Avoid monomorphization of a large function

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

.github/workflows/ci.yaml

@@ -349,7 +349,7 @@ jobs:
       - uses: actions/checkout@v4
         with:
           persist-credentials: false
-      - uses: astral-sh/setup-uv@v4
+      - uses: astral-sh/setup-uv@v5
       - uses: actions/download-artifact@v4
         name: Download Ruff binary to test
         id: download-cached-binary
@@ -613,7 +613,7 @@ jobs:
       - name: "Install Rust toolchain"
         run: rustup show
       - name: Install uv
-        uses: astral-sh/setup-uv@v4
+        uses: astral-sh/setup-uv@v5
       - uses: Swatinem/rust-cache@v2
       - name: "Install Insiders dependencies"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}

.github/workflows/daily_fuzz.yaml

@@ -34,7 +34,7 @@ jobs:
       - uses: actions/checkout@v4
         with:
           persist-credentials: false
-      - uses: astral-sh/setup-uv@v4
+      - uses: astral-sh/setup-uv@v5
       - name: "Install Rust toolchain"
         run: rustup show
       - name: "Install mold"

.github/workflows/publish-pypi.yml

@@ -22,7 +22,7 @@ jobs:
       id-token: write
     steps:
       - name: "Install uv"
-        uses: astral-sh/setup-uv@v4
+        uses: astral-sh/setup-uv@v5
       - uses: actions/download-artifact@v4
         with:
           pattern: wheels-*

.pre-commit-config.yaml

@@ -23,7 +23,7 @@ repos:
       - id: validate-pyproject
 
   - repo: https://github.com/executablebooks/mdformat
-    rev: 0.7.19
+    rev: 0.7.21
     hooks:
       - id: mdformat
         additional_dependencies:
@@ -59,7 +59,7 @@ repos:
           - black==24.10.0
 
   - repo: https://github.com/crate-ci/typos
-    rev: v1.28.3
+    rev: v1.28.4
     hooks:
       - id: typos
 
@@ -73,7 +73,7 @@ repos:
         pass_filenames: false # This makes it a lot faster
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.8.3
+    rev: v0.8.4
     hooks:
       - id: ruff-format
       - id: ruff
@@ -91,7 +91,7 @@ repos:
   # zizmor detects security vulnerabilities in GitHub Actions workflows.
   # Additional configuration for the tool is found in `.github/zizmor.yml`
   - repo: https://github.com/woodruffw/zizmor-pre-commit
-    rev: v0.9.2
+    rev: v0.10.0
     hooks:
       - id: zizmor
 
@@ -103,7 +103,7 @@ repos:
   # `actionlint` hook, for verifying correct syntax in GitHub Actions workflows.
   # Some additional configuration for `actionlint` can be found in `.github/actionlint.yaml`.
   - repo: https://github.com/rhysd/actionlint
-    rev: v1.7.4
+    rev: v1.7.5
     hooks:
       - id: actionlint
         stages:

CHANGELOG.md

@@ -1,5 +1,46 @@
 # Changelog
 
+## 0.8.5
+
+### Preview features
+
+- \[`airflow`\] Extend names moved from core to provider (`AIR303`) ([#15145](https://github.com/astral-sh/ruff/pull/15145), [#15159](https://github.com/astral-sh/ruff/pull/15159), [#15196](https://github.com/astral-sh/ruff/pull/15196), [#15216](https://github.com/astral-sh/ruff/pull/15216))
+- \[`airflow`\] Extend rule to check class attributes, methods, arguments (`AIR302`) ([#15054](https://github.com/astral-sh/ruff/pull/15054), [#15083](https://github.com/astral-sh/ruff/pull/15083))
+- \[`fastapi`\] Update `FAST002` to check keyword-only arguments ([#15119](https://github.com/astral-sh/ruff/pull/15119))
+- \[`flake8-type-checking`\] Disable `TC006` and `TC007` in stub files ([#15179](https://github.com/astral-sh/ruff/pull/15179))
+- \[`pylint`\] Detect nested methods correctly (`PLW1641`) ([#15032](https://github.com/astral-sh/ruff/pull/15032))
+- \[`ruff`\] Detect more strict-integer expressions (`RUF046`) ([#14833](https://github.com/astral-sh/ruff/pull/14833))
+- \[`ruff`\] Implement `falsy-dict-get-fallback` (`RUF056`) ([#15160](https://github.com/astral-sh/ruff/pull/15160))
+- \[`ruff`\] Implement `unnecessary-round` (`RUF057`) ([#14828](https://github.com/astral-sh/ruff/pull/14828))
+
+### Rule changes
+
+- Visit PEP 764 inline `TypedDict` keys as non-type-expressions ([#15073](https://github.com/astral-sh/ruff/pull/15073))
+- \[`flake8-comprehensions`\] Skip `C416` if comprehension contains unpacking ([#14909](https://github.com/astral-sh/ruff/pull/14909))
+- \[`flake8-pie`\] Allow `cast(SomeType, ...)` (`PIE796`) ([#15141](https://github.com/astral-sh/ruff/pull/15141))
+- \[`flake8-simplify`\] More precise inference for dictionaries (`SIM300`) ([#15164](https://github.com/astral-sh/ruff/pull/15164))
+- \[`flake8-use-pathlib`\] Catch redundant joins in `PTH201` and avoid syntax errors ([#15177](https://github.com/astral-sh/ruff/pull/15177))
+- \[`pycodestyle`\] Preserve original value format (`E731`) ([#15097](https://github.com/astral-sh/ruff/pull/15097))
+- \[`pydocstyle`\] Split on first whitespace character (`D403`) ([#15082](https://github.com/astral-sh/ruff/pull/15082))
+- \[`pyupgrade`\] Add all PEP-585 names to `UP006` rule ([#5454](https://github.com/astral-sh/ruff/pull/5454))
+
+### Configuration
+
+- \[`flake8-type-checking`\] Improve flexibility of `runtime-evaluated-decorators` ([#15204](https://github.com/astral-sh/ruff/pull/15204))
+- \[`pydocstyle`\] Add setting to ignore missing documentation for `*args` and `**kwargs` parameters (`D417`) ([#15210](https://github.com/astral-sh/ruff/pull/15210))
+- \[`ruff`\] Add an allowlist for `unsafe-markup-use` (`RUF035`) ([#15076](https://github.com/astral-sh/ruff/pull/15076))
+
+### Bug fixes
+
+- Fix type subscript on older python versions ([#15090](https://github.com/astral-sh/ruff/pull/15090))
+- Use `TypeChecker` for detecting `fastapi` routes ([#15093](https://github.com/astral-sh/ruff/pull/15093))
+- \[`pycodestyle`\] Avoid false positives and negatives related to type parameter default syntax (`E225`, `E251`) ([#15214](https://github.com/astral-sh/ruff/pull/15214))
+
+### Documentation
+
+- Fix incorrect doc in `shebang-not-executable` (`EXE001`) and add git+windows solution to executable bit ([#15208](https://github.com/astral-sh/ruff/pull/15208))
+- Rename rules currently not conforming to naming convention ([#15102](https://github.com/astral-sh/ruff/pull/15102))
+
 ## 0.8.4
 
 ### Preview features

CONTRIBUTING.md

@@ -467,7 +467,7 @@ cargo build --release && hyperfine --warmup 10 \
   "./target/release/ruff check ./crates/ruff_linter/resources/test/cpython/ --no-cache -e --select W505,E501"
 ```
 
-You can run `poetry install` from `./scripts/benchmarks` to create a working environment for the
+You can run `uv venv --project ./scripts/benchmarks`, activate the venv and then run `uv sync --project ./scripts/benchmarks` to create a working environment for the
 above. All reported benchmarks were computed using the versions specified by
 `./scripts/benchmarks/pyproject.toml` on Python 3.11.
 

Cargo.lock

@@ -117,9 +117,9 @@ dependencies = [
 
 [[package]]
 name = "anyhow"
-version = "1.0.94"
+version = "1.0.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c1fd03a028ef38ba2276dce7e33fcd6369c158a1bca17946c4b1b701891c1ff7"
+checksum = "34ac096ce696dc2fcabef30516bb13c0a68a11d30131d3df6f04711467681b04"
 
 [[package]]
 name = "append-only-vec"
@@ -413,7 +413,7 @@ dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -470,14 +470,14 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "117725a109d387c937a1533ce01b450cbde6b88abceea8473c4d7a85853cda3c"
 dependencies = [
  "lazy_static",
- "windows-sys 0.52.0",
+ "windows-sys 0.48.0",
 ]
 
 [[package]]
 name = "compact_str"
-version = "0.8.0"
+version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6050c3a16ddab2e412160b31f2c871015704239bca62f72f6e5f0be631d3f644"
+checksum = "3b79c4069c6cad78e2e0cdfcbd26275770669fb39fd308a752dc110e83b9af32"
 dependencies = [
  "castaway",
  "cfg-if",
@@ -693,7 +693,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "strsim 0.10.0",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -704,7 +704,7 @@ checksum = "a668eda54683121533a393014d8692171709ff57a7d61f187b6e782719f8933f"
 dependencies = [
  "darling_core",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -774,7 +774,7 @@ dependencies = [
  "glob",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -826,7 +826,7 @@ checksum = "97369cbbc041bc366949bc74d34658d6cda5621039731c6310521892a3a20ae0"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -877,9 +877,9 @@ dependencies = [
 
 [[package]]
 name = "env_logger"
-version = "0.11.5"
+version = "0.11.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e13fa619b91fb2381732789fc5de83b45675e882f66623b7d8cb4f643017018d"
+checksum = "dcaee3d8e3cfc3fd92428d477bc97fc29ec8716d180c0d74c643bb26166660e0"
 dependencies = [
  "anstream",
  "anstyle",
@@ -1019,9 +1019,9 @@ dependencies = [
 
 [[package]]
 name = "glob"
-version = "0.3.1"
+version = "0.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d2fabcfbdc87f4758337ca535fb41a6d701b65693ce38287d856d1674551ec9b"
+checksum = "a8d1add55171497b4705a648c6b583acafb01d58050a51727785f0b2c8e0a2b2"
 
 [[package]]
 name = "globset"
@@ -1246,7 +1246,7 @@ checksum = "1ec89e9337638ecdc08744df490b221a7399bf8d164eb52a665454e60e075ad6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -1420,7 +1420,7 @@ dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -1521,9 +1521,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.168"
+version = "0.2.169"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5aaeb2981e0606ca11d79718f8bb01164f1d6ed75080182d3abf017e6d244b6d"
+checksum = "b5aba8db14291edd000dfcc4d620c7ebfb122c613afb886ca8803fa4e128a20a"
 
 [[package]]
 name = "libcst"
@@ -1547,7 +1547,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a2ae40017ac09cd2c6a53504cb3c871c7f2b41466eac5bc66ba63f39073b467b"
 dependencies = [
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -1607,13 +1607,14 @@ checksum = "a7a70ba024b9dc04c27ea2f0c0548feb474ec5c54bba33a7f72f873a39d07b24"
 
 [[package]]
 name = "lsp-server"
-version = "0.7.7"
+version = "0.7.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "550446e84739dcaf6d48a4a093973850669e13e8a34d8f8d64851041be267cd9"
+checksum = "9462c4dc73e17f971ec1f171d44bfffb72e65a130117233388a0ebc7ec5656f9"
 dependencies = [
  "crossbeam-channel",
  "log",
  "serde",
+ "serde_derive",
  "serde_json",
 ]
 
@@ -2014,7 +2015,7 @@ dependencies = [
  "pest_meta",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -2161,7 +2162,7 @@ dependencies = [
  "newtype-uuid",
  "quick-xml",
  "strip-ansi-escapes",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "uuid",
 ]
 
@@ -2196,9 +2197,9 @@ dependencies = [
 
 [[package]]
 name = "quote"
-version = "1.0.37"
+version = "1.0.38"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b5b9d34b8991d19d98081b46eacdd8eb58c6f2b201139f7c5f643cc155a633af"
+checksum = "0e4dccaaaf89514f546c693ddc140f729f958c247918a13380cccc6078391acc"
 dependencies = [
  "proc-macro2",
 ]
@@ -2306,6 +2307,7 @@ dependencies = [
  "ruff_python_literal",
  "ruff_python_parser",
  "ruff_python_stdlib",
+ "ruff_python_trivia",
  "ruff_source_file",
  "ruff_text_size",
  "rustc-hash 2.1.0",
@@ -2315,7 +2317,7 @@ dependencies = [
  "static_assertions",
  "tempfile",
  "test-case",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tracing",
 ]
 
@@ -2412,7 +2414,7 @@ dependencies = [
  "rustc-hash 2.1.0",
  "salsa",
  "serde",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "toml",
  "tracing",
 ]
@@ -2518,7 +2520,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.8.4"
+version = "0.8.5"
 dependencies = [
  "anyhow",
  "argfile",
@@ -2565,7 +2567,7 @@ dependencies = [
  "strum",
  "tempfile",
  "test-case",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tikv-jemallocator",
  "toml",
  "tracing",
@@ -2635,7 +2637,7 @@ dependencies = [
  "salsa",
  "serde",
  "tempfile",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tracing",
  "tracing-subscriber",
  "tracing-tree",
@@ -2737,7 +2739,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_linter"
-version = "0.8.4"
+version = "0.8.5"
 dependencies = [
  "aho-corasick",
  "annotate-snippets 0.9.2",
@@ -2787,7 +2789,7 @@ dependencies = [
  "strum",
  "strum_macros",
  "test-case",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "toml",
  "typed-arena",
  "unicode-normalization",
@@ -2804,7 +2806,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "ruff_python_trivia",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -2821,7 +2823,7 @@ dependencies = [
  "serde_json",
  "serde_with",
  "test-case",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "uuid",
 ]
 
@@ -2893,7 +2895,7 @@ dependencies = [
  "similar",
  "smallvec",
  "static_assertions",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tracing",
 ]
 
@@ -2967,6 +2969,7 @@ dependencies = [
  "rustc-hash 2.1.0",
  "schemars",
  "serde",
+ "smallvec",
 ]
 
 [[package]]
@@ -3026,7 +3029,7 @@ dependencies = [
  "serde",
  "serde_json",
  "shellexpand",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tracing",
  "tracing-subscriber",
 ]
@@ -3052,7 +3055,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_wasm"
-version = "0.8.4"
+version = "0.8.5"
 dependencies = [
  "console_error_panic_hook",
  "console_log",
@@ -3225,7 +3228,7 @@ dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
  "synstructure",
 ]
 
@@ -3259,7 +3262,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "serde_derive_internals",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -3282,9 +3285,9 @@ checksum = "1c107b6f4780854c8b126e228ea8869f4d7b71260f962fefb57b996b8959ba6b"
 
 [[package]]
 name = "serde"
-version = "1.0.216"
+version = "1.0.217"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0b9781016e935a97e8beecf0c933758c97a5520d32930e460142b4cd80c6338e"
+checksum = "02fc4265df13d6fa1d00ecff087228cc0a2b5f3c0e87e258d8b94a156e984c70"
 dependencies = [
  "serde_derive",
 ]
@@ -3302,13 +3305,13 @@ dependencies = [
 
 [[package]]
 name = "serde_derive"
-version = "1.0.216"
+version = "1.0.217"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "46f859dbbf73865c6627ed570e78961cd3ac92407a2d117204c49232485da55e"
+checksum = "5a9bf7cf98d04a2b28aead066b7496853d4779c9cc183c440dbac457641e19a0"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -3319,14 +3322,14 @@ checksum = "330f01ce65a3a5fe59a60c82f3c9a024b573b8a6e875bd233fe5f934e71d54e3"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
 name = "serde_json"
-version = "1.0.133"
+version = "1.0.134"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c7fceb2473b9166b2294ef05efcb65a3db80803f0b03ef86a5fc88a2b85ee377"
+checksum = "d00f4175c42ee48b15416f6193a959ba3a0d67fc699a0db9ad12df9f83991c7d"
 dependencies = [
  "itoa",
  "memchr",
@@ -3342,7 +3345,7 @@ checksum = "6c64451ba24fc7a6a2d60fc75dd9c83c90903b19028d4eff35e88fc1e86564e9"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -3365,9 +3368,9 @@ dependencies = [
 
 [[package]]
 name = "serde_with"
-version = "3.11.0"
+version = "3.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8e28bdad6db2b8340e449f7108f020b3b092e8583a9e3fb82713e1d4e71fe817"
+checksum = "d6b6f7f2fcb69f747921f79f3926bd1e203fce4fef62c268dd3abfb6d86029aa"
 dependencies = [
  "serde",
  "serde_derive",
@@ -3376,14 +3379,14 @@ dependencies = [
 
 [[package]]
 name = "serde_with_macros"
-version = "3.11.0"
+version = "3.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9d846214a9854ef724f3da161b426242d8de7c1fc7de2f89bb1efcb154dca79d"
+checksum = "8d00caa5193a3c8362ac2b73be6b9e768aa5a4b2f721d8f4b339600c3cb51f8e"
 dependencies = [
  "darling",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -3497,7 +3500,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "rustversion",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -3519,9 +3522,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "2.0.90"
+version = "2.0.93"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "919d3b74a5dd0ccd15aeb8f93e7006bd9e14c295087c9896a110f490752bcf31"
+checksum = "9c786062daee0d6db1132800e623df74274a0a87322d8e183338e01b3d98d058"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3536,7 +3539,7 @@ checksum = "c8af7666ab7b6390ab78131fb5b0fce11d6b7a6951602017c35fa82800708971"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -3599,7 +3602,7 @@ dependencies = [
  "cfg-if",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -3610,7 +3613,7 @@ checksum = "5c89e72a01ed4c579669add59014b9a524d609c0c88c6a585ce37485879f6ffb"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
  "test-case-core",
 ]
 
@@ -3625,11 +3628,11 @@ dependencies = [
 
 [[package]]
 name = "thiserror"
-version = "2.0.7"
+version = "2.0.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "93605438cbd668185516ab499d589afb7ee1859ea3d5fc8f6b0755e1c7443767"
+checksum = "f072643fd0190df67a8bab670c20ef5d8737177d6ac6b2e9a236cb096206b2cc"
 dependencies = [
- "thiserror-impl 2.0.7",
+ "thiserror-impl 2.0.9",
 ]
 
 [[package]]
@@ -3640,18 +3643,18 @@ checksum = "b607164372e89797d78b8e23a6d67d5d1038c1c65efd52e1389ef8b77caba2a6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
 name = "thiserror-impl"
-version = "2.0.7"
+version = "2.0.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e1d8749b4531af2117677a5fcd12b1348a3fe2b81e36e61ffeac5c4aa3273e36"
+checksum = "7b50fa271071aae2e6ee85f842e2e28ba8cd2c5fb67f11fcb1fd70b276f9e7d4"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -3773,7 +3776,7 @@ checksum = "395ae124c09f9e6918a2310af6038fba074bcf474ac352496d5910dd59a2226d"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -4043,7 +4046,7 @@ checksum = "6b91f57fe13a38d0ce9e28a03463d8d3c2468ed03d75375110ec71d93b449a08"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -4138,7 +4141,7 @@ dependencies = [
  "once_cell",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
  "wasm-bindgen-shared",
 ]
 
@@ -4173,7 +4176,7 @@ checksum = "98c9ae5a76e46f4deecd0f0255cc223cfa18dc9b261213b8aa0c7b36f61b3f1d"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
  "wasm-bindgen-backend",
  "wasm-bindgen-shared",
 ]
@@ -4207,7 +4210,7 @@ checksum = "222ebde6ea87fbfa6bdd2e9f1fd8a91d60aee5db68792632176c4e16a74fc7d8"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -4510,7 +4513,7 @@ checksum = "28cc31741b18cb6f1d5ff12f5b7523e3d6eb0852bbbad19d73905511d9849b95"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
  "synstructure",
 ]
 
@@ -4531,7 +4534,7 @@ checksum = "9ce1b18ccd8e73a9321186f97e46f9f04b778851177567b1975109d26a08d2a6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]
@@ -4551,7 +4554,7 @@ checksum = "0ea7b4a3637ea8669cedf0f1fd5c286a17f3de97b8dd5a70a6c167a1730e63a5"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
  "synstructure",
 ]
 
@@ -4580,7 +4583,7 @@ checksum = "6eafa6dfb17584ea3e2bd6e76e0cc15ad7af12b09abdd1ca55961bed9b1063c6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.93",
 ]
 
 [[package]]

README.md

@@ -140,8 +140,8 @@ 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/0.8.4/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.8.4/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.8.5/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.8.5/install.ps1 | iex"
 ```
 
 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -174,7 +174,7 @@ 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: v0.8.4
+  rev: v0.8.5
   hooks:
     # Run the linter.
     - id: ruff
@@ -196,7 +196,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: astral-sh/ruff-action@v1
+      - uses: astral-sh/ruff-action@v3
 ```
 
 ### Configuration<a id="configuration"></a>

crates/red_knot_python_semantic/Cargo.toml

@@ -20,6 +20,7 @@ ruff_python_stdlib = { workspace = true }
 ruff_source_file = { workspace = true }
 ruff_text_size = { workspace = true }
 ruff_python_literal = { workspace = true }
+ruff_python_trivia = { workspace = true }
 
 anyhow = { workspace = true }
 bitflags = { workspace = true }

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

@@ -47,7 +47,9 @@ def f():
 
 ## `typing.Never`
 
-`typing.Never` is only available in Python 3.11 and later:
+`typing.Never` is only available in Python 3.11 and later.
+
+### Python 3.11
 
 ```toml
 [environment]
@@ -57,8 +59,17 @@ python-version = "3.11"
 ```py
 from typing import Never
 
-x: Never
-
-def f():
-    reveal_type(x)  # revealed: Never
+reveal_type(Never)  # revealed: typing.Never
+```
+
+### Python 3.10
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+# error: [unresolved-import]
+from typing import Never
 ```

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

@@ -33,8 +33,6 @@ b: tuple[int] = (42,)
 c: tuple[str, int] = ("42", 42)
 d: tuple[tuple[str, str], tuple[int, int]] = (("foo", "foo"), (42, 42))
 e: tuple[str, ...] = ()
-# TODO: we should not emit this error
-# error: [call-possibly-unbound-method] "Method `__class_getitem__` of type `Literal[tuple]` is possibly unbound"
 f: tuple[str, *tuple[int, ...], bytes] = ("42", b"42")
 g: tuple[str, Unpack[tuple[int, ...]], bytes] = ("42", b"42")
 h: tuple[list[int], list[int]] = ([], [])

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

@@ -32,13 +32,10 @@ def _(flag: bool):
 
 ```py
 if True or (x := 1):
-    # TODO: infer that the second arm is never executed, and raise `unresolved-reference`.
-    # error: [possibly-unresolved-reference]
-    reveal_type(x)  # revealed: Literal[1]
+    # error: [unresolved-reference]
+    reveal_type(x)  # revealed: Unknown
 
 if True and (x := 1):
-    # TODO: infer that the second arm is always executed, do not raise a diagnostic
-    # error: [possibly-unresolved-reference]
     reveal_type(x)  # revealed: Literal[1]
 ```
 

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

@@ -67,6 +67,6 @@ def _(flag: bool):
             def __call__(self) -> int: ...
 
     a = NonCallable()
-    # error: "Object of type `Literal[__call__] | Literal[1]` is not callable (due to union element `Literal[1]`)"
-    reveal_type(a())  # revealed: int | Unknown
+    # error: "Object of type `Literal[1] | Literal[__call__]` is not callable (due to union element `Literal[1]`)"
+    reveal_type(a())  # revealed: Unknown | int
 ```

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

@@ -31,10 +31,10 @@ class C:
     def __lt__(self, other) -> C: ...
 
 x = A() < B() < C()
-reveal_type(x)  # revealed: A | B
+reveal_type(x)  # revealed: A & ~AlwaysTruthy | B
 
 y = 0 < 1 < A() < 3
-reveal_type(y)  # revealed: bool | A
+reveal_type(y)  # revealed: Literal[False] | A
 
 z = 10 < 0 < A() < B() < C()
 reveal_type(z)  # revealed: Literal[False]

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

@@ -10,8 +10,8 @@ def _(foo: str):
     reveal_type(False or "z")  # revealed: Literal["z"]
     reveal_type(False or True)  # revealed: Literal[True]
     reveal_type(False or False)  # revealed: Literal[False]
-    reveal_type(foo or False)  # revealed: str | Literal[False]
-    reveal_type(foo or True)  # revealed: str | Literal[True]
+    reveal_type(foo or False)  # revealed: str & ~AlwaysFalsy | Literal[False]
+    reveal_type(foo or True)  # revealed: str & ~AlwaysFalsy | Literal[True]
 ```
 
 ## AND
@@ -20,8 +20,8 @@ def _(foo: str):
 def _(foo: str):
     reveal_type(True and False)  # revealed: Literal[False]
     reveal_type(False and True)  # revealed: Literal[False]
-    reveal_type(foo and False)  # revealed: str | Literal[False]
-    reveal_type(foo and True)  # revealed: str | Literal[True]
+    reveal_type(foo and False)  # revealed: str & ~AlwaysTruthy | Literal[False]
+    reveal_type(foo and True)  # revealed: str & ~AlwaysTruthy | Literal[True]
     reveal_type("x" and "y" and "z")  # revealed: Literal["z"]
     reveal_type("x" and "y" and "")  # revealed: Literal[""]
     reveal_type("" and "y")  # revealed: Literal[""]

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

@@ -7,7 +7,7 @@ def _(flag: bool):
     reveal_type(1 if flag else 2)  # revealed: Literal[1, 2]
 ```
 
-## Statically known branches
+## Statically known conditions in if-expressions
 
 ```py
 reveal_type(1 if True else 2)  # revealed: Literal[1]

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

@@ -1,7 +1,23 @@
 # Ellipsis literals
 
-## Simple
+## Python 3.9
+
+```toml
+[environment]
+python-version = "3.9"
+```
 
 ```py
-reveal_type(...)  # revealed: EllipsisType | ellipsis
+reveal_type(...)  # revealed: ellipsis
+```
+
+## Python 3.10
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+reveal_type(...)  # revealed: EllipsisType
 ```

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

@@ -95,10 +95,14 @@ def _(t: type[object]):
 
 ### Handling of `None`
 
+`types.NoneType` is only available in Python 3.10 and later:
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
 ```py
-# TODO: this error should ideally go away once we (1) understand `sys.version_info` branches,
-# and (2) set the target Python version for this test to 3.10.
-# error: [possibly-unbound-import] "Member `NoneType` of module `types` is possibly unbound"
 from types import NoneType
 
 def _(flag: bool):

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

@@ -219,3 +219,97 @@ else:
 # TODO: It should be A. We should improve UnionBuilder or IntersectionBuilder. (issue #15023)
 reveal_type(y)  # revealed: A & ~AlwaysTruthy | A & ~AlwaysFalsy
 ```
+
+## Truthiness of classes
+
+```py
+class MetaAmbiguous(type):
+    def __bool__(self) -> bool: ...
+
+class MetaFalsy(type):
+    def __bool__(self) -> Literal[False]: ...
+
+class MetaTruthy(type):
+    def __bool__(self) -> Literal[True]: ...
+
+class MetaDeferred(type):
+    def __bool__(self) -> MetaAmbiguous: ...
+
+class AmbiguousClass(metaclass=MetaAmbiguous): ...
+class FalsyClass(metaclass=MetaFalsy): ...
+class TruthyClass(metaclass=MetaTruthy): ...
+class DeferredClass(metaclass=MetaDeferred): ...
+
+def _(
+    a: type[AmbiguousClass],
+    t: type[TruthyClass],
+    f: type[FalsyClass],
+    d: type[DeferredClass],
+    ta: type[TruthyClass | AmbiguousClass],
+    af: type[AmbiguousClass] | type[FalsyClass],
+    flag: bool,
+):
+    reveal_type(ta)  # revealed: type[TruthyClass] | type[AmbiguousClass]
+    if ta:
+        reveal_type(ta)  # revealed: type[TruthyClass] | type[AmbiguousClass] & ~AlwaysFalsy
+
+    reveal_type(af)  # revealed: type[AmbiguousClass] | type[FalsyClass]
+    if af:
+        reveal_type(af)  # revealed: type[AmbiguousClass] & ~AlwaysFalsy
+
+    # TODO: Emit a diagnostic (`d` is not valid in boolean context)
+    if d:
+        # TODO: Should be `Unknown`
+        reveal_type(d)  # revealed: type[DeferredClass] & ~AlwaysFalsy
+
+    tf = TruthyClass if flag else FalsyClass
+    reveal_type(tf)  # revealed: Literal[TruthyClass, FalsyClass]
+
+    if tf:
+        reveal_type(tf)  # revealed: Literal[TruthyClass]
+    else:
+        reveal_type(tf)  # revealed: Literal[FalsyClass]
+```
+
+## Narrowing in chained boolean expressions
+
+```py
+from typing import Literal
+
+class A: ...
+
+def _(x: Literal[0, 1]):
+    reveal_type(x or A())  # revealed: Literal[1] | A
+    reveal_type(x and A())  # revealed: Literal[0] | A
+
+def _(x: str):
+    reveal_type(x or A())  # revealed: str & ~AlwaysFalsy | A
+    reveal_type(x and A())  # revealed: str & ~AlwaysTruthy | A
+
+def _(x: bool | str):
+    reveal_type(x or A())  # revealed: Literal[True] | str & ~AlwaysFalsy | A
+    reveal_type(x and A())  # revealed: Literal[False] | str & ~AlwaysTruthy | A
+
+class Falsy:
+    def __bool__(self) -> Literal[False]: ...
+
+class Truthy:
+    def __bool__(self) -> Literal[True]: ...
+
+def _(x: Falsy | Truthy):
+    reveal_type(x or A())  # revealed: Truthy | A
+    reveal_type(x and A())  # revealed: Falsy | A
+
+class MetaFalsy(type):
+    def __bool__(self) -> Literal[False]: ...
+
+class MetaTruthy(type):
+    def __bool__(self) -> Literal[True]: ...
+
+class FalsyClass(metaclass=MetaFalsy): ...
+class TruthyClass(metaclass=MetaTruthy): ...
+
+def _(x: type[FalsyClass] | type[TruthyClass]):
+    reveal_type(x or A())  # revealed: type[TruthyClass] | A
+    reveal_type(x and A())  # revealed: type[FalsyClass] | A
+```

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

@@ -25,3 +25,29 @@ def f(): ...
 
 f: int = 1
 ```
+
+## Explicit shadowing involving `def` statements
+
+Since a `def` statement is a declaration, one `def` can shadow another `def`, or shadow a previous
+non-`def` declaration, without error.
+
+```py
+f = 1
+reveal_type(f)  # revealed: Literal[1]
+
+def f(): ...
+
+reveal_type(f)  # revealed: Literal[f]
+
+def f(x: int) -> int:
+    raise NotImplementedError
+
+reveal_type(f)  # revealed: Literal[f]
+
+f: int = 1
+reveal_type(f)  # revealed: Literal[1]
+
+def f(): ...
+
+reveal_type(f)  # revealed: Literal[f]
+```

crates/red_knot_python_semantic/resources/mdtest/slots.md

@@ -0,0 +1,184 @@
+# `__slots__`
+
+## Not specified and empty
+
+```py
+class A: ...
+
+class B:
+    __slots__ = ()
+
+class C:
+    __slots__ = ("lorem", "ipsum")
+
+class AB(A, B): ...  # fine
+class AC(A, C): ...  # fine
+class BC(B, C): ...  # fine
+class ABC(A, B, C): ...  # fine
+```
+
+## Incompatible tuples
+
+```py
+class A:
+    __slots__ = ("a", "b")
+
+class B:
+    __slots__ = ("c", "d")
+
+class C(
+    A,  # error: [incompatible-slots]
+    B,  # error: [incompatible-slots]
+): ...
+```
+
+## Same value
+
+```py
+class A:
+    __slots__ = ("a", "b")
+
+class B:
+    __slots__ = ("a", "b")
+
+class C(
+    A,  # error: [incompatible-slots]
+    B,  # error: [incompatible-slots]
+): ...
+```
+
+## Strings
+
+```py
+class A:
+    __slots__ = "abc"
+
+class B:
+    __slots__ = ("abc",)
+
+class AB(
+    A,  # error: [incompatible-slots]
+    B,  # error: [incompatible-slots]
+): ...
+```
+
+## Invalid
+
+TODO: Emit diagnostics
+
+```py
+class NonString1:
+    __slots__ = 42
+
+class NonString2:
+    __slots__ = b"ar"
+
+class NonIdentifier1:
+    __slots__ = "42"
+
+class NonIdentifier2:
+    __slots__ = ("lorem", "42")
+
+class NonIdentifier3:
+    __slots__ = (e for e in ("lorem", "42"))
+```
+
+## Inheritance
+
+```py
+class A:
+    __slots__ = ("a", "b")
+
+class B(A): ...
+
+class C:
+    __slots__ = ("c", "d")
+
+class D(C): ...
+class E(
+    B,  # error: [incompatible-slots]
+    D,  # error: [incompatible-slots]
+): ...
+```
+
+## Single solid base
+
+```py
+class A:
+    __slots__ = ("a", "b")
+
+class B(A): ...
+class C(A): ...
+class D(B, A): ...  # fine
+class E(B, C, A): ...  # fine
+```
+
+## False negatives
+
+### Possibly unbound
+
+```py
+def _(flag: bool):
+    class A:
+        if flag:
+            __slots__ = ("a", "b")
+
+    class B:
+        __slots__ = ("c", "d")
+
+    # Might or might not be fine at runtime
+    class C(A, B): ...
+```
+
+### Bound but with different types
+
+```py
+def _(flag: bool):
+    class A:
+        if flag:
+            __slots__ = ("a", "b")
+        else:
+            __slots__ = ()
+
+    class B:
+        __slots__ = ("c", "d")
+
+    # Might or might not be fine at runtime
+    class C(A, B): ...
+```
+
+### Non-tuples
+
+```py
+class A:
+    __slots__ = ["a", "b"]  # This is treated as "dynamic"
+
+class B:
+    __slots__ = ("c", "d")
+
+# False negative: [incompatible-slots]
+class C(A, B): ...
+```
+
+### Post-hoc modifications
+
+```py
+class A:
+    __slots__ = ()
+    __slots__ += ("a", "b")
+
+reveal_type(A.__slots__)  # revealed: @Todo(Support for more binary expressions)
+
+class B:
+    __slots__ = ("c", "d")
+
+# False negative: [incompatible-slots]
+class C(A, B): ...
+```
+
+### Built-ins with implicit layouts
+
+```py
+# False negative: [incompatible-slots]
+class A(int, str): ...
+```

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

@@ -81,10 +81,7 @@ python-version = "3.9"
 ```
 
 ```py
-# TODO:
-#  * `tuple.__class_getitem__` is always bound on 3.9 (`sys.version_info`)
-#  * `tuple[int, str]` is a valid base (generics)
-# error: [call-possibly-unbound-method] "Method `__class_getitem__` of type `Literal[tuple]` is possibly unbound"
+# TODO: `tuple[int, str]` is a valid base (generics)
 # error: [invalid-base] "Invalid class base with type `GenericAlias` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
 class A(tuple[int, str]): ...
 

crates/red_knot_python_semantic/resources/mdtest/suppressions/knot_ignore.md

@@ -0,0 +1,182 @@
+# Suppressing errors with `knot: ignore`
+
+Type check errors can be suppressed by a `knot: ignore` comment on the same line as the violation.
+
+## Simple `knot: ignore`
+
+```py
+a = 4 + test  # knot: ignore
+```
+
+## Suppressing a specific code
+
+```py
+a = 4 + test  # knot: ignore[unresolved-reference]
+```
+
+## Unused suppression
+
+```py
+test = 10
+# error: [unused-ignore-comment] "Unused `knot: ignore` directive: 'possibly-unresolved-reference'"
+a = test + 3  # knot: ignore[possibly-unresolved-reference]
+```
+
+## Unused suppression if the error codes don't match
+
+```py
+# error: [unresolved-reference]
+# error: [unused-ignore-comment] "Unused `knot: ignore` directive: 'possibly-unresolved-reference'"
+a = test + 3  # knot: ignore[possibly-unresolved-reference]
+```
+
+## Suppressed unused comment
+
+```py
+# error: [unused-ignore-comment]
+a = 10 / 2  # knot: ignore[division-by-zero]
+a = 10 / 2  # knot: ignore[division-by-zero, unused-ignore-comment]
+a = 10 / 2  # knot: ignore[unused-ignore-comment, division-by-zero]
+a = 10 / 2  # knot: ignore[unused-ignore-comment] # type: ignore
+a = 10 / 2  # type: ignore # knot: ignore[unused-ignore-comment]
+```
+
+## Unused ignore comment
+
+```py
+# error: [unused-ignore-comment] "Unused `knot: ignore` directive: 'unused-ignore-comment'"
+a = 10 / 0  # knot: ignore[division-by-zero, unused-ignore-comment]
+```
+
+## Multiple unused comments
+
+Today, Red Knot emits a diagnostic for every unused code. We might want to group the codes by
+comment at some point in the future.
+
+```py
+# error: [unused-ignore-comment] "Unused `knot: ignore` directive: 'division-by-zero'"
+# error: [unused-ignore-comment] "Unused `knot: ignore` directive: 'unresolved-reference'"
+a = 10 / 2  # knot: ignore[division-by-zero, unresolved-reference]
+
+# error: [unused-ignore-comment] "Unused `knot: ignore` directive: 'invalid-assignment'"
+# error: [unused-ignore-comment] "Unused `knot: ignore` directive: 'unresolved-reference'"
+a = 10 / 0  # knot: ignore[invalid-assignment, division-by-zero, unresolved-reference]
+```
+
+## Multiple suppressions
+
+```py
+# fmt: off
+def test(a: f"f-string type annotation", b: b"byte-string-type-annotation"): ...  # knot: ignore[fstring-type-annotation, byte-string-type-annotation]
+```
+
+## Can't suppress syntax errors
+
+<!-- blacken-docs:off -->
+
+```py
+# error: [invalid-syntax]
+# error: [unused-ignore-comment]
+def test(  # knot: ignore
+```
+
+<!-- blacken-docs:on -->
+
+## Can't suppress `revealed-type` diagnostics
+
+```py
+a = 10
+# revealed: Literal[10]
+# error: [unknown-rule] "Unknown rule `revealed-type`"
+reveal_type(a)  # knot: ignore[revealed-type]
+```
+
+## Extra whitespace in type ignore comments is allowed
+
+```py
+a = 10 / 0  # knot   :   ignore
+a = 10 / 0  # knot: ignore  [    division-by-zero   ]
+```
+
+## Whitespace is optional
+
+```py
+# fmt: off
+a = 10 / 0  #knot:ignore[division-by-zero]
+```
+
+## Trailing codes comma
+
+Trailing commas in the codes section are allowed:
+
+```py
+a = 10 / 0  # knot: ignore[division-by-zero,]
+```
+
+## Invalid characters in codes
+
+```py
+# error: [division-by-zero]
+# error: [invalid-ignore-comment] "Invalid `knot: ignore` comment: expected a alphanumeric character or `-` or `_` as code"
+a = 10 / 0  # knot: ignore[*-*]
+```
+
+## Trailing whitespace
+
+<!-- blacken-docs:off -->
+
+```py
+a = 10 / 0  # knot: ignore[division-by-zero]      
+            #                               ^^^^^^ trailing whitespace
+```
+
+<!-- blacken-docs:on -->
+
+## Missing comma
+
+A missing comma results in an invalid suppression comment. We may want to recover from this in the
+future.
+
+```py
+# error: [unresolved-reference]
+# error: [invalid-ignore-comment] "Invalid `knot: ignore` comment: expected a comma separating the rule codes"
+a = x / 0  # knot: ignore[division-by-zero unresolved-reference]
+```
+
+## Missing closing bracket
+
+```py
+# error: [unresolved-reference] "Name `x` used when not defined"
+# error: [invalid-ignore-comment] "Invalid `knot: ignore` comment: expected a comma separating the rule codes"
+a = x / 2  # knot: ignore[unresolved-reference
+```
+
+## Empty codes
+
+An empty codes array suppresses no-diagnostics and is always useless
+
+```py
+# error: [division-by-zero]
+# error: [unused-ignore-comment] "Unused `knot: ignore` without a code"
+a = 4 / 0  # knot: ignore[]
+```
+
+## File-level suppression comments
+
+File level suppression comments are currently intentionally unsupported because we've yet to decide
+if they should use a different syntax that also supports enabling rules or changing the rule's
+severity: `knot: possibly-undefined-reference=error`
+
+```py
+# error: [unused-ignore-comment]
+# knot: ignore[division-by-zero]
+
+a = 4 / 0  # error: [division-by-zero]
+```
+
+## Unknown rule
+
+```py
+# error: [unknown-rule] "Unknown rule `is-equal-14`"
+a = 10 + 4  # knot: ignore[is-equal-14]
+```

crates/red_knot_python_semantic/resources/mdtest/suppressions/no_type_check.md

@@ -0,0 +1,118 @@
+# `@no_type_check`
+
+> If a type checker supports the `no_type_check` decorator for functions, it should suppress all
+> type errors for the def statement and its body including any nested functions or classes. It
+> should also ignore all parameter and return type annotations and treat the function as if it were
+> unannotated. [source](https://typing.readthedocs.io/en/latest/spec/directives.html#no-type-check)
+
+## Error in the function body
+
+```py
+from typing import no_type_check
+
+@no_type_check
+def test() -> int:
+    return a + 5
+```
+
+## Error in nested function
+
+```py
+from typing import no_type_check
+
+@no_type_check
+def test() -> int:
+    def nested():
+        return a + 5
+```
+
+## Error in nested class
+
+```py
+from typing import no_type_check
+
+@no_type_check
+def test() -> int:
+    class Nested:
+        def inner(self):
+            return a + 5
+```
+
+## Error in preceding decorator
+
+Don't suppress diagnostics for decorators appearing before the `no_type_check` decorator.
+
+```py
+from typing import no_type_check
+
+@unknown_decorator  # error: [unresolved-reference]
+@no_type_check
+def test() -> int:
+    return a + 5
+```
+
+## Error in following decorator
+
+Unlike Pyright and mypy, suppress diagnostics appearing after the `no_type_check` decorator. We do
+this because it more closely matches Python's runtime semantics of decorators. For more details, see
+the discussion on the
+[PR adding `@no_type_check` support](https://github.com/astral-sh/ruff/pull/15122#discussion_r1896869411).
+
+```py
+from typing import no_type_check
+
+@no_type_check
+@unknown_decorator
+def test() -> int:
+    return a + 5
+```
+
+## Error in default value
+
+```py
+from typing import no_type_check
+
+@no_type_check
+def test(a: int = "test"):
+    return x + 5
+```
+
+## Error in return value position
+
+```py
+from typing import no_type_check
+
+@no_type_check
+def test() -> Undefined:
+    return x + 5
+```
+
+## `no_type_check` on classes isn't supported
+
+Red Knot does not support decorating classes with `no_type_check`. The behaviour of `no_type_check`
+when applied to classes is
+[not specified currently](https://typing.readthedocs.io/en/latest/spec/directives.html#no-type-check),
+and is not supported by Pyright or mypy.
+
+A future improvement might be to emit a diagnostic if a `no_type_check` annotation is applied to a
+class.
+
+```py
+from typing import no_type_check
+
+@no_type_check
+class Test:
+    def test(self):
+        return a + 5  # error: [unresolved-reference]
+```
+
+## `type: ignore` comments in `@no_type_check` blocks
+
+```py
+from typing import no_type_check
+
+@no_type_check
+def test():
+    # error: [unused-ignore-comment] "Unused `knot: ignore` directive: 'unresolved-reference'"
+    return x + 5  # knot: ignore[unresolved-reference]
+```

crates/red_knot_python_semantic/resources/mdtest/suppressions/type_ignore.md

@@ -0,0 +1,162 @@
+# Suppressing errors with `type: ignore`
+
+Type check errors can be suppressed by a `type: ignore` comment on the same line as the violation.
+
+## Simple `type: ignore`
+
+```py
+a = 4 + test  # type: ignore
+```
+
+## Multiline ranges
+
+A diagnostic with a multiline range can be suppressed by a comment on the same line as the
+diagnostic's start or end. This is the same behavior as Mypy's.
+
+```py
+# fmt: off
+y = (
+    4 / 0  # type: ignore
+)
+
+y = (
+    4 /  # type: ignore
+    0
+)
+
+y = (
+    4 /
+    0  # type: ignore
+)
+```
+
+Pyright diverges from this behavior and instead applies a suppression if its range intersects with
+the diagnostic range. This can be problematic for nested expressions because a suppression in a
+child expression now suppresses errors in the outer expression.
+
+For example, the `type: ignore` comment in this example suppresses the error of adding `2` to
+`"test"` and adding `"other"` to the result of the cast.
+
+```py path=nested.py
+# fmt: off
+from typing import cast
+
+y = (
+    cast(int, "test" +
+            # TODO: Remove the expected error after implementing `invalid-operator` for binary expressions
+            # error: [unused-ignore-comment]
+            2 # type: ignore
+    )
+    + "other"  # TODO: expected-error[invalid-operator]
+)
+```
+
+Mypy flags the second usage.
+
+## Before opening parenthesis
+
+A suppression that applies to all errors before the opening parenthesis.
+
+```py
+a: Test = (  # type: ignore
+  Test()  # error: [unresolved-reference]
+)  # fmt: skip
+```
+
+## Multiline string
+
+```py
+a: int = 4
+a = """
+  This is a multiline string and the suppression is at its end
+"""  # type: ignore
+```
+
+## Line continuations
+
+Suppressions after a line continuation apply to all previous lines.
+
+```py
+# fmt: off
+a = test \
+  + 2  # type: ignore
+
+a = test \
+  + a \
+  + 2  # type: ignore
+```
+
+## Codes
+
+Mypy supports `type: ignore[code]`. Red Knot doesn't understand mypy's rule names. Therefore, ignore
+the codes and suppress all errors.
+
+```py
+a = test  # type: ignore[name-defined]
+```
+
+## Nested comments
+
+```py
+# fmt: off
+a = test \
+  + 2  # fmt: skip # type: ignore
+
+a = test \
+  + 2  # type: ignore # fmt: skip
+```
+
+## Misspelled `type: ignore`
+
+```py
+# error: [unresolved-reference]
+# error: [invalid-ignore-comment]
+a = test + 2  # type: ignoree
+```
+
+## Invalid - ignore on opening parentheses
+
+`type: ignore` comments after an opening parentheses suppress any type errors inside the parentheses
+in Pyright. Neither Ruff, nor mypy support this and neither does Red Knot.
+
+```py
+# fmt: off
+# error: [unused-ignore-comment]
+a = (  # type: ignore
+    test + 4  # error: [unresolved-reference]
+)
+```
+
+## File level suppression
+
+```py
+# type: ignore
+
+a = 10 / 0
+b = a / 0
+```
+
+## File level suppression with leading shebang
+
+```py
+#!/usr/bin/env/python
+# type: ignore
+
+a = 10 / 0
+b = a / 0
+```
+
+## Invalid own-line suppression
+
+```py
+"""
+File level suppressions must come before any non-trivia token,
+including module docstrings. 
+"""
+
+# error: [unused-ignore-comment] "Unused blanket `type: ignore` directive"
+# type: ignore
+
+a = 10 / 0  # error: [division-by-zero]
+b = a / 0  # error: [division-by-zero]
+```

crates/red_knot_python_semantic/resources/mdtest/sys_platform.md

@@ -0,0 +1,71 @@
+# `sys.platform`
+
+## Default value
+
+When no target platform is specified, we fall back to the type of `sys.platform` declared in
+typeshed:
+
+```toml
+[environment]
+# No python-platform entry
+```
+
+```py
+import sys
+
+reveal_type(sys.platform)  # revealed: str
+```
+
+## Explicit selection of `all` platforms
+
+```toml
+[environment]
+python-platform = "all"
+```
+
+```py
+import sys
+
+reveal_type(sys.platform)  # revealed: str
+```
+
+## Explicit selection of a specific platform
+
+```toml
+[environment]
+python-platform = "linux"
+```
+
+```py
+import sys
+
+reveal_type(sys.platform)  # revealed: Literal["linux"]
+```
+
+## Testing for a specific platform
+
+### Exact comparison
+
+```toml
+[environment]
+python-platform = "freebsd8"
+```
+
+```py
+import sys
+
+reveal_type(sys.platform == "freebsd8")  # revealed: Literal[True]
+reveal_type(sys.platform == "linux")  # revealed: Literal[False]
+```
+
+### Substring comparison
+
+It is [recommended](https://docs.python.org/3/library/sys.html#sys.platform) to use
+`sys.platform.startswith(...)` for platform checks. This is not yet supported in type inference:
+
+```py
+import sys
+
+reveal_type(sys.platform.startswith("freebsd"))  # revealed: @Todo(instance attributes)
+reveal_type(sys.platform.startswith("linux"))  # revealed: @Todo(instance attributes)
+```

crates/red_knot_python_semantic/resources/mdtest/unpacking.md

@@ -61,7 +61,7 @@ reveal_type(c)  # revealed: Literal[4]
 ### Uneven unpacking (1)
 
 ```py
-# TODO: Add diagnostic (there aren't enough values to unpack)
+# error: [invalid-assignment] "Not enough values to unpack (expected 3, got 2)"
 (a, b, c) = (1, 2)
 reveal_type(a)  # revealed: Literal[1]
 reveal_type(b)  # revealed: Literal[2]
@@ -71,7 +71,7 @@ reveal_type(c)  # revealed: Unknown
 ### Uneven unpacking (2)
 
 ```py
-# TODO: Add diagnostic (too many values to unpack)
+# error: [invalid-assignment] "Too many values to unpack (expected 2, got 3)"
 (a, b) = (1, 2, 3)
 reveal_type(a)  # revealed: Literal[1]
 reveal_type(b)  # revealed: Literal[2]
@@ -80,7 +80,7 @@ reveal_type(b)  # revealed: Literal[2]
 ### Starred expression (1)
 
 ```py
-# TODO: Add diagnostic (need more values to unpack)
+# error: [invalid-assignment] "Not enough values to unpack (expected 3 or more, got 2)"
 [a, *b, c, d] = (1, 2)
 reveal_type(a)  # revealed: Literal[1]
 # TODO: Should be list[Any] once support for assigning to starred expression is added
@@ -133,7 +133,7 @@ reveal_type(c)  # revealed: @Todo(starred unpacking)
 ### Starred expression (6)
 
 ```py
-# TODO: Add diagnostic (need more values to unpack)
+# error: [invalid-assignment] "Not enough values to unpack (expected 5 or more, got 1)"
 (a, b, c, *d, e, f) = (1,)
 reveal_type(a)  # revealed: Literal[1]
 reveal_type(b)  # revealed: Unknown
@@ -199,7 +199,7 @@ reveal_type(b)  # revealed: LiteralString
 ### Uneven unpacking (1)
 
 ```py
-# TODO: Add diagnostic (there aren't enough values to unpack)
+# error: [invalid-assignment] "Not enough values to unpack (expected 3, got 2)"
 a, b, c = "ab"
 reveal_type(a)  # revealed: LiteralString
 reveal_type(b)  # revealed: LiteralString
@@ -209,7 +209,7 @@ reveal_type(c)  # revealed: Unknown
 ### Uneven unpacking (2)
 
 ```py
-# TODO: Add diagnostic (too many values to unpack)
+# error: [invalid-assignment] "Too many values to unpack (expected 2, got 3)"
 a, b = "abc"
 reveal_type(a)  # revealed: LiteralString
 reveal_type(b)  # revealed: LiteralString
@@ -218,7 +218,7 @@ reveal_type(b)  # revealed: LiteralString
 ### Starred expression (1)
 
 ```py
-# TODO: Add diagnostic (need more values to unpack)
+# error: [invalid-assignment] "Not enough values to unpack (expected 3 or more, got 2)"
 (a, *b, c, d) = "ab"
 reveal_type(a)  # revealed: LiteralString
 # TODO: Should be list[LiteralString] once support for assigning to starred expression is added
@@ -271,7 +271,7 @@ reveal_type(c)  # revealed: @Todo(starred unpacking)
 ### Unicode
 
 ```py
-# TODO: Add diagnostic (need more values to unpack)
+# error: [invalid-assignment] "Not enough values to unpack (expected 2, got 1)"
 (a, b) = "é"
 
 reveal_type(a)  # revealed: LiteralString
@@ -281,7 +281,7 @@ reveal_type(b)  # revealed: Unknown
 ### Unicode escape (1)
 
 ```py
-# TODO: Add diagnostic (need more values to unpack)
+# error: [invalid-assignment] "Not enough values to unpack (expected 2, got 1)"
 (a, b) = "\u9E6C"
 
 reveal_type(a)  # revealed: LiteralString
@@ -291,7 +291,7 @@ reveal_type(b)  # revealed: Unknown
 ### Unicode escape (2)
 
 ```py
-# TODO: Add diagnostic (need more values to unpack)
+# error: [invalid-assignment] "Not enough values to unpack (expected 2, got 1)"
 (a, b) = "\U0010FFFF"
 
 reveal_type(a)  # revealed: LiteralString
@@ -306,3 +306,273 @@ reveal_type(b)  # revealed: Unknown
 reveal_type(a)  # revealed: LiteralString
 reveal_type(b)  # revealed: LiteralString
 ```
+
+## Union
+
+### Same types
+
+Union of two tuples of equal length and each element is of the same type.
+
+```py
+def _(arg: tuple[int, int] | tuple[int, int]):
+    (a, b) = arg
+    reveal_type(a)  # revealed: int
+    reveal_type(b)  # revealed: int
+```
+
+### Mixed types (1)
+
+Union of two tuples of equal length and one element differs in its type.
+
+```py
+def _(arg: tuple[int, int] | tuple[int, str]):
+    a, b = arg
+    reveal_type(a)  # revealed: int
+    reveal_type(b)  # revealed: int | str
+```
+
+### Mixed types (2)
+
+Union of two tuples of equal length and both the element types are different.
+
+```py
+def _(arg: tuple[int, str] | tuple[str, int]):
+    a, b = arg
+    reveal_type(a)  # revealed: int | str
+    reveal_type(b)  # revealed: str | int
+```
+
+### Mixed types (3)
+
+Union of three tuples of equal length and various combination of element types:
+
+1. All same types
+1. One different type
+1. All different types
+
+```py
+def _(arg: tuple[int, int, int] | tuple[int, str, bytes] | tuple[int, int, str]):
+    a, b, c = arg
+    reveal_type(a)  # revealed: int
+    reveal_type(b)  # revealed: int | str
+    reveal_type(c)  # revealed: int | bytes | str
+```
+
+### Nested
+
+```py
+def _(arg: tuple[int, tuple[str, bytes]] | tuple[tuple[int, bytes], Literal["ab"]]):
+    a, (b, c) = arg
+    reveal_type(a)  # revealed: int | tuple[int, bytes]
+    reveal_type(b)  # revealed: str
+    reveal_type(c)  # revealed: bytes | LiteralString
+```
+
+### Starred expression
+
+```py
+def _(arg: tuple[int, bytes, int] | tuple[int, int, str, int, bytes]):
+    a, *b, c = arg
+    reveal_type(a)  # revealed: int
+    # TODO: Should be `list[bytes | int | str]`
+    reveal_type(b)  # revealed: @Todo(starred unpacking)
+    reveal_type(c)  # revealed: int | bytes
+```
+
+### Size mismatch (1)
+
+```py
+def _(arg: tuple[int, bytes, int] | tuple[int, int, str, int, bytes]):
+    # error: [invalid-assignment] "Too many values to unpack (expected 2, got 3)"
+    # error: [invalid-assignment] "Too many values to unpack (expected 2, got 5)"
+    a, b = arg
+    reveal_type(a)  # revealed: int
+    reveal_type(b)  # revealed: bytes | int
+```
+
+### Size mismatch (2)
+
+```py
+def _(arg: tuple[int, bytes] | tuple[int, str]):
+    # error: [invalid-assignment] "Not enough values to unpack (expected 3, got 2)"
+    # error: [invalid-assignment] "Not enough values to unpack (expected 3, got 2)"
+    a, b, c = arg
+    reveal_type(a)  # revealed: int
+    reveal_type(b)  # revealed: bytes | str
+    reveal_type(c)  # revealed: Unknown
+```
+
+### Same literal types
+
+```py
+def _(flag: bool):
+    if flag:
+        value = (1, 2)
+    else:
+        value = (3, 4)
+
+    a, b = value
+    reveal_type(a)  # revealed: Literal[1, 3]
+    reveal_type(b)  # revealed: Literal[2, 4]
+```
+
+### Mixed literal types
+
+```py
+def _(flag: bool):
+    if flag:
+        value = (1, 2)
+    else:
+        value = ("a", "b")
+
+    a, b = value
+    reveal_type(a)  # revealed: Literal[1] | Literal["a"]
+    reveal_type(b)  # revealed: Literal[2] | Literal["b"]
+```
+
+### Typing literal
+
+```py
+from typing import Literal
+
+def _(arg: tuple[int, int] | Literal["ab"]):
+    a, b = arg
+    reveal_type(a)  # revealed: int | LiteralString
+    reveal_type(b)  # revealed: int | LiteralString
+```
+
+### Custom iterator (1)
+
+```py
+class Iterator:
+    def __next__(self) -> tuple[int, int] | tuple[int, str]:
+        return (1, 2)
+
+class Iterable:
+    def __iter__(self) -> Iterator:
+        return Iterator()
+
+((a, b), c) = Iterable()
+reveal_type(a)  # revealed: int
+reveal_type(b)  # revealed: int | str
+reveal_type(c)  # revealed: tuple[int, int] | tuple[int, str]
+```
+
+### Custom iterator (2)
+
+```py
+class Iterator:
+    def __next__(self) -> bytes:
+        return b""
+
+class Iterable:
+    def __iter__(self) -> Iterator:
+        return Iterator()
+
+def _(arg: tuple[int, str] | Iterable):
+    a, b = arg
+    reveal_type(a)  # revealed: int | bytes
+    reveal_type(b)  # revealed: str | bytes
+```
+
+## For statement
+
+Unpacking in a `for` statement.
+
+### Same types
+
+```py
+def _(arg: tuple[tuple[int, int], tuple[int, int]]):
+    for a, b in arg:
+        reveal_type(a)  # revealed: int
+        reveal_type(b)  # revealed: int
+```
+
+### Mixed types (1)
+
+```py
+def _(arg: tuple[tuple[int, int], tuple[int, str]]):
+    for a, b in arg:
+        reveal_type(a)  # revealed: int
+        reveal_type(b)  # revealed: int | str
+```
+
+### Mixed types (2)
+
+```py
+def _(arg: tuple[tuple[int, str], tuple[str, int]]):
+    for a, b in arg:
+        reveal_type(a)  # revealed: int | str
+        reveal_type(b)  # revealed: str | int
+```
+
+### Mixed types (3)
+
+```py
+def _(arg: tuple[tuple[int, int, int], tuple[int, str, bytes], tuple[int, int, str]]):
+    for a, b, c in arg:
+        reveal_type(a)  # revealed: int
+        reveal_type(b)  # revealed: int | str
+        reveal_type(c)  # revealed: int | bytes | str
+```
+
+### Same literal values
+
+```py
+for a, b in ((1, 2), (3, 4)):
+    reveal_type(a)  # revealed: Literal[1, 3]
+    reveal_type(b)  # revealed: Literal[2, 4]
+```
+
+### Mixed literal values (1)
+
+```py
+for a, b in ((1, 2), ("a", "b")):
+    reveal_type(a)  # revealed: Literal[1] | Literal["a"]
+    reveal_type(b)  # revealed: Literal[2] | Literal["b"]
+```
+
+### Mixed literals values (2)
+
+```py
+# error: "Object of type `Literal[1]` is not iterable"
+# error: "Object of type `Literal[2]` is not iterable"
+# error: "Object of type `Literal[4]` is not iterable"
+# error: [invalid-assignment] "Not enough values to unpack (expected 2, got 1)"
+for a, b in (1, 2, (3, "a"), 4, (5, "b"), "c"):
+    reveal_type(a)  # revealed: Unknown | Literal[3, 5] | LiteralString
+    reveal_type(b)  # revealed: Unknown | Literal["a", "b"]
+```
+
+### Custom iterator (1)
+
+```py
+class Iterator:
+    def __next__(self) -> tuple[int, int]:
+        return (1, 2)
+
+class Iterable:
+    def __iter__(self) -> Iterator:
+        return Iterator()
+
+for a, b in Iterable():
+    reveal_type(a)  # revealed: int
+    reveal_type(b)  # revealed: int
+```
+
+### Custom iterator (2)
+
+```py
+class Iterator:
+    def __next__(self) -> bytes:
+        return b""
+
+class Iterable:
+    def __iter__(self) -> Iterator:
+        return Iterator()
+
+def _(arg: tuple[tuple[int, str], Iterable]):
+    for a, b in arg:
+        reveal_type(a)  # revealed: int | bytes
+        reveal_type(b)  # revealed: str | bytes
+```

crates/red_knot_python_semantic/src/ast_node_ref.rs

@@ -43,7 +43,7 @@ impl<T> AstNodeRef<T> {
     }
 
     /// Returns a reference to the wrapped node.
-    pub fn node(&self) -> &T {
+    pub const fn node(&self) -> &T {
         // SAFETY: Holding on to `parsed` ensures that the AST to which `node` belongs is still
         // alive and not moved.
         unsafe { self.node.as_ref() }

crates/red_knot_python_semantic/src/db.rs

@@ -1,4 +1,4 @@
-use crate::lint::RuleSelection;
+use crate::lint::{LintRegistry, RuleSelection};
 use ruff_db::files::File;
 use ruff_db::{Db as SourceDb, Upcast};
 
@@ -8,6 +8,8 @@ pub trait Db: SourceDb + Upcast<dyn SourceDb> {
     fn is_file_open(&self, file: File) -> bool;
 
     fn rule_selection(&self) -> &RuleSelection;
+
+    fn lint_registry(&self) -> &LintRegistry;
 }
 
 #[cfg(test)]
@@ -16,10 +18,10 @@ pub(crate) mod tests {
 
     use crate::program::{Program, SearchPathSettings};
     use crate::python_version::PythonVersion;
-    use crate::{default_lint_registry, ProgramSettings};
+    use crate::{default_lint_registry, ProgramSettings, PythonPlatform};
 
     use super::Db;
-    use crate::lint::RuleSelection;
+    use crate::lint::{LintRegistry, RuleSelection};
     use anyhow::Context;
     use ruff_db::files::{File, Files};
     use ruff_db::system::{DbWithTestSystem, System, SystemPathBuf, TestSystem};
@@ -45,7 +47,7 @@ pub(crate) mod tests {
                 vendored: red_knot_vendored::file_system().clone(),
                 events: Arc::default(),
                 files: Files::default(),
-                rule_selection: Arc::new(RuleSelection::from_registry(&default_lint_registry())),
+                rule_selection: Arc::new(RuleSelection::from_registry(default_lint_registry())),
             }
         }
 
@@ -112,6 +114,10 @@ pub(crate) mod tests {
         fn rule_selection(&self) -> &RuleSelection {
             &self.rule_selection
         }
+
+        fn lint_registry(&self) -> &LintRegistry {
+            default_lint_registry()
+        }
     }
 
     #[salsa::db]
@@ -127,6 +133,8 @@ pub(crate) mod tests {
     pub(crate) struct TestDbBuilder<'a> {
         /// Target Python version
         python_version: PythonVersion,
+        /// Target Python platform
+        python_platform: PythonPlatform,
         /// Path to a custom typeshed directory
         custom_typeshed: Option<SystemPathBuf>,
         /// Path and content pairs for files that should be present
@@ -137,6 +145,7 @@ pub(crate) mod tests {
         pub(crate) fn new() -> Self {
             Self {
                 python_version: PythonVersion::default(),
+                python_platform: PythonPlatform::default(),
                 custom_typeshed: None,
                 files: vec![],
             }
@@ -173,6 +182,7 @@ pub(crate) mod tests {
                 &db,
                 &ProgramSettings {
                     python_version: self.python_version,
+                    python_platform: self.python_platform,
                     search_paths,
                 },
             )

crates/red_knot_python_semantic/src/lib.rs

@@ -3,10 +3,12 @@ use std::hash::BuildHasherDefault;
 use rustc_hash::FxHasher;
 
 use crate::lint::{LintRegistry, LintRegistryBuilder};
+use crate::suppression::{INVALID_IGNORE_COMMENT, UNKNOWN_RULE, UNUSED_IGNORE_COMMENT};
 pub use db::Db;
 pub use module_name::ModuleName;
 pub use module_resolver::{resolve_module, system_module_search_paths, KnownModule, Module};
 pub use program::{Program, ProgramSettings, SearchPathSettings, SitePackages};
+pub use python_platform::PythonPlatform;
 pub use python_version::PythonVersion;
 pub use semantic_model::{HasTy, SemanticModel};
 
@@ -17,26 +19,36 @@ mod module_name;
 mod module_resolver;
 mod node_key;
 mod program;
+mod python_platform;
 mod python_version;
 pub mod semantic_index;
 mod semantic_model;
 pub(crate) mod site_packages;
 mod stdlib;
+mod suppression;
 pub(crate) mod symbol;
 pub mod types;
 mod unpack;
 mod util;
+mod visibility_constraints;
 
 type FxOrderSet<V> = ordermap::set::OrderSet<V, BuildHasherDefault<FxHasher>>;
 
-/// Creates a new registry with all known semantic lints.
-pub fn default_lint_registry() -> LintRegistry {
-    let mut registry = LintRegistryBuilder::default();
-    register_lints(&mut registry);
-    registry.build()
+/// Returns the default registry with all known semantic lints.
+pub fn default_lint_registry() -> &'static LintRegistry {
+    static REGISTRY: std::sync::LazyLock<LintRegistry> = std::sync::LazyLock::new(|| {
+        let mut registry = LintRegistryBuilder::default();
+        register_lints(&mut registry);
+        registry.build()
+    });
+
+    &REGISTRY
 }
 
 /// Register all known semantic lints.
 pub fn register_lints(registry: &mut LintRegistryBuilder) {
     types::register_lints(registry);
+    registry.register_lint(&UNUSED_IGNORE_COMMENT);
+    registry.register_lint(&UNKNOWN_RULE);
+    registry.register_lint(&INVALID_IGNORE_COMMENT);
 }

crates/red_knot_python_semantic/src/lint.rs

@@ -321,7 +321,7 @@ impl LintRegistryBuilder {
     }
 }
 
-#[derive(Default, Debug)]
+#[derive(Default, Debug, Clone)]
 pub struct LintRegistry {
     lints: Vec<LintId>,
     by_name: FxHashMap<&'static str, LintEntry>,
@@ -374,7 +374,7 @@ impl LintRegistry {
     }
 }
 
-#[derive(Error, Debug, Clone)]
+#[derive(Error, Debug, Clone, PartialEq, Eq)]
 pub enum GetLintError {
     /// The name maps to this removed lint.
     #[error("lint {0} has been removed")]
@@ -385,7 +385,7 @@ pub enum GetLintError {
     Unknown(String),
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
 pub enum LintEntry {
     /// An existing lint rule. Can be in preview, stable or deprecated.
     Lint(LintId),
@@ -444,6 +444,11 @@ impl RuleSelection {
         self.lints.get(&lint).copied()
     }
 
+    /// Returns `true` if the `lint` is enabled.
+    pub fn is_enabled(&self, lint: LintId) -> bool {
+        self.severity(lint).is_some()
+    }
+
     /// Enables `lint` and configures with the given `severity`.
     ///
     /// Overrides any previous configuration for the lint.

crates/red_knot_python_semantic/src/module_resolver/resolver.rs

@@ -721,8 +721,8 @@ mod tests {
     use crate::module_name::ModuleName;
     use crate::module_resolver::module::ModuleKind;
     use crate::module_resolver::testing::{FileSpec, MockedTypeshed, TestCase, TestCaseBuilder};
-    use crate::ProgramSettings;
     use crate::PythonVersion;
+    use crate::{ProgramSettings, PythonPlatform};
 
     use super::*;
 
@@ -1262,7 +1262,7 @@ mod tests {
     fn symlink() -> anyhow::Result<()> {
         use anyhow::Context;
 
-        use crate::program::Program;
+        use crate::{program::Program, PythonPlatform};
         use ruff_db::system::{OsSystem, SystemPath};
 
         use crate::db::tests::TestDb;
@@ -1296,6 +1296,7 @@ mod tests {
             &db,
             &ProgramSettings {
                 python_version: PythonVersion::PY38,
+                python_platform: PythonPlatform::default(),
                 search_paths: SearchPathSettings {
                     extra_paths: vec![],
                     src_root: src.clone(),
@@ -1801,6 +1802,7 @@ not_a_directory
             &db,
             &ProgramSettings {
                 python_version: PythonVersion::default(),
+                python_platform: PythonPlatform::default(),
                 search_paths: SearchPathSettings {
                     extra_paths: vec![],
                     src_root: SystemPathBuf::from("/src"),

crates/red_knot_python_semantic/src/module_resolver/testing.rs

@@ -4,7 +4,7 @@ use ruff_db::vendored::VendoredPathBuf;
 use crate::db::tests::TestDb;
 use crate::program::{Program, SearchPathSettings};
 use crate::python_version::PythonVersion;
-use crate::{ProgramSettings, SitePackages};
+use crate::{ProgramSettings, PythonPlatform, SitePackages};
 
 /// A test case for the module resolver.
 ///
@@ -101,6 +101,7 @@ pub(crate) struct UnspecifiedTypeshed;
 pub(crate) struct TestCaseBuilder<T> {
     typeshed_option: T,
     python_version: PythonVersion,
+    python_platform: PythonPlatform,
     first_party_files: Vec<FileSpec>,
     site_packages_files: Vec<FileSpec>,
 }
@@ -147,6 +148,7 @@ impl TestCaseBuilder<UnspecifiedTypeshed> {
         Self {
             typeshed_option: UnspecifiedTypeshed,
             python_version: PythonVersion::default(),
+            python_platform: PythonPlatform::default(),
             first_party_files: vec![],
             site_packages_files: vec![],
         }
@@ -157,12 +159,14 @@ impl TestCaseBuilder<UnspecifiedTypeshed> {
         let TestCaseBuilder {
             typeshed_option: _,
             python_version,
+            python_platform,
             first_party_files,
             site_packages_files,
         } = self;
         TestCaseBuilder {
             typeshed_option: VendoredTypeshed,
             python_version,
+            python_platform,
             first_party_files,
             site_packages_files,
         }
@@ -176,6 +180,7 @@ impl TestCaseBuilder<UnspecifiedTypeshed> {
         let TestCaseBuilder {
             typeshed_option: _,
             python_version,
+            python_platform,
             first_party_files,
             site_packages_files,
         } = self;
@@ -183,6 +188,7 @@ impl TestCaseBuilder<UnspecifiedTypeshed> {
         TestCaseBuilder {
             typeshed_option: typeshed,
             python_version,
+            python_platform,
             first_party_files,
             site_packages_files,
         }
@@ -212,6 +218,7 @@ impl TestCaseBuilder<MockedTypeshed> {
         let TestCaseBuilder {
             typeshed_option,
             python_version,
+            python_platform,
             first_party_files,
             site_packages_files,
         } = self;
@@ -227,6 +234,7 @@ impl TestCaseBuilder<MockedTypeshed> {
             &db,
             &ProgramSettings {
                 python_version,
+                python_platform,
                 search_paths: SearchPathSettings {
                     extra_paths: vec![],
                     src_root: src.clone(),
@@ -269,6 +277,7 @@ impl TestCaseBuilder<VendoredTypeshed> {
         let TestCaseBuilder {
             typeshed_option: VendoredTypeshed,
             python_version,
+            python_platform,
             first_party_files,
             site_packages_files,
         } = self;
@@ -283,6 +292,7 @@ impl TestCaseBuilder<VendoredTypeshed> {
             &db,
             &ProgramSettings {
                 python_version,
+                python_platform,
                 search_paths: SearchPathSettings {
                     site_packages: SitePackages::Known(vec![site_packages.clone()]),
                     ..SearchPathSettings::new(src.clone())

crates/red_knot_python_semantic/src/program.rs

@@ -1,3 +1,4 @@
+use crate::python_platform::PythonPlatform;
 use crate::python_version::PythonVersion;
 use anyhow::Context;
 use salsa::Durability;
@@ -12,6 +13,8 @@ use crate::Db;
 pub struct Program {
     pub python_version: PythonVersion,
 
+    pub python_platform: PythonPlatform,
+
     #[return_ref]
     pub(crate) search_paths: SearchPaths,
 }
@@ -20,6 +23,7 @@ impl Program {
     pub fn from_settings(db: &dyn Db, settings: &ProgramSettings) -> anyhow::Result<Self> {
         let ProgramSettings {
             python_version,
+            python_platform,
             search_paths,
         } = settings;
 
@@ -28,9 +32,11 @@ impl Program {
         let search_paths = SearchPaths::from_settings(db, search_paths)
             .with_context(|| "Invalid search path settings")?;
 
-        Ok(Program::builder(settings.python_version, search_paths)
-            .durability(Durability::HIGH)
-            .new(db))
+        Ok(
+            Program::builder(*python_version, python_platform.clone(), search_paths)
+                .durability(Durability::HIGH)
+                .new(db),
+        )
     }
 
     pub fn update_search_paths(
@@ -57,6 +63,7 @@ impl Program {
 #[cfg_attr(feature = "serde", derive(serde::Serialize))]
 pub struct ProgramSettings {
     pub python_version: PythonVersion,
+    pub python_platform: PythonPlatform,
     pub search_paths: SearchPathSettings,
 }
 

crates/red_knot_python_semantic/src/python_platform.rs

@@ -0,0 +1,19 @@
+/// The target platform to assume when resolving types.
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Serialize, serde::Deserialize),
+    serde(rename_all = "kebab-case")
+)]
+pub enum PythonPlatform {
+    /// Do not make any assumptions about the target platform.
+    #[default]
+    All,
+    /// Assume a specific target platform like `linux`, `darwin` or `win32`.
+    ///
+    /// We use a string (instead of individual enum variants), as the set of possible platforms
+    /// may change over time. See <https://docs.python.org/3/library/sys.html#sys.platform> for
+    /// some known platform identifiers.
+    #[cfg_attr(feature = "serde", serde(untagged))]
+    Identifier(String),
+}

crates/red_knot_python_semantic/src/semantic_index.rs

@@ -29,7 +29,8 @@ pub mod symbol;
 mod use_def;
 
 pub(crate) use self::use_def::{
-    BindingWithConstraints, BindingWithConstraintsIterator, DeclarationsIterator,
+    BindingWithConstraints, BindingWithConstraintsIterator, DeclarationWithConstraint,
+    DeclarationsIterator, ScopedVisibilityConstraintId,
 };
 
 type SymbolMap = hashbrown::HashMap<ScopedSymbolId, (), FxBuildHasher>;
@@ -378,14 +379,12 @@ mod tests {
     impl UseDefMap<'_> {
         fn first_public_binding(&self, symbol: ScopedSymbolId) -> Option<Definition<'_>> {
             self.public_bindings(symbol)
-                .next()
-                .map(|constrained_binding| constrained_binding.binding)
+                .find_map(|constrained_binding| constrained_binding.binding)
         }
 
         fn first_binding_at_use(&self, use_id: ScopedUseId) -> Option<Definition<'_>> {
             self.bindings_at_use(use_id)
-                .next()
-                .map(|constrained_binding| constrained_binding.binding)
+                .find_map(|constrained_binding| constrained_binding.binding)
         }
     }
 

crates/red_knot_python_semantic/src/semantic_index/builder.rs

@@ -9,12 +9,12 @@ use ruff_index::IndexVec;
 use ruff_python_ast as ast;
 use ruff_python_ast::name::Name;
 use ruff_python_ast::visitor::{walk_expr, walk_pattern, walk_stmt, Visitor};
-use ruff_python_ast::{BoolOp, Expr};
 
 use crate::ast_node_ref::AstNodeRef;
 use crate::module_name::ModuleName;
 use crate::semantic_index::ast_ids::node_key::ExpressionNodeKey;
 use crate::semantic_index::ast_ids::AstIdsBuilder;
+use crate::semantic_index::constraint::PatternConstraintKind;
 use crate::semantic_index::definition::{
     AssignmentDefinitionNodeRef, ComprehensionDefinitionNodeRef, Definition, DefinitionNodeKey,
     DefinitionNodeRef, ForStmtDefinitionNodeRef, ImportFromDefinitionNodeRef,
@@ -24,9 +24,12 @@ use crate::semantic_index::symbol::{
     FileScopeId, NodeWithScopeKey, NodeWithScopeRef, Scope, ScopeId, ScopedSymbolId,
     SymbolTableBuilder,
 };
-use crate::semantic_index::use_def::{FlowSnapshot, UseDefMapBuilder};
+use crate::semantic_index::use_def::{
+    FlowSnapshot, ScopedConstraintId, ScopedVisibilityConstraintId, UseDefMapBuilder,
+};
 use crate::semantic_index::SemanticIndex;
-use crate::unpack::Unpack;
+use crate::unpack::{Unpack, UnpackValue};
+use crate::visibility_constraints::VisibilityConstraint;
 use crate::Db;
 
 use super::constraint::{Constraint, ConstraintNode, PatternConstraint};
@@ -285,11 +288,7 @@ impl<'db> SemanticIndexBuilder<'db> {
         constraint
     }
 
-    fn record_constraint(&mut self, constraint: Constraint<'db>) {
-        self.current_use_def_map_mut().record_constraint(constraint);
-    }
-
-    fn build_constraint(&mut self, constraint_node: &Expr) -> Constraint<'db> {
+    fn build_constraint(&mut self, constraint_node: &ast::Expr) -> Constraint<'db> {
         let expression = self.add_standalone_expression(constraint_node);
         Constraint {
             node: ConstraintNode::Expression(expression),
@@ -297,12 +296,89 @@ impl<'db> SemanticIndexBuilder<'db> {
         }
     }
 
-    fn record_negated_constraint(&mut self, constraint: Constraint<'db>) {
+    /// Adds a new constraint to the list of all constraints, but does not record it. Returns the
+    /// constraint ID for later recording using [`SemanticIndexBuilder::record_constraint_id`].
+    fn add_constraint(&mut self, constraint: Constraint<'db>) -> ScopedConstraintId {
+        self.current_use_def_map_mut().add_constraint(constraint)
+    }
+
+    /// Negates a constraint and adds it to the list of all constraints, does not record it.
+    fn add_negated_constraint(
+        &mut self,
+        constraint: Constraint<'db>,
+    ) -> (Constraint<'db>, ScopedConstraintId) {
+        let negated = Constraint {
+            node: constraint.node,
+            is_positive: false,
+        };
+        let id = self.current_use_def_map_mut().add_constraint(negated);
+        (negated, id)
+    }
+
+    /// Records a previously added constraint by adding it to all live bindings.
+    fn record_constraint_id(&mut self, constraint: ScopedConstraintId) {
         self.current_use_def_map_mut()
-            .record_constraint(Constraint {
-                node: constraint.node,
-                is_positive: false,
-            });
+            .record_constraint_id(constraint);
+    }
+
+    /// Adds and records a constraint, i.e. adds it to all live bindings.
+    fn record_constraint(&mut self, constraint: Constraint<'db>) {
+        self.current_use_def_map_mut().record_constraint(constraint);
+    }
+
+    /// Negates the given constraint and then adds it to all live bindings.
+    fn record_negated_constraint(&mut self, constraint: Constraint<'db>) -> ScopedConstraintId {
+        let (_, id) = self.add_negated_constraint(constraint);
+        self.record_constraint_id(id);
+        id
+    }
+
+    /// Adds a new visibility constraint, but does not record it. Returns the constraint ID
+    /// for later recording using [`SemanticIndexBuilder::record_visibility_constraint_id`].
+    fn add_visibility_constraint(
+        &mut self,
+        constraint: VisibilityConstraint<'db>,
+    ) -> ScopedVisibilityConstraintId {
+        self.current_use_def_map_mut()
+            .add_visibility_constraint(constraint)
+    }
+
+    /// Records a previously added visibility constraint by applying it to all live bindings
+    /// and declarations.
+    fn record_visibility_constraint_id(&mut self, constraint: ScopedVisibilityConstraintId) {
+        self.current_use_def_map_mut()
+            .record_visibility_constraint_id(constraint);
+    }
+
+    /// Negates the given visibility constraint and then adds it to all live bindings and declarations.
+    fn record_negated_visibility_constraint(
+        &mut self,
+        constraint: ScopedVisibilityConstraintId,
+    ) -> ScopedVisibilityConstraintId {
+        self.current_use_def_map_mut()
+            .record_visibility_constraint(VisibilityConstraint::VisibleIfNot(constraint))
+    }
+
+    /// Records a visibility constraint by applying it to all live bindings and declarations.
+    fn record_visibility_constraint(
+        &mut self,
+        constraint: Constraint<'db>,
+    ) -> ScopedVisibilityConstraintId {
+        self.current_use_def_map_mut()
+            .record_visibility_constraint(VisibilityConstraint::VisibleIf(constraint))
+    }
+
+    /// Records a [`VisibilityConstraint::Ambiguous`] constraint.
+    fn record_ambiguous_visibility(&mut self) -> ScopedVisibilityConstraintId {
+        self.current_use_def_map_mut()
+            .record_visibility_constraint(VisibilityConstraint::Ambiguous)
+    }
+
+    /// Simplifies (resets) visibility constraints on all live bindings and declarations that did
+    /// not see any new definitions since the given snapshot.
+    fn simplify_visibility_constraints(&mut self, snapshot: FlowSnapshot) {
+        self.current_use_def_map_mut()
+            .simplify_visibility_constraints(snapshot);
     }
 
     fn push_assignment(&mut self, assignment: CurrentAssignment<'db>) {
@@ -324,30 +400,37 @@ impl<'db> SemanticIndexBuilder<'db> {
 
     fn add_pattern_constraint(
         &mut self,
-        subject: &ast::Expr,
+        subject: Expression<'db>,
         pattern: &ast::Pattern,
-    ) -> PatternConstraint<'db> {
-        #[allow(unsafe_code)]
-        let (subject, pattern) = unsafe {
-            (
-                AstNodeRef::new(self.module.clone(), subject),
-                AstNodeRef::new(self.module.clone(), pattern),
-            )
+        guard: Option<&ast::Expr>,
+    ) -> Constraint<'db> {
+        let guard = guard.map(|guard| self.add_standalone_expression(guard));
+
+        let kind = match pattern {
+            ast::Pattern::MatchValue(pattern) => {
+                let value = self.add_standalone_expression(&pattern.value);
+                PatternConstraintKind::Value(value, guard)
+            }
+            ast::Pattern::MatchSingleton(singleton) => {
+                PatternConstraintKind::Singleton(singleton.value, guard)
+            }
+            _ => PatternConstraintKind::Unsupported,
         };
+
         let pattern_constraint = PatternConstraint::new(
             self.db,
             self.file,
             self.current_scope(),
             subject,
-            pattern,
+            kind,
             countme::Count::default(),
         );
-        self.current_use_def_map_mut()
-            .record_constraint(Constraint {
-                node: ConstraintNode::Pattern(pattern_constraint),
-                is_positive: true,
-            });
-        pattern_constraint
+        let constraint = Constraint {
+            node: ConstraintNode::Pattern(pattern_constraint),
+            is_positive: true,
+        };
+        self.current_use_def_map_mut().record_constraint(constraint);
+        constraint
     }
 
     /// Record an expression that needs to be a Salsa ingredient, because we need to infer its type
@@ -726,7 +809,7 @@ where
                                     unsafe {
                                         AstNodeRef::new(self.module.clone(), target)
                                     },
-                                    value,
+                                    UnpackValue::Assign(value),
                                     countme::Count::default(),
                                 )),
                             })
@@ -799,6 +882,10 @@ where
                 let constraint = self.record_expression_constraint(&node.test);
                 let mut constraints = vec![constraint];
                 self.visit_body(&node.body);
+
+                let visibility_constraint_id = self.record_visibility_constraint(constraint);
+                let mut vis_constraints = vec![visibility_constraint_id];
+
                 let mut post_clauses: Vec<FlowSnapshot> = vec![];
                 let elif_else_clauses = node
                     .elif_else_clauses
@@ -825,15 +912,31 @@ where
                     for constraint in &constraints {
                         self.record_negated_constraint(*constraint);
                     }
-                    if let Some(elif_test) = clause_test {
+
+                    let elif_constraint = if let Some(elif_test) = clause_test {
                         self.visit_expr(elif_test);
-                        constraints.push(self.record_expression_constraint(elif_test));
-                    }
+                        let constraint = self.record_expression_constraint(elif_test);
+                        constraints.push(constraint);
+                        Some(constraint)
+                    } else {
+                        None
+                    };
                     self.visit_body(clause_body);
+
+                    for id in &vis_constraints {
+                        self.record_negated_visibility_constraint(*id);
+                    }
+                    if let Some(elif_constraint) = elif_constraint {
+                        let id = self.record_visibility_constraint(elif_constraint);
+                        vis_constraints.push(id);
+                    }
                 }
+
                 for post_clause_state in post_clauses {
                     self.flow_merge(post_clause_state);
                 }
+
+                self.simplify_visibility_constraints(pre_if);
             }
             ast::Stmt::While(ast::StmtWhile {
                 test,
@@ -856,6 +959,8 @@ where
                 self.visit_body(body);
                 self.set_inside_loop(outer_loop_state);
 
+                let vis_constraint_id = self.record_visibility_constraint(constraint);
+
                 // Get the break states from the body of this loop, and restore the saved outer
                 // ones.
                 let break_states =
@@ -863,15 +968,21 @@ where
 
                 // We may execute the `else` clause without ever executing the body, so merge in
                 // the pre-loop state before visiting `else`.
-                self.flow_merge(pre_loop);
+                self.flow_merge(pre_loop.clone());
                 self.record_negated_constraint(constraint);
                 self.visit_body(orelse);
+                self.record_negated_visibility_constraint(vis_constraint_id);
 
                 // Breaking out of a while loop bypasses the `else` clause, so merge in the break
                 // states after visiting `else`.
                 for break_state in break_states {
-                    self.flow_merge(break_state);
+                    let snapshot = self.flow_snapshot();
+                    self.flow_restore(break_state);
+                    self.record_visibility_constraint(constraint);
+                    self.flow_merge(snapshot);
                 }
+
+                self.simplify_visibility_constraints(pre_loop);
             }
             ast::Stmt::With(ast::StmtWith {
                 items,
@@ -909,16 +1020,47 @@ where
                     orelse,
                 },
             ) => {
-                self.add_standalone_expression(iter);
+                debug_assert_eq!(&self.current_assignments, &[]);
+
+                let iter_expr = self.add_standalone_expression(iter);
                 self.visit_expr(iter);
 
+                self.record_ambiguous_visibility();
+
                 let pre_loop = self.flow_snapshot();
                 let saved_break_states = std::mem::take(&mut self.loop_break_states);
 
-                debug_assert_eq!(&self.current_assignments, &[]);
-                self.push_assignment(for_stmt.into());
+                let current_assignment = match &**target {
+                    ast::Expr::List(_) | ast::Expr::Tuple(_) => Some(CurrentAssignment::For {
+                        node: for_stmt,
+                        first: true,
+                        unpack: Some(Unpack::new(
+                            self.db,
+                            self.file,
+                            self.current_scope(),
+                            #[allow(unsafe_code)]
+                            unsafe {
+                                AstNodeRef::new(self.module.clone(), target)
+                            },
+                            UnpackValue::Iterable(iter_expr),
+                            countme::Count::default(),
+                        )),
+                    }),
+                    ast::Expr::Name(_) => Some(CurrentAssignment::For {
+                        node: for_stmt,
+                        unpack: None,
+                        first: false,
+                    }),
+                    _ => None,
+                };
+
+                if let Some(current_assignment) = current_assignment {
+                    self.push_assignment(current_assignment);
+                }
                 self.visit_expr(target);
-                self.pop_assignment();
+                if current_assignment.is_some() {
+                    self.pop_assignment();
+                }
 
                 // TODO: Definitions created by loop variables
                 // (and definitions created inside the body)
@@ -947,32 +1089,63 @@ where
                 cases,
                 range: _,
             }) => {
-                self.add_standalone_expression(subject);
+                let subject_expr = self.add_standalone_expression(subject);
                 self.visit_expr(subject);
 
                 let after_subject = self.flow_snapshot();
                 let Some((first, remaining)) = cases.split_first() else {
                     return;
                 };
-                self.add_pattern_constraint(subject, &first.pattern);
+
+                let first_constraint_id = self.add_pattern_constraint(
+                    subject_expr,
+                    &first.pattern,
+                    first.guard.as_deref(),
+                );
+
                 self.visit_match_case(first);
 
+                let first_vis_constraint_id =
+                    self.record_visibility_constraint(first_constraint_id);
+                let mut vis_constraints = vec![first_vis_constraint_id];
+
                 let mut post_case_snapshots = vec![];
                 for case in remaining {
                     post_case_snapshots.push(self.flow_snapshot());
                     self.flow_restore(after_subject.clone());
-                    self.add_pattern_constraint(subject, &case.pattern);
+                    let constraint_id = self.add_pattern_constraint(
+                        subject_expr,
+                        &case.pattern,
+                        case.guard.as_deref(),
+                    );
                     self.visit_match_case(case);
+
+                    for id in &vis_constraints {
+                        self.record_negated_visibility_constraint(*id);
+                    }
+                    let vis_constraint_id = self.record_visibility_constraint(constraint_id);
+                    vis_constraints.push(vis_constraint_id);
                 }
-                for post_clause_state in post_case_snapshots {
-                    self.flow_merge(post_clause_state);
-                }
+
+                // If there is no final wildcard match case, pretend there is one. This is similar to how
+                // we add an implicit `else` block in if-elif chains, in case it's not present.
                 if !cases
                     .last()
                     .is_some_and(|case| case.guard.is_none() && case.pattern.is_wildcard())
                 {
-                    self.flow_merge(after_subject);
+                    post_case_snapshots.push(self.flow_snapshot());
+                    self.flow_restore(after_subject.clone());
+
+                    for id in &vis_constraints {
+                        self.record_negated_visibility_constraint(*id);
+                    }
                 }
+
+                for post_clause_state in post_case_snapshots {
+                    self.flow_merge(post_clause_state);
+                }
+
+                self.simplify_visibility_constraints(after_subject);
             }
             ast::Stmt::Try(ast::StmtTry {
                 body,
@@ -982,6 +1155,8 @@ where
                 is_star,
                 range: _,
             }) => {
+                self.record_ambiguous_visibility();
+
                 // Save the state prior to visiting any of the `try` block.
                 //
                 // Potentially none of the `try` block could have been executed prior to executing
@@ -1136,12 +1311,18 @@ where
                         Some(CurrentAssignment::AugAssign(aug_assign)) => {
                             self.add_definition(symbol, aug_assign);
                         }
-                        Some(CurrentAssignment::For(node)) => {
+                        Some(CurrentAssignment::For {
+                            node,
+                            first,
+                            unpack,
+                        }) => {
                             self.add_definition(
                                 symbol,
                                 ForStmtDefinitionNodeRef {
+                                    unpack,
+                                    first,
                                     iterable: &node.iter,
-                                    target: name_node,
+                                    name: name_node,
                                     is_async: node.is_async,
                                 },
                             );
@@ -1177,7 +1358,9 @@ where
                     }
                 }
 
-                if let Some(CurrentAssignment::Assign { first, .. }) = self.current_assignment_mut()
+                if let Some(
+                    CurrentAssignment::Assign { first, .. } | CurrentAssignment::For { first, .. },
+                ) = self.current_assignment_mut()
                 {
                     *first = false;
                 }
@@ -1222,19 +1405,19 @@ where
             ast::Expr::If(ast::ExprIf {
                 body, test, orelse, ..
             }) => {
-                // TODO detect statically known truthy or falsy test (via type inference, not naive
-                // AST inspection, so we can't simplify here, need to record test expression for
-                // later checking)
                 self.visit_expr(test);
                 let pre_if = self.flow_snapshot();
                 let constraint = self.record_expression_constraint(test);
                 self.visit_expr(body);
+                let visibility_constraint = self.record_visibility_constraint(constraint);
                 let post_body = self.flow_snapshot();
-                self.flow_restore(pre_if);
+                self.flow_restore(pre_if.clone());
 
                 self.record_negated_constraint(constraint);
                 self.visit_expr(orelse);
+                self.record_negated_visibility_constraint(visibility_constraint);
                 self.flow_merge(post_body);
+                self.simplify_visibility_constraints(pre_if);
             }
             ast::Expr::ListComp(
                 list_comprehension @ ast::ExprListComp {
@@ -1291,27 +1474,55 @@ where
                 range: _,
                 op,
             }) => {
-                // TODO detect statically known truthy or falsy values (via type inference, not naive
-                // AST inspection, so we can't simplify here, need to record test expression for
-                // later checking)
+                let pre_op = self.flow_snapshot();
+
                 let mut snapshots = vec![];
+                let mut visibility_constraints = vec![];
 
                 for (index, value) in values.iter().enumerate() {
                     self.visit_expr(value);
-                    // In the last value we don't need to take a snapshot nor add a constraint
+
+                    for vid in &visibility_constraints {
+                        self.record_visibility_constraint_id(*vid);
+                    }
+
+                    // For the last value, we don't need to model control flow. There is short-circuiting
+                    // anymore.
                     if index < values.len() - 1 {
-                        // Snapshot is taken after visiting the expression but before adding the constraint.
-                        snapshots.push(self.flow_snapshot());
                         let constraint = self.build_constraint(value);
-                        match op {
-                            BoolOp::And => self.record_constraint(constraint),
-                            BoolOp::Or => self.record_negated_constraint(constraint),
+                        let (constraint, constraint_id) = match op {
+                            ast::BoolOp::And => (constraint, self.add_constraint(constraint)),
+                            ast::BoolOp::Or => self.add_negated_constraint(constraint),
+                        };
+                        let visibility_constraint = self
+                            .add_visibility_constraint(VisibilityConstraint::VisibleIf(constraint));
+
+                        let after_expr = self.flow_snapshot();
+
+                        // We first model the short-circuiting behavior. We take the short-circuit
+                        // path here if all of the previous short-circuit paths were not taken, so
+                        // we record all previously existing visibility constraints, and negate the
+                        // one for the current expression.
+                        for vid in &visibility_constraints {
+                            self.record_visibility_constraint_id(*vid);
                         }
+                        self.record_negated_visibility_constraint(visibility_constraint);
+                        snapshots.push(self.flow_snapshot());
+
+                        // Then we model the non-short-circuiting behavior. Here, we need to delay
+                        // the application of the visibility constraint until after the expression
+                        // has been evaluated, so we only push it onto the stack here.
+                        self.flow_restore(after_expr);
+                        self.record_constraint_id(constraint_id);
+                        visibility_constraints.push(visibility_constraint);
                     }
                 }
+
                 for snapshot in snapshots {
                     self.flow_merge(snapshot);
                 }
+
+                self.simplify_visibility_constraints(pre_op);
             }
             _ => {
                 walk_expr(self, expr);
@@ -1391,7 +1602,11 @@ enum CurrentAssignment<'a> {
     },
     AnnAssign(&'a ast::StmtAnnAssign),
     AugAssign(&'a ast::StmtAugAssign),
-    For(&'a ast::StmtFor),
+    For {
+        node: &'a ast::StmtFor,
+        first: bool,
+        unpack: Option<Unpack<'a>>,
+    },
     Named(&'a ast::ExprNamed),
     Comprehension {
         node: &'a ast::Comprehension,
@@ -1415,12 +1630,6 @@ impl<'a> From<&'a ast::StmtAugAssign> for CurrentAssignment<'a> {
     }
 }
 
-impl<'a> From<&'a ast::StmtFor> for CurrentAssignment<'a> {
-    fn from(value: &'a ast::StmtFor) -> Self {
-        Self::For(value)
-    }
-}
-
 impl<'a> From<&'a ast::ExprNamed> for CurrentAssignment<'a> {
     fn from(value: &'a ast::ExprNamed) -> Self {
         Self::Named(value)

crates/red_knot_python_semantic/src/semantic_index/constraint.rs

@@ -1,7 +1,6 @@
 use ruff_db::files::File;
-use ruff_python_ast as ast;
+use ruff_python_ast::Singleton;
 
-use crate::ast_node_ref::AstNodeRef;
 use crate::db::Db;
 use crate::semantic_index::expression::Expression;
 use crate::semantic_index::symbol::{FileScopeId, ScopeId};
@@ -18,6 +17,14 @@ pub(crate) enum ConstraintNode<'db> {
     Pattern(PatternConstraint<'db>),
 }
 
+/// Pattern kinds for which we support type narrowing and/or static visibility analysis.
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) enum PatternConstraintKind<'db> {
+    Singleton(Singleton, Option<Expression<'db>>),
+    Value(Expression<'db>, Option<Expression<'db>>),
+    Unsupported,
+}
+
 #[salsa::tracked]
 pub(crate) struct PatternConstraint<'db> {
     #[id]
@@ -28,11 +35,11 @@ pub(crate) struct PatternConstraint<'db> {
 
     #[no_eq]
     #[return_ref]
-    pub(crate) subject: AstNodeRef<ast::Expr>,
+    pub(crate) subject: Expression<'db>,
 
     #[no_eq]
     #[return_ref]
-    pub(crate) pattern: AstNodeRef<ast::Pattern>,
+    pub(crate) kind: PatternConstraintKind<'db>,
 
     #[no_eq]
     count: countme::Count<PatternConstraint<'static>>,

crates/red_knot_python_semantic/src/semantic_index/definition.rs

@@ -225,8 +225,10 @@ pub(crate) struct WithItemDefinitionNodeRef<'a> {
 
 #[derive(Copy, Clone, Debug)]
 pub(crate) struct ForStmtDefinitionNodeRef<'a> {
+    pub(crate) unpack: Option<Unpack<'a>>,
     pub(crate) iterable: &'a ast::Expr,
-    pub(crate) target: &'a ast::ExprName,
+    pub(crate) name: &'a ast::ExprName,
+    pub(crate) first: bool,
     pub(crate) is_async: bool,
 }
 
@@ -298,12 +300,16 @@ impl<'db> DefinitionNodeRef<'db> {
                 DefinitionKind::AugmentedAssignment(AstNodeRef::new(parsed, augmented_assignment))
             }
             DefinitionNodeRef::For(ForStmtDefinitionNodeRef {
+                unpack,
                 iterable,
-                target,
+                name,
+                first,
                 is_async,
             }) => DefinitionKind::For(ForStmtDefinitionKind {
+                target: TargetKind::from(unpack),
                 iterable: AstNodeRef::new(parsed.clone(), iterable),
-                target: AstNodeRef::new(parsed, target),
+                name: AstNodeRef::new(parsed, name),
+                first,
                 is_async,
             }),
             DefinitionNodeRef::Comprehension(ComprehensionDefinitionNodeRef {
@@ -382,10 +388,12 @@ impl<'db> DefinitionNodeRef<'db> {
             Self::AnnotatedAssignment(node) => node.into(),
             Self::AugmentedAssignment(node) => node.into(),
             Self::For(ForStmtDefinitionNodeRef {
+                unpack: _,
                 iterable: _,
-                target,
+                name,
+                first: _,
                 is_async: _,
-            }) => target.into(),
+            }) => name.into(),
             Self::Comprehension(ComprehensionDefinitionNodeRef { target, .. }) => target.into(),
             Self::VariadicPositionalParameter(node) => node.into(),
             Self::VariadicKeywordParameter(node) => node.into(),
@@ -452,7 +460,7 @@ pub enum DefinitionKind<'db> {
     Assignment(AssignmentDefinitionKind<'db>),
     AnnotatedAssignment(AstNodeRef<ast::StmtAnnAssign>),
     AugmentedAssignment(AstNodeRef<ast::StmtAugAssign>),
-    For(ForStmtDefinitionKind),
+    For(ForStmtDefinitionKind<'db>),
     Comprehension(ComprehensionDefinitionKind),
     VariadicPositionalParameter(AstNodeRef<ast::Parameter>),
     VariadicKeywordParameter(AstNodeRef<ast::Parameter>),
@@ -465,8 +473,14 @@ pub enum DefinitionKind<'db> {
     TypeVarTuple(AstNodeRef<ast::TypeParamTypeVarTuple>),
 }
 
-impl Ranged for DefinitionKind<'_> {
-    fn range(&self) -> TextRange {
+impl DefinitionKind<'_> {
+    /// Returns the [`TextRange`] of the definition target.
+    ///
+    /// A definition target would mainly be the node representing the symbol being defined i.e.,
+    /// [`ast::ExprName`] or [`ast::Identifier`] but could also be other nodes.
+    ///
+    /// This is mainly used for logging and debugging purposes.
+    pub(crate) fn target_range(&self) -> TextRange {
         match self {
             DefinitionKind::Import(alias) => alias.range(),
             DefinitionKind::ImportFrom(import) => import.alias().range(),
@@ -477,7 +491,7 @@ impl Ranged for DefinitionKind<'_> {
             DefinitionKind::Assignment(assignment) => assignment.name().range(),
             DefinitionKind::AnnotatedAssignment(assign) => assign.target.range(),
             DefinitionKind::AugmentedAssignment(aug_assign) => aug_assign.target.range(),
-            DefinitionKind::For(for_stmt) => for_stmt.target().range(),
+            DefinitionKind::For(for_stmt) => for_stmt.name().range(),
             DefinitionKind::Comprehension(comp) => comp.target().range(),
             DefinitionKind::VariadicPositionalParameter(parameter) => parameter.name.range(),
             DefinitionKind::VariadicKeywordParameter(parameter) => parameter.name.range(),
@@ -490,9 +504,7 @@ impl Ranged for DefinitionKind<'_> {
             DefinitionKind::TypeVarTuple(type_var_tuple) => type_var_tuple.name.range(),
         }
     }
-}
 
-impl DefinitionKind<'_> {
     pub(crate) fn category(&self) -> DefinitionCategory {
         match self {
             // functions, classes, and imports always bind, and we consider them declarations
@@ -665,22 +677,32 @@ impl WithItemDefinitionKind {
 }
 
 #[derive(Clone, Debug)]
-pub struct ForStmtDefinitionKind {
+pub struct ForStmtDefinitionKind<'db> {
+    target: TargetKind<'db>,
     iterable: AstNodeRef<ast::Expr>,
-    target: AstNodeRef<ast::ExprName>,
+    name: AstNodeRef<ast::ExprName>,
+    first: bool,
     is_async: bool,
 }
 
-impl ForStmtDefinitionKind {
+impl<'db> ForStmtDefinitionKind<'db> {
     pub(crate) fn iterable(&self) -> &ast::Expr {
         self.iterable.node()
     }
 
-    pub(crate) fn target(&self) -> &ast::ExprName {
-        self.target.node()
+    pub(crate) fn target(&self) -> TargetKind<'db> {
+        self.target
     }
 
-    pub(crate) fn is_async(&self) -> bool {
+    pub(crate) fn name(&self) -> &ast::ExprName {
+        self.name.node()
+    }
+
+    pub(crate) const fn is_first(&self) -> bool {
+        self.first
+    }
+
+    pub(crate) const fn is_async(&self) -> bool {
         self.is_async
     }
 }
@@ -756,12 +778,6 @@ impl From<&ast::StmtAugAssign> for DefinitionNodeKey {
     }
 }
 
-impl From<&ast::StmtFor> for DefinitionNodeKey {
-    fn from(value: &ast::StmtFor) -> Self {
-        Self(NodeKey::from_node(value))
-    }
-}
-
 impl From<&ast::Parameter> for DefinitionNodeKey {
     fn from(node: &ast::Parameter) -> Self {
         Self(NodeKey::from_node(node))

crates/red_knot_python_semantic/src/semantic_index/symbol.rs

@@ -463,10 +463,7 @@ impl NodeWithScopeKind {
     }
 
     pub fn expect_function(&self) -> &ast::StmtFunctionDef {
-        match self {
-            Self::Function(function) => function.node(),
-            _ => panic!("expected function"),
-        }
+        self.as_function().expect("expected function")
     }
 
     pub fn expect_type_alias(&self) -> &ast::StmtTypeAlias {
@@ -475,6 +472,13 @@ impl NodeWithScopeKind {
             _ => panic!("expected type alias"),
         }
     }
+
+    pub const fn as_function(&self) -> Option<&ast::StmtFunctionDef> {
+        match self {
+            Self::Function(function) => Some(function.node()),
+            _ => None,
+        }
+    }
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]

crates/red_knot_python_semantic/src/semantic_index/use_def.rs

@@ -169,17 +169,11 @@
 //! indexvecs in the [`UseDefMap`].
 //!
 //! There is another special kind of possible "definition" for a symbol: there might be a path from
-//! the scope entry to a given use in which the symbol is never bound.
-//!
-//! The simplest way to model "unbound" would be as a "binding" itself: the initial "binding" for
-//! each symbol in a scope. But actually modeling it this way would unnecessarily increase the
-//! number of [`Definition`]s that Salsa must track. Since "unbound" is special in that all symbols
-//! share it, and it doesn't have any additional per-symbol state, and constraints are irrelevant
-//! to it, we can represent it more efficiently: we use the `may_be_unbound` boolean on the
-//! [`SymbolBindings`] struct. If this flag is `true` for a use of a symbol, it means the symbol
-//! has a path to the use in which it is never bound. If this flag is `false`, it means we've
-//! eliminated the possibility of unbound: every control flow path to the use includes a binding
-//! for this symbol.
+//! the scope entry to a given use in which the symbol is never bound. We model this with a special
+//! "unbound" definition (a `None` entry at the start of the `all_definitions` vector). If that
+//! sentinel definition is present in the live bindings at a given use, it means that there is a
+//! possible path through control flow in which that symbol is unbound. Similarly, if that sentinel
+//! is present in the live declarations, it means that the symbol is (possibly) undeclared.
 //!
 //! To build a [`UseDefMap`], the [`UseDefMapBuilder`] is notified of each new use, definition, and
 //! constraint as they are encountered by the
@@ -190,11 +184,13 @@
 //! end of the scope, it records the state for each symbol as the public definitions of that
 //! symbol.
 //!
-//! Let's walk through the above example. Initially we record for `x` that it has no bindings, and
-//! may be unbound. When we see `x = 1`, we record that as the sole live binding of `x`, and flip
-//! `may_be_unbound` to `false`. Then we see `x = 2`, and we replace `x = 1` as the sole live
-//! binding of `x`. When we get to `y = x`, we record that the live bindings for that use of `x`
-//! are just the `x = 2` definition.
+//! Let's walk through the above example. Initially we do not have any record of `x`. When we add
+//! the new symbol (before we process the first binding), we create a new undefined `SymbolState`
+//! which has a single live binding (the "unbound" definition) and a single live declaration (the
+//! "undeclared" definition). When we see `x = 1`, we record that as the sole live binding of `x`.
+//! The "unbound" binding is no longer visible. Then we see `x = 2`, and we replace `x = 1` as the
+//! sole live binding of `x`. When we get to `y = x`, we record that the live bindings for that use
+//! of `x` are just the `x = 2` definition.
 //!
 //! Then we hit the `if` branch. We visit the `test` node (`flag` in this case), since that will
 //! happen regardless. Then we take a pre-branch snapshot of the current state for all symbols,
@@ -207,8 +203,8 @@
 //! be the pre-if conditions; if we are entering the `else` clause, we know that the `if` test
 //! failed and we didn't execute the `if` body. So we first reset the builder to the pre-if state,
 //! using the snapshot we took previously (meaning we now have `x = 2` as the sole binding for `x`
-//! again), then visit the `else` clause, where `x = 4` replaces `x = 2` as the sole live binding
-//! of `x`.
+//! again), and record a *negative* `flag` constraint for all live bindings (`x = 2`). We then
+//! visit the `else` clause, where `x = 4` replaces `x = 2` as the sole live binding of `x`.
 //!
 //! Now we reach the end of the if/else, and want to visit the following code. The state here needs
 //! to reflect that we might have gone through the `if` branch, or we might have gone through the
@@ -217,18 +213,58 @@
 //! snapshot (which has `x = 3` as the only live binding). The result of this merge is that we now
 //! have two live bindings of `x`: `x = 3` and `x = 4`.
 //!
+//! Another piece of information that the `UseDefMap` needs to provide are visibility constraints.
+//! These are similar to the narrowing constraints, but apply to bindings and declarations within a
+//! control flow path. Consider the following example:
+//! ```py
+//! x = 1
+//! if test:
+//!     x = 2
+//!     y = "y"
+//! ```
+//! In principle, there are two possible control flow paths here. However, if we can statically
+//! infer `test` to be always truthy or always falsy (that is, `__bool__` of `test` is of type
+//! `Literal[True]` or `Literal[False]`), we can rule out one of the possible paths. To support
+//! this feature, we record a visibility constraint of `test` to all live bindings and declarations
+//! *after* visiting the body of the `if` statement. And we record a negative visibility constraint
+//! `~test` to all live bindings/declarations in the (implicit) `else` branch. For the example
+//! above, we would record the following visibility constraints (adding the implicit "unbound"
+//! definitions for clarity):
+//! ```py
+//! x = <unbound>  # not live, shadowed by `x = 1`
+//! y = <unbound>  # visibility constraint: ~test
+//!
+//! x = 1  # visibility constraint: ~test
+//! if test:
+//!     x = 2  # visibility constraint: test
+//!     y = "y"  # visibility constraint: test
+//! ```
+//! When we encounter a use of `x` after this `if` statement, we would record two live bindings: `x
+//! = 1` with a constraint of `~test`, and `x = 2` with a constraint of `test`. In type inference,
+//! when we iterate over all live bindings, we can evaluate these constraints to determine if a
+//! particular binding is actually visible. For example, if `test` is always truthy, we only see
+//! the `x = 2` binding. If `test` is always falsy, we only see the `x = 1` binding. And if the
+//! `__bool__` method of `test` returns type `bool`, we can see both bindings.
+//!
+//! Note that we also record visibility constraints for the start of the scope. This is important
+//! to determine if a symbol is definitely bound, possibly unbound, or definitely unbound. In the
+//! example above, The `y = <unbound>` binding is constrained by `~test`, so `y` would only be
+//! definitely-bound if `test` is always truthy.
+//!
 //! The [`UseDefMapBuilder`] itself just exposes methods for taking a snapshot, resetting to a
 //! snapshot, and merging a snapshot into the current state. The logic using these methods lives in
 //! [`SemanticIndexBuilder`](crate::semantic_index::builder::SemanticIndexBuilder), e.g. where it
 //! visits a `StmtIf` node.
 use self::symbol_state::{
     BindingIdWithConstraintsIterator, ConstraintIdIterator, DeclarationIdIterator,
-    ScopedConstraintId, ScopedDefinitionId, SymbolBindings, SymbolDeclarations, SymbolState,
+    ScopedDefinitionId, SymbolBindings, SymbolDeclarations, SymbolState,
 };
+pub(crate) use self::symbol_state::{ScopedConstraintId, ScopedVisibilityConstraintId};
 use crate::semantic_index::ast_ids::ScopedUseId;
 use crate::semantic_index::definition::Definition;
 use crate::semantic_index::symbol::ScopedSymbolId;
-use crate::symbol::Boundness;
+use crate::semantic_index::use_def::symbol_state::DeclarationIdWithConstraint;
+use crate::visibility_constraints::{VisibilityConstraint, VisibilityConstraints};
 use ruff_index::IndexVec;
 use rustc_hash::FxHashMap;
 
@@ -237,14 +273,20 @@ use super::constraint::Constraint;
 mod bitset;
 mod symbol_state;
 
+type AllConstraints<'db> = IndexVec<ScopedConstraintId, Constraint<'db>>;
+
 /// Applicable definitions and constraints for every use of a name.
 #[derive(Debug, PartialEq, Eq)]
 pub(crate) struct UseDefMap<'db> {
-    /// Array of [`Definition`] in this scope.
-    all_definitions: IndexVec<ScopedDefinitionId, Definition<'db>>,
+    /// Array of [`Definition`] in this scope. Only the first entry should be `None`;
+    /// this represents the implicit "unbound"/"undeclared" definition of every symbol.
+    all_definitions: IndexVec<ScopedDefinitionId, Option<Definition<'db>>>,
 
     /// Array of [`Constraint`] in this scope.
-    all_constraints: IndexVec<ScopedConstraintId, Constraint<'db>>,
+    all_constraints: AllConstraints<'db>,
+
+    /// Array of [`VisibilityConstraint`]s in this scope.
+    visibility_constraints: VisibilityConstraints<'db>,
 
     /// [`SymbolBindings`] reaching a [`ScopedUseId`].
     bindings_by_use: IndexVec<ScopedUseId, SymbolBindings>,
@@ -275,14 +317,6 @@ impl<'db> UseDefMap<'db> {
         self.bindings_iterator(&self.bindings_by_use[use_id])
     }
 
-    pub(crate) fn use_boundness(&self, use_id: ScopedUseId) -> Boundness {
-        if self.bindings_by_use[use_id].may_be_unbound() {
-            Boundness::PossiblyUnbound
-        } else {
-            Boundness::Bound
-        }
-    }
-
     pub(crate) fn public_bindings(
         &self,
         symbol: ScopedSymbolId,
@@ -290,14 +324,6 @@ impl<'db> UseDefMap<'db> {
         self.bindings_iterator(self.public_symbols[symbol].bindings())
     }
 
-    pub(crate) fn public_boundness(&self, symbol: ScopedSymbolId) -> Boundness {
-        if self.public_symbols[symbol].may_be_unbound() {
-            Boundness::PossiblyUnbound
-        } else {
-            Boundness::Bound
-        }
-    }
-
     pub(crate) fn bindings_at_declaration(
         &self,
         declaration: Definition<'db>,
@@ -310,10 +336,10 @@ impl<'db> UseDefMap<'db> {
         }
     }
 
-    pub(crate) fn declarations_at_binding(
-        &self,
+    pub(crate) fn declarations_at_binding<'map>(
+        &'map self,
         binding: Definition<'db>,
-    ) -> DeclarationsIterator<'_, 'db> {
+    ) -> DeclarationsIterator<'map, 'db> {
         if let SymbolDefinitions::Declarations(declarations) =
             &self.definitions_by_definition[&binding]
         {
@@ -323,37 +349,34 @@ impl<'db> UseDefMap<'db> {
         }
     }
 
-    pub(crate) fn public_declarations(
-        &self,
+    pub(crate) fn public_declarations<'map>(
+        &'map self,
         symbol: ScopedSymbolId,
-    ) -> DeclarationsIterator<'_, 'db> {
+    ) -> DeclarationsIterator<'map, 'db> {
         let declarations = self.public_symbols[symbol].declarations();
         self.declarations_iterator(declarations)
     }
 
-    pub(crate) fn has_public_declarations(&self, symbol: ScopedSymbolId) -> bool {
-        !self.public_symbols[symbol].declarations().is_empty()
-    }
-
-    fn bindings_iterator<'a>(
-        &'a self,
-        bindings: &'a SymbolBindings,
-    ) -> BindingWithConstraintsIterator<'a, 'db> {
+    fn bindings_iterator<'map>(
+        &'map self,
+        bindings: &'map SymbolBindings,
+    ) -> BindingWithConstraintsIterator<'map, 'db> {
         BindingWithConstraintsIterator {
             all_definitions: &self.all_definitions,
             all_constraints: &self.all_constraints,
+            visibility_constraints: &self.visibility_constraints,
             inner: bindings.iter(),
         }
     }
 
-    fn declarations_iterator<'a>(
-        &'a self,
-        declarations: &'a SymbolDeclarations,
-    ) -> DeclarationsIterator<'a, 'db> {
+    fn declarations_iterator<'map>(
+        &'map self,
+        declarations: &'map SymbolDeclarations,
+    ) -> DeclarationsIterator<'map, 'db> {
         DeclarationsIterator {
             all_definitions: &self.all_definitions,
+            visibility_constraints: &self.visibility_constraints,
             inner: declarations.iter(),
-            may_be_undeclared: declarations.may_be_undeclared(),
         }
     }
 }
@@ -367,8 +390,9 @@ enum SymbolDefinitions {
 
 #[derive(Debug)]
 pub(crate) struct BindingWithConstraintsIterator<'map, 'db> {
-    all_definitions: &'map IndexVec<ScopedDefinitionId, Definition<'db>>,
-    all_constraints: &'map IndexVec<ScopedConstraintId, Constraint<'db>>,
+    all_definitions: &'map IndexVec<ScopedDefinitionId, Option<Definition<'db>>>,
+    all_constraints: &'map AllConstraints<'db>,
+    pub(crate) visibility_constraints: &'map VisibilityConstraints<'db>,
     inner: BindingIdWithConstraintsIterator<'map>,
 }
 
@@ -376,14 +400,17 @@ impl<'map, 'db> Iterator for BindingWithConstraintsIterator<'map, 'db> {
     type Item = BindingWithConstraints<'map, 'db>;
 
     fn next(&mut self) -> Option<Self::Item> {
+        let all_constraints = self.all_constraints;
+
         self.inner
             .next()
-            .map(|def_id_with_constraints| BindingWithConstraints {
-                binding: self.all_definitions[def_id_with_constraints.definition],
+            .map(|binding_id_with_constraints| BindingWithConstraints {
+                binding: self.all_definitions[binding_id_with_constraints.definition],
                 constraints: ConstraintsIterator {
-                    all_constraints: self.all_constraints,
-                    constraint_ids: def_id_with_constraints.constraint_ids,
+                    all_constraints,
+                    constraint_ids: binding_id_with_constraints.constraint_ids,
                 },
+                visibility_constraint: binding_id_with_constraints.visibility_constraint,
             })
     }
 }
@@ -391,12 +418,13 @@ impl<'map, 'db> Iterator for BindingWithConstraintsIterator<'map, 'db> {
 impl std::iter::FusedIterator for BindingWithConstraintsIterator<'_, '_> {}
 
 pub(crate) struct BindingWithConstraints<'map, 'db> {
-    pub(crate) binding: Definition<'db>,
+    pub(crate) binding: Option<Definition<'db>>,
     pub(crate) constraints: ConstraintsIterator<'map, 'db>,
+    pub(crate) visibility_constraint: ScopedVisibilityConstraintId,
 }
 
 pub(crate) struct ConstraintsIterator<'map, 'db> {
-    all_constraints: &'map IndexVec<ScopedConstraintId, Constraint<'db>>,
+    all_constraints: &'map AllConstraints<'db>,
     constraint_ids: ConstraintIdIterator<'map>,
 }
 
@@ -413,22 +441,31 @@ impl<'db> Iterator for ConstraintsIterator<'_, 'db> {
 impl std::iter::FusedIterator for ConstraintsIterator<'_, '_> {}
 
 pub(crate) struct DeclarationsIterator<'map, 'db> {
-    all_definitions: &'map IndexVec<ScopedDefinitionId, Definition<'db>>,
+    all_definitions: &'map IndexVec<ScopedDefinitionId, Option<Definition<'db>>>,
+    pub(crate) visibility_constraints: &'map VisibilityConstraints<'db>,
     inner: DeclarationIdIterator<'map>,
-    may_be_undeclared: bool,
 }
 
-impl DeclarationsIterator<'_, '_> {
-    pub(crate) fn may_be_undeclared(&self) -> bool {
-        self.may_be_undeclared
-    }
+pub(crate) struct DeclarationWithConstraint<'db> {
+    pub(crate) declaration: Option<Definition<'db>>,
+    pub(crate) visibility_constraint: ScopedVisibilityConstraintId,
 }
 
 impl<'db> Iterator for DeclarationsIterator<'_, 'db> {
-    type Item = Definition<'db>;
+    type Item = DeclarationWithConstraint<'db>;
 
     fn next(&mut self) -> Option<Self::Item> {
-        self.inner.next().map(|def_id| self.all_definitions[def_id])
+        self.inner.next().map(
+            |DeclarationIdWithConstraint {
+                 definition,
+                 visibility_constraint,
+             }| {
+                DeclarationWithConstraint {
+                    declaration: self.all_definitions[definition],
+                    visibility_constraint,
+                }
+            },
+        )
     }
 }
 
@@ -438,15 +475,25 @@ impl std::iter::FusedIterator for DeclarationsIterator<'_, '_> {}
 #[derive(Clone, Debug)]
 pub(super) struct FlowSnapshot {
     symbol_states: IndexVec<ScopedSymbolId, SymbolState>,
+    scope_start_visibility: ScopedVisibilityConstraintId,
 }
 
-#[derive(Debug, Default)]
+#[derive(Debug)]
 pub(super) struct UseDefMapBuilder<'db> {
     /// Append-only array of [`Definition`].
-    all_definitions: IndexVec<ScopedDefinitionId, Definition<'db>>,
+    all_definitions: IndexVec<ScopedDefinitionId, Option<Definition<'db>>>,
 
     /// Append-only array of [`Constraint`].
-    all_constraints: IndexVec<ScopedConstraintId, Constraint<'db>>,
+    all_constraints: AllConstraints<'db>,
+
+    /// Append-only array of [`VisibilityConstraint`].
+    visibility_constraints: VisibilityConstraints<'db>,
+
+    /// A constraint which describes the visibility of the unbound/undeclared state, i.e.
+    /// whether or not the start of the scope is visible. This is important for cases like
+    /// `if True: x = 1; use(x)` where we need to hide the implicit "x = unbound" binding
+    /// in the "else" branch.
+    scope_start_visibility: ScopedVisibilityConstraintId,
 
     /// Live bindings at each so-far-recorded use.
     bindings_by_use: IndexVec<ScopedUseId, SymbolBindings>,
@@ -458,14 +505,30 @@ pub(super) struct UseDefMapBuilder<'db> {
     symbol_states: IndexVec<ScopedSymbolId, SymbolState>,
 }
 
+impl Default for UseDefMapBuilder<'_> {
+    fn default() -> Self {
+        Self {
+            all_definitions: IndexVec::from_iter([None]),
+            all_constraints: IndexVec::new(),
+            visibility_constraints: VisibilityConstraints::default(),
+            scope_start_visibility: ScopedVisibilityConstraintId::ALWAYS_TRUE,
+            bindings_by_use: IndexVec::new(),
+            definitions_by_definition: FxHashMap::default(),
+            symbol_states: IndexVec::new(),
+        }
+    }
+}
+
 impl<'db> UseDefMapBuilder<'db> {
     pub(super) fn add_symbol(&mut self, symbol: ScopedSymbolId) {
-        let new_symbol = self.symbol_states.push(SymbolState::undefined());
+        let new_symbol = self
+            .symbol_states
+            .push(SymbolState::undefined(self.scope_start_visibility));
         debug_assert_eq!(symbol, new_symbol);
     }
 
     pub(super) fn record_binding(&mut self, symbol: ScopedSymbolId, binding: Definition<'db>) {
-        let def_id = self.all_definitions.push(binding);
+        let def_id = self.all_definitions.push(Some(binding));
         let symbol_state = &mut self.symbol_states[symbol];
         self.definitions_by_definition.insert(
             binding,
@@ -474,10 +537,82 @@ impl<'db> UseDefMapBuilder<'db> {
         symbol_state.record_binding(def_id);
     }
 
-    pub(super) fn record_constraint(&mut self, constraint: Constraint<'db>) {
-        let constraint_id = self.all_constraints.push(constraint);
+    pub(super) fn add_constraint(&mut self, constraint: Constraint<'db>) -> ScopedConstraintId {
+        self.all_constraints.push(constraint)
+    }
+
+    pub(super) fn record_constraint_id(&mut self, constraint: ScopedConstraintId) {
         for state in &mut self.symbol_states {
-            state.record_constraint(constraint_id);
+            state.record_constraint(constraint);
+        }
+    }
+
+    pub(super) fn record_constraint(&mut self, constraint: Constraint<'db>) -> ScopedConstraintId {
+        let new_constraint_id = self.add_constraint(constraint);
+        self.record_constraint_id(new_constraint_id);
+        new_constraint_id
+    }
+
+    pub(super) fn add_visibility_constraint(
+        &mut self,
+        constraint: VisibilityConstraint<'db>,
+    ) -> ScopedVisibilityConstraintId {
+        self.visibility_constraints.add(constraint)
+    }
+
+    pub(super) fn record_visibility_constraint_id(
+        &mut self,
+        constraint: ScopedVisibilityConstraintId,
+    ) {
+        for state in &mut self.symbol_states {
+            state.record_visibility_constraint(&mut self.visibility_constraints, constraint);
+        }
+
+        self.scope_start_visibility = self
+            .visibility_constraints
+            .add_and_constraint(self.scope_start_visibility, constraint);
+    }
+
+    pub(super) fn record_visibility_constraint(
+        &mut self,
+        constraint: VisibilityConstraint<'db>,
+    ) -> ScopedVisibilityConstraintId {
+        let new_constraint_id = self.add_visibility_constraint(constraint);
+        self.record_visibility_constraint_id(new_constraint_id);
+        new_constraint_id
+    }
+
+    /// This method resets the visibility constraints for all symbols to a previous state
+    /// *if* there have been no new declarations or bindings since then. Consider the
+    /// following example:
+    /// ```py
+    /// x = 0
+    /// y = 0
+    /// if test_a:
+    ///     y = 1
+    /// elif test_b:
+    ///     y = 2
+    /// elif test_c:
+    ///    y = 3
+    ///
+    /// # RESET
+    /// ```
+    /// We build a complex visibility constraint for the `y = 0` binding. We build the same
+    /// constraint for the `x = 0` binding as well, but at the `RESET` point, we can get rid
+    /// of it, as the `if`-`elif`-`elif` chain doesn't include any new bindings of `x`.
+    pub(super) fn simplify_visibility_constraints(&mut self, snapshot: FlowSnapshot) {
+        debug_assert!(self.symbol_states.len() >= snapshot.symbol_states.len());
+
+        self.scope_start_visibility = snapshot.scope_start_visibility;
+
+        // Note that this loop terminates when we reach a symbol not present in the snapshot.
+        // This means we keep visibility constraints for all new symbols, which is intended,
+        // since these symbols have been introduced in the corresponding branch, which might
+        // be subject to visibility constraints. We only simplify/reset visibility constraints
+        // for symbols that have the same bindings and declarations present compared to the
+        // snapshot.
+        for (current, snapshot) in self.symbol_states.iter_mut().zip(snapshot.symbol_states) {
+            current.simplify_visibility_constraints(snapshot);
         }
     }
 
@@ -486,7 +621,7 @@ impl<'db> UseDefMapBuilder<'db> {
         symbol: ScopedSymbolId,
         declaration: Definition<'db>,
     ) {
-        let def_id = self.all_definitions.push(declaration);
+        let def_id = self.all_definitions.push(Some(declaration));
         let symbol_state = &mut self.symbol_states[symbol];
         self.definitions_by_definition.insert(
             declaration,
@@ -501,7 +636,7 @@ impl<'db> UseDefMapBuilder<'db> {
         definition: Definition<'db>,
     ) {
         // We don't need to store anything in self.definitions_by_definition.
-        let def_id = self.all_definitions.push(definition);
+        let def_id = self.all_definitions.push(Some(definition));
         let symbol_state = &mut self.symbol_states[symbol];
         symbol_state.record_declaration(def_id);
         symbol_state.record_binding(def_id);
@@ -520,6 +655,7 @@ impl<'db> UseDefMapBuilder<'db> {
     pub(super) fn snapshot(&self) -> FlowSnapshot {
         FlowSnapshot {
             symbol_states: self.symbol_states.clone(),
+            scope_start_visibility: self.scope_start_visibility,
         }
     }
 
@@ -533,12 +669,15 @@ impl<'db> UseDefMapBuilder<'db> {
 
         // Restore the current visible-definitions state to the given snapshot.
         self.symbol_states = snapshot.symbol_states;
+        self.scope_start_visibility = snapshot.scope_start_visibility;
 
         // If the snapshot we are restoring is missing some symbols we've recorded since, we need
         // to fill them in so the symbol IDs continue to line up. Since they don't exist in the
         // snapshot, the correct state to fill them in with is "undefined".
-        self.symbol_states
-            .resize(num_symbols, SymbolState::undefined());
+        self.symbol_states.resize(
+            num_symbols,
+            SymbolState::undefined(self.scope_start_visibility),
+        );
     }
 
     /// Merge the given snapshot into the current state, reflecting that we might have taken either
@@ -553,13 +692,19 @@ impl<'db> UseDefMapBuilder<'db> {
         let mut snapshot_definitions_iter = snapshot.symbol_states.into_iter();
         for current in &mut self.symbol_states {
             if let Some(snapshot) = snapshot_definitions_iter.next() {
-                current.merge(snapshot);
+                current.merge(snapshot, &mut self.visibility_constraints);
             } else {
+                current.merge(
+                    SymbolState::undefined(snapshot.scope_start_visibility),
+                    &mut self.visibility_constraints,
+                );
                 // Symbol not present in snapshot, so it's unbound/undeclared from that path.
-                current.set_may_be_unbound();
-                current.set_may_be_undeclared();
             }
         }
+
+        self.scope_start_visibility = self
+            .visibility_constraints
+            .add_or_constraint(self.scope_start_visibility, snapshot.scope_start_visibility);
     }
 
     pub(super) fn finish(mut self) -> UseDefMap<'db> {
@@ -572,6 +717,7 @@ impl<'db> UseDefMapBuilder<'db> {
         UseDefMap {
             all_definitions: self.all_definitions,
             all_constraints: self.all_constraints,
+            visibility_constraints: self.visibility_constraints,
             bindings_by_use: self.bindings_by_use,
             public_symbols: self.symbol_states,
             definitions_by_definition: self.definitions_by_definition,

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

@@ -32,10 +32,6 @@ impl<const B: usize> BitSet<B> {
         bitset
     }
 
-    pub(super) fn is_empty(&self) -> bool {
-        self.blocks().iter().all(|&b| b == 0)
-    }
-
     /// Convert from Inline to Heap, if needed, and resize the Heap vector, if needed.
     fn resize(&mut self, value: u32) {
         let num_blocks_needed = (value / 64) + 1;
@@ -97,19 +93,6 @@ impl<const B: usize> BitSet<B> {
         }
     }
 
-    /// Union in-place with another [`BitSet`].
-    pub(super) fn union(&mut self, other: &BitSet<B>) {
-        let mut max_len = self.blocks().len();
-        let other_len = other.blocks().len();
-        if other_len > max_len {
-            max_len = other_len;
-            self.resize_blocks(max_len);
-        }
-        for (my_block, other_block) in self.blocks_mut().iter_mut().zip(other.blocks()) {
-            *my_block |= other_block;
-        }
-    }
-
     /// Return an iterator over the values (in ascending order) in this [`BitSet`].
     pub(super) fn iter(&self) -> BitSetIterator<'_, B> {
         let blocks = self.blocks();
@@ -239,59 +222,6 @@ mod tests {
         assert_bitset(&b1, &[89]);
     }
 
-    #[test]
-    fn union() {
-        let mut b1 = BitSet::<1>::with(2);
-        let b2 = BitSet::<1>::with(4);
-
-        b1.union(&b2);
-        assert_bitset(&b1, &[2, 4]);
-    }
-
-    #[test]
-    fn union_mixed_1() {
-        let mut b1 = BitSet::<1>::with(4);
-        let mut b2 = BitSet::<1>::with(4);
-        b1.insert(89);
-        b2.insert(5);
-
-        b1.union(&b2);
-        assert_bitset(&b1, &[4, 5, 89]);
-    }
-
-    #[test]
-    fn union_mixed_2() {
-        let mut b1 = BitSet::<1>::with(4);
-        let mut b2 = BitSet::<1>::with(4);
-        b1.insert(23);
-        b2.insert(89);
-
-        b1.union(&b2);
-        assert_bitset(&b1, &[4, 23, 89]);
-    }
-
-    #[test]
-    fn union_heap() {
-        let mut b1 = BitSet::<1>::with(4);
-        let mut b2 = BitSet::<1>::with(4);
-        b1.insert(89);
-        b2.insert(90);
-
-        b1.union(&b2);
-        assert_bitset(&b1, &[4, 89, 90]);
-    }
-
-    #[test]
-    fn union_heap_2() {
-        let mut b1 = BitSet::<1>::with(89);
-        let mut b2 = BitSet::<1>::with(89);
-        b1.insert(91);
-        b2.insert(90);
-
-        b1.union(&b2);
-        assert_bitset(&b1, &[89, 90, 91]);
-    }
-
     #[test]
     fn multiple_blocks() {
         let mut b = BitSet::<2>::with(120);
@@ -299,11 +229,4 @@ mod tests {
         assert!(matches!(b, BitSet::Inline(_)));
         assert_bitset(&b, &[45, 120]);
     }
-
-    #[test]
-    fn empty() {
-        let b = BitSet::<1>::default();
-
-        assert!(b.is_empty());
-    }
 }

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

@@ -43,6 +43,8 @@
 //!
 //! Tracking live declarations is simpler, since constraints are not involved, but otherwise very
 //! similar to tracking live bindings.
+use crate::semantic_index::use_def::VisibilityConstraints;
+
 use super::bitset::{BitSet, BitSetIterator};
 use ruff_index::newtype_index;
 use smallvec::SmallVec;
@@ -51,9 +53,18 @@ use smallvec::SmallVec;
 #[newtype_index]
 pub(super) struct ScopedDefinitionId;
 
+impl ScopedDefinitionId {
+    /// A special ID that is used to describe an implicit start-of-scope state. When
+    /// we see that this definition is live, we know that the symbol is (possibly)
+    /// unbound or undeclared at a given usage site.
+    /// When creating a use-def-map builder, we always add an empty `None` definition
+    /// at index 0, so this ID is always present.
+    pub(super) const UNBOUND: ScopedDefinitionId = ScopedDefinitionId::from_u32(0);
+}
+
 /// A newtype-index for a constraint expression in a particular scope.
 #[newtype_index]
-pub(super) struct ScopedConstraintId;
+pub(crate) struct ScopedConstraintId;
 
 /// Can reference this * 64 total definitions inline; more will fall back to the heap.
 const INLINE_BINDING_BLOCKS: usize = 3;
@@ -75,58 +86,97 @@ const INLINE_CONSTRAINT_BLOCKS: usize = 2;
 /// Can keep inline this many live bindings per symbol at a given time; more will go to heap.
 const INLINE_BINDINGS_PER_SYMBOL: usize = 4;
 
-/// One [`BitSet`] of applicable [`ScopedConstraintId`] per live binding.
-type InlineConstraintArray = [BitSet<INLINE_CONSTRAINT_BLOCKS>; INLINE_BINDINGS_PER_SYMBOL];
-type Constraints = SmallVec<InlineConstraintArray>;
-type ConstraintsIterator<'a> = std::slice::Iter<'a, BitSet<INLINE_CONSTRAINT_BLOCKS>>;
+/// Which constraints apply to a given binding?
+type Constraints = BitSet<INLINE_CONSTRAINT_BLOCKS>;
+
+type InlineConstraintArray = [Constraints; INLINE_BINDINGS_PER_SYMBOL];
+
+/// One [`BitSet`] of applicable [`ScopedConstraintId`]s per live binding.
+type ConstraintsPerBinding = SmallVec<InlineConstraintArray>;
+
+/// Iterate over all constraints for a single binding.
+type ConstraintsIterator<'a> = std::slice::Iter<'a, Constraints>;
 type ConstraintsIntoIterator = smallvec::IntoIter<InlineConstraintArray>;
 
-/// Live declarations for a single symbol at some point in control flow.
+/// A newtype-index for a visibility constraint in a particular scope.
+#[newtype_index]
+pub(crate) struct ScopedVisibilityConstraintId;
+
+impl ScopedVisibilityConstraintId {
+    /// A special ID that is used for an "always true" / "always visible" constraint.
+    /// When we create a new [`VisibilityConstraints`] object, this constraint is always
+    /// present at index 0.
+    pub(crate) const ALWAYS_TRUE: ScopedVisibilityConstraintId =
+        ScopedVisibilityConstraintId::from_u32(0);
+}
+
+const INLINE_VISIBILITY_CONSTRAINTS: usize = 4;
+type InlineVisibilityConstraintsArray =
+    [ScopedVisibilityConstraintId; INLINE_VISIBILITY_CONSTRAINTS];
+
+/// One [`ScopedVisibilityConstraintId`] per live declaration.
+type VisibilityConstraintPerDeclaration = SmallVec<InlineVisibilityConstraintsArray>;
+
+/// One [`ScopedVisibilityConstraintId`] per live binding.
+type VisibilityConstraintPerBinding = SmallVec<InlineVisibilityConstraintsArray>;
+
+/// Iterator over the visibility constraints for all live bindings/declarations.
+type VisibilityConstraintsIterator<'a> = std::slice::Iter<'a, ScopedVisibilityConstraintId>;
+
+type VisibilityConstraintsIntoIterator = smallvec::IntoIter<InlineVisibilityConstraintsArray>;
+
+/// Live declarations for a single symbol at some point in control flow, with their
+/// corresponding visibility constraints.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub(super) struct SymbolDeclarations {
     /// [`BitSet`]: which declarations (as [`ScopedDefinitionId`]) can reach the current location?
-    live_declarations: Declarations,
+    pub(crate) live_declarations: Declarations,
 
-    /// Could the symbol be un-declared at this point?
-    may_be_undeclared: bool,
+    /// For each live declaration, which visibility constraint applies to it?
+    pub(crate) visibility_constraints: VisibilityConstraintPerDeclaration,
 }
 
 impl SymbolDeclarations {
-    fn undeclared() -> Self {
+    fn undeclared(scope_start_visibility: ScopedVisibilityConstraintId) -> Self {
         Self {
-            live_declarations: Declarations::default(),
-            may_be_undeclared: true,
+            live_declarations: Declarations::with(0),
+            visibility_constraints: VisibilityConstraintPerDeclaration::from_iter([
+                scope_start_visibility,
+            ]),
         }
     }
 
     /// Record a newly-encountered declaration for this symbol.
     fn record_declaration(&mut self, declaration_id: ScopedDefinitionId) {
         self.live_declarations = Declarations::with(declaration_id.into());
-        self.may_be_undeclared = false;
+
+        self.visibility_constraints = VisibilityConstraintPerDeclaration::with_capacity(1);
+        self.visibility_constraints
+            .push(ScopedVisibilityConstraintId::ALWAYS_TRUE);
     }
 
-    /// Add undeclared as a possibility for this symbol.
-    fn set_may_be_undeclared(&mut self) {
-        self.may_be_undeclared = true;
+    /// Add given visibility constraint to all live declarations.
+    pub(super) fn record_visibility_constraint(
+        &mut self,
+        visibility_constraints: &mut VisibilityConstraints,
+        constraint: ScopedVisibilityConstraintId,
+    ) {
+        for existing in &mut self.visibility_constraints {
+            *existing = visibility_constraints.add_and_constraint(*existing, constraint);
+        }
     }
 
     /// Return an iterator over live declarations for this symbol.
     pub(super) fn iter(&self) -> DeclarationIdIterator {
         DeclarationIdIterator {
-            inner: self.live_declarations.iter(),
+            declarations: self.live_declarations.iter(),
+            visibility_constraints: self.visibility_constraints.iter(),
         }
     }
-
-    pub(super) fn is_empty(&self) -> bool {
-        self.live_declarations.is_empty()
-    }
-
-    pub(super) fn may_be_undeclared(&self) -> bool {
-        self.may_be_undeclared
-    }
 }
 
-/// Live bindings and narrowing constraints for a single symbol at some point in control flow.
+/// Live bindings for a single symbol at some point in control flow. Each live binding comes
+/// with a set of narrowing constraints and a visibility constraint.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub(super) struct SymbolBindings {
     /// [`BitSet`]: which bindings (as [`ScopedDefinitionId`]) can reach the current location?
@@ -136,34 +186,34 @@ pub(super) struct SymbolBindings {
     ///
     /// This is a [`smallvec::SmallVec`] which should always have one [`BitSet`] of constraints per
     /// binding in `live_bindings`.
-    constraints: Constraints,
+    constraints: ConstraintsPerBinding,
 
-    /// Could the symbol be unbound at this point?
-    may_be_unbound: bool,
+    /// For each live binding, which visibility constraint applies to it?
+    visibility_constraints: VisibilityConstraintPerBinding,
 }
 
 impl SymbolBindings {
-    fn unbound() -> Self {
+    fn unbound(scope_start_visibility: ScopedVisibilityConstraintId) -> Self {
         Self {
-            live_bindings: Bindings::default(),
-            constraints: Constraints::default(),
-            may_be_unbound: true,
+            live_bindings: Bindings::with(ScopedDefinitionId::UNBOUND.as_u32()),
+            constraints: ConstraintsPerBinding::from_iter([Constraints::default()]),
+            visibility_constraints: VisibilityConstraintPerBinding::from_iter([
+                scope_start_visibility,
+            ]),
         }
     }
 
-    /// Add Unbound as a possibility for this symbol.
-    fn set_may_be_unbound(&mut self) {
-        self.may_be_unbound = true;
-    }
-
     /// Record a newly-encountered binding for this symbol.
     pub(super) fn record_binding(&mut self, binding_id: ScopedDefinitionId) {
         // The new binding replaces all previous live bindings in this path, and has no
         // constraints.
         self.live_bindings = Bindings::with(binding_id.into());
-        self.constraints = Constraints::with_capacity(1);
-        self.constraints.push(BitSet::default());
-        self.may_be_unbound = false;
+        self.constraints = ConstraintsPerBinding::with_capacity(1);
+        self.constraints.push(Constraints::default());
+
+        self.visibility_constraints = VisibilityConstraintPerBinding::with_capacity(1);
+        self.visibility_constraints
+            .push(ScopedVisibilityConstraintId::ALWAYS_TRUE);
     }
 
     /// Add given constraint to all live bindings.
@@ -173,17 +223,25 @@ impl SymbolBindings {
         }
     }
 
-    /// Iterate over currently live bindings for this symbol.
+    /// Add given visibility constraint to all live bindings.
+    pub(super) fn record_visibility_constraint(
+        &mut self,
+        visibility_constraints: &mut VisibilityConstraints,
+        constraint: ScopedVisibilityConstraintId,
+    ) {
+        for existing in &mut self.visibility_constraints {
+            *existing = visibility_constraints.add_and_constraint(*existing, constraint);
+        }
+    }
+
+    /// Iterate over currently live bindings for this symbol
     pub(super) fn iter(&self) -> BindingIdWithConstraintsIterator {
         BindingIdWithConstraintsIterator {
             definitions: self.live_bindings.iter(),
             constraints: self.constraints.iter(),
+            visibility_constraints: self.visibility_constraints.iter(),
         }
     }
-
-    pub(super) fn may_be_unbound(&self) -> bool {
-        self.may_be_unbound
-    }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
@@ -194,20 +252,16 @@ pub(super) struct SymbolState {
 
 impl SymbolState {
     /// Return a new [`SymbolState`] representing an unbound, undeclared symbol.
-    pub(super) fn undefined() -> Self {
+    pub(super) fn undefined(scope_start_visibility: ScopedVisibilityConstraintId) -> Self {
         Self {
-            declarations: SymbolDeclarations::undeclared(),
-            bindings: SymbolBindings::unbound(),
+            declarations: SymbolDeclarations::undeclared(scope_start_visibility),
+            bindings: SymbolBindings::unbound(scope_start_visibility),
         }
     }
 
-    /// Add Unbound as a possibility for this symbol.
-    pub(super) fn set_may_be_unbound(&mut self) {
-        self.bindings.set_may_be_unbound();
-    }
-
     /// Record a newly-encountered binding for this symbol.
     pub(super) fn record_binding(&mut self, binding_id: ScopedDefinitionId) {
+        debug_assert_ne!(binding_id, ScopedDefinitionId::UNBOUND);
         self.bindings.record_binding(binding_id);
     }
 
@@ -216,9 +270,26 @@ impl SymbolState {
         self.bindings.record_constraint(constraint_id);
     }
 
-    /// Add undeclared as a possibility for this symbol.
-    pub(super) fn set_may_be_undeclared(&mut self) {
-        self.declarations.set_may_be_undeclared();
+    /// Add given visibility constraint to all live bindings.
+    pub(super) fn record_visibility_constraint(
+        &mut self,
+        visibility_constraints: &mut VisibilityConstraints,
+        constraint: ScopedVisibilityConstraintId,
+    ) {
+        self.bindings
+            .record_visibility_constraint(visibility_constraints, constraint);
+        self.declarations
+            .record_visibility_constraint(visibility_constraints, constraint);
+    }
+
+    pub(super) fn simplify_visibility_constraints(&mut self, snapshot_state: SymbolState) {
+        if self.bindings.live_bindings == snapshot_state.bindings.live_bindings {
+            self.bindings.visibility_constraints = snapshot_state.bindings.visibility_constraints;
+        }
+        if self.declarations.live_declarations == snapshot_state.declarations.live_declarations {
+            self.declarations.visibility_constraints =
+                snapshot_state.declarations.visibility_constraints;
+        }
     }
 
     /// Record a newly-encountered declaration of this symbol.
@@ -227,29 +298,31 @@ impl SymbolState {
     }
 
     /// Merge another [`SymbolState`] into this one.
-    pub(super) fn merge(&mut self, b: SymbolState) {
+    pub(super) fn merge(
+        &mut self,
+        b: SymbolState,
+        visibility_constraints: &mut VisibilityConstraints,
+    ) {
         let mut a = Self {
             bindings: SymbolBindings {
                 live_bindings: Bindings::default(),
-                constraints: Constraints::default(),
-                may_be_unbound: self.bindings.may_be_unbound || b.bindings.may_be_unbound,
+                constraints: ConstraintsPerBinding::default(),
+                visibility_constraints: VisibilityConstraintPerBinding::default(),
             },
             declarations: SymbolDeclarations {
                 live_declarations: self.declarations.live_declarations.clone(),
-                may_be_undeclared: self.declarations.may_be_undeclared
-                    || b.declarations.may_be_undeclared,
+                visibility_constraints: VisibilityConstraintPerDeclaration::default(),
             },
         };
 
         std::mem::swap(&mut a, self);
-        self.declarations
-            .live_declarations
-            .union(&b.declarations.live_declarations);
 
         let mut a_defs_iter = a.bindings.live_bindings.iter();
         let mut b_defs_iter = b.bindings.live_bindings.iter();
         let mut a_constraints_iter = a.bindings.constraints.into_iter();
         let mut b_constraints_iter = b.bindings.constraints.into_iter();
+        let mut a_vis_constraints_iter = a.bindings.visibility_constraints.into_iter();
+        let mut b_vis_constraints_iter = b.bindings.visibility_constraints.into_iter();
 
         let mut opt_a_def: Option<u32> = a_defs_iter.next();
         let mut opt_b_def: Option<u32> = b_defs_iter.next();
@@ -261,17 +334,30 @@ impl SymbolState {
         // path is irrelevant.
 
         // Helper to push `def`, with constraints in `constraints_iter`, onto `self`.
-        let push = |def, constraints_iter: &mut ConstraintsIntoIterator, merged: &mut Self| {
+        let push = |def,
+                    constraints_iter: &mut ConstraintsIntoIterator,
+                    visibility_constraints_iter: &mut VisibilityConstraintsIntoIterator,
+                    merged: &mut Self| {
             merged.bindings.live_bindings.insert(def);
-            // SAFETY: we only ever create SymbolState with either no definitions and no constraint
-            // bitsets (`::unbound`) or one definition and one constraint bitset (`::with`), and
-            // `::merge` always pushes one definition and one constraint bitset together (just
-            // below), so the number of definitions and the number of constraint bitsets can never
+            // SAFETY: we only ever create SymbolState using [`SymbolState::undefined`], which adds
+            // one "unbound" definition with corresponding narrowing and visibility constraints, or
+            // using [`SymbolState::record_binding`] or [`SymbolState::record_declaration`], which
+            // similarly add one definition with corresponding constraints. [`SymbolState::merge`]
+            // always pushes one definition and one constraint bitset and one visibility constraint
+            // together (just below), so the number of definitions and the number of constraints can
+            // never get out of sync.
             // get out of sync.
             let constraints = constraints_iter
                 .next()
                 .expect("definitions and constraints length mismatch");
+            let visibility_constraints = visibility_constraints_iter
+                .next()
+                .expect("definitions and visibility_constraints length mismatch");
             merged.bindings.constraints.push(constraints);
+            merged
+                .bindings
+                .visibility_constraints
+                .push(visibility_constraints);
         };
 
         loop {
@@ -279,50 +365,139 @@ impl SymbolState {
                 (Some(a_def), Some(b_def)) => match a_def.cmp(&b_def) {
                     std::cmp::Ordering::Less => {
                         // Next definition ID is only in `a`, push it to `self` and advance `a`.
-                        push(a_def, &mut a_constraints_iter, self);
+                        push(
+                            a_def,
+                            &mut a_constraints_iter,
+                            &mut a_vis_constraints_iter,
+                            self,
+                        );
                         opt_a_def = a_defs_iter.next();
                     }
                     std::cmp::Ordering::Greater => {
                         // Next definition ID is only in `b`, push it to `self` and advance `b`.
-                        push(b_def, &mut b_constraints_iter, self);
+                        push(
+                            b_def,
+                            &mut b_constraints_iter,
+                            &mut b_vis_constraints_iter,
+                            self,
+                        );
                         opt_b_def = b_defs_iter.next();
                     }
                     std::cmp::Ordering::Equal => {
                         // Next definition is in both; push to `self` and intersect constraints.
-                        push(a_def, &mut b_constraints_iter, self);
-                        // SAFETY: we only ever create SymbolState with either no definitions and
-                        // no constraint bitsets (`::unbound`) or one definition and one constraint
-                        // bitset (`::with`), and `::merge` always pushes one definition and one
-                        // constraint bitset together (just below), so the number of definitions
-                        // and the number of constraint bitsets can never get out of sync.
+                        push(
+                            a_def,
+                            &mut b_constraints_iter,
+                            &mut b_vis_constraints_iter,
+                            self,
+                        );
+
+                        // SAFETY: see comment in `push` above.
                         let a_constraints = a_constraints_iter
                             .next()
                             .expect("definitions and constraints length mismatch");
+                        let current_constraints = self.bindings.constraints.last_mut().unwrap();
+
                         // If the same definition is visible through both paths, any constraint
                         // that applies on only one path is irrelevant to the resulting type from
                         // unioning the two paths, so we intersect the constraints.
-                        self.bindings
-                            .constraints
-                            .last_mut()
-                            .unwrap()
-                            .intersect(&a_constraints);
+                        current_constraints.intersect(&a_constraints);
+
+                        // For visibility constraints, we merge them using a ternary OR operation:
+                        let a_vis_constraint = a_vis_constraints_iter
+                            .next()
+                            .expect("visibility_constraints length mismatch");
+                        let current_vis_constraint =
+                            self.bindings.visibility_constraints.last_mut().unwrap();
+                        *current_vis_constraint = visibility_constraints
+                            .add_or_constraint(*current_vis_constraint, a_vis_constraint);
+
                         opt_a_def = a_defs_iter.next();
                         opt_b_def = b_defs_iter.next();
                     }
                 },
                 (Some(a_def), None) => {
                     // We've exhausted `b`, just push the def from `a` and move on to the next.
-                    push(a_def, &mut a_constraints_iter, self);
+                    push(
+                        a_def,
+                        &mut a_constraints_iter,
+                        &mut a_vis_constraints_iter,
+                        self,
+                    );
                     opt_a_def = a_defs_iter.next();
                 }
                 (None, Some(b_def)) => {
                     // We've exhausted `a`, just push the def from `b` and move on to the next.
-                    push(b_def, &mut b_constraints_iter, self);
+                    push(
+                        b_def,
+                        &mut b_constraints_iter,
+                        &mut b_vis_constraints_iter,
+                        self,
+                    );
                     opt_b_def = b_defs_iter.next();
                 }
                 (None, None) => break,
             }
         }
+
+        // Same as above, but for declarations.
+        let mut a_decls_iter = a.declarations.live_declarations.iter();
+        let mut b_decls_iter = b.declarations.live_declarations.iter();
+        let mut a_vis_constraints_iter = a.declarations.visibility_constraints.into_iter();
+        let mut b_vis_constraints_iter = b.declarations.visibility_constraints.into_iter();
+
+        let mut opt_a_decl: Option<u32> = a_decls_iter.next();
+        let mut opt_b_decl: Option<u32> = b_decls_iter.next();
+
+        let push = |decl,
+                    vis_constraints_iter: &mut VisibilityConstraintsIntoIterator,
+                    merged: &mut Self| {
+            merged.declarations.live_declarations.insert(decl);
+            let vis_constraints = vis_constraints_iter
+                .next()
+                .expect("declarations and visibility_constraints length mismatch");
+            merged
+                .declarations
+                .visibility_constraints
+                .push(vis_constraints);
+        };
+
+        loop {
+            match (opt_a_decl, opt_b_decl) {
+                (Some(a_decl), Some(b_decl)) => match a_decl.cmp(&b_decl) {
+                    std::cmp::Ordering::Less => {
+                        push(a_decl, &mut a_vis_constraints_iter, self);
+                        opt_a_decl = a_decls_iter.next();
+                    }
+                    std::cmp::Ordering::Greater => {
+                        push(b_decl, &mut b_vis_constraints_iter, self);
+                        opt_b_decl = b_decls_iter.next();
+                    }
+                    std::cmp::Ordering::Equal => {
+                        push(a_decl, &mut b_vis_constraints_iter, self);
+
+                        let a_vis_constraint = a_vis_constraints_iter
+                            .next()
+                            .expect("declarations and visibility_constraints length mismatch");
+                        let current = self.declarations.visibility_constraints.last_mut().unwrap();
+                        *current =
+                            visibility_constraints.add_or_constraint(*current, a_vis_constraint);
+
+                        opt_a_decl = a_decls_iter.next();
+                        opt_b_decl = b_decls_iter.next();
+                    }
+                },
+                (Some(a_decl), None) => {
+                    push(a_decl, &mut a_vis_constraints_iter, self);
+                    opt_a_decl = a_decls_iter.next();
+                }
+                (None, Some(b_decl)) => {
+                    push(b_decl, &mut b_vis_constraints_iter, self);
+                    opt_b_decl = b_decls_iter.next();
+                }
+                (None, None) => break,
+            }
+        }
     }
 
     pub(super) fn bindings(&self) -> &SymbolBindings {
@@ -332,47 +507,44 @@ impl SymbolState {
     pub(super) fn declarations(&self) -> &SymbolDeclarations {
         &self.declarations
     }
-
-    /// Could the symbol be unbound?
-    pub(super) fn may_be_unbound(&self) -> bool {
-        self.bindings.may_be_unbound()
-    }
-}
-
-/// The default state of a symbol, if we've seen no definitions of it, is undefined (that is,
-/// both unbound and undeclared).
-impl Default for SymbolState {
-    fn default() -> Self {
-        SymbolState::undefined()
-    }
 }
 
 /// A single binding (as [`ScopedDefinitionId`]) with an iterator of its applicable
-/// [`ScopedConstraintId`].
+/// narrowing constraints ([`ScopedConstraintId`]) and a corresponding visibility
+/// visibility constraint ([`ScopedVisibilityConstraintId`]).
 #[derive(Debug)]
-pub(super) struct BindingIdWithConstraints<'a> {
+pub(super) struct BindingIdWithConstraints<'map> {
     pub(super) definition: ScopedDefinitionId,
-    pub(super) constraint_ids: ConstraintIdIterator<'a>,
+    pub(super) constraint_ids: ConstraintIdIterator<'map>,
+    pub(super) visibility_constraint: ScopedVisibilityConstraintId,
 }
 
 #[derive(Debug)]
-pub(super) struct BindingIdWithConstraintsIterator<'a> {
-    definitions: BindingsIterator<'a>,
-    constraints: ConstraintsIterator<'a>,
+pub(super) struct BindingIdWithConstraintsIterator<'map> {
+    definitions: BindingsIterator<'map>,
+    constraints: ConstraintsIterator<'map>,
+    visibility_constraints: VisibilityConstraintsIterator<'map>,
 }
 
-impl<'a> Iterator for BindingIdWithConstraintsIterator<'a> {
-    type Item = BindingIdWithConstraints<'a>;
+impl<'map> Iterator for BindingIdWithConstraintsIterator<'map> {
+    type Item = BindingIdWithConstraints<'map>;
 
     fn next(&mut self) -> Option<Self::Item> {
-        match (self.definitions.next(), self.constraints.next()) {
-            (None, None) => None,
-            (Some(def), Some(constraints)) => Some(BindingIdWithConstraints {
-                definition: ScopedDefinitionId::from_u32(def),
-                constraint_ids: ConstraintIdIterator {
-                    wrapped: constraints.iter(),
-                },
-            }),
+        match (
+            self.definitions.next(),
+            self.constraints.next(),
+            self.visibility_constraints.next(),
+        ) {
+            (None, None, None) => None,
+            (Some(def), Some(constraints), Some(visibility_constraint_id)) => {
+                Some(BindingIdWithConstraints {
+                    definition: ScopedDefinitionId::from_u32(def),
+                    constraint_ids: ConstraintIdIterator {
+                        wrapped: constraints.iter(),
+                    },
+                    visibility_constraint: *visibility_constraint_id,
+                })
+            }
             // SAFETY: see above.
             _ => unreachable!("definitions and constraints length mismatch"),
         }
@@ -396,16 +568,34 @@ impl Iterator for ConstraintIdIterator<'_> {
 
 impl std::iter::FusedIterator for ConstraintIdIterator<'_> {}
 
+/// A single declaration (as [`ScopedDefinitionId`]) with a corresponding visibility
+/// visibility constraint ([`ScopedVisibilityConstraintId`]).
 #[derive(Debug)]
-pub(super) struct DeclarationIdIterator<'a> {
-    inner: DeclarationsIterator<'a>,
+pub(super) struct DeclarationIdWithConstraint {
+    pub(super) definition: ScopedDefinitionId,
+    pub(super) visibility_constraint: ScopedVisibilityConstraintId,
+}
+
+pub(super) struct DeclarationIdIterator<'map> {
+    pub(crate) declarations: DeclarationsIterator<'map>,
+    pub(crate) visibility_constraints: VisibilityConstraintsIterator<'map>,
 }
 
 impl Iterator for DeclarationIdIterator<'_> {
-    type Item = ScopedDefinitionId;
+    type Item = DeclarationIdWithConstraint;
 
     fn next(&mut self) -> Option<Self::Item> {
-        self.inner.next().map(ScopedDefinitionId::from_u32)
+        match (self.declarations.next(), self.visibility_constraints.next()) {
+            (None, None) => None,
+            (Some(declaration), Some(&visibility_constraint)) => {
+                Some(DeclarationIdWithConstraint {
+                    definition: ScopedDefinitionId::from_u32(declaration),
+                    visibility_constraint,
+                })
+            }
+            // SAFETY: see above.
+            _ => unreachable!("declarations and visibility_constraints length mismatch"),
+        }
     }
 }
 
@@ -413,176 +603,172 @@ impl std::iter::FusedIterator for DeclarationIdIterator<'_> {}
 
 #[cfg(test)]
 mod tests {
-    use super::{ScopedConstraintId, ScopedDefinitionId, SymbolState};
+    use super::*;
 
-    fn assert_bindings(symbol: &SymbolState, may_be_unbound: bool, expected: &[&str]) {
-        assert_eq!(symbol.may_be_unbound(), may_be_unbound);
+    #[track_caller]
+    fn assert_bindings(symbol: &SymbolState, expected: &[&str]) {
         let actual = symbol
             .bindings()
             .iter()
             .map(|def_id_with_constraints| {
-                format!(
-                    "{}<{}>",
-                    def_id_with_constraints.definition.as_u32(),
-                    def_id_with_constraints
-                        .constraint_ids
-                        .map(ScopedConstraintId::as_u32)
-                        .map(|idx| idx.to_string())
-                        .collect::<Vec<_>>()
-                        .join(", ")
-                )
+                let def_id = def_id_with_constraints.definition;
+                let def = if def_id == ScopedDefinitionId::UNBOUND {
+                    "unbound".into()
+                } else {
+                    def_id.as_u32().to_string()
+                };
+                let constraints = def_id_with_constraints
+                    .constraint_ids
+                    .map(ScopedConstraintId::as_u32)
+                    .map(|idx| idx.to_string())
+                    .collect::<Vec<_>>()
+                    .join(", ");
+                format!("{def}<{constraints}>")
             })
             .collect::<Vec<_>>();
         assert_eq!(actual, expected);
     }
 
-    pub(crate) fn assert_declarations(
-        symbol: &SymbolState,
-        may_be_undeclared: bool,
-        expected: &[u32],
-    ) {
-        assert_eq!(symbol.declarations.may_be_undeclared(), may_be_undeclared);
+    #[track_caller]
+    pub(crate) fn assert_declarations(symbol: &SymbolState, expected: &[&str]) {
         let actual = symbol
             .declarations()
             .iter()
-            .map(ScopedDefinitionId::as_u32)
+            .map(
+                |DeclarationIdWithConstraint {
+                     definition,
+                     visibility_constraint: _,
+                 }| {
+                    if definition == ScopedDefinitionId::UNBOUND {
+                        "undeclared".into()
+                    } else {
+                        definition.as_u32().to_string()
+                    }
+                },
+            )
             .collect::<Vec<_>>();
         assert_eq!(actual, expected);
     }
 
     #[test]
     fn unbound() {
-        let sym = SymbolState::undefined();
+        let sym = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
 
-        assert_bindings(&sym, true, &[]);
+        assert_bindings(&sym, &["unbound<>"]);
     }
 
     #[test]
     fn with() {
-        let mut sym = SymbolState::undefined();
-        sym.record_binding(ScopedDefinitionId::from_u32(0));
+        let mut sym = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
+        sym.record_binding(ScopedDefinitionId::from_u32(1));
 
-        assert_bindings(&sym, false, &["0<>"]);
-    }
-
-    #[test]
-    fn set_may_be_unbound() {
-        let mut sym = SymbolState::undefined();
-        sym.record_binding(ScopedDefinitionId::from_u32(0));
-        sym.set_may_be_unbound();
-
-        assert_bindings(&sym, true, &["0<>"]);
+        assert_bindings(&sym, &["1<>"]);
     }
 
     #[test]
     fn record_constraint() {
-        let mut sym = SymbolState::undefined();
-        sym.record_binding(ScopedDefinitionId::from_u32(0));
+        let mut sym = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
+        sym.record_binding(ScopedDefinitionId::from_u32(1));
         sym.record_constraint(ScopedConstraintId::from_u32(0));
 
-        assert_bindings(&sym, false, &["0<0>"]);
+        assert_bindings(&sym, &["1<0>"]);
     }
 
     #[test]
     fn merge() {
+        let mut visibility_constraints = VisibilityConstraints::default();
+
         // merging the same definition with the same constraint keeps the constraint
-        let mut sym0a = SymbolState::undefined();
-        sym0a.record_binding(ScopedDefinitionId::from_u32(0));
-        sym0a.record_constraint(ScopedConstraintId::from_u32(0));
+        let mut sym1a = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
+        sym1a.record_binding(ScopedDefinitionId::from_u32(1));
+        sym1a.record_constraint(ScopedConstraintId::from_u32(0));
 
-        let mut sym0b = SymbolState::undefined();
-        sym0b.record_binding(ScopedDefinitionId::from_u32(0));
-        sym0b.record_constraint(ScopedConstraintId::from_u32(0));
+        let mut sym1b = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
+        sym1b.record_binding(ScopedDefinitionId::from_u32(1));
+        sym1b.record_constraint(ScopedConstraintId::from_u32(0));
 
-        sym0a.merge(sym0b);
-        let mut sym0 = sym0a;
-        assert_bindings(&sym0, false, &["0<0>"]);
+        sym1a.merge(sym1b, &mut visibility_constraints);
+        let mut sym1 = sym1a;
+        assert_bindings(&sym1, &["1<0>"]);
 
         // merging the same definition with differing constraints drops all constraints
-        let mut sym1a = SymbolState::undefined();
-        sym1a.record_binding(ScopedDefinitionId::from_u32(1));
-        sym1a.record_constraint(ScopedConstraintId::from_u32(1));
+        let mut sym2a = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
+        sym2a.record_binding(ScopedDefinitionId::from_u32(2));
+        sym2a.record_constraint(ScopedConstraintId::from_u32(1));
 
-        let mut sym1b = SymbolState::undefined();
-        sym1b.record_binding(ScopedDefinitionId::from_u32(1));
+        let mut sym1b = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
+        sym1b.record_binding(ScopedDefinitionId::from_u32(2));
         sym1b.record_constraint(ScopedConstraintId::from_u32(2));
 
-        sym1a.merge(sym1b);
-        let sym1 = sym1a;
-        assert_bindings(&sym1, false, &["1<>"]);
+        sym2a.merge(sym1b, &mut visibility_constraints);
+        let sym2 = sym2a;
+        assert_bindings(&sym2, &["2<>"]);
 
         // merging a constrained definition with unbound keeps both
-        let mut sym2a = SymbolState::undefined();
-        sym2a.record_binding(ScopedDefinitionId::from_u32(2));
-        sym2a.record_constraint(ScopedConstraintId::from_u32(3));
+        let mut sym3a = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
+        sym3a.record_binding(ScopedDefinitionId::from_u32(3));
+        sym3a.record_constraint(ScopedConstraintId::from_u32(3));
 
-        let sym2b = SymbolState::undefined();
+        let sym2b = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
 
-        sym2a.merge(sym2b);
-        let sym2 = sym2a;
-        assert_bindings(&sym2, true, &["2<3>"]);
+        sym3a.merge(sym2b, &mut visibility_constraints);
+        let sym3 = sym3a;
+        assert_bindings(&sym3, &["unbound<>", "3<3>"]);
 
         // merging different definitions keeps them each with their existing constraints
-        sym0.merge(sym2);
-        let sym = sym0;
-        assert_bindings(&sym, true, &["0<0>", "2<3>"]);
+        sym1.merge(sym3, &mut visibility_constraints);
+        let sym = sym1;
+        assert_bindings(&sym, &["unbound<>", "1<0>", "3<3>"]);
     }
 
     #[test]
     fn no_declaration() {
-        let sym = SymbolState::undefined();
+        let sym = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
 
-        assert_declarations(&sym, true, &[]);
+        assert_declarations(&sym, &["undeclared"]);
     }
 
     #[test]
     fn record_declaration() {
-        let mut sym = SymbolState::undefined();
+        let mut sym = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
         sym.record_declaration(ScopedDefinitionId::from_u32(1));
 
-        assert_declarations(&sym, false, &[1]);
+        assert_declarations(&sym, &["1"]);
     }
 
     #[test]
     fn record_declaration_override() {
-        let mut sym = SymbolState::undefined();
+        let mut sym = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
         sym.record_declaration(ScopedDefinitionId::from_u32(1));
         sym.record_declaration(ScopedDefinitionId::from_u32(2));
 
-        assert_declarations(&sym, false, &[2]);
+        assert_declarations(&sym, &["2"]);
     }
 
     #[test]
     fn record_declaration_merge() {
-        let mut sym = SymbolState::undefined();
+        let mut visibility_constraints = VisibilityConstraints::default();
+        let mut sym = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
         sym.record_declaration(ScopedDefinitionId::from_u32(1));
 
-        let mut sym2 = SymbolState::undefined();
+        let mut sym2 = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
         sym2.record_declaration(ScopedDefinitionId::from_u32(2));
 
-        sym.merge(sym2);
+        sym.merge(sym2, &mut visibility_constraints);
 
-        assert_declarations(&sym, false, &[1, 2]);
+        assert_declarations(&sym, &["1", "2"]);
     }
 
     #[test]
     fn record_declaration_merge_partial_undeclared() {
-        let mut sym = SymbolState::undefined();
+        let mut visibility_constraints = VisibilityConstraints::default();
+        let mut sym = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
         sym.record_declaration(ScopedDefinitionId::from_u32(1));
 
-        let sym2 = SymbolState::undefined();
+        let sym2 = SymbolState::undefined(ScopedVisibilityConstraintId::ALWAYS_TRUE);
 
-        sym.merge(sym2);
+        sym.merge(sym2, &mut visibility_constraints);
 
-        assert_declarations(&sym, true, &[1]);
-    }
-
-    #[test]
-    fn set_may_be_undeclared() {
-        let mut sym = SymbolState::undefined();
-        sym.record_declaration(ScopedDefinitionId::from_u32(0));
-        sym.set_may_be_undeclared();
-
-        assert_declarations(&sym, true, &[0]);
+        assert_declarations(&sym, &["undeclared", "1"]);
     }
 }

crates/red_knot_python_semantic/src/symbol.rs

@@ -35,7 +35,7 @@ impl Boundness {
 /// possibly_unbound:  Symbol::Type(Type::IntLiteral(2), Boundness::PossiblyUnbound),
 /// non_existent:      Symbol::Unbound,
 /// ```
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub(crate) enum Symbol<'db> {
     Type(Type<'db>, Boundness),
     Unbound,

crates/red_knot_python_semantic/src/types.rs

@@ -23,9 +23,11 @@ use crate::semantic_index::definition::Definition;
 use crate::semantic_index::symbol::{self as symbol, ScopeId, ScopedSymbolId};
 use crate::semantic_index::{
     global_scope, imported_modules, semantic_index, symbol_table, use_def_map,
-    BindingWithConstraints, BindingWithConstraintsIterator, DeclarationsIterator,
+    BindingWithConstraints, BindingWithConstraintsIterator, DeclarationWithConstraint,
+    DeclarationsIterator,
 };
 use crate::stdlib::{builtins_symbol, known_module_symbol, typing_extensions_symbol};
+use crate::suppression::check_suppressions;
 use crate::symbol::{Boundness, Symbol};
 use crate::types::call::{CallDunderResult, CallOutcome};
 use crate::types::class_base::ClassBase;
@@ -44,6 +46,7 @@ mod infer;
 mod mro;
 mod narrow;
 mod signatures;
+mod slots;
 mod string_annotation;
 mod unpacker;
 
@@ -64,10 +67,13 @@ pub fn check_types(db: &dyn Db, file: File) -> TypeCheckDiagnostics {
         diagnostics.extend(result.diagnostics());
     }
 
+    check_suppressions(db, file, &mut diagnostics);
+
     diagnostics
 }
 
 /// Infer the public type of a symbol (its type as seen from outside its scope).
+#[salsa::tracked]
 fn symbol_by_id<'db>(db: &'db dyn Db, scope: ScopeId<'db>, symbol: ScopedSymbolId) -> Symbol<'db> {
     let _span = tracing::trace_span!("symbol_by_id", ?symbol).entered();
 
@@ -75,51 +81,60 @@ fn symbol_by_id<'db>(db: &'db dyn Db, scope: ScopeId<'db>, symbol: ScopedSymbolI
 
     // If the symbol is declared, the public type is based on declarations; otherwise, it's based
     // on inference from bindings.
-    if use_def.has_public_declarations(symbol) {
-        let declarations = use_def.public_declarations(symbol);
-        // If the symbol is undeclared in some paths, include the inferred type in the public type.
-        let undeclared_ty = if declarations.may_be_undeclared() {
-            Some(
-                bindings_ty(db, use_def.public_bindings(symbol))
-                    .map(|bindings_ty| Symbol::Type(bindings_ty, use_def.public_boundness(symbol)))
-                    .unwrap_or(Symbol::Unbound),
-            )
-        } else {
-            None
-        };
-        // Intentionally ignore conflicting declared types; that's not our problem, it's the
-        // problem of the module we are importing from.
 
-        // TODO: Our handling of boundness currently only depends on bindings, and ignores
-        // declarations. This is inconsistent, since we only look at bindings if the symbol
-        // may be undeclared. Consider the following example:
-        // ```py
-        // x: int
-        //
-        // if flag:
-        //     y: int
-        // else
-        //     y = 3
-        // ```
-        // If we import from this module, we will currently report `x` as a definitely-bound
-        // symbol (even though it has no bindings at all!) but report `y` as possibly-unbound
-        // (even though every path has either a binding or a declaration for it.)
+    let declarations = use_def.public_declarations(symbol);
+    let declared = declarations_ty(db, declarations);
 
-        match undeclared_ty {
-            Some(Symbol::Type(ty, boundness)) => Symbol::Type(
-                declarations_ty(db, declarations, Some(ty)).unwrap_or_else(|(ty, _)| ty),
-                boundness,
-            ),
-            None | Some(Symbol::Unbound) => Symbol::Type(
-                declarations_ty(db, declarations, None).unwrap_or_else(|(ty, _)| ty),
-                Boundness::Bound,
-            ),
+    match declared {
+        // Symbol is declared, trust the declared type
+        Ok(symbol @ Symbol::Type(_, Boundness::Bound)) => symbol,
+        // Symbol is possibly declared
+        Ok(Symbol::Type(declared_ty, Boundness::PossiblyUnbound)) => {
+            let bindings = use_def.public_bindings(symbol);
+            let inferred = bindings_ty(db, bindings);
+
+            match inferred {
+                // Symbol is possibly undeclared and definitely unbound
+                Symbol::Unbound => {
+                    // TODO: We probably don't want to report `Bound` here. This requires a bit of
+                    // design work though as we might want a different behavior for stubs and for
+                    // normal modules.
+                    Symbol::Type(declared_ty, Boundness::Bound)
+                }
+                // Symbol is possibly undeclared and (possibly) bound
+                Symbol::Type(inferred_ty, boundness) => Symbol::Type(
+                    UnionType::from_elements(db, [inferred_ty, declared_ty].iter().copied()),
+                    boundness,
+                ),
+            }
+        }
+        // Symbol is undeclared, return the inferred type
+        Ok(Symbol::Unbound) => {
+            let bindings = use_def.public_bindings(symbol);
+            bindings_ty(db, bindings)
+        }
+        // Symbol is possibly undeclared
+        Err((declared_ty, _)) => {
+            // Intentionally ignore conflicting declared types; that's not our problem,
+            // it's the problem of the module we are importing from.
+            declared_ty.into()
         }
-    } else {
-        bindings_ty(db, use_def.public_bindings(symbol))
-            .map(|bindings_ty| Symbol::Type(bindings_ty, use_def.public_boundness(symbol)))
-            .unwrap_or(Symbol::Unbound)
     }
+
+    // TODO (ticket: https://github.com/astral-sh/ruff/issues/14297) Our handling of boundness
+    // currently only depends on bindings, and ignores declarations. This is inconsistent, since
+    // we only look at bindings if the symbol may be undeclared. Consider the following example:
+    // ```py
+    // x: int
+    //
+    // if flag:
+    //     y: int
+    // else
+    //     y = 3
+    // ```
+    // If we import from this module, we will currently report `x` as a definitely-bound symbol
+    // (even though it has no bindings at all!) but report `y` as possibly-unbound (even though
+    // every path has either a binding or a declaration for it.)
 }
 
 /// Shorthand for `symbol_by_id` that takes a symbol name instead of an ID.
@@ -132,6 +147,22 @@ fn symbol<'db>(db: &'db dyn Db, scope: ScopeId<'db>, name: &str) -> Symbol<'db>
     {
         return Symbol::Type(Type::BooleanLiteral(true), Boundness::Bound);
     }
+    if name == "platform"
+        && file_to_module(db, scope.file(db))
+            .is_some_and(|module| module.is_known(KnownModule::Sys))
+    {
+        match Program::get(db).python_platform(db) {
+            crate::PythonPlatform::Identifier(platform) => {
+                return Symbol::Type(
+                    Type::StringLiteral(StringLiteralType::new(db, platform.as_str())),
+                    Boundness::Bound,
+                );
+            }
+            crate::PythonPlatform::All => {
+                // Fall through to the looked up type
+            }
+        }
+    }
 
     let table = symbol_table(db, scope);
     table
@@ -247,46 +278,77 @@ fn definition_expression_ty<'db>(
 fn bindings_ty<'db>(
     db: &'db dyn Db,
     bindings_with_constraints: BindingWithConstraintsIterator<'_, 'db>,
-) -> Option<Type<'db>> {
-    let mut def_types = bindings_with_constraints.map(
+) -> Symbol<'db> {
+    let visibility_constraints = bindings_with_constraints.visibility_constraints;
+    let mut bindings_with_constraints = bindings_with_constraints.peekable();
+
+    let unbound_visibility = if let Some(BindingWithConstraints {
+        binding: None,
+        constraints: _,
+        visibility_constraint,
+    }) = bindings_with_constraints.peek()
+    {
+        visibility_constraints.evaluate(db, *visibility_constraint)
+    } else {
+        Truthiness::AlwaysFalse
+    };
+
+    let mut types = bindings_with_constraints.filter_map(
         |BindingWithConstraints {
              binding,
              constraints,
+             visibility_constraint,
          }| {
+            let binding = binding?;
+            let static_visibility = visibility_constraints.evaluate(db, visibility_constraint);
+
+            if static_visibility.is_always_false() {
+                return None;
+            }
+
             let mut constraint_tys = constraints
                 .filter_map(|constraint| narrowing_constraint(db, constraint, binding))
                 .peekable();
 
             let binding_ty = binding_ty(db, binding);
             if constraint_tys.peek().is_some() {
-                constraint_tys
+                let intersection_ty = constraint_tys
                     .fold(
                         IntersectionBuilder::new(db).add_positive(binding_ty),
                         IntersectionBuilder::add_positive,
                     )
-                    .build()
+                    .build();
+                Some(intersection_ty)
             } else {
-                binding_ty
+                Some(binding_ty)
             }
         },
     );
 
-    if let Some(first) = def_types.next() {
-        if let Some(second) = def_types.next() {
-            Some(UnionType::from_elements(
-                db,
-                [first, second].into_iter().chain(def_types),
-            ))
+    if let Some(first) = types.next() {
+        let boundness = match unbound_visibility {
+            Truthiness::AlwaysTrue => {
+                unreachable!("If we have at least one binding, the scope-start should not be definitely visible")
+            }
+            Truthiness::AlwaysFalse => Boundness::Bound,
+            Truthiness::Ambiguous => Boundness::PossiblyUnbound,
+        };
+
+        if let Some(second) = types.next() {
+            Symbol::Type(
+                UnionType::from_elements(db, [first, second].into_iter().chain(types)),
+                boundness,
+            )
         } else {
-            Some(first)
+            Symbol::Type(first, boundness)
         }
     } else {
-        None
+        Symbol::Unbound
     }
 }
 
 /// The result of looking up a declared type from declarations; see [`declarations_ty`].
-type DeclaredTypeResult<'db> = Result<Type<'db>, (Type<'db>, Box<[Type<'db>]>)>;
+type DeclaredTypeResult<'db> = Result<Symbol<'db>, (Type<'db>, Box<[Type<'db>]>)>;
 
 /// Build a declared type from a [`DeclarationsIterator`].
 ///
@@ -304,40 +366,68 @@ type DeclaredTypeResult<'db> = Result<Type<'db>, (Type<'db>, Box<[Type<'db>]>)>;
 fn declarations_ty<'db>(
     db: &'db dyn Db,
     declarations: DeclarationsIterator<'_, 'db>,
-    undeclared_ty: Option<Type<'db>>,
 ) -> DeclaredTypeResult<'db> {
-    let mut declaration_types = declarations.map(|declaration| declaration_ty(db, declaration));
+    let visibility_constraints = declarations.visibility_constraints;
+    let mut declarations = declarations.peekable();
 
-    let Some(first) = declaration_types.next() else {
-        if let Some(undeclared_ty) = undeclared_ty {
-            // Short-circuit to return the undeclared type if there are no declarations.
-            return Ok(undeclared_ty);
-        }
-        panic!("declarations_ty must not be called with zero declarations and no undeclared_ty");
+    let undeclared_visibility = if let Some(DeclarationWithConstraint {
+        declaration: None,
+        visibility_constraint,
+    }) = declarations.peek()
+    {
+        visibility_constraints.evaluate(db, *visibility_constraint)
+    } else {
+        Truthiness::AlwaysFalse
     };
 
-    let mut conflicting: Vec<Type<'db>> = vec![];
-    let mut builder = UnionBuilder::new(db).add(first);
-    for other in declaration_types {
-        if !first.is_equivalent_to(db, other) {
-            conflicting.push(other);
-        }
-        builder = builder.add(other);
-    }
-    // Avoid considering the undeclared type for the conflicting declaration diagnostics. It
-    // should still be part of the declared type.
-    if let Some(undeclared_ty) = undeclared_ty {
-        builder = builder.add(undeclared_ty);
-    }
-    let declared_ty = builder.build();
+    let mut types = declarations.filter_map(
+        |DeclarationWithConstraint {
+             declaration,
+             visibility_constraint,
+         }| {
+            let declaration = declaration?;
+            let static_visibility = visibility_constraints.evaluate(db, visibility_constraint);
 
-    if conflicting.is_empty() {
-        Ok(declared_ty)
+            if static_visibility.is_always_false() {
+                None
+            } else {
+                Some(declaration_ty(db, declaration))
+            }
+        },
+    );
+
+    if let Some(first) = types.next() {
+        let mut conflicting: Vec<Type<'db>> = vec![];
+        let declared_ty = if let Some(second) = types.next() {
+            let mut builder = UnionBuilder::new(db).add(first);
+            for other in std::iter::once(second).chain(types) {
+                if !first.is_equivalent_to(db, other) {
+                    conflicting.push(other);
+                }
+                builder = builder.add(other);
+            }
+            builder.build()
+        } else {
+            first
+        };
+        if conflicting.is_empty() {
+            let boundness = match undeclared_visibility {
+                Truthiness::AlwaysTrue => {
+                    unreachable!("If we have at least one declaration, the scope-start should not be definitely visible")
+                }
+                Truthiness::AlwaysFalse => Boundness::Bound,
+                Truthiness::Ambiguous => Boundness::PossiblyUnbound,
+            };
+
+            Ok(Symbol::Type(declared_ty, boundness))
+        } else {
+            Err((
+                declared_ty,
+                std::iter::once(first).chain(conflicting).collect(),
+            ))
+        }
     } else {
-        Err((
-            declared_ty,
-            [first].into_iter().chain(conflicting).collect(),
-        ))
+        Ok(Symbol::Unbound)
     }
 }
 
@@ -580,6 +670,13 @@ impl<'db> Type<'db> {
             .expect("Expected a Type::KnownInstance variant")
     }
 
+    pub const fn into_tuple(self) -> Option<TupleType<'db>> {
+        match self {
+            Type::Tuple(tuple_type) => Some(tuple_type),
+            _ => None,
+        }
+    }
+
     pub const fn is_boolean_literal(&self) -> bool {
         matches!(self, Type::BooleanLiteral(..))
     }
@@ -1113,14 +1210,6 @@ impl<'db> Type<'db> {
                 Type::SubclassOf(_),
             ) => true,
 
-            (Type::SubclassOf(_), _) | (_, Type::SubclassOf(_)) => {
-                // TODO: Once we have support for final classes, we can determine disjointness in some cases
-                // here. However, note that it might be better to turn `Type::SubclassOf('FinalClass')` into
-                // `Type::ClassLiteral('FinalClass')` during construction, instead of adding special cases for
-                // final classes inside `Type::SubclassOf` everywhere.
-                false
-            }
-
             (Type::AlwaysTruthy, ty) | (ty, Type::AlwaysTruthy) => {
                 // `Truthiness::Ambiguous` may include `AlwaysTrue` as a subset, so it's not guaranteed to be disjoint.
                 // Thus, they are only disjoint if `ty.bool() == AlwaysFalse`.
@@ -1131,6 +1220,14 @@ impl<'db> Type<'db> {
                 matches!(ty.bool(db), Truthiness::AlwaysTrue)
             }
 
+            (Type::SubclassOf(_), _) | (_, Type::SubclassOf(_)) => {
+                // TODO: Once we have support for final classes, we can determine disjointness in some cases
+                // here. However, note that it might be better to turn `Type::SubclassOf('FinalClass')` into
+                // `Type::ClassLiteral('FinalClass')` during construction, instead of adding special cases for
+                // final classes inside `Type::SubclassOf` everywhere.
+                false
+            }
+
             (Type::KnownInstance(left), right) => {
                 left.instance_fallback(db).is_disjoint_from(db, right)
             }
@@ -1580,20 +1677,18 @@ impl<'db> Type<'db> {
     ///
     /// This is used to determine the value that would be returned
     /// when `bool(x)` is called on an object `x`.
-    fn bool(&self, db: &'db dyn Db) -> Truthiness {
+    pub(crate) fn bool(&self, db: &'db dyn Db) -> Truthiness {
         match self {
             Type::Any | Type::Todo(_) | Type::Never | Type::Unknown => Truthiness::Ambiguous,
             Type::FunctionLiteral(_) => Truthiness::AlwaysTrue,
             Type::ModuleLiteral(_) => Truthiness::AlwaysTrue,
-            Type::ClassLiteral(_) => {
-                // TODO: lookup `__bool__` and `__len__` methods on the class's metaclass
-                // More info in https://docs.python.org/3/library/stdtypes.html#truth-value-testing
-                Truthiness::Ambiguous
-            }
-            Type::SubclassOf(_) => {
-                // TODO: see above
-                Truthiness::Ambiguous
+            Type::ClassLiteral(ClassLiteralType { class }) => {
+                class.metaclass(db).to_instance(db).bool(db)
             }
+            Type::SubclassOf(SubclassOfType { base }) => base
+                .into_class()
+                .map(|class| Type::class_literal(class).bool(db))
+                .unwrap_or(Truthiness::Ambiguous),
             Type::AlwaysTruthy => Truthiness::AlwaysTrue,
             Type::AlwaysFalsy => Truthiness::AlwaysFalse,
             instance_ty @ Type::Instance(InstanceType { class }) => {
@@ -2859,11 +2954,19 @@ pub enum Truthiness {
 }
 
 impl Truthiness {
-    const fn is_ambiguous(self) -> bool {
+    pub(crate) const fn is_ambiguous(self) -> bool {
         matches!(self, Truthiness::Ambiguous)
     }
 
-    const fn negate(self) -> Self {
+    pub(crate) const fn is_always_false(self) -> bool {
+        matches!(self, Truthiness::AlwaysFalse)
+    }
+
+    pub(crate) const fn is_always_true(self) -> bool {
+        matches!(self, Truthiness::AlwaysTrue)
+    }
+
+    pub(crate) const fn negate(self) -> Self {
         match self {
             Self::AlwaysTrue => Self::AlwaysFalse,
             Self::AlwaysFalse => Self::AlwaysTrue,
@@ -2871,6 +2974,14 @@ impl Truthiness {
         }
     }
 
+    pub(crate) const fn negate_if(self, condition: bool) -> Self {
+        if condition {
+            self.negate()
+        } else {
+            self
+        }
+    }
+
     fn into_type(self, db: &dyn Db) -> Type {
         match self {
             Self::AlwaysTrue => Type::BooleanLiteral(true),
@@ -2975,13 +3086,16 @@ pub enum KnownFunction {
     Len,
     /// `typing(_extensions).final`
     Final,
+
+    /// [`typing(_extensions).no_type_check`](https://typing.readthedocs.io/en/latest/spec/directives.html#no-type-check)
+    NoTypeCheck,
 }
 
 impl KnownFunction {
     pub fn constraint_function(self) -> Option<KnownConstraintFunction> {
         match self {
             Self::ConstraintFunction(f) => Some(f),
-            Self::RevealType | Self::Len | Self::Final => None,
+            Self::RevealType | Self::Len | Self::Final | Self::NoTypeCheck => None,
         }
     }
 
@@ -3000,6 +3114,9 @@ impl KnownFunction {
             ),
             "len" if definition.is_builtin_definition(db) => Some(KnownFunction::Len),
             "final" if definition.is_typing_definition(db) => Some(KnownFunction::Final),
+            "no_type_check" if definition.is_typing_definition(db) => {
+                Some(KnownFunction::NoTypeCheck)
+            }
             _ => None,
         }
     }

crates/red_knot_python_semantic/src/types/context.rs

@@ -8,13 +8,16 @@ use ruff_db::{
 use ruff_python_ast::AnyNodeRef;
 use ruff_text_size::Ranged;
 
+use super::{binding_ty, KnownFunction, TypeCheckDiagnostic, TypeCheckDiagnostics};
+
+use crate::semantic_index::semantic_index;
+use crate::semantic_index::symbol::ScopeId;
 use crate::{
     lint::{LintId, LintMetadata},
+    suppression::suppressions,
     Db,
 };
 
-use super::{TypeCheckDiagnostic, TypeCheckDiagnostics};
-
 /// Context for inferring the types of a single file.
 ///
 /// One context exists for at least for every inferred region but it's
@@ -29,17 +32,21 @@ use super::{TypeCheckDiagnostic, TypeCheckDiagnostics};
 /// on the current [`TypeInference`](super::infer::TypeInference) result.
 pub(crate) struct InferContext<'db> {
     db: &'db dyn Db,
+    scope: ScopeId<'db>,
     file: File,
     diagnostics: std::cell::RefCell<TypeCheckDiagnostics>,
+    no_type_check: InNoTypeCheck,
     bomb: DebugDropBomb,
 }
 
 impl<'db> InferContext<'db> {
-    pub(crate) fn new(db: &'db dyn Db, file: File) -> Self {
+    pub(crate) fn new(db: &'db dyn Db, scope: ScopeId<'db>) -> Self {
         Self {
             db,
-            file,
+            scope,
+            file: scope.file(db),
             diagnostics: std::cell::RefCell::new(TypeCheckDiagnostics::default()),
+            no_type_check: InNoTypeCheck::default(),
             bomb: DebugDropBomb::new("`InferContext` needs to be explicitly consumed by calling `::finish` to prevent accidental loss of diagnostics."),
         }
     }
@@ -57,9 +64,7 @@ impl<'db> InferContext<'db> {
     where
         T: WithDiagnostics,
     {
-        self.diagnostics
-            .get_mut()
-            .extend(other.diagnostics().iter().cloned());
+        self.diagnostics.get_mut().extend(other.diagnostics());
     }
 
     /// Reports a lint located at `node`.
@@ -67,13 +72,28 @@ impl<'db> InferContext<'db> {
         &self,
         lint: &'static LintMetadata,
         node: AnyNodeRef,
-        message: std::fmt::Arguments,
+        message: fmt::Arguments,
     ) {
+        if !self.db.is_file_open(self.file) {
+            return;
+        }
+
         // Skip over diagnostics if the rule is disabled.
         let Some(severity) = self.db.rule_selection().severity(LintId::of(lint)) else {
             return;
         };
 
+        if self.is_in_no_type_check() {
+            return;
+        }
+
+        let suppressions = suppressions(self.db, self.file);
+
+        if let Some(suppression) = suppressions.find_suppression(node.range(), LintId::of(lint)) {
+            self.diagnostics.borrow_mut().mark_used(suppression.id());
+            return;
+        }
+
         self.report_diagnostic(node, DiagnosticId::Lint(lint.name()), severity, message);
     }
 
@@ -85,7 +105,7 @@ impl<'db> InferContext<'db> {
         node: AnyNodeRef,
         id: DiagnosticId,
         severity: Severity,
-        message: std::fmt::Arguments,
+        message: fmt::Arguments,
     ) {
         if !self.db.is_file_open(self.file) {
             return;
@@ -96,7 +116,6 @@ impl<'db> InferContext<'db> {
         // * The rule is disabled for this file. We probably want to introduce a new query that
         //   returns a rule selector for a given file that respects the package's settings,
         //   any global pragma comments in the file, and any per-file-ignores.
-        // * Check for suppression comments, bump a counter if the diagnostic is suppressed.
 
         self.diagnostics.borrow_mut().push(TypeCheckDiagnostic {
             file: self.file,
@@ -107,6 +126,42 @@ impl<'db> InferContext<'db> {
         });
     }
 
+    pub(super) fn set_in_no_type_check(&mut self, no_type_check: InNoTypeCheck) {
+        self.no_type_check = no_type_check;
+    }
+
+    fn is_in_no_type_check(&self) -> bool {
+        match self.no_type_check {
+            InNoTypeCheck::Possibly => {
+                // Accessing the semantic index here is fine because
+                // the index belongs to the same file as for which we emit the diagnostic.
+                let index = semantic_index(self.db, self.file);
+
+                let scope_id = self.scope.file_scope_id(self.db);
+
+                // Inspect all ancestor function scopes by walking bottom up and infer the function's type.
+                let mut function_scope_tys = index
+                    .ancestor_scopes(scope_id)
+                    .filter_map(|(_, scope)| scope.node().as_function())
+                    .filter_map(|function| {
+                        binding_ty(self.db, index.definition(function)).into_function_literal()
+                    });
+
+                // Iterate over all functions and test if any is decorated with `@no_type_check`.
+                function_scope_tys.any(|function_ty| {
+                    function_ty
+                        .decorators(self.db)
+                        .iter()
+                        .filter_map(|decorator| decorator.into_function_literal())
+                        .any(|decorator_ty| {
+                            decorator_ty.is_known(self.db, KnownFunction::NoTypeCheck)
+                        })
+                })
+            }
+            InNoTypeCheck::Yes => true,
+        }
+    }
+
     #[must_use]
     pub(crate) fn finish(mut self) -> TypeCheckDiagnostics {
         self.bomb.defuse();
@@ -126,6 +181,17 @@ impl fmt::Debug for InferContext<'_> {
     }
 }
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
+pub(crate) enum InNoTypeCheck {
+    /// The inference might be in a `no_type_check` block but only if any
+    /// ancestor function is decorated with `@no_type_check`.
+    #[default]
+    Possibly,
+
+    /// The inference is known to be in an `@no_type_check` decorated function.
+    Yes,
+}
+
 pub(crate) trait WithDiagnostics {
     fn diagnostics(&self) -> &TypeCheckDiagnostics;
 }

crates/red_knot_python_semantic/src/types/diagnostic.rs

@@ -1,5 +1,7 @@
+use super::context::InferContext;
 use crate::declare_lint;
 use crate::lint::{Level, LintRegistryBuilder, LintStatus};
+use crate::suppression::FileSuppressionId;
 use crate::types::string_annotation::{
     BYTE_STRING_TYPE_ANNOTATION, ESCAPE_CHARACTER_IN_FORWARD_ANNOTATION, FSTRING_TYPE_ANNOTATION,
     IMPLICIT_CONCATENATED_STRING_TYPE_ANNOTATION, INVALID_SYNTAX_IN_FORWARD_ANNOTATION,
@@ -10,13 +12,12 @@ use ruff_db::diagnostic::{Diagnostic, DiagnosticId, Severity};
 use ruff_db::files::File;
 use ruff_python_ast::{self as ast, AnyNodeRef};
 use ruff_text_size::{Ranged, TextRange};
+use rustc_hash::FxHashSet;
 use std::borrow::Cow;
 use std::fmt::Formatter;
 use std::ops::Deref;
 use std::sync::Arc;
 
-use super::context::InferContext;
-
 /// Registers all known type check lints.
 pub(crate) fn register_lints(registry: &mut LintRegistryBuilder) {
     registry.register_lint(&CALL_NON_CALLABLE);
@@ -26,6 +27,7 @@ pub(crate) fn register_lints(registry: &mut LintRegistryBuilder) {
     registry.register_lint(&CYCLIC_CLASS_DEFINITION);
     registry.register_lint(&DIVISION_BY_ZERO);
     registry.register_lint(&DUPLICATE_BASE);
+    registry.register_lint(&INCOMPATIBLE_SLOTS);
     registry.register_lint(&INCONSISTENT_MRO);
     registry.register_lint(&INDEX_OUT_OF_BOUNDS);
     registry.register_lint(&INVALID_ASSIGNMENT);
@@ -147,6 +149,64 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Checks for classes whose bases define incompatible `__slots__`.
+    ///
+    /// ## Why is this bad?
+    /// Inheriting from bases with incompatible `__slots__`s
+    /// will lead to a `TypeError` at runtime.
+    ///
+    /// Classes with no or empty `__slots__` are always compatible:
+    ///
+    /// ```python
+    /// class A: ...
+    /// class B:
+    ///     __slots__ = ()
+    /// class C:
+    ///     __slots__ = ("a", "b")
+    ///
+    /// # fine
+    /// class D(A, B, C): ...
+    /// ```
+    ///
+    /// Multiple inheritance from more than one different class
+    /// defining non-empty `__slots__` is not allowed:
+    ///
+    /// ```python
+    /// class A:
+    ///     __slots__ = ("a", "b")
+    ///
+    /// class B:
+    ///     __slots__ = ("a", "b")  # Even if the values are the same
+    ///
+    /// # TypeError: multiple bases have instance lay-out conflict
+    /// class C(A, B): ...
+    /// ```
+    ///
+    /// ## Known problems
+    /// Dynamic (not tuple or string literal) `__slots__` are not checked.
+    /// Additionally, classes inheriting from built-in classes with implicit layouts
+    /// like `str` or `int` are also not checked.
+    ///
+    /// ```pycon
+    /// >>> hasattr(int, "__slots__")
+    /// False
+    /// >>> hasattr(str, "__slots__")
+    /// False
+    /// >>> class A(int, str): ...
+    /// Traceback (most recent call last):
+    ///   File "<python-input-0>", line 1, in <module>
+    ///     class A(int, str): ...
+    /// TypeError: multiple bases have instance lay-out conflict
+    /// ```
+    pub(crate) static INCOMPATIBLE_SLOTS = {
+        summary: "detects class definitions whose MRO has conflicting `__slots__`",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// TODO #14889
     pub(crate) static INCONSISTENT_MRO = {
@@ -512,11 +572,11 @@ declare_lint! {
 
 #[derive(Debug, Eq, PartialEq, Clone)]
 pub struct TypeCheckDiagnostic {
-    pub(super) id: DiagnosticId,
-    pub(super) message: String,
-    pub(super) range: TextRange,
-    pub(super) severity: Severity,
-    pub(super) file: File,
+    pub(crate) id: DiagnosticId,
+    pub(crate) message: String,
+    pub(crate) range: TextRange,
+    pub(crate) severity: Severity,
+    pub(crate) file: File,
 }
 
 impl TypeCheckDiagnostic {
@@ -570,41 +630,41 @@ impl Ranged for TypeCheckDiagnostic {
 /// each Salsa-struct comes with an overhead.
 #[derive(Default, Eq, PartialEq)]
 pub struct TypeCheckDiagnostics {
-    inner: Vec<std::sync::Arc<TypeCheckDiagnostic>>,
+    diagnostics: Vec<Arc<TypeCheckDiagnostic>>,
+    used_suppressions: FxHashSet<FileSuppressionId>,
 }
 
 impl TypeCheckDiagnostics {
-    pub(super) fn push(&mut self, diagnostic: TypeCheckDiagnostic) {
-        self.inner.push(Arc::new(diagnostic));
+    pub(crate) fn push(&mut self, diagnostic: TypeCheckDiagnostic) {
+        self.diagnostics.push(Arc::new(diagnostic));
+    }
+
+    pub(super) fn extend(&mut self, other: &TypeCheckDiagnostics) {
+        self.diagnostics.extend_from_slice(&other.diagnostics);
+        self.used_suppressions.extend(&other.used_suppressions);
+    }
+
+    pub(crate) fn mark_used(&mut self, suppression_id: FileSuppressionId) {
+        self.used_suppressions.insert(suppression_id);
+    }
+
+    pub(crate) fn is_used(&self, suppression_id: FileSuppressionId) -> bool {
+        self.used_suppressions.contains(&suppression_id)
+    }
+
+    pub(crate) fn used_len(&self) -> usize {
+        self.used_suppressions.len()
     }
 
     pub(crate) fn shrink_to_fit(&mut self) {
-        self.inner.shrink_to_fit();
-    }
-}
-
-impl Extend<TypeCheckDiagnostic> for TypeCheckDiagnostics {
-    fn extend<T: IntoIterator<Item = TypeCheckDiagnostic>>(&mut self, iter: T) {
-        self.inner.extend(iter.into_iter().map(std::sync::Arc::new));
-    }
-}
-
-impl Extend<std::sync::Arc<TypeCheckDiagnostic>> for TypeCheckDiagnostics {
-    fn extend<T: IntoIterator<Item = Arc<TypeCheckDiagnostic>>>(&mut self, iter: T) {
-        self.inner.extend(iter);
-    }
-}
-
-impl<'a> Extend<&'a std::sync::Arc<TypeCheckDiagnostic>> for TypeCheckDiagnostics {
-    fn extend<T: IntoIterator<Item = &'a Arc<TypeCheckDiagnostic>>>(&mut self, iter: T) {
-        self.inner
-            .extend(iter.into_iter().map(std::sync::Arc::clone));
+        self.used_suppressions.shrink_to_fit();
+        self.diagnostics.shrink_to_fit();
     }
 }
 
 impl std::fmt::Debug for TypeCheckDiagnostics {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
-        self.inner.fmt(f)
+        self.diagnostics.fmt(f)
     }
 }
 
@@ -612,7 +672,7 @@ impl Deref for TypeCheckDiagnostics {
     type Target = [std::sync::Arc<TypeCheckDiagnostic>];
 
     fn deref(&self) -> &Self::Target {
-        &self.inner
+        &self.diagnostics
     }
 }
 
@@ -621,7 +681,7 @@ impl IntoIterator for TypeCheckDiagnostics {
     type IntoIter = std::vec::IntoIter<std::sync::Arc<TypeCheckDiagnostic>>;
 
     fn into_iter(self) -> Self::IntoIter {
-        self.inner.into_iter()
+        self.diagnostics.into_iter()
     }
 }
 
@@ -630,7 +690,7 @@ impl<'a> IntoIterator for &'a TypeCheckDiagnostics {
     type IntoIter = std::slice::Iter<'a, std::sync::Arc<TypeCheckDiagnostic>>;
 
     fn into_iter(self) -> Self::IntoIter {
-        self.inner.iter()
+        self.diagnostics.iter()
     }
 }
 
@@ -812,3 +872,11 @@ pub(crate) fn report_invalid_exception_cause(context: &InferContext, node: &ast:
         ),
     );
 }
+
+pub(crate) fn report_base_with_incompatible_slots(context: &InferContext, node: &ast::Expr) {
+    context.report_lint(
+        &INCOMPATIBLE_SLOTS,
+        node.into(),
+        format_args!("Class base has incompatible `__slots__`"),
+    );
+}

crates/red_knot_python_semantic/src/types/display.rs

@@ -324,6 +324,12 @@ impl<'db> TypeArrayDisplay<'db> for Vec<Type<'db>> {
     }
 }
 
+impl<'db> TypeArrayDisplay<'db> for [Type<'db>] {
+    fn display(&self, db: &'db dyn Db) -> DisplayTypeArray {
+        DisplayTypeArray { types: self, db }
+    }
+}
+
 pub(crate) struct DisplayTypeArray<'b, 'db> {
     types: &'b [Type<'db>],
     db: &'db dyn Db,

crates/red_knot_python_semantic/src/types/infer.rs

@@ -31,7 +31,7 @@ use std::num::NonZeroU32;
 use itertools::Itertools;
 use ruff_db::files::File;
 use ruff_db::parsed::parsed_module;
-use ruff_python_ast::{self as ast, AnyNodeRef, ExprContext, UnaryOp};
+use ruff_python_ast::{self as ast, AnyNodeRef, ExprContext};
 use ruff_text_size::Ranged;
 use rustc_hash::{FxHashMap, FxHashSet};
 use salsa;
@@ -42,7 +42,7 @@ use crate::module_resolver::{file_to_module, resolve_module};
 use crate::semantic_index::ast_ids::{HasScopedExpressionId, HasScopedUseId, ScopedExpressionId};
 use crate::semantic_index::definition::{
     AssignmentDefinitionKind, Definition, DefinitionKind, DefinitionNodeKey,
-    ExceptHandlerDefinitionKind, TargetKind,
+    ExceptHandlerDefinitionKind, ForStmtDefinitionKind, TargetKind,
 };
 use crate::semantic_index::expression::Expression;
 use crate::semantic_index::semantic_index;
@@ -72,13 +72,14 @@ use crate::unpack::Unpack;
 use crate::util::subscript::{PyIndex, PySlice};
 use crate::Db;
 
-use super::context::{InferContext, WithDiagnostics};
+use super::context::{InNoTypeCheck, InferContext, WithDiagnostics};
 use super::diagnostic::{
     report_index_out_of_bounds, report_invalid_exception_caught, report_invalid_exception_cause,
     report_invalid_exception_raised, report_non_subscriptable,
     report_possibly_unresolved_reference, report_slice_step_size_zero, report_unresolved_reference,
     SUBCLASS_OF_FINAL_CLASS,
 };
+use super::slots::check_class_slots;
 use super::string_annotation::{
     parse_string_annotation, BYTE_STRING_TYPE_ANNOTATION, FSTRING_TYPE_ANNOTATION,
 };
@@ -131,7 +132,7 @@ pub(crate) fn infer_definition_types<'db>(
     let file = definition.file(db);
     let _span = tracing::trace_span!(
         "infer_definition_types",
-        range = ?definition.kind(db).range(),
+        range = ?definition.kind(db).target_range(),
         file = %file.path(db)
     )
     .entered();
@@ -154,7 +155,7 @@ pub(crate) fn infer_deferred_types<'db>(
     let _span = tracing::trace_span!(
         "infer_deferred_types",
         definition = ?definition.as_id(),
-        range = ?definition.kind(db).range(),
+        range = ?definition.kind(db).target_range(),
         file = %file.path(db)
     )
     .entered();
@@ -168,7 +169,6 @@ pub(crate) fn infer_deferred_types<'db>(
 /// Use rarely; only for cases where we'd otherwise risk double-inferring an expression: RHS of an
 /// assignment, which might be unpacking/multi-target and thus part of multiple definitions, or a
 /// type narrowing guard expression (e.g. if statement test node).
-#[allow(unused)]
 #[salsa::tracked(return_ref)]
 pub(crate) fn infer_expression_types<'db>(
     db: &'db dyn Db,
@@ -198,21 +198,16 @@ pub(crate) fn infer_expression_types<'db>(
 fn infer_unpack_types<'db>(db: &'db dyn Db, unpack: Unpack<'db>) -> UnpackResult<'db> {
     let file = unpack.file(db);
     let _span =
-        tracing::trace_span!("infer_unpack_types", unpack=?unpack.as_id(), file=%file.path(db))
+        tracing::trace_span!("infer_unpack_types", range=?unpack.range(db), file=%file.path(db))
             .entered();
 
-    let value = unpack.value(db);
-    let scope = unpack.scope(db);
-
-    let result = infer_expression_types(db, value);
-    let value_ty = result.expression_ty(value.node_ref(db).scoped_expression_id(db, scope));
-
-    let mut unpacker = Unpacker::new(db, file);
-    unpacker.unpack(unpack.target(db), value_ty, scope);
+    let mut unpacker = Unpacker::new(db, unpack.scope(db));
+    unpacker.unpack(unpack.target(db), unpack.value(db));
     unpacker.finish()
 }
 
 /// A region within which we can infer types.
+#[derive(Copy, Clone, Debug)]
 pub(crate) enum InferenceRegion<'db> {
     /// infer types for a standalone [`Expression`]
     Expression(Expression<'db>),
@@ -224,6 +219,18 @@ pub(crate) enum InferenceRegion<'db> {
     Scope(ScopeId<'db>),
 }
 
+impl<'db> InferenceRegion<'db> {
+    fn scope(self, db: &'db dyn Db) -> ScopeId<'db> {
+        match self {
+            InferenceRegion::Expression(expression) => expression.scope(db),
+            InferenceRegion::Definition(definition) | InferenceRegion::Deferred(definition) => {
+                definition.scope(db)
+            }
+            InferenceRegion::Scope(scope) => scope,
+        }
+    }
+}
+
 /// The inferred types for a single region.
 #[derive(Debug, Eq, PartialEq)]
 pub(crate) struct TypeInference<'db> {
@@ -382,16 +389,10 @@ impl<'db> TypeInferenceBuilder<'db> {
         region: InferenceRegion<'db>,
         index: &'db SemanticIndex<'db>,
     ) -> Self {
-        let (file, scope) = match region {
-            InferenceRegion::Expression(expression) => (expression.file(db), expression.scope(db)),
-            InferenceRegion::Definition(definition) | InferenceRegion::Deferred(definition) => {
-                (definition.file(db), definition.scope(db))
-            }
-            InferenceRegion::Scope(scope) => (scope.file(db), scope),
-        };
+        let scope = region.scope(db);
 
         Self {
-            context: InferContext::new(db, file),
+            context: InferContext::new(db, scope),
             index,
             region,
             deferred_state: DeferredExpressionState::None,
@@ -591,41 +592,44 @@ impl<'db> TypeInferenceBuilder<'db> {
             }
 
             // (3) Check that the class's MRO is resolvable
-            if let Err(mro_error) = class.try_mro(self.db()).as_ref() {
-                match mro_error.reason() {
-                    MroErrorKind::DuplicateBases(duplicates) => {
-                        let base_nodes = class_node.bases();
-                        for (index, duplicate) in duplicates {
-                            self.context.report_lint(
-                                &DUPLICATE_BASE,
-                                (&base_nodes[*index]).into(),
-                                format_args!("Duplicate base class `{}`", duplicate.name(self.db())),
-                            );
+            match class.try_mro(self.db()).as_ref() {
+                Err(mro_error) => {
+                    match mro_error.reason() {
+                        MroErrorKind::DuplicateBases(duplicates) => {
+                            let base_nodes = class_node.bases();
+                            for (index, duplicate) in duplicates {
+                                self.context.report_lint(
+                                    &DUPLICATE_BASE,
+                                    (&base_nodes[*index]).into(),
+                                    format_args!("Duplicate base class `{}`", duplicate.name(self.db())),
+                                );
+                            }
                         }
-                    }
-                    MroErrorKind::InvalidBases(bases) => {
-                        let base_nodes = class_node.bases();
-                        for (index, base_ty) in bases {
-                            self.context.report_lint(
-                                &INVALID_BASE,
-                                (&base_nodes[*index]).into(),
-                                format_args!(
-                                    "Invalid class base with type `{}` (all bases must be a class, `Any`, `Unknown` or `Todo`)",
-                                    base_ty.display(self.db())
-                                ),
-                            );
+                        MroErrorKind::InvalidBases(bases) => {
+                            let base_nodes = class_node.bases();
+                            for (index, base_ty) in bases {
+                                self.context.report_lint(
+                                    &INVALID_BASE,
+                                    (&base_nodes[*index]).into(),
+                                    format_args!(
+                                        "Invalid class base with type `{}` (all bases must be a class, `Any`, `Unknown` or `Todo`)",
+                                        base_ty.display(self.db())
+                                    ),
+                                );
+                            }
                         }
+                        MroErrorKind::UnresolvableMro { bases_list } => self.context.report_lint(
+                            &INCONSISTENT_MRO,
+                            class_node.into(),
+                            format_args!(
+                                "Cannot create a consistent method resolution order (MRO) for class `{}` with bases list `[{}]`",
+                                class.name(self.db()),
+                                bases_list.iter().map(|base| base.display(self.db())).join(", ")
+                            ),
+                        )
                     }
-                    MroErrorKind::UnresolvableMro { bases_list } => self.context.report_lint(
-                        &INCONSISTENT_MRO,
-                        class_node.into(),
-                        format_args!(
-                            "Cannot create a consistent method resolution order (MRO) for class `{}` with bases list `[{}]`",
-                            class.name(self.db()),
-                            bases_list.iter().map(|base| base.display(self.db())).join(", ")
-                        ),
-                    )
                 }
+                Ok(_) => check_class_slots(&self.context, class, class_node)
             }
 
             // (4) Check that the class's metaclass can be determined without error.
@@ -710,12 +714,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                 self.infer_augment_assignment_definition(augmented_assignment.node(), definition);
             }
             DefinitionKind::For(for_statement_definition) => {
-                self.infer_for_statement_definition(
-                    for_statement_definition.target(),
-                    for_statement_definition.iterable(),
-                    for_statement_definition.is_async(),
-                    definition,
-                );
+                self.infer_for_statement_definition(for_statement_definition, definition);
             }
             DefinitionKind::NamedExpression(named_expression) => {
                 self.infer_named_expression_definition(named_expression.node(), definition);
@@ -824,14 +823,10 @@ impl<'db> TypeInferenceBuilder<'db> {
         debug_assert!(binding.is_binding(self.db()));
         let use_def = self.index.use_def_map(binding.file_scope(self.db()));
         let declarations = use_def.declarations_at_binding(binding);
-        let undeclared_ty = if declarations.may_be_undeclared() {
-            Some(Type::Unknown)
-        } else {
-            None
-        };
         let mut bound_ty = ty;
-        let declared_ty = declarations_ty(self.db(), declarations, undeclared_ty).unwrap_or_else(
-            |(ty, conflicting)| {
+        let declared_ty = declarations_ty(self.db(), declarations)
+            .map(|s| s.ignore_possibly_unbound().unwrap_or(Type::Unknown))
+            .unwrap_or_else(|(ty, conflicting)| {
                 // TODO point out the conflicting declarations in the diagnostic?
                 let symbol_table = self.index.symbol_table(binding.file_scope(self.db()));
                 let symbol_name = symbol_table.symbol(binding.symbol(self.db())).name();
@@ -844,8 +839,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                     ),
                 );
                 ty
-            },
-        );
+            });
         if !bound_ty.is_assignable_to(self.db(), declared_ty) {
             report_invalid_assignment(&self.context, node, declared_ty, bound_ty);
             // allow declarations to override inference in case of invalid assignment
@@ -860,7 +854,9 @@ impl<'db> TypeInferenceBuilder<'db> {
         let use_def = self.index.use_def_map(declaration.file_scope(self.db()));
         let prior_bindings = use_def.bindings_at_declaration(declaration);
         // unbound_ty is Never because for this check we don't care about unbound
-        let inferred_ty = bindings_ty(self.db(), prior_bindings).unwrap_or(Type::Never);
+        let inferred_ty = bindings_ty(self.db(), prior_bindings)
+            .ignore_possibly_unbound()
+            .unwrap_or(Type::Never);
         let ty = if inferred_ty.is_assignable_to(self.db(), ty) {
             ty
         } else {
@@ -1032,10 +1028,20 @@ impl<'db> TypeInferenceBuilder<'db> {
             decorator_list,
         } = function;
 
-        let decorator_tys: Box<[Type]> = decorator_list
-            .iter()
-            .map(|decorator| self.infer_decorator(decorator))
-            .collect();
+        // Check if the function is decorated with the `no_type_check` decorator
+        // and, if so, suppress any errors that come after the decorators.
+        let mut decorator_tys = Vec::with_capacity(decorator_list.len());
+
+        for decorator in decorator_list {
+            let ty = self.infer_decorator(decorator);
+            decorator_tys.push(ty);
+
+            if let Type::FunctionLiteral(function) = ty {
+                if function.is_known(self.db(), KnownFunction::NoTypeCheck) {
+                    self.context.set_in_no_type_check(InNoTypeCheck::Yes);
+                }
+            }
+        }
 
         for default in parameters
             .iter_non_variadic_params()
@@ -1071,7 +1077,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             &name.id,
             function_kind,
             body_scope,
-            decorator_tys,
+            decorator_tys.into_boxed_slice(),
         ));
 
         self.add_declaration_with_binding(function.into(), definition, function_ty, function_ty);
@@ -1739,7 +1745,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                 guard,
             } = case;
             self.infer_match_pattern(pattern);
-            self.infer_optional_expression(guard.as_deref());
+            guard
+                .as_deref()
+                .map(|guard| self.infer_standalone_expression(guard));
             self.infer_body(body);
         }
     }
@@ -1764,13 +1772,24 @@ impl<'db> TypeInferenceBuilder<'db> {
     fn infer_match_pattern(&mut self, pattern: &ast::Pattern) {
         // TODO(dhruvmanila): Add a Salsa query for inferring pattern types and matching against
         // the subject expression: https://github.com/astral-sh/ruff/pull/13147#discussion_r1739424510
+        match pattern {
+            ast::Pattern::MatchValue(match_value) => {
+                self.infer_standalone_expression(&match_value.value);
+            }
+            _ => {
+                self.infer_match_pattern_impl(pattern);
+            }
+        }
+    }
+
+    fn infer_match_pattern_impl(&mut self, pattern: &ast::Pattern) {
         match pattern {
             ast::Pattern::MatchValue(match_value) => {
                 self.infer_expression(&match_value.value);
             }
             ast::Pattern::MatchSequence(match_sequence) => {
                 for pattern in &match_sequence.patterns {
-                    self.infer_match_pattern(pattern);
+                    self.infer_match_pattern_impl(pattern);
                 }
             }
             ast::Pattern::MatchMapping(match_mapping) => {
@@ -1784,7 +1803,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                     self.infer_expression(key);
                 }
                 for pattern in patterns {
-                    self.infer_match_pattern(pattern);
+                    self.infer_match_pattern_impl(pattern);
                 }
             }
             ast::Pattern::MatchClass(match_class) => {
@@ -1794,21 +1813,21 @@ impl<'db> TypeInferenceBuilder<'db> {
                     arguments,
                 } = match_class;
                 for pattern in &arguments.patterns {
-                    self.infer_match_pattern(pattern);
+                    self.infer_match_pattern_impl(pattern);
                 }
                 for keyword in &arguments.keywords {
-                    self.infer_match_pattern(&keyword.pattern);
+                    self.infer_match_pattern_impl(&keyword.pattern);
                 }
                 self.infer_expression(cls);
             }
             ast::Pattern::MatchAs(match_as) => {
                 if let Some(pattern) = &match_as.pattern {
-                    self.infer_match_pattern(pattern);
+                    self.infer_match_pattern_impl(pattern);
                 }
             }
             ast::Pattern::MatchOr(match_or) => {
                 for pattern in &match_or.patterns {
-                    self.infer_match_pattern(pattern);
+                    self.infer_match_pattern_impl(pattern);
                 }
             }
             ast::Pattern::MatchStar(_) | ast::Pattern::MatchSingleton(_) => {}
@@ -1823,18 +1842,28 @@ impl<'db> TypeInferenceBuilder<'db> {
         } = assignment;
 
         for target in targets {
-            self.infer_assignment_target(target, value);
+            self.infer_target(target, value);
         }
     }
 
-    // TODO: Remove the `value` argument once we handle all possible assignment targets.
-    fn infer_assignment_target(&mut self, target: &ast::Expr, value: &ast::Expr) {
+    /// Infer the definition types involved in a `target` expression.
+    ///
+    /// This is used for assignment statements, for statements, etc. with a single or multiple
+    /// targets (unpacking).
+    ///
+    /// # Panics
+    ///
+    /// If the `value` is not a standalone expression.
+    fn infer_target(&mut self, target: &ast::Expr, value: &ast::Expr) {
         match target {
             ast::Expr::Name(name) => self.infer_definition(name),
             ast::Expr::List(ast::ExprList { elts, .. })
             | ast::Expr::Tuple(ast::ExprTuple { elts, .. }) => {
                 for element in elts {
-                    self.infer_assignment_target(element, value);
+                    self.infer_target(element, value);
+                }
+                if elts.is_empty() {
+                    self.infer_standalone_expression(value);
                 }
             }
             _ => {
@@ -1853,10 +1882,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         let value = assignment.value();
         let name = assignment.name();
 
-        self.infer_standalone_expression(value);
-
-        let value_ty = self.expression_ty(value);
-        let name_ast_id = name.scoped_expression_id(self.db(), self.scope());
+        let value_ty = self.infer_standalone_expression(value);
 
         let mut target_ty = match assignment.target() {
             TargetKind::Sequence(unpack) => {
@@ -1867,6 +1893,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                     self.context.extend(unpacked);
                 }
 
+                let name_ast_id = name.scoped_expression_id(self.db(), self.scope());
                 unpacked.get(name_ast_id).unwrap_or(Type::Unknown)
             }
             TargetKind::Name => value_ty,
@@ -2094,36 +2121,41 @@ impl<'db> TypeInferenceBuilder<'db> {
             is_async: _,
         } = for_statement;
 
-        // TODO more complex assignment targets
-        if let ast::Expr::Name(name) = &**target {
-            self.infer_definition(name);
-        } else {
-            self.infer_standalone_expression(iter);
-            self.infer_expression(target);
-        }
+        self.infer_target(target, iter);
         self.infer_body(body);
         self.infer_body(orelse);
     }
 
     fn infer_for_statement_definition(
         &mut self,
-        target: &ast::ExprName,
-        iterable: &ast::Expr,
-        is_async: bool,
+        for_stmt: &ForStmtDefinitionKind<'db>,
         definition: Definition<'db>,
     ) {
+        let iterable = for_stmt.iterable();
+        let name = for_stmt.name();
+
         let iterable_ty = self.infer_standalone_expression(iterable);
 
-        let loop_var_value_ty = if is_async {
+        let loop_var_value_ty = if for_stmt.is_async() {
             todo_type!("async iterables/iterators")
         } else {
-            iterable_ty
-                .iterate(self.db())
-                .unwrap_with_diagnostic(&self.context, iterable.into())
+            match for_stmt.target() {
+                TargetKind::Sequence(unpack) => {
+                    let unpacked = infer_unpack_types(self.db(), unpack);
+                    if for_stmt.is_first() {
+                        self.context.extend(unpacked);
+                    }
+                    let name_ast_id = name.scoped_expression_id(self.db(), self.scope());
+                    unpacked.get(name_ast_id).unwrap_or(Type::Unknown)
+                }
+                TargetKind::Name => iterable_ty
+                    .iterate(self.db())
+                    .unwrap_with_diagnostic(&self.context, iterable.into()),
+            }
         };
 
-        self.store_expression_type(target, loop_var_value_ty);
-        self.add_binding(target.into(), definition, loop_var_value_ty);
+        self.store_expression_type(name, loop_var_value_ty);
+        self.add_binding(name.into(), definition, loop_var_value_ty);
     }
 
     fn infer_while_statement(&mut self, while_statement: &ast::StmtWhile) {
@@ -3094,28 +3126,24 @@ impl<'db> TypeInferenceBuilder<'db> {
         let use_def = self.index.use_def_map(file_scope_id);
 
         // If we're inferring types of deferred expressions, always treat them as public symbols
-        let (bindings_ty, boundness) = if self.is_deferred() {
+        let bindings_ty = if self.is_deferred() {
             if let Some(symbol) = self.index.symbol_table(file_scope_id).symbol_id_by_name(id) {
-                (
-                    bindings_ty(self.db(), use_def.public_bindings(symbol)),
-                    use_def.public_boundness(symbol),
-                )
+                bindings_ty(self.db(), use_def.public_bindings(symbol))
             } else {
                 assert!(
                     self.deferred_state.in_string_annotation(),
                     "Expected the symbol table to create a symbol for every Name node"
                 );
-                (None, Boundness::PossiblyUnbound)
+                Symbol::Unbound
             }
         } else {
             let use_id = name.scoped_use_id(self.db(), self.scope());
-            (
-                bindings_ty(self.db(), use_def.bindings_at_use(use_id)),
-                use_def.use_boundness(use_id),
-            )
+            bindings_ty(self.db(), use_def.bindings_at_use(use_id))
         };
 
-        if boundness == Boundness::PossiblyUnbound {
+        if let Symbol::Type(ty, Boundness::Bound) = bindings_ty {
+            ty
+        } else {
             match self.lookup_name(name) {
                 Symbol::Type(looked_up_ty, looked_up_boundness) => {
                     if looked_up_boundness == Boundness::PossiblyUnbound {
@@ -3123,20 +3151,22 @@ impl<'db> TypeInferenceBuilder<'db> {
                     }
 
                     bindings_ty
+                        .ignore_possibly_unbound()
                         .map(|ty| UnionType::from_elements(self.db(), [ty, looked_up_ty]))
                         .unwrap_or(looked_up_ty)
                 }
-                Symbol::Unbound => {
-                    if bindings_ty.is_some() {
+                Symbol::Unbound => match bindings_ty {
+                    Symbol::Type(ty, Boundness::PossiblyUnbound) => {
                         report_possibly_unresolved_reference(&self.context, name);
-                    } else {
-                        report_unresolved_reference(&self.context, name);
+                        ty
                     }
-                    bindings_ty.unwrap_or(Type::Unknown)
-                }
+                    Symbol::Unbound => {
+                        report_unresolved_reference(&self.context, name);
+                        Type::Unknown
+                    }
+                    Symbol::Type(_, Boundness::Bound) => unreachable!("Handled above"),
+                },
             }
-        } else {
-            bindings_ty.unwrap_or(Type::Unknown)
         }
     }
 
@@ -3225,17 +3255,19 @@ impl<'db> TypeInferenceBuilder<'db> {
             (_, Type::Never) => Type::Never,
             (_, Type::Unknown) => Type::Unknown,
 
-            (UnaryOp::UAdd, Type::IntLiteral(value)) => Type::IntLiteral(value),
-            (UnaryOp::USub, Type::IntLiteral(value)) => Type::IntLiteral(-value),
-            (UnaryOp::Invert, Type::IntLiteral(value)) => Type::IntLiteral(!value),
+            (ast::UnaryOp::UAdd, Type::IntLiteral(value)) => Type::IntLiteral(value),
+            (ast::UnaryOp::USub, Type::IntLiteral(value)) => Type::IntLiteral(-value),
+            (ast::UnaryOp::Invert, Type::IntLiteral(value)) => Type::IntLiteral(!value),
 
-            (UnaryOp::UAdd, Type::BooleanLiteral(bool)) => Type::IntLiteral(i64::from(bool)),
-            (UnaryOp::USub, Type::BooleanLiteral(bool)) => Type::IntLiteral(-i64::from(bool)),
-            (UnaryOp::Invert, Type::BooleanLiteral(bool)) => Type::IntLiteral(!i64::from(bool)),
+            (ast::UnaryOp::UAdd, Type::BooleanLiteral(bool)) => Type::IntLiteral(i64::from(bool)),
+            (ast::UnaryOp::USub, Type::BooleanLiteral(bool)) => Type::IntLiteral(-i64::from(bool)),
+            (ast::UnaryOp::Invert, Type::BooleanLiteral(bool)) => {
+                Type::IntLiteral(!i64::from(bool))
+            }
 
-            (UnaryOp::Not, ty) => ty.bool(self.db()).negate().into_type(self.db()),
+            (ast::UnaryOp::Not, ty) => ty.bool(self.db()).negate().into_type(self.db()),
             (
-                op @ (UnaryOp::UAdd | UnaryOp::USub | UnaryOp::Invert),
+                op @ (ast::UnaryOp::UAdd | ast::UnaryOp::USub | ast::UnaryOp::Invert),
                 Type::FunctionLiteral(_)
                 | Type::ModuleLiteral(_)
                 | Type::ClassLiteral(_)
@@ -3253,10 +3285,10 @@ impl<'db> TypeInferenceBuilder<'db> {
                 | Type::Tuple(_),
             ) => {
                 let unary_dunder_method = match op {
-                    UnaryOp::Invert => "__invert__",
-                    UnaryOp::UAdd => "__pos__",
-                    UnaryOp::USub => "__neg__",
-                    UnaryOp::Not => {
+                    ast::UnaryOp::Invert => "__invert__",
+                    ast::UnaryOp::UAdd => "__pos__",
+                    ast::UnaryOp::USub => "__neg__",
+                    ast::UnaryOp::Not => {
                         unreachable!("Not operator is handled in its own case");
                     }
                 };
@@ -3574,27 +3606,37 @@ impl<'db> TypeInferenceBuilder<'db> {
         n_values: usize,
     ) -> Type<'db> {
         let mut done = false;
-        UnionType::from_elements(
-            db,
-            values.into_iter().enumerate().map(|(i, ty)| {
-                if done {
-                    Type::Never
-                } else {
-                    let is_last = i == n_values - 1;
-                    match (ty.bool(db), is_last, op) {
-                        (Truthiness::Ambiguous, _, _) => ty,
-                        (Truthiness::AlwaysTrue, false, ast::BoolOp::And) => Type::Never,
-                        (Truthiness::AlwaysFalse, false, ast::BoolOp::Or) => Type::Never,
-                        (Truthiness::AlwaysFalse, _, ast::BoolOp::And)
-                        | (Truthiness::AlwaysTrue, _, ast::BoolOp::Or) => {
-                            done = true;
-                            ty
-                        }
-                        (_, true, _) => ty,
-                    }
+
+        let elements = values.into_iter().enumerate().map(|(i, ty)| {
+            if done {
+                return Type::Never;
+            }
+
+            let is_last = i == n_values - 1;
+
+            match (ty.bool(db), is_last, op) {
+                (Truthiness::AlwaysTrue, false, ast::BoolOp::And) => Type::Never,
+                (Truthiness::AlwaysFalse, false, ast::BoolOp::Or) => Type::Never,
+
+                (Truthiness::AlwaysFalse, _, ast::BoolOp::And)
+                | (Truthiness::AlwaysTrue, _, ast::BoolOp::Or) => {
+                    done = true;
+                    ty
                 }
-            }),
-        )
+
+                (Truthiness::Ambiguous, false, _) => IntersectionBuilder::new(db)
+                    .add_positive(ty)
+                    .add_negative(match op {
+                        ast::BoolOp::And => Type::AlwaysTruthy,
+                        ast::BoolOp::Or => Type::AlwaysFalsy,
+                    })
+                    .build(),
+
+                (_, true, _) => ty,
+            }
+        });
+
+        UnionType::from_elements(db, elements)
     }
 
     fn infer_compare_expression(&mut self, compare: &ast::ExprCompare) -> Type<'db> {
@@ -5191,7 +5233,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             }
             // for negative and positive numbers
             ast::Expr::UnaryOp(ref u)
-                if matches!(u.op, UnaryOp::USub | UnaryOp::UAdd)
+                if matches!(u.op, ast::UnaryOp::USub | ast::UnaryOp::UAdd)
                     && u.operand.is_number_literal_expr() =>
             {
                 self.infer_unary_expression(u)
@@ -6353,14 +6395,13 @@ mod tests {
     }
 
     // Incremental inference tests
-
+    #[track_caller]
     fn first_public_binding<'db>(db: &'db TestDb, file: File, name: &str) -> Definition<'db> {
         let scope = global_scope(db, file);
         use_def_map(db, scope)
             .public_bindings(symbol_table(db, scope).symbol_id_by_name(name).unwrap())
-            .next()
-            .unwrap()
-            .binding
+            .find_map(|b| b.binding)
+            .expect("no binding found")
     }
 
     #[test]

crates/red_knot_python_semantic/src/types/narrow.rs

@@ -1,5 +1,7 @@
 use crate::semantic_index::ast_ids::HasScopedExpressionId;
-use crate::semantic_index::constraint::{Constraint, ConstraintNode, PatternConstraint};
+use crate::semantic_index::constraint::{
+    Constraint, ConstraintNode, PatternConstraint, PatternConstraintKind,
+};
 use crate::semantic_index::definition::Definition;
 use crate::semantic_index::expression::Expression;
 use crate::semantic_index::symbol::{ScopeId, ScopedSymbolId, SymbolTable};
@@ -216,31 +218,12 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
     ) -> Option<NarrowingConstraints<'db>> {
         let subject = pattern.subject(self.db);
 
-        match pattern.pattern(self.db).node() {
-            ast::Pattern::MatchValue(_) => {
-                None // TODO
-            }
-            ast::Pattern::MatchSingleton(singleton_pattern) => {
-                self.evaluate_match_pattern_singleton(subject, singleton_pattern)
-            }
-            ast::Pattern::MatchSequence(_) => {
-                None // TODO
-            }
-            ast::Pattern::MatchMapping(_) => {
-                None // TODO
-            }
-            ast::Pattern::MatchClass(_) => {
-                None // TODO
-            }
-            ast::Pattern::MatchStar(_) => {
-                None // TODO
-            }
-            ast::Pattern::MatchAs(_) => {
-                None // TODO
-            }
-            ast::Pattern::MatchOr(_) => {
-                None // TODO
+        match pattern.kind(self.db) {
+            PatternConstraintKind::Singleton(singleton, _guard) => {
+                self.evaluate_match_pattern_singleton(*subject, *singleton)
             }
+            // TODO: support more pattern kinds
+            PatternConstraintKind::Value(..) | PatternConstraintKind::Unsupported => None,
         }
     }
 
@@ -483,14 +466,14 @@ impl<'db> NarrowingConstraintsBuilder<'db> {
 
     fn evaluate_match_pattern_singleton(
         &mut self,
-        subject: &ast::Expr,
-        pattern: &ast::PatternMatchSingleton,
+        subject: Expression<'db>,
+        singleton: ast::Singleton,
     ) -> Option<NarrowingConstraints<'db>> {
-        if let Some(ast::ExprName { id, .. }) = subject.as_name_expr() {
+        if let Some(ast::ExprName { id, .. }) = subject.node_ref(self.db).as_name_expr() {
             // SAFETY: we should always have a symbol for every Name node.
             let symbol = self.symbols().symbol_id_by_name(id).unwrap();
 
-            let ty = match pattern.value {
+            let ty = match singleton {
                 ast::Singleton::None => Type::none(self.db),
                 ast::Singleton::True => Type::BooleanLiteral(true),
                 ast::Singleton::False => Type::BooleanLiteral(false),

crates/red_knot_python_semantic/src/types/slots.rs

@@ -0,0 +1,103 @@
+use ruff_python_ast as ast;
+
+use crate::db::Db;
+use crate::symbol::{Boundness, Symbol};
+use crate::types::class_base::ClassBase;
+use crate::types::diagnostic::report_base_with_incompatible_slots;
+use crate::types::{Class, ClassLiteralType, Type};
+
+use super::InferContext;
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+enum SlotsKind {
+    /// `__slots__` is not found in the class.
+    NotSpecified,
+    /// `__slots__` is defined but empty: `__slots__ = ()`.
+    Empty,
+    /// `__slots__` is defined and is not empty: `__slots__ = ("a", "b")`.
+    NotEmpty,
+    /// `__slots__` is defined but its value is dynamic:
+    /// * `__slots__ = tuple(a for a in b)`
+    /// * `__slots__ = ["a", "b"]`
+    Dynamic,
+}
+
+impl SlotsKind {
+    fn from(db: &dyn Db, base: Class) -> Self {
+        let Symbol::Type(slots_ty, bound) = base.own_class_member(db, "__slots__") else {
+            return Self::NotSpecified;
+        };
+
+        if matches!(bound, Boundness::PossiblyUnbound) {
+            return Self::Dynamic;
+        };
+
+        match slots_ty {
+            // __slots__ = ("a", "b")
+            Type::Tuple(tuple) => {
+                if tuple.elements(db).is_empty() {
+                    Self::Empty
+                } else {
+                    Self::NotEmpty
+                }
+            }
+
+            // __slots__ = "abc"  # Same as `("abc",)`
+            Type::StringLiteral(_) => Self::NotEmpty,
+
+            _ => Self::Dynamic,
+        }
+    }
+}
+
+pub(super) fn check_class_slots(context: &InferContext, class: Class, node: &ast::StmtClassDef) {
+    let db = context.db();
+
+    let mut first_with_solid_base = None;
+    let mut common_solid_base = None;
+    let mut found_second = false;
+
+    for (index, base) in class.explicit_bases(db).iter().enumerate() {
+        let Type::ClassLiteral(ClassLiteralType { class: base }) = base else {
+            continue;
+        };
+
+        let solid_base = base.iter_mro(db).find_map(|current| {
+            let ClassBase::Class(current) = current else {
+                return None;
+            };
+
+            match SlotsKind::from(db, current) {
+                SlotsKind::NotEmpty => Some(current),
+                SlotsKind::NotSpecified | SlotsKind::Empty => None,
+                SlotsKind::Dynamic => None,
+            }
+        });
+
+        if solid_base.is_none() {
+            continue;
+        }
+
+        let base_node = &node.bases()[index];
+
+        if first_with_solid_base.is_none() {
+            first_with_solid_base = Some(index);
+            common_solid_base = solid_base;
+            continue;
+        }
+
+        if solid_base == common_solid_base {
+            continue;
+        }
+
+        found_second = true;
+        report_base_with_incompatible_slots(context, base_node);
+    }
+
+    if found_second {
+        if let Some(index) = first_with_solid_base {
+            let base_node = &node.bases()[index];
+            report_base_with_incompatible_slots(context, base_node);
+        };
+    }
+}

crates/red_knot_python_semantic/src/types/unpacker.rs

@@ -1,27 +1,33 @@
 use std::borrow::Cow;
+use std::cmp::Ordering;
 
-use ruff_db::files::File;
-use ruff_python_ast::{self as ast, AnyNodeRef};
 use rustc_hash::FxHashMap;
 
+use ruff_python_ast::{self as ast, AnyNodeRef};
+
 use crate::semantic_index::ast_ids::{HasScopedExpressionId, ScopedExpressionId};
 use crate::semantic_index::symbol::ScopeId;
-use crate::types::{todo_type, Type, TypeCheckDiagnostics};
+use crate::types::{infer_expression_types, todo_type, Type, TypeCheckDiagnostics};
+use crate::unpack::UnpackValue;
 use crate::Db;
 
 use super::context::{InferContext, WithDiagnostics};
+use super::diagnostic::INVALID_ASSIGNMENT;
+use super::{TupleType, UnionType};
 
 /// Unpacks the value expression type to their respective targets.
 pub(crate) struct Unpacker<'db> {
     context: InferContext<'db>,
+    scope: ScopeId<'db>,
     targets: FxHashMap<ScopedExpressionId, Type<'db>>,
 }
 
 impl<'db> Unpacker<'db> {
-    pub(crate) fn new(db: &'db dyn Db, file: File) -> Self {
+    pub(crate) fn new(db: &'db dyn Db, scope: ScopeId<'db>) -> Self {
         Self {
-            context: InferContext::new(db, file),
+            context: InferContext::new(db, scope),
             targets: FxHashMap::default(),
+            scope,
         }
     }
 
@@ -29,98 +35,211 @@ impl<'db> Unpacker<'db> {
         self.context.db()
     }
 
-    pub(crate) fn unpack(&mut self, target: &ast::Expr, value_ty: Type<'db>, scope: ScopeId<'db>) {
+    /// Unpack the value to the target expression.
+    pub(crate) fn unpack(&mut self, target: &ast::Expr, value: UnpackValue<'db>) {
+        debug_assert!(
+            matches!(target, ast::Expr::List(_) | ast::Expr::Tuple(_)),
+            "Unpacking target must be a list or tuple expression"
+        );
+
+        let mut value_ty = infer_expression_types(self.db(), value.expression())
+            .expression_ty(value.scoped_expression_id(self.db(), self.scope));
+
+        if value.is_iterable() {
+            // If the value is an iterable, then the type that needs to be unpacked is the iterator
+            // type.
+            value_ty = value_ty
+                .iterate(self.db())
+                .unwrap_with_diagnostic(&self.context, value.as_any_node_ref(self.db()));
+        }
+
+        self.unpack_inner(target, value_ty);
+    }
+
+    fn unpack_inner(&mut self, target: &ast::Expr, value_ty: Type<'db>) {
         match target {
             ast::Expr::Name(target_name) => {
-                self.targets
-                    .insert(target_name.scoped_expression_id(self.db(), scope), value_ty);
+                self.targets.insert(
+                    target_name.scoped_expression_id(self.db(), self.scope),
+                    value_ty,
+                );
             }
             ast::Expr::Starred(ast::ExprStarred { value, .. }) => {
-                self.unpack(value, value_ty, scope);
+                self.unpack_inner(value, value_ty);
             }
             ast::Expr::List(ast::ExprList { elts, .. })
-            | ast::Expr::Tuple(ast::ExprTuple { elts, .. }) => match value_ty {
-                Type::Tuple(tuple_ty) => {
-                    let starred_index = elts.iter().position(ast::Expr::is_starred_expr);
+            | ast::Expr::Tuple(ast::ExprTuple { elts, .. }) => {
+                // Initialize the vector of target types, one for each target.
+                //
+                // This is mainly useful for the union type where the target type at index `n` is
+                // going to be a union of types from every union type element at index `n`.
+                //
+                // For example, if the type is `tuple[int, int] | tuple[int, str]` and the target
+                // has two elements `(a, b)`, then
+                // * The type of `a` will be a union of `int` and `int` which are at index 0 in the
+                //   first and second tuple respectively which resolves to an `int`.
+                // * Similarly, the type of `b` will be a union of `int` and `str` which are at
+                //   index 1 in the first and second tuple respectively which will be `int | str`.
+                let mut target_types = vec![vec![]; elts.len()];
 
-                    let element_types = if let Some(starred_index) = starred_index {
-                        if tuple_ty.len(self.db()) >= elts.len() - 1 {
-                            let mut element_types = Vec::with_capacity(elts.len());
-                            element_types.extend_from_slice(
-                                // SAFETY: Safe because of the length check above.
-                                &tuple_ty.elements(self.db())[..starred_index],
-                            );
+                let unpack_types = match value_ty {
+                    Type::Union(union_ty) => union_ty.elements(self.db()),
+                    _ => std::slice::from_ref(&value_ty),
+                };
 
-                            // E.g., in `(a, *b, c, d) = ...`, the index of starred element `b`
-                            // is 1 and the remaining elements after that are 2.
-                            let remaining = elts.len() - (starred_index + 1);
-                            // This index represents the type of the last element that belongs
-                            // to the starred expression, in an exclusive manner.
-                            let starred_end_index = tuple_ty.len(self.db()) - remaining;
-                            // SAFETY: Safe because of the length check above.
-                            let _starred_element_types =
-                                &tuple_ty.elements(self.db())[starred_index..starred_end_index];
-                            // TODO: Combine the types into a list type. If the
-                            // starred_element_types is empty, then it should be `List[Any]`.
-                            // combine_types(starred_element_types);
-                            element_types.push(todo_type!("starred unpacking"));
+                for ty in unpack_types.iter().copied() {
+                    // Deconstruct certain types to delegate the inference back to the tuple type
+                    // for correct handling of starred expressions.
+                    let ty = match ty {
+                        Type::StringLiteral(string_literal_ty) => {
+                            // We could go further and deconstruct to an array of `StringLiteral`
+                            // with each individual character, instead of just an array of
+                            // `LiteralString`, but there would be a cost and it's not clear that
+                            // it's worth it.
+                            Type::tuple(
+                                self.db(),
+                                std::iter::repeat(Type::LiteralString)
+                                    .take(string_literal_ty.python_len(self.db())),
+                            )
+                        }
+                        _ => ty,
+                    };
 
-                            element_types.extend_from_slice(
-                                // SAFETY: Safe because of the length check above.
-                                &tuple_ty.elements(self.db())[starred_end_index..],
-                            );
-                            Cow::Owned(element_types)
-                        } else {
-                            let mut element_types = tuple_ty.elements(self.db()).to_vec();
-                            // Subtract 1 to insert the starred expression type at the correct
-                            // index.
-                            element_types.resize(elts.len() - 1, Type::Unknown);
-                            // TODO: This should be `list[Unknown]`
-                            element_types.insert(starred_index, todo_type!("starred unpacking"));
-                            Cow::Owned(element_types)
+                    if let Some(tuple_ty) = ty.into_tuple() {
+                        let tuple_ty_elements = self.tuple_ty_elements(target, elts, tuple_ty);
+
+                        match elts.len().cmp(&tuple_ty_elements.len()) {
+                            Ordering::Less => {
+                                self.context.report_lint(
+                                    &INVALID_ASSIGNMENT,
+                                    target.into(),
+                                    format_args!(
+                                        "Too many values to unpack (expected {}, got {})",
+                                        elts.len(),
+                                        tuple_ty_elements.len()
+                                    ),
+                                );
+                            }
+                            Ordering::Greater => {
+                                self.context.report_lint(
+                                    &INVALID_ASSIGNMENT,
+                                    target.into(),
+                                    format_args!(
+                                        "Not enough values to unpack (expected {}, got {})",
+                                        elts.len(),
+                                        tuple_ty_elements.len()
+                                    ),
+                                );
+                            }
+                            Ordering::Equal => {}
+                        }
+
+                        for (index, ty) in tuple_ty_elements.iter().enumerate() {
+                            if let Some(element_types) = target_types.get_mut(index) {
+                                element_types.push(*ty);
+                            }
                         }
                     } else {
-                        Cow::Borrowed(tuple_ty.elements(self.db()).as_ref())
-                    };
+                        let ty = if ty.is_literal_string() {
+                            Type::LiteralString
+                        } else {
+                            ty.iterate(self.db())
+                                .unwrap_with_diagnostic(&self.context, AnyNodeRef::from(target))
+                        };
+                        for target_type in &mut target_types {
+                            target_type.push(ty);
+                        }
+                    }
+                }
 
-                    for (index, element) in elts.iter().enumerate() {
-                        self.unpack(
-                            element,
-                            element_types.get(index).copied().unwrap_or(Type::Unknown),
-                            scope,
-                        );
-                    }
-                }
-                Type::StringLiteral(string_literal_ty) => {
-                    // Deconstruct the string literal to delegate the inference back to the
-                    // tuple type for correct handling of starred expressions. We could go
-                    // further and deconstruct to an array of `StringLiteral` with each
-                    // individual character, instead of just an array of `LiteralString`, but
-                    // there would be a cost and it's not clear that it's worth it.
-                    let value_ty = Type::tuple(
-                        self.db(),
-                        std::iter::repeat(Type::LiteralString)
-                            .take(string_literal_ty.python_len(self.db())),
-                    );
-                    self.unpack(target, value_ty, scope);
-                }
-                _ => {
-                    let value_ty = if value_ty.is_literal_string() {
-                        Type::LiteralString
-                    } else {
-                        value_ty
-                            .iterate(self.db())
-                            .unwrap_with_diagnostic(&self.context, AnyNodeRef::from(target))
+                for (index, element) in elts.iter().enumerate() {
+                    // SAFETY: `target_types` is initialized with the same length as `elts`.
+                    let element_ty = match target_types[index].as_slice() {
+                        [] => Type::Unknown,
+                        types => UnionType::from_elements(self.db(), types),
                     };
-                    for element in elts {
-                        self.unpack(element, value_ty, scope);
-                    }
+                    self.unpack_inner(element, element_ty);
                 }
-            },
+            }
             _ => {}
         }
     }
 
+    /// Returns the [`Type`] elements inside the given [`TupleType`] taking into account that there
+    /// can be a starred expression in the `elements`.
+    fn tuple_ty_elements(
+        &self,
+        expr: &ast::Expr,
+        targets: &[ast::Expr],
+        tuple_ty: TupleType<'db>,
+    ) -> Cow<'_, [Type<'db>]> {
+        // If there is a starred expression, it will consume all of the types at that location.
+        let Some(starred_index) = targets.iter().position(ast::Expr::is_starred_expr) else {
+            // Otherwise, the types will be unpacked 1-1 to the targets.
+            return Cow::Borrowed(tuple_ty.elements(self.db()).as_ref());
+        };
+
+        if tuple_ty.len(self.db()) >= targets.len() - 1 {
+            // This branch is only taken when there are enough elements in the tuple type to
+            // combine for the starred expression. So, the arithmetic and indexing operations are
+            // safe to perform.
+            let mut element_types = Vec::with_capacity(targets.len());
+
+            // Insert all the elements before the starred expression.
+            element_types.extend_from_slice(
+                // SAFETY: Safe because of the length check above.
+                &tuple_ty.elements(self.db())[..starred_index],
+            );
+
+            // The number of target expressions that are remaining after the starred expression.
+            // For example, in `(a, *b, c, d) = ...`, the index of starred element `b` is 1 and the
+            // remaining elements after that are 2.
+            let remaining = targets.len() - (starred_index + 1);
+
+            // This index represents the position of the last element that belongs to the starred
+            // expression, in an exclusive manner. For example, in `(a, *b, c) = (1, 2, 3, 4)`, the
+            // starred expression `b` will consume the elements `Literal[2]` and `Literal[3]` and
+            // the index value would be 3.
+            let starred_end_index = tuple_ty.len(self.db()) - remaining;
+
+            // SAFETY: Safe because of the length check above.
+            let _starred_element_types =
+                &tuple_ty.elements(self.db())[starred_index..starred_end_index];
+            // TODO: Combine the types into a list type. If the
+            // starred_element_types is empty, then it should be `List[Any]`.
+            // combine_types(starred_element_types);
+            element_types.push(todo_type!("starred unpacking"));
+
+            // Insert the types remaining that aren't consumed by the starred expression.
+            element_types.extend_from_slice(
+                // SAFETY: Safe because of the length check above.
+                &tuple_ty.elements(self.db())[starred_end_index..],
+            );
+
+            Cow::Owned(element_types)
+        } else {
+            self.context.report_lint(
+                &INVALID_ASSIGNMENT,
+                expr.into(),
+                format_args!(
+                    "Not enough values to unpack (expected {} or more, got {})",
+                    targets.len() - 1,
+                    tuple_ty.len(self.db())
+                ),
+            );
+
+            let mut element_types = tuple_ty.elements(self.db()).to_vec();
+
+            // Subtract 1 to insert the starred expression type at the correct
+            // index.
+            element_types.resize(targets.len() - 1, Type::Unknown);
+            // TODO: This should be `list[Unknown]`
+            element_types.insert(starred_index, todo_type!("starred unpacking"));
+
+            Cow::Owned(element_types)
+        }
+    }
+
     pub(crate) fn finish(mut self) -> UnpackResult<'db> {
         self.targets.shrink_to_fit();
         UnpackResult {

crates/red_knot_python_semantic/src/unpack.rs

@@ -1,7 +1,9 @@
 use ruff_db::files::File;
-use ruff_python_ast::{self as ast};
+use ruff_python_ast::{self as ast, AnyNodeRef};
+use ruff_text_size::{Ranged, TextRange};
 
 use crate::ast_node_ref::AstNodeRef;
+use crate::semantic_index::ast_ids::{HasScopedExpressionId, ScopedExpressionId};
 use crate::semantic_index::expression::Expression;
 use crate::semantic_index::symbol::{FileScopeId, ScopeId};
 use crate::Db;
@@ -41,7 +43,7 @@ pub(crate) struct Unpack<'db> {
     /// The ingredient representing the value expression of the unpacking. For example, in
     /// `(a, b) = (1, 2)`, the value expression is `(1, 2)`.
     #[no_eq]
-    pub(crate) value: Expression<'db>,
+    pub(crate) value: UnpackValue<'db>,
 
     #[no_eq]
     count: countme::Count<Unpack<'static>>,
@@ -52,4 +54,48 @@ impl<'db> Unpack<'db> {
     pub(crate) fn scope(self, db: &'db dyn Db) -> ScopeId<'db> {
         self.file_scope(db).to_scope_id(db, self.file(db))
     }
+
+    /// Returns the range of the unpack target expression.
+    pub(crate) fn range(self, db: &'db dyn Db) -> TextRange {
+        self.target(db).range()
+    }
+}
+
+/// The expression that is being unpacked.
+#[derive(Clone, Copy, Debug)]
+pub(crate) enum UnpackValue<'db> {
+    /// An iterable expression like the one in a `for` loop or a comprehension.
+    Iterable(Expression<'db>),
+    /// An expression that is being assigned to a target.
+    Assign(Expression<'db>),
+}
+
+impl<'db> UnpackValue<'db> {
+    /// Returns `true` if the value is an iterable expression.
+    pub(crate) const fn is_iterable(self) -> bool {
+        matches!(self, UnpackValue::Iterable(_))
+    }
+
+    /// Returns the underlying [`Expression`] that is being unpacked.
+    pub(crate) const fn expression(self) -> Expression<'db> {
+        match self {
+            UnpackValue::Assign(expr) | UnpackValue::Iterable(expr) => expr,
+        }
+    }
+
+    /// Returns the [`ScopedExpressionId`] of the underlying expression.
+    pub(crate) fn scoped_expression_id(
+        self,
+        db: &'db dyn Db,
+        scope: ScopeId<'db>,
+    ) -> ScopedExpressionId {
+        self.expression()
+            .node_ref(db)
+            .scoped_expression_id(db, scope)
+    }
+
+    /// Returns the expression as an [`AnyNodeRef`].
+    pub(crate) fn as_any_node_ref(self, db: &'db dyn Db) -> AnyNodeRef<'db> {
+        self.expression().node_ref(db).node().into()
+    }
 }

crates/red_knot_python_semantic/src/visibility_constraints.rs

@@ -0,0 +1,338 @@
+//! # Visibility constraints
+//!
+//! During semantic index building, we collect visibility constraints for each binding and
+//! declaration. These constraints are then used during type-checking to determine the static
+//! visibility of a certain definition. This allows us to re-analyze control flow during type
+//! checking, potentially "hiding" some branches that we can statically determine to never be
+//! taken. Consider the following example first. We added implicit "unbound" definitions at the
+//! start of the scope. Note how visibility constraints can apply to bindings outside of the
+//! if-statement:
+//! ```py
+//! x = <unbound>  # not a live binding for the use of x below, shadowed by `x = 1`
+//! y = <unbound>  # visibility constraint: ~test
+//!
+//! x = 1  # visibility constraint: ~test
+//! if test:
+//!     x = 2  # visibility constraint: test
+//!
+//!     y = 2  # visibility constraint: test
+//!
+//! use(x)
+//! use(y)
+//! ```
+//! The static truthiness of the `test` condition can either be always-false, ambiguous, or
+//! always-true. Similarly, we have the same three options when evaluating a visibility constraint.
+//! This outcome determines the visibility of a definition: always-true means that the definition
+//! is definitely visible for a given use, always-false means that the definition is definitely
+//! not visible, and ambiguous means that we might see this definition or not. In the latter case,
+//! we need to consider both options during type inference and boundness analysis. For the example
+//! above, these are the possible type inference / boundness results for the uses of `x` and `y`:
+//!
+//! ```text
+//!       | `test` truthiness | `~test` truthiness | type of `x`     | boundness of `y` |
+//!       |-------------------|--------------------|-----------------|------------------|
+//!       | always false      | always true        | `Literal[1]`    | unbound          |
+//!       | ambiguous         | ambiguous          | `Literal[1, 2]` | possibly unbound |
+//!       | always true       | always false       | `Literal[2]`    | bound            |
+//! ```
+//!
+//! ### Sequential constraints (ternary AND)
+//!
+//! As we have seen above, visibility constraints can apply outside of a control flow element.
+//! So we need to consider the possibility that multiple constraints apply to the same binding.
+//! Here, we consider what happens if multiple `if`-statements lead to a sequence of constraints.
+//! Consider the following example:
+//! ```py
+//! x = 0
+//!
+//! if test1:
+//!     x = 1
+//!
+//! if test2:
+//!     x = 2
+//! ```
+//! The binding `x = 2` is easy to analyze. Its visibility corresponds to the truthiness of `test2`.
+//! For the `x = 1` binding, things are a bit more interesting. It is always visible if `test1` is
+//! always-true *and* `test2` is always-false. It is never visible if `test1` is always-false *or*
+//! `test2` is always-true. And it is ambiguous otherwise. This corresponds to a ternary *test1 AND
+//! ~test2* operation in three-valued Kleene logic [Kleene]:
+//!
+//! ```text
+//!       | AND          | always-false | ambiguous    | always-true  |
+//!       |--------------|--------------|--------------|--------------|
+//!       | always false | always-false | always-false | always-false |
+//!       | ambiguous    | always-false | ambiguous    | ambiguous    |
+//!       | always true  | always-false | ambiguous    | always-true  |
+//! ```
+//!
+//! The `x = 0` binding can be handled similarly, with the difference that both `test1` and `test2`
+//! are negated:
+//! ```py
+//! x = 0  # ~test1 AND ~test2
+//!
+//! if test1:
+//!     x = 1  # test1 AND ~test2
+//!
+//! if test2:
+//!     x = 2  # test2
+//! ```
+//!
+//! ### Merged constraints (ternary OR)
+//!
+//! Finally, we consider what happens in "parallel" control flow. Consider the following example
+//! where we have omitted the test condition for the outer `if` for clarity:
+//! ```py
+//! x = 0
+//!
+//! if <…>:
+//!     if test1:
+//!         x = 1
+//! else:
+//!     if test2:
+//!         x = 2
+//!
+//! use(x)
+//! ```
+//! At the usage of `x`, i.e. after control flow has been merged again, the visibility of the `x =
+//! 0` binding behaves as follows: the binding is always visible if `test1` is always-false *or*
+//! `test2` is always-false; and it is never visible if `test1` is always-true *and* `test2` is
+//! always-true. This corresponds to a ternary *OR* operation in Kleene logic:
+//!
+//! ```text
+//!       | OR           | always-false | ambiguous    | always-true  |
+//!       |--------------|--------------|--------------|--------------|
+//!       | always false | always-false | ambiguous    | always-true  |
+//!       | ambiguous    | ambiguous    | ambiguous    | always-true  |
+//!       | always true  | always-true  | always-true  | always-true  |
+//! ```
+//!
+//! Using this, we can annotate the visibility constraints for the example above:
+//! ```py
+//! x = 0  # ~test1 OR ~test2
+//!
+//! if <…>:
+//!     if test1:
+//!         x = 1  # test1
+//! else:
+//!     if test2:
+//!         x = 2  # test2
+//!
+//! use(x)
+//! ```
+//!
+//! ### Explicit ambiguity
+//!
+//! In some cases, we explicitly add a `VisibilityConstraint::Ambiguous` constraint to all bindings
+//! in a certain control flow path. We do this when branching on something that we can not (or
+//! intentionally do not want to) analyze statically. `for` loops are one example:
+//! ```py
+//! x = <unbound>
+//!
+//! for _ in range(2):
+//!    x = 1
+//! ```
+//! Here, we report an ambiguous visibility constraint before branching off. If we don't do this,
+//! the `x = <unbound>` binding would be considered unconditionally visible in the no-loop case.
+//! And since the other branch does not have the live `x = <unbound>` binding, we would incorrectly
+//! create a state where the `x = <unbound>` binding is always visible.
+//!
+//!
+//! ### Properties
+//!
+//! The ternary `AND` and `OR` operations have the property that `~a OR ~b = ~(a AND b)`. This
+//! means we could, in principle, get rid of either of these two to simplify the representation.
+//!
+//! However, we already apply negative constraints `~test1` and `~test2` to the "branches not
+//! taken" in the example above. This means that the tree-representation `~test1 OR ~test2` is much
+//! cheaper/shallower than basically creating `~(~(~test1) AND ~(~test2))`. Similarly, if we wanted
+//! to get rid of `AND`, we would also have to create additional nodes. So for performance reasons,
+//! there is a small "duplication" in the code between those two constraint types.
+//!
+//! [Kleene]: <https://en.wikipedia.org/wiki/Three-valued_logic#Kleene_and_Priest_logics>
+
+use ruff_index::IndexVec;
+
+use crate::semantic_index::ScopedVisibilityConstraintId;
+use crate::semantic_index::{
+    ast_ids::HasScopedExpressionId,
+    constraint::{Constraint, ConstraintNode, PatternConstraintKind},
+};
+use crate::types::{infer_expression_types, Truthiness};
+use crate::Db;
+
+/// The maximum depth of recursion when evaluating visibility constraints.
+///
+/// This is a performance optimization that prevents us from descending deeply in case of
+/// pathological cases. The actual limit here has been derived from performance testing on
+/// the `black` codebase. When increasing the limit beyond 32, we see a 5x runtime increase
+/// resulting from a few files with a lot of boolean expressions and `if`-statements.
+const MAX_RECURSION_DEPTH: usize = 24;
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) enum VisibilityConstraint<'db> {
+    AlwaysTrue,
+    Ambiguous,
+    VisibleIf(Constraint<'db>),
+    VisibleIfNot(ScopedVisibilityConstraintId),
+    KleeneAnd(ScopedVisibilityConstraintId, ScopedVisibilityConstraintId),
+    KleeneOr(ScopedVisibilityConstraintId, ScopedVisibilityConstraintId),
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub(crate) struct VisibilityConstraints<'db> {
+    constraints: IndexVec<ScopedVisibilityConstraintId, VisibilityConstraint<'db>>,
+}
+
+impl Default for VisibilityConstraints<'_> {
+    fn default() -> Self {
+        Self {
+            constraints: IndexVec::from_iter([VisibilityConstraint::AlwaysTrue]),
+        }
+    }
+}
+
+impl<'db> VisibilityConstraints<'db> {
+    pub(crate) fn add(
+        &mut self,
+        constraint: VisibilityConstraint<'db>,
+    ) -> ScopedVisibilityConstraintId {
+        self.constraints.push(constraint)
+    }
+
+    pub(crate) fn add_or_constraint(
+        &mut self,
+        a: ScopedVisibilityConstraintId,
+        b: ScopedVisibilityConstraintId,
+    ) -> ScopedVisibilityConstraintId {
+        match (&self.constraints[a], &self.constraints[b]) {
+            (_, VisibilityConstraint::VisibleIfNot(id)) if a == *id => {
+                ScopedVisibilityConstraintId::ALWAYS_TRUE
+            }
+            (VisibilityConstraint::VisibleIfNot(id), _) if *id == b => {
+                ScopedVisibilityConstraintId::ALWAYS_TRUE
+            }
+            _ => self.add(VisibilityConstraint::KleeneOr(a, b)),
+        }
+    }
+
+    pub(crate) fn add_and_constraint(
+        &mut self,
+        a: ScopedVisibilityConstraintId,
+        b: ScopedVisibilityConstraintId,
+    ) -> ScopedVisibilityConstraintId {
+        if a == ScopedVisibilityConstraintId::ALWAYS_TRUE {
+            b
+        } else if b == ScopedVisibilityConstraintId::ALWAYS_TRUE {
+            a
+        } else {
+            self.add(VisibilityConstraint::KleeneAnd(a, b))
+        }
+    }
+
+    /// Analyze the statically known visibility for a given visibility constraint.
+    pub(crate) fn evaluate(&self, db: &'db dyn Db, id: ScopedVisibilityConstraintId) -> Truthiness {
+        self.evaluate_impl(db, id, MAX_RECURSION_DEPTH)
+    }
+
+    fn evaluate_impl(
+        &self,
+        db: &'db dyn Db,
+        id: ScopedVisibilityConstraintId,
+        max_depth: usize,
+    ) -> Truthiness {
+        if max_depth == 0 {
+            return Truthiness::Ambiguous;
+        }
+
+        let visibility_constraint = &self.constraints[id];
+        match visibility_constraint {
+            VisibilityConstraint::AlwaysTrue => Truthiness::AlwaysTrue,
+            VisibilityConstraint::Ambiguous => Truthiness::Ambiguous,
+            VisibilityConstraint::VisibleIf(constraint) => Self::analyze_single(db, constraint),
+            VisibilityConstraint::VisibleIfNot(negated) => {
+                self.evaluate_impl(db, *negated, max_depth - 1).negate()
+            }
+            VisibilityConstraint::KleeneAnd(lhs, rhs) => {
+                let lhs = self.evaluate_impl(db, *lhs, max_depth - 1);
+
+                if lhs == Truthiness::AlwaysFalse {
+                    return Truthiness::AlwaysFalse;
+                }
+
+                let rhs = self.evaluate_impl(db, *rhs, max_depth - 1);
+
+                if rhs == Truthiness::AlwaysFalse {
+                    Truthiness::AlwaysFalse
+                } else if lhs == Truthiness::AlwaysTrue && rhs == Truthiness::AlwaysTrue {
+                    Truthiness::AlwaysTrue
+                } else {
+                    Truthiness::Ambiguous
+                }
+            }
+            VisibilityConstraint::KleeneOr(lhs_id, rhs_id) => {
+                let lhs = self.evaluate_impl(db, *lhs_id, max_depth - 1);
+
+                if lhs == Truthiness::AlwaysTrue {
+                    return Truthiness::AlwaysTrue;
+                }
+
+                let rhs = self.evaluate_impl(db, *rhs_id, max_depth - 1);
+
+                if rhs == Truthiness::AlwaysTrue {
+                    Truthiness::AlwaysTrue
+                } else if lhs == Truthiness::AlwaysFalse && rhs == Truthiness::AlwaysFalse {
+                    Truthiness::AlwaysFalse
+                } else {
+                    Truthiness::Ambiguous
+                }
+            }
+        }
+    }
+
+    fn analyze_single(db: &dyn Db, constraint: &Constraint) -> Truthiness {
+        match constraint.node {
+            ConstraintNode::Expression(test_expr) => {
+                let inference = infer_expression_types(db, test_expr);
+                let scope = test_expr.scope(db);
+                let ty =
+                    inference.expression_ty(test_expr.node_ref(db).scoped_expression_id(db, scope));
+
+                ty.bool(db).negate_if(!constraint.is_positive)
+            }
+            ConstraintNode::Pattern(inner) => match inner.kind(db) {
+                PatternConstraintKind::Value(value, guard) => {
+                    let subject_expression = inner.subject(db);
+                    let inference = infer_expression_types(db, *subject_expression);
+                    let scope = subject_expression.scope(db);
+                    let subject_ty = inference.expression_ty(
+                        subject_expression
+                            .node_ref(db)
+                            .scoped_expression_id(db, scope),
+                    );
+
+                    let inference = infer_expression_types(db, *value);
+                    let scope = value.scope(db);
+                    let value_ty =
+                        inference.expression_ty(value.node_ref(db).scoped_expression_id(db, scope));
+
+                    if subject_ty.is_single_valued(db) {
+                        let truthiness =
+                            Truthiness::from(subject_ty.is_equivalent_to(db, value_ty));
+
+                        if truthiness.is_always_true() && guard.is_some() {
+                            // Fall back to ambiguous, the guard might change the result.
+                            Truthiness::Ambiguous
+                        } else {
+                            truthiness
+                        }
+                    } else {
+                        Truthiness::Ambiguous
+                    }
+                }
+                PatternConstraintKind::Singleton(..) | PatternConstraintKind::Unsupported => {
+                    Truthiness::Ambiguous
+                }
+            },
+        }
+    }
+}

crates/red_knot_test/src/config.rs

@@ -9,7 +9,7 @@
 //! ```
 
 use anyhow::Context;
-use red_knot_python_semantic::PythonVersion;
+use red_knot_python_semantic::{PythonPlatform, PythonVersion};
 use serde::Deserialize;
 
 #[derive(Deserialize, Debug, Default, Clone)]
@@ -28,13 +28,22 @@ impl MarkdownTestConfig {
     pub(crate) fn python_version(&self) -> Option<PythonVersion> {
         self.environment.as_ref().and_then(|env| env.python_version)
     }
+
+    pub(crate) fn python_platform(&self) -> Option<PythonPlatform> {
+        self.environment
+            .as_ref()
+            .and_then(|env| env.python_platform.clone())
+    }
 }
 
 #[derive(Deserialize, Debug, Default, Clone)]
 #[serde(rename_all = "kebab-case", deny_unknown_fields)]
 pub(crate) struct Environment {
-    /// Python version to assume when resolving types.
+    /// Target Python version to assume when resolving types.
     pub(crate) python_version: Option<PythonVersion>,
+
+    /// Target platform to assume when resolving types.
+    pub(crate) python_platform: Option<PythonPlatform>,
 }
 
 #[derive(Deserialize, Debug, Clone)]

crates/red_knot_test/src/db.rs

@@ -1,7 +1,7 @@
-use red_knot_python_semantic::lint::RuleSelection;
+use red_knot_python_semantic::lint::{LintRegistry, RuleSelection};
 use red_knot_python_semantic::{
-    default_lint_registry, Db as SemanticDb, Program, ProgramSettings, PythonVersion,
-    SearchPathSettings,
+    default_lint_registry, Db as SemanticDb, Program, ProgramSettings, PythonPlatform,
+    PythonVersion, SearchPathSettings,
 };
 use ruff_db::files::{File, Files};
 use ruff_db::system::{DbWithTestSystem, System, SystemPath, SystemPathBuf, TestSystem};
@@ -21,7 +21,7 @@ pub(crate) struct Db {
 
 impl Db {
     pub(crate) fn setup(workspace_root: SystemPathBuf) -> Self {
-        let rule_selection = RuleSelection::from_registry(&default_lint_registry());
+        let rule_selection = RuleSelection::from_registry(default_lint_registry());
 
         let db = Self {
             workspace_root,
@@ -40,6 +40,7 @@ impl Db {
             &db,
             &ProgramSettings {
                 python_version: PythonVersion::default(),
+                python_platform: PythonPlatform::default(),
                 search_paths: SearchPathSettings::new(db.workspace_root.clone()),
             },
         )
@@ -96,6 +97,10 @@ impl SemanticDb for Db {
     fn rule_selection(&self) -> &RuleSelection {
         &self.rule_selection
     }
+
+    fn lint_registry(&self) -> &LintRegistry {
+        default_lint_registry()
+    }
 }
 
 #[salsa::db]

crates/red_knot_test/src/lib.rs

@@ -52,6 +52,9 @@ pub fn run(path: &Utf8Path, long_title: &str, short_title: &str, test_name: &str
         Program::get(&db)
             .set_python_version(&mut db)
             .to(test.configuration().python_version().unwrap_or_default());
+        Program::get(&db)
+            .set_python_platform(&mut db)
+            .to(test.configuration().python_platform().unwrap_or_default());
 
         // Remove all files so that the db is in a "fresh" state.
         db.memory_file_system().remove_all();
@@ -97,7 +100,11 @@ fn run_test(db: &mut db::Db, test: &parser::MarkdownTest) -> Result<(), Failures
 
     let test_files: Vec<_> = test
         .files()
-        .map(|embedded| {
+        .filter_map(|embedded| {
+            if embedded.lang == "ignore" {
+                return None;
+            }
+
             assert!(
                 matches!(embedded.lang, "py" | "pyi"),
                 "Non-Python files not supported yet."
@@ -106,10 +113,10 @@ fn run_test(db: &mut db::Db, test: &parser::MarkdownTest) -> Result<(), Failures
             db.write_file(&full_path, embedded.code).unwrap();
             let file = system_path_to_file(db, full_path).unwrap();
 
-            TestFile {
+            Some(TestFile {
                 file,
                 backtick_offset: embedded.md_offset,
-            }
+            })
         })
         .collect();
 

crates/red_knot_vendored/vendor/typeshed/source_commit.txt

@@ -1 +1 @@
-fc11e835108394728930059c8db5b436209bc957
+2047b820730fdd65d37e6e8efcf29ca9af7ec3e7

crates/red_knot_vendored/vendor/typeshed/stdlib/_asyncio.pyi

@@ -65,7 +65,7 @@ class Task(Future[_T_co]):  # type: ignore[type-var]  # pyright: ignore[reportIn
             self,
             coro: _TaskCompatibleCoro[_T_co],
             *,
-            loop: AbstractEventLoop = ...,
+            loop: AbstractEventLoop | None = None,
             name: str | None = ...,
             context: Context | None = None,
             eager_start: bool = False,
@@ -75,13 +75,13 @@ class Task(Future[_T_co]):  # type: ignore[type-var]  # pyright: ignore[reportIn
             self,
             coro: _TaskCompatibleCoro[_T_co],
             *,
-            loop: AbstractEventLoop = ...,
+            loop: AbstractEventLoop | None = None,
             name: str | None = ...,
             context: Context | None = None,
         ) -> None: ...
     else:
         def __init__(
-            self, coro: _TaskCompatibleCoro[_T_co], *, loop: AbstractEventLoop = ..., name: str | None = ...
+            self, coro: _TaskCompatibleCoro[_T_co], *, loop: AbstractEventLoop | None = None, name: str | None = ...
         ) -> None: ...
 
     if sys.version_info >= (3, 12):

crates/red_knot_vendored/vendor/typeshed/stdlib/_blake2.pyi

@@ -22,8 +22,8 @@ class blake2b:
     digest_size: int
     name: str
     if sys.version_info >= (3, 9):
-        def __init__(
-            self,
+        def __new__(
+            cls,
             data: ReadableBuffer = b"",
             /,
             *,
@@ -39,10 +39,10 @@ class blake2b:
             inner_size: int = 0,
             last_node: bool = False,
             usedforsecurity: bool = True,
-        ) -> None: ...
+        ) -> Self: ...
     else:
-        def __init__(
-            self,
+        def __new__(
+            cls,
             data: ReadableBuffer = b"",
             /,
             *,
@@ -57,7 +57,7 @@ class blake2b:
             node_depth: int = 0,
             inner_size: int = 0,
             last_node: bool = False,
-        ) -> None: ...
+        ) -> Self: ...
 
     def copy(self) -> Self: ...
     def digest(self) -> bytes: ...
@@ -74,8 +74,8 @@ class blake2s:
     digest_size: int
     name: str
     if sys.version_info >= (3, 9):
-        def __init__(
-            self,
+        def __new__(
+            cls,
             data: ReadableBuffer = b"",
             /,
             *,
@@ -91,10 +91,10 @@ class blake2s:
             inner_size: int = 0,
             last_node: bool = False,
             usedforsecurity: bool = True,
-        ) -> None: ...
+        ) -> Self: ...
     else:
-        def __init__(
-            self,
+        def __new__(
+            cls,
             data: ReadableBuffer = b"",
             /,
             *,
@@ -109,7 +109,7 @@ class blake2s:
             node_depth: int = 0,
             inner_size: int = 0,
             last_node: bool = False,
-        ) -> None: ...
+        ) -> Self: ...
 
     def copy(self) -> Self: ...
     def digest(self) -> bytes: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_bz2.pyi

@@ -1,9 +1,15 @@
+import sys
 from _typeshed import ReadableBuffer
 from typing import final
+from typing_extensions import Self
 
 @final
 class BZ2Compressor:
-    def __init__(self, compresslevel: int = 9) -> None: ...
+    if sys.version_info >= (3, 12):
+        def __new__(cls, compresslevel: int = 9, /) -> Self: ...
+    else:
+        def __init__(self, compresslevel: int = 9, /) -> None: ...
+
     def compress(self, data: ReadableBuffer, /) -> bytes: ...
     def flush(self) -> bytes: ...
 

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

@@ -8,6 +8,7 @@ from typing import (  # noqa: Y022,Y038
     AsyncIterator as AsyncIterator,
     Awaitable as Awaitable,
     Callable as Callable,
+    ClassVar,
     Collection as Collection,
     Container as Container,
     Coroutine as Coroutine,
@@ -74,6 +75,7 @@ _VT_co = TypeVar("_VT_co", covariant=True)  # Value type covariant containers.
 class dict_keys(KeysView[_KT_co], Generic[_KT_co, _VT_co]):  # undocumented
     def __eq__(self, value: object, /) -> bool: ...
     def __reversed__(self) -> Iterator[_KT_co]: ...
+    __hash__: ClassVar[None]  # type: ignore[assignment]
     if sys.version_info >= (3, 13):
         def isdisjoint(self, other: Iterable[_KT_co], /) -> bool: ...
     if sys.version_info >= (3, 10):
@@ -91,6 +93,7 @@ class dict_values(ValuesView[_VT_co], Generic[_KT_co, _VT_co]):  # undocumented
 class dict_items(ItemsView[_KT_co, _VT_co]):  # undocumented
     def __eq__(self, value: object, /) -> bool: ...
     def __reversed__(self) -> Iterator[tuple[_KT_co, _VT_co]]: ...
+    __hash__: ClassVar[None]  # type: ignore[assignment]
     if sys.version_info >= (3, 13):
         def isdisjoint(self, other: Iterable[tuple[_KT_co, _VT_co]], /) -> bool: ...
     if sys.version_info >= (3, 10):

crates/red_knot_vendored/vendor/typeshed/stdlib/_contextvars.pyi

@@ -1,7 +1,7 @@
 import sys
 from collections.abc import Callable, Iterator, Mapping
 from typing import Any, ClassVar, Generic, TypeVar, final, overload
-from typing_extensions import ParamSpec
+from typing_extensions import ParamSpec, Self
 
 if sys.version_info >= (3, 9):
     from types import GenericAlias
@@ -13,9 +13,9 @@ _P = ParamSpec("_P")
 @final
 class ContextVar(Generic[_T]):
     @overload
-    def __init__(self, name: str) -> None: ...
+    def __new__(cls, name: str) -> Self: ...
     @overload
-    def __init__(self, name: str, *, default: _T) -> None: ...
+    def __new__(cls, name: str, *, default: _T) -> Self: ...
     def __hash__(self) -> int: ...
     @property
     def name(self) -> str: ...
@@ -37,6 +37,7 @@ class Token(Generic[_T]):
     @property
     def old_value(self) -> Any: ...  # returns either _T or MISSING, but that's hard to express
     MISSING: ClassVar[object]
+    __hash__: ClassVar[None]  # type: ignore[assignment]
     if sys.version_info >= (3, 9):
         def __class_getitem__(cls, item: Any, /) -> GenericAlias: ...
 
@@ -55,6 +56,7 @@ class Context(Mapping[ContextVar[Any], Any]):
     def get(self, key: ContextVar[_T], default: _D, /) -> _T | _D: ...
     def run(self, callable: Callable[_P, _T], *args: _P.args, **kwargs: _P.kwargs) -> _T: ...
     def copy(self) -> Context: ...
+    __hash__: ClassVar[None]  # type: ignore[assignment]
     def __getitem__(self, key: ContextVar[_T], /) -> _T: ...
     def __iter__(self) -> Iterator[ContextVar[Any]]: ...
     def __len__(self) -> int: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_csv.pyi

@@ -32,8 +32,8 @@ class Dialect:
     lineterminator: str
     quoting: _QuotingType
     strict: bool
-    def __init__(
-        self,
+    def __new__(
+        cls,
         dialect: _DialectLike | None = ...,
         delimiter: str = ",",
         doublequote: bool = True,
@@ -43,7 +43,7 @@ class Dialect:
         quoting: _QuotingType = 0,
         skipinitialspace: bool = False,
         strict: bool = False,
-    ) -> None: ...
+    ) -> Self: ...
 
 if sys.version_info >= (3, 10):
     # This class calls itself _csv.reader.
@@ -115,7 +115,7 @@ def reader(
 ) -> _reader: ...
 def register_dialect(
     name: str,
-    dialect: type[Dialect] = ...,
+    dialect: type[Dialect | csv.Dialect] = ...,
     *,
     delimiter: str = ",",
     quotechar: str | None = '"',

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

@@ -169,18 +169,18 @@ class CFuncPtr(_PointerLike, _CData, metaclass=_PyCFuncPtrType):
     # Abstract attribute that must be defined on subclasses
     _flags_: ClassVar[int]
     @overload
-    def __init__(self) -> None: ...
+    def __new__(cls) -> Self: ...
     @overload
-    def __init__(self, address: int, /) -> None: ...
+    def __new__(cls, address: int, /) -> Self: ...
     @overload
-    def __init__(self, callable: Callable[..., Any], /) -> None: ...
+    def __new__(cls, callable: Callable[..., Any], /) -> Self: ...
     @overload
-    def __init__(self, func_spec: tuple[str | int, CDLL], paramflags: tuple[_PF, ...] | None = ..., /) -> None: ...
+    def __new__(cls, func_spec: tuple[str | int, CDLL], paramflags: tuple[_PF, ...] | None = ..., /) -> Self: ...
     if sys.platform == "win32":
         @overload
-        def __init__(
-            self, vtbl_index: int, name: str, paramflags: tuple[_PF, ...] | None = ..., iid: _CData | _CDataType | None = ..., /
-        ) -> None: ...
+        def __new__(
+            cls, vtbl_index: int, name: str, paramflags: tuple[_PF, ...] | None = ..., iid: _CData | _CDataType | None = ..., /
+        ) -> Self: ...
 
     def __call__(self, *args: Any, **kwargs: Any) -> Any: ...
 

crates/red_knot_vendored/vendor/typeshed/stdlib/_curses.pyi

@@ -1,7 +1,7 @@
 import sys
-from _typeshed import ReadOnlyBuffer, SupportsRead
+from _typeshed import ReadOnlyBuffer, SupportsRead, SupportsWrite
 from curses import _ncurses_version
-from typing import IO, Any, final, overload
+from typing import Any, final, overload
 from typing_extensions import TypeAlias
 
 # NOTE: This module is ordinarily only available on Unix, but the windows-curses
@@ -517,7 +517,7 @@ class window:  # undocumented
     def overwrite(
         self, destwin: window, sminrow: int, smincol: int, dminrow: int, dmincol: int, dmaxrow: int, dmaxcol: int
     ) -> None: ...
-    def putwin(self, file: IO[Any], /) -> None: ...
+    def putwin(self, file: SupportsWrite[bytes], /) -> None: ...
     def redrawln(self, beg: int, num: int, /) -> None: ...
     def redrawwin(self) -> None: ...
     @overload

crates/red_knot_vendored/vendor/typeshed/stdlib/_frozen_importlib.pyi

@@ -5,7 +5,7 @@ import types
 from _typeshed.importlib import LoaderProtocol
 from collections.abc import Mapping, Sequence
 from types import ModuleType
-from typing import Any
+from typing import Any, ClassVar
 
 # Signature of `builtins.__import__` should be kept identical to `importlib.__import__`
 def __import__(
@@ -43,6 +43,7 @@ class ModuleSpec:
     def parent(self) -> str | None: ...
     has_location: bool
     def __eq__(self, other: object) -> bool: ...
+    __hash__: ClassVar[None]  # type: ignore[assignment]
 
 class BuiltinImporter(importlib.abc.MetaPathFinder, importlib.abc.InspectLoader):
     # MetaPathFinder

crates/red_knot_vendored/vendor/typeshed/stdlib/_io.pyi

@@ -112,7 +112,7 @@ class BufferedRandom(BufferedIOBase, _BufferedIOBase, BinaryIO):  # type: ignore
     def truncate(self, pos: int | None = None, /) -> int: ...
 
 class BufferedRWPair(BufferedIOBase, _BufferedIOBase):
-    def __init__(self, reader: RawIOBase, writer: RawIOBase, buffer_size: int = 8192) -> None: ...
+    def __init__(self, reader: RawIOBase, writer: RawIOBase, buffer_size: int = 8192, /) -> None: ...
     def peek(self, size: int = 0, /) -> bytes: ...
 
 class _TextIOBase(_IOBase):

crates/red_knot_vendored/vendor/typeshed/stdlib/_json.pyi

@@ -1,5 +1,6 @@
 from collections.abc import Callable
 from typing import Any, final
+from typing_extensions import Self
 
 @final
 class make_encoder:
@@ -19,8 +20,8 @@ class make_encoder:
     def encoder(self) -> Callable[[str], str]: ...
     @property
     def item_separator(self) -> str: ...
-    def __init__(
-        self,
+    def __new__(
+        cls,
         markers: dict[int, Any] | None,
         default: Callable[[Any], Any],
         encoder: Callable[[str], str],
@@ -30,7 +31,7 @@ class make_encoder:
         sort_keys: bool,
         skipkeys: bool,
         allow_nan: bool,
-    ) -> None: ...
+    ) -> Self: ...
     def __call__(self, obj: object, _current_indent_level: int) -> Any: ...
 
 @final
@@ -42,7 +43,7 @@ class make_scanner:
     parse_float: Any
     strict: bool
     # TODO: 'context' needs the attrs above (ducktype), but not __call__.
-    def __init__(self, context: make_scanner) -> None: ...
+    def __new__(cls, context: make_scanner) -> Self: ...
     def __call__(self, string: str, index: int) -> tuple[Any, int]: ...
 
 def encode_basestring(s: str, /) -> str: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_lzma.pyi

@@ -1,7 +1,8 @@
+import sys
 from _typeshed import ReadableBuffer
 from collections.abc import Mapping, Sequence
 from typing import Any, Final, final
-from typing_extensions import TypeAlias
+from typing_extensions import Self, TypeAlias
 
 _FilterChain: TypeAlias = Sequence[Mapping[str, Any]]
 
@@ -36,7 +37,11 @@ PRESET_EXTREME: int  # v big number
 
 @final
 class LZMADecompressor:
-    def __init__(self, format: int | None = ..., memlimit: int | None = ..., filters: _FilterChain | None = ...) -> None: ...
+    if sys.version_info >= (3, 12):
+        def __new__(cls, format: int | None = ..., memlimit: int | None = ..., filters: _FilterChain | None = ...) -> Self: ...
+    else:
+        def __init__(self, format: int | None = ..., memlimit: int | None = ..., filters: _FilterChain | None = ...) -> None: ...
+
     def decompress(self, data: ReadableBuffer, max_length: int = -1) -> bytes: ...
     @property
     def check(self) -> int: ...
@@ -49,9 +54,15 @@ class LZMADecompressor:
 
 @final
 class LZMACompressor:
-    def __init__(
-        self, format: int | None = ..., check: int = ..., preset: int | None = ..., filters: _FilterChain | None = ...
-    ) -> None: ...
+    if sys.version_info >= (3, 12):
+        def __new__(
+            cls, format: int | None = ..., check: int = ..., preset: int | None = ..., filters: _FilterChain | None = ...
+        ) -> Self: ...
+    else:
+        def __init__(
+            self, format: int | None = ..., check: int = ..., preset: int | None = ..., filters: _FilterChain | None = ...
+        ) -> None: ...
+
     def compress(self, data: ReadableBuffer, /) -> bytes: ...
     def flush(self) -> bytes: ...
 

crates/red_knot_vendored/vendor/typeshed/stdlib/_pickle.pyi

@@ -66,7 +66,6 @@ class Pickler:
         self,
         file: SupportsWrite[bytes],
         protocol: int | None = None,
-        *,
         fix_imports: bool = True,
         buffer_callback: _BufferCallback = None,
     ) -> None: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_ssl.pyi

@@ -12,7 +12,7 @@ from ssl import (
     SSLWantWriteError as SSLWantWriteError,
     SSLZeroReturnError as SSLZeroReturnError,
 )
-from typing import Any, Literal, TypedDict, final, overload
+from typing import Any, ClassVar, Literal, TypedDict, final, overload
 from typing_extensions import NotRequired, Self, TypeAlias
 
 _PasswordType: TypeAlias = Callable[[], str | bytes | bytearray] | str | bytes | bytearray
@@ -119,6 +119,7 @@ class MemoryBIO:
 
 @final
 class SSLSession:
+    __hash__: ClassVar[None]  # type: ignore[assignment]
     @property
     def has_ticket(self) -> bool: ...
     @property

crates/red_knot_vendored/vendor/typeshed/stdlib/_thread.pyi

@@ -13,17 +13,11 @@ error = RuntimeError
 
 def _count() -> int: ...
 @final
-class LockType:
+class RLock:
     def acquire(self, blocking: bool = True, timeout: float = -1) -> bool: ...
     def release(self) -> None: ...
-    def locked(self) -> bool: ...
-    def acquire_lock(self, blocking: bool = True, timeout: float = -1) -> bool: ...
-    def release_lock(self) -> None: ...
-    def locked_lock(self) -> bool: ...
-    def __enter__(self) -> bool: ...
-    def __exit__(
-        self, type: type[BaseException] | None, value: BaseException | None, traceback: TracebackType | None
-    ) -> None: ...
+    __enter__ = acquire
+    def __exit__(self, t: type[BaseException] | None, v: BaseException | None, tb: TracebackType | None) -> None: ...
 
 if sys.version_info >= (3, 13):
     @final
@@ -37,7 +31,33 @@ if sys.version_info >= (3, 13):
     def start_joinable_thread(
         function: Callable[[], object], handle: _ThreadHandle | None = None, daemon: bool = True
     ) -> _ThreadHandle: ...
-    lock = LockType
+    @final
+    class lock:
+        def acquire(self, blocking: bool = True, timeout: float = -1) -> bool: ...
+        def release(self) -> None: ...
+        def locked(self) -> bool: ...
+        def acquire_lock(self, blocking: bool = True, timeout: float = -1) -> bool: ...
+        def release_lock(self) -> None: ...
+        def locked_lock(self) -> bool: ...
+        def __enter__(self) -> bool: ...
+        def __exit__(
+            self, type: type[BaseException] | None, value: BaseException | None, traceback: TracebackType | None
+        ) -> None: ...
+
+    LockType = lock
+else:
+    @final
+    class LockType:
+        def acquire(self, blocking: bool = True, timeout: float = -1) -> bool: ...
+        def release(self) -> None: ...
+        def locked(self) -> bool: ...
+        def acquire_lock(self, blocking: bool = True, timeout: float = -1) -> bool: ...
+        def release_lock(self) -> None: ...
+        def locked_lock(self) -> bool: ...
+        def __enter__(self) -> bool: ...
+        def __exit__(
+            self, type: type[BaseException] | None, value: BaseException | None, traceback: TracebackType | None
+        ) -> None: ...
 
 @overload
 def start_new_thread(function: Callable[[Unpack[_Ts]], object], args: tuple[Unpack[_Ts]], /) -> int: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/_weakrefset.pyi

@@ -1,6 +1,6 @@
 import sys
 from collections.abc import Iterable, Iterator, MutableSet
-from typing import Any, TypeVar, overload
+from typing import Any, ClassVar, TypeVar, overload
 from typing_extensions import Self
 
 if sys.version_info >= (3, 9):
@@ -21,6 +21,7 @@ class WeakSet(MutableSet[_T]):
     def copy(self) -> Self: ...
     def remove(self, item: _T) -> None: ...
     def update(self, other: Iterable[_T]) -> None: ...
+    __hash__: ClassVar[None]  # type: ignore[assignment]
     def __contains__(self, item: object) -> bool: ...
     def __len__(self) -> int: ...
     def __iter__(self) -> Iterator[_T]: ...

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

@@ -1,8 +1,8 @@
 import sys
-from _typeshed import sentinel
+from _typeshed import SupportsWrite, sentinel
 from collections.abc import Callable, Generator, Iterable, Sequence
 from re import Pattern
-from typing import IO, Any, Final, Generic, NewType, NoReturn, Protocol, TypeVar, overload
+from typing import IO, Any, ClassVar, Final, Generic, NewType, NoReturn, Protocol, TypeVar, overload
 from typing_extensions import Self, TypeAlias, deprecated
 
 __all__ = [
@@ -207,8 +207,8 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         help: str | None = None,
         metavar: str | None = None,
     ) -> _SubParsersAction[_ArgumentParserT]: ...
-    def print_usage(self, file: IO[str] | None = None) -> None: ...
-    def print_help(self, file: IO[str] | None = None) -> None: ...
+    def print_usage(self, file: SupportsWrite[str] | None = None) -> None: ...
+    def print_help(self, file: SupportsWrite[str] | None = None) -> None: ...
     def format_usage(self) -> str: ...
     def format_help(self) -> str: ...
     @overload
@@ -254,7 +254,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
     def _get_value(self, action: Action, arg_string: str) -> Any: ...
     def _check_value(self, action: Action, value: Any) -> None: ...
     def _get_formatter(self) -> HelpFormatter: ...
-    def _print_message(self, message: str, file: IO[str] | None = None) -> None: ...
+    def _print_message(self, message: str, file: SupportsWrite[str] | None = None) -> None: ...
 
 class HelpFormatter:
     # undocumented
@@ -456,6 +456,7 @@ class Namespace(_AttributeHolder):
     def __setattr__(self, name: str, value: Any, /) -> None: ...
     def __contains__(self, key: str) -> bool: ...
     def __eq__(self, other: object) -> bool: ...
+    __hash__: ClassVar[None]  # type: ignore[assignment]
 
 class FileType:
     # undocumented

crates/red_knot_vendored/vendor/typeshed/stdlib/array.pyi

@@ -3,7 +3,7 @@ from _typeshed import ReadableBuffer, SupportsRead, SupportsWrite
 from collections.abc import Iterable
 
 # pytype crashes if array inherits from collections.abc.MutableSequence instead of typing.MutableSequence
-from typing import Any, Literal, MutableSequence, SupportsIndex, TypeVar, overload  # noqa: Y022
+from typing import Any, ClassVar, Literal, MutableSequence, SupportsIndex, TypeVar, overload  # noqa: Y022
 from typing_extensions import Self, TypeAlias
 
 if sys.version_info >= (3, 12):
@@ -24,19 +24,21 @@ class array(MutableSequence[_T]):
     @property
     def itemsize(self) -> int: ...
     @overload
-    def __init__(self: array[int], typecode: _IntTypeCode, initializer: bytes | bytearray | Iterable[int] = ..., /) -> None: ...
+    def __new__(
+        cls: type[array[int]], typecode: _IntTypeCode, initializer: bytes | bytearray | Iterable[int] = ..., /
+    ) -> array[int]: ...
     @overload
-    def __init__(
-        self: array[float], typecode: _FloatTypeCode, initializer: bytes | bytearray | Iterable[float] = ..., /
-    ) -> None: ...
+    def __new__(
+        cls: type[array[float]], typecode: _FloatTypeCode, initializer: bytes | bytearray | Iterable[float] = ..., /
+    ) -> array[float]: ...
     @overload
-    def __init__(
-        self: array[str], typecode: _UnicodeTypeCode, initializer: bytes | bytearray | Iterable[str] = ..., /
-    ) -> None: ...
+    def __new__(
+        cls: type[array[str]], typecode: _UnicodeTypeCode, initializer: bytes | bytearray | Iterable[str] = ..., /
+    ) -> array[str]: ...
     @overload
-    def __init__(self, typecode: str, initializer: Iterable[_T], /) -> None: ...
+    def __new__(cls, typecode: str, initializer: Iterable[_T], /) -> Self: ...
     @overload
-    def __init__(self, typecode: str, initializer: bytes | bytearray = ..., /) -> None: ...
+    def __new__(cls, typecode: str, initializer: bytes | bytearray = ..., /) -> Self: ...
     def append(self, v: _T, /) -> None: ...
     def buffer_info(self) -> tuple[int, int]: ...
     def byteswap(self) -> None: ...
@@ -62,6 +64,7 @@ class array(MutableSequence[_T]):
         def fromstring(self, buffer: str | ReadableBuffer, /) -> None: ...
         def tostring(self) -> bytes: ...
 
+    __hash__: ClassVar[None]  # type: ignore[assignment]
     def __len__(self) -> int: ...
     @overload
     def __getitem__(self, key: SupportsIndex, /) -> _T: ...

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

@@ -7,7 +7,7 @@ from _ast import (
     PyCF_TYPE_COMMENTS as PyCF_TYPE_COMMENTS,
 )
 from _typeshed import ReadableBuffer, Unused
-from collections.abc import Iterator
+from collections.abc import Iterable, Iterator
 from typing import Any, ClassVar, Generic, Literal, TypedDict, TypeVar as _TypeVar, overload
 from typing_extensions import Self, Unpack, deprecated
 
@@ -1154,6 +1154,7 @@ class Tuple(expr):
     if sys.version_info >= (3, 14):
         def __replace__(self, *, elts: list[expr] = ..., ctx: expr_context = ..., **kwargs: Unpack[_Attributes]) -> Self: ...
 
+@deprecated("Deprecated since Python 3.9.")
 class slice(AST): ...  # deprecated and moved to ast.py for >= (3, 9)
 
 if sys.version_info >= (3, 9):
@@ -1185,22 +1186,38 @@ class Slice(_Slice):
             **kwargs: Unpack[_SliceAttributes],
         ) -> Self: ...
 
+@deprecated("Deprecated since Python 3.9. Use ast.Tuple instead.")
 class ExtSlice(slice):  # deprecated and moved to ast.py if sys.version_info >= (3, 9)
-    dims: list[slice]
-    def __init__(self, dims: list[slice], **kwargs: Unpack[_SliceAttributes]) -> None: ...
+    if sys.version_info >= (3, 9):
+        def __new__(cls, dims: Iterable[slice] = (), **kwargs: Unpack[_SliceAttributes]) -> Tuple: ...  # type: ignore[misc]
+    else:
+        dims: list[slice]
+        def __init__(self, dims: list[slice], **kwargs: Unpack[_SliceAttributes]) -> None: ...
 
+@deprecated("Deprecated since Python 3.9. Use the index value directly instead.")
 class Index(slice):  # deprecated and moved to ast.py if sys.version_info >= (3, 9)
-    value: expr
-    def __init__(self, value: expr, **kwargs: Unpack[_SliceAttributes]) -> None: ...
+    if sys.version_info >= (3, 9):
+        def __new__(cls, value: expr, **kwargs: Unpack[_SliceAttributes]) -> expr: ...  # type: ignore[misc]
+    else:
+        value: expr
+        def __init__(self, value: expr, **kwargs: Unpack[_SliceAttributes]) -> None: ...
 
 class expr_context(AST): ...
+
+@deprecated("Deprecated since Python 3.9. Unused in Python 3.")
 class AugLoad(expr_context): ...  # deprecated and moved to ast.py if sys.version_info >= (3, 9)
+
+@deprecated("Deprecated since Python 3.9. Unused in Python 3.")
 class AugStore(expr_context): ...  # deprecated and moved to ast.py if sys.version_info >= (3, 9)
+
+@deprecated("Deprecated since Python 3.9. Unused in Python 3.")
 class Param(expr_context): ...  # deprecated and moved to ast.py if sys.version_info >= (3, 9)
 
+@deprecated("Deprecated since Python 3.9. Unused in Python 3.")
 class Suite(mod):  # deprecated and moved to ast.py if sys.version_info >= (3, 9)
-    body: list[stmt]
-    def __init__(self, body: list[stmt]) -> None: ...
+    if sys.version_info < (3, 9):
+        body: list[stmt]
+        def __init__(self, body: list[stmt]) -> None: ...
 
 class Load(expr_context): ...
 class Store(expr_context): ...

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/base_events.pyi

@@ -13,6 +13,7 @@ from socket import AddressFamily, SocketKind, _Address, _RetAddress, socket
 from typing import IO, Any, Literal, TypeVar, overload
 from typing_extensions import TypeAlias, TypeVarTuple, Unpack
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.version_info >= (3, 9):
     __all__ = ("BaseEventLoop", "Server")
 else:
@@ -452,6 +453,7 @@ class BaseEventLoop(AbstractEventLoop):
         bufsize: Literal[0] = 0,
         encoding: None = None,
         errors: None = None,
+        text: Literal[False] | None = None,
         **kwargs: Any,
     ) -> tuple[SubprocessTransport, _ProtocolT]: ...
     def add_reader(self, fd: FileDescriptorLike, callback: Callable[[Unpack[_Ts]], Any], *args: Unpack[_Ts]) -> None: ...

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/coroutines.pyi

@@ -3,6 +3,7 @@ from collections.abc import Awaitable, Callable, Coroutine
 from typing import Any, TypeVar, overload
 from typing_extensions import ParamSpec, TypeGuard, TypeIs
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.version_info >= (3, 11):
     __all__ = ("iscoroutinefunction", "iscoroutine")
 else:

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/events.pyi

@@ -22,6 +22,7 @@ from .tasks import Task
 from .transports import BaseTransport, DatagramTransport, ReadTransport, SubprocessTransport, Transport, WriteTransport
 from .unix_events import AbstractChildWatcher
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.version_info >= (3, 14):
     __all__ = (
         "AbstractEventLoopPolicy",

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/exceptions.pyi

@@ -1,5 +1,6 @@
 import sys
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.version_info >= (3, 11):
     __all__ = (
         "BrokenBarrierError",

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/futures.pyi

@@ -5,6 +5,7 @@ from typing_extensions import TypeIs
 
 from .events import AbstractEventLoop
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 __all__ = ("Future", "wrap_future", "isfuture")
 
 _T = TypeVar("_T")

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/locks.pyi

@@ -15,6 +15,7 @@ if sys.version_info >= (3, 10):
 else:
     _LoopBoundMixin = object
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.version_info >= (3, 11):
     __all__ = ("Lock", "Event", "Condition", "Semaphore", "BoundedSemaphore", "Barrier")
 else:

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/protocols.pyi

@@ -2,6 +2,7 @@ from _typeshed import ReadableBuffer
 from asyncio import transports
 from typing import Any
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 __all__ = ("BaseProtocol", "Protocol", "DatagramProtocol", "SubprocessProtocol", "BufferedProtocol")
 
 class BaseProtocol:

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/queues.pyi

@@ -13,6 +13,7 @@ else:
 class QueueEmpty(Exception): ...
 class QueueFull(Exception): ...
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.version_info >= (3, 13):
     __all__ = ("Queue", "PriorityQueue", "LifoQueue", "QueueFull", "QueueEmpty", "QueueShutDown")
 

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/runners.pyi

@@ -7,6 +7,7 @@ from typing_extensions import Self
 
 from .events import AbstractEventLoop
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.version_info >= (3, 11):
     __all__ = ("Runner", "run")
 else:

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/streams.pyi

@@ -9,6 +9,7 @@ from typing_extensions import Self, TypeAlias
 from . import events, protocols, transports
 from .base_events import Server
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.platform == "win32":
     __all__ = ("StreamReader", "StreamWriter", "StreamReaderProtocol", "open_connection", "start_server")
 else:

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/subprocess.pyi

@@ -5,6 +5,7 @@ from asyncio import events, protocols, streams, transports
 from collections.abc import Callable, Collection
 from typing import IO, Any, Literal
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 __all__ = ("create_subprocess_exec", "create_subprocess_shell")
 
 PIPE: int

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/taskgroups.pyi

@@ -8,6 +8,7 @@ from . import _CoroutineLike
 from .events import AbstractEventLoop
 from .tasks import Task
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.version_info >= (3, 12):
     __all__ = ("TaskGroup",)
 else:

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

@@ -18,6 +18,7 @@ from .futures import Future
 if sys.version_info >= (3, 11):
     from contextvars import Context
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.version_info >= (3, 12):
     __all__ = (
         "Task",

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/threads.pyi

@@ -2,6 +2,7 @@ from collections.abc import Callable
 from typing import TypeVar
 from typing_extensions import ParamSpec
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 __all__ = ("to_thread",)
 _P = ParamSpec("_P")
 _R = TypeVar("_R")

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/timeouts.pyi

@@ -2,6 +2,7 @@ from types import TracebackType
 from typing import final
 from typing_extensions import Self
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 __all__ = ("Timeout", "timeout", "timeout_at")
 
 @final

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/transports.pyi

@@ -4,6 +4,7 @@ from collections.abc import Iterable, Mapping
 from socket import _Address
 from typing import Any
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 __all__ = ("BaseTransport", "ReadTransport", "WriteTransport", "Transport", "DatagramTransport", "SubprocessTransport")
 
 class BaseTransport:

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

@@ -13,10 +13,12 @@ from .selector_events import BaseSelectorEventLoop
 
 _Ts = TypeVarTuple("_Ts")
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.platform != "win32":
     if sys.version_info >= (3, 14):
         __all__ = ("SelectorEventLoop", "DefaultEventLoopPolicy", "EventLoop")
     elif sys.version_info >= (3, 13):
+        # Adds EventLoop
         __all__ = (
             "SelectorEventLoop",
             "AbstractChildWatcher",
@@ -29,6 +31,7 @@ if sys.platform != "win32":
             "EventLoop",
         )
     elif sys.version_info >= (3, 9):
+        # adds PidfdChildWatcher
         __all__ = (
             "SelectorEventLoop",
             "AbstractChildWatcher",

crates/red_knot_vendored/vendor/typeshed/stdlib/asyncio/windows_events.pyi

@@ -6,6 +6,7 @@ from typing import IO, Any, ClassVar, Final, NoReturn
 
 from . import events, futures, proactor_events, selector_events, streams, windows_utils
 
+# Keep asyncio.__all__ updated with any changes to __all__ here
 if sys.platform == "win32":
     if sys.version_info >= (3, 13):
         # 3.13 added `EventLoop`.

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

@@ -1489,18 +1489,18 @@ def locals() -> dict[str, Any]: ...
 
 class map(Generic[_S]):
     @overload
-    def __new__(cls, func: Callable[[_T1], _S], iter1: Iterable[_T1], /) -> Self: ...
+    def __new__(cls, func: Callable[[_T1], _S], iterable: Iterable[_T1], /) -> Self: ...
     @overload
-    def __new__(cls, func: Callable[[_T1, _T2], _S], iter1: Iterable[_T1], iter2: Iterable[_T2], /) -> Self: ...
+    def __new__(cls, func: Callable[[_T1, _T2], _S], iterable: Iterable[_T1], iter2: Iterable[_T2], /) -> Self: ...
     @overload
     def __new__(
-        cls, func: Callable[[_T1, _T2, _T3], _S], iter1: Iterable[_T1], iter2: Iterable[_T2], iter3: Iterable[_T3], /
+        cls, func: Callable[[_T1, _T2, _T3], _S], iterable: Iterable[_T1], iter2: Iterable[_T2], iter3: Iterable[_T3], /
     ) -> Self: ...
     @overload
     def __new__(
         cls,
         func: Callable[[_T1, _T2, _T3, _T4], _S],
-        iter1: Iterable[_T1],
+        iterable: Iterable[_T1],
         iter2: Iterable[_T2],
         iter3: Iterable[_T3],
         iter4: Iterable[_T4],
@@ -1510,7 +1510,7 @@ class map(Generic[_S]):
     def __new__(
         cls,
         func: Callable[[_T1, _T2, _T3, _T4, _T5], _S],
-        iter1: Iterable[_T1],
+        iterable: Iterable[_T1],
         iter2: Iterable[_T2],
         iter3: Iterable[_T3],
         iter4: Iterable[_T4],
@@ -1521,7 +1521,7 @@ class map(Generic[_S]):
     def __new__(
         cls,
         func: Callable[..., _S],
-        iter1: Iterable[Any],
+        iterable: Iterable[Any],
         iter2: Iterable[Any],
         iter3: Iterable[Any],
         iter4: Iterable[Any],
@@ -1964,9 +1964,7 @@ class NameError(Exception):
 
 class ReferenceError(Exception): ...
 class RuntimeError(Exception): ...
-
-class StopAsyncIteration(Exception):
-    value: Any
+class StopAsyncIteration(Exception): ...
 
 class SyntaxError(Exception):
     msg: str

crates/red_knot_vendored/vendor/typeshed/stdlib/codecs.pyi

@@ -254,6 +254,8 @@ class StreamReaderWriter(TextIO):
     def writable(self) -> bool: ...
 
 class StreamRecoder(BinaryIO):
+    data_encoding: str
+    file_encoding: str
     def __init__(
         self,
         stream: _Stream,