Make CallArguments salsa::interned

.github/ISSUE_TEMPLATE/1_bug_report.yaml

@@ -1,31 +0,0 @@
-name: Bug report
-description: Report an error or unexpected behavior
-body:
-  - type: markdown
-    attributes:
-      value: |
-        Thank you for taking the time to report an issue! We're glad to have you involved with Ruff.
-
-        **Before reporting, please make sure to search through [existing issues](https://github.com/astral-sh/ruff/issues?q=is:issue+is:open+label:bug) (including [closed](https://github.com/astral-sh/ruff/issues?q=is:issue%20state:closed%20label:bug)).**
-
-  - type: textarea
-    attributes:
-      label: Summary
-      description: |
-        A clear and concise description of the bug, including a minimal reproducible example.
-
-        Be sure to include the command you invoked (e.g., `ruff check /path/to/file.py --fix`), ideally including the `--isolated` flag and
-        the current Ruff settings (e.g., relevant sections from your `pyproject.toml`).
-
-        If possible, try to include the [playground](https://play.ruff.rs) link that reproduces this issue.
-
-    validations:
-      required: true
-
-  - type: input
-    attributes:
-      label: Version
-      description: What version of ruff are you using? (see `ruff version`)
-      placeholder: e.g., ruff 0.9.3 (90589372d 2025-01-23)
-    validations:
-      required: false

.github/ISSUE_TEMPLATE/2_rule_request.yaml

@@ -1,10 +0,0 @@
-name: Rule request
-description: Anything related to lint rules (proposing new rules, changes to existing rules, auto-fixes, etc.)
-body:
-  - type: textarea
-    attributes:
-      label: Summary
-      description: |
-        A clear and concise description of the relevant request. If applicable, please describe the current behavior as well.
-    validations:
-      required: true

.github/ISSUE_TEMPLATE/3_question.yaml

@@ -1,18 +0,0 @@
-name: Question
-description: Ask a question about Ruff
-labels: ["question"]
-body:
-  - type: textarea
-    attributes:
-      label: Question
-      description: Describe your question in detail.
-    validations:
-      required: true
-
-  - type: input
-    attributes:
-      label: Version
-      description: What version of ruff are you using? (see `ruff version`)
-      placeholder: e.g., ruff 0.9.3 (90589372d 2025-01-23)
-    validations:
-      required: false

.github/ISSUE_TEMPLATE/config.yml

@@ -1,8 +1,2 @@
-blank_issues_enabled: true
-contact_links:
-  - name: Documentation
-    url: https://docs.astral.sh/ruff
-    about: Please consult the documentation before creating an issue.
-  - name: Community
-    url: https://discord.com/invite/astral-sh
-    about: Join our Discord community to ask questions and collaborate.
+# This file cannot use the extension `.yaml`.
+blank_issues_enabled: false

.github/ISSUE_TEMPLATE/issue.yaml

@@ -0,0 +1,22 @@
+name: New issue
+description: A generic issue
+
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thank you for taking the time to report an issue! We're glad to have you involved with Ruff.
+
+        If you're filing a bug report, please consider including the following information:
+
+        * List of keywords you searched for before creating this issue. Write them down here so that others can find this issue more easily and help provide feedback.
+        e.g. "RUF001", "unused variable", "Jupyter notebook"
+        * A minimal code snippet that reproduces the bug.
+        * The command you invoked (e.g., `ruff /path/to/file.py --fix`), ideally including the `--isolated` flag.
+        * The current Ruff settings (any relevant sections from your `pyproject.toml`).
+        * The current Ruff version (`ruff --version`).
+
+  - type: textarea
+    attributes:
+      label: Description
+      description: A description of the issue

.github/renovate.json5

@@ -58,6 +58,12 @@
       description: "Disable PRs updating GitHub runners (e.g. 'runs-on: macos-14')",
       enabled: false,
     },
+    {
+      // TODO: Remove this once the codebase is upgrade to v4 (https://github.com/astral-sh/ruff/pull/16069)
+      matchPackageNames: ["tailwindcss"],
+      matchManagers: ["npm"],
+      enabled: false,
+    },
     {
       // Disable updates of `zip-rs`; intentionally pinned for now due to ownership change
       // See: https://github.com/astral-sh/uv/issues/3642
@@ -95,7 +101,14 @@
       matchManagers: ["cargo"],
       matchPackageNames: ["strum"],
       description: "Weekly update of strum dependencies",
-    }
+    },
+    {
+      groupName: "ESLint",
+      matchManagers: ["npm"],
+      matchPackageNames: ["eslint"],
+      allowedVersions: "<9",
+      description: "Constraint ESLint to version 8 until TypeScript-eslint supports ESLint 9", // https://github.com/typescript-eslint/typescript-eslint/issues/8211
+    },
   ],
   vulnerabilityAlerts: {
     commitMessageSuffix: "",

.github/workflows/build-docker.yml

@@ -163,7 +163,7 @@ jobs:
         # Mapping of base image followed by a comma followed by one or more base tags (comma separated)
         # Note, org.opencontainers.image.version label will use the first base tag (use the most specific tag first)
         image-mapping:
-          - alpine:3.21,alpine3.21,alpine
+          - alpine:3.20,alpine3.20,alpine
           - debian:bookworm-slim,bookworm-slim,debian-slim
           - buildpack-deps:bookworm,bookworm,debian
     steps:

.github/workflows/daily_property_tests.yaml

@@ -47,7 +47,6 @@ jobs:
         run: |
           export QUICKCHECK_TESTS=100000
           for _ in {1..5}; do
-            cargo test --locked --release --package red_knot_python_semantic -- --ignored list::property_tests
             cargo test --locked --release --package red_knot_python_semantic -- --ignored types::property_tests::stable
           done
 

.github/workflows/mypy_primer.yaml

@@ -1,93 +0,0 @@
-name: Run mypy_primer
-
-permissions: {}
-
-on:
-  pull_request:
-    paths:
-      - "crates/red_knot*/**"
-      - "crates/ruff_db"
-      - "crates/ruff_python_ast"
-      - "crates/ruff_python_parser"
-      - ".github/workflows/mypy_primer.yaml"
-      - ".github/workflows/mypy_primer_comment.yaml"
-
-concurrency:
-  group: ${{ github.workflow }}-${{ github.ref_name }}-${{ github.event.pull_request.number || github.sha }}
-  cancel-in-progress: true
-
-env:
-  CARGO_INCREMENTAL: 0
-  CARGO_NET_RETRY: 10
-  CARGO_TERM_COLOR: always
-  RUSTUP_MAX_RETRIES: 10
-
-jobs:
-  mypy_primer:
-    name: Run mypy_primer
-    runs-on: ubuntu-24.04
-    timeout-minutes: 20
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          path: ruff
-          fetch-depth: 0
-          persist-credentials: false
-
-      - name: Install the latest version of uv
-        uses: astral-sh/setup-uv@v5
-
-      - uses: Swatinem/rust-cache@v2
-        with:
-          workspaces: "ruff"
-      - name: Install Rust toolchain
-        run: rustup show
-
-      - name: Install mypy_primer
-        run: |
-          uv tool install "git+https://github.com/astral-sh/mypy_primer.git@add-red-knot-support"
-
-      - name: Run mypy_primer
-        shell: bash
-        run: |
-          cd ruff
-
-          echo "new commit"
-          git rev-list --format=%s --max-count=1 "$GITHUB_SHA"
-
-          MERGE_BASE="$(git merge-base "$GITHUB_SHA" "origin/$GITHUB_BASE_REF")"
-          git checkout -b base_commit "$MERGE_BASE"
-          echo "base commit"
-          git rev-list --format=%s --max-count=1 base_commit
-
-          cd ..
-
-          # Allow the exit code to be 0 or 1, only fail for actual mypy_primer crashes/bugs
-          uvx mypy_primer \
-            --repo ruff \
-            --type-checker knot \
-            --old base_commit \
-            --new "$GITHUB_SHA" \
-            --project-selector '/(mypy_primer|black|pyp|git-revise|zipp|arrow)$' \
-            --output concise \
-            --debug > mypy_primer.diff || [ $? -eq 1 ]
-
-          # Output diff with ANSI color codes
-          cat mypy_primer.diff
-
-          # Remove ANSI color codes before uploading
-          sed -ie 's/\x1b\[[0-9;]*m//g' mypy_primer.diff
-
-          echo ${{ github.event.number }} > pr-number
-
-      - name: Upload diff
-        uses: actions/upload-artifact@v4
-        with:
-          name: mypy_primer_diff
-          path: mypy_primer.diff
-
-      - name: Upload pr-number
-        uses: actions/upload-artifact@v4
-        with:
-          name: pr-number
-          path: pr-number

.github/workflows/mypy_primer_comment.yaml

@@ -1,97 +0,0 @@
-name: PR comment (mypy_primer)
-
-on: # zizmor: ignore[dangerous-triggers]
-  workflow_run:
-    workflows: [Run mypy_primer]
-    types: [completed]
-  workflow_dispatch:
-    inputs:
-      workflow_run_id:
-        description: The mypy_primer workflow that triggers the workflow run
-        required: true
-
-jobs:
-  comment:
-    runs-on: ubuntu-24.04
-    permissions:
-      pull-requests: write
-    steps:
-      - uses: dawidd6/action-download-artifact@v8
-        name: Download PR number
-        with:
-          name: pr-number
-          run_id: ${{ github.event.workflow_run.id ||  github.event.inputs.workflow_run_id }}
-          if_no_artifact_found: ignore
-          allow_forks: true
-
-      - name: Parse pull request number
-        id: pr-number
-        run: |
-          if [[ -f pr-number ]]
-          then
-            echo "pr-number=$(<pr-number)" >> "$GITHUB_OUTPUT"
-          fi
-
-      - uses: dawidd6/action-download-artifact@v8
-        name: "Download mypy_primer results"
-        id: download-mypy_primer_diff
-        if: steps.pr-number.outputs.pr-number
-        with:
-          name: mypy_primer_diff
-          workflow: mypy_primer.yaml
-          pr: ${{ steps.pr-number.outputs.pr-number }}
-          path: pr/mypy_primer_diff
-          workflow_conclusion: completed
-          if_no_artifact_found: ignore
-          allow_forks: true
-
-      - name: Generate comment content
-        id: generate-comment
-        if: steps.download-mypy_primer_diff.outputs.found_artifact == 'true'
-        run: |
-          # Guard against malicious mypy_primer results that symlink to a secret
-          # file on this runner
-          if [[ -L pr/mypy_primer_diff/mypy_primer.diff ]]
-          then
-              echo "Error: mypy_primer.diff cannot be a symlink"
-              exit 1
-          fi
-
-          # Note this identifier is used to find the comment to update on
-          # subsequent runs
-          echo '<!-- generated-comment mypy_primer -->' >> comment.txt
-
-          echo '## `mypy_primer` results' >> comment.txt
-          if [ -s "pr/mypy_primer_diff/mypy_primer.diff" ]; then
-            echo '<details>' >> comment.txt
-            echo '<summary>Changes were detected when running on open source projects</summary>' >> comment.txt
-            echo '' >> comment.txt
-            echo '```diff' >> comment.txt
-            cat pr/mypy_primer_diff/mypy_primer.diff >> comment.txt
-            echo '```' >> comment.txt
-            echo '</details>' >> comment.txt
-          else
-            echo 'No ecosystem changes detected ✅' >> comment.txt
-          fi
-
-          echo 'comment<<EOF' >> "$GITHUB_OUTPUT"
-          cat comment.txt >> "$GITHUB_OUTPUT"
-          echo 'EOF' >> "$GITHUB_OUTPUT"
-
-      - name: Find existing comment
-        uses: peter-evans/find-comment@v3
-        if: steps.generate-comment.outcome == 'success'
-        id: find-comment
-        with:
-          issue-number: ${{ steps.pr-number.outputs.pr-number }}
-          comment-author: "github-actions[bot]"
-          body-includes: "<!-- generated-comment mypy_primer -->"
-
-      - name: Create or update comment
-        if: steps.find-comment.outcome == 'success'
-        uses: peter-evans/create-or-update-comment@v4
-        with:
-          comment-id: ${{ steps.find-comment.outputs.comment-id }}
-          issue-number: ${{ steps.pr-number.outputs.pr-number }}
-          body-path: comment.txt
-          edit-mode: replace

.pre-commit-config.yaml

@@ -60,7 +60,7 @@ repos:
           - black==25.1.0
 
   - repo: https://github.com/crate-ci/typos
-    rev: v1.30.0
+    rev: v1.29.7
     hooks:
       - id: typos
 
@@ -74,7 +74,7 @@ repos:
         pass_filenames: false # This makes it a lot faster
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.9.9
+    rev: v0.9.6
     hooks:
       - id: ruff-format
       - id: ruff
@@ -84,7 +84,7 @@ repos:
 
   # Prettier
   - repo: https://github.com/rbubley/mirrors-prettier
-    rev: v3.5.2
+    rev: v3.5.1
     hooks:
       - id: prettier
         types: [yaml]
@@ -92,12 +92,12 @@ repos:
   # zizmor detects security vulnerabilities in GitHub Actions workflows.
   # Additional configuration for the tool is found in `.github/zizmor.yml`
   - repo: https://github.com/woodruffw/zizmor-pre-commit
-    rev: v1.4.1
+    rev: v1.3.1
     hooks:
       - id: zizmor
 
   - repo: https://github.com/python-jsonschema/check-jsonschema
-    rev: 0.31.2
+    rev: 0.31.1
     hooks:
       - id: check-github-workflows
 

BREAKING_CHANGES.md

@@ -1,46 +1,5 @@
 # Breaking Changes
 
-## 0.10.0
-
-- **Changes to how the Python version is inferred when a `target-version` is not specified** ([#16319](https://github.com/astral-sh/ruff/pull/16319))
-
-    In previous versions of Ruff, you could specify your Python version with:
-
-    - The `target-version` option in a `ruff.toml` file or the `[tool.ruff]` section of a pyproject.toml file.
-    - The `project.requires-python` field in a `pyproject.toml` file with a `[tool.ruff]` section.
-
-    These options worked well in most cases, and are still recommended for fine control of the Python version. However, because of the way Ruff discovers config files, `pyproject.toml` files without a `[tool.ruff]` section would be ignored, including the `requires-python` setting. Ruff would then use the default Python version (3.9 as of this writing) instead, which is surprising when you've attempted to request another version.
-
-    In v0.10, config discovery has been updated to address this issue:
-
-    - If Ruff finds a `ruff.toml` file without a `target-version`, it will check
-        for a `pyproject.toml` file in the same directory and respect its
-        `requires-python` version, even if it does not contain a `[tool.ruff]`
-        section.
-    - If Ruff finds a user-level configuration, the `requires-python` field of the closest `pyproject.toml` in a parent directory will take precedence.
-    - If there is no config file (`ruff.toml`or `pyproject.toml` with a
-        `[tool.ruff]` section) in the directory of the file being checked, Ruff will
-        search for the closest `pyproject.toml` in the parent directories and use its
-        `requires-python` setting.
-
-- **Updated `TYPE_CHECKING` behavior** ([#16669](https://github.com/astral-sh/ruff/pull/16669))
-
-    Previously, Ruff only recognized typechecking blocks that tested the `typing.TYPE_CHECKING` symbol. Now, Ruff recognizes any local variable named `TYPE_CHECKING`. This release also removes support for the legacy `if 0:` and `if False:` typechecking checks. Use a local `TYPE_CHECKING` variable instead.
-
-- **More robust noqa parsing** ([#16483](https://github.com/astral-sh/ruff/pull/16483))
-
-    The syntax for both file-level and in-line suppression comments has been unified and made more robust to certain errors. In most cases, this will result in more suppression comments being read by Ruff, but there are a few instances where previously read comments will now log an error to the user instead. Please refer to the documentation on [_Error suppression_](https://docs.astral.sh/ruff/linter/#error-suppression) for the full specification.
-
-- **Avoid unnecessary parentheses around with statements with a single context manager and a trailing comment** ([#14005](https://github.com/astral-sh/ruff/pull/14005))
-
-    This change fixes a bug in the formatter where it introduced unnecessary parentheses around with statements with a single context manager and a trailing comment. This change may result in a change in formatting for some users.
-
-- **Bump alpine default tag to 3.21 for derived Docker images** ([#16456](https://github.com/astral-sh/ruff/pull/16456))
-
-    Alpine 3.21 was released in Dec 2024 and is used in the official Alpine-based Python images. Now the ruff:alpine image will use 3.21 instead of 3.20 and ruff:alpine3.20 will no longer be updated.
-
-- **\[`unsafe-markup-use`\]: `RUF035` has been recoded to `S704`** ([#15957](https://github.com/astral-sh/ruff/pull/15957))
-
 ## 0.9.0
 
 Ruff now formats your code according to the 2025 style guide. As a result, your code might now get formatted differently. See the [changelog](./CHANGELOG.md#090) for a detailed list of changes.

CHANGELOG.md

@@ -1,200 +1,5 @@
 # Changelog
 
-## 0.10.0
-
-Check out the [blog post](https://astral.sh/blog/ruff-v0.10.0) for a migration guide and overview of the changes!
-
-### Breaking changes
-
-See also, the "Remapped rules" section which may result in disabled rules.
-
-- **Changes to how the Python version is inferred when a `target-version` is not specified** ([#16319](https://github.com/astral-sh/ruff/pull/16319))
-
-    In previous versions of Ruff, you could specify your Python version with:
-
-    - The `target-version` option in a `ruff.toml` file or the `[tool.ruff]` section of a pyproject.toml file.
-    - The `project.requires-python` field in a `pyproject.toml` file with a `[tool.ruff]` section.
-
-    These options worked well in most cases, and are still recommended for fine control of the Python version. However, because of the way Ruff discovers config files, `pyproject.toml` files without a `[tool.ruff]` section would be ignored, including the `requires-python` setting. Ruff would then use the default Python version (3.9 as of this writing) instead, which is surprising when you've attempted to request another version.
-
-    In v0.10, config discovery has been updated to address this issue:
-
-    - If Ruff finds a `ruff.toml` file without a `target-version`, it will check
-        for a `pyproject.toml` file in the same directory and respect its
-        `requires-python` version, even if it does not contain a `[tool.ruff]`
-        section.
-    - If Ruff finds a user-level configuration, the `requires-python` field of the closest `pyproject.toml` in a parent directory will take precedence.
-    - If there is no config file (`ruff.toml`or `pyproject.toml` with a
-        `[tool.ruff]` section) in the directory of the file being checked, Ruff will
-        search for the closest `pyproject.toml` in the parent directories and use its
-        `requires-python` setting.
-
-- **Updated `TYPE_CHECKING` behavior** ([#16669](https://github.com/astral-sh/ruff/pull/16669))
-
-    Previously, Ruff only recognized typechecking blocks that tested the `typing.TYPE_CHECKING` symbol. Now, Ruff recognizes any local variable named `TYPE_CHECKING`. This release also removes support for the legacy `if 0:` and `if False:` typechecking checks. Use a local `TYPE_CHECKING` variable instead.
-
-- **More robust noqa parsing** ([#16483](https://github.com/astral-sh/ruff/pull/16483))
-
-    The syntax for both file-level and in-line suppression comments has been unified and made more robust to certain errors. In most cases, this will result in more suppression comments being read by Ruff, but there are a few instances where previously read comments will now log an error to the user instead. Please refer to the documentation on [_Error suppression_](https://docs.astral.sh/ruff/linter/#error-suppression) for the full specification.
-
-- **Avoid unnecessary parentheses around with statements with a single context manager and a trailing comment** ([#14005](https://github.com/astral-sh/ruff/pull/14005))
-
-    This change fixes a bug in the formatter where it introduced unnecessary parentheses around with statements with a single context manager and a trailing comment. This change may result in a change in formatting for some users.
-
-- **Bump alpine default tag to 3.21 for derived Docker images** ([#16456](https://github.com/astral-sh/ruff/pull/16456))
-
-    Alpine 3.21 was released in Dec 2024 and is used in the official Alpine-based Python images. Now the ruff:alpine image will use 3.21 instead of 3.20 and ruff:alpine3.20 will no longer be updated.
-
-### Deprecated Rules
-
-The following rules have been deprecated:
-
-- [`non-pep604-isinstance`](https://docs.astral.sh/ruff/rules/non-pep604-isinstance/) (`UP038`)
-- [`suspicious-xmle-tree-usage`](https://docs.astral.sh/ruff/rules/suspicious-xmle-tree-usage/) (`S320`)
-
-### Remapped rules
-
-The following rules have been remapped to new rule codes:
-
-- \[`unsafe-markup-use`\]: `RUF035` to `S704`
-
-### Stabilization
-
-The following rules have been stabilized and are no longer in preview:
-
-- [`batched-without-explicit-strict`](https://docs.astral.sh/ruff/rules/batched-without-explicit-strict) (`B911`)
-- [`unnecessary-dict-comprehension-for-iterable`](https://docs.astral.sh/ruff/rules/unnecessary-dict-comprehension-for-iterable) (`C420`)
-- [`datetime-min-max`](https://docs.astral.sh/ruff/rules/datetime-min-max) (`DTZ901`)
-- [`fast-api-unused-path-parameter`](https://docs.astral.sh/ruff/rules/fast-api-unused-path-parameter) (`FAST003`)
-- [`root-logger-call`](https://docs.astral.sh/ruff/rules/root-logger-call) (`LOG015`)
-- [`len-test`](https://docs.astral.sh/ruff/rules/len-test) (`PLC1802`)
-- [`shallow-copy-environ`](https://docs.astral.sh/ruff/rules/shallow-copy-environ) (`PLW1507`)
-- [`os-listdir`](https://docs.astral.sh/ruff/rules/os-listdir) (`PTH208`)
-- [`invalid-pathlib-with-suffix`](https://docs.astral.sh/ruff/rules/invalid-pathlib-with-suffix) (`PTH210`)
-- [`invalid-assert-message-literal-argument`](https://docs.astral.sh/ruff/rules/invalid-assert-message-literal-argument) (`RUF040`)
-- [`unnecessary-nested-literal`](https://docs.astral.sh/ruff/rules/unnecessary-nested-literal) (`RUF041`)
-- [`unnecessary-cast-to-int`](https://docs.astral.sh/ruff/rules/unnecessary-cast-to-int) (`RUF046`)
-- [`map-int-version-parsing`](https://docs.astral.sh/ruff/rules/map-int-version-parsing) (`RUF048`)
-- [`if-key-in-dict-del`](https://docs.astral.sh/ruff/rules/if-key-in-dict-del) (`RUF051`)
-- [`unsafe-markup-use`](https://docs.astral.sh/ruff/rules/unsafe-markup-use) (`S704`). This rule has also been renamed from `RUF035`.
-- [`split-static-string`](https://docs.astral.sh/ruff/rules/split-static-string) (`SIM905`)
-- [`runtime-cast-value`](https://docs.astral.sh/ruff/rules/runtime-cast-value) (`TC006`)
-- [`unquoted-type-alias`](https://docs.astral.sh/ruff/rules/unquoted-type-alias) (`TC007`)
-- [`non-pep646-unpack`](https://docs.astral.sh/ruff/rules/non-pep646-unpack) (`UP044`)
-
-The following behaviors have been stabilized:
-
-- [`bad-staticmethod-argument`](https://docs.astral.sh/ruff/rules/bad-staticmethod-argument/) (`PLW0211`) [`invalid-first-argument-name-for-class-method`](https://docs.astral.sh/ruff/rules/invalid-first-argument-name-for-class-method/) (`N804`): `__new__` methods are now no longer flagged by `invalid-first-argument-name-for-class-method` (`N804`) but instead by `bad-staticmethod-argument` (`PLW0211`)
-- [`bad-str-strip-call`](https://docs.astral.sh/ruff/rules/bad-str-strip-call/) (`PLE1310`): The rule now applies to objects which are known to have type `str` or `bytes`.
-- [`blanket-noqa`](https://docs.astral.sh/ruff/rules/blanket-noqa/) (`PGH004`): Also detect blanked file-level noqa comments (and not just line level comments).
-- [`custom-type-var-for-self`](https://docs.astral.sh/ruff/rules/custom-type-var-for-self/) (`PYI019`): More accurate detection of custom `TypeVars` replaceable by `Self`. The range of the diagnostic is now the full function header rather than just the return annotation.
-- [`invalid-argument-name`](https://docs.astral.sh/ruff/rules/invalid-argument-name/) (`N803`): Ignore argument names of functions decorated with `typing.override`
-- [`invalid-envvar-default`](https://docs.astral.sh/ruff/rules/invalid-envvar-default/) (`PLW1508`): Detect default value arguments to `os.environ.get` with invalid type.
-- [`pytest-raises-with-multiple-statements`](https://docs.astral.sh/ruff/rules/pytest-raises-with-multiple-statements/) (`PT012`) [`pytest-warns-with-multiple-statements`](https://docs.astral.sh/ruff/rules/pytest-warns-with-multiple-statements/) (`PT031`): Allow `for` statements with an empty body in `pytest.raises` and `pytest.warns` `with` statements.
-- [`redundant-open-modes`](https://docs.astral.sh/ruff/rules/redundant-open-modes/) (`UP015`): The diagnostic range is now the range of the redundant mode argument where it previously was the range of the entire open call. You may have to replace your `noqa` comments when suppressing `UP015`.
-- [`stdlib-module-shadowing`](https://docs.astral.sh/ruff/rules/stdlib-module-shadowing/) (`A005`): Changes the default value of `lint.flake8-builtins.strict-checking` from `true` to `false`.
-- [`type-none-comparison`](https://docs.astral.sh/ruff/rules/type-none-comparison/) (`FURB169`): Now also recognizes `type(expr) is type(None)` comparisons where `expr` isn't a name expression.
-
-The following fixes or improvements to fixes have been stabilized:
-
-- [`repeated-equality-comparison`](https://docs.astral.sh/ruff/rules/repeated-equality-comparison/) (`PLR1714`) ([#16685](https://github.com/astral-sh/ruff/pull/16685))
-- [`needless-bool`](https://docs.astral.sh/ruff/rules/needless-bool/) (`SIM103`) ([#16684](https://github.com/astral-sh/ruff/pull/16684))
-- [`unused-private-type-var`](https://docs.astral.sh/ruff/rules/unused-private-type-var/) (`PYI018`) ([#16682](https://github.com/astral-sh/ruff/pull/16682))
-
-### Server
-
-- Remove logging output for `ruff.printDebugInformation` ([#16617](https://github.com/astral-sh/ruff/pull/16617))
-
-### Configuration
-
-- \[`flake8-builtins`\] Deprecate the `builtins-` prefixed options in favor of the unprefixed options (e.g. `builtins-allowed-modules` is now deprecated in favor of `allowed-modules`) ([#16092](https://github.com/astral-sh/ruff/pull/16092))
-
-### Bug fixes
-
-- [flake8-bandit] Fix mixed-case hash algorithm names (S324) ([#16552](https://github.com/astral-sh/ruff/pull/16552))
-
-### CLI
-
-- [ruff] Fix `last_tag`/`commits_since_last_tag` for `version` command ([#16686](https://github.com/astral-sh/ruff/pull/16686))
-
-## 0.9.10
-
-### Preview features
-
-- \[`ruff`\] Add new rule `RUF059`: Unused unpacked assignment ([#16449](https://github.com/astral-sh/ruff/pull/16449))
-- \[`syntax-errors`\] Detect assignment expressions before Python 3.8 ([#16383](https://github.com/astral-sh/ruff/pull/16383))
-- \[`syntax-errors`\] Named expressions in decorators before Python 3.9 ([#16386](https://github.com/astral-sh/ruff/pull/16386))
-- \[`syntax-errors`\] Parenthesized keyword argument names after Python 3.8 ([#16482](https://github.com/astral-sh/ruff/pull/16482))
-- \[`syntax-errors`\] Positional-only parameters before Python 3.8 ([#16481](https://github.com/astral-sh/ruff/pull/16481))
-- \[`syntax-errors`\] Tuple unpacking in `return` and `yield` before Python 3.8 ([#16485](https://github.com/astral-sh/ruff/pull/16485))
-- \[`syntax-errors`\] Type parameter defaults before Python 3.13 ([#16447](https://github.com/astral-sh/ruff/pull/16447))
-- \[`syntax-errors`\] Type parameter lists before Python 3.12 ([#16479](https://github.com/astral-sh/ruff/pull/16479))
-- \[`syntax-errors`\] `except*` before Python 3.11 ([#16446](https://github.com/astral-sh/ruff/pull/16446))
-- \[`syntax-errors`\] `type` statements before Python 3.12 ([#16478](https://github.com/astral-sh/ruff/pull/16478))
-
-### Bug fixes
-
-- Escape template filenames in glob patterns in configuration ([#16407](https://github.com/astral-sh/ruff/pull/16407))
-- \[`flake8-simplify`\] Exempt unittest context methods for `SIM115` rule ([#16439](https://github.com/astral-sh/ruff/pull/16439))
-- Formatter: Fix syntax error location in notebooks ([#16499](https://github.com/astral-sh/ruff/pull/16499))
-- \[`pyupgrade`\] Do not offer fix when at least one target is `global`/`nonlocal` (`UP028`) ([#16451](https://github.com/astral-sh/ruff/pull/16451))
-- \[`flake8-builtins`\] Ignore variables matching module attribute names (`A001`) ([#16454](https://github.com/astral-sh/ruff/pull/16454))
-- \[`pylint`\] Convert `code` keyword argument to a positional argument in fix for (`PLR1722`) ([#16424](https://github.com/astral-sh/ruff/pull/16424))
-
-### CLI
-
-- Move rule code from `description` to `check_name` in GitLab output serializer ([#16437](https://github.com/astral-sh/ruff/pull/16437))
-
-### Documentation
-
-- \[`pydocstyle`\] Clarify that `D417` only checks docstrings with an arguments section ([#16494](https://github.com/astral-sh/ruff/pull/16494))
-
-## 0.9.9
-
-### Preview features
-
-- Fix caching of unsupported-syntax errors ([#16425](https://github.com/astral-sh/ruff/pull/16425))
-
-### Bug fixes
-
-- Only show unsupported-syntax errors in editors when preview mode is enabled ([#16429](https://github.com/astral-sh/ruff/pull/16429))
-
-## 0.9.8
-
-### Preview features
-
-- Start detecting version-related syntax errors in the parser ([#16090](https://github.com/astral-sh/ruff/pull/16090))
-
-### Rule changes
-
-- \[`pylint`\] Mark fix unsafe (`PLW1507`) ([#16343](https://github.com/astral-sh/ruff/pull/16343))
-- \[`pylint`\] Catch `case np.nan`/`case math.nan` in `match` statements (`PLW0177`) ([#16378](https://github.com/astral-sh/ruff/pull/16378))
-- \[`ruff`\] Add more Pydantic models variants to the list of default copy semantics (`RUF012`) ([#16291](https://github.com/astral-sh/ruff/pull/16291))
-
-### Server
-
-- Avoid indexing the project if `configurationPreference` is `editorOnly` ([#16381](https://github.com/astral-sh/ruff/pull/16381))
-- Avoid unnecessary info at non-trace server log level ([#16389](https://github.com/astral-sh/ruff/pull/16389))
-- Expand `ruff.configuration` to allow inline config ([#16296](https://github.com/astral-sh/ruff/pull/16296))
-- Notify users for invalid client settings ([#16361](https://github.com/astral-sh/ruff/pull/16361))
-
-### Configuration
-
-- Add `per-file-target-version` option ([#16257](https://github.com/astral-sh/ruff/pull/16257))
-
-### Bug fixes
-
-- \[`refurb`\] Do not consider docstring(s) (`FURB156`) ([#16391](https://github.com/astral-sh/ruff/pull/16391))
-- \[`flake8-self`\] Ignore attribute accesses on instance-like variables (`SLF001`) ([#16149](https://github.com/astral-sh/ruff/pull/16149))
-- \[`pylint`\] Fix false positives, add missing methods, and support positional-only parameters (`PLE0302`) ([#16263](https://github.com/astral-sh/ruff/pull/16263))
-- \[`flake8-pyi`\] Mark `PYI030` fix unsafe when comments are deleted ([#16322](https://github.com/astral-sh/ruff/pull/16322))
-
-### Documentation
-
-- Fix example for `S611` ([#16316](https://github.com/astral-sh/ruff/pull/16316))
-- Normalize inconsistent markdown headings in docstrings ([#16364](https://github.com/astral-sh/ruff/pull/16364))
-- Document MSRV policy ([#16384](https://github.com/astral-sh/ruff/pull/16384))
-
 ## 0.9.7
 
 ### Preview features
@@ -208,7 +13,16 @@ The following fixes or improvements to fixes have been stabilized:
 
 ### Rule changes
 
+- \[`flake8-comprehensions`\]: Handle trailing comma in `C403` fix ([#16110](https://github.com/astral-sh/ruff/pull/16110))
 - \[`flake8-debugger`\] Also flag `sys.breakpointhook` and `sys.__breakpointhook__` (`T100`) ([#16191](https://github.com/astral-sh/ruff/pull/16191))
+- \[`pydocstyle`\] Handle arguments with the same names as sections (`D417`) ([#16011](https://github.com/astral-sh/ruff/pull/16011))
+- \[`pylint`\] Correct ordering of arguments in fix for `if-stmt-min-max` (`PLR1730`) ([#16080](https://github.com/astral-sh/ruff/pull/16080))
+- \[`pylint`\] Do not offer fix for raw strings (`PLE251`) ([#16132](https://github.com/astral-sh/ruff/pull/16132))
+- \[`pyupgrade`\] Do not upgrade functional `TypedDicts` with private field names to the class-based syntax (`UP013`) ([#16219](https://github.com/astral-sh/ruff/pull/16219))
+- \[`pyupgrade`\] Handle micro version numbers correctly (`UP036`) ([#16091](https://github.com/astral-sh/ruff/pull/16091))
+- \[`pyupgrade`\] Unwrap unary expressions correctly (`UP018`) ([#15919](https://github.com/astral-sh/ruff/pull/15919))
+- \[`ruff`\] Skip `RUF001` diagnostics when visiting string type definitions ([#16122](https://github.com/astral-sh/ruff/pull/16122))
+- \[`flake8-pyi`\] Avoid flagging `custom-typevar-for-self` on metaclass methods (`PYI019`) ([#16141](https://github.com/astral-sh/ruff/pull/16141))
 - \[`pycodestyle`\] Exempt `site.addsitedir(...)` calls (`E402`) ([#16251](https://github.com/astral-sh/ruff/pull/16251))
 
 ### Formatter
@@ -229,16 +43,7 @@ The following fixes or improvements to fixes have been stabilized:
 
 ### Bug fixes
 
-- \[`flake8-comprehensions`\] Handle trailing comma in `C403` fix ([#16110](https://github.com/astral-sh/ruff/pull/16110))
-- \[`flake8-pyi`\] Avoid flagging `custom-typevar-for-self` on metaclass methods (`PYI019`) ([#16141](https://github.com/astral-sh/ruff/pull/16141))
-- \[`pydocstyle`\] Handle arguments with the same names as sections (`D417`) ([#16011](https://github.com/astral-sh/ruff/pull/16011))
-- \[`pylint`\] Correct ordering of arguments in fix for `if-stmt-min-max` (`PLR1730`) ([#16080](https://github.com/astral-sh/ruff/pull/16080))
-- \[`pylint`\] Do not offer fix for raw strings (`PLE251`) ([#16132](https://github.com/astral-sh/ruff/pull/16132))
-- \[`pyupgrade`\] Do not upgrade functional `TypedDicts` with private field names to the class-based syntax (`UP013`) ([#16219](https://github.com/astral-sh/ruff/pull/16219))
-- \[`pyupgrade`\] Handle micro version numbers correctly (`UP036`) ([#16091](https://github.com/astral-sh/ruff/pull/16091))
-- \[`pyupgrade`\] Unwrap unary expressions correctly (`UP018`) ([#15919](https://github.com/astral-sh/ruff/pull/15919))
 - \[`refurb`\] Correctly handle lengths of literal strings in `slice-to-remove-prefix-or-suffix` (`FURB188`) ([#16237](https://github.com/astral-sh/ruff/pull/16237))
-- \[`ruff`\] Skip `RUF001` diagnostics when visiting string type definitions ([#16122](https://github.com/astral-sh/ruff/pull/16122))
 
 ### Documentation
 
@@ -1448,7 +1253,7 @@ The following fixes have been stabilized:
 
 ## 0.5.6
 
-Ruff 0.5.6 automatically enables linting and formatting of notebooks in _preview mode_.
+Ruff 0.5.6 automatically enables linting and formatting of notebooks in *preview mode*.
 You can opt-out of this behavior by adding `*.ipynb` to the `extend-exclude` setting.
 
 ```toml
@@ -2201,7 +2006,7 @@ To setup `ruff server` with your editor, refer to the [README.md](https://github
 
 ### Server
 
-_This section is devoted to updates for our new language server, written in Rust._
+*This section is devoted to updates for our new language server, written in Rust.*
 
 - Enable ruff-specific source actions ([#10916](https://github.com/astral-sh/ruff/pull/10916))
 - Refreshes diagnostics for open files when file configuration is changed ([#10988](https://github.com/astral-sh/ruff/pull/10988))
@@ -3608,7 +3413,7 @@ Read Ruff's new [versioning policy](https://docs.astral.sh/ruff/versioning/).
 - \[`refurb`\] Add `single-item-membership-test` (`FURB171`) ([#7815](https://github.com/astral-sh/ruff/pull/7815))
 - \[`pylint`\] Add `and-or-ternary` (`R1706`) ([#7811](https://github.com/astral-sh/ruff/pull/7811))
 
-_New rules are added in [preview](https://docs.astral.sh/ruff/preview/)._
+*New rules are added in [preview](https://docs.astral.sh/ruff/preview/).*
 
 ### Configuration
 

Cargo.toml

@@ -4,7 +4,7 @@ resolver = "2"
 
 [workspace.package]
 edition = "2021"
-rust-version = "1.83"
+rust-version = "1.80"
 homepage = "https://docs.astral.sh/ruff"
 documentation = "https://docs.astral.sh/ruff"
 repository = "https://github.com/astral-sh/ruff"
@@ -123,7 +123,7 @@ rayon = { version = "1.10.0" }
 regex = { version = "1.10.2" }
 rustc-hash = { version = "2.0.0" }
 # When updating salsa, make sure to also update the revision in `fuzz/Cargo.toml`
-salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "095d8b2b8115c3cf8bf31914dd9ea74648bb7cf9" }
+salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "351d9cf0037be949d17800d0c7b4838e533c2ed6" }
 schemars = { version = "0.8.16" }
 seahash = { version = "4.1.0" }
 serde = { version = "1.0.197", features = ["derive"] }

README.md

@@ -149,8 +149,8 @@ curl -LsSf https://astral.sh/ruff/install.sh | sh
 powershell -c "irm https://astral.sh/ruff/install.ps1 | iex"
 
 # For a specific version.
-curl -LsSf https://astral.sh/ruff/0.10.0/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.10.0/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.9.7/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.9.7/install.ps1 | iex"
 ```
 
 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -183,7 +183,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.10.0
+  rev: v0.9.7
   hooks:
     # Run the linter.
     - id: ruff

_typos.toml

@@ -23,10 +23,6 @@ extend-ignore-re = [
     # Line ignore with trailing "spellchecker:disable-line"
     "(?Rm)^.*#\\s*spellchecker:disable-line$",
     "LICENSEs",
-    # Various third party dependencies uses `typ` as struct field names (e.g., lsp_types::LogMessageParams)
-    "typ",
-    # TODO: Remove this once the `TYP` redirects are removed from `rule_redirects.rs`
-    "TYP",
 ]
 
 [default.extend-identifiers]

crates/red_knot/Cargo.toml

@@ -19,7 +19,6 @@ ruff_db = { workspace = true, features = ["os", "cache"] }
 ruff_python_ast = { workspace = true }
 
 anyhow = { workspace = true }
-argfile = { workspace = true }
 chrono = { workspace = true }
 clap = { workspace = true, features = ["wrap_help"] }
 colored = { workspace = true }
@@ -32,7 +31,6 @@ tracing = { workspace = true, features = ["release_max_level_debug"] }
 tracing-subscriber = { workspace = true, features = ["env-filter", "fmt"] }
 tracing-flame = { workspace = true }
 tracing-tree = { workspace = true }
-wild = { workspace = true }
 
 [dev-dependencies]
 ruff_db = { workspace = true, features = ["testing"] }

crates/red_knot/docs/mypy_primer.md

@@ -1,61 +0,0 @@
-# Running `mypy_primer`
-
-## Basics
-
-For now, we use our own [fork of mypy primer]. It can be run using `uvx --from "…" mypy_primer`. For example, to see the help message, run:
-
-```sh
-uvx --from "git+https://github.com/astral-sh/mypy_primer.git@add-red-knot-support" mypy_primer -h
-```
-
-Alternatively, you can install the forked version of `mypy_primer` using:
-
-```sh
-uv tool install "git+https://github.com/astral-sh/mypy_primer.git@add-red-knot-support"
-```
-
-and then run it using `uvx mypy_primer` or just `mypy_primer`, if your `PATH` is set up accordingly (see: [Tool executables]).
-
-## Showing the diagnostics diff between two Git revisions
-
-To show the diagnostics diff between two Git revisions (e.g. your feature branch and `main`), run:
-
-```sh
-mypy_primer \
-    --type-checker knot \
-    --old origin/main \
-    --new my/feature \
-    --debug \
-    --output concise \
-    --project-selector '/black$'
-```
-
-This will show the diagnostics diff for the `black` project between the `main` branch and your `my/feature` branch. To run the
-diff for all projects, you currently need to copy the project-selector regex from the CI pipeline in `.github/workflows/mypy_primer.yaml`.
-
-You can also take a look at the [full list of ecosystem projects]. Note that some of them might still need a `knot_paths` configuration
-option to work correctly.
-
-## Avoiding recompilation
-
-If you want to run `mypy_primer` repeatedly, e.g. for different projects, but for the same combination of `--old` and `--new`, you
-can use set the `MYPY_PRIMER_NO_REBUILD` environment variable to avoid recompilation of Red Knot:
-
-```sh
-MYPY_PRIMER_NO_REBUILD=1 mypy_primer …
-```
-
-## Running from a local copy of the repository
-
-If you are working on a local branch, you can use `mypy_primer`'s `--repo` option to specify the path to your local copy of the `ruff` repository.
-This allows `mypy_primer` to check out local branches:
-
-```sh
-mypy_primer --repo /path/to/ruff --old origin/main --new my/local-branch …
-```
-
-Note that you might need to clean up `/tmp/mypy_primer` in order for this to work correctly.
-
-[fork of mypy primer]: https://github.com/astral-sh/mypy_primer/tree/add-red-knot-support
-[full list of ecosystem projects]: https://github.com/astral-sh/mypy_primer/blob/add-red-knot-support/mypy_primer/projects.py
-[tool executables]: https://docs.astral.sh/uv/concepts/tools/#tool-executables

crates/red_knot/src/args.rs

@@ -32,13 +32,6 @@ pub(crate) enum Command {
 
 #[derive(Debug, Parser)]
 pub(crate) struct CheckCommand {
-    /// List of files or directories to check.
-    #[clap(
-        help = "List of files or directories to check [default: the project root]",
-        value_name = "PATH"
-    )]
-    pub paths: Vec<SystemPathBuf>,
-
     /// Run the command within the given project directory.
     ///
     /// All `pyproject.toml` files will be discovered by walking up the directory tree from the given project directory,
@@ -48,14 +41,12 @@ pub(crate) struct CheckCommand {
     #[arg(long, value_name = "PROJECT")]
     pub(crate) project: Option<SystemPathBuf>,
 
-    /// Path to the Python installation from which Red Knot resolves type information and third-party dependencies.
+    /// Path to the virtual environment the project uses.
     ///
-    /// Red Knot will search in the path's `site-packages` directories for type information and
-    /// third-party imports.
-    ///
-    /// This option is commonly used to specify the path to a virtual environment.
+    /// If provided, red-knot will use the `site-packages` directory of this virtual environment
+    /// to resolve type information for the project's third-party dependencies.
     #[arg(long, value_name = "PATH")]
-    pub(crate) python: Option<SystemPathBuf>,
+    pub(crate) venv_path: Option<SystemPathBuf>,
 
     /// Custom directory to use for stdlib typeshed stubs.
     #[arg(long, value_name = "PATH", alias = "custom-typeshed-dir")]
@@ -83,7 +74,7 @@ pub(crate) struct CheckCommand {
     #[arg(long)]
     pub(crate) exit_zero: bool,
 
-    /// Watch files for changes and recheck files related to the changed files.
+    /// Run in watch mode by re-running whenever files change.
     #[arg(long, short = 'W')]
     pub(crate) watch: bool,
 }
@@ -106,7 +97,7 @@ impl CheckCommand {
                 python_version: self
                     .python_version
                     .map(|version| RangedValue::cli(version.into())),
-                python: self.python.map(RelativePathBuf::cli),
+                venv_path: self.venv_path.map(RelativePathBuf::cli),
                 typeshed: self.typeshed.map(RelativePathBuf::cli),
                 extra_paths: self.extra_search_path.map(|extra_search_paths| {
                     extra_search_paths

crates/red_knot/src/main.rs

@@ -1,4 +1,4 @@
-use std::io::{self, stdout, BufWriter, Write};
+use std::io::{self, BufWriter, Write};
 use std::process::{ExitCode, Termination};
 
 use anyhow::Result;
@@ -15,8 +15,8 @@ use red_knot_project::watch::ProjectWatcher;
 use red_knot_project::{watch, Db};
 use red_knot_project::{ProjectDatabase, ProjectMetadata};
 use red_knot_server::run_server;
-use ruff_db::diagnostic::{DisplayDiagnosticConfig, OldDiagnosticTrait, Severity};
-use ruff_db::system::{OsSystem, SystemPath, SystemPathBuf};
+use ruff_db::diagnostic::{Diagnostic, DisplayDiagnosticConfig, Severity};
+use ruff_db::system::{OsSystem, System, SystemPath, SystemPathBuf};
 use salsa::plumbing::ZalsaDatabase;
 
 mod args;
@@ -39,15 +39,6 @@ pub fn main() -> ExitStatus {
         // the configuration it is help to chain errors ("resolving configuration failed" ->
         // "failed to read file: subdir/pyproject.toml")
         for cause in error.chain() {
-            // Exit "gracefully" on broken pipe errors.
-            //
-            // See: https://github.com/BurntSushi/ripgrep/blob/bf63fe8f258afc09bae6caa48f0ae35eaf115005/crates/core/main.rs#L47C1-L61C14
-            if let Some(ioerr) = cause.downcast_ref::<io::Error>() {
-                if ioerr.kind() == io::ErrorKind::BrokenPipe {
-                    return ExitStatus::Success;
-                }
-            }
-
             writeln!(stderr, "  {} {cause}", "Cause:".bold()).ok();
         }
 
@@ -56,10 +47,7 @@ pub fn main() -> ExitStatus {
 }
 
 fn run() -> anyhow::Result<ExitStatus> {
-    let args = wild::args_os();
-    let args = argfile::expand_args_from(args, argfile::parse_fromfile, argfile::PREFIX)
-        .context("Failed to read CLI arguments from file")?;
-    let args = Args::parse_from(args);
+    let args = Args::parse_from(std::env::args());
 
     match args.command {
         Command::Server => run_server().map(|()| ExitStatus::Success),
@@ -81,7 +69,7 @@ fn run_check(args: CheckCommand) -> anyhow::Result<ExitStatus> {
     let _guard = setup_tracing(verbosity)?;
 
     // The base path to which all CLI arguments are relative to.
-    let cwd = {
+    let cli_base_path = {
         let cwd = std::env::current_dir().context("Failed to get the current working directory")?;
         SystemPathBuf::from_path_buf(cwd)
             .map_err(|path| {
@@ -92,42 +80,30 @@ fn run_check(args: CheckCommand) -> anyhow::Result<ExitStatus> {
             })?
     };
 
-    let project_path = args
+    let cwd = args
         .project
         .as_ref()
-        .map(|project| {
-            if project.as_std_path().is_dir() {
-                Ok(SystemPath::absolute(project, &cwd))
+        .map(|cwd| {
+            if cwd.as_std_path().is_dir() {
+                Ok(SystemPath::absolute(cwd, &cli_base_path))
             } else {
-                Err(anyhow!(
-                    "Provided project path `{project}` is not a directory"
-                ))
+                Err(anyhow!("Provided project path `{cwd}` is not a directory"))
             }
         })
         .transpose()?
-        .unwrap_or_else(|| cwd.clone());
-
-    let check_paths: Vec<_> = args
-        .paths
-        .iter()
-        .map(|path| SystemPath::absolute(path, &cwd))
-        .collect();
+        .unwrap_or_else(|| cli_base_path.clone());
 
     let system = OsSystem::new(cwd);
     let watch = args.watch;
     let exit_zero = args.exit_zero;
 
     let cli_options = args.into_options();
-    let mut project_metadata = ProjectMetadata::discover(&project_path, &system)?;
+    let mut project_metadata = ProjectMetadata::discover(system.current_directory(), &system)?;
     project_metadata.apply_cli_options(cli_options.clone());
     project_metadata.apply_configuration_files(&system)?;
 
     let mut db = ProjectDatabase::new(project_metadata, system)?;
 
-    if !check_paths.is_empty() {
-        db.project().set_included_paths(&mut db, check_paths);
-    }
-
     let (main_loop, main_loop_cancellation_token) = MainLoop::new(cli_options);
 
     // Listen to Ctrl+C and abort the watch mode.
@@ -143,7 +119,7 @@ fn run_check(args: CheckCommand) -> anyhow::Result<ExitStatus> {
     let exit_status = if watch {
         main_loop.watch(&mut db)?
     } else {
-        main_loop.run(&mut db)?
+        main_loop.run(&mut db)
     };
 
     tracing::trace!("Counts for entire CLI run:\n{}", countme::get_all());
@@ -203,7 +179,7 @@ impl MainLoop {
         )
     }
 
-    fn watch(mut self, db: &mut ProjectDatabase) -> Result<ExitStatus> {
+    fn watch(mut self, db: &mut ProjectDatabase) -> anyhow::Result<ExitStatus> {
         tracing::debug!("Starting watch mode");
         let sender = self.sender.clone();
         let watcher = watch::directory_watcher(move |event| {
@@ -212,12 +188,12 @@ impl MainLoop {
 
         self.watcher = Some(ProjectWatcher::new(watcher, db));
 
-        self.run(db)?;
+        self.run(db);
 
         Ok(ExitStatus::Success)
     }
 
-    fn run(mut self, db: &mut ProjectDatabase) -> Result<ExitStatus> {
+    fn run(mut self, db: &mut ProjectDatabase) -> ExitStatus {
         self.sender.send(MainLoopMessage::CheckWorkspace).unwrap();
 
         let result = self.main_loop(db);
@@ -227,7 +203,7 @@ impl MainLoop {
         result
     }
 
-    fn main_loop(&mut self, db: &mut ProjectDatabase) -> Result<ExitStatus> {
+    fn main_loop(&mut self, db: &mut ProjectDatabase) -> ExitStatus {
         // Schedule the first check.
         tracing::debug!("Starting main loop");
 
@@ -265,43 +241,14 @@ impl MainLoop {
                             Severity::Error
                         };
 
+                    let failed = result
+                        .iter()
+                        .any(|diagnostic| diagnostic.severity() >= min_error_severity);
+
                     if check_revision == revision {
-                        if db.project().files(db).is_empty() {
-                            tracing::warn!("No python files found under the given path(s)");
-                        }
-
-                        let mut stdout = stdout().lock();
-
-                        if result.is_empty() {
-                            writeln!(stdout, "All checks passed!")?;
-
-                            if self.watcher.is_none() {
-                                return Ok(ExitStatus::Success);
-                            }
-                        } else {
-                            let mut failed = false;
-                            let diagnostics_count = result.len();
-
-                            for diagnostic in result {
-                                writeln!(stdout, "{}", diagnostic.display(db, &display_config))?;
-
-                                failed |= diagnostic.severity() >= min_error_severity;
-                            }
-
-                            writeln!(
-                                stdout,
-                                "Found {} diagnostic{}",
-                                diagnostics_count,
-                                if diagnostics_count > 1 { "s" } else { "" }
-                            )?;
-
-                            if self.watcher.is_none() {
-                                return Ok(if failed {
-                                    ExitStatus::Failure
-                                } else {
-                                    ExitStatus::Success
-                                });
-                            }
+                        #[allow(clippy::print_stdout)]
+                        for diagnostic in result {
+                            println!("{}", diagnostic.display(db, &display_config));
                         }
                     } else {
                         tracing::debug!(
@@ -309,6 +256,14 @@ impl MainLoop {
                         );
                     }
 
+                    if self.watcher.is_none() {
+                        return if failed {
+                            ExitStatus::Failure
+                        } else {
+                            ExitStatus::Success
+                        };
+                    }
+
                     tracing::trace!("Counts after last check:\n{}", countme::get_all());
                 }
 
@@ -326,14 +281,14 @@ impl MainLoop {
                     // TODO: Don't use Salsa internal APIs
                     //  [Zulip-Thread](https://salsa.zulipchat.com/#narrow/stream/333573-salsa-3.2E0/topic/Expose.20an.20API.20to.20cancel.20other.20queries)
                     let _ = db.zalsa_mut();
-                    return Ok(ExitStatus::Success);
+                    return ExitStatus::Success;
                 }
             }
 
             tracing::debug!("Waiting for next main loop message.");
         }
 
-        Ok(ExitStatus::Success)
+        ExitStatus::Success
     }
 }
 
@@ -353,8 +308,7 @@ impl MainLoopCancellationToken {
 enum MainLoopMessage {
     CheckWorkspace,
     CheckCompleted {
-        /// The diagnostics that were found during the check.
-        result: Vec<Box<dyn OldDiagnosticTrait>>,
+        result: Vec<Box<dyn Diagnostic>>,
         revision: u64,
     },
     ApplyChanges(Vec<watch::ChangeEvent>),

crates/red_knot/tests/cli.rs

@@ -28,7 +28,7 @@ fn config_override() -> anyhow::Result<()> {
         ),
     ])?;
 
-    assert_cmd_snapshot!(case.command(), @r"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -40,18 +40,16 @@ fn config_override() -> anyhow::Result<()> {
       |       ^^^^^^^^^^^^ Type `<module 'sys'>` has no attribute `last_exc`
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    ");
+    "###);
 
     assert_cmd_snapshot!(case.command().arg("--python-version").arg("3.12"), @r"
-    success: true
-    exit_code: 0
-    ----- stdout -----
-    All checks passed!
+        success: true
+        exit_code: 0
+        ----- stdout -----
 
-    ----- stderr -----
+        ----- stderr -----
     ");
 
     Ok(())
@@ -86,7 +84,7 @@ fn cli_arguments_are_relative_to_the_current_directory() -> anyhow::Result<()> {
             "libs/utils.py",
             r#"
             def add(a: int, b: int) -> int:
-                return a + b
+                a + b
             "#,
         ),
         (
@@ -100,7 +98,7 @@ fn cli_arguments_are_relative_to_the_current_directory() -> anyhow::Result<()> {
     ])?;
 
     // Make sure that the CLI fails when the `libs` directory is not in the search path.
-    assert_cmd_snapshot!(case.command().current_dir(case.root().join("child")), @r"
+    assert_cmd_snapshot!(case.command().current_dir(case.root().join("child")), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -113,18 +111,16 @@ fn cli_arguments_are_relative_to_the_current_directory() -> anyhow::Result<()> {
     4 | stat = add(10, 15)
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    ");
+    "###);
 
     assert_cmd_snapshot!(case.command().current_dir(case.root().join("child")).arg("--extra-search-path").arg("../libs"), @r"
-    success: true
-    exit_code: 0
-    ----- stdout -----
-    All checks passed!
+        success: true
+        exit_code: 0
+        ----- stdout -----
 
-    ----- stderr -----
+        ----- stderr -----
     ");
 
     Ok(())
@@ -158,7 +154,7 @@ fn paths_in_configuration_files_are_relative_to_the_project_root() -> anyhow::Re
             "libs/utils.py",
             r#"
             def add(a: int, b: int) -> int:
-                return a + b
+                a + b
             "#,
         ),
         (
@@ -172,12 +168,11 @@ fn paths_in_configuration_files_are_relative_to_the_project_root() -> anyhow::Re
     ])?;
 
     assert_cmd_snapshot!(case.command().current_dir(case.root().join("child")), @r"
-    success: true
-    exit_code: 0
-    ----- stdout -----
-    All checks passed!
+        success: true
+        exit_code: 0
+        ----- stdout -----
 
-    ----- stderr -----
+        ----- stderr -----
     ");
 
     Ok(())
@@ -200,7 +195,7 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
 
     // Assert that there's a possibly unresolved reference diagnostic
     // and that division-by-zero has a severity of error by default.
-    assert_cmd_snapshot!(case.command(), @r"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -222,10 +217,9 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
       |       - Name `x` used when possibly not defined
       |
 
-    Found 2 diagnostics
 
     ----- stderr -----
-    ");
+    "###);
 
     case.write_file(
         "pyproject.toml",
@@ -236,7 +230,7 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
     "#,
     )?;
 
-    assert_cmd_snapshot!(case.command(), @r"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -249,10 +243,9 @@ fn configuration_rule_severity() -> anyhow::Result<()> {
     4 | for a in range(0, y):
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -276,7 +269,7 @@ fn cli_rule_severity() -> anyhow::Result<()> {
 
     // Assert that there's a possibly unresolved reference diagnostic
     // and that division-by-zero has a severity of error by default.
-    assert_cmd_snapshot!(case.command(), @r"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -309,10 +302,9 @@ fn cli_rule_severity() -> anyhow::Result<()> {
       |       - Name `x` used when possibly not defined
       |
 
-    Found 3 diagnostics
 
     ----- stderr -----
-    ");
+    "###);
 
     assert_cmd_snapshot!(
         case
@@ -323,7 +315,7 @@ fn cli_rule_severity() -> anyhow::Result<()> {
             .arg("division-by-zero")
             .arg("--warn")
             .arg("unresolved-import"),
-        @r"
+        @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -347,10 +339,9 @@ fn cli_rule_severity() -> anyhow::Result<()> {
     6 | for a in range(0, y):
       |
 
-    Found 2 diagnostics
 
     ----- stderr -----
-    "
+    "###
     );
 
     Ok(())
@@ -374,7 +365,7 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
 
     // Assert that there's a possibly unresolved reference diagnostic
     // and that division-by-zero has a severity of error by default.
-    assert_cmd_snapshot!(case.command(), @r"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -396,10 +387,9 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
       |       - Name `x` used when possibly not defined
       |
 
-    Found 2 diagnostics
 
     ----- stderr -----
-    ");
+    "###);
 
     assert_cmd_snapshot!(
         case
@@ -411,7 +401,7 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
             // Override the error severity with warning
             .arg("--ignore")
             .arg("possibly-unresolved-reference"),
-        @r"
+        @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -424,10 +414,9 @@ fn cli_rule_severity_precedence() -> anyhow::Result<()> {
     4 | for a in range(0, y):
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    "
+    "###
     );
 
     Ok(())
@@ -447,7 +436,7 @@ fn configuration_unknown_rules() -> anyhow::Result<()> {
         ("test.py", "print(10)"),
     ])?;
 
-    assert_cmd_snapshot!(case.command(), @r#"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -459,10 +448,9 @@ fn configuration_unknown_rules() -> anyhow::Result<()> {
       | --------------- Unknown lint rule `division-by-zer`
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    "#);
+    "###);
 
     Ok(())
 }
@@ -472,16 +460,15 @@ fn configuration_unknown_rules() -> anyhow::Result<()> {
 fn cli_unknown_rules() -> anyhow::Result<()> {
     let case = TestCase::with_file("test.py", "print(10)")?;
 
-    assert_cmd_snapshot!(case.command().arg("--ignore").arg("division-by-zer"), @r"
+    assert_cmd_snapshot!(case.command().arg("--ignore").arg("division-by-zer"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
     warning: unknown-rule: Unknown lint rule `division-by-zer`
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -490,7 +477,7 @@ fn cli_unknown_rules() -> anyhow::Result<()> {
 fn exit_code_only_warnings() -> anyhow::Result<()> {
     let case = TestCase::with_file("test.py", r"print(x)  # [unresolved-reference]")?;
 
-    assert_cmd_snapshot!(case.command(), @r"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -501,10 +488,9 @@ fn exit_code_only_warnings() -> anyhow::Result<()> {
       |       - Name `x` used when not defined
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -519,7 +505,7 @@ fn exit_code_only_info() -> anyhow::Result<()> {
         "#,
     )?;
 
-    assert_cmd_snapshot!(case.command(), @r"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -531,10 +517,9 @@ fn exit_code_only_info() -> anyhow::Result<()> {
       | -------------- info: Revealed type is `Literal[1]`
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -549,7 +534,7 @@ fn exit_code_only_info_and_error_on_warning_is_true() -> anyhow::Result<()> {
         "#,
     )?;
 
-    assert_cmd_snapshot!(case.command().arg("--error-on-warning"), @r"
+    assert_cmd_snapshot!(case.command().arg("--error-on-warning"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -561,10 +546,9 @@ fn exit_code_only_info_and_error_on_warning_is_true() -> anyhow::Result<()> {
       | -------------- info: Revealed type is `Literal[1]`
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -573,7 +557,7 @@ fn exit_code_only_info_and_error_on_warning_is_true() -> anyhow::Result<()> {
 fn exit_code_no_errors_but_error_on_warning_is_true() -> anyhow::Result<()> {
     let case = TestCase::with_file("test.py", r"print(x)  # [unresolved-reference]")?;
 
-    assert_cmd_snapshot!(case.command().arg("--error-on-warning"), @r"
+    assert_cmd_snapshot!(case.command().arg("--error-on-warning"), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -584,10 +568,9 @@ fn exit_code_no_errors_but_error_on_warning_is_true() -> anyhow::Result<()> {
       |       - Name `x` used when not defined
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -605,7 +588,7 @@ fn exit_code_no_errors_but_error_on_warning_is_enabled_in_configuration() -> any
         ),
     ])?;
 
-    assert_cmd_snapshot!(case.command(), @r"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -616,10 +599,9 @@ fn exit_code_no_errors_but_error_on_warning_is_enabled_in_configuration() -> any
       |       - Name `x` used when not defined
       |
 
-    Found 1 diagnostic
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -634,7 +616,7 @@ fn exit_code_both_warnings_and_errors() -> anyhow::Result<()> {
         "#,
     )?;
 
-    assert_cmd_snapshot!(case.command(), @r"
+    assert_cmd_snapshot!(case.command(), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -654,10 +636,9 @@ fn exit_code_both_warnings_and_errors() -> anyhow::Result<()> {
       |       ^ Cannot subscript object of type `Literal[4]` with no `__getitem__` method
       |
 
-    Found 2 diagnostics
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -672,7 +653,7 @@ fn exit_code_both_warnings_and_errors_and_error_on_warning_is_true() -> anyhow::
         "###,
     )?;
 
-    assert_cmd_snapshot!(case.command().arg("--error-on-warning"), @r"
+    assert_cmd_snapshot!(case.command().arg("--error-on-warning"), @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -692,10 +673,9 @@ fn exit_code_both_warnings_and_errors_and_error_on_warning_is_true() -> anyhow::
       |       ^ Cannot subscript object of type `Literal[4]` with no `__getitem__` method
       |
 
-    Found 2 diagnostics
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -710,7 +690,7 @@ fn exit_code_exit_zero_is_true() -> anyhow::Result<()> {
         "#,
     )?;
 
-    assert_cmd_snapshot!(case.command().arg("--exit-zero"), @r"
+    assert_cmd_snapshot!(case.command().arg("--exit-zero"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -730,10 +710,9 @@ fn exit_code_exit_zero_is_true() -> anyhow::Result<()> {
       |       ^ Cannot subscript object of type `Literal[4]` with no `__getitem__` method
       |
 
-    Found 2 diagnostics
 
     ----- stderr -----
-    ");
+    "###);
 
     Ok(())
 }
@@ -770,7 +749,7 @@ fn user_configuration() -> anyhow::Result<()> {
 
     assert_cmd_snapshot!(
         case.command().current_dir(case.root().join("project")).env(config_env_var, config_directory.as_os_str()),
-        @r"
+        @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -792,10 +771,9 @@ fn user_configuration() -> anyhow::Result<()> {
       |       - Name `x` used when possibly not defined
       |
 
-    Found 2 diagnostics
 
     ----- stderr -----
-    "
+    "###
     );
 
     // The user-level configuration promotes `possibly-unresolved-reference` to an error.
@@ -812,7 +790,7 @@ fn user_configuration() -> anyhow::Result<()> {
 
     assert_cmd_snapshot!(
         case.command().current_dir(case.root().join("project")).env(config_env_var, config_directory.as_os_str()),
-        @r"
+        @r###"
     success: false
     exit_code: 1
     ----- stdout -----
@@ -834,134 +812,9 @@ fn user_configuration() -> anyhow::Result<()> {
       |       ^ Name `x` used when possibly not defined
       |
 
-    Found 2 diagnostics
 
     ----- stderr -----
-    "
-    );
-
-    Ok(())
-}
-
-#[test]
-fn check_specific_paths() -> anyhow::Result<()> {
-    let case = TestCase::with_files([
-        (
-            "project/main.py",
-            r#"
-            y = 4 / 0  # error: division-by-zero
-            "#,
-        ),
-        (
-            "project/tests/test_main.py",
-            r#"
-            import does_not_exist  # error: unresolved-import
-            "#,
-        ),
-        (
-            "project/other.py",
-            r#"
-            from main2 import z  # error: unresolved-import
-
-            print(z)
-            "#,
-        ),
-    ])?;
-
-    assert_cmd_snapshot!(
-        case.command(),
-        @r"
-    success: false
-    exit_code: 1
-    ----- stdout -----
-    error: lint:unresolved-import
-     --> <temp_dir>/project/tests/test_main.py:2:8
-      |
-    2 | import does_not_exist  # error: unresolved-import
-      |        ^^^^^^^^^^^^^^ Cannot resolve import `does_not_exist`
-      |
-
-    error: lint:division-by-zero
-     --> <temp_dir>/project/main.py:2:5
-      |
-    2 | y = 4 / 0  # error: division-by-zero
-      |     ^^^^^ Cannot divide object of type `Literal[4]` by zero
-      |
-
-    error: lint:unresolved-import
-     --> <temp_dir>/project/other.py:2:6
-      |
-    2 | from main2 import z  # error: unresolved-import
-      |      ^^^^^ Cannot resolve import `main2`
-    3 |
-    4 | print(z)
-      |
-
-    Found 3 diagnostics
-
-    ----- stderr -----
-    "
-    );
-
-    // Now check only the `tests` and `other.py` files.
-    // We should no longer see any diagnostics related to `main.py`.
-    assert_cmd_snapshot!(
-        case.command().arg("project/tests").arg("project/other.py"),
-        @r"
-    success: false
-    exit_code: 1
-    ----- stdout -----
-    error: lint:unresolved-import
-     --> <temp_dir>/project/tests/test_main.py:2:8
-      |
-    2 | import does_not_exist  # error: unresolved-import
-      |        ^^^^^^^^^^^^^^ Cannot resolve import `does_not_exist`
-      |
-
-    error: lint:unresolved-import
-     --> <temp_dir>/project/other.py:2:6
-      |
-    2 | from main2 import z  # error: unresolved-import
-      |      ^^^^^ Cannot resolve import `main2`
-    3 |
-    4 | print(z)
-      |
-
-    Found 2 diagnostics
-
-    ----- stderr -----
-    "
-    );
-
-    Ok(())
-}
-
-#[test]
-fn check_non_existing_path() -> anyhow::Result<()> {
-    let case = TestCase::with_files([])?;
-
-    let mut settings = insta::Settings::clone_current();
-    settings.add_filter(
-        &regex::escape("The system cannot find the path specified. (os error 3)"),
-        "No such file or directory (os error 2)",
-    );
-    let _s = settings.bind_to_scope();
-
-    assert_cmd_snapshot!(
-        case.command().arg("project/main.py").arg("project/tests"),
-        @r"
-    success: false
-    exit_code: 1
-    ----- stdout -----
-    error: io: `<temp_dir>/project/main.py`: No such file or directory (os error 2)
-
-    error: io: `<temp_dir>/project/tests`: No such file or directory (os error 2)
-
-    Found 2 diagnostics
-
-    ----- stderr -----
-    WARN No python files found under the given path(s)
-    "
+    "###
     );
 
     Ok(())

crates/red_knot/tests/file_watching.rs

@@ -1,6 +1,5 @@
 #![allow(clippy::disallowed_names)]
 
-use std::collections::HashSet;
 use std::io::Write;
 use std::time::{Duration, Instant};
 
@@ -194,29 +193,11 @@ impl TestCase {
         Ok(())
     }
 
-    #[track_caller]
-    fn assert_indexed_project_files(&self, expected: impl IntoIterator<Item = File>) {
-        let mut expected: HashSet<_> = expected.into_iter().collect();
-
-        let actual = self.db().project().files(self.db());
-        for file in &actual {
-            assert!(
-                expected.remove(&file),
-                "Indexed project files contains '{}' which was not expected.",
-                file.path(self.db())
-            );
-        }
-
-        if !expected.is_empty() {
-            let paths: Vec<_> = expected
-                .iter()
-                .map(|file| file.path(self.db()).as_str())
-                .collect();
-            panic!(
-                "Indexed project files are missing the following files: {:?}",
-                paths.join(", ")
-            );
-        }
+    fn collect_project_files(&self) -> Vec<File> {
+        let files = self.db().project().files(self.db());
+        let mut collected: Vec<_> = files.into_iter().collect();
+        collected.sort_unstable_by_key(|file| file.path(self.db()).as_system_path().unwrap());
+        collected
     }
 
     fn system_file(&self, path: impl AsRef<SystemPath>) -> Result<File, FileError> {
@@ -241,15 +222,13 @@ where
     }
 }
 
-trait Setup {
-    fn setup(self, context: &mut SetupContext) -> anyhow::Result<()>;
+trait SetupFiles {
+    fn setup(self, context: &SetupContext) -> anyhow::Result<()>;
 }
 
 struct SetupContext<'a> {
     system: &'a OsSystem,
     root_path: &'a SystemPath,
-    options: Option<Options>,
-    included_paths: Option<Vec<SystemPathBuf>>,
 }
 
 impl<'a> SetupContext<'a> {
@@ -272,77 +251,55 @@ impl<'a> SetupContext<'a> {
     fn join_root_path(&self, relative: impl AsRef<SystemPath>) -> SystemPathBuf {
         self.root_path().join(relative)
     }
-
-    fn write_project_file(
-        &self,
-        relative_path: impl AsRef<SystemPath>,
-        content: &str,
-    ) -> anyhow::Result<()> {
-        let relative_path = relative_path.as_ref();
-        let absolute_path = self.join_project_path(relative_path);
-        Self::write_file_impl(absolute_path, content)
-    }
-
-    fn write_file(
-        &self,
-        relative_path: impl AsRef<SystemPath>,
-        content: &str,
-    ) -> anyhow::Result<()> {
-        let relative_path = relative_path.as_ref();
-        let absolute_path = self.join_root_path(relative_path);
-        Self::write_file_impl(absolute_path, content)
-    }
-
-    fn write_file_impl(path: impl AsRef<SystemPath>, content: &str) -> anyhow::Result<()> {
-        let path = path.as_ref();
-        if let Some(parent) = path.parent() {
-            std::fs::create_dir_all(parent)
-                .with_context(|| format!("Failed to create parent directory for file `{path}`"))?;
-        }
-
-        let mut file = std::fs::File::create(path.as_std_path())
-            .with_context(|| format!("Failed to open file `{path}`"))?;
-        file.write_all(content.as_bytes())
-            .with_context(|| format!("Failed to write to file `{path}`"))?;
-        file.sync_data()?;
-
-        Ok(())
-    }
-
-    fn set_options(&mut self, options: Options) {
-        self.options = Some(options);
-    }
-
-    fn set_included_paths(&mut self, paths: Vec<SystemPathBuf>) {
-        self.included_paths = Some(paths);
-    }
 }
 
-impl<const N: usize, P> Setup for [(P, &'static str); N]
+impl<const N: usize, P> SetupFiles for [(P, &'static str); N]
 where
     P: AsRef<SystemPath>,
 {
-    fn setup(self, context: &mut SetupContext) -> anyhow::Result<()> {
+    fn setup(self, context: &SetupContext) -> anyhow::Result<()> {
         for (relative_path, content) in self {
-            context.write_project_file(relative_path, content)?;
+            let relative_path = relative_path.as_ref();
+            let absolute_path = context.join_project_path(relative_path);
+            if let Some(parent) = absolute_path.parent() {
+                std::fs::create_dir_all(parent).with_context(|| {
+                    format!("Failed to create parent directory for file `{relative_path}`")
+                })?;
+            }
+
+            let mut file = std::fs::File::create(absolute_path.as_std_path())
+                .with_context(|| format!("Failed to open file `{relative_path}`"))?;
+            file.write_all(content.as_bytes())
+                .with_context(|| format!("Failed to write to file `{relative_path}`"))?;
+            file.sync_data()?;
         }
 
         Ok(())
     }
 }
 
-impl<F> Setup for F
+impl<F> SetupFiles for F
 where
-    F: FnOnce(&mut SetupContext) -> anyhow::Result<()>,
+    F: FnOnce(&SetupContext) -> anyhow::Result<()>,
 {
-    fn setup(self, context: &mut SetupContext) -> anyhow::Result<()> {
+    fn setup(self, context: &SetupContext) -> anyhow::Result<()> {
         self(context)
     }
 }
 
 fn setup<F>(setup_files: F) -> anyhow::Result<TestCase>
 where
-    F: Setup,
+    F: SetupFiles,
+{
+    setup_with_options(setup_files, |_context| None)
+}
+
+fn setup_with_options<F>(
+    setup_files: F,
+    create_options: impl FnOnce(&SetupContext) -> Option<Options>,
+) -> anyhow::Result<TestCase>
+where
+    F: SetupFiles,
 {
     let temp_dir = tempfile::tempdir()?;
 
@@ -368,18 +325,16 @@ where
         .with_context(|| format!("Failed to create project directory `{project_path}`"))?;
 
     let system = OsSystem::new(&project_path);
-    let mut setup_context = SetupContext {
+    let setup_context = SetupContext {
         system: &system,
         root_path: &root_path,
-        options: None,
-        included_paths: None,
     };
 
     setup_files
-        .setup(&mut setup_context)
+        .setup(&setup_context)
         .context("Failed to setup test files")?;
 
-    if let Some(options) = setup_context.options {
+    if let Some(options) = create_options(&setup_context) {
         std::fs::write(
             project_path.join("pyproject.toml").as_std_path(),
             toml::to_string(&PyProject {
@@ -393,8 +348,6 @@ where
         .context("Failed to write configuration")?;
     }
 
-    let included_paths = setup_context.included_paths;
-
     let mut project = ProjectMetadata::discover(&project_path, &system)?;
     project.apply_configuration_files(&system)?;
 
@@ -410,11 +363,7 @@ where
             .with_context(|| format!("Failed to create search path `{path}`"))?;
     }
 
-    let mut db = ProjectDatabase::new(project, system)?;
-
-    if let Some(included_paths) = included_paths {
-        db.project().set_included_paths(&mut db, included_paths);
-    }
+    let db = ProjectDatabase::new(project, system)?;
 
     let (sender, receiver) = crossbeam::channel::unbounded();
     let watcher = directory_watcher(move |events| sender.send(events).unwrap())
@@ -476,7 +425,7 @@ fn new_file() -> anyhow::Result<()> {
     let foo_path = case.project_path("foo.py");
 
     assert_eq!(case.system_file(&foo_path), Err(FileError::NotFound));
-    case.assert_indexed_project_files([bar_file]);
+    assert_eq!(&case.collect_project_files(), &[bar_file]);
 
     std::fs::write(foo_path.as_std_path(), "print('Hello')")?;
 
@@ -486,7 +435,7 @@ fn new_file() -> anyhow::Result<()> {
 
     let foo = case.system_file(&foo_path).expect("foo.py to exist.");
 
-    case.assert_indexed_project_files([bar_file, foo]);
+    assert_eq!(&case.collect_project_files(), &[bar_file, foo]);
 
     Ok(())
 }
@@ -499,7 +448,7 @@ fn new_ignored_file() -> anyhow::Result<()> {
     let foo_path = case.project_path("foo.py");
 
     assert_eq!(case.system_file(&foo_path), Err(FileError::NotFound));
-    case.assert_indexed_project_files([bar_file]);
+    assert_eq!(&case.collect_project_files(), &[bar_file]);
 
     std::fs::write(foo_path.as_std_path(), "print('Hello')")?;
 
@@ -508,132 +457,7 @@ fn new_ignored_file() -> anyhow::Result<()> {
     case.apply_changes(changes);
 
     assert!(case.system_file(&foo_path).is_ok());
-    case.assert_indexed_project_files([bar_file]);
-
-    Ok(())
-}
-
-#[test]
-fn new_non_project_file() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
-        context.write_project_file("bar.py", "")?;
-        context.set_options(Options {
-            environment: Some(EnvironmentOptions {
-                extra_paths: Some(vec![RelativePathBuf::cli(
-                    context.join_root_path("site_packages"),
-                )]),
-                ..EnvironmentOptions::default()
-            }),
-            ..Options::default()
-        });
-
-        Ok(())
-    })?;
-
-    let bar_path = case.project_path("bar.py");
-    let bar_file = case.system_file(&bar_path).unwrap();
-
-    case.assert_indexed_project_files([bar_file]);
-
-    // Add a file to site packages
-    let black_path = case.root_path().join("site_packages/black.py");
-    std::fs::write(black_path.as_std_path(), "print('Hello')")?;
-
-    let changes = case.stop_watch(event_for_file("black.py"));
-
-    case.apply_changes(changes);
-
-    assert!(case.system_file(&black_path).is_ok());
-
-    // The file should not have been added to the project files
-    case.assert_indexed_project_files([bar_file]);
-
-    Ok(())
-}
-
-#[test]
-fn new_files_with_explicit_included_paths() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
-        context.write_project_file("src/main.py", "")?;
-        context.write_project_file("src/sub/__init__.py", "")?;
-        context.write_project_file("src/test.py", "")?;
-        context.set_included_paths(vec![
-            context.join_project_path("src/main.py"),
-            context.join_project_path("src/sub"),
-        ]);
-        Ok(())
-    })?;
-
-    let main_path = case.project_path("src/main.py");
-    let main_file = case.system_file(&main_path).unwrap();
-
-    let sub_init_path = case.project_path("src/sub/__init__.py");
-    let sub_init = case.system_file(&sub_init_path).unwrap();
-
-    case.assert_indexed_project_files([main_file, sub_init]);
-
-    // Write a new file to `sub` which is an included path
-    let sub_a_path = case.project_path("src/sub/a.py");
-    std::fs::write(sub_a_path.as_std_path(), "print('Hello')")?;
-
-    // and write a second file in the root directory -- this should not be included
-    let test2_path = case.project_path("src/test2.py");
-    std::fs::write(test2_path.as_std_path(), "print('Hello')")?;
-
-    let changes = case.stop_watch(event_for_file("test2.py"));
-
-    case.apply_changes(changes);
-
-    let sub_a_file = case.system_file(&sub_a_path).expect("sub/a.py to exist");
-
-    case.assert_indexed_project_files([main_file, sub_init, sub_a_file]);
-
-    Ok(())
-}
-
-#[test]
-fn new_file_in_included_out_of_project_directory() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
-        context.write_project_file("src/main.py", "")?;
-        context.write_project_file("script.py", "")?;
-        context.write_file("outside_project/a.py", "")?;
-
-        context.set_included_paths(vec![
-            context.join_root_path("outside_project"),
-            context.join_project_path("src"),
-        ]);
-        Ok(())
-    })?;
-
-    let main_path = case.project_path("src/main.py");
-    let main_file = case.system_file(&main_path).unwrap();
-
-    let outside_a_path = case.root_path().join("outside_project/a.py");
-    let outside_a = case.system_file(&outside_a_path).unwrap();
-
-    case.assert_indexed_project_files([outside_a, main_file]);
-
-    // Write a new file to `src` which should be watched
-    let src_a = case.project_path("src/a.py");
-    std::fs::write(src_a.as_std_path(), "print('Hello')")?;
-
-    // and write a second file to `outside_project` which should be watched too
-    let outside_b_path = case.root_path().join("outside_project/b.py");
-    std::fs::write(outside_b_path.as_std_path(), "print('Hello')")?;
-
-    // and a third file in the project's root that should not be included
-    let script2_path = case.project_path("script2.py");
-    std::fs::write(script2_path.as_std_path(), "print('Hello')")?;
-
-    let changes = case.stop_watch(event_for_file("script2.py"));
-
-    case.apply_changes(changes);
-
-    let src_a_file = case.system_file(&src_a).unwrap();
-    let outside_b_file = case.system_file(&outside_b_path).unwrap();
-
-    // The file should not have been added to the project files
-    case.assert_indexed_project_files([main_file, outside_a, outside_b_file, src_a_file]);
+    assert_eq!(&case.collect_project_files(), &[bar_file]);
 
     Ok(())
 }
@@ -646,7 +470,7 @@ fn changed_file() -> anyhow::Result<()> {
 
     let foo = case.system_file(&foo_path)?;
     assert_eq!(source_text(case.db(), foo).as_str(), foo_source);
-    case.assert_indexed_project_files([foo]);
+    assert_eq!(&case.collect_project_files(), &[foo]);
 
     update_file(&foo_path, "print('Version 2')")?;
 
@@ -657,7 +481,7 @@ fn changed_file() -> anyhow::Result<()> {
     case.apply_changes(changes);
 
     assert_eq!(source_text(case.db(), foo).as_str(), "print('Version 2')");
-    case.assert_indexed_project_files([foo]);
+    assert_eq!(&case.collect_project_files(), &[foo]);
 
     Ok(())
 }
@@ -671,7 +495,7 @@ fn deleted_file() -> anyhow::Result<()> {
     let foo = case.system_file(&foo_path)?;
 
     assert!(foo.exists(case.db()));
-    case.assert_indexed_project_files([foo]);
+    assert_eq!(&case.collect_project_files(), &[foo]);
 
     std::fs::remove_file(foo_path.as_std_path())?;
 
@@ -680,7 +504,7 @@ fn deleted_file() -> anyhow::Result<()> {
     case.apply_changes(changes);
 
     assert!(!foo.exists(case.db()));
-    case.assert_indexed_project_files([]);
+    assert_eq!(&case.collect_project_files(), &[] as &[File]);
 
     Ok(())
 }
@@ -700,7 +524,7 @@ fn move_file_to_trash() -> anyhow::Result<()> {
     let foo = case.system_file(&foo_path)?;
 
     assert!(foo.exists(case.db()));
-    case.assert_indexed_project_files([foo]);
+    assert_eq!(&case.collect_project_files(), &[foo]);
 
     std::fs::rename(
         foo_path.as_std_path(),
@@ -712,7 +536,7 @@ fn move_file_to_trash() -> anyhow::Result<()> {
     case.apply_changes(changes);
 
     assert!(!foo.exists(case.db()));
-    case.assert_indexed_project_files([]);
+    assert_eq!(&case.collect_project_files(), &[] as &[File]);
 
     Ok(())
 }
@@ -730,7 +554,7 @@ fn move_file_to_project() -> anyhow::Result<()> {
     let foo_in_project = case.project_path("foo.py");
 
     assert!(case.system_file(&foo_path).is_ok());
-    case.assert_indexed_project_files([bar]);
+    assert_eq!(&case.collect_project_files(), &[bar]);
 
     std::fs::rename(foo_path.as_std_path(), foo_in_project.as_std_path())?;
 
@@ -741,7 +565,7 @@ fn move_file_to_project() -> anyhow::Result<()> {
     let foo_in_project = case.system_file(&foo_in_project)?;
 
     assert!(foo_in_project.exists(case.db()));
-    case.assert_indexed_project_files([bar, foo_in_project]);
+    assert_eq!(&case.collect_project_files(), &[bar, foo_in_project]);
 
     Ok(())
 }
@@ -755,7 +579,7 @@ fn rename_file() -> anyhow::Result<()> {
 
     let foo = case.system_file(&foo_path)?;
 
-    case.assert_indexed_project_files([foo]);
+    assert_eq!(case.collect_project_files(), [foo]);
 
     std::fs::rename(foo_path.as_std_path(), bar_path.as_std_path())?;
 
@@ -768,7 +592,7 @@ fn rename_file() -> anyhow::Result<()> {
     let bar = case.system_file(&bar_path)?;
 
     assert!(bar.exists(case.db()));
-    case.assert_indexed_project_files([bar]);
+    assert_eq!(case.collect_project_files(), [bar]);
 
     Ok(())
 }
@@ -794,7 +618,7 @@ fn directory_moved_to_project() -> anyhow::Result<()> {
     );
 
     assert_eq!(sub_a_module, None);
-    case.assert_indexed_project_files([bar]);
+    assert_eq!(case.collect_project_files(), &[bar]);
 
     let sub_new_path = case.project_path("sub");
     std::fs::rename(sub_original_path.as_std_path(), sub_new_path.as_std_path())
@@ -818,7 +642,7 @@ fn directory_moved_to_project() -> anyhow::Result<()> {
     )
     .is_some());
 
-    case.assert_indexed_project_files([bar, init_file, a_file]);
+    assert_eq!(case.collect_project_files(), &[bar, init_file, a_file]);
 
     Ok(())
 }
@@ -846,7 +670,7 @@ fn directory_moved_to_trash() -> anyhow::Result<()> {
         .system_file(sub_path.join("a.py"))
         .expect("a.py to exist");
 
-    case.assert_indexed_project_files([bar, init_file, a_file]);
+    assert_eq!(case.collect_project_files(), &[bar, init_file, a_file]);
 
     std::fs::create_dir(case.root_path().join(".trash").as_std_path())?;
     let trashed_sub = case.root_path().join(".trash/sub");
@@ -867,7 +691,7 @@ fn directory_moved_to_trash() -> anyhow::Result<()> {
     assert!(!init_file.exists(case.db()));
     assert!(!a_file.exists(case.db()));
 
-    case.assert_indexed_project_files([bar]);
+    assert_eq!(case.collect_project_files(), &[bar]);
 
     Ok(())
 }
@@ -901,7 +725,7 @@ fn directory_renamed() -> anyhow::Result<()> {
         .system_file(sub_path.join("a.py"))
         .expect("a.py to exist");
 
-    case.assert_indexed_project_files([bar, sub_init, sub_a]);
+    assert_eq!(case.collect_project_files(), &[bar, sub_init, sub_a]);
 
     let foo_baz = case.project_path("foo/baz");
 
@@ -943,7 +767,10 @@ fn directory_renamed() -> anyhow::Result<()> {
     assert!(foo_baz_init.exists(case.db()));
     assert!(foo_baz_a.exists(case.db()));
 
-    case.assert_indexed_project_files([bar, foo_baz_init, foo_baz_a]);
+    assert_eq!(
+        case.collect_project_files(),
+        &[bar, foo_baz_init, foo_baz_a]
+    );
 
     Ok(())
 }
@@ -972,7 +799,7 @@ fn directory_deleted() -> anyhow::Result<()> {
     let a_file = case
         .system_file(sub_path.join("a.py"))
         .expect("a.py to exist");
-    case.assert_indexed_project_files([bar, init_file, a_file]);
+    assert_eq!(case.collect_project_files(), &[bar, init_file, a_file]);
 
     std::fs::remove_dir_all(sub_path.as_std_path())
         .with_context(|| "Failed to remove the sub directory")?;
@@ -990,17 +817,15 @@ fn directory_deleted() -> anyhow::Result<()> {
 
     assert!(!init_file.exists(case.db()));
     assert!(!a_file.exists(case.db()));
-    case.assert_indexed_project_files([bar]);
+    assert_eq!(case.collect_project_files(), &[bar]);
 
     Ok(())
 }
 
 #[test]
 fn search_path() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
-        context.write_project_file("bar.py", "import sub.a")?;
-
-        context.set_options(Options {
+    let mut case = setup_with_options([("bar.py", "import sub.a")], |context| {
+        Some(Options {
             environment: Some(EnvironmentOptions {
                 extra_paths: Some(vec![RelativePathBuf::cli(
                     context.join_root_path("site_packages"),
@@ -1008,8 +833,7 @@ fn search_path() -> anyhow::Result<()> {
                 ..EnvironmentOptions::default()
             }),
             ..Options::default()
-        });
-        Ok(())
+        })
     })?;
 
     let site_packages = case.root_path().join("site_packages");
@@ -1026,7 +850,10 @@ fn search_path() -> anyhow::Result<()> {
     case.apply_changes(changes);
 
     assert!(resolve_module(case.db().upcast(), &ModuleName::new_static("a").unwrap()).is_some());
-    case.assert_indexed_project_files([case.system_file(case.project_path("bar.py")).unwrap()]);
+    assert_eq!(
+        case.collect_project_files(),
+        &[case.system_file(case.project_path("bar.py")).unwrap()]
+    );
 
     Ok(())
 }
@@ -1063,9 +890,8 @@ fn add_search_path() -> anyhow::Result<()> {
 
 #[test]
 fn remove_search_path() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
-        context.write_project_file("bar.py", "import sub.a")?;
-        context.set_options(Options {
+    let mut case = setup_with_options([("bar.py", "import sub.a")], |context| {
+        Some(Options {
             environment: Some(EnvironmentOptions {
                 extra_paths: Some(vec![RelativePathBuf::cli(
                     context.join_root_path("site_packages"),
@@ -1073,9 +899,7 @@ fn remove_search_path() -> anyhow::Result<()> {
                 ..EnvironmentOptions::default()
             }),
             ..Options::default()
-        });
-
-        Ok(())
+        })
     })?;
 
     // Remove site packages from the search path settings.
@@ -1098,30 +922,30 @@ fn remove_search_path() -> anyhow::Result<()> {
 
 #[test]
 fn change_python_version_and_platform() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
+    let mut case = setup_with_options(
         // `sys.last_exc` is a Python 3.12 only feature
         // `os.getegid()` is Unix only
-        context.write_project_file(
+        [(
             "bar.py",
             r#"
 import sys
 import os
 print(sys.last_exc, os.getegid())
 "#,
-        )?;
-        context.set_options(Options {
-            environment: Some(EnvironmentOptions {
-                python_version: Some(RangedValue::cli(PythonVersion::PY311)),
-                python_platform: Some(RangedValue::cli(PythonPlatform::Identifier(
-                    "win32".to_string(),
-                ))),
-                ..EnvironmentOptions::default()
-            }),
-            ..Options::default()
-        });
-
-        Ok(())
-    })?;
+        )],
+        |_context| {
+            Some(Options {
+                environment: Some(EnvironmentOptions {
+                    python_version: Some(RangedValue::cli(PythonVersion::PY311)),
+                    python_platform: Some(RangedValue::cli(PythonPlatform::Identifier(
+                        "win32".to_string(),
+                    ))),
+                    ..EnvironmentOptions::default()
+                }),
+                ..Options::default()
+            })
+        },
+    )?;
 
     let diagnostics = case.db.check().context("Failed to check project.")?;
 
@@ -1156,35 +980,38 @@ print(sys.last_exc, os.getegid())
 
 #[test]
 fn changed_versions_file() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
-        std::fs::write(
-            context.join_project_path("bar.py").as_std_path(),
-            "import sub.a",
-        )?;
-        std::fs::create_dir_all(context.join_root_path("typeshed/stdlib").as_std_path())?;
-        std::fs::write(
-            context
-                .join_root_path("typeshed/stdlib/VERSIONS")
-                .as_std_path(),
-            "",
-        )?;
-        std::fs::write(
-            context
-                .join_root_path("typeshed/stdlib/os.pyi")
-                .as_std_path(),
-            "# not important",
-        )?;
+    let mut case = setup_with_options(
+        |context: &SetupContext| {
+            std::fs::write(
+                context.join_project_path("bar.py").as_std_path(),
+                "import sub.a",
+            )?;
+            std::fs::create_dir_all(context.join_root_path("typeshed/stdlib").as_std_path())?;
+            std::fs::write(
+                context
+                    .join_root_path("typeshed/stdlib/VERSIONS")
+                    .as_std_path(),
+                "",
+            )?;
+            std::fs::write(
+                context
+                    .join_root_path("typeshed/stdlib/os.pyi")
+                    .as_std_path(),
+                "# not important",
+            )?;
 
-        context.set_options(Options {
-            environment: Some(EnvironmentOptions {
-                typeshed: Some(RelativePathBuf::cli(context.join_root_path("typeshed"))),
-                ..EnvironmentOptions::default()
-            }),
-            ..Options::default()
-        });
-
-        Ok(())
-    })?;
+            Ok(())
+        },
+        |context| {
+            Some(Options {
+                environment: Some(EnvironmentOptions {
+                    typeshed: Some(RelativePathBuf::cli(context.join_root_path("typeshed"))),
+                    ..EnvironmentOptions::default()
+                }),
+                ..Options::default()
+            })
+        },
+    )?;
 
     // Unset the custom typeshed directory.
     assert_eq!(
@@ -1229,7 +1056,7 @@ fn changed_versions_file() -> anyhow::Result<()> {
 /// we're seeing is that Windows only emits a single event, similar to Linux.
 #[test]
 fn hard_links_in_project() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
+    let mut case = setup(|context: &SetupContext| {
         let foo_path = context.join_project_path("foo.py");
         std::fs::write(foo_path.as_std_path(), "print('Version 1')")?;
 
@@ -1248,7 +1075,6 @@ fn hard_links_in_project() -> anyhow::Result<()> {
 
     assert_eq!(source_text(case.db(), foo).as_str(), "print('Version 1')");
     assert_eq!(source_text(case.db(), bar).as_str(), "print('Version 1')");
-    case.assert_indexed_project_files([bar, foo]);
 
     // Write to the hard link target.
     update_file(foo_path, "print('Version 2')").context("Failed to update foo.py")?;
@@ -1301,7 +1127,7 @@ fn hard_links_in_project() -> anyhow::Result<()> {
     ignore = "windows doesn't support observing changes to hard linked files."
 )]
 fn hard_links_to_target_outside_project() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
+    let mut case = setup(|context: &SetupContext| {
         let foo_path = context.join_root_path("foo.py");
         std::fs::write(foo_path.as_std_path(), "print('Version 1')")?;
 
@@ -1409,7 +1235,7 @@ mod unix {
         ignore = "FSEvents doesn't emit change events for symlinked directories outside of the watched paths."
     )]
     fn symlink_target_outside_watched_paths() -> anyhow::Result<()> {
-        let mut case = setup(|context: &mut SetupContext| {
+        let mut case = setup(|context: &SetupContext| {
             // Set up the symlink target.
             let link_target = context.join_root_path("bar");
             std::fs::create_dir_all(link_target.as_std_path())
@@ -1490,7 +1316,7 @@ mod unix {
     /// ```
     #[test]
     fn symlink_inside_project() -> anyhow::Result<()> {
-        let mut case = setup(|context: &mut SetupContext| {
+        let mut case = setup(|context: &SetupContext| {
             // Set up the symlink target.
             let link_target = context.join_project_path("patched/bar");
             std::fs::create_dir_all(link_target.as_std_path())
@@ -1528,8 +1354,6 @@ mod unix {
         );
         assert_eq!(baz.file().path(case.db()).as_system_path(), Some(&*bar_baz));
 
-        case.assert_indexed_project_files([patched_bar_baz_file]);
-
         // Write to the symlink target.
         update_file(&patched_bar_baz, "def baz(): print('Version 2')")
             .context("Failed to update bar/baz.py")?;
@@ -1565,7 +1389,6 @@ mod unix {
             bar_baz_text = bar_baz_text.as_str()
         );
 
-        case.assert_indexed_project_files([patched_bar_baz_file]);
         Ok(())
     }
 
@@ -1583,39 +1406,43 @@ mod unix {
     /// ```
     #[test]
     fn symlinked_module_search_path() -> anyhow::Result<()> {
-        let mut case = setup(|context: &mut SetupContext| {
-            // Set up the symlink target.
-            let site_packages = context.join_root_path("site-packages");
-            let bar = site_packages.join("bar");
-            std::fs::create_dir_all(bar.as_std_path()).context("Failed to create bar directory")?;
-            let baz_original = bar.join("baz.py");
-            std::fs::write(baz_original.as_std_path(), "def baz(): ...")
-                .context("Failed to write baz.py")?;
+        let mut case = setup_with_options(
+            |context: &SetupContext| {
+                // Set up the symlink target.
+                let site_packages = context.join_root_path("site-packages");
+                let bar = site_packages.join("bar");
+                std::fs::create_dir_all(bar.as_std_path())
+                    .context("Failed to create bar directory")?;
+                let baz_original = bar.join("baz.py");
+                std::fs::write(baz_original.as_std_path(), "def baz(): ...")
+                    .context("Failed to write baz.py")?;
 
-            // Symlink the site packages in the venv to the global site packages
-            let venv_site_packages =
-                context.join_project_path(".venv/lib/python3.12/site-packages");
-            std::fs::create_dir_all(venv_site_packages.parent().unwrap())
-                .context("Failed to create .venv directory")?;
-            std::os::unix::fs::symlink(
-                site_packages.as_std_path(),
-                venv_site_packages.as_std_path(),
-            )
-            .context("Failed to create symlink to site-packages")?;
+                // Symlink the site packages in the venv to the global site packages
+                let venv_site_packages =
+                    context.join_project_path(".venv/lib/python3.12/site-packages");
+                std::fs::create_dir_all(venv_site_packages.parent().unwrap())
+                    .context("Failed to create .venv directory")?;
+                std::os::unix::fs::symlink(
+                    site_packages.as_std_path(),
+                    venv_site_packages.as_std_path(),
+                )
+                .context("Failed to create symlink to site-packages")?;
 
-            context.set_options(Options {
-                environment: Some(EnvironmentOptions {
-                    extra_paths: Some(vec![RelativePathBuf::cli(
-                        ".venv/lib/python3.12/site-packages",
-                    )]),
-                    python_version: Some(RangedValue::cli(PythonVersion::PY312)),
-                    ..EnvironmentOptions::default()
-                }),
-                ..Options::default()
-            });
-
-            Ok(())
-        })?;
+                Ok(())
+            },
+            |_context| {
+                Some(Options {
+                    environment: Some(EnvironmentOptions {
+                        extra_paths: Some(vec![RelativePathBuf::cli(
+                            ".venv/lib/python3.12/site-packages",
+                        )]),
+                        python_version: Some(RangedValue::cli(PythonVersion::PY312)),
+                        ..EnvironmentOptions::default()
+                    }),
+                    ..Options::default()
+                })
+            },
+        )?;
 
         let baz = resolve_module(
             case.db().upcast(),
@@ -1642,8 +1469,6 @@ mod unix {
             Some(&*baz_original)
         );
 
-        case.assert_indexed_project_files([]);
-
         // Write to the symlink target.
         update_file(&baz_original, "def baz(): print('Version 2')")
             .context("Failed to update bar/baz.py")?;
@@ -1669,15 +1494,13 @@ mod unix {
             "def baz(): print('Version 2')"
         );
 
-        case.assert_indexed_project_files([]);
-
         Ok(())
     }
 }
 
 #[test]
 fn nested_projects_delete_root() -> anyhow::Result<()> {
-    let mut case = setup(|context: &mut SetupContext| {
+    let mut case = setup(|context: &SetupContext| {
         std::fs::write(
             context.join_project_path("pyproject.toml").as_std_path(),
             r#"
@@ -1719,7 +1542,7 @@ fn nested_projects_delete_root() -> anyhow::Result<()> {
 fn changes_to_user_configuration() -> anyhow::Result<()> {
     let mut _config_dir_override: Option<UserConfigDirectoryOverrideGuard> = None;
 
-    let mut case = setup(|context: &mut SetupContext| {
+    let mut case = setup(|context: &SetupContext| {
         std::fs::write(
             context.join_project_path("pyproject.toml").as_std_path(),
             r#"

crates/red_knot_project/src/combine.rs

@@ -1,6 +1,6 @@
 use std::{collections::HashMap, hash::BuildHasher};
 
-use red_knot_python_semantic::{PythonPath, PythonPlatform};
+use red_knot_python_semantic::{PythonPlatform, SitePackages};
 use ruff_db::system::SystemPathBuf;
 use ruff_python_ast::PythonVersion;
 
@@ -128,7 +128,7 @@ macro_rules! impl_noop_combine {
 
 impl_noop_combine!(SystemPathBuf);
 impl_noop_combine!(PythonPlatform);
-impl_noop_combine!(PythonPath);
+impl_noop_combine!(SitePackages);
 impl_noop_combine!(PythonVersion);
 
 // std types

crates/red_knot_project/src/db.rs

@@ -5,7 +5,7 @@ use crate::DEFAULT_LINT_REGISTRY;
 use crate::{Project, ProjectMetadata};
 use red_knot_python_semantic::lint::{LintRegistry, RuleSelection};
 use red_knot_python_semantic::{Db as SemanticDb, Program};
-use ruff_db::diagnostic::OldDiagnosticTrait;
+use ruff_db::diagnostic::Diagnostic;
 use ruff_db::files::{File, Files};
 use ruff_db::system::System;
 use ruff_db::vendored::VendoredFileSystem;
@@ -55,11 +55,11 @@ impl ProjectDatabase {
     }
 
     /// Checks all open files in the project and its dependencies.
-    pub fn check(&self) -> Result<Vec<Box<dyn OldDiagnosticTrait>>, Cancelled> {
+    pub fn check(&self) -> Result<Vec<Box<dyn Diagnostic>>, Cancelled> {
         self.with_db(|db| db.project().check(db))
     }
 
-    pub fn check_file(&self, file: File) -> Result<Vec<Box<dyn OldDiagnosticTrait>>, Cancelled> {
+    pub fn check_file(&self, file: File) -> Result<Vec<Box<dyn Diagnostic>>, Cancelled> {
         let _span = tracing::debug_span!("check_file", file=%file.path(self)).entered();
 
         self.with_db(|db| self.project().check_file(db, file))

crates/red_knot_project/src/db/changes.rs

@@ -2,20 +2,20 @@ use crate::db::{Db, ProjectDatabase};
 use crate::metadata::options::Options;
 use crate::watch::{ChangeEvent, CreatedKind, DeletedKind};
 use crate::{Project, ProjectMetadata};
-use std::collections::BTreeSet;
 
-use crate::walk::ProjectFilesWalker;
 use red_knot_python_semantic::Program;
-use ruff_db::files::{File, Files};
+use ruff_db::files::{system_path_to_file, File, Files};
+use ruff_db::system::walk_directory::WalkState;
 use ruff_db::system::SystemPath;
 use ruff_db::Db as _;
+use ruff_python_ast::PySourceType;
 use rustc_hash::FxHashSet;
 
 impl ProjectDatabase {
     #[tracing::instrument(level = "debug", skip(self, changes, cli_options))]
     pub fn apply_changes(&mut self, changes: Vec<ChangeEvent>, cli_options: Option<&Options>) {
         let mut project = self.project();
-        let project_root = project.root(self).to_path_buf();
+        let project_path = project.root(self).to_path_buf();
         let program = Program::get(self);
         let custom_stdlib_versions_path = program
             .custom_stdlib_search_path(self)
@@ -30,7 +30,7 @@ impl ProjectDatabase {
 
         // Deduplicate the `sync` calls. Many file watchers emit multiple events for the same path.
         let mut synced_files = FxHashSet::default();
-        let mut sync_recursively = BTreeSet::default();
+        let mut synced_recursively = FxHashSet::default();
 
         let mut sync_path = |db: &mut ProjectDatabase, path: &SystemPath| {
             if synced_files.insert(path.to_path_buf()) {
@@ -38,9 +38,13 @@ impl ProjectDatabase {
             }
         };
 
-        for change in changes {
-            tracing::trace!("Handle change: {:?}", change);
+        let mut sync_recursively = |db: &mut ProjectDatabase, path: &SystemPath| {
+            if synced_recursively.insert(path.to_path_buf()) {
+                Files::sync_recursively(db, path);
+            }
+        };
 
+        for change in changes {
             if let Some(path) = change.system_path() {
                 if matches!(
                     path.file_name(),
@@ -66,27 +70,16 @@ impl ProjectDatabase {
                     match kind {
                         CreatedKind::File => sync_path(self, &path),
                         CreatedKind::Directory | CreatedKind::Any => {
-                            sync_recursively.insert(path.clone());
+                            sync_recursively(self, &path);
                         }
                     }
 
-                    // Unlike other files, it's not only important to update the status of existing
-                    // and known `File`s (`sync_recursively`), it's also important to discover new files
-                    // that were added in the project's root (or any of the paths included for checking).
-                    //
-                    // This is important because `Project::check` iterates over all included files.
-                    // The code below walks the `added_paths` and adds all files that
-                    // should be included in the project. We can skip this check for
-                    // paths that aren't part of the project or shouldn't be included
-                    // when checking the project.
-                    if project.is_path_included(self, &path) {
-                        if self.system().is_file(&path) {
-                            // Add the parent directory because `walkdir` always visits explicitly passed files
-                            // even if they match an exclude filter.
-                            added_paths.insert(path.parent().unwrap().to_path_buf());
-                        } else {
-                            added_paths.insert(path);
-                        }
+                    if self.system().is_file(&path) {
+                        // Add the parent directory because `walkdir` always visits explicitly passed files
+                        // even if they match an exclude filter.
+                        added_paths.insert(path.parent().unwrap().to_path_buf());
+                    } else {
+                        added_paths.insert(path);
                     }
                 }
 
@@ -110,7 +103,7 @@ impl ProjectDatabase {
                             project.remove_file(self, file);
                         }
                     } else {
-                        sync_recursively.insert(path.clone());
+                        sync_recursively(self, &path);
 
                         if custom_stdlib_versions_path
                             .as_ref()
@@ -119,19 +112,11 @@ impl ProjectDatabase {
                             custom_stdlib_change = true;
                         }
 
-                        if project.is_path_included(self, &path) || path == project_root {
-                            // TODO: Shouldn't it be enough to simply traverse the project files and remove all
-                            // that start with the given path?
-                            tracing::debug!(
-                                "Reload project because of a path that could have been a directory."
-                            );
-
-                            // Perform a full-reload in case the deleted directory contained the pyproject.toml.
-                            // We may want to make this more clever in the future, to e.g. iterate over the
-                            // indexed files and remove the once that start with the same path, unless
-                            // the deleted path is the project configuration.
-                            project_changed = true;
-                        }
+                        // Perform a full-reload in case the deleted directory contained the pyproject.toml.
+                        // We may want to make this more clever in the future, to e.g. iterate over the
+                        // indexed files and remove the once that start with the same path, unless
+                        // the deleted path is the project configuration.
+                        project_changed = true;
                     }
                 }
 
@@ -148,29 +133,13 @@ impl ProjectDatabase {
                 ChangeEvent::Rescan => {
                     project_changed = true;
                     Files::sync_all(self);
-                    sync_recursively.clear();
                     break;
                 }
             }
         }
 
-        let sync_recursively = sync_recursively.into_iter();
-        let mut last = None;
-
-        for path in sync_recursively {
-            // Avoid re-syncing paths that are sub-paths of each other.
-            if let Some(last) = &last {
-                if path.starts_with(last) {
-                    continue;
-                }
-            }
-
-            Files::sync_recursively(self, &path);
-            last = Some(path);
-        }
-
         if project_changed {
-            match ProjectMetadata::discover(&project_root, self.system()) {
+            match ProjectMetadata::discover(&project_path, self.system()) {
                 Ok(mut metadata) => {
                     if let Some(cli_options) = cli_options {
                         metadata.apply_cli_options(cli_options.clone());
@@ -217,24 +186,50 @@ impl ProjectDatabase {
             }
         }
 
-        let diagnostics = if let Some(walker) = ProjectFilesWalker::incremental(self, added_paths) {
-            // Use directory walking to discover newly added files.
-            let (files, diagnostics) = walker.collect_vec(self);
+        let mut added_paths = added_paths.into_iter();
 
-            for file in files {
-                project.add_file(self, file);
+        // Use directory walking to discover newly added files.
+        if let Some(path) = added_paths.next() {
+            let mut walker = self.system().walk_directory(&path);
+
+            for extra_path in added_paths {
+                walker = walker.add(&extra_path);
             }
 
-            diagnostics
-        } else {
-            Vec::new()
-        };
+            let added_paths = std::sync::Mutex::new(Vec::default());
 
-        // Note: We simply replace all IO related diagnostics here. This isn't ideal, because
-        // it removes IO errors that may still be relevant. However, tracking IO errors correctly
-        // across revisions doesn't feel essential, considering that they're rare. However, we could
-        // implement a `BTreeMap` or similar and only prune the diagnostics from paths that we've
-        // re-scanned (or that were removed etc).
-        project.replace_index_diagnostics(self, diagnostics);
+            walker.run(|| {
+                Box::new(|entry| {
+                    let Ok(entry) = entry else {
+                        return WalkState::Continue;
+                    };
+
+                    if !entry.file_type().is_file() {
+                        return WalkState::Continue;
+                    }
+
+                    if entry
+                        .path()
+                        .extension()
+                        .and_then(PySourceType::try_from_extension)
+                        .is_some()
+                    {
+                        let mut paths = added_paths.lock().unwrap();
+
+                        paths.push(entry.into_path());
+                    }
+
+                    WalkState::Continue
+                })
+            });
+
+            for path in added_paths.into_inner().unwrap() {
+                let file = system_path_to_file(self, &path);
+
+                if let Ok(file) = file {
+                    project.add_file(self, file);
+                }
+            }
+        }
     }
 }

crates/red_knot_project/src/files.rs

@@ -8,7 +8,10 @@ use salsa::Setter;
 use ruff_db::files::File;
 
 use crate::db::Db;
-use crate::{IOErrorDiagnostic, Project};
+use crate::Project;
+
+/// Cheap cloneable hash set of files.
+type FileSet = Arc<FxHashSet<File>>;
 
 /// The indexed files of a project.
 ///
@@ -32,9 +35,9 @@ impl IndexedFiles {
         }
     }
 
-    fn indexed(inner: Arc<IndexedInner>) -> Self {
+    fn indexed(files: FileSet) -> Self {
         Self {
-            state: std::sync::Mutex::new(State::Indexed(inner)),
+            state: std::sync::Mutex::new(State::Indexed(files)),
         }
     }
 
@@ -43,8 +46,8 @@ impl IndexedFiles {
 
         match &*state {
             State::Lazy => Index::Lazy(LazyFiles { files: state }),
-            State::Indexed(inner) => Index::Indexed(Indexed {
-                inner: Arc::clone(inner),
+            State::Indexed(files) => Index::Indexed(Indexed {
+                files: Arc::clone(files),
                 _lifetime: PhantomData,
             }),
         }
@@ -91,7 +94,7 @@ impl IndexedFiles {
         Some(IndexedMut {
             db: Some(db),
             project,
-            indexed,
+            files: indexed,
             did_change: false,
         })
     }
@@ -109,7 +112,7 @@ enum State {
     Lazy,
 
     /// The files are indexed. Stores the known files of a package.
-    Indexed(Arc<IndexedInner>),
+    Indexed(FileSet),
 }
 
 pub(super) enum Index<'db> {
@@ -126,48 +129,32 @@ pub(super) struct LazyFiles<'db> {
 
 impl<'db> LazyFiles<'db> {
     /// Sets the indexed files of a package to `files`.
-    pub(super) fn set(
-        mut self,
-        files: FxHashSet<File>,
-        diagnostics: Vec<IOErrorDiagnostic>,
-    ) -> Indexed<'db> {
+    pub(super) fn set(mut self, files: FxHashSet<File>) -> Indexed<'db> {
         let files = Indexed {
-            inner: Arc::new(IndexedInner { files, diagnostics }),
+            files: Arc::new(files),
             _lifetime: PhantomData,
         };
-        *self.files = State::Indexed(Arc::clone(&files.inner));
+        *self.files = State::Indexed(Arc::clone(&files.files));
         files
     }
 }
 
-/// The indexed files of the project.
+/// The indexed files of a package.
 ///
 /// Note: This type is intentionally non-cloneable. Making it cloneable requires
 /// revisiting the locking behavior in [`IndexedFiles::indexed_mut`].
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Eq)]
 pub struct Indexed<'db> {
-    inner: Arc<IndexedInner>,
+    files: FileSet,
     // Preserve the lifetime of `PackageFiles`.
     _lifetime: PhantomData<&'db ()>,
 }
 
-#[derive(Debug)]
-struct IndexedInner {
-    files: FxHashSet<File>,
-    diagnostics: Vec<IOErrorDiagnostic>,
-}
-
-impl Indexed<'_> {
-    pub(super) fn diagnostics(&self) -> &[IOErrorDiagnostic] {
-        &self.inner.diagnostics
-    }
-}
-
 impl Deref for Indexed<'_> {
     type Target = FxHashSet<File>;
 
     fn deref(&self) -> &Self::Target {
-        &self.inner.files
+        &self.files
     }
 }
 
@@ -178,7 +165,7 @@ impl<'a> IntoIterator for &'a Indexed<'_> {
     type IntoIter = IndexedIter<'a>;
 
     fn into_iter(self) -> Self::IntoIter {
-        self.inner.files.iter().copied()
+        self.files.iter().copied()
     }
 }
 
@@ -189,13 +176,13 @@ impl<'a> IntoIterator for &'a Indexed<'_> {
 pub(super) struct IndexedMut<'db> {
     db: Option<&'db mut dyn Db>,
     project: Project,
-    indexed: Arc<IndexedInner>,
+    files: FileSet,
     did_change: bool,
 }
 
 impl IndexedMut<'_> {
     pub(super) fn insert(&mut self, file: File) -> bool {
-        if self.inner_mut().files.insert(file) {
+        if self.files_mut().insert(file) {
             self.did_change = true;
             true
         } else {
@@ -204,7 +191,7 @@ impl IndexedMut<'_> {
     }
 
     pub(super) fn remove(&mut self, file: File) -> bool {
-        if self.inner_mut().files.remove(&file) {
+        if self.files_mut().remove(&file) {
             self.did_change = true;
             true
         } else {
@@ -212,13 +199,8 @@ impl IndexedMut<'_> {
         }
     }
 
-    pub(super) fn set_diagnostics(&mut self, diagnostics: Vec<IOErrorDiagnostic>) {
-        self.inner_mut().diagnostics = diagnostics;
-    }
-
-    fn inner_mut(&mut self) -> &mut IndexedInner {
-        Arc::get_mut(&mut self.indexed)
-            .expect("All references to `FilesSet` should have been dropped")
+    fn files_mut(&mut self) -> &mut FxHashSet<File> {
+        Arc::get_mut(&mut self.files).expect("All references to `FilesSet` to have been dropped")
     }
 
     fn set_impl(&mut self) {
@@ -226,16 +208,16 @@ impl IndexedMut<'_> {
             return;
         };
 
-        let indexed = Arc::clone(&self.indexed);
+        let files = Arc::clone(&self.files);
 
         if self.did_change {
             // If there are changes, set the new file_set to trigger a salsa revision change.
             self.project
                 .set_file_set(db)
-                .to(IndexedFiles::indexed(indexed));
+                .to(IndexedFiles::indexed(files));
         } else {
             // The `indexed_mut` replaced the `state` with Lazy. Restore it back to the indexed state.
-            *self.project.file_set(db).state.lock().unwrap() = State::Indexed(indexed);
+            *self.project.file_set(db).state.lock().unwrap() = State::Indexed(files);
         }
     }
 }
@@ -255,7 +237,7 @@ mod tests {
     use crate::files::Index;
     use crate::ProjectMetadata;
     use ruff_db::files::system_path_to_file;
-    use ruff_db::system::{DbWithWritableSystem as _, SystemPathBuf};
+    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
     use ruff_python_ast::name::Name;
 
     #[test]
@@ -270,7 +252,7 @@ mod tests {
         let file = system_path_to_file(&db, "test.py").unwrap();
 
         let files = match project.file_set(&db).get() {
-            Index::Lazy(lazy) => lazy.set(FxHashSet::from_iter([file]), Vec::new()),
+            Index::Lazy(lazy) => lazy.set(FxHashSet::from_iter([file])),
             Index::Indexed(files) => files,
         };
 

crates/red_knot_project/src/lib.rs

@@ -1,7 +1,6 @@
 #![allow(clippy::ref_option)]
 
 use crate::metadata::options::OptionDiagnostic;
-use crate::walk::{ProjectFilesFilter, ProjectFilesWalker};
 pub use db::{Db, ProjectDatabase};
 use files::{Index, Indexed, IndexedFiles};
 use metadata::settings::Settings;
@@ -9,24 +8,24 @@ pub use metadata::{ProjectDiscoveryError, ProjectMetadata};
 use red_knot_python_semantic::lint::{LintRegistry, LintRegistryBuilder, RuleSelection};
 use red_knot_python_semantic::register_lints;
 use red_knot_python_semantic::types::check_types;
-use ruff_db::diagnostic::{DiagnosticId, OldDiagnosticTrait, OldParseDiagnostic, Severity, Span};
-use ruff_db::files::File;
+use ruff_db::diagnostic::{Diagnostic, DiagnosticId, ParseDiagnostic, Severity, Span};
+use ruff_db::files::{system_path_to_file, File};
 use ruff_db::parsed::parsed_module;
 use ruff_db::source::{source_text, SourceTextError};
-use ruff_db::system::{SystemPath, SystemPathBuf};
-use rustc_hash::FxHashSet;
+use ruff_db::system::walk_directory::WalkState;
+use ruff_db::system::{FileType, SystemPath};
+use ruff_python_ast::PySourceType;
+use rustc_hash::{FxBuildHasher, FxHashSet};
 use salsa::Durability;
 use salsa::Setter;
 use std::borrow::Cow;
 use std::sync::Arc;
-use thiserror::Error;
 
 pub mod combine;
 
 mod db;
 mod files;
 pub mod metadata;
-mod walk;
 pub mod watch;
 
 pub static DEFAULT_LINT_REGISTRY: std::sync::LazyLock<LintRegistry> =
@@ -72,30 +71,6 @@ pub struct Project {
     #[return_ref]
     pub settings: Settings,
 
-    /// The paths that should be included when checking this project.
-    ///
-    /// The default (when this list is empty) is to include all files in the project root
-    /// (that satisfy the configured include and exclude patterns).
-    /// However, it's sometimes desired to only check a subset of the project, e.g. to see
-    /// the diagnostics for a single file or a folder.
-    ///
-    /// This list gets initialized by the paths passed to `knot check <paths>`
-    ///
-    /// ## How is this different from `open_files`?
-    ///
-    /// The `included_paths` is closely related to `open_files`. The only difference is that
-    /// `open_files` is already a resolved set of files whereas `included_paths` is only a list of paths
-    /// that are resolved to files by indexing them. The other difference is that
-    /// new files added to any directory in `included_paths` will be indexed and added to the project
-    /// whereas `open_files` needs to be updated manually (e.g. by the IDE).
-    ///
-    /// In short, `open_files` is cheaper in contexts where the set of files is known, like
-    /// in an IDE when the user only wants to check the open tabs. This could be modeled
-    /// with `included_paths` too but it would require an explicit walk dir step that's simply unnecessary.
-    #[default]
-    #[return_ref]
-    included_paths_list: Vec<SystemPathBuf>,
-
     /// Diagnostics that were generated when resolving the project settings.
     #[return_ref]
     settings_diagnostics: Vec<OptionDiagnostic>,
@@ -131,16 +106,6 @@ impl Project {
         self.settings(db).to_rules()
     }
 
-    /// Returns `true` if `path` is both part of the project and included (see `included_paths_list`).
-    ///
-    /// Unlike [Self::files], this method does not respect `.gitignore` files. It only checks
-    /// the project's include and exclude settings as well as the paths that were passed to `knot check <paths>`.
-    /// This means, that this method is an over-approximation of `Self::files` and may return `true` for paths
-    /// that won't be included when checking the project because they're ignored in a `.gitignore` file.
-    pub fn is_path_included(self, db: &dyn Db, path: &SystemPath) -> bool {
-        ProjectFilesFilter::from_project(db, self).is_included(path)
-    }
-
     pub fn reload(self, db: &mut dyn Db, metadata: ProjectMetadata) {
         tracing::debug!("Reloading project");
         assert_eq!(self.root(db), metadata.root());
@@ -163,22 +128,15 @@ impl Project {
     }
 
     /// Checks all open files in the project and its dependencies.
-    pub(crate) fn check(self, db: &ProjectDatabase) -> Vec<Box<dyn OldDiagnosticTrait>> {
+    pub(crate) fn check(self, db: &ProjectDatabase) -> Vec<Box<dyn Diagnostic>> {
         let project_span = tracing::debug_span!("Project::check");
         let _span = project_span.enter();
 
         tracing::debug!("Checking project '{name}'", name = self.name(db));
 
-        let mut diagnostics: Vec<Box<dyn OldDiagnosticTrait>> = Vec::new();
+        let mut diagnostics: Vec<Box<dyn Diagnostic>> = Vec::new();
         diagnostics.extend(self.settings_diagnostics(db).iter().map(|diagnostic| {
-            let diagnostic: Box<dyn OldDiagnosticTrait> = Box::new(diagnostic.clone());
-            diagnostic
-        }));
-
-        let files = ProjectFiles::new(db, self);
-
-        diagnostics.extend(files.diagnostics().iter().cloned().map(|diagnostic| {
-            let diagnostic: Box<dyn OldDiagnosticTrait> = Box::new(diagnostic);
+            let diagnostic: Box<dyn Diagnostic> = Box::new(diagnostic.clone());
             diagnostic
         }));
 
@@ -189,6 +147,7 @@ impl Project {
         let project_span = project_span.clone();
 
         rayon::scope(move |scope| {
+            let files = ProjectFiles::new(&db, self);
             for file in &files {
                 let result = inner_result.clone();
                 let db = db.clone();
@@ -207,12 +166,12 @@ impl Project {
         Arc::into_inner(result).unwrap().into_inner().unwrap()
     }
 
-    pub(crate) fn check_file(self, db: &dyn Db, file: File) -> Vec<Box<dyn OldDiagnosticTrait>> {
+    pub(crate) fn check_file(self, db: &dyn Db, file: File) -> Vec<Box<dyn Diagnostic>> {
         let mut file_diagnostics: Vec<_> = self
             .settings_diagnostics(db)
             .iter()
             .map(|diagnostic| {
-                let diagnostic: Box<dyn OldDiagnosticTrait> = Box::new(diagnostic.clone());
+                let diagnostic: Box<dyn Diagnostic> = Box::new(diagnostic.clone());
                 diagnostic
             })
             .collect();
@@ -248,30 +207,6 @@ impl Project {
         removed
     }
 
-    pub fn set_included_paths(self, db: &mut dyn Db, paths: Vec<SystemPathBuf>) {
-        tracing::debug!("Setting included paths: {paths}", paths = paths.len());
-
-        self.set_included_paths_list(db).to(paths);
-        self.reload_files(db);
-    }
-
-    /// Returns the paths that should be checked.
-    ///
-    /// The default is to check the entire project in which case this method returns
-    /// the project root. However, users can specify to only check specific sub-folders or
-    /// even files of a project by using `knot check <paths>`. In that case, this method
-    /// returns the provided absolute paths.
-    ///
-    /// Note: The CLI doesn't prohibit users from specifying paths outside the project root.
-    /// This can be useful to check arbitrary files, but it isn't something we recommend.
-    /// We should try to support this use case but it's okay if there are some limitations around it.
-    fn included_paths_or_root(self, db: &dyn Db) -> &[SystemPathBuf] {
-        match &**self.included_paths_list(db) {
-            [] => std::slice::from_ref(&self.metadata(db).root),
-            paths => paths,
-        }
-    }
-
     /// Returns the open files in the project or `None` if the entire project should be checked.
     pub fn open_files(self, db: &dyn Db) -> Option<&FxHashSet<File>> {
         self.open_fileset(db).as_deref()
@@ -354,17 +289,6 @@ impl Project {
         index.insert(file);
     }
 
-    /// Replaces the diagnostics from indexing the project files with `diagnostics`.
-    ///
-    /// This is a no-op if the project files haven't been indexed yet.
-    pub fn replace_index_diagnostics(self, db: &mut dyn Db, diagnostics: Vec<IOErrorDiagnostic>) {
-        let Some(mut index) = IndexedFiles::indexed_mut(db, self) else {
-            return;
-        };
-
-        index.set_diagnostics(diagnostics);
-    }
-
     /// Returns the files belonging to this project.
     pub fn files(self, db: &dyn Db) -> Indexed<'_> {
         let files = self.file_set(db);
@@ -372,14 +296,12 @@ impl Project {
         let indexed = match files.get() {
             Index::Lazy(vacant) => {
                 let _entered =
-                    tracing::debug_span!("Project::index_files", project = %self.name(db))
+                    tracing::debug_span!("Project::index_files", package = %self.name(db))
                         .entered();
 
-                let walker = ProjectFilesWalker::new(db);
-                let (files, diagnostics) = walker.collect_set(db);
-
-                tracing::info!("Indexed {} file(s)", files.len());
-                vacant.set(files, diagnostics)
+                let files = discover_project_files(db, self);
+                tracing::info!("Found {} files in project `{}`", files.len(), self.name(db));
+                vacant.set(files)
             }
             Index::Indexed(indexed) => indexed,
         };
@@ -397,29 +319,28 @@ impl Project {
     }
 }
 
-fn check_file_impl(db: &dyn Db, file: File) -> Vec<Box<dyn OldDiagnosticTrait>> {
-    let mut diagnostics: Vec<Box<dyn OldDiagnosticTrait>> = Vec::new();
+fn check_file_impl(db: &dyn Db, file: File) -> Vec<Box<dyn Diagnostic>> {
+    let mut diagnostics: Vec<Box<dyn Diagnostic>> = Vec::new();
 
     // Abort checking if there are IO errors.
     let source = source_text(db.upcast(), file);
 
     if let Some(read_error) = source.read_error() {
         diagnostics.push(Box::new(IOErrorDiagnostic {
-            file: Some(file),
-            error: read_error.clone().into(),
+            file,
+            error: read_error.clone(),
         }));
         return diagnostics;
     }
 
     let parsed = parsed_module(db.upcast(), file);
     diagnostics.extend(parsed.errors().iter().map(|error| {
-        let diagnostic: Box<dyn OldDiagnosticTrait> =
-            Box::new(OldParseDiagnostic::new(file, error.clone()));
+        let diagnostic: Box<dyn Diagnostic> = Box::new(ParseDiagnostic::new(file, error.clone()));
         diagnostic
     }));
 
     diagnostics.extend(check_types(db.upcast(), file).iter().map(|diagnostic| {
-        let boxed: Box<dyn OldDiagnosticTrait> = Box::new(diagnostic.clone());
+        let boxed: Box<dyn Diagnostic> = Box::new(diagnostic.clone());
         boxed
     }));
 
@@ -434,6 +355,53 @@ fn check_file_impl(db: &dyn Db, file: File) -> Vec<Box<dyn OldDiagnosticTrait>>
     diagnostics
 }
 
+fn discover_project_files(db: &dyn Db, project: Project) -> FxHashSet<File> {
+    let paths = std::sync::Mutex::new(Vec::new());
+
+    db.system().walk_directory(project.root(db)).run(|| {
+        Box::new(|entry| {
+            match entry {
+                Ok(entry) => {
+                    // Skip over any non python files to avoid creating too many entries in `Files`.
+                    match entry.file_type() {
+                        FileType::File => {
+                            if entry
+                                .path()
+                                .extension()
+                                .and_then(PySourceType::try_from_extension)
+                                .is_some()
+                            {
+                                let mut paths = paths.lock().unwrap();
+                                paths.push(entry.into_path());
+                            }
+                        }
+                        FileType::Directory | FileType::Symlink => {}
+                    }
+                }
+                Err(error) => {
+                    // TODO Handle error
+                    tracing::error!("Failed to walk path: {error}");
+                }
+            }
+
+            WalkState::Continue
+        })
+    });
+
+    let paths = paths.into_inner().unwrap();
+    let mut files = FxHashSet::with_capacity_and_hasher(paths.len(), FxBuildHasher);
+
+    for path in paths {
+        // If this returns `None`, then the file was deleted between the `walk_directory` call and now.
+        // We can ignore this.
+        if let Ok(file) = system_path_to_file(db.upcast(), &path) {
+            files.insert(file);
+        }
+    }
+
+    files
+}
+
 #[derive(Debug)]
 enum ProjectFiles<'a> {
     OpenFiles(&'a FxHashSet<File>),
@@ -448,13 +416,6 @@ impl<'a> ProjectFiles<'a> {
             ProjectFiles::Indexed(project.files(db))
         }
     }
-
-    fn diagnostics(&self) -> &[IOErrorDiagnostic] {
-        match self {
-            ProjectFiles::OpenFiles(_) => &[],
-            ProjectFiles::Indexed(indexed) => indexed.diagnostics(),
-        }
-    }
 }
 
 impl<'a> IntoIterator for &'a ProjectFiles<'a> {
@@ -487,13 +448,13 @@ impl Iterator for ProjectFilesIter<'_> {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug)]
 pub struct IOErrorDiagnostic {
-    file: Option<File>,
-    error: IOErrorKind,
+    file: File,
+    error: SourceTextError,
 }
 
-impl OldDiagnosticTrait for IOErrorDiagnostic {
+impl Diagnostic for IOErrorDiagnostic {
     fn id(&self) -> DiagnosticId {
         DiagnosticId::Io
     }
@@ -503,7 +464,7 @@ impl OldDiagnosticTrait for IOErrorDiagnostic {
     }
 
     fn span(&self) -> Option<Span> {
-        self.file.map(Span::from)
+        Some(Span::from(self.file))
     }
 
     fn severity(&self) -> Severity {
@@ -511,24 +472,15 @@ impl OldDiagnosticTrait for IOErrorDiagnostic {
     }
 }
 
-#[derive(Error, Debug, Clone)]
-enum IOErrorKind {
-    #[error(transparent)]
-    Walk(#[from] walk::WalkError),
-
-    #[error(transparent)]
-    SourceText(#[from] SourceTextError),
-}
-
 #[cfg(test)]
 mod tests {
     use crate::db::tests::TestDb;
     use crate::{check_file_impl, ProjectMetadata};
     use red_knot_python_semantic::types::check_types;
-    use ruff_db::diagnostic::OldDiagnosticTrait;
+    use ruff_db::diagnostic::Diagnostic;
     use ruff_db::files::system_path_to_file;
     use ruff_db::source::source_text;
-    use ruff_db::system::{DbWithTestSystem, DbWithWritableSystem as _, SystemPath, SystemPathBuf};
+    use ruff_db::system::{DbWithTestSystem, SystemPath, SystemPathBuf};
     use ruff_db::testing::assert_function_query_was_not_run;
     use ruff_python_ast::name::Name;
 

crates/red_knot_project/src/metadata.rs

@@ -77,10 +77,10 @@ impl ProjectMetadata {
         // If the `options` don't specify a python version but the `project.requires-python` field is set,
         // use that as a lower bound instead.
         if let Some(project) = project {
-            if options
+            if !options
                 .environment
                 .as_ref()
-                .is_none_or(|env| env.python_version.is_none())
+                .is_some_and(|env| env.python_version.is_some())
             {
                 if let Some(requires_python) = project.resolve_requires_python_lower_bound()? {
                     let mut environment = options.environment.unwrap_or_default();
@@ -321,7 +321,7 @@ mod tests {
 
         system
             .memory_file_system()
-            .write_files_all([(root.join("foo.py"), ""), (root.join("bar.py"), "")])
+            .write_files([(root.join("foo.py"), ""), (root.join("bar.py"), "")])
             .context("Failed to write files")?;
 
         let project =
@@ -349,7 +349,7 @@ mod tests {
 
         system
             .memory_file_system()
-            .write_files_all([
+            .write_files([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -393,7 +393,7 @@ mod tests {
 
         system
             .memory_file_system()
-            .write_files_all([
+            .write_files([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -432,7 +432,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files_all([
+            .write_files([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -482,7 +482,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files_all([
+            .write_files([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -532,7 +532,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files_all([
+            .write_files([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -572,7 +572,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files_all([
+            .write_files([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -623,7 +623,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_files_all([
+            .write_files([
                 (
                     root.join("pyproject.toml"),
                     r#"
@@ -673,7 +673,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file_all(
+            .write_file(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -703,7 +703,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file_all(
+            .write_file(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -735,7 +735,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file_all(
+            .write_file(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -765,7 +765,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file_all(
+            .write_file(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -795,7 +795,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file_all(
+            .write_file(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -828,7 +828,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file_all(
+            .write_file(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -861,7 +861,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file_all(
+            .write_file(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -886,7 +886,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file_all(
+            .write_file(
                 root.join("pyproject.toml"),
                 r#"
                 [project]
@@ -911,7 +911,7 @@ expected `.`, `]`
 
         system
             .memory_file_system()
-            .write_file_all(
+            .write_file(
                 root.join("pyproject.toml"),
                 r#"
                 [project]

crates/red_knot_project/src/metadata/options.rs

@@ -1,8 +1,8 @@
 use crate::metadata::value::{RangedValue, RelativePathBuf, ValueSource, ValueSourceGuard};
 use crate::Db;
 use red_knot_python_semantic::lint::{GetLintError, Level, LintSource, RuleSelection};
-use red_knot_python_semantic::{ProgramSettings, PythonPath, PythonPlatform, SearchPathSettings};
-use ruff_db::diagnostic::{DiagnosticId, OldDiagnosticTrait, Severity, Span};
+use red_knot_python_semantic::{ProgramSettings, PythonPlatform, SearchPathSettings, SitePackages};
+use ruff_db::diagnostic::{Diagnostic, DiagnosticId, Severity, Span};
 use ruff_db::files::system_path_to_file;
 use ruff_db::system::{System, SystemPath};
 use ruff_macros::Combine;
@@ -90,7 +90,7 @@ impl Options {
             .map(|env| {
                 (
                     env.extra_paths.clone(),
-                    env.python.clone(),
+                    env.venv_path.clone(),
                     env.typeshed.clone(),
                 )
             })
@@ -104,11 +104,11 @@ impl Options {
                 .collect(),
             src_roots,
             custom_typeshed: typeshed.map(|path| path.absolute(project_root, system)),
-            python_path: python
-                .map(|python_path| {
-                    PythonPath::SysPrefix(python_path.absolute(project_root, system))
+            site_packages: python
+                .map(|venv_path| SitePackages::Derived {
+                    venv_path: venv_path.absolute(project_root, system),
                 })
-                .unwrap_or(PythonPath::KnownSitePackages(vec![])),
+                .unwrap_or(SitePackages::Known(vec![])),
         }
     }
 
@@ -236,14 +236,10 @@ pub struct EnvironmentOptions {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub typeshed: Option<RelativePathBuf>,
 
-    /// Path to the Python installation from which Red Knot resolves type information and third-party dependencies.
-    ///
-    /// Red Knot will search in the path's `site-packages` directories for type information and
-    /// third-party imports.
-    ///
-    /// This option is commonly used to specify the path to a virtual environment.
+    // TODO: Rename to python, see https://github.com/astral-sh/ruff/issues/15530
+    /// The path to the user's `site-packages` directory, where third-party packages from ``PyPI`` are installed.
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub python: Option<RelativePathBuf>,
+    pub venv_path: Option<RelativePathBuf>,
 }
 
 #[derive(Debug, Default, Clone, Eq, PartialEq, Combine, Serialize, Deserialize)]
@@ -376,7 +372,7 @@ impl OptionDiagnostic {
     }
 }
 
-impl OldDiagnosticTrait for OptionDiagnostic {
+impl Diagnostic for OptionDiagnostic {
     fn id(&self) -> DiagnosticId {
         self.id
     }

crates/red_knot_project/src/walk.rs

@@ -1,256 +0,0 @@
-use crate::{Db, IOErrorDiagnostic, IOErrorKind, Project};
-use ruff_db::files::{system_path_to_file, File};
-use ruff_db::system::walk_directory::{ErrorKind, WalkDirectoryBuilder, WalkState};
-use ruff_db::system::{FileType, SystemPath, SystemPathBuf};
-use ruff_python_ast::PySourceType;
-use rustc_hash::{FxBuildHasher, FxHashSet};
-use std::path::PathBuf;
-use thiserror::Error;
-
-/// Filter that decides which files are included in the project.
-///
-/// In the future, this will hold a reference to the `include` and `exclude` pattern.
-///
-/// This struct mainly exists because `dyn Db` isn't `Send` or `Sync`, making it impossible
-/// to access fields from within the walker.
-#[derive(Default, Debug)]
-pub(crate) struct ProjectFilesFilter<'a> {
-    /// The same as [`Project::included_paths_or_root`].
-    included_paths: &'a [SystemPathBuf],
-
-    /// The filter skips checking if the path is in `included_paths` if set to `true`.
-    ///
-    /// Skipping this check is useful when the walker only walks over `included_paths`.
-    skip_included_paths: bool,
-}
-
-impl<'a> ProjectFilesFilter<'a> {
-    pub(crate) fn from_project(db: &'a dyn Db, project: Project) -> Self {
-        Self {
-            included_paths: project.included_paths_or_root(db),
-            skip_included_paths: false,
-        }
-    }
-
-    /// Returns `true` if a file is part of the project and included in the paths to check.
-    ///
-    /// A file is included in the checked files if it is a sub path of the project's root
-    /// (when no CLI path arguments are specified) or if it is a sub path of any path provided on the CLI (`knot check <paths>`) AND:
-    ///
-    /// * It matches a positive `include` pattern and isn't excluded by a later negative `include` pattern.
-    /// * It doesn't match a positive `exclude` pattern or is re-included by a later negative `exclude` pattern.
-    ///
-    /// ## Note
-    ///
-    /// This method may return `true` for files that don't end up being included when walking the
-    /// project tree because it doesn't consider `.gitignore` and other ignore files when deciding
-    /// if a file's included.
-    pub(crate) fn is_included(&self, path: &SystemPath) -> bool {
-        #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
-        enum CheckPathMatch {
-            /// The path is a partial match of the checked path (it's a sub path)
-            Partial,
-
-            /// The path matches a check path exactly.
-            Full,
-        }
-
-        let m = if self.skip_included_paths {
-            Some(CheckPathMatch::Partial)
-        } else {
-            self.included_paths
-                .iter()
-                .filter_map(|included_path| {
-                    if let Ok(relative_path) = path.strip_prefix(included_path) {
-                        // Exact matches are always included
-                        if relative_path.as_str().is_empty() {
-                            Some(CheckPathMatch::Full)
-                        } else {
-                            Some(CheckPathMatch::Partial)
-                        }
-                    } else {
-                        None
-                    }
-                })
-                .max()
-        };
-
-        match m {
-            None => false,
-            Some(CheckPathMatch::Partial) => {
-                // TODO: For partial matches, only include the file if it is included by the project's include/exclude settings.
-                true
-            }
-            Some(CheckPathMatch::Full) => true,
-        }
-    }
-}
-
-pub(crate) struct ProjectFilesWalker<'a> {
-    walker: WalkDirectoryBuilder,
-
-    filter: ProjectFilesFilter<'a>,
-}
-
-impl<'a> ProjectFilesWalker<'a> {
-    pub(crate) fn new(db: &'a dyn Db) -> Self {
-        let project = db.project();
-
-        let mut filter = ProjectFilesFilter::from_project(db, project);
-        // It's unnecessary to filter on included paths because it only iterates over those to start with.
-        filter.skip_included_paths = true;
-
-        Self::from_paths(db, project.included_paths_or_root(db), filter)
-            .expect("included_paths_or_root to never return an empty iterator")
-    }
-
-    /// Creates a walker for indexing the project files incrementally.
-    ///
-    /// The main difference to a full project walk is that `paths` may contain paths
-    /// that aren't part of the included files.
-    pub(crate) fn incremental<P>(db: &'a dyn Db, paths: impl IntoIterator<Item = P>) -> Option<Self>
-    where
-        P: AsRef<SystemPath>,
-    {
-        let project = db.project();
-
-        let filter = ProjectFilesFilter::from_project(db, project);
-
-        Self::from_paths(db, paths, filter)
-    }
-
-    fn from_paths<P>(
-        db: &'a dyn Db,
-        paths: impl IntoIterator<Item = P>,
-        filter: ProjectFilesFilter<'a>,
-    ) -> Option<Self>
-    where
-        P: AsRef<SystemPath>,
-    {
-        let mut paths = paths.into_iter();
-
-        let mut walker = db.system().walk_directory(paths.next()?.as_ref());
-
-        for path in paths {
-            walker = walker.add(path);
-        }
-
-        Some(Self { walker, filter })
-    }
-
-    /// Walks the project paths and collects the paths of all files that
-    /// are included in the project.
-    pub(crate) fn walk_paths(self) -> (Vec<SystemPathBuf>, Vec<IOErrorDiagnostic>) {
-        let paths = std::sync::Mutex::new(Vec::new());
-        let diagnostics = std::sync::Mutex::new(Vec::new());
-
-        self.walker.run(|| {
-            Box::new(|entry| {
-                match entry {
-                    Ok(entry) => {
-                        if !self.filter.is_included(entry.path()) {
-                            tracing::debug!("Ignoring not-included path: {}", entry.path());
-                            return WalkState::Skip;
-                        }
-
-                        // Skip over any non python files to avoid creating too many entries in `Files`.
-                        match entry.file_type() {
-                            FileType::File => {
-                                if entry
-                                    .path()
-                                    .extension()
-                                    .and_then(PySourceType::try_from_extension)
-                                    .is_some()
-                                {
-                                    let mut paths = paths.lock().unwrap();
-                                    paths.push(entry.into_path());
-                                }
-                            }
-                            FileType::Directory | FileType::Symlink => {}
-                        }
-                    }
-                    Err(error) => match error.kind() {
-                        ErrorKind::Loop { .. } => {
-                            unreachable!("Loops shouldn't be possible without following symlinks.")
-                        }
-                        ErrorKind::Io { path, err } => {
-                            let mut diagnostics = diagnostics.lock().unwrap();
-                            let error = if let Some(path) = path {
-                                WalkError::IOPathError {
-                                    path: path.clone(),
-                                    error: err.to_string(),
-                                }
-                            } else {
-                                WalkError::IOError {
-                                    error: err.to_string(),
-                                }
-                            };
-
-                            diagnostics.push(IOErrorDiagnostic {
-                                file: None,
-                                error: IOErrorKind::Walk(error),
-                            });
-                        }
-                        ErrorKind::NonUtf8Path { path } => {
-                            diagnostics.lock().unwrap().push(IOErrorDiagnostic {
-                                file: None,
-                                error: IOErrorKind::Walk(WalkError::NonUtf8Path {
-                                    path: path.clone(),
-                                }),
-                            });
-                        }
-                    },
-                }
-
-                WalkState::Continue
-            })
-        });
-
-        (
-            paths.into_inner().unwrap(),
-            diagnostics.into_inner().unwrap(),
-        )
-    }
-
-    pub(crate) fn collect_vec(self, db: &dyn Db) -> (Vec<File>, Vec<IOErrorDiagnostic>) {
-        let (paths, diagnostics) = self.walk_paths();
-
-        (
-            paths
-                .into_iter()
-                .filter_map(move |path| {
-                    // If this returns `None`, then the file was deleted between the `walk_directory` call and now.
-                    // We can ignore this.
-                    system_path_to_file(db.upcast(), &path).ok()
-                })
-                .collect(),
-            diagnostics,
-        )
-    }
-
-    pub(crate) fn collect_set(self, db: &dyn Db) -> (FxHashSet<File>, Vec<IOErrorDiagnostic>) {
-        let (paths, diagnostics) = self.walk_paths();
-
-        let mut files = FxHashSet::with_capacity_and_hasher(paths.len(), FxBuildHasher);
-
-        for path in paths {
-            if let Ok(file) = system_path_to_file(db.upcast(), &path) {
-                files.insert(file);
-            }
-        }
-
-        (files, diagnostics)
-    }
-}
-
-#[derive(Error, Debug, Clone)]
-pub(crate) enum WalkError {
-    #[error("`{path}`: {error}")]
-    IOPathError { path: SystemPathBuf, error: String },
-
-    #[error("Failed to walk project directory: {error}")]
-    IOError { error: String },
-
-    #[error("`{path}` is not a valid UTF-8 path")]
-    NonUtf8Path { path: PathBuf },
-}

crates/red_knot_project/src/watch/project_watcher.rs

@@ -6,7 +6,7 @@ use tracing::info;
 use red_knot_python_semantic::system_module_search_paths;
 use ruff_cache::{CacheKey, CacheKeyHasher};
 use ruff_db::system::{SystemPath, SystemPathBuf};
-use ruff_db::Upcast;
+use ruff_db::{Db as _, Upcast};
 
 use crate::db::{Db, ProjectDatabase};
 use crate::watch::Watcher;
@@ -42,9 +42,9 @@ impl ProjectWatcher {
 
     pub fn update(&mut self, db: &ProjectDatabase) {
         let search_paths: Vec<_> = system_module_search_paths(db.upcast()).collect();
-        let project_path = db.project().root(db);
+        let project_path = db.project().root(db).to_path_buf();
 
-        let new_cache_key = Self::compute_cache_key(project_path, &search_paths);
+        let new_cache_key = Self::compute_cache_key(&project_path, &search_paths);
 
         if self.cache_key == Some(new_cache_key) {
             return;
@@ -68,47 +68,41 @@ impl ProjectWatcher {
 
         self.has_errored_paths = false;
 
+        let project_path = db
+            .system()
+            .canonicalize_path(&project_path)
+            .unwrap_or(project_path);
+
         let config_paths = db
             .project()
             .metadata(db)
             .extra_configuration_paths()
             .iter()
-            .map(SystemPathBuf::as_path);
-
-        // Watch both the project root and any paths provided by the user on the CLI (removing any redundant nested paths).
-        // This is necessary to observe changes to files that are outside the project root.
-        // We always need to watch the project root to observe changes to its configuration.
-        let included_paths = ruff_db::system::deduplicate_nested_paths(
-            std::iter::once(project_path).chain(
-                db.project()
-                    .included_paths_list(db)
-                    .iter()
-                    .map(SystemPathBuf::as_path),
-            ),
-        );
+            .cloned();
 
         // Find the non-overlapping module search paths and filter out paths that are already covered by the project.
         // Module search paths are already canonicalized.
         let unique_module_paths = ruff_db::system::deduplicate_nested_paths(
             search_paths
                 .into_iter()
-                .filter(|path| !path.starts_with(project_path)),
-        );
+                .filter(|path| !path.starts_with(&project_path)),
+        )
+        .map(SystemPath::to_path_buf);
 
         // Now add the new paths, first starting with the project path and then
         // adding the library search paths, and finally the paths for configurations.
-        for path in included_paths
+        for path in std::iter::once(project_path)
             .chain(unique_module_paths)
             .chain(config_paths)
         {
             // Log a warning. It's not worth aborting if registering a single folder fails because
             // Ruff otherwise stills works as expected.
-            if let Err(error) = self.watcher.watch(path) {
+            if let Err(error) = self.watcher.watch(&path) {
                 // TODO: Log a user-facing warning.
                 tracing::warn!("Failed to setup watcher for path `{path}`: {error}. You have to restart Ruff after making changes to files under this path or you might see stale results.");
                 self.has_errored_paths = true;
             } else {
-                self.watched_paths.push(path.to_path_buf());
+                self.watched_paths.push(path);
             }
         }
 

crates/red_knot_project/tests/check.rs

@@ -117,7 +117,7 @@ fn run_corpus_tests(pattern: &str) -> anyhow::Result<()> {
         let code = std::fs::read_to_string(source)?;
 
         let mut check_with_file_name = |path: &SystemPath| {
-            memory_fs.write_file_all(path, &code).unwrap();
+            memory_fs.write_file(path, &code).unwrap();
             File::sync_path(&mut db, path);
 
             // this test is only asserting that we can pull every expression type without a panic
@@ -216,17 +216,6 @@ impl SourceOrderVisitor<'_> for PullTypesVisitor<'_> {
                 self.visit_body(&for_stmt.orelse);
                 return;
             }
-            Stmt::With(with_stmt) => {
-                for item in &with_stmt.items {
-                    if let Some(target) = &item.optional_vars {
-                        self.visit_target(target);
-                    }
-                    self.visit_expr(&item.context_expr);
-                }
-
-                self.visit_body(&with_stmt.body);
-                return;
-            }
             Stmt::AnnAssign(_)
             | Stmt::Return(_)
             | Stmt::Delete(_)
@@ -234,6 +223,7 @@ impl SourceOrderVisitor<'_> for PullTypesVisitor<'_> {
             | Stmt::TypeAlias(_)
             | Stmt::While(_)
             | Stmt::If(_)
+            | Stmt::With(_)
             | Stmt::Match(_)
             | Stmt::Raise(_)
             | Stmt::Try(_)
@@ -279,4 +269,18 @@ impl SourceOrderVisitor<'_> for PullTypesVisitor<'_> {
 
 /// Whether or not the .py/.pyi version of this file is expected to fail
 #[rustfmt::skip]
-const KNOWN_FAILURES: &[(&str, bool, bool)] = &[];
+const KNOWN_FAILURES: &[(&str, bool, bool)] = &[
+    // related to circular references in nested functions
+    ("crates/ruff_linter/resources/test/fixtures/flake8_return/RET503.py", false, true),
+    // related to circular references in class definitions
+    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_26.py", true, true),
+    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_27.py", true, true),
+    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F811_19.py", true, false),
+    ("crates/ruff_linter/resources/test/fixtures/pyupgrade/UP039.py", true, false),
+    // related to circular references in type aliases (salsa cycle panic):
+    ("crates/ruff_python_parser/resources/inline/err/type_alias_invalid_value_expr.py", true, true),
+    ("crates/ruff_linter/resources/test/fixtures/flake8_type_checking/TC008.py", true, true),
+    // related to circular references in f-string annotations (invalid syntax)
+    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_15.py", true, true),
+    ("crates/ruff_linter/resources/test/fixtures/pyflakes/F821_14.py", false, true),
+];

crates/red_knot_python_semantic/Cargo.toml

@@ -42,8 +42,6 @@ smallvec = { workspace = true }
 static_assertions = { workspace = true }
 test-case = { workspace = true }
 memchr = { workspace = true }
-strum = { workspace = true}
-strum_macros = { workspace = true}
 
 [dev-dependencies]
 ruff_db = { workspace = true, features = ["testing", "os"] }

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

@@ -1,211 +0,0 @@
-# Callable
-
-References:
-
-- <https://typing.readthedocs.io/en/latest/spec/callables.html#callable>
-
-TODO: Use `collections.abc` as importing from `typing` is deprecated but this requires support for
-`*` imports. See: <https://docs.python.org/3/library/typing.html#deprecated-aliases>.
-
-## Invalid forms
-
-The `Callable` special form requires _exactly_ two arguments where the first argument is either a
-parameter type list, parameter specification, `typing.Concatenate`, or `...` and the second argument
-is the return type. Here, we explore various invalid forms.
-
-### Empty
-
-A bare `Callable` without any type arguments:
-
-```py
-from typing import Callable
-
-def _(c: Callable):
-    reveal_type(c)  # revealed: (...) -> Unknown
-```
-
-### Invalid parameter type argument
-
-When it's not a list:
-
-```py
-from typing import Callable
-
-# error: [invalid-type-form] "The first argument to `Callable` must be either a list of types, ParamSpec, Concatenate, or `...`"
-def _(c: Callable[int, str]):
-    reveal_type(c)  # revealed: (...) -> Unknown
-```
-
-Or, when it's a literal type:
-
-```py
-# error: [invalid-type-form] "The first argument to `Callable` must be either a list of types, ParamSpec, Concatenate, or `...`"
-def _(c: Callable[42, str]):
-    reveal_type(c)  # revealed: (...) -> Unknown
-```
-
-Or, when one of the parameter type is invalid in the list:
-
-```py
-def _(c: Callable[[int, 42, str, False], None]):
-    # revealed: (int, @Todo(number literal in type expression), str, @Todo(boolean literal in type expression), /) -> None
-    reveal_type(c)
-```
-
-### Missing return type
-
-Using a parameter list:
-
-```py
-from typing import Callable
-
-# error: [invalid-type-form] "Special form `typing.Callable` expected exactly two arguments (parameter types and return type)"
-def _(c: Callable[[int, str]]):
-    reveal_type(c)  # revealed: (int, str, /) -> Unknown
-```
-
-Or, an ellipsis:
-
-```py
-# error: [invalid-type-form] "Special form `typing.Callable` expected exactly two arguments (parameter types and return type)"
-def _(c: Callable[...]):
-    reveal_type(c)  # revealed: (...) -> Unknown
-```
-
-### More than two arguments
-
-We can't reliably infer the callable type if there are more then 2 arguments because we don't know
-which argument corresponds to either the parameters or the return type.
-
-```py
-from typing import Callable
-
-# error: [invalid-type-form] "Special form `typing.Callable` expected exactly two arguments (parameter types and return type)"
-def _(c: Callable[[int], str, str]):
-    reveal_type(c)  # revealed: (...) -> Unknown
-```
-
-## Simple
-
-A simple `Callable` with multiple parameters and a return type:
-
-```py
-from typing import Callable
-
-def _(c: Callable[[int, str], int]):
-    reveal_type(c)  # revealed: (int, str, /) -> int
-```
-
-## Nested
-
-A nested `Callable` as one of the parameter types:
-
-```py
-from typing import Callable
-
-def _(c: Callable[[Callable[[int], str]], int]):
-    reveal_type(c)  # revealed: ((int, /) -> str, /) -> int
-```
-
-And, as the return type:
-
-```py
-def _(c: Callable[[int, str], Callable[[int], int]]):
-    reveal_type(c)  # revealed: (int, str, /) -> (int, /) -> int
-```
-
-## Gradual form
-
-The `Callable` special form supports the use of `...` in place of the list of parameter types. This
-is a [gradual form] indicating that the type is consistent with any input signature:
-
-```py
-from typing import Callable
-
-def gradual_form(c: Callable[..., str]):
-    reveal_type(c)  # revealed: (...) -> str
-```
-
-## Using `typing.Concatenate`
-
-Using `Concatenate` as the first argument to `Callable`:
-
-```py
-from typing_extensions import Callable, Concatenate
-
-def _(c: Callable[Concatenate[int, str, ...], int]):
-    reveal_type(c)  # revealed: (*args: @Todo(todo signature *args), **kwargs: @Todo(todo signature **kwargs)) -> int
-```
-
-And, as one of the parameter types:
-
-```py
-def _(c: Callable[[Concatenate[int, str, ...], int], int]):
-    reveal_type(c)  # revealed: (*args: @Todo(todo signature *args), **kwargs: @Todo(todo signature **kwargs)) -> int
-```
-
-## Using `typing.ParamSpec`
-
-Using a `ParamSpec` in a `Callable` annotation:
-
-```py
-from typing_extensions import Callable
-
-# TODO: Not an error; remove once `ParamSpec` is supported
-# error: [invalid-type-form]
-def _[**P1](c: Callable[P1, int]):
-    reveal_type(c)  # revealed: (...) -> Unknown
-```
-
-And, using the legacy syntax:
-
-```py
-from typing_extensions import ParamSpec
-
-P2 = ParamSpec("P2")
-
-# TODO: Not an error; remove once `ParamSpec` is supported
-# error: [invalid-type-form]
-def _(c: Callable[P2, int]):
-    reveal_type(c)  # revealed: (...) -> Unknown
-```
-
-## Using `typing.Unpack`
-
-Using the unpack operator (`*`):
-
-```py
-from typing_extensions import Callable, TypeVarTuple
-
-Ts = TypeVarTuple("Ts")
-
-def _(c: Callable[[int, *Ts], int]):
-    reveal_type(c)  # revealed: (*args: @Todo(todo signature *args), **kwargs: @Todo(todo signature **kwargs)) -> int
-```
-
-And, using the legacy syntax using `Unpack`:
-
-```py
-from typing_extensions import Unpack
-
-def _(c: Callable[[int, Unpack[Ts]], int]):
-    reveal_type(c)  # revealed: (*args: @Todo(todo signature *args), **kwargs: @Todo(todo signature **kwargs)) -> int
-```
-
-## Member lookup
-
-```py
-from typing import Callable
-
-def _(c: Callable[[int], int]):
-    reveal_type(c.__init__)  # revealed: Literal[__init__]
-    reveal_type(c.__class__)  # revealed: type
-
-    # TODO: The member lookup for `Callable` uses `object` which does not have a `__call__`
-    # attribute. We could special case `__call__` in this context. Refer to
-    # https://github.com/astral-sh/ruff/pull/16493#discussion_r1985098508 for more details.
-    # error: [unresolved-attribute] "Type `(int, /) -> int` has no attribute `__call__`"
-    reveal_type(c.__call__)  # revealed: Unknown
-```
-
-[gradual form]: https://typing.readthedocs.io/en/latest/spec/glossary.html#term-gradual-form

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

@@ -38,8 +38,7 @@ If `__future__.annotations` is imported, annotations *are* deferred.
 ```py
 from __future__ import annotations
 
-def get_foo() -> Foo:
-    return Foo()
+def get_foo() -> Foo: ...
 
 class Foo: ...
 

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

@@ -1,45 +0,0 @@
-# Tests for invalid types in type expressions
-
-## Invalid types are rejected
-
-Many types are illegal in the context of a type expression:
-
-```py
-import typing
-from knot_extensions import AlwaysTruthy, AlwaysFalsy
-from typing_extensions import Literal, Never
-
-def _(
-    a: type[int],
-    b: AlwaysTruthy,
-    c: AlwaysFalsy,
-    d: Literal[True],
-    e: Literal["bar"],
-    f: Literal[b"foo"],
-    g: tuple[int, str],
-    h: Never,
-):
-    def foo(): ...
-    def invalid(
-        i: a,  # error: [invalid-type-form] "Variable of type `type[int]` is not allowed in a type expression"
-        j: b,  # error: [invalid-type-form]
-        k: c,  # error: [invalid-type-form]
-        l: d,  # error: [invalid-type-form]
-        m: e,  # error: [invalid-type-form]
-        n: f,  # error: [invalid-type-form]
-        o: g,  # error: [invalid-type-form]
-        p: h,  # error: [invalid-type-form]
-        q: typing,  # error: [invalid-type-form]
-        r: foo,  # error: [invalid-type-form]
-    ):
-        reveal_type(i)  # revealed: Unknown
-        reveal_type(j)  # revealed: Unknown
-        reveal_type(k)  # revealed: Unknown
-        reveal_type(l)  # revealed: Unknown
-        reveal_type(m)  # revealed: Unknown
-        reveal_type(n)  # revealed: Unknown
-        reveal_type(o)  # revealed: Unknown
-        reveal_type(p)  # revealed: Unknown
-        reveal_type(q)  # revealed: Unknown
-        reveal_type(r)  # revealed: Unknown
-```

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

@@ -73,12 +73,12 @@ qux = (foo, bar)
 reveal_type(qux)  # revealed: tuple[Literal["foo"], Literal["bar"]]
 
 # TODO: Infer "LiteralString"
-reveal_type(foo.join(qux))  # revealed: @Todo(return type of decorated function)
+reveal_type(foo.join(qux))  # revealed: @Todo(decorated method)
 
 template: LiteralString = "{}, {}"
 reveal_type(template)  # revealed: Literal["{}, {}"]
 # TODO: Infer `LiteralString`
-reveal_type(template.format(foo, bar))  # revealed: @Todo(return type of decorated function)
+reveal_type(template.format(foo, bar))  # revealed: @Todo(decorated method)
 ```
 
 ### Assignability

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

@@ -70,7 +70,8 @@ import typing
 
 class ListSubclass(typing.List): ...
 
-# revealed: tuple[Literal[ListSubclass], Literal[list], Literal[MutableSequence], Literal[Sequence], Literal[Reversible], Literal[Collection], Literal[Iterable], Literal[Container], @Todo(protocol), Literal[object]]
+# TODO: should have `Generic`, should not have `Unknown`
+# revealed: tuple[Literal[ListSubclass], Literal[list], Unknown, Literal[object]]
 reveal_type(ListSubclass.__mro__)
 
 class DictSubclass(typing.Dict): ...

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

@@ -116,8 +116,8 @@ MyType = int
 class Aliases:
     MyType = str
 
-    forward: "MyType" = "value"
-    not_forward: MyType = "value"
+    forward: "MyType"
+    not_forward: MyType
 
 reveal_type(Aliases.forward)  # revealed: str
 reveal_type(Aliases.not_forward)  # revealed: str

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

@@ -18,7 +18,7 @@ def f(*args: Unpack[Ts]) -> tuple[Unpack[Ts]]:
     # TODO: should understand the annotation
     reveal_type(args)  # revealed: tuple
 
-    reveal_type(Alias)  # revealed: @Todo(Invalid or unsupported `KnownInstanceType` in `Type::to_type_expression`)
+    reveal_type(Alias)  # revealed: @Todo(Unsupported or invalid type in a type expression)
 
 def g() -> TypeGuard[int]: ...
 def h() -> TypeIs[int]: ...
@@ -29,13 +29,11 @@ def i(callback: Callable[Concatenate[int, P], R_co], *args: P.args, **kwargs: P.
     # TODO: should understand the annotation
     reveal_type(kwargs)  # revealed: dict
 
-    # TODO: not an error; remove once `call` is implemented for `Callable`
-    # error: [call-non-callable]
     return callback(42, *args, **kwargs)
 
 class Foo:
     def method(self, x: Self):
-        reveal_type(x)  # revealed: @Todo(Invalid or unsupported `KnownInstanceType` in `Type::to_type_expression`)
+        reveal_type(x)  # revealed: @Todo(Unsupported or invalid type in a type expression)
 ```
 
 ## Inheritance

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

@@ -75,7 +75,8 @@ def _(flag: bool):
 
     f = Foo()
 
-    # error: [unsupported-operator] "Operator `+=` is unsupported between objects of type `Foo` and `Literal["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

crates/red_knot_python_semantic/resources/mdtest/attributes.md

@@ -54,12 +54,13 @@ c_instance.declared_and_bound = False
 # error: [invalid-assignment] "Object of type `Literal["incompatible"]` is not assignable to attribute `declared_and_bound` of type `bool`"
 c_instance.declared_and_bound = "incompatible"
 
+# TODO: we already show an error here but the message might be improved?
 # mypy shows no error here, but pyright raises "reportAttributeAccessIssue"
-# error: [unresolved-attribute] "Attribute `inferred_from_value` can only be accessed on instances, not on the class object `Literal[C]` itself."
+# error: [unresolved-attribute] "Type `Literal[C]` has no attribute `inferred_from_value`"
 reveal_type(C.inferred_from_value)  # revealed: Unknown
 
+# TODO: this should be an error (pure instance variables cannot be accessed on the class)
 # mypy shows no error here, but pyright raises "reportAttributeAccessIssue"
-# error: [invalid-attribute-access] "Cannot assign to instance attribute `inferred_from_value` from the class object `Literal[C]`"
 C.inferred_from_value = "overwritten on class"
 
 # This assignment is fine:
@@ -89,13 +90,13 @@ c_instance = C()
 
 reveal_type(c_instance.declared_and_bound)  # revealed: str | None
 
-# Note that both mypy and pyright show no error in this case! So we may reconsider this in
-# the future, if it turns out to produce too many false positives. We currently emit:
-# error: [unresolved-attribute] "Attribute `declared_and_bound` can only be accessed on instances, not on the class object `Literal[C]` itself."
-reveal_type(C.declared_and_bound)  # revealed: Unknown
+# TODO: we currently plan to emit a diagnostic here. Note that both mypy
+# and pyright show no error in this case! So we may reconsider this in
+# the future, if it turns out to produce too many false positives.
+reveal_type(C.declared_and_bound)  # revealed: str | None
 
-# Same as above. Mypy and pyright do not show an error here.
-# error: [invalid-attribute-access] "Cannot assign to instance attribute `declared_and_bound` from the class object `Literal[C]`"
+# TODO: same as above. We plan to emit a diagnostic here, even if both mypy
+# and pyright allow this.
 C.declared_and_bound = "overwritten on class"
 
 # error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to attribute `declared_and_bound` of type `str | None`"
@@ -115,11 +116,11 @@ c_instance = C()
 
 reveal_type(c_instance.only_declared)  # revealed: str
 
-# Mypy and pyright do not show an error here. We treat this as a pure instance variable.
-# error: [unresolved-attribute] "Attribute `only_declared` can only be accessed on instances, not on the class object `Literal[C]` itself."
-reveal_type(C.only_declared)  # revealed: Unknown
+# TODO: mypy and pyright do not show an error here, but we plan to emit a diagnostic.
+# The type could be changed to 'Unknown' if we decide to emit an error?
+reveal_type(C.only_declared)  # revealed: str
 
-# error: [invalid-attribute-access] "Cannot assign to instance attribute `only_declared` from the class object `Literal[C]`"
+# TODO: mypy and pyright do not show an error here, but we plan to emit one.
 C.only_declared = "overwritten on class"
 ```
 
@@ -155,9 +156,7 @@ reveal_type(c_instance.declared_in_body_and_init)  # revealed: str | None
 
 reveal_type(c_instance.declared_in_body_defined_in_init)  # revealed: str | None
 
-# TODO: This should be `str | None`. Fixing this requires an overhaul of the `Symbol` API,
-# which is planned in https://github.com/astral-sh/ruff/issues/14297
-reveal_type(c_instance.bound_in_body_declared_in_init)  # revealed: Unknown | str | None
+reveal_type(c_instance.bound_in_body_declared_in_init)  # revealed: str | None
 
 reveal_type(c_instance.bound_in_body_and_init)  # revealed: Unknown | None | Literal["a"]
 ```
@@ -192,10 +191,11 @@ reveal_type(c_instance.declared_only)  # revealed: bytes
 
 reveal_type(c_instance.declared_and_bound)  # revealed: bool
 
-# error: [unresolved-attribute] "Attribute `inferred_from_value` can only be accessed on instances, not on the class object `Literal[C]` itself."
+# TODO: We already show an error here, but the message might be improved?
+# error: [unresolved-attribute]
 reveal_type(C.inferred_from_value)  # revealed: Unknown
 
-# error: [invalid-attribute-access] "Cannot assign to instance attribute `inferred_from_value` from the class object `Literal[C]`"
+# TODO: this should be an error
 C.inferred_from_value = "overwritten on class"
 ```
 
@@ -348,11 +348,8 @@ reveal_type(C().y)  # revealed: Unknown | str
 
 ```py
 class ContextManager:
-    def __enter__(self) -> int | None:
-        return 1
-
-    def __exit__(self, exc_type, exc_value, traceback) -> None:
-        pass
+    def __enter__(self) -> int | None: ...
+    def __exit__(self, exc_type, exc_value, traceback) -> None: ...
 
 class C:
     def __init__(self) -> None:
@@ -361,28 +358,9 @@ class C:
 
 c_instance = C()
 
-reveal_type(c_instance.x)  # revealed: Unknown | int | None
-```
-
-#### Attributes defined in `with` statements, but with unpacking
-
-```py
-class ContextManager:
-    def __enter__(self) -> tuple[int | None, int]:
-        return 1, 2
-
-    def __exit__(self, exc_type, exc_value, traceback) -> None:
-        pass
-
-class C:
-    def __init__(self) -> None:
-        with ContextManager() as (self.x, self.y):
-            pass
-
-c_instance = C()
-
-reveal_type(c_instance.x)  # revealed: Unknown | int | None
-reveal_type(c_instance.y)  # revealed: Unknown | int
+# TODO: Should be `Unknown | int | None`
+# error: [unresolved-attribute]
+reveal_type(c_instance.x)  # revealed: Unknown
 ```
 
 #### Attributes defined in comprehensions
@@ -620,9 +598,6 @@ C.class_method()
 # error: [unresolved-attribute]
 reveal_type(C.pure_class_variable)  # revealed: Unknown
 
-# TODO: should be no error when descriptor protocol is supported
-# and the assignment is properly attributed to the class method.
-# error: [invalid-attribute-access] "Cannot assign to instance attribute `pure_class_variable` from the class object `Literal[C]`"
 C.pure_class_variable = "overwritten on class"
 
 # TODO: should be  `Unknown | Literal["value set in class method"]` or
@@ -728,90 +703,7 @@ reveal_type(Derived().declared_in_body)  # revealed: int | None
 reveal_type(Derived().defined_in_init)  # revealed: str | None
 ```
 
-## Accessing attributes on class objects
-
-When accessing attributes on class objects, they are always looked up on the type of the class
-object first, i.e. on the metaclass:
-
-```py
-from typing import Literal
-
-class Meta1:
-    attr: Literal["metaclass value"] = "metaclass value"
-
-class C1(metaclass=Meta1): ...
-
-reveal_type(C1.attr)  # revealed: Literal["metaclass value"]
-```
-
-However, the metaclass attribute only takes precedence over a class-level attribute if it is a data
-descriptor. If it is a non-data descriptor or a normal attribute, the class-level attribute is used
-instead (see the [descriptor protocol tests] for data/non-data descriptor attributes):
-
-```py
-class Meta2:
-    attr: str = "metaclass value"
-
-class C2(metaclass=Meta2):
-    attr: Literal["class value"] = "class value"
-
-reveal_type(C2.attr)  # revealed: Literal["class value"]
-```
-
-If the class-level attribute is only partially defined, we union the metaclass attribute with the
-class-level attribute:
-
-```py
-def _(flag: bool):
-    class Meta3:
-        attr1 = "metaclass value"
-        attr2: Literal["metaclass value"] = "metaclass value"
-
-    class C3(metaclass=Meta3):
-        if flag:
-            attr1 = "class value"
-            # TODO: Neither mypy nor pyright show an error here, but we could consider emitting a conflicting-declaration diagnostic here.
-            attr2: Literal["class value"] = "class value"
-
-    reveal_type(C3.attr1)  # revealed: Unknown | Literal["metaclass value", "class value"]
-    reveal_type(C3.attr2)  # revealed: Literal["metaclass value", "class value"]
-```
-
-If the *metaclass* attribute is only partially defined, we emit a `possibly-unbound-attribute`
-diagnostic:
-
-```py
-def _(flag: bool):
-    class Meta4:
-        if flag:
-            attr1: str = "metaclass value"
-
-    class C4(metaclass=Meta4): ...
-    # error: [possibly-unbound-attribute]
-    reveal_type(C4.attr1)  # revealed: str
-```
-
-Finally, if both the metaclass attribute and the class-level attribute are only partially defined,
-we union them and emit a `possibly-unbound-attribute` diagnostic:
-
-```py
-def _(flag1: bool, flag2: bool):
-    class Meta5:
-        if flag1:
-            attr1 = "metaclass value"
-
-    class C5(metaclass=Meta5):
-        if flag2:
-            attr1 = "class value"
-
-    # error: [possibly-unbound-attribute]
-    reveal_type(C5.attr1)  # revealed: Unknown | Literal["metaclass value", "class value"]
-```
-
-## Unions of attributes
-
-If the (meta)class is a union type or if the attribute on the (meta) class has a union type, we
-infer those union types accordingly:
+## Union of attributes
 
 ```py
 def _(flag: bool):
@@ -823,186 +715,14 @@ def _(flag: bool):
         class C1:
             x = 2
 
-    reveal_type(C1.x)  # revealed: Unknown | Literal[1, 2]
-
     class C2:
         if flag:
             x = 3
         else:
             x = 4
 
+    reveal_type(C1.x)  # revealed: Unknown | Literal[1, 2]
     reveal_type(C2.x)  # revealed: Unknown | Literal[3, 4]
-
-    if flag:
-        class Meta3(type):
-            x = 5
-
-    else:
-        class Meta3(type):
-            x = 6
-
-    class C3(metaclass=Meta3): ...
-    reveal_type(C3.x)  # revealed: Unknown | Literal[5, 6]
-
-    class Meta4(type):
-        if flag:
-            x = 7
-        else:
-            x = 8
-
-    class C4(metaclass=Meta4): ...
-    reveal_type(C4.x)  # revealed: Unknown | Literal[7, 8]
-```
-
-## Unions with possibly unbound paths
-
-### Definite boundness within a class
-
-In this example, the `x` attribute is not defined in the `C2` element of the union:
-
-```py
-def _(flag1: bool, flag2: bool):
-    class C1:
-        x = 1
-
-    class C2: ...
-
-    class C3:
-        x = 3
-
-    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: Unknown | Literal[1, 3]
-
-    # error: [possibly-unbound-attribute] "Attribute `x` on type `C1 | C2 | C3` is possibly unbound"
-    reveal_type(C().x)  # revealed: Unknown | Literal[1, 3]
-```
-
-### Possibly-unbound within a class
-
-We raise the same diagnostic if the attribute is possibly-unbound in at least one element of the
-union:
-
-```py
-def _(flag: bool, flag1: bool, flag2: bool):
-    class C1:
-        x = 1
-
-    class C2:
-        if flag:
-            x = 2
-
-    class C3:
-        x = 3
-
-    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: Unknown | Literal[1, 2, 3]
-
-    # Note: we might want to consider ignoring possibly-unbound diagnostics for instance attributes eventually,
-    # see the "Possibly unbound/undeclared instance attribute" section below.
-    # error: [possibly-unbound-attribute] "Attribute `x` on type `C1 | C2 | C3` is possibly unbound"
-    reveal_type(C().x)  # revealed: Unknown | Literal[1, 2, 3]
-```
-
-### Possibly-unbound within gradual types
-
-```py
-from typing import Any
-
-def _(flag: bool):
-    class Base:
-        x: Any
-
-    class Derived(Base):
-        if flag:
-            # Redeclaring `x` with a more static type is okay in terms of LSP.
-            x: int
-
-    reveal_type(Derived().x)  # revealed: int | Any
-```
-
-### Attribute possibly unbound on a subclass but not on a superclass
-
-```py
-def _(flag: bool):
-    class Foo:
-        x = 1
-
-    class Bar(Foo):
-        if flag:
-            x = 2
-
-    reveal_type(Bar.x)  # revealed: Unknown | Literal[2, 1]
-
-    reveal_type(Bar().x)  # revealed: Unknown | Literal[2, 1]
-```
-
-### Attribute possibly unbound on a subclass and on a superclass
-
-```py
-def _(flag: bool):
-    class Foo:
-        if flag:
-            x = 1
-
-    class Bar(Foo):
-        if flag:
-            x = 2
-
-    # error: [possibly-unbound-attribute]
-    reveal_type(Bar.x)  # revealed: Unknown | Literal[2, 1]
-
-    # error: [possibly-unbound-attribute]
-    reveal_type(Bar().x)  # revealed: Unknown | Literal[2, 1]
-```
-
-### Possibly unbound/undeclared instance attribute
-
-#### Possibly unbound and undeclared
-
-```py
-def _(flag: bool):
-    class Foo:
-        if flag:
-            x: int
-
-        def __init(self):
-            if flag:
-                self.x = 1
-
-    # error: [possibly-unbound-attribute]
-    reveal_type(Foo().x)  # revealed: int | Unknown
-```
-
-#### Possibly unbound
-
-```py
-def _(flag: bool):
-    class Foo:
-        def __init(self):
-            if flag:
-                self.x = 1
-
-    # Emitting a diagnostic in a case like this is not something we support, and it's unclear
-    # if we ever will (or want to)
-    reveal_type(Foo().x)  # revealed: Unknown | Literal[1]
-```
-
-### Unions with all paths unbound
-
-If the symbol is unbound in all elements of the union, we detect that:
-
-```py
-def _(flag: bool):
-    class C1: ...
-    class C2: ...
-    C = C1 if flag else C2
-
-    # error: [unresolved-attribute] "Type `Literal[C1, C2]` has no attribute `x`"
-    reveal_type(C.x)  # revealed: Unknown
 ```
 
 ## Inherited class attributes
@@ -1042,133 +762,82 @@ reveal_type(A.__mro__)
 reveal_type(A.X)  # revealed: Unknown | Literal[42]
 ```
 
-## Intersections of attributes
+## Unions with possibly unbound paths
 
-### Attribute only available on one element
+### Definite boundness within a class
+
+In this example, the `x` attribute is not defined in the `C2` element of the union:
 
 ```py
-from knot_extensions import Intersection
+def _(flag1: bool, flag2: bool):
+    class C1:
+        x = 1
 
-class A:
-    x: int = 1
+    class C2: ...
 
-class B: ...
+    class C3:
+        x = 3
 
-def _(a_and_b: Intersection[A, B]):
-    reveal_type(a_and_b.x)  # revealed: int
+    C = C1 if flag1 else C2 if flag2 else C3
 
-# Same for class objects
-def _(a_and_b: Intersection[type[A], type[B]]):
-    reveal_type(a_and_b.x)  # revealed: int
+    # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
+    reveal_type(C.x)  # revealed: Unknown | Literal[1, 3]
 ```
 
-### Attribute available on both elements
+### Possibly-unbound within a class
+
+We raise the same diagnostic if the attribute is possibly-unbound in at least one element of the
+union:
 
 ```py
-from knot_extensions import Intersection
+def _(flag: bool, flag1: bool, flag2: bool):
+    class C1:
+        x = 1
 
-class P: ...
-class Q: ...
+    class C2:
+        if flag:
+            x = 2
 
-class A:
-    x: P = P()
+    class C3:
+        x = 3
 
-class B:
-    x: Q = Q()
+    C = C1 if flag1 else C2 if flag2 else C3
 
-def _(a_and_b: Intersection[A, B]):
-    reveal_type(a_and_b.x)  # revealed: P & Q
-
-# Same for class objects
-def _(a_and_b: Intersection[type[A], type[B]]):
-    reveal_type(a_and_b.x)  # revealed: P & Q
+    # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
+    reveal_type(C.x)  # revealed: Unknown | Literal[1, 2, 3]
 ```
 
-### Possible unboundness
+### Attribute possibly unbound on a subclass but not on a superclass
 
 ```py
-from knot_extensions import Intersection
-
-class P: ...
-class Q: ...
-
 def _(flag: bool):
-    class A1:
+    class Foo:
+        x = 1
+
+    class Bar(Foo):
         if flag:
-            x: P = P()
+            x = 2
 
-    class B1: ...
-
-    def inner1(a_and_b: Intersection[A1, B1]):
-        # error: [possibly-unbound-attribute]
-        reveal_type(a_and_b.x)  # revealed: P
-    # Same for class objects
-    def inner1_class(a_and_b: Intersection[type[A1], type[B1]]):
-        # error: [possibly-unbound-attribute]
-        reveal_type(a_and_b.x)  # revealed: P
-
-    class A2:
-        if flag:
-            x: P = P()
-
-    class B1:
-        x: Q = Q()
-
-    def inner2(a_and_b: Intersection[A2, B1]):
-        reveal_type(a_and_b.x)  # revealed: P & Q
-    # Same for class objects
-    def inner2_class(a_and_b: Intersection[type[A2], type[B1]]):
-        reveal_type(a_and_b.x)  # revealed: P & Q
-
-    class A3:
-        if flag:
-            x: P = P()
-
-    class B3:
-        if flag:
-            x: Q = Q()
-
-    def inner3(a_and_b: Intersection[A3, B3]):
-        # error: [possibly-unbound-attribute]
-        reveal_type(a_and_b.x)  # revealed: P & Q
-    # Same for class objects
-    def inner3_class(a_and_b: Intersection[type[A3], type[B3]]):
-        # error: [possibly-unbound-attribute]
-        reveal_type(a_and_b.x)  # revealed: P & Q
-
-    class A4: ...
-    class B4: ...
-
-    def inner4(a_and_b: Intersection[A4, B4]):
-        # error: [unresolved-attribute]
-        reveal_type(a_and_b.x)  # revealed: Unknown
-    # Same for class objects
-    def inner4_class(a_and_b: Intersection[type[A4], type[B4]]):
-        # error: [unresolved-attribute]
-        reveal_type(a_and_b.x)  # revealed: Unknown
+    reveal_type(Bar.x)  # revealed: Unknown | Literal[2, 1]
 ```
 
-### Intersection of implicit instance attributes
+### Attribute possibly unbound on a subclass and on a superclass
 
 ```py
-from knot_extensions import Intersection
+def _(flag: bool):
+    class Foo:
+        if flag:
+            x = 1
 
-class P: ...
-class Q: ...
+    class Bar(Foo):
+        if flag:
+            x = 2
 
-class A:
-    def __init__(self):
-        self.x: P = P()
-
-class B:
-    def __init__(self):
-        self.x: Q = Q()
-
-def _(a_and_b: Intersection[A, B]):
-    reveal_type(a_and_b.x)  # revealed: P & Q
+    # error: [possibly-unbound-attribute]
+    reveal_type(Bar.x)  # revealed: Unknown | Literal[2, 1]
 ```
 
-## Attribute access on `Any`
+### Attribute access on `Any`
 
 The union of the set of types that `Any` could materialise to is equivalent to `object`. It follows
 from this that attribute access on `Any` resolves to `Any` if the attribute does not exist on
@@ -1199,112 +868,29 @@ reveal_type(C.__mro__)  # revealed: tuple[Literal[C], Literal[B], Any, Literal[A
 reveal_type(C.x)  # revealed: Literal[1] & Any
 ```
 
-## Classes with custom `__getattr__` methods
+### Unions with all paths unbound
 
-### Basic
-
-If a type provides a custom `__getattr__` method, we use the return type of that method as the type
-for unknown attributes. Consider the following `CustomGetAttr` class:
+If the symbol is unbound in all elements of the union, we detect that:
 
 ```py
-from typing import Literal
+def _(flag: bool):
+    class C1: ...
+    class C2: ...
+    C = C1 if flag else C2
 
-def flag() -> bool:
-    return True
-
-class GetAttrReturnType: ...
-
-class CustomGetAttr:
-    class_attr: int = 1
-
-    if flag():
-        possibly_unbound: bytes = b"a"
-
-    def __init__(self) -> None:
-        self.instance_attr: str = "a"
-
-    def __getattr__(self, name: str) -> GetAttrReturnType:
-        return GetAttrReturnType()
-```
-
-We can access arbitrary attributes on instances of this class, and the type of the attribute will be
-`GetAttrReturnType`:
-
-```py
-c = CustomGetAttr()
-
-reveal_type(c.whatever)  # revealed: GetAttrReturnType
-```
-
-If an attribute is defined on the class, it takes precedence over the `__getattr__` method:
-
-```py
-reveal_type(c.class_attr)  # revealed: int
-```
-
-If the class attribute is possibly unbound, we union the type of the attribute with the fallback
-type of the `__getattr__` method:
-
-```py
-reveal_type(c.possibly_unbound)  # revealed: bytes | GetAttrReturnType
-```
-
-Instance attributes also take precedence over the `__getattr__` method:
-
-```py
-# Note: we could attempt to union with the fallback type of `__getattr__` here, as we currently do not
-# attempt to determine if instance attributes are always bound or not. Neither mypy nor pyright do this,
-# so it's not a priority.
-reveal_type(c.instance_attr)  # revealed: str
-```
-
-### Type of the `name` parameter
-
-If the `name` parameter of the `__getattr__` method is annotated with a (union of) literal type(s),
-we only consider the attribute access to be valid if the accessed attribute is one of them:
-
-```py
-from typing import Literal
-
-class Date:
-    def __getattr__(self, name: Literal["day", "month", "year"]) -> int:
-        return 0
-
-date = Date()
-
-reveal_type(date.day)  # revealed: int
-reveal_type(date.month)  # revealed: int
-reveal_type(date.year)  # revealed: int
-
-# error: [unresolved-attribute] "Type `Date` has no attribute `century`"
-reveal_type(date.century)  # revealed: Unknown
-```
-
-### `argparse.Namespace`
-
-A standard library example of a class with a custom `__getattr__` method is `argparse.Namespace`:
-
-```py
-import argparse
-
-def _(ns: argparse.Namespace):
-    reveal_type(ns.whatever)  # revealed: Any
+    # 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
 
-The type of `x.__class__` is the same as `x`'s meta-type. `x.__class__` is always the same value as
-`type(x)`.
-
 ```py
 import typing_extensions
 
 reveal_type(typing_extensions.__class__)  # revealed: Literal[ModuleType]
-reveal_type(type(typing_extensions))  # revealed: Literal[ModuleType]
 
 a = 42
 reveal_type(a.__class__)  # revealed: Literal[int]
-reveal_type(type(a))  # revealed: Literal[int]
 
 b = "42"
 reveal_type(b.__class__)  # revealed: Literal[str]
@@ -1320,13 +906,8 @@ 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(type(a))  # revealed: type[int]
-
     reveal_type(b.__class__)  # revealed: Literal[str]
-    reveal_type(type(b))  # revealed: Literal[str]
-
     reveal_type(c.__class__)  # revealed: type[int] | type[str]
-    reveal_type(type(c))  # 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,
@@ -1343,8 +924,6 @@ reveal_type(Foo.__class__)  # revealed: Literal[type]
 
 ## Module attributes
 
-### Basic
-
 `mod.py`:
 
 ```py
@@ -1379,7 +958,7 @@ for mod.global_symbol in IntIterable():
     pass
 ```
 
-### Nested module attributes
+## Nested attributes
 
 `outer/__init__.py`:
 
@@ -1453,8 +1032,8 @@ Most attribute accesses on bool-literal types are delegated to `builtins.bool`,
 bools are instances of that class:
 
 ```py
-reveal_type(True.__and__)  # revealed: <bound method `__and__` of `Literal[True]`>
-reveal_type(False.__or__)  # revealed: <bound method `__or__` of `Literal[False]`>
+reveal_type(True.__and__)  # revealed: @Todo(decorated method)
+reveal_type(False.__or__)  # revealed: @Todo(decorated method)
 ```
 
 Some attributes are special-cased, however:
@@ -1557,20 +1136,6 @@ class C:
 reveal_type(C().x)  # revealed: Unknown
 ```
 
-### Accessing attributes on `Never`
-
-Arbitrary attributes can be accessed on `Never` without emitting any errors:
-
-```py
-from typing_extensions import Never
-
-def f(never: Never):
-    reveal_type(never.arbitrary_attribute)  # revealed: Never
-
-    # Assigning `Never` to an attribute on `Never` is also allowed:
-    never.another_attribute = never
-```
-
 ### Builtin types attributes
 
 This test can probably be removed eventually, but we currently include it because we do not yet
@@ -1610,7 +1175,6 @@ reveal_type(C.a_none)  # revealed: None
 Some of the tests in the *Class and instance variables* section draw inspiration from
 [pyright's documentation] on this topic.
 
-[descriptor protocol tests]: descriptor_protocol.md
 [pyright's documentation]: https://microsoft.github.io/pyright/#/type-concepts-advanced?id=class-and-instance-variables
 [typing spec on `classvar`]: https://typing.readthedocs.io/en/latest/spec/class-compat.html#classvar
 [`typing.classvar`]: https://docs.python.org/3/library/typing.html#typing.ClassVar

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

@@ -259,17 +259,11 @@ class A:
 class B:
     __add__ = A()
 
-reveal_type(B() + B())  # revealed: Unknown | int
-```
-
-Note that we union with `Unknown` here because `__add__` is not declared. We do infer just `int` if
-the callable is declared:
-
-```py
-class B2:
-    __add__: A = A()
-
-reveal_type(B2() + B2())  # revealed: int
+# TODO: this could be `int` if we declare `B.__add__` using a `Callable` type
+# TODO: Should not be an error: `A` instance is not a method descriptor, don't prepend `self` arg.
+#   Revealed type should be `Unknown | int`.
+# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `B` and `B`"
+reveal_type(B() + B())  # revealed: Unknown
 ```
 
 ## Integration test: numbers from typeshed
@@ -312,7 +306,7 @@ reveal_type(1 + A())  # revealed: A
 reveal_type(A() + "foo")  # revealed: A
 # TODO should be `A` since `str.__add__` doesn't support `A` instances
 # TODO overloads
-reveal_type("foo" + A())  # revealed: @Todo(return type of decorated function)
+reveal_type("foo" + A())  # revealed: @Todo(return type)
 
 reveal_type(A() + b"foo")  # revealed: A
 # TODO should be `A` since `bytes.__add__` doesn't support `A` instances
@@ -320,7 +314,7 @@ reveal_type(b"foo" + A())  # revealed: bytes
 
 reveal_type(A() + ())  # revealed: A
 # TODO this should be `A`, since `tuple.__add__` doesn't support `A` instances
-reveal_type(() + A())  # revealed: @Todo(return type of decorated function)
+reveal_type(() + A())  # revealed: @Todo(return type)
 
 literal_string_instance = "foo" * 1_000_000_000
 # the test is not testing what it's meant to be testing if this isn't a `LiteralString`:
@@ -329,7 +323,7 @@ reveal_type(literal_string_instance)  # revealed: LiteralString
 reveal_type(A() + literal_string_instance)  # revealed: A
 # TODO should be `A` since `str.__add__` doesn't support `A` instances
 # TODO overloads
-reveal_type(literal_string_instance + A())  # revealed: @Todo(return type of decorated function)
+reveal_type(literal_string_instance + A())  # revealed: @Todo(return type)
 ```
 
 ## Operations involving instances of classes inheriting from `Any`
@@ -357,20 +351,6 @@ class Y(Foo): ...
 reveal_type(X() + Y())  # revealed: int
 ```
 
-## Operations involving types with invalid `__bool__` methods
-
-<!-- snapshot-diagnostics -->
-
-```py
-class NotBoolable:
-    __bool__ = 3
-
-a = NotBoolable()
-
-# error: [unsupported-bool-conversion]
-10 and a and True
-```
-
 ## Unsupported
 
 ### Dunder as instance attribute
@@ -406,12 +386,10 @@ A left-hand dunder method doesn't apply for the right-hand operand, or vice vers
 
 ```py
 class A:
-    def __add__(self, other) -> int:
-        return 1
+    def __add__(self, other) -> int: ...
 
 class B:
-    def __radd__(self, other) -> int:
-        return 1
+    def __radd__(self, other) -> int: ...
 
 class C: ...
 

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

@@ -10,7 +10,8 @@ reveal_type(-3 // 3)  # revealed: Literal[-1]
 reveal_type(-3 / 3)  # revealed: float
 reveal_type(5 % 3)  # revealed: Literal[2]
 
-# error: [unsupported-operator] "Operator `+` is unsupported between objects of type `Literal[2]` and `Literal["f"]`"
+# TODO: Should emit `unsupported-operator` but we don't understand the bases of `str`, so we think
+#       it inherits `Unknown`, so we think `str.__radd__` is `Unknown` instead of nonexistent.
 reveal_type(2 + "f")  # revealed: Unknown
 
 def lhs(x: int):
@@ -50,9 +51,9 @@ reveal_type(1 ** (largest_u32 + 1))  # revealed: int
 reveal_type(2**largest_u32)  # revealed: int
 
 def variable(x: int):
-    reveal_type(x**2)  # revealed: @Todo(return type of decorated function)
-    reveal_type(2**x)  # revealed: @Todo(return type of decorated function)
-    reveal_type(x**x)  # revealed: @Todo(return type of decorated function)
+    reveal_type(x**2)  # revealed: @Todo(return type)
+    reveal_type(2**x)  # revealed: @Todo(return type)
+    reveal_type(x**x)  # revealed: @Todo(return type)
 ```
 
 ## Division by Zero

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

@@ -1,51 +0,0 @@
-# Binary operations on union types
-
-Binary operations on union types are only available if they are supported for all possible
-combinations of types:
-
-```py
-def f1(i: int, u: int | None):
-    # error: [unsupported-operator] "Operator `+` is unsupported between objects of type `int` and `int | None`"
-    reveal_type(i + u)  # revealed: Unknown
-    # error: [unsupported-operator] "Operator `+` is unsupported between objects of type `int | None` and `int`"
-    reveal_type(u + i)  # revealed: Unknown
-```
-
-`int` can be added to `int`, and `str` can be added to `str`, but expressions of type `int | str`
-cannot be added, because that would require addition of `int` and `str` or vice versa:
-
-```py
-def f2(i: int, s: str, int_or_str: int | str):
-    i + i
-    s + s
-    # error: [unsupported-operator] "Operator `+` is unsupported between objects of type `int | str` and `int | str`"
-    reveal_type(int_or_str + int_or_str)  # revealed: Unknown
-```
-
-However, if an operation is supported for all possible combinations, the result will be a union of
-the possible outcomes:
-
-```py
-from typing import Literal
-
-def f3(two_or_three: Literal[2, 3], a_or_b: Literal["a", "b"]):
-    reveal_type(two_or_three + two_or_three)  # revealed: Literal[4, 5, 6]
-    reveal_type(two_or_three**two_or_three)  # revealed: Literal[4, 8, 9, 27]
-
-    reveal_type(a_or_b + a_or_b)  # revealed: Literal["aa", "ab", "ba", "bb"]
-
-    reveal_type(two_or_three * a_or_b)  # revealed: Literal["aa", "bb", "aaa", "bbb"]
-```
-
-We treat a type annotation of `float` as a union of `int` and `float`, so union handling is relevant
-here:
-
-```py
-def f4(x: float, y: float):
-    reveal_type(x + y)  # revealed: int | float
-    reveal_type(x - y)  # revealed: int | float
-    reveal_type(x * y)  # revealed: int | float
-    reveal_type(x / y)  # revealed: int | float
-    reveal_type(x // y)  # revealed: int | float
-    reveal_type(x % y)  # revealed: int | float
-```

crates/red_knot_python_semantic/resources/mdtest/boundness_declaredness/public.md

@@ -69,8 +69,7 @@ without raising an error.
 from typing import Any
 
 def any() -> Any: ...
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 a: int
 b: str
@@ -127,8 +126,7 @@ inferred types:
 from typing import Any
 
 def any() -> Any: ...
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 a = 1
 b = 2
@@ -166,8 +164,7 @@ error for both `a` and `b`:
 ```py
 from typing import Any
 
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 if flag():
     a: Any = 1
@@ -197,8 +194,7 @@ seems inconsistent when compared to the case just above.
 `mod.py`:
 
 ```py
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 if flag():
     a: int
@@ -252,8 +248,7 @@ inconsistent when compared to the "possibly-undeclared-and-possibly-unbound" cas
 `mod.py`:
 
 ```py
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 if flag:
     a = 1

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

@@ -1,40 +0,0 @@
-# Calling builtins
-
-## `bool` with incorrect arguments
-
-```py
-class NotBool:
-    __bool__ = None
-
-# error: [too-many-positional-arguments] "Too many positional arguments to class `bool`: expected 1, got 2"
-bool(1, 2)
-
-# TODO: We should emit an `unsupported-bool-conversion` error here because the argument doesn't implement `__bool__` correctly.
-bool(NotBool())
-```
-
-## Calls to `type()`
-
-A single-argument call to `type()` returns an object that has the argument's meta-type. (This is
-tested more extensively in `crates/red_knot_python_semantic/resources/mdtest/attributes.md`,
-alongside the tests for the `__class__` attribute.)
-
-```py
-reveal_type(type(1))  # revealed: Literal[int]
-```
-
-But a three-argument call to type creates a dynamic instance of the `type` class:
-
-```py
-reveal_type(type("Foo", (), {}))  # revealed: type
-```
-
-Other numbers of arguments are invalid
-
-```py
-# error: [no-matching-overload] "No overload of class `type` matches arguments"
-type("Foo", ())
-
-# error: [no-matching-overload] "No overload of class `type` matches arguments"
-type("Foo", (), {}, weird_other_arg=42)
-```

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

@@ -25,8 +25,7 @@ reveal_type(b)  # revealed: Unknown
 def _(flag: bool):
     class PossiblyNotCallable:
         if flag:
-            def __call__(self) -> int:
-                return 1
+            def __call__(self) -> int: ...
 
     a = PossiblyNotCallable()
     result = a()  # error: "Object of type `PossiblyNotCallable` is not callable (possibly unbound `__call__` method)"
@@ -39,8 +38,7 @@ def _(flag: bool):
 def _(flag: bool):
     if flag:
         class PossiblyUnbound:
-            def __call__(self) -> int:
-                return 1
+            def __call__(self) -> int: ...
 
     # error: [possibly-unresolved-reference]
     a = PossiblyUnbound()
@@ -66,8 +64,7 @@ def _(flag: bool):
         if flag:
             __call__ = 1
         else:
-            def __call__(self) -> int:
-                return 1
+            def __call__(self) -> int: ...
 
     a = NonCallable()
     # error: [call-non-callable] "Object of type `Literal[1]` is not callable"
@@ -85,7 +82,7 @@ class C:
 
 c = C()
 
-# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 2 (`x`) of bound method `__call__`; expected type `int`"
+# error: 15 [invalid-argument-type] "Object of type `Literal["foo"]` cannot be assigned to parameter 2 (`x`) of function `__call__`; expected type `int`"
 reveal_type(c("foo"))  # revealed: int
 ```
 
@@ -99,7 +96,7 @@ class C:
 
 c = C()
 
-# error: 13 [invalid-argument-type] "Object of type `C` cannot be assigned to parameter 1 (`self`) of bound method `__call__`; expected type `int`"
+# error: 13 [invalid-argument-type] "Object of type `C` cannot be assigned to parameter 1 (`self`) of function `__call__`; expected type `int`"
 reveal_type(c())  # revealed: int
 ```
 

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

@@ -1,219 +0,0 @@
-# Dunder calls
-
-## Introduction
-
-This test suite explains and documents how dunder methods are looked up and called. Throughout the
-document, we use `__getitem__` as an example, but the same principles apply to other dunder methods.
-
-Dunder methods are implicitly called when using certain syntax. For example, the index operator
-`obj[key]` calls the `__getitem__` method under the hood. Exactly *how* a dunder method is looked up
-and called works slightly different from regular methods. Dunder methods are not looked up on `obj`
-directly, but rather on `type(obj)`. But in many ways, they still *act* as if they were called on
-`obj` directly. If the `__getitem__` member of `type(obj)` is a descriptor, it is called with `obj`
-as the `instance` argument to `__get__`. A desugared version of `obj[key]` is roughly equivalent to
-`getitem_desugared(obj, key)` as defined below:
-
-```py
-from typing import Any
-
-def find_name_in_mro(typ: type, name: str) -> Any:
-    # See implementation in https://docs.python.org/3/howto/descriptor.html#invocation-from-an-instance
-    pass
-
-def getitem_desugared(obj: object, key: object) -> object:
-    getitem_callable = find_name_in_mro(type(obj), "__getitem__")
-    if hasattr(getitem_callable, "__get__"):
-        getitem_callable = getitem_callable.__get__(obj, type(obj))
-
-    return getitem_callable(key)
-```
-
-In the following tests, we demonstrate that we implement this behavior correctly.
-
-## Operating on class objects
-
-If we invoke a dunder method on a class, it is looked up on the *meta* class, since any class is an
-instance of its metaclass:
-
-```py
-class Meta(type):
-    def __getitem__(cls, key: int) -> str:
-        return str(key)
-
-class DunderOnMetaclass(metaclass=Meta):
-    pass
-
-reveal_type(DunderOnMetaclass[0])  # revealed: str
-```
-
-If the dunder method is only present on the class itself, it will not be called:
-
-```py
-class ClassWithNormalDunder:
-    def __getitem__(self, key: int) -> str:
-        return str(key)
-
-# error: [non-subscriptable]
-ClassWithNormalDunder[0]
-```
-
-## Operating on instances
-
-When invoking a dunder method on an instance of a class, it is looked up on the class:
-
-```py
-class ClassWithNormalDunder:
-    def __getitem__(self, key: int) -> str:
-        return str(key)
-
-class_with_normal_dunder = ClassWithNormalDunder()
-
-reveal_type(class_with_normal_dunder[0])  # revealed: str
-```
-
-Which can be demonstrated by trying to attach a dunder method to an instance, which will not work:
-
-```py
-def external_getitem(instance, key: int) -> str:
-    return str(key)
-
-class ThisFails:
-    def __init__(self):
-        self.__getitem__ = external_getitem
-
-this_fails = ThisFails()
-
-# error: [non-subscriptable] "Cannot subscript object of type `ThisFails` with no `__getitem__` method"
-reveal_type(this_fails[0])  # revealed: Unknown
-```
-
-However, the attached dunder method *can* be called if accessed directly:
-
-```py
-reveal_type(this_fails.__getitem__(this_fails, 0))  # revealed: Unknown | str
-```
-
-The instance-level method is also not called when the class-level method is present:
-
-```py
-def external_getitem1(instance, key) -> str:
-    return "a"
-
-def external_getitem2(key) -> int:
-    return 1
-
-def _(flag: bool):
-    class ThisFails:
-        if flag:
-            __getitem__ = external_getitem1
-
-        def __init__(self):
-            self.__getitem__ = external_getitem2
-
-    this_fails = ThisFails()
-
-    # error: [call-possibly-unbound-method]
-    reveal_type(this_fails[0])  # revealed: Unknown | str
-```
-
-## When the dunder is not a method
-
-A dunder can also be a non-method callable:
-
-```py
-class SomeCallable:
-    def __call__(self, key: int) -> str:
-        return str(key)
-
-class ClassWithNonMethodDunder:
-    __getitem__: SomeCallable = SomeCallable()
-
-class_with_callable_dunder = ClassWithNonMethodDunder()
-
-reveal_type(class_with_callable_dunder[0])  # revealed: str
-```
-
-## Dunders are looked up using the descriptor protocol
-
-Here, we demonstrate that the descriptor protocol is invoked when looking up a dunder method. Note
-that the `instance` argument is on object of type `ClassWithDescriptorDunder`:
-
-```py
-from __future__ import annotations
-
-class SomeCallable:
-    def __call__(self, key: int) -> str:
-        return str(key)
-
-class Descriptor:
-    def __get__(self, instance: ClassWithDescriptorDunder, owner: type[ClassWithDescriptorDunder]) -> SomeCallable:
-        return SomeCallable()
-
-class ClassWithDescriptorDunder:
-    __getitem__: Descriptor = Descriptor()
-
-class_with_descriptor_dunder = ClassWithDescriptorDunder()
-
-reveal_type(class_with_descriptor_dunder[0])  # revealed: str
-```
-
-## Dunders can not be overwritten on instances
-
-If we attempt to overwrite a dunder method on an instance, it does not affect the behavior of
-implicit dunder calls:
-
-```py
-class C:
-    def __getitem__(self, key: int) -> str:
-        return str(key)
-
-    def f(self):
-        # TODO: This should emit an `invalid-assignment` diagnostic once we understand the type of `self`
-        self.__getitem__ = None
-
-# This is still fine, and simply calls the `__getitem__` method on the class
-reveal_type(C()[0])  # revealed: str
-```
-
-## Calling a union of dunder methods
-
-```py
-def _(flag: bool):
-    class C:
-        if flag:
-            def __getitem__(self, key: int) -> str:
-                return str(key)
-        else:
-            def __getitem__(self, key: int) -> bytes:
-                return bytes()
-
-    c = C()
-    reveal_type(c[0])  # revealed: str | bytes
-
-    if flag:
-        class D:
-            def __getitem__(self, key: int) -> str:
-                return str(key)
-
-    else:
-        class D:
-            def __getitem__(self, key: int) -> bytes:
-                return bytes()
-
-    d = D()
-    reveal_type(d[0])  # revealed: str | bytes
-```
-
-## Calling a possibly-unbound dunder method
-
-```py
-def _(flag: bool):
-    class C:
-        if flag:
-            def __getitem__(self, key: int) -> str:
-                return str(key)
-
-    c = C()
-    # error: [call-possibly-unbound-method]
-    reveal_type(c[0])  # revealed: str
-```

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

@@ -37,8 +37,6 @@ def foo() -> int:
     return 42
 
 def decorator(func) -> Callable[[], int]:
-    # TODO: no error
-    # error: [invalid-return-type]
     return foo
 
 @decorator
@@ -46,7 +44,7 @@ def bar() -> str:
     return "bar"
 
 # TODO: should reveal `int`, as the decorator replaces `bar` with `foo`
-reveal_type(bar())  # revealed: @Todo(return type of decorated function)
+reveal_type(bar())  # revealed: @Todo(return type)
 ```
 
 ## Invalid callable

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

@@ -12,7 +12,7 @@ import inspect
 
 class Descriptor:
     def __get__(self, instance, owner) -> str:
-        return "a"
+        return 1
 
 class C:
     normal: int = 1
@@ -59,7 +59,7 @@ import sys
 reveal_type(inspect.getattr_static(sys, "platform"))  # revealed: LiteralString
 reveal_type(inspect.getattr_static(inspect, "getattr_static"))  # revealed: Literal[getattr_static]
 
-reveal_type(inspect.getattr_static(1, "real"))  # revealed: Literal[real]
+reveal_type(inspect.getattr_static(1, "real"))  # revealed: Literal[1]
 ```
 
 (Implicit) instance attributes can also be accessed through `inspect.getattr_static`:
@@ -72,23 +72,6 @@ class D:
 reveal_type(inspect.getattr_static(D(), "instance_attr"))  # revealed: int
 ```
 
-And attributes on metaclasses can be accessed when probing the class:
-
-```py
-class Meta(type):
-    attr: int = 1
-
-class E(metaclass=Meta): ...
-
-reveal_type(inspect.getattr_static(E, "attr"))  # revealed: int
-```
-
-Metaclass attributes can not be added when probing an instance of the class:
-
-```py
-reveal_type(inspect.getattr_static(E(), "attr", "non_existent"))  # revealed: Literal["non_existent"]
-```
-
 ## Error cases
 
 We can only infer precise types if the attribute is a literal string. In all other cases, we fall

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

@@ -235,198 +235,24 @@ method_wrapper(C(), None)
 method_wrapper(None, C)
 
 # Passing `None` without an `owner` argument is an
-# error: [no-matching-overload] "No overload of method wrapper `__get__` of function `f` matches arguments"
+# error: [missing-argument] "No argument provided for required parameter `owner`"
 method_wrapper(None)
 
 # Passing something that is not assignable to `type` as the `owner` argument is an
-# error: [no-matching-overload] "No overload of method wrapper `__get__` of function `f` matches arguments"
+# error: [invalid-argument-type] "Object of type `Literal[1]` cannot be assigned to parameter 2 (`owner`); expected type `type`"
 method_wrapper(None, 1)
 
 # Passing `None` as the `owner` argument when `instance` is `None` is an
-# error: [no-matching-overload] "No overload of method wrapper `__get__` of function `f` matches arguments"
+# error: [invalid-argument-type] "Object of type `None` cannot be assigned to parameter 2 (`owner`); expected type `type`"
 method_wrapper(None, None)
 
 # Calling `__get__` without any arguments is an
-# error: [no-matching-overload] "No overload of method wrapper `__get__` of function `f` matches arguments"
+# error: [missing-argument] "No argument provided for required parameter `instance`"
 method_wrapper()
 
 # Calling `__get__` with too many positional arguments is an
-# error: [no-matching-overload] "No overload of method wrapper `__get__` of function `f` matches arguments"
+# error: [too-many-positional-arguments] "Too many positional arguments: expected 2, got 3"
 method_wrapper(C(), C, "one too many")
 ```
 
-## Fallback to metaclass
-
-When a method is accessed on a class object, it is looked up on the metaclass if it is not found on
-the class itself. This also creates a bound method that is bound to the class object itself:
-
-```py
-from __future__ import annotations
-
-class Meta(type):
-    def f(cls, arg: int) -> str:
-        return "a"
-
-class C(metaclass=Meta):
-    pass
-
-reveal_type(C.f)  # revealed: <bound method `f` of `Literal[C]`>
-reveal_type(C.f(1))  # revealed: str
-```
-
-The method `f` can not be accessed from an instance of the class:
-
-```py
-# error: [unresolved-attribute] "Type `C` has no attribute `f`"
-C().f
-```
-
-A metaclass function can be shadowed by a method on the class:
-
-```py
-from typing import Any, Literal
-
-class D(metaclass=Meta):
-    def f(arg: int) -> Literal["a"]:
-        return "a"
-
-reveal_type(D.f(1))  # revealed: Literal["a"]
-```
-
-If the class method is possibly unbound, we union the return types:
-
-```py
-def flag() -> bool:
-    return True
-
-class E(metaclass=Meta):
-    if flag():
-        def f(arg: int) -> Any:
-            return "a"
-
-reveal_type(E.f(1))  # revealed: str | Any
-```
-
-## `@classmethod`
-
-### Basic
-
-When a `@classmethod` attribute is accessed, it returns a bound method object, even when accessed on
-the class object itself:
-
-```py
-from __future__ import annotations
-
-class C:
-    @classmethod
-    def f(cls: type[C], x: int) -> str:
-        return "a"
-
-reveal_type(C.f)  # revealed: <bound method `f` of `Literal[C]`>
-reveal_type(C().f)  # revealed: <bound method `f` of `type[C]`>
-```
-
-The `cls` method argument is then implicitly passed as the first argument when calling the method:
-
-```py
-reveal_type(C.f(1))  # revealed: str
-reveal_type(C().f(1))  # revealed: str
-```
-
-When the class method is called incorrectly, we detect it:
-
-```py
-C.f("incorrect")  # error: [invalid-argument-type]
-C.f()  # error: [missing-argument]
-C.f(1, 2)  # error: [too-many-positional-arguments]
-```
-
-If the `cls` parameter is wrongly annotated, we emit an error at the call site:
-
-```py
-class D:
-    @classmethod
-    def f(cls: D):
-        # This function is wrongly annotated, it should be `type[D]` instead of `D`
-        pass
-
-# error: [invalid-argument-type] "Object of type `Literal[D]` cannot be assigned to parameter 1 (`cls`) of bound method `f`; expected type `D`"
-D.f()
-```
-
-When a class method is accessed on a derived class, it is bound to that derived class:
-
-```py
-class Derived(C):
-    pass
-
-reveal_type(Derived.f)  # revealed: <bound method `f` of `Literal[Derived]`>
-reveal_type(Derived().f)  # revealed: <bound method `f` of `type[Derived]`>
-
-reveal_type(Derived.f(1))  # revealed: str
-reveal_type(Derived().f(1))  # revealed: str
-```
-
-### Accessing the classmethod as a static member
-
-Accessing a `@classmethod`-decorated function at runtime returns a `classmethod` object. We
-currently don't model this explicitly:
-
-```py
-from inspect import getattr_static
-
-class C:
-    @classmethod
-    def f(cls): ...
-
-reveal_type(getattr_static(C, "f"))  # revealed: Literal[f]
-reveal_type(getattr_static(C, "f").__get__)  # revealed: <method-wrapper `__get__` of `f`>
-```
-
-But we correctly model how the `classmethod` descriptor works:
-
-```py
-reveal_type(getattr_static(C, "f").__get__(None, C))  # revealed: <bound method `f` of `Literal[C]`>
-reveal_type(getattr_static(C, "f").__get__(C(), C))  # revealed: <bound method `f` of `Literal[C]`>
-reveal_type(getattr_static(C, "f").__get__(C()))  # revealed: <bound method `f` of `type[C]`>
-```
-
-The `owner` argument takes precedence over the `instance` argument:
-
-```py
-reveal_type(getattr_static(C, "f").__get__("dummy", C))  # revealed: <bound method `f` of `Literal[C]`>
-```
-
-### Classmethods mixed with other decorators
-
-When a `@classmethod` is additionally decorated with another decorator, it is still treated as a
-class method:
-
-```py
-from __future__ import annotations
-
-def does_nothing[T](f: T) -> T:
-    return f
-
-class C:
-    @classmethod
-    @does_nothing
-    def f1(cls: type[C], x: int) -> str:
-        return "a"
-
-    @does_nothing
-    @classmethod
-    def f2(cls: type[C], x: int) -> str:
-        return "a"
-
-# TODO: We do not support decorators yet (only limited special cases). Eventually,
-# these should all return `str`:
-
-reveal_type(C.f1(1))  # revealed: @Todo(return type of decorated function)
-reveal_type(C().f1(1))  # revealed: @Todo(return type of decorated function)
-
-reveal_type(C.f2(1))  # revealed: @Todo(return type of decorated function)
-reveal_type(C().f2(1))  # revealed: @Todo(return type of decorated function)
-```
-
 [functions and methods]: https://docs.python.org/3/howto/descriptor.html#functions-and-methods

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

@@ -1,12 +0,0 @@
-# Never is callable
-
-The type `Never` is callable with an arbitrary set of arguments. The result is always `Never`.
-
-```py
-from typing_extensions import Never
-
-def f(never: Never):
-    reveal_type(never())  # revealed: Never
-    reveal_type(never(1))  # revealed: Never
-    reveal_type(never(1, "a", never, x=None))  # revealed: Never
-```

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

@@ -1,50 +0,0 @@
-# Call `type[...]`
-
-## Single class
-
-### Trivial constructor
-
-```py
-class C: ...
-
-def _(subclass_of_c: type[C]):
-    reveal_type(subclass_of_c())  # revealed: C
-```
-
-### Non-trivial constructor
-
-```py
-class C:
-    def __init__(self, x: int): ...
-
-def _(subclass_of_c: type[C]):
-    reveal_type(subclass_of_c(1))  # revealed: C
-
-    # TODO: Those should all be errors
-    reveal_type(subclass_of_c("a"))  # revealed: C
-    reveal_type(subclass_of_c())  # revealed: C
-    reveal_type(subclass_of_c(1, 2))  # revealed: C
-```
-
-## Dynamic base
-
-```py
-from typing import Any
-from knot_extensions import Unknown
-
-def _(subclass_of_any: type[Any], subclass_of_unknown: type[Unknown]):
-    reveal_type(subclass_of_any())  # revealed: Any
-    reveal_type(subclass_of_any("any", "args", 1, 2))  # revealed: Any
-    reveal_type(subclass_of_unknown())  # revealed: Unknown
-    reveal_type(subclass_of_unknown("any", "args", 1, 2))  # revealed: Unknown
-```
-
-## Unions of classes
-
-```py
-class A: ...
-class B: ...
-
-def _(subclass_of_ab: type[A | B]):
-    reveal_type(subclass_of_ab())  # revealed: A | B
-```

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

@@ -56,7 +56,6 @@ def _(flag: bool, flag2: bool):
     else:
         def f() -> int:
             return 1
-    # TODO we should mention all non-callable elements of the union
     # error: [call-non-callable] "Object of type `Literal[1]` is not callable"
     # revealed: int | Unknown
     reveal_type(f())
@@ -82,12 +81,8 @@ def _(flag: bool):
 Calling a union where the arguments don't match the signature of all variants.
 
 ```py
-def f1(a: int) -> int:
-    return a
-
-def f2(a: str) -> str:
-    return a
-
+def f1(a: int) -> int: ...
+def f2(a: str) -> str: ...
 def _(flag: bool):
     if flag:
         f = f1
@@ -113,38 +108,3 @@ def _(flag: bool):
     x = f(3)
     reveal_type(x)  # revealed: Unknown
 ```
-
-## Union of binding errors
-
-```py
-def f1(): ...
-def f2(): ...
-def _(flag: bool):
-    if flag:
-        f = f1
-    else:
-        f = f2
-
-    # TODO: we should show all errors from the union, not arbitrarily pick one union element
-    # error: [too-many-positional-arguments] "Too many positional arguments to function `f1`: expected 0, got 1"
-    x = f(3)
-    reveal_type(x)  # revealed: Unknown
-```
-
-## One not-callable, one wrong argument
-
-```py
-class C: ...
-
-def f1(): ...
-def _(flag: bool):
-    if flag:
-        f = f1
-    else:
-        f = C()
-
-    # TODO: we should either show all union errors here, or prioritize the not-callable error
-    # error: [too-many-positional-arguments] "Too many positional arguments to function `f1`: expected 0, got 1"
-    x = f(3)
-    reveal_type(x)  # revealed: Unknown
-```

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

@@ -160,45 +160,3 @@ reveal_type(42 in A())  # revealed: bool
 # error: [unsupported-operator] "Operator `in` is not supported for types `str` and `A`, in comparing `Literal["hello"]` with `A`"
 reveal_type("hello" in A())  # revealed: bool
 ```
-
-## Return type that doesn't implement `__bool__` correctly
-
-`in` and `not in` operations will fail at runtime if the object on the right-hand side of the
-operation has a `__contains__` method that returns a type which is not convertible to `bool`. This
-is because of the way these operations are handled by the Python interpreter at runtime. If we
-assume that `y` is an object that has a `__contains__` method, the Python expression `x in y`
-desugars to a `contains(y, x)` call, where `contains` looks something like this:
-
-```ignore
-def contains(y, x):
-    return bool(type(y).__contains__(y, x))
-```
-
-where the `bool()` conversion itself implicitly calls `__bool__` under the hood.
-
-TODO: Ideally the message would explain to the user what's wrong. E.g,
-
-```ignore
-error: [operator] cannot use `in` operator on object of type `WithContains`
-    note: This is because the `in` operator implicitly calls `WithContains.__contains__`, but `WithContains.__contains__` is invalidly defined
-    note: `WithContains.__contains__` is invalidly defined because it returns an instance of `NotBoolable`, which cannot be evaluated in a boolean context
-    note: `NotBoolable` cannot be evaluated in a boolean context because its `__bool__` attribute is not callable
-```
-
-It may also be more appropriate to use `unsupported-operator` as the error code.
-
-<!-- snapshot-diagnostics -->
-
-```py
-class NotBoolable:
-    __bool__ = 3
-
-class WithContains:
-    def __contains__(self, item) -> NotBoolable:
-        return NotBoolable()
-
-# error: [unsupported-bool-conversion]
-10 in WithContains()
-# error: [unsupported-bool-conversion]
-10 not in WithContains()
-```

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

@@ -154,7 +154,7 @@ reveal_type(B() >= A())  # revealed: LeReturnType
 
 class C:
     def __gt__(self, other: C) -> EqReturnType:
-        return EqReturnType()
+        return 42
 
     def __ge__(self, other: C) -> NeReturnType:
         return NeReturnType()
@@ -345,47 +345,3 @@ def f(x: bool, y: int):
     reveal_type(4.2 < x)  # revealed: bool
     reveal_type(x < 4.2)  # revealed: bool
 ```
-
-## Chained comparisons with objects that don't implement `__bool__` correctly
-
-<!-- snapshot-diagnostics -->
-
-Python implicitly calls `bool` on the comparison result of preceding elements (but not for the last
-element) of a chained comparison.
-
-```py
-class NotBoolable:
-    __bool__ = 3
-
-class Comparable:
-    def __lt__(self, item) -> NotBoolable:
-        return NotBoolable()
-
-    def __gt__(self, item) -> NotBoolable:
-        return NotBoolable()
-
-# error: [unsupported-bool-conversion]
-10 < Comparable() < 20
-# error: [unsupported-bool-conversion]
-10 < Comparable() < Comparable()
-
-Comparable() < Comparable()  # fine
-```
-
-## Callables as comparison dunders
-
-```py
-from typing import Literal
-
-class AlwaysTrue:
-    def __call__(self, other: object) -> Literal[True]:
-        return True
-
-class A:
-    __eq__: AlwaysTrue = AlwaysTrue()
-    __lt__: AlwaysTrue = AlwaysTrue()
-
-reveal_type(A() == A())  # revealed: Literal[True]
-reveal_type(A() < A())  # revealed: Literal[True]
-reveal_type(A() > A())  # revealed: Literal[True]
-```

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

@@ -110,8 +110,7 @@ given operator:
 
 ```py
 class Container:
-    def __contains__(self, x) -> bool:
-        return False
+    def __contains__(self, x) -> bool: ...
 
 class NonContainer: ...
 
@@ -131,8 +130,7 @@ unsupported for the given operator:
 
 ```py
 class Container:
-    def __contains__(self, x) -> bool:
-        return False
+    def __contains__(self, x) -> bool: ...
 
 class NonContainer: ...
 

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

@@ -22,19 +22,14 @@ Walking through examples:
 from __future__ import annotations
 
 class A:
-    def __lt__(self, other) -> A:
-        return self
-
-    def __gt__(self, other) -> bool:
-        return False
+    def __lt__(self, other) -> A: ...
+    def __gt__(self, other) -> bool: ...
 
 class B:
-    def __lt__(self, other) -> B:
-        return self
+    def __lt__(self, other) -> B: ...
 
 class C:
-    def __lt__(self, other) -> C:
-        return self
+    def __lt__(self, other) -> C: ...
 
 x = A() < B() < C()
 reveal_type(x)  # revealed: A & ~AlwaysTruthy | B

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

@@ -197,7 +197,7 @@ class LtReturnTypeOnB: ...
 
 class B:
     def __lt__(self, o: B) -> LtReturnTypeOnB:
-        return LtReturnTypeOnB()
+        return set()
 
 reveal_type((A(), B()) < (A(), B()))  # revealed: LtReturnType | LtReturnTypeOnB | Literal[False]
 ```
@@ -334,61 +334,3 @@ reveal_type(a is not c)  # revealed: Literal[True]
 For tuples like `tuple[int, ...]`, `tuple[Any, ...]`
 
 // TODO
-
-## Chained comparisons with elements that incorrectly implement `__bool__`
-
-<!-- snapshot-diagnostics -->
-
-For an operation `A() < A()` to succeed at runtime, the `A.__lt__` method does not necessarily need
-to return an object that is convertible to a `bool`. However, the return type _does_ need to be
-convertible to a `bool` for the operation `A() < A() < A()` (a _chained_ comparison) to succeed.
-This is because `A() < A() < A()` desugars to something like this, which involves several implicit
-conversions to `bool`:
-
-```ignore
-def compute_chained_comparison():
-  a1 = A()
-  a2 = A()
-  first_comparison = a1 < a2
-  return first_comparison and (a2 < A())
-```
-
-```py
-class NotBoolable:
-    __bool__ = 5
-
-class Comparable:
-    def __lt__(self, other) -> NotBoolable:
-        return NotBoolable()
-
-    def __gt__(self, other) -> NotBoolable:
-        return NotBoolable()
-
-a = (1, Comparable())
-b = (1, Comparable())
-
-# error: [unsupported-bool-conversion]
-a < b < b
-
-a < b  # fine
-```
-
-## Equality with elements that incorrectly implement `__bool__`
-
-<!-- snapshot-diagnostics -->
-
-Python does not generally attempt to coerce the result of `==` and `!=` operations between two
-arbitrary objects to a `bool`, but a comparison of tuples will fail if the result of comparing any
-pair of elements at equivalent positions cannot be converted to a `bool`:
-
-```py
-class A:
-    def __eq__(self, other) -> NotBoolable:
-        return NotBoolable()
-
-class NotBoolable:
-    __bool__ = None
-
-# error: [unsupported-bool-conversion]
-(A(),) == (A(),)
-```

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

@@ -104,8 +104,7 @@ class Iterator:
         return 42
 
 class Iterable:
-    def __iter__(self) -> Iterator:
-        return Iterator()
+    def __iter__(self) -> Iterator: ...
 
 # This is fine:
 x = [*Iterable()]

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

@@ -35,13 +35,3 @@ def _(flag: bool):
     x = 1 if flag else None
     reveal_type(x)  # revealed: Literal[1] | None
 ```
-
-## Condition with object that implements `__bool__` incorrectly
-
-```py
-class NotBoolable:
-    __bool__ = 3
-
-# error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable"
-3 if NotBoolable() else 4
-```

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

@@ -147,17 +147,3 @@ def _(flag: bool):
 
     reveal_type(y)  # revealed: Literal[0, 1]
 ```
-
-## Condition with object that implements `__bool__` incorrectly
-
-```py
-class NotBoolable:
-    __bool__ = 3
-
-# error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable"
-if NotBoolable():
-    ...
-# error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable"
-elif NotBoolable():
-    ...
-```

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

@@ -43,21 +43,3 @@ def _(target: int):
 
     reveal_type(y)  # revealed: Literal[2, 3, 4]
 ```
-
-## Guard with object that implements `__bool__` incorrectly
-
-```py
-class NotBoolable:
-    __bool__ = 3
-
-def _(target: int, flag: NotBoolable):
-    y = 1
-    match target:
-        # error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable"
-        case 1 if flag:
-            y = 2
-        case 2:
-            y = 3
-
-    reveal_type(y)  # revealed: Literal[1, 2, 3]
-```

crates/red_knot_python_semantic/resources/mdtest/descriptor_protocol.md

@@ -6,9 +6,7 @@ A descriptor is an attribute value that has one of the methods in the descriptor
 methods are `__get__()`, `__set__()`, and `__delete__()`. If any of those methods are defined for an
 attribute, it is said to be a descriptor.
 
-## Basic properties
-
-### Example
+## Basic example
 
 An introductory example, modeled after a [simple example] in the primer on descriptors, involving a
 descriptor that returns a constant value:
@@ -33,17 +31,21 @@ reveal_type(c.ten)  # revealed: Literal[10]
 reveal_type(C.ten)  # revealed: Literal[10]
 
 # These are fine:
-c.ten = 10
+# TODO: This should not be an error
+c.ten = 10  # error: [invalid-assignment]
 C.ten = 10
 
-# error: [invalid-assignment] "Object of type `Literal[11]` is not assignable to attribute `ten` of type `Literal[10]`"
+# TODO: This should be an error (as the wrong type is being implicitly passed to `Ten.__set__`),
+# but the error message is misleading.
+# error: [invalid-assignment] "Object of type `Literal[11]` is not assignable to attribute `ten` of type `Ten`"
 c.ten = 11
 
+# TODO: same as above
 # error: [invalid-assignment] "Object of type `Literal[11]` is not assignable to attribute `ten` of type `Literal[10]`"
 C.ten = 11
 ```
 
-### Different types for `__get__` and `__set__`
+## Different types for `__get__` and `__set__`
 
 The return type of `__get__` and the value type of `__set__` can be different:
 
@@ -65,25 +67,28 @@ c = C()
 
 reveal_type(c.flexible_int)  # revealed: int | None
 
+# TODO: These should not be errors
+# error: [invalid-assignment]
 c.flexible_int = 42  # okay
-# TODO: This should not be an error
 # error: [invalid-assignment]
 c.flexible_int = "42"  # also okay!
 
 reveal_type(c.flexible_int)  # revealed: int | None
 
-# TODO: This should be an error
+# TODO: This should be an error, but the message needs to be improved.
+# error: [invalid-assignment] "Object of type `None` is not assignable to attribute `flexible_int` of type `FlexibleInt`"
 c.flexible_int = None  # not okay
 
 reveal_type(c.flexible_int)  # revealed: int | None
 ```
 
-### Data and non-data descriptors
+## Data and non-data descriptors
 
-Descriptors that define `__set__` or `__delete__` are called *data descriptors*. An example of a
-data descriptor is a `property` with a setter and/or a deleter. Descriptors that only define
-`__get__`, meanwhile, are called *non-data descriptors*. Examples include functions, `classmethod`
-or `staticmethod`.
+Descriptors that define `__set__` or `__delete__` are called *data descriptors*. An example\
+of a data descriptor is a `property` with a setter and/or a deleter.\
+Descriptors that only define `__get__`, meanwhile, are called *non-data descriptors*. Examples
+include\
+functions, `classmethod` or `staticmethod`).
 
 The precedence chain for attribute access is (1) data descriptors, (2) instance attributes, and (3)
 non-data descriptors.
@@ -95,7 +100,7 @@ class DataDescriptor:
     def __get__(self, instance: object, owner: type | None = None) -> Literal["data"]:
         return "data"
 
-    def __set__(self, instance: object, value: int) -> None:
+    def __set__(self, instance: int, value) -> None:
         pass
 
 class NonDataDescriptor:
@@ -119,7 +124,12 @@ class C:
 
 c = C()
 
-reveal_type(c.data_descriptor)  # revealed: Unknown | Literal["data"]
+# TODO: This should ideally be `Unknown | Literal["data"]`.
+#
+#     - Pyright also wrongly shows `int | Literal['data']` here
+#     - Mypy shows Literal["data"] here, but also shows Literal["non-data"] below.
+#
+reveal_type(c.data_descriptor)  # revealed: Unknown | Literal["data", 1]
 
 reveal_type(c.non_data_descriptor)  # revealed: Unknown | Literal["non-data", 1]
 
@@ -133,58 +143,79 @@ reveal_type(C.non_data_descriptor)  # revealed: Unknown | Literal["non-data"]
 C.data_descriptor = "something else"  # This is okay
 ```
 
-### Partial fall back
+## Built-in `property` descriptor
 
-Our implementation of the descriptor protocol takes into account that symbols can be possibly
-unbound. In those cases, we fall back to lower precedence steps of the descriptor protocol and union
-all possible results accordingly. We start by defining a data and a non-data descriptor:
+The built-in `property` decorator creates a descriptor. The names for attribute reads/writes are
+determined by the return type of the `name` method and the parameter type of the setter,
+respectively.
 
 ```py
-from typing import Literal
+class C:
+    _name: str | None = None
 
-class DataDescriptor:
-    def __get__(self, instance: object, owner: type | None = None) -> Literal["data"]:
-        return "data"
+    @property
+    def name(self) -> str:
+        return self._name or "Unset"
+    # TODO: No diagnostic should be emitted here
+    # error: [unresolved-attribute] "Type `Literal[name]` has no attribute `setter`"
+    @name.setter
+    def name(self, value: str | None) -> None:
+        self._value = value
 
-    def __set__(self, instance: object, value: int) -> None:
-        pass
+c = C()
 
-class NonDataDescriptor:
-    def __get__(self, instance: object, owner: type | None = None) -> Literal["non-data"]:
-        return "non-data"
+reveal_type(c._name)  # revealed: str | None
+
+# Should be `str`
+reveal_type(c.name)  # revealed: @Todo(decorated method)
+
+# Should be `builtins.property`
+reveal_type(C.name)  # revealed: Literal[name]
+
+# This is fine:
+c.name = "new"
+
+c.name = None
+
+# TODO: this should be an error
+c.name = 42
 ```
 
-Then, we demonstrate that we fall back to an instance attribute if a data descriptor is possibly
-unbound:
+## Built-in `classmethod` descriptor
+
+Similarly to `property`, `classmethod` decorator creates an implicit descriptor that binds the first
+argument to the class instead of the instance.
 
 ```py
-def f1(flag: bool):
-    class C1:
-        if flag:
-            attr = DataDescriptor()
+class C:
+    def __init__(self, value: str) -> None:
+        self._name: str = value
 
-        def f(self):
-            self.attr = "normal"
+    @classmethod
+    def factory(cls, value: str) -> "C":
+        return cls(value)
 
-    reveal_type(C1().attr)  # revealed: Unknown | Literal["data", "normal"]
+    @classmethod
+    def get_name(cls) -> str:
+        return cls.__name__
+
+c1 = C.factory("test")  # okay
+
+# TODO: should be `C`
+reveal_type(c1)  # revealed: @Todo(return type)
+
+# TODO: should be `str`
+reveal_type(C.get_name())  # revealed: @Todo(return type)
+
+# TODO: should be `str`
+reveal_type(C("42").get_name())  # revealed: @Todo(decorated method)
 ```
 
-We never treat implicit instance attributes as definitely bound, so we fall back to the non-data
-descriptor here:
+## Descriptors only work when used as class variables
 
-```py
-def f2(flag: bool):
-    class C2:
-        def f(self):
-            self.attr = "normal"
-        attr = NonDataDescriptor()
+From the descriptor guide:
 
-    reveal_type(C2().attr)  # revealed: Unknown | Literal["non-data", "normal"]
-```
-
-### Descriptors only work when used as class variables
-
-Descriptors only work when used as class variables. When put in instances, they have no effect.
+> Descriptors only work when used as class variables. When put in instances, they have no effect.
 
 ```py
 from typing import Literal
@@ -197,182 +228,8 @@ class C:
     def __init__(self):
         self.ten: Ten = Ten()
 
-reveal_type(C().ten)  # revealed: Ten
-```
-
-## Descriptor protocol for class objects
-
-When attributes are accessed on a class object, the following [precedence chain] is used:
-
-- Data descriptor on the metaclass
-- Data or non-data descriptor on the class
-- Class attribute
-- Non-data descriptor on the metaclass
-- Metaclass attribute
-
-To verify this, we define a data and a non-data descriptor:
-
-```py
-from typing import Literal, Any
-
-class DataDescriptor:
-    def __get__(self, instance: object, owner: type | None = None) -> Literal["data"]:
-        return "data"
-
-    def __set__(self, instance: object, value: str) -> None:
-        pass
-
-class NonDataDescriptor:
-    def __get__(self, instance: object, owner: type | None = None) -> Literal["non-data"]:
-        return "non-data"
-```
-
-First, we make sure that the descriptors are correctly accessed when defined on the metaclass or the
-class:
-
-```py
-class Meta1(type):
-    meta_data_descriptor: DataDescriptor = DataDescriptor()
-    meta_non_data_descriptor: NonDataDescriptor = NonDataDescriptor()
-
-class C1(metaclass=Meta1):
-    class_data_descriptor: DataDescriptor = DataDescriptor()
-    class_non_data_descriptor: NonDataDescriptor = NonDataDescriptor()
-
-reveal_type(C1.meta_data_descriptor)  # revealed: Literal["data"]
-reveal_type(C1.meta_non_data_descriptor)  # revealed: Literal["non-data"]
-
-reveal_type(C1.class_data_descriptor)  # revealed: Literal["data"]
-reveal_type(C1.class_non_data_descriptor)  # revealed: Literal["non-data"]
-```
-
-Next, we demonstrate that a *metaclass data descriptor* takes precedence over all class-level
-attributes:
-
-```py
-class Meta2(type):
-    meta_data_descriptor1: DataDescriptor = DataDescriptor()
-    meta_data_descriptor2: DataDescriptor = DataDescriptor()
-
-class ClassLevelDataDescriptor:
-    def __get__(self, instance: object, owner: type | None = None) -> Literal["class level data descriptor"]:
-        return "class level data descriptor"
-
-    def __set__(self, instance: object, value: str) -> None:
-        pass
-
-class C2(metaclass=Meta2):
-    meta_data_descriptor1: Literal["value on class"] = "value on class"
-    meta_data_descriptor2: ClassLevelDataDescriptor = ClassLevelDataDescriptor()
-
-reveal_type(C2.meta_data_descriptor1)  # revealed: Literal["data"]
-reveal_type(C2.meta_data_descriptor2)  # revealed: Literal["data"]
-```
-
-On the other hand, normal metaclass attributes and metaclass non-data descriptors are shadowed by
-class-level attributes (descriptor or not):
-
-```py
-class Meta3(type):
-    meta_attribute1: Literal["value on metaclass"] = "value on metaclass"
-    meta_attribute2: Literal["value on metaclass"] = "value on metaclass"
-    meta_non_data_descriptor1: NonDataDescriptor = NonDataDescriptor()
-    meta_non_data_descriptor2: NonDataDescriptor = NonDataDescriptor()
-
-class C3(metaclass=Meta3):
-    meta_attribute1: Literal["value on class"] = "value on class"
-    meta_attribute2: ClassLevelDataDescriptor = ClassLevelDataDescriptor()
-    meta_non_data_descriptor1: Literal["value on class"] = "value on class"
-    meta_non_data_descriptor2: ClassLevelDataDescriptor = ClassLevelDataDescriptor()
-
-reveal_type(C3.meta_attribute1)  # revealed: Literal["value on class"]
-reveal_type(C3.meta_attribute2)  # revealed: Literal["class level data descriptor"]
-reveal_type(C3.meta_non_data_descriptor1)  # revealed: Literal["value on class"]
-reveal_type(C3.meta_non_data_descriptor2)  # revealed: Literal["class level data descriptor"]
-```
-
-Finally, metaclass attributes and metaclass non-data descriptors are only accessible when they are
-not shadowed by class-level attributes:
-
-```py
-class Meta4(type):
-    meta_attribute: Literal["value on metaclass"] = "value on metaclass"
-    meta_non_data_descriptor: NonDataDescriptor = NonDataDescriptor()
-
-class C4(metaclass=Meta4): ...
-
-reveal_type(C4.meta_attribute)  # revealed: Literal["value on metaclass"]
-reveal_type(C4.meta_non_data_descriptor)  # revealed: Literal["non-data"]
-```
-
-When a metaclass data descriptor is possibly unbound, we union the result type of its `__get__`
-method with an underlying class level attribute, if present:
-
-```py
-def _(flag: bool):
-    class Meta5(type):
-        if flag:
-            meta_data_descriptor1: DataDescriptor = DataDescriptor()
-            meta_data_descriptor2: DataDescriptor = DataDescriptor()
-
-    class C5(metaclass=Meta5):
-        meta_data_descriptor1: Literal["value on class"] = "value on class"
-
-    reveal_type(C5.meta_data_descriptor1)  # revealed: Literal["data", "value on class"]
-    # error: [possibly-unbound-attribute]
-    reveal_type(C5.meta_data_descriptor2)  # revealed: Literal["data"]
-```
-
-When a class-level attribute is possibly unbound, we union its (descriptor protocol) type with the
-metaclass attribute (unless it's a data descriptor, which always takes precedence):
-
-```py
-from typing import Any
-
-def _(flag: bool):
-    class Meta6(type):
-        attribute1: DataDescriptor = DataDescriptor()
-        attribute2: NonDataDescriptor = NonDataDescriptor()
-        attribute3: Literal["value on metaclass"] = "value on metaclass"
-
-    class C6(metaclass=Meta6):
-        if flag:
-            attribute1: Literal["value on class"] = "value on class"
-            attribute2: Literal["value on class"] = "value on class"
-            attribute3: Literal["value on class"] = "value on class"
-            attribute4: Literal["value on class"] = "value on class"
-
-    reveal_type(C6.attribute1)  # revealed: Literal["data"]
-    reveal_type(C6.attribute2)  # revealed: Literal["non-data", "value on class"]
-    reveal_type(C6.attribute3)  # revealed: Literal["value on metaclass", "value on class"]
-    # error: [possibly-unbound-attribute]
-    reveal_type(C6.attribute4)  # revealed: Literal["value on class"]
-```
-
-Finally, we can also have unions of various types of attributes:
-
-```py
-def _(flag: bool):
-    class Meta7(type):
-        if flag:
-            union_of_metaclass_attributes: Literal[1] = 1
-            union_of_metaclass_data_descriptor_and_attribute: DataDescriptor = DataDescriptor()
-        else:
-            union_of_metaclass_attributes: Literal[2] = 2
-            union_of_metaclass_data_descriptor_and_attribute: Literal[2] = 2
-
-    class C7(metaclass=Meta7):
-        if flag:
-            union_of_class_attributes: Literal[1] = 1
-            union_of_class_data_descriptor_and_attribute: DataDescriptor = DataDescriptor()
-        else:
-            union_of_class_attributes: Literal[2] = 2
-            union_of_class_data_descriptor_and_attribute: Literal[2] = 2
-
-    reveal_type(C7.union_of_metaclass_attributes)  # revealed: Literal[1, 2]
-    reveal_type(C7.union_of_metaclass_data_descriptor_and_attribute)  # revealed: Literal["data", 2]
-    reveal_type(C7.union_of_class_attributes)  # revealed: Literal[1, 2]
-    reveal_type(C7.union_of_class_data_descriptor_and_attribute)  # revealed: Literal["data", 2]
+# TODO: Should be Ten
+reveal_type(C().ten)  # revealed: Literal[10]
 ```
 
 ## Descriptors distinguishing between class and instance access
@@ -405,12 +262,63 @@ reveal_type(C.d)  # revealed: LiteralString
 reveal_type(C().d)  # revealed: LiteralString
 ```
 
-## Descriptor protocol for dunder methods
+## Undeclared descriptor arguments
 
-Dunder methods are always looked up on the meta-type. There is no instance fallback. This means that
-an implicit dunder call on an instance-like object will not only look up the dunder method on the
-class object, without considering instance attributes. And an implicit dunder call on a class object
-will look up the dunder method on the metaclass, without considering class attributes.
+If a descriptor attribute is not declared, we union with `Unknown`, just like for regular
+attributes, since that attribute could be overwritten externally. Even a data descriptor with a
+`__set__` method can be overwritten when accessed through a class object.
+
+```py
+class Descriptor:
+    def __get__(self, instance: object, owner: type | None = None) -> int:
+        return 1
+
+    def __set__(self, instance: object, value: int) -> None:
+        pass
+
+class C:
+    descriptor = Descriptor()
+
+C.descriptor = "something else"
+
+# This could also be `Literal["something else"]` if we support narrowing of attribute types based on assignments
+reveal_type(C.descriptor)  # revealed: Unknown | int
+```
+
+## Descriptors with incorrect `__get__` signature
+
+```py
+class Descriptor:
+    # `__get__` method with missing parameters:
+    def __get__(self) -> int:
+        return 1
+
+class C:
+    descriptor: Descriptor = Descriptor()
+
+# TODO: This should be an error
+reveal_type(C.descriptor)  # revealed: Descriptor
+```
+
+## Possibly-unbound `__get__` method
+
+```py
+def _(flag: bool):
+    class MaybeDescriptor:
+        if flag:
+            def __get__(self, instance: object, owner: type | None = None) -> int:
+                return 1
+
+    class C:
+        descriptor: MaybeDescriptor = MaybeDescriptor()
+
+    # TODO: This should be `MaybeDescriptor | int`
+    reveal_type(C.descriptor)  # revealed: int
+```
+
+## Dunder methods
+
+Dunder methods are looked up on the meta type, but we still need to invoke the descriptor protocol:
 
 ```py
 class SomeCallable:
@@ -430,77 +338,7 @@ reveal_type(b_instance(1))  # revealed: str
 b_instance("bla")  # error: [invalid-argument-type]
 ```
 
-## Special descriptors
-
-### Built-in `property` descriptor
-
-The built-in `property` decorator creates a descriptor. The names for attribute reads/writes are
-determined by the return type of the `name` method and the parameter type of the setter,
-respectively.
-
-```py
-class C:
-    _name: str | None = None
-
-    @property
-    def name(self) -> str:
-        return self._name or "Unset"
-    # TODO: No diagnostic should be emitted here
-    # error: [unresolved-attribute] "Type `Literal[name]` has no attribute `setter`"
-    @name.setter
-    def name(self, value: str | None) -> None:
-        self._value = value
-
-c = C()
-
-reveal_type(c._name)  # revealed: str | None
-
-# TODO: Should be `str`
-reveal_type(c.name)  # revealed: <bound method `name` of `C`>
-
-# Should be `builtins.property`
-reveal_type(C.name)  # revealed: Literal[name]
-
-# TODO: These should not emit errors
-# error: [invalid-assignment]
-c.name = "new"
-
-# error: [invalid-assignment]
-c.name = None
-
-# TODO: this should be an error, but with a proper error message
-# error: [invalid-assignment] "Object of type `Literal[42]` is not assignable to attribute `name` of type `<bound method `name` of `C`>`"
-c.name = 42
-```
-
-### Built-in `classmethod` descriptor
-
-Similarly to `property`, `classmethod` decorator creates an implicit descriptor that binds the first
-argument to the class instead of the instance.
-
-```py
-class C:
-    def __init__(self, value: str) -> None:
-        self._name: str = value
-
-    @classmethod
-    def factory(cls, value: str) -> "C":
-        return cls(value)
-
-    @classmethod
-    def get_name(cls) -> str:
-        return cls.__name__
-
-c1 = C.factory("test")  # okay
-
-reveal_type(c1)  # revealed: C
-
-reveal_type(C.get_name())  # revealed: str
-
-reveal_type(C("42").get_name())  # revealed: str
-```
-
-### Functions as descriptors
+## Functions as descriptors
 
 Functions are descriptors because they implement a `__get__` method. This is crucial in making sure
 that method calls work as expected. See [this test suite](./call/methods.md) for more information.
@@ -550,202 +388,32 @@ Finally, we test some error cases for the call to the wrapper descriptor:
 
 ```py
 # Calling the wrapper descriptor without any arguments is an
-# error: [no-matching-overload] "No overload of wrapper descriptor `FunctionType.__get__` matches arguments"
+# error: [missing-argument] "No arguments provided for required parameters `self`, `instance`"
 wrapper_descriptor()
 
 # Calling it without the `instance` argument is an also an
-# error: [no-matching-overload] "No overload of wrapper descriptor `FunctionType.__get__` matches arguments"
+# error: [missing-argument] "No argument provided for required parameter `instance`"
 wrapper_descriptor(f)
 
 # Calling it without the `owner` argument if `instance` is not `None` is an
-# error: [no-matching-overload] "No overload of wrapper descriptor `FunctionType.__get__` matches arguments"
+# error: [missing-argument] "No argument provided for required parameter `owner`"
 wrapper_descriptor(f, None)
 
 # But calling it with an instance is fine (in this case, the `owner` argument is optional):
 wrapper_descriptor(f, C())
 
 # Calling it with something that is not a `FunctionType` as the first argument is an
-# error: [no-matching-overload] "No overload of wrapper descriptor `FunctionType.__get__` matches arguments"
+# error: [invalid-argument-type] "Object of type `Literal[1]` cannot be assigned to parameter 1 (`self`); expected type `FunctionType`"
 wrapper_descriptor(1, None, type(f))
 
 # Calling it with something that is not a `type` as the `owner` argument is an
-# error: [no-matching-overload] "No overload of wrapper descriptor `FunctionType.__get__` matches arguments"
+# error: [invalid-argument-type] "Object of type `Literal[f]` cannot be assigned to parameter 3 (`owner`); expected type `type`"
 wrapper_descriptor(f, None, f)
 
 # Calling it with too many positional arguments is an
-# error: [no-matching-overload] "No overload of wrapper descriptor `FunctionType.__get__` matches arguments"
+# error: [too-many-positional-arguments] "Too many positional arguments: expected 3, got 4"
 wrapper_descriptor(f, None, type(f), "one too many")
 ```
 
-## Error handling and edge cases
-
-### `__get__` is called with correct arguments
-
-This test makes sure that we call `__get__` with the right argument types for various scenarios:
-
-```py
-from __future__ import annotations
-
-class TailoredForClassObjectAccess:
-    def __get__(self, instance: None, owner: type[C]) -> int:
-        return 1
-
-class TailoredForInstanceAccess:
-    def __get__(self, instance: C, owner: type[C] | None = None) -> str:
-        return "a"
-
-class TailoredForMetaclassAccess:
-    def __get__(self, instance: type[C], owner: type[Meta]) -> bytes:
-        return b"a"
-
-class Meta(type):
-    metaclass_access: TailoredForMetaclassAccess = TailoredForMetaclassAccess()
-
-class C(metaclass=Meta):
-    class_object_access: TailoredForClassObjectAccess = TailoredForClassObjectAccess()
-    instance_access: TailoredForInstanceAccess = TailoredForInstanceAccess()
-
-reveal_type(C.class_object_access)  # revealed: int
-reveal_type(C().instance_access)  # revealed: str
-reveal_type(C.metaclass_access)  # revealed: bytes
-
-# TODO: These should emit a diagnostic
-reveal_type(C().class_object_access)  # revealed: TailoredForClassObjectAccess
-reveal_type(C.instance_access)  # revealed: TailoredForInstanceAccess
-```
-
-### Descriptors with incorrect `__get__` signature
-
-```py
-class Descriptor:
-    # `__get__` method with missing parameters:
-    def __get__(self) -> int:
-        return 1
-
-class C:
-    descriptor: Descriptor = Descriptor()
-
-# TODO: This should be an error
-reveal_type(C.descriptor)  # revealed: Descriptor
-
-# TODO: This should be an error
-reveal_type(C().descriptor)  # revealed: Descriptor
-```
-
-### Undeclared descriptor arguments
-
-If a descriptor attribute is not declared, we union with `Unknown`, just like for regular
-attributes, since that attribute could be overwritten externally. Even a data descriptor with a
-`__set__` method can be overwritten when accessed through a class object.
-
-```py
-class Descriptor:
-    def __get__(self, instance: object, owner: type | None = None) -> int:
-        return 1
-
-    def __set__(self, instance: object, value: int) -> None:
-        pass
-
-class C:
-    descriptor = Descriptor()
-
-C.descriptor = "something else"
-
-# This could also be `Literal["something else"]` if we support narrowing of attribute types based on assignments
-reveal_type(C.descriptor)  # revealed: Unknown | int
-```
-
-### Possibly unbound descriptor attributes
-
-```py
-class DataDescriptor:
-    def __get__(self, instance: object, owner: type | None = None) -> int:
-        return 1
-
-    def __set__(self, instance: int, value) -> None:
-        pass
-
-class NonDataDescriptor:
-    def __get__(self, instance: object, owner: type | None = None) -> int:
-        return 1
-
-def _(flag: bool):
-    class PossiblyUnbound:
-        if flag:
-            non_data: NonDataDescriptor = NonDataDescriptor()
-            data: DataDescriptor = DataDescriptor()
-
-    # error: [possibly-unbound-attribute] "Attribute `non_data` on type `Literal[PossiblyUnbound]` is possibly unbound"
-    reveal_type(PossiblyUnbound.non_data)  # revealed: int
-
-    # error: [possibly-unbound-attribute] "Attribute `non_data` on type `PossiblyUnbound` is possibly unbound"
-    reveal_type(PossiblyUnbound().non_data)  # revealed: int
-
-    # error: [possibly-unbound-attribute] "Attribute `data` on type `Literal[PossiblyUnbound]` is possibly unbound"
-    reveal_type(PossiblyUnbound.data)  # revealed: int
-
-    # error: [possibly-unbound-attribute] "Attribute `data` on type `PossiblyUnbound` is possibly unbound"
-    reveal_type(PossiblyUnbound().data)  # revealed: int
-```
-
-### Possibly-unbound `__get__` method
-
-```py
-def _(flag: bool):
-    class MaybeDescriptor:
-        if flag:
-            def __get__(self, instance: object, owner: type | None = None) -> int:
-                return 1
-
-    class C:
-        descriptor: MaybeDescriptor = MaybeDescriptor()
-
-    reveal_type(C.descriptor)  # revealed: int | MaybeDescriptor
-
-    reveal_type(C().descriptor)  # revealed: int | MaybeDescriptor
-```
-
-### Descriptors with non-function `__get__` callables that are descriptors themselves
-
-The descriptor protocol is recursive, i.e. looking up `__get__` can involve triggering the
-descriptor protocol on the callable's `__call__` method:
-
-```py
-from __future__ import annotations
-
-class ReturnedCallable2:
-    def __call__(self, descriptor: Descriptor1, instance: None, owner: type[C]) -> int:
-        return 1
-
-class ReturnedCallable1:
-    def __call__(self, descriptor: Descriptor2, instance: Callable1, owner: type[Callable1]) -> ReturnedCallable2:
-        return ReturnedCallable2()
-
-class Callable3:
-    def __call__(self, descriptor: Descriptor3, instance: Callable2, owner: type[Callable2]) -> ReturnedCallable1:
-        return ReturnedCallable1()
-
-class Descriptor3:
-    __get__: Callable3 = Callable3()
-
-class Callable2:
-    __call__: Descriptor3 = Descriptor3()
-
-class Descriptor2:
-    __get__: Callable2 = Callable2()
-
-class Callable1:
-    __call__: Descriptor2 = Descriptor2()
-
-class Descriptor1:
-    __get__: Callable1 = Callable1()
-
-class C:
-    d: Descriptor1 = Descriptor1()
-
-reveal_type(C.d)  # revealed: int
-```
-
 [descriptors]: https://docs.python.org/3/howto/descriptor.html
-[precedence chain]: https://github.com/python/cpython/blob/3.13/Objects/typeobject.c#L5393-L5481
 [simple example]: https://docs.python.org/3/howto/descriptor.html#simple-example-a-descriptor-that-returns-a-constant

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

@@ -182,16 +182,3 @@ class C:
 c = C()
 c("wrong")  # error: [invalid-argument-type]
 ```
-
-## Calls to methods
-
-Tests that we also see a reference to a function if the callable is a bound method.
-
-```py
-class C:
-    def square(self, x: int) -> int:
-        return x * x
-
-c = C()
-c.square("hello")  # error: [invalid-argument-type]
-```

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

@@ -1,14 +0,0 @@
-# No matching overload diagnostics
-
-<!-- snapshot-diagnostics -->
-
-## Calls to overloaded functions
-
-TODO: Note that we do not yet support the `@overload` decorator to define overloaded functions in
-real Python code. We are instead testing a special-cased function where we create an overloaded
-signature internally. Update this to an `@overload` function in the Python snippet itself once we
-can.
-
-```py
-type("Foo", ())  # error: [no-matching-overload]
-```

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

@@ -1,9 +0,0 @@
-## Condition with object that implements `__bool__` incorrectly
-
-```py
-class NotBoolable:
-    __bool__ = 3
-
-# error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable"
-assert NotBoolable()
-```

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

@@ -101,55 +101,3 @@ reveal_type(bool([]))  # revealed: bool
 reveal_type(bool({}))  # revealed: bool
 reveal_type(bool(set()))  # revealed: bool
 ```
-
-## `__bool__` returning `NoReturn`
-
-```py
-from typing import NoReturn
-
-class NotBoolable:
-    def __bool__(self) -> NoReturn:
-        raise NotImplementedError("This object can't be converted to a boolean")
-
-# TODO: This should emit an error that `NotBoolable` can't be converted to a bool but it currently doesn't
-#   because `Never` is assignable to `bool`. This probably requires dead code analysis to fix.
-if NotBoolable():
-    ...
-```
-
-## Not callable `__bool__`
-
-```py
-class NotBoolable:
-    __bool__ = None
-
-# error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable"
-if NotBoolable():
-    ...
-```
-
-## Not-boolable union
-
-```py
-def test(cond: bool):
-    class NotBoolable:
-        __bool__ = None if cond else 3
-
-    # error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; it incorrectly implements `__bool__`"
-    if NotBoolable():
-        ...
-```
-
-## Union with some variants implementing `__bool__` incorrectly
-
-```py
-def test(cond: bool):
-    class NotBoolable:
-        __bool__ = None
-
-    a = 10 if cond else NotBoolable()
-
-    # error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `Literal[10] | NotBoolable`; its `__bool__` method isn't callable"
-    if a:
-        ...
-```

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

@@ -1,100 +0,0 @@
-# `lambda` expression
-
-## No parameters
-
-`lambda` expressions can be defined without any parameters.
-
-```py
-reveal_type(lambda: 1)  # revealed: () -> @Todo(lambda return type)
-
-# error: [unresolved-reference]
-reveal_type(lambda: a)  # revealed: () -> @Todo(lambda return type)
-```
-
-## With parameters
-
-Unlike parameters in function definition, the parameters in a `lambda` expression cannot be
-annotated.
-
-```py
-reveal_type(lambda a: a)  # revealed: (a) -> @Todo(lambda return type)
-reveal_type(lambda a, b: a + b)  # revealed: (a, b) -> @Todo(lambda return type)
-```
-
-But, it can have default values:
-
-```py
-reveal_type(lambda a=1: a)  # revealed: (a=Literal[1]) -> @Todo(lambda return type)
-reveal_type(lambda a, b=2: a)  # revealed: (a, b=Literal[2]) -> @Todo(lambda return type)
-```
-
-And, positional-only parameters:
-
-```py
-reveal_type(lambda a, b, /, c: c)  # revealed: (a, b, /, c) -> @Todo(lambda return type)
-```
-
-And, keyword-only parameters:
-
-```py
-reveal_type(lambda a, *, b=2, c: b)  # revealed: (a, *, b=Literal[2], c) -> @Todo(lambda return type)
-```
-
-And, variadic parameter:
-
-```py
-reveal_type(lambda *args: args)  # revealed: (*args) -> @Todo(lambda return type)
-```
-
-And, keyword-varidic parameter:
-
-```py
-reveal_type(lambda **kwargs: kwargs)  # revealed: (**kwargs) -> @Todo(lambda return type)
-```
-
-Mixing all of them together:
-
-```py
-# revealed: (a, b, /, c=Literal[True], *args, *, d=Literal["default"], e=Literal[5], **kwargs) -> @Todo(lambda return type)
-reveal_type(lambda a, b, /, c=True, *args, d="default", e=5, **kwargs: None)
-```
-
-## Parameter type
-
-In addition to correctly inferring the `lambda` expression, the parameters should also be inferred
-correctly.
-
-Using a parameter with no default value:
-
-```py
-lambda x: reveal_type(x)  # revealed: Unknown
-```
-
-Using a parameter with default value:
-
-```py
-lambda x=1: reveal_type(x)  # revealed: Unknown | Literal[1]
-```
-
-Using a variadic paramter:
-
-```py
-# TODO: should be `tuple[Unknown, ...]` (needs generics)
-lambda *args: reveal_type(args)  # revealed: tuple
-```
-
-Using a keyword-varidic parameter:
-
-```py
-# TODO: should be `dict[str, Unknown]` (needs generics)
-lambda **kwargs: reveal_type(kwargs)  # revealed: dict
-```
-
-## Nested `lambda` expressions
-
-Here, a `lambda` expression is used as the default value for a parameter in another `lambda`
-expression.
-
-```py
-reveal_type(lambda a=lambda x, y: 0: 2)  # revealed: (a=(x, y) -> @Todo(lambda return type)) -> @Todo(lambda return type)
-```

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

@@ -99,28 +99,22 @@ The returned value of `__len__` is implicitly and recursively converted to `int`
 from typing import Literal
 
 class Zero:
-    def __len__(self) -> Literal[0]:
-        return 0
+    def __len__(self) -> Literal[0]: ...
 
 class ZeroOrOne:
-    def __len__(self) -> Literal[0, 1]:
-        return 0
+    def __len__(self) -> Literal[0, 1]: ...
 
 class ZeroOrTrue:
-    def __len__(self) -> Literal[0, True]:
-        return 0
+    def __len__(self) -> Literal[0, True]: ...
 
 class OneOrFalse:
-    def __len__(self) -> Literal[1] | Literal[False]:
-        return 1
+    def __len__(self) -> Literal[1] | Literal[False]: ...
 
 class OneOrFoo:
-    def __len__(self) -> Literal[1, "foo"]:
-        return 1
+    def __len__(self) -> Literal[1, "foo"]: ...
 
 class ZeroOrStr:
-    def __len__(self) -> Literal[0] | str:
-        return 0
+    def __len__(self) -> Literal[0] | str: ...
 
 reveal_type(len(Zero()))  # revealed: Literal[0]
 reveal_type(len(ZeroOrOne()))  # revealed: Literal[0, 1]
@@ -140,12 +134,10 @@ reveal_type(len(ZeroOrStr()))  # revealed: int
 from typing import Literal
 
 class LiteralTrue:
-    def __len__(self) -> Literal[True]:
-        return True
+    def __len__(self) -> Literal[True]: ...
 
 class LiteralFalse:
-    def __len__(self) -> Literal[False]:
-        return False
+    def __len__(self) -> Literal[False]: ...
 
 reveal_type(len(LiteralTrue()))  # revealed: Literal[1]
 reveal_type(len(LiteralFalse()))  # revealed: Literal[0]
@@ -165,24 +157,19 @@ class SomeEnum(Enum):
     INT_2 = 3_2
 
 class Auto:
-    def __len__(self) -> Literal[SomeEnum.AUTO]:
-        return SomeEnum.AUTO
+    def __len__(self) -> Literal[SomeEnum.AUTO]: ...
 
 class Int:
-    def __len__(self) -> Literal[SomeEnum.INT]:
-        return SomeEnum.INT
+    def __len__(self) -> Literal[SomeEnum.INT]: ...
 
 class Str:
-    def __len__(self) -> Literal[SomeEnum.STR]:
-        return SomeEnum.STR
+    def __len__(self) -> Literal[SomeEnum.STR]: ...
 
 class Tuple:
-    def __len__(self) -> Literal[SomeEnum.TUPLE]:
-        return SomeEnum.TUPLE
+    def __len__(self) -> Literal[SomeEnum.TUPLE]: ...
 
 class IntUnion:
-    def __len__(self) -> Literal[SomeEnum.INT, SomeEnum.INT_2]:
-        return SomeEnum.INT
+    def __len__(self) -> Literal[SomeEnum.INT, SomeEnum.INT_2]: ...
 
 reveal_type(len(Auto()))  # revealed: int
 reveal_type(len(Int()))  # revealed: int
@@ -197,8 +184,7 @@ reveal_type(len(IntUnion()))  # revealed: int
 from typing import Literal
 
 class Negative:
-    def __len__(self) -> Literal[-1]:
-        return -1
+    def __len__(self) -> Literal[-1]: ...
 
 # TODO: Emit a diagnostic
 reveal_type(len(Negative()))  # revealed: int
@@ -210,12 +196,10 @@ reveal_type(len(Negative()))  # revealed: int
 from typing import Literal
 
 class SecondOptionalArgument:
-    def __len__(self, v: int = 0) -> Literal[0]:
-        return 0
+    def __len__(self, v: int = 0) -> Literal[0]: ...
 
 class SecondRequiredArgument:
-    def __len__(self, v: int) -> Literal[1]:
-        return 1
+    def __len__(self, v: int) -> Literal[1]: ...
 
 # TODO: Emit a diagnostic
 reveal_type(len(SecondOptionalArgument()))  # revealed: Literal[0]

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

@@ -1,245 +0,0 @@
-# Function return type
-
-When a function's return type is annotated, all return statements are checked to ensure that the
-type of the returned value is assignable to the annotated return type.
-
-## Basic examples
-
-A return value assignable to the annotated return type is valid.
-
-```py
-def f() -> int:
-    return 1
-```
-
-The type of the value obtained by calling a function is the annotated return type, not the inferred
-return type.
-
-```py
-reveal_type(f())  # revealed: int
-```
-
-A `raise` is equivalent to a return of `Never`, which is assignable to any annotated return type.
-
-```py
-def f() -> str:
-    raise ValueError()
-
-reveal_type(f())  # revealed: str
-```
-
-## Stub functions
-
-"Stub" function definitions (that is, function definitions with an empty body) are permissible in
-stub files, or in a few other locations: Protocol method definitions, abstract methods, and
-overloads. In this case the function body is considered to be omitted (thus no return type checking
-is performed on it), not assumed to implicitly return `None`.
-
-A stub function's "empty" body may contain only an optional docstring, followed (optionally) by an
-ellipsis (`...`) or `pass`.
-
-### In stub file
-
-```pyi
-def f() -> int: ...
-
-def f() -> int:
-    pass
-
-def f() -> int:
-    """Some docstring"""
-
-def f() -> int:
-    """Some docstring"""
-    ...
-```
-
-### In Protocol
-
-```py
-from typing import Protocol
-
-class Bar(Protocol):
-    # TODO: no error
-    # error: [invalid-return-type]
-    def f(self) -> int: ...
-```
-
-### In abstract method
-
-```py
-from abc import ABC, abstractmethod
-
-class Foo(ABC):
-    @abstractmethod
-    # TODO: no error
-    # error: [invalid-return-type]
-    def f(self) -> int: ...
-    @abstractmethod
-    # error: [invalid-return-type]
-    def g[T](self, x: T) -> T: ...
-```
-
-### In overload
-
-```py
-from typing import overload
-
-@overload
-def f(x: int) -> int: ...
-@overload
-def f(x: str) -> str: ...
-def f(x: int | str):
-    return x
-```
-
-## Conditional return type
-
-```py
-def f(cond: bool) -> int:
-    if cond:
-        return 1
-    else:
-        return 2
-
-def f(cond: bool) -> int | None:
-    if cond:
-        return 1
-    else:
-        return
-
-def f(cond: bool) -> int:
-    if cond:
-        return 1
-    else:
-        raise ValueError()
-
-def f(cond: bool) -> str | int:
-    if cond:
-        return "a"
-    else:
-        return 1
-```
-
-## Implicit return type
-
-```py
-def f(cond: bool) -> int | None:
-    if cond:
-        return 1
-
-# no implicit return
-def f() -> int:
-    if True:
-        return 1
-
-# no implicit return
-def f(cond: bool) -> int:
-    cond = True
-    if cond:
-        return 1
-
-def f(cond: bool) -> int:
-    if cond:
-        cond = True
-    else:
-        return 1
-    if cond:
-        return 2
-```
-
-## Invalid return type
-
-<!-- snapshot-diagnostics -->
-
-```py
-# error: [invalid-return-type]
-def f() -> int:
-    1
-
-def f() -> str:
-    # error: [invalid-return-type]
-    return 1
-
-def f() -> int:
-    # error: [invalid-return-type]
-    return
-
-from typing import TypeVar
-
-T = TypeVar("T")
-
-# TODO: `invalid-return-type` error should be emitted
-def m(x: T) -> T: ...
-```
-
-## Invalid return type in stub file
-
-<!-- snapshot-diagnostics -->
-
-```pyi
-def f() -> int:
-    # error: [invalid-return-type]
-    return ...
-
-# error: [invalid-return-type]
-def foo() -> int:
-    print("...")
-    ...
-
-# error: [invalid-return-type]
-def foo() -> int:
-    f"""{foo} is a function that ..."""
-    ...
-```
-
-## Invalid conditional return type
-
-<!-- snapshot-diagnostics -->
-
-```py
-def f(cond: bool) -> str:
-    if cond:
-        return "a"
-    else:
-        # error: [invalid-return-type]
-        return 1
-
-def f(cond: bool) -> str:
-    if cond:
-        # error: [invalid-return-type]
-        return 1
-    else:
-        # error: [invalid-return-type]
-        return 2
-```
-
-## Invalid implicit return type
-
-<!-- snapshot-diagnostics -->
-
-```py
-def f() -> None:
-    if False:
-        # error: [invalid-return-type]
-        return 1
-
-# error: [invalid-return-type]
-def f(cond: bool) -> int:
-    if cond:
-        return 1
-
-# error: [invalid-return-type]
-def f(cond: bool) -> int:
-    if cond:
-        raise ValueError()
-
-# error: [invalid-return-type]
-def f(cond: bool) -> int:
-    if cond:
-        cond = False
-    else:
-        return 1
-    if cond:
-        return 2
-```

crates/red_knot_python_semantic/resources/mdtest/generics.md

@@ -0,0 +1,81 @@
+# PEP 695 Generics
+
+## Class Declarations
+
+Basic PEP 695 generics
+
+```py
+class MyBox[T]:
+    data: T
+    box_model_number = 695
+
+    def __init__(self, data: T):
+        self.data = data
+
+box: MyBox[int] = MyBox(5)
+
+# TODO should emit a diagnostic here (str is not assignable to int)
+wrong_innards: MyBox[int] = MyBox("five")
+
+# TODO reveal int, do not leak the typevar
+reveal_type(box.data)  # revealed: T
+
+reveal_type(MyBox.box_model_number)  # revealed: Unknown | Literal[695]
+```
+
+## Subclassing
+
+```py
+class MyBox[T]:
+    data: T
+
+    def __init__(self, data: T):
+        self.data = data
+
+# TODO not error on the subscripting
+# error: [non-subscriptable]
+class MySecureBox[T](MyBox[T]): ...
+
+secure_box: MySecureBox[int] = MySecureBox(5)
+reveal_type(secure_box)  # revealed: MySecureBox
+# TODO reveal int
+# The @Todo(…) is misleading here. We currently treat `MyBox[T]` as a dynamic base class because we
+# don't understand generics and therefore infer `Unknown` for the `MyBox[T]` base of `MySecureBox[T]`.
+reveal_type(secure_box.data)  # revealed: @Todo(instance attribute on class with dynamic base)
+```
+
+## Cyclical class definition
+
+In type stubs, classes can reference themselves in their base class definitions. For example, in
+`typeshed`, we have `class str(Sequence[str]): ...`.
+
+This should hold true even with generics at play.
+
+```pyi
+class Seq[T]: ...
+
+# TODO not error on the subscripting
+class S[T](Seq[S]): ...  # error: [non-subscriptable]
+
+reveal_type(S)  # revealed: Literal[S]
+```
+
+## Type params
+
+A PEP695 type variable defines a value of type `typing.TypeVar`.
+
+```py
+def f[T]():
+    reveal_type(T)  # revealed: T
+    reveal_type(T.__name__)  # revealed: Literal["T"]
+```
+
+## Minimum two constraints
+
+A typevar with less than two constraints emits a diagnostic:
+
+```py
+# 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/generics/classes.md

@@ -1,200 +0,0 @@
-# Generic classes
-
-## PEP 695 syntax
-
-TODO: Add a `red_knot_extension` function that asserts whether a function or class is generic.
-
-This is a generic class defined using PEP 695 syntax:
-
-```py
-class C[T]: ...
-```
-
-A class that inherits from a generic class, and fills its type parameters with typevars, is generic:
-
-```py
-# TODO: no error
-# error: [non-subscriptable]
-class D[U](C[U]): ...
-```
-
-A class that inherits from a generic class, but fills its type parameters with concrete types, is
-_not_ generic:
-
-```py
-# TODO: no error
-# error: [non-subscriptable]
-class E(C[int]): ...
-```
-
-A class that inherits from a generic class, and doesn't fill its type parameters at all, implicitly
-uses the default value for the typevar. In this case, that default type is `Unknown`, so `F`
-inherits from `C[Unknown]` and is not itself generic.
-
-```py
-class F(C): ...
-```
-
-## Legacy syntax
-
-This is a generic class defined using the legacy syntax:
-
-```py
-from typing import Generic, TypeVar
-
-T = TypeVar("T")
-
-# TODO: no error
-# error: [invalid-base]
-class C(Generic[T]): ...
-```
-
-A class that inherits from a generic class, and fills its type parameters with typevars, is generic.
-
-```py
-class D(C[T]): ...
-```
-
-(Examples `E` and `F` from above do not have analogues in the legacy syntax.)
-
-## Inferring generic class parameters
-
-The type parameter can be specified explicitly:
-
-```py
-class C[T]:
-    x: T
-
-# TODO: no error
-# TODO: revealed: C[int]
-# error: [non-subscriptable]
-reveal_type(C[int]())  # revealed: C
-```
-
-We can infer the type parameter from a type context:
-
-```py
-c: C[int] = C()
-# TODO: revealed: C[int]
-reveal_type(c)  # revealed: C
-```
-
-The typevars of a fully specialized generic class should no longer be visible:
-
-```py
-# TODO: revealed: int
-reveal_type(c.x)  # revealed: T
-```
-
-If the type parameter is not specified explicitly, and there are no constraints that let us infer a
-specific type, we infer the typevar's default type:
-
-```py
-class D[T = int]: ...
-
-# TODO: revealed: D[int]
-reveal_type(D())  # revealed: D
-```
-
-If a typevar does not provide a default, we use `Unknown`:
-
-```py
-# TODO: revealed: C[Unknown]
-reveal_type(C())  # revealed: C
-```
-
-If the type of a constructor parameter is a class typevar, we can use that to infer the type
-parameter:
-
-```py
-class E[T]:
-    def __init__(self, x: T) -> None: ...
-
-# TODO: revealed: E[int] or E[Literal[1]]
-reveal_type(E(1))  # revealed: E
-```
-
-The types inferred from a type context and from a constructor parameter must be consistent with each
-other:
-
-```py
-# TODO: error
-wrong_innards: E[int] = E("five")
-```
-
-## Generic subclass
-
-When a generic subclass fills its superclass's type parameter with one of its own, the actual types
-propagate through:
-
-```py
-class Base[T]:
-    x: T | None = None
-
-# TODO: no error
-# error: [non-subscriptable]
-class Sub[U](Base[U]): ...
-
-# TODO: no error
-# TODO: revealed: int | None
-# error: [non-subscriptable]
-reveal_type(Base[int].x)  # revealed: T | None
-# TODO: revealed: int | None
-# error: [non-subscriptable]
-reveal_type(Sub[int].x)  # revealed: T | None
-```
-
-## Cyclic class definition
-
-A class can use itself as the type parameter of one of its superclasses. (This is also known as the
-[curiously recurring template pattern][crtp] or [F-bounded quantification][f-bound].)
-
-Here, `Sub` is not a generic class, since it fills its superclass's type parameter (with itself).
-
-`stub.pyi`:
-
-```pyi
-class Base[T]: ...
-# TODO: no error
-# error: [non-subscriptable]
-class Sub(Base[Sub]): ...
-
-reveal_type(Sub)  # revealed: Literal[Sub]
-```
-
-A similar case can work in a non-stub file, if forward references are stringified:
-
-`string_annotation.py`:
-
-```py
-class Base[T]: ...
-
-# TODO: no error
-# error: [non-subscriptable]
-class Sub(Base["Sub"]): ...
-
-reveal_type(Sub)  # revealed: Literal[Sub]
-```
-
-In a non-stub file, without stringified forward references, this raises a `NameError`:
-
-`bare_annotation.py`:
-
-```py
-class Base[T]: ...
-
-# TODO: error: [unresolved-reference]
-# error: [non-subscriptable]
-class Sub(Base[Sub]): ...
-```
-
-## Another cyclic case
-
-```pyi
-# TODO no error (generics)
-# error: [invalid-base]
-class Derived[T](list[Derived[T]]): ...
-```
-
-[crtp]: https://en.wikipedia.org/wiki/Curiously_recurring_template_pattern
-[f-bound]: https://en.wikipedia.org/wiki/Bounded_quantification#F-bounded_quantification

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

@@ -1,246 +0,0 @@
-# Generic functions
-
-## Typevar must be used at least twice
-
-If you're only using a typevar for a single parameter, you don't need the typevar — just use
-`object` (or the typevar's upper bound):
-
-```py
-# TODO: error, should be (x: object)
-def typevar_not_needed[T](x: T) -> None:
-    pass
-
-# TODO: error, should be (x: int)
-def bounded_typevar_not_needed[T: int](x: T) -> None:
-    pass
-```
-
-Typevars are only needed if you use them more than once. For instance, to specify that two
-parameters must both have the same type:
-
-```py
-def two_params[T](x: T, y: T) -> T:
-    return x
-```
-
-or to specify that a return value is the same as a parameter:
-
-```py
-def return_value[T](x: T) -> T:
-    return x
-```
-
-Each typevar must also appear _somewhere_ in the parameter list:
-
-```py
-def absurd[T]() -> T:
-    # There's no way to construct a T!
-    raise ValueError("absurd")
-```
-
-## Inferring generic function parameter types
-
-If the type of a generic function parameter is a typevar, then we can infer what type that typevar
-is bound to at each call site.
-
-TODO: Note that some of the TODO revealed types have two options, since we haven't decided yet
-whether we want to infer a more specific `Literal` type where possible, or use heuristics to weaken
-the inferred type to e.g. `int`.
-
-```py
-def f[T](x: T) -> T:
-    return x
-
-# TODO: no error
-# TODO: revealed: int or Literal[1]
-# error: [invalid-argument-type]
-reveal_type(f(1))  # revealed: T
-
-# TODO: no error
-# TODO: revealed: float
-# error: [invalid-argument-type]
-reveal_type(f(1.0))  # revealed: T
-
-# TODO: no error
-# TODO: revealed: bool or Literal[true]
-# error: [invalid-argument-type]
-reveal_type(f(True))  # revealed: T
-
-# TODO: no error
-# TODO: revealed: str or Literal["string"]
-# error: [invalid-argument-type]
-reveal_type(f("string"))  # revealed: T
-```
-
-## Inferring “deep” generic parameter types
-
-The matching up of call arguments and discovery of constraints on typevars can be a recursive
-process for arbitrarily-nested generic types in parameters.
-
-```py
-def f[T](x: list[T]) -> T:
-    return x[0]
-
-# TODO: revealed: float
-reveal_type(f([1.0, 2.0]))  # revealed: T
-```
-
-## Typevar constraints
-
-If a type parameter has an upper bound, that upper bound constrains which types can be used for that
-typevar. This effectively adds the upper bound as an intersection to every appearance of the typevar
-in the function.
-
-```py
-def good_param[T: int](x: T) -> None:
-    # TODO: revealed: T & int
-    reveal_type(x)  # revealed: T
-```
-
-If the function is annotated as returning the typevar, this means that the upper bound is _not_
-assignable to that typevar, since return types are contravariant. In `bad`, we can infer that
-`x + 1` has type `int`. But `T` might be instantiated with a narrower type than `int`, and so the
-return value is not guaranteed to be compatible for all `T: int`.
-
-```py
-def good_return[T: int](x: T) -> T:
-    return x
-
-def bad_return[T: int](x: T) -> T:
-    # TODO: error: int is not assignable to T
-    # error: [unsupported-operator] "Operator `+` is unsupported between objects of type `T` and `Literal[1]`"
-    return x + 1
-```
-
-## All occurrences of the same typevar have the same type
-
-If a typevar appears multiple times in a function signature, all occurrences have the same type.
-
-```py
-def different_types[T, S](cond: bool, t: T, s: S) -> T:
-    if cond:
-        return t
-    else:
-        # error: [invalid-return-type] "Object of type `S` is not assignable to return type `T`"
-        return s
-
-def same_types[T](cond: bool, t1: T, t2: T) -> T:
-    if cond:
-        return t1
-    else:
-        return t2
-```
-
-## All occurrences of the same constrained typevar have the same type
-
-The above is true even when the typevars are constrained. Here, both `int` and `str` have `__add__`
-methods that are compatible with the return type, so the `return` expression is always well-typed:
-
-```py
-def same_constrained_types[T: (int, str)](t1: T, t2: T) -> T:
-    # TODO: no error
-    # error: [unsupported-operator] "Operator `+` is unsupported between objects of type `T` and `T`"
-    return t1 + t2
-```
-
-This is _not_ the same as a union type, because of this additional constraint that the two
-occurrences have the same type. In `unions_are_different`, `t1` and `t2` might have different types,
-and an `int` and a `str` cannot be added together:
-
-```py
-def unions_are_different(t1: int | str, t2: int | str) -> int | str:
-    # error: [unsupported-operator] "Operator `+` is unsupported between objects of type `int | str` and `int | str`"
-    return t1 + t2
-```
-
-## Typevar inference is a unification problem
-
-When inferring typevar assignments in a generic function call, we cannot simply solve constraints
-eagerly for each parameter in turn. We must solve a unification problem involving all of the
-parameters simultaneously.
-
-```py
-def two_params[T](x: T, y: T) -> T:
-    return x
-
-# TODO: no error
-# TODO: revealed: str
-# error: [invalid-argument-type]
-# error: [invalid-argument-type]
-reveal_type(two_params("a", "b"))  # revealed: T
-
-# TODO: no error
-# TODO: revealed: str | int
-# error: [invalid-argument-type]
-# error: [invalid-argument-type]
-reveal_type(two_params("a", 1))  # revealed: T
-```
-
-```py
-def param_with_union[T](x: T | int, y: T) -> T:
-    return y
-
-# TODO: no error
-# TODO: revealed: str
-# error: [invalid-argument-type]
-reveal_type(param_with_union(1, "a"))  # revealed: T
-
-# TODO: no error
-# TODO: revealed: str
-# error: [invalid-argument-type]
-# error: [invalid-argument-type]
-reveal_type(param_with_union("a", "a"))  # revealed: T
-
-# TODO: no error
-# TODO: revealed: int
-# error: [invalid-argument-type]
-reveal_type(param_with_union(1, 1))  # revealed: T
-
-# TODO: no error
-# TODO: revealed: str | int
-# error: [invalid-argument-type]
-# error: [invalid-argument-type]
-reveal_type(param_with_union("a", 1))  # revealed: T
-```
-
-```py
-def tuple_param[T, S](x: T | S, y: tuple[T, S]) -> tuple[T, S]:
-    return y
-
-# TODO: no error
-# TODO: revealed: tuple[str, int]
-# error: [invalid-argument-type]
-# error: [invalid-argument-type]
-reveal_type(tuple_param("a", ("a", 1)))  # revealed: tuple[T, S]
-
-# TODO: no error
-# TODO: revealed: tuple[str, int]
-# error: [invalid-argument-type]
-# error: [invalid-argument-type]
-reveal_type(tuple_param(1, ("a", 1)))  # revealed: tuple[T, S]
-```
-
-## Inferring nested generic function calls
-
-We can infer type assignments in nested calls to multiple generic functions. If they use the same
-type variable, we do not confuse the two; `T@f` and `T@g` have separate types in each example below.
-
-```py
-def f[T](x: T) -> tuple[T, int]:
-    return (x, 1)
-
-def g[T](x: T) -> T | None:
-    return x
-
-# TODO: no error
-# TODO: revealed: tuple[str | None, int]
-# error: [invalid-argument-type]
-# error: [invalid-argument-type]
-reveal_type(f(g("a")))  # revealed: tuple[T, int]
-
-# TODO: no error
-# TODO: revealed: tuple[str, int] | None
-# error: [invalid-argument-type]
-# error: [invalid-argument-type]
-reveal_type(g(f("a")))  # revealed: T | None
-```

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

@@ -1,72 +0,0 @@
-# Legacy type variables
-
-The tests in this file focus on how type variables are defined using the legacy notation. Most
-_uses_ of type variables are tested in other files in this directory; we do not duplicate every test
-for both type variable syntaxes.
-
-Unless otherwise specified, all quotations come from the [Generics] section of the typing spec.
-
-## Type variables
-
-### Defining legacy type variables
-
-> Generics can be parameterized by using a factory available in `typing` called `TypeVar`.
-
-This was the only way to create type variables prior to PEP 695/Python 3.12. It is still available
-in newer Python releases.
-
-```py
-from typing import TypeVar
-
-T = TypeVar("T")
-```
-
-### Directly assigned to a variable
-
-> A `TypeVar()` expression must always directly be assigned to a variable (it should not be used as
-> part of a larger expression).
-
-```py
-from typing import TypeVar
-
-# TODO: error
-TestList = list[TypeVar("W")]
-```
-
-### `TypeVar` parameter must match variable name
-
-> The argument to `TypeVar()` must be a string equal to the variable name to which it is assigned.
-
-```py
-from typing import TypeVar
-
-# TODO: error
-T = TypeVar("Q")
-```
-
-### No redefinition
-
-> Type variables must not be redefined.
-
-```py
-from typing import TypeVar
-
-T = TypeVar("T")
-
-# TODO: error
-T = TypeVar("T")
-```
-
-### Cannot have only one constraint
-
-> `TypeVar` supports constraining parametric types to a fixed set of possible types...There should
-> be at least two constraints, if any; specifying a single constraint is disallowed.
-
-```py
-from typing import TypeVar
-
-# TODO: error: [invalid-type-variable-constraints]
-T = TypeVar("T", int)
-```
-
-[generics]: https://typing.readthedocs.io/en/latest/spec/generics.html

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

@@ -1,51 +0,0 @@
-# PEP 695 Generics
-
-[PEP 695] and Python 3.12 introduced new, more ergonomic syntax for type variables.
-
-## Type variables
-
-### Defining PEP 695 type variables
-
-PEP 695 introduces a new syntax for defining type variables. The resulting type variables are
-instances of `typing.TypeVar`, just like legacy type variables.
-
-```py
-def f[T]():
-    reveal_type(type(T))  # revealed: Literal[TypeVar]
-    reveal_type(T)  # revealed: T
-    reveal_type(T.__name__)  # revealed: Literal["T"]
-```
-
-### Cannot have only one constraint
-
-> `TypeVar` supports constraining parametric types to a fixed set of possible types...There should
-> be at least two constraints, if any; specifying a single constraint is disallowed.
-
-```py
-# error: [invalid-type-variable-constraints] "TypeVar must have at least two constrained types"
-def f[T: (int,)]():
-    pass
-```
-
-## Invalid uses
-
-Note that many of the invalid uses of legacy typevars do not apply to PEP 695 typevars, since the
-PEP 695 syntax is only allowed places where typevars are allowed.
-
-## Displaying typevars
-
-We use a suffix when displaying the typevars of a generic function or class. This helps distinguish
-different uses of the same typevar.
-
-```py
-def f[T](x: T, y: T) -> None:
-    # TODO: revealed: T@f
-    reveal_type(x)  # revealed: T
-
-class C[T]:
-    def m(self, x: T) -> None:
-        # TODO: revealed: T@c
-        reveal_type(x)  # revealed: T
-```
-
-[pep 695]: https://peps.python.org/pep-0695/

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

@@ -1,270 +0,0 @@
-# Scoping rules for type variables
-
-Most of these tests come from the [Scoping rules for type variables][scoping] section of the typing
-spec.
-
-## Typevar used outside of generic function or class
-
-Typevars may only be used in generic function or class definitions.
-
-```py
-from typing import TypeVar
-
-T = TypeVar("T")
-
-# TODO: error
-x: T
-
-class C:
-    # TODO: error
-    x: T
-
-def f() -> None:
-    # TODO: error
-    x: T
-```
-
-## Legacy typevar used multiple times
-
-> A type variable used in a generic function could be inferred to represent different types in the
-> same code block.
-
-This only applies to typevars defined using the legacy syntax, since the PEP 695 syntax creates a
-new distinct typevar for each occurrence.
-
-```py
-from typing import TypeVar
-
-T = TypeVar("T")
-
-def f1(x: T) -> T:
-    return x
-
-def f2(x: T) -> T:
-    return x
-
-f1(1)
-f2("a")
-```
-
-## Typevar inferred multiple times
-
-> A type variable used in a generic function could be inferred to represent different types in the
-> same code block.
-
-This also applies to a single generic function being used multiple times, instantiating the typevar
-to a different type each time.
-
-```py
-def f[T](x: T) -> T:
-    return x
-
-# TODO: no error
-# TODO: revealed: int or Literal[1]
-# error: [invalid-argument-type]
-reveal_type(f(1))  # revealed: T
-# TODO: no error
-# TODO: revealed: str or Literal["a"]
-# error: [invalid-argument-type]
-reveal_type(f("a"))  # revealed: T
-```
-
-## Methods can mention class typevars
-
-> A type variable used in a method of a generic class that coincides with one of the variables that
-> parameterize this class is always bound to that variable.
-
-```py
-class C[T]:
-    def m1(self, x: T) -> T:
-        return x
-
-    def m2(self, x: T) -> T:
-        return x
-
-c: C[int] = C()
-# TODO: no error
-# error: [invalid-argument-type]
-c.m1(1)
-# TODO: no error
-# error: [invalid-argument-type]
-c.m2(1)
-# TODO: expected type `int`
-# error: [invalid-argument-type] "Object of type `Literal["string"]` cannot be assigned to parameter 2 (`x`) of bound method `m2`; expected type `T`"
-c.m2("string")
-```
-
-## Methods can mention other typevars
-
-> A type variable used in a method that does not match any of the variables that parameterize the
-> class makes this method a generic function in that variable.
-
-```py
-from typing import TypeVar, Generic
-
-T = TypeVar("T")
-S = TypeVar("S")
-
-# TODO: no error
-# error: [invalid-base]
-class Legacy(Generic[T]):
-    def m(self, x: T, y: S) -> S:
-        return y
-
-legacy: Legacy[int] = Legacy()
-# TODO: revealed: str
-reveal_type(legacy.m(1, "string"))  # revealed: @Todo(Invalid or unsupported `Instance` in `Type::to_type_expression`)
-```
-
-With PEP 695 syntax, it is clearer that the method uses a separate typevar:
-
-```py
-class C[T]:
-    def m[S](self, x: T, y: S) -> S:
-        return y
-
-c: C[int] = C()
-# TODO: no errors
-# TODO: revealed: str
-# error: [invalid-argument-type]
-# error: [invalid-argument-type]
-reveal_type(c.m(1, "string"))  # revealed: S
-```
-
-## Unbound typevars
-
-> Unbound type variables should not appear in the bodies of generic functions, or in the class
-> bodies apart from method definitions.
-
-This is true with the legacy syntax:
-
-```py
-from typing import TypeVar, Generic
-
-T = TypeVar("T")
-S = TypeVar("S")
-
-def f(x: T) -> None:
-    x: list[T] = []
-    # TODO: error
-    y: list[S] = []
-
-# TODO: no error
-# error: [invalid-base]
-class C(Generic[T]):
-    # TODO: error
-    x: list[S] = []
-
-    # This is not an error, as shown in the previous test
-    def m(self, x: S) -> S:
-        return x
-```
-
-This is true with PEP 695 syntax, as well, though we must use the legacy syntax to define the
-unbound typevars:
-
-`pep695.py`:
-
-```py
-from typing import TypeVar
-
-S = TypeVar("S")
-
-def f[T](x: T) -> None:
-    x: list[T] = []
-    # TODO: error
-    y: list[S] = []
-
-class C[T]:
-    # TODO: error
-    x: list[S] = []
-
-    def m1(self, x: S) -> S:
-        return x
-
-    def m2[S](self, x: S) -> S:
-        return x
-```
-
-## Nested formal typevars must be distinct
-
-Generic functions and classes can be nested in each other, but it is an error for the same typevar
-to be used in nested generic definitions.
-
-Note that the typing spec only mentions two specific versions of this rule:
-
-> A generic class definition that appears inside a generic function should not use type variables
-> that parameterize the generic function.
-
-and
-
-> A generic class nested in another generic class cannot use the same type variables.
-
-We assume that the more general form holds.
-
-### Generic function within generic function
-
-```py
-def f[T](x: T, y: T) -> None:
-    def ok[S](a: S, b: S) -> None: ...
-
-    # TODO: error
-    def bad[T](a: T, b: T) -> None: ...
-```
-
-### Generic method within generic class
-
-```py
-class C[T]:
-    def ok[S](self, a: S, b: S) -> None: ...
-
-    # TODO: error
-    def bad[T](self, a: T, b: T) -> None: ...
-```
-
-### Generic class within generic function
-
-```py
-from typing import Iterable
-
-def f[T](x: T, y: T) -> None:
-    class Ok[S]: ...
-    # TODO: error for reuse of typevar
-    class Bad1[T]: ...
-    # TODO: no non-subscriptable error, error for reuse of typevar
-    # error: [non-subscriptable]
-    class Bad2(Iterable[T]): ...
-```
-
-### Generic class within generic class
-
-```py
-from typing import Iterable
-
-class C[T]:
-    class Ok1[S]: ...
-    # TODO: error for reuse of typevar
-    class Bad1[T]: ...
-    # TODO: no non-subscriptable error, error for reuse of typevar
-    # error: [non-subscriptable]
-    class Bad2(Iterable[T]): ...
-```
-
-## Class scopes do not cover inner scopes
-
-Just like regular symbols, the typevars of a generic class are only available in that class's scope,
-and are not available in nested scopes.
-
-```py
-class C[T]:
-    ok1: list[T] = []
-
-    class Bad:
-        # TODO: error
-        bad: list[T] = []
-
-    class Inner[S]: ...
-    ok2: Inner[T]
-```
-
-[scoping]: https://typing.readthedocs.io/en/latest/spec/generics.html#scoping-rules-for-type-variables

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

@@ -1,131 +0,0 @@
-# Case Sensitive Imports
-
-```toml
-# TODO: This test should use the real file system instead of the memory file system.
-# but we can't change the file system yet because the tests would then start failing for 
-# case-insensitive file systems.
-#system = "os"
-```
-
-Python's import system is case-sensitive even on case-insensitive file system. This means, importing
-a module `a` should fail if the file in the search paths is named `A.py`. See
-[PEP 235](https://peps.python.org/pep-0235/).
-
-## Correct casing
-
-Importing a module where the name matches the file name's casing should succeed.
-
-`a.py`:
-
-```py
-class Foo:
-    x: int = 1
-```
-
-```python
-from a import Foo
-
-reveal_type(Foo().x)  # revealed: int
-```
-
-## Incorrect casing
-
-Importing a module where the name does not match the file name's casing should fail.
-
-`A.py`:
-
-```py
-class Foo:
-    x: int = 1
-```
-
-```python
-# error: [unresolved-import]
-from a import Foo
-```
-
-## Multiple search paths with different cased modules
-
-The resolved module is the first matching the file name's casing but Python falls back to later
-search paths if the file name's casing does not match.
-
-```toml
-[environment]
-extra-paths = ["/search-1", "/search-2"]
-```
-
-`/search-1/A.py`:
-
-```py
-class Foo:
-    x: int = 1
-```
-
-`/search-2/a.py`:
-
-```py
-class Bar:
-    x: str = "test"
-```
-
-```python
-from A import Foo
-from a import Bar
-
-reveal_type(Foo().x)  # revealed: int
-reveal_type(Bar().x)  # revealed: str
-```
-
-## Intermediate segments
-
-`db/__init__.py`:
-
-```py
-```
-
-`db/a.py`:
-
-```py
-class Foo:
-    x: int = 1
-```
-
-`correctly_cased.py`:
-
-```python
-from db.a import Foo
-
-reveal_type(Foo().x)  # revealed: int
-```
-
-Imports where some segments are incorrectly cased should fail.
-
-`incorrectly_cased.py`:
-
-```python
-# error: [unresolved-import]
-from DB.a import Foo
-
-# error: [unresolved-import]
-from DB.A import Foo
-
-# error: [unresolved-import]
-from db.A import Foo
-```
-
-## Incorrect extension casing
-
-The extension of imported python modules must be `.py` or `.pyi` but not `.PY` or `Py` or any
-variant where some characters are uppercase.
-
-`a.PY`:
-
-```py
-class Foo:
-    x: int = 1
-```
-
-```python
-# error: [unresolved-import]
-from a import Foo
-```

crates/red_knot_python_semantic/resources/mdtest/invalid_syntax.md

@@ -91,16 +91,3 @@ match while:
 for x in foo.pass:
     pass
 ```
-
-## Invalid annotation
-
-### `typing.Callable`
-
-```py
-from typing import Callable
-
-# error: [invalid-syntax] "Expected index or slice expression"
-# error: [invalid-type-form] "Special form `typing.Callable` expected exactly two arguments (parameter types and return type)"
-def _(c: Callable[]):
-    reveal_type(c)  # revealed: (...) -> Unknown
-```

crates/red_knot_python_semantic/resources/mdtest/known_constants.md

@@ -26,6 +26,23 @@ from typing import TYPE_CHECKING as TC
 reveal_type(TC)  # revealed: Literal[True]
 ```
 
+### Must originate from `typing`
+
+Make sure we only use our special handling for `typing.TYPE_CHECKING` and not for other constants
+with the same name:
+
+`constants.py`:
+
+```py
+TYPE_CHECKING: bool = False
+```
+
+```py
+from constants import TYPE_CHECKING
+
+reveal_type(TYPE_CHECKING)  # revealed: bool
+```
+
 ### `typing_extensions` re-export
 
 This should behave in the same way as `typing.TYPE_CHECKING`:
@@ -35,117 +52,3 @@ from typing_extensions import TYPE_CHECKING
 
 reveal_type(TYPE_CHECKING)  # revealed: Literal[True]
 ```
-
-## User-defined `TYPE_CHECKING`
-
-If we set `TYPE_CHECKING = False` directly instead of importing it from the `typing` module, it will
-still be treated as `True` during type checking. This behavior is for compatibility with other major
-type checkers, e.g. mypy and pyright.
-
-### With no type annotation
-
-```py
-TYPE_CHECKING = False
-reveal_type(TYPE_CHECKING)  # revealed: Literal[True]
-if TYPE_CHECKING:
-    type_checking = True
-if not TYPE_CHECKING:
-    runtime = True
-
-# type_checking is treated as unconditionally assigned.
-reveal_type(type_checking)  # revealed: Literal[True]
-# error: [unresolved-reference]
-reveal_type(runtime)  # revealed: Unknown
-```
-
-### With a type annotation
-
-We can also define `TYPE_CHECKING` with a type annotation. The type must be one to which `bool` can
-be assigned. Even in this case, the type of `TYPE_CHECKING` is still inferred to be `Literal[True]`.
-
-```py
-TYPE_CHECKING: bool = False
-reveal_type(TYPE_CHECKING)  # revealed: Literal[True]
-if TYPE_CHECKING:
-    type_checking = True
-if not TYPE_CHECKING:
-    runtime = True
-
-reveal_type(type_checking)  # revealed: Literal[True]
-# error: [unresolved-reference]
-reveal_type(runtime)  # revealed: Unknown
-```
-
-### Importing user-defined `TYPE_CHECKING`
-
-`constants.py`:
-
-```py
-TYPE_CHECKING = False
-```
-
-`stub.pyi`:
-
-```pyi
-TYPE_CHECKING: bool
-# or
-TYPE_CHECKING: bool = ...
-```
-
-```py
-from constants import TYPE_CHECKING
-
-reveal_type(TYPE_CHECKING)  # revealed: Literal[True]
-
-from stub import TYPE_CHECKING
-
-reveal_type(TYPE_CHECKING)  # revealed: Literal[True]
-```
-
-### Invalid assignment to `TYPE_CHECKING`
-
-Only `False` can be assigned to `TYPE_CHECKING`; any assignment other than `False` will result in an
-error. A type annotation to which `bool` is not assignable is also an error.
-
-```py
-from typing import Literal
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING = True
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: bool = True
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: int = 1
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: str = "str"
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: str = False
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: Literal[False] = False
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: Literal[True] = False
-```
-
-The same rules apply in a stub file:
-
-```pyi
-from typing import Literal
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: str
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: str = False
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: Literal[False] = ...
-
-# error: [invalid-type-checking-constant]
-TYPE_CHECKING: object = "str"
-```

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

@@ -105,11 +105,7 @@ reveal_type(x)
 
 ## With non-callable iterator
 
-<!-- snapshot-diagnostics -->
-
 ```py
-from typing_extensions import reveal_type
-
 def _(flag: bool):
     class NotIterable:
         if flag:
@@ -117,8 +113,7 @@ def _(flag: bool):
         else:
             __iter__: None = None
 
-    # error: [not-iterable]
-    for x in NotIterable():
+    for x in NotIterable():  # error: "Object of type `NotIterable` is not iterable"
         pass
 
     # revealed: Unknown
@@ -128,25 +123,21 @@ def _(flag: bool):
 
 ## Invalid iterable
 
-<!-- snapshot-diagnostics -->
-
 ```py
 nonsense = 123
-for x in nonsense:  # error: [not-iterable]
+for x in nonsense:  # error: "Object of type `Literal[123]` is not iterable"
     pass
 ```
 
 ## New over old style iteration protocol
 
-<!-- snapshot-diagnostics -->
-
 ```py
 class NotIterable:
     def __getitem__(self, key: int) -> int:
         return 42
     __iter__: None = None
 
-for x in NotIterable():  # error: [not-iterable]
+for x in NotIterable():  # error: "Object of type `NotIterable` is not iterable"
     pass
 ```
 
@@ -230,11 +221,7 @@ def _(flag: bool):
 
 ## Union type as iterable where one union element has no `__iter__` method
 
-<!-- snapshot-diagnostics -->
-
 ```py
-from typing_extensions import reveal_type
-
 class TestIter:
     def __next__(self) -> int:
         return 42
@@ -244,18 +231,14 @@ class Test:
         return TestIter()
 
 def _(flag: bool):
-    # error: [not-iterable]
+    # 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
 
-<!-- snapshot-diagnostics -->
-
 ```py
-from typing_extensions import reveal_type
-
 class TestIter:
     def __next__(self) -> int:
         return 42
@@ -270,7 +253,7 @@ class Test2:
 
 def _(flag: bool):
     # TODO: Improve error message to state which union variant isn't iterable (https://github.com/astral-sh/ruff/issues/13989)
-    # error: [not-iterable]
+    # error: "Object of type `Test | Test2` is not iterable"
     for x in Test() if flag else Test2():
         reveal_type(x)  # revealed: int
 ```
@@ -286,464 +269,7 @@ class Test:
     def __iter__(self) -> TestIter | int:
         return TestIter()
 
-# error: [not-iterable] "Object of type `Test` may not be iterable because its `__iter__` method returns an object of type `TestIter | int`, which may not have a `__next__` method"
+# error: [not-iterable] "Object of type `Test` is not iterable"
 for x in Test():
     reveal_type(x)  # revealed: int
 ```
-
-## Possibly-not-callable `__iter__` method
-
-```py
-def _(flag: bool):
-    class Iterator:
-        def __next__(self) -> int:
-            return 42
-
-    class CustomCallable:
-        if flag:
-            def __call__(self, *args, **kwargs) -> Iterator:
-                return Iterator()
-        else:
-            __call__: None = None
-
-    class Iterable1:
-        __iter__: CustomCallable = CustomCallable()
-
-    class Iterable2:
-        if flag:
-            def __iter__(self) -> Iterator:
-                return Iterator()
-        else:
-            __iter__: None = None
-
-    # error: [not-iterable] "Object of type `Iterable1` may not be iterable because its `__iter__` attribute (with type `CustomCallable`) may not be callable"
-    for x in Iterable1():
-        # TODO... `int` might be ideal here?
-        reveal_type(x)  # revealed: int | Unknown
-
-    # error: [not-iterable] "Object of type `Iterable2` may not be iterable because its `__iter__` attribute (with type `<bound method `__iter__` of `Iterable2`> | None`) may not be callable"
-    for y in Iterable2():
-        # TODO... `int` might be ideal here?
-        reveal_type(y)  # revealed: int | Unknown
-```
-
-## `__iter__` method with a bad signature
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-class Iterator:
-    def __next__(self) -> int:
-        return 42
-
-class Iterable:
-    def __iter__(self, extra_arg) -> Iterator:
-        return Iterator()
-
-# error: [not-iterable]
-for x in Iterable():
-    reveal_type(x)  # revealed: int
-```
-
-## `__iter__` does not return an iterator
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-class Bad:
-    def __iter__(self) -> int:
-        return 42
-
-# error: [not-iterable]
-for x in Bad():
-    reveal_type(x)  # revealed: Unknown
-```
-
-## `__iter__` returns an object with a possibly unbound `__next__` method
-
-```py
-def _(flag: bool):
-    class Iterator:
-        if flag:
-            def __next__(self) -> int:
-                return 42
-
-    class Iterable:
-        def __iter__(self) -> Iterator:
-            return Iterator()
-
-    # error: [not-iterable] "Object of type `Iterable` may not be iterable because its `__iter__` method returns an object of type `Iterator`, which may not have a `__next__` method"
-    for x in Iterable():
-        reveal_type(x)  # revealed: int
-```
-
-## `__iter__` returns an iterator with an invalid `__next__` method
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-class Iterator1:
-    def __next__(self, extra_arg) -> int:
-        return 42
-
-class Iterator2:
-    __next__: None = None
-
-class Iterable1:
-    def __iter__(self) -> Iterator1:
-        return Iterator1()
-
-class Iterable2:
-    def __iter__(self) -> Iterator2:
-        return Iterator2()
-
-# error: [not-iterable]
-for x in Iterable1():
-    reveal_type(x)  # revealed: int
-
-# error: [not-iterable]
-for y in Iterable2():
-    reveal_type(y)  # revealed: Unknown
-```
-
-## Possibly unbound `__iter__` and bad `__getitem__` method
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-def _(flag: bool):
-    class Iterator:
-        def __next__(self) -> int:
-            return 42
-
-    class Iterable:
-        if flag:
-            def __iter__(self) -> Iterator:
-                return Iterator()
-        # invalid signature because it only accepts a `str`,
-        # but the old-style iteration protocol will pass it an `int`
-        def __getitem__(self, key: str) -> bytes:
-            return bytes()
-
-    # error: [not-iterable]
-    for x in Iterable():
-        reveal_type(x)  # revealed: int | bytes
-```
-
-## Possibly unbound `__iter__` and not-callable `__getitem__`
-
-This snippet tests that we infer the element type correctly in the following edge case:
-
-- `__iter__` is a method with the correct parameter spec that returns a valid iterator; BUT
-- `__iter__` is possibly unbound; AND
-- `__getitem__` is set to a non-callable type
-
-It's important that we emit a diagnostic here, but it's also important that we still use the return
-type of the iterator's `__next__` method as the inferred type of `x` in the `for` loop:
-
-```py
-def _(flag: bool):
-    class Iterator:
-        def __next__(self) -> int:
-            return 42
-
-    class Iterable:
-        if flag:
-            def __iter__(self) -> Iterator:
-                return Iterator()
-        __getitem__: None = None
-
-    # error: [not-iterable] "Object of type `Iterable` may not be iterable because it may not have an `__iter__` method and its `__getitem__` attribute has type `None`, which is not callable"
-    for x in Iterable():
-        reveal_type(x)  # revealed: int
-```
-
-## Possibly unbound `__iter__` and possibly unbound `__getitem__`
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-class Iterator:
-    def __next__(self) -> int:
-        return 42
-
-def _(flag1: bool, flag2: bool):
-    class Iterable:
-        if flag1:
-            def __iter__(self) -> Iterator:
-                return Iterator()
-        if flag2:
-            def __getitem__(self, key: int) -> bytes:
-                return bytes()
-
-    # error: [not-iterable]
-    for x in Iterable():
-        reveal_type(x)  # revealed: int | bytes
-```
-
-## No `__iter__` method and `__getitem__` is not callable
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-class Bad:
-    __getitem__: None = None
-
-# error: [not-iterable]
-for x in Bad():
-    reveal_type(x)  # revealed: Unknown
-```
-
-## Possibly-not-callable `__getitem__` method
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-def _(flag: bool):
-    class CustomCallable:
-        if flag:
-            def __call__(self, *args, **kwargs) -> int:
-                return 42
-        else:
-            __call__: None = None
-
-    class Iterable1:
-        __getitem__: CustomCallable = CustomCallable()
-
-    class Iterable2:
-        if flag:
-            def __getitem__(self, key: int) -> int:
-                return 42
-        else:
-            __getitem__: None = None
-
-    # error: [not-iterable]
-    for x in Iterable1():
-        # TODO... `int` might be ideal here?
-        reveal_type(x)  # revealed: int | Unknown
-
-    # error: [not-iterable]
-    for y in Iterable2():
-        # TODO... `int` might be ideal here?
-        reveal_type(y)  # revealed: int | Unknown
-```
-
-## Bad `__getitem__` method
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-class Iterable:
-    # invalid because it will implicitly be passed an `int`
-    # by the interpreter
-    def __getitem__(self, key: str) -> int:
-        return 42
-
-# error: [not-iterable]
-for x in Iterable():
-    reveal_type(x)  # revealed: int
-```
-
-## Possibly unbound `__iter__` but definitely bound `__getitem__`
-
-Here, we should not emit a diagnostic: if `__iter__` is unbound, we should fallback to
-`__getitem__`:
-
-```py
-class Iterator:
-    def __next__(self) -> str:
-        return "foo"
-
-def _(flag: bool):
-    class Iterable:
-        if flag:
-            def __iter__(self) -> Iterator:
-                return Iterator()
-
-        def __getitem__(self, key: int) -> bytes:
-            return b"foo"
-
-    for x in Iterable():
-        reveal_type(x)  # revealed: str | bytes
-```
-
-## Possibly invalid `__iter__` methods
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-class Iterator:
-    def __next__(self) -> int:
-        return 42
-
-def _(flag: bool):
-    class Iterable1:
-        if flag:
-            def __iter__(self) -> Iterator:
-                return Iterator()
-        else:
-            def __iter__(self, invalid_extra_arg) -> Iterator:
-                return Iterator()
-
-    # error: [not-iterable]
-    for x in Iterable1():
-        reveal_type(x)  # revealed: int
-
-    class Iterable2:
-        if flag:
-            def __iter__(self) -> Iterator:
-                return Iterator()
-        else:
-            __iter__: None = None
-
-    # error: [not-iterable]
-    for x in Iterable2():
-        # TODO: `int` would probably be better here:
-        reveal_type(x)  # revealed: int | Unknown
-```
-
-## Possibly invalid `__next__` method
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-def _(flag: bool):
-    class Iterator1:
-        if flag:
-            def __next__(self) -> int:
-                return 42
-        else:
-            def __next__(self, invalid_extra_arg) -> str:
-                return "foo"
-
-    class Iterator2:
-        if flag:
-            def __next__(self) -> int:
-                return 42
-        else:
-            __next__: None = None
-
-    class Iterable1:
-        def __iter__(self) -> Iterator1:
-            return Iterator1()
-
-    class Iterable2:
-        def __iter__(self) -> Iterator2:
-            return Iterator2()
-
-    # error: [not-iterable]
-    for x in Iterable1():
-        reveal_type(x)  # revealed: int | str
-
-    # error: [not-iterable]
-    for y in Iterable2():
-        # TODO: `int` would probably be better here:
-        reveal_type(y)  # revealed: int | Unknown
-```
-
-## Possibly invalid `__getitem__` methods
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-def _(flag: bool):
-    class Iterable1:
-        if flag:
-            def __getitem__(self, item: int) -> str:
-                return "foo"
-        else:
-            __getitem__: None = None
-
-    class Iterable2:
-        if flag:
-            def __getitem__(self, item: int) -> str:
-                return "foo"
-        else:
-            def __getitem__(self, item: str) -> int:
-                return 42
-
-    # error: [not-iterable]
-    for x in Iterable1():
-        # TODO: `str` might be better
-        reveal_type(x)  # revealed: str | Unknown
-
-    # error: [not-iterable]
-    for y in Iterable2():
-        reveal_type(y)  # revealed: str | int
-```
-
-## Possibly unbound `__iter__` and possibly invalid `__getitem__`
-
-<!-- snapshot-diagnostics -->
-
-```py
-from typing_extensions import reveal_type
-
-class Iterator:
-    def __next__(self) -> bytes:
-        return b"foo"
-
-def _(flag: bool, flag2: bool):
-    class Iterable1:
-        if flag:
-            def __getitem__(self, item: int) -> str:
-                return "foo"
-        else:
-            __getitem__: None = None
-
-        if flag2:
-            def __iter__(self) -> Iterator:
-                return Iterator()
-
-    class Iterable2:
-        if flag:
-            def __getitem__(self, item: int) -> str:
-                return "foo"
-        else:
-            def __getitem__(self, item: str) -> int:
-                return 42
-        if flag2:
-            def __iter__(self) -> Iterator:
-                return Iterator()
-
-    # error: [not-iterable]
-    for x in Iterable1():
-        # TODO: `bytes | str` might be better
-        reveal_type(x)  # revealed: bytes | str | Unknown
-
-    # error: [not-iterable]
-    for y in Iterable2():
-        reveal_type(y)  # revealed: bytes | str | int
-```
-
-## Never is iterable
-
-```py
-from typing_extensions import Never
-
-def f(never: Never):
-    for x in never:
-        reveal_type(x)  # revealed: Never
-```

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

@@ -10,8 +10,7 @@ class Iterator:
         return 42
 
 class Iterable:
-    def __iter__(self) -> Iterator:
-        return Iterator()
+    def __iter__(self) -> Iterator: ...
 
 def generator_function():
     yield from Iterable()

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

@@ -116,14 +116,3 @@ def _(flag: bool, flag2: bool):
     # error: [possibly-unresolved-reference]
     y
 ```
-
-## Condition with object that implements `__bool__` incorrectly
-
-```py
-class NotBoolable:
-    __bool__ = 3
-
-# error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `NotBoolable`; its `__bool__` method isn't callable"
-while NotBoolable():
-    ...
-```

crates/red_knot_python_semantic/resources/mdtest/metaclass.md

@@ -163,11 +163,10 @@ reveal_type(B.__class__)  # revealed: Literal[M]
 ## Non-class
 
 When a class has an explicit `metaclass` that is not a class, but is a callable that accepts
-`type.__new__` arguments, we should return the meta-type of its return type.
+`type.__new__` arguments, we should return the meta type of its return type.
 
 ```py
-def f(*args, **kwargs) -> int:
-    return 1
+def f(*args, **kwargs) -> int: ...
 
 class A(metaclass=f): ...
 

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

@@ -22,13 +22,11 @@ def _(flag: bool):
 
     # invalid invocation, too many positional args
     reveal_type(x)  # revealed: Literal[1] | None
-    # error: [too-many-positional-arguments] "Too many positional arguments to class `bool`: expected 1, got 2"
-    if bool(x is not None, 5):
+    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
-    # error: [unknown-argument] "Argument `y` does not match any known parameter of class `bool`"
-    if bool(x is not None, y=5):
+    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/isinstance.md

@@ -97,7 +97,12 @@ else:
 ## No narrowing for instances of `builtins.type`
 
 ```py
-def _(flag: bool, t: type):
+def _(flag: bool):
+    t = type("t", (), {})
+
+    # 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):

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

@@ -112,7 +112,8 @@ def _(flag: bool):
         reveal_type(t)  # revealed: Literal[NoneType]
 
     if issubclass(t, type(None)):
-        reveal_type(t)  # revealed: Literal[NoneType]
+        # TODO: this should be just `Literal[NoneType]`
+        reveal_type(t)  # revealed: Literal[int, NoneType]
 ```
 
 ## `classinfo` contains multiple types
@@ -170,8 +171,7 @@ if issubclass(t, int):
 def issubclass(c, ci):
     return True
 
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 t = int if flag() else str
 if issubclass(t, int):
@@ -183,8 +183,7 @@ if issubclass(t, int):
 ```py
 issubclass_alias = issubclass
 
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 t = int if flag() else str
 if issubclass_alias(t, int):
@@ -196,8 +195,7 @@ if issubclass_alias(t, int):
 ```py
 from builtins import issubclass as imported_issubclass
 
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 t = int if flag() else str
 if imported_issubclass(t, int):
@@ -209,8 +207,7 @@ if imported_issubclass(t, int):
 ```py
 from typing import Any
 
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 t = int if flag() else str
 
@@ -233,8 +230,7 @@ if issubclass(t, Any):
 ### Do not narrow if there are keyword arguments
 
 ```py
-def flag() -> bool:
-    return True
+def flag() -> bool: ...
 
 t = int if flag() else str
 

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

@@ -20,8 +20,7 @@ def _(flag: bool):
 ## Class patterns
 
 ```py
-def get_object() -> object:
-    return object()
+def get_object() -> object: ...
 
 class A: ...
 class B: ...
@@ -43,12 +42,10 @@ reveal_type(x)  # revealed: object
 ## Class pattern with guard
 
 ```py
-def get_object() -> object:
-    return object()
+def get_object() -> object: ...
 
 class A:
-    def y() -> int:
-        return 1
+    def y() -> int: ...
 
 class B: ...
 

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

@@ -233,20 +233,16 @@ reveal_type(y)  # revealed: A
 from typing import Literal
 
 class MetaAmbiguous(type):
-    def __bool__(self) -> bool:
-        return True
+    def __bool__(self) -> bool: ...
 
 class MetaFalsy(type):
-    def __bool__(self) -> Literal[False]:
-        return False
+    def __bool__(self) -> Literal[False]: ...
 
 class MetaTruthy(type):
-    def __bool__(self) -> Literal[True]:
-        return True
+    def __bool__(self) -> Literal[True]: ...
 
 class MetaDeferred(type):
-    def __bool__(self) -> MetaAmbiguous:
-        return MetaAmbiguous()
+    def __bool__(self) -> MetaAmbiguous: ...
 
 class AmbiguousClass(metaclass=MetaAmbiguous): ...
 class FalsyClass(metaclass=MetaFalsy): ...
@@ -270,7 +266,7 @@ def _(
     if af:
         reveal_type(af)  # revealed: type[AmbiguousClass] & ~AlwaysFalsy
 
-    # error: [unsupported-bool-conversion] "Boolean conversion is unsupported for type `MetaDeferred`; the return type of its bool method (`MetaAmbiguous`) isn't assignable to `bool"
+    # TODO: Emit a diagnostic (`d` is not valid in boolean context)
     if d:
         # TODO: Should be `Unknown`
         reveal_type(d)  # revealed: type[DeferredClass] & ~AlwaysFalsy
@@ -304,24 +300,20 @@ def _(x: bool | str):
     reveal_type(x and A())  # revealed: Literal[False] | str & ~AlwaysTruthy | A
 
 class Falsy:
-    def __bool__(self) -> Literal[False]:
-        return False
+    def __bool__(self) -> Literal[False]: ...
 
 class Truthy:
-    def __bool__(self) -> Literal[True]:
-        return True
+    def __bool__(self) -> Literal[True]: ...
 
 def _(x: Falsy | Truthy):
     reveal_type(x or A())  # revealed: Truthy | A
     reveal_type(x and A())  # revealed: Falsy | A
 
 class MetaFalsy(type):
-    def __bool__(self) -> Literal[False]:
-        return False
+    def __bool__(self) -> Literal[False]: ...
 
 class MetaTruthy(type):
-    def __bool__(self) -> Literal[True]:
-        return True
+    def __bool__(self) -> Literal[True]: ...
 
 class FalsyClass(metaclass=MetaFalsy): ...
 class TruthyClass(metaclass=MetaTruthy): ...

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

@@ -88,7 +88,7 @@ def _(x: str | int):
 
 ```py
 def _(x: str | int):
-    # error: [no-matching-overload] "No overload of class `type` matches arguments"
+    # TODO: we could issue a diagnostic here
     if type(object=x) is str:
         reveal_type(x)  # revealed: str | int
 ```

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

@@ -9,8 +9,7 @@ is retained after the loop.
 ## Basic `while` loop
 
 ```py
-def next_item() -> int | None:
-    return 1
+def next_item() -> int | None: ...
 
 x = next_item()
 
@@ -24,8 +23,7 @@ reveal_type(x)  # revealed: None
 ## `while` loop with `else`
 
 ```py
-def next_item() -> int | None:
-    return 1
+def next_item() -> int | None: ...
 
 x = next_item()
 
@@ -43,8 +41,7 @@ reveal_type(x)  # revealed: None
 ```py
 from typing import Literal
 
-def next_item() -> Literal[1, 2, 3]:
-    raise NotImplementedError
+def next_item() -> Literal[1, 2, 3]: ...
 
 x = next_item()
 

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

@@ -341,12 +341,10 @@ annotation are looked up lazily, even if they occur in an eager scope.
 ### Eager annotations in a Python file
 
 ```py
-from typing import ClassVar
-
 x = int
 
 class C:
-    var: ClassVar[x]
+    var: x
 
 reveal_type(C.var)  # revealed: int
 
@@ -358,12 +356,10 @@ x = str
 ```py
 from __future__ import annotations
 
-from typing import ClassVar
-
 x = int
 
 class C:
-    var: ClassVar[x]
+    var: x
 
 reveal_type(C.var)  # revealed: Unknown | str
 
@@ -373,12 +369,10 @@ x = str
 ### Deferred annotations in a stub file
 
 ```pyi
-from typing import ClassVar
-
 x = int
 
 class C:
-    var: ClassVar[x]
+    var: x
 
 reveal_type(C.var)  # revealed: Unknown | str
 

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

@@ -9,7 +9,7 @@ is unbound.
 ```py
 reveal_type(__name__)  # revealed: str
 reveal_type(__file__)  # revealed: str | None
-reveal_type(__loader__)  # revealed: LoaderProtocol | None
+reveal_type(__loader__)  # revealed: @Todo(instance attribute on class with dynamic base) | None
 reveal_type(__package__)  # revealed: str | None
 reveal_type(__doc__)  # revealed: str | None
 
@@ -136,43 +136,3 @@ if returns_bool():
 reveal_type(__file__)  # revealed: Literal[42]
 reveal_type(__name__)  # revealed: Literal[1] | str
 ```
-
-## Implicit global attributes in the current module override implicit globals from builtins
-
-Here, we take the type of the implicit global symbol `__name__` from the `types.ModuleType` stub
-(which in this custom typeshed specifies the type as `bytes`). This is because the `main` module has
-an implicit `__name__` global that shadows the builtin `__name__` symbol.
-
-```toml
-[environment]
-typeshed = "/typeshed"
-```
-
-`/typeshed/stdlib/builtins.pyi`:
-
-```pyi
-class object: ...
-class int: ...
-class bytes: ...
-
-__name__: int = 42
-```
-
-`/typeshed/stdlib/types.pyi`:
-
-```pyi
-class ModuleType:
-    __name__: bytes
-```
-
-`/typeshed/stdlib/typing_extensions.pyi`:
-
-```pyi
-def reveal_type(obj, /): ...
-```
-
-`main.py`:
-
-```py
-reveal_type(__name__)  # revealed: bytes
-```

crates/red_knot_python_semantic/resources/mdtest/slots.md

@@ -167,7 +167,7 @@ class A:
     __slots__ = ()
     __slots__ += ("a", "b")
 
-reveal_type(A.__slots__)  # revealed: @Todo(return type of decorated function)
+reveal_type(A.__slots__)  # revealed: @Todo(return type)
 
 class B:
     __slots__ = ("c", "d")

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

@@ -1,52 +0,0 @@
----
-source: crates/red_knot_test/src/lib.rs
-expression: snapshot
----
----
-mdtest name: for.md - For loops - Bad `__getitem__` method
-mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
----
-
-# Python source files
-
-## mdtest_snippet.py
-
-```
- 1 | from typing_extensions import reveal_type
- 2 | 
- 3 | class Iterable:
- 4 |     # invalid because it will implicitly be passed an `int`
- 5 |     # by the interpreter
- 6 |     def __getitem__(self, key: str) -> int:
- 7 |         return 42
- 8 | 
- 9 | # error: [not-iterable]
-10 | for x in Iterable():
-11 |     reveal_type(x)  # revealed: int
-```
-
-# Diagnostics
-
-```
-error: lint:not-iterable
-  --> /src/mdtest_snippet.py:10:10
-   |
- 9 | # error: [not-iterable]
-10 | for x in Iterable():
-   |          ^^^^^^^^^^ Object of type `Iterable` is not iterable because it has no `__iter__` method and its `__getitem__` method has an incorrect signature for the old-style iteration protocol (expected a signature at least as permissive as `def __getitem__(self, key: int): ...`)
-11 |     reveal_type(x)  # revealed: int
-   |
-
-```
-
-```
-info: revealed-type
-  --> /src/mdtest_snippet.py:11:5
-   |
- 9 | # error: [not-iterable]
-10 | for x in Iterable():
-11 |     reveal_type(x)  # revealed: int
-   |     -------------- info: Revealed type is `int`
-   |
-
-```

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

@@ -1,32 +0,0 @@
----
-source: crates/red_knot_test/src/lib.rs
-expression: snapshot
----
----
-mdtest name: for.md - For loops - Invalid iterable
-mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
----
-
-# Python source files
-
-## mdtest_snippet.py
-
-```
-1 | nonsense = 123
-2 | for x in nonsense:  # error: [not-iterable]
-3 |     pass
-```
-
-# Diagnostics
-
-```
-error: lint:not-iterable
- --> /src/mdtest_snippet.py:2:10
-  |
-1 | nonsense = 123
-2 | for x in nonsense:  # error: [not-iterable]
-  |          ^^^^^^^^ Object of type `Literal[123]` is not iterable because it doesn't have an `__iter__` method or a `__getitem__` method
-3 |     pass
-  |
-
-```

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

@@ -1,37 +0,0 @@
----
-source: crates/red_knot_test/src/lib.rs
-expression: snapshot
----
----
-mdtest name: for.md - For loops - New over old style iteration protocol
-mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
----
-
-# Python source files
-
-## mdtest_snippet.py
-
-```
-1 | class NotIterable:
-2 |     def __getitem__(self, key: int) -> int:
-3 |         return 42
-4 |     __iter__: None = None
-5 | 
-6 | for x in NotIterable():  # error: [not-iterable]
-7 |     pass
-```
-
-# Diagnostics
-
-```
-error: lint:not-iterable
- --> /src/mdtest_snippet.py:6:10
-  |
-4 |     __iter__: None = None
-5 |
-6 | for x in NotIterable():  # error: [not-iterable]
-  |          ^^^^^^^^^^^^^ Object of type `NotIterable` is not iterable because its `__iter__` attribute has type `None`, which is not callable
-7 |     pass
-  |
-
-```

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

@@ -1,49 +0,0 @@
----
-source: crates/red_knot_test/src/lib.rs
-expression: snapshot
----
----
-mdtest name: for.md - For loops - No `__iter__` method and `__getitem__` is not callable
-mdtest path: crates/red_knot_python_semantic/resources/mdtest/loops/for.md
----
-
-# Python source files
-
-## mdtest_snippet.py
-
-```
-1 | from typing_extensions import reveal_type
-2 | 
-3 | class Bad:
-4 |     __getitem__: None = None
-5 | 
-6 | # error: [not-iterable]
-7 | for x in Bad():
-8 |     reveal_type(x)  # revealed: Unknown
-```
-
-# Diagnostics
-
-```
-error: lint:not-iterable
- --> /src/mdtest_snippet.py:7:10
-  |
-6 | # error: [not-iterable]
-7 | for x in Bad():
-  |          ^^^^^ Object of type `Bad` is not iterable because it has no `__iter__` method and its `__getitem__` attribute has type `None`, which is not callable
-8 |     reveal_type(x)  # revealed: Unknown
-  |
-
-```
-
-```
-info: revealed-type
- --> /src/mdtest_snippet.py:8:5
-  |
-6 | # error: [not-iterable]
-7 | for x in Bad():
-8 |     reveal_type(x)  # revealed: Unknown
-  |     -------------- info: Revealed type is `Unknown`
-  |
-
-```