Avoid cloning live declarations

## Summary

Simplify unions of `T` and `~T` to `object`.

## Test Plan

Adapted existing tests.

.github/renovate.json5

@@ -45,7 +45,7 @@
       groupName: "Artifact GitHub Actions dependencies",
       matchManagers: ["github-actions"],
       matchDatasources: ["gitea-tags", "github-tags"],
-      matchPackagePatterns: ["actions/.*-artifact"],
+      matchPackageNames: ["actions/.*-artifact"],
       description: "Weekly update of artifact-related GitHub Actions dependencies",
     },
     {
@@ -61,7 +61,7 @@
     {
       // Disable updates of `zip-rs`; intentionally pinned for now due to ownership change
       // See: https://github.com/astral-sh/uv/issues/3642
-      matchPackagePatterns: ["zip"],
+      matchPackageNames: ["zip"],
       matchManagers: ["cargo"],
       enabled: false,
     },
@@ -70,7 +70,7 @@
       // with `mkdocs-material-insider`.
       // See: https://squidfunk.github.io/mkdocs-material/insiders/upgrade/
       matchManagers: ["pip_requirements"],
-      matchPackagePatterns: ["mkdocs-material"],
+      matchPackageNames: ["mkdocs-material"],
       enabled: false,
     },
     {
@@ -87,13 +87,13 @@
     {
       groupName: "Monaco",
       matchManagers: ["npm"],
-      matchPackagePatterns: ["monaco"],
+      matchPackageNames: ["monaco"],
       description: "Weekly update of the Monaco editor",
     },
     {
       groupName: "strum",
       matchManagers: ["cargo"],
-      matchPackagePatterns: ["strum"],
+      matchPackageNames: ["strum"],
       description: "Weekly update of strum dependencies",
     },
     {

.github/workflows/build-docker.yml

@@ -48,11 +48,13 @@ jobs:
 
       - name: Check tag consistency
         if: ${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
+        env:
+          TAG: ${{ inputs.plan != '' && fromJson(inputs.plan).announcement_tag || 'dry-run' }}
         run: |
           version=$(grep "version = " pyproject.toml | sed -e 's/version = "\(.*\)"/\1/g')
-          if [ "${{ fromJson(inputs.plan).announcement_tag }}" != "${version}" ]; then
+          if [ "${TAG}" != "${version}" ]; then
             echo "The input tag does not match the version from pyproject.toml:" >&2
-            echo "${{ fromJson(inputs.plan).announcement_tag }}" >&2
+            echo "${TAG}" >&2
             echo "${version}" >&2
             exit 1
           else
@@ -175,6 +177,8 @@ jobs:
 
       - name: Generate Dynamic Dockerfile Tags
         shell: bash
+        env:
+          TAG_VALUE: ${{ fromJson(inputs.plan).announcement_tag }}
         run: |
           set -euo pipefail
 
@@ -195,8 +199,8 @@ jobs:
           # Loop through all base tags and append its docker metadata pattern to the list
           # Order is on purpose such that the label org.opencontainers.image.version has the first pattern with the full version
           IFS=','; for TAG in ${BASE_TAGS}; do
-            TAG_PATTERNS="${TAG_PATTERNS}type=pep440,pattern={{ version }},suffix=-${TAG},value=${{ fromJson(inputs.plan).announcement_tag }}\n"
-            TAG_PATTERNS="${TAG_PATTERNS}type=pep440,pattern={{ major }}.{{ minor }},suffix=-${TAG},value=${{ fromJson(inputs.plan).announcement_tag }}\n"
+            TAG_PATTERNS="${TAG_PATTERNS}type=pep440,pattern={{ version }},suffix=-${TAG},value=${TAG_VALUE}\n"
+            TAG_PATTERNS="${TAG_PATTERNS}type=pep440,pattern={{ major }}.{{ minor }},suffix=-${TAG},value=${TAG_VALUE}\n"
             TAG_PATTERNS="${TAG_PATTERNS}type=raw,value=${TAG}\n"
           done
 

.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
@@ -386,7 +386,7 @@ jobs:
       - name: "Install Rust toolchain"
         run: rustup component add rustfmt
       - uses: Swatinem/rust-cache@v2
-      - run: ./scripts/add_rule.py --name DoTheThing --prefix PL --code C0999 --linter pylint
+      - run: ./scripts/add_rule.py --name DoTheThing --prefix F --code 999 --linter pyflakes
       - run: cargo check
       - run: cargo fmt --all --check
       - run: |
@@ -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"
@@ -73,6 +73,6 @@ jobs:
               owner: "astral-sh",
               repo: "ruff",
               title: `Daily parser fuzz failed on ${new Date().toDateString()}`,
-              body: "Runs listed here: https://github.com/astral-sh/ruff/actions/workflows/daily_fuzz.yml",
+              body: "Run listed here: https://github.com/${{ github.repository }}/actions/runs/${{ github.run_id }}",
               labels: ["bug", "parser", "fuzzer"],
             })

.github/workflows/daily_property_tests.yaml

@@ -0,0 +1,71 @@
+name: Daily property test run
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 12 * * *"
+  pull_request:
+    paths:
+      - ".github/workflows/daily_property_tests.yaml"
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+env:
+  CARGO_INCREMENTAL: 0
+  CARGO_NET_RETRY: 10
+  CARGO_TERM_COLOR: always
+  RUSTUP_MAX_RETRIES: 10
+  FORCE_COLOR: 1
+
+jobs:
+  property_tests:
+    name: Property tests
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    # Don't run the cron job on forks:
+    if: ${{ github.repository == 'astral-sh/ruff' || github.event_name != 'schedule' }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      - name: "Install Rust toolchain"
+        run: rustup show
+      - name: "Install mold"
+        uses: rui314/setup-mold@v1
+      - uses: Swatinem/rust-cache@v2
+      - name: Build Red Knot
+        # A release build takes longer (2 min vs 1 min), but the property tests run much faster in release
+        # mode (1.5 min vs 14 min), so the overall time is shorter with a release build.
+        run: cargo build --locked --release --package red_knot_python_semantic --tests
+      - name: Run property tests
+        shell: bash
+        run: |
+          export QUICKCHECK_TESTS=100000
+          for _ in {1..5}; do
+            cargo test --locked --release --package red_knot_python_semantic -- --ignored types::property_tests::stable
+          done
+
+  create-issue-on-failure:
+    name: Create an issue if the daily property test run surfaced any bugs
+    runs-on: ubuntu-latest
+    needs: property_tests
+    if: ${{ github.repository == 'astral-sh/ruff' && always() && github.event_name == 'schedule' && needs.property_tests.result == 'failure' }}
+    permissions:
+      issues: write
+    steps:
+      - uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            await github.rest.issues.create({
+              owner: "astral-sh",
+              repo: "ruff",
+              title: `Daily property test run failed on ${new Date().toDateString()}`,
+              body: "Run listed here: https://github.com/${{ github.repository }}/actions/runs/${{ github.run_id }}",
+              labels: ["bug", "red-knot", "testing"],
+            })

.github/workflows/publish-docs.yml

@@ -33,8 +33,9 @@ jobs:
           python-version: 3.12
 
       - name: "Set docs version"
+        env:
+          version: ${{ (inputs.plan != '' && fromJson(inputs.plan).announcement_tag) || inputs.ref }}
         run: |
-          version="${{ (inputs.plan != '' && fromJson(inputs.plan).announcement_tag) || inputs.ref }}"
           # if version is missing, use 'latest'
           if [ -z "$version" ]; then
             echo "Using 'latest' as version"

.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-*

.github/zizmor.yml

@@ -1,6 +1,12 @@
 # Configuration for the zizmor static analysis tool, run via pre-commit in CI
 # https://woodruffw.github.io/zizmor/configuration/
+#
+# TODO: can we remove the ignores here so that our workflows are more secure?
 rules:
   dangerous-triggers:
     ignore:
       - pr-comment.yaml
+  cache-poisoning:
+    ignore:
+      - build-docker.yml
+      - publish-playground.yml

.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: v1.29.4
     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: v0.8.6
     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: v1.0.0
     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: v1.7.6
     hooks:
       - id: actionlint
         stages:

BREAKING_CHANGES.md

@@ -1,5 +1,9 @@
 # Breaking Changes
 
+## 0.9.0
+
+Ruff now formats your code according to the 2025 style guide. As a result, your code might now get formatted differently. See the [changelog](./CHANGELOG.md#090) for a detailed list of changes.
+
 ## 0.8.0
 
 - **Default to Python 3.9**

CHANGELOG.md

@@ -1,5 +1,180 @@
 # Changelog
 
+## 0.9.1
+
+### Preview features
+
+- \[`pycodestyle`\] Run `too-many-newlines-at-end-of-file` on each cell in notebooks (`W391`) ([#15308](https://github.com/astral-sh/ruff/pull/15308))
+- \[`ruff`\] Omit diagnostic for shadowed private function parameters in `used-dummy-variable` (`RUF052`) ([#15376](https://github.com/astral-sh/ruff/pull/15376))
+
+### Rule changes
+
+- \[`flake8-bugbear`\] Improve `assert-raises-exception` message (`B017`) ([#15389](https://github.com/astral-sh/ruff/pull/15389))
+
+### Formatter
+
+- Preserve trailing end-of line comments for the last string literal in implicitly concatenated strings ([#15378](https://github.com/astral-sh/ruff/pull/15378))
+
+### Server
+
+- Fix a bug where the server and client notebooks were out of sync after reordering cells ([#15398](https://github.com/astral-sh/ruff/pull/15398))
+
+### Bug fixes
+
+- \[`flake8-pie`\] Correctly remove wrapping parentheses (`PIE800`) ([#15394](https://github.com/astral-sh/ruff/pull/15394))
+- \[`pyupgrade`\] Handle comments and multiline expressions correctly (`UP037`) ([#15337](https://github.com/astral-sh/ruff/pull/15337))
+
+## 0.9.0
+
+Check out the [blog post](https://astral.sh/blog/ruff-v0.9.0) for a migration guide and overview of the changes!
+
+### Breaking changes
+
+Ruff now formats your code according to the 2025 style guide. As a result, your code might now get formatted differently. See the formatter section for a detailed list of changes.
+
+This release doesn’t remove or remap any existing stable rules.
+
+### Stabilization
+
+The following rules have been stabilized and are no longer in preview:
+
+- [`stdlib-module-shadowing`](https://docs.astral.sh/ruff/rules/stdlib-module-shadowing/) (`A005`).
+    This rule has also been renamed: previously, it was called `builtin-module-shadowing`.
+- [`builtin-lambda-argument-shadowing`](https://docs.astral.sh/ruff/rules/builtin-lambda-argument-shadowing/) (`A006`)
+- [`slice-to-remove-prefix-or-suffix`](https://docs.astral.sh/ruff/rules/slice-to-remove-prefix-or-suffix/) (`FURB188`)
+- [`boolean-chained-comparison`](https://docs.astral.sh/ruff/rules/boolean-chained-comparison/) (`PLR1716`)
+- [`decimal-from-float-literal`](https://docs.astral.sh/ruff/rules/decimal-from-float-literal/) (`RUF032`)
+- [`post-init-default`](https://docs.astral.sh/ruff/rules/post-init-default/) (`RUF033`)
+- [`useless-if-else`](https://docs.astral.sh/ruff/rules/useless-if-else/) (`RUF034`)
+
+The following behaviors have been stabilized:
+
+- [`pytest-parametrize-names-wrong-type`](https://docs.astral.sh/ruff/rules/pytest-parametrize-names-wrong-type/) (`PT006`): Detect [`pytest.parametrize`](https://docs.pytest.org/en/7.1.x/how-to/parametrize.html#parametrize) calls outside decorators and calls with keyword arguments.
+- [`module-import-not-at-top-of-file`](https://docs.astral.sh/ruff/rules/module-import-not-at-top-of-file/) (`E402`): Ignore [`pytest.importorskip`](https://docs.pytest.org/en/7.1.x/reference/reference.html#pytest-importorskip) calls between import statements.
+- [`mutable-dataclass-default`](https://docs.astral.sh/ruff/rules/mutable-dataclass-default/) (`RUF008`) and [`function-call-in-dataclass-default-argument`](https://docs.astral.sh/ruff/rules/function-call-in-dataclass-default-argument/) (`RUF009`): Add support for [`attrs`](https://www.attrs.org/en/stable/).
+- [`bad-version-info-comparison`](https://docs.astral.sh/ruff/rules/bad-version-info-comparison/) (`PYI006`): Extend the rule to check non-stub files.
+
+The following fixes or improvements to fixes have been stabilized:
+
+- [`redundant-numeric-union`](https://docs.astral.sh/ruff/rules/redundant-numeric-union/) (`PYI041`)
+- [`duplicate-union-members`](https://docs.astral.sh/ruff/rules/duplicate-union-member/) (`PYI016`)
+
+### Formatter
+
+This release introduces the new 2025 stable style ([#13371](https://github.com/astral-sh/ruff/issues/13371)), stabilizing the following changes:
+
+- Format expressions in f-string elements ([#7594](https://github.com/astral-sh/ruff/issues/7594))
+- Alternate quotes for strings inside f-strings ([#13860](https://github.com/astral-sh/ruff/pull/13860))
+- Preserve the casing of hex codes in f-string debug expressions ([#14766](https://github.com/astral-sh/ruff/issues/14766))
+- Choose the quote style for each string literal in an implicitly concatenated f-string rather than for the entire string ([#13539](https://github.com/astral-sh/ruff/pull/13539))
+- Automatically join an implicitly concatenated string into a single string literal if it fits on a single line ([#9457](https://github.com/astral-sh/ruff/issues/9457))
+- Remove the [`ISC001`](https://docs.astral.sh/ruff/rules/single-line-implicit-string-concatenation/) incompatibility warning ([#15123](https://github.com/astral-sh/ruff/pull/15123))
+- Prefer parenthesizing the `assert` message over breaking the assertion expression ([#9457](https://github.com/astral-sh/ruff/issues/9457))
+- Automatically parenthesize over-long `if` guards in `match` `case` clauses ([#13513](https://github.com/astral-sh/ruff/pull/13513))
+- More consistent formatting for `match` `case` patterns ([#6933](https://github.com/astral-sh/ruff/issues/6933))
+- Avoid unnecessary parentheses around return type annotations ([#13381](https://github.com/astral-sh/ruff/pull/13381))
+- Keep the opening parentheses on the same line as the `if` keyword for comprehensions where the condition has a leading comment ([#12282](https://github.com/astral-sh/ruff/pull/12282))
+- More consistent formatting for `with` statements with a single context manager for Python 3.8 or older ([#10276](https://github.com/astral-sh/ruff/pull/10276))
+- Correctly calculate the line-width for code blocks in docstrings when using `max-doc-code-line-length = "dynamic"` ([#13523](https://github.com/astral-sh/ruff/pull/13523))
+
+### Preview features
+
+- \[`flake8-bugbear`\] Implement `class-as-data-structure` (`B903`) ([#9601](https://github.com/astral-sh/ruff/pull/9601))
+- \[`flake8-type-checking`\] Apply `quoted-type-alias` more eagerly in `TYPE_CHECKING` blocks and ignore it in stubs (`TC008`) ([#15180](https://github.com/astral-sh/ruff/pull/15180))
+- \[`pylint`\] Ignore `eq-without-hash` in stub files (`PLW1641`) ([#15310](https://github.com/astral-sh/ruff/pull/15310))
+- \[`pyupgrade`\] Split `UP007` into two individual rules: `UP007` for `Union` and `UP045` for `Optional` (`UP007`, `UP045`) ([#15313](https://github.com/astral-sh/ruff/pull/15313))
+- \[`ruff`\] New rule that detects classes that are both an enum and a `dataclass` (`RUF049`) ([#15299](https://github.com/astral-sh/ruff/pull/15299))
+- \[`ruff`\] Recode `RUF025` to `RUF037` (`RUF037`) ([#15258](https://github.com/astral-sh/ruff/pull/15258))
+
+### Rule changes
+
+- \[`flake8-builtins`\] Ignore [`stdlib-module-shadowing`](https://docs.astral.sh/ruff/rules/stdlib-module-shadowing/) in stub files(`A005`) ([#15350](https://github.com/astral-sh/ruff/pull/15350))
+- \[`flake8-return`\] Add support for functions returning `typing.Never` (`RET503`) ([#15298](https://github.com/astral-sh/ruff/pull/15298))
+
+### Server
+
+- Improve the observability by removing the need for the ["trace" value](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#traceValue) to turn on or off logging. The server logging is solely controlled using the [`logLevel` server setting](https://docs.astral.sh/ruff/editors/settings/#loglevel)
+    which defaults to `info`. This addresses the issue where users were notified about an error and told to consult the log, but it didn’t contain any messages. ([#15232](https://github.com/astral-sh/ruff/pull/15232))
+- Ignore diagnostics from other sources for code action requests ([#15373](https://github.com/astral-sh/ruff/pull/15373))
+
+### CLI
+
+- Improve the error message for `--config key=value` when the `key` is for a table and it’s a simple `value`
+
+### Bug fixes
+
+- \[`eradicate`\] Ignore metadata blocks directly followed by normal blocks (`ERA001`) ([#15330](https://github.com/astral-sh/ruff/pull/15330))
+- \[`flake8-django`\] Recognize other magic methods (`DJ012`) ([#15365](https://github.com/astral-sh/ruff/pull/15365))
+- \[`pycodestyle`\] Avoid false positives related to type aliases (`E252`) ([#15356](https://github.com/astral-sh/ruff/pull/15356))
+- \[`pydocstyle`\] Avoid treating newline-separated sections as sub-sections (`D405`) ([#15311](https://github.com/astral-sh/ruff/pull/15311))
+- \[`pyflakes`\] Remove call when removing final argument from `format` (`F523`) ([#15309](https://github.com/astral-sh/ruff/pull/15309))
+- \[`refurb`\] Mark fix as unsafe when the right-hand side is a string (`FURB171`) ([#15273](https://github.com/astral-sh/ruff/pull/15273))
+- \[`ruff`\] Treat `)` as a regex metacharacter (`RUF043`, `RUF055`) ([#15318](https://github.com/astral-sh/ruff/pull/15318))
+- \[`ruff`\] Parenthesize the `int`-call argument when removing the `int` call would change semantics (`RUF046`) ([#15277](https://github.com/astral-sh/ruff/pull/15277))
+
+## 0.8.6
+
+### Preview features
+
+- \[`format`\]: Preserve multiline implicit concatenated strings in docstring positions ([#15126](https://github.com/astral-sh/ruff/pull/15126))
+- \[`ruff`\] Add rule to detect empty literal in deque call (`RUF025`) ([#15104](https://github.com/astral-sh/ruff/pull/15104))
+- \[`ruff`\] Avoid reporting when `ndigits` is possibly negative (`RUF057`) ([#15234](https://github.com/astral-sh/ruff/pull/15234))
+
+### Rule changes
+
+- \[`flake8-todos`\] remove issue code length restriction (`TD003`) ([#15175](https://github.com/astral-sh/ruff/pull/15175))
+- \[`pyflakes`\] Ignore errors in `@no_type_check` string annotations (`F722`, `F821`) ([#15215](https://github.com/astral-sh/ruff/pull/15215))
+
+### CLI
+
+- Show errors for attempted fixes only when passed `--verbose` ([#15237](https://github.com/astral-sh/ruff/pull/15237))
+
+### Bug fixes
+
+- \[`ruff`\] Avoid syntax error when removing int over multiple lines (`RUF046`) ([#15230](https://github.com/astral-sh/ruff/pull/15230))
+- \[`pyupgrade`\] Revert "Add all PEP-585 names to `UP006` rule" ([#15250](https://github.com/astral-sh/ruff/pull/15250))
+
+## 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"
@@ -220,9 +220,9 @@ checksum = "7f839cdf7e2d3198ac6ca003fd8ebc61715755f41c1cad15ff13df67531e00ed"
 
 [[package]]
 name = "bstr"
-version = "1.11.1"
+version = "1.11.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "786a307d683a5bf92e6fd5fd69a7eb613751668d1d8d67d802846dfe367c62c8"
+checksum = "531a9155a481e2ee699d4f98f43c0ca4ff8ee1bfd55c31e9e98fb29d2b176fe0"
 dependencies = [
  "memchr",
  "regex-automata 0.4.8",
@@ -291,12 +291,6 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
-[[package]]
-name = "cfg_aliases"
-version = "0.1.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fd16c4719339c4530435d38e511904438d07cce7950afa3718a84ac36c10e89e"
-
 [[package]]
 name = "cfg_aliases"
 version = "0.2.1"
@@ -413,7 +407,7 @@ dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -424,15 +418,15 @@ checksum = "f46ad14479a25103f283c0f10005961cf086d8dc42205bb44c46ac563475dca6"
 
 [[package]]
 name = "clearscreen"
-version = "3.0.0"
+version = "4.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2f8c93eb5f77c9050c7750e14f13ef1033a40a0aac70c6371535b6763a01438c"
+checksum = "8c41dc435a7b98e4608224bbf65282309f5403719df9113621b30f8b6f74e2f4"
 dependencies = [
- "nix 0.28.0",
+ "nix",
  "terminfo",
- "thiserror 1.0.67",
+ "thiserror 2.0.9",
  "which",
- "winapi",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -470,14 +464,14 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "117725a109d387c937a1533ce01b450cbde6b88abceea8473c4d7a85853cda3c"
 dependencies = [
  "lazy_static",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[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",
@@ -668,7 +662,7 @@ version = "3.4.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "90eeab0aa92f3f9b4e87f258c72b139c207d251f9cbc1080a0086b86a8870dd3"
 dependencies = [
- "nix 0.29.0",
+ "nix",
  "windows-sys 0.59.0",
 ]
 
@@ -693,7 +687,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "strsim 0.10.0",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -704,7 +698,7 @@ checksum = "a668eda54683121533a393014d8692171709ff57a7d61f187b6e782719f8933f"
 dependencies = [
  "darling_core",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -774,16 +768,7 @@ dependencies = [
  "glob",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
-]
-
-[[package]]
-name = "dirs"
-version = "4.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ca3aa72a6f96ea37bbc5aa912f6788242832f75369bdfdadcb0e38423f100059"
-dependencies = [
- "dirs-sys 0.3.7",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -792,18 +777,7 @@ version = "5.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "44c45a9d03d6676652bcb5e724c7e988de1acad23a711b5217ab9cbecbec2225"
 dependencies = [
- "dirs-sys 0.4.1",
-]
-
-[[package]]
-name = "dirs-sys"
-version = "0.3.7"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b1d1d91c932ef41c0f2663aa8b0ca0342d444d842c06914aa0a7e352d0bada6"
-dependencies = [
- "libc",
- "redox_users",
- "winapi",
+ "dirs-sys",
 ]
 
 [[package]]
@@ -826,7 +800,7 @@ checksum = "97369cbbc041bc366949bc74d34658d6cda5621039731c6310521892a3a20ae0"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -876,10 +850,16 @@ dependencies = [
 ]
 
 [[package]]
-name = "env_logger"
-version = "0.11.5"
+name = "env_home"
+version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e13fa619b91fb2381732789fc5de83b45675e882f66623b7d8cb4f643017018d"
+checksum = "c7f84e12ccf0a7ddc17a6c41c93326024c42920d7ee630d04950e6926645c0fe"
+
+[[package]]
+name = "env_logger"
+version = "0.11.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dcaee3d8e3cfc3fd92428d477bc97fc29ec8716d180c0d74c643bb26166660e0"
 dependencies = [
  "anstream",
  "anstyle",
@@ -1019,9 +999,9 @@ 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 +1226,7 @@ checksum = "1ec89e9337638ecdc08744df490b221a7399bf8d164eb52a665454e60e075ad6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -1365,14 +1345,14 @@ dependencies = [
 
 [[package]]
 name = "insta"
-version = "1.41.1"
+version = "1.42.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7e9ffc4d4892617c50a928c52b2961cb5174b6fc6ebf252b2fac9d21955c48b8"
+checksum = "6513e4067e16e69ed1db5ab56048ed65db32d10ba5fc1217f5393f8f17d8b5a5"
 dependencies = [
  "console",
  "globset",
- "lazy_static",
  "linked-hash-map",
+ "once_cell",
  "pest",
  "pest_derive",
  "regex",
@@ -1420,7 +1400,7 @@ dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -1462,6 +1442,15 @@ dependencies = [
  "either",
 ]
 
+[[package]]
+name = "itertools"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b192c782037fadd9cfa75548310488aabdbf3d2da73885b31bd0abd03351285"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itoa"
 version = "1.0.11"
@@ -1521,9 +1510,9 @@ 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 +1536,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a2ae40017ac09cd2c6a53504cb3c871c7f2b41466eac5bc66ba63f39073b467b"
 dependencies = [
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -1607,13 +1596,14 @@ 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",
 ]
 
@@ -1646,9 +1636,9 @@ checksum = "2532096657941c2fea9c289d370a250971c689d4f143798ff67113ec042024a5"
 
 [[package]]
 name = "matchit"
-version = "0.8.5"
+version = "0.8.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bd0aa4b8ca861b08d68afc8702af3250776898c1508b278e1da9d01e01d4b45c"
+checksum = "2f926ade0c4e170215ae43342bf13b9310a437609c81f29f86c5df6657582ef9"
 
 [[package]]
 name = "memchr"
@@ -1718,18 +1708,6 @@ dependencies = [
  "uuid",
 ]
 
-[[package]]
-name = "nix"
-version = "0.28.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ab2156c4fce2f8df6c499cc1c763e4394b7482525bf2a9701c9d79d215f519e4"
-dependencies = [
- "bitflags 2.6.0",
- "cfg-if",
- "cfg_aliases 0.1.1",
- "libc",
-]
-
 [[package]]
 name = "nix"
 version = "0.29.0"
@@ -1738,7 +1716,7 @@ checksum = "71e2746dc3a24dd78b3cfcb7be93368c6de9963d30f43a6a73998a9cf4b17b46"
 dependencies = [
  "bitflags 2.6.0",
  "cfg-if",
- "cfg_aliases 0.2.1",
+ "cfg_aliases",
  "libc",
 ]
 
@@ -2014,7 +1992,7 @@ dependencies = [
  "pest_meta",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -2161,7 +2139,7 @@ dependencies = [
  "newtype-uuid",
  "quick-xml",
  "strip-ansi-escapes",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "uuid",
 ]
 
@@ -2196,9 +2174,9 @@ 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",
 ]
@@ -2292,7 +2270,7 @@ dependencies = [
  "hashbrown 0.15.2",
  "indexmap",
  "insta",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "memchr",
  "ordermap",
  "quickcheck",
@@ -2306,6 +2284,7 @@ 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 +2294,7 @@ dependencies = [
  "static_assertions",
  "tempfile",
  "test-case",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tracing",
 ]
 
@@ -2412,7 +2391,7 @@ dependencies = [
  "rustc-hash 2.1.0",
  "salsa",
  "serde",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "toml",
  "tracing",
 ]
@@ -2518,7 +2497,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.8.4"
+version = "0.9.1"
 dependencies = [
  "anyhow",
  "argfile",
@@ -2538,7 +2517,7 @@ dependencies = [
  "insta",
  "insta-cmd",
  "is-macro",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "log",
  "mimalloc",
  "notify",
@@ -2565,7 +2544,7 @@ dependencies = [
  "strum",
  "tempfile",
  "test-case",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tikv-jemallocator",
  "toml",
  "tracing",
@@ -2604,7 +2583,7 @@ dependencies = [
  "filetime",
  "glob",
  "globset",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "regex",
  "ruff_macros",
  "seahash",
@@ -2635,7 +2614,7 @@ dependencies = [
  "salsa",
  "serde",
  "tempfile",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tracing",
  "tracing-subscriber",
  "tracing-tree",
@@ -2653,7 +2632,7 @@ dependencies = [
  "imara-diff",
  "indicatif",
  "indoc",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "libcst",
  "pretty_assertions",
  "rayon",
@@ -2737,7 +2716,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_linter"
-version = "0.8.4"
+version = "0.9.1"
 dependencies = [
  "aho-corasick",
  "annotate-snippets 0.9.2",
@@ -2753,7 +2732,7 @@ dependencies = [
  "insta",
  "is-macro",
  "is-wsl",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "libcst",
  "log",
  "memchr",
@@ -2766,6 +2745,7 @@ dependencies = [
  "regex",
  "ruff_cache",
  "ruff_diagnostics",
+ "ruff_index",
  "ruff_macros",
  "ruff_notebook",
  "ruff_python_ast",
@@ -2787,7 +2767,7 @@ dependencies = [
  "strum",
  "strum_macros",
  "test-case",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "toml",
  "typed-arena",
  "unicode-normalization",
@@ -2800,11 +2780,11 @@ dependencies = [
 name = "ruff_macros"
 version = "0.0.0"
 dependencies = [
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "proc-macro2",
  "quote",
  "ruff_python_trivia",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -2812,7 +2792,7 @@ name = "ruff_notebook"
 version = "0.0.0"
 dependencies = [
  "anyhow",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "rand",
  "ruff_diagnostics",
  "ruff_source_file",
@@ -2821,7 +2801,7 @@ dependencies = [
  "serde_json",
  "serde_with",
  "test-case",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "uuid",
 ]
 
@@ -2833,7 +2813,7 @@ dependencies = [
  "bitflags 2.6.0",
  "compact_str",
  "is-macro",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "memchr",
  "ruff_cache",
  "ruff_macros",
@@ -2875,7 +2855,7 @@ dependencies = [
  "clap",
  "countme",
  "insta",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "memchr",
  "regex",
  "ruff_cache",
@@ -2893,7 +2873,7 @@ dependencies = [
  "similar",
  "smallvec",
  "static_assertions",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tracing",
 ]
 
@@ -2913,7 +2893,7 @@ name = "ruff_python_literal"
 version = "0.0.0"
 dependencies = [
  "bitflags 2.6.0",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "ruff_python_ast",
  "unic-ucd-category",
 ]
@@ -2967,6 +2947,7 @@ dependencies = [
  "rustc-hash 2.1.0",
  "schemars",
  "serde",
+ "smallvec",
 ]
 
 [[package]]
@@ -2981,7 +2962,7 @@ dependencies = [
 name = "ruff_python_trivia"
 version = "0.0.0"
 dependencies = [
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "ruff_source_file",
  "ruff_text_size",
  "unicode-ident",
@@ -3026,7 +3007,7 @@ dependencies = [
  "serde",
  "serde_json",
  "shellexpand",
- "thiserror 2.0.7",
+ "thiserror 2.0.9",
  "tracing",
  "tracing-subscriber",
 ]
@@ -3052,7 +3033,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_wasm"
-version = "0.8.4"
+version = "0.9.1"
 dependencies = [
  "console_error_panic_hook",
  "console_log",
@@ -3086,7 +3067,7 @@ dependencies = [
  "globset",
  "ignore",
  "is-macro",
- "itertools 0.13.0",
+ "itertools 0.14.0",
  "log",
  "matchit",
  "path-absolutize",
@@ -3194,7 +3175,7 @@ checksum = "e86697c916019a8588c99b5fac3cead74ec0b4b819707a682fd4d23fa0ce1ba1"
 [[package]]
 name = "salsa"
 version = "0.18.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=3c7f1694c9efba751dbeeacfbc93b227586e316a#3c7f1694c9efba751dbeeacfbc93b227586e316a"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=88a1d7774d78f048fbd77d40abca9ebd729fd1f0#88a1d7774d78f048fbd77d40abca9ebd729fd1f0"
 dependencies = [
  "append-only-vec",
  "arc-swap",
@@ -3202,7 +3183,6 @@ dependencies = [
  "dashmap 6.1.0",
  "hashlink",
  "indexmap",
- "lazy_static",
  "parking_lot",
  "rayon",
  "rustc-hash 2.1.0",
@@ -3215,17 +3195,17 @@ dependencies = [
 [[package]]
 name = "salsa-macro-rules"
 version = "0.1.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=3c7f1694c9efba751dbeeacfbc93b227586e316a#3c7f1694c9efba751dbeeacfbc93b227586e316a"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=88a1d7774d78f048fbd77d40abca9ebd729fd1f0#88a1d7774d78f048fbd77d40abca9ebd729fd1f0"
 
 [[package]]
 name = "salsa-macros"
 version = "0.18.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=3c7f1694c9efba751dbeeacfbc93b227586e316a#3c7f1694c9efba751dbeeacfbc93b227586e316a"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=88a1d7774d78f048fbd77d40abca9ebd729fd1f0#88a1d7774d78f048fbd77d40abca9ebd729fd1f0"
 dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
  "synstructure",
 ]
 
@@ -3259,7 +3239,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "serde_derive_internals",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -3282,9 +3262,9 @@ 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 +3282,13 @@ 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 2.0.95",
 ]
 
 [[package]]
@@ -3319,14 +3299,14 @@ checksum = "330f01ce65a3a5fe59a60c82f3c9a024b573b8a6e875bd233fe5f934e71d54e3"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[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 +3322,7 @@ checksum = "6c64451ba24fc7a6a2d60fc75dd9c83c90903b19028d4eff35e88fc1e86564e9"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -3365,9 +3345,9 @@ 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 +3356,14 @@ 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 2.0.95",
 ]
 
 [[package]]
@@ -3412,7 +3392,7 @@ version = "3.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "da03fa3b94cc19e3ebfc88c4229c49d8f08cdbd1228870a45f0ffdf84988e14b"
 dependencies = [
- "dirs 5.0.1",
+ "dirs",
 ]
 
 [[package]]
@@ -3497,7 +3477,7 @@ dependencies = [
  "proc-macro2",
  "quote",
  "rustversion",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -3519,9 +3499,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "2.0.90"
+version = "2.0.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "919d3b74a5dd0ccd15aeb8f93e7006bd9e14c295087c9896a110f490752bcf31"
+checksum = "46f71c0377baf4ef1cc3e3402ded576dccc315800fbc62dfc7fe04b009773b4a"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3536,7 +3516,7 @@ checksum = "c8af7666ab7b6390ab78131fb5b0fce11d6b7a6951602017c35fa82800708971"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -3564,11 +3544,10 @@ dependencies = [
 
 [[package]]
 name = "terminfo"
-version = "0.8.0"
+version = "0.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "666cd3a6681775d22b200409aad3b089c5b99fb11ecdd8a204d9d62f8148498f"
+checksum = "d4ea810f0692f9f51b382fff5893887bb4580f5fa246fde546e0b13e7fcee662"
 dependencies = [
- "dirs 4.0.0",
  "fnv",
  "nom",
  "phf",
@@ -3599,7 +3578,7 @@ dependencies = [
  "cfg-if",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -3610,7 +3589,7 @@ checksum = "5c89e72a01ed4c579669add59014b9a524d609c0c88c6a585ce37485879f6ffb"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
  "test-case-core",
 ]
 
@@ -3625,11 +3604,11 @@ 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 +3619,18 @@ checksum = "b607164372e89797d78b8e23a6d67d5d1038c1c65efd52e1389ef8b77caba2a6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[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 2.0.95",
 ]
 
 [[package]]
@@ -3773,7 +3752,7 @@ checksum = "395ae124c09f9e6918a2310af6038fba074bcf474ac352496d5910dd59a2226d"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -4043,7 +4022,7 @@ checksum = "6b91f57fe13a38d0ce9e28a03463d8d3c2468ed03d75375110ec71d93b449a08"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -4138,7 +4117,7 @@ dependencies = [
  "once_cell",
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
  "wasm-bindgen-shared",
 ]
 
@@ -4173,7 +4152,7 @@ checksum = "98c9ae5a76e46f4deecd0f0255cc223cfa18dc9b261213b8aa0c7b36f61b3f1d"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
  "wasm-bindgen-backend",
  "wasm-bindgen-shared",
 ]
@@ -4207,7 +4186,7 @@ checksum = "222ebde6ea87fbfa6bdd2e9f1fd8a91d60aee5db68792632176c4e16a74fc7d8"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -4241,12 +4220,12 @@ dependencies = [
 
 [[package]]
 name = "which"
-version = "6.0.1"
+version = "7.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8211e4f58a2b2805adfbefbc07bab82958fc91e3836339b1ab7ae32465dce0d7"
+checksum = "fb4a9e33648339dc1642b0e36e21b3385e6148e289226f657c809dee59df5028"
 dependencies = [
  "either",
- "home",
+ "env_home",
  "rustix",
  "winsafe",
 ]
@@ -4510,7 +4489,7 @@ checksum = "28cc31741b18cb6f1d5ff12f5b7523e3d6eb0852bbbad19d73905511d9849b95"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
  "synstructure",
 ]
 
@@ -4531,7 +4510,7 @@ checksum = "9ce1b18ccd8e73a9321186f97e46f9f04b778851177567b1975109d26a08d2a6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]
@@ -4551,7 +4530,7 @@ checksum = "0ea7b4a3637ea8669cedf0f1fd5c286a17f3de97b8dd5a70a6c167a1730e63a5"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
  "synstructure",
 ]
 
@@ -4580,7 +4559,7 @@ checksum = "6eafa6dfb17584ea3e2bd6e76e0cc15ad7af12b09abdd1ca55961bed9b1063c6"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.90",
+ "syn 2.0.95",
 ]
 
 [[package]]

Cargo.toml

@@ -55,7 +55,7 @@ camino = { version = "1.1.7" }
 chrono = { version = "0.4.35", default-features = false, features = ["clock"] }
 clap = { version = "4.5.3", features = ["derive"] }
 clap_complete_command = { version = "0.6.0" }
-clearscreen = { version = "3.0.0" }
+clearscreen = { version = "4.0.0" }
 codspeed-criterion-compat = { version = "2.6.0", default-features = false }
 colored = { version = "2.1.0" }
 console_error_panic_hook = { version = "0.1.7" }
@@ -89,7 +89,7 @@ insta = { version = "1.35.1" }
 insta-cmd = { version = "0.6.0" }
 is-macro = { version = "0.3.5" }
 is-wsl = { version = "0.4.0" }
-itertools = { version = "0.13.0" }
+itertools = { version = "0.14.0" }
 js-sys = { version = "0.3.69" }
 jod-thread = { version = "0.1.2" }
 libc = { version = "0.2.153" }
@@ -119,7 +119,7 @@ rayon = { version = "1.10.0" }
 regex = { version = "1.10.2" }
 rustc-hash = { version = "2.0.0" }
 # When updating salsa, make sure to also update the revision in `fuzz/Cargo.toml`
-salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "3c7f1694c9efba751dbeeacfbc93b227586e316a" }
+salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "88a1d7774d78f048fbd77d40abca9ebd729fd1f0" }
 schemars = { version = "0.8.16" }
 seahash = { version = "4.1.0" }
 serde = { version = "1.0.197", features = ["derive"] }
@@ -211,6 +211,9 @@ redundant_clone = "warn"
 debug_assert_with_mut_call = "warn"
 unused_peekable = "warn"
 
+# Diagnostics are not actionable: Enable once https://github.com/rust-lang/rust-clippy/issues/13774 is resolved.
+large_stack_arrays = "allow"
+
 [profile.release]
 # Note that we set these explicitly, and these values
 # were chosen based on a trade-off between compile times

README.md

@@ -116,12 +116,21 @@ For more, see the [documentation](https://docs.astral.sh/ruff/).
 
 ### Installation
 
-Ruff is available as [`ruff`](https://pypi.org/project/ruff/) on PyPI:
+Ruff is available as [`ruff`](https://pypi.org/project/ruff/) on PyPI.
+
+Invoke Ruff directly with [`uvx`](https://docs.astral.sh/uv/):
+
+```shell
+uvx ruff check   # Lint all files in the current directory.
+uvx ruff format  # Format all files in the current directory.
+```
+
+Or install Ruff with `uv` (recommended), `pip`, or `pipx`:
 
 ```shell
 # With uv.
-uv add --dev ruff     # to add ruff to your project
-uv tool install ruff  # to install ruff globally
+uv tool install ruff@latest  # Install Ruff globally.
+uv add --dev ruff            # Or add Ruff to your project.
 
 # With pip.
 pip install ruff
@@ -140,8 +149,8 @@ curl -LsSf https://astral.sh/ruff/install.sh | sh
 powershell -c "irm https://astral.sh/ruff/install.ps1 | iex"
 
 # For a specific version.
-curl -LsSf https://astral.sh/ruff/0.8.4/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.8.4/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.9.1/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.9.1/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 +183,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.8.4
+  rev: v0.9.1
   hooks:
     # Run the linter.
     - id: ruff
@@ -196,7 +205,7 @@ 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/literal.md

@@ -9,8 +9,6 @@ from typing import Literal
 from enum import Enum
 
 mode: Literal["w", "r"]
-mode2: Literal["w"] | Literal["r"]
-union_var: Literal[Literal[Literal[1, 2, 3], "foo"], 5, None]
 a1: Literal[26]
 a2: Literal[0x1A]
 a3: Literal[-4]
@@ -19,7 +17,6 @@ a5: Literal[b"hello world"]
 a6: Literal[True]
 a7: Literal[None]
 a8: Literal[Literal[1]]
-a9: Literal[Literal["w"], Literal["r"], Literal[Literal["w+"]]]
 
 class Color(Enum):
     RED = 0
@@ -30,9 +27,6 @@ b1: Literal[Color.RED]
 
 def f():
     reveal_type(mode)  # revealed: Literal["w", "r"]
-    reveal_type(mode2)  # revealed: Literal["w", "r"]
-    # TODO: should be revealed: Literal[1, 2, 3, "foo", 5] | None
-    reveal_type(union_var)  # revealed: Literal[1, 2, 3, 5] | Literal["foo"] | None
     reveal_type(a1)  # revealed: Literal[26]
     reveal_type(a2)  # revealed: Literal[26]
     reveal_type(a3)  # revealed: Literal[-4]
@@ -41,7 +35,6 @@ def f():
     reveal_type(a6)  # revealed: Literal[True]
     reveal_type(a7)  # revealed: None
     reveal_type(a8)  # revealed: Literal[1]
-    reveal_type(a9)  # revealed: Literal["w", "r", "w+"]
     # TODO: This should be Color.RED
     reveal_type(b1)  # revealed: Literal[0]
 
@@ -61,6 +54,63 @@ invalid4: Literal[
 ]
 ```
 
+## Shortening unions of literals
+
+When a Literal is parameterized with more than one value, it’s treated as exactly to equivalent to
+the union of those types.
+
+```py
+from typing import Literal
+
+def x(
+    a1: Literal[Literal[Literal[1, 2, 3], "foo"], 5, None],
+    a2: Literal["w"] | Literal["r"],
+    a3: Literal[Literal["w"], Literal["r"], Literal[Literal["w+"]]],
+    a4: Literal[True] | Literal[1, 2] | Literal["foo"],
+):
+    reveal_type(a1)  # revealed: Literal[1, 2, 3, "foo", 5] | None
+    reveal_type(a2)  # revealed: Literal["w", "r"]
+    reveal_type(a3)  # revealed: Literal["w", "r", "w+"]
+    reveal_type(a4)  # revealed: Literal[True, 1, 2, "foo"]
+```
+
+## Display of heterogeneous unions of literals
+
+```py
+from typing import Literal, Union
+
+def foo(x: int) -> int:
+    return x + 1
+
+def bar(s: str) -> str:
+    return s
+
+class A: ...
+class B: ...
+
+def union_example(
+    x: Union[
+        # unknown type
+        # error: [unresolved-reference]
+        y,
+        Literal[-1],
+        Literal["A"],
+        Literal[b"A"],
+        Literal[b"\x00"],
+        Literal[b"\x07"],
+        Literal[0],
+        Literal[1],
+        Literal["B"],
+        Literal["foo"],
+        Literal["bar"],
+        Literal["B"],
+        Literal[True],
+        None,
+    ]
+):
+    reveal_type(x)  # revealed: Unknown | Literal[-1, "A", b"A", b"\x00", b"\x07", 0, 1, "B", "foo", "bar", True] | None
+```
+
 ## Detecting Literal outside typing and typing_extensions
 
 Only Literal that is defined in typing and typing_extension modules is detected as the special

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

@@ -107,7 +107,7 @@ def _(flag: bool):
     qux_2: Literal["qux"] = baz_2  # error: [invalid-assignment]
 
     baz_3 = "foo" if flag else 1
-    reveal_type(baz_3)  # revealed: Literal["foo"] | Literal[1]
+    reveal_type(baz_3)  # revealed: Literal["foo", 1]
     qux_3: LiteralString = baz_3  # error: [invalid-assignment]
 ```
 

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/annotations/string.md

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

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]] = ([], [])
@@ -124,3 +122,10 @@ class Foo: ...
 x = Foo()
 reveal_type(x)  # revealed: Foo
 ```
+
+## Annotated assignments in stub files are inferred correctly
+
+```pyi path=main.pyi
+x: int = 1
+reveal_type(x) # revealed: Literal[1]
+```

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

@@ -40,9 +40,9 @@ class C:
         return 42
 
 x = C()
+# error: [invalid-argument-type]
 x -= 1
 
-# TODO: should error, once operand type check is implemented
 reveal_type(x)  # revealed: int
 ```
 

crates/red_knot_python_semantic/resources/mdtest/attributes.md

@@ -1,4 +1,6 @@
-# Class attributes
+# Attributes
+
+Tests for attribute access on various kinds of types.
 
 ## Union of attributes
 
@@ -155,3 +157,67 @@ class Foo: ...
 
 reveal_type(Foo.__class__)  # revealed: Literal[type]
 ```
+
+## Function-literal attributes
+
+Most attribute accesses on function-literal types are delegated to `types.FunctionType`, since all
+functions are instances of that class:
+
+```py path=a.py
+def f(): ...
+
+reveal_type(f.__defaults__)  # revealed: @Todo(instance attributes)
+reveal_type(f.__kwdefaults__)  # revealed: @Todo(instance attributes)
+```
+
+Some attributes are special-cased, however:
+
+```py path=b.py
+def f(): ...
+
+reveal_type(f.__get__)  # revealed: @Todo(`__get__` method on functions)
+reveal_type(f.__call__)  # revealed: @Todo(`__call__` method on functions)
+```
+
+## Int-literal attributes
+
+Most attribute accesses on int-literal types are delegated to `builtins.int`, since all literal
+integers are instances of that class:
+
+```py path=a.py
+reveal_type((2).bit_length)  # revealed: @Todo(instance attributes)
+reveal_type((2).denominator)  # revealed: @Todo(instance attributes)
+```
+
+Some attributes are special-cased, however:
+
+```py path=b.py
+reveal_type((2).numerator)  # revealed: Literal[2]
+reveal_type((2).real)  # revealed: Literal[2]
+```
+
+## Literal `bool` attributes
+
+Most attribute accesses on bool-literal types are delegated to `builtins.bool`, since all literal
+bols are instances of that class:
+
+```py path=a.py
+reveal_type(True.__and__)  # revealed: @Todo(instance attributes)
+reveal_type(False.__or__)  # revealed: @Todo(instance attributes)
+```
+
+Some attributes are special-cased, however:
+
+```py path=b.py
+reveal_type(True.numerator)  # revealed: Literal[1]
+reveal_type(False.real)  # revealed: Literal[0]
+```
+
+## Bytes-literal attributes
+
+All attribute access on literal `bytes` types is currently delegated to `buitins.bytes`:
+
+```py
+reveal_type(b"foo".join)  # revealed: @Todo(instance attributes)
+reveal_type(b"foo".endswith)  # revealed: @Todo(instance attributes)
+```

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

@@ -46,3 +46,50 @@ reveal_type(a | b)  # revealed: Literal[True]
 reveal_type(b | a)  # revealed: Literal[True]
 reveal_type(b | b)  # revealed: Literal[False]
 ```
+
+## Arithmetic with a variable
+
+```py
+a = True
+b = False
+
+def lhs_is_int(x: int):
+    reveal_type(x + a)  # revealed: int
+    reveal_type(x - a)  # revealed: int
+    reveal_type(x * a)  # revealed: int
+    reveal_type(x // a)  # revealed: int
+    reveal_type(x / a)  # revealed: float
+    reveal_type(x % a)  # revealed: int
+
+def rhs_is_int(x: int):
+    reveal_type(a + x)  # revealed: int
+    reveal_type(a - x)  # revealed: int
+    reveal_type(a * x)  # revealed: int
+    reveal_type(a // x)  # revealed: int
+    reveal_type(a / x)  # revealed: float
+    reveal_type(a % x)  # revealed: int
+
+def lhs_is_bool(x: bool):
+    reveal_type(x + a)  # revealed: int
+    reveal_type(x - a)  # revealed: int
+    reveal_type(x * a)  # revealed: int
+    reveal_type(x // a)  # revealed: int
+    reveal_type(x / a)  # revealed: float
+    reveal_type(x % a)  # revealed: int
+
+def rhs_is_bool(x: bool):
+    reveal_type(a + x)  # revealed: int
+    reveal_type(a - x)  # revealed: int
+    reveal_type(a * x)  # revealed: int
+    reveal_type(a // x)  # revealed: int
+    reveal_type(a / x)  # revealed: float
+    reveal_type(a % x)  # revealed: int
+
+def both_are_bool(x: bool, y: bool):
+    reveal_type(x + y)  # revealed: int
+    reveal_type(x - y)  # revealed: int
+    reveal_type(x * y)  # revealed: int
+    reveal_type(x // y)  # revealed: int
+    reveal_type(x / y)  # revealed: float
+    reveal_type(x % y)  # revealed: int
+```

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

@@ -0,0 +1,27 @@
+# Binary operations on classes
+
+## Union of two classes
+
+Unioning two classes via the `|` operator is only available in Python 3.10 and later.
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+class A: ...
+class B: ...
+
+reveal_type(A | B)  # revealed: UnionType
+```
+
+## Union of two classes (prior to 3.10)
+
+```py
+class A: ...
+class B: ...
+
+# error: "Operator `|` is unsupported between objects of type `Literal[A]` and `Literal[B]`"
+reveal_type(A | B)  # revealed: Unknown
+```

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

@@ -0,0 +1,371 @@
+# Custom binary operations
+
+## Class instances
+
+```py
+class Yes:
+    def __add__(self, other) -> Literal["+"]:
+        return "+"
+
+    def __sub__(self, other) -> Literal["-"]:
+        return "-"
+
+    def __mul__(self, other) -> Literal["*"]:
+        return "*"
+
+    def __matmul__(self, other) -> Literal["@"]:
+        return "@"
+
+    def __truediv__(self, other) -> Literal["/"]:
+        return "/"
+
+    def __mod__(self, other) -> Literal["%"]:
+        return "%"
+
+    def __pow__(self, other) -> Literal["**"]:
+        return "**"
+
+    def __lshift__(self, other) -> Literal["<<"]:
+        return "<<"
+
+    def __rshift__(self, other) -> Literal[">>"]:
+        return ">>"
+
+    def __or__(self, other) -> Literal["|"]:
+        return "|"
+
+    def __xor__(self, other) -> Literal["^"]:
+        return "^"
+
+    def __and__(self, other) -> Literal["&"]:
+        return "&"
+
+    def __floordiv__(self, other) -> Literal["//"]:
+        return "//"
+
+class Sub(Yes): ...
+class No: ...
+
+# Yes implements all of the dunder methods.
+reveal_type(Yes() + Yes())  # revealed: Literal["+"]
+reveal_type(Yes() - Yes())  # revealed: Literal["-"]
+reveal_type(Yes() * Yes())  # revealed: Literal["*"]
+reveal_type(Yes() @ Yes())  # revealed: Literal["@"]
+reveal_type(Yes() / Yes())  # revealed: Literal["/"]
+reveal_type(Yes() % Yes())  # revealed: Literal["%"]
+reveal_type(Yes() ** Yes())  # revealed: Literal["**"]
+reveal_type(Yes() << Yes())  # revealed: Literal["<<"]
+reveal_type(Yes() >> Yes())  # revealed: Literal[">>"]
+reveal_type(Yes() | Yes())  # revealed: Literal["|"]
+reveal_type(Yes() ^ Yes())  # revealed: Literal["^"]
+reveal_type(Yes() & Yes())  # revealed: Literal["&"]
+reveal_type(Yes() // Yes())  # revealed: Literal["//"]
+
+# Sub inherits Yes's implementation of the dunder methods.
+reveal_type(Sub() + Sub())  # revealed: Literal["+"]
+reveal_type(Sub() - Sub())  # revealed: Literal["-"]
+reveal_type(Sub() * Sub())  # revealed: Literal["*"]
+reveal_type(Sub() @ Sub())  # revealed: Literal["@"]
+reveal_type(Sub() / Sub())  # revealed: Literal["/"]
+reveal_type(Sub() % Sub())  # revealed: Literal["%"]
+reveal_type(Sub() ** Sub())  # revealed: Literal["**"]
+reveal_type(Sub() << Sub())  # revealed: Literal["<<"]
+reveal_type(Sub() >> Sub())  # revealed: Literal[">>"]
+reveal_type(Sub() | Sub())  # revealed: Literal["|"]
+reveal_type(Sub() ^ Sub())  # revealed: Literal["^"]
+reveal_type(Sub() & Sub())  # revealed: Literal["&"]
+reveal_type(Sub() // Sub())  # revealed: Literal["//"]
+
+# No does not implement any of the dunder methods.
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `No` and `No`"
+reveal_type(No() + No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `-` is unsupported between objects of type `No` and `No`"
+reveal_type(No() - No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `*` is unsupported between objects of type `No` and `No`"
+reveal_type(No() * No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `@` is unsupported between objects of type `No` and `No`"
+reveal_type(No() @ No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `/` is unsupported between objects of type `No` and `No`"
+reveal_type(No() / No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `%` is unsupported between objects of type `No` and `No`"
+reveal_type(No() % No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `**` is unsupported between objects of type `No` and `No`"
+reveal_type(No() ** No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `<<` is unsupported between objects of type `No` and `No`"
+reveal_type(No() << No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `>>` is unsupported between objects of type `No` and `No`"
+reveal_type(No() >> No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `|` is unsupported between objects of type `No` and `No`"
+reveal_type(No() | No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `^` is unsupported between objects of type `No` and `No`"
+reveal_type(No() ^ No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `&` is unsupported between objects of type `No` and `No`"
+reveal_type(No() & No())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `//` is unsupported between objects of type `No` and `No`"
+reveal_type(No() // No())  # revealed: Unknown
+
+# Yes does not implement any of the reflected dunder methods.
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() + Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `-` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() - Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `*` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() * Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `@` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() @ Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `/` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() / Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `%` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() % Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `**` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() ** Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `<<` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() << Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `>>` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() >> Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `|` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() | Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `^` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() ^ Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `&` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() & Yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `//` is unsupported between objects of type `No` and `Yes`"
+reveal_type(No() // Yes())  # revealed: Unknown
+```
+
+## Subclass reflections override superclass dunders
+
+```py
+class Yes:
+    def __add__(self, other) -> Literal["+"]:
+        return "+"
+
+    def __sub__(self, other) -> Literal["-"]:
+        return "-"
+
+    def __mul__(self, other) -> Literal["*"]:
+        return "*"
+
+    def __matmul__(self, other) -> Literal["@"]:
+        return "@"
+
+    def __truediv__(self, other) -> Literal["/"]:
+        return "/"
+
+    def __mod__(self, other) -> Literal["%"]:
+        return "%"
+
+    def __pow__(self, other) -> Literal["**"]:
+        return "**"
+
+    def __lshift__(self, other) -> Literal["<<"]:
+        return "<<"
+
+    def __rshift__(self, other) -> Literal[">>"]:
+        return ">>"
+
+    def __or__(self, other) -> Literal["|"]:
+        return "|"
+
+    def __xor__(self, other) -> Literal["^"]:
+        return "^"
+
+    def __and__(self, other) -> Literal["&"]:
+        return "&"
+
+    def __floordiv__(self, other) -> Literal["//"]:
+        return "//"
+
+class Sub(Yes):
+    def __radd__(self, other) -> Literal["r+"]:
+        return "r+"
+
+    def __rsub__(self, other) -> Literal["r-"]:
+        return "r-"
+
+    def __rmul__(self, other) -> Literal["r*"]:
+        return "r*"
+
+    def __rmatmul__(self, other) -> Literal["r@"]:
+        return "r@"
+
+    def __rtruediv__(self, other) -> Literal["r/"]:
+        return "r/"
+
+    def __rmod__(self, other) -> Literal["r%"]:
+        return "r%"
+
+    def __rpow__(self, other) -> Literal["r**"]:
+        return "r**"
+
+    def __rlshift__(self, other) -> Literal["r<<"]:
+        return "r<<"
+
+    def __rrshift__(self, other) -> Literal["r>>"]:
+        return "r>>"
+
+    def __ror__(self, other) -> Literal["r|"]:
+        return "r|"
+
+    def __rxor__(self, other) -> Literal["r^"]:
+        return "r^"
+
+    def __rand__(self, other) -> Literal["r&"]:
+        return "r&"
+
+    def __rfloordiv__(self, other) -> Literal["r//"]:
+        return "r//"
+
+class No:
+    def __radd__(self, other) -> Literal["r+"]:
+        return "r+"
+
+    def __rsub__(self, other) -> Literal["r-"]:
+        return "r-"
+
+    def __rmul__(self, other) -> Literal["r*"]:
+        return "r*"
+
+    def __rmatmul__(self, other) -> Literal["r@"]:
+        return "r@"
+
+    def __rtruediv__(self, other) -> Literal["r/"]:
+        return "r/"
+
+    def __rmod__(self, other) -> Literal["r%"]:
+        return "r%"
+
+    def __rpow__(self, other) -> Literal["r**"]:
+        return "r**"
+
+    def __rlshift__(self, other) -> Literal["r<<"]:
+        return "r<<"
+
+    def __rrshift__(self, other) -> Literal["r>>"]:
+        return "r>>"
+
+    def __ror__(self, other) -> Literal["r|"]:
+        return "r|"
+
+    def __rxor__(self, other) -> Literal["r^"]:
+        return "r^"
+
+    def __rand__(self, other) -> Literal["r&"]:
+        return "r&"
+
+    def __rfloordiv__(self, other) -> Literal["r//"]:
+        return "r//"
+
+# Subclass reflected dunder methods take precedence over the superclass's regular dunders.
+reveal_type(Yes() + Sub())  # revealed: Literal["r+"]
+reveal_type(Yes() - Sub())  # revealed: Literal["r-"]
+reveal_type(Yes() * Sub())  # revealed: Literal["r*"]
+reveal_type(Yes() @ Sub())  # revealed: Literal["r@"]
+reveal_type(Yes() / Sub())  # revealed: Literal["r/"]
+reveal_type(Yes() % Sub())  # revealed: Literal["r%"]
+reveal_type(Yes() ** Sub())  # revealed: Literal["r**"]
+reveal_type(Yes() << Sub())  # revealed: Literal["r<<"]
+reveal_type(Yes() >> Sub())  # revealed: Literal["r>>"]
+reveal_type(Yes() | Sub())  # revealed: Literal["r|"]
+reveal_type(Yes() ^ Sub())  # revealed: Literal["r^"]
+reveal_type(Yes() & Sub())  # revealed: Literal["r&"]
+reveal_type(Yes() // Sub())  # revealed: Literal["r//"]
+
+# But for an unrelated class, the superclass regular dunders are used.
+reveal_type(Yes() + No())  # revealed: Literal["+"]
+reveal_type(Yes() - No())  # revealed: Literal["-"]
+reveal_type(Yes() * No())  # revealed: Literal["*"]
+reveal_type(Yes() @ No())  # revealed: Literal["@"]
+reveal_type(Yes() / No())  # revealed: Literal["/"]
+reveal_type(Yes() % No())  # revealed: Literal["%"]
+reveal_type(Yes() ** No())  # revealed: Literal["**"]
+reveal_type(Yes() << No())  # revealed: Literal["<<"]
+reveal_type(Yes() >> No())  # revealed: Literal[">>"]
+reveal_type(Yes() | No())  # revealed: Literal["|"]
+reveal_type(Yes() ^ No())  # revealed: Literal["^"]
+reveal_type(Yes() & No())  # revealed: Literal["&"]
+reveal_type(Yes() // No())  # revealed: Literal["//"]
+```
+
+## Classes
+
+Dunder methods defined in a class are available to instances of that class, but not to the class
+itself. (For these operators to work on the class itself, they would have to be defined on the
+class's type, i.e. `type`.)
+
+```py
+class Yes:
+    def __add__(self, other) -> Literal["+"]:
+        return "+"
+
+class Sub(Yes): ...
+class No: ...
+
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `Literal[Yes]` and `Literal[Yes]`"
+reveal_type(Yes + Yes)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `Literal[Sub]` and `Literal[Sub]`"
+reveal_type(Sub + Sub)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `Literal[No]` and `Literal[No]`"
+reveal_type(No + No)  # revealed: Unknown
+```
+
+## Subclass
+
+```py
+class Yes:
+    def __add__(self, other) -> Literal["+"]:
+        return "+"
+
+class Sub(Yes): ...
+class No: ...
+
+def yes() -> type[Yes]:
+    return Yes
+
+def sub() -> type[Sub]:
+    return Sub
+
+def no() -> type[No]:
+    return No
+
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `type[Yes]` and `type[Yes]`"
+reveal_type(yes() + yes())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `type[Sub]` and `type[Sub]`"
+reveal_type(sub() + sub())  # revealed: Unknown
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `type[No]` and `type[No]`"
+reveal_type(no() + no())  # revealed: Unknown
+```
+
+## Function literals
+
+```py
+def f():
+    pass
+
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f + f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `-` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f - f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `*` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f * f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `@` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f @ f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `/` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f / f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `%` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f % f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `**` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f**f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `<<` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f << f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `>>` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f >> f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `|` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f | f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `^` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f ^ f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `&` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f & f)  # revealed: Unknown
+# error: [unsupported-operator] "Operator `//` is unsupported between objects of type `Literal[f]` and `Literal[f]`"
+reveal_type(f // f)  # revealed: Unknown
+```

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

@@ -9,6 +9,34 @@ reveal_type(3 * -1)  # revealed: Literal[-3]
 reveal_type(-3 // 3)  # revealed: Literal[-1]
 reveal_type(-3 / 3)  # revealed: float
 reveal_type(5 % 3)  # revealed: Literal[2]
+
+# TODO: We don't currently verify that the actual parameter to int.__add__ matches the declared
+# formal parameter type.
+reveal_type(2 + "f")  # revealed: int
+
+def lhs(x: int):
+    reveal_type(x + 1)  # revealed: int
+    reveal_type(x - 4)  # revealed: int
+    reveal_type(x * -1)  # revealed: int
+    reveal_type(x // 3)  # revealed: int
+    reveal_type(x / 3)  # revealed: float
+    reveal_type(x % 3)  # revealed: int
+
+def rhs(x: int):
+    reveal_type(2 + x)  # revealed: int
+    reveal_type(3 - x)  # revealed: int
+    reveal_type(3 * x)  # revealed: int
+    reveal_type(-3 // x)  # revealed: int
+    reveal_type(-3 / x)  # revealed: float
+    reveal_type(5 % x)  # revealed: int
+
+def both(x: int):
+    reveal_type(x + x)  # revealed: int
+    reveal_type(x - x)  # revealed: int
+    reveal_type(x * x)  # revealed: int
+    reveal_type(x // x)  # revealed: int
+    reveal_type(x / x)  # revealed: float
+    reveal_type(x % x)  # revealed: int
 ```
 
 ## Power
@@ -21,6 +49,11 @@ largest_u32 = 4_294_967_295
 reveal_type(2**2)  # revealed: Literal[4]
 reveal_type(1 ** (largest_u32 + 1))  # revealed: int
 reveal_type(2**largest_u32)  # revealed: int
+
+def variable(x: int):
+    reveal_type(x**2)  # revealed: @Todo(return type)
+    reveal_type(2**x)  # revealed: @Todo(return type)
+    reveal_type(x**x)  # revealed: @Todo(return type)
 ```
 
 ## Division by Zero

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 +67,35 @@ 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
+```
+
+## Call binding errors
+
+### Wrong argument type
+
+```py
+class C:
+    def __call__(self, x: int) -> int:
+        return 1
+
+c = C()
+
+# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 2 (`x`) of function `__call__`; expected type `int`"
+reveal_type(c("foo"))  # revealed: int
+```
+
+### Wrong argument type on `self`
+
+```py
+class C:
+    # TODO this definition should also be an error; `C` must be assignable to type of `self`
+    def __call__(self: int) -> int:
+        return 1
+
+c = C()
+
+# error: 13 [invalid-argument-type] "Object of type `C` cannot be assigned to parameter 1 (`self`) of function `__call__`; expected type `int`"
+reveal_type(c())  # revealed: int
 ```

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

@@ -64,3 +64,260 @@ def _(flag: bool):
     # error: [possibly-unresolved-reference]
     reveal_type(foo())  # revealed: int
 ```
+
+## Wrong argument type
+
+### Positional argument, positional-or-keyword parameter
+
+```py
+def f(x: int) -> int:
+    return 1
+
+# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 1 (`x`) of function `f`; expected type `int`"
+reveal_type(f("foo"))  # revealed: int
+```
+
+### Positional argument, positional-only parameter
+
+```py
+def f(x: int, /) -> int:
+    return 1
+
+# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 1 (`x`) of function `f`; expected type `int`"
+reveal_type(f("foo"))  # revealed: int
+```
+
+### Positional argument, variadic parameter
+
+```py
+def f(*args: int) -> int:
+    return 1
+
+# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter `*args` of function `f`; expected type `int`"
+reveal_type(f("foo"))  # revealed: int
+```
+
+### Keyword argument, positional-or-keyword parameter
+
+```py
+def f(x: int) -> int:
+    return 1
+
+# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter `x` of function `f`; expected type `int`"
+reveal_type(f(x="foo"))  # revealed: int
+```
+
+### Keyword argument, keyword-only parameter
+
+```py
+def f(*, x: int) -> int:
+    return 1
+
+# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter `x` of function `f`; expected type `int`"
+reveal_type(f(x="foo"))  # revealed: int
+```
+
+### Keyword argument, keywords parameter
+
+```py
+def f(**kwargs: int) -> int:
+    return 1
+
+# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter `**kwargs` of function `f`; expected type `int`"
+reveal_type(f(x="foo"))  # revealed: int
+```
+
+### Correctly match keyword out-of-order
+
+```py
+def f(x: int = 1, y: str = "foo") -> int:
+    return 1
+
+# error: 15 [invalid-argument-type] "Object of type `Literal[2]` cannot be assigned to parameter `y` of function `f`; expected type `str`"
+# error: 20 [invalid-argument-type] "Object of type `Literal["bar"]` cannot be assigned to parameter `x` of function `f`; expected type `int`"
+reveal_type(f(y=2, x="bar"))  # revealed: int
+```
+
+## Too many positional arguments
+
+### One too many
+
+```py
+def f() -> int:
+    return 1
+
+# error: 15 [too-many-positional-arguments] "Too many positional arguments to function `f`: expected 0, got 1"
+reveal_type(f("foo"))  # revealed: int
+```
+
+### Two too many
+
+```py
+def f() -> int:
+    return 1
+
+# error: 15 [too-many-positional-arguments] "Too many positional arguments to function `f`: expected 0, got 2"
+reveal_type(f("foo", "bar"))  # revealed: int
+```
+
+### No too-many-positional if variadic is taken
+
+```py
+def f(*args: int) -> int:
+    return 1
+
+reveal_type(f(1, 2, 3))  # revealed: int
+```
+
+## Missing arguments
+
+### No defaults or variadic
+
+```py
+def f(x: int) -> int:
+    return 1
+
+# error: 13 [missing-argument] "No argument provided for required parameter `x` of function `f`"
+reveal_type(f())  # revealed: int
+```
+
+### With default
+
+```py
+def f(x: int, y: str = "foo") -> int:
+    return 1
+
+# error: 13 [missing-argument] "No argument provided for required parameter `x` of function `f`"
+reveal_type(f())  # revealed: int
+```
+
+### Defaulted argument is not required
+
+```py
+def f(x: int = 1) -> int:
+    return 1
+
+reveal_type(f())  # revealed: int
+```
+
+### With variadic
+
+```py
+def f(x: int, *y: str) -> int:
+    return 1
+
+# error: 13 [missing-argument] "No argument provided for required parameter `x` of function `f`"
+reveal_type(f())  # revealed: int
+```
+
+### Variadic argument is not required
+
+```py
+def f(*args: int) -> int:
+    return 1
+
+reveal_type(f())  # revealed: int
+```
+
+### Keywords argument is not required
+
+```py
+def f(**kwargs: int) -> int:
+    return 1
+
+reveal_type(f())  # revealed: int
+```
+
+### Multiple
+
+```py
+def f(x: int, y: int) -> int:
+    return 1
+
+# error: 13 [missing-argument] "No arguments provided for required parameters `x`, `y` of function `f`"
+reveal_type(f())  # revealed: int
+```
+
+## Unknown argument
+
+```py
+def f(x: int) -> int:
+    return 1
+
+# error: 20 [unknown-argument] "Argument `y` does not match any known parameter of function `f`"
+reveal_type(f(x=1, y=2))  # revealed: int
+```
+
+## Parameter already assigned
+
+```py
+def f(x: int) -> int:
+    return 1
+
+# error: 18 [parameter-already-assigned] "Multiple values provided for parameter `x` of function `f`"
+reveal_type(f(1, x=2))  # revealed: int
+```
+
+## Special functions
+
+Some functions require special handling in type inference. Here, we make sure that we still emit
+proper diagnostics in case of missing or superfluous arguments.
+
+### `reveal_type`
+
+```py
+from typing_extensions import reveal_type
+
+# error: [missing-argument] "No argument provided for required parameter `obj` of function `reveal_type`"
+reveal_type()  # revealed: Unknown
+
+# error: [too-many-positional-arguments] "Too many positional arguments to function `reveal_type`: expected 1, got 2"
+reveal_type(1, 2)  # revealed: Literal[1]
+```
+
+### `static_assert`
+
+```py
+from knot_extensions import static_assert
+
+# error: [missing-argument] "No argument provided for required parameter `condition` of function `static_assert`"
+# error: [static-assert-error]
+static_assert()
+
+# error: [too-many-positional-arguments] "Too many positional arguments to function `static_assert`: expected 2, got 3"
+static_assert(True, 2, 3)
+```
+
+### `len`
+
+```py
+# error: [missing-argument] "No argument provided for required parameter `obj` of function `len`"
+len()
+
+# error: [too-many-positional-arguments] "Too many positional arguments to function `len`: expected 1, got 2"
+len([], 1)
+```
+
+### Type API predicates
+
+```py
+from knot_extensions import is_subtype_of, is_fully_static
+
+# error: [missing-argument]
+is_subtype_of()
+
+# error: [missing-argument]
+is_subtype_of(int)
+
+# error: [too-many-positional-arguments]
+is_subtype_of(int, int, int)
+
+# error: [too-many-positional-arguments]
+is_subtype_of(int, int, int, int)
+
+# error: [missing-argument]
+is_fully_static()
+
+# error: [too-many-positional-arguments]
+is_fully_static(int, int)
+```

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

@@ -0,0 +1,44 @@
+# Invalid signatures
+
+## Multiple arguments with the same name
+
+We always map a keyword argument to the first parameter of that name.
+
+```py
+# error: [invalid-syntax] "Duplicate parameter "x""
+def f(x: int, x: str) -> int:
+    return 1
+
+# error: 13 [missing-argument] "No argument provided for required parameter `x` of function `f`"
+# error: 18 [parameter-already-assigned] "Multiple values provided for parameter `x` of function `f`"
+reveal_type(f(1, x=2))  # revealed: int
+```
+
+## Positional after non-positional
+
+When parameter kinds are given in an invalid order, we emit a diagnostic and implicitly reorder them
+to the valid order:
+
+```py
+# error: [invalid-syntax] "Parameter cannot follow var-keyword parameter"
+def f(**kw: int, x: str) -> int:
+    return 1
+
+# error: 15 [invalid-argument-type] "Object of type `Literal[1]` cannot be assigned to parameter 1 (`x`) of function `f`; expected type `str`"
+reveal_type(f(1))  # revealed: int
+```
+
+## Non-defaulted after defaulted
+
+We emit a syntax diagnostic for this, but it doesn't cause any problems for binding.
+
+```py
+# error: [invalid-syntax] "Parameter without a default cannot follow a parameter with a default"
+def f(x: int = 1, y: str) -> int:
+    return 1
+
+reveal_type(f(y="foo"))  # revealed: int
+# error: [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 1 (`x`) of function `f`; expected type `int`"
+# error: [missing-argument] "No argument provided for required parameter `y` of function `f`"
+reveal_type(f("foo"))  # revealed: int
+```

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

@@ -56,7 +56,7 @@ def _(flag: bool, flag2: bool):
     else:
         def f() -> int:
             return 1
-    # error: "Object of type `Literal[1] | Literal["foo"] | Literal[f]` is not callable (due to union elements Literal[1], Literal["foo"])"
+    # error: "Object of type `Literal[1, "foo"] | Literal[f]` is not callable (due to union elements Literal[1], Literal["foo"])"
     # revealed: Unknown | int
     reveal_type(f())
 ```
@@ -72,6 +72,6 @@ def _(flag: bool):
     else:
         f = "foo"
 
-    x = f()  # error: "Object of type `Literal[1] | Literal["foo"]` is not callable"
+    x = f()  # error: "Object of type `Literal[1, "foo"]` is not callable"
     reveal_type(x)  # revealed: Unknown
 ```

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/comparison/unsupported.md

@@ -22,7 +22,7 @@ def _(flag: bool, flag1: bool, flag2: bool):
     reveal_type(d)  # revealed: bool
 
     int_literal_or_str_literal = 1 if flag else "foo"
-    # error: "Operator `in` is not supported for types `Literal[42]` and `Literal[1]`, in comparing `Literal[42]` with `Literal[1] | Literal["foo"]`"
+    # error: "Operator `in` is not supported for types `Literal[42]` and `Literal[1]`, in comparing `Literal[42]` with `Literal[1, "foo"]`"
     e = 42 in int_literal_or_str_literal
     reveal_type(e)  # revealed: bool
 

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

@@ -115,3 +115,35 @@ def _(flag: bool, flag2: bool):
 
     reveal_type(y)  # revealed: Literal[2, 3, 4]
 ```
+
+## if-elif with assignment expressions in tests
+
+```py
+def check(x: int) -> bool:
+    return bool(x)
+
+if check(x := 1):
+    x = 2
+elif check(x := 3):
+    x = 4
+
+reveal_type(x)  # revealed: Literal[2, 3, 4]
+```
+
+## constraints apply to later test expressions
+
+```py
+def check(x) -> bool:
+    return bool(x)
+
+def _(flag: bool):
+    x = 1 if flag else None
+    y = 0
+
+    if x is None:
+        pass
+    elif check(y := x):
+        pass
+
+    reveal_type(y)  # revealed: Literal[0, 1]
+```

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

@@ -0,0 +1,142 @@
+# `assert_type`
+
+## Basic
+
+```py
+from typing_extensions import assert_type
+
+def _(x: int):
+    assert_type(x, int)  # fine
+    assert_type(x, str)  # error: [type-assertion-failure]
+```
+
+## Narrowing
+
+The asserted type is checked against the inferred type, not the declared type.
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+from typing_extensions import assert_type
+
+def _(x: int | str):
+    if isinstance(x, int):
+        reveal_type(x)  # revealed: int
+        assert_type(x, int)  # fine
+```
+
+## Equivalence
+
+The actual type must match the asserted type precisely.
+
+```py
+from typing import Any, Type, Union
+from typing_extensions import assert_type
+
+# Subtype does not count
+def _(x: bool):
+    assert_type(x, int)  # error: [type-assertion-failure]
+
+def _(a: type[int], b: type[Any]):
+    assert_type(a, type[Any])  # error: [type-assertion-failure]
+    assert_type(b, type[int])  # error: [type-assertion-failure]
+
+# The expression constructing the type is not taken into account
+def _(a: type[int]):
+    assert_type(a, Type[int])  # fine
+```
+
+## Gradual types
+
+```py
+from typing import Any
+from typing_extensions import Literal, assert_type
+
+from knot_extensions import Unknown
+
+# Any and Unknown are considered equivalent
+def _(a: Unknown, b: Any):
+    reveal_type(a)  # revealed: Unknown
+    assert_type(a, Any)  # fine
+
+    reveal_type(b)  # revealed: Any
+    assert_type(b, Unknown)  # fine
+
+def _(a: type[Unknown], b: type[Any]):
+    reveal_type(a)  # revealed: type[Unknown]
+    assert_type(a, type[Any])  # fine
+
+    reveal_type(b)  # revealed: type[Any]
+    assert_type(b, type[Unknown])  # fine
+```
+
+## Tuples
+
+Tuple types with the same elements are the same.
+
+```py
+from typing_extensions import assert_type
+
+from knot_extensions import Unknown
+
+def _(a: tuple[int, str, bytes]):
+    assert_type(a, tuple[int, str, bytes])  # fine
+
+    assert_type(a, tuple[int, str])  # error: [type-assertion-failure]
+    assert_type(a, tuple[int, str, bytes, None])  # error: [type-assertion-failure]
+    assert_type(a, tuple[int, bytes, str])  # error: [type-assertion-failure]
+
+def _(a: tuple[Any, ...], b: tuple[Unknown, ...]):
+    assert_type(a, tuple[Any, ...])  # fine
+    assert_type(a, tuple[Unknown, ...])  # fine
+
+    assert_type(b, tuple[Unknown, ...])  # fine
+    assert_type(b, tuple[Any, ...])  # fine
+```
+
+## Unions
+
+Unions with the same elements are the same, regardless of order.
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+from typing_extensions import assert_type
+
+def _(a: str | int):
+    assert_type(a, str | int)  # fine
+
+    # TODO: Order-independent union handling in type equivalence
+    assert_type(a, int | str)  # error: [type-assertion-failure]
+```
+
+## Intersections
+
+Intersections are the same when their positive and negative parts are respectively the same,
+regardless of order.
+
+```py
+from typing_extensions import assert_type
+
+from knot_extensions import Intersection, Not
+
+class A: ...
+class B: ...
+class C: ...
+class D: ...
+
+def _(a: A):
+    if isinstance(a, B) and not isinstance(a, C) and not isinstance(a, D):
+        reveal_type(a)  # revealed: A & B & ~C & ~D
+
+        assert_type(a, Intersection[A, B, Not[C], Not[D]])  # fine
+
+        # TODO: Order-independent intersection handling in type equivalence
+        assert_type(a, Intersection[B, A, Not[D], Not[C]])  # error: [type-assertion-failure]
+```

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

@@ -17,7 +17,7 @@ def _(flag: bool):
 
     reveal_type(A.always_bound)  # revealed: Literal[1]
 
-    reveal_type(A.union)  # revealed: Literal[1] | Literal["abc"]
+    reveal_type(A.union)  # revealed: Literal[1, "abc"]
 
     # error: [possibly-unbound-attribute] "Attribute `possibly_unbound` on type `Literal[A]` is possibly unbound"
     reveal_type(A.possibly_unbound)  # revealed: Literal["abc"]

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]
@@ -31,9 +31,9 @@ The test inside an if expression should not affect code outside of the expressio
 def _(flag: bool):
     x: Literal[42, "hello"] = 42 if flag else "hello"
 
-    reveal_type(x)  # revealed: Literal[42] | Literal["hello"]
+    reveal_type(x)  # revealed: Literal[42, "hello"]
 
     _ = ... if isinstance(x, str) else ...
 
-    reveal_type(x)  # revealed: Literal[42] | Literal["hello"]
+    reveal_type(x)  # revealed: Literal[42, "hello"]
 ```

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

@@ -119,7 +119,7 @@ class ZeroOrStr:
 reveal_type(len(Zero()))  # revealed: Literal[0]
 reveal_type(len(ZeroOrOne()))  # revealed: Literal[0, 1]
 reveal_type(len(ZeroOrTrue()))  # revealed: Literal[0, 1]
-reveal_type(len(OneOrFalse()))  # revealed: Literal[0, 1]
+reveal_type(len(OneOrFalse()))  # revealed: Literal[1, 0]
 
 # TODO: Emit a diagnostic
 reveal_type(len(OneOrFoo()))  # revealed: int

crates/red_knot_python_semantic/resources/mdtest/final.md

@@ -0,0 +1,31 @@
+# Tests for the `@typing(_extensions).final` decorator
+
+## Cannot subclass
+
+Don't do this:
+
+```py
+import typing_extensions
+from typing import final
+
+@final
+class A: ...
+
+class B(A): ...  # error: 9 [subclass-of-final-class] "Class `B` cannot inherit from final class `A`"
+
+@typing_extensions.final
+class C: ...
+
+class D(C): ...  # error: [subclass-of-final-class]
+class E: ...
+class F: ...
+class G: ...
+
+# fmt: off
+class H(
+    E,
+    F,
+    A,  # error: [subclass-of-final-class]
+    G,
+): ...
+```

crates/red_knot_python_semantic/resources/mdtest/intersection_types.md

@@ -0,0 +1,748 @@
+# Intersection types
+
+## Introduction
+
+This test suite covers certain properties of intersection types and makes sure that we can apply
+various simplification strategies. We use `Intersection` (`&`) and `Not` (`~`) to construct
+intersection types (note that we display negative contributions at the end; the order does not
+matter):
+
+```py
+from knot_extensions import Intersection, Not
+
+class P: ...
+class Q: ...
+
+def _(
+    i1: Intersection[P, Q],
+    i2: Intersection[P, Not[Q]],
+    i3: Intersection[Not[P], Q],
+    i4: Intersection[Not[P], Not[Q]],
+) -> None:
+    reveal_type(i1)  # revealed: P & Q
+    reveal_type(i2)  # revealed: P & ~Q
+    reveal_type(i3)  # revealed: Q & ~P
+    reveal_type(i4)  # revealed: ~P & ~Q
+```
+
+## Notation
+
+Throughout this document, we use the following types as representatives for certain equivalence
+classes.
+
+### Non-disjoint types
+
+We use `P`, `Q`, `R`, … to denote types that are non-disjoint:
+
+```py
+from knot_extensions import static_assert, is_disjoint_from
+
+class P: ...
+class Q: ...
+class R: ...
+
+static_assert(not is_disjoint_from(P, Q))
+static_assert(not is_disjoint_from(P, R))
+static_assert(not is_disjoint_from(Q, R))
+```
+
+Although `P` is not a subtype of `Q` and `Q` is not a subtype of `P`, the two types are not disjoint
+because it would be possible to create a class `S` that inherits from both `P` and `Q` using
+multiple inheritance. An instance of `S` would be a member of the `P` type _and_ the `Q` type.
+
+### Disjoint types
+
+We use `Literal[1]`, `Literal[2]`, … as examples of pairwise-disjoint types, and `int` as a joint
+supertype of these:
+
+```py
+from knot_extensions import static_assert, is_disjoint_from, is_subtype_of
+from typing import Literal
+
+static_assert(is_disjoint_from(Literal[1], Literal[2]))
+static_assert(is_disjoint_from(Literal[1], Literal[3]))
+static_assert(is_disjoint_from(Literal[2], Literal[3]))
+
+static_assert(is_subtype_of(Literal[1], int))
+static_assert(is_subtype_of(Literal[2], int))
+static_assert(is_subtype_of(Literal[3], int))
+```
+
+### Subtypes
+
+Finally, we use `A <: B <: C` and `A <: B1`, `A <: B2` to denote hierarchies of (proper) subtypes:
+
+```py
+from knot_extensions import static_assert, is_subtype_of, is_disjoint_from
+
+class A: ...
+class B(A): ...
+class C(B): ...
+
+static_assert(is_subtype_of(B, A))
+static_assert(is_subtype_of(C, B))
+static_assert(is_subtype_of(C, A))
+
+static_assert(not is_subtype_of(A, B))
+static_assert(not is_subtype_of(B, C))
+static_assert(not is_subtype_of(A, C))
+
+class B1(A): ...
+class B2(A): ...
+
+static_assert(is_subtype_of(B1, A))
+static_assert(is_subtype_of(B2, A))
+
+static_assert(not is_subtype_of(A, B1))
+static_assert(not is_subtype_of(A, B2))
+
+static_assert(not is_subtype_of(B1, B2))
+static_assert(not is_subtype_of(B2, B1))
+```
+
+## Structural properties
+
+This section covers structural properties of intersection types and documents some decisions on how
+to represent mixtures of intersections and unions.
+
+### Single-element intersections
+
+If we have an intersection with a single element, we can simplify to that element. Similarly, we
+show an intersection with a single negative contribution as just the negation of that element.
+
+```py
+from knot_extensions import Intersection, Not
+
+class P: ...
+
+def _(
+    i1: Intersection[P],
+    i2: Intersection[Not[P]],
+) -> None:
+    reveal_type(i1)  # revealed: P
+    reveal_type(i2)  # revealed: ~P
+```
+
+### Flattening of nested intersections
+
+We eagerly flatten nested intersections types.
+
+```py
+from knot_extensions import Intersection, Not
+
+class P: ...
+class Q: ...
+class R: ...
+class S: ...
+
+def positive_contributions(
+    i1: Intersection[P, Intersection[Q, R]],
+    i2: Intersection[Intersection[P, Q], R],
+) -> None:
+    reveal_type(i1)  # revealed: P & Q & R
+    reveal_type(i2)  # revealed: P & Q & R
+
+def negative_contributions(
+    i1: Intersection[Not[P], Intersection[Not[Q], Not[R]]],
+    i2: Intersection[Intersection[Not[P], Not[Q]], Not[R]],
+) -> None:
+    reveal_type(i1)  # revealed: ~P & ~Q & ~R
+    reveal_type(i2)  # revealed: ~P & ~Q & ~R
+
+def mixed(
+    i1: Intersection[P, Intersection[Not[Q], R]],
+    i2: Intersection[Intersection[P, Not[Q]], R],
+    i3: Intersection[Not[P], Intersection[Q, Not[R]]],
+    i4: Intersection[Intersection[Q, Not[R]], Not[P]],
+) -> None:
+    reveal_type(i1)  # revealed: P & R & ~Q
+    reveal_type(i2)  # revealed: P & R & ~Q
+    reveal_type(i3)  # revealed: Q & ~P & ~R
+    reveal_type(i4)  # revealed: Q & ~R & ~P
+
+def multiple(
+    i1: Intersection[Intersection[P, Q], Intersection[R, S]],
+):
+    reveal_type(i1)  # revealed: P & Q & R & S
+
+def nested(
+    i1: Intersection[Intersection[Intersection[P, Q], R], S],
+    i2: Intersection[P, Intersection[Q, Intersection[R, S]]],
+):
+    reveal_type(i1)  # revealed: P & Q & R & S
+    reveal_type(i2)  # revealed: P & Q & R & S
+```
+
+### Union of intersections
+
+We always normalize our representation to a _union of intersections_, so when we add a _union to an
+intersection_, we distribute the union over the respective elements:
+
+```py
+from knot_extensions import Intersection, Not
+
+class P: ...
+class Q: ...
+class R: ...
+class S: ...
+
+def _(
+    i1: Intersection[P, Q | R | S],
+    i2: Intersection[P | Q | R, S],
+    i3: Intersection[P | Q, R | S],
+) -> None:
+    reveal_type(i1)  # revealed: P & Q | P & R | P & S
+    reveal_type(i2)  # revealed: P & S | Q & S | R & S
+    reveal_type(i3)  # revealed: P & R | Q & R | P & S | Q & S
+
+def simplifications_for_same_elements(
+    i1: Intersection[P, Q | P],
+    i2: Intersection[Q, P | Q],
+    i3: Intersection[P | Q, Q | R],
+    i4: Intersection[P | Q, P | Q],
+    i5: Intersection[P | Q, Q | P],
+) -> None:
+    #   P & (Q | P)
+    # = P & Q | P & P
+    # = P & Q | P
+    # = P
+    # (because P is a supertype of P & Q)
+    reveal_type(i1)  # revealed: P
+    # similar here:
+    reveal_type(i2)  # revealed: Q
+
+    #   (P | Q) & (Q | R)
+    # = P & Q | P & R | Q & Q | Q & R
+    # = P & Q | P & R | Q | Q & R
+    # = Q | P & R
+    # (again, because Q is a supertype of P & Q and of Q & R)
+    reveal_type(i3)  # revealed: Q | P & R
+
+    #   (P | Q) & (P | Q)
+    # = P & P | P & Q | Q & P | Q & Q
+    # = P | P & Q | Q
+    # = P | Q
+    reveal_type(i4)  # revealed: P | Q
+```
+
+### Negation distributes over union
+
+Distribution also applies to a negation operation. This is a manifestation of one of
+[De Morgan's laws], namely `~(P | Q) = ~P & ~Q`:
+
+```py
+from knot_extensions import Not
+from typing import Literal
+
+class P: ...
+class Q: ...
+class R: ...
+
+def _(i1: Not[P | Q], i2: Not[P | Q | R]) -> None:
+    reveal_type(i1)  # revealed: ~P & ~Q
+    reveal_type(i2)  # revealed: ~P & ~Q & ~R
+
+def example_literals(i: Not[Literal[1, 2]]) -> None:
+    reveal_type(i)  # revealed: ~Literal[1] & ~Literal[2]
+```
+
+### Negation of intersections
+
+The other of [De Morgan's laws], `~(P & Q) = ~P | ~Q`, also holds:
+
+```py
+from knot_extensions import Intersection, Not
+
+class P: ...
+class Q: ...
+class R: ...
+
+def _(
+    i1: Not[Intersection[P, Q]],
+    i2: Not[Intersection[P, Q, R]],
+) -> None:
+    reveal_type(i1)  # revealed: ~P | ~Q
+    reveal_type(i2)  # revealed: ~P | ~Q | ~R
+```
+
+### `Never` is dual to `object`
+
+`Never` represents the empty set of values, while `object` represents the set of all values, so
+`~Never` is equivalent to `object`, and `~object` is equivalent to `Never`. This is a manifestation
+of the [complement laws] of set theory.
+
+```py
+from knot_extensions import Intersection, Not
+from typing_extensions import Never
+
+def _(
+    not_never: Not[Never],
+    not_object: Not[object],
+) -> None:
+    reveal_type(not_never)  # revealed: object
+    reveal_type(not_object)  # revealed: Never
+```
+
+### Intersection of a type and its negation
+
+Continuing with more [complement laws], if we see both `P` and `~P` in an intersection, we can
+simplify to `Never`, even in the presence of other types:
+
+```py
+from knot_extensions import Intersection, Not
+from typing import Any
+
+class P: ...
+class Q: ...
+
+def _(
+    i1: Intersection[P, Not[P]],
+    i2: Intersection[Not[P], P],
+    i3: Intersection[P, Q, Not[P]],
+    i4: Intersection[Not[P], Q, P],
+    i5: Intersection[P, Any, Not[P]],
+    i6: Intersection[Not[P], Any, P],
+) -> None:
+    reveal_type(i1)  # revealed: Never
+    reveal_type(i2)  # revealed: Never
+    reveal_type(i3)  # revealed: Never
+    reveal_type(i4)  # revealed: Never
+    reveal_type(i5)  # revealed: Never
+    reveal_type(i6)  # revealed: Never
+```
+
+### Union of a type and its negation
+
+Similarly, if we have both `P` and `~P` in a _union_, we can simplify that to `object`.
+
+```py
+from knot_extensions import Intersection, Not
+
+class P: ...
+class Q: ...
+
+def _(
+    i1: P | Not[P],
+    i2: Not[P] | P,
+    i3: P | Q | Not[P],
+    i4: Not[P] | Q | P,
+) -> None:
+    reveal_type(i1)  # revealed: object
+    reveal_type(i2)  # revealed: object
+    reveal_type(i3)  # revealed: object
+    reveal_type(i4)  # revealed: object
+```
+
+### Negation is an involution
+
+The final of the [complement laws] states that negating twice is equivalent to not negating at all:
+
+```py
+from knot_extensions import Not
+
+class P: ...
+
+def _(
+    i1: Not[P],
+    i2: Not[Not[P]],
+    i3: Not[Not[Not[P]]],
+    i4: Not[Not[Not[Not[P]]]],
+) -> None:
+    reveal_type(i1)  # revealed: ~P
+    reveal_type(i2)  # revealed: P
+    reveal_type(i3)  # revealed: ~P
+    reveal_type(i4)  # revealed: P
+```
+
+## Simplification strategies
+
+In this section, we present various simplification strategies that go beyond the structure of the
+representation.
+
+### `Never` in intersections
+
+If we intersect with `Never`, we can simplify the whole intersection to `Never`, even if there are
+dynamic types involved:
+
+```py
+from knot_extensions import Intersection, Not
+from typing_extensions import Never, Any
+
+class P: ...
+class Q: ...
+
+def _(
+    i1: Intersection[P, Never],
+    i2: Intersection[Never, P],
+    i3: Intersection[Any, Never],
+    i4: Intersection[Never, Not[Any]],
+) -> None:
+    reveal_type(i1)  # revealed: Never
+    reveal_type(i2)  # revealed: Never
+    reveal_type(i3)  # revealed: Never
+    reveal_type(i4)  # revealed: Never
+```
+
+### Simplifications using disjointness
+
+#### Positive contributions
+
+If we intersect disjoint types, we can simplify to `Never`, even in the presence of other types:
+
+```py
+from knot_extensions import Intersection, Not
+from typing import Literal, Any
+
+class P: ...
+
+def _(
+    i01: Intersection[Literal[1], Literal[2]],
+    i02: Intersection[Literal[2], Literal[1]],
+    i03: Intersection[Literal[1], Literal[2], P],
+    i04: Intersection[Literal[1], P, Literal[2]],
+    i05: Intersection[P, Literal[1], Literal[2]],
+    i06: Intersection[Literal[1], Literal[2], Any],
+    i07: Intersection[Literal[1], Any, Literal[2]],
+    i08: Intersection[Any, Literal[1], Literal[2]],
+) -> None:
+    reveal_type(i01)  # revealed: Never
+    reveal_type(i02)  # revealed: Never
+    reveal_type(i03)  # revealed: Never
+    reveal_type(i04)  # revealed: Never
+    reveal_type(i05)  # revealed: Never
+    reveal_type(i06)  # revealed: Never
+    reveal_type(i07)  # revealed: Never
+    reveal_type(i08)  # revealed: Never
+
+# `bool` is final and can not be subclassed, so `type[bool]` is equivalent to `Literal[bool]`, which
+# is disjoint from `type[str]`:
+def example_type_bool_type_str(
+    i: Intersection[type[bool], type[str]],
+) -> None:
+    reveal_type(i)  # revealed: Never
+```
+
+#### Positive and negative contributions
+
+If we intersect a type `X` with the negation `~Y` of a disjoint type `Y`, we can remove the negative
+contribution `~Y`, as `~Y` must fully contain the positive contribution `X` as a subtype:
+
+```py
+from knot_extensions import Intersection, Not
+from typing import Literal
+
+def _(
+    i1: Intersection[Literal[1], Not[Literal[2]]],
+    i2: Intersection[Not[Literal[2]], Literal[1]],
+    i3: Intersection[Literal[1], Not[Literal[2]], int],
+    i4: Intersection[Literal[1], int, Not[Literal[2]]],
+    i5: Intersection[int, Literal[1], Not[Literal[2]]],
+) -> None:
+    reveal_type(i1)  # revealed: Literal[1]
+    reveal_type(i2)  # revealed: Literal[1]
+    reveal_type(i3)  # revealed: Literal[1]
+    reveal_type(i4)  # revealed: Literal[1]
+    reveal_type(i5)  # revealed: Literal[1]
+
+# None is disjoint from int, so this simplification applies here
+def example_none(
+    i1: Intersection[int, Not[None]],
+    i2: Intersection[Not[None], int],
+) -> None:
+    reveal_type(i1)  # revealed: int
+    reveal_type(i2)  # revealed: int
+```
+
+### Simplifications using subtype relationships
+
+#### Positive type and positive subtype
+
+Subtypes are contained within their supertypes, so we can simplify intersections by removing
+superfluous supertypes:
+
+```py
+from knot_extensions import Intersection, Not
+from typing import Any
+
+class A: ...
+class B(A): ...
+class C(B): ...
+class Unrelated: ...
+
+def _(
+    i01: Intersection[A, B],
+    i02: Intersection[B, A],
+    i03: Intersection[A, C],
+    i04: Intersection[C, A],
+    i05: Intersection[B, C],
+    i06: Intersection[C, B],
+    i07: Intersection[A, B, C],
+    i08: Intersection[C, B, A],
+    i09: Intersection[B, C, A],
+    i10: Intersection[A, B, Unrelated],
+    i11: Intersection[B, A, Unrelated],
+    i12: Intersection[B, Unrelated, A],
+    i13: Intersection[A, Unrelated, B],
+    i14: Intersection[Unrelated, A, B],
+    i15: Intersection[Unrelated, B, A],
+    i16: Intersection[A, B, Any],
+    i17: Intersection[B, A, Any],
+    i18: Intersection[B, Any, A],
+    i19: Intersection[A, Any, B],
+    i20: Intersection[Any, A, B],
+    i21: Intersection[Any, B, A],
+) -> None:
+    reveal_type(i01)  # revealed: B
+    reveal_type(i02)  # revealed: B
+    reveal_type(i03)  # revealed: C
+    reveal_type(i04)  # revealed: C
+    reveal_type(i05)  # revealed: C
+    reveal_type(i06)  # revealed: C
+    reveal_type(i07)  # revealed: C
+    reveal_type(i08)  # revealed: C
+    reveal_type(i09)  # revealed: C
+    reveal_type(i10)  # revealed: B & Unrelated
+    reveal_type(i11)  # revealed: B & Unrelated
+    reveal_type(i12)  # revealed: B & Unrelated
+    reveal_type(i13)  # revealed: Unrelated & B
+    reveal_type(i14)  # revealed: Unrelated & B
+    reveal_type(i15)  # revealed: Unrelated & B
+    reveal_type(i16)  # revealed: B & Any
+    reveal_type(i17)  # revealed: B & Any
+    reveal_type(i18)  # revealed: B & Any
+    reveal_type(i19)  # revealed: Any & B
+    reveal_type(i20)  # revealed: Any & B
+    reveal_type(i21)  # revealed: Any & B
+```
+
+#### Negative type and negative subtype
+
+For negative contributions, this property is reversed. Here we can remove superfluous _subtypes_:
+
+```py
+from knot_extensions import Intersection, Not
+from typing import Any
+
+class A: ...
+class B(A): ...
+class C(B): ...
+class Unrelated: ...
+
+def _(
+    i01: Intersection[Not[B], Not[A]],
+    i02: Intersection[Not[A], Not[B]],
+    i03: Intersection[Not[A], Not[C]],
+    i04: Intersection[Not[C], Not[A]],
+    i05: Intersection[Not[B], Not[C]],
+    i06: Intersection[Not[C], Not[B]],
+    i07: Intersection[Not[A], Not[B], Not[C]],
+    i08: Intersection[Not[C], Not[B], Not[A]],
+    i09: Intersection[Not[B], Not[C], Not[A]],
+    i10: Intersection[Not[B], Not[A], Unrelated],
+    i11: Intersection[Not[A], Not[B], Unrelated],
+    i12: Intersection[Not[A], Unrelated, Not[B]],
+    i13: Intersection[Not[B], Unrelated, Not[A]],
+    i14: Intersection[Unrelated, Not[A], Not[B]],
+    i15: Intersection[Unrelated, Not[B], Not[A]],
+    i16: Intersection[Not[B], Not[A], Any],
+    i17: Intersection[Not[A], Not[B], Any],
+    i18: Intersection[Not[A], Any, Not[B]],
+    i19: Intersection[Not[B], Any, Not[A]],
+    i20: Intersection[Any, Not[A], Not[B]],
+    i21: Intersection[Any, Not[B], Not[A]],
+) -> None:
+    reveal_type(i01)  # revealed: ~A
+    reveal_type(i02)  # revealed: ~A
+    reveal_type(i03)  # revealed: ~A
+    reveal_type(i04)  # revealed: ~A
+    reveal_type(i05)  # revealed: ~B
+    reveal_type(i06)  # revealed: ~B
+    reveal_type(i07)  # revealed: ~A
+    reveal_type(i08)  # revealed: ~A
+    reveal_type(i09)  # revealed: ~A
+    reveal_type(i10)  # revealed: Unrelated & ~A
+    reveal_type(i11)  # revealed: Unrelated & ~A
+    reveal_type(i12)  # revealed: Unrelated & ~A
+    reveal_type(i13)  # revealed: Unrelated & ~A
+    reveal_type(i14)  # revealed: Unrelated & ~A
+    reveal_type(i15)  # revealed: Unrelated & ~A
+    reveal_type(i16)  # revealed: Any & ~A
+    reveal_type(i17)  # revealed: Any & ~A
+    reveal_type(i18)  # revealed: Any & ~A
+    reveal_type(i19)  # revealed: Any & ~A
+    reveal_type(i20)  # revealed: Any & ~A
+    reveal_type(i21)  # revealed: Any & ~A
+```
+
+#### Negative type and multiple negative subtypes
+
+If there are multiple negative subtypes, all of them can be removed:
+
+```py
+from knot_extensions import Intersection, Not
+
+class A: ...
+class B1(A): ...
+class B2(A): ...
+
+def _(
+    i1: Intersection[Not[A], Not[B1], Not[B2]],
+    i2: Intersection[Not[A], Not[B2], Not[B1]],
+    i3: Intersection[Not[B1], Not[A], Not[B2]],
+    i4: Intersection[Not[B1], Not[B2], Not[A]],
+    i5: Intersection[Not[B2], Not[A], Not[B1]],
+    i6: Intersection[Not[B2], Not[B1], Not[A]],
+) -> None:
+    reveal_type(i1)  # revealed: ~A
+    reveal_type(i2)  # revealed: ~A
+    reveal_type(i3)  # revealed: ~A
+    reveal_type(i4)  # revealed: ~A
+    reveal_type(i5)  # revealed: ~A
+    reveal_type(i6)  # revealed: ~A
+```
+
+#### Negative type and positive subtype
+
+When `A` is a supertype of `B`, its negation `~A` is disjoint from `B`, so we can simplify the
+intersection to `Never`:
+
+```py
+from knot_extensions import Intersection, Not
+from typing import Any
+
+class A: ...
+class B(A): ...
+class C(B): ...
+class Unrelated: ...
+
+def _(
+    i1: Intersection[Not[A], B],
+    i2: Intersection[B, Not[A]],
+    i3: Intersection[Not[A], C],
+    i4: Intersection[C, Not[A]],
+    i5: Intersection[Unrelated, Not[A], B],
+    i6: Intersection[B, Not[A], Not[Unrelated]],
+    i7: Intersection[Any, Not[A], B],
+    i8: Intersection[B, Not[A], Not[Any]],
+) -> None:
+    reveal_type(i1)  # revealed: Never
+    reveal_type(i2)  # revealed: Never
+    reveal_type(i3)  # revealed: Never
+    reveal_type(i4)  # revealed: Never
+    reveal_type(i5)  # revealed: Never
+    reveal_type(i6)  # revealed: Never
+    reveal_type(i7)  # revealed: Never
+    reveal_type(i8)  # revealed: Never
+```
+
+## Non fully-static types
+
+### Negation of dynamic types
+
+`Any` represents the dynamic type, an unknown set of runtime values. The negation of that, `~Any`,
+is still an unknown set of runtime values, so `~Any` is equivalent to `Any`. We therefore eagerly
+simplify `~Any` to `Any` in intersections. The same applies to `Unknown`.
+
+```py
+from knot_extensions import Intersection, Not, Unknown
+from typing_extensions import Any, Never
+
+class P: ...
+
+def any(
+    i1: Not[Any],
+    i2: Intersection[P, Not[Any]],
+    i3: Intersection[Never, Not[Any]],
+) -> None:
+    reveal_type(i1)  # revealed: Any
+    reveal_type(i2)  # revealed: P & Any
+    reveal_type(i3)  # revealed: Never
+
+def unknown(
+    i1: Not[Unknown],
+    i2: Intersection[P, Not[Unknown]],
+    i3: Intersection[Never, Not[Unknown]],
+) -> None:
+    reveal_type(i1)  # revealed: Unknown
+    reveal_type(i2)  # revealed: P & Unknown
+    reveal_type(i3)  # revealed: Never
+```
+
+### Collapsing of multiple `Any`/`Unknown` contributions
+
+The intersection of an unknown set of runtime values with (another) unknown set of runtime values is
+still an unknown set of runtime values:
+
+```py
+from knot_extensions import Intersection, Not, Unknown
+from typing_extensions import Any
+
+class P: ...
+
+def any(
+    i1: Intersection[Any, Any],
+    i2: Intersection[P, Any, Any],
+    i3: Intersection[Any, P, Any],
+    i4: Intersection[Any, Any, P],
+) -> None:
+    reveal_type(i1)  # revealed: Any
+    reveal_type(i2)  # revealed: P & Any
+    reveal_type(i3)  # revealed: Any & P
+    reveal_type(i4)  # revealed: Any & P
+
+def unknown(
+    i1: Intersection[Unknown, Unknown],
+    i2: Intersection[P, Unknown, Unknown],
+    i3: Intersection[Unknown, P, Unknown],
+    i4: Intersection[Unknown, Unknown, P],
+) -> None:
+    reveal_type(i1)  # revealed: Unknown
+    reveal_type(i2)  # revealed: P & Unknown
+    reveal_type(i3)  # revealed: Unknown & P
+    reveal_type(i4)  # revealed: Unknown & P
+```
+
+### No self-cancellation
+
+Dynamic types do not cancel each other out. Intersecting an unknown set of values with the negation
+of another unknown set of values is not necessarily empty, so we keep the positive contribution:
+
+```py
+from knot_extensions import Intersection, Not, Unknown
+
+def any(
+    i1: Intersection[Any, Not[Any]],
+    i2: Intersection[Not[Any], Any],
+) -> None:
+    reveal_type(i1)  # revealed: Any
+    reveal_type(i2)  # revealed: Any
+
+def unknown(
+    i1: Intersection[Unknown, Not[Unknown]],
+    i2: Intersection[Not[Unknown], Unknown],
+) -> None:
+    reveal_type(i1)  # revealed: Unknown
+    reveal_type(i2)  # revealed: Unknown
+```
+
+### Mixed dynamic types
+
+We currently do not simplify mixed dynamic types, but might consider doing so in the future:
+
+```py
+from knot_extensions import Intersection, Not, Unknown
+
+def mixed(
+    i1: Intersection[Any, Unknown],
+    i2: Intersection[Any, Not[Unknown]],
+    i3: Intersection[Not[Any], Unknown],
+    i4: Intersection[Not[Any], Not[Unknown]],
+) -> None:
+    reveal_type(i1)  # revealed: Any & Unknown
+    reveal_type(i2)  # revealed: Any & Unknown
+    reveal_type(i3)  # revealed: Any & Unknown
+    reveal_type(i4)  # revealed: Any & Unknown
+```
+
+[complement laws]: https://en.wikipedia.org/wiki/Complement_(set_theory)
+[de morgan's laws]: https://en.wikipedia.org/wiki/De_Morgan%27s_laws

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/loops/for.md

@@ -98,7 +98,7 @@ reveal_type(x)
 for x in (1, "a", b"foo"):
     pass
 
-# revealed: Literal[1] | Literal["a"] | Literal[b"foo"]
+# revealed: Literal[1, "a", b"foo"]
 # error: [possibly-unresolved-reference]
 reveal_type(x)
 ```

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

@@ -41,7 +41,7 @@ def _(flag: bool, flag2: bool):
         x = 3
 
     reveal_type(x)  # revealed: Literal[2, 3]
-    reveal_type(y)  # revealed: Literal[1, 2, 4]
+    reveal_type(y)  # revealed: Literal[4, 1, 2]
 ```
 
 ## Nested `while` loops

crates/red_knot_python_semantic/resources/mdtest/metaclass.md

@@ -170,8 +170,35 @@ def f(*args, **kwargs) -> int: ...
 
 class A(metaclass=f): ...
 
-# TODO should be `type[int]`
-reveal_type(A.__class__)  # revealed: @Todo(metaclass not a class)
+# TODO: Should be `int`
+reveal_type(A)  # revealed: Literal[A]
+reveal_type(A.__class__)  # revealed: type[int]
+
+def _(n: int):
+    # error: [invalid-metaclass]
+    class B(metaclass=n): ...
+    # TODO: Should be `Unknown`
+    reveal_type(B)  # revealed: Literal[B]
+    reveal_type(B.__class__)  # revealed: type[Unknown]
+
+def _(flag: bool):
+    m = f if flag else 42
+
+    # error: [invalid-metaclass]
+    class C(metaclass=m): ...
+    # TODO: Should be `int | Unknown`
+    reveal_type(C)  # revealed: Literal[C]
+    reveal_type(C.__class__)  # revealed: type[Unknown]
+
+class SignatureMismatch: ...
+
+# TODO: Emit a diagnostic
+class D(metaclass=SignatureMismatch): ...
+
+# TODO: Should be `Unknown`
+reveal_type(D)  # revealed: Literal[D]
+# TODO: Should be `type[Unknown]`
+reveal_type(D.__class__)  # revealed: Literal[SignatureMismatch]
 ```
 
 ## Cyclic

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

@@ -56,7 +56,7 @@ def _(x_flag: bool, y_flag: bool):
 def _(flag1: bool, flag2: bool):
     x = None if flag1 else (1 if flag2 else True)
 
-    reveal_type(x)  # revealed: None | Literal[1] | Literal[True]
+    reveal_type(x)  # revealed: None | Literal[1, True]
     if x is None:
         reveal_type(x)  # revealed: None
     elif x is True:

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

@@ -17,7 +17,7 @@ def _(flag: bool):
             reveal_type(x)  # revealed: Never
 
     if isinstance(x, (int, object)):
-        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+        reveal_type(x)  # revealed: Literal[1, "a"]
 ```
 
 ## `classinfo` is a tuple of types
@@ -30,7 +30,7 @@ def _(flag: bool, flag1: bool, flag2: bool):
     x = 1 if flag else "a"
 
     if isinstance(x, (int, str)):
-        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+        reveal_type(x)  # revealed: Literal[1, "a"]
     else:
         reveal_type(x)  # revealed: Never
 
@@ -43,19 +43,19 @@ def _(flag: bool, flag1: bool, flag2: bool):
     # No narrowing should occur if a larger type is also
     # one of the possibilities:
     if isinstance(x, (int, object)):
-        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+        reveal_type(x)  # revealed: Literal[1, "a"]
     else:
         reveal_type(x)  # revealed: Never
 
     y = 1 if flag1 else "a" if flag2 else b"b"
     if isinstance(y, (int, str)):
-        reveal_type(y)  # revealed: Literal[1] | Literal["a"]
+        reveal_type(y)  # revealed: Literal[1, "a"]
 
     if isinstance(y, (int, bytes)):
-        reveal_type(y)  # revealed: Literal[1] | Literal[b"b"]
+        reveal_type(y)  # revealed: Literal[1, b"b"]
 
     if isinstance(y, (str, bytes)):
-        reveal_type(y)  # revealed: Literal["a"] | Literal[b"b"]
+        reveal_type(y)  # revealed: Literal["a", b"b"]
 ```
 
 ## `classinfo` is a nested tuple of types
@@ -107,7 +107,7 @@ def _(flag: bool):
     x = 1 if flag else "foo"
 
     if isinstance(x, t):
-        reveal_type(x)  # revealed: Literal[1] | Literal["foo"]
+        reveal_type(x)  # revealed: Literal[1, "foo"]
 ```
 
 ## Do not use custom `isinstance` for narrowing
@@ -119,7 +119,7 @@ def _(flag: bool):
     x = 1 if flag else "a"
 
     if isinstance(x, int):
-        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+        reveal_type(x)  # revealed: Literal[1, "a"]
 ```
 
 ## Do support narrowing if `isinstance` is aliased
@@ -155,12 +155,12 @@ def _(flag: bool):
     # TODO: this should cause us to emit a diagnostic during
     # type checking
     if isinstance(x, "a"):
-        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+        reveal_type(x)  # revealed: Literal[1, "a"]
 
     # TODO: this should cause us to emit a diagnostic during
     # type checking
     if isinstance(x, "int"):
-        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+        reveal_type(x)  # revealed: Literal[1, "a"]
 ```
 
 ## Do not narrow if there are keyword arguments
@@ -169,8 +169,15 @@ def _(flag: bool):
 def _(flag: bool):
     x = 1 if flag else "a"
 
-    # TODO: this should cause us to emit a diagnostic
-    # (`isinstance` has no `foo` parameter)
+    # error: [unknown-argument]
     if isinstance(x, int, foo="bar"):
-        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+        reveal_type(x)  # revealed: Literal[1, "a"]
+```
+
+## `type[]` types are narrowed as well as class-literal types
+
+```py
+def _(x: object, y: type[int]):
+    if isinstance(x, y):
+        reveal_type(x)  # revealed: int
 ```

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

@@ -90,15 +90,19 @@ def _(t: type[object]):
         if issubclass(t, B):
             reveal_type(t)  # revealed: type[A] & type[B]
     else:
-        reveal_type(t)  # revealed: type[object] & ~type[A]
+        reveal_type(t)  # revealed: type & ~type[A]
 ```
 
 ### 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):
@@ -142,7 +146,7 @@ class A: ...
 
 t = object()
 
-# TODO: we should emit a diagnostic here
+# error: [invalid-argument-type]
 if issubclass(t, A):
     reveal_type(t)  # revealed: type[A]
 ```
@@ -156,7 +160,7 @@ branch:
 ```py
 t = 1
 
-# TODO: we should emit a diagnostic here
+# error: [invalid-argument-type]
 if issubclass(t, int):
     reveal_type(t)  # revealed: Never
 ```
@@ -230,8 +234,15 @@ def flag() -> bool: ...
 
 t = int if flag() else str
 
-# TODO: this should cause us to emit a diagnostic
-# (`issubclass` has no `foo` parameter)
+# error: [unknown-argument]
 if issubclass(t, int, foo="bar"):
     reveal_type(t)  # revealed: Literal[int, str]
 ```
+
+### `type[]` types are narrowed as well as class-literal types
+
+```py
+def _(x: type, y: type[int]):
+    if issubclass(x, y):
+        reveal_type(x)  # revealed: type[int]
+```

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

@@ -16,3 +16,48 @@ def _(flag: bool):
 
     reveal_type(y)  # revealed: Literal[0] | None
 ```
+
+## Class patterns
+
+```py
+def get_object() -> object: ...
+
+class A: ...
+class B: ...
+
+x = get_object()
+
+reveal_type(x)  # revealed: object
+
+match x:
+    case A():
+        reveal_type(x)  # revealed: A
+    case B():
+        # TODO could be `B & ~A`
+        reveal_type(x)  # revealed: B
+
+reveal_type(x)  # revealed: object
+```
+
+## Class pattern with guard
+
+```py
+def get_object() -> object: ...
+
+class A:
+    def y() -> int: ...
+
+class B: ...
+
+x = get_object()
+
+reveal_type(x)  # revealed: object
+
+match x:
+    case A() if reveal_type(x):  # revealed: A
+        pass
+    case B() if reveal_type(x):  # revealed: B
+        pass
+
+reveal_type(x)  # revealed: object
+```

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

@@ -9,39 +9,39 @@ def foo() -> Literal[0, -1, True, False, "", "foo", b"", b"bar", None] | tuple[(
 x = foo()
 
 if x:
-    reveal_type(x)  # revealed: Literal[-1] | Literal[True] | Literal["foo"] | Literal[b"bar"]
+    reveal_type(x)  # revealed: Literal[-1, True, "foo", b"bar"]
 else:
-    reveal_type(x)  # revealed: Literal[0] | Literal[False] | Literal[""] | Literal[b""] | None | tuple[()]
+    reveal_type(x)  # revealed: Literal[0, False, "", b""] | None | tuple[()]
 
 if not x:
-    reveal_type(x)  # revealed: Literal[0] | Literal[False] | Literal[""] | Literal[b""] | None | tuple[()]
+    reveal_type(x)  # revealed: Literal[0, False, "", b""] | None | tuple[()]
 else:
-    reveal_type(x)  # revealed: Literal[-1] | Literal[True] | Literal["foo"] | Literal[b"bar"]
+    reveal_type(x)  # revealed: Literal[-1, True, "foo", b"bar"]
 
 if x and not x:
     reveal_type(x)  # revealed: Never
 else:
-    reveal_type(x)  # revealed: Literal[-1, 0] | bool | Literal["", "foo"] | Literal[b"", b"bar"] | None | tuple[()]
+    reveal_type(x)  # revealed: Literal[0, -1, "", "foo", b"", b"bar"] | bool | None | tuple[()]
 
 if not (x and not x):
-    reveal_type(x)  # revealed: Literal[-1, 0] | bool | Literal["", "foo"] | Literal[b"", b"bar"] | None | tuple[()]
+    reveal_type(x)  # revealed: Literal[0, -1, "", "foo", b"", b"bar"] | bool | None | tuple[()]
 else:
     reveal_type(x)  # revealed: Never
 
 if x or not x:
-    reveal_type(x)  # revealed: Literal[-1, 0] | bool | Literal["foo", ""] | Literal[b"bar", b""] | None | tuple[()]
+    reveal_type(x)  # revealed: Literal[0, -1, "", "foo", b"", b"bar"] | bool | None | tuple[()]
 else:
     reveal_type(x)  # revealed: Never
 
 if not (x or not x):
     reveal_type(x)  # revealed: Never
 else:
-    reveal_type(x)  # revealed: Literal[-1, 0] | bool | Literal["foo", ""] | Literal[b"bar", b""] | None | tuple[()]
+    reveal_type(x)  # revealed: Literal[0, -1, "", "foo", b"", b"bar"] | bool | None | tuple[()]
 
 if (isinstance(x, int) or isinstance(x, str)) and x:
-    reveal_type(x)  # revealed: Literal[-1] | Literal[True] | Literal["foo"]
+    reveal_type(x)  # revealed: Literal[-1, True, "foo"]
 else:
-    reveal_type(x)  # revealed: Literal[b"", b"bar"] | None | tuple[()] | Literal[0] | Literal[False] | Literal[""]
+    reveal_type(x)  # revealed: Literal[b"", b"bar", 0, False, ""] | None | tuple[()]
 ```
 
 ## Function Literals
@@ -87,10 +87,10 @@ def f(x: A | B):
     if x and not x:
         reveal_type(x)  # revealed: A & ~AlwaysFalsy & ~AlwaysTruthy | B & ~AlwaysFalsy & ~AlwaysTruthy
     else:
-        reveal_type(x)  # revealed: A & ~AlwaysTruthy | B & ~AlwaysTruthy | A & ~AlwaysFalsy | B & ~AlwaysFalsy
+        reveal_type(x)  # revealed: A | B
 
     if x or not x:
-        reveal_type(x)  # revealed: A & ~AlwaysFalsy | B & ~AlwaysFalsy | A & ~AlwaysTruthy | B & ~AlwaysTruthy
+        reveal_type(x)  # revealed: A | B
     else:
         reveal_type(x)  # revealed: A & ~AlwaysTruthy & ~AlwaysFalsy | B & ~AlwaysTruthy & ~AlwaysFalsy
 ```
@@ -166,16 +166,16 @@ y = literals()
 
 if isinstance(x, str) and not isinstance(x, B):
     reveal_type(x)  # revealed: A & str & ~B
-    reveal_type(y)  # revealed: Literal[0, 42] | Literal["", "hello"]
+    reveal_type(y)  # revealed: Literal[0, 42, "", "hello"]
 
     z = x if flag() else y
 
-    reveal_type(z)  # revealed: A & str & ~B | Literal[0, 42] | Literal["", "hello"]
+    reveal_type(z)  # revealed: A & str & ~B | Literal[0, 42, "", "hello"]
 
     if z:
-        reveal_type(z)  # revealed: A & str & ~B & ~AlwaysFalsy | Literal[42] | Literal["hello"]
+        reveal_type(z)  # revealed: A & str & ~B & ~AlwaysFalsy | Literal[42, "hello"]
     else:
-        reveal_type(z)  # revealed: A & str & ~B & ~AlwaysTruthy | Literal[0] | Literal[""]
+        reveal_type(z)  # revealed: A & str & ~B & ~AlwaysTruthy | Literal[0, ""]
 ```
 
 ## Narrowing Multiple Variables
@@ -214,8 +214,101 @@ if x and not x:
     reveal_type(y)  # revealed: A & ~AlwaysFalsy & ~AlwaysTruthy
 else:
     y = x
-    reveal_type(y)  # revealed: A & ~AlwaysTruthy | A & ~AlwaysFalsy
+    reveal_type(y)  # revealed: A
 
-# TODO: It should be A. We should improve UnionBuilder or IntersectionBuilder. (issue #15023)
-reveal_type(y)  # revealed: A & ~AlwaysTruthy | A & ~AlwaysFalsy
+reveal_type(y)  # revealed: A
+```
+
+## 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/scopes/unbound.md

@@ -37,7 +37,7 @@ class C:
     # error: [possibly-unresolved-reference]
     y = x
 
-reveal_type(C.y)  # revealed: Literal[1] | Literal["abc"]
+reveal_type(C.y)  # revealed: Literal[1, "abc"]
 ```
 
 ## Unbound function local

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(return type)
+
+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/stubs/ellipsis.md

@@ -0,0 +1,78 @@
+# Ellipsis
+
+## Function and methods
+
+The ellipsis literal `...` can be used as a placeholder default value for a function parameter, in a
+stub file only, regardless of the type of the parameter.
+
+```py path=test.pyi
+def f(x: int = ...) -> None:
+    reveal_type(x)  # revealed: int
+
+def f2(x: str = ...) -> None:
+    reveal_type(x)  # revealed: str
+```
+
+## Class and module symbols
+
+The ellipsis literal can be assigned to a class or module symbol, regardless of its declared type,
+in a stub file only.
+
+```py path=test.pyi
+y: bytes = ...
+reveal_type(y)  # revealed: bytes
+x = ...
+reveal_type(x)  # revealed: Unknown
+
+class Foo:
+    y: int = ...
+
+reveal_type(Foo.y)  # revealed: int
+```
+
+## Unpacking ellipsis literal in assignment
+
+No diagnostic is emitted if an ellipsis literal is "unpacked" in a stub file as part of an
+assignment statement:
+
+```py path=test.pyi
+x, y = ...
+reveal_type(x)  # revealed: Unknown
+reveal_type(y)  # revealed: Unknown
+```
+
+## Unpacking ellipsis literal in for loops
+
+Iterating over an ellipsis literal as part of a `for` loop in a stub is invalid, however, and
+results in a diagnostic:
+
+```py path=test.pyi
+# error: [not-iterable] "Object of type `ellipsis` is not iterable"
+for a, b in ...:
+    reveal_type(a)  # revealed: Unknown
+    reveal_type(b)  # revealed: Unknown
+```
+
+## Ellipsis usage in non stub file
+
+In a non-stub file, there's no special treatment of ellipsis literals. An ellipsis literal can only
+be assigned if `EllipsisType` is actually assignable to the annotated type.
+
+```py
+# error: 7 [invalid-parameter-default] "Default value of type `ellipsis` is not assignable to annotated parameter type `int`"
+def f(x: int = ...) -> None: ...
+
+# error: 1 [invalid-assignment] "Object of type `ellipsis` is not assignable to `int`"
+a: int = ...
+b = ...
+reveal_type(b)  # revealed: ellipsis
+```
+
+## Use of `Ellipsis` symbol
+
+There is no special treatment of the builtin name `Ellipsis` in stubs, only of `...` literals.
+
+```py path=test.pyi
+# error: 7 [invalid-parameter-default] "Default value of type `ellipsis` is not assignable to annotated parameter type `int`"
+def f(x: int = Ellipsis) -> None: ...
+```

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/type_api.md

@@ -0,0 +1,352 @@
+# Type API (`knot_extensions`)
+
+This document describes the internal `knot_extensions` API for creating and manipulating types as
+well as testing various type system properties.
+
+## Type extensions
+
+The Python language itself allows us to perform a variety of operations on types. For example, we
+can build a union of types like `int | None`, or we can use type constructors such as `list[int]`
+and `type[int]` to create new types. But some type-level operations that we rely on in Red Knot,
+like intersections, cannot yet be expressed in Python. The `knot_extensions` module provides the
+`Intersection` and `Not` type constructors (special forms) which allow us to construct these types
+directly.
+
+### Negation
+
+```py
+from knot_extensions import Not, static_assert
+
+def negate(n1: Not[int], n2: Not[Not[int]], n3: Not[Not[Not[int]]]) -> None:
+    reveal_type(n1)  # revealed: ~int
+    reveal_type(n2)  # revealed: int
+    reveal_type(n3)  # revealed: ~int
+
+def static_truthiness(not_one: Not[Literal[1]]) -> None:
+    static_assert(not_one != 1)
+    static_assert(not (not_one == 1))
+
+# error: "Special form `knot_extensions.Not` expected exactly one type parameter"
+n: Not[int, str]
+```
+
+### Intersection
+
+```py
+from knot_extensions import Intersection, Not, is_subtype_of, static_assert
+from typing_extensions import Never
+
+class S: ...
+class T: ...
+
+def x(x1: Intersection[S, T], x2: Intersection[S, Not[T]]) -> None:
+    reveal_type(x1)  # revealed: S & T
+    reveal_type(x2)  # revealed: S & ~T
+
+def y(y1: Intersection[int, object], y2: Intersection[int, bool], y3: Intersection[int, Never]) -> None:
+    reveal_type(y1)  # revealed: int
+    reveal_type(y2)  # revealed: bool
+    reveal_type(y3)  # revealed: Never
+
+def z(z1: Intersection[int, Not[Literal[1]], Not[Literal[2]]]) -> None:
+    reveal_type(z1)  # revealed: int & ~Literal[1] & ~Literal[2]
+
+class A: ...
+class B: ...
+class C: ...
+
+type ABC = Intersection[A, B, C]
+
+static_assert(is_subtype_of(ABC, A))
+static_assert(is_subtype_of(ABC, B))
+static_assert(is_subtype_of(ABC, C))
+
+class D: ...
+
+static_assert(not is_subtype_of(ABC, D))
+```
+
+### Unknown type
+
+The `Unknown` type is a special type that we use to represent actually unknown types (no
+annotation), as opposed to `Any` which represents an explicitly unknown type.
+
+```py
+from knot_extensions import Unknown, static_assert, is_assignable_to, is_fully_static
+
+static_assert(is_assignable_to(Unknown, int))
+static_assert(is_assignable_to(int, Unknown))
+
+static_assert(not is_fully_static(Unknown))
+
+def explicit_unknown(x: Unknown, y: tuple[str, Unknown], z: Unknown = 1) -> None:
+    reveal_type(x)  # revealed: Unknown
+    reveal_type(y)  # revealed: tuple[str, Unknown]
+    reveal_type(z)  # revealed: Unknown | Literal[1]
+
+# Unknown can be subclassed, just like Any
+class C(Unknown): ...
+
+# revealed: tuple[Literal[C], Unknown, Literal[object]]
+reveal_type(C.__mro__)
+
+# error: "Special form `knot_extensions.Unknown` expected no type parameter"
+u: Unknown[str]
+```
+
+## Static assertions
+
+### Basics
+
+The `knot_extensions` module provides a `static_assert` function that can be used to enforce
+properties at type-check time. The function takes an arbitrary expression and raises a type error if
+the expression is not of statically known truthiness.
+
+```py
+from knot_extensions import static_assert
+from typing import TYPE_CHECKING
+import sys
+
+static_assert(True)
+static_assert(False)  # error: "Static assertion error: argument evaluates to `False`"
+
+static_assert(False or True)
+static_assert(True and True)
+static_assert(False or False)  # error: "Static assertion error: argument evaluates to `False`"
+static_assert(False and True)  # error: "Static assertion error: argument evaluates to `False`"
+
+static_assert(1 + 1 == 2)
+static_assert(1 + 1 == 3)  # error: "Static assertion error: argument evaluates to `False`"
+
+static_assert("a" in "abc")
+static_assert("d" in "abc")  # error: "Static assertion error: argument evaluates to `False`"
+
+n = None
+static_assert(n is None)
+
+static_assert(TYPE_CHECKING)
+
+static_assert(sys.version_info >= (3, 6))
+```
+
+### Narrowing constraints
+
+Static assertions can be used to enforce narrowing constraints:
+
+```py
+from knot_extensions import static_assert
+
+def f(x: int) -> None:
+    if x != 0:
+        static_assert(x != 0)
+    else:
+        # `int` can be subclassed, so we cannot assert that `x == 0` here:
+        # error: "Static assertion error: argument of type `bool` has an ambiguous static truthiness"
+        static_assert(x == 0)
+```
+
+### Truthy expressions
+
+See also: <https://docs.python.org/3/library/stdtypes.html#truth-value-testing>
+
+```py
+from knot_extensions import static_assert
+
+static_assert(True)
+static_assert(False)  # error: "Static assertion error: argument evaluates to `False`"
+
+static_assert(None)  # error: "Static assertion error: argument of type `None` is statically known to be falsy"
+
+static_assert(1)
+static_assert(0)  # error: "Static assertion error: argument of type `Literal[0]` is statically known to be falsy"
+
+static_assert((0,))
+static_assert(())  # error: "Static assertion error: argument of type `tuple[()]` is statically known to be falsy"
+
+static_assert("a")
+static_assert("")  # error: "Static assertion error: argument of type `Literal[""]` is statically known to be falsy"
+
+static_assert(b"a")
+static_assert(b"")  # error: "Static assertion error: argument of type `Literal[b""]` is statically known to be falsy"
+```
+
+### Error messages
+
+We provide various tailored error messages for wrong argument types to `static_assert`:
+
+```py
+from knot_extensions import static_assert
+
+static_assert(2 * 3 == 6)
+
+# error: "Static assertion error: argument evaluates to `False`"
+static_assert(2 * 3 == 7)
+
+# error: "Static assertion error: argument of type `bool` has an ambiguous static truthiness"
+static_assert(int(2.0 * 3.0) == 6)
+
+class InvalidBoolDunder:
+    def __bool__(self) -> int:
+        return 1
+
+# error: "Static assertion error: argument of type `InvalidBoolDunder` has an ambiguous static truthiness"
+static_assert(InvalidBoolDunder())
+```
+
+### Custom error messages
+
+Alternatively, users can provide custom error messages:
+
+```py
+from knot_extensions import static_assert
+
+# error: "Static assertion error: I really want this to be true"
+static_assert(1 + 1 == 3, "I really want this to be true")
+
+error_message = "A custom message "
+error_message += "constructed from multiple string literals"
+# error: "Static assertion error: A custom message constructed from multiple string literals"
+static_assert(False, error_message)
+
+# There are limitations to what we can still infer as a string literal. In those cases,
+# we simply fall back to the default message.
+shouted_message = "A custom message".upper()
+# error: "Static assertion error: argument evaluates to `False`"
+static_assert(False, shouted_message)
+```
+
+## Type predicates
+
+The `knot_extensions` module also provides predicates to test various properties of types. These are
+implemented as functions that return `Literal[True]` or `Literal[False]` depending on the result of
+the test.
+
+### Equivalence
+
+```py
+from knot_extensions import is_equivalent_to, static_assert
+from typing_extensions import Never, Union
+
+static_assert(is_equivalent_to(type, type[object]))
+static_assert(is_equivalent_to(tuple[int, Never], Never))
+static_assert(is_equivalent_to(int | str, Union[int, str]))
+
+static_assert(not is_equivalent_to(int, str))
+static_assert(not is_equivalent_to(int | str, int | str | bytes))
+```
+
+### Subtyping
+
+```py
+from knot_extensions import is_subtype_of, static_assert
+
+static_assert(is_subtype_of(bool, int))
+static_assert(not is_subtype_of(str, int))
+
+static_assert(is_subtype_of(bool, int | str))
+static_assert(is_subtype_of(str, int | str))
+static_assert(not is_subtype_of(bytes, int | str))
+
+class Base: ...
+class Derived(Base): ...
+class Unrelated: ...
+
+static_assert(is_subtype_of(Derived, Base))
+static_assert(not is_subtype_of(Base, Derived))
+static_assert(is_subtype_of(Base, Base))
+
+static_assert(not is_subtype_of(Unrelated, Base))
+static_assert(not is_subtype_of(Base, Unrelated))
+```
+
+### Assignability
+
+```py
+from knot_extensions import is_assignable_to, static_assert
+from typing import Any
+
+static_assert(is_assignable_to(int, Any))
+static_assert(is_assignable_to(Any, str))
+static_assert(not is_assignable_to(int, str))
+```
+
+### Disjointness
+
+```py
+from knot_extensions import is_disjoint_from, static_assert
+
+static_assert(is_disjoint_from(None, int))
+static_assert(not is_disjoint_from(Literal[2] | str, int))
+```
+
+### Fully static types
+
+```py
+from knot_extensions import is_fully_static, static_assert
+from typing import Any
+
+static_assert(is_fully_static(int | str))
+static_assert(is_fully_static(type[int]))
+
+static_assert(not is_fully_static(int | Any))
+static_assert(not is_fully_static(type[Any]))
+```
+
+### Singleton types
+
+```py
+from knot_extensions import is_singleton, static_assert
+
+static_assert(is_singleton(None))
+static_assert(is_singleton(Literal[True]))
+
+static_assert(not is_singleton(int))
+static_assert(not is_singleton(Literal["a"]))
+```
+
+### Single-valued types
+
+```py
+from knot_extensions import is_single_valued, static_assert
+
+static_assert(is_single_valued(None))
+static_assert(is_single_valued(Literal[True]))
+static_assert(is_single_valued(Literal["a"]))
+
+static_assert(not is_single_valued(int))
+static_assert(not is_single_valued(Literal["a"] | Literal["b"]))
+```
+
+## `TypeOf`
+
+We use `TypeOf` to get the inferred type of an expression. This is useful when we want to refer to
+it in a type expression. For example, if we want to make sure that the class literal type `str` is a
+subtype of `type[str]`, we can not use `is_subtype_of(str, type[str])`, as that would test if the
+type `str` itself is a subtype of `type[str]`. Instead, we can use `TypeOf[str]` to get the type of
+the expression `str`:
+
+```py
+from knot_extensions import TypeOf, is_subtype_of, static_assert
+
+# This is incorrect and therefore fails with ...
+# error: "Static assertion error: argument evaluates to `False`"
+static_assert(is_subtype_of(str, type[str]))
+
+# Correct, returns True:
+static_assert(is_subtype_of(TypeOf[str], type[str]))
+
+class Base: ...
+class Derived(Base): ...
+
+# `TypeOf` can be used in annotations:
+def type_of_annotation() -> None:
+    t1: TypeOf[Base] = Base
+    t2: TypeOf[Base] = Derived  # error: [invalid-assignment]
+
+    # Note how this is different from `type[…]` which includes subclasses:
+    s1: type[Base] = Base
+    s2: type[Base] = Derived  # no error here
+
+# error: "Special form `knot_extensions.TypeOf` expected exactly one type parameter"
+t: TypeOf[int, str, bytes]
+```

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

@@ -142,3 +142,25 @@ class Foo(type[int]): ...
 # TODO: should be `tuple[Literal[Foo], Literal[type], Literal[object]]
 reveal_type(Foo.__mro__)  # revealed: tuple[Literal[Foo], Unknown, Literal[object]]
 ```
+
+## `@final` classes
+
+`type[]` types are eagerly converted to class-literal types if a class decorated with `@final` is
+used as the type argument. This applies to standard-library classes and user-defined classes:
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+from types import EllipsisType
+from typing import final
+
+@final
+class Foo: ...
+
+def _(x: type[Foo], y: type[EllipsisType]):
+    reveal_type(x)  # revealed: Literal[Foo]
+    reveal_type(y)  # revealed: Literal[EllipsisType]
+```

crates/red_knot_python_semantic/resources/mdtest/type_of/dynamic.md

@@ -47,9 +47,8 @@ x: type = A()  # error: [invalid-assignment]
 
 ```py
 def f(x: type[object]):
-    reveal_type(x)  # revealed: type[object]
-    # TODO: bound method types
-    reveal_type(x.__repr__)  # revealed: Literal[__repr__]
+    reveal_type(x)  # revealed: type
+    reveal_type(x.__repr__)  # revealed: @Todo(instance attributes)
 
 class A: ...
 

crates/red_knot_python_semantic/resources/mdtest/type_properties/is_assignable_to.md

@@ -0,0 +1,352 @@
+# Assignable-to relation
+
+The `is_assignable_to(S, T)` relation below checks if type `S` is assignable to type `T` (target).
+This allows us to check if a type `S` can be used in a context where a type `T` is expected
+(function arguments, variable assignments). See the [typing documentation] for a precise definition
+of this concept.
+
+## Basic types
+
+### Fully static
+
+Fully static types participate in subtyping. If a type `S` is a subtype of `T`, `S` will also be
+assignable to `T`. Two equivalent types are subtypes of each other:
+
+```py
+from knot_extensions import static_assert, is_assignable_to
+
+class Parent: ...
+class Child1(Parent): ...
+class Child2(Parent): ...
+class Grandchild(Child1, Child2): ...
+class Unrelated: ...
+
+static_assert(is_assignable_to(int, int))
+static_assert(is_assignable_to(Parent, Parent))
+static_assert(is_assignable_to(Child1, Parent))
+static_assert(is_assignable_to(Grandchild, Parent))
+static_assert(is_assignable_to(Unrelated, Unrelated))
+
+static_assert(not is_assignable_to(str, int))
+static_assert(not is_assignable_to(object, int))
+static_assert(not is_assignable_to(Parent, Child1))
+static_assert(not is_assignable_to(Unrelated, Parent))
+static_assert(not is_assignable_to(Child1, Child2))
+```
+
+### Gradual types
+
+Gradual types do not participate in subtyping, but can still be assignable to other types (and
+static types can be assignable to gradual types):
+
+```py
+from knot_extensions import static_assert, is_assignable_to, Unknown
+from typing import Any
+
+static_assert(is_assignable_to(Unknown, Literal[1]))
+static_assert(is_assignable_to(Any, Literal[1]))
+static_assert(is_assignable_to(Literal[1], Unknown))
+static_assert(is_assignable_to(Literal[1], Any))
+```
+
+## Literal types
+
+### Boolean literals
+
+`Literal[True]` and `Literal[False]` are both subtypes of (and therefore assignable to) `bool`,
+which is in turn a subtype of `int`:
+
+```py
+from knot_extensions import static_assert, is_assignable_to
+from typing import Literal
+
+static_assert(is_assignable_to(Literal[True], Literal[True]))
+static_assert(is_assignable_to(Literal[True], bool))
+static_assert(is_assignable_to(Literal[True], int))
+
+static_assert(not is_assignable_to(Literal[True], Literal[False]))
+static_assert(not is_assignable_to(bool, Literal[True]))
+```
+
+### Integer literals
+
+```py
+from knot_extensions import static_assert, is_assignable_to
+from typing import Literal
+
+static_assert(is_assignable_to(Literal[1], Literal[1]))
+static_assert(is_assignable_to(Literal[1], int))
+
+static_assert(not is_assignable_to(Literal[1], Literal[2]))
+static_assert(not is_assignable_to(int, Literal[1]))
+static_assert(not is_assignable_to(Literal[1], str))
+```
+
+### String literals and `LiteralString`
+
+All string-literal types are subtypes of (and therefore assignable to) `LiteralString`, which is in
+turn a subtype of `str`:
+
+```py
+from knot_extensions import static_assert, is_assignable_to
+from typing_extensions import Literal, LiteralString
+
+static_assert(is_assignable_to(Literal["foo"], Literal["foo"]))
+static_assert(is_assignable_to(Literal["foo"], LiteralString))
+static_assert(is_assignable_to(Literal["foo"], str))
+
+static_assert(is_assignable_to(LiteralString, str))
+
+static_assert(not is_assignable_to(Literal["foo"], Literal["bar"]))
+static_assert(not is_assignable_to(str, Literal["foo"]))
+static_assert(not is_assignable_to(str, LiteralString))
+```
+
+### Byte literals
+
+```py
+from knot_extensions import static_assert, is_assignable_to
+from typing_extensions import Literal, LiteralString
+
+static_assert(is_assignable_to(Literal[b"foo"], bytes))
+static_assert(is_assignable_to(Literal[b"foo"], Literal[b"foo"]))
+
+static_assert(not is_assignable_to(Literal[b"foo"], str))
+static_assert(not is_assignable_to(Literal[b"foo"], LiteralString))
+static_assert(not is_assignable_to(Literal[b"foo"], Literal[b"bar"]))
+static_assert(not is_assignable_to(Literal[b"foo"], Literal["foo"]))
+static_assert(not is_assignable_to(Literal["foo"], Literal[b"foo"]))
+```
+
+## `type[…]` and class literals
+
+In the following tests, `TypeOf[str]` is a singleton type with a single inhabitant, the class `str`.
+This contrasts with `type[str]`, which represents "all possible subclasses of `str`".
+
+Both `TypeOf[str]` and `type[str]` are subtypes of `type` and `type[object]`, which both represent
+"all possible instances of `type`"; therefore both `type[str]` and `TypeOf[str]` are assignable to
+`type`. `type[Any]`, on the other hand, represents a type of unknown size or inhabitants, but which
+is known to be no larger than the set of possible objects represented by `type`.
+
+```py
+from knot_extensions import static_assert, is_assignable_to, Unknown, TypeOf
+from typing import Any
+
+static_assert(is_assignable_to(type, type))
+static_assert(is_assignable_to(type[object], type[object]))
+
+static_assert(is_assignable_to(type, type[object]))
+static_assert(is_assignable_to(type[object], type))
+
+static_assert(is_assignable_to(type[str], type[object]))
+static_assert(is_assignable_to(TypeOf[str], type[object]))
+static_assert(is_assignable_to(type[str], type))
+static_assert(is_assignable_to(TypeOf[str], type))
+
+static_assert(is_assignable_to(type[str], type[str]))
+static_assert(is_assignable_to(TypeOf[str], type[str]))
+
+static_assert(not is_assignable_to(TypeOf[int], type[str]))
+static_assert(not is_assignable_to(type, type[str]))
+static_assert(not is_assignable_to(type[object], type[str]))
+
+static_assert(is_assignable_to(type[Any], type[Any]))
+static_assert(is_assignable_to(type[Any], type[object]))
+static_assert(is_assignable_to(type[object], type[Any]))
+static_assert(is_assignable_to(type, type[Any]))
+static_assert(is_assignable_to(type[Any], type[str]))
+static_assert(is_assignable_to(type[str], type[Any]))
+static_assert(is_assignable_to(TypeOf[str], type[Any]))
+
+static_assert(is_assignable_to(type[Unknown], type[Unknown]))
+static_assert(is_assignable_to(type[Unknown], type[object]))
+static_assert(is_assignable_to(type[object], type[Unknown]))
+static_assert(is_assignable_to(type, type[Unknown]))
+static_assert(is_assignable_to(type[Unknown], type[str]))
+static_assert(is_assignable_to(type[str], type[Unknown]))
+static_assert(is_assignable_to(TypeOf[str], type[Unknown]))
+
+static_assert(is_assignable_to(type[Unknown], type[Any]))
+static_assert(is_assignable_to(type[Any], type[Unknown]))
+
+static_assert(not is_assignable_to(object, type[Any]))
+static_assert(not is_assignable_to(str, type[Any]))
+
+class Meta(type): ...
+
+static_assert(is_assignable_to(type[Any], Meta))
+static_assert(is_assignable_to(type[Unknown], Meta))
+static_assert(is_assignable_to(Meta, type[Any]))
+static_assert(is_assignable_to(Meta, type[Unknown]))
+```
+
+## Tuple types
+
+```py
+from knot_extensions import static_assert, is_assignable_to
+from typing import Literal, Any
+
+static_assert(is_assignable_to(tuple[()], tuple[()]))
+static_assert(is_assignable_to(tuple[int], tuple[int]))
+static_assert(is_assignable_to(tuple[int], tuple[Any]))
+static_assert(is_assignable_to(tuple[Any], tuple[int]))
+static_assert(is_assignable_to(tuple[int, str], tuple[int, str]))
+static_assert(is_assignable_to(tuple[Literal[1], Literal[2]], tuple[int, int]))
+static_assert(is_assignable_to(tuple[Any, Literal[2]], tuple[int, int]))
+static_assert(is_assignable_to(tuple[Literal[1], Any], tuple[int, int]))
+
+static_assert(not is_assignable_to(tuple[()], tuple[int]))
+static_assert(not is_assignable_to(tuple[int], tuple[str]))
+static_assert(not is_assignable_to(tuple[int], tuple[int, str]))
+static_assert(not is_assignable_to(tuple[int, str], tuple[int]))
+static_assert(not is_assignable_to(tuple[int, int], tuple[Literal[1], int]))
+static_assert(not is_assignable_to(tuple[Any, Literal[2]], tuple[int, str]))
+```
+
+## Union types
+
+```py
+from knot_extensions import static_assert, is_assignable_to, Unknown
+from typing import Literal, Any
+
+static_assert(is_assignable_to(int, int | str))
+static_assert(is_assignable_to(str, int | str))
+static_assert(is_assignable_to(int | str, int | str))
+static_assert(is_assignable_to(str | int, int | str))
+static_assert(is_assignable_to(Literal[1], int | str))
+static_assert(is_assignable_to(Literal[1], Unknown | str))
+static_assert(is_assignable_to(Literal[1] | Literal[2], Literal[1] | Literal[2]))
+static_assert(is_assignable_to(Literal[1] | Literal[2], int))
+static_assert(is_assignable_to(Literal[1] | None, int | None))
+static_assert(is_assignable_to(Any, int | str))
+static_assert(is_assignable_to(Any | int, int))
+static_assert(is_assignable_to(str, int | Any))
+
+static_assert(not is_assignable_to(int | None, int))
+static_assert(not is_assignable_to(int | None, str | None))
+static_assert(not is_assignable_to(Literal[1] | None, int))
+static_assert(not is_assignable_to(Literal[1] | None, str | None))
+static_assert(not is_assignable_to(Any | int | str, int))
+```
+
+## Intersection types
+
+```py
+from knot_extensions import static_assert, is_assignable_to, Intersection, Not
+from typing_extensions import Any, Literal
+
+class Parent: ...
+class Child1(Parent): ...
+class Child2(Parent): ...
+class Grandchild(Child1, Child2): ...
+class Unrelated: ...
+
+static_assert(is_assignable_to(Intersection[Child1, Child2], Child1))
+static_assert(is_assignable_to(Intersection[Child1, Child2], Child2))
+static_assert(is_assignable_to(Intersection[Child1, Child2], Parent))
+static_assert(is_assignable_to(Intersection[Child1, Parent], Parent))
+
+static_assert(is_assignable_to(Intersection[Parent, Unrelated], Parent))
+static_assert(is_assignable_to(Intersection[Child1, Unrelated], Child1))
+
+static_assert(is_assignable_to(Intersection[Child1, Not[Child2]], Child1))
+static_assert(is_assignable_to(Intersection[Child1, Not[Child2]], Parent))
+static_assert(is_assignable_to(Intersection[Child1, Not[Grandchild]], Parent))
+
+static_assert(is_assignable_to(Intersection[Child1, Child2], Intersection[Child1, Child2]))
+static_assert(is_assignable_to(Intersection[Child1, Child2], Intersection[Child2, Child1]))
+static_assert(is_assignable_to(Grandchild, Intersection[Child1, Child2]))
+
+static_assert(not is_assignable_to(Parent, Intersection[Parent, Unrelated]))
+static_assert(not is_assignable_to(int, Intersection[int, Not[Literal[1]]]))
+static_assert(not is_assignable_to(int, Not[int]))
+static_assert(not is_assignable_to(int, Not[Literal[1]]))
+
+static_assert(not is_assignable_to(Intersection[Any, Parent], Unrelated))
+
+# TODO: The following assertions should not fail (see https://github.com/astral-sh/ruff/issues/14899)
+# error: [static-assert-error]
+static_assert(is_assignable_to(Intersection[Any, int], int))
+
+# error: [static-assert-error]
+static_assert(is_assignable_to(Intersection[Unrelated, Any], Intersection[Unrelated, Any]))
+# error: [static-assert-error]
+static_assert(is_assignable_to(Intersection[Unrelated, Any], Intersection[Unrelated, Not[Any]]))
+# error: [static-assert-error]
+static_assert(is_assignable_to(Intersection[Unrelated, Any], Not[tuple[Unrelated, Any]]))
+```
+
+## General properties
+
+See also: our property tests in `property_tests.rs`.
+
+### Everything is assignable to `object`
+
+`object` is Python's top type; the set of all possible objects at runtime:
+
+```py
+from knot_extensions import static_assert, is_assignable_to, Unknown
+from typing import Literal, Any
+
+static_assert(is_assignable_to(str, object))
+static_assert(is_assignable_to(Literal[1], object))
+static_assert(is_assignable_to(object, object))
+static_assert(is_assignable_to(type, object))
+static_assert(is_assignable_to(Any, object))
+static_assert(is_assignable_to(Unknown, object))
+static_assert(is_assignable_to(type[object], object))
+static_assert(is_assignable_to(type[str], object))
+static_assert(is_assignable_to(type[Any], object))
+```
+
+### Every type is assignable to `Any` / `Unknown`
+
+`Any` and `Unknown` are gradual types. They could materialize to any given type at runtime, and so
+any type is assignable to them:
+
+```py
+from knot_extensions import static_assert, is_assignable_to, Unknown
+from typing import Literal, Any
+
+static_assert(is_assignable_to(str, Any))
+static_assert(is_assignable_to(Literal[1], Any))
+static_assert(is_assignable_to(object, Any))
+static_assert(is_assignable_to(type, Any))
+static_assert(is_assignable_to(Any, Any))
+static_assert(is_assignable_to(Unknown, Any))
+static_assert(is_assignable_to(type[object], Any))
+static_assert(is_assignable_to(type[str], Any))
+static_assert(is_assignable_to(type[Any], Any))
+
+static_assert(is_assignable_to(str, Unknown))
+static_assert(is_assignable_to(Literal[1], Unknown))
+static_assert(is_assignable_to(object, Unknown))
+static_assert(is_assignable_to(type, Unknown))
+static_assert(is_assignable_to(Any, Unknown))
+static_assert(is_assignable_to(Unknown, Unknown))
+static_assert(is_assignable_to(type[object], Unknown))
+static_assert(is_assignable_to(type[str], Unknown))
+static_assert(is_assignable_to(type[Any], Unknown))
+```
+
+### `Never` is assignable to every type
+
+`Never` is Python's bottom type: the empty set, a type with no inhabitants. It is therefore
+assignable to any arbitrary type.
+
+```py
+from knot_extensions import static_assert, is_assignable_to, Unknown
+from typing_extensions import Never, Any
+
+static_assert(is_assignable_to(Never, str))
+static_assert(is_assignable_to(Never, Literal[1]))
+static_assert(is_assignable_to(Never, object))
+static_assert(is_assignable_to(Never, type))
+static_assert(is_assignable_to(Never, Any))
+static_assert(is_assignable_to(Never, Unknown))
+static_assert(is_assignable_to(Never, type[object]))
+static_assert(is_assignable_to(Never, type[str]))
+static_assert(is_assignable_to(Never, type[Any]))
+```
+
+[typing documentation]: https://typing.readthedocs.io/en/latest/spec/concepts.html#the-assignable-to-or-consistent-subtyping-relation

crates/red_knot_python_semantic/resources/mdtest/type_properties/tuples_containing_never.md

@@ -0,0 +1,33 @@
+# Tuples containing `Never`
+
+A heterogeneous `tuple[…]` type that contains `Never` as a type argument simplifies to `Never`. One
+way to think about this is the following: in order to construct a tuple, you need to have an object
+of every element type. But since there is no object of type `Never`, you cannot construct the tuple.
+Such a tuple type is therefore uninhabited and equivalent to `Never`.
+
+In the language of algebraic data types, a tuple type is a product type and `Never` acts like the
+zero element in multiplication, similar to how a Cartesian product with the empty set is the empty
+set.
+
+```py
+from knot_extensions import static_assert, is_equivalent_to
+from typing_extensions import Never, NoReturn
+
+static_assert(is_equivalent_to(Never, tuple[Never]))
+static_assert(is_equivalent_to(Never, tuple[Never, int]))
+static_assert(is_equivalent_to(Never, tuple[int, Never]))
+static_assert(is_equivalent_to(Never, tuple[int, Never, str]))
+static_assert(is_equivalent_to(Never, tuple[int, tuple[str, Never]]))
+static_assert(is_equivalent_to(Never, tuple[tuple[str, Never], int]))
+
+# The empty tuple is *not* equivalent to Never!
+static_assert(not is_equivalent_to(Never, tuple[()]))
+
+# NoReturn is just a different spelling of Never, so the same is true for NoReturn
+static_assert(is_equivalent_to(NoReturn, tuple[NoReturn]))
+static_assert(is_equivalent_to(NoReturn, tuple[NoReturn, int]))
+static_assert(is_equivalent_to(NoReturn, tuple[int, NoReturn]))
+static_assert(is_equivalent_to(NoReturn, tuple[int, NoReturn, str]))
+static_assert(is_equivalent_to(NoReturn, tuple[int, tuple[str, NoReturn]]))
+static_assert(is_equivalent_to(NoReturn, tuple[tuple[str, NoReturn], int]))
+```

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

@@ -34,6 +34,10 @@ reveal_type(~No())  # revealed: Unknown
 
 ## Classes
 
+Dunder methods defined in a class are available to instances of that class, but not to the class
+itself. (For these operators to work on the class itself, they would have to be defined on the
+class's type, i.e. `type`.)
+
 ```py
 class Yes:
     def __pos__(self) -> bool:

crates/red_knot_python_semantic/resources/mdtest/union_types.md

@@ -0,0 +1,143 @@
+# Union types
+
+This test suite covers certain basic properties and simplification strategies for union types.
+
+## Basic unions
+
+```py
+from typing import Literal
+
+def _(u1: int | str, u2: Literal[0] | Literal[1]) -> None:
+    reveal_type(u1)  # revealed: int | str
+    reveal_type(u2)  # revealed: Literal[0, 1]
+```
+
+## Duplicate elements are collapsed
+
+```py
+def _(u1: int | int | str, u2: int | str | int) -> None:
+    reveal_type(u1)  # revealed: int | str
+    reveal_type(u2)  # revealed: int | str
+```
+
+## `Never` is removed
+
+`Never` is an empty set, a type with no inhabitants. Its presence in a union is always redundant,
+and so we eagerly simplify it away. `NoReturn` is equivalent to `Never`.
+
+```py
+from typing_extensions import Never, NoReturn
+
+def never(u1: int | Never, u2: int | Never | str) -> None:
+    reveal_type(u1)  # revealed: int
+    reveal_type(u2)  # revealed:  int | str
+
+def noreturn(u1: int | NoReturn, u2: int | NoReturn | str) -> None:
+    reveal_type(u1)  # revealed: int
+    reveal_type(u2)  # revealed:  int | str
+```
+
+## Flattening of nested unions
+
+```py
+from typing import Literal
+
+def _(
+    u1: (int | str) | bytes,
+    u2: int | (str | bytes),
+    u3: int | (str | (bytes | complex)),
+) -> None:
+    reveal_type(u1)  # revealed: int | str | bytes
+    reveal_type(u2)  # revealed: int | str | bytes
+    reveal_type(u3)  # revealed: int | str | bytes | complex
+```
+
+## Simplification using subtyping
+
+The type `S | T` can be simplified to `T` if `S` is a subtype of `T`:
+
+```py
+from typing_extensions import Literal, LiteralString
+
+def _(
+    u1: str | LiteralString, u2: LiteralString | str, u3: Literal["a"] | str | LiteralString, u4: str | bytes | LiteralString
+) -> None:
+    reveal_type(u1)  # revealed: str
+    reveal_type(u2)  # revealed: str
+    reveal_type(u3)  # revealed: str
+    reveal_type(u4)  # revealed: str | bytes
+```
+
+## Boolean literals
+
+The union `Literal[True] | Literal[False]` is exactly equivalent to `bool`:
+
+```py
+from typing import Literal
+
+def _(
+    u1: Literal[True, False],
+    u2: bool | Literal[True],
+    u3: Literal[True] | bool,
+    u4: Literal[True] | Literal[True, 17],
+    u5: Literal[True, False, True, 17],
+) -> None:
+    reveal_type(u1)  # revealed: bool
+    reveal_type(u2)  # revealed: bool
+    reveal_type(u3)  # revealed: bool
+    reveal_type(u4)  # revealed: Literal[True, 17]
+    reveal_type(u5)  # revealed: bool | Literal[17]
+```
+
+## Do not erase `Unknown`
+
+```py
+from knot_extensions import Unknown
+
+def _(u1: Unknown | str, u2: str | Unknown) -> None:
+    reveal_type(u1)  # revealed: Unknown | str
+    reveal_type(u2)  # revealed: str | Unknown
+```
+
+## Collapse multiple `Unknown`s
+
+Since `Unknown` is a gradual type, it is not a subtype of anything, but multiple `Unknown`s in a
+union are still redundant:
+
+```py
+from knot_extensions import Unknown
+
+def _(u1: Unknown | Unknown | str, u2: Unknown | str | Unknown, u3: str | Unknown | Unknown) -> None:
+    reveal_type(u1)  # revealed: Unknown | str
+    reveal_type(u2)  # revealed: Unknown | str
+    reveal_type(u3)  # revealed: str | Unknown
+```
+
+## Subsume multiple elements
+
+Simplifications still apply when `Unknown` is present.
+
+```py
+from knot_extensions import Unknown
+
+def _(u1: str | Unknown | int | object):
+    reveal_type(u1)  # revealed: Unknown | object
+```
+
+## Union of intersections
+
+We can simplify unions of intersections:
+
+```py
+from knot_extensions import Intersection, Not
+
+class P: ...
+class Q: ...
+
+def _(
+    i1: Intersection[P, Q] | Intersection[P, Q],
+    i2: Intersection[P, Q] | Intersection[Q, P],
+) -> None:
+    reveal_type(i1)  # revealed: P & Q
+    reveal_type(i2)  # revealed: P & Q
+```

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, "a"]
+    reveal_type(b)  # revealed: Literal[2, "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, "a"]
+    reveal_type(b)  # revealed: Literal[2, "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, Module};
+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/mod.rs

@@ -1,6 +1,6 @@
 use std::iter::FusedIterator;
 
-pub use module::Module;
+pub use module::{KnownModule, Module};
 pub use resolver::resolve_module;
 pub(crate) use resolver::{file_to_module, SearchPaths};
 use ruff_db::system::SystemPath;

crates/red_knot_python_semantic/src/module_resolver/module.rs

@@ -19,12 +19,14 @@ impl Module {
         search_path: SearchPath,
         file: File,
     ) -> Self {
+        let known = KnownModule::try_from_search_path_and_name(&search_path, &name);
         Self {
             inner: Arc::new(ModuleInner {
                 name,
                 kind,
                 search_path,
                 file,
+                known,
             }),
         }
     }
@@ -39,6 +41,16 @@ impl Module {
         self.inner.file
     }
 
+    /// Is this a module that we special-case somehow? If so, which one?
+    pub fn known(&self) -> Option<KnownModule> {
+        self.inner.known
+    }
+
+    /// Does this module represent the given known module?
+    pub fn is_known(&self, known_module: KnownModule) -> bool {
+        self.known() == Some(known_module)
+    }
+
     /// The search path from which the module was resolved.
     pub(crate) fn search_path(&self) -> &SearchPath {
         &self.inner.search_path
@@ -67,6 +79,7 @@ struct ModuleInner {
     kind: ModuleKind,
     search_path: SearchPath,
     file: File,
+    known: Option<KnownModule>,
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
@@ -83,3 +96,69 @@ impl ModuleKind {
         matches!(self, ModuleKind::Package)
     }
 }
+
+/// Enumeration of various core stdlib modules in which important types are located
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum KnownModule {
+    Builtins,
+    Types,
+    Typeshed,
+    TypingExtensions,
+    Typing,
+    Sys,
+    #[allow(dead_code)]
+    Abc, // currently only used in tests
+    Collections,
+    KnotExtensions,
+}
+
+impl KnownModule {
+    pub const fn as_str(self) -> &'static str {
+        match self {
+            Self::Builtins => "builtins",
+            Self::Types => "types",
+            Self::Typing => "typing",
+            Self::Typeshed => "_typeshed",
+            Self::TypingExtensions => "typing_extensions",
+            Self::Sys => "sys",
+            Self::Abc => "abc",
+            Self::Collections => "collections",
+            Self::KnotExtensions => "knot_extensions",
+        }
+    }
+
+    pub fn name(self) -> ModuleName {
+        let self_as_str = self.as_str();
+        ModuleName::new_static(self_as_str)
+            .unwrap_or_else(|| panic!("{self_as_str} should be a valid module name!"))
+    }
+
+    pub(crate) fn try_from_search_path_and_name(
+        search_path: &SearchPath,
+        name: &ModuleName,
+    ) -> Option<Self> {
+        if !search_path.is_standard_library() {
+            return None;
+        }
+        match name.as_str() {
+            "builtins" => Some(Self::Builtins),
+            "types" => Some(Self::Types),
+            "typing" => Some(Self::Typing),
+            "_typeshed" => Some(Self::Typeshed),
+            "typing_extensions" => Some(Self::TypingExtensions),
+            "sys" => Some(Self::Sys),
+            "abc" => Some(Self::Abc),
+            "collections" => Some(Self::Collections),
+            "knot_extensions" => Some(Self::KnotExtensions),
+            _ => None,
+        }
+    }
+
+    pub const fn is_typing(self) -> bool {
+        matches!(self, Self::Typing)
+    }
+
+    pub const fn is_knot_extensions(self) -> bool {
+        matches!(self, Self::KnotExtensions)
+    }
+}

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 +400,52 @@ 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> {
+        // This is called for the top-level pattern of each match arm. We need to create a
+        // standalone expression for each arm of a match statement, since they can introduce
+        // constraints on the match subject. (Or more accurately, for the match arm's pattern,
+        // since its the pattern that introduces any constraints, not the body.) Ideally, that
+        // standalone expression would wrap the match arm's pattern as a whole. But a standalone
+        // expression can currently only wrap an ast::Expr, which patterns are not. So, we need to
+        // choose an Expr that can “stand in” for the pattern, which we can wrap in a standalone
+        // expression.
+        //
+        // See the comment in TypeInferenceBuilder::infer_match_pattern for more details.
+
+        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)
+            }
+            ast::Pattern::MatchClass(pattern) => {
+                let cls = self.add_standalone_expression(&pattern.cls);
+                PatternConstraintKind::Class(cls, 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 +824,7 @@ where
                                     unsafe {
                                         AstNodeRef::new(self.module.clone(), target)
                                     },
-                                    value,
+                                    UnpackValue::Assign(value),
                                     countme::Count::default(),
                                 )),
                             })
@@ -795,10 +893,13 @@ where
             }
             ast::Stmt::If(node) => {
                 self.visit_expr(&node.test);
-                let pre_if = self.flow_snapshot();
-                let constraint = self.record_expression_constraint(&node.test);
-                let mut constraints = vec![constraint];
+                let mut no_branch_taken = self.flow_snapshot();
+                let mut last_constraint = self.record_expression_constraint(&node.test);
                 self.visit_body(&node.body);
+
+                let visibility_constraint_id = self.record_visibility_constraint(last_constraint);
+                let mut vis_constraints = vec![visibility_constraint_id];
+
                 let mut post_clauses: Vec<FlowSnapshot> = vec![];
                 let elif_else_clauses = node
                     .elif_else_clauses
@@ -820,20 +921,37 @@ where
                     // the state that we merge the other snapshots into
                     post_clauses.push(self.flow_snapshot());
                     // we can only take an elif/else branch if none of the previous ones were
-                    // taken, so the block entry state is always `pre_if`
-                    self.flow_restore(pre_if.clone());
-                    for constraint in &constraints {
-                        self.record_negated_constraint(*constraint);
-                    }
-                    if let Some(elif_test) = clause_test {
+                    // taken
+                    self.flow_restore(no_branch_taken.clone());
+                    self.record_negated_constraint(last_constraint);
+
+                    let elif_constraint = if let Some(elif_test) = clause_test {
                         self.visit_expr(elif_test);
-                        constraints.push(self.record_expression_constraint(elif_test));
-                    }
+                        // A test expression is evaluated whether the branch is taken or not
+                        no_branch_taken = self.flow_snapshot();
+                        let constraint = self.record_expression_constraint(elif_test);
+                        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 {
+                        last_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(no_branch_taken);
             }
             ast::Stmt::While(ast::StmtWhile {
                 test,
@@ -856,6 +974,8 @@ 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 +983,21 @@ 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 +1035,47 @@ 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 +1104,61 @@ where
                 cases,
                 range: _,
             }) => {
-                self.add_standalone_expression(subject);
-                self.visit_expr(subject);
+                debug_assert_eq!(self.current_match_case, None);
 
-                let after_subject = self.flow_snapshot();
-                let Some((first, remaining)) = cases.split_first() else {
+                let subject_expr = self.add_standalone_expression(subject);
+                self.visit_expr(subject);
+                if cases.is_empty() {
                     return;
                 };
-                self.add_pattern_constraint(subject, &first.pattern);
-                self.visit_match_case(first);
 
+                let after_subject = self.flow_snapshot();
+                let mut vis_constraints = vec![];
                 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);
-                    self.visit_match_case(case);
-                }
-                for post_clause_state in post_case_snapshots {
-                    self.flow_merge(post_clause_state);
+                for (i, case) in cases.iter().enumerate() {
+                    if i != 0 {
+                        post_case_snapshots.push(self.flow_snapshot());
+                        self.flow_restore(after_subject.clone());
+                    }
+
+                    self.current_match_case = Some(CurrentMatchCase::new(&case.pattern));
+                    self.visit_pattern(&case.pattern);
+                    self.current_match_case = None;
+                    let constraint_id = self.add_pattern_constraint(
+                        subject_expr,
+                        &case.pattern,
+                        case.guard.as_deref(),
+                    );
+                    if let Some(expr) = &case.guard {
+                        self.visit_expr(expr);
+                    }
+                    self.visit_body(&case.body);
+                    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);
                 }
+
+                // 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 +1168,8 @@ 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 +1324,18 @@ 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 +1371,9 @@ 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 +1418,19 @@ 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 +1487,55 @@ 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);
@@ -1327,18 +1551,6 @@ where
         }
     }
 
-    fn visit_match_case(&mut self, match_case: &'ast ast::MatchCase) {
-        debug_assert!(self.current_match_case.is_none());
-        self.current_match_case = Some(CurrentMatchCase::new(&match_case.pattern));
-        self.visit_pattern(&match_case.pattern);
-        self.current_match_case = None;
-
-        if let Some(expr) = &match_case.guard {
-            self.visit_expr(expr);
-        }
-        self.visit_body(&match_case.body);
-    }
-
     fn visit_pattern(&mut self, pattern: &'ast ast::Pattern) {
         if let ast::Pattern::MatchStar(ast::PatternMatchStar {
             name: Some(name),
@@ -1391,7 +1603,11 @@ 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,
@@ -1415,18 +1631,13 @@ 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)
     }
 }
 
+#[derive(Debug, PartialEq)]
 struct CurrentMatchCase<'a> {
     /// The pattern that's part of the current match case.
     pattern: &'a ast::Pattern,

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 +17,15 @@ 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>>),
+    Class(Expression<'db>, Option<Expression<'db>>),
+    Unsupported,
+}
+
 #[salsa::tracked]
 pub(crate) struct PatternConstraint<'db> {
     #[id]
@@ -28,11 +36,11 @@ 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

@@ -8,7 +8,7 @@ use crate::module_resolver::file_to_module;
 use crate::node_key::NodeKey;
 use crate::semantic_index::symbol::{FileScopeId, ScopeId, ScopedSymbolId};
 use crate::unpack::Unpack;
-use crate::Db;
+use crate::{Db, KnownModule};
 
 /// A definition of a symbol.
 ///
@@ -63,17 +63,21 @@ impl<'db> Definition<'db> {
     }
 
     pub(crate) fn is_builtin_definition(self, db: &'db dyn Db) -> bool {
-        file_to_module(db, self.file(db)).is_some_and(|module| {
-            module.search_path().is_standard_library() && matches!(&**module.name(), "builtins")
-        })
+        file_to_module(db, self.file(db))
+            .is_some_and(|module| module.is_known(KnownModule::Builtins))
     }
 
     /// Return true if this symbol was defined in the `typing` or `typing_extensions` modules
     pub(crate) fn is_typing_definition(self, db: &'db dyn Db) -> bool {
-        file_to_module(db, self.file(db)).is_some_and(|module| {
-            module.search_path().is_standard_library()
-                && matches!(&**module.name(), "typing" | "typing_extensions")
-        })
+        matches!(
+            file_to_module(db, self.file(db)).and_then(|module| module.known()),
+            Some(KnownModule::Typing | KnownModule::TypingExtensions)
+        )
+    }
+
+    pub(crate) fn is_knot_extensions_definition(self, db: &'db dyn Db) -> bool {
+        file_to_module(db, self.file(db))
+            .is_some_and(|module| module.is_known(KnownModule::KnotExtensions))
     }
 }
 
@@ -226,8 +230,10 @@ 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,
 }
 
@@ -299,12 +305,16 @@ 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 {
@@ -383,10 +393,12 @@ 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(),
@@ -453,7 +465,7 @@ 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>),
@@ -466,8 +478,14 @@ 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(),
@@ -478,7 +496,7 @@ 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(),
@@ -491,9 +509,7 @@ 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
@@ -666,22 +682,32 @@ 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
     }
 }
@@ -757,12 +783,6 @@ 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,
+                live_declarations: Declarations::default(),
+                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/stdlib.rs

@@ -1,55 +1,19 @@
-use crate::module_name::ModuleName;
-use crate::module_resolver::resolve_module;
+use crate::module_resolver::{resolve_module, KnownModule};
 use crate::semantic_index::global_scope;
 use crate::semantic_index::symbol::ScopeId;
 use crate::symbol::Symbol;
 use crate::types::global_symbol;
 use crate::Db;
 
-/// Enumeration of various core stdlib modules, for which we have dedicated Salsa queries.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub(crate) enum CoreStdlibModule {
-    Builtins,
-    Types,
-    Typeshed,
-    TypingExtensions,
-    Typing,
-    Sys,
-    #[allow(dead_code)]
-    Abc, // currently only used in tests
-    Collections,
-}
-
-impl CoreStdlibModule {
-    pub(crate) const fn as_str(self) -> &'static str {
-        match self {
-            Self::Builtins => "builtins",
-            Self::Types => "types",
-            Self::Typing => "typing",
-            Self::Typeshed => "_typeshed",
-            Self::TypingExtensions => "typing_extensions",
-            Self::Sys => "sys",
-            Self::Abc => "abc",
-            Self::Collections => "collections",
-        }
-    }
-
-    pub(crate) fn name(self) -> ModuleName {
-        let self_as_str = self.as_str();
-        ModuleName::new_static(self_as_str)
-            .unwrap_or_else(|| panic!("{self_as_str} should be a valid module name!"))
-    }
-}
-
-/// Lookup the type of `symbol` in a given core module
+/// Lookup the type of `symbol` in a given known module
 ///
-/// Returns `Symbol::Unbound` if the given core module cannot be resolved for some reason
-pub(crate) fn core_module_symbol<'db>(
+/// Returns `Symbol::Unbound` if the given known module cannot be resolved for some reason
+pub(crate) fn known_module_symbol<'db>(
     db: &'db dyn Db,
-    core_module: CoreStdlibModule,
+    known_module: KnownModule,
     symbol: &str,
 ) -> Symbol<'db> {
-    resolve_module(db, &core_module.name())
+    resolve_module(db, &known_module.name())
         .map(|module| global_symbol(db, module.file(), symbol))
         .unwrap_or(Symbol::Unbound)
 }
@@ -59,7 +23,7 @@ pub(crate) fn core_module_symbol<'db>(
 /// Returns `Symbol::Unbound` if the `builtins` module isn't available for some reason.
 #[inline]
 pub(crate) fn builtins_symbol<'db>(db: &'db dyn Db, symbol: &str) -> Symbol<'db> {
-    core_module_symbol(db, CoreStdlibModule::Builtins, symbol)
+    known_module_symbol(db, KnownModule::Builtins, symbol)
 }
 
 /// Lookup the type of `symbol` in the `typing` module namespace.
@@ -68,7 +32,7 @@ pub(crate) fn builtins_symbol<'db>(db: &'db dyn Db, symbol: &str) -> Symbol<'db>
 #[inline]
 #[cfg(test)]
 pub(crate) fn typing_symbol<'db>(db: &'db dyn Db, symbol: &str) -> Symbol<'db> {
-    core_module_symbol(db, CoreStdlibModule::Typing, symbol)
+    known_module_symbol(db, KnownModule::Typing, symbol)
 }
 
 /// Lookup the type of `symbol` in the `typing_extensions` module namespace.
@@ -76,13 +40,13 @@ pub(crate) fn typing_symbol<'db>(db: &'db dyn Db, symbol: &str) -> Symbol<'db> {
 /// Returns `Symbol::Unbound` if the `typing_extensions` module isn't available for some reason.
 #[inline]
 pub(crate) fn typing_extensions_symbol<'db>(db: &'db dyn Db, symbol: &str) -> Symbol<'db> {
-    core_module_symbol(db, CoreStdlibModule::TypingExtensions, symbol)
+    known_module_symbol(db, KnownModule::TypingExtensions, symbol)
 }
 
 /// Get the scope of a core stdlib module.
 ///
 /// Can return `None` if a custom typeshed is used that is missing the core module in question.
-fn core_module_scope(db: &dyn Db, core_module: CoreStdlibModule) -> Option<ScopeId<'_>> {
+fn core_module_scope(db: &dyn Db, core_module: KnownModule) -> Option<ScopeId<'_>> {
     resolve_module(db, &core_module.name()).map(|module| global_scope(db, module.file()))
 }
 
@@ -90,5 +54,5 @@ fn core_module_scope(db: &dyn Db, core_module: CoreStdlibModule) -> Option<Scope
 ///
 /// Can return `None` if a custom typeshed is used that is missing `builtins.pyi`.
 pub(crate) fn builtins_module_scope(db: &dyn Db) -> Option<ScopeId<'_>> {
-    core_module_scope(db, CoreStdlibModule::Builtins)
+    core_module_scope(db, KnownModule::Builtins)
 }

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/builder.rs

@@ -65,6 +65,8 @@ impl<'db> UnionBuilder<'db> {
 
                 let mut to_add = ty;
                 let mut to_remove = SmallVec::<[usize; 2]>::new();
+                let ty_negated = ty.negate(self.db);
+
                 for (index, element) in self.elements.iter().enumerate() {
                     if Some(*element) == bool_pair {
                         to_add = KnownClass::Bool.to_instance(self.db);
@@ -80,6 +82,17 @@ impl<'db> UnionBuilder<'db> {
                         return self;
                     } else if element.is_subtype_of(self.db, ty) {
                         to_remove.push(index);
+                    } else if ty_negated.is_subtype_of(self.db, *element) {
+                        // We add `ty` to the union. We just checked that `~ty` is a subtype of an existing `element`.
+                        // This also means that `~ty | ty` is a subtype of `element | ty`, because both elements in the
+                        // first union are subtypes of the corresponding elements in the second union. But `~ty | ty` is
+                        // just `object`. Since `object` is a subtype of `element | ty`, we can only conclude that
+                        // `element | ty` must be `object` (object has no other supertypes). This means we can simplify
+                        // the whole union to just `object`, since all other potential elements would also be subtypes of
+                        // `object`.
+                        self.elements.clear();
+                        self.elements.push(KnownClass::Object.to_instance(self.db));
+                        return self;
                     }
                 }
                 match to_remove[..] {
@@ -321,7 +334,15 @@ impl<'db> InnerIntersectionBuilder<'db> {
                     self.add_positive(db, *neg);
                 }
             }
-            ty @ (Type::Any | Type::Unknown | Type::Todo(_)) => {
+            Type::Never => {
+                // Adding ~Never to an intersection is a no-op.
+            }
+            Type::Instance(instance) if instance.class.is_known(db, KnownClass::Object) => {
+                // Adding ~object to an intersection results in Never.
+                *self = Self::default();
+                self.positive.insert(Type::Never);
+            }
+            ty @ Type::Dynamic(_) => {
                 // Adding any of these types to the negative side of an intersection
                 // is equivalent to adding it to the positive side. We do this to
                 // simplify the representation.
@@ -386,18 +407,34 @@ impl<'db> InnerIntersectionBuilder<'db> {
 
 #[cfg(test)]
 mod tests {
-    use super::{IntersectionBuilder, IntersectionType, Type, UnionType};
+    use super::{IntersectionBuilder, Type, UnionBuilder, UnionType};
 
-    use crate::db::tests::{setup_db, TestDb};
-    use crate::types::{global_symbol, todo_type, KnownClass, Truthiness, UnionBuilder};
+    use crate::db::tests::setup_db;
+    use crate::types::{KnownClass, Truthiness};
 
-    use ruff_db::files::system_path_to_file;
-    use ruff_db::system::DbWithTestSystem;
     use test_case::test_case;
 
     #[test]
-    fn build_union() {
+    fn build_union_no_elements() {
         let db = setup_db();
+
+        let empty_union = UnionBuilder::new(&db).build();
+        assert_eq!(empty_union, Type::Never);
+    }
+
+    #[test]
+    fn build_union_single_element() {
+        let db = setup_db();
+
+        let t0 = Type::IntLiteral(0);
+        let union = UnionType::from_elements(&db, [t0]);
+        assert_eq!(union, t0);
+    }
+
+    #[test]
+    fn build_union_two_elements() {
+        let db = setup_db();
+
         let t0 = Type::IntLiteral(0);
         let t1 = Type::IntLiteral(1);
         let union = UnionType::from_elements(&db, [t0, t1]).expect_union();
@@ -405,605 +442,12 @@ mod tests {
         assert_eq!(union.elements(&db), &[t0, t1]);
     }
 
-    #[test]
-    fn build_union_single() {
-        let db = setup_db();
-        let t0 = Type::IntLiteral(0);
-        let ty = UnionType::from_elements(&db, [t0]);
-        assert_eq!(ty, t0);
-    }
-
-    #[test]
-    fn build_union_empty() {
-        let db = setup_db();
-        let ty = UnionBuilder::new(&db).build();
-        assert_eq!(ty, Type::Never);
-    }
-
-    #[test]
-    fn build_union_never() {
-        let db = setup_db();
-        let t0 = Type::IntLiteral(0);
-        let ty = UnionType::from_elements(&db, [t0, Type::Never]);
-        assert_eq!(ty, t0);
-    }
-
-    #[test]
-    fn build_union_bool() {
-        let db = setup_db();
-        let bool_instance_ty = KnownClass::Bool.to_instance(&db);
-
-        let t0 = Type::BooleanLiteral(true);
-        let t1 = Type::BooleanLiteral(true);
-        let t2 = Type::BooleanLiteral(false);
-        let t3 = Type::IntLiteral(17);
-
-        let union = UnionType::from_elements(&db, [t0, t1, t3]).expect_union();
-        assert_eq!(union.elements(&db), &[t0, t3]);
-
-        let union = UnionType::from_elements(&db, [t0, t1, t2, t3]).expect_union();
-        assert_eq!(union.elements(&db), &[bool_instance_ty, t3]);
-
-        let result_ty = UnionType::from_elements(&db, [bool_instance_ty, t0]);
-        assert_eq!(result_ty, bool_instance_ty);
-
-        let result_ty = UnionType::from_elements(&db, [t0, bool_instance_ty]);
-        assert_eq!(result_ty, bool_instance_ty);
-    }
-
-    #[test]
-    fn build_union_flatten() {
-        let db = setup_db();
-        let t0 = Type::IntLiteral(0);
-        let t1 = Type::IntLiteral(1);
-        let t2 = Type::IntLiteral(2);
-        let u1 = UnionType::from_elements(&db, [t0, t1]);
-        let union = UnionType::from_elements(&db, [u1, t2]).expect_union();
-
-        assert_eq!(union.elements(&db), &[t0, t1, t2]);
-    }
-
-    #[test]
-    fn build_union_simplify_subtype() {
-        let db = setup_db();
-        let t0 = KnownClass::Str.to_instance(&db);
-        let t1 = Type::LiteralString;
-        let u0 = UnionType::from_elements(&db, [t0, t1]);
-        let u1 = UnionType::from_elements(&db, [t1, t0]);
-
-        assert_eq!(u0, t0);
-        assert_eq!(u1, t0);
-    }
-
-    #[test]
-    fn build_union_no_simplify_unknown() {
-        let db = setup_db();
-        let t0 = KnownClass::Str.to_instance(&db);
-        let t1 = Type::Unknown;
-        let u0 = UnionType::from_elements(&db, [t0, t1]);
-        let u1 = UnionType::from_elements(&db, [t1, t0]);
-
-        assert_eq!(u0.expect_union().elements(&db), &[t0, t1]);
-        assert_eq!(u1.expect_union().elements(&db), &[t1, t0]);
-    }
-
-    #[test]
-    fn build_union_simplify_multiple_unknown() {
-        let db = setup_db();
-        let t0 = KnownClass::Str.to_instance(&db);
-        let t1 = Type::Unknown;
-
-        let u = UnionType::from_elements(&db, [t0, t1, t1]);
-
-        assert_eq!(u.expect_union().elements(&db), &[t0, t1]);
-    }
-
-    #[test]
-    fn build_union_subsume_multiple() {
-        let db = setup_db();
-        let str_ty = KnownClass::Str.to_instance(&db);
-        let int_ty = KnownClass::Int.to_instance(&db);
-        let object_ty = KnownClass::Object.to_instance(&db);
-        let unknown_ty = Type::Unknown;
-
-        let u0 = UnionType::from_elements(&db, [str_ty, unknown_ty, int_ty, object_ty]);
-
-        assert_eq!(u0.expect_union().elements(&db), &[unknown_ty, object_ty]);
-    }
-
-    impl<'db> IntersectionType<'db> {
-        fn pos_vec(self, db: &'db TestDb) -> Vec<Type<'db>> {
-            self.positive(db).into_iter().copied().collect()
-        }
-
-        fn neg_vec(self, db: &'db TestDb) -> Vec<Type<'db>> {
-            self.negative(db).into_iter().copied().collect()
-        }
-    }
-
-    #[test]
-    fn build_intersection() {
-        let db = setup_db();
-        let t0 = Type::IntLiteral(0);
-        let ta = Type::Any;
-        let intersection = IntersectionBuilder::new(&db)
-            .add_positive(ta)
-            .add_negative(t0)
-            .build()
-            .expect_intersection();
-
-        assert_eq!(intersection.pos_vec(&db), &[ta]);
-        assert_eq!(intersection.neg_vec(&db), &[t0]);
-    }
-
     #[test]
     fn build_intersection_empty_intersection_equals_object() {
         let db = setup_db();
 
-        let ty = IntersectionBuilder::new(&db).build();
-
-        assert_eq!(ty, KnownClass::Object.to_instance(&db));
-    }
-
-    #[test]
-    fn build_intersection_flatten_positive() {
-        let db = setup_db();
-        let ta = Type::Any;
-        let t1 = Type::IntLiteral(1);
-        let t2 = Type::IntLiteral(2);
-        let i0 = IntersectionBuilder::new(&db)
-            .add_positive(ta)
-            .add_negative(t1)
-            .build();
-        let intersection = IntersectionBuilder::new(&db)
-            .add_positive(t2)
-            .add_positive(i0)
-            .build()
-            .expect_intersection();
-
-        assert_eq!(intersection.pos_vec(&db), &[t2, ta]);
-        assert_eq!(intersection.neg_vec(&db), &[]);
-    }
-
-    #[test]
-    fn build_intersection_flatten_negative() {
-        let db = setup_db();
-        let ta = Type::Any;
-        let t1 = Type::IntLiteral(1);
-        let t2 = KnownClass::Int.to_instance(&db);
-        // i0 = Any & ~Literal[1]
-        let i0 = IntersectionBuilder::new(&db)
-            .add_positive(ta)
-            .add_negative(t1)
-            .build();
-        // ta_not_i0 = int & ~(Any & ~Literal[1])
-        // -> int & (~Any  | Literal[1])
-        // (~Any is equivalent to Any)
-        // -> (int & Any) | (int & Literal[1])
-        // -> (int & Any) | Literal[1]
-        let ta_not_i0 = IntersectionBuilder::new(&db)
-            .add_positive(t2)
-            .add_negative(i0)
-            .build();
-
-        assert_eq!(ta_not_i0.display(&db).to_string(), "int & Any | Literal[1]");
-    }
-
-    #[test]
-    fn build_intersection_simplify_negative_any() {
-        let db = setup_db();
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(Type::Any)
-            .build();
-        assert_eq!(ty, Type::Any);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(Type::Never)
-            .add_negative(Type::Any)
-            .build();
-        assert_eq!(ty, Type::Never);
-    }
-
-    #[test]
-    fn build_intersection_simplify_multiple_unknown() {
-        let db = setup_db();
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(Type::Unknown)
-            .add_positive(Type::Unknown)
-            .build();
-        assert_eq!(ty, Type::Unknown);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(Type::Unknown)
-            .add_negative(Type::Unknown)
-            .build();
-        assert_eq!(ty, Type::Unknown);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(Type::Unknown)
-            .add_negative(Type::Unknown)
-            .build();
-        assert_eq!(ty, Type::Unknown);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(Type::Unknown)
-            .add_positive(Type::IntLiteral(0))
-            .add_negative(Type::Unknown)
-            .build();
-        assert_eq!(
-            ty,
-            IntersectionBuilder::new(&db)
-                .add_positive(Type::Unknown)
-                .add_positive(Type::IntLiteral(0))
-                .build()
-        );
-    }
-
-    #[test]
-    fn intersection_distributes_over_union() {
-        let db = setup_db();
-        let t0 = Type::IntLiteral(0);
-        let t1 = Type::IntLiteral(1);
-        let ta = Type::Any;
-        let u0 = UnionType::from_elements(&db, [t0, t1]);
-
-        let union = IntersectionBuilder::new(&db)
-            .add_positive(ta)
-            .add_positive(u0)
-            .build()
-            .expect_union();
-        let [Type::Intersection(i0), Type::Intersection(i1)] = union.elements(&db)[..] else {
-            panic!("expected a union of two intersections");
-        };
-        assert_eq!(i0.pos_vec(&db), &[ta, t0]);
-        assert_eq!(i1.pos_vec(&db), &[ta, t1]);
-    }
-
-    #[test]
-    fn intersection_negation_distributes_over_union() {
-        let mut db = setup_db();
-        db.write_dedented(
-            "/src/module.py",
-            r#"
-            class A: ...
-            class B: ...
-            "#,
-        )
-        .unwrap();
-        let module = ruff_db::files::system_path_to_file(&db, "/src/module.py").unwrap();
-
-        let a = global_symbol(&db, module, "A")
-            .expect_type()
-            .to_instance(&db);
-        let b = global_symbol(&db, module, "B")
-            .expect_type()
-            .to_instance(&db);
-
-        // intersection: A & B
-        let intersection = IntersectionBuilder::new(&db)
-            .add_positive(a)
-            .add_positive(b)
-            .build()
-            .expect_intersection();
-        assert_eq!(intersection.pos_vec(&db), &[a, b]);
-        assert_eq!(intersection.neg_vec(&db), &[]);
-
-        // ~intersection => ~A | ~B
-        let negated_intersection = IntersectionBuilder::new(&db)
-            .add_negative(Type::Intersection(intersection))
-            .build()
-            .expect_union();
-
-        // should have as elements ~A and ~B
-        let not_a = a.negate(&db);
-        let not_b = b.negate(&db);
-        assert_eq!(negated_intersection.elements(&db), &[not_a, not_b]);
-    }
-
-    #[test]
-    fn mixed_intersection_negation_distributes_over_union() {
-        let mut db = setup_db();
-        db.write_dedented(
-            "/src/module.py",
-            r#"
-            class A: ...
-            class B: ...
-            "#,
-        )
-        .unwrap();
-        let module = ruff_db::files::system_path_to_file(&db, "/src/module.py").unwrap();
-
-        let a = global_symbol(&db, module, "A")
-            .expect_type()
-            .to_instance(&db);
-        let b = global_symbol(&db, module, "B")
-            .expect_type()
-            .to_instance(&db);
-        let int = KnownClass::Int.to_instance(&db);
-
-        // a_not_b: A & ~B
-        let a_not_b = IntersectionBuilder::new(&db)
-            .add_positive(a)
-            .add_negative(b)
-            .build()
-            .expect_intersection();
-        assert_eq!(a_not_b.pos_vec(&db), &[a]);
-        assert_eq!(a_not_b.neg_vec(&db), &[b]);
-
-        // let's build
-        //         int & ~(A & ~B)
-        //       = int & ~(A & ~B)
-        //       = int & (~A | B)
-        //       = (int & ~A) | (int & B)
-        let t = IntersectionBuilder::new(&db)
-            .add_positive(int)
-            .add_negative(Type::Intersection(a_not_b))
-            .build();
-        assert_eq!(t.display(&db).to_string(), "int & ~A | int & B");
-    }
-
-    #[test]
-    fn build_intersection_self_negation() {
-        let db = setup_db();
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(Type::none(&db))
-            .add_negative(Type::none(&db))
-            .build();
-
-        assert_eq!(ty, Type::Never);
-    }
-
-    #[test]
-    fn build_intersection_simplify_negative_never() {
-        let db = setup_db();
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(Type::none(&db))
-            .add_negative(Type::Never)
-            .build();
-
-        assert_eq!(ty, Type::none(&db));
-    }
-
-    #[test]
-    fn build_intersection_simplify_positive_never() {
-        let db = setup_db();
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(Type::none(&db))
-            .add_positive(Type::Never)
-            .build();
-
-        assert_eq!(ty, Type::Never);
-    }
-
-    #[test]
-    fn build_intersection_simplify_negative_none() {
-        let db = setup_db();
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(Type::none(&db))
-            .add_positive(Type::IntLiteral(1))
-            .build();
-        assert_eq!(ty, Type::IntLiteral(1));
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(Type::IntLiteral(1))
-            .add_negative(Type::none(&db))
-            .build();
-        assert_eq!(ty, Type::IntLiteral(1));
-    }
-
-    #[test]
-    fn build_negative_union_de_morgan() {
-        let db = setup_db();
-
-        let union = UnionBuilder::new(&db)
-            .add(Type::IntLiteral(1))
-            .add(Type::IntLiteral(2))
-            .build();
-        assert_eq!(union.display(&db).to_string(), "Literal[1, 2]");
-
-        let ty = IntersectionBuilder::new(&db).add_negative(union).build();
-
-        let expected = IntersectionBuilder::new(&db)
-            .add_negative(Type::IntLiteral(1))
-            .add_negative(Type::IntLiteral(2))
-            .build();
-
-        assert_eq!(ty.display(&db).to_string(), "~Literal[1] & ~Literal[2]");
-        assert_eq!(ty, expected);
-    }
-
-    #[test]
-    fn build_intersection_simplify_positive_type_and_positive_subtype() {
-        let db = setup_db();
-
-        let t = KnownClass::Str.to_instance(&db);
-        let s = Type::LiteralString;
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(t)
-            .add_positive(s)
-            .build();
-        assert_eq!(ty, s);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(s)
-            .add_positive(t)
-            .build();
-        assert_eq!(ty, s);
-
-        let literal = Type::string_literal(&db, "a");
-        let expected = IntersectionBuilder::new(&db)
-            .add_positive(s)
-            .add_negative(literal)
-            .build();
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(t)
-            .add_negative(literal)
-            .add_positive(s)
-            .build();
-        assert_eq!(ty, expected);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(s)
-            .add_negative(literal)
-            .add_positive(t)
-            .build();
-        assert_eq!(ty, expected);
-    }
-
-    #[test]
-    fn build_intersection_simplify_negative_type_and_negative_subtype() {
-        let db = setup_db();
-
-        let t = KnownClass::Str.to_instance(&db);
-        let s = Type::LiteralString;
-
-        let expected = IntersectionBuilder::new(&db).add_negative(t).build();
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(t)
-            .add_negative(s)
-            .build();
-        assert_eq!(ty, expected);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(s)
-            .add_negative(t)
-            .build();
-        assert_eq!(ty, expected);
-
-        let object = KnownClass::Object.to_instance(&db);
-        let expected = IntersectionBuilder::new(&db)
-            .add_negative(t)
-            .add_positive(object)
-            .build();
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(t)
-            .add_positive(object)
-            .add_negative(s)
-            .build();
-        assert_eq!(ty, expected);
-    }
-
-    #[test]
-    fn build_intersection_simplify_negative_type_and_multiple_negative_subtypes() {
-        let db = setup_db();
-
-        let s1 = Type::IntLiteral(1);
-        let s2 = Type::IntLiteral(2);
-        let t = KnownClass::Int.to_instance(&db);
-
-        let expected = IntersectionBuilder::new(&db).add_negative(t).build();
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(s1)
-            .add_negative(s2)
-            .add_negative(t)
-            .build();
-        assert_eq!(ty, expected);
-    }
-
-    #[test]
-    fn build_intersection_simplify_negative_type_and_positive_subtype() {
-        let db = setup_db();
-
-        let t = KnownClass::Str.to_instance(&db);
-        let s = Type::LiteralString;
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(t)
-            .add_positive(s)
-            .build();
-        assert_eq!(ty, Type::Never);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(s)
-            .add_negative(t)
-            .build();
-        assert_eq!(ty, Type::Never);
-
-        // This should also work in the presence of additional contributions:
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(KnownClass::Object.to_instance(&db))
-            .add_negative(t)
-            .add_positive(s)
-            .build();
-        assert_eq!(ty, Type::Never);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(s)
-            .add_negative(Type::string_literal(&db, "a"))
-            .add_negative(t)
-            .build();
-        assert_eq!(ty, Type::Never);
-    }
-
-    #[test]
-    fn build_intersection_simplify_disjoint_positive_types() {
-        let db = setup_db();
-
-        let t1 = Type::IntLiteral(1);
-        let t2 = Type::none(&db);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(t1)
-            .add_positive(t2)
-            .build();
-        assert_eq!(ty, Type::Never);
-
-        // If there are any negative contributions, they should
-        // be removed too.
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(KnownClass::Str.to_instance(&db))
-            .add_negative(Type::LiteralString)
-            .add_positive(t2)
-            .build();
-        assert_eq!(ty, Type::Never);
-    }
-
-    #[test]
-    fn build_intersection_simplify_disjoint_positive_and_negative_types() {
-        let db = setup_db();
-
-        let t_p = KnownClass::Int.to_instance(&db);
-        let t_n = Type::string_literal(&db, "t_n");
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(t_p)
-            .add_negative(t_n)
-            .build();
-        assert_eq!(ty, t_p);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(t_n)
-            .add_positive(t_p)
-            .build();
-        assert_eq!(ty, t_p);
-
-        let int_literal = Type::IntLiteral(1);
-        let expected = IntersectionBuilder::new(&db)
-            .add_positive(t_p)
-            .add_negative(int_literal)
-            .build();
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_positive(t_p)
-            .add_negative(int_literal)
-            .add_negative(t_n)
-            .build();
-        assert_eq!(ty, expected);
-
-        let ty = IntersectionBuilder::new(&db)
-            .add_negative(t_n)
-            .add_negative(int_literal)
-            .add_positive(t_p)
-            .build();
-        assert_eq!(ty, expected);
+        let intersection = IntersectionBuilder::new(&db).build();
+        assert_eq!(intersection, KnownClass::Object.to_instance(&db));
     }
 
     #[test_case(Type::BooleanLiteral(true))]
@@ -1048,85 +492,4 @@ mod tests {
             .build();
         assert_eq!(ty, Type::BooleanLiteral(!bool_value));
     }
-
-    #[test_case(Type::Any)]
-    #[test_case(Type::Unknown)]
-    #[test_case(todo_type!())]
-    fn build_intersection_t_and_negative_t_does_not_simplify(ty: Type) {
-        let db = setup_db();
-
-        let result = IntersectionBuilder::new(&db)
-            .add_positive(ty)
-            .add_negative(ty)
-            .build();
-        assert_eq!(result, ty);
-
-        let result = IntersectionBuilder::new(&db)
-            .add_negative(ty)
-            .add_positive(ty)
-            .build();
-        assert_eq!(result, ty);
-    }
-
-    #[test]
-    fn build_intersection_of_two_unions_simplify() {
-        let mut db = setup_db();
-        db.write_dedented(
-            "/src/module.py",
-            "
-            class A: ...
-            class B: ...
-            a = A()
-            b = B()
-        ",
-        )
-        .unwrap();
-
-        let file = system_path_to_file(&db, "src/module.py").expect("file to exist");
-
-        let a = global_symbol(&db, file, "a").expect_type();
-        let b = global_symbol(&db, file, "b").expect_type();
-        let union = UnionBuilder::new(&db).add(a).add(b).build();
-        assert_eq!(union.display(&db).to_string(), "A | B");
-        let reversed_union = UnionBuilder::new(&db).add(b).add(a).build();
-        assert_eq!(reversed_union.display(&db).to_string(), "B | A");
-        let intersection = IntersectionBuilder::new(&db)
-            .add_positive(union)
-            .add_positive(reversed_union)
-            .build();
-        assert_eq!(intersection.display(&db).to_string(), "B | A");
-    }
-
-    #[test]
-    fn build_union_of_two_intersections_simplify() {
-        let mut db = setup_db();
-        db.write_dedented(
-            "/src/module.py",
-            "
-            class A: ...
-            class B: ...
-            a = A()
-            b = B()
-        ",
-        )
-        .unwrap();
-
-        let file = system_path_to_file(&db, "src/module.py").expect("file to exist");
-
-        let a = global_symbol(&db, file, "a").expect_type();
-        let b = global_symbol(&db, file, "b").expect_type();
-        let intersection = IntersectionBuilder::new(&db)
-            .add_positive(a)
-            .add_positive(b)
-            .build();
-        let reversed_intersection = IntersectionBuilder::new(&db)
-            .add_positive(b)
-            .add_positive(a)
-            .build();
-        let union = UnionBuilder::new(&db)
-            .add(intersection)
-            .add(reversed_intersection)
-            .build();
-        assert_eq!(union.display(&db).to_string(), "A & B");
-    }
 }

crates/red_knot_python_semantic/src/types/call.rs

@@ -1,17 +1,32 @@
 use super::context::InferContext;
-use super::diagnostic::CALL_NON_CALLABLE;
-use super::{Severity, Type, TypeArrayDisplay, UnionBuilder};
+use super::diagnostic::{CALL_NON_CALLABLE, TYPE_ASSERTION_FAILURE};
+use super::{Severity, Signature, Type, TypeArrayDisplay, UnionBuilder};
+use crate::types::diagnostic::STATIC_ASSERT_ERROR;
 use crate::Db;
 use ruff_db::diagnostic::DiagnosticId;
 use ruff_python_ast as ast;
 
+mod arguments;
+mod bind;
+
+pub(super) use arguments::{Argument, CallArguments};
+pub(super) use bind::{bind_call, CallBinding};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) enum StaticAssertionErrorKind<'db> {
+    ArgumentIsFalse,
+    ArgumentIsFalsy(Type<'db>),
+    ArgumentTruthinessIsAmbiguous(Type<'db>),
+    CustomError(&'db str),
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub(super) enum CallOutcome<'db> {
     Callable {
-        return_ty: Type<'db>,
+        binding: CallBinding<'db>,
     },
     RevealType {
-        return_ty: Type<'db>,
+        binding: CallBinding<'db>,
         revealed_ty: Type<'db>,
     },
     NotCallable {
@@ -25,12 +40,20 @@ pub(super) enum CallOutcome<'db> {
         called_ty: Type<'db>,
         call_outcome: Box<CallOutcome<'db>>,
     },
+    StaticAssertionError {
+        binding: CallBinding<'db>,
+        error_kind: StaticAssertionErrorKind<'db>,
+    },
+    AssertType {
+        binding: CallBinding<'db>,
+        asserted_ty: Type<'db>,
+    },
 }
 
 impl<'db> CallOutcome<'db> {
     /// Create a new `CallOutcome::Callable` with given return type.
-    pub(super) fn callable(return_ty: Type<'db>) -> CallOutcome<'db> {
-        CallOutcome::Callable { return_ty }
+    pub(super) fn callable(binding: CallBinding<'db>) -> CallOutcome<'db> {
+        CallOutcome::Callable { binding }
     }
 
     /// Create a new `CallOutcome::NotCallable` with given not-callable type.
@@ -39,9 +62,9 @@ impl<'db> CallOutcome<'db> {
     }
 
     /// Create a new `CallOutcome::RevealType` with given revealed and return types.
-    pub(super) fn revealed(return_ty: Type<'db>, revealed_ty: Type<'db>) -> CallOutcome<'db> {
+    pub(super) fn revealed(binding: CallBinding<'db>, revealed_ty: Type<'db>) -> CallOutcome<'db> {
         CallOutcome::RevealType {
-            return_ty,
+            binding,
             revealed_ty,
         }
     }
@@ -57,14 +80,22 @@ impl<'db> CallOutcome<'db> {
         }
     }
 
+    /// Create a new `CallOutcome::AssertType` with given revealed and return types.
+    pub(super) fn asserted(binding: CallBinding<'db>, asserted_ty: Type<'db>) -> CallOutcome<'db> {
+        CallOutcome::AssertType {
+            binding,
+            asserted_ty,
+        }
+    }
+
     /// Get the return type of the call, or `None` if not callable.
     pub(super) fn return_ty(&self, db: &'db dyn Db) -> Option<Type<'db>> {
         match self {
-            Self::Callable { return_ty } => Some(*return_ty),
+            Self::Callable { binding } => Some(binding.return_ty()),
             Self::RevealType {
-                return_ty,
+                binding,
                 revealed_ty: _,
-            } => Some(*return_ty),
+            } => Some(binding.return_ty()),
             Self::NotCallable { not_callable_ty: _ } => None,
             Self::Union {
                 outcomes,
@@ -78,11 +109,16 @@ impl<'db> CallOutcome<'db> {
                     match (acc, ty) {
                         (None, None) => None,
                         (None, Some(ty)) => Some(UnionBuilder::new(db).add(ty)),
-                        (Some(builder), ty) => Some(builder.add(ty.unwrap_or(Type::Unknown))),
+                        (Some(builder), ty) => Some(builder.add(ty.unwrap_or(Type::unknown()))),
                     }
                 })
                 .map(UnionBuilder::build),
             Self::PossiblyUnboundDunderCall { call_outcome, .. } => call_outcome.return_ty(db),
+            Self::StaticAssertionError { .. } => Some(Type::none(db)),
+            Self::AssertType {
+                binding,
+                asserted_ty: _,
+            } => Some(binding.return_ty()),
         }
     }
 
@@ -163,23 +199,30 @@ impl<'db> CallOutcome<'db> {
         context: &InferContext<'db>,
         node: ast::AnyNodeRef,
     ) -> Result<Type<'db>, NotCallableError<'db>> {
+        // TODO should this method emit diagnostics directly, or just return results that allow the
+        // caller to decide about emitting diagnostics? Currently it emits binding diagnostics, but
+        // only non-callable diagnostics in the union case, which is inconsistent.
         match self {
-            Self::Callable { return_ty } => Ok(*return_ty),
+            Self::Callable { binding } => {
+                binding.report_diagnostics(context, node);
+                Ok(binding.return_ty())
+            }
             Self::RevealType {
-                return_ty,
+                binding,
                 revealed_ty,
             } => {
+                binding.report_diagnostics(context, node);
                 context.report_diagnostic(
                     node,
                     DiagnosticId::RevealedType,
                     Severity::Info,
                     format_args!("Revealed type is `{}`", revealed_ty.display(context.db())),
                 );
-                Ok(*return_ty)
+                Ok(binding.return_ty())
             }
             Self::NotCallable { not_callable_ty } => Err(NotCallableError::Type {
                 not_callable_ty: *not_callable_ty,
-                return_ty: Type::Unknown,
+                return_ty: Type::unknown(),
             }),
             Self::PossiblyUnboundDunderCall {
                 called_ty,
@@ -188,7 +231,7 @@ impl<'db> CallOutcome<'db> {
                 callable_ty: *called_ty,
                 return_ty: call_outcome
                     .return_ty(context.db())
-                    .unwrap_or(Type::Unknown),
+                    .unwrap_or(Type::unknown()),
             }),
             Self::Union {
                 outcomes,
@@ -201,14 +244,14 @@ impl<'db> CallOutcome<'db> {
                     let return_ty = match outcome {
                         Self::NotCallable { not_callable_ty } => {
                             not_callable.push(*not_callable_ty);
-                            Type::Unknown
+                            Type::unknown()
                         }
                         Self::RevealType {
-                            return_ty,
+                            binding,
                             revealed_ty: _,
                         } => {
                             if revealed {
-                                *return_ty
+                                binding.return_ty()
                             } else {
                                 revealed = true;
                                 outcome.unwrap_with_diagnostic(context, node)
@@ -237,6 +280,73 @@ impl<'db> CallOutcome<'db> {
                     }),
                 }
             }
+            CallOutcome::StaticAssertionError {
+                binding,
+                error_kind,
+            } => {
+                binding.report_diagnostics(context, node);
+
+                match error_kind {
+                    StaticAssertionErrorKind::ArgumentIsFalse => {
+                        context.report_lint(
+                            &STATIC_ASSERT_ERROR,
+                            node,
+                            format_args!("Static assertion error: argument evaluates to `False`"),
+                        );
+                    }
+                    StaticAssertionErrorKind::ArgumentIsFalsy(parameter_ty) => {
+                        context.report_lint(
+                            &STATIC_ASSERT_ERROR,
+                            node,
+                            format_args!(
+                                "Static assertion error: argument of type `{parameter_ty}` is statically known to be falsy",
+                                parameter_ty=parameter_ty.display(context.db())
+                            ),
+                        );
+                    }
+                    StaticAssertionErrorKind::ArgumentTruthinessIsAmbiguous(parameter_ty) => {
+                        context.report_lint(
+                            &STATIC_ASSERT_ERROR,
+                            node,
+                            format_args!(
+                                "Static assertion error: argument of type `{parameter_ty}` has an ambiguous static truthiness",
+                                parameter_ty=parameter_ty.display(context.db())
+                            ),
+                        );
+                    }
+                    StaticAssertionErrorKind::CustomError(message) => {
+                        context.report_lint(
+                            &STATIC_ASSERT_ERROR,
+                            node,
+                            format_args!("Static assertion error: {message}"),
+                        );
+                    }
+                }
+
+                Ok(Type::unknown())
+            }
+            CallOutcome::AssertType {
+                binding,
+                asserted_ty,
+            } => {
+                let [actual_ty, _asserted] = binding.parameter_tys() else {
+                    return Ok(binding.return_ty());
+                };
+
+                if !actual_ty.is_gradual_equivalent_to(context.db(), *asserted_ty) {
+                    context.report_lint(
+                        &TYPE_ASSERTION_FAILURE,
+                        node,
+                        format_args!(
+                            "Actual type `{}` is not the same as asserted type `{}`",
+                            actual_ty.display(context.db()),
+                            asserted_ty.display(context.db()),
+                        ),
+                    );
+                }
+
+                Ok(binding.return_ty())
+            }
         }
     }
 }

crates/red_knot_python_semantic/src/types/call/arguments.rs

@@ -0,0 +1,73 @@
+use super::Type;
+
+/// Typed arguments for a single call, in source order.
+#[derive(Clone, Debug, Default)]
+pub(crate) struct CallArguments<'a, 'db>(Vec<Argument<'a, 'db>>);
+
+impl<'a, 'db> CallArguments<'a, 'db> {
+    /// Create a [`CallArguments`] from an iterator over non-variadic positional argument types.
+    pub(crate) fn positional(positional_tys: impl IntoIterator<Item = Type<'db>>) -> Self {
+        positional_tys
+            .into_iter()
+            .map(Argument::Positional)
+            .collect()
+    }
+
+    /// Prepend an extra positional argument.
+    pub(crate) fn with_self(&self, self_ty: Type<'db>) -> Self {
+        let mut arguments = Vec::with_capacity(self.0.len() + 1);
+        arguments.push(Argument::Synthetic(self_ty));
+        arguments.extend_from_slice(&self.0);
+        Self(arguments)
+    }
+
+    pub(crate) fn iter(&self) -> impl Iterator<Item = &Argument<'a, 'db>> {
+        self.0.iter()
+    }
+
+    // TODO this should be eliminated in favor of [`bind_call`]
+    pub(crate) fn first_argument(&self) -> Option<Type<'db>> {
+        self.0.first().map(Argument::ty)
+    }
+}
+
+impl<'db, 'a, 'b> IntoIterator for &'b CallArguments<'a, 'db> {
+    type Item = &'b Argument<'a, 'db>;
+    type IntoIter = std::slice::Iter<'b, Argument<'a, 'db>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.iter()
+    }
+}
+
+impl<'a, 'db> FromIterator<Argument<'a, 'db>> for CallArguments<'a, 'db> {
+    fn from_iter<T: IntoIterator<Item = Argument<'a, 'db>>>(iter: T) -> Self {
+        Self(iter.into_iter().collect())
+    }
+}
+
+#[derive(Clone, Debug)]
+pub(crate) enum Argument<'a, 'db> {
+    /// The synthetic `self` or `cls` argument, which doesn't appear explicitly at the call site.
+    Synthetic(Type<'db>),
+    /// A positional argument.
+    Positional(Type<'db>),
+    /// A starred positional argument (e.g. `*args`).
+    Variadic(Type<'db>),
+    /// A keyword argument (e.g. `a=1`).
+    Keyword { name: &'a str, ty: Type<'db> },
+    /// The double-starred keywords argument (e.g. `**kwargs`).
+    Keywords(Type<'db>),
+}
+
+impl<'db> Argument<'_, 'db> {
+    fn ty(&self) -> Type<'db> {
+        match self {
+            Self::Synthetic(ty) => *ty,
+            Self::Positional(ty) => *ty,
+            Self::Variadic(ty) => *ty,
+            Self::Keyword { name: _, ty } => *ty,
+            Self::Keywords(ty) => *ty,
+        }
+    }
+}

crates/red_knot_python_semantic/src/types/call/bind.rs

@@ -0,0 +1,411 @@
+use super::{Argument, CallArguments, InferContext, Signature, Type};
+use crate::db::Db;
+use crate::types::diagnostic::{
+    INVALID_ARGUMENT_TYPE, MISSING_ARGUMENT, PARAMETER_ALREADY_ASSIGNED,
+    TOO_MANY_POSITIONAL_ARGUMENTS, UNKNOWN_ARGUMENT,
+};
+use crate::types::signatures::Parameter;
+use crate::types::UnionType;
+use ruff_python_ast as ast;
+
+/// Bind a [`CallArguments`] against a callable [`Signature`].
+///
+/// The returned [`CallBinding`] provides the return type of the call, the bound types for all
+/// parameters, and any errors resulting from binding the call.
+pub(crate) fn bind_call<'db>(
+    db: &'db dyn Db,
+    arguments: &CallArguments<'_, 'db>,
+    signature: &Signature<'db>,
+    callable_ty: Option<Type<'db>>,
+) -> CallBinding<'db> {
+    let parameters = signature.parameters();
+    // The type assigned to each parameter at this call site.
+    let mut parameter_tys = vec![None; parameters.len()];
+    let mut errors = vec![];
+    let mut next_positional = 0;
+    let mut first_excess_positional = None;
+    let mut num_synthetic_args = 0;
+    let get_argument_index = |argument_index: usize, num_synthetic_args: usize| {
+        if argument_index >= num_synthetic_args {
+            // Adjust the argument index to skip synthetic args, which don't appear at the call
+            // site and thus won't be in the Call node arguments list.
+            Some(argument_index - num_synthetic_args)
+        } else {
+            // we are erroring on a synthetic argument, we'll just emit the diagnostic on the
+            // entire Call node, since there's no argument node for this argument at the call site
+            None
+        }
+    };
+    for (argument_index, argument) in arguments.iter().enumerate() {
+        let (index, parameter, argument_ty, positional) = match argument {
+            Argument::Positional(ty) | Argument::Synthetic(ty) => {
+                if matches!(argument, Argument::Synthetic(_)) {
+                    num_synthetic_args += 1;
+                }
+                let Some((index, parameter)) = parameters
+                    .get_positional(next_positional)
+                    .map(|param| (next_positional, param))
+                    .or_else(|| parameters.variadic())
+                else {
+                    first_excess_positional.get_or_insert(argument_index);
+                    next_positional += 1;
+                    continue;
+                };
+                next_positional += 1;
+                (index, parameter, ty, !parameter.is_variadic())
+            }
+            Argument::Keyword { name, ty } => {
+                let Some((index, parameter)) = parameters
+                    .keyword_by_name(name)
+                    .or_else(|| parameters.keyword_variadic())
+                else {
+                    errors.push(CallBindingError::UnknownArgument {
+                        argument_name: ast::name::Name::new(name),
+                        argument_index: get_argument_index(argument_index, num_synthetic_args),
+                    });
+                    continue;
+                };
+                (index, parameter, ty, false)
+            }
+
+            Argument::Variadic(_) | Argument::Keywords(_) => {
+                // TODO
+                continue;
+            }
+        };
+        if let Some(expected_ty) = parameter.annotated_ty() {
+            if !argument_ty.is_assignable_to(db, expected_ty) {
+                errors.push(CallBindingError::InvalidArgumentType {
+                    parameter: ParameterContext::new(parameter, index, positional),
+                    argument_index: get_argument_index(argument_index, num_synthetic_args),
+                    expected_ty,
+                    provided_ty: *argument_ty,
+                });
+            }
+        }
+        if let Some(existing) = parameter_tys[index].replace(*argument_ty) {
+            if parameter.is_variadic() {
+                let union = UnionType::from_elements(db, [existing, *argument_ty]);
+                parameter_tys[index].replace(union);
+            } else {
+                errors.push(CallBindingError::ParameterAlreadyAssigned {
+                    argument_index: get_argument_index(argument_index, num_synthetic_args),
+                    parameter: ParameterContext::new(parameter, index, positional),
+                });
+            }
+        }
+    }
+    if let Some(first_excess_argument_index) = first_excess_positional {
+        errors.push(CallBindingError::TooManyPositionalArguments {
+            first_excess_argument_index: get_argument_index(
+                first_excess_argument_index,
+                num_synthetic_args,
+            ),
+            expected_positional_count: parameters.positional().count(),
+            provided_positional_count: next_positional,
+        });
+    }
+    let mut missing = vec![];
+    for (index, bound_ty) in parameter_tys.iter().enumerate() {
+        if bound_ty.is_none() {
+            let param = &parameters[index];
+            if param.is_variadic() || param.is_keyword_variadic() || param.default_ty().is_some() {
+                // variadic/keywords and defaulted arguments are not required
+                continue;
+            }
+            missing.push(ParameterContext::new(param, index, false));
+        }
+    }
+
+    if !missing.is_empty() {
+        errors.push(CallBindingError::MissingArguments {
+            parameters: ParameterContexts(missing),
+        });
+    }
+
+    CallBinding {
+        callable_ty,
+        return_ty: signature.return_ty.unwrap_or(Type::unknown()),
+        parameter_tys: parameter_tys
+            .into_iter()
+            .map(|opt_ty| opt_ty.unwrap_or(Type::unknown()))
+            .collect(),
+        errors,
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) struct CallBinding<'db> {
+    /// Type of the callable object (function, class...)
+    callable_ty: Option<Type<'db>>,
+
+    /// Return type of the call.
+    return_ty: Type<'db>,
+
+    /// Bound types for parameters, in parameter source order.
+    parameter_tys: Box<[Type<'db>]>,
+
+    /// Call binding errors, if any.
+    errors: Vec<CallBindingError<'db>>,
+}
+
+impl<'db> CallBinding<'db> {
+    // TODO remove this constructor and construct always from `bind_call`
+    pub(crate) fn from_return_ty(return_ty: Type<'db>) -> Self {
+        Self {
+            callable_ty: None,
+            return_ty,
+            parameter_tys: Box::default(),
+            errors: vec![],
+        }
+    }
+
+    pub(crate) fn set_return_ty(&mut self, return_ty: Type<'db>) {
+        self.return_ty = return_ty;
+    }
+
+    pub(crate) fn return_ty(&self) -> Type<'db> {
+        self.return_ty
+    }
+
+    pub(crate) fn parameter_tys(&self) -> &[Type<'db>] {
+        &self.parameter_tys
+    }
+
+    pub(crate) fn one_parameter_ty(&self) -> Option<Type<'db>> {
+        match self.parameter_tys() {
+            [ty] => Some(*ty),
+            _ => None,
+        }
+    }
+
+    pub(crate) fn two_parameter_tys(&self) -> Option<(Type<'db>, Type<'db>)> {
+        match self.parameter_tys() {
+            [first, second] => Some((*first, *second)),
+            _ => None,
+        }
+    }
+
+    fn callable_name(&self, db: &'db dyn Db) -> Option<&str> {
+        match self.callable_ty {
+            Some(Type::FunctionLiteral(function)) => Some(function.name(db)),
+            Some(Type::ClassLiteral(class_type)) => Some(class_type.class.name(db)),
+            _ => None,
+        }
+    }
+
+    pub(super) fn report_diagnostics(&self, context: &InferContext<'db>, node: ast::AnyNodeRef) {
+        let callable_name = self.callable_name(context.db());
+        for error in &self.errors {
+            error.report_diagnostic(context, node, callable_name);
+        }
+    }
+}
+
+/// Information needed to emit a diagnostic regarding a parameter.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) struct ParameterContext {
+    name: Option<ast::name::Name>,
+    index: usize,
+
+    /// Was the argument for this parameter passed positionally, and matched to a non-variadic
+    /// positional parameter? (If so, we will provide the index in the diagnostic, not just the
+    /// name.)
+    positional: bool,
+}
+
+impl ParameterContext {
+    fn new(parameter: &Parameter, index: usize, positional: bool) -> Self {
+        Self {
+            name: parameter.display_name(),
+            index,
+            positional,
+        }
+    }
+}
+
+impl std::fmt::Display for ParameterContext {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if let Some(name) = &self.name {
+            if self.positional {
+                write!(f, "{} (`{name}`)", self.index + 1)
+            } else {
+                write!(f, "`{name}`")
+            }
+        } else {
+            write!(f, "{}", self.index + 1)
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) struct ParameterContexts(Vec<ParameterContext>);
+
+impl std::fmt::Display for ParameterContexts {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut iter = self.0.iter();
+        if let Some(first) = iter.next() {
+            write!(f, "{first}")?;
+            for param in iter {
+                f.write_str(", ")?;
+                write!(f, "{param}")?;
+            }
+        }
+        Ok(())
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub(crate) enum CallBindingError<'db> {
+    /// The type of an argument is not assignable to the annotated type of its corresponding
+    /// parameter.
+    InvalidArgumentType {
+        parameter: ParameterContext,
+        argument_index: Option<usize>,
+        expected_ty: Type<'db>,
+        provided_ty: Type<'db>,
+    },
+    /// One or more required parameters (that is, with no default) is not supplied by any argument.
+    MissingArguments { parameters: ParameterContexts },
+    /// A call argument can't be matched to any parameter.
+    UnknownArgument {
+        argument_name: ast::name::Name,
+        argument_index: Option<usize>,
+    },
+    /// More positional arguments are provided in the call than can be handled by the signature.
+    TooManyPositionalArguments {
+        first_excess_argument_index: Option<usize>,
+        expected_positional_count: usize,
+        provided_positional_count: usize,
+    },
+    /// Multiple arguments were provided for a single parameter.
+    ParameterAlreadyAssigned {
+        argument_index: Option<usize>,
+        parameter: ParameterContext,
+    },
+}
+
+impl<'db> CallBindingError<'db> {
+    pub(super) fn report_diagnostic(
+        &self,
+        context: &InferContext<'db>,
+        node: ast::AnyNodeRef,
+        callable_name: Option<&str>,
+    ) {
+        match self {
+            Self::InvalidArgumentType {
+                parameter,
+                argument_index,
+                expected_ty,
+                provided_ty,
+            } => {
+                let provided_ty_display = provided_ty.display(context.db());
+                let expected_ty_display = expected_ty.display(context.db());
+                context.report_lint(
+                    &INVALID_ARGUMENT_TYPE,
+                    Self::get_node(node, *argument_index),
+                    format_args!(
+                        "Object of type `{provided_ty_display}` cannot be assigned to \
+                        parameter {parameter}{}; expected type `{expected_ty_display}`",
+                        if let Some(callable_name) = callable_name {
+                            format!(" of function `{callable_name}`")
+                        } else {
+                            String::new()
+                        }
+                    ),
+                );
+            }
+
+            Self::TooManyPositionalArguments {
+                first_excess_argument_index,
+                expected_positional_count,
+                provided_positional_count,
+            } => {
+                context.report_lint(
+                    &TOO_MANY_POSITIONAL_ARGUMENTS,
+                    Self::get_node(node, *first_excess_argument_index),
+                    format_args!(
+                        "Too many positional arguments{}: expected \
+                        {expected_positional_count}, got {provided_positional_count}",
+                        if let Some(callable_name) = callable_name {
+                            format!(" to function `{callable_name}`")
+                        } else {
+                            String::new()
+                        }
+                    ),
+                );
+            }
+
+            Self::MissingArguments { parameters } => {
+                let s = if parameters.0.len() == 1 { "" } else { "s" };
+                context.report_lint(
+                    &MISSING_ARGUMENT,
+                    node,
+                    format_args!(
+                        "No argument{s} provided for required parameter{s} {parameters}{}",
+                        if let Some(callable_name) = callable_name {
+                            format!(" of function `{callable_name}`")
+                        } else {
+                            String::new()
+                        }
+                    ),
+                );
+            }
+
+            Self::UnknownArgument {
+                argument_name,
+                argument_index,
+            } => {
+                context.report_lint(
+                    &UNKNOWN_ARGUMENT,
+                    Self::get_node(node, *argument_index),
+                    format_args!(
+                        "Argument `{argument_name}` does not match any known parameter{}",
+                        if let Some(callable_name) = callable_name {
+                            format!(" of function `{callable_name}`")
+                        } else {
+                            String::new()
+                        }
+                    ),
+                );
+            }
+
+            Self::ParameterAlreadyAssigned {
+                argument_index,
+                parameter,
+            } => {
+                context.report_lint(
+                    &PARAMETER_ALREADY_ASSIGNED,
+                    Self::get_node(node, *argument_index),
+                    format_args!(
+                        "Multiple values provided for parameter {parameter}{}",
+                        if let Some(callable_name) = callable_name {
+                            format!(" of function `{callable_name}`")
+                        } else {
+                            String::new()
+                        }
+                    ),
+                );
+            }
+        }
+    }
+
+    fn get_node(node: ast::AnyNodeRef, argument_index: Option<usize>) -> ast::AnyNodeRef {
+        // If we have a Call node and an argument index, report the diagnostic on the correct
+        // argument node; otherwise, report it on the entire provided node.
+        match (node, argument_index) {
+            (ast::AnyNodeRef::ExprCall(call_node), Some(argument_index)) => {
+                match call_node
+                    .arguments
+                    .arguments_source_order()
+                    .nth(argument_index)
+                    .expect("argument index should not be out of range")
+                {
+                    ast::ArgOrKeyword::Arg(expr) => expr.into(),
+                    ast::ArgOrKeyword::Keyword(keyword) => keyword.into(),
+                }
+            }
+            _ => node,
+        }
+    }
+}

crates/red_knot_python_semantic/src/types/class_base.rs

@@ -1,5 +1,5 @@
 use crate::types::{
-    todo_type, Class, ClassLiteralType, KnownClass, KnownInstanceType, TodoType, Type,
+    todo_type, Class, ClassLiteralType, DynamicType, KnownClass, KnownInstanceType, Type,
 };
 use crate::Db;
 use itertools::Either;
@@ -8,16 +8,29 @@ use itertools::Either;
 ///
 /// This is much more limited than the [`Type`] enum:
 /// all types that would be invalid to have as a class base are
-/// transformed into [`ClassBase::Unknown`]
+/// transformed into [`ClassBase::unknown`]
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, salsa::Update)]
 pub enum ClassBase<'db> {
-    Any,
-    Unknown,
-    Todo(TodoType),
+    Dynamic(DynamicType),
     Class(Class<'db>),
 }
 
 impl<'db> ClassBase<'db> {
+    pub const fn any() -> Self {
+        Self::Dynamic(DynamicType::Any)
+    }
+
+    pub const fn unknown() -> Self {
+        Self::Dynamic(DynamicType::Unknown)
+    }
+
+    pub const fn is_dynamic(self) -> bool {
+        match self {
+            ClassBase::Dynamic(_) => true,
+            ClassBase::Class(_) => false,
+        }
+    }
+
     pub fn display(self, db: &'db dyn Db) -> impl std::fmt::Display + 'db {
         struct Display<'db> {
             base: ClassBase<'db>,
@@ -27,9 +40,7 @@ impl<'db> ClassBase<'db> {
         impl std::fmt::Display for Display<'_> {
             fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
                 match self.base {
-                    ClassBase::Any => f.write_str("Any"),
-                    ClassBase::Todo(todo) => todo.fmt(f),
-                    ClassBase::Unknown => f.write_str("Unknown"),
+                    ClassBase::Dynamic(dynamic) => dynamic.fmt(f),
                     ClassBase::Class(class) => write!(f, "<class '{}'>", class.name(self.db)),
                 }
             }
@@ -43,7 +54,7 @@ impl<'db> ClassBase<'db> {
         KnownClass::Object
             .to_class_literal(db)
             .into_class_literal()
-            .map_or(Self::Unknown, |ClassLiteralType { class }| {
+            .map_or(Self::unknown(), |ClassLiteralType { class }| {
                 Self::Class(class)
             })
     }
@@ -53,9 +64,7 @@ impl<'db> ClassBase<'db> {
     /// Return `None` if `ty` is not an acceptable type for a class base.
     pub(super) fn try_from_ty(db: &'db dyn Db, ty: Type<'db>) -> Option<Self> {
         match ty {
-            Type::Any => Some(Self::Any),
-            Type::Unknown => Some(Self::Unknown),
-            Type::Todo(todo) => Some(Self::Todo(todo)),
+            Type::Dynamic(dynamic) => Some(Self::Dynamic(dynamic)),
             Type::ClassLiteral(ClassLiteralType { class }) => Some(Self::Class(class)),
             Type::Union(_) => None, // TODO -- forces consideration of multiple possible MROs?
             Type::Intersection(_) => None, // TODO -- probably incorrect?
@@ -93,8 +102,12 @@ impl<'db> ClassBase<'db> {
                 | KnownInstanceType::Required
                 | KnownInstanceType::TypeAlias
                 | KnownInstanceType::ReadOnly
-                | KnownInstanceType::Optional => None,
-                KnownInstanceType::Any => Some(Self::Any),
+                | KnownInstanceType::Optional
+                | KnownInstanceType::Not
+                | KnownInstanceType::Intersection
+                | KnownInstanceType::TypeOf => None,
+                KnownInstanceType::Unknown => Some(Self::unknown()),
+                KnownInstanceType::Any => Some(Self::any()),
                 // TODO: Classes inheriting from `typing.Type` et al. also have `Generic` in their MRO
                 KnownInstanceType::Dict => {
                     Self::try_from_ty(db, KnownClass::Dict.to_class_literal(db))
@@ -139,7 +152,7 @@ impl<'db> ClassBase<'db> {
     pub(super) fn into_class(self) -> Option<Class<'db>> {
         match self {
             Self::Class(class) => Some(class),
-            _ => None,
+            Self::Dynamic(_) => None,
         }
     }
 
@@ -149,13 +162,7 @@ impl<'db> ClassBase<'db> {
         db: &'db dyn Db,
     ) -> Either<impl Iterator<Item = ClassBase<'db>>, impl Iterator<Item = ClassBase<'db>>> {
         match self {
-            ClassBase::Any => Either::Left([ClassBase::Any, ClassBase::object(db)].into_iter()),
-            ClassBase::Unknown => {
-                Either::Left([ClassBase::Unknown, ClassBase::object(db)].into_iter())
-            }
-            ClassBase::Todo(todo) => {
-                Either::Left([ClassBase::Todo(todo), ClassBase::object(db)].into_iter())
-            }
+            ClassBase::Dynamic(_) => Either::Left([self, ClassBase::object(db)].into_iter()),
             ClassBase::Class(class) => Either::Right(class.iter_mro(db)),
         }
     }
@@ -170,9 +177,7 @@ impl<'db> From<Class<'db>> for ClassBase<'db> {
 impl<'db> From<ClassBase<'db>> for Type<'db> {
     fn from(value: ClassBase<'db>) -> Self {
         match value {
-            ClassBase::Any => Type::Any,
-            ClassBase::Todo(todo) => Type::Todo(todo),
-            ClassBase::Unknown => Type::Unknown,
+            ClassBase::Dynamic(dynamic) => Type::Dynamic(dynamic),
             ClassBase::Class(class) => Type::class_literal(class),
         }
     }

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 +126,47 @@ 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,
+        }
+    }
+
+    /// Are we currently inferring types in a stub file?
+    pub(crate) fn in_stub(&self) -> bool {
+        self.file.is_stub(self.db().upcast())
+    }
+
     #[must_use]
     pub(crate) fn finish(mut self) -> TypeCheckDiagnostics {
         self.bomb.defuse();
@@ -126,6 +186,17 @@ 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);
@@ -26,28 +27,38 @@ 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_ARGUMENT_TYPE);
     registry.register_lint(&INVALID_ASSIGNMENT);
     registry.register_lint(&INVALID_BASE);
     registry.register_lint(&INVALID_CONTEXT_MANAGER);
     registry.register_lint(&INVALID_DECLARATION);
     registry.register_lint(&INVALID_EXCEPTION_CAUGHT);
+    registry.register_lint(&INVALID_METACLASS);
     registry.register_lint(&INVALID_PARAMETER_DEFAULT);
     registry.register_lint(&INVALID_RAISE);
     registry.register_lint(&INVALID_TYPE_FORM);
     registry.register_lint(&INVALID_TYPE_VARIABLE_CONSTRAINTS);
+    registry.register_lint(&MISSING_ARGUMENT);
     registry.register_lint(&NON_SUBSCRIPTABLE);
     registry.register_lint(&NOT_ITERABLE);
+    registry.register_lint(&PARAMETER_ALREADY_ASSIGNED);
     registry.register_lint(&POSSIBLY_UNBOUND_ATTRIBUTE);
     registry.register_lint(&POSSIBLY_UNBOUND_IMPORT);
     registry.register_lint(&POSSIBLY_UNRESOLVED_REFERENCE);
+    registry.register_lint(&SUBCLASS_OF_FINAL_CLASS);
+    registry.register_lint(&TYPE_ASSERTION_FAILURE);
+    registry.register_lint(&TOO_MANY_POSITIONAL_ARGUMENTS);
     registry.register_lint(&UNDEFINED_REVEAL);
+    registry.register_lint(&UNKNOWN_ARGUMENT);
     registry.register_lint(&UNRESOLVED_ATTRIBUTE);
     registry.register_lint(&UNRESOLVED_IMPORT);
     registry.register_lint(&UNRESOLVED_REFERENCE);
     registry.register_lint(&UNSUPPORTED_OPERATOR);
     registry.register_lint(&ZERO_STEPSIZE_IN_SLICE);
+    registry.register_lint(&STATIC_ASSERT_ERROR);
 
     // String annotations
     registry.register_lint(&BYTE_STRING_TYPE_ANNOTATION);
@@ -146,6 +157,64 @@ 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 = {
@@ -165,6 +234,27 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Detects call arguments whose type is not assignable to the corresponding typed parameter.
+    ///
+    /// ## Why is this bad?
+    /// Passing an argument of a type the function (or callable object) does not accept violates
+    /// the expectations of the function author and may cause unexpected runtime errors within the
+    /// body of the function.
+    ///
+    /// ## Examples
+    /// ```python
+    /// def func(x: int): ...
+    /// func("foo")  # error: [invalid-argument-type]
+    /// ```
+    pub(crate) static INVALID_ARGUMENT_TYPE = {
+        summary: "detects call arguments whose type is not assignable to the corresponding typed parameter",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// TODO #14889
     pub(crate) static INVALID_ASSIGNMENT = {
@@ -202,6 +292,7 @@ declare_lint! {
 }
 
 declare_lint! {
+    /// ## What it does
     /// Checks for exception handlers that catch non-exception classes.
     ///
     /// ## Why is this bad?
@@ -236,6 +327,33 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Checks for arguments to `metaclass=` that are invalid.
+    ///
+    /// ## Why is this bad?
+    /// Python allows arbitrary expressions to be used as the argument to `metaclass=`.
+    /// These expressions, however, need to be callable and accept the same arguments
+    /// as `type.__new__`.
+    ///
+    /// ## Example
+    ///
+    /// ```python
+    /// def f(): ...
+    ///
+    /// # TypeError: f() takes 0 positional arguments but 3 were given
+    /// class B(metaclass=f): ...
+    /// ```
+    ///
+    /// ## References
+    /// - [Python documentation: Metaclasses](https://docs.python.org/3/reference/datamodel.html#metaclasses)
+    pub(crate) static INVALID_METACLASS = {
+        summary: "detects invalid `metaclass=` arguments",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// ## What it does
     /// Checks for default values that can't be assigned to the parameter's annotated type.
@@ -314,6 +432,25 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Checks for missing required arguments in a call.
+    ///
+    /// ## Why is this bad?
+    /// Failing to provide a required argument will raise a `TypeError` at runtime.
+    ///
+    /// ## Examples
+    /// ```python
+    /// def func(x: int): ...
+    /// func()  # TypeError: func() missing 1 required positional argument: 'x'
+    /// ```
+    pub(crate) static MISSING_ARGUMENT = {
+        summary: "detects missing required arguments in a call",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// ## What it does
     /// Checks for subscripting objects that do not support subscripting.
@@ -352,6 +489,27 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Checks for calls which provide more than one argument for a single parameter.
+    ///
+    /// ## Why is this bad?
+    /// Providing multiple values for a single parameter will raise a `TypeError` at runtime.
+    ///
+    /// ## Examples
+    ///
+    /// ```python
+    /// def f(x: int) -> int: ...
+    ///
+    /// f(1, x=2)  # Error raised here
+    /// ```
+    pub(crate) static PARAMETER_ALREADY_ASSIGNED = {
+        summary: "detects multiple arguments for the same parameter",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// ## What it does
     /// Checks for possibly unbound attributes.
@@ -395,6 +553,72 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Checks for classes that subclass final classes.
+    ///
+    /// ## Why is this bad?
+    /// Decorating a class with `@final` declares to the type checker that it should not be subclassed.
+    ///
+    /// ## Example
+    ///
+    /// ```python
+    /// from typing import final
+    ///
+    /// @final
+    /// class A: ...
+    /// class B(A): ...  # Error raised here
+    /// ```
+    pub(crate) static SUBCLASS_OF_FINAL_CLASS = {
+        summary: "detects subclasses of final classes",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for `assert_type()` calls where the actual type
+    /// is not the same as the asserted type.
+    ///
+    /// ## Why is this bad?
+    /// `assert_type()` allows confirming the inferred type of a certain value.
+    ///
+    /// ## Example
+    ///
+    /// ```python
+    /// def _(x: int):
+    ///     assert_type(x, int)  # fine
+    ///     assert_type(x, str)  # error: Actual type does not match asserted type
+    /// ```
+    pub(crate) static TYPE_ASSERTION_FAILURE = {
+        summary: "detects failed type assertions",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for calls that pass more positional arguments than the callable can accept.
+    ///
+    /// ## Why is this bad?
+    /// Passing too many positional arguments will raise `TypeError` at runtime.
+    ///
+    /// ## Example
+    ///
+    /// ```python
+    /// def f(): ...
+    ///
+    /// f("foo")  # Error raised here
+    /// ```
+    pub(crate) static TOO_MANY_POSITIONAL_ARGUMENTS = {
+        summary: "detects calls passing too many positional arguments",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// ## What it does
     /// Checks for calls to `reveal_type` without importing it.
@@ -411,6 +635,27 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Checks for keyword arguments in calls that don't match any parameter of the callable.
+    ///
+    /// ## Why is this bad?
+    /// Providing an unknown keyword argument will raise `TypeError` at runtime.
+    ///
+    /// ## Example
+    ///
+    /// ```python
+    /// def f(x: int) -> int: ...
+    ///
+    /// f(x=1, y=2)  # Error raised here
+    /// ```
+    pub(crate) static UNKNOWN_ARGUMENT = {
+        summary: "detects unknown keyword arguments in calls",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 declare_lint! {
     /// ## What it does
     /// Checks for unresolved attributes.
@@ -486,13 +731,32 @@ declare_lint! {
     }
 }
 
+declare_lint! {
+    /// ## What it does
+    /// Makes sure that the argument of `static_assert` is statically known to be true.
+    ///
+    /// ## Examples
+    /// ```python
+    /// from knot_extensions import static_assert
+    ///
+    /// static_assert(1 + 1 == 3)  # error: evaluates to `False`
+    ///
+    /// static_assert(int(2.0 * 3.0) == 6)  # error: does not have a statically known truthiness
+    /// ```
+    pub(crate) static STATIC_ASSERT_ERROR = {
+        summary: "Failed static assertion",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 #[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 {
@@ -546,41 +810,41 @@ 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)
     }
 }
 
@@ -588,7 +852,7 @@ impl Deref for TypeCheckDiagnostics {
     type Target = [std::sync::Arc<TypeCheckDiagnostic>];
 
     fn deref(&self) -> &Self::Target {
-        &self.inner
+        &self.diagnostics
     }
 }
 
@@ -597,7 +861,7 @@ 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()
     }
 }
 
@@ -606,7 +870,7 @@ 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()
     }
 }
 
@@ -788,3 +1052,11 @@ 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

@@ -8,8 +8,8 @@ use ruff_python_literal::escape::AsciiEscape;
 
 use crate::types::class_base::ClassBase;
 use crate::types::{
-    ClassLiteralType, InstanceType, IntersectionType, KnownClass, StringLiteralType,
-    SubclassOfType, Type, UnionType,
+    ClassLiteralType, InstanceType, IntersectionType, KnownClass, StringLiteralType, Type,
+    UnionType,
 };
 use crate::Db;
 use rustc_hash::FxHashMap;
@@ -65,9 +65,8 @@ struct DisplayRepresentation<'db> {
 impl Display for DisplayRepresentation<'_> {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         match self.ty {
-            Type::Any => f.write_str("Any"),
+            Type::Dynamic(dynamic) => dynamic.fmt(f),
             Type::Never => f.write_str("Never"),
-            Type::Unknown => f.write_str("Unknown"),
             Type::Instance(InstanceType { class }) => {
                 let representation = match class.known(self.db) {
                     Some(KnownClass::NoneType) => "None",
@@ -76,24 +75,17 @@ impl Display for DisplayRepresentation<'_> {
                 };
                 f.write_str(representation)
             }
-            // `[Type::Todo]`'s display should be explicit that is not a valid display of
-            // any other type
-            Type::Todo(todo) => write!(f, "@Todo{todo}"),
             Type::ModuleLiteral(module) => {
                 write!(f, "<module '{}'>", module.module(self.db).name())
             }
             // TODO functions and classes should display using a fully qualified name
             Type::ClassLiteral(ClassLiteralType { class }) => f.write_str(class.name(self.db)),
-            Type::SubclassOf(SubclassOfType {
-                base: ClassBase::Class(class),
-            }) => {
+            Type::SubclassOf(subclass_of_ty) => match subclass_of_ty.subclass_of() {
                 // Only show the bare class name here; ClassBase::display would render this as
                 // type[<class 'Foo'>] instead of type[Foo].
-                write!(f, "type[{}]", class.name(self.db))
-            }
-            Type::SubclassOf(SubclassOfType { base }) => {
-                write!(f, "type[{}]", base.display(self.db))
-            }
+                ClassBase::Class(class) => write!(f, "type[{}]", class.name(self.db)),
+                ClassBase::Dynamic(dynamic) => write!(f, "type[{dynamic}]"),
+            },
             Type::KnownInstance(known_instance) => f.write_str(known_instance.repr(self.db)),
             Type::FunctionLiteral(function) => f.write_str(function.name(self.db)),
             Type::Union(union) => union.display(self.db).fmt(f),
@@ -177,12 +169,9 @@ impl Display for DisplayUnionType<'_> {
 
         for element in elements {
             if let Ok(kind) = CondensedDisplayTypeKind::try_from(*element) {
-                let Some(mut condensed_kind) = grouped_condensed_kinds.remove(&kind) else {
+                let Some(condensed_kind) = grouped_condensed_kinds.remove(&kind) else {
                     continue;
                 };
-                if kind == CondensedDisplayTypeKind::Int {
-                    condensed_kind.sort_unstable_by_key(|ty| ty.expect_int_literal());
-                }
                 join.entry(&DisplayLiteralGroup {
                     literals: condensed_kind,
                     db: self.db,
@@ -223,17 +212,12 @@ impl Display for DisplayLiteralGroup<'_> {
 
 /// Enumeration of literal types that are displayed in a "condensed way" inside `Literal` slices.
 ///
-/// For example, `Literal[1] | Literal[2]` is displayed as `"Literal[1, 2]"`.
-/// Not all `Literal` types are displayed using `Literal` slices
-/// (e.g. it would be inappropriate to display `LiteralString`
-/// as `Literal[LiteralString]`).
+/// For example, `Literal[1] | Literal[2] | Literal["s"]` is displayed as `"Literal[1, 2, "s"]"`.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
 enum CondensedDisplayTypeKind {
     Class,
     Function,
-    Int,
-    String,
-    Bytes,
+    LiteralExpression,
 }
 
 impl TryFrom<Type<'_>> for CondensedDisplayTypeKind {
@@ -243,9 +227,10 @@ impl TryFrom<Type<'_>> for CondensedDisplayTypeKind {
         match value {
             Type::ClassLiteral(_) => Ok(Self::Class),
             Type::FunctionLiteral(_) => Ok(Self::Function),
-            Type::IntLiteral(_) => Ok(Self::Int),
-            Type::StringLiteral(_) => Ok(Self::String),
-            Type::BytesLiteral(_) => Ok(Self::Bytes),
+            Type::IntLiteral(_)
+            | Type::StringLiteral(_)
+            | Type::BytesLiteral(_)
+            | Type::BooleanLiteral(_) => Ok(Self::LiteralExpression),
             _ => Err(()),
         }
     }
@@ -324,6 +309,12 @@ 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,
@@ -366,64 +357,8 @@ impl Display for DisplayStringLiteralType<'_> {
 
 #[cfg(test)]
 mod tests {
-    use ruff_db::files::system_path_to_file;
-    use ruff_db::system::DbWithTestSystem;
-
     use crate::db::tests::setup_db;
-    use crate::types::{global_symbol, SliceLiteralType, StringLiteralType, Type, UnionType};
-
-    #[test]
-    fn test_condense_literal_display_by_type() -> anyhow::Result<()> {
-        let mut db = setup_db();
-
-        db.write_dedented(
-            "src/main.py",
-            "
-            def foo(x: int) -> int:
-                return x + 1
-
-            def bar(s: str) -> str:
-                return s
-
-            class A: ...
-            class B: ...
-            ",
-        )?;
-        let mod_file = system_path_to_file(&db, "src/main.py").expect("file to exist");
-
-        let union_elements = &[
-            Type::Unknown,
-            Type::IntLiteral(-1),
-            global_symbol(&db, mod_file, "A").expect_type(),
-            Type::string_literal(&db, "A"),
-            Type::bytes_literal(&db, &[0u8]),
-            Type::bytes_literal(&db, &[7u8]),
-            Type::IntLiteral(0),
-            Type::IntLiteral(1),
-            Type::string_literal(&db, "B"),
-            global_symbol(&db, mod_file, "foo").expect_type(),
-            global_symbol(&db, mod_file, "bar").expect_type(),
-            global_symbol(&db, mod_file, "B").expect_type(),
-            Type::BooleanLiteral(true),
-            Type::none(&db),
-        ];
-        let union = UnionType::from_elements(&db, union_elements).expect_union();
-        let display = format!("{}", union.display(&db));
-        assert_eq!(
-            display,
-            concat!(
-                "Unknown | ",
-                "Literal[-1, 0, 1] | ",
-                "Literal[A, B] | ",
-                "Literal[\"A\", \"B\"] | ",
-                "Literal[b\"\\x00\", b\"\\x07\"] | ",
-                "Literal[foo, bar] | ",
-                "Literal[True] | ",
-                "None"
-            )
-        );
-        Ok(())
-    }
+    use crate::types::{SliceLiteralType, StringLiteralType, Type};
 
     #[test]
     fn test_slice_literal_display() {