Revert certain double quotes from workflow shell script (#14939)

Follow-up from #14938

.github/workflows/build-binaries.yml

@@ -53,9 +53,9 @@ jobs:
           args: --out dist
       - name: "Test sdist"
         run: |
-          pip install dist/${{ env.PACKAGE_NAME }}-*.tar.gz --force-reinstall
-          ${{ env.MODULE_NAME }} --help
-          python -m ${{ env.MODULE_NAME }} --help
+          pip install dist/${PACKAGE_NAME}-*.tar.gz --force-reinstall
+          "${MODULE_NAME}" --help
+          python -m "${MODULE_NAME}" --help
       - name: "Upload sdist"
         uses: actions/upload-artifact@v4
         with:
@@ -125,7 +125,7 @@ jobs:
           args: --release --locked --out dist
       - name: "Test wheel - aarch64"
         run: |
-          pip install dist/${{ env.PACKAGE_NAME }}-*.whl --force-reinstall
+          pip install dist/${PACKAGE_NAME}-*.whl --force-reinstall
           ruff --help
           python -m ruff --help
       - name: "Upload wheels"
@@ -186,9 +186,9 @@ jobs:
         if: ${{ !startsWith(matrix.platform.target, 'aarch64') }}
         shell: bash
         run: |
-          python -m pip install dist/${{ env.PACKAGE_NAME }}-*.whl --force-reinstall
-          ${{ env.MODULE_NAME }} --help
-          python -m ${{ env.MODULE_NAME }} --help
+          python -m pip install dist/${PACKAGE_NAME}-*.whl --force-reinstall
+          "${MODULE_NAME}" --help
+          python -m "${MODULE_NAME}" --help
       - name: "Upload wheels"
         uses: actions/upload-artifact@v4
         with:
@@ -236,9 +236,9 @@ jobs:
       - name: "Test wheel"
         if: ${{ startsWith(matrix.target, 'x86_64') }}
         run: |
-          pip install dist/${{ env.PACKAGE_NAME }}-*.whl --force-reinstall
-          ${{ env.MODULE_NAME }} --help
-          python -m ${{ env.MODULE_NAME }} --help
+          pip install dist/${PACKAGE_NAME}-*.whl --force-reinstall
+          "${MODULE_NAME}" --help
+          python -m "${MODULE_NAME}" --help
       - name: "Upload wheels"
         uses: actions/upload-artifact@v4
         with:

.github/workflows/build-docker.yml

@@ -72,7 +72,7 @@ jobs:
       - name: Normalize Platform Pair (replace / with -)
         run: |
           platform=${{ matrix.platform }}
-          echo "PLATFORM_TUPLE=${platform//\//-}" >> $GITHUB_ENV
+          echo "PLATFORM_TUPLE=${platform//\//-}" >> "$GITHUB_ENV"
 
       # Adapted from https://docs.docker.com/build/ci/github-actions/multi-platform/
       - name: Build and push by digest
@@ -87,9 +87,10 @@ jobs:
           outputs: type=image,name=${{ env.RUFF_BASE_IMG }},push-by-digest=true,name-canonical=true,push=${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
 
       - name: Export digests
+        env:
+          digest: ${{ steps.build.outputs.digest }}
         run: |
           mkdir -p /tmp/digests
-          digest="${{ steps.build.outputs.digest }}"
           touch "/tmp/digests/${digest#sha256:}"
 
       - name: Upload digests
@@ -143,7 +144,7 @@ jobs:
         run: |
           docker buildx imagetools create \
             $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
-            $(printf '${{ env.RUFF_BASE_IMG }}@sha256:%s ' *)
+            $(printf "${RUFF_BASE_IMG}@sha256:%s " *)
 
   docker-publish-extra:
     name: Publish additional Docker image based on ${{ matrix.image-mapping }}
@@ -182,7 +183,7 @@ jobs:
           # Generate Dockerfile content
           cat <<EOF > Dockerfile
           FROM ${BASE_IMAGE}
-          COPY --from=${{ env.RUFF_BASE_IMG }}:latest /ruff /usr/local/bin/ruff
+          COPY --from=${RUFF_BASE_IMG}:latest /ruff /usr/local/bin/ruff
           ENTRYPOINT []
           CMD ["/usr/local/bin/ruff"]
           EOF
@@ -202,14 +203,14 @@ jobs:
           TAG_PATTERNS="${TAG_PATTERNS%\\n}"
 
           # Export image cache name
-          echo "IMAGE_REF=${BASE_IMAGE//:/-}" >> $GITHUB_ENV
+          echo "IMAGE_REF=${BASE_IMAGE//:/-}" >> "$GITHUB_ENV"
 
           # Export tag patterns using the multiline env var syntax
           {
             echo "TAG_PATTERNS<<EOF"
             echo -e "${TAG_PATTERNS}"
             echo EOF
-          } >> $GITHUB_ENV
+          } >> "$GITHUB_ENV"
 
       - name: Extract metadata (tags, labels) for Docker
         id: meta
@@ -288,4 +289,4 @@ jobs:
           docker buildx imagetools create \
             "${annotations[@]}" \
             $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
-            $(printf '${{ env.RUFF_BASE_IMG }}@sha256:%s ' *)
+            $(printf "${RUFF_BASE_IMG}@sha256:%s " *)

.github/workflows/publish-docs.yml

@@ -49,13 +49,11 @@ jobs:
 
       - name: "Set branch name"
         run: |
-          version="${{ env.version }}"
-          display_name="${{ env.display_name }}"
           timestamp="$(date +%s)"
 
           # create branch_display_name from display_name by replacing all
           # characters disallowed in git branch names with hyphens
-          branch_display_name="$(echo "$display_name" | tr -c '[:alnum:]._' '-' | tr -s '-')"
+          branch_display_name="$(echo "${display_name}" | tr -c '[:alnum:]._' '-' | tr -s '-')"
 
           echo "branch_name=update-docs-$branch_display_name-$timestamp" >> $GITHUB_ENV
           echo "timestamp=$timestamp" >> $GITHUB_ENV
@@ -93,9 +91,7 @@ jobs:
         run: mkdocs build --strict -f mkdocs.public.yml
 
       - name: "Clone docs repo"
-        run: |
-          version="${{ env.version }}"
-          git clone https://${{ secrets.ASTRAL_DOCS_PAT }}@github.com/astral-sh/docs.git astral-docs
+        run: git clone https://${{ secrets.ASTRAL_DOCS_PAT }}@github.com/astral-sh/docs.git astral-docs
 
       - name: "Copy docs"
         run: rm -rf astral-docs/site/ruff && mkdir -p astral-docs/site && cp -r site/ruff astral-docs/site/
@@ -103,12 +99,10 @@ jobs:
       - name: "Commit docs"
         working-directory: astral-docs
         run: |
-          branch_name="${{ env.branch_name }}"
-
           git config user.name "astral-docs-bot"
           git config user.email "176161322+astral-docs-bot@users.noreply.github.com"
 
-          git checkout -b $branch_name
+          git checkout -b "${branch_name}"
           git add site/ruff
           git commit -m "Update ruff documentation for $version"
 
@@ -117,12 +111,8 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.ASTRAL_DOCS_PAT }}
         run: |
-          version="${{ env.version }}"
-          display_name="${{ env.display_name }}"
-          branch_name="${{ env.branch_name }}"
-
           # set the PR title
-          pull_request_title="Update ruff documentation for $display_name"
+          pull_request_title="Update ruff documentation for "${display_name}""
 
           # Delete any existing pull requests that are open for this version
           # by checking against pull_request_title because the new PR will
@@ -131,12 +121,12 @@ jobs:
             xargs -I {} gh pr close {}
 
           # push the branch to GitHub
-          git push origin $branch_name
+          git push origin "${branch_name}"
 
           # create the PR
-          gh pr create --base main --head $branch_name \
+          gh pr create --base main --head "${branch_name}" \
             --title "$pull_request_title" \
-            --body "Automated documentation update for $display_name" \
+            --body "Automated documentation update for "${display_name}"" \
             --label "documentation"
 
       - name: "Merge Pull Request"
@@ -145,9 +135,7 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.ASTRAL_DOCS_PAT }}
         run: |
-          branch_name="${{ env.branch_name }}"
-
           # auto-merge the PR if the build was triggered by a release. Manual builds should be reviewed by a human.
           # give the PR a few seconds to be created before trying to auto-merge it
           sleep 10
-          gh pr merge --squash $branch_name
+          gh pr merge --squash "${branch_name}"

.github/workflows/sync_typeshed.yaml

@@ -31,7 +31,7 @@ jobs:
         with:
           repository: python/typeshed
           path: typeshed
-          persist-credentials: true
+          persist-credentials: false
       - name: Setup git
         run: |
           git config --global user.name typeshedbot

.pre-commit-config.yaml

@@ -95,8 +95,6 @@ repos:
         # `release.yml` is autogenerated by `dist`; security issues need to be fixed there
         # (https://opensource.axo.dev/cargo-dist/)
         exclude: .github/workflows/release.yml
-        # We could consider enabling the low-severity warnings, but they're noisy
-        args: [--min-severity=medium]
 
   - repo: https://github.com/python-jsonschema/check-jsonschema
     rev: 0.30.0

CHANGELOG.md

@@ -1,5 +1,40 @@
 # Changelog
 
+## 0.8.3
+
+### Preview features
+
+- Fix fstring formatting removing overlong implicit concatenated string in expression part ([#14811](https://github.com/astral-sh/ruff/pull/14811))
+- \[`airflow`\] Add fix to remove deprecated keyword arguments (`AIR302`) ([#14887](https://github.com/astral-sh/ruff/pull/14887))
+- \[`airflow`\]: Extend rule to include deprecated names for Airflow 3.0 (`AIR302`) ([#14765](https://github.com/astral-sh/ruff/pull/14765) and [#14804](https://github.com/astral-sh/ruff/pull/14804))
+- \[`flake8-bugbear`\] Improve error messages for `except*` (`B025`, `B029`, `B030`, `B904`) ([#14815](https://github.com/astral-sh/ruff/pull/14815))
+- \[`flake8-bugbear`\] `itertools.batched()` without explicit `strict` (`B911`) ([#14408](https://github.com/astral-sh/ruff/pull/14408))
+- \[`flake8-use-pathlib`\] Dotless suffix passed to `Path.with_suffix()` (`PTH210`) ([#14779](https://github.com/astral-sh/ruff/pull/14779))
+- \[`pylint`\] Include parentheses and multiple comparators in check for `boolean-chained-comparison` (`PLR1716`) ([#14781](https://github.com/astral-sh/ruff/pull/14781))
+- \[`ruff`\] Do not simplify `round()` calls (`RUF046`) ([#14832](https://github.com/astral-sh/ruff/pull/14832))
+- \[`ruff`\] Don't emit `used-dummy-variable` on function parameters (`RUF052`) ([#14818](https://github.com/astral-sh/ruff/pull/14818))
+- \[`ruff`\] Implement `if-key-in-dict-del` (`RUF051`) ([#14553](https://github.com/astral-sh/ruff/pull/14553))
+- \[`ruff`\] Mark autofix for `RUF052` as always unsafe ([#14824](https://github.com/astral-sh/ruff/pull/14824))
+- \[`ruff`\] Teach autofix for `used-dummy-variable` about TypeVars etc. (`RUF052`) ([#14819](https://github.com/astral-sh/ruff/pull/14819))
+
+### Rule changes
+
+- \[`flake8-bugbear`\] Offer unsafe autofix for `no-explicit-stacklevel` (`B028`) ([#14829](https://github.com/astral-sh/ruff/pull/14829))
+- \[`flake8-pyi`\] Skip all type definitions in `string-or-bytes-too-long` (`PYI053`) ([#14797](https://github.com/astral-sh/ruff/pull/14797))
+- \[`pyupgrade`\] Do not report when a UTF-8 comment is followed by a non-UTF-8 one (`UP009`) ([#14728](https://github.com/astral-sh/ruff/pull/14728))
+- \[`pyupgrade`\] Mark fixes for `convert-typed-dict-functional-to-class` and `convert-named-tuple-functional-to-class` as unsafe if they will remove comments (`UP013`, `UP014`) ([#14842](https://github.com/astral-sh/ruff/pull/14842))
+
+### Bug fixes
+
+- Raise syntax error for mixing `except` and `except*` ([#14895](https://github.com/astral-sh/ruff/pull/14895))
+- \[`flake8-bugbear`\] Fix `B028` to allow `stacklevel` to be explicitly assigned as a positional argument ([#14868](https://github.com/astral-sh/ruff/pull/14868))
+- \[`flake8-bugbear`\] Skip `B028` if `warnings.warn` is called with `*args` or `**kwargs` ([#14870](https://github.com/astral-sh/ruff/pull/14870))
+- \[`flake8-comprehensions`\] Skip iterables with named expressions in `unnecessary-map` (`C417`) ([#14827](https://github.com/astral-sh/ruff/pull/14827))
+- \[`flake8-pyi`\] Also remove `self` and `cls`'s annotation (`PYI034`) ([#14801](https://github.com/astral-sh/ruff/pull/14801))
+- \[`flake8-pytest-style`\] Fix `pytest-parametrize-names-wrong-type` (`PT006`) to edit both `argnames` and `argvalues` if both of them are single-element tuples/lists ([#14699](https://github.com/astral-sh/ruff/pull/14699))
+- \[`perflint`\] Improve autofix for `PERF401` ([#14369](https://github.com/astral-sh/ruff/pull/14369))
+- \[`pylint`\] Fix `PLW1508` false positive for default string created via a mult operation ([#14841](https://github.com/astral-sh/ruff/pull/14841))
+
 ## 0.8.2
 
 ### Preview features

Cargo.lock

@@ -2300,6 +2300,7 @@ dependencies = [
  "red_knot_vendored",
  "ruff_db",
  "ruff_index",
+ "ruff_macros",
  "ruff_python_ast",
  "ruff_python_literal",
  "ruff_python_parser",
@@ -2516,7 +2517,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.8.2"
+version = "0.8.3"
 dependencies = [
  "anyhow",
  "argfile",
@@ -2735,7 +2736,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_linter"
-version = "0.8.2"
+version = "0.8.3"
 dependencies = [
  "aho-corasick",
  "annotate-snippets 0.9.2",
@@ -3050,7 +3051,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_wasm"
-version = "0.8.2"
+version = "0.8.3"
 dependencies = [
  "console_error_panic_hook",
  "console_log",

README.md

@@ -140,8 +140,8 @@ curl -LsSf https://astral.sh/ruff/install.sh | sh
 powershell -c "irm https://astral.sh/ruff/install.ps1 | iex"
 
 # For a specific version.
-curl -LsSf https://astral.sh/ruff/0.8.2/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.8.2/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.8.3/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.8.3/install.ps1 | iex"
 ```
 
 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -174,7 +174,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.8.2
+  rev: v0.8.3
   hooks:
     # Run the linter.
     - id: ruff

crates/red_knot_python_semantic/Cargo.toml

@@ -13,6 +13,7 @@ license = { workspace = true }
 [dependencies]
 ruff_db = { workspace = true }
 ruff_index = { workspace = true }
+ruff_macros = { workspace = true }
 ruff_python_ast = { workspace = true }
 ruff_python_parser = { workspace = true }
 ruff_python_stdlib = { workspace = true }

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

@@ -34,8 +34,7 @@ If you define your own class named `Any`, using that in a type expression refers
 isn't a spelling of the Any type.
 
 ```py
-class Any:
-    pass
+class Any: ...
 
 x: Any
 
@@ -59,8 +58,7 @@ assignable to `int`.
 ```py
 from typing import Any
 
-class Subclass(Any):
-    pass
+class Subclass(Any): ...
 
 reveal_type(Subclass.__mro__)  # revealed: tuple[Literal[Subclass], Any, Literal[object]]
 
@@ -68,8 +66,18 @@ x: Subclass = 1  # error: [invalid-assignment]
 # TODO: no diagnostic
 y: int = Subclass()  # error: [invalid-assignment]
 
-def f() -> Subclass:
-    pass
-
-reveal_type(f())  # revealed: Subclass
+def _(s: Subclass):
+    reveal_type(s)  # revealed: Subclass
+```
+
+## Invalid
+
+`Any` cannot be parameterized:
+
+```py
+from typing import Any
+
+# error: [invalid-type-parameter] "Type `typing.Any` expected no type parameter"
+def f(x: Any[int]):
+    reveal_type(x)  # revealed: Unknown
 ```

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

@@ -89,28 +89,26 @@ vice versa.
 ```py
 from typing_extensions import Literal, LiteralString
 
-def coinflip() -> bool:
-    return True
+def _(flag: bool):
+    foo_1: Literal["foo"] = "foo"
+    bar_1: LiteralString = foo_1  # fine
 
-foo_1: Literal["foo"] = "foo"
-bar_1: LiteralString = foo_1  # fine
+    foo_2 = "foo" if flag else "bar"
+    reveal_type(foo_2)  # revealed: Literal["foo", "bar"]
+    bar_2: LiteralString = foo_2  # fine
 
-foo_2 = "foo" if coinflip() else "bar"
-reveal_type(foo_2)  # revealed: Literal["foo", "bar"]
-bar_2: LiteralString = foo_2  # fine
+    foo_3: LiteralString = "foo" * 1_000_000_000
+    bar_3: str = foo_2  # fine
 
-foo_3: LiteralString = "foo" * 1_000_000_000
-bar_3: str = foo_2  # fine
+    baz_1: str = str()
+    qux_1: LiteralString = baz_1  # error: [invalid-assignment]
 
-baz_1: str = str()
-qux_1: LiteralString = baz_1  # error: [invalid-assignment]
+    baz_2: LiteralString = "baz" * 1_000_000_000
+    qux_2: Literal["qux"] = baz_2  # error: [invalid-assignment]
 
-baz_2: LiteralString = "baz" * 1_000_000_000
-qux_2: Literal["qux"] = baz_2  # error: [invalid-assignment]
-
-baz_3 = "foo" if coinflip() else 1
-reveal_type(baz_3)  # revealed: Literal["foo"] | Literal[1]
-qux_3: LiteralString = baz_3  # error: [invalid-assignment]
+    baz_3 = "foo" if flag else 1
+    reveal_type(baz_3)  # revealed: Literal["foo"] | Literal[1]
+    qux_3: LiteralString = baz_3  # error: [invalid-assignment]
 ```
 
 ### Narrowing

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

@@ -3,75 +3,56 @@
 ## Simple
 
 ```py
-def f() -> "int":
-    return 1
-
-reveal_type(f())  # revealed: int
+def f(v: "int"):
+    reveal_type(v)  # revealed: int
 ```
 
 ## Nested
 
 ```py
-def f() -> "'int'":
-    return 1
-
-reveal_type(f())  # revealed: int
+def f(v: "'int'"):
+    reveal_type(v)  # revealed: int
 ```
 
 ## Type expression
 
 ```py
-def f1() -> "int | str":
-    return 1
-
-def f2() -> "tuple[int, str]":
-    return 1
-
-reveal_type(f1())  # revealed: int | str
-reveal_type(f2())  # revealed: tuple[int, str]
+def f1(v: "int | str", w: "tuple[int, str]"):
+    reveal_type(v)  # revealed: int | str
+    reveal_type(w)  # revealed: tuple[int, str]
 ```
 
 ## Partial
 
 ```py
-def f() -> tuple[int, "str"]:
-    return 1
-
-reveal_type(f())  # revealed: tuple[int, str]
+def f(v: tuple[int, "str"]):
+    reveal_type(v)  # revealed: tuple[int, str]
 ```
 
 ## Deferred
 
 ```py
-def f() -> "Foo":
-    return Foo()
+def f(v: "Foo"):
+    reveal_type(v)  # revealed: Foo
 
-class Foo:
-    pass
-
-reveal_type(f())  # revealed: Foo
+class Foo: ...
 ```
 
 ## Deferred (undefined)
 
 ```py
 # error: [unresolved-reference]
-def f() -> "Foo":
-    pass
-
-reveal_type(f())  # revealed: Unknown
+def f(v: "Foo"):
+    reveal_type(v)  # revealed: Unknown
 ```
 
 ## Partial deferred
 
 ```py
-def f() -> int | "Foo":
-    return 1
+def f(v: int | "Foo"):
+    reveal_type(v)  # revealed: int | Foo
 
-class Foo:
-    pass
-
-reveal_type(f())  # revealed: int | Foo
+class Foo: ...
 ```
 
 ## `typing.Literal`
@@ -79,65 +60,43 @@ reveal_type(f())  # revealed: int | Foo
 ```py
 from typing import Literal
 
-def f1() -> Literal["Foo", "Bar"]:
-    return "Foo"
+def f1(v: Literal["Foo", "Bar"], w: 'Literal["Foo", "Bar"]'):
+    reveal_type(v)  # revealed: Literal["Foo", "Bar"]
+    reveal_type(w)  # revealed: Literal["Foo", "Bar"]
 
-def f2() -> 'Literal["Foo", "Bar"]':
-    return "Foo"
-
-class Foo:
-    pass
-
-reveal_type(f1())  # revealed: Literal["Foo", "Bar"]
-reveal_type(f2())  # revealed: Literal["Foo", "Bar"]
+class Foo: ...
 ```
 
 ## Various string kinds
 
 ```py
-# error: [annotation-raw-string] "Type expressions cannot use raw string literal"
-def f1() -> r"int":
-    return 1
-
-# error: [annotation-f-string] "Type expressions cannot use f-strings"
-def f2() -> f"int":
-    return 1
-
-# error: [annotation-byte-string] "Type expressions cannot use bytes literal"
-def f3() -> b"int":
-    return 1
-
-def f4() -> "int":
-    return 1
-
-# error: [annotation-implicit-concat] "Type expressions cannot span multiple string literals"
-def f5() -> "in" "t":
-    return 1
-
-# error: [annotation-escape-character] "Type expressions cannot contain escape characters"
-def f6() -> "\N{LATIN SMALL LETTER I}nt":
-    return 1
-
-# error: [annotation-escape-character] "Type expressions cannot contain escape characters"
-def f7() -> "\x69nt":
-    return 1
-
-def f8() -> """int""":
-    return 1
-
-# error: [annotation-byte-string] "Type expressions cannot use bytes literal"
-def f9() -> "b'int'":
-    return 1
-
-reveal_type(f1())  # revealed: Unknown
-reveal_type(f2())  # revealed: Unknown
-reveal_type(f3())  # revealed: Unknown
-reveal_type(f4())  # revealed: int
-reveal_type(f5())  # revealed: Unknown
-reveal_type(f6())  # revealed: Unknown
-reveal_type(f7())  # revealed: Unknown
-reveal_type(f8())  # revealed: int
-reveal_type(f9())  # revealed: Unknown
+def f1(
+    # error: [raw-string-type-annotation] "Type expressions cannot use raw string literal"
+    a: r"int",
+    # error: [fstring-type-annotation] "Type expressions cannot use f-strings"
+    b: f"int",
+    # error: [byte-string-type-annotation] "Type expressions cannot use bytes literal"
+    c: b"int",
+    d: "int",
+    # error: [implicit-concatenated-string-type-annotation] "Type expressions cannot span multiple string literals"
+    e: "in" "t",
+    # error: [escape-character-in-forward-annotation] "Type expressions cannot contain escape characters"
+    f: "\N{LATIN SMALL LETTER I}nt",
+    # error: [escape-character-in-forward-annotation] "Type expressions cannot contain escape characters"
+    g: "\x69nt",
+    h: """int""",
+    # error: [byte-string-type-annotation] "Type expressions cannot use bytes literal"
+    i: "b'int'",
+):
+    reveal_type(a)  # revealed: Unknown
+    reveal_type(b)  # revealed: Unknown
+    reveal_type(c)  # revealed: Unknown
+    reveal_type(d)  # revealed: int
+    reveal_type(e)  # revealed: Unknown
+    reveal_type(f)  # revealed: Unknown
+    reveal_type(g)  # revealed: Unknown
+    reveal_type(h)  # revealed: int
+    reveal_type(i)  # revealed: Unknown
 ```
 
 ## Various string kinds in `typing.Literal`
@@ -145,10 +104,8 @@ reveal_type(f9())  # revealed: Unknown
 ```py
 from typing import Literal
 
-def f() -> Literal["a", r"b", b"c", "d" "e", "\N{LATIN SMALL LETTER F}", "\x67", """h"""]:
-    return "normal"
-
-reveal_type(f())  # revealed: Literal["a", "b", "de", "f", "g", "h"] | Literal[b"c"]
+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"]
 ```
 
 ## Class variables
@@ -175,8 +132,7 @@ c: "Foo"
 # error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to `Foo`"
 d: "Foo" = 1
 
-class Foo:
-    pass
+class Foo: ...
 
 c = Foo()
 
@@ -208,9 +164,9 @@ i: "{i for i in range(5)}"
 j: "{i: i for i in range(5)}"
 k: "(i for i in range(5))"
 l: "await 1"
-# error: [forward-annotation-syntax-error]
+# error: [invalid-syntax-in-forward-annotation]
 m: "yield 1"
-# error: [forward-annotation-syntax-error]
+# error: [invalid-syntax-in-forward-annotation]
 n: "yield from 1"
 o: "1 < 2"
 p: "call()"

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

@@ -78,20 +78,10 @@ c: tuple[str | int, str] = ([], "foo")
 ## PEP-604 annotations are supported
 
 ```py
-def foo() -> str | int | None:
-    return None
-
-reveal_type(foo())  # revealed: str | int | None
-
-def bar() -> str | str | None:
-    return None
-
-reveal_type(bar())  # revealed: str | None
-
-def baz() -> str | str:
-    return "Hello, world!"
-
-reveal_type(baz())  # revealed: str
+def foo(v: str | int | None, w: str | str | None, x: str | str):
+    reveal_type(v)  # revealed: str | int | None
+    reveal_type(w)  # revealed: str | None
+    reveal_type(x)  # revealed: str
 ```
 
 ## Attribute expressions in type annotations are understood
@@ -118,8 +108,7 @@ from __future__ import annotations
 
 x: Foo
 
-class Foo:
-    pass
+class Foo: ...
 
 x = Foo()
 reveal_type(x)  # revealed: Foo
@@ -130,8 +119,7 @@ reveal_type(x)  # revealed: Foo
 ```pyi path=main.pyi
 x: Foo
 
-class Foo:
-    pass
+class Foo: ...
 
 x = Foo()
 reveal_type(x)  # revealed: Foo

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

@@ -49,134 +49,116 @@ reveal_type(x)  # revealed: int
 ## Method union
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class Foo:
+        if flag:
+            def __iadd__(self, other: int) -> str:
+                return "Hello, world!"
+        else:
+            def __iadd__(self, other: int) -> int:
+                return 42
 
-flag = bool_instance()
+    f = Foo()
+    f += 12
 
-class Foo:
-    if bool_instance():
-        def __iadd__(self, other: int) -> str:
-            return "Hello, world!"
-    else:
-        def __iadd__(self, other: int) -> int:
-            return 42
-
-f = Foo()
-f += 12
-
-reveal_type(f)  # revealed: str | int
+    reveal_type(f)  # revealed: str | int
 ```
 
 ## Partially bound `__iadd__`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class Foo:
+        if flag:
+            def __iadd__(self, other: str) -> int:
+                return 42
 
-class Foo:
-    if bool_instance():
-        def __iadd__(self, other: str) -> int:
-            return 42
+    f = Foo()
 
-f = Foo()
+    # TODO: We should emit an `unsupported-operator` error here, possibly with the information
+    # that `Foo.__iadd__` may be unbound as additional context.
+    f += "Hello, world!"
 
-# TODO: We should emit an `unsupported-operator` error here, possibly with the information
-# that `Foo.__iadd__` may be unbound as additional context.
-f += "Hello, world!"
-
-reveal_type(f)  # revealed: int | Unknown
+    reveal_type(f)  # revealed: int | Unknown
 ```
 
 ## Partially bound with `__add__`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class Foo:
+        def __add__(self, other: str) -> str:
+            return "Hello, world!"
+        if flag:
+            def __iadd__(self, other: str) -> int:
+                return 42
 
-class Foo:
-    def __add__(self, other: str) -> str:
-        return "Hello, world!"
-    if bool_instance():
-        def __iadd__(self, other: str) -> int:
-            return 42
+    f = Foo()
+    f += "Hello, world!"
 
-f = Foo()
-f += "Hello, world!"
-
-reveal_type(f)  # revealed: int | str
+    reveal_type(f)  # revealed: int | str
 ```
 
 ## Partially bound target union
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    class Foo:
+        def __add__(self, other: int) -> str:
+            return "Hello, world!"
+        if flag1:
+            def __iadd__(self, other: int) -> int:
+                return 42
 
-class Foo:
-    def __add__(self, other: int) -> str:
-        return "Hello, world!"
-    if bool_instance():
-        def __iadd__(self, other: int) -> int:
-            return 42
+    if flag2:
+        f = Foo()
+    else:
+        f = 42.0
+    f += 12
 
-if bool_instance():
-    f = Foo()
-else:
-    f = 42.0
-f += 12
-
-reveal_type(f)  # revealed: int | str | float
+    reveal_type(f)  # revealed: int | str | float
 ```
 
 ## Target union
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class Foo:
+        def __iadd__(self, other: int) -> str:
+            return "Hello, world!"
 
-flag = bool_instance()
+    if flag:
+        f = Foo()
+    else:
+        f = 42.0
+    f += 12
 
-class Foo:
-    def __iadd__(self, other: int) -> str:
-        return "Hello, world!"
-
-if flag:
-    f = Foo()
-else:
-    f = 42.0
-f += 12
-
-reveal_type(f)  # revealed: str | float
+    reveal_type(f)  # revealed: str | float
 ```
 
 ## Partially bound target union with `__add__`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def f(flag: bool, flag2: bool):
+    class Foo:
+        def __add__(self, other: int) -> str:
+            return "Hello, world!"
+        if flag:
+            def __iadd__(self, other: int) -> int:
+                return 42
 
-flag = bool_instance()
+    class Bar:
+        def __add__(self, other: int) -> bytes:
+            return b"Hello, world!"
 
-class Foo:
-    def __add__(self, other: int) -> str:
-        return "Hello, world!"
-    if bool_instance():
-        def __iadd__(self, other: int) -> int:
-            return 42
+        def __iadd__(self, other: int) -> float:
+            return 42.0
 
-class Bar:
-    def __add__(self, other: int) -> bytes:
-        return b"Hello, world!"
+    if flag2:
+        f = Foo()
+    else:
+        f = Bar()
+    f += 12
 
-    def __iadd__(self, other: int) -> float:
-        return 42.0
-
-if flag:
-    f = Foo()
-else:
-    f = Bar()
-f += 12
-
-reveal_type(f)  # revealed: int | str | float
+    reveal_type(f)  # revealed: int | str | float
 ```

crates/red_knot_python_semantic/resources/mdtest/attributes.md

@@ -3,27 +3,23 @@
 ## Union of attributes
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-
-if flag:
-    class C1:
-        x = 1
-
-else:
-    class C1:
-        x = 2
-
-class C2:
+def _(flag: bool):
     if flag:
-        x = 3
-    else:
-        x = 4
+        class C1:
+            x = 1
 
-reveal_type(C1.x)  # revealed: Literal[1, 2]
-reveal_type(C2.x)  # revealed: Literal[3, 4]
+    else:
+        class C1:
+            x = 2
+
+    class C2:
+        if flag:
+            x = 3
+        else:
+            x = 4
+
+    reveal_type(C1.x)  # revealed: Literal[1, 2]
+    reveal_type(C2.x)  # revealed: Literal[3, 4]
 ```
 
 ## Inherited attributes
@@ -68,24 +64,19 @@ reveal_type(A.X)  # revealed: Literal[42]
 In this example, the `x` attribute is not defined in the `C2` element of the union:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    class C1:
+        x = 1
 
-class C1:
-    x = 1
+    class C2: ...
 
-class C2: ...
+    class C3:
+        x = 3
 
-class C3:
-    x = 3
+    C = C1 if flag1 else C2 if flag2 else C3
 
-flag1 = bool_instance()
-flag2 = bool_instance()
-
-C = C1 if flag1 else C2 if flag2 else C3
-
-# error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
-reveal_type(C.x)  # revealed: Literal[1, 3]
+    # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
+    reveal_type(C.x)  # revealed: Literal[1, 3]
 ```
 
 ### Possibly-unbound within a class
@@ -94,26 +85,21 @@ We raise the same diagnostic if the attribute is possibly-unbound in at least on
 union:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag1: bool, flag2: bool):
+    class C1:
+        x = 1
 
-class C1:
-    x = 1
+    class C2:
+        if flag:
+            x = 2
 
-class C2:
-    if bool_instance():
-        x = 2
+    class C3:
+        x = 3
 
-class C3:
-    x = 3
+    C = C1 if flag1 else C2 if flag2 else C3
 
-flag1 = bool_instance()
-flag2 = bool_instance()
-
-C = C1 if flag1 else C2 if flag2 else C3
-
-# error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
-reveal_type(C.x)  # revealed: Literal[1, 2, 3]
+    # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
+    reveal_type(C.x)  # revealed: Literal[1, 2, 3]
 ```
 
 ## Unions with all paths unbound
@@ -121,16 +107,51 @@ reveal_type(C.x)  # revealed: Literal[1, 2, 3]
 If the symbol is unbound in all elements of the union, we detect that:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class C1: ...
+    class C2: ...
+    C = C1 if flag else C2
 
-class C1: ...
-class C2: ...
-
-flag = bool_instance()
-
-C = C1 if flag else C2
-
-# error: [unresolved-attribute] "Type `Literal[C1, C2]` has no attribute `x`"
-reveal_type(C.x)  # revealed: Unknown
+    # error: [unresolved-attribute] "Type `Literal[C1, C2]` has no attribute `x`"
+    reveal_type(C.x)  # revealed: Unknown
+```
+
+## Objects of all types have a `__class__` method
+
+```py
+import typing_extensions
+
+reveal_type(typing_extensions.__class__)  # revealed: Literal[ModuleType]
+
+a = 42
+reveal_type(a.__class__)  # revealed: Literal[int]
+
+b = "42"
+reveal_type(b.__class__)  # revealed: Literal[str]
+
+c = b"42"
+reveal_type(c.__class__)  # revealed: Literal[bytes]
+
+d = True
+reveal_type(d.__class__)  # revealed: Literal[bool]
+
+e = (42, 42)
+reveal_type(e.__class__)  # revealed: Literal[tuple]
+
+def f(a: int, b: typing_extensions.LiteralString, c: int | str, d: type[str]):
+    reveal_type(a.__class__)  # revealed: type[int]
+    reveal_type(b.__class__)  # revealed: Literal[str]
+    reveal_type(c.__class__)  # revealed: type[int] | type[str]
+
+    # `type[type]`, a.k.a., either the class `type` or some subclass of `type`.
+    # It would be incorrect to infer `Literal[type]` here,
+    # as `c` could be some subclass of `str` with a custom metaclass.
+    # All we know is that the metaclass must be a (non-strict) subclass of `type`.
+    reveal_type(d.__class__)  # revealed: type[type]
+
+reveal_type(f.__class__)  # revealed: Literal[FunctionType]
+
+class Foo: ...
+
+reveal_type(Foo.__class__)  # revealed: Literal[type]
 ```

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

@@ -281,20 +281,12 @@ reveal_type(42 + 4.2)  # revealed: int
 # TODO should be complex, need to check arg type and fall back to `rhs.__radd__`
 reveal_type(3 + 3j)  # revealed: int
 
-def returns_int() -> int:
-    return 42
+def _(x: bool, y: int):
+    reveal_type(x + y)  # revealed: int
+    reveal_type(4.2 + x)  # revealed: float
 
-def returns_bool() -> bool:
-    return True
-
-x = returns_bool()
-y = returns_int()
-
-reveal_type(x + y)  # revealed: int
-reveal_type(4.2 + x)  # revealed: float
-
-# TODO should be float, need to check arg type and fall back to `rhs.__radd__`
-reveal_type(y + 4.12)  # revealed: int
+    # TODO should be float, need to check arg type and fall back to `rhs.__radd__`
+    reveal_type(y + 4.12)  # revealed: int
 ```
 
 ## With literal types

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

@@ -7,29 +7,25 @@ Similarly, in `and` expressions, if the left-hand side is falsy, the right-hand
 evaluated.
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag or (x := 1):
+        # error: [possibly-unresolved-reference]
+        reveal_type(x)  # revealed: Literal[1]
 
-if bool_instance() or (x := 1):
-    # error: [possibly-unresolved-reference]
-    reveal_type(x)  # revealed: Literal[1]
-
-if bool_instance() and (x := 1):
-    # error: [possibly-unresolved-reference]
-    reveal_type(x)  # revealed: Literal[1]
+    if flag and (x := 1):
+        # error: [possibly-unresolved-reference]
+        reveal_type(x)  # revealed: Literal[1]
 ```
 
 ## First expression is always evaluated
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if (x := 1) or flag:
+        reveal_type(x)  # revealed: Literal[1]
 
-if (x := 1) or bool_instance():
-    reveal_type(x)  # revealed: Literal[1]
-
-if (x := 1) and bool_instance():
-    reveal_type(x)  # revealed: Literal[1]
+    if (x := 1) and flag:
+        reveal_type(x)  # revealed: Literal[1]
 ```
 
 ## Statically known truthiness
@@ -49,30 +45,26 @@ if True and (x := 1):
 ## Later expressions can always use variables from earlier expressions
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    flag or (x := 1) or reveal_type(x)  # revealed: Literal[1]
 
-bool_instance() or (x := 1) or reveal_type(x)  # revealed: Literal[1]
-
-# error: [unresolved-reference]
-bool_instance() or reveal_type(y) or (y := 1)  # revealed: Unknown
+    # error: [unresolved-reference]
+    flag or reveal_type(y) or (y := 1)  # revealed: Unknown
 ```
 
 ## Nested expressions
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    if flag1 or ((x := 1) and flag2):
+        # error: [possibly-unresolved-reference]
+        reveal_type(x)  # revealed: Literal[1]
+
+    if ((y := 1) and flag1) or flag2:
+        reveal_type(y)  # revealed: Literal[1]
 
-if bool_instance() or ((x := 1) and bool_instance()):
     # error: [possibly-unresolved-reference]
-    reveal_type(x)  # revealed: Literal[1]
-
-if ((y := 1) and bool_instance()) or bool_instance():
-    reveal_type(y)  # revealed: Literal[1]
-
-# error: [possibly-unresolved-reference]
-if (bool_instance() and (z := 1)) or reveal_type(z):  # revealed: Literal[1]
-    # error: [possibly-unresolved-reference]
-    reveal_type(z)  # revealed: Literal[1]
+    if (flag1 and (z := 1)) or reveal_type(z):  # revealed: Literal[1]
+        # error: [possibly-unresolved-reference]
+        reveal_type(z)  # revealed: Literal[1]
 ```

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

@@ -22,29 +22,27 @@ reveal_type(b)  # revealed: Unknown
 ## Possibly unbound `__call__` method
 
 ```py
-def flag() -> bool: ...
+def _(flag: bool):
+    class PossiblyNotCallable:
+        if flag:
+            def __call__(self) -> int: ...
 
-class PossiblyNotCallable:
-    if flag():
-        def __call__(self) -> int: ...
-
-a = PossiblyNotCallable()
-result = a()  # error: "Object of type `PossiblyNotCallable` is not callable (possibly unbound `__call__` method)"
-reveal_type(result)  # revealed: int
+    a = PossiblyNotCallable()
+    result = a()  # error: "Object of type `PossiblyNotCallable` is not callable (possibly unbound `__call__` method)"
+    reveal_type(result)  # revealed: int
 ```
 
 ## Possibly unbound callable
 
 ```py
-def flag() -> bool: ...
+def _(flag: bool):
+    if flag:
+        class PossiblyUnbound:
+            def __call__(self) -> int: ...
 
-if flag():
-    class PossiblyUnbound:
-        def __call__(self) -> int: ...
-
-# error: [possibly-unresolved-reference]
-a = PossiblyUnbound()
-reveal_type(a())  # revealed: int
+    # error: [possibly-unresolved-reference]
+    a = PossiblyUnbound()
+    reveal_type(a())  # revealed: int
 ```
 
 ## Non-callable `__call__`
@@ -61,15 +59,14 @@ reveal_type(a())  # revealed: Unknown
 ## Possibly non-callable `__call__`
 
 ```py
-def flag() -> bool: ...
+def _(flag: bool):
+    class NonCallable:
+        if flag:
+            __call__ = 1
+        else:
+            def __call__(self) -> int: ...
 
-class NonCallable:
-    if flag():
-        __call__ = 1
-    else:
-        def __call__(self) -> int: ...
-
-a = NonCallable()
-# error: "Object of type `Literal[1] | Literal[__call__]` is not callable (due to union element `Literal[1]`)"
-reveal_type(a())  # revealed: Unknown | int
+    a = NonCallable()
+    # error: "Object of type `Literal[1] | Literal[__call__]` is not callable (due to union element `Literal[1]`)"
+    reveal_type(a())  # revealed: Unknown | int
 ```

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

@@ -57,12 +57,10 @@ x = nonsense()  # error: "Object of type `Literal[123]` is not callable"
 ## Potentially unbound function
 
 ```py
-def flag() -> bool: ...
-
-if flag():
-    def foo() -> int:
-        return 42
-
-# error: [possibly-unresolved-reference]
-reveal_type(foo())  # revealed: int
+def _(flag: bool):
+    if flag:
+        def foo() -> int:
+            return 42
+    # error: [possibly-unresolved-reference]
+    reveal_type(foo())  # revealed: int
 ```

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

@@ -3,22 +3,14 @@
 ## Union of return types
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-
-if flag:
-
-    def f() -> int:
-        return 1
-
-else:
-
-    def f() -> str:
-        return "foo"
-
-reveal_type(f())  # revealed: int | str
+def _(flag: bool):
+    if flag:
+        def f() -> int:
+            return 1
+    else:
+        def f() -> str:
+            return "foo"
+    reveal_type(f())  # revealed: int | str
 ```
 
 ## Calling with an unknown union
@@ -26,13 +18,10 @@ reveal_type(f())  # revealed: int | str
 ```py
 from nonexistent import f  # error: [unresolved-import] "Cannot resolve import `nonexistent`"
 
-def bool_instance() -> bool:
+def coinflip() -> bool:
     return True
 
-flag = bool_instance()
-
-if flag:
-
+if coinflip():
     def f() -> int:
         return 1
 
@@ -44,20 +33,14 @@ reveal_type(f())  # revealed: Unknown | int
 Calling a union with a non-callable element should emit a diagnostic.
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-
-if flag:
-    f = 1
-else:
-
-    def f() -> int:
-        return 1
-
-x = f()  # error: "Object of type `Literal[1] | Literal[f]` is not callable (due to union element `Literal[1]`)"
-reveal_type(x)  # revealed: Unknown | int
+def _(flag: bool):
+    if flag:
+        f = 1
+    else:
+        def f() -> int:
+            return 1
+    x = f()  # error: "Object of type `Literal[1] | Literal[f]` is not callable (due to union element `Literal[1]`)"
+    reveal_type(x)  # revealed: Unknown | int
 ```
 
 ## Multiple non-callable elements in a union
@@ -65,23 +48,17 @@ reveal_type(x)  # revealed: Unknown | int
 Calling a union with multiple non-callable elements should mention all of them in the diagnostic.
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-flag, flag2 = bool_instance(), bool_instance()
-
-if flag:
-    f = 1
-elif flag2:
-    f = "foo"
-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"])"
-# revealed: Unknown | int
-reveal_type(f())
+def _(flag: bool, flag2: bool):
+    if flag:
+        f = 1
+    elif flag2:
+        f = "foo"
+    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"])"
+    # revealed: Unknown | int
+    reveal_type(f())
 ```
 
 ## All non-callable union elements
@@ -89,16 +66,12 @@ reveal_type(f())
 Calling a union with no callable elements can emit a simpler diagnostic.
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        f = 1
+    else:
+        f = "foo"
 
-flag = bool_instance()
-
-if flag:
-    f = 1
-else:
-    f = "foo"
-
-x = f()  # error: "Object of type `Literal[1] | Literal["foo"]` is not callable"
-reveal_type(x)  # revealed: Unknown
+    x = f()  # error: "Object of type `Literal[1] | Literal["foo"]` is not callable"
+    reveal_type(x)  # revealed: Unknown
 ```

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

@@ -3,38 +3,31 @@
 ```py
 class A: ...
 
-def get_a() -> A: ...
-def get_object() -> object: ...
+def _(a1: A, a2: A, o: object):
+    n1 = None
+    n2 = None
 
-a1 = get_a()
-a2 = get_a()
+    reveal_type(a1 is a1)  # revealed: bool
+    reveal_type(a1 is a2)  # revealed: bool
 
-n1 = None
-n2 = None
+    reveal_type(n1 is n1)  # revealed: Literal[True]
+    reveal_type(n1 is n2)  # revealed: Literal[True]
 
-o = get_object()
+    reveal_type(a1 is n1)  # revealed: Literal[False]
+    reveal_type(n1 is a1)  # revealed: Literal[False]
 
-reveal_type(a1 is a1)  # revealed: bool
-reveal_type(a1 is a2)  # revealed: bool
+    reveal_type(a1 is o)  # revealed: bool
+    reveal_type(n1 is o)  # revealed: bool
 
-reveal_type(n1 is n1)  # revealed: Literal[True]
-reveal_type(n1 is n2)  # revealed: Literal[True]
+    reveal_type(a1 is not a1)  # revealed: bool
+    reveal_type(a1 is not a2)  # revealed: bool
 
-reveal_type(a1 is n1)  # revealed: Literal[False]
-reveal_type(n1 is a1)  # revealed: Literal[False]
+    reveal_type(n1 is not n1)  # revealed: Literal[False]
+    reveal_type(n1 is not n2)  # revealed: Literal[False]
 
-reveal_type(a1 is o)  # revealed: bool
-reveal_type(n1 is o)  # revealed: bool
+    reveal_type(a1 is not n1)  # revealed: Literal[True]
+    reveal_type(n1 is not a1)  # revealed: Literal[True]
 
-reveal_type(a1 is not a1)  # revealed: bool
-reveal_type(a1 is not a2)  # revealed: bool
-
-reveal_type(n1 is not n1)  # revealed: Literal[False]
-reveal_type(n1 is not n2)  # revealed: Literal[False]
-
-reveal_type(a1 is not n1)  # revealed: Literal[True]
-reveal_type(n1 is not a1)  # revealed: Literal[True]
-
-reveal_type(a1 is not o)  # revealed: bool
-reveal_type(n1 is not o)  # revealed: bool
+    reveal_type(a1 is not o)  # revealed: bool
+    reveal_type(n1 is not o)  # revealed: bool
 ```

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

@@ -312,17 +312,9 @@ reveal_type(1 <= 2j)  # revealed: bool
 reveal_type(1 > 2j)  # revealed: bool
 reveal_type(1 >= 2j)  # revealed: bool
 
-def bool_instance() -> bool:
-    return True
-
-def int_instance() -> int:
-    return 42
-
-x = bool_instance()
-y = int_instance()
-
-reveal_type(x < y)  # revealed: bool
-reveal_type(y < x)  # revealed: bool
-reveal_type(4.2 < x)  # revealed: bool
-reveal_type(x < 4.2)  # revealed: bool
+def f(x: bool, y: int):
+    reveal_type(x < y)  # revealed: bool
+    reveal_type(y < x)  # revealed: bool
+    reveal_type(4.2 < x)  # revealed: bool
+    reveal_type(x < 4.2)  # revealed: bool
 ```

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

@@ -20,10 +20,8 @@ reveal_type(1 <= "" and 0 < 1)  # revealed: bool
 
 ```py
 # TODO: implement lookup of `__eq__` on typeshed `int` stub.
-def int_instance() -> int:
-    return 42
-
-reveal_type(1 == int_instance())  # revealed: bool
-reveal_type(9 < int_instance())  # revealed: bool
-reveal_type(int_instance() < int_instance())  # revealed: bool
+def _(a: int, b: int):
+    reveal_type(1 == a)  # revealed: bool
+    reveal_type(9 < a)  # revealed: bool
+    reveal_type(a < b)  # revealed: bool
 ```

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

@@ -14,21 +14,19 @@ class Child1(Base):
 
 class Child2(Base): ...
 
-def get_base() -> Base: ...
+def _(x: Base):
+    c1 = Child1()
 
-x = get_base()
-c1 = Child1()
+    # Create an intersection type through narrowing:
+    if isinstance(x, Child1):
+        if isinstance(x, Child2):
+            reveal_type(x)  # revealed: Child1 & Child2
 
-# Create an intersection type through narrowing:
-if isinstance(x, Child1):
-    if isinstance(x, Child2):
-        reveal_type(x)  # revealed: Child1 & Child2
+            reveal_type(x == 1)  # revealed: Literal[True]
 
-        reveal_type(x == 1)  # revealed: Literal[True]
-
-        # Other comparison operators fall back to the base type:
-        reveal_type(x > 1)  # revealed: bool
-        reveal_type(x is c1)  # revealed: bool
+            # Other comparison operators fall back to the base type:
+            reveal_type(x > 1)  # revealed: bool
+            reveal_type(x is c1)  # revealed: bool
 ```
 
 ## Negative contributions
@@ -73,18 +71,15 @@ if x != "abc":
 #### Integers
 
 ```py
-def get_int() -> int: ...
+def _(x: int):
+    if x != 1:
+        reveal_type(x)  # revealed: int & ~Literal[1]
 
-x = get_int()
+        reveal_type(x != 1)  # revealed: Literal[True]
+        reveal_type(x != 2)  # revealed: bool
 
-if x != 1:
-    reveal_type(x)  # revealed: int & ~Literal[1]
-
-    reveal_type(x != 1)  # revealed: Literal[True]
-    reveal_type(x != 2)  # revealed: bool
-
-    reveal_type(x == 1)  # revealed: Literal[False]
-    reveal_type(x == 2)  # revealed: bool
+        reveal_type(x == 1)  # revealed: Literal[False]
+        reveal_type(x == 2)  # revealed: bool
 ```
 
 ### Identity comparisons
@@ -92,18 +87,15 @@ if x != 1:
 ```py
 class A: ...
 
-def get_object() -> object: ...
+def _(o: object):
+    a = A()
+    n = None
 
-o = object()
+    if o is not None:
+        reveal_type(o)  # revealed: object & ~None
 
-a = A()
-n = None
-
-if o is not None:
-    reveal_type(o)  # revealed: object & ~None
-
-    reveal_type(o is n)  # revealed: Literal[False]
-    reveal_type(o is not n)  # revealed: Literal[True]
+        reveal_type(o is n)  # revealed: Literal[False]
+        reveal_type(o is not n)  # revealed: Literal[True]
 ```
 
 ## Diagnostics
@@ -119,16 +111,13 @@ class Container:
 
 class NonContainer: ...
 
-def get_object() -> object: ...
+def _(x: object):
+    if isinstance(x, Container):
+        if isinstance(x, NonContainer):
+            reveal_type(x)  # revealed: Container & NonContainer
 
-x = get_object()
-
-if isinstance(x, Container):
-    if isinstance(x, NonContainer):
-        reveal_type(x)  # revealed: Container & NonContainer
-
-        # error: [unsupported-operator] "Operator `in` is not supported for types `int` and `NonContainer`"
-        reveal_type(2 in x)  # revealed: bool
+            # error: [unsupported-operator] "Operator `in` is not supported for types `int` and `NonContainer`"
+            reveal_type(2 in x)  # revealed: bool
 ```
 
 ### Unsupported operators for negative contributions
@@ -142,14 +131,11 @@ class Container:
 
 class NonContainer: ...
 
-def get_object() -> object: ...
+def _(x: object):
+    if isinstance(x, Container):
+        if not isinstance(x, NonContainer):
+            reveal_type(x)  # revealed: Container & ~NonContainer
 
-x = get_object()
-
-if isinstance(x, Container):
-    if not isinstance(x, NonContainer):
-        reveal_type(x)  # revealed: Container & ~NonContainer
-
-        # No error here!
-        reveal_type(2 in x)  # revealed: bool
+            # No error here!
+            reveal_type(2 in x)  # revealed: bool
 ```

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

@@ -3,18 +3,17 @@
 ## String literals
 
 ```py
-def str_instance() -> str: ...
+def _(x: str):
+    reveal_type("abc" == "abc")  # revealed: Literal[True]
+    reveal_type("ab_cd" <= "ab_ce")  # revealed: Literal[True]
+    reveal_type("abc" in "ab cd")  # revealed: Literal[False]
+    reveal_type("" not in "hello")  # revealed: Literal[False]
+    reveal_type("--" is "--")  # revealed: bool
+    reveal_type("A" is "B")  # revealed: Literal[False]
+    reveal_type("--" is not "--")  # revealed: bool
+    reveal_type("A" is not "B")  # revealed: Literal[True]
+    reveal_type(x < "...")  # revealed: bool
 
-reveal_type("abc" == "abc")  # revealed: Literal[True]
-reveal_type("ab_cd" <= "ab_ce")  # revealed: Literal[True]
-reveal_type("abc" in "ab cd")  # revealed: Literal[False]
-reveal_type("" not in "hello")  # revealed: Literal[False]
-reveal_type("--" is "--")  # revealed: bool
-reveal_type("A" is "B")  # revealed: Literal[False]
-reveal_type("--" is not "--")  # revealed: bool
-reveal_type("A" is not "B")  # revealed: Literal[True]
-reveal_type(str_instance() < "...")  # revealed: bool
-
-# ensure we're not comparing the interned salsa symbols, which compare by order of declaration.
-reveal_type("ab" < "ab_cd")  # revealed: Literal[True]
+    # ensure we're not comparing the interned salsa symbols, which compare by order of declaration.
+    reveal_type("ab" < "ab_cd")  # revealed: Literal[True]
 ```

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

@@ -58,28 +58,23 @@ reveal_type(c >= d)  # revealed: Literal[True]
 #### Results with Ambiguity
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(x: bool, y: int):
+    a = (x,)
+    b = (y,)
 
-def int_instance() -> int:
-    return 42
+    reveal_type(a == a)  # revealed: bool
+    reveal_type(a != a)  # revealed: bool
+    reveal_type(a < a)  # revealed: bool
+    reveal_type(a <= a)  # revealed: bool
+    reveal_type(a > a)  # revealed: bool
+    reveal_type(a >= a)  # revealed: bool
 
-a = (bool_instance(),)
-b = (int_instance(),)
-
-reveal_type(a == a)  # revealed: bool
-reveal_type(a != a)  # revealed: bool
-reveal_type(a < a)  # revealed: bool
-reveal_type(a <= a)  # revealed: bool
-reveal_type(a > a)  # revealed: bool
-reveal_type(a >= a)  # revealed: bool
-
-reveal_type(a == b)  # revealed: bool
-reveal_type(a != b)  # revealed: bool
-reveal_type(a < b)  # revealed: bool
-reveal_type(a <= b)  # revealed: bool
-reveal_type(a > b)  # revealed: bool
-reveal_type(a >= b)  # revealed: bool
+    reveal_type(a == b)  # revealed: bool
+    reveal_type(a != b)  # revealed: bool
+    reveal_type(a < b)  # revealed: bool
+    reveal_type(a <= b)  # revealed: bool
+    reveal_type(a > b)  # revealed: bool
+    reveal_type(a >= b)  # revealed: bool
 ```
 
 #### Comparison Unsupported
@@ -197,7 +192,7 @@ reveal_type((A(), B()) < (A(), B()))  # revealed: float | set | Literal[False]
 
 #### Special Handling of Eq and NotEq in Lexicographic Comparisons
 
-> Example: `(int_instance(), "foo") == (int_instance(), "bar")`
+> Example: `(<int instance>, "foo") == (<int instance>, "bar")`
 
 `Eq` and `NotEq` have unique behavior compared to other operators in lexicographic comparisons.
 Specifically, for `Eq`, if any non-equal pair exists within the tuples being compared, we can
@@ -208,42 +203,38 @@ In contrast, with operators like `<` and `>`, the comparison must consider each
 sequentially, and the final outcome might remain ambiguous until all pairs are compared.
 
 ```py
-def str_instance() -> str:
-    return "hello"
+def _(x: str, y: int):
+    reveal_type("foo" == "bar")  # revealed: Literal[False]
+    reveal_type(("foo",) == ("bar",))  # revealed: Literal[False]
+    reveal_type((4, "foo") == (4, "bar"))  # revealed: Literal[False]
+    reveal_type((y, "foo") == (y, "bar"))  # revealed: Literal[False]
 
-def int_instance() -> int:
-    return 42
+    a = (x, y, "foo")
 
-reveal_type("foo" == "bar")  # revealed: Literal[False]
-reveal_type(("foo",) == ("bar",))  # revealed: Literal[False]
-reveal_type((4, "foo") == (4, "bar"))  # revealed: Literal[False]
-reveal_type((int_instance(), "foo") == (int_instance(), "bar"))  # revealed: Literal[False]
+    reveal_type(a == a)  # revealed: bool
+    reveal_type(a != a)  # revealed: bool
+    reveal_type(a < a)  # revealed: bool
+    reveal_type(a <= a)  # revealed: bool
+    reveal_type(a > a)  # revealed: bool
+    reveal_type(a >= a)  # revealed: bool
 
-a = (str_instance(), int_instance(), "foo")
+    b = (x, y, "bar")
 
-reveal_type(a == a)  # revealed: bool
-reveal_type(a != a)  # revealed: bool
-reveal_type(a < a)  # revealed: bool
-reveal_type(a <= a)  # revealed: bool
-reveal_type(a > a)  # revealed: bool
-reveal_type(a >= a)  # revealed: bool
+    reveal_type(a == b)  # revealed: Literal[False]
+    reveal_type(a != b)  # revealed: Literal[True]
+    reveal_type(a < b)  # revealed: bool
+    reveal_type(a <= b)  # revealed: bool
+    reveal_type(a > b)  # revealed: bool
+    reveal_type(a >= b)  # revealed: bool
 
-b = (str_instance(), int_instance(), "bar")
+    c = (x, y, "foo", "different_length")
 
-reveal_type(a == b)  # revealed: Literal[False]
-reveal_type(a != b)  # revealed: Literal[True]
-reveal_type(a < b)  # revealed: bool
-reveal_type(a <= b)  # revealed: bool
-reveal_type(a > b)  # revealed: bool
-reveal_type(a >= b)  # revealed: bool
-
-c = (str_instance(), int_instance(), "foo", "different_length")
-reveal_type(a == c)  # revealed: Literal[False]
-reveal_type(a != c)  # revealed: Literal[True]
-reveal_type(a < c)  # revealed: bool
-reveal_type(a <= c)  # revealed: bool
-reveal_type(a > c)  # revealed: bool
-reveal_type(a >= c)  # revealed: bool
+    reveal_type(a == c)  # revealed: Literal[False]
+    reveal_type(a != c)  # revealed: Literal[True]
+    reveal_type(a < c)  # revealed: bool
+    reveal_type(a <= c)  # revealed: bool
+    reveal_type(a > c)  # revealed: bool
+    reveal_type(a >= c)  # revealed: bool
 ```
 
 #### Error Propagation
@@ -252,42 +243,36 @@ Errors occurring within a tuple comparison should propagate outward. However, if
 comparison can clearly conclude before encountering an error, the error should not be raised.
 
 ```py
-def int_instance() -> int:
-    return 42
+def _(n: int, s: str):
+    class A: ...
+    # error: [unsupported-operator] "Operator `<` is not supported for types `A` and `A`"
+    A() < A()
+    # error: [unsupported-operator] "Operator `<=` is not supported for types `A` and `A`"
+    A() <= A()
+    # error: [unsupported-operator] "Operator `>` is not supported for types `A` and `A`"
+    A() > A()
+    # error: [unsupported-operator] "Operator `>=` is not supported for types `A` and `A`"
+    A() >= A()
 
-def str_instance() -> str:
-    return "hello"
+    a = (0, n, A())
 
-class A: ...
+    # error: [unsupported-operator] "Operator `<` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
+    reveal_type(a < a)  # revealed: Unknown
+    # error: [unsupported-operator] "Operator `<=` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
+    reveal_type(a <= a)  # revealed: Unknown
+    # error: [unsupported-operator] "Operator `>` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
+    reveal_type(a > a)  # revealed: Unknown
+    # error: [unsupported-operator] "Operator `>=` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
+    reveal_type(a >= a)  # revealed: Unknown
 
-# error: [unsupported-operator] "Operator `<` is not supported for types `A` and `A`"
-A() < A()
-# error: [unsupported-operator] "Operator `<=` is not supported for types `A` and `A`"
-A() <= A()
-# error: [unsupported-operator] "Operator `>` is not supported for types `A` and `A`"
-A() > A()
-# error: [unsupported-operator] "Operator `>=` is not supported for types `A` and `A`"
-A() >= A()
+    # Comparison between `a` and `b` should only involve the first elements, `Literal[0]` and `Literal[99999]`,
+    # and should terminate immediately.
+    b = (99999, n, A())
 
-a = (0, int_instance(), A())
-
-# error: [unsupported-operator] "Operator `<` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
-reveal_type(a < a)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `<=` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
-reveal_type(a <= a)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `>` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
-reveal_type(a > a)  # revealed: Unknown
-# error: [unsupported-operator] "Operator `>=` is not supported for types `A` and `A`, in comparing `tuple[Literal[0], int, A]` with `tuple[Literal[0], int, A]`"
-reveal_type(a >= a)  # revealed: Unknown
-
-# Comparison between `a` and `b` should only involve the first elements, `Literal[0]` and `Literal[99999]`,
-# and should terminate immediately.
-b = (99999, int_instance(), A())
-
-reveal_type(a < b)  # revealed: Literal[True]
-reveal_type(a <= b)  # revealed: Literal[True]
-reveal_type(a > b)  # revealed: Literal[False]
-reveal_type(a >= b)  # revealed: Literal[False]
+    reveal_type(a < b)  # revealed: Literal[True]
+    reveal_type(a <= b)  # revealed: Literal[True]
+    reveal_type(a > b)  # revealed: Literal[False]
+    reveal_type(a >= b)  # revealed: Literal[False]
 ```
 
 ### Membership Test Comparisons
@@ -295,22 +280,20 @@ reveal_type(a >= b)  # revealed: Literal[False]
 "Membership Test Comparisons" refers to the operators `in` and `not in`.
 
 ```py
-def int_instance() -> int:
-    return 42
+def _(n: int):
+    a = (1, 2)
+    b = ((3, 4), (1, 2))
+    c = ((1, 2, 3), (4, 5, 6))
+    d = ((n, n), (n, n))
 
-a = (1, 2)
-b = ((3, 4), (1, 2))
-c = ((1, 2, 3), (4, 5, 6))
-d = ((int_instance(), int_instance()), (int_instance(), int_instance()))
+    reveal_type(a in b)  # revealed: Literal[True]
+    reveal_type(a not in b)  # revealed: Literal[False]
 
-reveal_type(a in b)  # revealed: Literal[True]
-reveal_type(a not in b)  # revealed: Literal[False]
+    reveal_type(a in c)  # revealed: Literal[False]
+    reveal_type(a not in c)  # revealed: Literal[True]
 
-reveal_type(a in c)  # revealed: Literal[False]
-reveal_type(a not in c)  # revealed: Literal[True]
-
-reveal_type(a in d)  # revealed: bool
-reveal_type(a not in d)  # revealed: bool
+    reveal_type(a in d)  # revealed: bool
+    reveal_type(a not in d)  # revealed: bool
 ```
 
 ### Identity Comparisons

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

@@ -5,49 +5,46 @@
 Comparisons on union types need to consider all possible cases:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    one_or_two = 1 if flag else 2
 
-flag = bool_instance()
-one_or_two = 1 if flag else 2
+    reveal_type(one_or_two <= 2)  # revealed: Literal[True]
+    reveal_type(one_or_two <= 1)  # revealed: bool
+    reveal_type(one_or_two <= 0)  # revealed: Literal[False]
 
-reveal_type(one_or_two <= 2)  # revealed: Literal[True]
-reveal_type(one_or_two <= 1)  # revealed: bool
-reveal_type(one_or_two <= 0)  # revealed: Literal[False]
+    reveal_type(2 >= one_or_two)  # revealed: Literal[True]
+    reveal_type(1 >= one_or_two)  # revealed: bool
+    reveal_type(0 >= one_or_two)  # revealed: Literal[False]
 
-reveal_type(2 >= one_or_two)  # revealed: Literal[True]
-reveal_type(1 >= one_or_two)  # revealed: bool
-reveal_type(0 >= one_or_two)  # revealed: Literal[False]
+    reveal_type(one_or_two < 1)  # revealed: Literal[False]
+    reveal_type(one_or_two < 2)  # revealed: bool
+    reveal_type(one_or_two < 3)  # revealed: Literal[True]
 
-reveal_type(one_or_two < 1)  # revealed: Literal[False]
-reveal_type(one_or_two < 2)  # revealed: bool
-reveal_type(one_or_two < 3)  # revealed: Literal[True]
+    reveal_type(one_or_two > 0)  # revealed: Literal[True]
+    reveal_type(one_or_two > 1)  # revealed: bool
+    reveal_type(one_or_two > 2)  # revealed: Literal[False]
 
-reveal_type(one_or_two > 0)  # revealed: Literal[True]
-reveal_type(one_or_two > 1)  # revealed: bool
-reveal_type(one_or_two > 2)  # revealed: Literal[False]
+    reveal_type(one_or_two == 3)  # revealed: Literal[False]
+    reveal_type(one_or_two == 1)  # revealed: bool
 
-reveal_type(one_or_two == 3)  # revealed: Literal[False]
-reveal_type(one_or_two == 1)  # revealed: bool
+    reveal_type(one_or_two != 3)  # revealed: Literal[True]
+    reveal_type(one_or_two != 1)  # revealed: bool
 
-reveal_type(one_or_two != 3)  # revealed: Literal[True]
-reveal_type(one_or_two != 1)  # revealed: bool
+    a_or_ab = "a" if flag else "ab"
 
-a_or_ab = "a" if flag else "ab"
+    reveal_type(a_or_ab in "ab")  # revealed: Literal[True]
+    reveal_type("a" in a_or_ab)  # revealed: Literal[True]
 
-reveal_type(a_or_ab in "ab")  # revealed: Literal[True]
-reveal_type("a" in a_or_ab)  # revealed: Literal[True]
+    reveal_type("c" not in a_or_ab)  # revealed: Literal[True]
+    reveal_type("a" not in a_or_ab)  # revealed: Literal[False]
 
-reveal_type("c" not in a_or_ab)  # revealed: Literal[True]
-reveal_type("a" not in a_or_ab)  # revealed: Literal[False]
+    reveal_type("b" in a_or_ab)  # revealed: bool
+    reveal_type("b" not in a_or_ab)  # revealed: bool
 
-reveal_type("b" in a_or_ab)  # revealed: bool
-reveal_type("b" not in a_or_ab)  # revealed: bool
+    one_or_none = 1 if flag else None
 
-one_or_none = 1 if flag else None
-
-reveal_type(one_or_none is None)  # revealed: bool
-reveal_type(one_or_none is not None)  # revealed: bool
+    reveal_type(one_or_none is None)  # revealed: bool
+    reveal_type(one_or_none is not None)  # revealed: bool
 ```
 
 ## Union on both sides of the comparison
@@ -56,18 +53,15 @@ With unions on both sides, we need to consider the full cross product of options
 resulting (union) type:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag_s: bool, flag_l: bool):
+    small = 1 if flag_s else 2
+    large = 2 if flag_l else 3
 
-flag_s, flag_l = bool_instance(), bool_instance()
-small = 1 if flag_s else 2
-large = 2 if flag_l else 3
+    reveal_type(small <= large)  # revealed: Literal[True]
+    reveal_type(small >= large)  # revealed: bool
 
-reveal_type(small <= large)  # revealed: Literal[True]
-reveal_type(small >= large)  # revealed: bool
-
-reveal_type(small < large)  # revealed: bool
-reveal_type(small > large)  # revealed: Literal[False]
+    reveal_type(small < large)  # revealed: bool
+    reveal_type(small > large)  # revealed: Literal[False]
 ```
 
 ## Unsupported operations
@@ -77,12 +71,9 @@ back to `bool` for the result type instead of trying to infer something more pre
 (supported) variants:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = [1, 2] if flag else 1
 
-flag = bool_instance()
-x = [1, 2] if flag else 1
-
-result = 1 in x  # error: "Operator `in` is not supported"
-reveal_type(result)  # revealed: bool
+    result = 1 in x  # error: "Operator `in` is not supported"
+    reveal_type(result)  # revealed: bool
 ```

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

@@ -1,42 +1,38 @@
 # Comparison: Unsupported operators
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag1: bool, flag2: bool):
+    class A: ...
+    a = 1 in 7  # error: "Operator `in` is not supported for types `Literal[1]` and `Literal[7]`"
+    reveal_type(a)  # revealed: bool
 
-class A: ...
+    b = 0 not in 10  # error: "Operator `not in` is not supported for types `Literal[0]` and `Literal[10]`"
+    reveal_type(b)  # revealed: bool
 
-a = 1 in 7  # error: "Operator `in` is not supported for types `Literal[1]` and `Literal[7]`"
-reveal_type(a)  # revealed: bool
+    # TODO: should error, once operand type check is implemented
+    # ("Operator `<` is not supported for types `object` and `int`")
+    c = object() < 5
+    # TODO: should be Unknown, once operand type check is implemented
+    reveal_type(c)  # revealed: bool
 
-b = 0 not in 10  # error: "Operator `not in` is not supported for types `Literal[0]` and `Literal[10]`"
-reveal_type(b)  # revealed: bool
+    # TODO: should error, once operand type check is implemented
+    # ("Operator `<` is not supported for types `int` and `object`")
+    d = 5 < object()
+    # TODO: should be Unknown, once operand type check is implemented
+    reveal_type(d)  # revealed: bool
 
-# TODO: should error, once operand type check is implemented
-# ("Operator `<` is not supported for types `object` and `int`")
-c = object() < 5
-# TODO: should be Unknown, once operand type check is implemented
-reveal_type(c)  # 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"]`"
+    e = 42 in int_literal_or_str_literal
+    reveal_type(e)  # revealed: bool
 
-# TODO: should error, once operand type check is implemented
-# ("Operator `<` is not supported for types `int` and `object`")
-d = 5 < object()
-# TODO: should be Unknown, once operand type check is implemented
-reveal_type(d)  # revealed: bool
+    # TODO: should error, need to check if __lt__ signature is valid for right operand
+    # error may be "Operator `<` is not supported for types `int` and `str`, in comparing `tuple[Literal[1], Literal[2]]` with `tuple[Literal[1], Literal["hello"]]`
+    f = (1, 2) < (1, "hello")
+    # TODO: should be Unknown, once operand type check is implemented
+    reveal_type(f)  # revealed: bool
 
-flag = bool_instance()
-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"]`"
-e = 42 in int_literal_or_str_literal
-reveal_type(e)  # revealed: bool
-
-# TODO: should error, need to check if __lt__ signature is valid for right operand
-# error may be "Operator `<` is not supported for types `int` and `str`, in comparing `tuple[Literal[1], Literal[2]]` with `tuple[Literal[1], Literal["hello"]]`
-f = (1, 2) < (1, "hello")
-# TODO: should be Unknown, once operand type check is implemented
-reveal_type(f)  # revealed: bool
-
-# error: [unsupported-operator] "Operator `<` is not supported for types `A` and `A`, in comparing `tuple[bool, A]` with `tuple[bool, A]`"
-g = (bool_instance(), A()) < (bool_instance(), A())
-reveal_type(g)  # revealed: Unknown
+    # error: [unsupported-operator] "Operator `<` is not supported for types `A` and `A`, in comparing `tuple[bool, A]` with `tuple[bool, A]`"
+    g = (flag1, A()) < (flag2, A())
+    reveal_type(g)  # revealed: Unknown
 ```

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

@@ -3,47 +3,35 @@
 ## Simple if-expression
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-x = 1 if flag else 2
-reveal_type(x)  # revealed: Literal[1, 2]
+def _(flag: bool):
+    x = 1 if flag else 2
+    reveal_type(x)  # revealed: Literal[1, 2]
 ```
 
 ## If-expression with walrus operator
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-y = 0
-z = 0
-x = (y := 1) if flag else (z := 2)
-reveal_type(x)  # revealed: Literal[1, 2]
-reveal_type(y)  # revealed: Literal[0, 1]
-reveal_type(z)  # revealed: Literal[0, 2]
+def _(flag: bool):
+    y = 0
+    z = 0
+    x = (y := 1) if flag else (z := 2)
+    reveal_type(x)  # revealed: Literal[1, 2]
+    reveal_type(y)  # revealed: Literal[0, 1]
+    reveal_type(z)  # revealed: Literal[0, 2]
 ```
 
 ## Nested if-expression
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-flag, flag2 = bool_instance(), bool_instance()
-x = 1 if flag else 2 if flag2 else 3
-reveal_type(x)  # revealed: Literal[1, 2, 3]
+def _(flag: bool, flag2: bool):
+    x = 1 if flag else 2 if flag2 else 3
+    reveal_type(x)  # revealed: Literal[1, 2, 3]
 ```
 
 ## None
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-x = 1 if flag else None
-reveal_type(x)  # revealed: Literal[1] | None
+def _(flag: bool):
+    x = 1 if flag else None
+    reveal_type(x)  # revealed: Literal[1] | None
 ```

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

@@ -3,128 +3,115 @@
 ## Simple if
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    y = 1
+    y = 2
 
-flag = bool_instance()
-y = 1
-y = 2
+    if flag:
+        y = 3
 
-if flag:
-    y = 3
-
-reveal_type(y)  # revealed: Literal[2, 3]
+    reveal_type(y)  # revealed: Literal[2, 3]
 ```
 
 ## Simple if-elif-else
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag2: bool):
+    y = 1
+    y = 2
 
-flag, flag2 = bool_instance(), bool_instance()
-y = 1
-y = 2
-if flag:
-    y = 3
-elif flag2:
-    y = 4
-else:
-    r = y
-    y = 5
-    s = y
-x = y
+    if flag:
+        y = 3
+    elif flag2:
+        y = 4
+    else:
+        r = y
+        y = 5
+        s = y
+    x = y
 
-reveal_type(x)  # revealed: Literal[3, 4, 5]
+    reveal_type(x)  # revealed: Literal[3, 4, 5]
 
-# revealed: Literal[2]
-# error: [possibly-unresolved-reference]
-reveal_type(r)
+    # revealed: Literal[2]
+    # error: [possibly-unresolved-reference]
+    reveal_type(r)
 
-# revealed: Literal[5]
-# error: [possibly-unresolved-reference]
-reveal_type(s)
+    # revealed: Literal[5]
+    # error: [possibly-unresolved-reference]
+    reveal_type(s)
 ```
 
 ## Single symbol across if-elif-else
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag2: bool):
+    if flag:
+        y = 1
+    elif flag2:
+        y = 2
+    else:
+        y = 3
 
-flag, flag2 = bool_instance(), bool_instance()
-
-if flag:
-    y = 1
-elif flag2:
-    y = 2
-else:
-    y = 3
-reveal_type(y)  # revealed: Literal[1, 2, 3]
+    reveal_type(y)  # revealed: Literal[1, 2, 3]
 ```
 
 ## if-elif-else without else assignment
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag2: bool):
+    y = 0
 
-flag, flag2 = bool_instance(), bool_instance()
-y = 0
-if flag:
-    y = 1
-elif flag2:
-    y = 2
-else:
-    pass
-reveal_type(y)  # revealed: Literal[0, 1, 2]
+    if flag:
+        y = 1
+    elif flag2:
+        y = 2
+    else:
+        pass
+
+    reveal_type(y)  # revealed: Literal[0, 1, 2]
 ```
 
 ## if-elif-else with intervening assignment
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag2: bool):
+    y = 0
 
-flag, flag2 = bool_instance(), bool_instance()
-y = 0
-if flag:
-    y = 1
-    z = 3
-elif flag2:
-    y = 2
-else:
-    pass
-reveal_type(y)  # revealed: Literal[0, 1, 2]
+    if flag:
+        y = 1
+        z = 3
+    elif flag2:
+        y = 2
+    else:
+        pass
+
+    reveal_type(y)  # revealed: Literal[0, 1, 2]
 ```
 
 ## Nested if statement
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag2: bool):
+    y = 0
 
-flag, flag2 = bool_instance(), bool_instance()
-y = 0
-if flag:
-    if flag2:
-        y = 1
-reveal_type(y)  # revealed: Literal[0, 1]
+    if flag:
+        if flag2:
+            y = 1
+
+    reveal_type(y)  # revealed: Literal[0, 1]
 ```
 
 ## if-elif without else
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag2: bool):
+    y = 1
+    y = 2
 
-flag, flag2 = bool_instance(), bool_instance()
-y = 1
-y = 2
-if flag:
-    y = 3
-elif flag2:
-    y = 4
+    if flag:
+        y = 3
+    elif flag2:
+        y = 4
 
-reveal_type(y)  # revealed: Literal[2, 3, 4]
+    reveal_type(y)  # revealed: Literal[2, 3, 4]
 ```

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

@@ -31,6 +31,7 @@ reveal_type(y)
 ```py
 y = 1
 y = 2
+
 match 0:
     case 1:
         y = 3

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

@@ -10,42 +10,35 @@ x: str  # error: [invalid-declaration] "Cannot declare type `str` for inferred t
 ## Incompatible declarations
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        x: str
+    else:
+        x: int
 
-flag = bool_instance()
-if flag:
-    x: str
-else:
-    x: int
-x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: str, int"
+    x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: str, int"
 ```
 
 ## Partial declarations
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        x: int
 
-flag = bool_instance()
-if flag:
-    x: int
-x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: Unknown, int"
+    x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: Unknown, int"
 ```
 
 ## Incompatible declarations with bad assignment
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        x: str
+    else:
+        x: int
 
-flag = bool_instance()
-if flag:
-    x: str
-else:
-    x: int
-
-# error: [conflicting-declarations]
-# error: [invalid-assignment]
-x = b"foo"
+    # error: [conflicting-declarations]
+    # error: [invalid-assignment]
+    x = b"foo"
 ```

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

@@ -49,12 +49,44 @@ def foo(
     try:
         help()
     except x as e:
-        # TODO: should be `AttributeError`
-        reveal_type(e)  # revealed: @Todo(exception type)
+        reveal_type(e)  # revealed: AttributeError
     except y as f:
-        # TODO: should be `OSError | RuntimeError`
-        reveal_type(f)  # revealed: @Todo(exception type)
+        reveal_type(f)  # revealed: OSError | RuntimeError
     except z as g:
         # TODO: should be `BaseException`
-        reveal_type(g)  # revealed: @Todo(exception type)
+        reveal_type(g)  # revealed: @Todo(full tuple[...] support)
+```
+
+## Invalid exception handlers
+
+```py
+try:
+    pass
+# error: [invalid-exception-caught] "Cannot catch object of type `Literal[3]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
+except 3 as e:
+    reveal_type(e)  # revealed: Unknown
+
+try:
+    pass
+# error: [invalid-exception-caught] "Cannot catch object of type `Literal["foo"]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
+# error: [invalid-exception-caught] "Cannot catch object of type `Literal[b"bar"]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
+except (ValueError, OSError, "foo", b"bar") as e:
+    reveal_type(e)  # revealed: ValueError | OSError | Unknown
+
+def foo(
+    x: type[str],
+    y: tuple[type[OSError], type[RuntimeError], int],
+    z: tuple[type[str], ...],
+):
+    try:
+        help()
+    # error: [invalid-exception-caught]
+    except x as e:
+        reveal_type(e)  # revealed: Unknown
+    # error: [invalid-exception-caught]
+    except y as f:
+        reveal_type(f)  # revealed: OSError | RuntimeError | Unknown
+    except z as g:
+        # TODO: should emit a diagnostic here:
+        reveal_type(g)  # revealed: @Todo(full tuple[...] support)
 ```

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

@@ -1,30 +1,59 @@
-# Except star
+# `except*`
 
-## Except\* with BaseException
+## `except*` with `BaseException`
 
 ```py
 try:
     help()
 except* BaseException as e:
+    # TODO: should be `BaseExceptionGroup[BaseException]` --Alex
     reveal_type(e)  # revealed: BaseExceptionGroup
 ```
 
-## Except\* with specific exception
+## `except*` with specific exception
 
 ```py
 try:
     help()
 except* OSError as e:
-    # TODO(Alex): more precise would be `ExceptionGroup[OSError]`
+    # TODO: more precise would be `ExceptionGroup[OSError]` --Alex
+    # (needs homogenous tuples + generics)
     reveal_type(e)  # revealed: BaseExceptionGroup
 ```
 
-## Except\* with multiple exceptions
+## `except*` with multiple exceptions
 
 ```py
 try:
     help()
 except* (TypeError, AttributeError) as e:
-    # TODO(Alex): more precise would be `ExceptionGroup[TypeError | AttributeError]`.
+    # TODO: more precise would be `ExceptionGroup[TypeError | AttributeError]` --Alex
+    # (needs homogenous tuples + generics)
+    reveal_type(e)  # revealed: BaseExceptionGroup
+```
+
+## `except*` with mix of `Exception`s and `BaseException`s
+
+```py
+try:
+    help()
+except* (KeyboardInterrupt, AttributeError) as e:
+    # TODO: more precise would be `BaseExceptionGroup[KeyboardInterrupt | AttributeError]` --Alex
+    reveal_type(e)  # revealed: BaseExceptionGroup
+```
+
+## Invalid `except*` handlers
+
+```py
+try:
+    help()
+except* 3 as e:  # error: [invalid-exception-caught]
+    # TODO: Should be `BaseExceptionGroup[Unknown]` --Alex
+    reveal_type(e)  # revealed: BaseExceptionGroup
+
+try:
+    help()
+except* (AttributeError, 42) as e:  # error: [invalid-exception-caught]
+    # TODO: Should be `BaseExceptionGroup[AttributeError | Unknown]` --Alex
     reveal_type(e)  # revealed: BaseExceptionGroup
 ```

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

@@ -9,5 +9,4 @@ try:
     print
 except as e:  # error: [invalid-syntax]
     reveal_type(e)  # revealed: Unknown
-
 ```

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

@@ -3,26 +3,25 @@
 ## Boundness
 
 ```py
-def flag() -> bool: ...
+def _(flag: bool):
+    class A:
+        always_bound = 1
 
-class A:
-    always_bound = 1
+        if flag:
+            union = 1
+        else:
+            union = "abc"
 
-    if flag():
-        union = 1
-    else:
-        union = "abc"
+        if flag:
+            possibly_unbound = "abc"
 
-    if flag():
-        possibly_unbound = "abc"
+    reveal_type(A.always_bound)  # revealed: Literal[1]
 
-reveal_type(A.always_bound)  # revealed: Literal[1]
+    reveal_type(A.union)  # revealed: Literal[1] | Literal["abc"]
 
-reveal_type(A.union)  # revealed: Literal[1] | Literal["abc"]
+    # error: [possibly-unbound-attribute] "Attribute `possibly_unbound` on type `Literal[A]` is possibly unbound"
+    reveal_type(A.possibly_unbound)  # revealed: Literal["abc"]
 
-# error: [possibly-unbound-attribute] "Attribute `possibly_unbound` on type `Literal[A]` is possibly unbound"
-reveal_type(A.possibly_unbound)  # revealed: Literal["abc"]
-
-# error: [unresolved-attribute] "Type `Literal[A]` has no attribute `non_existent`"
-reveal_type(A.non_existent)  # revealed: Unknown
+    # error: [unresolved-attribute] "Type `Literal[A]` has no attribute `non_existent`"
+    reveal_type(A.non_existent)  # revealed: Unknown
 ```

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

@@ -3,54 +3,45 @@
 ## OR
 
 ```py
-def foo() -> str:
-    pass
-
-reveal_type(True or False)  # revealed: Literal[True]
-reveal_type("x" or "y" or "z")  # revealed: Literal["x"]
-reveal_type("" or "y" or "z")  # revealed: Literal["y"]
-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]
+def _(foo: str):
+    reveal_type(True or False)  # revealed: Literal[True]
+    reveal_type("x" or "y" or "z")  # revealed: Literal["x"]
+    reveal_type("" or "y" or "z")  # revealed: Literal["y"]
+    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]
 ```
 
 ## AND
 
 ```py
-def foo() -> str:
-    pass
-
-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("x" and "y" and "z")  # revealed: Literal["z"]
-reveal_type("x" and "y" and "")  # revealed: Literal[""]
-reveal_type("" and "y")  # revealed: Literal[""]
+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("x" and "y" and "z")  # revealed: Literal["z"]
+    reveal_type("x" and "y" and "")  # revealed: Literal[""]
+    reveal_type("" and "y")  # revealed: Literal[""]
 ```
 
 ## Simple function calls to bool
 
 ```py
-def returns_bool() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        x = True
+    else:
+        x = False
 
-if returns_bool():
-    x = True
-else:
-    x = False
-
-reveal_type(x)  # revealed: bool
+    reveal_type(x)  # revealed: bool
 ```
 
 ## Complex
 
 ```py
-def foo() -> str:
-    pass
-
 reveal_type("x" and "y" or "z")  # revealed: Literal["y"]
 reveal_type("x" or "y" and "z")  # revealed: Literal["x"]
 reveal_type("" and "y" or "z")  # revealed: Literal["z"]

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

@@ -3,10 +3,8 @@
 ## Union
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-reveal_type(1 if bool_instance() else 2)  # revealed: Literal[1, 2]
+def _(flag: bool):
+    reveal_type(1 if flag else 2)  # revealed: Literal[1, 2]
 ```
 
 ## Statically known branches
@@ -30,14 +28,12 @@ reveal_type(1 if 0 else 2)  # revealed: Literal[2]
 The test inside an if expression should not affect code outside of the expression.
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x: Literal[42, "hello"] = 42 if flag else "hello"
 
-x: Literal[42, "hello"] = 42 if bool_instance() else "hello"
+    reveal_type(x)  # revealed: Literal[42] | Literal["hello"]
 
-reveal_type(x)  # revealed: Literal[42] | Literal["hello"]
+    _ = ... if isinstance(x, str) else ...
 
-_ = ... if isinstance(x, str) else ...
-
-reveal_type(x)  # revealed: Literal[42] | Literal["hello"]
+    reveal_type(x)  # revealed: Literal[42] | Literal["hello"]
 ```

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

@@ -211,8 +211,7 @@ reveal_type(len(SecondRequiredArgument()))  # revealed: Literal[1]
 ### No `__len__`
 
 ```py
-class NoDunderLen:
-    pass
+class NoDunderLen: ...
 
 # TODO: Emit a diagnostic
 reveal_type(len(NoDunderLen()))  # revealed: int

crates/red_knot_python_semantic/resources/mdtest/generics.md

@@ -73,7 +73,7 @@ def f[T]():
 A typevar with less than two constraints emits a diagnostic:
 
 ```py
-# error: [invalid-typevar-constraints] "TypeVar must have at least two constrained types"
+# error: [invalid-type-variable-constraints] "TypeVar must have at least two constrained types"
 def f[T: (int,)]():
     pass
 ```

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

@@ -3,11 +3,10 @@
 ## Maybe unbound
 
 ```py path=maybe_unbound.py
-def bool_instance() -> bool:
+def coinflip() -> bool:
     return True
 
-flag = bool_instance()
-if flag:
+if coinflip():
     y = 3
 
 x = y  # error: [possibly-unresolved-reference]
@@ -31,13 +30,12 @@ reveal_type(y)  # revealed: Literal[3]
 ## Maybe unbound annotated
 
 ```py path=maybe_unbound_annotated.py
-def bool_instance() -> bool:
+def coinflip() -> bool:
     return True
 
-flag = bool_instance()
-
-if flag:
+if coinflip():
     y: int = 3
+
 x = y  # error: [possibly-unresolved-reference]
 
 # revealed: Literal[3]
@@ -63,10 +61,10 @@ reveal_type(y)  # revealed: int
 Importing a possibly undeclared name still gives us its declared type:
 
 ```py path=maybe_undeclared.py
-def bool_instance() -> bool:
+def coinflip() -> bool:
     return True
 
-if bool_instance():
+if coinflip():
     x: int
 ```
 
@@ -83,14 +81,12 @@ def f(): ...
 ```
 
 ```py path=b.py
-def bool_instance() -> bool:
+def coinflip() -> bool:
     return True
 
-flag = bool_instance()
-if flag:
+if coinflip():
     from c import f
 else:
-
     def f(): ...
 ```
 
@@ -111,11 +107,10 @@ x: int
 ```
 
 ```py path=b.py
-def bool_instance() -> bool:
+def coinflip() -> bool:
     return True
 
-flag = bool_instance()
-if flag:
+if coinflip():
     from c import x
 else:
     x = 1

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

@@ -106,23 +106,19 @@ reveal_type(x)
 ## With non-callable iterator
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class NotIterable:
+        if flag:
+            __iter__ = 1
+        else:
+            __iter__ = None
 
-flag = bool_instance()
+    for x in NotIterable():  # error: "Object of type `NotIterable` is not iterable"
+        pass
 
-class NotIterable:
-    if flag:
-        __iter__ = 1
-    else:
-        __iter__ = None
-
-for x in NotIterable():  # error: "Object of type `NotIterable` is not iterable"
-    pass
-
-# revealed: Unknown
-# error: [possibly-unresolved-reference]
-reveal_type(x)
+    # revealed: Unknown
+    # error: [possibly-unresolved-reference]
+    reveal_type(x)
 ```
 
 ## Invalid iterable
@@ -160,13 +156,9 @@ class Test2:
     def __iter__(self) -> TestIter:
         return TestIter()
 
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-
-for x in Test() if flag else Test2():
-    reveal_type(x)  # revealed: int
+def _(flag: bool):
+    for x in Test() if flag else Test2():
+        reveal_type(x)  # revealed: int
 ```
 
 ## Union type as iterator
@@ -215,13 +207,9 @@ class Test2:
     def __iter__(self) -> TestIter3 | TestIter4:
         return TestIter3()
 
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-
-for x in Test() if flag else Test2():
-    reveal_type(x)  # revealed: int | Exception | str | tuple[int, int] | bytes | memoryview
+def _(flag: bool):
+    for x in Test() if flag else Test2():
+        reveal_type(x)  # revealed: int | Exception | str | tuple[int, int] | bytes | memoryview
 ```
 
 ## Union type as iterable where one union element has no `__iter__` method
@@ -235,12 +223,10 @@ class Test:
     def __iter__(self) -> TestIter:
         return TestIter()
 
-def coinflip() -> bool:
-    return True
-
-# error: [not-iterable] "Object of type `Test | Literal[42]` is not iterable because its `__iter__` method is possibly unbound"
-for x in Test() if coinflip() else 42:
-    reveal_type(x)  # revealed: int
+def _(flag: bool):
+    # error: [not-iterable] "Object of type `Test | Literal[42]` is not iterable because its `__iter__` method is possibly unbound"
+    for x in Test() if flag else 42:
+        reveal_type(x)  # revealed: int
 ```
 
 ## Union type as iterable where one union element has invalid `__iter__` method
@@ -258,12 +244,10 @@ class Test2:
     def __iter__(self) -> int:
         return 42
 
-def coinflip() -> bool:
-    return True
-
-# error: "Object of type `Test | Test2` is not iterable"
-for x in Test() if coinflip() else Test2():
-    reveal_type(x)  # revealed: Unknown
+def _(flag: bool):
+    # error: "Object of type `Test | Test2` is not iterable"
+    for x in Test() if flag else Test2():
+        reveal_type(x)  # revealed: Unknown
 ```
 
 ## Union type as iterator where one union element has no `__next__` method

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

@@ -3,54 +3,45 @@
 ## Basic While Loop
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1
+    while flag:
+        x = 2
 
-flag = bool_instance()
-x = 1
-while flag:
-    x = 2
-
-reveal_type(x)  # revealed: Literal[1, 2]
+    reveal_type(x)  # revealed: Literal[1, 2]
 ```
 
 ## While with else (no break)
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1
+    while flag:
+        x = 2
+    else:
+        reveal_type(x)  # revealed: Literal[1, 2]
+        x = 3
 
-flag = bool_instance()
-x = 1
-while flag:
-    x = 2
-else:
-    reveal_type(x)  # revealed: Literal[1, 2]
-    x = 3
-
-reveal_type(x)  # revealed: Literal[3]
+    reveal_type(x)  # revealed: Literal[3]
 ```
 
 ## While with Else (may break)
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag2: bool):
+    x = 1
+    y = 0
+    while flag:
+        x = 2
+        if flag2:
+            y = 4
+            break
+    else:
+        y = x
+        x = 3
 
-flag, flag2 = bool_instance(), bool_instance()
-x = 1
-y = 0
-while flag:
-    x = 2
-    if flag2:
-        y = 4
-        break
-else:
-    y = x
-    x = 3
-
-reveal_type(x)  # revealed: Literal[2, 3]
-reveal_type(y)  # revealed: Literal[1, 2, 4]
+    reveal_type(x)  # revealed: Literal[2, 3]
+    reveal_type(y)  # revealed: Literal[1, 2, 4]
 ```
 
 ## Nested while loops

crates/red_knot_python_semantic/resources/mdtest/metaclass.md

@@ -179,9 +179,9 @@ reveal_type(A.__class__)  # revealed: @Todo(metaclass not a class)
 Retrieving the metaclass of a cyclically defined class should not cause an infinite loop.
 
 ```py path=a.pyi
-class A(B): ...  # error: [cyclic-class-def]
-class B(C): ...  # error: [cyclic-class-def]
-class C(A): ...  # error: [cyclic-class-def]
+class A(B): ...  # error: [cyclic-class-definition]
+class B(C): ...  # error: [cyclic-class-definition]
+class C(A): ...  # error: [cyclic-class-definition]
 
 reveal_type(A.__class__)  # revealed: Unknown
 ```

crates/red_knot_python_semantic/resources/mdtest/mro.md

@@ -348,14 +348,14 @@ reveal_type(unknown_object.__mro__)  # revealed: Unknown
 These are invalid, but we need to be able to handle them gracefully without panicking.
 
 ```py path=a.pyi
-class Foo(Foo): ...  # error: [cyclic-class-def]
+class Foo(Foo): ...  # error: [cyclic-class-definition]
 
 reveal_type(Foo)  # revealed: Literal[Foo]
 reveal_type(Foo.__mro__)  # revealed: tuple[Literal[Foo], Unknown, Literal[object]]
 
 class Bar: ...
 class Baz: ...
-class Boz(Bar, Baz, Boz): ...  # error: [cyclic-class-def]
+class Boz(Bar, Baz, Boz): ...  # error: [cyclic-class-definition]
 
 reveal_type(Boz)  # revealed: Literal[Boz]
 reveal_type(Boz.__mro__)  # revealed: tuple[Literal[Boz], Unknown, Literal[object]]
@@ -366,9 +366,9 @@ reveal_type(Boz.__mro__)  # revealed: tuple[Literal[Boz], Unknown, Literal[objec
 These are similarly unlikely, but we still shouldn't crash:
 
 ```py path=a.pyi
-class Foo(Bar): ...  # error: [cyclic-class-def]
-class Bar(Baz): ...  # error: [cyclic-class-def]
-class Baz(Foo): ...  # error: [cyclic-class-def]
+class Foo(Bar): ...  # error: [cyclic-class-definition]
+class Bar(Baz): ...  # error: [cyclic-class-definition]
+class Baz(Foo): ...  # error: [cyclic-class-definition]
 
 reveal_type(Foo.__mro__)  # revealed: tuple[Literal[Foo], Unknown, Literal[object]]
 reveal_type(Bar.__mro__)  # revealed: tuple[Literal[Bar], Unknown, Literal[object]]
@@ -379,9 +379,9 @@ reveal_type(Baz.__mro__)  # revealed: tuple[Literal[Baz], Unknown, Literal[objec
 
 ```py path=a.pyi
 class Spam: ...
-class Foo(Bar): ...  # error: [cyclic-class-def]
-class Bar(Baz): ...  # error: [cyclic-class-def]
-class Baz(Foo, Spam): ...  # error: [cyclic-class-def]
+class Foo(Bar): ...  # error: [cyclic-class-definition]
+class Bar(Baz): ...  # error: [cyclic-class-definition]
+class Baz(Foo, Spam): ...  # error: [cyclic-class-definition]
 
 reveal_type(Foo.__mro__)  # revealed: tuple[Literal[Foo], Unknown, Literal[object]]
 reveal_type(Bar.__mro__)  # revealed: tuple[Literal[Bar], Unknown, Literal[object]]
@@ -391,16 +391,16 @@ reveal_type(Baz.__mro__)  # revealed: tuple[Literal[Baz], Unknown, Literal[objec
 ## Classes with cycles in their MRO, and a sub-graph
 
 ```py path=a.pyi
-class FooCycle(BarCycle): ...  # error: [cyclic-class-def]
+class FooCycle(BarCycle): ...  # error: [cyclic-class-definition]
 class Foo: ...
-class BarCycle(FooCycle): ...  # error: [cyclic-class-def]
+class BarCycle(FooCycle): ...  # error: [cyclic-class-definition]
 class Bar(Foo): ...
 
 # TODO: can we avoid emitting the errors for these?
 # The classes have cyclic superclasses,
 # but are not themselves cyclic...
-class Baz(Bar, BarCycle): ...  # error: [cyclic-class-def]
-class Spam(Baz): ...  # error: [cyclic-class-def]
+class Baz(Bar, BarCycle): ...  # error: [cyclic-class-definition]
+class Spam(Baz): ...  # error: [cyclic-class-definition]
 
 reveal_type(FooCycle.__mro__)  # revealed: tuple[Literal[FooCycle], Unknown, Literal[object]]
 reveal_type(BarCycle.__mro__)  # revealed: tuple[Literal[BarCycle], Unknown, Literal[object]]

crates/red_knot_python_semantic/resources/mdtest/narrow/bool-call.md

@@ -1,32 +1,32 @@
 ## Narrowing for `bool(..)` checks
 
 ```py
-def flag() -> bool: ...
+def _(flag: bool):
 
-x = 1 if flag() else None
+    x = 1 if flag else None
 
-# valid invocation, positive
-reveal_type(x)  # revealed: Literal[1] | None
-if bool(x is not None):
-    reveal_type(x)  # revealed: Literal[1]
-
-# valid invocation, negative
-reveal_type(x)  # revealed: Literal[1] | None
-if not bool(x is not None):
-    reveal_type(x)  # revealed: None
-
-# no args/narrowing
-reveal_type(x)  # revealed: Literal[1] | None
-if not bool():
+    # valid invocation, positive
     reveal_type(x)  # revealed: Literal[1] | None
+    if bool(x is not None):
+        reveal_type(x)  # revealed: Literal[1]
 
-# invalid invocation, too many positional args
-reveal_type(x)  # revealed: Literal[1] | None
-if bool(x is not None, 5):  # TODO diagnostic
+    # valid invocation, negative
     reveal_type(x)  # revealed: Literal[1] | None
+    if not bool(x is not None):
+        reveal_type(x)  # revealed: None
 
-# invalid invocation, too many kwargs
-reveal_type(x)  # revealed: Literal[1] | None
-if bool(x is not None, y=5):  # TODO diagnostic
+    # no args/narrowing
     reveal_type(x)  # revealed: Literal[1] | None
+    if not bool():
+        reveal_type(x)  # revealed: Literal[1] | None
+
+    # invalid invocation, too many positional args
+    reveal_type(x)  # revealed: Literal[1] | None
+    if bool(x is not None, 5):  # TODO diagnostic
+        reveal_type(x)  # revealed: Literal[1] | None
+
+    # invalid invocation, too many kwargs
+    reveal_type(x)  # revealed: Literal[1] | None
+    if bool(x is not None, y=5):  # TODO diagnostic
+        reveal_type(x)  # revealed: Literal[1] | None
 ```

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

@@ -9,85 +9,67 @@ Similarly, in `and` expressions, the right-hand side is evaluated only if the le
 ## Narrowing in `or`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class A: ...
+    x: A | None = A() if flag else None
 
-class A: ...
-
-x: A | None = A() if bool_instance() else None
-
-isinstance(x, A) or reveal_type(x)  # revealed: None
-x is None or reveal_type(x)  # revealed: A
-reveal_type(x)  # revealed: A | None
+    isinstance(x, A) or reveal_type(x)  # revealed: None
+    x is None or reveal_type(x)  # revealed: A
+    reveal_type(x)  # revealed: A | None
 ```
 
 ## Narrowing in `and`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class A: ...
+    x: A | None = A() if flag else None
 
-class A: ...
-
-x: A | None = A() if bool_instance() else None
-
-isinstance(x, A) and reveal_type(x)  # revealed: A
-x is None and reveal_type(x)  # revealed: None
-reveal_type(x)  # revealed: A | None
+    isinstance(x, A) and reveal_type(x)  # revealed: A
+    x is None and reveal_type(x)  # revealed: None
+    reveal_type(x)  # revealed: A | None
 ```
 
 ## Multiple `and` arms
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool, flag3: bool, flag4: bool):
+    class A: ...
+    x: A | None = A() if flag1 else None
 
-class A: ...
-
-x: A | None = A() if bool_instance() else None
-
-bool_instance() and isinstance(x, A) and reveal_type(x)  # revealed: A
-isinstance(x, A) and bool_instance() and reveal_type(x)  # revealed: A
-reveal_type(x) and isinstance(x, A) and bool_instance()  # revealed: A | None
+    flag2 and isinstance(x, A) and reveal_type(x)  # revealed: A
+    isinstance(x, A) and flag2 and reveal_type(x)  # revealed: A
+    reveal_type(x) and isinstance(x, A) and flag3  # revealed: A | None
 ```
 
 ## Multiple `or` arms
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool, flag3: bool, flag4: bool):
+    class A: ...
+    x: A | None = A() if flag1 else None
 
-class A: ...
-
-x: A | None = A() if bool_instance() else None
-
-bool_instance() or isinstance(x, A) or reveal_type(x)  # revealed: None
-isinstance(x, A) or bool_instance() or reveal_type(x)  # revealed: None
-reveal_type(x) or isinstance(x, A) or bool_instance()  # revealed: A | None
+    flag2 or isinstance(x, A) or reveal_type(x)  # revealed: None
+    isinstance(x, A) or flag3 or reveal_type(x)  # revealed: None
+    reveal_type(x) or isinstance(x, A) or flag4  # revealed: A | None
 ```
 
 ## Multiple predicates
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    class A: ...
+    x: A | None | Literal[1] = A() if flag1 else None if flag2 else 1
 
-class A: ...
-
-x: A | None | Literal[1] = A() if bool_instance() else None if bool_instance() else 1
-
-x is None or isinstance(x, A) or reveal_type(x)  # revealed: Literal[1]
+    x is None or isinstance(x, A) or reveal_type(x)  # revealed: Literal[1]
 ```
 
 ## Mix of `and` and `or`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    class A: ...
+    x: A | None | Literal[1] = A() if flag1 else None if flag2 else 1
 
-class A: ...
-
-x: A | None | Literal[1] = A() if bool_instance() else None if bool_instance() else 1
-
-isinstance(x, A) or x is not None and reveal_type(x)  # revealed: Literal[1]
+    isinstance(x, A) or x is not None and reveal_type(x)  # revealed: Literal[1]
 ```

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

@@ -6,15 +6,11 @@
 class A: ...
 class B: ...
 
-def instance() -> A | B:
-    return A()
-
-x = instance()
-
-if isinstance(x, A) and isinstance(x, B):
-    reveal_type(x)  # revealed:  A & B
-else:
-    reveal_type(x)  # revealed:  B & ~A | A & ~B
+def _(x: A | B):
+    if isinstance(x, A) and isinstance(x, B):
+        reveal_type(x)  # revealed:  A & B
+    else:
+        reveal_type(x)  # revealed:  B & ~A | A & ~B
 ```
 
 ## Arms might not add narrowing constraints
@@ -23,25 +19,18 @@ else:
 class A: ...
 class B: ...
 
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, x: A | B):
+    if isinstance(x, A) and flag:
+        reveal_type(x)  # revealed: A
+    else:
+        reveal_type(x)  # revealed: A | B
 
-def instance() -> A | B:
-    return A()
+    if flag and isinstance(x, A):
+        reveal_type(x)  # revealed: A
+    else:
+        reveal_type(x)  # revealed: A | B
 
-x = instance()
-
-if isinstance(x, A) and bool_instance():
-    reveal_type(x)  # revealed: A
-else:
     reveal_type(x)  # revealed: A | B
-
-if bool_instance() and isinstance(x, A):
-    reveal_type(x)  # revealed: A
-else:
-    reveal_type(x)  # revealed: A | B
-
-reveal_type(x)  # revealed: A | B
 ```
 
 ## Statically known arms
@@ -50,39 +39,35 @@ reveal_type(x)  # revealed: A | B
 class A: ...
 class B: ...
 
-def instance() -> A | B:
-    return A()
+def _(x: A | B):
+    if isinstance(x, A) and True:
+        reveal_type(x)  # revealed: A
+    else:
+        reveal_type(x)  # revealed: B & ~A
 
-x = instance()
+    if True and isinstance(x, A):
+        reveal_type(x)  # revealed: A
+    else:
+        reveal_type(x)  # revealed: B & ~A
 
-if isinstance(x, A) and True:
-    reveal_type(x)  # revealed: A
-else:
-    reveal_type(x)  # revealed: B & ~A
+    if False and isinstance(x, A):
+        # TODO: should emit an `unreachable code` diagnostic
+        reveal_type(x)  # revealed: A
+    else:
+        reveal_type(x)  # revealed: A | B
 
-if True and isinstance(x, A):
-    reveal_type(x)  # revealed: A
-else:
-    reveal_type(x)  # revealed: B & ~A
+    if False or isinstance(x, A):
+        reveal_type(x)  # revealed: A
+    else:
+        reveal_type(x)  # revealed: B & ~A
+
+    if True or isinstance(x, A):
+        reveal_type(x)  # revealed: A | B
+    else:
+        # TODO: should emit an `unreachable code` diagnostic
+        reveal_type(x)  # revealed: B & ~A
 
-if False and isinstance(x, A):
-    # TODO: should emit an `unreachable code` diagnostic
-    reveal_type(x)  # revealed: A
-else:
     reveal_type(x)  # revealed: A | B
-
-if False or isinstance(x, A):
-    reveal_type(x)  # revealed: A
-else:
-    reveal_type(x)  # revealed: B & ~A
-
-if True or isinstance(x, A):
-    reveal_type(x)  # revealed: A | B
-else:
-    # TODO: should emit an `unreachable code` diagnostic
-    reveal_type(x)  # revealed: B & ~A
-
-reveal_type(x)  # revealed: A | B
 ```
 
 ## The type of multiple symbols can be narrowed down
@@ -91,22 +76,17 @@ reveal_type(x)  # revealed: A | B
 class A: ...
 class B: ...
 
-def instance() -> A | B:
-    return A()
+def _(x: A | B, y: A | B):
+    if isinstance(x, A) and isinstance(y, B):
+        reveal_type(x)  # revealed: A
+        reveal_type(y)  # revealed: B
+    else:
+        # No narrowing: Only-one or both checks might have failed
+        reveal_type(x)  # revealed: A | B
+        reveal_type(y)  # revealed: A | B
 
-x = instance()
-y = instance()
-
-if isinstance(x, A) and isinstance(y, B):
-    reveal_type(x)  # revealed: A
-    reveal_type(y)  # revealed: B
-else:
-    # No narrowing: Only-one or both checks might have failed
     reveal_type(x)  # revealed: A | B
     reveal_type(y)  # revealed: A | B
-
-reveal_type(x)  # revealed: A | B
-reveal_type(y)  # revealed: A | B
 ```
 
 ## Narrowing in `or` conditional
@@ -116,15 +96,11 @@ class A: ...
 class B: ...
 class C: ...
 
-def instance() -> A | B | C:
-    return A()
-
-x = instance()
-
-if isinstance(x, A) or isinstance(x, B):
-    reveal_type(x)  # revealed:  A | B
-else:
-    reveal_type(x)  # revealed:  C & ~A & ~B
+def _(x: A | B | C):
+    if isinstance(x, A) or isinstance(x, B):
+        reveal_type(x)  # revealed:  A | B
+    else:
+        reveal_type(x)  # revealed:  C & ~A & ~B
 ```
 
 ## In `or`, all arms should add constraint in order to narrow
@@ -134,18 +110,11 @@ class A: ...
 class B: ...
 class C: ...
 
-def instance() -> A | B | C:
-    return A()
-
-def bool_instance() -> bool:
-    return True
-
-x = instance()
-
-if isinstance(x, A) or isinstance(x, B) or bool_instance():
-    reveal_type(x)  # revealed:  A | B | C
-else:
-    reveal_type(x)  # revealed:  C & ~A & ~B
+def _(flag: bool, x: A | B | C):
+    if isinstance(x, A) or isinstance(x, B) or flag:
+        reveal_type(x)  # revealed:  A | B | C
+    else:
+        reveal_type(x)  # revealed:  C & ~A & ~B
 ```
 
 ## in `or`, all arms should narrow the same set of symbols
@@ -155,28 +124,23 @@ class A: ...
 class B: ...
 class C: ...
 
-def instance() -> A | B | C:
-    return A()
+def _(x: A | B | C, y: A | B | C):
+    if isinstance(x, A) or isinstance(y, A):
+        # The predicate might be satisfied by the right side, so the type of `x` can’t be narrowed down here.
+        reveal_type(x)  # revealed:  A | B | C
+        # The same for `y`
+        reveal_type(y)  # revealed:  A | B | C
+    else:
+        reveal_type(x)  # revealed:  B & ~A | C & ~A
+        reveal_type(y)  # revealed:  B & ~A | C & ~A
 
-x = instance()
-y = instance()
-
-if isinstance(x, A) or isinstance(y, A):
-    # The predicate might be satisfied by the right side, so the type of `x` can’t be narrowed down here.
-    reveal_type(x)  # revealed:  A | B | C
-    # The same for `y`
-    reveal_type(y)  # revealed:  A | B | C
-else:
-    reveal_type(x)  # revealed:  B & ~A | C & ~A
-    reveal_type(y)  # revealed:  B & ~A | C & ~A
-
-if (isinstance(x, A) and isinstance(y, A)) or (isinstance(x, B) and isinstance(y, B)):
-    # Here, types of `x` and `y` can be narrowd since all `or` arms constraint them.
-    reveal_type(x)  # revealed:  A | B
-    reveal_type(y)  # revealed:  A | B
-else:
-    reveal_type(x)  # revealed:  A | B | C
-    reveal_type(y)  # revealed:  A | B | C
+    if (isinstance(x, A) and isinstance(y, A)) or (isinstance(x, B) and isinstance(y, B)):
+        # Here, types of `x` and `y` can be narrowd since all `or` arms constraint them.
+        reveal_type(x)  # revealed:  A | B
+        reveal_type(y)  # revealed:  A | B
+    else:
+        reveal_type(x)  # revealed:  A | B | C
+        reveal_type(y)  # revealed:  A | B | C
 ```
 
 ## mixing `and` and `not`
@@ -186,16 +150,12 @@ class A: ...
 class B: ...
 class C: ...
 
-def instance() -> A | B | C:
-    return A()
-
-x = instance()
-
-if isinstance(x, B) and not isinstance(x, C):
-    reveal_type(x)  # revealed:  B & ~C
-else:
-    # ~(B & ~C) -> ~B | C -> (A & ~B) | (C & ~B) | C -> (A & ~B) | C
-    reveal_type(x)  # revealed: A & ~B | C
+def _(x: A | B | C):
+    if isinstance(x, B) and not isinstance(x, C):
+        reveal_type(x)  # revealed:  B & ~C
+    else:
+        # ~(B & ~C) -> ~B | C -> (A & ~B) | (C & ~B) | C -> (A & ~B) | C
+        reveal_type(x)  # revealed: A & ~B | C
 ```
 
 ## mixing `or` and `not`
@@ -205,15 +165,11 @@ class A: ...
 class B: ...
 class C: ...
 
-def instance() -> A | B | C:
-    return A()
-
-x = instance()
-
-if isinstance(x, B) or not isinstance(x, C):
-    reveal_type(x)  # revealed: B | A & ~C
-else:
-    reveal_type(x)  # revealed: C & ~B
+def _(x: A | B | C):
+    if isinstance(x, B) or not isinstance(x, C):
+        reveal_type(x)  # revealed: B | A & ~C
+    else:
+        reveal_type(x)  # revealed: C & ~B
 ```
 
 ## `or` with nested `and`
@@ -223,16 +179,12 @@ class A: ...
 class B: ...
 class C: ...
 
-def instance() -> A | B | C:
-    return A()
-
-x = instance()
-
-if isinstance(x, A) or (isinstance(x, B) and not isinstance(x, C)):
-    reveal_type(x)  # revealed:  A | B & ~C
-else:
-    # ~(A | (B & ~C)) -> ~A & ~(B & ~C) -> ~A & (~B | C) -> (~A & C) | (~A ~ B)
-    reveal_type(x)  # revealed:  C & ~A
+def _(x: A | B | C):
+    if isinstance(x, A) or (isinstance(x, B) and not isinstance(x, C)):
+        reveal_type(x)  # revealed:  A | B & ~C
+    else:
+        # ~(A | (B & ~C)) -> ~A & ~(B & ~C) -> ~A & (~B | C) -> (~A & C) | (~A ~ B)
+        reveal_type(x)  # revealed:  C & ~A
 ```
 
 ## `and` with nested `or`
@@ -242,41 +194,32 @@ class A: ...
 class B: ...
 class C: ...
 
-def instance() -> A | B | C:
-    return A()
-
-x = instance()
-
-if isinstance(x, A) and (isinstance(x, B) or not isinstance(x, C)):
-    # A & (B | ~C) -> (A & B) | (A & ~C)
-    reveal_type(x)  # revealed:  A & B | A & ~C
-else:
-    # ~((A & B) | (A & ~C)) ->
-    # ~(A & B) & ~(A & ~C) ->
-    # (~A | ~B) & (~A | C) ->
-    # [(~A | ~B) & ~A] | [(~A | ~B) & C] ->
-    # ~A | (~A & C) | (~B & C) ->
-    # ~A | (C & ~B) ->
-    # ~A | (C & ~B)  The positive side of ~A is  A | B | C ->
-    reveal_type(x)  # revealed:  B & ~A | C & ~A | C & ~B
+def _(x: A | B | C):
+    if isinstance(x, A) and (isinstance(x, B) or not isinstance(x, C)):
+        # A & (B | ~C) -> (A & B) | (A & ~C)
+        reveal_type(x)  # revealed:  A & B | A & ~C
+    else:
+        # ~((A & B) | (A & ~C)) ->
+        # ~(A & B) & ~(A & ~C) ->
+        # (~A | ~B) & (~A | C) ->
+        # [(~A | ~B) & ~A] | [(~A | ~B) & C] ->
+        # ~A | (~A & C) | (~B & C) ->
+        # ~A | (C & ~B) ->
+        # ~A | (C & ~B)  The positive side of ~A is  A | B | C ->
+        reveal_type(x)  # revealed:  B & ~A | C & ~A | C & ~B
 ```
 
 ## Boolean expression internal narrowing
 
 ```py
-def optional_string() -> str | None:
-    return None
+def _(x: str | None, y: str | None):
+    if x is None and y is not x:
+        reveal_type(y)  # revealed: str
 
-x = optional_string()
-y = optional_string()
+    # Neither of the conditions alone is sufficient for narrowing y's type:
+    if x is None:
+        reveal_type(y)  # revealed: str | None
 
-if x is None and y is not x:
-    reveal_type(y)  # revealed: str
-
-# Neither of the conditions alone is sufficient for narrowing y's type:
-if x is None:
-    reveal_type(y)  # revealed: str | None
-
-if y is not x:
-    reveal_type(y)  # revealed: str | None
+    if y is not x:
+        reveal_type(y)  # revealed: str | None
 ```

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

@@ -3,55 +3,47 @@
 ## Positive contributions become negative in elif-else blocks
 
 ```py
-def int_instance() -> int:
-    return 42
-
-x = int_instance()
-
-if x == 1:
-    # cannot narrow; could be a subclass of `int`
-    reveal_type(x)  # revealed: int
-elif x == 2:
-    reveal_type(x)  # revealed: int & ~Literal[1]
-elif x != 3:
-    reveal_type(x)  # revealed: int & ~Literal[1] & ~Literal[2] & ~Literal[3]
+def _(x: int):
+    if x == 1:
+        # cannot narrow; could be a subclass of `int`
+        reveal_type(x)  # revealed: int
+    elif x == 2:
+        reveal_type(x)  # revealed: int & ~Literal[1]
+    elif x != 3:
+        reveal_type(x)  # revealed: int & ~Literal[1] & ~Literal[2] & ~Literal[3]
 ```
 
 ## Positive contributions become negative in elif-else blocks, with simplification
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    x = 1 if flag1 else 2 if flag2 else 3
 
-x = 1 if bool_instance() else 2 if bool_instance() else 3
-
-if x == 1:
-    # TODO should be Literal[1]
-    reveal_type(x)  # revealed: Literal[1, 2, 3]
-elif x == 2:
-    # TODO should be Literal[2]
-    reveal_type(x)  # revealed: Literal[2, 3]
-else:
-    reveal_type(x)  # revealed: Literal[3]
+    if x == 1:
+        # TODO should be Literal[1]
+        reveal_type(x)  # revealed: Literal[1, 2, 3]
+    elif x == 2:
+        # TODO should be Literal[2]
+        reveal_type(x)  # revealed: Literal[2, 3]
+    else:
+        reveal_type(x)  # revealed: Literal[3]
 ```
 
 ## Multiple negative contributions using elif, with simplification
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    x = 1 if flag1 else 2 if flag2 else 3
 
-x = 1 if bool_instance() else 2 if bool_instance() else 3
-
-if x != 1:
-    reveal_type(x)  # revealed: Literal[2, 3]
-elif x != 2:
-    # TODO should be `Literal[1]`
-    reveal_type(x)  # revealed: Literal[1, 3]
-elif x == 3:
-    # TODO should be Never
-    reveal_type(x)  # revealed: Literal[1, 2, 3]
-else:
-    # TODO should be Never
-    reveal_type(x)  # revealed: Literal[1, 2]
+    if x != 1:
+        reveal_type(x)  # revealed: Literal[2, 3]
+    elif x != 2:
+        # TODO should be `Literal[1]`
+        reveal_type(x)  # revealed: Literal[1, 3]
+    elif x == 3:
+        # TODO should be Never
+        reveal_type(x)  # revealed: Literal[1, 2, 3]
+    else:
+        # TODO should be Never
+        reveal_type(x)  # revealed: Literal[1, 2]
 ```

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

@@ -3,77 +3,64 @@
 ## `is None`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = None if flag else 1
 
-flag = bool_instance()
-x = None if flag else 1
+    if x is None:
+        reveal_type(x)  # revealed: None
+    else:
+        reveal_type(x)  # revealed: Literal[1]
 
-if x is None:
-    reveal_type(x)  # revealed: None
-else:
-    reveal_type(x)  # revealed: Literal[1]
-
-reveal_type(x)  # revealed: None | Literal[1]
+    reveal_type(x)  # revealed: None | Literal[1]
 ```
 
 ## `is` for other types
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class A: ...
+    x = A()
+    y = x if flag else None
 
-flag = bool_instance()
+    if y is x:
+        reveal_type(y)  # revealed: A
+    else:
+        reveal_type(y)  # revealed: A | None
 
-class A: ...
-
-x = A()
-y = x if flag else None
-
-if y is x:
-    reveal_type(y)  # revealed: A
-else:
     reveal_type(y)  # revealed: A | None
-
-reveal_type(y)  # revealed: A | None
 ```
 
 ## `is` in chained comparisons
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(x_flag: bool, y_flag: bool):
+    x = True if x_flag else False
+    y = True if y_flag else False
 
-x_flag, y_flag = bool_instance(), bool_instance()
-x = True if x_flag else False
-y = True if y_flag else False
-
-reveal_type(x)  # revealed: bool
-reveal_type(y)  # revealed: bool
-
-if y is x is False:  # Interpreted as `(y is x) and (x is False)`
-    reveal_type(x)  # revealed: Literal[False]
-    reveal_type(y)  # revealed: bool
-else:
-    # The negation of the clause above is (y is not x) or (x is not False)
-    # So we can't narrow the type of x or y here, because each arm of the `or` could be true
     reveal_type(x)  # revealed: bool
     reveal_type(y)  # revealed: bool
+
+    if y is x is False:  # Interpreted as `(y is x) and (x is False)`
+        reveal_type(x)  # revealed: Literal[False]
+        reveal_type(y)  # revealed: bool
+    else:
+        # The negation of the clause above is (y is not x) or (x is not False)
+        # So we can't narrow the type of x or y here, because each arm of the `or` could be true
+        reveal_type(x)  # revealed: bool
+        reveal_type(y)  # revealed: bool
 ```
 
 ## `is` in elif clause
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    x = None if flag1 else (1 if flag2 else True)
 
-x = None if bool_instance() else (1 if bool_instance() else True)
-
-reveal_type(x)  # revealed: None | Literal[1] | Literal[True]
-if x is None:
-    reveal_type(x)  # revealed: None
-elif x is True:
-    reveal_type(x)  # revealed: Literal[True]
-else:
-    reveal_type(x)  # revealed: Literal[1]
+    reveal_type(x)  # revealed: None | Literal[1] | Literal[True]
+    if x is None:
+        reveal_type(x)  # revealed: None
+    elif x is True:
+        reveal_type(x)  # revealed: Literal[True]
+    else:
+        reveal_type(x)  # revealed: Literal[1]
 ```

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

@@ -5,34 +5,28 @@
 The type guard removes `None` from the union type:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = None if flag else 1
 
-flag = bool_instance()
-x = None if flag else 1
+    if x is not None:
+        reveal_type(x)  # revealed: Literal[1]
+    else:
+        reveal_type(x)  # revealed: None
 
-if x is not None:
-    reveal_type(x)  # revealed: Literal[1]
-else:
-    reveal_type(x)  # revealed: None
-
-reveal_type(x)  # revealed: None | Literal[1]
+    reveal_type(x)  # revealed: None | Literal[1]
 ```
 
 ## `is not` for other singleton types
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = True if flag else False
+    reveal_type(x)  # revealed: bool
 
-flag = bool_instance()
-x = True if flag else False
-reveal_type(x)  # revealed: bool
-
-if x is not False:
-    reveal_type(x)  # revealed: Literal[True]
-else:
-    reveal_type(x)  # revealed: Literal[False]
+    if x is not False:
+        reveal_type(x)  # revealed: Literal[True]
+    else:
+        reveal_type(x)  # revealed: Literal[False]
 ```
 
 ## `is not` for non-singleton types
@@ -53,20 +47,17 @@ else:
 ## `is not` for other types
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class A: ...
+    x = A()
+    y = x if flag else None
 
-class A: ...
+    if y is not x:
+        reveal_type(y)  # revealed: A | None
+    else:
+        reveal_type(y)  # revealed: A
 
-x = A()
-y = x if bool_instance() else None
-
-if y is not x:
     reveal_type(y)  # revealed: A | None
-else:
-    reveal_type(y)  # revealed: A
-
-reveal_type(y)  # revealed: A | None
 ```
 
 ## `is not` in chained comparisons
@@ -74,23 +65,20 @@ reveal_type(y)  # revealed: A | None
 The type guard removes `False` from the union type of the tested value only.
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-x_flag, y_flag = bool_instance(), bool_instance()
-x = True if x_flag else False
-y = True if y_flag else False
-
-reveal_type(x)  # revealed: bool
-reveal_type(y)  # revealed: bool
-
-if y is not x is not False:  # Interpreted as `(y is not x) and (x is not False)`
-    reveal_type(x)  # revealed: Literal[True]
-    reveal_type(y)  # revealed: bool
-else:
-    # The negation of the clause above is (y is x) or (x is False)
-    # So we can't narrow the type of x or y here, because each arm of the `or` could be true
+def _(x_flag: bool, y_flag: bool):
+    x = True if x_flag else False
+    y = True if y_flag else False
 
     reveal_type(x)  # revealed: bool
     reveal_type(y)  # revealed: bool
+
+    if y is not x is not False:  # Interpreted as `(y is not x) and (x is not False)`
+        reveal_type(x)  # revealed: Literal[True]
+        reveal_type(y)  # revealed: bool
+    else:
+        # The negation of the clause above is (y is x) or (x is False)
+        # So we can't narrow the type of x or y here, because each arm of the `or` could be true
+
+        reveal_type(x)  # revealed: bool
+        reveal_type(y)  # revealed: bool
 ```

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

@@ -3,54 +3,45 @@
 ## Multiple negative contributions
 
 ```py
-def int_instance() -> int:
-    return 42
-
-x = int_instance()
-
-if x != 1:
-    if x != 2:
-        if x != 3:
-            reveal_type(x)  # revealed: int & ~Literal[1] & ~Literal[2] & ~Literal[3]
+def _(x: int):
+    if x != 1:
+        if x != 2:
+            if x != 3:
+                reveal_type(x)  # revealed: int & ~Literal[1] & ~Literal[2] & ~Literal[3]
 ```
 
 ## Multiple negative contributions with simplification
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    x = 1 if flag1 else 2 if flag2 else 3
 
-flag1, flag2 = bool_instance(), bool_instance()
-x = 1 if flag1 else 2 if flag2 else 3
-
-if x != 1:
-    reveal_type(x)  # revealed: Literal[2, 3]
-    if x != 2:
-        reveal_type(x)  # revealed: Literal[3]
+    if x != 1:
+        reveal_type(x)  # revealed: Literal[2, 3]
+        if x != 2:
+            reveal_type(x)  # revealed: Literal[3]
 ```
 
 ## elif-else blocks
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    x = 1 if flag1 else 2 if flag2 else 3
 
-x = 1 if bool_instance() else 2 if bool_instance() else 3
-
-if x != 1:
-    reveal_type(x)  # revealed: Literal[2, 3]
-    if x == 2:
-        # TODO should be `Literal[2]`
+    if x != 1:
         reveal_type(x)  # revealed: Literal[2, 3]
-    elif x == 3:
-        reveal_type(x)  # revealed: Literal[3]
-    else:
-        reveal_type(x)  # revealed: Never
+        if x == 2:
+            # TODO should be `Literal[2]`
+            reveal_type(x)  # revealed: Literal[2, 3]
+        elif x == 3:
+            reveal_type(x)  # revealed: Literal[3]
+        else:
+            reveal_type(x)  # revealed: Never
 
-elif x != 2:
-    # TODO should be Literal[1]
-    reveal_type(x)  # revealed: Literal[1, 3]
-else:
-    # TODO should be Never
-    reveal_type(x)  # revealed: Literal[1, 2, 3]
+    elif x != 2:
+        # TODO should be Literal[1]
+        reveal_type(x)  # revealed: Literal[1, 3]
+    else:
+        # TODO should be Never
+        reveal_type(x)  # revealed: Literal[1, 2, 3]
 ```

crates/red_knot_python_semantic/resources/mdtest/narrow/conditionals/not.md

@@ -5,29 +5,25 @@ The `not` operator negates a constraint.
 ## `not is None`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = None if flag else 1
 
-x = None if bool_instance() else 1
+    if not x is None:
+        reveal_type(x)  # revealed: Literal[1]
+    else:
+        reveal_type(x)  # revealed: None
 
-if not x is None:
-    reveal_type(x)  # revealed: Literal[1]
-else:
-    reveal_type(x)  # revealed: None
-
-reveal_type(x)  # revealed: None | Literal[1]
+    reveal_type(x)  # revealed: None | Literal[1]
 ```
 
 ## `not isinstance`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1 if flag else "a"
 
-x = 1 if bool_instance() else "a"
-
-if not isinstance(x, (int)):
-    reveal_type(x)  # revealed: Literal["a"]
-else:
-    reveal_type(x)  # revealed: Literal[1]
+    if not isinstance(x, (int)):
+        reveal_type(x)  # revealed: Literal["a"]
+    else:
+        reveal_type(x)  # revealed: Literal[1]
 ```

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

@@ -3,82 +3,66 @@
 ## `x != None`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = None if flag else 1
 
-flag = bool_instance()
-x = None if flag else 1
-
-if x != None:
-    reveal_type(x)  # revealed: Literal[1]
-else:
-    # TODO should be None
-    reveal_type(x)  # revealed: None | Literal[1]
+    if x != None:
+        reveal_type(x)  # revealed: Literal[1]
+    else:
+        # TODO should be None
+        reveal_type(x)  # revealed: None | Literal[1]
 ```
 
 ## `!=` for other singleton types
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = True if flag else False
 
-flag = bool_instance()
-x = True if flag else False
-
-if x != False:
-    reveal_type(x)  # revealed: Literal[True]
-else:
-    # TODO should be Literal[False]
-    reveal_type(x)  # revealed: bool
+    if x != False:
+        reveal_type(x)  # revealed: Literal[True]
+    else:
+        # TODO should be Literal[False]
+        reveal_type(x)  # revealed: bool
 ```
 
 ## `x != y` where `y` is of literal type
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1 if flag else 2
 
-flag = bool_instance()
-x = 1 if flag else 2
-
-if x != 1:
-    reveal_type(x)  # revealed: Literal[2]
+    if x != 1:
+        reveal_type(x)  # revealed: Literal[2]
 ```
 
 ## `x != y` where `y` is a single-valued type
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class A: ...
+    class B: ...
+    C = A if flag else B
 
-flag = bool_instance()
-
-class A: ...
-class B: ...
-
-C = A if flag else B
-
-if C != A:
-    reveal_type(C)  # revealed: Literal[B]
-else:
-    # TODO should be Literal[A]
-    reveal_type(C)  # revealed: Literal[A, B]
+    if C != A:
+        reveal_type(C)  # revealed: Literal[B]
+    else:
+        # TODO should be Literal[A]
+        reveal_type(C)  # revealed: Literal[A, B]
 ```
 
 ## `x != y` where `y` has multiple single-valued options
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    x = 1 if flag1 else 2
+    y = 2 if flag2 else 3
 
-x = 1 if bool_instance() else 2
-y = 2 if bool_instance() else 3
-
-if x != y:
-    reveal_type(x)  # revealed: Literal[1, 2]
-else:
-    # TODO should be Literal[2]
-    reveal_type(x)  # revealed: Literal[1, 2]
+    if x != y:
+        reveal_type(x)  # revealed: Literal[1, 2]
+    else:
+        # TODO should be Literal[2]
+        reveal_type(x)  # revealed: Literal[1, 2]
 ```
 
 ## `!=` for non-single-valued types
@@ -86,34 +70,22 @@ else:
 Only single-valued types should narrow the type:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, a: int, y: int):
+    x = a if flag else None
 
-def int_instance() -> int:
-    return 42
-
-flag = bool_instance()
-x = int_instance() if flag else None
-y = int_instance()
-
-if x != y:
-    reveal_type(x)  # revealed: int | None
+    if x != y:
+        reveal_type(x)  # revealed: int | None
 ```
 
 ## Mix of single-valued and non-single-valued types
 
 ```py
-def int_instance() -> int:
-    return 42
+def _(flag1: bool, flag2: bool, a: int):
+    x = 1 if flag1 else 2
+    y = 2 if flag2 else a
 
-def bool_instance() -> bool:
-    return True
-
-x = 1 if bool_instance() else 2
-y = 2 if bool_instance() else int_instance()
-
-if x != y:
-    reveal_type(x)  # revealed: Literal[1, 2]
-else:
-    reveal_type(x)  # revealed: Literal[1, 2]
+    if x != y:
+        reveal_type(x)  # revealed: Literal[1, 2]
+    else:
+        reveal_type(x)  # revealed: Literal[1, 2]
 ```

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

@@ -5,23 +5,19 @@ Narrowing for `isinstance(object, classinfo)` expressions.
 ## `classinfo` is a single type
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1 if flag else "a"
 
-flag = bool_instance()
-
-x = 1 if flag else "a"
-
-if isinstance(x, int):
-    reveal_type(x)  # revealed: Literal[1]
-
-if isinstance(x, str):
-    reveal_type(x)  # revealed: Literal["a"]
     if isinstance(x, int):
-        reveal_type(x)  # revealed: Never
+        reveal_type(x)  # revealed: Literal[1]
 
-if isinstance(x, (int, object)):
-    reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+    if isinstance(x, str):
+        reveal_type(x)  # revealed: Literal["a"]
+        if isinstance(x, int):
+            reveal_type(x)  # revealed: Never
+
+    if isinstance(x, (int, object)):
+        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
 ```
 
 ## `classinfo` is a tuple of types
@@ -30,56 +26,48 @@ Note: `isinstance(x, (int, str))` should not be confused with `isinstance(x, tup
 The former is equivalent to `isinstance(x, int | str)`:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag1: bool, flag2: bool):
+    x = 1 if flag else "a"
 
-flag, flag1, flag2 = bool_instance(), bool_instance(), bool_instance()
+    if isinstance(x, (int, str)):
+        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+    else:
+        reveal_type(x)  # revealed: Never
 
-x = 1 if flag else "a"
+    if isinstance(x, (int, bytes)):
+        reveal_type(x)  # revealed: Literal[1]
 
-if isinstance(x, (int, str)):
-    reveal_type(x)  # revealed: Literal[1] | Literal["a"]
-else:
-    reveal_type(x)  # revealed: Never
+    if isinstance(x, (bytes, str)):
+        reveal_type(x)  # revealed: Literal["a"]
 
-if isinstance(x, (int, bytes)):
-    reveal_type(x)  # revealed: Literal[1]
+    # 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"]
+    else:
+        reveal_type(x)  # revealed: Never
 
-if isinstance(x, (bytes, str)):
-    reveal_type(x)  # revealed: Literal["a"]
+    y = 1 if flag1 else "a" if flag2 else b"b"
+    if isinstance(y, (int, str)):
+        reveal_type(y)  # revealed: Literal[1] | Literal["a"]
 
-# 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"]
-else:
-    reveal_type(x)  # revealed: Never
+    if isinstance(y, (int, bytes)):
+        reveal_type(y)  # revealed: Literal[1] | Literal[b"b"]
 
-y = 1 if flag1 else "a" if flag2 else b"b"
-if isinstance(y, (int, str)):
-    reveal_type(y)  # revealed: Literal[1] | Literal["a"]
-
-if isinstance(y, (int, bytes)):
-    reveal_type(y)  # revealed: Literal[1] | Literal[b"b"]
-
-if isinstance(y, (str, bytes)):
-    reveal_type(y)  # revealed: Literal["a"] | Literal[b"b"]
+    if isinstance(y, (str, bytes)):
+        reveal_type(y)  # revealed: Literal["a"] | Literal[b"b"]
 ```
 
 ## `classinfo` is a nested tuple of types
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1 if flag else "a"
 
-flag = bool_instance()
-
-x = 1 if flag else "a"
-
-if isinstance(x, (bool, (bytes, int))):
-    reveal_type(x)  # revealed: Literal[1]
-else:
-    reveal_type(x)  # revealed: Literal["a"]
+    if isinstance(x, (bool, (bytes, int))):
+        reveal_type(x)  # revealed: Literal[1]
+    else:
+        reveal_type(x)  # revealed: Literal["a"]
 ```
 
 ## Class types
@@ -89,9 +77,7 @@ class A: ...
 class B: ...
 class C: ...
 
-def get_object() -> object: ...
-
-x = get_object()
+x = object()
 
 if isinstance(x, A):
     reveal_type(x)  # revealed: A
@@ -112,50 +98,40 @@ else:
 ## No narrowing for instances of `builtins.type`
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    t = type("t", (), {})
 
-flag = bool_instance()
+    # This isn't testing what we want it to test if we infer anything more precise here:
+    reveal_type(t)  # revealed: type
 
-t = type("t", (), {})
+    x = 1 if flag else "foo"
 
-# This isn't testing what we want it to test if we infer anything more precise here:
-reveal_type(t)  # revealed: type
-x = 1 if flag else "foo"
-
-if isinstance(x, t):
-    reveal_type(x)  # revealed: Literal[1] | Literal["foo"]
+    if isinstance(x, t):
+        reveal_type(x)  # revealed: Literal[1] | Literal["foo"]
 ```
 
 ## Do not use custom `isinstance` for narrowing
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    def isinstance(x, t):
+        return True
+    x = 1 if flag else "a"
 
-flag = bool_instance()
-
-def isinstance(x, t):
-    return True
-
-x = 1 if flag else "a"
-if isinstance(x, int):
-    reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+    if isinstance(x, int):
+        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
 ```
 
 ## Do support narrowing if `isinstance` is aliased
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    isinstance_alias = isinstance
 
-flag = bool_instance()
+    x = 1 if flag else "a"
 
-isinstance_alias = isinstance
-
-x = 1 if flag else "a"
-if isinstance_alias(x, int):
-    reveal_type(x)  # revealed: Literal[1]
+    if isinstance_alias(x, int):
+        reveal_type(x)  # revealed: Literal[1]
 ```
 
 ## Do support narrowing if `isinstance` is imported
@@ -163,46 +139,38 @@ if isinstance_alias(x, int):
 ```py
 from builtins import isinstance as imported_isinstance
 
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1 if flag else "a"
 
-flag = bool_instance()
-x = 1 if flag else "a"
-if imported_isinstance(x, int):
-    reveal_type(x)  # revealed: Literal[1]
+    if imported_isinstance(x, int):
+        reveal_type(x)  # revealed: Literal[1]
 ```
 
 ## Do not narrow if second argument is not a type
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1 if flag else "a"
 
-flag = bool_instance()
-x = 1 if flag else "a"
+    # TODO: this should cause us to emit a diagnostic during
+    # type checking
+    if isinstance(x, "a"):
+        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
 
-# TODO: this should cause us to emit a diagnostic during
-# type checking
-if isinstance(x, "a"):
-    reveal_type(x)  # revealed: Literal[1] | Literal["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"]
+    # TODO: this should cause us to emit a diagnostic during
+    # type checking
+    if isinstance(x, "int"):
+        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
 ```
 
 ## Do not narrow if there are keyword arguments
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1 if flag else "a"
 
-flag = bool_instance()
-x = 1 if flag else "a"
-
-# TODO: this should cause us to emit a diagnostic
-# (`isinstance` has no `foo` parameter)
-if isinstance(x, int, foo="bar"):
-    reveal_type(x)  # revealed: Literal[1] | Literal["a"]
+    # TODO: this should cause us to emit a diagnostic
+    # (`isinstance` has no `foo` parameter)
+    if isinstance(x, int, foo="bar"):
+        reveal_type(x)  # revealed: Literal[1] | Literal["a"]
 ```

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

@@ -7,45 +7,43 @@ Narrowing for `issubclass(class, classinfo)` expressions.
 ### Basic example
 
 ```py
-def flag() -> bool: ...
+def _(flag: bool):
+    t = int if flag else str
 
-t = int if flag() else str
-
-if issubclass(t, bytes):
-    reveal_type(t)  # revealed: Never
-
-if issubclass(t, object):
-    reveal_type(t)  # revealed: Literal[int, str]
-
-if issubclass(t, int):
-    reveal_type(t)  # revealed: Literal[int]
-else:
-    reveal_type(t)  # revealed: Literal[str]
-
-if issubclass(t, str):
-    reveal_type(t)  # revealed: Literal[str]
-    if issubclass(t, int):
+    if issubclass(t, bytes):
         reveal_type(t)  # revealed: Never
+
+    if issubclass(t, object):
+        reveal_type(t)  # revealed: Literal[int, str]
+
+    if issubclass(t, int):
+        reveal_type(t)  # revealed: Literal[int]
+    else:
+        reveal_type(t)  # revealed: Literal[str]
+
+    if issubclass(t, str):
+        reveal_type(t)  # revealed: Literal[str]
+        if issubclass(t, int):
+            reveal_type(t)  # revealed: Never
 ```
 
 ### Proper narrowing in `elif` and `else` branches
 
 ```py
-def flag() -> bool: ...
+def _(flag1: bool, flag2: bool):
+    t = int if flag1 else str if flag2 else bytes
 
-t = int if flag() else str if flag() else bytes
+    if issubclass(t, int):
+        reveal_type(t)  # revealed: Literal[int]
+    else:
+        reveal_type(t)  # revealed: Literal[str, bytes]
 
-if issubclass(t, int):
-    reveal_type(t)  # revealed: Literal[int]
-else:
-    reveal_type(t)  # revealed: Literal[str, bytes]
-
-if issubclass(t, int):
-    reveal_type(t)  # revealed: Literal[int]
-elif issubclass(t, str):
-    reveal_type(t)  # revealed: Literal[str]
-else:
-    reveal_type(t)  # revealed: Literal[bytes]
+    if issubclass(t, int):
+        reveal_type(t)  # revealed: Literal[int]
+    elif issubclass(t, str):
+        reveal_type(t)  # revealed: Literal[str]
+    else:
+        reveal_type(t)  # revealed: Literal[bytes]
 ```
 
 ### Multiple derived classes
@@ -56,29 +54,28 @@ class Derived1(Base): ...
 class Derived2(Base): ...
 class Unrelated: ...
 
-def flag() -> bool: ...
+def _(flag1: bool, flag2: bool, flag3: bool):
+    t1 = Derived1 if flag1 else Derived2
 
-t1 = Derived1 if flag() else Derived2
+    if issubclass(t1, Base):
+        reveal_type(t1)  # revealed: Literal[Derived1, Derived2]
 
-if issubclass(t1, Base):
-    reveal_type(t1)  # revealed: Literal[Derived1, Derived2]
+    if issubclass(t1, Derived1):
+        reveal_type(t1)  # revealed: Literal[Derived1]
+    else:
+        reveal_type(t1)  # revealed: Literal[Derived2]
 
-if issubclass(t1, Derived1):
-    reveal_type(t1)  # revealed: Literal[Derived1]
-else:
-    reveal_type(t1)  # revealed: Literal[Derived2]
+    t2 = Derived1 if flag2 else Base
 
-t2 = Derived1 if flag() else Base
+    if issubclass(t2, Base):
+        reveal_type(t2)  # revealed: Literal[Derived1, Base]
 
-if issubclass(t2, Base):
-    reveal_type(t2)  # revealed: Literal[Derived1, Base]
+    t3 = Derived1 if flag3 else Unrelated
 
-t3 = Derived1 if flag() else Unrelated
-
-if issubclass(t3, Base):
-    reveal_type(t3)  # revealed: Literal[Derived1]
-else:
-    reveal_type(t3)  # revealed: Literal[Unrelated]
+    if issubclass(t3, Base):
+        reveal_type(t3)  # revealed: Literal[Derived1]
+    else:
+        reveal_type(t3)  # revealed: Literal[Unrelated]
 ```
 
 ### Narrowing for non-literals
@@ -87,16 +84,13 @@ else:
 class A: ...
 class B: ...
 
-def get_class() -> type[object]: ...
-
-t = get_class()
-
-if issubclass(t, A):
-    reveal_type(t)  # revealed: type[A]
-    if issubclass(t, B):
-        reveal_type(t)  # revealed: type[A] & type[B]
-else:
-    reveal_type(t)  # revealed: type[object] & ~type[A]
+def _(t: type[object]):
+    if issubclass(t, A):
+        reveal_type(t)  # revealed: type[A]
+        if issubclass(t, B):
+            reveal_type(t)  # revealed: type[A] & type[B]
+    else:
+        reveal_type(t)  # revealed: type[object] & ~type[A]
 ```
 
 ### Handling of `None`
@@ -107,16 +101,15 @@ else:
 # error: [possibly-unbound-import] "Member `NoneType` of module `types` is possibly unbound"
 from types import NoneType
 
-def flag() -> bool: ...
+def _(flag: bool):
+    t = int if flag else NoneType
 
-t = int if flag() else NoneType
+    if issubclass(t, NoneType):
+        reveal_type(t)  # revealed: Literal[NoneType]
 
-if issubclass(t, NoneType):
-    reveal_type(t)  # revealed: Literal[NoneType]
-
-if issubclass(t, type(None)):
-    # TODO: this should be just `Literal[NoneType]`
-    reveal_type(t)  # revealed: Literal[int, NoneType]
+    if issubclass(t, type(None)):
+        # TODO: this should be just `Literal[NoneType]`
+        reveal_type(t)  # revealed: Literal[int, NoneType]
 ```
 
 ## `classinfo` contains multiple types
@@ -126,14 +119,13 @@ if issubclass(t, type(None)):
 ```py
 class Unrelated: ...
 
-def flag() -> bool: ...
+def _(flag1: bool, flag2: bool):
+    t = int if flag1 else str if flag2 else bytes
 
-t = int if flag() else str if flag() else bytes
-
-if issubclass(t, (int, (Unrelated, (bytes,)))):
-    reveal_type(t)  # revealed: Literal[int, bytes]
-else:
-    reveal_type(t)  # revealed: Literal[str]
+    if issubclass(t, (int, (Unrelated, (bytes,)))):
+        reveal_type(t)  # revealed: Literal[int, bytes]
+    else:
+        reveal_type(t)  # revealed: Literal[str]
 ```
 
 ## Special cases
@@ -148,9 +140,7 @@ to `issubclass`:
 ```py
 class A: ...
 
-def get_object() -> object: ...
-
-t = get_object()
+t = object()
 
 # TODO: we should emit a diagnostic here
 if issubclass(t, A):

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

@@ -3,19 +3,16 @@
 ## Single `match` pattern
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = None if flag else 1
 
-flag = bool_instance()
+    reveal_type(x)  # revealed: None | Literal[1]
 
-x = None if flag else 1
-reveal_type(x)  # revealed: None | Literal[1]
+    y = 0
 
-y = 0
+    match x:
+        case None:
+            y = x
 
-match x:
-    case None:
-        y = x
-
-reveal_type(y)  # revealed: Literal[0] | None
+    reveal_type(y)  # revealed: Literal[0] | None
 ```

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

@@ -3,62 +3,49 @@
 ## After if-else statements, narrowing has no effect if the variable is not mutated in any branch
 
 ```py
-def optional_int() -> int | None: ...
+def _(x: int | None):
+    if x is None:
+        pass
+    else:
+        pass
 
-x = optional_int()
-
-if x is None:
-    pass
-else:
-    pass
-
-reveal_type(x)  # revealed: int | None
+    reveal_type(x)  # revealed: int | None
 ```
 
 ## Narrowing can have a persistent effect if the variable is mutated in one branch
 
 ```py
-def optional_int() -> int | None: ...
+def _(x: int | None):
+    if x is None:
+        x = 10
+    else:
+        pass
 
-x = optional_int()
-
-if x is None:
-    x = 10
-else:
-    pass
-
-reveal_type(x)  # revealed: int
+    reveal_type(x)  # revealed: int
 ```
 
 ## An if statement without an explicit `else` branch is equivalent to one with a no-op `else` branch
 
 ```py
-def optional_int() -> int | None: ...
+def _(x: int | None, y: int | None):
+    if x is None:
+        x = 0
 
-x = optional_int()
-y = optional_int()
+    if y is None:
+        pass
 
-if x is None:
-    x = 0
-
-if y is None:
-    pass
-
-reveal_type(x)  # revealed: int
-reveal_type(y)  # revealed: int | None
+    reveal_type(x)  # revealed: int
+    reveal_type(y)  # revealed: int | None
 ```
 
 ## An if-elif without an explicit else branch is equivalent to one with an empty else branch
 
 ```py
-def optional_int() -> int | None: ...
+def _(x: int | None):
+    if x is None:
+        x = 0
+    elif x > 50:
+        x = 50
 
-x = optional_int()
-
-if x is None:
-    x = 0
-elif x > 50:
-    x = 50
-
-reveal_type(x)  # revealed: int
+    reveal_type(x)  # revealed: int
 ```

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

@@ -6,18 +6,14 @@
 class A: ...
 class B: ...
 
-def get_a_or_b() -> A | B:
-    return A()
-
-x = get_a_or_b()
-
-if type(x) is A:
-    reveal_type(x)  # revealed: A
-else:
-    # It would be wrong to infer `B` here. The type
-    # of `x` could be a subclass of `A`, so we need
-    # to infer the full union type:
-    reveal_type(x)  # revealed: A | B
+def _(x: A | B):
+    if type(x) is A:
+        reveal_type(x)  # revealed: A
+    else:
+        # It would be wrong to infer `B` here. The type
+        # of `x` could be a subclass of `A`, so we need
+        # to infer the full union type:
+        reveal_type(x)  # revealed: A | B
 ```
 
 ## `type(x) is not C`
@@ -26,16 +22,12 @@ else:
 class A: ...
 class B: ...
 
-def get_a_or_b() -> A | B:
-    return A()
-
-x = get_a_or_b()
-
-if type(x) is not A:
-    # Same reasoning as above: no narrowing should occur here.
-    reveal_type(x)  # revealed: A | B
-else:
-    reveal_type(x)  # revealed: A
+def _(x: A | B):
+    if type(x) is not A:
+        # Same reasoning as above: no narrowing should occur here.
+        reveal_type(x)  # revealed: A | B
+    else:
+        reveal_type(x)  # revealed: A
 ```
 
 ## `type(x) == C`, `type(x) != C`
@@ -54,16 +46,12 @@ class IsEqualToEverything(type):
 class A(metaclass=IsEqualToEverything): ...
 class B(metaclass=IsEqualToEverything): ...
 
-def get_a_or_b() -> A | B:
-    return B()
+def _(x: A | B):
+    if type(x) == A:
+        reveal_type(x)  # revealed: A | B
 
-x = get_a_or_b()
-
-if type(x) == A:
-    reveal_type(x)  # revealed: A | B
-
-if type(x) != A:
-    reveal_type(x)  # revealed: A | B
+    if type(x) != A:
+        reveal_type(x)  # revealed: A | B
 ```
 
 ## No narrowing for custom `type` callable
@@ -75,15 +63,11 @@ class B: ...
 def type(x):
     return int
 
-def get_a_or_b() -> A | B:
-    return A()
-
-x = get_a_or_b()
-
-if type(x) is A:
-    reveal_type(x)  # revealed: A | B
-else:
-    reveal_type(x)  # revealed: A | B
+def _(x: A | B):
+    if type(x) is A:
+        reveal_type(x)  # revealed: A | B
+    else:
+        reveal_type(x)  # revealed: A | B
 ```
 
 ## No narrowing for multiple arguments
@@ -91,15 +75,11 @@ else:
 No narrowing should occur if `type` is used to dynamically create a class:
 
 ```py
-def get_str_or_int() -> str | int:
-    return "test"
-
-x = get_str_or_int()
-
-if type(x, (), {}) is str:
-    reveal_type(x)  # revealed: str | int
-else:
-    reveal_type(x)  # revealed: str | int
+def _(x: str | int):
+    if type(x, (), {}) is str:
+        reveal_type(x)  # revealed: str | int
+    else:
+        reveal_type(x)  # revealed: str | int
 ```
 
 ## No narrowing for keyword arguments
@@ -107,14 +87,10 @@ else:
 `type` can't be used with a keyword argument:
 
 ```py
-def get_str_or_int() -> str | int:
-    return "test"
-
-x = get_str_or_int()
-
-# TODO: we could issue a diagnostic here
-if type(object=x) is str:
-    reveal_type(x)  # revealed: str | int
+def _(x: str | int):
+    # TODO: we could issue a diagnostic here
+    if type(object=x) is str:
+        reveal_type(x)  # revealed: str | int
 ```
 
 ## Narrowing if `type` is aliased
@@ -125,13 +101,9 @@ class B: ...
 
 alias_for_type = type
 
-def get_a_or_b() -> A | B:
-    return A()
-
-x = get_a_or_b()
-
-if alias_for_type(x) is A:
-    reveal_type(x)  # revealed: A
+def _(x: A | B):
+    if alias_for_type(x) is A:
+        reveal_type(x)  # revealed: A
 ```
 
 ## Limitations
@@ -140,13 +112,9 @@ if alias_for_type(x) is A:
 class Base: ...
 class Derived(Base): ...
 
-def get_base() -> Base:
-    return Base()
-
-x = get_base()
-
-if type(x) is Base:
-    # Ideally, this could be narrower, but there is now way to
-    # express a constraint like `Base & ~ProperSubtypeOf[Base]`.
-    reveal_type(x)  # revealed: Base
+def _(x: Base):
+    if type(x) is Base:
+        # Ideally, this could be narrower, but there is now way to
+        # express a constraint like `Base & ~ProperSubtypeOf[Base]`.
+        reveal_type(x)  # revealed: Base
 ```

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

@@ -59,7 +59,7 @@ reveal_type(typing.__init__)  # revealed: Literal[__init__]
 # These come from `builtins.object`, not `types.ModuleType`:
 reveal_type(typing.__eq__)  # revealed: Literal[__eq__]
 
-reveal_type(typing.__class__)  # revealed: Literal[type]
+reveal_type(typing.__class__)  # revealed: Literal[ModuleType]
 
 # TODO: needs support for attribute access on instances, properties and generics;
 # should be `dict[str, Any]`

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

@@ -5,10 +5,10 @@
 Name lookups within a class scope fall back to globals, but lookups of class attributes don't.
 
 ```py
-def bool_instance() -> bool:
+def coinflip() -> bool:
     return True
 
-flag = bool_instance()
+flag = coinflip()
 x = 1
 
 class C:
@@ -24,14 +24,14 @@ reveal_type(C.y)  # revealed: Literal[1]
 ## Possibly unbound in class and global scope
 
 ```py
-def bool_instance() -> bool:
+def coinflip() -> bool:
     return True
 
-if bool_instance():
+if coinflip():
     x = "abc"
 
 class C:
-    if bool_instance():
+    if coinflip():
         x = 1
 
     # error: [possibly-unresolved-reference]

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

@@ -3,14 +3,11 @@
 ## Shadow after incompatible declarations is OK
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        x: str
+    else:
+        x: int
 
-flag = bool_instance()
-
-if flag:
-    x: str
-else:
-    x: int
-x: bytes = b"foo"
+    x: bytes = b"foo"
 ```

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

@@ -22,12 +22,10 @@ reveal_type(x)  # revealed: Unknown
 y = b[-6]  # error: [index-out-of-bounds] "Index -6 is out of bounds for bytes literal `Literal[b"\x00abc\xff"]` with length 5"
 reveal_type(y)  # revealed: Unknown
 
-def int_instance() -> int:
-    return 42
-
-a = b"abcde"[int_instance()]
-# TODO: Support overloads... Should be `bytes`
-reveal_type(a)  # revealed: @Todo(return type)
+def _(n: int):
+    a = b"abcde"[n]
+    # TODO: Support overloads... Should be `bytes`
+    reveal_type(a)  # revealed: @Todo(return type)
 ```
 
 ## Slices
@@ -43,15 +41,13 @@ b[:4:0]  # error: [zero-stepsize-in-slice]
 b[0::0]  # error: [zero-stepsize-in-slice]
 b[::0]  # error: [zero-stepsize-in-slice]
 
-def int_instance() -> int: ...
+def _(m: int, n: int):
+    byte_slice1 = b[m:n]
+    # TODO: Support overloads... Should be `bytes`
+    reveal_type(byte_slice1)  # revealed: @Todo(return type)
 
-byte_slice1 = b[int_instance() : int_instance()]
-# TODO: Support overloads... Should be `bytes`
-reveal_type(byte_slice1)  # revealed: @Todo(return type)
-
-def bytes_instance() -> bytes: ...
-
-byte_slice2 = bytes_instance()[0:5]
-# TODO: Support overloads... Should be `bytes`
-reveal_type(byte_slice2)  # revealed: @Todo(return type)
+def _(s: bytes) -> bytes:
+    byte_slice2 = s[0:5]
+    # TODO: Support overloads... Should be `bytes`
+    reveal_type(byte_slice2)  # revealed: @Todo(return type)
 ```

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

@@ -21,77 +21,66 @@ reveal_type(Identity[0])  # revealed: str
 ## Class getitem union
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class UnionClassGetItem:
+        if flag:
+            def __class_getitem__(cls, item: int) -> str:
+                return item
+        else:
+            def __class_getitem__(cls, item: int) -> int:
+                return item
 
-class UnionClassGetItem:
-    if bool_instance():
-
-        def __class_getitem__(cls, item: int) -> str:
-            return item
-    else:
-
-        def __class_getitem__(cls, item: int) -> int:
-            return item
-
-reveal_type(UnionClassGetItem[0])  # revealed: str | int
+    reveal_type(UnionClassGetItem[0])  # revealed: str | int
 ```
 
 ## Class getitem with class union
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class A:
+        def __class_getitem__(cls, item: int) -> str:
+            return item
 
-class A:
-    def __class_getitem__(cls, item: int) -> str:
-        return item
+    class B:
+        def __class_getitem__(cls, item: int) -> int:
+            return item
 
-class B:
-    def __class_getitem__(cls, item: int) -> int:
-        return item
+    x = A if flag else B
 
-x = A if bool_instance() else B
-
-reveal_type(x)  # revealed: Literal[A, B]
-reveal_type(x[0])  # revealed: str | int
+    reveal_type(x)  # revealed: Literal[A, B]
+    reveal_type(x[0])  # revealed: str | int
 ```
 
 ## Class getitem with unbound method union
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        class Spam:
+            def __class_getitem__(self, x: int) -> str:
+                return "foo"
 
-if bool_instance():
-    class Spam:
-        def __class_getitem__(self, x: int) -> str:
-            return "foo"
-
-else:
-    class Spam: ...
-
-# error: [call-possibly-unbound-method] "Method `__class_getitem__` of type `Literal[Spam, Spam]` is possibly unbound"
-# revealed: str
-reveal_type(Spam[42])
+    else:
+        class Spam: ...
+    # error: [call-possibly-unbound-method] "Method `__class_getitem__` of type `Literal[Spam, Spam]` is possibly unbound"
+    # revealed: str
+    reveal_type(Spam[42])
 ```
 
 ## TODO: Class getitem non-class union
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        class Eggs:
+            def __class_getitem__(self, x: int) -> str:
+                return "foo"
 
-if bool_instance():
-    class Eggs:
-        def __class_getitem__(self, x: int) -> str:
-            return "foo"
+    else:
+        Eggs = 1
 
-else:
-    Eggs = 1
+    a = Eggs[42]  # error: "Cannot subscript object of type `Literal[Eggs] | Literal[1]` with no `__getitem__` method"
 
-a = Eggs[42]  # error: "Cannot subscript object of type `Literal[Eggs] | Literal[1]` with no `__getitem__` method"
-
-# TODO: should _probably_ emit `str | Unknown`
-reveal_type(a)  # revealed: Unknown
+    # TODO: should _probably_ emit `str | Unknown`
+    reveal_type(a)  # revealed: Unknown
 ```

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

@@ -30,18 +30,14 @@ reveal_type(Identity()[0])  # revealed: int
 ## Getitem union
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class Identity:
+        if flag:
+            def __getitem__(self, index: int) -> int:
+                return index
+        else:
+            def __getitem__(self, index: int) -> str:
+                return str(index)
 
-class Identity:
-    if bool_instance():
-
-        def __getitem__(self, index: int) -> int:
-            return index
-    else:
-
-        def __getitem__(self, index: int) -> str:
-            return str(index)
-
-reveal_type(Identity()[0])  # revealed: int | str
+    reveal_type(Identity()[0])  # revealed: int | str
 ```

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

@@ -19,11 +19,10 @@ reveal_type(a)  # revealed: Unknown
 b = s[-8]  # error: [index-out-of-bounds] "Index -8 is out of bounds for string `Literal["abcde"]` with length 5"
 reveal_type(b)  # revealed: Unknown
 
-def int_instance() -> int: ...
-
-a = "abcde"[int_instance()]
-# TODO: Support overloads... Should be `str`
-reveal_type(a)  # revealed: @Todo(return type)
+def _(n: int):
+    a = "abcde"[n]
+    # TODO: Support overloads... Should be `str`
+    reveal_type(a)  # revealed: @Todo(return type)
 ```
 
 ## Slices
@@ -74,17 +73,14 @@ s[:4:0]  # error: [zero-stepsize-in-slice]
 s[0::0]  # error: [zero-stepsize-in-slice]
 s[::0]  # error: [zero-stepsize-in-slice]
 
-def int_instance() -> int: ...
+def _(m: int, n: int, s2: str):
+    substring1 = s[m:n]
+    # TODO: Support overloads... Should be `LiteralString`
+    reveal_type(substring1)  # revealed: @Todo(return type)
 
-substring1 = s[int_instance() : int_instance()]
-# TODO: Support overloads... Should be `LiteralString`
-reveal_type(substring1)  # revealed: @Todo(return type)
-
-def str_instance() -> str: ...
-
-substring2 = str_instance()[0:5]
-# TODO: Support overloads... Should be `str`
-reveal_type(substring2)  # revealed: @Todo(return type)
+    substring2 = s2[0:5]
+    # TODO: Support overloads... Should be `str`
+    reveal_type(substring2)  # revealed: @Todo(return type)
 ```
 
 ## Unsupported slice types

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

@@ -67,9 +67,60 @@ t[:4:0]  # error: [zero-stepsize-in-slice]
 t[0::0]  # error: [zero-stepsize-in-slice]
 t[::0]  # error: [zero-stepsize-in-slice]
 
-def int_instance() -> int: ...
-
-tuple_slice = t[int_instance() : int_instance()]
-# TODO: Support overloads... Should be `tuple[Literal[1, 'a', b"b"] | None, ...]`
-reveal_type(tuple_slice)  # revealed: @Todo(return type)
+def _(m: int, n: int):
+    tuple_slice = t[m:n]
+    # TODO: Support overloads... Should be `tuple[Literal[1, 'a', b"b"] | None, ...]`
+    reveal_type(tuple_slice)  # revealed: @Todo(return type)
+```
+
+## Inheritance
+
+```toml
+[environment]
+target-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"
+# error: [invalid-base] "Invalid class base with type `GenericAlias` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
+class A(tuple[int, str]): ...
+
+# Runtime value: `(A, tuple, object)`
+# TODO: Generics
+reveal_type(A.__mro__)  # revealed: tuple[Literal[A], Unknown, Literal[object]]
+```
+
+## `typing.Tuple`
+
+### Correspondence with `tuple`
+
+`typing.Tuple` can be used interchangeably with `tuple`:
+
+```py
+from typing import Tuple
+
+class A: ...
+
+def _(c: Tuple, d: Tuple[int, A], e: Tuple[Any, ...]):
+    reveal_type(c)  # revealed: tuple
+    reveal_type(d)  # revealed: tuple[int, A]
+    reveal_type(e)  # revealed: @Todo(full tuple[...] support)
+```
+
+### Inheritance
+
+Inheriting from `Tuple` results in a MRO with `builtins.tuple` and `typing.Generic`. `Tuple` itself
+is not a class.
+
+```py
+from typing import Tuple
+
+class C(Tuple): ...
+
+# Runtime value: `(C, tuple, typing.Generic, object)`
+# TODO: Add `Generic` to the MRO
+reveal_type(C.__mro__)  # revealed: tuple[Literal[C], Literal[tuple], Unknown, Literal[object]]
 ```

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

@@ -0,0 +1,53 @@
+# type[Any]
+
+## Simple
+
+```py
+def f(x: type[Any]):
+    reveal_type(x)  # revealed: type[Any]
+    # TODO: could be `<object.__repr__ type> & Any`
+    reveal_type(x.__repr__)  # revealed: Any
+
+class A: ...
+
+x: type[Any] = object
+x: type[Any] = type
+x: type[Any] = A
+x: type[Any] = A()  # error: [invalid-assignment]
+```
+
+## Bare type
+
+The interpretation of bare `type` is not clear: existing wording in the spec does not match the
+behavior of mypy or pyright. For now we interpret it as simply "an instance of `builtins.type`",
+which is equivalent to `type[object]`. This is similar to the current behavior of mypy, and pyright
+in strict mode.
+
+```py
+def f(x: type):
+    reveal_type(x)  # revealed: type
+    reveal_type(x.__repr__)  # revealed: @Todo(instance attributes)
+
+class A: ...
+
+x: type = object
+x: type = type
+x: type = A
+x: type = A()  # error: [invalid-assignment]
+```
+
+## type[object] != type[Any]
+
+```py
+def f(x: type[object]):
+    reveal_type(x)  # revealed: type[object]
+    # TODO: bound method types
+    reveal_type(x.__repr__)  # revealed: Literal[__repr__]
+
+class A: ...
+
+x: type[object] = object
+x: type[object] = type
+x: type[object] = A
+x: type[object] = A()  # error: [invalid-assignment]
+```

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

@@ -5,10 +5,8 @@
 ```py
 class A: ...
 
-def f() -> type[A]:
-    return A
-
-reveal_type(f())  # revealed: type[A]
+def _(c: type[A]):
+    reveal_type(c)  # revealed: type[A]
 ```
 
 ## Nested class literal
@@ -17,10 +15,8 @@ reveal_type(f())  # revealed: type[A]
 class A:
     class B: ...
 
-def f() -> type[A.B]:
-    return A.B
-
-reveal_type(f())  # revealed: type[B]
+def f(c: type[A.B]):
+    reveal_type(c)  # revealed: type[B]
 ```
 
 ## Deeply nested class literal
@@ -30,10 +26,8 @@ class A:
     class B:
         class C: ...
 
-def f() -> type[A.B.C]:
-    return A.B.C
-
-reveal_type(f())  # revealed: type[C]
+def f(c: type[A.B.C]):
+    reveal_type(c)  # revealed: type[C]
 ```
 
 ## Class literal from another module
@@ -41,10 +35,8 @@ reveal_type(f())  # revealed: type[C]
 ```py
 from a import A
 
-def f() -> type[A]:
-    return A
-
-reveal_type(f())  # revealed: type[A]
+def f(c: type[A]):
+    reveal_type(c)  # revealed: type[A]
 ```
 
 ```py path=a.py
@@ -56,10 +48,8 @@ class A: ...
 ```py
 import a
 
-def f() -> type[a.B]:
-    return a.B
-
-reveal_type(f())  # revealed: type[B]
+def f(c: type[a.B]):
+    reveal_type(c)  # revealed: type[B]
 ```
 
 ```py path=a.py
@@ -73,12 +63,8 @@ import a.b
 
 # TODO: no diagnostic
 # error: [unresolved-attribute]
-def f() -> type[a.b.C]:
-    # TODO: no diagnostic
-    # error: [unresolved-attribute]
-    return a.b.C
-
-reveal_type(f())  # revealed: @Todo(unsupported type[X] special form)
+def f(c: type[a.b.C]):
+    reveal_type(c)  # revealed: @Todo(unsupported type[X] special form)
 ```
 
 ```py path=a/__init__.py
@@ -88,7 +74,7 @@ reveal_type(f())  # revealed: @Todo(unsupported type[X] special form)
 class C: ...
 ```
 
-## Union of classes
+## New-style union of classes
 
 ```py
 class BasicUser: ...
@@ -98,11 +84,44 @@ class A:
     class B:
         class C: ...
 
-def get_user() -> type[BasicUser | ProUser | A.B.C]:
-    return BasicUser
+def _(u: type[BasicUser | ProUser | A.B.C]):
+    # revealed: type[BasicUser] | type[ProUser] | type[C]
+    reveal_type(u)
+```
 
-# revealed: type[BasicUser] | type[ProUser] | type[C]
-reveal_type(get_user())
+## Old-style union of classes
+
+```py
+from typing import Union
+
+class BasicUser: ...
+class ProUser: ...
+
+class A:
+    class B:
+        class C: ...
+
+def f(a: type[Union[BasicUser, ProUser, A.B.C]], b: type[Union[str]], c: type[Union[BasicUser, Union[ProUser, A.B.C]]]):
+    reveal_type(a)  # revealed: type[BasicUser] | type[ProUser] | type[C]
+    reveal_type(b)  # revealed: type[str]
+    reveal_type(c)  # revealed: type[BasicUser] | type[ProUser] | type[C]
+```
+
+## New-style and old-style unions in combination
+
+```py
+from typing import Union
+
+class BasicUser: ...
+class ProUser: ...
+
+class A:
+    class B:
+        class C: ...
+
+def f(a: type[BasicUser | Union[ProUser, A.B.C]], b: type[Union[BasicUser | Union[ProUser, A.B.C | str]]]):
+    reveal_type(a)  # revealed: type[BasicUser] | type[ProUser] | type[C]
+    reveal_type(b)  # revealed: type[BasicUser] | type[ProUser] | type[C] | type[str]
 ```
 
 ## Illegal parameters
@@ -112,6 +131,16 @@ class A: ...
 class B: ...
 
 # error: [invalid-type-form]
-def get_user() -> type[A, B]:
-    return A
+_: type[A, B]
+```
+
+## As a base class
+
+```py
+# TODO: this is a false positive
+# error: [invalid-base] "Invalid class base with type `GenericAlias` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
+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]]
 ```

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

@@ -0,0 +1,32 @@
+# `typing.Type`
+
+## Annotation
+
+`typing.Type` can be used interchangeably with `type`:
+
+```py
+from typing import Type
+
+class A: ...
+
+def _(c: Type, d: Type[A], e: Type[A]):
+    reveal_type(c)  # revealed: type
+    reveal_type(d)  # revealed: type[A]
+    c = d  # fine
+    d = c  # fine
+```
+
+## Inheritance
+
+Inheriting from `Type` results in a MRO with `builtins.type` and `typing.Generic`. `Type` itself is
+not a class.
+
+```py
+from typing import Type
+
+class C(Type): ...
+
+# Runtime value: `(C, type, typing.Generic, object)`
+# TODO: Add `Generic` to the MRO
+reveal_type(C.__mro__)  # revealed: tuple[Literal[C], Literal[type], Literal[object]]
+```

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

@@ -35,29 +35,25 @@ y = 1
 ## Union
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        p = 1
+        q = 3.3
+        r = "hello"
+        s = "world"
+        t = 0
+    else:
+        p = "hello"
+        q = 4
+        r = ""
+        s = 0
+        t = ""
 
-flag = bool_instance()
-
-if flag:
-    p = 1
-    q = 3.3
-    r = "hello"
-    s = "world"
-    t = 0
-else:
-    p = "hello"
-    q = 4
-    r = ""
-    s = 0
-    t = ""
-
-reveal_type(not p)  # revealed: Literal[False]
-reveal_type(not q)  # revealed: bool
-reveal_type(not r)  # revealed: bool
-reveal_type(not s)  # revealed: bool
-reveal_type(not t)  # revealed: Literal[True]
+    reveal_type(not p)  # revealed: Literal[False]
+    reveal_type(not q)  # revealed: bool
+    reveal_type(not r)  # revealed: bool
+    reveal_type(not s)  # revealed: bool
+    reveal_type(not t)  # revealed: Literal[True]
 ```
 
 ## Integer literal

crates/red_knot_python_semantic/resources/mdtest/with/sync.md

@@ -21,25 +21,23 @@ with Manager() as f:
 ## Union context manager
 
 ```py
-def coinflip() -> bool:
-    return True
+def _(flag: bool):
+    class Manager1:
+        def __enter__(self) -> str:
+            return "foo"
 
-class Manager1:
-    def __enter__(self) -> str:
-        return "foo"
+        def __exit__(self, exc_type, exc_value, traceback): ...
 
-    def __exit__(self, exc_type, exc_value, traceback): ...
+    class Manager2:
+        def __enter__(self) -> int:
+            return 42
 
-class Manager2:
-    def __enter__(self) -> int:
-        return 42
+        def __exit__(self, exc_type, exc_value, traceback): ...
 
-    def __exit__(self, exc_type, exc_value, traceback): ...
+    context_expr = Manager1() if flag else Manager2()
 
-context_expr = Manager1() if coinflip() else Manager2()
-
-with context_expr as f:
-    reveal_type(f)  # revealed: str | int
+    with context_expr as f:
+        reveal_type(f)  # revealed: str | int
 ```
 
 ## Context manager without an `__enter__` or `__exit__` method
@@ -103,39 +101,34 @@ with Manager():
 ## Context expression with possibly-unbound union variants
 
 ```py
-def coinflip() -> bool:
-    return True
+def _(flag: bool):
+    class Manager1:
+        def __enter__(self) -> str:
+            return "foo"
 
-class Manager1:
-    def __enter__(self) -> str:
-        return "foo"
+        def __exit__(self, exc_type, exc_value, traceback): ...
 
-    def __exit__(self, exc_type, exc_value, traceback): ...
+    class NotAContextManager: ...
+    context_expr = Manager1() if flag else NotAContextManager()
 
-class NotAContextManager: ...
-
-context_expr = Manager1() if coinflip() else NotAContextManager()
-
-# error: [invalid-context-manager] "Object of type `Manager1 | NotAContextManager` cannot be used with `with` because the method `__enter__` is possibly unbound"
-# error: [invalid-context-manager] "Object of type `Manager1 | NotAContextManager` cannot be used with `with` because the method `__exit__` is possibly unbound"
-with context_expr as f:
-    reveal_type(f)  # revealed: str
+    # error: [invalid-context-manager] "Object of type `Manager1 | NotAContextManager` cannot be used with `with` because the method `__enter__` is possibly unbound"
+    # error: [invalid-context-manager] "Object of type `Manager1 | NotAContextManager` cannot be used with `with` because the method `__exit__` is possibly unbound"
+    with context_expr as f:
+        reveal_type(f)  # revealed: str
 ```
 
 ## Context expression with "sometimes" callable `__enter__` method
 
 ```py
-def coinflip() -> bool:
-    return True
+def _(flag: bool):
+    class Manager:
+        if flag:
+            def __enter__(self) -> str:
+                return "abcd"
 
-class Manager:
-    if coinflip():
-        def __enter__(self) -> str:
-            return "abcd"
+        def __exit__(self, *args): ...
 
-    def __exit__(self, *args): ...
-
-# error: [invalid-context-manager] "Object of type `Manager` cannot be used with `with` because the method `__enter__` is possibly unbound"
-with Manager() as f:
-    reveal_type(f)  # revealed: str
+    # error: [invalid-context-manager] "Object of type `Manager` cannot be used with `with` because the method `__enter__` is possibly unbound"
+    with Manager() as f:
+        reveal_type(f)  # revealed: str
 ```

crates/red_knot_python_semantic/src/db.rs

@@ -1,3 +1,4 @@
+use crate::lint::RuleSelection;
 use ruff_db::files::File;
 use ruff_db::{Db as SourceDb, Upcast};
 
@@ -5,6 +6,8 @@ use ruff_db::{Db as SourceDb, Upcast};
 #[salsa::db]
 pub trait Db: SourceDb + Upcast<dyn SourceDb> {
     fn is_file_open(&self, file: File) -> bool;
+
+    fn rule_selection(&self) -> &RuleSelection;
 }
 
 #[cfg(test)]
@@ -13,23 +16,24 @@ pub(crate) mod tests {
 
     use crate::program::{Program, SearchPathSettings};
     use crate::python_version::PythonVersion;
-    use crate::ProgramSettings;
+    use crate::{default_lint_registry, ProgramSettings};
 
+    use super::Db;
+    use crate::lint::RuleSelection;
     use anyhow::Context;
     use ruff_db::files::{File, Files};
     use ruff_db::system::{DbWithTestSystem, System, SystemPathBuf, TestSystem};
     use ruff_db::vendored::VendoredFileSystem;
     use ruff_db::{Db as SourceDb, Upcast};
 
-    use super::Db;
-
     #[salsa::db]
     pub(crate) struct TestDb {
         storage: salsa::Storage<Self>,
         files: Files,
         system: TestSystem,
         vendored: VendoredFileSystem,
-        events: std::sync::Arc<std::sync::Mutex<Vec<salsa::Event>>>,
+        events: Arc<std::sync::Mutex<Vec<salsa::Event>>>,
+        rule_selection: Arc<RuleSelection>,
     }
 
     impl TestDb {
@@ -38,8 +42,9 @@ pub(crate) mod tests {
                 storage: salsa::Storage::default(),
                 system: TestSystem::default(),
                 vendored: red_knot_vendored::file_system().clone(),
-                events: std::sync::Arc::default(),
+                events: Arc::default(),
                 files: Files::default(),
+                rule_selection: Arc::new(RuleSelection::from_registry(&default_lint_registry())),
             }
         }
 
@@ -102,6 +107,10 @@ pub(crate) mod tests {
         fn is_file_open(&self, file: File) -> bool {
             !file.path(self).is_vendored_path()
         }
+
+        fn rule_selection(&self) -> &RuleSelection {
+            &self.rule_selection
+        }
     }
 
     #[salsa::db]

crates/red_knot_python_semantic/src/lib.rs

@@ -2,6 +2,7 @@ use std::hash::BuildHasherDefault;
 
 use rustc_hash::FxHasher;
 
+use crate::lint::{LintRegistry, LintRegistryBuilder};
 pub use db::Db;
 pub use module_name::ModuleName;
 pub use module_resolver::{resolve_module, system_module_search_paths, Module};
@@ -11,6 +12,7 @@ pub use semantic_model::{HasTy, SemanticModel};
 
 pub mod ast_node_ref;
 mod db;
+pub mod lint;
 mod module_name;
 mod module_resolver;
 mod node_key;
@@ -26,3 +28,15 @@ mod unpack;
 mod util;
 
 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()
+}
+
+/// Register all known semantic lints.
+pub fn register_lints(registry: &mut LintRegistryBuilder) {
+    types::register_lints(registry);
+}

crates/red_knot_python_semantic/src/lint.rs

@@ -0,0 +1,465 @@
+use itertools::Itertools;
+use ruff_db::diagnostic::{LintName, Severity};
+use rustc_hash::FxHashMap;
+use std::hash::Hasher;
+use thiserror::Error;
+
+#[derive(Debug, Clone)]
+pub struct LintMetadata {
+    /// The unique identifier for the lint.
+    pub name: LintName,
+
+    /// A one-sentence summary of what the lint catches.
+    pub summary: &'static str,
+
+    /// An in depth explanation of the lint in markdown. Covers what the lint does, why it's bad and possible fixes.
+    ///
+    /// The documentation may require post-processing to be rendered correctly. For example, lines
+    /// might have leading or trailing whitespace that should be removed.
+    pub raw_documentation: &'static str,
+
+    /// The default level of the lint if the user doesn't specify one.
+    pub default_level: Level,
+
+    pub status: LintStatus,
+
+    /// The source file in which the lint is declared.
+    pub file: &'static str,
+
+    /// The 1-based line number in the source `file` where the lint is declared.
+    pub line: u32,
+}
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd)]
+pub enum Level {
+    /// The lint is disabled and should not run.
+    Ignore,
+
+    /// The lint is enabled and diagnostic should have a warning severity.
+    Warn,
+
+    /// The lint is enabled and diagnostics have an error severity.
+    Error,
+}
+
+impl Level {
+    pub const fn is_error(self) -> bool {
+        matches!(self, Level::Error)
+    }
+
+    pub const fn is_warn(self) -> bool {
+        matches!(self, Level::Warn)
+    }
+
+    pub const fn is_ignore(self) -> bool {
+        matches!(self, Level::Ignore)
+    }
+}
+
+impl TryFrom<Level> for Severity {
+    type Error = ();
+
+    fn try_from(level: Level) -> Result<Self, ()> {
+        match level {
+            Level::Ignore => Err(()),
+            Level::Warn => Ok(Severity::Warning),
+            Level::Error => Ok(Severity::Error),
+        }
+    }
+}
+
+impl LintMetadata {
+    pub fn name(&self) -> LintName {
+        self.name
+    }
+
+    pub fn summary(&self) -> &str {
+        self.summary
+    }
+
+    /// Returns the documentation line by line with one leading space and all trailing whitespace removed.
+    pub fn documentation_lines(&self) -> impl Iterator<Item = &str> {
+        self.raw_documentation
+            .lines()
+            .map(|line| line.strip_prefix(' ').unwrap_or(line).trim_end())
+    }
+
+    /// Returns the documentation as a single string.
+    pub fn documentation(&self) -> String {
+        self.documentation_lines().join("\n")
+    }
+
+    pub fn default_level(&self) -> Level {
+        self.default_level
+    }
+
+    pub fn status(&self) -> &LintStatus {
+        &self.status
+    }
+
+    pub fn file(&self) -> &str {
+        self.file
+    }
+
+    pub fn line(&self) -> u32 {
+        self.line
+    }
+}
+
+#[doc(hidden)]
+pub const fn lint_metadata_defaults() -> LintMetadata {
+    LintMetadata {
+        name: LintName::of(""),
+        summary: "",
+        raw_documentation: "",
+        default_level: Level::Error,
+        status: LintStatus::preview("0.0.0"),
+        file: "",
+        line: 1,
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum LintStatus {
+    /// The lint has been added to the linter, but is not yet stable.
+    Preview {
+        /// The version in which the lint was added.
+        since: &'static str,
+    },
+
+    /// The lint is stable.
+    Stable {
+        /// The version in which the lint was stabilized.
+        since: &'static str,
+    },
+
+    /// The lint is deprecated and no longer recommended for use.
+    Deprecated {
+        /// The version in which the lint was deprecated.
+        since: &'static str,
+
+        /// The reason why the lint has been deprecated.
+        ///
+        /// This should explain why the lint has been deprecated and if there's a replacement lint that users
+        /// can use instead.
+        reason: &'static str,
+    },
+
+    /// The lint has been removed and can no longer be used.
+    Removed {
+        /// The version in which the lint was removed.
+        since: &'static str,
+
+        /// The reason why the lint has been removed.
+        reason: &'static str,
+    },
+}
+
+impl LintStatus {
+    pub const fn preview(since: &'static str) -> Self {
+        LintStatus::Preview { since }
+    }
+
+    pub const fn stable(since: &'static str) -> Self {
+        LintStatus::Stable { since }
+    }
+
+    pub const fn deprecated(since: &'static str, reason: &'static str) -> Self {
+        LintStatus::Deprecated { since, reason }
+    }
+
+    pub const fn removed(since: &'static str, reason: &'static str) -> Self {
+        LintStatus::Removed { since, reason }
+    }
+
+    pub const fn is_removed(&self) -> bool {
+        matches!(self, LintStatus::Removed { .. })
+    }
+}
+
+/// Declares a lint rule with the given metadata.
+///
+/// ```rust
+/// use red_knot_python_semantic::declare_lint;
+/// use red_knot_python_semantic::lint::{LintStatus, Level};
+///
+/// declare_lint! {
+///     /// ## What it does
+///     /// Checks for references to names that are not defined.
+///     ///
+///     /// ## Why is this bad?
+///     /// Using an undefined variable will raise a `NameError` at runtime.
+///     ///
+///     /// ## Example
+///     ///
+///     /// ```python
+///     /// print(x)  # NameError: name 'x' is not defined
+///     /// ```
+///     pub(crate) static UNRESOLVED_REFERENCE = {
+///         summary: "detects references to names that are not defined",
+///         status: LintStatus::preview("1.0.0"),
+///         default_level: Level::Warn,
+///     }
+/// }
+/// ```
+#[macro_export]
+macro_rules! declare_lint {
+    (
+        $(#[doc = $doc:literal])+
+        $vis: vis static $name: ident = {
+            summary: $summary: literal,
+            status: $status: expr,
+            // Optional properties
+            $( $key:ident: $value:expr, )*
+        }
+    ) => {
+        $( #[doc = $doc] )+
+        #[allow(clippy::needless_update)]
+        $vis static $name: $crate::lint::LintMetadata = $crate::lint::LintMetadata {
+            name: ruff_db::diagnostic::LintName::of(ruff_macros::kebab_case!($name)),
+            summary: $summary,
+            raw_documentation: concat!($($doc,)+ "\n"),
+            status: $status,
+            file: file!(),
+            line: line!(),
+            $( $key: $value, )*
+            ..$crate::lint::lint_metadata_defaults()
+        };
+    };
+}
+
+/// A unique identifier for a lint rule.
+///
+/// Implements `PartialEq`, `Eq`, and `Hash` based on the `LintMetadata` pointer
+/// for fast comparison and lookup.
+#[derive(Debug, Clone, Copy)]
+pub struct LintId {
+    definition: &'static LintMetadata,
+}
+
+impl LintId {
+    pub const fn of(definition: &'static LintMetadata) -> Self {
+        LintId { definition }
+    }
+}
+
+impl PartialEq for LintId {
+    fn eq(&self, other: &Self) -> bool {
+        std::ptr::eq(self.definition, other.definition)
+    }
+}
+
+impl Eq for LintId {}
+
+impl std::hash::Hash for LintId {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        std::ptr::hash(self.definition, state);
+    }
+}
+
+impl std::ops::Deref for LintId {
+    type Target = LintMetadata;
+
+    fn deref(&self) -> &Self::Target {
+        self.definition
+    }
+}
+
+#[derive(Default, Debug)]
+pub struct LintRegistryBuilder {
+    /// Registered lints that haven't been removed.
+    lints: Vec<LintId>,
+
+    /// Lints indexed by name, including aliases and removed rules.
+    by_name: FxHashMap<&'static str, LintEntry>,
+}
+
+impl LintRegistryBuilder {
+    #[track_caller]
+    pub fn register_lint(&mut self, lint: &'static LintMetadata) {
+        assert_eq!(
+            self.by_name.insert(&*lint.name, lint.into()),
+            None,
+            "duplicate lint registration for '{name}'",
+            name = lint.name
+        );
+
+        if !lint.status.is_removed() {
+            self.lints.push(LintId::of(lint));
+        }
+    }
+
+    #[track_caller]
+    pub fn register_alias(&mut self, from: LintName, to: &'static LintMetadata) {
+        let target = match self.by_name.get(to.name.as_str()) {
+            Some(LintEntry::Lint(target) | LintEntry::Removed(target)) => target,
+            Some(LintEntry::Alias(target)) => {
+                panic!(
+                    "lint alias {from} -> {to:?} points to another alias {target:?}",
+                    target = target.name()
+                )
+            }
+            None => panic!(
+                "lint alias {from} -> {to} points to non-registered lint",
+                to = to.name
+            ),
+        };
+
+        assert_eq!(
+            self.by_name
+                .insert(from.as_str(), LintEntry::Alias(*target)),
+            None,
+            "duplicate lint registration for '{from}'",
+        );
+    }
+
+    pub fn build(self) -> LintRegistry {
+        LintRegistry {
+            lints: self.lints,
+            by_name: self.by_name,
+        }
+    }
+}
+
+#[derive(Default, Debug)]
+pub struct LintRegistry {
+    lints: Vec<LintId>,
+    by_name: FxHashMap<&'static str, LintEntry>,
+}
+
+impl LintRegistry {
+    /// Looks up a lint by its name.
+    pub fn get(&self, code: &str) -> Result<LintId, GetLintError> {
+        match self.by_name.get(code) {
+            Some(LintEntry::Lint(metadata)) => Ok(*metadata),
+            Some(LintEntry::Alias(lint)) => {
+                if lint.status.is_removed() {
+                    Err(GetLintError::Removed(lint.name()))
+                } else {
+                    Ok(*lint)
+                }
+            }
+            Some(LintEntry::Removed(lint)) => Err(GetLintError::Removed(lint.name())),
+            None => Err(GetLintError::Unknown(code.to_string())),
+        }
+    }
+
+    /// Returns all registered, non-removed lints.
+    pub fn lints(&self) -> &[LintId] {
+        &self.lints
+    }
+
+    /// Returns an iterator over all known aliases and to their target lints.
+    ///
+    /// This iterator includes aliases that point to removed lints.
+    pub fn aliases(&self) -> impl Iterator<Item = (LintName, LintId)> + '_ {
+        self.by_name.iter().filter_map(|(key, value)| {
+            if let LintEntry::Alias(alias) = value {
+                Some((LintName::of(key), *alias))
+            } else {
+                None
+            }
+        })
+    }
+
+    /// Iterates over all removed lints.
+    pub fn removed(&self) -> impl Iterator<Item = LintId> + '_ {
+        self.by_name.iter().filter_map(|(_, value)| {
+            if let LintEntry::Removed(metadata) = value {
+                Some(*metadata)
+            } else {
+                None
+            }
+        })
+    }
+}
+
+#[derive(Error, Debug, Clone)]
+pub enum GetLintError {
+    /// The name maps to this removed lint.
+    #[error("lint {0} has been removed")]
+    Removed(LintName),
+
+    /// No lint with the given name is known.
+    #[error("unknown lint {0}")]
+    Unknown(String),
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum LintEntry {
+    /// An existing lint rule. Can be in preview, stable or deprecated.
+    Lint(LintId),
+    /// A lint rule that has been removed.
+    Removed(LintId),
+    Alias(LintId),
+}
+
+impl From<&'static LintMetadata> for LintEntry {
+    fn from(metadata: &'static LintMetadata) -> Self {
+        if metadata.status.is_removed() {
+            LintEntry::Removed(LintId::of(metadata))
+        } else {
+            LintEntry::Lint(LintId::of(metadata))
+        }
+    }
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct RuleSelection {
+    /// Map with the severity for each enabled lint rule.
+    ///
+    /// If a rule isn't present in this map, then it should be considered disabled.
+    lints: FxHashMap<LintId, Severity>,
+}
+
+impl RuleSelection {
+    /// Creates a new rule selection from all known lints in the registry that are enabled
+    /// according to their default severity.
+    pub fn from_registry(registry: &LintRegistry) -> Self {
+        let lints = registry
+            .lints()
+            .iter()
+            .filter_map(|lint| {
+                Severity::try_from(lint.default_level())
+                    .ok()
+                    .map(|severity| (*lint, severity))
+            })
+            .collect();
+
+        RuleSelection { lints }
+    }
+
+    /// Returns an iterator over all enabled lints.
+    pub fn enabled(&self) -> impl Iterator<Item = LintId> + '_ {
+        self.lints.keys().copied()
+    }
+
+    /// Returns an iterator over all enabled lints and their severity.
+    pub fn iter(&self) -> impl ExactSizeIterator<Item = (LintId, Severity)> + '_ {
+        self.lints.iter().map(|(&lint, &severity)| (lint, severity))
+    }
+
+    /// Returns the configured severity for the lint with the given id or `None` if the lint is disabled.
+    pub fn severity(&self, lint: LintId) -> Option<Severity> {
+        self.lints.get(&lint).copied()
+    }
+
+    /// Enables `lint` and configures with the given `severity`.
+    ///
+    /// Overrides any previous configuration for the lint.
+    pub fn enable(&mut self, lint: LintId, severity: Severity) {
+        self.lints.insert(lint, severity);
+    }
+
+    /// Disables `lint` if it was previously enabled.
+    pub fn disable(&mut self, lint: LintId) {
+        self.lints.remove(&lint);
+    }
+
+    /// Merges the enabled lints from `other` into this selection.
+    ///
+    /// Lints from `other` will override any existing configuration.
+    pub fn merge(&mut self, other: &RuleSelection) {
+        self.lints.extend(other.iter());
+    }
+}

crates/red_knot_python_semantic/src/semantic_index/use_def.rs

@@ -47,7 +47,7 @@
 //! The **declared type** represents the code author's declaration (usually through a type
 //! annotation) that a given variable should not be assigned any type outside the declared type. In
 //! our model, declared types are also control-flow-sensitive; we allow the code author to
-//! explicitly re-declare the same variable with a different type. So for a given binding of a
+//! explicitly redeclare the same variable with a different type. So for a given binding of a
 //! variable, we will want to ask which declarations of that variable can reach that binding, in
 //! order to determine whether the binding is permitted, or should be a type error. For example:
 //!
@@ -62,7 +62,7 @@
 //! assignable to `str`. This is the purpose of declared types: they prevent accidental assignment
 //! of the wrong type to a variable.
 //!
-//! But in some cases it is useful to "shadow" or "re-declare" a variable with a new type, and we
+//! But in some cases it is useful to "shadow" or "redeclare" a variable with a new type, and we
 //! permit this, as long as it is done with an explicit re-annotation. So `path: Path =
 //! Path(path)`, with the explicit `: Path` annotation, is permitted.
 //!

crates/red_knot_python_semantic/src/types.rs

@@ -2,11 +2,12 @@ use std::hash::Hash;
 
 use indexmap::IndexSet;
 use itertools::Itertools;
-
+use ruff_db::diagnostic::Severity;
 use ruff_db::files::File;
 use ruff_python_ast as ast;
 
 pub(crate) use self::builder::{IntersectionBuilder, UnionBuilder};
+pub(crate) use self::diagnostic::register_lints;
 pub use self::diagnostic::{TypeCheckDiagnostic, TypeCheckDiagnostics};
 pub(crate) use self::display::TypeArrayDisplay;
 pub(crate) use self::infer::{
@@ -25,12 +26,14 @@ use crate::stdlib::{
     builtins_symbol, core_module_symbol, typing_extensions_symbol, CoreStdlibModule,
 };
 use crate::symbol::{Boundness, Symbol};
+use crate::types::call::{CallDunderResult, CallOutcome};
 use crate::types::diagnostic::TypeCheckDiagnosticsBuilder;
 use crate::types::mro::{ClassBase, Mro, MroError, MroIterator};
 use crate::types::narrow::narrowing_constraint;
 use crate::{Db, FxOrderSet, Module, Program, PythonVersion};
 
 mod builder;
+mod call;
 mod diagnostic;
 mod display;
 mod infer;
@@ -225,18 +228,6 @@ fn definition_expression_ty<'db>(
     }
 }
 
-/// Get the type of an expression from an arbitrary scope.
-///
-/// Can cause query cycles if used carelessly; caller must be sure that type inference isn't
-/// currently in progress for the expression's scope.
-fn expression_ty<'db>(db: &'db dyn Db, file: File, expression: &ast::Expr) -> Type<'db> {
-    let index = semantic_index(db, file);
-    let file_scope = index.expression_scope_id(expression);
-    let scope = file_scope.to_scope_id(db, file);
-    let expr_id = expression.scoped_expression_id(db, scope);
-    infer_scope_types(db, scope).expression_ty(expr_id)
-}
-
 /// Infer the combined type of an iterator of bindings.
 ///
 /// Will return a union if there is more than one binding.
@@ -572,7 +563,11 @@ impl<'db> Type<'db> {
     }
 
     pub const fn subclass_of(class: Class<'db>) -> Self {
-        Self::SubclassOf(SubclassOfType { class })
+        Self::subclass_of_base(ClassBase::Class(class))
+    }
+
+    pub const fn subclass_of_base(base: ClassBase<'db>) -> Self {
+        Self::SubclassOf(SubclassOfType { base })
     }
 
     pub fn string_literal(db: &'db dyn Db, string: &str) -> Self {
@@ -617,8 +612,6 @@ impl<'db> Type<'db> {
             return false;
         }
         match (self, target) {
-            (Type::Unknown | Type::Any | Type::Todo(_), _) => false,
-            (_, Type::Unknown | Type::Any | Type::Todo(_)) => false,
             (Type::Never, _) => true,
             (_, Type::Never) => false,
             (_, Type::Instance(InstanceType { class }))
@@ -661,19 +654,31 @@ impl<'db> Type<'db> {
                         },
                     )
             }
-            (Type::ClassLiteral(..), Type::Instance(InstanceType { class }))
-                if class.is_known(db, KnownClass::Type) =>
-            {
-                true
-            }
             (Type::ClassLiteral(self_class), Type::SubclassOf(target_class)) => {
-                self_class.class.is_subclass_of(db, target_class.class)
-            }
-            (Type::SubclassOf(self_class), Type::SubclassOf(target_class)) => {
-                self_class.class.is_subclass_of(db, target_class.class)
+                self_class.class.is_subclass_of_base(db, target_class.base)
             }
             (
-                Type::SubclassOf(SubclassOfType { class: self_class }),
+                Type::Instance(InstanceType { class: self_class }),
+                Type::SubclassOf(target_class),
+            ) if self_class.is_known(db, KnownClass::Type) => {
+                self_class.is_subclass_of_base(db, target_class.base)
+            }
+            (
+                Type::SubclassOf(SubclassOfType {
+                    base: ClassBase::Class(self_class),
+                }),
+                Type::SubclassOf(SubclassOfType {
+                    base: ClassBase::Class(target_class),
+                }),
+            ) => self_class.is_subclass_of(db, target_class),
+            // C ⊆ type
+            // type[C] ⊆ type
+            // Though note that this works regardless of which metaclass C has, not just for type.
+            (
+                Type::ClassLiteral(ClassLiteralType { class: self_class })
+                | Type::SubclassOf(SubclassOfType {
+                    base: ClassBase::Class(self_class),
+                }),
                 Type::Instance(InstanceType {
                     class: target_class,
                 }),
@@ -770,6 +775,30 @@ impl<'db> Type<'db> {
                         },
                     )
             }
+            (
+                Type::SubclassOf(SubclassOfType {
+                    base: ClassBase::Any,
+                }),
+                Type::SubclassOf(_),
+            ) => true,
+            (
+                Type::SubclassOf(SubclassOfType {
+                    base: ClassBase::Any,
+                }),
+                Type::Instance(target),
+            ) if target.class.is_known(db, KnownClass::Type) => true,
+            (
+                Type::Instance(class),
+                Type::SubclassOf(SubclassOfType {
+                    base: ClassBase::Any,
+                }),
+            ) if class.class.is_known(db, KnownClass::Type) => true,
+            (
+                Type::ClassLiteral(_) | Type::SubclassOf(_),
+                Type::SubclassOf(SubclassOfType {
+                    base: ClassBase::Any,
+                }),
+            ) => true,
             // TODO other types containing gradual forms (e.g. generics containing Any/Unknown)
             _ => self.is_subtype_of(db, target),
         }
@@ -785,27 +814,56 @@ impl<'db> Type<'db> {
             return false;
         }
 
+        // TODO: The following is a workaround that is required to unify the two different versions
+        // of `NoneType` and `NoDefaultType` in typeshed. This should not be required anymore once
+        // we understand `sys.version_info` branches.
+        if let (
+            Type::Instance(InstanceType { class: self_class }),
+            Type::Instance(InstanceType {
+                class: target_class,
+            }),
+        ) = (self, other)
+        {
+            let self_known = self_class.known(db);
+            if matches!(
+                self_known,
+                Some(KnownClass::NoneType | KnownClass::NoDefaultType)
+            ) && self_known == target_class.known(db)
+            {
+                return true;
+            }
+        }
+
+        // type[object] ≡ type
+        if let (
+            Type::SubclassOf(SubclassOfType {
+                base: ClassBase::Class(object_class),
+            }),
+            Type::Instance(InstanceType { class: type_class }),
+        )
+        | (
+            Type::Instance(InstanceType { class: type_class }),
+            Type::SubclassOf(SubclassOfType {
+                base: ClassBase::Class(object_class),
+            }),
+        ) = (self, other)
+        {
+            // This is the only case where "instance of a class" is equivalent to "subclass of a
+            // class", so we don't need to fall through if we're not looking at instance[type] and
+            // type[object] specifically.
+            return object_class.is_known(db, KnownClass::Object)
+                && type_class.is_known(db, KnownClass::Type);
+        }
+
         // TODO equivalent but not identical structural types, differently-ordered unions and
         // intersections, other cases?
 
         // TODO: Once we have support for final classes, we can establish that
         // `Type::SubclassOf('FinalClass')` is equivalent to `Type::ClassLiteral('FinalClass')`.
 
-        // TODO: The following is a workaround that is required to unify the two different versions
-        // of `NoneType` and `NoDefaultType` in typeshed. This should not be required anymore once
-        // we understand `sys.version_info` branches.
+        // For all other cases, types are equivalent iff they have the same internal
+        // representation.
         self == other
-            || matches!((self, other),
-                (
-                    Type::Instance(InstanceType { class: self_class }),
-                    Type::Instance(InstanceType { class: target_class })
-                )
-                if {
-                    let self_known = self_class.known(db);
-                    matches!(self_known, Some(KnownClass::NoneType | KnownClass::NoDefaultType))
-                        && self_known == target_class.known(db)
-                }
-            )
     }
 
     /// Returns true if both `self` and `other` are the same gradual form
@@ -872,7 +930,7 @@ impl<'db> Type<'db> {
 
             (Type::SubclassOf(type_class), Type::ClassLiteral(class_literal))
             | (Type::ClassLiteral(class_literal), Type::SubclassOf(type_class)) => {
-                !class_literal.class.is_subclass_of(db, type_class.class)
+                !class_literal.class.is_subclass_of_base(db, type_class.base)
             }
             (Type::SubclassOf(_), Type::SubclassOf(_)) => false,
             (Type::SubclassOf(_), Type::Instance(_)) | (Type::Instance(_), Type::SubclassOf(_)) => {
@@ -1039,7 +1097,8 @@ impl<'db> Type<'db> {
             | Type::BytesLiteral(_)
             | Type::SliceLiteral(_)
             | Type::KnownInstance(_) => true,
-            Type::ClassLiteral(_) | Type::SubclassOf(_) | Type::Instance(_) => {
+            Type::SubclassOf(SubclassOfType { base }) => matches!(base, ClassBase::Class(_)),
+            Type::ClassLiteral(_) | Type::Instance(_) => {
                 // TODO: Ideally, we would iterate over the MRO of the class, check if all
                 // bases are fully static, and only return `true` if that is the case.
                 //
@@ -1185,6 +1244,8 @@ impl<'db> Type<'db> {
                     | KnownClass::Set
                     | KnownClass::Dict
                     | KnownClass::Slice
+                    | KnownClass::BaseException
+                    | KnownClass::BaseExceptionGroup
                     | KnownClass::GenericAlias
                     | KnownClass::ModuleType
                     | KnownClass::FunctionType
@@ -1211,6 +1272,10 @@ impl<'db> Type<'db> {
     /// as accessed from instances of the `Bar` class.
     #[must_use]
     pub(crate) fn member(&self, db: &'db dyn Db, name: &str) -> Symbol<'db> {
+        if name == "__class__" {
+            return self.to_meta_type(db).into();
+        }
+
         match self {
             Type::Any => Type::Any.into(),
             Type::Never => {
@@ -1599,12 +1664,6 @@ impl<'db> Type<'db> {
             };
         }
 
-        if matches!(self, Type::Unknown | Type::Any | Type::Todo(_)) {
-            // Explicit handling of `Unknown` and `Any` necessary until `type[Unknown]` and
-            // `type[Any]` are not defined as `Todo` anymore.
-            return IterationOutcome::Iterable { element_ty: self };
-        }
-
         let dunder_iter_result = self.call_dunder(db, "__iter__", &[self]);
         match dunder_iter_result {
             CallDunderResult::CallOutcome(ref call_outcome)
@@ -1662,7 +1721,10 @@ impl<'db> Type<'db> {
             Type::Unknown => Type::Unknown,
             Type::Never => Type::Never,
             Type::ClassLiteral(ClassLiteralType { class }) => Type::instance(*class),
-            Type::SubclassOf(SubclassOfType { class }) => Type::instance(*class),
+            Type::SubclassOf(SubclassOfType {
+                base: ClassBase::Class(class),
+            }) => Type::instance(*class),
+            Type::SubclassOf(_) => Type::Any,
             Type::Union(union) => union.map(db, |element| element.to_instance(db)),
             // TODO: we can probably do better here: --Alex
             Type::Intersection(_) => todo_type!(),
@@ -1691,7 +1753,12 @@ impl<'db> Type<'db> {
     #[must_use]
     pub fn in_type_expression(&self, db: &'db dyn Db) -> Type<'db> {
         match self {
+            // In a type expression, a bare `type` is interpreted as "instance of `type`", which is
+            // equivalent to `type[object]`.
             Type::ClassLiteral(_) | Type::SubclassOf(_) => self.to_instance(db),
+            // We treat `typing.Type` exactly the same as `builtins.type`:
+            Type::KnownInstance(KnownInstanceType::Type) => KnownClass::Type.to_instance(db),
+            Type::KnownInstance(KnownInstanceType::Tuple) => KnownClass::Tuple.to_instance(db),
             Type::Union(union) => union.map(db, |element| element.in_type_expression(db)),
             Type::Unknown => Type::Unknown,
             // TODO map this to a new `Type::TypeVar` variant
@@ -1750,9 +1817,7 @@ impl<'db> Type<'db> {
     pub fn to_meta_type(&self, db: &'db dyn Db) -> Type<'db> {
         match self {
             Type::Never => Type::Never,
-            Type::Instance(InstanceType { class }) => {
-                Type::SubclassOf(SubclassOfType { class: *class })
-            }
+            Type::Instance(InstanceType { class }) => Type::subclass_of(*class),
             Type::KnownInstance(known_instance) => known_instance.class().to_class_literal(db),
             Type::Union(union) => union.map(db, |ty| ty.to_meta_type(db)),
             Type::BooleanLiteral(_) => KnownClass::Bool.to_class_literal(db),
@@ -1763,7 +1828,9 @@ impl<'db> Type<'db> {
             Type::ModuleLiteral(_) => KnownClass::ModuleType.to_class_literal(db),
             Type::Tuple(_) => KnownClass::Tuple.to_class_literal(db),
             Type::ClassLiteral(ClassLiteralType { class }) => class.metaclass(db),
-            Type::SubclassOf(SubclassOfType { class }) => Type::subclass_of(
+            Type::SubclassOf(SubclassOfType {
+                base: ClassBase::Class(class),
+            }) => Type::subclass_of(
                 class
                     .try_metaclass(db)
                     .ok()
@@ -1771,10 +1838,9 @@ impl<'db> Type<'db> {
                     .unwrap_or_else(|| KnownClass::Type.to_class_literal(db).expect_class_literal())
                     .class,
             ),
+            Type::SubclassOf(_) => Type::Any,
             Type::StringLiteral(_) | Type::LiteralString => KnownClass::Str.to_class_literal(db),
-            // TODO: `type[Any]`?
             Type::Any => Type::Any,
-            // TODO: `type[Unknown]`?
             Type::Unknown => Type::Unknown,
             // TODO intersections
             Type::Intersection(_) => todo_type!(),
@@ -1857,6 +1923,8 @@ pub enum KnownClass {
     Set,
     Dict,
     Slice,
+    BaseException,
+    BaseExceptionGroup,
     // Types
     GenericAlias,
     ModuleType,
@@ -1887,6 +1955,8 @@ impl<'db> KnownClass {
             Self::List => "list",
             Self::Type => "type",
             Self::Slice => "slice",
+            Self::BaseException => "BaseException",
+            Self::BaseExceptionGroup => "BaseExceptionGroup",
             Self::GenericAlias => "GenericAlias",
             Self::ModuleType => "ModuleType",
             Self::FunctionType => "FunctionType",
@@ -1914,6 +1984,12 @@ impl<'db> KnownClass {
             .unwrap_or(Type::Unknown)
     }
 
+    pub fn to_subclass_of(self, db: &'db dyn Db) -> Option<Type<'db>> {
+        self.to_class_literal(db)
+            .into_class_literal()
+            .map(|ClassLiteralType { class }| Type::subclass_of(class))
+    }
+
     /// Return the module in which we should look up the definition for this class
     pub(crate) fn canonical_module(self, db: &'db dyn Db) -> CoreStdlibModule {
         match self {
@@ -1928,6 +2004,8 @@ impl<'db> KnownClass {
             | Self::Tuple
             | Self::Set
             | Self::Dict
+            | Self::BaseException
+            | Self::BaseExceptionGroup
             | Self::Slice => CoreStdlibModule::Builtins,
             Self::VersionInfo => CoreStdlibModule::Sys,
             Self::GenericAlias | Self::ModuleType | Self::FunctionType => CoreStdlibModule::Types,
@@ -1971,6 +2049,8 @@ impl<'db> KnownClass {
             | Self::ModuleType
             | Self::FunctionType
             | Self::SpecialForm
+            | Self::BaseException
+            | Self::BaseExceptionGroup
             | Self::TypeVar => false,
         }
     }
@@ -1992,6 +2072,8 @@ impl<'db> KnownClass {
             "dict" => Self::Dict,
             "list" => Self::List,
             "slice" => Self::Slice,
+            "BaseException" => Self::BaseException,
+            "BaseExceptionGroup" => Self::BaseExceptionGroup,
             "GenericAlias" => Self::GenericAlias,
             "NoneType" => Self::NoneType,
             "ModuleType" => Self::ModuleType,
@@ -2028,6 +2110,8 @@ impl<'db> KnownClass {
             | Self::GenericAlias
             | Self::ModuleType
             | Self::VersionInfo
+            | Self::BaseException
+            | Self::BaseExceptionGroup
             | Self::FunctionType => module.name() == self.canonical_module(db).as_str(),
             Self::NoneType => matches!(module.name().as_str(), "_typeshed" | "types"),
             Self::SpecialForm | Self::TypeVar | Self::TypeAliasType | Self::NoDefaultType => {
@@ -2054,6 +2138,10 @@ pub enum KnownInstanceType<'db> {
     Never,
     /// The symbol `typing.Any` (which can also be found as `typing_extensions.Any`)
     Any,
+    /// The symbol `typing.Tuple` (which can also be found as `typing_extensions.Tuple`)
+    Tuple,
+    /// The symbol `typing.Type` (which can also be found as `typing_extensions.Type`)
+    Type,
     /// A single instance of `typing.TypeVar`
     TypeVar(TypeVarInstance<'db>),
     /// A single instance of `typing.TypeAliasType` (PEP 695 type alias)
@@ -2072,6 +2160,8 @@ impl<'db> KnownInstanceType<'db> {
             Self::NoReturn => "NoReturn",
             Self::Never => "Never",
             Self::Any => "Any",
+            Self::Tuple => "Tuple",
+            Self::Type => "Type",
             Self::TypeAliasType(_) => "TypeAliasType",
         }
     }
@@ -2087,6 +2177,8 @@ impl<'db> KnownInstanceType<'db> {
             | Self::NoReturn
             | Self::Never
             | Self::Any
+            | Self::Tuple
+            | Self::Type
             | Self::TypeAliasType(_) => Truthiness::AlwaysTrue,
         }
     }
@@ -2101,6 +2193,8 @@ impl<'db> KnownInstanceType<'db> {
             Self::NoReturn => "typing.NoReturn",
             Self::Never => "typing.Never",
             Self::Any => "typing.Any",
+            Self::Tuple => "typing.Tuple",
+            Self::Type => "typing.Type",
             Self::TypeVar(typevar) => typevar.name(db),
             Self::TypeAliasType(_) => "typing.TypeAliasType",
         }
@@ -2116,6 +2210,8 @@ impl<'db> KnownInstanceType<'db> {
             Self::NoReturn => KnownClass::SpecialForm,
             Self::Never => KnownClass::SpecialForm,
             Self::Any => KnownClass::Object,
+            Self::Tuple => KnownClass::SpecialForm,
+            Self::Type => KnownClass::SpecialForm,
             Self::TypeVar(_) => KnownClass::TypeVar,
             Self::TypeAliasType(_) => KnownClass::TypeAliasType,
         }
@@ -2142,6 +2238,8 @@ impl<'db> KnownInstanceType<'db> {
             ("typing" | "typing_extensions", "Union") => Some(Self::Union),
             ("typing" | "typing_extensions", "NoReturn") => Some(Self::NoReturn),
             ("typing" | "typing_extensions", "Never") => Some(Self::Never),
+            ("typing" | "typing_extensions", "Tuple") => Some(Self::Tuple),
+            ("typing" | "typing_extensions", "Type") => Some(Self::Type),
             _ => None,
         }
     }
@@ -2206,312 +2304,6 @@ pub enum TypeVarBoundOrConstraints<'db> {
     Constraints(TupleType<'db>),
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
-enum CallOutcome<'db> {
-    Callable {
-        return_ty: Type<'db>,
-    },
-    RevealType {
-        return_ty: Type<'db>,
-        revealed_ty: Type<'db>,
-    },
-    NotCallable {
-        not_callable_ty: Type<'db>,
-    },
-    Union {
-        called_ty: Type<'db>,
-        outcomes: Box<[CallOutcome<'db>]>,
-    },
-    PossiblyUnboundDunderCall {
-        called_ty: Type<'db>,
-        call_outcome: Box<CallOutcome<'db>>,
-    },
-}
-
-impl<'db> CallOutcome<'db> {
-    /// Create a new `CallOutcome::Callable` with given return type.
-    fn callable(return_ty: Type<'db>) -> CallOutcome<'db> {
-        CallOutcome::Callable { return_ty }
-    }
-
-    /// Create a new `CallOutcome::NotCallable` with given not-callable type.
-    fn not_callable(not_callable_ty: Type<'db>) -> CallOutcome<'db> {
-        CallOutcome::NotCallable { not_callable_ty }
-    }
-
-    /// Create a new `CallOutcome::RevealType` with given revealed and return types.
-    fn revealed(return_ty: Type<'db>, revealed_ty: Type<'db>) -> CallOutcome<'db> {
-        CallOutcome::RevealType {
-            return_ty,
-            revealed_ty,
-        }
-    }
-
-    /// Create a new `CallOutcome::Union` with given wrapped outcomes.
-    fn union(
-        called_ty: Type<'db>,
-        outcomes: impl IntoIterator<Item = CallOutcome<'db>>,
-    ) -> CallOutcome<'db> {
-        CallOutcome::Union {
-            called_ty,
-            outcomes: outcomes.into_iter().collect(),
-        }
-    }
-
-    /// Get the return type of the call, or `None` if not callable.
-    fn return_ty(&self, db: &'db dyn Db) -> Option<Type<'db>> {
-        match self {
-            Self::Callable { return_ty } => Some(*return_ty),
-            Self::RevealType {
-                return_ty,
-                revealed_ty: _,
-            } => Some(*return_ty),
-            Self::NotCallable { not_callable_ty: _ } => None,
-            Self::Union {
-                outcomes,
-                called_ty: _,
-            } => outcomes
-                .iter()
-                // If all outcomes are NotCallable, we return None; if some outcomes are callable
-                // and some are not, we return a union including Unknown.
-                .fold(None, |acc, outcome| {
-                    let ty = outcome.return_ty(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))),
-                    }
-                })
-                .map(UnionBuilder::build),
-            Self::PossiblyUnboundDunderCall { call_outcome, .. } => call_outcome.return_ty(db),
-        }
-    }
-
-    /// Get the return type of the call, emitting default diagnostics if needed.
-    fn unwrap_with_diagnostic<'a>(
-        &self,
-        db: &'db dyn Db,
-        node: ast::AnyNodeRef,
-        diagnostics: &'a mut TypeCheckDiagnosticsBuilder<'db>,
-    ) -> Type<'db> {
-        match self.return_ty_result(db, node, diagnostics) {
-            Ok(return_ty) => return_ty,
-            Err(NotCallableError::Type {
-                not_callable_ty,
-                return_ty,
-            }) => {
-                diagnostics.add(
-                    node,
-                    "call-non-callable",
-                    format_args!(
-                        "Object of type `{}` is not callable",
-                        not_callable_ty.display(db)
-                    ),
-                );
-                return_ty
-            }
-            Err(NotCallableError::UnionElement {
-                not_callable_ty,
-                called_ty,
-                return_ty,
-            }) => {
-                diagnostics.add(
-                    node,
-                    "call-non-callable",
-                    format_args!(
-                        "Object of type `{}` is not callable (due to union element `{}`)",
-                        called_ty.display(db),
-                        not_callable_ty.display(db),
-                    ),
-                );
-                return_ty
-            }
-            Err(NotCallableError::UnionElements {
-                not_callable_tys,
-                called_ty,
-                return_ty,
-            }) => {
-                diagnostics.add(
-                    node,
-                    "call-non-callable",
-                    format_args!(
-                        "Object of type `{}` is not callable (due to union elements {})",
-                        called_ty.display(db),
-                        not_callable_tys.display(db),
-                    ),
-                );
-                return_ty
-            }
-            Err(NotCallableError::PossiblyUnboundDunderCall {
-                callable_ty: called_ty,
-                return_ty,
-            }) => {
-                diagnostics.add(
-                    node,
-                    "call-non-callable",
-                    format_args!(
-                        "Object of type `{}` is not callable (possibly unbound `__call__` method)",
-                        called_ty.display(db)
-                    ),
-                );
-                return_ty
-            }
-        }
-    }
-
-    /// Get the return type of the call as a result.
-    fn return_ty_result<'a>(
-        &self,
-        db: &'db dyn Db,
-        node: ast::AnyNodeRef,
-        diagnostics: &'a mut TypeCheckDiagnosticsBuilder<'db>,
-    ) -> Result<Type<'db>, NotCallableError<'db>> {
-        match self {
-            Self::Callable { return_ty } => Ok(*return_ty),
-            Self::RevealType {
-                return_ty,
-                revealed_ty,
-            } => {
-                diagnostics.add(
-                    node,
-                    "revealed-type",
-                    format_args!("Revealed type is `{}`", revealed_ty.display(db)),
-                );
-                Ok(*return_ty)
-            }
-            Self::NotCallable { not_callable_ty } => Err(NotCallableError::Type {
-                not_callable_ty: *not_callable_ty,
-                return_ty: Type::Unknown,
-            }),
-            Self::PossiblyUnboundDunderCall {
-                called_ty,
-                call_outcome,
-            } => Err(NotCallableError::PossiblyUnboundDunderCall {
-                callable_ty: *called_ty,
-                return_ty: call_outcome.return_ty(db).unwrap_or(Type::Unknown),
-            }),
-            Self::Union {
-                outcomes,
-                called_ty,
-            } => {
-                let mut not_callable = vec![];
-                let mut union_builder = UnionBuilder::new(db);
-                let mut revealed = false;
-                for outcome in outcomes {
-                    let return_ty = match outcome {
-                        Self::NotCallable { not_callable_ty } => {
-                            not_callable.push(*not_callable_ty);
-                            Type::Unknown
-                        }
-                        Self::RevealType {
-                            return_ty,
-                            revealed_ty: _,
-                        } => {
-                            if revealed {
-                                *return_ty
-                            } else {
-                                revealed = true;
-                                outcome.unwrap_with_diagnostic(db, node, diagnostics)
-                            }
-                        }
-                        _ => outcome.unwrap_with_diagnostic(db, node, diagnostics),
-                    };
-                    union_builder = union_builder.add(return_ty);
-                }
-                let return_ty = union_builder.build();
-                match not_callable[..] {
-                    [] => Ok(return_ty),
-                    [elem] => Err(NotCallableError::UnionElement {
-                        not_callable_ty: elem,
-                        called_ty: *called_ty,
-                        return_ty,
-                    }),
-                    _ if not_callable.len() == outcomes.len() => Err(NotCallableError::Type {
-                        not_callable_ty: *called_ty,
-                        return_ty,
-                    }),
-                    _ => Err(NotCallableError::UnionElements {
-                        not_callable_tys: not_callable.into_boxed_slice(),
-                        called_ty: *called_ty,
-                        return_ty,
-                    }),
-                }
-            }
-        }
-    }
-}
-
-enum CallDunderResult<'db> {
-    CallOutcome(CallOutcome<'db>),
-    PossiblyUnbound(CallOutcome<'db>),
-    MethodNotAvailable,
-}
-
-impl<'db> CallDunderResult<'db> {
-    fn return_ty(&self, db: &'db dyn Db) -> Option<Type<'db>> {
-        match self {
-            Self::CallOutcome(outcome) => outcome.return_ty(db),
-            Self::PossiblyUnbound { .. } => None,
-            Self::MethodNotAvailable => None,
-        }
-    }
-}
-
-#[derive(Debug, Clone, PartialEq, Eq)]
-enum NotCallableError<'db> {
-    /// The type is not callable.
-    Type {
-        not_callable_ty: Type<'db>,
-        return_ty: Type<'db>,
-    },
-    /// A single union element is not callable.
-    UnionElement {
-        not_callable_ty: Type<'db>,
-        called_ty: Type<'db>,
-        return_ty: Type<'db>,
-    },
-    /// Multiple (but not all) union elements are not callable.
-    UnionElements {
-        not_callable_tys: Box<[Type<'db>]>,
-        called_ty: Type<'db>,
-        return_ty: Type<'db>,
-    },
-    PossiblyUnboundDunderCall {
-        callable_ty: Type<'db>,
-        return_ty: Type<'db>,
-    },
-}
-
-impl<'db> NotCallableError<'db> {
-    /// The return type that should be used when a call is not callable.
-    fn return_ty(&self) -> Type<'db> {
-        match self {
-            Self::Type { return_ty, .. } => *return_ty,
-            Self::UnionElement { return_ty, .. } => *return_ty,
-            Self::UnionElements { return_ty, .. } => *return_ty,
-            Self::PossiblyUnboundDunderCall { return_ty, .. } => *return_ty,
-        }
-    }
-
-    /// The resolved type that was not callable.
-    ///
-    /// For unions, returns the union type itself, which may contain a mix of callable and
-    /// non-callable types.
-    fn called_ty(&self) -> Type<'db> {
-        match self {
-            Self::Type {
-                not_callable_ty, ..
-            } => *not_callable_ty,
-            Self::UnionElement { called_ty, .. } => *called_ty,
-            Self::UnionElements { called_ty, .. } => *called_ty,
-            Self::PossiblyUnboundDunderCall {
-                callable_ty: called_ty,
-                ..
-            } => *called_ty,
-        }
-    }
-}
-
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum IterationOutcome<'db> {
     Iterable {
@@ -2917,15 +2709,11 @@ impl<'db> Class<'db> {
             return Type::tuple(db, &tuple_elements).into();
         }
 
-        if name == "__class__" {
-            return self.metaclass(db).into();
-        }
-
         for superclass in self.iter_mro(db) {
             match superclass {
                 // TODO we may instead want to record the fact that we encountered dynamic, and intersect it with
                 // the type found on the next "real" class.
-                ClassBase::Any | ClassBase::Unknown | ClassBase::Todo => {
+                ClassBase::Any | ClassBase::Unknown | ClassBase::Todo(_) => {
                     return Type::from(superclass).member(db, name)
                 }
                 ClassBase::Class(class) => {
@@ -3033,12 +2821,12 @@ impl<'db> From<ClassLiteralType<'db>> for Type<'db> {
 /// A type that represents `type[C]`, i.e. the class literal `C` and class literals that are subclasses of `C`.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, salsa::Update)]
 pub struct SubclassOfType<'db> {
-    class: Class<'db>,
+    base: ClassBase<'db>,
 }
 
 impl<'db> SubclassOfType<'db> {
     fn member(self, db: &'db dyn Db, name: &str) -> Symbol<'db> {
-        self.class.class_member(db, name)
+        Type::from(self.base).member(db, name)
     }
 }
 
@@ -3257,6 +3045,8 @@ pub(crate) mod tests {
         Union(Vec<Ty>),
         Intersection { pos: Vec<Ty>, neg: Vec<Ty> },
         Tuple(Vec<Ty>),
+        SubclassOfAny,
+        SubclassOfBuiltinClass(&'static str),
     }
 
     impl Ty {
@@ -3294,6 +3084,13 @@ pub(crate) mod tests {
                     let elements = tys.into_iter().map(|ty| ty.into_type(db));
                     Type::tuple(db, elements)
                 }
+                Ty::SubclassOfAny => Type::subclass_of_base(ClassBase::Any),
+                Ty::SubclassOfBuiltinClass(s) => Type::subclass_of(
+                    builtins_symbol(db, s)
+                        .expect_type()
+                        .expect_class_literal()
+                        .class,
+                ),
             }
         }
     }
@@ -3331,6 +3128,26 @@ pub(crate) mod tests {
     )]
     #[test_case(Ty::Tuple(vec![Ty::Todo]), Ty::Tuple(vec![Ty::IntLiteral(2)]))]
     #[test_case(Ty::Tuple(vec![Ty::IntLiteral(2)]), Ty::Tuple(vec![Ty::Todo]))]
+    #[test_case(Ty::SubclassOfAny, Ty::SubclassOfAny)]
+    #[test_case(Ty::SubclassOfAny, Ty::SubclassOfBuiltinClass("object"))]
+    #[test_case(Ty::SubclassOfAny, Ty::SubclassOfBuiltinClass("str"))]
+    #[test_case(Ty::SubclassOfAny, Ty::BuiltinInstance("type"))]
+    #[test_case(Ty::SubclassOfBuiltinClass("object"), Ty::SubclassOfAny)]
+    #[test_case(
+        Ty::SubclassOfBuiltinClass("object"),
+        Ty::SubclassOfBuiltinClass("object")
+    )]
+    #[test_case(Ty::SubclassOfBuiltinClass("object"), Ty::BuiltinInstance("type"))]
+    #[test_case(Ty::SubclassOfBuiltinClass("str"), Ty::SubclassOfAny)]
+    #[test_case(
+        Ty::SubclassOfBuiltinClass("str"),
+        Ty::SubclassOfBuiltinClass("object")
+    )]
+    #[test_case(Ty::SubclassOfBuiltinClass("str"), Ty::SubclassOfBuiltinClass("str"))]
+    #[test_case(Ty::SubclassOfBuiltinClass("str"), Ty::BuiltinInstance("type"))]
+    #[test_case(Ty::BuiltinInstance("type"), Ty::SubclassOfAny)]
+    #[test_case(Ty::BuiltinInstance("type"), Ty::SubclassOfBuiltinClass("object"))]
+    #[test_case(Ty::BuiltinInstance("type"), Ty::BuiltinInstance("type"))]
     fn is_assignable_to(from: Ty, to: Ty) {
         let db = setup_db();
         assert!(from.into_type(&db).is_assignable_to(&db, to.into_type(&db)));
@@ -3348,6 +3165,11 @@ pub(crate) mod tests {
         Ty::Union(vec![Ty::IntLiteral(1), Ty::None]),
         Ty::Union(vec![Ty::BuiltinInstance("str"), Ty::None])
     )]
+    #[test_case(
+        Ty::SubclassOfBuiltinClass("object"),
+        Ty::SubclassOfBuiltinClass("str")
+    )]
+    #[test_case(Ty::BuiltinInstance("type"), Ty::SubclassOfBuiltinClass("str"))]
     fn is_not_assignable_to(from: Ty, to: Ty) {
         let db = setup_db();
         assert!(!from.into_type(&db).is_assignable_to(&db, to.into_type(&db)));
@@ -3502,10 +3324,13 @@ pub(crate) mod tests {
         Ty::Union(vec![Ty::IntLiteral(1), Ty::IntLiteral(2)]),
         Ty::Union(vec![Ty::IntLiteral(1), Ty::IntLiteral(2)])
     )]
+    #[test_case(Ty::SubclassOfBuiltinClass("object"), Ty::BuiltinInstance("type"))]
     fn is_equivalent_to(from: Ty, to: Ty) {
         let db = setup_db();
-
-        assert!(from.into_type(&db).is_equivalent_to(&db, to.into_type(&db)));
+        let from = from.into_type(&db);
+        let to = to.into_type(&db);
+        assert!(from.is_equivalent_to(&db, to));
+        assert!(to.is_equivalent_to(&db, from));
     }
 
     #[test_case(Ty::Any, Ty::Any)]
@@ -3516,8 +3341,10 @@ pub(crate) mod tests {
     #[test_case(Ty::Union(vec![Ty::IntLiteral(1), Ty::IntLiteral(2)]), Ty::Union(vec![Ty::IntLiteral(1), Ty::IntLiteral(2), Ty::IntLiteral(3)]))]
     fn is_not_equivalent_to(from: Ty, to: Ty) {
         let db = setup_db();
-
-        assert!(!from.into_type(&db).is_equivalent_to(&db, to.into_type(&db)));
+        let from = from.into_type(&db);
+        let to = to.into_type(&db);
+        assert!(!from.is_equivalent_to(&db, to));
+        assert!(!to.is_equivalent_to(&db, from));
     }
 
     #[test_case(Ty::Never, Ty::Never)]
@@ -3779,6 +3606,9 @@ pub(crate) mod tests {
     #[test_case(Ty::Intersection{pos: vec![Ty::KnownClassInstance(KnownClass::Str)], neg: vec![Ty::LiteralString]})]
     #[test_case(Ty::Tuple(vec![]))]
     #[test_case(Ty::Tuple(vec![Ty::KnownClassInstance(KnownClass::Int), Ty::KnownClassInstance(KnownClass::Object)]))]
+    #[test_case(Ty::BuiltinInstance("type"))]
+    #[test_case(Ty::SubclassOfBuiltinClass("object"))]
+    #[test_case(Ty::SubclassOfBuiltinClass("str"))]
     fn is_fully_static(from: Ty) {
         let db = setup_db();
 
@@ -3792,6 +3622,7 @@ pub(crate) mod tests {
     #[test_case(Ty::Union(vec![Ty::KnownClassInstance(KnownClass::Str), Ty::Unknown]))]
     #[test_case(Ty::Intersection{pos: vec![Ty::Any], neg: vec![Ty::LiteralString]})]
     #[test_case(Ty::Tuple(vec![Ty::KnownClassInstance(KnownClass::Int), Ty::Any]))]
+    #[test_case(Ty::SubclassOfAny)]
     fn is_not_fully_static(from: Ty) {
         let db = setup_db();
 

crates/red_knot_python_semantic/src/types/call.rs

@@ -0,0 +1,312 @@
+use super::diagnostic::{TypeCheckDiagnosticsBuilder, CALL_NON_CALLABLE};
+use super::{Severity, Type, TypeArrayDisplay, UnionBuilder};
+use crate::Db;
+use ruff_db::diagnostic::DiagnosticId;
+use ruff_python_ast as ast;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) enum CallOutcome<'db> {
+    Callable {
+        return_ty: Type<'db>,
+    },
+    RevealType {
+        return_ty: Type<'db>,
+        revealed_ty: Type<'db>,
+    },
+    NotCallable {
+        not_callable_ty: Type<'db>,
+    },
+    Union {
+        called_ty: Type<'db>,
+        outcomes: Box<[CallOutcome<'db>]>,
+    },
+    PossiblyUnboundDunderCall {
+        called_ty: Type<'db>,
+        call_outcome: Box<CallOutcome<'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 }
+    }
+
+    /// Create a new `CallOutcome::NotCallable` with given not-callable type.
+    pub(super) fn not_callable(not_callable_ty: Type<'db>) -> CallOutcome<'db> {
+        CallOutcome::NotCallable { not_callable_ty }
+    }
+
+    /// 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> {
+        CallOutcome::RevealType {
+            return_ty,
+            revealed_ty,
+        }
+    }
+
+    /// Create a new `CallOutcome::Union` with given wrapped outcomes.
+    pub(super) fn union(
+        called_ty: Type<'db>,
+        outcomes: impl IntoIterator<Item = CallOutcome<'db>>,
+    ) -> CallOutcome<'db> {
+        CallOutcome::Union {
+            called_ty,
+            outcomes: outcomes.into_iter().collect(),
+        }
+    }
+
+    /// 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::RevealType {
+                return_ty,
+                revealed_ty: _,
+            } => Some(*return_ty),
+            Self::NotCallable { not_callable_ty: _ } => None,
+            Self::Union {
+                outcomes,
+                called_ty: _,
+            } => outcomes
+                .iter()
+                // If all outcomes are NotCallable, we return None; if some outcomes are callable
+                // and some are not, we return a union including Unknown.
+                .fold(None, |acc, outcome| {
+                    let ty = outcome.return_ty(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))),
+                    }
+                })
+                .map(UnionBuilder::build),
+            Self::PossiblyUnboundDunderCall { call_outcome, .. } => call_outcome.return_ty(db),
+        }
+    }
+
+    /// Get the return type of the call, emitting default diagnostics if needed.
+    pub(super) fn unwrap_with_diagnostic<'a>(
+        &self,
+        db: &'db dyn Db,
+        node: ast::AnyNodeRef,
+        diagnostics: &'a mut TypeCheckDiagnosticsBuilder<'db>,
+    ) -> Type<'db> {
+        match self.return_ty_result(db, node, diagnostics) {
+            Ok(return_ty) => return_ty,
+            Err(NotCallableError::Type {
+                not_callable_ty,
+                return_ty,
+            }) => {
+                diagnostics.add_lint(
+                    &CALL_NON_CALLABLE,
+                    node,
+                    format_args!(
+                        "Object of type `{}` is not callable",
+                        not_callable_ty.display(db)
+                    ),
+                );
+                return_ty
+            }
+            Err(NotCallableError::UnionElement {
+                not_callable_ty,
+                called_ty,
+                return_ty,
+            }) => {
+                diagnostics.add_lint(
+                    &CALL_NON_CALLABLE,
+                    node,
+                    format_args!(
+                        "Object of type `{}` is not callable (due to union element `{}`)",
+                        called_ty.display(db),
+                        not_callable_ty.display(db),
+                    ),
+                );
+                return_ty
+            }
+            Err(NotCallableError::UnionElements {
+                not_callable_tys,
+                called_ty,
+                return_ty,
+            }) => {
+                diagnostics.add_lint(
+                    &CALL_NON_CALLABLE,
+                    node,
+                    format_args!(
+                        "Object of type `{}` is not callable (due to union elements {})",
+                        called_ty.display(db),
+                        not_callable_tys.display(db),
+                    ),
+                );
+                return_ty
+            }
+            Err(NotCallableError::PossiblyUnboundDunderCall {
+                callable_ty: called_ty,
+                return_ty,
+            }) => {
+                diagnostics.add_lint(
+                    &CALL_NON_CALLABLE,
+                    node,
+                    format_args!(
+                        "Object of type `{}` is not callable (possibly unbound `__call__` method)",
+                        called_ty.display(db)
+                    ),
+                );
+                return_ty
+            }
+        }
+    }
+
+    /// Get the return type of the call as a result.
+    pub(super) fn return_ty_result<'a>(
+        &self,
+        db: &'db dyn Db,
+        node: ast::AnyNodeRef,
+        diagnostics: &'a mut TypeCheckDiagnosticsBuilder<'db>,
+    ) -> Result<Type<'db>, NotCallableError<'db>> {
+        match self {
+            Self::Callable { return_ty } => Ok(*return_ty),
+            Self::RevealType {
+                return_ty,
+                revealed_ty,
+            } => {
+                diagnostics.add(
+                    node,
+                    DiagnosticId::RevealedType,
+                    Severity::Info,
+                    format_args!("Revealed type is `{}`", revealed_ty.display(db)),
+                );
+                Ok(*return_ty)
+            }
+            Self::NotCallable { not_callable_ty } => Err(NotCallableError::Type {
+                not_callable_ty: *not_callable_ty,
+                return_ty: Type::Unknown,
+            }),
+            Self::PossiblyUnboundDunderCall {
+                called_ty,
+                call_outcome,
+            } => Err(NotCallableError::PossiblyUnboundDunderCall {
+                callable_ty: *called_ty,
+                return_ty: call_outcome.return_ty(db).unwrap_or(Type::Unknown),
+            }),
+            Self::Union {
+                outcomes,
+                called_ty,
+            } => {
+                let mut not_callable = vec![];
+                let mut union_builder = UnionBuilder::new(db);
+                let mut revealed = false;
+                for outcome in outcomes {
+                    let return_ty = match outcome {
+                        Self::NotCallable { not_callable_ty } => {
+                            not_callable.push(*not_callable_ty);
+                            Type::Unknown
+                        }
+                        Self::RevealType {
+                            return_ty,
+                            revealed_ty: _,
+                        } => {
+                            if revealed {
+                                *return_ty
+                            } else {
+                                revealed = true;
+                                outcome.unwrap_with_diagnostic(db, node, diagnostics)
+                            }
+                        }
+                        _ => outcome.unwrap_with_diagnostic(db, node, diagnostics),
+                    };
+                    union_builder = union_builder.add(return_ty);
+                }
+                let return_ty = union_builder.build();
+                match not_callable[..] {
+                    [] => Ok(return_ty),
+                    [elem] => Err(NotCallableError::UnionElement {
+                        not_callable_ty: elem,
+                        called_ty: *called_ty,
+                        return_ty,
+                    }),
+                    _ if not_callable.len() == outcomes.len() => Err(NotCallableError::Type {
+                        not_callable_ty: *called_ty,
+                        return_ty,
+                    }),
+                    _ => Err(NotCallableError::UnionElements {
+                        not_callable_tys: not_callable.into_boxed_slice(),
+                        called_ty: *called_ty,
+                        return_ty,
+                    }),
+                }
+            }
+        }
+    }
+}
+
+pub(super) enum CallDunderResult<'db> {
+    CallOutcome(CallOutcome<'db>),
+    PossiblyUnbound(CallOutcome<'db>),
+    MethodNotAvailable,
+}
+
+impl<'db> CallDunderResult<'db> {
+    pub(super) fn return_ty(&self, db: &'db dyn Db) -> Option<Type<'db>> {
+        match self {
+            Self::CallOutcome(outcome) => outcome.return_ty(db),
+            Self::PossiblyUnbound { .. } => None,
+            Self::MethodNotAvailable => None,
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) enum NotCallableError<'db> {
+    /// The type is not callable.
+    Type {
+        not_callable_ty: Type<'db>,
+        return_ty: Type<'db>,
+    },
+    /// A single union element is not callable.
+    UnionElement {
+        not_callable_ty: Type<'db>,
+        called_ty: Type<'db>,
+        return_ty: Type<'db>,
+    },
+    /// Multiple (but not all) union elements are not callable.
+    UnionElements {
+        not_callable_tys: Box<[Type<'db>]>,
+        called_ty: Type<'db>,
+        return_ty: Type<'db>,
+    },
+    PossiblyUnboundDunderCall {
+        callable_ty: Type<'db>,
+        return_ty: Type<'db>,
+    },
+}
+
+impl<'db> NotCallableError<'db> {
+    /// The return type that should be used when a call is not callable.
+    pub(super) fn return_ty(&self) -> Type<'db> {
+        match self {
+            Self::Type { return_ty, .. } => *return_ty,
+            Self::UnionElement { return_ty, .. } => *return_ty,
+            Self::UnionElements { return_ty, .. } => *return_ty,
+            Self::PossiblyUnboundDunderCall { return_ty, .. } => *return_ty,
+        }
+    }
+
+    /// The resolved type that was not callable.
+    ///
+    /// For unions, returns the union type itself, which may contain a mix of callable and
+    /// non-callable types.
+    pub(super) fn called_ty(&self) -> Type<'db> {
+        match self {
+            Self::Type {
+                not_callable_ty, ..
+            } => *not_callable_ty,
+            Self::UnionElement { called_ty, .. } => *called_ty,
+            Self::UnionElements { called_ty, .. } => *called_ty,
+            Self::PossiblyUnboundDunderCall {
+                callable_ty: called_ty,
+                ..
+            } => *called_ty,
+        }
+    }
+}

crates/red_knot_python_semantic/src/types/diagnostic.rs

@@ -1,6 +1,12 @@
+use crate::lint::{Level, LintId, LintMetadata, LintRegistryBuilder, LintStatus};
+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,
+    RAW_STRING_TYPE_ANNOTATION,
+};
 use crate::types::{ClassLiteralType, Type};
-use crate::Db;
-use ruff_db::diagnostic::{Diagnostic, Severity};
+use crate::{declare_lint, Db};
+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};
@@ -9,18 +15,466 @@ use std::fmt::Formatter;
 use std::ops::Deref;
 use std::sync::Arc;
 
+/// Registers all known type check lints.
+pub(crate) fn register_lints(registry: &mut LintRegistryBuilder) {
+    registry.register_lint(&UNRESOLVED_REFERENCE);
+    registry.register_lint(&POSSIBLY_UNRESOLVED_REFERENCE);
+    registry.register_lint(&NOT_ITERABLE);
+    registry.register_lint(&INDEX_OUT_OF_BOUNDS);
+    registry.register_lint(&NON_SUBSCRIPTABLE);
+    registry.register_lint(&UNRESOLVED_IMPORT);
+    registry.register_lint(&POSSIBLY_UNBOUND_IMPORT);
+    registry.register_lint(&ZERO_STEPSIZE_IN_SLICE);
+    registry.register_lint(&INVALID_ASSIGNMENT);
+    registry.register_lint(&INVALID_DECLARATION);
+    registry.register_lint(&CONFLICTING_DECLARATIONS);
+    registry.register_lint(&DIVISION_BY_ZERO);
+    registry.register_lint(&CALL_NON_CALLABLE);
+    registry.register_lint(&INVALID_TYPE_PARAMETER);
+    registry.register_lint(&INVALID_TYPE_VARIABLE_CONSTRAINTS);
+    registry.register_lint(&CYCLIC_CLASS_DEFINITION);
+    registry.register_lint(&DUPLICATE_BASE);
+    registry.register_lint(&INVALID_BASE);
+    registry.register_lint(&INCONSISTENT_MRO);
+    registry.register_lint(&INVALID_LITERAL_PARAMETER);
+    registry.register_lint(&CALL_POSSIBLY_UNBOUND_METHOD);
+    registry.register_lint(&POSSIBLY_UNBOUND_ATTRIBUTE);
+    registry.register_lint(&UNRESOLVED_ATTRIBUTE);
+    registry.register_lint(&CONFLICTING_METACLASS);
+    registry.register_lint(&UNSUPPORTED_OPERATOR);
+    registry.register_lint(&INVALID_CONTEXT_MANAGER);
+    registry.register_lint(&UNDEFINED_REVEAL);
+    registry.register_lint(&INVALID_PARAMETER_DEFAULT);
+    registry.register_lint(&INVALID_TYPE_FORM);
+    registry.register_lint(&INVALID_EXCEPTION_CAUGHT);
+
+    // String annotations
+    registry.register_lint(&FSTRING_TYPE_ANNOTATION);
+    registry.register_lint(&BYTE_STRING_TYPE_ANNOTATION);
+    registry.register_lint(&RAW_STRING_TYPE_ANNOTATION);
+    registry.register_lint(&IMPLICIT_CONCATENATED_STRING_TYPE_ANNOTATION);
+    registry.register_lint(&INVALID_SYNTAX_IN_FORWARD_ANNOTATION);
+    registry.register_lint(&ESCAPE_CHARACTER_IN_FORWARD_ANNOTATION);
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for references to names that are not defined.
+    ///
+    /// ## Why is this bad?
+    /// Using an undefined variable will raise a `NameError` at runtime.
+    ///
+    /// ## Example
+    ///
+    /// ```python
+    /// print(x)  # NameError: name 'x' is not defined
+    /// ```
+    pub(crate) static UNRESOLVED_REFERENCE = {
+        summary: "detects references to names that are not defined",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Warn,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for references to names that are possibly not defined.
+    ///
+    /// ## Why is this bad?
+    /// Using an undefined variable will raise a `NameError` at runtime.
+    ///
+    /// ## Example
+    ///
+    /// ```python
+    /// for i in range(0):
+    ///     x = i
+    ///
+    /// print(x)  # NameError: name 'x' is not defined
+    /// ```
+    pub(crate) static POSSIBLY_UNRESOLVED_REFERENCE = {
+        summary: "detects references to possibly undefined names",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Warn,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for objects that are not iterable but are used in a context that requires them to be.
+    ///
+    /// ## Why is this bad?
+    /// Iterating over an object that is not iterable will raise a `TypeError` at runtime.
+    ///
+    /// ## Examples
+    ///
+    /// ```python
+    /// for i in 34:  # TypeError: 'int' object is not iterable
+    ///     pass
+    /// ```
+    pub(crate) static NOT_ITERABLE = {
+        summary: "detects iteration over an object that is not iterable",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// TODO #14889
+    pub(crate) static INDEX_OUT_OF_BOUNDS = {
+        summary: "detects index out of bounds errors",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for subscripting objects that do not support subscripting.
+    ///
+    /// ## Why is this bad?
+    /// Subscripting an object that does not support it will raise a `TypeError` at runtime.
+    ///
+    /// ## Examples
+    /// ```python
+    /// 4[1]  # TypeError: 'int' object is not subscriptable
+    /// ```
+    pub(crate) static NON_SUBSCRIPTABLE = {
+        summary: "detects subscripting objects that do not support subscripting",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for import statements for which the module cannot be resolved.
+    ///
+    /// ## Why is this bad?
+    /// Importing a module that cannot be resolved will raise an `ImportError` at runtime.
+    pub(crate) static UNRESOLVED_IMPORT = {
+        summary: "detects unresolved imports",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static POSSIBLY_UNBOUND_IMPORT = {
+        summary: "detects possibly unbound imports",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Warn,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for step size 0 in slices.
+    ///
+    /// ## Why is this bad?
+    /// A slice with a step size of zero will raise a `ValueError` at runtime.
+    ///
+    /// ## Examples
+    /// ```python
+    ///  l = list(range(10))
+    /// l[1:10:0]  # ValueError: slice step cannot be zero
+    pub(crate) static ZERO_STEPSIZE_IN_SLICE = {
+        summary: "detects a slice step size of zero",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static INVALID_ASSIGNMENT = {
+        summary: "detects invalid assignments",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static INVALID_DECLARATION = {
+        summary: "detects invalid declarations",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static CONFLICTING_DECLARATIONS = {
+        summary: "detects conflicting declarations",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// It detects division by zero.
+    ///
+    /// ## Why is this bad?
+    /// Dividing by zero raises a `ZeroDivisionError` at runtime.
+    ///
+    /// ## Examples
+    /// ```python
+    /// 5 / 0
+    /// ```
+    pub(crate) static DIVISION_BY_ZERO = {
+        summary: "detects division by zero",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for calls to non-callable objects.
+    ///
+    /// ## Why is this bad?
+    /// Calling a non-callable object will raise a `TypeError` at runtime.
+    ///
+    /// ## Examples
+    /// ```python
+    /// 4()  # TypeError: 'int' object is not callable
+    /// ```
+    pub(crate) static CALL_NON_CALLABLE = {
+        summary: "detects calls to non-callable objects",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// TODO #14889
+    pub(crate) static INVALID_TYPE_PARAMETER = {
+        summary: "detects invalid type parameters",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static INVALID_TYPE_VARIABLE_CONSTRAINTS = {
+        summary: "detects invalid type variable constraints",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for class definitions with a cyclic inheritance chain.
+    ///
+    /// ## Why is it bad?
+    /// TODO #14889
+    pub(crate) static CYCLIC_CLASS_DEFINITION = {
+        summary: "detects cyclic class definitions",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static DUPLICATE_BASE = {
+        summary: "detects class definitions with duplicate bases",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static INVALID_BASE = {
+        summary: "detects class definitions with an invalid base",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static INCONSISTENT_MRO = {
+        summary: "detects class definitions with an inconsistent MRO",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for invalid parameters to `typing.Literal`.
+    ///
+    /// TODO #14889
+    pub(crate) static INVALID_LITERAL_PARAMETER = {
+        summary: "detects invalid literal parameters",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for calls to possibly unbound methods.
+    ///
+    /// TODO #14889
+    pub(crate) static CALL_POSSIBLY_UNBOUND_METHOD = {
+        summary: "detects calls to possibly unbound methods",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Warn,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for possibly unbound attributes.
+    ///
+    /// TODO #14889
+    pub(crate) static POSSIBLY_UNBOUND_ATTRIBUTE = {
+        summary: "detects references to possibly unbound attributes",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Warn,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for unresolved attributes.
+    ///
+    /// TODO #14889
+    pub(crate) static UNRESOLVED_ATTRIBUTE = {
+        summary: "detects references to unresolved attributes",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static CONFLICTING_METACLASS = {
+        summary: "detects conflicting metaclasses",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for binary expressions, comparisons, and unary expressions where the operands don't support the operator.
+    ///
+    /// TODO #14889
+    pub(crate) static UNSUPPORTED_OPERATOR = {
+        summary: "detects binary, unary, or comparison expressions where the operands don't support the operator",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static INVALID_CONTEXT_MANAGER = {
+        summary: "detects expressions used in with statements that don't implement the context manager protocol",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for calls to `reveal_type` without importing it.
+    ///
+    /// ## Why is this bad?
+    /// Using `reveal_type` without importing it will raise a `NameError` at runtime.
+    ///
+    /// ## Examples
+    /// TODO #14889
+    pub(crate) static UNDEFINED_REVEAL = {
+        summary: "detects usages of `reveal_type` without importing it",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Warn,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for default values that can't be assigned to the parameter's annotated type.
+    ///
+    /// ## Why is this bad?
+    /// TODO #14889
+    pub(crate) static INVALID_PARAMETER_DEFAULT = {
+        summary: "detects default values that can't be assigned to the parameter's annotated type",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for invalid type expressions.
+    ///
+    /// ## Why is this bad?
+    /// TODO #14889
+    pub(crate) static INVALID_TYPE_FORM = {
+        summary: "detects invalid type forms",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// Checks for exception handlers that catch non-exception classes.
+    ///
+    /// ## Why is this bad?
+    /// Catching classes that do not inherit from `BaseException` will raise a TypeError at runtime.
+    ///
+    /// ## Example
+    /// ```python
+    /// try:
+    ///     1 / 0
+    /// except 1:
+    ///     ...
+    /// ```
+    ///
+    /// Use instead:
+    /// ```python
+    /// try:
+    ///     1 / 0
+    /// except ZeroDivisionError:
+    ///     ...
+    /// ```
+    ///
+    /// ## References
+    /// - [Python documentation: except clause](https://docs.python.org/3/reference/compound_stmts.html#except-clause)
+    /// - [Python documentation: Built-in Exceptions](https://docs.python.org/3/library/exceptions.html#built-in-exceptions)
+    ///
+    /// ## Ruff rule
+    ///  This rule corresponds to Ruff's [`except-with-non-exception-classes` (`B030`)](https://docs.astral.sh/ruff/rules/except-with-non-exception-classes)
+    pub(crate) static INVALID_EXCEPTION_CAUGHT = {
+        summary: "detects exception handlers that catch classes that do not inherit from `BaseException`",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
 #[derive(Debug, Eq, PartialEq, Clone)]
 pub struct TypeCheckDiagnostic {
-    // TODO: Don't use string keys for rules
-    pub(super) rule: String,
+    pub(super) id: DiagnosticId,
     pub(super) message: String,
     pub(super) range: TextRange,
+    pub(super) severity: Severity,
     pub(super) file: File,
 }
 
 impl TypeCheckDiagnostic {
-    pub fn rule(&self) -> &str {
-        &self.rule
+    pub fn id(&self) -> DiagnosticId {
+        self.id
     }
 
     pub fn message(&self) -> &str {
@@ -33,8 +487,8 @@ impl TypeCheckDiagnostic {
 }
 
 impl Diagnostic for TypeCheckDiagnostic {
-    fn rule(&self) -> &str {
-        TypeCheckDiagnostic::rule(self)
+    fn id(&self) -> DiagnosticId {
+        self.id
     }
 
     fn message(&self) -> Cow<str> {
@@ -50,7 +504,7 @@ impl Diagnostic for TypeCheckDiagnostic {
     }
 
     fn severity(&self) -> Severity {
-        Severity::Error
+        self.severity
     }
 }
 
@@ -150,9 +604,9 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
 
     /// Emit a diagnostic declaring that the object represented by `node` is not iterable
     pub(super) fn add_not_iterable(&mut self, node: AnyNodeRef, not_iterable_ty: Type<'db>) {
-        self.add(
+        self.add_lint(
+            &NOT_ITERABLE,
             node,
-            "not-iterable",
             format_args!(
                 "Object of type `{}` is not iterable",
                 not_iterable_ty.display(self.db)
@@ -167,9 +621,9 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
         node: AnyNodeRef,
         element_ty: Type<'db>,
     ) {
-        self.add(
+        self.add_lint(
+            &NOT_ITERABLE,
             node,
-            "not-iterable",
             format_args!(
                 "Object of type `{}` is not iterable because its `__iter__` method is possibly unbound",
                 element_ty.display(self.db)
@@ -186,9 +640,9 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
         length: usize,
         index: i64,
     ) {
-        self.add(
+        self.add_lint(
+            &INDEX_OUT_OF_BOUNDS,
             node,
-            "index-out-of-bounds",
             format_args!(
                 "Index {index} is out of bounds for {kind} `{}` with length {length}",
                 tuple_ty.display(self.db)
@@ -203,9 +657,9 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
         non_subscriptable_ty: Type<'db>,
         method: &str,
     ) {
-        self.add(
+        self.add_lint(
+            &NON_SUBSCRIPTABLE,
             node,
-            "non-subscriptable",
             format_args!(
                 "Cannot subscript object of type `{}` with no `{method}` method",
                 non_subscriptable_ty.display(self.db)
@@ -219,9 +673,9 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
         level: u32,
         module: Option<&str>,
     ) {
-        self.add(
+        self.add_lint(
+            &UNRESOLVED_IMPORT,
             import_node.into(),
-            "unresolved-import",
             format_args!(
                 "Cannot resolve import `{}{}`",
                 ".".repeat(level as usize),
@@ -231,9 +685,9 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
     }
 
     pub(super) fn add_slice_step_size_zero(&mut self, node: AnyNodeRef) {
-        self.add(
+        self.add_lint(
+            &ZERO_STEPSIZE_IN_SLICE,
             node,
-            "zero-stepsize-in-slice",
             format_args!("Slice step size can not be zero"),
         );
     }
@@ -246,19 +700,19 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
     ) {
         match declared_ty {
             Type::ClassLiteral(ClassLiteralType { class }) => {
-                self.add(node, "invalid-assignment", format_args!(
+                self.add_lint(&INVALID_ASSIGNMENT, node, format_args!(
                         "Implicit shadowing of class `{}`; annotate to make it explicit if this is intentional",
                         class.name(self.db)));
             }
             Type::FunctionLiteral(function) => {
-                self.add(node, "invalid-assignment", format_args!(
+                self.add_lint(&INVALID_ASSIGNMENT, node, format_args!(
                         "Implicit shadowing of function `{}`; annotate to make it explicit if this is intentional",
                         function.name(self.db)));
             }
             _ => {
-                self.add(
+                self.add_lint(
+                    &INVALID_ASSIGNMENT,
                     node,
-                    "invalid-assignment",
                     format_args!(
                         "Object of type `{}` is not assignable to `{}`",
                         assigned_ty.display(self.db),
@@ -272,9 +726,9 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
     pub(super) fn add_possibly_unresolved_reference(&mut self, expr_name_node: &ast::ExprName) {
         let ast::ExprName { id, .. } = expr_name_node;
 
-        self.add(
+        self.add_lint(
+            &POSSIBLY_UNRESOLVED_REFERENCE,
             expr_name_node.into(),
-            "possibly-unresolved-reference",
             format_args!("Name `{id}` used when possibly not defined"),
         );
     }
@@ -282,17 +736,49 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
     pub(super) fn add_unresolved_reference(&mut self, expr_name_node: &ast::ExprName) {
         let ast::ExprName { id, .. } = expr_name_node;
 
-        self.add(
+        self.add_lint(
+            &UNRESOLVED_REFERENCE,
             expr_name_node.into(),
-            "unresolved-reference",
             format_args!("Name `{id}` used when not defined"),
         );
     }
 
+    pub(super) fn add_invalid_exception_caught(&mut self, db: &dyn Db, node: &ast::Expr, ty: Type) {
+        self.add_lint(
+            &INVALID_EXCEPTION_CAUGHT,
+            node.into(),
+            format_args!(
+                "Cannot catch object of type `{}` in an exception handler \
+                (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)",
+                ty.display(db)
+            ),
+        );
+    }
+
+    pub(super) fn add_lint(
+        &mut self,
+        lint: &'static LintMetadata,
+        node: AnyNodeRef,
+        message: std::fmt::Arguments,
+    ) {
+        // Skip over diagnostics if the rule is disabled.
+        let Some(severity) = self.db.rule_selection().severity(LintId::of(lint)) else {
+            return;
+        };
+
+        self.add(node, DiagnosticId::Lint(lint.name()), severity, message);
+    }
+
     /// Adds a new diagnostic.
     ///
     /// The diagnostic does not get added if the rule isn't enabled for this file.
-    pub(super) fn add(&mut self, node: AnyNodeRef, rule: &str, message: std::fmt::Arguments) {
+    pub(super) fn add(
+        &mut self,
+        node: AnyNodeRef,
+        id: DiagnosticId,
+        severity: Severity,
+        message: std::fmt::Arguments,
+    ) {
         if !self.db.is_file_open(self.file) {
             return;
         }
@@ -305,9 +791,10 @@ impl<'db> TypeCheckDiagnosticsBuilder<'db> {
 
         self.diagnostics.push(TypeCheckDiagnostic {
             file: self.file,
-            rule: rule.to_string(),
+            id,
             message: message.to_string(),
             range: node.range(),
+            severity,
         });
     }
 

crates/red_knot_python_semantic/src/types/display.rs

@@ -6,6 +6,7 @@ use ruff_db::display::FormatterJoinExtension;
 use ruff_python_ast::str::Quote;
 use ruff_python_literal::escape::AsciiEscape;
 
+use crate::types::mro::ClassBase;
 use crate::types::{
     ClassLiteralType, InstanceType, IntersectionType, KnownClass, StringLiteralType,
     SubclassOfType, Type, UnionType,
@@ -83,9 +84,16 @@ impl Display for DisplayRepresentation<'_> {
             }
             // 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 { class }) => {
+            Type::SubclassOf(SubclassOfType {
+                base: ClassBase::Class(class),
+            }) => {
+                // 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))
+            }
             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),

crates/red_knot_python_semantic/src/types/infer.rs

@@ -31,7 +31,7 @@ use std::num::NonZeroU32;
 use itertools::Itertools;
 use ruff_db::files::File;
 use ruff_db::parsed::parsed_module;
-use ruff_python_ast::{self as ast, AnyNodeRef, Expr, ExprContext, UnaryOp};
+use ruff_python_ast::{self as ast, AnyNodeRef, ExprContext, UnaryOp};
 use rustc_hash::{FxHashMap, FxHashSet};
 use salsa;
 use salsa::plumbing::AsId;
@@ -48,8 +48,16 @@ use crate::semantic_index::semantic_index;
 use crate::semantic_index::symbol::{NodeWithScopeKind, NodeWithScopeRef, ScopeId};
 use crate::semantic_index::SemanticIndex;
 use crate::stdlib::builtins_module_scope;
-use crate::types::diagnostic::{TypeCheckDiagnostics, TypeCheckDiagnosticsBuilder};
-use crate::types::mro::MroErrorKind;
+use crate::types::diagnostic::{
+    TypeCheckDiagnostics, TypeCheckDiagnosticsBuilder, CALL_NON_CALLABLE,
+    CALL_POSSIBLY_UNBOUND_METHOD, CONFLICTING_DECLARATIONS, CONFLICTING_METACLASS,
+    CYCLIC_CLASS_DEFINITION, DIVISION_BY_ZERO, DUPLICATE_BASE, INCONSISTENT_MRO, INVALID_BASE,
+    INVALID_CONTEXT_MANAGER, INVALID_DECLARATION, INVALID_LITERAL_PARAMETER,
+    INVALID_PARAMETER_DEFAULT, INVALID_TYPE_FORM, INVALID_TYPE_PARAMETER,
+    INVALID_TYPE_VARIABLE_CONSTRAINTS, POSSIBLY_UNBOUND_ATTRIBUTE, POSSIBLY_UNBOUND_IMPORT,
+    UNDEFINED_REVEAL, UNRESOLVED_ATTRIBUTE, UNRESOLVED_IMPORT, UNSUPPORTED_OPERATOR,
+};
+use crate::types::mro::{ClassBase, MroErrorKind};
 use crate::types::unpacker::{UnpackResult, Unpacker};
 use crate::types::{
     bindings_ty, builtins_symbol, declarations_ty, global_symbol, symbol, todo_type,
@@ -63,8 +71,9 @@ use crate::unpack::Unpack;
 use crate::util::subscript::{PyIndex, PySlice};
 use crate::Db;
 
-use super::expression_ty;
-use super::string_annotation::parse_string_annotation;
+use super::string_annotation::{
+    parse_string_annotation, BYTE_STRING_TYPE_ANNOTATION, FSTRING_TYPE_ANNOTATION,
+};
 
 /// Infer all types for a [`ScopeId`], including all definitions and expressions in that scope.
 /// Use when checking a scope, or needing to provide a type for an arbitrary expression in the
@@ -407,13 +416,37 @@ impl<'db> TypeInferenceBuilder<'db> {
 
     /// Get the already-inferred type of an expression node.
     ///
-    /// PANIC if no type has been inferred for this node.
+    /// ## Panics
+    /// If the expression is not within this region, or if no type has yet been inferred for
+    /// this node.
     #[track_caller]
     fn expression_ty(&self, expr: &ast::Expr) -> Type<'db> {
         self.types
             .expression_ty(expr.scoped_expression_id(self.db, self.scope()))
     }
 
+    /// Get the type of an expression from any scope in the same file.
+    ///
+    /// If the expression is in the current scope, and we are inferring the entire scope, just look
+    /// up the expression in our own results, otherwise call [`infer_scope_types()`] for the scope
+    /// of the expression.
+    ///
+    /// ## Panics
+    ///
+    /// If the expression is in the current scope but we haven't yet inferred a type for it.
+    ///
+    /// Can cause query cycles if the expression is from a different scope and type inference is
+    /// already in progress for that scope (further up the stack).
+    fn file_expression_ty(&self, expression: &ast::Expr) -> Type<'db> {
+        let file_scope = self.index.expression_scope_id(expression);
+        let expr_scope = file_scope.to_scope_id(self.db, self.file);
+        let expr_id = expression.scoped_expression_id(self.db, expr_scope);
+        match self.region {
+            InferenceRegion::Scope(scope) if scope == expr_scope => self.expression_ty(expression),
+            _ => infer_scope_types(self.db, expr_scope).expression_ty(expr_id),
+        }
+    }
+
     /// Infers types in the given [`InferenceRegion`].
     fn infer_region(&mut self) {
         match self.region {
@@ -502,9 +535,9 @@ impl<'db> TypeInferenceBuilder<'db> {
         for (class, class_node) in class_definitions {
             // (1) Check that the class does not have a cyclic definition
             if class.is_cyclically_defined(self.db) {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &CYCLIC_CLASS_DEFINITION,
                     class_node.into(),
-                    "cyclic-class-def",
                     format_args!(
                         "Cyclic definition of `{}` or bases of `{}` (class cannot inherit from itself)",
                         class.name(self.db),
@@ -522,9 +555,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                     MroErrorKind::DuplicateBases(duplicates) => {
                         let base_nodes = class_node.bases();
                         for (index, duplicate) in duplicates {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &DUPLICATE_BASE,
                                 (&base_nodes[*index]).into(),
-                                "duplicate-base",
                                 format_args!("Duplicate base class `{}`", duplicate.name(self.db)),
                             );
                         }
@@ -532,9 +565,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                     MroErrorKind::InvalidBases(bases) => {
                         let base_nodes = class_node.bases();
                         for (index, base_ty) in bases {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &INVALID_BASE,
                                 (&base_nodes[*index]).into(),
-                                "invalid-base",
                                 format_args!(
                                     "Invalid class base with type `{}` (all bases must be a class, `Any`, `Unknown` or `Todo`)",
                                     base_ty.display(self.db)
@@ -542,9 +575,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                             );
                         }
                     }
-                    MroErrorKind::UnresolvableMro { bases_list } => self.diagnostics.add(
+                    MroErrorKind::UnresolvableMro { bases_list } => self.diagnostics.add_lint(
+                        &INCONSISTENT_MRO,
                         class_node.into(),
-                        "inconsistent-mro",
                         format_args!(
                             "Cannot create a consistent method resolution order (MRO) for class `{}` with bases list `[{}]`",
                             class.name(self.db),
@@ -572,9 +605,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                     } => {
                         let node = class_node.into();
                         if *candidate1_is_base_class {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &CONFLICTING_METACLASS,
                                 node,
-                                "conflicting-metaclass",
                                 format_args!(
                                     "The metaclass of a derived class (`{class}`) must be a subclass of the metaclasses of all its bases, \
                                     but `{metaclass1}` (metaclass of base class `{base1}`) and `{metaclass2}` (metaclass of base class `{base2}`) \
@@ -584,12 +617,12 @@ impl<'db> TypeInferenceBuilder<'db> {
                                     base1 = class1.name(self.db),
                                     metaclass2 = metaclass2.name(self.db),
                                     base2 = class2.name(self.db),
-                                )
+                                ),
                             );
                         } else {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &CONFLICTING_METACLASS,
                                 node,
-                                "conflicting-metaclass",
                                 format_args!(
                                     "The metaclass of a derived class (`{class}`) must be a subclass of the metaclasses of all its bases, \
                                     but `{metaclass_of_class}` (metaclass of `{class}`) and `{metaclass_of_base}` (metaclass of base class `{base}`) \
@@ -598,7 +631,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                                     metaclass_of_class = metaclass1.name(self.db),
                                     metaclass_of_base = metaclass2.name(self.db),
                                     base = class2.name(self.db),
-                                )
+                                ),
                             );
                         }
                     }
@@ -736,9 +769,9 @@ impl<'db> TypeInferenceBuilder<'db> {
             _ => return,
         };
 
-        self.diagnostics.add(
+        self.diagnostics.add_lint(
+            &DIVISION_BY_ZERO,
             expr.into(),
-            "division-by-zero",
             format_args!(
                 "Cannot {op} object of type `{}` {by_zero}",
                 left.display(self.db)
@@ -761,9 +794,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                 // TODO point out the conflicting declarations in the diagnostic?
                 let symbol_table = self.index.symbol_table(binding.file_scope(self.db));
                 let symbol_name = symbol_table.symbol(binding.symbol(self.db)).name();
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &CONFLICTING_DECLARATIONS,
                     node,
-                    "conflicting-declarations",
                     format_args!(
                         "Conflicting declared types for `{symbol_name}`: {}",
                         conflicting.display(self.db)
@@ -791,9 +824,9 @@ impl<'db> TypeInferenceBuilder<'db> {
         let ty = if inferred_ty.is_assignable_to(self.db, ty) {
             ty
         } else {
-            self.diagnostics.add(
+            self.diagnostics.add_lint(
+                &INVALID_DECLARATION,
                 node,
-                "invalid-declaration",
                 format_args!(
                     "Cannot declare type `{}` for inferred type `{}`",
                     ty.display(self.db),
@@ -1081,19 +1114,19 @@ impl<'db> TypeInferenceBuilder<'db> {
         } = parameter_with_default;
         let default_ty = default
             .as_ref()
-            .map(|default| expression_ty(self.db, self.file, default));
+            .map(|default| self.file_expression_ty(default));
         if let Some(annotation) = parameter.annotation.as_ref() {
-            let declared_ty = expression_ty(self.db, self.file, annotation);
+            let declared_ty = self.file_expression_ty(annotation);
             let inferred_ty = if let Some(default_ty) = default_ty {
                 if default_ty.is_assignable_to(self.db, declared_ty) {
                     UnionType::from_elements(self.db, [declared_ty, default_ty])
                 } else {
-                    self.diagnostics.add(
+                    self.diagnostics.add_lint(
+                        &INVALID_PARAMETER_DEFAULT,
                         parameter_with_default.into(),
-                        "invalid-parameter-default",
                         format_args!(
                             "Default value of type `{}` is not assignable to annotated parameter type `{}`",
-                            default_ty.display(self.db), declared_ty.display(self.db))
+                            default_ty.display(self.db), declared_ty.display(self.db)),
                     );
                     declared_ty
                 }
@@ -1127,7 +1160,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         definition: Definition<'db>,
     ) {
         if let Some(annotation) = parameter.annotation.as_ref() {
-            let _annotated_ty = expression_ty(self.db, self.file, annotation);
+            let _annotated_ty = self.file_expression_ty(annotation);
             // TODO `tuple[annotated_ty, ...]`
             let ty = KnownClass::Tuple.to_instance(self.db);
             self.add_declaration_with_binding(parameter.into(), definition, ty, ty);
@@ -1152,7 +1185,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         definition: Definition<'db>,
     ) {
         if let Some(annotation) = parameter.annotation.as_ref() {
-            let _annotated_ty = expression_ty(self.db, self.file, annotation);
+            let _annotated_ty = self.file_expression_ty(annotation);
             // TODO `dict[str, annotated_ty]`
             let ty = KnownClass::Dict.to_instance(self.db);
             self.add_declaration_with_binding(parameter.into(), definition, ty, ty);
@@ -1400,9 +1433,9 @@ impl<'db> TypeInferenceBuilder<'db> {
         // TODO: Make use of Protocols when we support it (the manager be assignable to `contextlib.AbstractContextManager`).
         match (enter, exit) {
             (Symbol::Unbound, Symbol::Unbound) => {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &INVALID_CONTEXT_MANAGER,
                     context_expression.into(),
-                    "invalid-context-manager",
                     format_args!(
                         "Object of type `{}` cannot be used with `with` because it doesn't implement `__enter__` and `__exit__`",
                         context_expression_ty.display(self.db)
@@ -1411,9 +1444,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                 Type::Unknown
             }
             (Symbol::Unbound, _) => {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &INVALID_CONTEXT_MANAGER,
                     context_expression.into(),
-                    "invalid-context-manager",
                     format_args!(
                         "Object of type `{}` cannot be used with `with` because it doesn't implement `__enter__`",
                         context_expression_ty.display(self.db)
@@ -1423,9 +1456,9 @@ impl<'db> TypeInferenceBuilder<'db> {
             }
             (Symbol::Type(enter_ty, enter_boundness), exit) => {
                 if enter_boundness == Boundness::PossiblyUnbound {
-                    self.diagnostics.add(
+                    self.diagnostics.add_lint(
+                        &INVALID_CONTEXT_MANAGER,
                         context_expression.into(),
-                        "invalid-context-manager",
                         format_args!(
                             "Object of type `{context_expression}` cannot be used with `with` because the method `__enter__` is possibly unbound",
                             context_expression = context_expression_ty.display(self.db),
@@ -1437,9 +1470,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                     .call(self.db, &[context_expression_ty])
                     .return_ty_result(self.db, context_expression.into(), &mut self.diagnostics)
                     .unwrap_or_else(|err| {
-                        self.diagnostics.add(
+                        self.diagnostics.add_lint(
+                            &INVALID_CONTEXT_MANAGER,
                             context_expression.into(),
-                            "invalid-context-manager",
                             format_args!("
                                 Object of type `{context_expression}` cannot be used with `with` because the method `__enter__` of type `{enter_ty}` is not callable", context_expression = context_expression_ty.display(self.db), enter_ty = enter_ty.display(self.db)
                             ),
@@ -1449,9 +1482,9 @@ impl<'db> TypeInferenceBuilder<'db> {
 
                 match exit {
                     Symbol::Unbound => {
-                        self.diagnostics.add(
+                        self.diagnostics.add_lint(
+                            &INVALID_CONTEXT_MANAGER,
                             context_expression.into(),
-                            "invalid-context-manager",
                             format_args!(
                                 "Object of type `{}` cannot be used with `with` because it doesn't implement `__exit__`",
                                 context_expression_ty.display(self.db)
@@ -1462,9 +1495,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                         // TODO: Use the `exit_ty` to determine if any raised exception is suppressed.
 
                         if exit_boundness == Boundness::PossiblyUnbound {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &INVALID_CONTEXT_MANAGER,
                                 context_expression.into(),
-                                "invalid-context-manager",
                                 format_args!(
                                     "Object of type `{context_expression}` cannot be used with `with` because the method `__exit__` is possibly unbound",
                                     context_expression = context_expression_ty.display(self.db),
@@ -1489,9 +1522,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                             )
                             .is_err()
                         {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &INVALID_CONTEXT_MANAGER,
                                 context_expression.into(),
-                                "invalid-context-manager",
                                 format_args!(
                                     "Object of type `{context_expression}` cannot be used with `with` because the method `__exit__` of type `{exit_ty}` is not callable",
                                     context_expression = context_expression_ty.display(self.db),
@@ -1512,40 +1545,56 @@ impl<'db> TypeInferenceBuilder<'db> {
         except_handler_definition: &ExceptHandlerDefinitionKind,
         definition: Definition<'db>,
     ) {
-        let node_ty = except_handler_definition
-            .handled_exceptions()
-            .map(|ty| self.infer_expression(ty))
-            // If there is no handled exception, it's invalid syntax;
-            // a diagnostic will have already been emitted
-            .unwrap_or(Type::Unknown);
+        let node = except_handler_definition.handled_exceptions();
+
+        // If there is no handled exception, it's invalid syntax;
+        // a diagnostic will have already been emitted
+        let node_ty = node.map_or(Type::Unknown, |ty| self.infer_expression(ty));
+
+        // If it's an `except*` handler, this won't actually be the type of the bound symbol;
+        // it will actually be the type of the generic parameters to `BaseExceptionGroup` or `ExceptionGroup`.
+        let symbol_ty = if let Type::Tuple(tuple) = node_ty {
+            let type_base_exception = KnownClass::BaseException
+                .to_subclass_of(self.db)
+                .unwrap_or(Type::Unknown);
+            let mut builder = UnionBuilder::new(self.db);
+            for element in tuple.elements(self.db).iter().copied() {
+                builder = builder.add(if element.is_assignable_to(self.db, type_base_exception) {
+                    element.to_instance(self.db)
+                } else {
+                    if let Some(node) = node {
+                        self.diagnostics
+                            .add_invalid_exception_caught(self.db, node, element);
+                    }
+                    Type::Unknown
+                });
+            }
+            builder.build()
+        } else if node_ty.is_subtype_of(self.db, KnownClass::Tuple.to_instance(self.db)) {
+            todo_type!("Homogeneous tuple in exception handler")
+        } else {
+            let type_base_exception = KnownClass::BaseException
+                .to_subclass_of(self.db)
+                .unwrap_or(Type::Unknown);
+            if node_ty.is_assignable_to(self.db, type_base_exception) {
+                node_ty.to_instance(self.db)
+            } else {
+                if let Some(node) = node {
+                    self.diagnostics
+                        .add_invalid_exception_caught(self.db, node, node_ty);
+                }
+                Type::Unknown
+            }
+        };
 
         let symbol_ty = if except_handler_definition.is_star() {
-            // TODO should be generic --Alex
+            // TODO: we should infer `ExceptionGroup` if `node_ty` is a subtype of `tuple[type[Exception], ...]`
+            // (needs support for homogeneous tuples).
             //
-            // TODO should infer `ExceptionGroup` if all caught exceptions
-            // are subclasses of `Exception` --Alex
-            builtins_symbol(self.db, "BaseExceptionGroup")
-                .ignore_possibly_unbound()
-                .unwrap_or(Type::Unknown)
-                .to_instance(self.db)
+            // TODO: should be generic with `symbol_ty` as the generic parameter
+            KnownClass::BaseExceptionGroup.to_instance(self.db)
         } else {
-            // TODO: anything that's a consistent subtype of
-            // `type[BaseException] | tuple[type[BaseException], ...]` should be valid;
-            // anything else is invalid and should lead to a diagnostic being reported --Alex
-            match node_ty {
-                Type::Any | Type::Unknown => node_ty,
-                Type::ClassLiteral(ClassLiteralType { class }) => Type::instance(class),
-                Type::Tuple(tuple) => UnionType::from_elements(
-                    self.db,
-                    tuple.elements(self.db).iter().map(|ty| {
-                        ty.into_class_literal().map_or(
-                            todo_type!("exception type"),
-                            |ClassLiteralType { class }| Type::instance(class),
-                        )
-                    }),
-                ),
-                _ => todo_type!("exception type"),
-            }
+            symbol_ty
         };
 
         self.add_binding(
@@ -1569,9 +1618,9 @@ impl<'db> TypeInferenceBuilder<'db> {
         let bound_or_constraint = match bound.as_deref() {
             Some(expr @ ast::Expr::Tuple(ast::ExprTuple { elts, .. })) => {
                 if elts.len() < 2 {
-                    self.diagnostics.add(
+                    self.diagnostics.add_lint(
+                        &INVALID_TYPE_VARIABLE_CONSTRAINTS,
                         expr.into(),
-                        "invalid-typevar-constraints",
                         format_args!("TypeVar must have at least two constrained types"),
                     );
                     self.infer_expression(expr);
@@ -1892,9 +1941,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                     ) {
                         Ok(t) => t,
                         Err(e) => {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &UNSUPPORTED_OPERATOR,
                                 assignment.into(),
-                                "unsupported-operator",
                                 format_args!(
                                     "Operator `{op}=` is unsupported between objects of type `{}` and `{}`",
                                     target_type.display(self.db),
@@ -1913,9 +1962,9 @@ impl<'db> TypeInferenceBuilder<'db> {
 
                             let binary_return_ty = self.infer_binary_expression_type(left_ty, right_ty, op)
                                 .unwrap_or_else(|| {
-                                    self.diagnostics.add(
+                                    self.diagnostics.add_lint(
+                                        &UNSUPPORTED_OPERATOR,
                                         assignment.into(),
-                                        "unsupported-operator",
                                         format_args!(
                                             "Operator `{op}=` is unsupported between objects of type `{}` and `{}`",
                                             left_ty.display(self.db),
@@ -1942,9 +1991,9 @@ impl<'db> TypeInferenceBuilder<'db> {
 
         self.infer_binary_expression_type(left_ty, right_ty, op)
             .unwrap_or_else(|| {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &UNSUPPORTED_OPERATOR,
                     assignment.into(),
-                    "unsupported-operator",
                     format_args!(
                         "Operator `{op}=` is unsupported between objects of type `{}` and `{}`",
                         left_ty.display(self.db),
@@ -1974,11 +2023,11 @@ impl<'db> TypeInferenceBuilder<'db> {
 
         // Resolve the target type, assuming a load context.
         let target_type = match &**target {
-            Expr::Name(name) => {
+            ast::Expr::Name(name) => {
                 self.store_expression_type(target, Type::Never);
                 self.infer_name_load(name)
             }
-            Expr::Attribute(attr) => {
+            ast::Expr::Attribute(attr) => {
                 self.store_expression_type(target, Type::Never);
                 self.infer_attribute_load(attr)
             }
@@ -2195,19 +2244,19 @@ impl<'db> TypeInferenceBuilder<'db> {
                     match module_ty.member(self.db, &ast::name::Name::new(&name.id)) {
                         Symbol::Type(ty, boundness) => {
                             if boundness == Boundness::PossiblyUnbound {
-                                self.diagnostics.add(
+                                self.diagnostics.add_lint(
+                                    &POSSIBLY_UNBOUND_IMPORT,
                                     AnyNodeRef::Alias(alias),
-                                    "possibly-unbound-import",
-                                    format_args!("Member `{name}` of module `{module_name}` is possibly unbound",),
+                                    format_args!("Member `{name}` of module `{module_name}` is possibly unbound", ),
                                 );
                             }
 
                             ty
                         }
                         Symbol::Unbound => {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &UNRESOLVED_IMPORT,
                                 AnyNodeRef::Alias(alias),
-                                "unresolved-import",
                                 format_args!("Module `{module_name}` has no member `{name}`",),
                             );
                             Type::Unknown
@@ -2912,9 +2961,9 @@ impl<'db> TypeInferenceBuilder<'db> {
             {
                 let mut builtins_symbol = builtins_symbol(self.db, name);
                 if builtins_symbol.is_unbound() && name == "reveal_type" {
-                    self.diagnostics.add(
+                    self.diagnostics.add_lint(
+                        &UNDEFINED_REVEAL,
                         name_node.into(),
-                        "undefined-reveal",
                         format_args!(
                             "`reveal_type` used without importing it; this is allowed for debugging convenience but will fail at runtime"),
                     );
@@ -3009,9 +3058,9 @@ impl<'db> TypeInferenceBuilder<'db> {
         match value_ty.member(self.db, &attr.id) {
             Symbol::Type(member_ty, boundness) => {
                 if boundness == Boundness::PossiblyUnbound {
-                    self.diagnostics.add(
+                    self.diagnostics.add_lint(
+                        &POSSIBLY_UNBOUND_ATTRIBUTE,
                         attribute.into(),
-                        "possibly-unbound-attribute",
                         format_args!(
                             "Attribute `{}` on type `{}` is possibly unbound",
                             attr.id,
@@ -3023,9 +3072,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                 member_ty
             }
             Symbol::Unbound => {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &UNRESOLVED_ATTRIBUTE,
                     attribute.into(),
-                    "unresolved-attribute",
                     format_args!(
                         "Type `{}` has no attribute `{}`",
                         value_ty.display(self.db),
@@ -3104,9 +3153,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                     ) {
                         Ok(t) => t,
                         Err(e) => {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &UNSUPPORTED_OPERATOR,
                                 unary.into(),
-                                "unsupported-operator",
                                 format_args!(
                                     "Unary operator `{op}` is unsupported for type `{}`",
                                     operand_type.display(self.db),
@@ -3116,9 +3165,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                         }
                     }
                 } else {
-                    self.diagnostics.add(
+                    self.diagnostics.add_lint(
+                        &UNSUPPORTED_OPERATOR,
                         unary.into(),
-                        "unsupported-operator",
                         format_args!(
                             "Unary operator `{op}` is unsupported for type `{}`",
                             operand_type.display(self.db),
@@ -3157,9 +3206,9 @@ impl<'db> TypeInferenceBuilder<'db> {
 
         self.infer_binary_expression_type(left_ty, right_ty, *op)
             .unwrap_or_else(|| {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &UNSUPPORTED_OPERATOR,
                     binary.into(),
-                    "unsupported-operator",
                     format_args!(
                         "Operator `{op}` is unsupported between objects of type `{}` and `{}`",
                         left_ty.display(self.db),
@@ -3467,9 +3516,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                     self.infer_binary_type_comparison(left_ty, *op, right_ty)
                         .unwrap_or_else(|error| {
                             // Handle unsupported operators (diagnostic, `bool`/`Unknown` outcome)
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &UNSUPPORTED_OPERATOR,
                                 AnyNodeRef::ExprCompare(compare),
-                                "unsupported-operator",
                                 format_args!(
                                     "Operator `{}` is not supported for types `{}` and `{}`{}",
                                     error.op,
@@ -4124,9 +4173,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                     Symbol::Unbound => {}
                     Symbol::Type(dunder_getitem_method, boundness) => {
                         if boundness == Boundness::PossiblyUnbound {
-                            self.diagnostics.add(
+                            self.diagnostics.add_lint(
+                                &CALL_POSSIBLY_UNBOUND_METHOD,
                                 value_node.into(),
-                                "call-possibly-unbound-method",
                                 format_args!(
                                     "Method `__getitem__` of type `{}` is possibly unbound",
                                     value_ty.display(self.db),
@@ -4138,9 +4187,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                             .call(self.db, &[slice_ty])
                             .return_ty_result(self.db, value_node.into(), &mut self.diagnostics)
                             .unwrap_or_else(|err| {
-                                self.diagnostics.add(
+                                self.diagnostics.add_lint(
+                                    &CALL_NON_CALLABLE,
                                     value_node.into(),
-                                    "call-non-callable",
                                     format_args!(
                                         "Method `__getitem__` of type `{}` is not callable on object of type `{}`",
                                         err.called_ty().display(self.db),
@@ -4168,9 +4217,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                         Symbol::Unbound => {}
                         Symbol::Type(ty, boundness) => {
                             if boundness == Boundness::PossiblyUnbound {
-                                self.diagnostics.add(
+                                self.diagnostics.add_lint(
+                                    &CALL_POSSIBLY_UNBOUND_METHOD,
                                     value_node.into(),
-                                    "call-possibly-unbound-method",
                                     format_args!(
                                         "Method `__class_getitem__` of type `{}` is possibly unbound",
                                         value_ty.display(self.db),
@@ -4182,9 +4231,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                                 .call(self.db, &[slice_ty])
                                 .return_ty_result(self.db, value_node.into(), &mut self.diagnostics)
                                 .unwrap_or_else(|err| {
-                                    self.diagnostics.add(
+                                    self.diagnostics.add_lint(
+                                        &CALL_NON_CALLABLE,
                                         value_node.into(),
-                                        "call-non-callable",
                                         format_args!(
                                             "Method `__class_getitem__` of type `{}` is not callable on object of type `{}`",
                                             err.called_ty().display(self.db),
@@ -4324,18 +4373,18 @@ impl<'db> TypeInferenceBuilder<'db> {
             ast::Expr::Starred(starred) => self.infer_starred_expression(starred),
 
             ast::Expr::BytesLiteral(bytes) => {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &BYTE_STRING_TYPE_ANNOTATION,
                     bytes.into(),
-                    "annotation-byte-string",
                     format_args!("Type expressions cannot use bytes literal"),
                 );
                 Type::Unknown
             }
 
             ast::Expr::FString(fstring) => {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &FSTRING_TYPE_ANNOTATION,
                     fstring.into(),
-                    "annotation-f-string",
                     format_args!("Type expressions cannot use f-strings"),
                 );
                 self.infer_fstring_expression(fstring);
@@ -4657,10 +4706,12 @@ impl<'db> TypeInferenceBuilder<'db> {
         match slice {
             ast::Expr::Name(_) | ast::Expr::Attribute(_) => {
                 let name_ty = self.infer_expression(slice);
-                if let Some(ClassLiteralType { class }) = name_ty.into_class_literal() {
-                    Type::subclass_of(class)
-                } else {
-                    todo_type!("unsupported type[X] special form")
+                match name_ty {
+                    Type::ClassLiteral(ClassLiteralType { class }) => Type::subclass_of(class),
+                    Type::KnownInstance(KnownInstanceType::Any) => {
+                        Type::subclass_of_base(ClassBase::Any)
+                    }
+                    _ => todo_type!("unsupported type[X] special form"),
                 }
             }
             ast::Expr::BinOp(binary) if binary.op == ast::Operator::BitOr => {
@@ -4677,13 +4728,40 @@ impl<'db> TypeInferenceBuilder<'db> {
             }
             ast::Expr::Tuple(_) => {
                 self.infer_type_expression(slice);
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &INVALID_TYPE_FORM,
                     slice.into(),
-                    "invalid-type-form",
                     format_args!("type[...] must have exactly one type argument"),
                 );
                 Type::Unknown
             }
+            ast::Expr::Subscript(ast::ExprSubscript {
+                value,
+                slice: parameters,
+                ..
+            }) => {
+                let parameters_ty = match self.infer_expression(value) {
+                    Type::KnownInstance(KnownInstanceType::Union) => match &**parameters {
+                        ast::Expr::Tuple(tuple) => {
+                            let ty = UnionType::from_elements(
+                                self.db,
+                                tuple
+                                    .iter()
+                                    .map(|element| self.infer_subclass_of_type_expression(element)),
+                            );
+                            self.store_expression_type(parameters, ty);
+                            ty
+                        }
+                        _ => self.infer_subclass_of_type_expression(parameters),
+                    },
+                    _ => {
+                        self.infer_type_expression(parameters);
+                        todo_type!("unsupported nested subscript in type[X]")
+                    }
+                };
+                self.store_expression_type(slice, parameters_ty);
+                parameters_ty
+            }
             // TODO: subscripts, etc.
             _ => {
                 self.infer_type_expression(slice);
@@ -4726,9 +4804,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                 Ok(ty) => ty,
                 Err(nodes) => {
                     for node in nodes {
-                        self.diagnostics.add(
+                        self.diagnostics.add_lint(
+                            &INVALID_LITERAL_PARAMETER,
                             node.into(),
-                            "invalid-literal-parameter",
                             format_args!(
                                 "Type arguments for `Literal` must be `None`, \
                                     a literal value (int, bool, str, or bytes), or an enum value"
@@ -4762,9 +4840,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                 todo_type!("generic type alias")
             }
             KnownInstanceType::NoReturn | KnownInstanceType::Never => {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &INVALID_TYPE_PARAMETER,
                     subscript.into(),
-                    "invalid-type-parameter",
                     format_args!(
                         "Type `{}` expected no type parameter",
                         known_instance.repr(self.db)
@@ -4773,9 +4851,9 @@ impl<'db> TypeInferenceBuilder<'db> {
                 Type::Unknown
             }
             KnownInstanceType::LiteralString => {
-                self.diagnostics.add(
+                self.diagnostics.add_lint(
+                    &INVALID_TYPE_PARAMETER,
                     subscript.into(),
-                    "invalid-type-parameter",
                     format_args!(
                         "Type `{}` expected no type parameter. Did you mean to use `Literal[...]` instead?",
                         known_instance.repr(self.db)
@@ -4783,7 +4861,19 @@ impl<'db> TypeInferenceBuilder<'db> {
                 );
                 Type::Unknown
             }
-            KnownInstanceType::Any => Type::Any,
+            KnownInstanceType::Type => self.infer_subclass_of_type_expression(parameters),
+            KnownInstanceType::Tuple => self.infer_tuple_type_expression(parameters),
+            KnownInstanceType::Any => {
+                self.diagnostics.add_lint(
+                    &INVALID_TYPE_PARAMETER,
+                    subscript.into(),
+                    format_args!(
+                        "Type `{}` expected no type parameter",
+                        known_instance.repr(self.db)
+                    ),
+                );
+                Type::Unknown
+            }
         }
     }
 

crates/red_knot_python_semantic/src/types/mro.rs

@@ -4,8 +4,8 @@ use std::ops::Deref;
 use itertools::Either;
 use rustc_hash::FxHashSet;
 
-use super::{Class, ClassLiteralType, KnownClass, KnownInstanceType, Type};
-use crate::{types::todo_type, Db};
+use super::{Class, ClassLiteralType, KnownClass, KnownInstanceType, TodoType, Type};
+use crate::Db;
 
 /// The inferred method resolution order of a given class.
 ///
@@ -76,21 +76,14 @@ impl<'db> Mro<'db> {
             // This *could* theoretically be handled by the final branch below,
             // but it's a common case (i.e., worth optimizing for),
             // and the `c3_merge` function requires lots of allocations.
-            [single_base] => {
-                let single_base = ClassBase::try_from_ty(*single_base).ok_or(*single_base);
-                single_base.map_or_else(
-                    |invalid_base_ty| {
-                        let bases_info = Box::from([(0, invalid_base_ty)]);
-                        Err(MroErrorKind::InvalidBases(bases_info))
-                    },
-                    |single_base| {
-                        let mro = std::iter::once(ClassBase::Class(class))
-                            .chain(single_base.mro(db))
-                            .collect();
-                        Ok(mro)
-                    },
-                )
-            }
+            [single_base] => ClassBase::try_from_ty(db, *single_base).map_or_else(
+                || Err(MroErrorKind::InvalidBases(Box::from([(0, *single_base)]))),
+                |single_base| {
+                    Ok(std::iter::once(ClassBase::Class(class))
+                        .chain(single_base.mro(db))
+                        .collect())
+                },
+            ),
 
             // The class has multiple explicit bases.
             //
@@ -102,9 +95,9 @@ impl<'db> Mro<'db> {
                 let mut invalid_bases = vec![];
 
                 for (i, base) in multiple_bases.iter().enumerate() {
-                    match ClassBase::try_from_ty(*base).ok_or(*base) {
-                        Ok(valid_base) => valid_bases.push(valid_base),
-                        Err(invalid_base) => invalid_bases.push((i, invalid_base)),
+                    match ClassBase::try_from_ty(db, *base) {
+                        Some(valid_base) => valid_bases.push(valid_base),
+                        None => invalid_bases.push((i, *base)),
                     }
                 }
 
@@ -299,16 +292,16 @@ pub(super) enum MroErrorKind<'db> {
 /// 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`]
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-pub(super) enum ClassBase<'db> {
+#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, salsa::Update)]
+pub enum ClassBase<'db> {
     Any,
     Unknown,
-    Todo,
+    Todo(TodoType),
     Class(Class<'db>),
 }
 
 impl<'db> ClassBase<'db> {
-    pub(super) fn display(self, db: &'db dyn Db) -> impl std::fmt::Display + 'db {
+    pub fn display(self, db: &'db dyn Db) -> impl std::fmt::Display + 'db {
         struct Display<'db> {
             base: ClassBase<'db>,
             db: &'db dyn Db,
@@ -318,7 +311,7 @@ impl<'db> ClassBase<'db> {
             fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
                 match self.base {
                     ClassBase::Any => f.write_str("Any"),
-                    ClassBase::Todo => f.write_str("Todo"),
+                    ClassBase::Todo(todo) => todo.fmt(f),
                     ClassBase::Unknown => f.write_str("Unknown"),
                     ClassBase::Class(class) => write!(f, "<class '{}'>", class.name(self.db)),
                 }
@@ -341,11 +334,11 @@ impl<'db> ClassBase<'db> {
     /// Attempt to resolve `ty` into a `ClassBase`.
     ///
     /// Return `None` if `ty` is not an acceptable type for a class base.
-    fn try_from_ty(ty: Type<'db>) -> Option<Self> {
+    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(_) => Some(Self::Todo),
+            Type::Todo(todo) => Some(Self::Todo(todo)),
             Type::ClassLiteral(ClassLiteralType { class }) => Some(Self::Class(class)),
             Type::Union(_) => None, // TODO -- forces consideration of multiple possible MROs?
             Type::Intersection(_) => None, // TODO -- probably incorrect?
@@ -371,6 +364,13 @@ impl<'db> ClassBase<'db> {
                 | KnownInstanceType::Never
                 | KnownInstanceType::Optional => None,
                 KnownInstanceType::Any => Some(Self::Any),
+                // TODO: Classes inheriting from `typing.Type` et al. also have `Generic` in their MRO
+                KnownInstanceType::Type => {
+                    ClassBase::try_from_ty(db, KnownClass::Type.to_class_literal(db))
+                }
+                KnownInstanceType::Tuple => {
+                    ClassBase::try_from_ty(db, KnownClass::Tuple.to_class_literal(db))
+                }
             },
         }
     }
@@ -392,7 +392,9 @@ impl<'db> ClassBase<'db> {
             ClassBase::Unknown => {
                 Either::Left([ClassBase::Unknown, ClassBase::object(db)].into_iter())
             }
-            ClassBase::Todo => Either::Left([ClassBase::Todo, ClassBase::object(db)].into_iter()),
+            ClassBase::Todo(todo) => {
+                Either::Left([ClassBase::Todo(todo), ClassBase::object(db)].into_iter())
+            }
             ClassBase::Class(class) => Either::Right(class.iter_mro(db)),
         }
     }
@@ -408,7 +410,7 @@ impl<'db> From<ClassBase<'db>> for Type<'db> {
     fn from(value: ClassBase<'db>) -> Self {
         match value {
             ClassBase::Any => Type::Any,
-            ClassBase::Todo => todo_type!(),
+            ClassBase::Todo(todo) => Type::Todo(todo),
             ClassBase::Unknown => Type::Unknown,
             ClassBase::Class(class) => Type::class_literal(class),
         }

crates/red_knot_python_semantic/src/types/property_tests.rs

@@ -64,6 +64,10 @@ fn arbitrary_core_type(g: &mut Gen) -> Ty {
         Ty::BuiltinClassLiteral("int"),
         Ty::BuiltinClassLiteral("bool"),
         Ty::BuiltinClassLiteral("object"),
+        Ty::BuiltinInstance("type"),
+        Ty::SubclassOfAny,
+        Ty::SubclassOfBuiltinClass("object"),
+        Ty::SubclassOfBuiltinClass("str"),
     ])
     .unwrap()
     .clone()
@@ -163,13 +167,13 @@ mod stable {
     // `T` is equivalent to itself.
     type_property_test!(
         equivalent_to_is_reflexive, db,
-        forall types t. t.is_equivalent_to(db, t)
+        forall types t. t.is_fully_static(db) => t.is_equivalent_to(db, t)
     );
 
     // `T` is a subtype of itself.
     type_property_test!(
         subtype_of_is_reflexive, db,
-        forall types t. t.is_subtype_of(db, t)
+        forall types t. t.is_fully_static(db) => t.is_subtype_of(db, t)
     );
 
     // `S <: T` and `T <: U` implies that `S <: U`.
@@ -214,6 +218,12 @@ mod stable {
         forall types t. t.is_singleton(db) => t.is_single_valued(db)
     );
 
+    // If `T` contains a gradual form, it should not participate in equivalence
+    type_property_test!(
+        non_fully_static_types_do_not_participate_in_equivalence, db,
+        forall types s, t. !s.is_fully_static(db) => !s.is_equivalent_to(db, t) && !t.is_equivalent_to(db, s)
+    );
+
     // If `T` contains a gradual form, it should not participate in subtyping
     type_property_test!(
         non_fully_static_types_do_not_participate_in_subtyping, db,

crates/red_knot_python_semantic/src/types/string_annotation.rs

@@ -5,8 +5,127 @@ use ruff_python_ast::{self as ast, ModExpression, StringFlags};
 use ruff_python_parser::{parse_expression_range, Parsed};
 use ruff_text_size::Ranged;
 
+use crate::lint::{Level, LintStatus};
 use crate::types::diagnostic::{TypeCheckDiagnostics, TypeCheckDiagnosticsBuilder};
-use crate::Db;
+use crate::{declare_lint, Db};
+
+declare_lint! {
+    /// ## What it does
+    /// Checks for f-strings in type annotation positions.
+    ///
+    /// ## Why is this bad?
+    /// Static analysis tools like Red Knot can't analyse type annotations that use f-string notation.
+    ///
+    /// ## Examples
+    /// ```python
+    /// def test(): -> f"int":
+    ///     ...
+    /// ```
+    ///
+    /// Use instead:
+    /// ```python
+    /// def test(): -> "int":
+    ///     ...
+    /// ```
+    pub(crate) static FSTRING_TYPE_ANNOTATION = {
+        summary: "detects F-strings in type annotation positions",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+        /// ## What it does
+        /// Checks for byte-strings in type annotation positions.
+        ///
+        /// ## Why is this bad?
+        /// Static analysis tools like Red Knot can't analyse type annotations that use byte-string notation.
+        ///
+        /// ## Examples
+        /// ```python
+        /// def test(): -> b"int":
+        ///     ...
+        /// ```
+        ///
+        /// Use instead:
+        /// ```python
+        /// def test(): -> "int":
+        ///     ...
+        /// ```
+    pub(crate) static BYTE_STRING_TYPE_ANNOTATION = {
+        summary: "detects byte strings in type annotation positions",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+        /// ## What it does
+        /// Checks for raw-strings in type annotation positions.
+        ///
+        /// ## Why is this bad?
+        /// Static analysis tools like Red Knot can't analyse type annotations that use raw-string notation.
+        ///
+        /// ## Examples
+        /// ```python
+        /// def test(): -> r"int":
+        ///     ...
+        /// ```
+        ///
+        /// Use instead:
+        /// ```python
+        /// def test(): -> "int":
+        ///     ...
+        /// ```
+    pub(crate) static RAW_STRING_TYPE_ANNOTATION = {
+        summary: "detects raw strings in type annotation positions",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+        /// ## What it does
+        /// Checks for implicit concatenated strings in type annotation positions.
+        ///
+        /// ## Why is this bad?
+        /// Static analysis tools like Red Knot can't analyse type annotations that use implicit concatenated strings.
+        ///
+        /// ## Examples
+        /// ```python
+        /// def test(): -> "Literal[" "5" "]":
+        ///     ...
+        /// ```
+        ///
+        /// Use instead:
+        /// ```python
+        /// def test(): -> "Literal[5]":
+        ///     ...
+        /// ```
+    pub(crate) static IMPLICIT_CONCATENATED_STRING_TYPE_ANNOTATION = {
+        summary: "detects implicit concatenated strings in type annotations",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static INVALID_SYNTAX_IN_FORWARD_ANNOTATION = {
+        summary: "detects invalid syntax in forward annotations",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
+
+declare_lint! {
+    /// TODO #14889
+    pub(crate) static ESCAPE_CHARACTER_IN_FORWARD_ANNOTATION = {
+        summary: "detects forward type annotations with escape characters",
+        status: LintStatus::preview("1.0.0"),
+        default_level: Level::Error,
+    }
+}
 
 type AnnotationParseResult = Result<Parsed<ModExpression>, TypeCheckDiagnostics>;
 
@@ -25,9 +144,9 @@ pub(crate) fn parse_string_annotation(
     if let [string_literal] = string_expr.value.as_slice() {
         let prefix = string_literal.flags.prefix();
         if prefix.is_raw() {
-            diagnostics.add(
+            diagnostics.add_lint(
+                &RAW_STRING_TYPE_ANNOTATION,
                 string_literal.into(),
-                "annotation-raw-string",
                 format_args!("Type expressions cannot use raw string literal"),
             );
         // Compare the raw contents (without quotes) of the expression with the parsed contents
@@ -49,26 +168,26 @@ pub(crate) fn parse_string_annotation(
             // ```
             match parse_expression_range(source.as_str(), range_excluding_quotes) {
                 Ok(parsed) => return Ok(parsed),
-                Err(parse_error) => diagnostics.add(
+                Err(parse_error) => diagnostics.add_lint(
+                    &INVALID_SYNTAX_IN_FORWARD_ANNOTATION,
                     string_literal.into(),
-                    "forward-annotation-syntax-error",
                     format_args!("Syntax error in forward annotation: {}", parse_error.error),
                 ),
             }
         } else {
             // The raw contents of the string doesn't match the parsed content. This could be the
             // case for annotations that contain escape sequences.
-            diagnostics.add(
+            diagnostics.add_lint(
+                &ESCAPE_CHARACTER_IN_FORWARD_ANNOTATION,
                 string_expr.into(),
-                "annotation-escape-character",
                 format_args!("Type expressions cannot contain escape characters"),
             );
         }
     } else {
         // String is implicitly concatenated.
-        diagnostics.add(
+        diagnostics.add_lint(
+            &IMPLICIT_CONCATENATED_STRING_TYPE_ANNOTATION,
             string_expr.into(),
-            "annotation-implicit-concat",
             format_args!("Type expressions cannot span multiple string literals"),
         );
     }

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

@@ -86,14 +86,15 @@ fn to_lsp_diagnostic(
 
     let severity = match diagnostic.severity() {
         Severity::Info => DiagnosticSeverity::INFORMATION,
-        Severity::Error => DiagnosticSeverity::ERROR,
+        Severity::Warning => DiagnosticSeverity::WARNING,
+        Severity::Error | Severity::Fatal => DiagnosticSeverity::ERROR,
     };
 
     Diagnostic {
         range,
         severity: Some(severity),
         tags: None,
-        code: Some(NumberOrString::String(diagnostic.rule().to_string())),
+        code: Some(NumberOrString::String(diagnostic.id().to_string())),
         code_description: None,
         source: Some("red-knot".into()),
         message: diagnostic.message().into_owned(),

crates/red_knot_test/src/db.rs

@@ -1,5 +1,7 @@
+use red_knot_python_semantic::lint::RuleSelection;
 use red_knot_python_semantic::{
-    Db as SemanticDb, Program, ProgramSettings, PythonVersion, SearchPathSettings,
+    default_lint_registry, Db as SemanticDb, Program, ProgramSettings, PythonVersion,
+    SearchPathSettings,
 };
 use ruff_db::files::{File, Files};
 use ruff_db::system::{DbWithTestSystem, System, SystemPath, SystemPathBuf, TestSystem};
@@ -13,16 +15,20 @@ pub(crate) struct Db {
     files: Files,
     system: TestSystem,
     vendored: VendoredFileSystem,
+    rule_selection: RuleSelection,
 }
 
 impl Db {
     pub(crate) fn setup(workspace_root: SystemPathBuf) -> Self {
+        let rule_selection = RuleSelection::from_registry(&default_lint_registry());
+
         let db = Self {
             workspace_root,
             storage: salsa::Storage::default(),
             system: TestSystem::default(),
             vendored: red_knot_vendored::file_system().clone(),
             files: Files::default(),
+            rule_selection,
         };
 
         db.memory_file_system()
@@ -85,6 +91,10 @@ impl SemanticDb for Db {
     fn is_file_open(&self, file: File) -> bool {
         !file.path(self).is_vendored_path()
     }
+
+    fn rule_selection(&self) -> &RuleSelection {
+        &self.rule_selection
+    }
 }
 
 #[salsa::db]

crates/red_knot_test/src/diagnostic.rs

@@ -144,7 +144,7 @@ struct DiagnosticWithLine<T> {
 mod tests {
     use crate::db::Db;
     use crate::diagnostic::Diagnostic;
-    use ruff_db::diagnostic::Severity;
+    use ruff_db::diagnostic::{DiagnosticId, LintName, Severity};
     use ruff_db::files::{system_path_to_file, File};
     use ruff_db::source::line_index;
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
@@ -190,8 +190,8 @@ mod tests {
     }
 
     impl Diagnostic for DummyDiagnostic {
-        fn rule(&self) -> &str {
-            "dummy"
+        fn id(&self) -> DiagnosticId {
+            DiagnosticId::Lint(LintName::of("dummy"))
         }
 
         fn message(&self) -> Cow<str> {

crates/red_knot_test/src/matcher.rs

@@ -4,7 +4,7 @@ use crate::assertion::{Assertion, ErrorAssertion, InlineFileAssertions};
 use crate::db::Db;
 use crate::diagnostic::SortedDiagnostics;
 use colored::Colorize;
-use ruff_db::diagnostic::Diagnostic;
+use ruff_db::diagnostic::{Diagnostic, DiagnosticAsStrError, DiagnosticId};
 use ruff_db::files::File;
 use ruff_db::source::{line_index, source_text, SourceText};
 use ruff_source_file::{LineIndex, OneIndexed};
@@ -146,7 +146,7 @@ fn maybe_add_undefined_reveal_clarification<T: Diagnostic>(
     diagnostic: &T,
     original: std::fmt::Arguments,
 ) -> String {
-    if diagnostic.rule() == "undefined-reveal" {
+    if diagnostic.id().is_lint_named("undefined-reveal") {
         format!(
             "{} add a `# revealed` assertion on this line (original diagnostic: {original})",
             "used built-in `reveal_type`:".yellow()
@@ -161,9 +161,14 @@ where
     T: Diagnostic,
 {
     fn unmatched(&self) -> String {
+        let id = self.id();
+        let id = id.as_str().unwrap_or_else(|error| match error {
+            DiagnosticAsStrError::Category { name, .. } => name,
+        });
+
         maybe_add_undefined_reveal_clarification(
             self,
-            format_args!(r#"[{}] "{}""#, self.rule(), self.message()),
+            format_args!(r#"[{id}] "{message}""#, message = self.message()),
         )
     }
 }
@@ -173,9 +178,14 @@ where
     T: Diagnostic,
 {
     fn unmatched_with_column(&self, column: OneIndexed) -> String {
+        let id = self.id();
+        let id = id.as_str().unwrap_or_else(|error| match error {
+            DiagnosticAsStrError::Category { name, .. } => name,
+        });
+
         maybe_add_undefined_reveal_clarification(
             self,
-            format_args!(r#"{column} [{}] "{}""#, self.rule(), self.message()),
+            format_args!(r#"{column} [{id}] "{message}""#, message = self.message()),
         )
     }
 }
@@ -270,10 +280,11 @@ impl Matcher {
         match assertion {
             Assertion::Error(error) => {
                 let position = unmatched.iter().position(|diagnostic| {
-                    !error.rule.is_some_and(|rule| rule != diagnostic.rule())
-                        && !error
-                            .column
-                            .is_some_and(|col| col != self.column(*diagnostic))
+                    !error.rule.is_some_and(|rule| {
+                        !(diagnostic.id().is_lint_named(rule) || diagnostic.id().matches(rule))
+                    }) && !error
+                        .column
+                        .is_some_and(|col| col != self.column(*diagnostic))
                         && !error
                             .message_contains
                             .is_some_and(|needle| !diagnostic.message().contains(needle))
@@ -294,12 +305,12 @@ impl Matcher {
                 let expected_reveal_type_message = format!("Revealed type is `{expected_type}`");
                 for (index, diagnostic) in unmatched.iter().enumerate() {
                     if matched_revealed_type.is_none()
-                        && diagnostic.rule() == "revealed-type"
+                        && diagnostic.id() == DiagnosticId::RevealedType
                         && diagnostic.message() == expected_reveal_type_message
                     {
                         matched_revealed_type = Some(index);
                     } else if matched_undefined_reveal.is_none()
-                        && diagnostic.rule() == "undefined-reveal"
+                        && diagnostic.id().is_lint_named("undefined-reveal")
                     {
                         matched_undefined_reveal = Some(index);
                     }
@@ -323,7 +334,7 @@ impl Matcher {
 #[cfg(test)]
 mod tests {
     use super::FailuresByLine;
-    use ruff_db::diagnostic::{Diagnostic, Severity};
+    use ruff_db::diagnostic::{Diagnostic, DiagnosticId, Severity};
     use ruff_db::files::{system_path_to_file, File};
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
     use ruff_python_trivia::textwrap::dedent;
@@ -332,16 +343,16 @@ mod tests {
     use std::borrow::Cow;
 
     struct ExpectedDiagnostic {
-        rule: &'static str,
+        id: DiagnosticId,
         message: &'static str,
         range: TextRange,
     }
 
     impl ExpectedDiagnostic {
-        fn new(rule: &'static str, message: &'static str, offset: usize) -> Self {
+        fn new(id: DiagnosticId, message: &'static str, offset: usize) -> Self {
             let offset: u32 = offset.try_into().unwrap();
             Self {
-                rule,
+                id,
                 message,
                 range: TextRange::new(offset.into(), (offset + 1).into()),
             }
@@ -349,7 +360,7 @@ mod tests {
 
         fn into_diagnostic(self, file: File) -> TestDiagnostic {
             TestDiagnostic {
-                rule: self.rule,
+                id: self.id,
                 message: self.message,
                 range: self.range,
                 file,
@@ -359,15 +370,15 @@ mod tests {
 
     #[derive(Debug)]
     struct TestDiagnostic {
-        rule: &'static str,
+        id: DiagnosticId,
         message: &'static str,
         range: TextRange,
         file: File,
     }
 
     impl Diagnostic for TestDiagnostic {
-        fn rule(&self) -> &str {
-            self.rule
+        fn id(&self) -> DiagnosticId {
+            self.id
         }
 
         fn message(&self) -> Cow<str> {
@@ -437,7 +448,7 @@ mod tests {
         let result = get_result(
             "x # revealed: Foo",
             vec![ExpectedDiagnostic::new(
-                "revealed-type",
+                DiagnosticId::RevealedType,
                 "Revealed type is `Foo`",
                 0,
             )],
@@ -451,7 +462,7 @@ mod tests {
         let result = get_result(
             "x # revealed: Foo",
             vec![ExpectedDiagnostic::new(
-                "not-revealed-type",
+                DiagnosticId::lint("not-revealed-type"),
                 "Revealed type is `Foo`",
                 0,
             )],
@@ -474,7 +485,7 @@ mod tests {
         let result = get_result(
             "x # revealed: Foo",
             vec![ExpectedDiagnostic::new(
-                "revealed-type",
+                DiagnosticId::RevealedType,
                 "Something else",
                 0,
             )],
@@ -504,8 +515,12 @@ mod tests {
         let result = get_result(
             "x # revealed: Foo",
             vec![
-                ExpectedDiagnostic::new("revealed-type", "Revealed type is `Foo`", 0),
-                ExpectedDiagnostic::new("undefined-reveal", "Doesn't matter", 0),
+                ExpectedDiagnostic::new(DiagnosticId::RevealedType, "Revealed type is `Foo`", 0),
+                ExpectedDiagnostic::new(
+                    DiagnosticId::lint("undefined-reveal"),
+                    "Doesn't matter",
+                    0,
+                ),
             ],
         );
 
@@ -517,7 +532,7 @@ mod tests {
         let result = get_result(
             "x # revealed: Foo",
             vec![ExpectedDiagnostic::new(
-                "undefined-reveal",
+                DiagnosticId::lint("undefined-reveal"),
                 "Doesn't matter",
                 0,
             )],
@@ -531,8 +546,12 @@ mod tests {
         let result = get_result(
             "x # revealed: Foo",
             vec![
-                ExpectedDiagnostic::new("revealed-type", "Revealed type is `Bar`", 0),
-                ExpectedDiagnostic::new("undefined-reveal", "Doesn't matter", 0),
+                ExpectedDiagnostic::new(DiagnosticId::RevealedType, "Revealed type is `Bar`", 0),
+                ExpectedDiagnostic::new(
+                    DiagnosticId::lint("undefined-reveal"),
+                    "Doesn't matter",
+                    0,
+                ),
             ],
         );
 
@@ -553,8 +572,16 @@ mod tests {
         let result = get_result(
             "reveal_type(1)",
             vec![
-                ExpectedDiagnostic::new("undefined-reveal", "undefined reveal message", 0),
-                ExpectedDiagnostic::new("revealed-type", "Revealed type is `Literal[1]`", 12),
+                ExpectedDiagnostic::new(
+                    DiagnosticId::lint("undefined-reveal"),
+                    "undefined reveal message",
+                    0,
+                ),
+                ExpectedDiagnostic::new(
+                    DiagnosticId::RevealedType,
+                    "Revealed type is `Literal[1]`",
+                    12,
+                ),
             ],
         );
 
@@ -576,8 +603,16 @@ mod tests {
         let result = get_result(
             "reveal_type(1) # error: [something-else]",
             vec![
-                ExpectedDiagnostic::new("undefined-reveal", "undefined reveal message", 0),
-                ExpectedDiagnostic::new("revealed-type", "Revealed type is `Literal[1]`", 12),
+                ExpectedDiagnostic::new(
+                    DiagnosticId::lint("undefined-reveal"),
+                    "undefined reveal message",
+                    0,
+                ),
+                ExpectedDiagnostic::new(
+                    DiagnosticId::RevealedType,
+                    "Revealed type is `Literal[1]`",
+                    12,
+                ),
             ],
         );
 
@@ -606,7 +641,11 @@ mod tests {
     fn error_match_rule() {
         let result = get_result(
             "x # error: [some-rule]",
-            vec![ExpectedDiagnostic::new("some-rule", "Any message", 0)],
+            vec![ExpectedDiagnostic::new(
+                DiagnosticId::lint("some-rule"),
+                "Any message",
+                0,
+            )],
         );
 
         assert_ok(&result);
@@ -616,7 +655,11 @@ mod tests {
     fn error_wrong_rule() {
         let result = get_result(
             "x # error: [some-rule]",
-            vec![ExpectedDiagnostic::new("anything", "Any message", 0)],
+            vec![ExpectedDiagnostic::new(
+                DiagnosticId::lint("anything"),
+                "Any message",
+                0,
+            )],
         );
 
         assert_fail(
@@ -636,7 +679,7 @@ mod tests {
         let result = get_result(
             r#"x # error: "contains this""#,
             vec![ExpectedDiagnostic::new(
-                "anything",
+                DiagnosticId::lint("anything"),
                 "message contains this",
                 0,
             )],
@@ -649,7 +692,11 @@ mod tests {
     fn error_wrong_message() {
         let result = get_result(
             r#"x # error: "contains this""#,
-            vec![ExpectedDiagnostic::new("anything", "Any message", 0)],
+            vec![ExpectedDiagnostic::new(
+                DiagnosticId::lint("anything"),
+                "Any message",
+                0,
+            )],
         );
 
         assert_fail(
@@ -668,7 +715,11 @@ mod tests {
     fn error_match_column_and_rule() {
         let result = get_result(
             "x # error: 1 [some-rule]",
-            vec![ExpectedDiagnostic::new("some-rule", "Any message", 0)],
+            vec![ExpectedDiagnostic::new(
+                DiagnosticId::lint("some-rule"),
+                "Any message",
+                0,
+            )],
         );
 
         assert_ok(&result);
@@ -678,7 +729,11 @@ mod tests {
     fn error_wrong_column() {
         let result = get_result(
             "x # error: 2 [rule]",
-            vec![ExpectedDiagnostic::new("rule", "Any message", 0)],
+            vec![ExpectedDiagnostic::new(
+                DiagnosticId::lint("rule"),
+                "Any message",
+                0,
+            )],
         );
 
         assert_fail(
@@ -698,7 +753,7 @@ mod tests {
         let result = get_result(
             r#"x # error: 1 "contains this""#,
             vec![ExpectedDiagnostic::new(
-                "anything",
+                DiagnosticId::lint("anything"),
                 "message contains this",
                 0,
             )],
@@ -712,7 +767,7 @@ mod tests {
         let result = get_result(
             r#"x # error: [a-rule] "contains this""#,
             vec![ExpectedDiagnostic::new(
-                "a-rule",
+                DiagnosticId::lint("a-rule"),
                 "message contains this",
                 0,
             )],
@@ -726,7 +781,7 @@ mod tests {
         let result = get_result(
             r#"x # error: 1 [a-rule] "contains this""#,
             vec![ExpectedDiagnostic::new(
-                "a-rule",
+                DiagnosticId::lint("a-rule"),
                 "message contains this",
                 0,
             )],
@@ -740,7 +795,7 @@ mod tests {
         let result = get_result(
             r#"x # error: 2 [some-rule] "contains this""#,
             vec![ExpectedDiagnostic::new(
-                "some-rule",
+                DiagnosticId::lint("some-rule"),
                 "message contains this",
                 0,
             )],
@@ -763,7 +818,7 @@ mod tests {
         let result = get_result(
             r#"x # error: 1 [some-rule] "contains this""#,
             vec![ExpectedDiagnostic::new(
-                "other-rule",
+                DiagnosticId::lint("other-rule"),
                 "message contains this",
                 0,
             )],
@@ -785,7 +840,11 @@ mod tests {
     fn error_match_all_wrong_message() {
         let result = get_result(
             r#"x # error: 1 [some-rule] "contains this""#,
-            vec![ExpectedDiagnostic::new("some-rule", "Any message", 0)],
+            vec![ExpectedDiagnostic::new(
+                DiagnosticId::lint("some-rule"),
+                "Any message",
+                0,
+            )],
         );
 
         assert_fail(
@@ -818,9 +877,9 @@ mod tests {
         let result = get_result(
             &source,
             vec![
-                ExpectedDiagnostic::new("line-two", "msg", two),
-                ExpectedDiagnostic::new("line-three", "msg", three),
-                ExpectedDiagnostic::new("line-five", "msg", five),
+                ExpectedDiagnostic::new(DiagnosticId::lint("line-two"), "msg", two),
+                ExpectedDiagnostic::new(DiagnosticId::lint("line-three"), "msg", three),
+                ExpectedDiagnostic::new(DiagnosticId::lint("line-five"), "msg", five),
             ],
         );
 
@@ -849,8 +908,8 @@ mod tests {
         let result = get_result(
             &source,
             vec![
-                ExpectedDiagnostic::new("line-one", "msg", one),
-                ExpectedDiagnostic::new("line-two", "msg", two),
+                ExpectedDiagnostic::new(DiagnosticId::lint("line-one"), "msg", one),
+                ExpectedDiagnostic::new(DiagnosticId::lint("line-two"), "msg", two),
             ],
         );
 
@@ -870,8 +929,8 @@ mod tests {
         let result = get_result(
             &source,
             vec![
-                ExpectedDiagnostic::new("one-rule", "msg", x),
-                ExpectedDiagnostic::new("other-rule", "msg", x),
+                ExpectedDiagnostic::new(DiagnosticId::lint("one-rule"), "msg", x),
+                ExpectedDiagnostic::new(DiagnosticId::lint("other-rule"), "msg", x),
             ],
         );
 
@@ -891,8 +950,8 @@ mod tests {
         let result = get_result(
             &source,
             vec![
-                ExpectedDiagnostic::new("one-rule", "msg", x),
-                ExpectedDiagnostic::new("one-rule", "msg", x),
+                ExpectedDiagnostic::new(DiagnosticId::lint("one-rule"), "msg", x),
+                ExpectedDiagnostic::new(DiagnosticId::lint("one-rule"), "msg", x),
             ],
         );
 
@@ -912,9 +971,9 @@ mod tests {
         let result = get_result(
             &source,
             vec![
-                ExpectedDiagnostic::new("one-rule", "msg", x),
-                ExpectedDiagnostic::new("other-rule", "msg", x),
-                ExpectedDiagnostic::new("third-rule", "msg", x),
+                ExpectedDiagnostic::new(DiagnosticId::lint("one-rule"), "msg", x),
+                ExpectedDiagnostic::new(DiagnosticId::lint("other-rule"), "msg", x),
+                ExpectedDiagnostic::new(DiagnosticId::lint("third-rule"), "msg", x),
             ],
         );
 
@@ -938,8 +997,12 @@ mod tests {
         let result = get_result(
             &source,
             vec![
-                ExpectedDiagnostic::new("undefined-reveal", "msg", reveal),
-                ExpectedDiagnostic::new("revealed-type", "Revealed type is `Literal[5]`", reveal),
+                ExpectedDiagnostic::new(DiagnosticId::lint("undefined-reveal"), "msg", reveal),
+                ExpectedDiagnostic::new(
+                    DiagnosticId::RevealedType,
+                    "Revealed type is `Literal[5]`",
+                    reveal,
+                ),
             ],
         );
 
@@ -952,7 +1015,11 @@ mod tests {
         let x = source.find('x').unwrap();
         let result = get_result(
             source,
-            vec![ExpectedDiagnostic::new("some-rule", "some message", x)],
+            vec![ExpectedDiagnostic::new(
+                DiagnosticId::lint("some-rule"),
+                "some message",
+                x,
+            )],
         );
 
         assert_fail(
@@ -973,7 +1040,11 @@ mod tests {
         let x = source.find('x').unwrap();
         let result = get_result(
             source,
-            vec![ExpectedDiagnostic::new("some-rule", "some message", x)],
+            vec![ExpectedDiagnostic::new(
+                DiagnosticId::lint("some-rule"),
+                "some message",
+                x,
+            )],
         );
 
         assert_fail(

crates/red_knot_wasm/tests/api.rs

@@ -19,6 +19,6 @@ fn check() {
 
     assert_eq!(
         result,
-        vec!["error[unresolved-import] /test.py:1:8 Cannot resolve import `random22`"]
+        vec!["error[lint:unresolved-import] /test.py:1:8 Cannot resolve import `random22`"]
     );
 }

crates/red_knot_workspace/src/db.rs

@@ -1,16 +1,17 @@
 use std::panic::RefUnwindSafe;
 use std::sync::Arc;
 
-use salsa::plumbing::ZalsaDatabase;
-use salsa::{Cancelled, Event};
-
 use crate::workspace::{check_file, Workspace, WorkspaceMetadata};
+use crate::DEFAULT_LINT_REGISTRY;
+use red_knot_python_semantic::lint::RuleSelection;
 use red_knot_python_semantic::{Db as SemanticDb, Program};
 use ruff_db::diagnostic::Diagnostic;
 use ruff_db::files::{File, Files};
 use ruff_db::system::System;
 use ruff_db::vendored::VendoredFileSystem;
 use ruff_db::{Db as SourceDb, Upcast};
+use salsa::plumbing::ZalsaDatabase;
+use salsa::{Cancelled, Event};
 
 mod changes;
 
@@ -25,6 +26,7 @@ pub struct RootDatabase {
     storage: salsa::Storage<RootDatabase>,
     files: Files,
     system: Arc<dyn System + Send + Sync + RefUnwindSafe>,
+    rule_selection: Arc<RuleSelection>,
 }
 
 impl RootDatabase {
@@ -32,11 +34,14 @@ impl RootDatabase {
     where
         S: System + 'static + Send + Sync + RefUnwindSafe,
     {
+        let rule_selection = RuleSelection::from_registry(&DEFAULT_LINT_REGISTRY);
+
         let mut db = Self {
             workspace: None,
             storage: salsa::Storage::default(),
             files: Files::default(),
             system: Arc::new(system),
+            rule_selection: Arc::new(rule_selection),
         };
 
         // Initialize the `Program` singleton
@@ -83,6 +88,7 @@ impl RootDatabase {
             storage: self.storage.clone(),
             files: self.files.snapshot(),
             system: Arc::clone(&self.system),
+            rule_selection: Arc::clone(&self.rule_selection),
         }
     }
 }
@@ -116,6 +122,10 @@ impl SemanticDb for RootDatabase {
 
         workspace.is_file_open(self, file)
     }
+
+    fn rule_selection(&self) -> &RuleSelection {
+        &self.rule_selection
+    }
 }
 
 #[salsa::db]
@@ -162,6 +172,7 @@ pub(crate) mod tests {
 
     use salsa::Event;
 
+    use red_knot_python_semantic::lint::RuleSelection;
     use red_knot_python_semantic::Db as SemanticDb;
     use ruff_db::files::Files;
     use ruff_db::system::{DbWithTestSystem, System, TestSystem};
@@ -170,14 +181,16 @@ pub(crate) mod tests {
 
     use crate::db::Db;
     use crate::workspace::{Workspace, WorkspaceMetadata};
+    use crate::DEFAULT_LINT_REGISTRY;
 
     #[salsa::db]
     pub(crate) struct TestDb {
         storage: salsa::Storage<Self>,
-        events: std::sync::Arc<std::sync::Mutex<Vec<salsa::Event>>>,
+        events: Arc<std::sync::Mutex<Vec<Event>>>,
         files: Files,
         system: TestSystem,
         vendored: VendoredFileSystem,
+        rule_selection: RuleSelection,
         workspace: Option<Workspace>,
     }
 
@@ -189,6 +202,7 @@ pub(crate) mod tests {
                 vendored: red_knot_vendored::file_system().clone(),
                 files: Files::default(),
                 events: Arc::default(),
+                rule_selection: RuleSelection::from_registry(&DEFAULT_LINT_REGISTRY),
                 workspace: None,
             };
 
@@ -259,6 +273,10 @@ pub(crate) mod tests {
         fn is_file_open(&self, file: ruff_db::files::File) -> bool {
             !file.path(self).is_vendored_path()
         }
+
+        fn rule_selection(&self) -> &RuleSelection {
+            &self.rule_selection
+        }
     }
 
     #[salsa::db]

crates/red_knot_workspace/src/lib.rs

@@ -1,3 +1,15 @@
+use red_knot_python_semantic::lint::{LintRegistry, LintRegistryBuilder};
+use red_knot_python_semantic::register_lints;
+
 pub mod db;
 pub mod watch;
 pub mod workspace;
+
+pub static DEFAULT_LINT_REGISTRY: std::sync::LazyLock<LintRegistry> =
+    std::sync::LazyLock::new(default_lints_registry);
+
+pub fn default_lints_registry() -> LintRegistry {
+    let mut builder = LintRegistryBuilder::default();
+    register_lints(&mut builder);
+    builder.build()
+}

crates/red_knot_workspace/src/workspace.rs

@@ -6,7 +6,7 @@ use crate::workspace::files::{Index, Indexed, IndexedIter, PackageFiles};
 pub use metadata::{PackageMetadata, WorkspaceDiscoveryError, WorkspaceMetadata};
 use red_knot_python_semantic::types::check_types;
 use red_knot_python_semantic::SearchPathSettings;
-use ruff_db::diagnostic::{Diagnostic, ParseDiagnostic, Severity};
+use ruff_db::diagnostic::{Diagnostic, DiagnosticId, ParseDiagnostic, Severity};
 use ruff_db::parsed::parsed_module;
 use ruff_db::source::{source_text, SourceTextError};
 use ruff_db::system::FileType;
@@ -533,8 +533,8 @@ pub struct IOErrorDiagnostic {
 }
 
 impl Diagnostic for IOErrorDiagnostic {
-    fn rule(&self) -> &str {
-        "io"
+    fn id(&self) -> DiagnosticId {
+        DiagnosticId::Io
     }
 
     fn message(&self) -> Cow<str> {

crates/ruff/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff"
-version = "0.8.2"
+version = "0.8.3"
 publish = true
 authors = { workspace = true }
 edition = { workspace = true }

crates/ruff/build.rs

@@ -1,4 +1,8 @@
-use std::{fs, path::Path, process::Command};
+use std::{
+    fs,
+    path::{Path, PathBuf},
+    process::Command,
+};
 
 fn main() {
     // The workspace root directory is not available without walking up the tree
@@ -21,27 +25,22 @@ fn commit_info(workspace_root: &Path) {
         return;
     }
 
-    let git_head_path = git_dir.join("HEAD");
-    println!(
-        "cargo::rerun-if-changed={}",
-        git_head_path.as_path().display()
-    );
+    if let Some(git_head_path) = git_head(&git_dir) {
+        println!("cargo:rerun-if-changed={}", git_head_path.display());
 
-    let git_head_contents = fs::read_to_string(git_head_path);
-    if let Ok(git_head_contents) = git_head_contents {
-        // The contents are either a commit or a reference in the following formats
-        // - "<commit>" when the head is detached
-        // - "ref <ref>" when working on a branch
-        // If a commit, checking if the HEAD file has changed is sufficient
-        // If a ref, we need to add the head file for that ref to rebuild on commit
-        let mut git_ref_parts = git_head_contents.split_whitespace();
-        git_ref_parts.next();
-        if let Some(git_ref) = git_ref_parts.next() {
-            let git_ref_path = git_dir.join(git_ref);
-            println!(
-                "cargo::rerun-if-changed={}",
-                git_ref_path.as_path().display()
-            );
+        let git_head_contents = fs::read_to_string(git_head_path);
+        if let Ok(git_head_contents) = git_head_contents {
+            // The contents are either a commit or a reference in the following formats
+            // - "<commit>" when the head is detached
+            // - "ref <ref>" when working on a branch
+            // If a commit, checking if the HEAD file has changed is sufficient
+            // If a ref, we need to add the head file for that ref to rebuild on commit
+            let mut git_ref_parts = git_head_contents.split_whitespace();
+            git_ref_parts.next();
+            if let Some(git_ref) = git_ref_parts.next() {
+                let git_ref_path = git_dir.join(git_ref);
+                println!("cargo:rerun-if-changed={}", git_ref_path.display());
+            }
         }
     }
 
@@ -78,3 +77,30 @@ fn commit_info(workspace_root: &Path) {
         );
     }
 }
+
+fn git_head(git_dir: &Path) -> Option<PathBuf> {
+    // The typical case is a standard git repository.
+    let git_head_path = git_dir.join("HEAD");
+    if git_head_path.exists() {
+        return Some(git_head_path);
+    }
+    if !git_dir.is_file() {
+        return None;
+    }
+    // If `.git/HEAD` doesn't exist and `.git` is actually a file,
+    // then let's try to attempt to read it as a worktree. If it's
+    // a worktree, then its contents will look like this, e.g.:
+    //
+    //     gitdir: /home/andrew/astral/uv/main/.git/worktrees/pr2
+    //
+    // And the HEAD file we want to watch will be at:
+    //
+    //     /home/andrew/astral/uv/main/.git/worktrees/pr2/HEAD
+    let contents = fs::read_to_string(git_dir).ok()?;
+    let (label, worktree_path) = contents.split_once(':')?;
+    if label != "gitdir" {
+        return None;
+    }
+    let worktree_path = worktree_path.trim();
+    Some(PathBuf::from(worktree_path))
+}

crates/ruff_benchmark/benches/red_knot.rs

@@ -25,30 +25,30 @@ const TOMLLIB_312_URL: &str = "https://raw.githubusercontent.com/python/cpython/
 
 static EXPECTED_DIAGNOSTICS: &[&str] = &[
     // We don't support `*` imports yet:
-    "error[unresolved-import] /src/tomllib/_parser.py:7:29 Module `collections.abc` has no member `Iterable`",
+    "error[lint:unresolved-import] /src/tomllib/_parser.py:7:29 Module `collections.abc` has no member `Iterable`",
     // We don't support terminal statements in control flow yet:
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:66:18 Name `s` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:98:12 Name `char` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:101:12 Name `char` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:104:14 Name `char` used when possibly not defined",
-    "error[conflicting-declarations] /src/tomllib/_parser.py:108:17 Conflicting declared types for `second_char`: Unknown, str | None",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:115:14 Name `char` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:126:12 Name `char` used when possibly not defined",
-    "error[conflicting-declarations] /src/tomllib/_parser.py:267:9 Conflicting declared types for `char`: Unknown, str | None",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:348:20 Name `nest` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:353:5 Name `nest` used when possibly not defined",
-    "error[conflicting-declarations] /src/tomllib/_parser.py:364:9 Conflicting declared types for `char`: Unknown, str | None",
-    "error[conflicting-declarations] /src/tomllib/_parser.py:381:13 Conflicting declared types for `char`: Unknown, str | None",
-    "error[conflicting-declarations] /src/tomllib/_parser.py:395:9 Conflicting declared types for `char`: Unknown, str | None",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:453:24 Name `nest` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:455:9 Name `nest` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:482:16 Name `char` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:566:12 Name `char` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:573:12 Name `char` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:579:12 Name `char` used when possibly not defined",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:580:63 Name `char` used when possibly not defined",
-    "error[conflicting-declarations] /src/tomllib/_parser.py:590:9 Conflicting declared types for `char`: Unknown, str | None",
-    "error[possibly-unresolved-reference] /src/tomllib/_parser.py:629:38 Name `datetime_obj` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:66:18 Name `s` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:98:12 Name `char` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:101:12 Name `char` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:104:14 Name `char` used when possibly not defined",
+    "error[lint:conflicting-declarations] /src/tomllib/_parser.py:108:17 Conflicting declared types for `second_char`: Unknown, str | None",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:115:14 Name `char` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:126:12 Name `char` used when possibly not defined",
+    "error[lint:conflicting-declarations] /src/tomllib/_parser.py:267:9 Conflicting declared types for `char`: Unknown, str | None",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:348:20 Name `nest` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:353:5 Name `nest` used when possibly not defined",
+    "error[lint:conflicting-declarations] /src/tomllib/_parser.py:364:9 Conflicting declared types for `char`: Unknown, str | None",
+    "error[lint:conflicting-declarations] /src/tomllib/_parser.py:381:13 Conflicting declared types for `char`: Unknown, str | None",
+    "error[lint:conflicting-declarations] /src/tomllib/_parser.py:395:9 Conflicting declared types for `char`: Unknown, str | None",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:453:24 Name `nest` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:455:9 Name `nest` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:482:16 Name `char` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:566:12 Name `char` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:573:12 Name `char` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:579:12 Name `char` used when possibly not defined",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:580:63 Name `char` used when possibly not defined",
+    "error[lint:conflicting-declarations] /src/tomllib/_parser.py:590:9 Conflicting declared types for `char`: Unknown, str | None",
+    "warning[lint:possibly-unresolved-reference] /src/tomllib/_parser.py:629:38 Name `datetime_obj` used when possibly not defined",
 ];
 
 fn get_test_file(name: &str) -> TestFile {

crates/ruff_db/src/diagnostic.rs

@@ -1,16 +1,156 @@
+use std::borrow::Cow;
+use std::fmt::Formatter;
+
+use thiserror::Error;
+
+use ruff_python_parser::ParseError;
+use ruff_text_size::TextRange;
+
 use crate::{
     files::File,
     source::{line_index, source_text},
     Db,
 };
-use ruff_python_parser::ParseError;
-use ruff_text_size::TextRange;
-use std::borrow::Cow;
+
+/// A string identifier for a lint rule.
+///
+/// This string is used in command line and configuration interfaces. The name should always
+/// be in kebab case, e.g. `no-foo` (all lower case).
+///
+/// Rules use kebab case, e.g. `no-foo`.
+#[derive(Debug, Copy, Clone, PartialOrd, Ord, PartialEq, Eq, Hash)]
+pub struct LintName(&'static str);
+
+impl LintName {
+    pub const fn of(name: &'static str) -> Self {
+        Self(name)
+    }
+
+    pub const fn as_str(&self) -> &'static str {
+        self.0
+    }
+}
+
+impl std::ops::Deref for LintName {
+    type Target = str;
+
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+
+impl std::fmt::Display for LintName {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        f.write_str(self.0)
+    }
+}
+
+impl PartialEq<str> for LintName {
+    fn eq(&self, other: &str) -> bool {
+        self.0 == other
+    }
+}
+
+impl PartialEq<&str> for LintName {
+    fn eq(&self, other: &&str) -> bool {
+        self.0 == *other
+    }
+}
+
+/// Uniquely identifies the kind of a diagnostic.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, PartialOrd, Ord, Hash)]
+pub enum DiagnosticId {
+    /// Some I/O operation failed
+    Io,
+
+    /// Some code contains a syntax error
+    InvalidSyntax,
+
+    /// A lint violation.
+    ///
+    /// Lints can be suppressed and some lints can be enabled or disabled in the configuration.
+    Lint(LintName),
+
+    /// A revealed type: Created by `reveal_type(expression)`.
+    RevealedType,
+}
+
+impl DiagnosticId {
+    /// Creates a new `DiagnosticId` for a lint with the given name.
+    pub const fn lint(name: &'static str) -> Self {
+        Self::Lint(LintName::of(name))
+    }
+
+    /// Returns `true` if this `DiagnosticId` represents a lint.
+    pub fn is_lint(&self) -> bool {
+        matches!(self, DiagnosticId::Lint(_))
+    }
+
+    /// Returns `true` if this `DiagnosticId` represents a lint with the given name.
+    pub fn is_lint_named(&self, name: &str) -> bool {
+        matches!(self, DiagnosticId::Lint(self_name) if self_name == name)
+    }
+
+    /// Returns `true` if this `DiagnosticId` matches the given name.
+    ///
+    /// ## Examples
+    /// ```
+    /// use ruff_db::diagnostic::DiagnosticId;
+    ///
+    /// assert!(DiagnosticId::Io.matches("io"));
+    /// assert!(DiagnosticId::lint("test").matches("lint:test"));
+    /// assert!(!DiagnosticId::lint("test").matches("test"));
+    /// ```
+    pub fn matches(&self, expected_name: &str) -> bool {
+        match self.as_str() {
+            Ok(id) => id == expected_name,
+            Err(DiagnosticAsStrError::Category { category, name }) => expected_name
+                .strip_prefix(category)
+                .and_then(|prefix| prefix.strip_prefix(":"))
+                .is_some_and(|rest| rest == name),
+        }
+    }
+
+    pub fn as_str(&self) -> Result<&str, DiagnosticAsStrError> {
+        match self {
+            DiagnosticId::Io => Ok("io"),
+            DiagnosticId::InvalidSyntax => Ok("invalid-syntax"),
+            DiagnosticId::Lint(name) => Err(DiagnosticAsStrError::Category {
+                category: "lint",
+                name: name.as_str(),
+            }),
+            DiagnosticId::RevealedType => Ok("revealed-type"),
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Error)]
+pub enum DiagnosticAsStrError {
+    /// The id can't be converted to a string because it belongs to a sub-category.
+    #[error("id from a sub-category: {category}:{name}")]
+    Category {
+        /// The id's category.
+        category: &'static str,
+        /// The diagnostic id in this category.
+        name: &'static str,
+    },
+}
+
+impl std::fmt::Display for DiagnosticId {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match self.as_str() {
+            Ok(name) => f.write_str(name),
+            Err(DiagnosticAsStrError::Category { category, name }) => {
+                write!(f, "{category}:{name}")
+            }
+        }
+    }
+}
 
 pub trait Diagnostic: Send + Sync + std::fmt::Debug {
-    fn rule(&self) -> &str;
+    fn id(&self) -> DiagnosticId;
 
-    fn message(&self) -> std::borrow::Cow<str>;
+    fn message(&self) -> Cow<str>;
 
     fn file(&self) -> File;
 
@@ -29,10 +169,12 @@ pub trait Diagnostic: Send + Sync + std::fmt::Debug {
     }
 }
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Ord, PartialOrd)]
 pub enum Severity {
     Info,
+    Warning,
     Error,
+    Fatal,
 }
 
 pub struct DisplayDiagnostic<'db> {
@@ -50,13 +192,15 @@ impl std::fmt::Display for DisplayDiagnostic<'_> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self.diagnostic.severity() {
             Severity::Info => f.write_str("info")?,
+            Severity::Warning => f.write_str("warning")?,
             Severity::Error => f.write_str("error")?,
+            Severity::Fatal => f.write_str("fatal")?,
         }
 
         write!(
             f,
             "[{rule}] {path}",
-            rule = self.diagnostic.rule(),
+            rule = self.diagnostic.id(),
             path = self.diagnostic.file().path(self.db)
         )?;
 
@@ -77,8 +221,8 @@ impl<T> Diagnostic for Box<T>
 where
     T: Diagnostic,
 {
-    fn rule(&self) -> &str {
-        (**self).rule()
+    fn id(&self) -> DiagnosticId {
+        (**self).id()
     }
 
     fn message(&self) -> Cow<str> {
@@ -102,8 +246,8 @@ impl<T> Diagnostic for std::sync::Arc<T>
 where
     T: Diagnostic,
 {
-    fn rule(&self) -> &str {
-        (**self).rule()
+    fn id(&self) -> DiagnosticId {
+        (**self).id()
     }
 
     fn message(&self) -> std::borrow::Cow<str> {
@@ -124,8 +268,8 @@ where
 }
 
 impl Diagnostic for Box<dyn Diagnostic> {
-    fn rule(&self) -> &str {
-        (**self).rule()
+    fn id(&self) -> DiagnosticId {
+        (**self).id()
     }
 
     fn message(&self) -> Cow<str> {
@@ -158,8 +302,8 @@ impl ParseDiagnostic {
 }
 
 impl Diagnostic for ParseDiagnostic {
-    fn rule(&self) -> &str {
-        "invalid-syntax"
+    fn id(&self) -> DiagnosticId {
+        DiagnosticId::InvalidSyntax
     }
 
     fn message(&self) -> Cow<str> {

crates/ruff_formatter/src/buffer.rs

@@ -656,7 +656,7 @@ where
         let elements = buffer.elements();
 
         let recorded = if self.start > elements.len() {
-            // May happen if buffer was rewinded.
+            // May happen if buffer was rewound.
             &[]
         } else {
             &elements[self.start..]

crates/ruff_graph/src/db.rs

@@ -1,6 +1,8 @@
 use anyhow::Result;
+use std::sync::Arc;
 use zip::CompressionMethod;
 
+use red_knot_python_semantic::lint::RuleSelection;
 use red_knot_python_semantic::{Db, Program, ProgramSettings, PythonVersion, SearchPathSettings};
 use ruff_db::files::{File, Files};
 use ruff_db::system::{OsSystem, System, SystemPathBuf};
@@ -19,6 +21,7 @@ pub struct ModuleDb {
     storage: salsa::Storage<Self>,
     files: Files,
     system: OsSystem,
+    rule_selection: Arc<RuleSelection>,
 }
 
 impl ModuleDb {
@@ -60,6 +63,7 @@ impl ModuleDb {
             storage: self.storage.clone(),
             system: self.system.clone(),
             files: self.files.snapshot(),
+            rule_selection: Arc::clone(&self.rule_selection),
         }
     }
 }
@@ -93,6 +97,10 @@ impl Db for ModuleDb {
     fn is_file_open(&self, file: File) -> bool {
         !file.path(self).is_vendored_path()
     }
+
+    fn rule_selection(&self) -> &RuleSelection {
+        &self.rule_selection
+    }
 }
 
 #[salsa::db]

crates/ruff_linter/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff_linter"
-version = "0.8.2"
+version = "0.8.3"
 publish = false
 authors = { workspace = true }
 edition = { workspace = true }

crates/ruff_linter/resources/test/fixtures/flake8_bugbear/B028.py

@@ -5,13 +5,23 @@ Should emit:
 B028 - on lines 8 and 9
 """
 
-warnings.warn(DeprecationWarning("test"))
-warnings.warn(DeprecationWarning("test"), source=None)
-warnings.warn(DeprecationWarning("test"), source=None, stacklevel=2)
-warnings.warn(DeprecationWarning("test"), stacklevel=1)
+warnings.warn("test", DeprecationWarning)
+warnings.warn("test", DeprecationWarning, source=None)
+warnings.warn("test", DeprecationWarning, source=None, stacklevel=2)
+warnings.warn("test", DeprecationWarning, stacklevel=1)
+warnings.warn("test", DeprecationWarning, 1)
+warnings.warn("test", category=DeprecationWarning, stacklevel=1)
+args = ("test", DeprecationWarning, 1)
+warnings.warn(*args)
+kwargs = {"message": "test", "category": DeprecationWarning, "stacklevel": 1}
+warnings.warn(**kwargs)
+args = ("test", DeprecationWarning)
+kwargs = {"stacklevel": 1}
+warnings.warn(*args, **kwargs)
 
 warnings.warn(
-        DeprecationWarning("test"),
+        "test",
+        DeprecationWarning,
         # some comments here
         source = None # no trailing comma
     )