff_vendored::file_system().clone(),
+                vendored: red_knot_vendored::file_system().clone(),
                 events: std::sync::Arc::default(),
                 files: Files::default(),
             }

crates/red_knot_python_semantic/src/module_resolver/resolver.rs

@@ -17,7 +17,7 @@ use super::module::{Module, ModuleKind};
 use super::path::{ModulePath, SearchPath, SearchPathValidationError};
 
 /// Resolves a module name to a module.
-pub fn resolve_module(db: &dyn Db, module_name: ModuleName) -> Option<Module> {
+pub fn resolve_module(db: &dyn Db, module_name: &ModuleName) -> Option<Module> {
     let interned_name = ModuleNameIngredient::new(db, module_name);
 
     resolve_module_query(db, interned_name)
@@ -36,14 +36,14 @@ pub(crate) fn resolve_module_query<'db>(
     let _span = tracing::trace_span!("resolve_module", %name).entered();
 
     let Some((search_path, module_file, kind)) = resolve_name(db, name) else {
-        tracing::debug!("Module '{name}' not found in the search paths.");
+        tracing::debug!("Module `{name}` not found in search paths");
         return None;
     };
 
     let module = Module::new(name.clone(), kind, search_path, module_file);
 
     tracing::trace!(
-        "Resolved module '{name}' to '{path}'.",
+        "Resolved module `{name}` to `{path}`",
         path = module_file.path(db)
     );
 
@@ -103,7 +103,7 @@ pub(crate) fn file_to_module(db: &dyn Db, file: File) -> Option<Module> {
     // If it doesn't, then that means that multiple modules have the same name in different
     // root paths, but that the module corresponding to `path` is in a lower priority search path,
     // in which case we ignore it.
-    let module = resolve_module(db, module_name)?;
+    let module = resolve_module(db, &module_name)?;
 
     if file == module.file() {
         Some(module)
@@ -324,7 +324,7 @@ pub(crate) fn dynamic_resolution_paths(db: &dyn Db) -> Vec<SearchPath> {
 
         let site_packages_root = files
             .root(db.upcast(), site_packages_dir)
-            .expect("Site-package root to have been created.");
+            .expect("Site-package root to have been created");
 
         // This query needs to be re-executed each time a `.pth` file
         // is added, modified or removed from the `site-packages` directory.
@@ -728,11 +728,11 @@ mod tests {
             .build();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
 
         assert_eq!(
             Some(&foo_module),
-            resolve_module(&db, foo_module_name.clone()).as_ref()
+            resolve_module(&db, &foo_module_name).as_ref()
         );
 
         assert_eq!("foo", foo_module.name());
@@ -755,7 +755,7 @@ mod tests {
             .build();
 
         let builtins_module_name = ModuleName::new_static("builtins").unwrap();
-        let builtins = resolve_module(&db, builtins_module_name).expect("builtins to resolve");
+        let builtins = resolve_module(&db, &builtins_module_name).expect("builtins to resolve");
 
         assert_eq!(builtins.file().path(&db), &stdlib.join("builtins.pyi"));
     }
@@ -776,7 +776,7 @@ mod tests {
             .build();
 
         let builtins_module_name = ModuleName::new_static("builtins").unwrap();
-        let builtins = resolve_module(&db, builtins_module_name).expect("builtins to resolve");
+        let builtins = resolve_module(&db, &builtins_module_name).expect("builtins to resolve");
 
         assert_eq!(builtins.file().path(&db), &stdlib.join("builtins.pyi"));
     }
@@ -794,11 +794,11 @@ mod tests {
             .build();
 
         let functools_module_name = ModuleName::new_static("functools").unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
 
         assert_eq!(
             Some(&functools_module),
-            resolve_module(&db, functools_module_name).as_ref()
+            resolve_module(&db, &functools_module_name).as_ref()
         );
 
         assert_eq!(&stdlib, functools_module.search_path());
@@ -848,7 +848,7 @@ mod tests {
 
         let existing_modules = create_module_names(&["asyncio", "functools", "xml.etree"]);
         for module_name in existing_modules {
-            let resolved_module = resolve_module(&db, module_name.clone()).unwrap_or_else(|| {
+            let resolved_module = resolve_module(&db, &module_name).unwrap_or_else(|| {
                 panic!("Expected module {module_name} to exist in the mock stdlib")
             });
             let search_path = resolved_module.search_path();
@@ -901,7 +901,7 @@ mod tests {
 
         for module_name in nonexisting_modules {
             assert!(
-                resolve_module(&db, module_name.clone()).is_none(),
+                resolve_module(&db, &module_name).is_none(),
                 "Unexpectedly resolved a module for {module_name}"
             );
         }
@@ -944,7 +944,7 @@ mod tests {
         ]);
 
         for module_name in existing_modules {
-            let resolved_module = resolve_module(&db, module_name.clone()).unwrap_or_else(|| {
+            let resolved_module = resolve_module(&db, &module_name).unwrap_or_else(|| {
                 panic!("Expected module {module_name} to exist in the mock stdlib")
             });
             let search_path = resolved_module.search_path();
@@ -980,7 +980,7 @@ mod tests {
         let nonexisting_modules = create_module_names(&["importlib", "xml", "xml.etree"]);
         for module_name in nonexisting_modules {
             assert!(
-                resolve_module(&db, module_name.clone()).is_none(),
+                resolve_module(&db, &module_name).is_none(),
                 "Unexpectedly resolved a module for {module_name}"
             );
         }
@@ -1002,11 +1002,11 @@ mod tests {
             .build();
 
         let functools_module_name = ModuleName::new_static("functools").unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
 
         assert_eq!(
             Some(&functools_module),
-            resolve_module(&db, functools_module_name).as_ref()
+            resolve_module(&db, &functools_module_name).as_ref()
         );
         assert_eq!(&src, functools_module.search_path());
         assert_eq!(ModuleKind::Module, functools_module.kind());
@@ -1026,7 +1026,7 @@ mod tests {
             .build();
 
         let pydoc_data_topics_name = ModuleName::new_static("pydoc_data.topics").unwrap();
-        let pydoc_data_topics = resolve_module(&db, pydoc_data_topics_name).unwrap();
+        let pydoc_data_topics = resolve_module(&db, &pydoc_data_topics_name).unwrap();
 
         assert_eq!("pydoc_data.topics", pydoc_data_topics.name());
         assert_eq!(pydoc_data_topics.search_path(), &stdlib);
@@ -1043,7 +1043,7 @@ mod tests {
             .build();
 
         let foo_path = src.join("foo/__init__.py");
-        let foo_module = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
+        let foo_module = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
 
         assert_eq!("foo", foo_module.name());
         assert_eq!(&src, foo_module.search_path());
@@ -1070,7 +1070,7 @@ mod tests {
 
         let TestCase { db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
 
-        let foo_module = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
+        let foo_module = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
         let foo_init_path = src.join("foo/__init__.py");
 
         assert_eq!(&src, foo_module.search_path());
@@ -1098,11 +1098,11 @@ mod tests {
         let foo_bar_module_name = ModuleName::new_static("foo.bar").unwrap();
 
         // `foo.py` takes priority over the `foo` namespace package
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
         assert_eq!(foo_module.file().path(&db), &src.join("foo.py"));
 
         // `foo.bar` isn't recognised as a module
-        let foo_bar_module = resolve_module(&db, foo_bar_module_name.clone());
+        let foo_bar_module = resolve_module(&db, &foo_bar_module_name);
         assert_eq!(foo_bar_module, None);
     }
 
@@ -1112,7 +1112,7 @@ mod tests {
 
         let TestCase { db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
 
-        let foo = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
+        let foo = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
         let foo_stub = src.join("foo.pyi");
 
         assert_eq!(&src, foo.search_path());
@@ -1136,7 +1136,7 @@ mod tests {
         let TestCase { db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
 
         let baz_module =
-            resolve_module(&db, ModuleName::new_static("foo.bar.baz").unwrap()).unwrap();
+            resolve_module(&db, &ModuleName::new_static("foo.bar.baz").unwrap()).unwrap();
         let baz_path = src.join("foo/bar/baz.py");
 
         assert_eq!(&src, baz_module.search_path());
@@ -1175,14 +1175,14 @@ mod tests {
         let one_module_name = ModuleName::new_static("parent.child.one").unwrap();
         let one_module_path = FilePath::System(src.join("parent/child/one.py"));
         assert_eq!(
-            resolve_module(&db, one_module_name),
+            resolve_module(&db, &one_module_name),
             path_to_module(&db, &one_module_path)
         );
 
         let two_module_name = ModuleName::new_static("parent.child.two").unwrap();
         let two_module_path = FilePath::System(site_packages.join("parent/child/two.py"));
         assert_eq!(
-            resolve_module(&db, two_module_name),
+            resolve_module(&db, &two_module_name),
             path_to_module(&db, &two_module_path)
         );
     }
@@ -1215,12 +1215,12 @@ mod tests {
 
         let one_module_path = FilePath::System(src.join("parent/child/one.py"));
         let one_module_name =
-            resolve_module(&db, ModuleName::new_static("parent.child.one").unwrap());
+            resolve_module(&db, &ModuleName::new_static("parent.child.one").unwrap());
         assert_eq!(one_module_name, path_to_module(&db, &one_module_path));
 
         assert_eq!(
             None,
-            resolve_module(&db, ModuleName::new_static("parent.child.two").unwrap())
+            resolve_module(&db, &ModuleName::new_static("parent.child.two").unwrap())
         );
     }
 
@@ -1236,7 +1236,7 @@ mod tests {
             .with_site_packages_files(&[("foo.py", "")])
             .build();
 
-        let foo_module = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
+        let foo_module = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
         let foo_src_path = src.join("foo.py");
 
         assert_eq!(&src, foo_module.search_path());
@@ -1301,8 +1301,8 @@ mod tests {
         )
         .context("Invalid program settings")?;
 
-        let foo_module = resolve_module(&db, ModuleName::new_static("foo").unwrap()).unwrap();
-        let bar_module = resolve_module(&db, ModuleName::new_static("bar").unwrap()).unwrap();
+        let foo_module = resolve_module(&db, &ModuleName::new_static("foo").unwrap()).unwrap();
+        let bar_module = resolve_module(&db, &ModuleName::new_static("bar").unwrap()).unwrap();
 
         assert_ne!(foo_module, bar_module);
 
@@ -1337,7 +1337,7 @@ mod tests {
             .build();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
 
         let bar_path = src.join("bar.py");
         let bar = system_path_to_file(&db, &bar_path).expect("bar.py to exist");
@@ -1351,7 +1351,7 @@ mod tests {
         // Re-query the foo module. The foo module should still be cached because `bar.py` isn't relevant
         // for resolving `foo`.
 
-        let foo_module2 = resolve_module(&db, foo_module_name);
+        let foo_module2 = resolve_module(&db, &foo_module_name);
 
         assert!(!db
             .take_salsa_events()
@@ -1368,14 +1368,14 @@ mod tests {
         let foo_path = src.join("foo.py");
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        assert_eq!(resolve_module(&db, foo_module_name.clone()), None);
+        assert_eq!(resolve_module(&db, &foo_module_name), None);
 
         // Now write the foo file
         db.write_file(&foo_path, "x = 1")?;
 
         let foo_file = system_path_to_file(&db, &foo_path).expect("foo.py to exist");
 
-        let foo_module = resolve_module(&db, foo_module_name).expect("Foo module to resolve");
+        let foo_module = resolve_module(&db, &foo_module_name).expect("Foo module to resolve");
         assert_eq!(foo_file, foo_module.file());
 
         Ok(())
@@ -1389,7 +1389,7 @@ mod tests {
         let TestCase { mut db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).expect("foo module to exist");
+        let foo_module = resolve_module(&db, &foo_module_name).expect("foo module to exist");
         let foo_init_path = src.join("foo/__init__.py");
 
         assert_eq!(&foo_init_path, foo_module.file().path(&db));
@@ -1401,7 +1401,7 @@ mod tests {
         File::sync_path(&mut db, &foo_init_path);
         File::sync_path(&mut db, foo_init_path.parent().unwrap());
 
-        let foo_module = resolve_module(&db, foo_module_name).expect("Foo module to resolve");
+        let foo_module = resolve_module(&db, &foo_module_name).expect("Foo module to resolve");
         assert_eq!(&src.join("foo.py"), foo_module.file().path(&db));
 
         Ok(())
@@ -1427,7 +1427,7 @@ mod tests {
         let functools_module_name = ModuleName::new_static("functools").unwrap();
         let stdlib_functools_path = stdlib.join("functools.pyi");
 
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &stdlib);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1440,7 +1440,7 @@ mod tests {
         let site_packages_functools_path = site_packages.join("functools.py");
         db.write_file(&site_packages_functools_path, "f: int")
             .unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         let events = db.take_salsa_events();
         assert_function_query_was_not_run(
             &db,
@@ -1473,7 +1473,7 @@ mod tests {
             .build();
 
         let functools_module_name = ModuleName::new_static("functools").unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &stdlib);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1484,7 +1484,7 @@ mod tests {
         // since first-party files take higher priority in module resolution:
         let src_functools_path = src.join("functools.py");
         db.write_file(&src_functools_path, "FOO: int").unwrap();
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &src);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1515,7 +1515,7 @@ mod tests {
         let functools_module_name = ModuleName::new_static("functools").unwrap();
         let src_functools_path = src.join("functools.py");
 
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &src);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1528,7 +1528,7 @@ mod tests {
             .remove_file(&src_functools_path)
             .unwrap();
         File::sync_path(&mut db, &src_functools_path);
-        let functools_module = resolve_module(&db, functools_module_name.clone()).unwrap();
+        let functools_module = resolve_module(&db, &functools_module_name).unwrap();
         assert_eq!(functools_module.search_path(), &stdlib);
         assert_eq!(
             Ok(functools_module.file()),
@@ -1550,8 +1550,8 @@ mod tests {
         let foo_module_name = ModuleName::new_static("foo").unwrap();
         let foo_bar_module_name = ModuleName::new_static("foo.bar").unwrap();
 
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
-        let foo_bar_module = resolve_module(&db, foo_bar_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
+        let foo_bar_module = resolve_module(&db, &foo_bar_module_name).unwrap();
 
         assert_eq!(
             foo_module.file().path(&db),
@@ -1579,11 +1579,11 @@ mod tests {
 
         // Lines with leading whitespace in `.pth` files do not parse:
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        assert_eq!(resolve_module(&db, foo_module_name), None);
+        assert_eq!(resolve_module(&db, &foo_module_name), None);
 
         // Lines with trailing whitespace in `.pth` files do:
         let bar_module_name = ModuleName::new_static("bar").unwrap();
-        let bar_module = resolve_module(&db, bar_module_name.clone()).unwrap();
+        let bar_module = resolve_module(&db, &bar_module_name).unwrap();
         assert_eq!(
             bar_module.file().path(&db),
             &FilePath::system("/y/src/bar.py")
@@ -1602,7 +1602,7 @@ mod tests {
             .build();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
 
         assert_eq!(
             foo_module.file().path(&db),
@@ -1650,10 +1650,10 @@ not_a_directory
         let b_module_name = ModuleName::new_static("b").unwrap();
         let spam_module_name = ModuleName::new_static("spam").unwrap();
 
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
-        let a_module = resolve_module(&db, a_module_name.clone()).unwrap();
-        let b_module = resolve_module(&db, b_module_name.clone()).unwrap();
-        let spam_module = resolve_module(&db, spam_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
+        let a_module = resolve_module(&db, &a_module_name).unwrap();
+        let b_module = resolve_module(&db, &b_module_name).unwrap();
+        let spam_module = resolve_module(&db, &spam_module_name).unwrap();
 
         assert_eq!(
             foo_module.file().path(&db),
@@ -1681,14 +1681,14 @@ not_a_directory
         let foo_module_name = ModuleName::new_static("foo").unwrap();
         let bar_module_name = ModuleName::new_static("bar").unwrap();
 
-        let foo_module = resolve_module(&db, foo_module_name).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
         assert_eq!(
             foo_module.file().path(&db),
             &FilePath::system("/x/src/foo.py")
         );
 
         db.clear_salsa_events();
-        let bar_module = resolve_module(&db, bar_module_name).unwrap();
+        let bar_module = resolve_module(&db, &bar_module_name).unwrap();
         assert_eq!(
             bar_module.file().path(&db),
             &FilePath::system("/y/src/bar.py")
@@ -1713,7 +1713,7 @@ not_a_directory
         db.write_files(x_directory).unwrap();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
         assert_eq!(
             foo_module.file().path(&db),
             &FilePath::system("/x/src/foo.py")
@@ -1725,7 +1725,7 @@ not_a_directory
 
         File::sync_path(&mut db, &site_packages.join("_foo.pth"));
 
-        assert_eq!(resolve_module(&db, foo_module_name.clone()), None);
+        assert_eq!(resolve_module(&db, &foo_module_name), None);
     }
 
     #[test]
@@ -1740,7 +1740,7 @@ not_a_directory
         db.write_files(x_directory).unwrap();
 
         let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_module = resolve_module(&db, foo_module_name.clone()).unwrap();
+        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
         let src_path = SystemPathBuf::from("/x/src");
         assert_eq!(
             foo_module.file().path(&db),
@@ -1753,7 +1753,7 @@ not_a_directory
         db.memory_file_system().remove_directory(&src_path).unwrap();
         File::sync_path(&mut db, &src_path.join("foo.py"));
         File::sync_path(&mut db, &src_path);
-        assert_eq!(resolve_module(&db, foo_module_name.clone()), None);
+        assert_eq!(resolve_module(&db, &foo_module_name), None);
     }
 
     #[test]
@@ -1812,7 +1812,7 @@ not_a_directory
         // The editable installs discovered from the `.pth` file in the first `site-packages` directory
         // take precedence over the second `site-packages` directory...
         let a_module_name = ModuleName::new_static("a").unwrap();
-        let a_module = resolve_module(&db, a_module_name.clone()).unwrap();
+        let a_module = resolve_module(&db, &a_module_name).unwrap();
         assert_eq!(a_module.file().path(&db), &editable_install_location);
 
         db.memory_file_system()
@@ -1823,7 +1823,7 @@ not_a_directory
         // ...But now that the `.pth` file in the first `site-packages` directory has been deleted,
         // the editable install no longer exists, so the module now resolves to the file in the
         // second `site-packages` directory
-        let a_module = resolve_module(&db, a_module_name).unwrap();
+        let a_module = resolve_module(&db, &a_module_name).unwrap();
         assert_eq!(a_module.file().path(&db), &system_site_packages_location);
     }
 }

crates/red_knot_python_semantic/src/module_resolver/typeshed.rs

@@ -391,7 +391,7 @@ mod tests {
         let db = TestDb::new();
         let vendored_typeshed_versions = vendored_typeshed_versions(&db);
         let vendored_typeshed_dir =
-            Path::new(env!("CARGO_MANIFEST_DIR")).join("../ruff_vendored/vendor/typeshed");
+            Path::new(env!("CARGO_MANIFEST_DIR")).join("../red_knot_vendored/vendor/typeshed");
 
         let mut empty_iterator = true;
 

crates/red_knot_python_semantic/src/semantic_index.rs

@@ -1,7 +1,7 @@
 use std::iter::FusedIterator;
 use std::sync::Arc;
 
-use rustc_hash::FxHashMap;
+use rustc_hash::{FxBuildHasher, FxHashMap};
 use salsa::plumbing::AsId;
 
 use ruff_db::files::File;
@@ -31,7 +31,7 @@ pub(crate) use self::use_def::{
     BindingWithConstraints, BindingWithConstraintsIterator, DeclarationsIterator,
 };
 
-type SymbolMap = hashbrown::HashMap<ScopedSymbolId, (), ()>;
+type SymbolMap = hashbrown::HashMap<ScopedSymbolId, (), FxBuildHasher>;
 
 /// Returns the semantic index for `file`.
 ///
@@ -994,7 +994,7 @@ class C[T]:
         let ast::Expr::NumberLiteral(ast::ExprNumberLiteral {
             value: ast::Number::Int(num),
             ..
-        }) = &*assignment.assignment().value
+        }) = assignment.value()
         else {
             panic!("should be a number literal")
         };

crates/red_knot_python_semantic/src/semantic_index/builder.rs

@@ -1,5 +1,6 @@
 use std::sync::Arc;
 
+use except_handlers::TryNodeContextStackManager;
 use rustc_hash::FxHashMap;
 
 use ruff_db::files::File;
@@ -28,22 +29,27 @@ use crate::Db;
 
 use super::constraint::{Constraint, PatternConstraint};
 use super::definition::{
-    DefinitionCategory, ExceptHandlerDefinitionNodeRef, MatchPatternDefinitionNodeRef,
-    WithItemDefinitionNodeRef,
+    AssignmentKind, DefinitionCategory, ExceptHandlerDefinitionNodeRef,
+    MatchPatternDefinitionNodeRef, WithItemDefinitionNodeRef,
 };
 
+mod except_handlers;
+
 pub(super) struct SemanticIndexBuilder<'db> {
     // Builder state
     db: &'db dyn Db,
     file: File,
     module: &'db ParsedModule,
     scope_stack: Vec<FileScopeId>,
-    /// The assignment we're currently visiting.
-    current_assignment: Option<CurrentAssignment<'db>>,
+    /// The assignments we're currently visiting, with
+    /// the most recent visit at the end of the Vec
+    current_assignments: Vec<CurrentAssignment<'db>>,
     /// The match case we're currently visiting.
     current_match_case: Option<CurrentMatchCase<'db>>,
     /// Flow states at each `break` in the current loop.
     loop_break_states: Vec<FlowSnapshot>,
+    /// Per-scope contexts regarding nested `try`/`except` statements
+    try_node_context_stack_manager: TryNodeContextStackManager,
 
     /// Flags about the file's global scope
     has_future_annotations: bool,
@@ -67,9 +73,10 @@ impl<'db> SemanticIndexBuilder<'db> {
             file,
             module: parsed,
             scope_stack: Vec::new(),
-            current_assignment: None,
+            current_assignments: vec![],
             current_match_case: None,
             loop_break_states: vec![],
+            try_node_context_stack_manager: TryNodeContextStackManager::default(),
 
             has_future_annotations: false,
 
@@ -110,6 +117,7 @@ impl<'db> SemanticIndexBuilder<'db> {
             kind: node.scope_kind(),
             descendents: children_start..children_start,
         };
+        self.try_node_context_stack_manager.enter_nested_scope();
 
         let file_scope_id = self.scopes.push(scope);
         self.symbol_tables.push(SymbolTableBuilder::new());
@@ -139,6 +147,7 @@ impl<'db> SemanticIndexBuilder<'db> {
         let children_end = self.scopes.next_index();
         let scope = &mut self.scopes[id];
         scope.descendents = scope.descendents.start..children_end;
+        self.try_node_context_stack_manager.exit_scope();
         id
     }
 
@@ -227,6 +236,10 @@ impl<'db> SemanticIndexBuilder<'db> {
             DefinitionCategory::Binding => use_def.record_binding(symbol, definition),
         }
 
+        let mut try_node_stack_manager = std::mem::take(&mut self.try_node_context_stack_manager);
+        try_node_stack_manager.record_definition(self);
+        self.try_node_context_stack_manager = try_node_stack_manager;
+
         definition
     }
 
@@ -238,6 +251,19 @@ impl<'db> SemanticIndexBuilder<'db> {
         expression
     }
 
+    fn push_assignment(&mut self, assignment: CurrentAssignment<'db>) {
+        self.current_assignments.push(assignment);
+    }
+
+    fn pop_assignment(&mut self) {
+        let popped_assignment = self.current_assignments.pop();
+        debug_assert!(popped_assignment.is_some());
+    }
+
+    fn current_assignment(&self) -> Option<&CurrentAssignment<'db>> {
+        self.current_assignments.last()
+    }
+
     fn add_pattern_constraint(
         &mut self,
         subject: &ast::Expr,
@@ -359,12 +385,12 @@ impl<'db> SemanticIndexBuilder<'db> {
         self.visit_expr(&generator.iter);
         self.push_scope(scope);
 
-        self.current_assignment = Some(CurrentAssignment::Comprehension {
+        self.push_assignment(CurrentAssignment::Comprehension {
             node: generator,
             first: true,
         });
         self.visit_expr(&generator.target);
-        self.current_assignment = None;
+        self.pop_assignment();
 
         for expr in &generator.ifs {
             self.visit_expr(expr);
@@ -374,12 +400,12 @@ impl<'db> SemanticIndexBuilder<'db> {
             self.add_standalone_expression(&generator.iter);
             self.visit_expr(&generator.iter);
 
-            self.current_assignment = Some(CurrentAssignment::Comprehension {
+            self.push_assignment(CurrentAssignment::Comprehension {
                 node: generator,
                 first: false,
             });
             self.visit_expr(&generator.target);
-            self.current_assignment = None;
+            self.pop_assignment();
 
             for expr in &generator.ifs {
                 self.visit_expr(expr);
@@ -415,7 +441,7 @@ impl<'db> SemanticIndexBuilder<'db> {
         self.pop_scope();
         assert!(self.scope_stack.is_empty());
 
-        assert!(self.current_assignment.is_none());
+        assert_eq!(&self.current_assignments, &[]);
 
         let mut symbol_tables: IndexVec<_, _> = self
             .symbol_tables
@@ -563,24 +589,38 @@ where
                 }
             }
             ast::Stmt::Assign(node) => {
-                debug_assert!(self.current_assignment.is_none());
+                debug_assert_eq!(&self.current_assignments, &[]);
                 self.visit_expr(&node.value);
                 self.add_standalone_expression(&node.value);
-                self.current_assignment = Some(node.into());
-                for target in &node.targets {
+                for (target_index, target) in node.targets.iter().enumerate() {
+                    let kind = match target {
+                        ast::Expr::List(_) | ast::Expr::Tuple(_) => Some(AssignmentKind::Sequence),
+                        ast::Expr::Name(_) => Some(AssignmentKind::Name),
+                        _ => None,
+                    };
+                    if let Some(kind) = kind {
+                        self.push_assignment(CurrentAssignment::Assign {
+                            assignment: node,
+                            target_index,
+                            kind,
+                        });
+                    }
                     self.visit_expr(target);
+                    if kind.is_some() {
+                        // only need to pop in the case where we pushed something
+                        self.pop_assignment();
+                    }
                 }
-                self.current_assignment = None;
             }
             ast::Stmt::AnnAssign(node) => {
-                debug_assert!(self.current_assignment.is_none());
+                debug_assert_eq!(&self.current_assignments, &[]);
                 self.visit_expr(&node.annotation);
                 if let Some(value) = &node.value {
                     self.visit_expr(value);
                 }
-                self.current_assignment = Some(node.into());
+                self.push_assignment(node.into());
                 self.visit_expr(&node.target);
-                self.current_assignment = None;
+                self.pop_assignment();
             }
             ast::Stmt::AugAssign(
                 aug_assign @ ast::StmtAugAssign {
@@ -590,11 +630,11 @@ where
                     value,
                 },
             ) => {
-                debug_assert!(self.current_assignment.is_none());
+                debug_assert_eq!(&self.current_assignments, &[]);
                 self.visit_expr(value);
-                self.current_assignment = Some(aug_assign.into());
+                self.push_assignment(aug_assign.into());
                 self.visit_expr(target);
-                self.current_assignment = None;
+                self.pop_assignment();
             }
             ast::Stmt::If(node) => {
                 self.visit_expr(&node.test);
@@ -662,9 +702,9 @@ where
                     self.visit_expr(&item.context_expr);
                     if let Some(optional_vars) = item.optional_vars.as_deref() {
                         self.add_standalone_expression(&item.context_expr);
-                        self.current_assignment = Some(item.into());
+                        self.push_assignment(item.into());
                         self.visit_expr(optional_vars);
-                        self.current_assignment = None;
+                        self.pop_assignment();
                     }
                 }
                 self.visit_body(body);
@@ -689,10 +729,10 @@ where
                 let pre_loop = self.flow_snapshot();
                 let saved_break_states = std::mem::take(&mut self.loop_break_states);
 
-                debug_assert!(self.current_assignment.is_none());
-                self.current_assignment = Some(for_stmt.into());
+                debug_assert_eq!(&self.current_assignments, &[]);
+                self.push_assignment(for_stmt.into());
                 self.visit_expr(target);
-                self.current_assignment = None;
+                self.pop_assignment();
 
                 // TODO: Definitions created by loop variables
                 // (and definitions created inside the body)
@@ -753,40 +793,104 @@ where
                 is_star,
                 range: _,
             }) => {
+                // Save the state prior to visiting any of the `try` block.
+                //
+                // Potentially none of the `try` block could have been executed prior to executing
+                // the `except` block(s) and/or the `finally` block.
+                // We will merge this state with all of the intermediate
+                // states during the `try` block before visiting those suites.
+                let pre_try_block_state = self.flow_snapshot();
+
+                self.try_node_context_stack_manager.push_context();
+
+                // Visit the `try` block!
                 self.visit_body(body);
 
-                for except_handler in handlers {
-                    let ast::ExceptHandler::ExceptHandler(except_handler) = except_handler;
-                    let ast::ExceptHandlerExceptHandler {
-                        name: symbol_name,
-                        type_: handled_exceptions,
-                        body: handler_body,
-                        range: _,
-                    } = except_handler;
+                let mut post_except_states = vec![];
 
-                    if let Some(handled_exceptions) = handled_exceptions {
-                        self.visit_expr(handled_exceptions);
+                // Take a record also of all the intermediate states we encountered
+                // while visiting the `try` block
+                let try_block_snapshots = self.try_node_context_stack_manager.pop_context();
+
+                if !handlers.is_empty() {
+                    // Save the state immediately *after* visiting the `try` block
+                    // but *before* we prepare for visiting the `except` block(s).
+                    //
+                    // We will revert to this state prior to visiting the the `else` block,
+                    // as there necessarily must have been 0 `except` blocks executed
+                    // if we hit the `else` block.
+                    let post_try_block_state = self.flow_snapshot();
+
+                    // Prepare for visiting the `except` block(s)
+                    self.flow_restore(pre_try_block_state);
+                    for state in try_block_snapshots {
+                        self.flow_merge(state);
                     }
 
-                    // If `handled_exceptions` above was `None`, it's something like `except as e:`,
-                    // which is invalid syntax. However, it's still pretty obvious here that the user
-                    // *wanted* `e` to be bound, so we should still create a definition here nonetheless.
-                    if let Some(symbol_name) = symbol_name {
-                        let symbol = self.add_symbol(symbol_name.id.clone());
+                    let pre_except_state = self.flow_snapshot();
+                    let num_handlers = handlers.len();
 
-                        self.add_definition(
-                            symbol,
-                            DefinitionNodeRef::ExceptHandler(ExceptHandlerDefinitionNodeRef {
-                                handler: except_handler,
-                                is_star: *is_star,
-                            }),
-                        );
+                    for (i, except_handler) in handlers.iter().enumerate() {
+                        let ast::ExceptHandler::ExceptHandler(except_handler) = except_handler;
+                        let ast::ExceptHandlerExceptHandler {
+                            name: symbol_name,
+                            type_: handled_exceptions,
+                            body: handler_body,
+                            range: _,
+                        } = except_handler;
+
+                        if let Some(handled_exceptions) = handled_exceptions {
+                            self.visit_expr(handled_exceptions);
+                        }
+
+                        // If `handled_exceptions` above was `None`, it's something like `except as e:`,
+                        // which is invalid syntax. However, it's still pretty obvious here that the user
+                        // *wanted* `e` to be bound, so we should still create a definition here nonetheless.
+                        if let Some(symbol_name) = symbol_name {
+                            let symbol = self.add_symbol(symbol_name.id.clone());
+
+                            self.add_definition(
+                                symbol,
+                                DefinitionNodeRef::ExceptHandler(ExceptHandlerDefinitionNodeRef {
+                                    handler: except_handler,
+                                    is_star: *is_star,
+                                }),
+                            );
+                        }
+
+                        self.visit_body(handler_body);
+                        // Each `except` block is mutually exclusive with all other `except` blocks.
+                        post_except_states.push(self.flow_snapshot());
+
+                        // It's unnecessary to do the `self.flow_restore()` call for the final except handler,
+                        // as we'll immediately call `self.flow_restore()` to a different state
+                        // as soon as this loop over the handlers terminates.
+                        if i < (num_handlers - 1) {
+                            self.flow_restore(pre_except_state.clone());
+                        }
                     }
 
-                    self.visit_body(handler_body);
+                    // If we get to the `else` block, we know that 0 of the `except` blocks can have been executed,
+                    // and the entire `try` block must have been executed:
+                    self.flow_restore(post_try_block_state);
                 }
 
                 self.visit_body(orelse);
+
+                for post_except_state in post_except_states {
+                    self.flow_merge(post_except_state);
+                }
+
+                // TODO: there's lots of complexity here that isn't yet handled by our model.
+                // In order to accurately model the semantics of `finally` suites, we in fact need to visit
+                // the suite twice: once under the (current) assumption that either the `try + else` suite
+                // ran to completion or exactly one `except` branch ran to completion, and then again under
+                // the assumption that potentially none of the branches ran to completion and we in fact
+                // jumped from a `try`, `else` or `except` branch straight into the `finally` branch.
+                // This requires rethinking some fundamental assumptions semantic indexing makes.
+                // For more details, see:
+                // - https://astral-sh.notion.site/Exception-handler-control-flow-11348797e1ca80bb8ce1e9aedbbe439d
+                // - https://github.com/astral-sh/ruff/pull/13633#discussion_r1788626702
                 self.visit_body(finalbody);
             }
             _ => {
@@ -802,7 +906,7 @@ where
 
         match expr {
             ast::Expr::Name(name_node @ ast::ExprName { id, ctx, .. }) => {
-                let (is_use, is_definition) = match (ctx, self.current_assignment) {
+                let (is_use, is_definition) = match (ctx, self.current_assignment()) {
                     (ast::ExprContext::Store, Some(CurrentAssignment::AugAssign(_))) => {
                         // For augmented assignment, the target expression is also used.
                         (true, true)
@@ -813,14 +917,21 @@ where
                     (ast::ExprContext::Invalid, _) => (false, false),
                 };
                 let symbol = self.add_symbol(id.clone());
+
                 if is_definition {
-                    match self.current_assignment {
-                        Some(CurrentAssignment::Assign(assignment)) => {
+                    match self.current_assignment().copied() {
+                        Some(CurrentAssignment::Assign {
+                            assignment,
+                            target_index,
+                            kind,
+                        }) => {
                             self.add_definition(
                                 symbol,
                                 AssignmentDefinitionNodeRef {
                                     assignment,
-                                    target: name_node,
+                                    target_index,
+                                    name: name_node,
+                                    kind,
                                 },
                             );
                         }
@@ -879,12 +990,11 @@ where
                 walk_expr(self, expr);
             }
             ast::Expr::Named(node) => {
-                debug_assert!(self.current_assignment.is_none());
                 // TODO walrus in comprehensions is implicitly nonlocal
                 self.visit_expr(&node.value);
-                self.current_assignment = Some(node.into());
+                self.push_assignment(node.into());
                 self.visit_expr(&node.target);
-                self.current_assignment = None;
+                self.pop_assignment();
             }
             ast::Expr::Lambda(lambda) => {
                 if let Some(parameters) = &lambda.parameters {
@@ -1043,9 +1153,13 @@ where
     }
 }
 
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, PartialEq)]
 enum CurrentAssignment<'a> {
-    Assign(&'a ast::StmtAssign),
+    Assign {
+        assignment: &'a ast::StmtAssign,
+        target_index: usize,
+        kind: AssignmentKind,
+    },
     AnnAssign(&'a ast::StmtAnnAssign),
     AugAssign(&'a ast::StmtAugAssign),
     For(&'a ast::StmtFor),
@@ -1057,12 +1171,6 @@ enum CurrentAssignment<'a> {
     WithItem(&'a ast::WithItem),
 }
 
-impl<'a> From<&'a ast::StmtAssign> for CurrentAssignment<'a> {
-    fn from(value: &'a ast::StmtAssign) -> Self {
-        Self::Assign(value)
-    }
-}
-
 impl<'a> From<&'a ast::StmtAnnAssign> for CurrentAssignment<'a> {
     fn from(value: &'a ast::StmtAnnAssign) -> Self {
         Self::AnnAssign(value)

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

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

crates/red_knot_python_semantic/src/semantic_index/definition.rs

@@ -3,6 +3,7 @@ use ruff_db::parsed::ParsedModule;
 use ruff_python_ast as ast;
 
 use crate::ast_node_ref::AstNodeRef;
+use crate::module_resolver::file_to_module;
 use crate::node_key::NodeKey;
 use crate::semantic_index::symbol::{FileScopeId, ScopeId, ScopedSymbolId};
 use crate::Db;
@@ -45,6 +46,14 @@ impl<'db> Definition<'db> {
     pub(crate) fn is_binding(self, db: &'db dyn Db) -> bool {
         self.kind(db).category().is_binding()
     }
+
+    /// Return true if this is a symbol was defined in the `typing` or `typing_extensions` modules
+    pub(crate) fn is_typing_definition(self, db: &'db dyn Db) -> bool {
+        file_to_module(db, self.file(db)).is_some_and(|module| {
+            module.search_path().is_standard_library()
+                && matches!(&**module.name(), "typing" | "typing_extensions")
+        })
+    }
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -152,7 +161,9 @@ pub(crate) struct ImportFromDefinitionNodeRef<'a> {
 #[derive(Copy, Clone, Debug)]
 pub(crate) struct AssignmentDefinitionNodeRef<'a> {
     pub(crate) assignment: &'a ast::StmtAssign,
-    pub(crate) target: &'a ast::ExprName,
+    pub(crate) target_index: usize,
+    pub(crate) name: &'a ast::ExprName,
+    pub(crate) kind: AssignmentKind,
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -215,12 +226,17 @@ impl DefinitionNodeRef<'_> {
             DefinitionNodeRef::NamedExpression(named) => {
                 DefinitionKind::NamedExpression(AstNodeRef::new(parsed, named))
             }
-            DefinitionNodeRef::Assignment(AssignmentDefinitionNodeRef { assignment, target }) => {
-                DefinitionKind::Assignment(AssignmentDefinitionKind {
-                    assignment: AstNodeRef::new(parsed.clone(), assignment),
-                    target: AstNodeRef::new(parsed, target),
-                })
-            }
+            DefinitionNodeRef::Assignment(AssignmentDefinitionNodeRef {
+                assignment,
+                target_index,
+                name,
+                kind,
+            }) => DefinitionKind::Assignment(AssignmentDefinitionKind {
+                assignment: AstNodeRef::new(parsed.clone(), assignment),
+                target_index,
+                name: AstNodeRef::new(parsed, name),
+                kind,
+            }),
             DefinitionNodeRef::AnnotatedAssignment(assign) => {
                 DefinitionKind::AnnotatedAssignment(AstNodeRef::new(parsed, assign))
             }
@@ -291,8 +307,10 @@ impl DefinitionNodeRef<'_> {
             Self::NamedExpression(node) => node.into(),
             Self::Assignment(AssignmentDefinitionNodeRef {
                 assignment: _,
-                target,
-            }) => target.into(),
+                target_index: _,
+                name,
+                kind: _,
+            }) => name.into(),
             Self::AnnotatedAssignment(node) => node.into(),
             Self::AugmentedAssignment(node) => node.into(),
             Self::For(ForStmtDefinitionNodeRef {
@@ -476,17 +494,34 @@ impl ImportFromDefinitionKind {
 #[derive(Clone, Debug)]
 pub struct AssignmentDefinitionKind {
     assignment: AstNodeRef<ast::StmtAssign>,
-    target: AstNodeRef<ast::ExprName>,
+    target_index: usize,
+    name: AstNodeRef<ast::ExprName>,
+    kind: AssignmentKind,
 }
 
 impl AssignmentDefinitionKind {
-    pub(crate) fn assignment(&self) -> &ast::StmtAssign {
-        self.assignment.node()
+    pub(crate) fn value(&self) -> &ast::Expr {
+        &self.assignment.node().value
     }
 
-    pub(crate) fn target(&self) -> &ast::ExprName {
-        self.target.node()
+    pub(crate) fn target(&self) -> &ast::Expr {
+        &self.assignment.node().targets[self.target_index]
     }
+
+    pub(crate) fn name(&self) -> &ast::ExprName {
+        self.name.node()
+    }
+
+    pub(crate) fn kind(&self) -> AssignmentKind {
+        self.kind
+    }
+}
+
+/// The kind of assignment target expression.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum AssignmentKind {
+    Sequence,
+    Name,
 }
 
 #[derive(Clone, Debug)]

crates/red_knot_python_semantic/src/semantic_model.rs

@@ -35,7 +35,7 @@ impl<'db> SemanticModel<'db> {
         line_index(self.db.upcast(), self.file)
     }
 
-    pub fn resolve_module(&self, module_name: ModuleName) -> Option<Module> {
+    pub fn resolve_module(&self, module_name: &ModuleName) -> Option<Module> {
         resolve_module(self.db, module_name)
     }
 

crates/red_knot_python_semantic/src/site_packages.rs

@@ -192,7 +192,7 @@ impl VirtualEnvironment {
             } else {
                 tracing::warn!(
                     "Failed to resolve `sys.prefix` of the system Python installation \
-from the `home` value in the `pyvenv.cfg` file at '{}'. \
+from the `home` value in the `pyvenv.cfg` file at `{}`. \
 System site-packages will not be used for module resolution.",
                     venv_path.join("pyvenv.cfg")
                 );
@@ -426,7 +426,7 @@ impl Deref for SysPrefixPath {
 
 impl fmt::Display for SysPrefixPath {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "`sys.prefix` path '{}'", self.0)
+        write!(f, "`sys.prefix` path `{}`", self.0)
     }
 }
 
@@ -483,7 +483,7 @@ impl Deref for PythonHomePath {
 
 impl fmt::Display for PythonHomePath {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "`home` location '{}'", self.0)
+        write!(f, "`home` location `{}`", self.0)
     }
 }
 

crates/red_knot_python_semantic/src/stdlib.rs

@@ -35,8 +35,15 @@ fn core_module_symbol_ty<'db>(
     core_module: CoreStdlibModule,
     symbol: &str,
 ) -> Type<'db> {
-    resolve_module(db, core_module.name())
+    resolve_module(db, &core_module.name())
         .map(|module| global_symbol_ty(db, module.file(), symbol))
+        .map(|ty| {
+            if ty.is_unbound() {
+                ty
+            } else {
+                ty.replace_unbound_with(db, Type::Never)
+            }
+        })
         .unwrap_or(Type::Unbound)
 }
 
@@ -76,7 +83,7 @@ pub(crate) fn typing_extensions_symbol_ty<'db>(db: &'db dyn Db, symbol: &str) ->
 ///
 /// Can return `None` if a custom typeshed is used that is missing the core module in question.
 fn core_module_scope(db: &dyn Db, core_module: CoreStdlibModule) -> Option<ScopeId<'_>> {
-    resolve_module(db, core_module.name()).map(|module| global_scope(db, module.file()))
+    resolve_module(db, &core_module.name()).map(|module| global_scope(db, module.file()))
 }
 
 /// Get the `builtins` module scope.

crates/red_knot_python_semantic/src/types/builder.rs

@@ -25,10 +25,12 @@
 //!   * No type in an intersection can be a supertype of any other type in the intersection (just
 //!     eliminate the supertype from the intersection).
 //!   * An intersection containing two non-overlapping types should simplify to [`Type::Never`].
-use crate::types::{builtins_symbol_ty, IntersectionType, Type, UnionType};
+use crate::types::{IntersectionType, Type, UnionType};
 use crate::{Db, FxOrderSet};
 use smallvec::SmallVec;
 
+use super::KnownClass;
+
 pub(crate) struct UnionBuilder<'db> {
     elements: Vec<Type<'db>>,
     db: &'db dyn Db,
@@ -64,7 +66,7 @@ impl<'db> UnionBuilder<'db> {
                 let mut to_remove = SmallVec::<[usize; 2]>::new();
                 for (index, element) in self.elements.iter().enumerate() {
                     if Some(*element) == bool_pair {
-                        to_add = builtins_symbol_ty(self.db, "bool");
+                        to_add = KnownClass::Bool.to_instance(self.db);
                         to_remove.push(index);
                         // The type we are adding is a BooleanLiteral, which doesn't have any
                         // subtypes. And we just found that the union already contained our
@@ -109,7 +111,7 @@ impl<'db> UnionBuilder<'db> {
         match self.elements.len() {
             0 => Type::Never,
             1 => self.elements[0],
-            _ => Type::Union(UnionType::new(self.db, self.elements.into())),
+            _ => Type::Union(UnionType::new(self.db, self.elements.into_boxed_slice())),
         }
     }
 }
@@ -215,6 +217,7 @@ impl<'db> InnerIntersectionBuilder<'db> {
 
     /// Adds a positive type to this intersection.
     fn add_positive(&mut self, db: &'db dyn Db, ty: Type<'db>) {
+        // TODO `Any`/`Unknown`/`Todo` actually should not self-cancel
         match ty {
             Type::Intersection(inter) => {
                 let pos = inter.positive(db);
@@ -234,7 +237,7 @@ impl<'db> InnerIntersectionBuilder<'db> {
 
     /// Adds a negative type to this intersection.
     fn add_negative(&mut self, db: &'db dyn Db, ty: Type<'db>) {
-        // TODO Any/Unknown actually should not self-cancel
+        // TODO `Any`/`Unknown`/`Todo` actually should not self-cancel
         match ty {
             Type::Intersection(intersection) => {
                 let pos = intersection.negative(db);
@@ -299,7 +302,7 @@ mod tests {
     use crate::db::tests::TestDb;
     use crate::program::{Program, SearchPathSettings};
     use crate::python_version::PythonVersion;
-    use crate::types::{builtins_symbol_ty, UnionBuilder};
+    use crate::types::{KnownClass, UnionBuilder};
     use crate::ProgramSettings;
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
 
@@ -359,7 +362,7 @@ mod tests {
     #[test]
     fn build_union_bool() {
         let db = setup_db();
-        let bool_ty = builtins_symbol_ty(&db, "bool");
+        let bool_instance_ty = KnownClass::Bool.to_instance(&db);
 
         let t0 = Type::BooleanLiteral(true);
         let t1 = Type::BooleanLiteral(true);
@@ -370,7 +373,7 @@ mod tests {
         assert_eq!(union.elements(&db), &[t0, t3]);
 
         let union = UnionType::from_elements(&db, [t0, t1, t2, t3]).expect_union();
-        assert_eq!(union.elements(&db), &[bool_ty, t3]);
+        assert_eq!(union.elements(&db), &[bool_instance_ty, t3]);
     }
 
     #[test]
@@ -388,7 +391,7 @@ mod tests {
     #[test]
     fn build_union_simplify_subtype() {
         let db = setup_db();
-        let t0 = builtins_symbol_ty(&db, "str").to_instance(&db);
+        let t0 = KnownClass::Str.to_instance(&db);
         let t1 = Type::LiteralString;
         let u0 = UnionType::from_elements(&db, [t0, t1]);
         let u1 = UnionType::from_elements(&db, [t1, t0]);
@@ -400,7 +403,7 @@ mod tests {
     #[test]
     fn build_union_no_simplify_unknown() {
         let db = setup_db();
-        let t0 = builtins_symbol_ty(&db, "str").to_instance(&db);
+        let t0 = KnownClass::Str.to_instance(&db);
         let t1 = Type::Unknown;
         let u0 = UnionType::from_elements(&db, [t0, t1]);
         let u1 = UnionType::from_elements(&db, [t1, t0]);
@@ -412,9 +415,9 @@ mod tests {
     #[test]
     fn build_union_subsume_multiple() {
         let db = setup_db();
-        let str_ty = builtins_symbol_ty(&db, "str").to_instance(&db);
-        let int_ty = builtins_symbol_ty(&db, "int").to_instance(&db);
-        let object_ty = builtins_symbol_ty(&db, "object").to_instance(&db);
+        let str_ty = KnownClass::Str.to_instance(&db);
+        let int_ty = KnownClass::Int.to_instance(&db);
+        let object_ty = KnownClass::Object.to_instance(&db);
         let unknown_ty = Type::Unknown;
 
         let u0 = UnionType::from_elements(&db, [str_ty, unknown_ty, int_ty, object_ty]);

crates/red_knot_python_semantic/src/types/display.rs

@@ -36,9 +36,8 @@ impl Display for DisplayType<'_> {
                 | Type::BytesLiteral(_)
                 | Type::Class(_)
                 | Type::Function(_)
-                | Type::RevealTypeFunction(_)
         ) {
-            write!(f, "Literal[{representation}]",)
+            write!(f, "Literal[{representation}]")
         } else {
             representation.fmt(f)
         }
@@ -67,15 +66,16 @@ impl Display for DisplayRepresentation<'_> {
             Type::Unknown => f.write_str("Unknown"),
             Type::Unbound => f.write_str("Unbound"),
             Type::None => f.write_str("None"),
+            // `[Type::Todo]`'s display should be explicit that is not a valid display of
+            // any other type
+            Type::Todo => f.write_str("@Todo"),
             Type::Module(file) => {
                 write!(f, "<module '{:?}'>", file.path(self.db))
             }
             // TODO functions and classes should display using a fully qualified name
             Type::Class(class) => f.write_str(class.name(self.db)),
             Type::Instance(class) => f.write_str(class.name(self.db)),
-            Type::Function(function) | Type::RevealTypeFunction(function) => {
-                f.write_str(function.name(self.db))
-            }
+            Type::Function(function) => f.write_str(function.name(self.db)),
             Type::Union(union) => union.display(self.db).fmt(f),
             Type::Intersection(intersection) => intersection.display(self.db).fmt(f),
             Type::IntLiteral(n) => n.fmt(f),
@@ -194,7 +194,7 @@ impl TryFrom<Type<'_>> for LiteralTypeKind {
     fn try_from(value: Type<'_>) -> Result<Self, Self::Error> {
         match value {
             Type::Class(_) => Ok(Self::Class),
-            Type::Function(_) | Type::RevealTypeFunction(_) => Ok(Self::Function),
+            Type::Function(_) => Ok(Self::Function),
             Type::IntLiteral(_) => Ok(Self::IntLiteral),
             Type::StringLiteral(_) => Ok(Self::StringLiteral),
             Type::BytesLiteral(_) => Ok(Self::BytesLiteral),
@@ -335,18 +335,18 @@ mod tests {
             class B: ...
             ",
         )?;
-        let mod_file = system_path_to_file(&db, "src/main.py").expect("Expected file to exist.");
+        let mod_file = system_path_to_file(&db, "src/main.py").expect("file to exist");
 
         let union_elements = &[
             Type::Unknown,
             Type::IntLiteral(-1),
             global_symbol_ty(&db, mod_file, "A"),
-            Type::StringLiteral(StringLiteralType::new(&db, Box::from("A"))),
-            Type::BytesLiteral(BytesLiteralType::new(&db, Box::from([0]))),
-            Type::BytesLiteral(BytesLiteralType::new(&db, Box::from([7]))),
+            Type::StringLiteral(StringLiteralType::new(&db, "A")),
+            Type::BytesLiteral(BytesLiteralType::new(&db, [0u8].as_slice())),
+            Type::BytesLiteral(BytesLiteralType::new(&db, [7u8].as_slice())),
             Type::IntLiteral(0),
             Type::IntLiteral(1),
-            Type::StringLiteral(StringLiteralType::new(&db, Box::from("B"))),
+            Type::StringLiteral(StringLiteralType::new(&db, "B")),
             global_symbol_ty(&db, mod_file, "foo"),
             global_symbol_ty(&db, mod_file, "bar"),
             global_symbol_ty(&db, mod_file, "B"),

crates/red_knot_python_semantic/src/types/narrow.rs

@@ -155,13 +155,24 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
             let inference = infer_expression_types(self.db, expression);
             for (op, comparator) in std::iter::zip(&**ops, &**comparators) {
                 let comp_ty = inference.expression_ty(comparator.scoped_ast_id(self.db, scope));
-                if matches!(op, ast::CmpOp::IsNot) {
-                    let ty = IntersectionBuilder::new(self.db)
-                        .add_negative(comp_ty)
-                        .build();
-                    self.constraints.insert(symbol, ty);
-                };
-                // TODO other comparison types
+                match op {
+                    ast::CmpOp::IsNot => {
+                        if comp_ty.is_singleton() {
+                            let ty = IntersectionBuilder::new(self.db)
+                                .add_negative(comp_ty)
+                                .build();
+                            self.constraints.insert(symbol, ty);
+                        } else {
+                            // Non-singletons cannot be safely narrowed using `is not`
+                        }
+                    }
+                    ast::CmpOp::Is => {
+                        self.constraints.insert(symbol, comp_ty);
+                    }
+                    _ => {
+                        // TODO other comparison types
+                    }
+                }
             }
         }
     }

crates/red_knot_python_semantic/tests/mdtest.rs

@@ -0,0 +1,14 @@
+use red_knot_test::run;
+use std::path::PathBuf;
+
+/// See `crates/red_knot_test/README.md` for documentation on these tests.
+#[rstest::rstest]
+fn mdtest(#[files("resources/mdtest/**/*.md")] path: PathBuf) {
+    let crate_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .join("resources")
+        .join("mdtest")
+        .canonicalize()
+        .unwrap();
+    let title = path.strip_prefix(crate_dir).unwrap();
+    run(&path, title.as_os_str().to_str().unwrap());
+}

crates/red_knot_server/src/server/api/requests/diagnostic.rs

@@ -47,7 +47,7 @@ impl BackgroundDocumentRequestHandler for DocumentDiagnosticRequestHandler {
 fn compute_diagnostics(snapshot: &DocumentSnapshot, db: &RootDatabase) -> Vec<Diagnostic> {
     let Some(file) = snapshot.file(db) else {
         tracing::info!(
-            "No file found for snapshot for '{}'",
+            "No file found for snapshot for `{}`",
             snapshot.query().file_url()
         );
         return vec![];

crates/red_knot_test/Cargo.toml

@@ -0,0 +1,33 @@
+[package]
+name = "red_knot_test"
+version = "0.0.0"
+publish = false
+edition.workspace = true
+rust-version.workspace = true
+homepage.workspace = true
+documentation.workspace = true
+repository.workspace = true
+authors.workspace = true
+license.workspace = true
+
+[dependencies]
+red_knot_python_semantic = { workspace = true }
+red_knot_vendored = { workspace = true }
+ruff_db = { workspace = true }
+ruff_index = { workspace = true }
+ruff_python_trivia = { workspace = true }
+ruff_source_file = { workspace = true }
+ruff_text_size = { workspace = true }
+
+anyhow = { workspace = true }
+colored = { workspace = true }
+once_cell = { workspace = true }
+regex = { workspace = true }
+rustc-hash = { workspace = true }
+salsa = { workspace = true }
+smallvec = { workspace = true }
+
+[dev-dependencies]
+
+[lints]
+workspace = true

crates/red_knot_test/README.md

@@ -0,0 +1,470 @@
+# Writing type-checking / type-inference tests
+
+Any Markdown file can be a test suite.
+
+In order for it to be run as one, `red_knot_test::run` must be called with its path; see
+`crates/red_knot_python_semantic/tests/mdtest.rs` for an example that treats all Markdown files
+under a certain directory as test suites.
+
+A Markdown test suite can contain any number of tests. A test consists of one or more embedded
+"files", each defined by a triple-backticks fenced code block. The code block must have a tag string
+specifying its language; currently only `py` (Python files) and `pyi` (type stub files) are
+supported.
+
+The simplest possible test suite consists of just a single test, with a single embedded file:
+
+````markdown
+```py
+reveal_type(1)  # revealed: Literal[1]
+```
+````
+
+When running this test, the mdtest framework will write a file with these contents to the default
+file path (`/src/test.py`) in its in-memory file system, run a type check on that file, and then
+match the resulting diagnostics with the assertions in the test. Assertions are in the form of
+Python comments. If all diagnostics and all assertions are matched, the test passes; otherwise, it
+fails.
+
+<!---
+(If you are reading this document in raw Markdown source rather than rendered Markdown, note that
+the quadruple-backtick-fenced "markdown" language code block above is NOT itself part of the mdtest
+syntax, it's just how this README embeds an example mdtest Markdown document.)
+--->
+
+See actual example mdtest suites in
+[`crates/red_knot_python_semantic/resources/mdtest`](https://github.com/astral-sh/ruff/tree/main/crates/red_knot_python_semantic/resources/mdtest).
+
+> ℹ️ Note: If you use `rstest` to generate a separate test for all Markdown files in a certain directory,
+> as with the example in `crates/red_knot_python_semantic/tests/mdtest.rs`,
+> you will likely want to also make sure that the crate the tests are in is rebuilt every time a
+> Markdown file is added or removed from the directory. See
+> [`crates/red_knot_python_semantic/build.rs`](https://github.com/astral-sh/ruff/tree/main/crates/red_knot_python_semantic/build.rs)
+> for an example of how to do this.
+>
+> This is because `rstest` generates its tests at build time rather than at runtime.
+> Without the `build.rs` file to force a rebuild when a Markdown file is added or removed,
+> a new Markdown test suite might not be run unless some other change in the crate caused a rebuild
+> following the addition of the new test file.
+
+## Assertions
+
+Two kinds of assertions are supported: `# revealed:` (shown above) and `# error:`.
+
+### Assertion kinds
+
+#### revealed
+
+A `# revealed:` assertion should always be paired with a call to the `reveal_type` utility, which
+reveals (via a diagnostic) the inferred type of its argument (which can be any expression). The text
+after `# revealed:` must match exactly with the displayed form of the revealed type of that
+expression.
+
+The `reveal_type` function can be imported from the `typing` standard library module (or, for older
+Python versions, from the `typing_extensions` pseudo-standard-library module[^extensions]):
+
+```py
+from typing import reveal_type
+
+reveal_type("foo")  # revealed: Literal["foo"]
+```
+
+For convenience, type checkers also pretend that `reveal_type` is a built-in, so that this import is
+not required. Using `reveal_type` without importing it issues a diagnostic warning that it was used
+without importing it, in addition to the diagnostic revealing the type of the expression.
+
+The `# revealed:` assertion must always match a revealed-type diagnostic, and will also match the
+undefined-reveal diagnostic, if present, so it's safe to use `reveal_type` in tests either with or
+without importing it. (Style preference is to not import it in tests, unless specifically testing
+something about the behavior of importing it.)
+
+#### error
+
+A comment beginning with `# error:` is an assertion that a type checker diagnostic will be emitted,
+with text span starting on that line. The matching can be narrowed in three ways:
+
+- `# error: [invalid-assignment]` requires that the matched diagnostic have the rule code
+    `invalid-assignment`. (The square brackets are required.)
+- `# error: "Some text"` requires that the diagnostic's full message contain the text `Some text`.
+    (The double quotes are required in the assertion comment; they are not part of the matched text.)
+- `# error: 8 [rule-code]` or `# error: 8 "Some text"` additionally requires that the matched
+    diagnostic's text span begins on column 8 (one-indexed) of this line.
+
+Assertions must contain either a rule code or a contains-text, or both, and may optionally also
+include a column number. They must come in order: first column, if present; then rule code, if
+present; then contains-text, if present. For example, an assertion using all three would look like
+`# error: 8 [invalid-assignment] "Some text"`.
+
+Error assertions in tests intended to test type checker semantics should primarily use rule-code
+assertions, with occasional contains-text assertions where needed to disambiguate or validate some
+details of the diagnostic message.
+
+### Assertion locations
+
+An assertion comment may be a line-trailing comment, in which case it applies to the line it is on:
+
+```py
+x: str = 1  # error: [invalid-assignment]
+```
+
+Or it may be a comment on its own line, in which case it applies to the next line that does not
+contain an assertion comment:
+
+```py
+# error: [invalid-assignment]
+x: str = 1
+```
+
+Multiple assertions applying to the same line may be stacked:
+
+```py
+# error: [invalid-assignment]
+# revealed: Literal[1]
+x: str = reveal_type(1)
+```
+
+Intervening empty lines or non-assertion comments are not allowed; an assertion stack must be one
+assertion per line, immediately following each other, with the line immediately following the last
+assertion as the line of source code on which the matched diagnostics are emitted.
+
+## Multi-file tests
+
+Some tests require multiple files, with imports from one file into another. Multiple fenced code
+blocks represent multiple embedded files. Since files must have unique names, at most one file can
+use the default name of `/src/test.py`. Other files must explicitly specify their file name:
+
+````markdown
+```py
+from b import C
+reveal_type(C)  # revealed: Literal[C]
+```
+
+```py path=b.py
+class C: pass
+```
+````
+
+Relative file names are always relative to the "workspace root", which is also an import root (that
+is, the equivalent of a runtime entry on `sys.path`).
+
+The default workspace root is `/src/`. Currently it is not possible to customize this in a test, but
+this is a feature we will want to add in the future.
+
+So the above test creates two files, `/src/test.py` and `/src/b.py`, and sets the workspace root to
+`/src/`, allowing `test.py` to import from `b.py` using the module name `b`.
+
+## Multi-test suites
+
+A single test suite (Markdown file) can contain multiple tests, by demarcating them using Markdown
+header lines:
+
+````markdown
+# Same-file invalid assignment
+
+```py
+x: int = "foo"  # error: [invalid-assignment]
+```
+
+# Cross-file invalid assignment
+
+```py
+from b import y
+x: int = y  # error: [invalid-assignment]
+```
+
+```py path=b.py
+y = "foo"
+```
+````
+
+This test suite contains two tests, one named "Same-file invalid assignment" and the other named
+"Cross-file invalid assignment". The first test involves only a single embedded file, and the second
+test involves two embedded files.
+
+The tests are run independently, in independent in-memory file systems and with new red-knot
+[Salsa](https://github.com/salsa-rs/salsa) databases. This means that each is a from-scratch run of
+the type checker, with no data persisting from any previous test.
+
+Due to `cargo test` limitations, an entire test suite (Markdown file) is run as a single Rust test,
+so it's not possible to select individual tests within it to run.
+
+## Structured test suites
+
+Markdown headers can also be used to group related tests within a suite:
+
+````markdown
+# Literals
+
+## Numbers
+
+### Integer
+
+```py
+reveal_type(1)  # revealed: Literal[1]
+```
+
+### Float
+
+```py
+reveal_type(1.0)  # revealed: float
+```
+
+## Strings
+
+```py
+reveal_type("foo")  # revealed: Literal["foo"]
+```
+````
+
+This test suite contains three tests, named "Literals - Numbers - Integer", "Literals - Numbers -
+Float", and "Literals - Strings".
+
+A header-demarcated section must either be a test or a grouping header; it cannot be both. That is,
+a header section can either contain embedded files (making it a test), or it can contain more
+deeply-nested headers (headers with more `#`), but it cannot contain both.
+
+## Documentation of tests
+
+Arbitrary Markdown syntax (including of course normal prose paragraphs) is permitted (and ignored by
+the test framework) between fenced code blocks. This permits natural documentation of
+why a test exists, and what it intends to assert:
+
+````markdown
+Assigning a string to a variable annotated as `int` is not permitted:
+
+```py
+x: int = "foo"  # error: [invalid-assignment]
+```
+````
+
+## Planned features
+
+There are some designed features that we intend for the test framework to have, but have not yet
+implemented:
+
+### Multi-line diagnostic assertions
+
+We may want to be able to assert that a diagnostic spans multiple lines, and to assert the columns it
+begins and/or ends on. The planned syntax for this will use `<<<` and `>>>` to mark the start and end lines for
+an assertion:
+
+```py
+(3  # error: 2 [unsupported-operands] <<<
+  +
+ "foo")  # error: 6 >>>
+```
+
+The column assertion `6` on the ending line should be optional.
+
+In cases of overlapping such assertions, resolve ambiguity using more angle brackets: `<<<<` begins
+an assertion ended by `>>>>`, etc.
+
+### Non-Python files
+
+Some tests may need to specify non-Python embedded files: typeshed `stdlib/VERSIONS`, `pth` files,
+`py.typed` files, `pyvenv.cfg` files...
+
+We will allow specifying any of these using the `text` language in the code block tag string:
+
+````markdown
+```text path=/third-party/foo/py.typed
+partial
+```
+````
+
+We may want to also support testing Jupyter notebooks as embedded files; exact syntax for this is
+yet to be determined.
+
+Of course, red-knot is only run directly on `py` and `pyi` files, and assertion comments are only
+possible in these files.
+
+A fenced code block with no language will always be an error.
+
+### Configuration
+
+We will add the ability to specify non-default red-knot configurations to use in tests, by including
+a TOML code block:
+
+````markdown
+```toml
+[tool.knot]
+warn-on-any = true
+```
+
+```py
+from typing import Any
+
+def f(x: Any):  # error: [use-of-any]
+    pass
+```
+````
+
+It should be possible to include a TOML code block in a single test (as shown), or in a grouping
+section, in which case it applies to all nested tests within that grouping section. Configurations
+at multiple level are allowed and merged, with the most-nested (closest to the test) taking
+precedence.
+
+### Running just a single test from a suite
+
+Having each test in a suite always run as a distinct Rust test would require writing our own test
+runner or code-generating tests in a build script; neither of these is planned.
+
+We could still allow running just a single test from a suite, for debugging purposes, either via
+some "focus" syntax that could be easily temporarily added to a test, or via an environment
+variable.
+
+### Configuring search paths and kinds
+
+The red-knot TOML configuration format hasn't been designed yet, and we may want to implement
+support in the test framework for configuring search paths before it is designed. If so, we can
+define some configuration options for now under the `[tool.knot.tests]` namespace. In the future,
+perhaps some of these can be replaced by real red-knot configuration options; some or all may also
+be kept long-term as test-specific options.
+
+Some configuration options we will want to provide:
+
+- We should be able to configure the default workspace root to something other than `/src/` using a
+    `workspace-root` configuration option.
+
+- We should be able to add a third-party root using the `third-party-root` configuration option.
+
+- We may want to add additional configuration options for setting additional search path kinds.
+
+Paths for `workspace-root` and `third-party-root` must be absolute.
+
+Relative embedded-file paths are relative to the workspace root, even if it is explicitly set to a
+non-default value using the `workspace-root` config.
+
+### Specifying a custom typeshed
+
+Some tests will need to override the default typeshed with custom files. The `[tool.knot.tests]`
+configuration option `typeshed-root` should be usable for this:
+
+````markdown
+```toml
+[tool.knot.tests]
+typeshed-root = "/typeshed"
+```
+
+This file is importable as part of our custom typeshed, because it is within `/typeshed`, which we
+configured above as our custom typeshed root:
+
+```py path=/typeshed/stdlib/builtins.pyi
+I_AM_THE_ONLY_BUILTIN = 1
+```
+
+This file is written to `/src/test.py`, because the default workspace root is `/src/ and the default
+file path is `test.py`:
+
+```py
+reveal_type(I_AM_THE_ONLY_BUILTIN)  # revealed: Literal[1]
+```
+
+````
+
+A fenced code block with language `text` can be used to provide a `stdlib/VERSIONS` file in the
+custom typeshed root. If no such file is created explicitly, one should be created implicitly
+including entries enabling all specified `<typeshed-root>/stdlib` files for all supported Python
+versions.
+
+### I/O errors
+
+We could use an `error=` configuration option in the tag string to make an embedded file cause an
+I/O error on read.
+
+### Asserting on full diagnostic output
+
+The inline comment diagnostic assertions are useful for making quick, readable assertions about
+diagnostics in a particular location. But sometimes we will want to assert on the full diagnostic
+output of checking an embedded Python file. Or sometimes (see “incremental tests” below) we will
+want to assert on diagnostics in a file, without impacting the contents of that file by changing a
+comment in it. In these cases, a Python code block in a test could be followed by a fenced code
+block with language `output`; this would contain the full diagnostic output for the preceding test
+file:
+
+````markdown
+# full output
+
+```py
+x = 1
+reveal_type(x)
+```
+
+This is just an example, not a proposal that red-knot would ever actually output diagnostics in
+precisely this format:
+
+```output
+test.py, line 1, col 1: revealed type is 'Literal[1]'
+```
+````
+
+We will want to build tooling to automatically capture and update these “full diagnostic output”
+blocks, when tests are run in an update-output mode (probably specified by an environment variable.)
+
+By default, an `output` block will specify diagnostic output for the file `<workspace-root>/test.py`.
+An `output` block can have a `path=` option, to explicitly specify the Python file for which it
+asserts diagnostic output, and a `stage=` option, to specify which stage of an incremental test it
+specifies diagnostic output at. (See “incremental tests” below.)
+
+It is an error for an `output` block to exist, if there is no `py` or `python` block in the same
+test for the same file path.
+
+### Incremental tests
+
+Some tests should validate incremental checking, by initially creating some files, checking them,
+and then modifying/adding/deleting files and checking again.
+
+We should add the capability to create an incremental test by using the `stage=` option on some
+fenced code blocks in the test:
+
+````markdown
+# Incremental
+
+## modify a file
+
+Initial version of `test.py` and `b.py`:
+
+```py
+from b import x
+reveal_type(x)
+```
+
+```py path=b.py
+x = 1
+```
+
+Initial expected output for `test.py`:
+
+```output
+/src/test.py, line 1, col 1: revealed type is 'Literal[1]'
+```
+
+Now in our first incremental stage, modify the contents of `b.py`:
+
+```py path=b.py stage=1
+# b.py
+x = 2
+```
+
+And this is our updated expected output for `test.py` at stage 1:
+
+```output stage=1
+/src/test.py, line 1, col 1: revealed type is 'Literal[2]'
+```
+
+(One reason to use full-diagnostic-output blocks in this test is that updating
+inline-comment diagnostic assertions for `test.py` would require specifying new
+contents for `test.py` in stage 1, which we don't want to do in this test.)
+````
+
+It will be possible to provide any number of stages in an incremental test. If a stage re-specifies
+a filename that was specified in a previous stage (or the initial stage), that file is modified. A
+new filename appearing for the first time in a new stage will create a new file. To delete a
+previously created file, specify that file with the tag `delete` in its tag string (in this case, it
+is an error to provide non-empty contents). Any previously-created files that are not re-specified
+in a later stage continue to exist with their previously-specified contents, and are not "touched".
+
+All stages should be run in order, incrementally, and then the final state should also be re-checked
+cold, to validate equivalence of cold and incremental check results.
+
+[^extensions]: `typing-extensions` is a third-party module, but typeshed, and thus type checkers
+    also, treat it as part of the standard library.

crates/red_knot_test/src/assertion.rs

@@ -0,0 +1,621 @@
+//! Parse type and type-error assertions in Python comment form.
+//!
+//! Parses comments of the form `# revealed: SomeType` and `# error: 8 [rule-code] "message text"`.
+//! In the latter case, the `8` is a column number, and `"message text"` asserts that the full
+//! diagnostic message contains the text `"message text"`; all three are optional (`# error:` will
+//! match any error.)
+//!
+//! Assertion comments may be placed at end-of-line:
+//!
+//! ```py
+//! x: int = "foo"  # error: [invalid-assignment]
+//! ```
+//!
+//! Or as a full-line comment on the preceding line:
+//!
+//! ```py
+//! # error: [invalid-assignment]
+//! x: int = "foo"
+//! ```
+//!
+//! Multiple assertion comments may apply to the same line; in this case all (or all but the last)
+//! must be full-line comments:
+//!
+//! ```py
+//! # error: [unbound-name]
+//! reveal_type(x)  # revealed: Unbound
+//! ```
+//!
+//! or
+//!
+//! ```py
+//! # error: [unbound-name]
+//! # revealed: Unbound
+//! reveal_type(x)
+//! ```
+
+use crate::db::Db;
+use once_cell::sync::Lazy;
+use regex::Regex;
+use ruff_db::files::File;
+use ruff_db::parsed::parsed_module;
+use ruff_db::source::{line_index, source_text, SourceText};
+use ruff_python_trivia::CommentRanges;
+use ruff_source_file::{LineIndex, Locator, OneIndexed};
+use ruff_text_size::{Ranged, TextRange};
+use smallvec::SmallVec;
+use std::ops::Deref;
+
+/// Diagnostic assertion comments in a single embedded file.
+#[derive(Debug)]
+pub(crate) struct InlineFileAssertions {
+    comment_ranges: CommentRanges,
+    source: SourceText,
+    lines: LineIndex,
+}
+
+impl InlineFileAssertions {
+    pub(crate) fn from_file(db: &Db, file: File) -> Self {
+        let source = source_text(db, file);
+        let lines = line_index(db, file);
+        let parsed = parsed_module(db, file);
+        let comment_ranges = CommentRanges::from(parsed.tokens());
+        Self {
+            comment_ranges,
+            source,
+            lines,
+        }
+    }
+
+    fn locator(&self) -> Locator {
+        Locator::with_index(&self.source, self.lines.clone())
+    }
+
+    fn line_number(&self, range: &impl Ranged) -> OneIndexed {
+        self.lines.line_index(range.start())
+    }
+
+    fn is_own_line_comment(&self, ranged_assertion: &AssertionWithRange) -> bool {
+        CommentRanges::is_own_line(ranged_assertion.start(), &self.locator())
+    }
+}
+
+impl<'a> IntoIterator for &'a InlineFileAssertions {
+    type Item = LineAssertions<'a>;
+    type IntoIter = LineAssertionsIterator<'a>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        Self::IntoIter {
+            file_assertions: self,
+            inner: AssertionWithRangeIterator {
+                file_assertions: self,
+                inner: self.comment_ranges.into_iter(),
+            }
+            .peekable(),
+        }
+    }
+}
+
+/// An [`Assertion`] with the [`TextRange`] of its original inline comment.
+#[derive(Debug)]
+struct AssertionWithRange<'a>(Assertion<'a>, TextRange);
+
+impl<'a> Deref for AssertionWithRange<'a> {
+    type Target = Assertion<'a>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl Ranged for AssertionWithRange<'_> {
+    fn range(&self) -> TextRange {
+        self.1
+    }
+}
+
+impl<'a> From<AssertionWithRange<'a>> for Assertion<'a> {
+    fn from(value: AssertionWithRange<'a>) -> Self {
+        value.0
+    }
+}
+
+/// Iterator that yields all assertions within a single embedded Python file.
+#[derive(Debug)]
+struct AssertionWithRangeIterator<'a> {
+    file_assertions: &'a InlineFileAssertions,
+    inner: std::iter::Copied<std::slice::Iter<'a, TextRange>>,
+}
+
+impl<'a> Iterator for AssertionWithRangeIterator<'a> {
+    type Item = AssertionWithRange<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let locator = self.file_assertions.locator();
+        loop {
+            let inner_next = self.inner.next()?;
+            let comment = locator.slice(inner_next);
+            if let Some(assertion) = Assertion::from_comment(comment) {
+                return Some(AssertionWithRange(assertion, inner_next));
+            };
+        }
+    }
+}
+
+impl std::iter::FusedIterator for AssertionWithRangeIterator<'_> {}
+
+/// A vector of [`Assertion`]s belonging to a single line.
+///
+/// Most lines will have zero or one assertion, so we use a [`SmallVec`] optimized for a single
+/// element to avoid most heap vector allocations.
+type AssertionVec<'a> = SmallVec<[Assertion<'a>; 1]>;
+
+#[derive(Debug)]
+pub(crate) struct LineAssertionsIterator<'a> {
+    file_assertions: &'a InlineFileAssertions,
+    inner: std::iter::Peekable<AssertionWithRangeIterator<'a>>,
+}
+
+impl<'a> Iterator for LineAssertionsIterator<'a> {
+    type Item = LineAssertions<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let file = self.file_assertions;
+        let ranged_assertion = self.inner.next()?;
+        let mut collector = AssertionVec::new();
+        let mut line_number = file.line_number(&ranged_assertion);
+        // Collect all own-line comments on consecutive lines; these all apply to the same line of
+        // code. For example:
+        //
+        // ```py
+        // # error: [unbound-name]
+        // # revealed: Unbound
+        // reveal_type(x)
+        // ```
+        //
+        if file.is_own_line_comment(&ranged_assertion) {
+            collector.push(ranged_assertion.into());
+            let mut only_own_line = true;
+            while let Some(ranged_assertion) = self.inner.peek() {
+                let next_line_number = line_number.saturating_add(1);
+                if file.line_number(ranged_assertion) == next_line_number {
+                    if !file.is_own_line_comment(ranged_assertion) {
+                        only_own_line = false;
+                    }
+                    line_number = next_line_number;
+                    collector.push(self.inner.next().unwrap().into());
+                    // If we see an end-of-line comment, it has to be the end of the stack,
+                    // otherwise we'd botch this case, attributing all three errors to the `bar`
+                    // line:
+                    //
+                    // ```py
+                    // # error:
+                    // foo  # error:
+                    // bar  # error:
+                    // ```
+                    //
+                    if !only_own_line {
+                        break;
+                    }
+                } else {
+                    break;
+                }
+            }
+            if only_own_line {
+                // The collected comments apply to the _next_ line in the code.
+                line_number = line_number.saturating_add(1);
+            }
+        } else {
+            // We have a line-trailing comment; it applies to its own line, and is not grouped.
+            collector.push(ranged_assertion.into());
+        }
+        Some(LineAssertions {
+            line_number,
+            assertions: collector,
+        })
+    }
+}
+
+impl std::iter::FusedIterator for LineAssertionsIterator<'_> {}
+
+/// One or more assertions referring to the same line of code.
+#[derive(Debug)]
+pub(crate) struct LineAssertions<'a> {
+    /// The line these assertions refer to.
+    ///
+    /// Not necessarily the same line the assertion comment is located on; for an own-line comment,
+    /// it's the next non-assertion line.
+    pub(crate) line_number: OneIndexed,
+
+    /// The assertions referring to this line.
+    pub(crate) assertions: AssertionVec<'a>,
+}
+
+impl<'a> Deref for LineAssertions<'a> {
+    type Target = [Assertion<'a>];
+
+    fn deref(&self) -> &Self::Target {
+        &self.assertions
+    }
+}
+
+static TYPE_RE: Lazy<Regex> =
+    Lazy::new(|| Regex::new(r"^#\s*revealed:\s*(?<ty_display>.+?)\s*$").unwrap());
+
+static ERROR_RE: Lazy<Regex> = Lazy::new(|| {
+    Regex::new(
+        r#"^#\s*error:(\s*(?<column>\d+))?(\s*\[(?<rule>.+?)\])?(\s*"(?<message>.+?)")?\s*$"#,
+    )
+    .unwrap()
+});
+
+/// A single diagnostic assertion comment.
+#[derive(Debug)]
+pub(crate) enum Assertion<'a> {
+    /// A `revealed: ` assertion.
+    Revealed(&'a str),
+
+    /// An `error: ` assertion.
+    Error(ErrorAssertion<'a>),
+}
+
+impl<'a> Assertion<'a> {
+    fn from_comment(comment: &'a str) -> Option<Self> {
+        if let Some(caps) = TYPE_RE.captures(comment) {
+            Some(Self::Revealed(caps.name("ty_display").unwrap().as_str()))
+        } else {
+            ERROR_RE.captures(comment).map(|caps| {
+                Self::Error(ErrorAssertion {
+                    rule: caps.name("rule").map(|m| m.as_str()),
+                    column: caps.name("column").and_then(|m| m.as_str().parse().ok()),
+                    message_contains: caps.name("message").map(|m| m.as_str()),
+                })
+            })
+        }
+    }
+}
+
+impl std::fmt::Display for Assertion<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Revealed(expected_type) => write!(f, "revealed: {expected_type}"),
+            Self::Error(assertion) => assertion.fmt(f),
+        }
+    }
+}
+
+/// An `error: ` assertion comment.
+#[derive(Debug)]
+pub(crate) struct ErrorAssertion<'a> {
+    /// The diagnostic rule code we expect.
+    pub(crate) rule: Option<&'a str>,
+
+    /// The column we expect the diagnostic range to start at.
+    pub(crate) column: Option<OneIndexed>,
+
+    /// A string we expect to be contained in the diagnostic message.
+    pub(crate) message_contains: Option<&'a str>,
+}
+
+impl std::fmt::Display for ErrorAssertion<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("error:")?;
+        if let Some(column) = self.column {
+            write!(f, " {column}")?;
+        }
+        if let Some(rule) = self.rule {
+            write!(f, " [{rule}]")?;
+        }
+        if let Some(message) = self.message_contains {
+            write!(f, r#" "{message}""#)?;
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{Assertion, InlineFileAssertions, LineAssertions};
+    use ruff_db::files::system_path_to_file;
+    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+    use ruff_python_trivia::textwrap::dedent;
+    use ruff_source_file::OneIndexed;
+
+    fn get_assertions(source: &str) -> InlineFileAssertions {
+        let mut db = crate::db::Db::setup(SystemPathBuf::from("/src"));
+        db.write_file("/src/test.py", source).unwrap();
+        let file = system_path_to_file(&db, "/src/test.py").unwrap();
+        InlineFileAssertions::from_file(&db, file)
+    }
+
+    fn as_vec(assertions: &InlineFileAssertions) -> Vec<LineAssertions> {
+        assertions.into_iter().collect()
+    }
+
+    #[test]
+    fn ty_display() {
+        let assertions = get_assertions(&dedent(
+            "
+            reveal_type(1)  # revealed: Literal[1]
+            ",
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(1));
+
+        let [assert] = &line.assertions[..] else {
+            panic!("expected one assertion");
+        };
+
+        assert_eq!(format!("{assert}"), "revealed: Literal[1]");
+    }
+
+    #[test]
+    fn error() {
+        let assertions = get_assertions(&dedent(
+            "
+            x  # error:
+            ",
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(1));
+
+        let [assert] = &line.assertions[..] else {
+            panic!("expected one assertion");
+        };
+
+        assert_eq!(format!("{assert}"), "error:");
+    }
+
+    #[test]
+    fn prior_line() {
+        let assertions = get_assertions(&dedent(
+            "
+            # revealed: Literal[1]
+            reveal_type(1)
+            ",
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(2));
+
+        let [assert] = &line.assertions[..] else {
+            panic!("expected one assertion");
+        };
+
+        assert_eq!(format!("{assert}"), "revealed: Literal[1]");
+    }
+
+    #[test]
+    fn stacked_prior_line() {
+        let assertions = get_assertions(&dedent(
+            "
+            # revealed: Unbound
+            # error: [unbound-name]
+            reveal_type(x)
+            ",
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(3));
+
+        let [assert1, assert2] = &line.assertions[..] else {
+            panic!("expected two assertions");
+        };
+
+        assert_eq!(format!("{assert1}"), "revealed: Unbound");
+        assert_eq!(format!("{assert2}"), "error: [unbound-name]");
+    }
+
+    #[test]
+    fn stacked_mixed() {
+        let assertions = get_assertions(&dedent(
+            "
+            # revealed: Unbound
+            reveal_type(x) # error: [unbound-name]
+            ",
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(2));
+
+        let [assert1, assert2] = &line.assertions[..] else {
+            panic!("expected two assertions");
+        };
+
+        assert_eq!(format!("{assert1}"), "revealed: Unbound");
+        assert_eq!(format!("{assert2}"), "error: [unbound-name]");
+    }
+
+    #[test]
+    fn multiple_lines() {
+        let assertions = get_assertions(&dedent(
+            r#"
+            # error: [invalid-assignment]
+            x: int = "foo"
+            y  # error: [unbound-name]
+            "#,
+        ));
+
+        let [line1, line2] = &as_vec(&assertions)[..] else {
+            panic!("expected two lines");
+        };
+
+        assert_eq!(line1.line_number, OneIndexed::from_zero_indexed(2));
+        assert_eq!(line2.line_number, OneIndexed::from_zero_indexed(3));
+
+        let [Assertion::Error(error1)] = &line1.assertions[..] else {
+            panic!("expected one error assertion");
+        };
+
+        assert_eq!(error1.rule, Some("invalid-assignment"));
+
+        let [Assertion::Error(error2)] = &line2.assertions[..] else {
+            panic!("expected one error assertion");
+        };
+
+        assert_eq!(error2.rule, Some("unbound-name"));
+    }
+
+    #[test]
+    fn multiple_lines_mixed_stack() {
+        let assertions = get_assertions(&dedent(
+            r#"
+            # error: [invalid-assignment]
+            x: int = reveal_type("foo")  # revealed: str
+            y  # error: [unbound-name]
+            "#,
+        ));
+
+        let [line1, line2] = &as_vec(&assertions)[..] else {
+            panic!("expected two lines");
+        };
+
+        assert_eq!(line1.line_number, OneIndexed::from_zero_indexed(2));
+        assert_eq!(line2.line_number, OneIndexed::from_zero_indexed(3));
+
+        let [Assertion::Error(error1), Assertion::Revealed(expected_ty)] = &line1.assertions[..]
+        else {
+            panic!("expected one error assertion and one Revealed assertion");
+        };
+
+        assert_eq!(error1.rule, Some("invalid-assignment"));
+        assert_eq!(*expected_ty, "str");
+
+        let [Assertion::Error(error2)] = &line2.assertions[..] else {
+            panic!("expected one error assertion");
+        };
+
+        assert_eq!(error2.rule, Some("unbound-name"));
+    }
+
+    #[test]
+    fn error_with_rule() {
+        let assertions = get_assertions(&dedent(
+            "
+            x  # error: [unbound-name]
+            ",
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(1));
+
+        let [assert] = &line.assertions[..] else {
+            panic!("expected one assertion");
+        };
+
+        assert_eq!(format!("{assert}"), "error: [unbound-name]");
+    }
+
+    #[test]
+    fn error_with_rule_and_column() {
+        let assertions = get_assertions(&dedent(
+            "
+            x  # error: 1 [unbound-name]
+            ",
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(1));
+
+        let [assert] = &line.assertions[..] else {
+            panic!("expected one assertion");
+        };
+
+        assert_eq!(format!("{assert}"), "error: 1 [unbound-name]");
+    }
+
+    #[test]
+    fn error_with_rule_and_message() {
+        let assertions = get_assertions(&dedent(
+            r#"
+            # error: [unbound-name] "`x` is unbound"
+            x
+            "#,
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(2));
+
+        let [assert] = &line.assertions[..] else {
+            panic!("expected one assertion");
+        };
+
+        assert_eq!(
+            format!("{assert}"),
+            r#"error: [unbound-name] "`x` is unbound""#
+        );
+    }
+
+    #[test]
+    fn error_with_message_and_column() {
+        let assertions = get_assertions(&dedent(
+            r#"
+            # error: 1 "`x` is unbound"
+            x
+            "#,
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(2));
+
+        let [assert] = &line.assertions[..] else {
+            panic!("expected one assertion");
+        };
+
+        assert_eq!(format!("{assert}"), r#"error: 1 "`x` is unbound""#);
+    }
+
+    #[test]
+    fn error_with_rule_and_message_and_column() {
+        let assertions = get_assertions(&dedent(
+            r#"
+            # error: 1 [unbound-name] "`x` is unbound"
+            x
+            "#,
+        ));
+
+        let [line] = &as_vec(&assertions)[..] else {
+            panic!("expected one line");
+        };
+
+        assert_eq!(line.line_number, OneIndexed::from_zero_indexed(2));
+
+        let [assert] = &line.assertions[..] else {
+            panic!("expected one assertion");
+        };
+
+        assert_eq!(
+            format!("{assert}"),
+            r#"error: 1 [unbound-name] "`x` is unbound""#
+        );
+    }
+}

crates/red_knot_test/src/db.rs

@@ -0,0 +1,88 @@
+use red_knot_python_semantic::{
+    Db as SemanticDb, Program, ProgramSettings, PythonVersion, SearchPathSettings,
+};
+use ruff_db::files::{File, Files};
+use ruff_db::system::SystemPathBuf;
+use ruff_db::system::{DbWithTestSystem, System, TestSystem};
+use ruff_db::vendored::VendoredFileSystem;
+use ruff_db::{Db as SourceDb, Upcast};
+
+#[salsa::db]
+pub(crate) struct Db {
+    storage: salsa::Storage<Self>,
+    files: Files,
+    system: TestSystem,
+    vendored: VendoredFileSystem,
+}
+
+impl Db {
+    pub(crate) fn setup(workspace_root: SystemPathBuf) -> Self {
+        let db = Self {
+            storage: salsa::Storage::default(),
+            system: TestSystem::default(),
+            vendored: red_knot_vendored::file_system().clone(),
+            files: Files::default(),
+        };
+
+        db.memory_file_system()
+            .create_directory_all(&workspace_root)
+            .unwrap();
+
+        Program::from_settings(
+            &db,
+            &ProgramSettings {
+                target_version: PythonVersion::default(),
+                search_paths: SearchPathSettings::new(workspace_root),
+            },
+        )
+        .expect("Invalid search path settings");
+
+        db
+    }
+}
+
+impl DbWithTestSystem for Db {
+    fn test_system(&self) -> &TestSystem {
+        &self.system
+    }
+
+    fn test_system_mut(&mut self) -> &mut TestSystem {
+        &mut self.system
+    }
+}
+
+#[salsa::db]
+impl SourceDb for Db {
+    fn vendored(&self) -> &VendoredFileSystem {
+        &self.vendored
+    }
+
+    fn system(&self) -> &dyn System {
+        &self.system
+    }
+
+    fn files(&self) -> &Files {
+        &self.files
+    }
+}
+
+impl Upcast<dyn SourceDb> for Db {
+    fn upcast(&self) -> &(dyn SourceDb + 'static) {
+        self
+    }
+    fn upcast_mut(&mut self) -> &mut (dyn SourceDb + 'static) {
+        self
+    }
+}
+
+#[salsa::db]
+impl SemanticDb for Db {
+    fn is_file_open(&self, file: File) -> bool {
+        !file.path(self).is_vendored_path()
+    }
+}
+
+#[salsa::db]
+impl salsa::Database for Db {
+    fn salsa_event(&self, _event: &dyn Fn() -> salsa::Event) {}
+}

crates/red_knot_test/src/diagnostic.rs

@@ -0,0 +1,173 @@
+//! Sort and group diagnostics by line number, so they can be correlated with assertions.
+//!
+//! We don't assume that we will get the diagnostics in source order.
+
+use ruff_source_file::{LineIndex, OneIndexed};
+use ruff_text_size::Ranged;
+use std::ops::{Deref, Range};
+
+/// All diagnostics for one embedded Python file, sorted and grouped by start line number.
+///
+/// The diagnostics are kept in a flat vector, sorted by line number. A separate vector of
+/// [`LineDiagnosticRange`] has one entry for each contiguous slice of the diagnostics vector
+/// containing diagnostics which all start on the same line.
+#[derive(Debug)]
+pub(crate) struct SortedDiagnostics<T> {
+    diagnostics: Vec<T>,
+    line_ranges: Vec<LineDiagnosticRange>,
+}
+
+impl<T> SortedDiagnostics<T>
+where
+    T: Ranged + Clone,
+{
+    pub(crate) fn new(diagnostics: impl IntoIterator<Item = T>, line_index: &LineIndex) -> Self {
+        let mut diagnostics: Vec<_> = diagnostics
+            .into_iter()
+            .map(|diagnostic| DiagnosticWithLine {
+                line_number: line_index.line_index(diagnostic.start()),
+                diagnostic,
+            })
+            .collect();
+        diagnostics.sort_unstable_by_key(|diagnostic_with_line| diagnostic_with_line.line_number);
+
+        let mut diags = Self {
+            diagnostics: Vec::with_capacity(diagnostics.len()),
+            line_ranges: vec![],
+        };
+
+        let mut current_line_number = None;
+        let mut start = 0;
+        for DiagnosticWithLine {
+            line_number,
+            diagnostic,
+        } in diagnostics
+        {
+            match current_line_number {
+                None => {
+                    current_line_number = Some(line_number);
+                }
+                Some(current) => {
+                    if line_number != current {
+                        let end = diags.diagnostics.len();
+                        diags.line_ranges.push(LineDiagnosticRange {
+                            line_number: current,
+                            diagnostic_index_range: start..end,
+                        });
+                        start = end;
+                        current_line_number = Some(line_number);
+                    }
+                }
+            }
+            diags.diagnostics.push(diagnostic);
+        }
+        if let Some(line_number) = current_line_number {
+            diags.line_ranges.push(LineDiagnosticRange {
+                line_number,
+                diagnostic_index_range: start..diags.diagnostics.len(),
+            });
+        }
+
+        diags
+    }
+
+    pub(crate) fn iter_lines(&self) -> LineDiagnosticsIterator<T> {
+        LineDiagnosticsIterator {
+            diagnostics: self.diagnostics.as_slice(),
+            inner: self.line_ranges.iter(),
+        }
+    }
+}
+
+/// Range delineating diagnostics in [`SortedDiagnostics`] that begin on a single line.
+#[derive(Debug)]
+struct LineDiagnosticRange {
+    line_number: OneIndexed,
+    diagnostic_index_range: Range<usize>,
+}
+
+/// Iterator to group sorted diagnostics by line.
+pub(crate) struct LineDiagnosticsIterator<'a, T> {
+    diagnostics: &'a [T],
+    inner: std::slice::Iter<'a, LineDiagnosticRange>,
+}
+
+impl<'a, T> Iterator for LineDiagnosticsIterator<'a, T>
+where
+    T: Ranged + Clone,
+{
+    type Item = LineDiagnostics<'a, T>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let LineDiagnosticRange {
+            line_number,
+            diagnostic_index_range,
+        } = self.inner.next()?;
+        Some(LineDiagnostics {
+            line_number: *line_number,
+            diagnostics: &self.diagnostics[diagnostic_index_range.clone()],
+        })
+    }
+}
+
+impl<T> std::iter::FusedIterator for LineDiagnosticsIterator<'_, T> where T: Clone + Ranged {}
+
+/// All diagnostics that start on a single line of source code in one embedded Python file.
+#[derive(Debug)]
+pub(crate) struct LineDiagnostics<'a, T> {
+    /// Line number on which these diagnostics start.
+    pub(crate) line_number: OneIndexed,
+
+    /// Diagnostics starting on this line.
+    pub(crate) diagnostics: &'a [T],
+}
+
+impl<T> Deref for LineDiagnostics<'_, T> {
+    type Target = [T];
+
+    fn deref(&self) -> &Self::Target {
+        self.diagnostics
+    }
+}
+
+#[derive(Debug)]
+struct DiagnosticWithLine<T> {
+    line_number: OneIndexed,
+    diagnostic: T,
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::db::Db;
+    use ruff_db::files::system_path_to_file;
+    use ruff_db::source::line_index;
+    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+    use ruff_source_file::OneIndexed;
+    use ruff_text_size::{TextRange, TextSize};
+
+    #[test]
+    fn sort_and_group() {
+        let mut db = Db::setup(SystemPathBuf::from("/src"));
+        db.write_file("/src/test.py", "one\ntwo\n").unwrap();
+        let file = system_path_to_file(&db, "/src/test.py").unwrap();
+        let lines = line_index(&db, file);
+
+        let ranges = vec![
+            TextRange::new(TextSize::new(0), TextSize::new(1)),
+            TextRange::new(TextSize::new(5), TextSize::new(10)),
+            TextRange::new(TextSize::new(1), TextSize::new(7)),
+        ];
+
+        let sorted = super::SortedDiagnostics::new(&ranges, &lines);
+        let grouped = sorted.iter_lines().collect::<Vec<_>>();
+
+        let [line1, line2] = &grouped[..] else {
+            panic!("expected two lines");
+        };
+
+        assert_eq!(line1.line_number, OneIndexed::from_zero_indexed(0));
+        assert_eq!(line1.diagnostics.len(), 2);
+        assert_eq!(line2.line_number, OneIndexed::from_zero_indexed(1));
+        assert_eq!(line2.diagnostics.len(), 1);
+    }
+}

crates/red_knot_test/src/lib.rs

@@ -0,0 +1,95 @@
+use colored::Colorize;
+use parser as test_parser;
+use red_knot_python_semantic::types::check_types;
+use ruff_db::files::system_path_to_file;
+use ruff_db::parsed::parsed_module;
+use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+use std::collections::BTreeMap;
+use std::path::PathBuf;
+
+type Failures = BTreeMap<SystemPathBuf, matcher::FailuresByLine>;
+
+mod assertion;
+mod db;
+mod diagnostic;
+mod matcher;
+mod parser;
+
+/// Run `path` as a markdown test suite with given `title`.
+///
+/// Panic on test failure, and print failure details.
+#[allow(clippy::print_stdout)]
+pub fn run(path: &PathBuf, title: &str) {
+    let source = std::fs::read_to_string(path).unwrap();
+    let suite = match test_parser::parse(title, &source) {
+        Ok(suite) => suite,
+        Err(err) => {
+            panic!("Error parsing `{}`: {err}", path.to_str().unwrap())
+        }
+    };
+
+    let mut any_failures = false;
+    for test in suite.tests() {
+        if let Err(failures) = run_test(&test) {
+            any_failures = true;
+            println!("\n{}\n", test.name().bold().underline());
+
+            for (path, by_line) in failures {
+                println!("{}", path.as_str().bold());
+                for (line_number, failures) in by_line.iter() {
+                    for failure in failures {
+                        let line_info = format!("line {line_number}:").cyan();
+                        println!("    {line_info} {failure}");
+                    }
+                }
+                println!();
+            }
+        }
+    }
+
+    println!("{}\n", "-".repeat(50));
+
+    assert!(!any_failures, "Some tests failed.");
+}
+
+fn run_test(test: &parser::MarkdownTest) -> Result<(), Failures> {
+    let workspace_root = SystemPathBuf::from("/src");
+    let mut db = db::Db::setup(workspace_root.clone());
+
+    let mut system_paths = vec![];
+
+    for file in test.files() {
+        assert!(
+            matches!(file.lang, "py" | "pyi"),
+            "Non-Python files not supported yet."
+        );
+        let full_path = workspace_root.join(file.path);
+        db.write_file(&full_path, file.code).unwrap();
+        system_paths.push(full_path);
+    }
+
+    let mut failures = BTreeMap::default();
+
+    for path in system_paths {
+        let file = system_path_to_file(&db, path.clone()).unwrap();
+        let parsed = parsed_module(&db, file);
+
+        // TODO allow testing against code with syntax errors
+        assert!(
+            parsed.errors().is_empty(),
+            "Python syntax errors in {}, {:?}: {:?}",
+            test.name(),
+            path,
+            parsed.errors()
+        );
+
+        matcher::match_file(&db, file, check_types(&db, file)).unwrap_or_else(|line_failures| {
+            failures.insert(path, line_failures);
+        });
+    }
+    if failures.is_empty() {
+        Ok(())
+    } else {
+        Err(failures)
+    }
+}