Make symbol_by_id a salsa query

## Summary

This PR adds initial support for `type: ignore`. It doesn't do anything
fancy yet like:

* Detecting invalid type ignore comments
* Detecting type ignore comments that are part of another suppression
comment: `# fmt: skip # type: ignore`
* Suppressing specific lints `type: ignore [code]`
* Detecting unsused type ignore comments
* ...

The goal is to add this functionality in separate PRs.

## Test Plan

---------

Co-authored-by: Carl Meyer <carl@astral.sh>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

.github/actionlint.yaml

@@ -0,0 +1,9 @@
+# Configuration for the actionlint tool, which we run via pre-commit
+# to verify the correctness of the syntax in our GitHub Actions workflows.
+
+self-hosted-runner:
+  # Various runners we use that aren't recognized out-of-the-box by actionlint:
+  labels:
+    - depot-ubuntu-latest-8
+    - depot-ubuntu-22.04-16
+    - windows-latest-xlarge

.github/workflows/build-binaries.yml

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

.github/workflows/build-docker.yml

@@ -72,7 +72,7 @@ jobs:
       - name: Normalize Platform Pair (replace / with -)
         run: |
           platform=${{ matrix.platform }}
-          echo "PLATFORM_TUPLE=${platform//\//-}" >> $GITHUB_ENV
+          echo "PLATFORM_TUPLE=${platform//\//-}" >> "$GITHUB_ENV"
 
       # Adapted from https://docs.docker.com/build/ci/github-actions/multi-platform/
       - name: Build and push by digest
@@ -87,9 +87,10 @@ jobs:
           outputs: type=image,name=${{ env.RUFF_BASE_IMG }},push-by-digest=true,name-canonical=true,push=${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
 
       - name: Export digests
+        env:
+          digest: ${{ steps.build.outputs.digest }}
         run: |
           mkdir -p /tmp/digests
-          digest="${{ steps.build.outputs.digest }}"
           touch "/tmp/digests/${digest#sha256:}"
 
       - name: Upload digests
@@ -141,9 +142,10 @@ jobs:
         # The printf will expand the base image with the `<RUFF_BASE_IMG>@sha256:<sha256> ...` for each sha256 in the directory
         # The final command becomes `docker buildx imagetools create -t tag1 -t tag2 ... <RUFF_BASE_IMG>@sha256:<sha256_1> <RUFF_BASE_IMG>@sha256:<sha256_2> ...`
         run: |
+          # shellcheck disable=SC2046
           docker buildx imagetools create \
             $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
-            $(printf '${{ env.RUFF_BASE_IMG }}@sha256:%s ' *)
+            $(printf "${RUFF_BASE_IMG}@sha256:%s " *)
 
   docker-publish-extra:
     name: Publish additional Docker image based on ${{ matrix.image-mapping }}
@@ -182,7 +184,7 @@ jobs:
           # Generate Dockerfile content
           cat <<EOF > Dockerfile
           FROM ${BASE_IMAGE}
-          COPY --from=${{ env.RUFF_BASE_IMG }}:latest /ruff /usr/local/bin/ruff
+          COPY --from=${RUFF_BASE_IMG}:latest /ruff /usr/local/bin/ruff
           ENTRYPOINT []
           CMD ["/usr/local/bin/ruff"]
           EOF
@@ -202,14 +204,14 @@ jobs:
           TAG_PATTERNS="${TAG_PATTERNS%\\n}"
 
           # Export image cache name
-          echo "IMAGE_REF=${BASE_IMAGE//:/-}" >> $GITHUB_ENV
+          echo "IMAGE_REF=${BASE_IMAGE//:/-}" >> "$GITHUB_ENV"
 
           # Export tag patterns using the multiline env var syntax
           {
             echo "TAG_PATTERNS<<EOF"
             echo -e "${TAG_PATTERNS}"
             echo EOF
-          } >> $GITHUB_ENV
+          } >> "$GITHUB_ENV"
 
       - name: Extract metadata (tags, labels) for Docker
         id: meta
@@ -285,7 +287,9 @@ jobs:
         # The final command becomes `docker buildx imagetools create -t tag1 -t tag2 ... <RUFF_BASE_IMG>@sha256:<sha256_1> <RUFF_BASE_IMG>@sha256:<sha256_2> ...`
         run: |
           readarray -t lines <<< "$DOCKER_METADATA_OUTPUT_ANNOTATIONS"; annotations=(); for line in "${lines[@]}"; do annotations+=(--annotation "$line"); done
+
+          # shellcheck disable=SC2046
           docker buildx imagetools create \
             "${annotations[@]}" \
             $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
-            $(printf '${{ env.RUFF_BASE_IMG }}@sha256:%s ' *)
+            $(printf "${RUFF_BASE_IMG}@sha256:%s " *)

.github/workflows/ci.yaml

@@ -290,7 +290,9 @@ jobs:
           file: "Cargo.toml"
           field: "workspace.package.rust-version"
       - name: "Install Rust toolchain"
-        run: rustup default ${{ steps.msrv.outputs.value }}
+        env:
+          MSRV: ${{ steps.msrv.outputs.value }}
+        run: rustup default "${MSRV}"
       - name: "Install mold"
         uses: rui314/setup-mold@v1
       - name: "Install cargo nextest"
@@ -306,13 +308,14 @@ jobs:
         shell: bash
         env:
           NEXTEST_PROFILE: "ci"
-        run: cargo +${{ steps.msrv.outputs.value }} insta test --all-features --unreferenced reject --test-runner nextest
+          MSRV: ${{ steps.msrv.outputs.value }}
+        run: cargo "+${MSRV}" insta test --all-features --unreferenced reject --test-runner nextest
 
   cargo-fuzz-build:
     name: "cargo fuzz build"
     runs-on: ubuntu-latest
     needs: determine_changes
-    if: ${{ github.ref == 'refs/heads/main' || needs.determine_changes.outputs.fuzz == 'true' }}
+    if: ${{ github.ref == 'refs/heads/main' || needs.determine_changes.outputs.fuzz == 'true' || needs.determine_changes.outputs.code == 'true' }}
     timeout-minutes: 10
     steps:
       - uses: actions/checkout@v4
@@ -354,16 +357,18 @@ jobs:
           name: ruff
           path: ruff-to-test
       - name: Fuzz
+        env:
+          DOWNLOAD_PATH: ${{ steps.download-cached-binary.outputs.download-path }}
         run: |
           # Make executable, since artifact download doesn't preserve this
-          chmod +x ${{ steps.download-cached-binary.outputs.download-path }}/ruff
+          chmod +x "${DOWNLOAD_PATH}/ruff"
 
           (
             uvx \
-            --python=${{ env.PYTHON_VERSION }} \
+            --python="${PYTHON_VERSION}" \
             --from=./python/py-fuzzer \
             fuzz \
-            --test-executable=${{ steps.download-cached-binary.outputs.download-path }}/ruff \
+            --test-executable="${DOWNLOAD_PATH}/ruff" \
             --bin=ruff \
             0-500
           )
@@ -429,64 +434,72 @@ jobs:
 
       - name: Run `ruff check` stable ecosystem check
         if: ${{ needs.determine_changes.outputs.linter == 'true' }}
+        env:
+          DOWNLOAD_PATH: ${{ steps.ruff-target.outputs.download-path }}
         run: |
           # Make executable, since artifact download doesn't preserve this
-          chmod +x ./ruff ${{ steps.ruff-target.outputs.download-path }}/ruff
+          chmod +x ./ruff "${DOWNLOAD_PATH}/ruff"
 
           # Set pipefail to avoid hiding errors with tee
           set -eo pipefail
 
-          ruff-ecosystem check ./ruff ${{ steps.ruff-target.outputs.download-path }}/ruff --cache ./checkouts --output-format markdown | tee ecosystem-result-check-stable
+          ruff-ecosystem check ./ruff "${DOWNLOAD_PATH}/ruff" --cache ./checkouts --output-format markdown | tee ecosystem-result-check-stable
 
-          cat ecosystem-result-check-stable > $GITHUB_STEP_SUMMARY
+          cat ecosystem-result-check-stable > "$GITHUB_STEP_SUMMARY"
           echo "### Linter (stable)"  > ecosystem-result
           cat ecosystem-result-check-stable >> ecosystem-result
           echo "" >> ecosystem-result
 
       - name: Run `ruff check` preview ecosystem check
         if: ${{ needs.determine_changes.outputs.linter == 'true' }}
+        env:
+          DOWNLOAD_PATH: ${{ steps.ruff-target.outputs.download-path }}
         run: |
           # Make executable, since artifact download doesn't preserve this
-          chmod +x ./ruff ${{ steps.ruff-target.outputs.download-path }}/ruff
+          chmod +x ./ruff "${DOWNLOAD_PATH}/ruff"
 
           # Set pipefail to avoid hiding errors with tee
           set -eo pipefail
 
-          ruff-ecosystem check ./ruff ${{ steps.ruff-target.outputs.download-path }}/ruff --cache ./checkouts --output-format markdown --force-preview | tee ecosystem-result-check-preview
+          ruff-ecosystem check ./ruff "${DOWNLOAD_PATH}/ruff" --cache ./checkouts --output-format markdown --force-preview | tee ecosystem-result-check-preview
 
-          cat ecosystem-result-check-preview > $GITHUB_STEP_SUMMARY
+          cat ecosystem-result-check-preview > "$GITHUB_STEP_SUMMARY"
           echo "### Linter (preview)" >> ecosystem-result
           cat ecosystem-result-check-preview >> ecosystem-result
           echo "" >> ecosystem-result
 
       - name: Run `ruff format` stable ecosystem check
         if: ${{ needs.determine_changes.outputs.formatter == 'true' }}
+        env:
+          DOWNLOAD_PATH: ${{ steps.ruff-target.outputs.download-path }}
         run: |
           # Make executable, since artifact download doesn't preserve this
-          chmod +x ./ruff ${{ steps.ruff-target.outputs.download-path }}/ruff
+          chmod +x ./ruff "${DOWNLOAD_PATH}/ruff"
 
           # Set pipefail to avoid hiding errors with tee
           set -eo pipefail
 
-          ruff-ecosystem format ./ruff ${{ steps.ruff-target.outputs.download-path }}/ruff --cache ./checkouts --output-format markdown | tee ecosystem-result-format-stable
+          ruff-ecosystem format ./ruff "${DOWNLOAD_PATH}/ruff" --cache ./checkouts --output-format markdown | tee ecosystem-result-format-stable
 
-          cat ecosystem-result-format-stable > $GITHUB_STEP_SUMMARY
+          cat ecosystem-result-format-stable > "$GITHUB_STEP_SUMMARY"
           echo "### Formatter (stable)" >> ecosystem-result
           cat ecosystem-result-format-stable >> ecosystem-result
           echo "" >> ecosystem-result
 
       - name: Run `ruff format` preview ecosystem check
         if: ${{ needs.determine_changes.outputs.formatter == 'true' }}
+        env:
+          DOWNLOAD_PATH: ${{ steps.ruff-target.outputs.download-path }}
         run: |
           # Make executable, since artifact download doesn't preserve this
-          chmod +x ./ruff ${{ steps.ruff-target.outputs.download-path }}/ruff
+          chmod +x ./ruff "${DOWNLOAD_PATH}/ruff"
 
           # Set pipefail to avoid hiding errors with tee
           set -eo pipefail
 
-          ruff-ecosystem format ./ruff ${{ steps.ruff-target.outputs.download-path }}/ruff --cache ./checkouts --output-format markdown --force-preview | tee ecosystem-result-format-preview
+          ruff-ecosystem format ./ruff "${DOWNLOAD_PATH}/ruff" --cache ./checkouts --output-format markdown --force-preview | tee ecosystem-result-format-preview
 
-          cat ecosystem-result-format-preview > $GITHUB_STEP_SUMMARY
+          cat ecosystem-result-format-preview > "$GITHUB_STEP_SUMMARY"
           echo "### Formatter (preview)" >> ecosystem-result
           cat ecosystem-result-format-preview >> ecosystem-result
           echo "" >> ecosystem-result
@@ -541,7 +554,7 @@ jobs:
           args: --out dist
       - name: "Test wheel"
         run: |
-          pip install --force-reinstall --find-links dist ${{ env.PACKAGE_NAME }}
+          pip install --force-reinstall --find-links dist "${PACKAGE_NAME}"
           ruff --help
           python -m ruff --help
       - name: "Remove wheels from cache"
@@ -570,13 +583,14 @@ jobs:
           key: pre-commit-${{ hashFiles('.pre-commit-config.yaml') }}
       - name: "Run pre-commit"
         run: |
-          echo '```console' > $GITHUB_STEP_SUMMARY
+          echo '```console' > "$GITHUB_STEP_SUMMARY"
           # Enable color output for pre-commit and remove it for the summary
-          SKIP=cargo-fmt,clippy,dev-generate-all pre-commit run --all-files --show-diff-on-failure --color=always | \
-            tee >(sed -E 's/\x1B\[([0-9]{1,2}(;[0-9]{1,2})*)?[mGK]//g' >> $GITHUB_STEP_SUMMARY) >&1
-          exit_code=${PIPESTATUS[0]}
-          echo '```' >> $GITHUB_STEP_SUMMARY
-          exit $exit_code
+          # Use --hook-stage=manual to enable slower pre-commit hooks that are skipped by default
+          SKIP=cargo-fmt,clippy,dev-generate-all pre-commit run --all-files --show-diff-on-failure --color=always --hook-stage=manual | \
+            tee >(sed -E 's/\x1B\[([0-9]{1,2}(;[0-9]{1,2})*)?[mGK]//g' >> "$GITHUB_STEP_SUMMARY") >&1
+          exit_code="${PIPESTATUS[0]}"
+          echo '```' >> "$GITHUB_STEP_SUMMARY"
+          exit "$exit_code"
 
   docs:
     name: "mkdocs"
@@ -637,7 +651,7 @@ jobs:
       - name: "Run checks"
         run: scripts/formatter_ecosystem_checks.sh
       - name: "Github step summary"
-        run: cat target/formatter-ecosystem/stats.txt > $GITHUB_STEP_SUMMARY
+        run: cat target/formatter-ecosystem/stats.txt > "$GITHUB_STEP_SUMMARY"
       - name: "Remove checkouts from cache"
         run: rm -r target/formatter-ecosystem
 
@@ -676,11 +690,13 @@ jobs:
           just install
 
       - name: Run ruff-lsp tests
+        env:
+          DOWNLOAD_PATH: ${{ steps.ruff-target.outputs.download-path }}
         run: |
           # Setup development binary
           pip uninstall --yes ruff
-          chmod +x ${{ steps.ruff-target.outputs.download-path }}/ruff
-          export PATH=${{ steps.ruff-target.outputs.download-path }}:$PATH
+          chmod +x "${DOWNLOAD_PATH}/ruff"
+          export PATH="${DOWNLOAD_PATH}:${PATH}"
           ruff version
 
           just test

.github/workflows/daily_fuzz.yaml

@@ -46,6 +46,7 @@ jobs:
         run: cargo build --locked
       - name: Fuzz
         run: |
+          # shellcheck disable=SC2046
           (
             uvx \
             --python=3.12 \

.github/workflows/pr-comment.yaml

@@ -10,12 +10,11 @@ on:
         description: The ecosystem workflow that triggers the workflow run
         required: true
 
-permissions:
-  pull-requests: write
-
 jobs:
   comment:
     runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
     steps:
       - uses: dawidd6/action-download-artifact@v7
         name: Download pull request number
@@ -30,7 +29,7 @@ jobs:
         run: |
           if [[ -f pr-number ]]
           then
-            echo "pr-number=$(<pr-number)" >> $GITHUB_OUTPUT
+            echo "pr-number=$(<pr-number)" >> "$GITHUB_OUTPUT"
           fi
 
       - uses: dawidd6/action-download-artifact@v7
@@ -66,9 +65,9 @@ jobs:
           cat pr/ecosystem/ecosystem-result >> comment.txt
           echo "" >> comment.txt
 
-          echo 'comment<<EOF' >> $GITHUB_OUTPUT
-          cat comment.txt >> $GITHUB_OUTPUT
-          echo 'EOF' >> $GITHUB_OUTPUT
+          echo 'comment<<EOF' >> "$GITHUB_OUTPUT"
+          cat comment.txt >> "$GITHUB_OUTPUT"
+          echo 'EOF' >> "$GITHUB_OUTPUT"
 
       - name: Find existing comment
         uses: peter-evans/find-comment@v3

.github/workflows/publish-docs.yml

@@ -44,21 +44,19 @@ jobs:
           # Use version as display name for now
           display_name="$version"
 
-          echo "version=$version" >> $GITHUB_ENV
-          echo "display_name=$display_name" >> $GITHUB_ENV
+          echo "version=$version" >> "$GITHUB_ENV"
+          echo "display_name=$display_name" >> "$GITHUB_ENV"
 
       - name: "Set branch name"
         run: |
-          version="${{ env.version }}"
-          display_name="${{ env.display_name }}"
           timestamp="$(date +%s)"
 
           # create branch_display_name from display_name by replacing all
           # characters disallowed in git branch names with hyphens
-          branch_display_name="$(echo "$display_name" | tr -c '[:alnum:]._' '-' | tr -s '-')"
+          branch_display_name="$(echo "${display_name}" | tr -c '[:alnum:]._' '-' | tr -s '-')"
 
-          echo "branch_name=update-docs-$branch_display_name-$timestamp" >> $GITHUB_ENV
-          echo "timestamp=$timestamp" >> $GITHUB_ENV
+          echo "branch_name=update-docs-$branch_display_name-$timestamp" >> "$GITHUB_ENV"
+          echo "timestamp=$timestamp" >> "$GITHUB_ENV"
 
       - name: "Add SSH key"
         if: ${{ env.MKDOCS_INSIDERS_SSH_KEY_EXISTS == 'true' }}
@@ -93,9 +91,7 @@ jobs:
         run: mkdocs build --strict -f mkdocs.public.yml
 
       - name: "Clone docs repo"
-        run: |
-          version="${{ env.version }}"
-          git clone https://${{ secrets.ASTRAL_DOCS_PAT }}@github.com/astral-sh/docs.git astral-docs
+        run: git clone https://${{ secrets.ASTRAL_DOCS_PAT }}@github.com/astral-sh/docs.git astral-docs
 
       - name: "Copy docs"
         run: rm -rf astral-docs/site/ruff && mkdir -p astral-docs/site && cp -r site/ruff astral-docs/site/
@@ -103,12 +99,10 @@ jobs:
       - name: "Commit docs"
         working-directory: astral-docs
         run: |
-          branch_name="${{ env.branch_name }}"
-
           git config user.name "astral-docs-bot"
           git config user.email "176161322+astral-docs-bot@users.noreply.github.com"
 
-          git checkout -b $branch_name
+          git checkout -b "${branch_name}"
           git add site/ruff
           git commit -m "Update ruff documentation for $version"
 
@@ -117,12 +111,8 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.ASTRAL_DOCS_PAT }}
         run: |
-          version="${{ env.version }}"
-          display_name="${{ env.display_name }}"
-          branch_name="${{ env.branch_name }}"
-
           # set the PR title
-          pull_request_title="Update ruff documentation for $display_name"
+          pull_request_title="Update ruff documentation for ${display_name}"
 
           # Delete any existing pull requests that are open for this version
           # by checking against pull_request_title because the new PR will
@@ -131,13 +121,15 @@ jobs:
             xargs -I {} gh pr close {}
 
           # push the branch to GitHub
-          git push origin $branch_name
+          git push origin "${branch_name}"
 
           # create the PR
-          gh pr create --base main --head $branch_name \
-            --title "$pull_request_title" \
-            --body "Automated documentation update for $display_name" \
-            --label "documentation"
+          gh pr create \
+            --base=main \
+            --head="${branch_name}" \
+            --title="${pull_request_title}" \
+            --body="Automated documentation update for ${display_name}" \
+            --label="documentation"
 
       - name: "Merge Pull Request"
         if: ${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
@@ -145,9 +137,7 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.ASTRAL_DOCS_PAT }}
         run: |
-          branch_name="${{ env.branch_name }}"
-
           # auto-merge the PR if the build was triggered by a release. Manual builds should be reviewed by a human.
           # give the PR a few seconds to be created before trying to auto-merge it
           sleep 10
-          gh pr merge --squash $branch_name
+          gh pr merge --squash "${branch_name}"

.github/workflows/sync_typeshed.yaml

@@ -31,7 +31,7 @@ jobs:
         with:
           repository: python/typeshed
           path: typeshed
-          persist-credentials: true
+          persist-credentials: false
       - name: Setup git
         run: |
           git config --global user.name typeshedbot
@@ -59,7 +59,7 @@ jobs:
         run: |
           cd ruff
           git push --force origin typeshedbot/sync-typeshed
-          gh pr list --repo $GITHUB_REPOSITORY --head typeshedbot/sync-typeshed --json id --jq length | grep 1 && exit 0 # exit if there is existing pr
+          gh pr list --repo "$GITHUB_REPOSITORY" --head typeshedbot/sync-typeshed --json id --jq length | grep 1 && exit 0 # exit if there is existing pr
           gh pr create --title "Sync vendored typeshed stubs" --body "Close and reopen this PR to trigger CI" --label "internal"
 
   create-issue-on-failure:

.github/zizmor.yml

@@ -0,0 +1,6 @@
+# Configuration for the zizmor static analysis tool, run via pre-commit in CI
+# https://woodruffw.github.io/zizmor/configuration/
+rules:
+  dangerous-triggers:
+    ignore:
+      - pr-comment.yaml

.markdownlint.yaml

@@ -21,3 +21,11 @@ MD014: false
 MD024:
   # Allow when nested under different parents e.g. CHANGELOG.md
   siblings_only: true
+
+# MD046/code-block-style
+#
+# Ignore this because it conflicts with the code block style used in content
+# tabs of mkdocs-material which is to add a blank line after the content title.
+#
+# Ref: https://github.com/astral-sh/ruff/pull/15011#issuecomment-2544790854
+MD046: false

.pre-commit-config.yaml

@@ -2,6 +2,7 @@ fail_fast: false
 
 exclude: |
   (?x)^(
+    .github/workflows/release.yml|
     crates/red_knot_vendored/vendor/.*|
     crates/red_knot_workspace/resources/.*|
     crates/ruff_linter/resources/.*|
@@ -26,9 +27,8 @@ repos:
     hooks:
       - id: mdformat
         additional_dependencies:
-          - mdformat-mkdocs
-          - mdformat-admon
-          - mdformat-footnote
+          - mdformat-mkdocs==4.0.0
+          - mdformat-footnote==0.1.1
         exclude: |
           (?x)^(
             docs/formatter/black\.md
@@ -59,7 +59,7 @@ repos:
           - black==24.10.0
 
   - repo: https://github.com/crate-ci/typos
-    rev: v1.28.2
+    rev: v1.28.3
     hooks:
       - id: typos
 
@@ -73,7 +73,7 @@ repos:
         pass_filenames: false # This makes it a lot faster
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.8.2
+    rev: v0.8.3
     hooks:
       - id: ruff-format
       - id: ruff
@@ -88,20 +88,37 @@ repos:
       - id: prettier
         types: [yaml]
 
+  # zizmor detects security vulnerabilities in GitHub Actions workflows.
+  # Additional configuration for the tool is found in `.github/zizmor.yml`
   - repo: https://github.com/woodruffw/zizmor-pre-commit
-    rev: v0.8.0
+    rev: v0.9.2
     hooks:
       - id: zizmor
-        # `release.yml` is autogenerated by `dist`; security issues need to be fixed there
-        # (https://opensource.axo.dev/cargo-dist/)
-        exclude: .github/workflows/release.yml
-        # We could consider enabling the low-severity warnings, but they're noisy
-        args: [--min-severity=medium]
 
   - repo: https://github.com/python-jsonschema/check-jsonschema
     rev: 0.30.0
     hooks:
       - id: check-github-workflows
 
+  # `actionlint` hook, for verifying correct syntax in GitHub Actions workflows.
+  # Some additional configuration for `actionlint` can be found in `.github/actionlint.yaml`.
+  - repo: https://github.com/rhysd/actionlint
+    rev: v1.7.4
+    hooks:
+      - id: actionlint
+        stages:
+          # This hook is disabled by default, since it's quite slow.
+          # To run all hooks *including* this hook, use `uvx pre-commit run -a --hook-stage=manual`.
+          # To run *just* this hook, use `uvx pre-commit run -a actionlint --hook-stage=manual`.
+          - manual
+        args:
+          - "-ignore=SC2129" # ignorable stylistic lint from shellcheck
+          - "-ignore=SC2016" # another shellcheck lint: seems to have false positives?
+        additional_dependencies:
+          # actionlint has a shellcheck integration which extracts shell scripts in `run:` steps from GitHub Actions
+          # and checks these with shellcheck. This is arguably its most useful feature,
+          # but the integration only works if shellcheck is installed
+          - "github.com/wasilibs/go-shellcheck/cmd/shellcheck@v0.10.0"
+
 ci:
   skip: [cargo-fmt, dev-generate-all]

CHANGELOG.md

@@ -1,5 +1,68 @@
 # Changelog
 
+## 0.8.4
+
+### Preview features
+
+- \[`airflow`\] Extend `AIR302` with additional functions and classes ([#15015](https://github.com/astral-sh/ruff/pull/15015))
+- \[`airflow`\] Implement `moved-to-provider-in-3` for modules that has been moved to Airflow providers (`AIR303`) ([#14764](https://github.com/astral-sh/ruff/pull/14764))
+- \[`flake8-use-pathlib`\] Extend check for invalid path suffix to include the case `"."` (`PTH210`) ([#14902](https://github.com/astral-sh/ruff/pull/14902))
+- \[`perflint`\] Fix panic in `PERF401` when list variable is after the `for` loop ([#14971](https://github.com/astral-sh/ruff/pull/14971))
+- \[`perflint`\] Simplify finding the loop target in `PERF401` ([#15025](https://github.com/astral-sh/ruff/pull/15025))
+- \[`pylint`\] Preserve original value format (`PLR6104`) ([#14978](https://github.com/astral-sh/ruff/pull/14978))
+- \[`ruff`\] Avoid false positives for `RUF027` for typing context bindings ([#15037](https://github.com/astral-sh/ruff/pull/15037))
+- \[`ruff`\] Check for ambiguous pattern passed to `pytest.raises()` (`RUF043`) ([#14966](https://github.com/astral-sh/ruff/pull/14966))
+
+### Rule changes
+
+- \[`flake8-bandit`\] Check `S105` for annotated assignment ([#15059](https://github.com/astral-sh/ruff/pull/15059))
+- \[`flake8-pyi`\] More autofixes for `redundant-none-literal` (`PYI061`) ([#14872](https://github.com/astral-sh/ruff/pull/14872))
+- \[`pydocstyle`\] Skip leading whitespace for `D403` ([#14963](https://github.com/astral-sh/ruff/pull/14963))
+- \[`ruff`\] Skip `SQLModel` base classes for `mutable-class-default` (`RUF012`) ([#14949](https://github.com/astral-sh/ruff/pull/14949))
+
+### Bug
+
+- \[`perflint`\] Parenthesize walrus expressions in autofix for `manual-list-comprehension` (`PERF401`) ([#15050](https://github.com/astral-sh/ruff/pull/15050))
+
+### Server
+
+- Check diagnostic refresh support from client capability which enables dynamic configuration for various editors ([#15014](https://github.com/astral-sh/ruff/pull/15014))
+
+## 0.8.3
+
+### Preview features
+
+- Fix fstring formatting removing overlong implicit concatenated string in expression part ([#14811](https://github.com/astral-sh/ruff/pull/14811))
+- \[`airflow`\] Add fix to remove deprecated keyword arguments (`AIR302`) ([#14887](https://github.com/astral-sh/ruff/pull/14887))
+- \[`airflow`\]: Extend rule to include deprecated names for Airflow 3.0 (`AIR302`) ([#14765](https://github.com/astral-sh/ruff/pull/14765) and [#14804](https://github.com/astral-sh/ruff/pull/14804))
+- \[`flake8-bugbear`\] Improve error messages for `except*` (`B025`, `B029`, `B030`, `B904`) ([#14815](https://github.com/astral-sh/ruff/pull/14815))
+- \[`flake8-bugbear`\] `itertools.batched()` without explicit `strict` (`B911`) ([#14408](https://github.com/astral-sh/ruff/pull/14408))
+- \[`flake8-use-pathlib`\] Dotless suffix passed to `Path.with_suffix()` (`PTH210`) ([#14779](https://github.com/astral-sh/ruff/pull/14779))
+- \[`pylint`\] Include parentheses and multiple comparators in check for `boolean-chained-comparison` (`PLR1716`) ([#14781](https://github.com/astral-sh/ruff/pull/14781))
+- \[`ruff`\] Do not simplify `round()` calls (`RUF046`) ([#14832](https://github.com/astral-sh/ruff/pull/14832))
+- \[`ruff`\] Don't emit `used-dummy-variable` on function parameters (`RUF052`) ([#14818](https://github.com/astral-sh/ruff/pull/14818))
+- \[`ruff`\] Implement `if-key-in-dict-del` (`RUF051`) ([#14553](https://github.com/astral-sh/ruff/pull/14553))
+- \[`ruff`\] Mark autofix for `RUF052` as always unsafe ([#14824](https://github.com/astral-sh/ruff/pull/14824))
+- \[`ruff`\] Teach autofix for `used-dummy-variable` about TypeVars etc. (`RUF052`) ([#14819](https://github.com/astral-sh/ruff/pull/14819))
+
+### Rule changes
+
+- \[`flake8-bugbear`\] Offer unsafe autofix for `no-explicit-stacklevel` (`B028`) ([#14829](https://github.com/astral-sh/ruff/pull/14829))
+- \[`flake8-pyi`\] Skip all type definitions in `string-or-bytes-too-long` (`PYI053`) ([#14797](https://github.com/astral-sh/ruff/pull/14797))
+- \[`pyupgrade`\] Do not report when a UTF-8 comment is followed by a non-UTF-8 one (`UP009`) ([#14728](https://github.com/astral-sh/ruff/pull/14728))
+- \[`pyupgrade`\] Mark fixes for `convert-typed-dict-functional-to-class` and `convert-named-tuple-functional-to-class` as unsafe if they will remove comments (`UP013`, `UP014`) ([#14842](https://github.com/astral-sh/ruff/pull/14842))
+
+### Bug fixes
+
+- Raise syntax error for mixing `except` and `except*` ([#14895](https://github.com/astral-sh/ruff/pull/14895))
+- \[`flake8-bugbear`\] Fix `B028` to allow `stacklevel` to be explicitly assigned as a positional argument ([#14868](https://github.com/astral-sh/ruff/pull/14868))
+- \[`flake8-bugbear`\] Skip `B028` if `warnings.warn` is called with `*args` or `**kwargs` ([#14870](https://github.com/astral-sh/ruff/pull/14870))
+- \[`flake8-comprehensions`\] Skip iterables with named expressions in `unnecessary-map` (`C417`) ([#14827](https://github.com/astral-sh/ruff/pull/14827))
+- \[`flake8-pyi`\] Also remove `self` and `cls`'s annotation (`PYI034`) ([#14801](https://github.com/astral-sh/ruff/pull/14801))
+- \[`flake8-pytest-style`\] Fix `pytest-parametrize-names-wrong-type` (`PT006`) to edit both `argnames` and `argvalues` if both of them are single-element tuples/lists ([#14699](https://github.com/astral-sh/ruff/pull/14699))
+- \[`perflint`\] Improve autofix for `PERF401` ([#14369](https://github.com/astral-sh/ruff/pull/14369))
+- \[`pylint`\] Fix `PLW1508` false positive for default string created via a mult operation ([#14841](https://github.com/astral-sh/ruff/pull/14841))
+
 ## 0.8.2
 
 ### Preview features

Cargo.lock

@@ -220,9 +220,9 @@ checksum = "7f839cdf7e2d3198ac6ca003fd8ebc61715755f41c1cad15ff13df67531e00ed"
 
 [[package]]
 name = "bstr"
-version = "1.11.0"
+version = "1.11.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1a68f1f47cdf0ec8ee4b941b2eee2a80cb796db73118c0dd09ac63fbe405be22"
+checksum = "786a307d683a5bf92e6fd5fd69a7eb613751668d1d8d67d802846dfe367c62c8"
 dependencies = [
  "memchr",
  "regex-automata 0.4.8",
@@ -314,9 +314,9 @@ dependencies = [
 
 [[package]]
 name = "chrono"
-version = "0.4.38"
+version = "0.4.39"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a21f936df1771bf62b77f047b726c4625ff2e8aa607c01ec06e5a05bd8463401"
+checksum = "7e36cc9d416881d2e24f9a963be5fb1cd90966419ac844274161d10488b3e825"
 dependencies = [
  "android-tzdata",
  "iana-time-zone",
@@ -465,12 +465,12 @@ checksum = "acbf1af155f9b9ef647e42cdc158db4b64a1b61f743629225fde6f3e0be2a7c7"
 
 [[package]]
 name = "colored"
-version = "2.1.0"
+version = "2.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cbf2150cce219b664a8a70df7a1f933836724b503f8a413af9365b4dcc4d90b8"
+checksum = "117725a109d387c937a1533ce01b450cbde6b88abceea8473c4d7a85853cda3c"
 dependencies = [
  "lazy_static",
- "windows-sys 0.48.0",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -923,9 +923,9 @@ checksum = "e8c02a5121d4ea3eb16a80748c74f5549a5665e4c21333c6098f283870fbdea6"
 
 [[package]]
 name = "fern"
-version = "0.7.0"
+version = "0.7.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "69ff9c9d5fb3e6da8ac2f77ab76fe7e8087d512ce095200f8f29ac5b656cf6dc"
+checksum = "4316185f709b23713e41e3195f90edef7fb00c3ed4adc79769cf09cc762a3b29"
 dependencies = [
  "log",
 ]
@@ -1521,9 +1521,9 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.167"
+version = "0.2.168"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "09d6582e104315a817dff97f75133544b2e094ee22447d2acf4a74e189ba06fc"
+checksum = "5aaeb2981e0606ca11d79718f8bb01164f1d6ed75080182d3abf017e6d244b6d"
 
 [[package]]
 name = "libcst"
@@ -2161,7 +2161,7 @@ dependencies = [
  "newtype-uuid",
  "quick-xml",
  "strip-ansi-escapes",
- "thiserror 2.0.6",
+ "thiserror 2.0.7",
  "uuid",
 ]
 
@@ -2288,6 +2288,7 @@ dependencies = [
  "compact_str",
  "countme",
  "dir-test",
+ "drop_bomb",
  "hashbrown 0.15.2",
  "indexmap",
  "insta",
@@ -2300,6 +2301,7 @@ dependencies = [
  "red_knot_vendored",
  "ruff_db",
  "ruff_index",
+ "ruff_macros",
  "ruff_python_ast",
  "ruff_python_literal",
  "ruff_python_parser",
@@ -2313,7 +2315,7 @@ dependencies = [
  "static_assertions",
  "tempfile",
  "test-case",
- "thiserror 2.0.6",
+ "thiserror 2.0.7",
  "tracing",
 ]
 
@@ -2410,7 +2412,7 @@ dependencies = [
  "rustc-hash 2.1.0",
  "salsa",
  "serde",
- "thiserror 2.0.6",
+ "thiserror 2.0.7",
  "toml",
  "tracing",
 ]
@@ -2516,7 +2518,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.8.2"
+version = "0.8.4"
 dependencies = [
  "anyhow",
  "argfile",
@@ -2563,7 +2565,7 @@ dependencies = [
  "strum",
  "tempfile",
  "test-case",
- "thiserror 2.0.6",
+ "thiserror 2.0.7",
  "tikv-jemallocator",
  "toml",
  "tracing",
@@ -2633,7 +2635,7 @@ dependencies = [
  "salsa",
  "serde",
  "tempfile",
- "thiserror 2.0.6",
+ "thiserror 2.0.7",
  "tracing",
  "tracing-subscriber",
  "tracing-tree",
@@ -2735,7 +2737,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_linter"
-version = "0.8.2"
+version = "0.8.4"
 dependencies = [
  "aho-corasick",
  "annotate-snippets 0.9.2",
@@ -2785,7 +2787,7 @@ dependencies = [
  "strum",
  "strum_macros",
  "test-case",
- "thiserror 2.0.6",
+ "thiserror 2.0.7",
  "toml",
  "typed-arena",
  "unicode-normalization",
@@ -2819,7 +2821,7 @@ dependencies = [
  "serde_json",
  "serde_with",
  "test-case",
- "thiserror 2.0.6",
+ "thiserror 2.0.7",
  "uuid",
 ]
 
@@ -2891,7 +2893,7 @@ dependencies = [
  "similar",
  "smallvec",
  "static_assertions",
- "thiserror 2.0.6",
+ "thiserror 2.0.7",
  "tracing",
 ]
 
@@ -3024,7 +3026,7 @@ dependencies = [
  "serde",
  "serde_json",
  "shellexpand",
- "thiserror 2.0.6",
+ "thiserror 2.0.7",
  "tracing",
  "tracing-subscriber",
 ]
@@ -3050,7 +3052,7 @@ dependencies = [
 
 [[package]]
 name = "ruff_wasm"
-version = "0.8.2"
+version = "0.8.4"
 dependencies = [
  "console_error_panic_hook",
  "console_log",
@@ -3192,7 +3194,7 @@ checksum = "e86697c916019a8588c99b5fac3cead74ec0b4b819707a682fd4d23fa0ce1ba1"
 [[package]]
 name = "salsa"
 version = "0.18.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=254c749b02cde2fd29852a7463a33e800b771758#254c749b02cde2fd29852a7463a33e800b771758"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=3c7f1694c9efba751dbeeacfbc93b227586e316a#3c7f1694c9efba751dbeeacfbc93b227586e316a"
 dependencies = [
  "append-only-vec",
  "arc-swap",
@@ -3202,6 +3204,7 @@ dependencies = [
  "indexmap",
  "lazy_static",
  "parking_lot",
+ "rayon",
  "rustc-hash 2.1.0",
  "salsa-macro-rules",
  "salsa-macros",
@@ -3212,12 +3215,12 @@ dependencies = [
 [[package]]
 name = "salsa-macro-rules"
 version = "0.1.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=254c749b02cde2fd29852a7463a33e800b771758#254c749b02cde2fd29852a7463a33e800b771758"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=3c7f1694c9efba751dbeeacfbc93b227586e316a#3c7f1694c9efba751dbeeacfbc93b227586e316a"
 
 [[package]]
 name = "salsa-macros"
 version = "0.18.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=254c749b02cde2fd29852a7463a33e800b771758#254c749b02cde2fd29852a7463a33e800b771758"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=3c7f1694c9efba751dbeeacfbc93b227586e316a#3c7f1694c9efba751dbeeacfbc93b227586e316a"
 dependencies = [
  "heck",
  "proc-macro2",
@@ -3279,9 +3282,9 @@ checksum = "1c107b6f4780854c8b126e228ea8869f4d7b71260f962fefb57b996b8959ba6b"
 
 [[package]]
 name = "serde"
-version = "1.0.215"
+version = "1.0.216"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6513c1ad0b11a9376da888e3e0baa0077f1aed55c17f50e7b2397136129fb88f"
+checksum = "0b9781016e935a97e8beecf0c933758c97a5520d32930e460142b4cd80c6338e"
 dependencies = [
  "serde_derive",
 ]
@@ -3299,9 +3302,9 @@ dependencies = [
 
 [[package]]
 name = "serde_derive"
-version = "1.0.215"
+version = "1.0.216"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ad1e866f866923f252f05c889987993144fb74e722403468a4ebd70c3cd756c0"
+checksum = "46f859dbbf73865c6627ed570e78961cd3ac92407a2d117204c49232485da55e"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -3622,11 +3625,11 @@ dependencies = [
 
 [[package]]
 name = "thiserror"
-version = "2.0.6"
+version = "2.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8fec2a1820ebd077e2b90c4df007bebf344cd394098a13c563957d0afc83ea47"
+checksum = "93605438cbd668185516ab499d589afb7ee1859ea3d5fc8f6b0755e1c7443767"
 dependencies = [
- "thiserror-impl 2.0.6",
+ "thiserror-impl 2.0.7",
 ]
 
 [[package]]
@@ -3642,9 +3645,9 @@ dependencies = [
 
 [[package]]
 name = "thiserror-impl"
-version = "2.0.6"
+version = "2.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d65750cab40f4ff1929fb1ba509e9914eb756131cef4210da8d5d700d26f6312"
+checksum = "e1d8749b4531af2117677a5fcd12b1348a3fe2b81e36e61ffeac5c4aa3273e36"
 dependencies = [
  "proc-macro2",
  "quote",

Cargo.toml

@@ -118,7 +118,8 @@ rand = { version = "0.8.5" }
 rayon = { version = "1.10.0" }
 regex = { version = "1.10.2" }
 rustc-hash = { version = "2.0.0" }
-salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "254c749b02cde2fd29852a7463a33e800b771758" }
+# When updating salsa, make sure to also update the revision in `fuzz/Cargo.toml`
+salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "3c7f1694c9efba751dbeeacfbc93b227586e316a" }
 schemars = { version = "0.8.16" }
 seahash = { version = "4.1.0" }
 serde = { version = "1.0.197", features = ["derive"] }

README.md

@@ -140,8 +140,8 @@ curl -LsSf https://astral.sh/ruff/install.sh | sh
 powershell -c "irm https://astral.sh/ruff/install.ps1 | iex"
 
 # For a specific version.
-curl -LsSf https://astral.sh/ruff/0.8.2/install.sh | sh
-powershell -c "irm https://astral.sh/ruff/0.8.2/install.ps1 | iex"
+curl -LsSf https://astral.sh/ruff/0.8.4/install.sh | sh
+powershell -c "irm https://astral.sh/ruff/0.8.4/install.ps1 | iex"
 ```
 
 You can also install Ruff via [Homebrew](https://formulae.brew.sh/formula/ruff), [Conda](https://anaconda.org/conda-forge/ruff),
@@ -174,7 +174,7 @@ Ruff can also be used as a [pre-commit](https://pre-commit.com/) hook via [`ruff
 ```yaml
 - repo: https://github.com/astral-sh/ruff-pre-commit
   # Ruff version.
-  rev: v0.8.2
+  rev: v0.8.4
   hooks:
     # Run the linter.
     - id: ruff

crates/red_knot/src/main.rs

@@ -5,6 +5,7 @@ use anyhow::{anyhow, Context};
 use clap::Parser;
 use colored::Colorize;
 use crossbeam::channel as crossbeam_channel;
+use python_version::PythonVersion;
 use red_knot_python_semantic::SitePackages;
 use red_knot_server::run_server;
 use red_knot_workspace::db::RootDatabase;
@@ -15,12 +16,11 @@ use red_knot_workspace::workspace::WorkspaceMetadata;
 use ruff_db::diagnostic::Diagnostic;
 use ruff_db::system::{OsSystem, System, SystemPath, SystemPathBuf};
 use salsa::plumbing::ZalsaDatabase;
-use target_version::TargetVersion;
 
 use crate::logging::{setup_tracing, Verbosity};
 
 mod logging;
-mod target_version;
+mod python_version;
 mod verbosity;
 
 #[derive(Debug, Parser)]
@@ -34,54 +34,39 @@ struct Args {
     #[command(subcommand)]
     pub(crate) command: Option<Command>,
 
-    #[arg(
-        long,
-        help = "Changes the current working directory.",
-        long_help = "Changes the current working directory before any specified operations. This affects the workspace and configuration discovery.",
-        value_name = "PATH"
-    )]
-    current_directory: Option<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,
+    /// as will the project's virtual environment (`.venv`) unless the `venv-path` option is set.
+    ///
+    /// Other command-line arguments (such as relative paths) will be resolved relative to the current working directory.
+    #[arg(long, value_name = "PROJECT")]
+    project: Option<SystemPathBuf>,
 
-    #[arg(
-        long,
-        help = "Path to the virtual environment the project uses",
-        long_help = "\
-Path to the virtual environment the project uses. \
-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.",
-        value_name = "PATH"
-    )]
+    /// Path to the virtual environment the project uses.
+    ///
+    /// 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")]
     venv_path: Option<SystemPathBuf>,
 
-    #[arg(
-        long,
-        value_name = "DIRECTORY",
-        help = "Custom directory to use for stdlib typeshed stubs"
-    )]
-    custom_typeshed_dir: Option<SystemPathBuf>,
+    /// Custom directory to use for stdlib typeshed stubs.
+    #[arg(long, value_name = "PATH", alias = "custom-typeshed-dir")]
+    typeshed: Option<SystemPathBuf>,
 
-    #[arg(
-        long,
-        value_name = "PATH",
-        help = "Additional path to use as a module-resolution source (can be passed multiple times)"
-    )]
+    /// Additional path to use as a module-resolution source (can be passed multiple times).
+    #[arg(long, value_name = "PATH")]
     extra_search_path: Option<Vec<SystemPathBuf>>,
 
-    #[arg(
-        long,
-        help = "Python version to assume when resolving types",
-        value_name = "VERSION"
-    )]
-    target_version: Option<TargetVersion>,
+    /// Python version to assume when resolving types.
+    #[arg(long, value_name = "VERSION", alias = "target-version")]
+    python_version: Option<PythonVersion>,
 
     #[clap(flatten)]
     verbosity: Verbosity,
 
-    #[arg(
-        long,
-        help = "Run in watch mode by re-running whenever files change",
-        short = 'W'
-    )]
+    /// Run in watch mode by re-running whenever files change.
+    #[arg(long, short = 'W')]
     watch: bool,
 }
 
@@ -89,8 +74,8 @@ impl Args {
     fn to_configuration(&self, cli_cwd: &SystemPath) -> Configuration {
         let mut configuration = Configuration::default();
 
-        if let Some(target_version) = self.target_version {
-            configuration.target_version = Some(target_version.into());
+        if let Some(python_version) = self.python_version {
+            configuration.python_version = Some(python_version.into());
         }
 
         if let Some(venv_path) = &self.venv_path {
@@ -99,9 +84,8 @@ impl Args {
             });
         }
 
-        if let Some(custom_typeshed_dir) = &self.custom_typeshed_dir {
-            configuration.search_paths.custom_typeshed =
-                Some(SystemPath::absolute(custom_typeshed_dir, cli_cwd));
+        if let Some(typeshed) = &self.typeshed {
+            configuration.search_paths.typeshed = Some(SystemPath::absolute(typeshed, cli_cwd));
         }
 
         if let Some(extra_search_paths) = &self.extra_search_path {
@@ -167,15 +151,13 @@ fn run() -> anyhow::Result<ExitStatus> {
     };
 
     let cwd = args
-        .current_directory
+        .project
         .as_ref()
         .map(|cwd| {
             if cwd.as_std_path().is_dir() {
                 Ok(SystemPath::absolute(cwd, &cli_base_path))
             } else {
-                Err(anyhow!(
-                    "Provided current-directory path `{cwd}` is not a directory"
-                ))
+                Err(anyhow!("Provided project path `{cwd}` is not a directory"))
             }
         })
         .transpose()?
@@ -297,7 +279,7 @@ impl MainLoop {
         while let Ok(message) = self.receiver.recv() {
             match message {
                 MainLoopMessage::CheckWorkspace => {
-                    let db = db.snapshot();
+                    let db = db.clone();
                     let sender = self.sender.clone();
 
                     // Spawn a new task that checks the workspace. This needs to be done in a separate thread

crates/red_knot/src/python_version.rs

@@ -0,0 +1,68 @@
+/// Enumeration of all supported Python versions
+///
+/// TODO: unify with the `PythonVersion` enum in the linter/formatter crates?
+#[derive(Copy, Clone, Hash, Debug, PartialEq, Eq, PartialOrd, Ord, Default, clap::ValueEnum)]
+pub enum PythonVersion {
+    #[value(name = "3.7")]
+    Py37,
+    #[value(name = "3.8")]
+    Py38,
+    #[default]
+    #[value(name = "3.9")]
+    Py39,
+    #[value(name = "3.10")]
+    Py310,
+    #[value(name = "3.11")]
+    Py311,
+    #[value(name = "3.12")]
+    Py312,
+    #[value(name = "3.13")]
+    Py313,
+}
+
+impl PythonVersion {
+    const fn as_str(self) -> &'static str {
+        match self {
+            Self::Py37 => "3.7",
+            Self::Py38 => "3.8",
+            Self::Py39 => "3.9",
+            Self::Py310 => "3.10",
+            Self::Py311 => "3.11",
+            Self::Py312 => "3.12",
+            Self::Py313 => "3.13",
+        }
+    }
+}
+
+impl std::fmt::Display for PythonVersion {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+impl From<PythonVersion> for red_knot_python_semantic::PythonVersion {
+    fn from(value: PythonVersion) -> Self {
+        match value {
+            PythonVersion::Py37 => Self::PY37,
+            PythonVersion::Py38 => Self::PY38,
+            PythonVersion::Py39 => Self::PY39,
+            PythonVersion::Py310 => Self::PY310,
+            PythonVersion::Py311 => Self::PY311,
+            PythonVersion::Py312 => Self::PY312,
+            PythonVersion::Py313 => Self::PY313,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::python_version::PythonVersion;
+
+    #[test]
+    fn same_default_as_python_version() {
+        assert_eq!(
+            red_knot_python_semantic::PythonVersion::from(PythonVersion::default()),
+            red_knot_python_semantic::PythonVersion::default()
+        );
+    }
+}

crates/red_knot/src/target_version.rs

@@ -1,62 +0,0 @@
-/// Enumeration of all supported Python versions
-///
-/// TODO: unify with the `PythonVersion` enum in the linter/formatter crates?
-#[derive(Copy, Clone, Hash, Debug, PartialEq, Eq, PartialOrd, Ord, Default, clap::ValueEnum)]
-pub enum TargetVersion {
-    Py37,
-    Py38,
-    #[default]
-    Py39,
-    Py310,
-    Py311,
-    Py312,
-    Py313,
-}
-
-impl TargetVersion {
-    const fn as_str(self) -> &'static str {
-        match self {
-            Self::Py37 => "py37",
-            Self::Py38 => "py38",
-            Self::Py39 => "py39",
-            Self::Py310 => "py310",
-            Self::Py311 => "py311",
-            Self::Py312 => "py312",
-            Self::Py313 => "py313",
-        }
-    }
-}
-
-impl std::fmt::Display for TargetVersion {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        f.write_str(self.as_str())
-    }
-}
-
-impl From<TargetVersion> for red_knot_python_semantic::PythonVersion {
-    fn from(value: TargetVersion) -> Self {
-        match value {
-            TargetVersion::Py37 => Self::PY37,
-            TargetVersion::Py38 => Self::PY38,
-            TargetVersion::Py39 => Self::PY39,
-            TargetVersion::Py310 => Self::PY310,
-            TargetVersion::Py311 => Self::PY311,
-            TargetVersion::Py312 => Self::PY312,
-            TargetVersion::Py313 => Self::PY313,
-        }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use crate::target_version::TargetVersion;
-    use red_knot_python_semantic::PythonVersion;
-
-    #[test]
-    fn same_default_as_python_version() {
-        assert_eq!(
-            PythonVersion::from(TargetVersion::default()),
-            PythonVersion::default()
-        );
-    }
-}

crates/red_knot/tests/file_watching.rs

@@ -282,7 +282,7 @@ where
         .extra_paths
         .iter()
         .flatten()
-        .chain(search_paths.custom_typeshed.iter())
+        .chain(search_paths.typeshed.iter())
         .chain(search_paths.site_packages.iter().flat_map(|site_packages| {
             if let SitePackages::Known(path) = site_packages {
                 path.as_slice()
@@ -296,7 +296,7 @@ where
     }
 
     let configuration = Configuration {
-        target_version: Some(PythonVersion::PY312),
+        python_version: Some(PythonVersion::PY312),
         search_paths,
     };
 
@@ -888,7 +888,7 @@ fn changed_versions_file() -> anyhow::Result<()> {
             Ok(())
         },
         |root_path, _workspace_path| SearchPathConfiguration {
-            custom_typeshed: Some(root_path.join("typeshed")),
+            typeshed: Some(root_path.join("typeshed")),
             ..SearchPathConfiguration::default()
         },
     )?;

crates/red_knot_python_semantic/Cargo.toml

@@ -13,6 +13,7 @@ license = { workspace = true }
 [dependencies]
 ruff_db = { workspace = true }
 ruff_index = { workspace = true }
+ruff_macros = { workspace = true }
 ruff_python_ast = { workspace = true }
 ruff_python_parser = { workspace = true }
 ruff_python_stdlib = { workspace = true }
@@ -25,6 +26,7 @@ bitflags = { workspace = true }
 camino = { workspace = true }
 compact_str = { workspace = true }
 countme = { workspace = true }
+drop_bomb = { workspace = true }
 indexmap = { workspace = true }
 itertools = { workspace = true }
 ordermap = { workspace = true }
@@ -52,5 +54,8 @@ tempfile = { workspace = true }
 quickcheck = { version = "1.0.3", default-features = false }
 quickcheck_macros = { version = "1.0.0" }
 
+[features]
+serde = ["ruff_db/serde", "dep:serde"]
+
 [lints]
 workspace = true

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

@@ -0,0 +1,94 @@
+# `Annotated`
+
+`Annotated` attaches arbitrary metadata to a given type.
+
+## Usages
+
+`Annotated[T, ...]` is equivalent to `T`: All metadata arguments are simply ignored.
+
+```py
+from typing_extensions import Annotated
+
+def _(x: Annotated[int, "foo"]):
+    reveal_type(x)  # revealed: int
+
+def _(x: Annotated[int, lambda: 0 + 1 * 2 // 3, _(4)]):
+    reveal_type(x)  # revealed: int
+
+def _(x: Annotated[int, "arbitrary", "metadata", "elements", "are", "fine"]):
+    reveal_type(x)  # revealed: int
+
+def _(x: Annotated[tuple[str, int], bytes]):
+    reveal_type(x)  # revealed: tuple[str, int]
+```
+
+## Parameterization
+
+It is invalid to parameterize `Annotated` with less than two arguments.
+
+```py
+from typing_extensions import Annotated
+
+# error: [invalid-type-form] "`Annotated` requires at least two arguments when used in an annotation or type expression"
+def _(x: Annotated):
+    reveal_type(x)  # revealed: Unknown
+
+def _(flag: bool):
+    if flag:
+        X = Annotated
+    else:
+        X = bool
+
+    # error: [invalid-type-form] "`Annotated` requires at least two arguments when used in an annotation or type expression"
+    def f(y: X):
+        reveal_type(y)  # revealed: Unknown | bool
+
+# error: [invalid-type-form] "`Annotated` requires at least two arguments when used in an annotation or type expression"
+def _(x: Annotated | bool):
+    reveal_type(x)  # revealed: Unknown | bool
+
+# error: [invalid-type-form]
+def _(x: Annotated[()]):
+    reveal_type(x)  # revealed: Unknown
+
+# error: [invalid-type-form]
+def _(x: Annotated[int]):
+    # `Annotated[T]` is invalid and will raise an error at runtime,
+    # but we treat it the same as `T` to provide better diagnostics later on.
+    # The subscription itself is still reported, regardless.
+    # Same for the `(int,)` form below.
+    reveal_type(x)  # revealed: int
+
+# error: [invalid-type-form]
+def _(x: Annotated[(int,)]):
+    reveal_type(x)  # revealed: int
+```
+
+## Inheritance
+
+### Correctly parameterized
+
+Inheriting from `Annotated[T, ...]` is equivalent to inheriting from `T` itself.
+
+```py
+from typing_extensions import Annotated
+
+# TODO: False positive
+# error: [invalid-base]
+class C(Annotated[int, "foo"]): ...
+
+# TODO: Should be `tuple[Literal[C], Literal[int], Literal[object]]`
+reveal_type(C.__mro__)  # revealed: tuple[Literal[C], Unknown, Literal[object]]
+```
+
+### Not parameterized
+
+```py
+from typing_extensions import Annotated
+
+# At runtime, this is an error.
+# error: [invalid-base]
+class C(Annotated): ...
+
+reveal_type(C.__mro__)  # revealed: tuple[Literal[C], Unknown, Literal[object]]
+```

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

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

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

@@ -45,19 +45,19 @@ def f():
     # TODO: This should be Color.RED
     reveal_type(b1)  # revealed: Literal[0]
 
-# error: [invalid-literal-parameter]
+# error: [invalid-type-form]
 invalid1: Literal[3 + 4]
-# error: [invalid-literal-parameter]
+# error: [invalid-type-form]
 invalid2: Literal[4 + 3j]
-# error: [invalid-literal-parameter]
+# error: [invalid-type-form]
 invalid3: Literal[(3, 4)]
 
 hello = "hello"
 invalid4: Literal[
-    1 + 2,  # error: [invalid-literal-parameter]
+    1 + 2,  # error: [invalid-type-form]
     "foo",
-    hello,  # error: [invalid-literal-parameter]
-    (1, 2, 3),  # error: [invalid-literal-parameter]
+    hello,  # error: [invalid-type-form]
+    (1, 2, 3),  # error: [invalid-type-form]
 ]
 ```
 
@@ -91,3 +91,13 @@ a1: Literal[26]
 def f():
     reveal_type(a1)  # revealed: Literal[26]
 ```
+
+## Invalid
+
+```py
+from typing import Literal
+
+# error: [invalid-type-form] "`Literal` requires at least one argument when used in a type expression"
+def _(x: Literal):
+    reveal_type(x)  # revealed: Unknown
+```

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

@@ -27,19 +27,19 @@ def f():
 ```py
 from typing_extensions import Literal, LiteralString
 
-bad_union: Literal["hello", LiteralString]  # error: [invalid-literal-parameter]
-bad_nesting: Literal[LiteralString]  # error: [invalid-literal-parameter]
+bad_union: Literal["hello", LiteralString]  # error: [invalid-type-form]
+bad_nesting: Literal[LiteralString]  # error: [invalid-type-form]
 ```
 
-### Parametrized
+### Parameterized
 
-`LiteralString` cannot be parametrized.
+`LiteralString` cannot be parameterized.
 
 ```py
 from typing_extensions import LiteralString
 
-a: LiteralString[str]  # error: [invalid-type-parameter]
-b: LiteralString["foo"]  # error: [invalid-type-parameter]
+a: LiteralString[str]  # error: [invalid-type-form]
+b: LiteralString["foo"]  # error: [invalid-type-form]
 ```
 
 ### As a base class
@@ -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(call todo)
+reveal_type(foo.join(qux))  # revealed: @Todo(Attribute access on `StringLiteral` types)
 
 template: LiteralString = "{}, {}"
 reveal_type(template)  # revealed: Literal["{}, {}"]
 # TODO: Infer `LiteralString`
-reveal_type(template.format(foo, bar))  # revealed: @Todo(call todo)
+reveal_type(template.format(foo, bar))  # revealed: @Todo(Attribute access on `StringLiteral` types)
 ```
 
 ### Assignability
@@ -89,28 +89,26 @@ vice versa.
 ```py
 from typing_extensions import Literal, LiteralString
 
-def coinflip() -> bool:
-    return True
+def _(flag: bool):
+    foo_1: Literal["foo"] = "foo"
+    bar_1: LiteralString = foo_1  # fine
 
-foo_1: Literal["foo"] = "foo"
-bar_1: LiteralString = foo_1  # fine
+    foo_2 = "foo" if flag else "bar"
+    reveal_type(foo_2)  # revealed: Literal["foo", "bar"]
+    bar_2: LiteralString = foo_2  # fine
 
-foo_2 = "foo" if coinflip() else "bar"
-reveal_type(foo_2)  # revealed: Literal["foo", "bar"]
-bar_2: LiteralString = foo_2  # fine
+    foo_3: LiteralString = "foo" * 1_000_000_000
+    bar_3: str = foo_2  # fine
 
-foo_3: LiteralString = "foo" * 1_000_000_000
-bar_3: str = foo_2  # fine
+    baz_1: str = str()
+    qux_1: LiteralString = baz_1  # error: [invalid-assignment]
 
-baz_1: str = str()
-qux_1: LiteralString = baz_1  # error: [invalid-assignment]
+    baz_2: LiteralString = "baz" * 1_000_000_000
+    qux_2: Literal["qux"] = baz_2  # error: [invalid-assignment]
 
-baz_2: LiteralString = "baz" * 1_000_000_000
-qux_2: Literal["qux"] = baz_2  # error: [invalid-assignment]
-
-baz_3 = "foo" if coinflip() else 1
-reveal_type(baz_3)  # revealed: Literal["foo"] | Literal[1]
-qux_3: LiteralString = baz_3  # error: [invalid-assignment]
+    baz_3 = "foo" if flag else 1
+    reveal_type(baz_3)  # revealed: Literal["foo"] | Literal[1]
+    qux_3: LiteralString = baz_3  # error: [invalid-assignment]
 ```
 
 ### Narrowing
@@ -137,7 +135,7 @@ if "" < lorem == "ipsum":
 
 ```toml
 [environment]
-target-version = "3.11"
+python-version = "3.11"
 ```
 
 ```py

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

@@ -21,7 +21,7 @@ reveal_type(stop())
 ```py
 from typing_extensions import NoReturn, Never, Any
 
-# error: [invalid-type-parameter] "Type `typing.Never` expected no type parameter"
+# error: [invalid-type-form] "Type `typing.Never` expected no type parameter"
 x: Never[int]
 a1: NoReturn
 a2: Never
@@ -51,7 +51,7 @@ def f():
 
 ```toml
 [environment]
-target-version = "3.11"
+python-version = "3.11"
 ```
 
 ```py

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

@@ -0,0 +1,127 @@
+# Typing-module aliases to other stdlib classes
+
+The `typing` module has various aliases to other stdlib classes. These are a legacy feature, but
+still need to be supported by a type checker.
+
+## Correspondence
+
+All of the following symbols can be mapped one-to-one with the actual type:
+
+```py
+import typing
+
+def f(
+    list_bare: typing.List,
+    list_parametrized: typing.List[int],
+    dict_bare: typing.Dict,
+    dict_parametrized: typing.Dict[int, str],
+    set_bare: typing.Set,
+    set_parametrized: typing.Set[int],
+    frozen_set_bare: typing.FrozenSet,
+    frozen_set_parametrized: typing.FrozenSet[str],
+    chain_map_bare: typing.ChainMap,
+    chain_map_parametrized: typing.ChainMap[int],
+    counter_bare: typing.Counter,
+    counter_parametrized: typing.Counter[int],
+    default_dict_bare: typing.DefaultDict,
+    default_dict_parametrized: typing.DefaultDict[str, int],
+    deque_bare: typing.Deque,
+    deque_parametrized: typing.Deque[str],
+    ordered_dict_bare: typing.OrderedDict,
+    ordered_dict_parametrized: typing.OrderedDict[int, str],
+):
+    reveal_type(list_bare)  # revealed: list
+    reveal_type(list_parametrized)  # revealed: list
+
+    reveal_type(dict_bare)  # revealed: dict
+    reveal_type(dict_parametrized)  # revealed: dict
+
+    reveal_type(set_bare)  # revealed: set
+    reveal_type(set_parametrized)  # revealed: set
+
+    reveal_type(frozen_set_bare)  # revealed: frozenset
+    reveal_type(frozen_set_parametrized)  # revealed: frozenset
+
+    reveal_type(chain_map_bare)  # revealed: ChainMap
+    reveal_type(chain_map_parametrized)  # revealed: ChainMap
+
+    reveal_type(counter_bare)  # revealed: Counter
+    reveal_type(counter_parametrized)  # revealed: Counter
+
+    reveal_type(default_dict_bare)  # revealed: defaultdict
+    reveal_type(default_dict_parametrized)  # revealed: defaultdict
+
+    reveal_type(deque_bare)  # revealed: deque
+    reveal_type(deque_parametrized)  # revealed: deque
+
+    reveal_type(ordered_dict_bare)  # revealed: OrderedDict
+    reveal_type(ordered_dict_parametrized)  # revealed: OrderedDict
+```
+
+## Inheritance
+
+The aliases can be inherited from. Some of these are still partially or wholly TODOs.
+
+```py
+import typing
+
+####################
+### Built-ins
+
+class ListSubclass(typing.List): ...
+
+# 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): ...
+
+# TODO: should have `Generic`, should not have `Unknown`
+# revealed: tuple[Literal[DictSubclass], Literal[dict], Unknown, Literal[object]]
+reveal_type(DictSubclass.__mro__)
+
+class SetSubclass(typing.Set): ...
+
+# TODO: should have `Generic`, should not have `Unknown`
+# revealed: tuple[Literal[SetSubclass], Literal[set], Unknown, Literal[object]]
+reveal_type(SetSubclass.__mro__)
+
+class FrozenSetSubclass(typing.FrozenSet): ...
+
+# TODO: should have `Generic`, should not have `Unknown`
+# revealed: tuple[Literal[FrozenSetSubclass], Literal[frozenset], Unknown, Literal[object]]
+reveal_type(FrozenSetSubclass.__mro__)
+
+####################
+### `collections`
+
+class ChainMapSubclass(typing.ChainMap): ...
+
+# TODO: Should be (ChainMapSubclass, ChainMap, MutableMapping, Mapping, Collection, Sized, Iterable, Container, Generic, object)
+# revealed: tuple[Literal[ChainMapSubclass], Literal[ChainMap], Unknown, Literal[object]]
+reveal_type(ChainMapSubclass.__mro__)
+
+class CounterSubclass(typing.Counter): ...
+
+# TODO: Should be (CounterSubclass, Counter, dict, MutableMapping, Mapping, Collection, Sized, Iterable, Container, Generic, object)
+# revealed: tuple[Literal[CounterSubclass], Literal[Counter], Unknown, Literal[object]]
+reveal_type(CounterSubclass.__mro__)
+
+class DefaultDictSubclass(typing.DefaultDict): ...
+
+# TODO: Should be (DefaultDictSubclass, defaultdict, dict, MutableMapping, Mapping, Collection, Sized, Iterable, Container, Generic, object)
+# revealed: tuple[Literal[DefaultDictSubclass], Literal[defaultdict], Unknown, Literal[object]]
+reveal_type(DefaultDictSubclass.__mro__)
+
+class DequeSubclass(typing.Deque): ...
+
+# TODO: Should be (DequeSubclass, deque, MutableSequence, Sequence, Reversible, Collection, Sized, Iterable, Container, Generic, object)
+# revealed: tuple[Literal[DequeSubclass], Literal[deque], Unknown, Literal[object]]
+reveal_type(DequeSubclass.__mro__)
+
+class OrderedDictSubclass(typing.OrderedDict): ...
+
+# TODO: Should be (OrderedDictSubclass, OrderedDict, dict, MutableMapping, Mapping, Collection, Sized, Iterable, Container, Generic, object)
+# revealed: tuple[Literal[OrderedDictSubclass], Literal[OrderedDict], Unknown, Literal[object]]
+reveal_type(OrderedDictSubclass.__mro__)
+```

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

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

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

@@ -0,0 +1,71 @@
+# Unsupported special forms
+
+## Not yet supported
+
+Several special forms are unsupported by red-knot currently. However, we also don't emit
+false-positive errors if you use one in an annotation:
+
+```py
+from typing_extensions import Self, TypeVarTuple, Unpack, TypeGuard, TypeIs, Concatenate, ParamSpec, TypeAlias, Callable, TypeVar
+
+P = ParamSpec("P")
+Ts = TypeVarTuple("Ts")
+R_co = TypeVar("R_co", covariant=True)
+
+Alias: TypeAlias = int
+
+def f(*args: Unpack[Ts]) -> tuple[Unpack[Ts]]:
+    # TODO: should understand the annotation
+    reveal_type(args)  # revealed: tuple
+
+    reveal_type(Alias)  # revealed: @Todo(Unsupported or invalid type in a type expression)
+
+def g() -> TypeGuard[int]: ...
+def h() -> TypeIs[int]: ...
+def i(callback: Callable[Concatenate[int, P], R_co], *args: P.args, **kwargs: P.kwargs) -> R_co:
+    # TODO: should understand the annotation
+    reveal_type(args)  # revealed: tuple
+
+    # TODO: should understand the annotation
+    reveal_type(kwargs)  # revealed: dict
+
+    return callback(42, *args, **kwargs)
+
+class Foo:
+    def method(self, x: Self):
+        reveal_type(x)  # revealed: @Todo(Unsupported or invalid type in a type expression)
+```
+
+## Inheritance
+
+You can't inherit from most of these. `typing.Callable` is an exception.
+
+```py
+from typing import Callable
+from typing_extensions import Self, Unpack, TypeGuard, TypeIs, Concatenate
+
+class A(Self): ...  # error: [invalid-base]
+class B(Unpack): ...  # error: [invalid-base]
+class C(TypeGuard): ...  # error: [invalid-base]
+class D(TypeIs): ...  # error: [invalid-base]
+class E(Concatenate): ...  # error: [invalid-base]
+class F(Callable): ...
+
+reveal_type(F.__mro__)  # revealed: tuple[Literal[F], @Todo(Support for Callable as a base class), Literal[object]]
+```
+
+## Subscriptability
+
+Some of these are not subscriptable:
+
+```py
+from typing_extensions import Self, TypeAlias
+
+X: TypeAlias[T] = int  # error: [invalid-type-form]
+
+class Foo[T]:
+    # error: [invalid-type-form] "Special form `typing.Self` expected no type parameter"
+    # error: [invalid-type-form] "Special form `typing.Self` expected no type parameter"
+    def method(self: Self[int]) -> Self[int]:
+        reveal_type(self)  # revealed: Unknown
+```

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

@@ -0,0 +1,37 @@
+# Unsupported type qualifiers
+
+## Not yet supported
+
+Several type qualifiers are unsupported by red-knot currently. However, we also don't emit
+false-positive errors if you use one in an annotation:
+
+```py
+from typing_extensions import Final, ClassVar, Required, NotRequired, ReadOnly, TypedDict
+
+X: Final = 42
+Y: Final[int] = 42
+
+class Foo:
+    A: ClassVar[int] = 42
+
+# TODO: `TypedDict` is actually valid as a base
+# error: [invalid-base]
+class Bar(TypedDict):
+    x: Required[int]
+    y: NotRequired[str]
+    z: ReadOnly[bytes]
+```
+
+## Inheritance
+
+You can't inherit from a type qualifier.
+
+```py
+from typing_extensions import Final, ClassVar, Required, NotRequired, ReadOnly
+
+class A(Final): ...  # error: [invalid-base]
+class B(ClassVar): ...  # error: [invalid-base]
+class C(Required): ...  # error: [invalid-base]
+class D(NotRequired): ...  # error: [invalid-base]
+class E(ReadOnly): ...  # error: [invalid-base]
+```

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

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

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

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

crates/red_knot_python_semantic/resources/mdtest/attributes.md

@@ -1,29 +1,27 @@
-# Class attributes
+# Attributes
+
+Tests for attribute access on various kinds of types.
 
 ## Union of attributes
 
 ```py
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-
-if flag:
-    class C1:
-        x = 1
-
-else:
-    class C1:
-        x = 2
-
-class C2:
+def _(flag: bool):
     if flag:
-        x = 3
-    else:
-        x = 4
+        class C1:
+            x = 1
 
-reveal_type(C1.x)  # revealed: Literal[1, 2]
-reveal_type(C2.x)  # revealed: Literal[3, 4]
+    else:
+        class C1:
+            x = 2
+
+    class C2:
+        if flag:
+            x = 3
+        else:
+            x = 4
+
+    reveal_type(C1.x)  # revealed: Literal[1, 2]
+    reveal_type(C2.x)  # revealed: Literal[3, 4]
 ```
 
 ## Inherited attributes
@@ -68,24 +66,19 @@ reveal_type(A.X)  # revealed: Literal[42]
 In this example, the `x` attribute is not defined in the `C2` element of the union:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    class C1:
+        x = 1
 
-class C1:
-    x = 1
+    class C2: ...
 
-class C2: ...
+    class C3:
+        x = 3
 
-class C3:
-    x = 3
+    C = C1 if flag1 else C2 if flag2 else C3
 
-flag1 = bool_instance()
-flag2 = bool_instance()
-
-C = C1 if flag1 else C2 if flag2 else C3
-
-# error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
-reveal_type(C.x)  # revealed: Literal[1, 3]
+    # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
+    reveal_type(C.x)  # revealed: Literal[1, 3]
 ```
 
 ### Possibly-unbound within a class
@@ -94,26 +87,21 @@ We raise the same diagnostic if the attribute is possibly-unbound in at least on
 union:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool, flag1: bool, flag2: bool):
+    class C1:
+        x = 1
 
-class C1:
-    x = 1
+    class C2:
+        if flag:
+            x = 2
 
-class C2:
-    if bool_instance():
-        x = 2
+    class C3:
+        x = 3
 
-class C3:
-    x = 3
+    C = C1 if flag1 else C2 if flag2 else C3
 
-flag1 = bool_instance()
-flag2 = bool_instance()
-
-C = C1 if flag1 else C2 if flag2 else C3
-
-# error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
-reveal_type(C.x)  # revealed: Literal[1, 2, 3]
+    # error: [possibly-unbound-attribute] "Attribute `x` on type `Literal[C1, C2, C3]` is possibly unbound"
+    reveal_type(C.x)  # revealed: Literal[1, 2, 3]
 ```
 
 ## Unions with all paths unbound
@@ -121,16 +109,115 @@ reveal_type(C.x)  # revealed: Literal[1, 2, 3]
 If the symbol is unbound in all elements of the union, we detect that:
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    class C1: ...
+    class C2: ...
+    C = C1 if flag else C2
 
-class C1: ...
-class C2: ...
-
-flag = bool_instance()
-
-C = C1 if flag else C2
-
-# error: [unresolved-attribute] "Type `Literal[C1, C2]` has no attribute `x`"
-reveal_type(C.x)  # revealed: Unknown
+    # error: [unresolved-attribute] "Type `Literal[C1, C2]` has no attribute `x`"
+    reveal_type(C.x)  # revealed: Unknown
+```
+
+## Objects of all types have a `__class__` method
+
+```py
+import typing_extensions
+
+reveal_type(typing_extensions.__class__)  # revealed: Literal[ModuleType]
+
+a = 42
+reveal_type(a.__class__)  # revealed: Literal[int]
+
+b = "42"
+reveal_type(b.__class__)  # revealed: Literal[str]
+
+c = b"42"
+reveal_type(c.__class__)  # revealed: Literal[bytes]
+
+d = True
+reveal_type(d.__class__)  # revealed: Literal[bool]
+
+e = (42, 42)
+reveal_type(e.__class__)  # revealed: Literal[tuple]
+
+def f(a: int, b: typing_extensions.LiteralString, c: int | str, d: type[str]):
+    reveal_type(a.__class__)  # revealed: type[int]
+    reveal_type(b.__class__)  # revealed: Literal[str]
+    reveal_type(c.__class__)  # revealed: type[int] | type[str]
+
+    # `type[type]`, a.k.a., either the class `type` or some subclass of `type`.
+    # It would be incorrect to infer `Literal[type]` here,
+    # as `c` could be some subclass of `str` with a custom metaclass.
+    # All we know is that the metaclass must be a (non-strict) subclass of `type`.
+    reveal_type(d.__class__)  # revealed: type[type]
+
+reveal_type(f.__class__)  # revealed: Literal[FunctionType]
+
+class Foo: ...
+
+reveal_type(Foo.__class__)  # revealed: Literal[type]
+```
+
+## Function-literal attributes
+
+Most attribute accesses on function-literal types are delegated to `types.FunctionType`, since all
+functions are instances of that class:
+
+```py path=a.py
+def f(): ...
+
+reveal_type(f.__defaults__)  # revealed: @Todo(instance attributes)
+reveal_type(f.__kwdefaults__)  # revealed: @Todo(instance attributes)
+```
+
+Some attributes are special-cased, however:
+
+```py path=b.py
+def f(): ...
+
+reveal_type(f.__get__)  # revealed: @Todo(`__get__` method on functions)
+reveal_type(f.__call__)  # revealed: @Todo(`__call__` method on functions)
+```
+
+## Int-literal attributes
+
+Most attribute accesses on int-literal types are delegated to `builtins.int`, since all literal
+integers are instances of that class:
+
+```py path=a.py
+reveal_type((2).bit_length)  # revealed: @Todo(instance attributes)
+reveal_type((2).denominator)  # revealed: @Todo(instance attributes)
+```
+
+Some attributes are special-cased, however:
+
+```py path=b.py
+reveal_type((2).numerator)  # revealed: Literal[2]
+reveal_type((2).real)  # revealed: Literal[2]
+```
+
+## Literal `bool` attributes
+
+Most attribute accesses on bool-literal types are delegated to `builtins.bool`, since all literal
+bols are instances of that class:
+
+```py path=a.py
+reveal_type(True.__and__)  # revealed: @Todo(instance attributes)
+reveal_type(False.__or__)  # revealed: @Todo(instance attributes)
+```
+
+Some attributes are special-cased, however:
+
+```py path=b.py
+reveal_type(True.numerator)  # revealed: Literal[1]
+reveal_type(False.real)  # revealed: Literal[0]
+```
+
+## Bytes-literal attributes
+
+All attribute access on literal `bytes` types is currently delegated to `buitins.bytes`:
+
+```py
+reveal_type(b"foo".join)  # revealed: @Todo(instance attributes)
+reveal_type(b"foo".endswith)  # revealed: @Todo(instance attributes)
 ```

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

@@ -3,39 +3,43 @@
 ## With wildcard
 
 ```py
-match 0:
-    case 1:
-        y = 2
-    case _:
-        y = 3
+def _(target: int):
+    match target:
+        case 1:
+            y = 2
+        case _:
+            y = 3
 
-reveal_type(y)  # revealed: Literal[2, 3]
+    reveal_type(y)  # revealed: Literal[2, 3]
 ```
 
 ## Without wildcard
 
 ```py
-match 0:
-    case 1:
-        y = 2
-    case 2:
-        y = 3
+def _(target: int):
+    match target:
+        case 1:
+            y = 2
+        case 2:
+            y = 3
 
-# revealed: Literal[2, 3]
-# error: [possibly-unresolved-reference]
-reveal_type(y)
+    # revealed: Literal[2, 3]
+    # error: [possibly-unresolved-reference]
+    reveal_type(y)
 ```
 
 ## Basic match
 
 ```py
-y = 1
-y = 2
-match 0:
-    case 1:
-        y = 3
-    case 2:
-        y = 4
+def _(target: int):
+    y = 1
+    y = 2
 
-reveal_type(y)  # revealed: Literal[2, 3, 4]
+    match target:
+        case 1:
+            y = 3
+        case 2:
+            y = 4
+
+    reveal_type(y)  # revealed: Literal[2, 3, 4]
 ```

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

@@ -10,42 +10,66 @@ x: str  # error: [invalid-declaration] "Cannot declare type `str` for inferred t
 ## Incompatible declarations
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        x: str
+    else:
+        x: int
 
-flag = bool_instance()
-if flag:
-    x: str
-else:
-    x: int
-x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: str, int"
+    x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: str, int"
 ```
 
-## Partial declarations
+## Incompatible declarations for 2 (out of 3) types
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag1: bool, flag2: bool):
+    if flag1:
+        x: str
+    elif flag2:
+        x: int
 
-flag = bool_instance()
-if flag:
-    x: int
-x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: Unknown, int"
+    # Here, the declared type for `x` is `int | str | Unknown`.
+    x = 1  # error: [conflicting-declarations] "Conflicting declared types for `x`: str, int"
 ```
 
 ## Incompatible declarations with bad assignment
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    if flag:
+        x: str
+    else:
+        x: int
 
-flag = bool_instance()
-if flag:
-    x: str
-else:
-    x: int
-
-# error: [conflicting-declarations]
-# error: [invalid-assignment]
-x = b"foo"
+    # error: [conflicting-declarations]
+    # error: [invalid-assignment]
+    x = b"foo"
+```
+
+## No errors
+
+Currently, we avoid raising the conflicting-declarations for the following cases:
+
+### Partial declarations
+
+```py
+def _(flag: bool):
+    if flag:
+        x: int
+
+    x = 1
+```
+
+### Partial declarations in try-except
+
+Refer to <https://github.com/astral-sh/ruff/issues/13966>
+
+```py
+def _():
+    try:
+        x: int = 1
+    except:
+        x = 2
+
+    x = 3
 ```

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

@@ -49,12 +49,124 @@ def foo(
     try:
         help()
     except x as e:
-        # TODO: should be `AttributeError`
-        reveal_type(e)  # revealed: @Todo(exception type)
+        reveal_type(e)  # revealed: AttributeError
     except y as f:
-        # TODO: should be `OSError | RuntimeError`
-        reveal_type(f)  # revealed: @Todo(exception type)
+        reveal_type(f)  # revealed: OSError | RuntimeError
     except z as g:
         # TODO: should be `BaseException`
-        reveal_type(g)  # revealed: @Todo(exception type)
+        reveal_type(g)  # revealed: @Todo(full tuple[...] support)
+```
+
+## Invalid exception handlers
+
+```py
+try:
+    pass
+# error: [invalid-exception-caught] "Cannot catch object of type `Literal[3]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
+except 3 as e:
+    reveal_type(e)  # revealed: Unknown
+
+try:
+    pass
+# error: [invalid-exception-caught] "Cannot catch object of type `Literal["foo"]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
+# error: [invalid-exception-caught] "Cannot catch object of type `Literal[b"bar"]` in an exception handler (must be a `BaseException` subclass or a tuple of `BaseException` subclasses)"
+except (ValueError, OSError, "foo", b"bar") as e:
+    reveal_type(e)  # revealed: ValueError | OSError | Unknown
+
+def foo(
+    x: type[str],
+    y: tuple[type[OSError], type[RuntimeError], int],
+    z: tuple[type[str], ...],
+):
+    try:
+        help()
+    # error: [invalid-exception-caught]
+    except x as e:
+        reveal_type(e)  # revealed: Unknown
+    # error: [invalid-exception-caught]
+    except y as f:
+        reveal_type(f)  # revealed: OSError | RuntimeError | Unknown
+    except z as g:
+        # TODO: should emit a diagnostic here:
+        reveal_type(g)  # revealed: @Todo(full tuple[...] support)
+```
+
+## Object raised is not an exception
+
+```py
+try:
+    raise AttributeError()  # fine
+except:
+    ...
+
+try:
+    raise FloatingPointError  # fine
+except:
+    ...
+
+try:
+    raise 1  # error: [invalid-raise]
+except:
+    ...
+
+try:
+    raise int  # error: [invalid-raise]
+except:
+    ...
+
+def _(e: Exception | type[Exception]):
+    raise e  # fine
+
+def _(e: Exception | type[Exception] | None):
+    raise e  # error: [invalid-raise]
+```
+
+## Exception cause is not an exception
+
+```py
+try:
+    raise EOFError() from GeneratorExit  # fine
+except:
+    ...
+
+try:
+    raise StopIteration from MemoryError()  # fine
+except:
+    ...
+
+try:
+    raise BufferError() from None  # fine
+except:
+    ...
+
+try:
+    raise ZeroDivisionError from False  # error: [invalid-raise]
+except:
+    ...
+
+try:
+    raise SystemExit from bool()  # error: [invalid-raise]
+except:
+    ...
+
+try:
+    raise
+except KeyboardInterrupt as e:  # fine
+    reveal_type(e)  # revealed: KeyboardInterrupt
+    raise LookupError from e  # fine
+
+try:
+    raise
+except int as e:  # error: [invalid-exception-caught]
+    reveal_type(e)  # revealed: Unknown
+    raise KeyError from e
+
+def _(e: Exception | type[Exception]):
+    raise ModuleNotFoundError from e  # fine
+
+def _(e: Exception | type[Exception] | None):
+    raise IndexError from e  # fine
+
+def _(e: int | None):
+    raise IndexError from e  # error: [invalid-raise]
 ```

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

@@ -1,30 +1,66 @@
-# Except star
+# `except*`
 
-## Except\* with BaseException
+`except*` is only available in Python 3.11 and later:
+
+```toml
+[environment]
+python-version = "3.11"
+```
+
+## `except*` with `BaseException`
 
 ```py
 try:
     help()
 except* BaseException as e:
+    # TODO: should be `BaseExceptionGroup[BaseException]` --Alex
     reveal_type(e)  # revealed: BaseExceptionGroup
 ```
 
-## Except\* with specific exception
+## `except*` with specific exception
 
 ```py
 try:
     help()
 except* OSError as e:
-    # TODO(Alex): more precise would be `ExceptionGroup[OSError]`
+    # TODO: more precise would be `ExceptionGroup[OSError]` --Alex
+    # (needs homogenous tuples + generics)
     reveal_type(e)  # revealed: BaseExceptionGroup
 ```
 
-## Except\* with multiple exceptions
+## `except*` with multiple exceptions
 
 ```py
 try:
     help()
 except* (TypeError, AttributeError) as e:
-    # TODO(Alex): more precise would be `ExceptionGroup[TypeError | AttributeError]`.
+    # TODO: more precise would be `ExceptionGroup[TypeError | AttributeError]` --Alex
+    # (needs homogenous tuples + generics)
+    reveal_type(e)  # revealed: BaseExceptionGroup
+```
+
+## `except*` with mix of `Exception`s and `BaseException`s
+
+```py
+try:
+    help()
+except* (KeyboardInterrupt, AttributeError) as e:
+    # TODO: more precise would be `BaseExceptionGroup[KeyboardInterrupt | AttributeError]` --Alex
+    reveal_type(e)  # revealed: BaseExceptionGroup
+```
+
+## Invalid `except*` handlers
+
+```py
+try:
+    help()
+except* 3 as e:  # error: [invalid-exception-caught]
+    # TODO: Should be `BaseExceptionGroup[Unknown]` --Alex
+    reveal_type(e)  # revealed: BaseExceptionGroup
+
+try:
+    help()
+except* (AttributeError, 42) as e:  # error: [invalid-exception-caught]
+    # TODO: Should be `BaseExceptionGroup[AttributeError | Unknown]` --Alex
     reveal_type(e)  # revealed: BaseExceptionGroup
 ```

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

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

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

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

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

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

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

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

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

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

crates/red_knot_python_semantic/resources/mdtest/final.md

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

crates/red_knot_python_semantic/resources/mdtest/generics.md

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

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

@@ -25,3 +25,82 @@ reveal_type(D)  # revealed: Literal[C]
 ```py path=b.py
 class C: ...
 ```
+
+## Nested
+
+```py
+import a.b
+
+reveal_type(a.b.C)  # revealed: Literal[C]
+```
+
+```py path=a/__init__.py
+```
+
+```py path=a/b.py
+class C: ...
+```
+
+## Deeply nested
+
+```py
+import a.b.c
+
+reveal_type(a.b.c.C)  # revealed: Literal[C]
+```
+
+```py path=a/__init__.py
+```
+
+```py path=a/b/__init__.py
+```
+
+```py path=a/b/c.py
+class C: ...
+```
+
+## Nested with rename
+
+```py
+import a.b as b
+
+reveal_type(b.C)  # revealed: Literal[C]
+```
+
+```py path=a/__init__.py
+```
+
+```py path=a/b.py
+class C: ...
+```
+
+## Deeply nested with rename
+
+```py
+import a.b.c as c
+
+reveal_type(c.C)  # revealed: Literal[C]
+```
+
+```py path=a/__init__.py
+```
+
+```py path=a/b/__init__.py
+```
+
+```py path=a/b/c.py
+class C: ...
+```
+
+## Unresolvable submodule imports
+
+```py
+# Topmost component resolvable, submodule not resolvable:
+import a.foo  # error: [unresolved-import] "Cannot resolve import `a.foo`"
+
+# Topmost component unresolvable:
+import b.foo  # error: [unresolved-import] "Cannot resolve import `b.foo`"
+```
+
+```py path=a/__init__.py
+```

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

@@ -3,6 +3,6 @@
 ```py
 import builtins
 
-x = builtins.copyright
-reveal_type(x)  # revealed: Literal[copyright]
+x = builtins.chr
+reveal_type(x)  # revealed: Literal[chr]
 ```

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

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

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

@@ -0,0 +1,75 @@
+# Conflicting attributes and submodules
+
+## Via import
+
+```py
+import a.b
+
+reveal_type(a.b)  # revealed: <module 'a.b'>
+```
+
+```py path=a/__init__.py
+b = 42
+```
+
+```py path=a/b.py
+```
+
+## Via from/import
+
+```py
+from a import b
+
+reveal_type(b)  # revealed: Literal[42]
+```
+
+```py path=a/__init__.py
+b = 42
+```
+
+```py path=a/b.py
+```
+
+## Via both
+
+```py
+import a.b
+from a import b
+
+reveal_type(b)  # revealed: <module 'a.b'>
+reveal_type(a.b)  # revealed: <module 'a.b'>
+```
+
+```py path=a/__init__.py
+b = 42
+```
+
+```py path=a/b.py
+```
+
+## Via both (backwards)
+
+In this test, we infer a different type for `b` than the runtime behavior of the Python interpreter.
+The interpreter will not load the submodule `a.b` during the `from a import b` statement, since `a`
+contains a non-module attribute named `b`. (See the [definition][from-import] of a `from...import`
+statement for details.) However, because our import tracking is flow-insensitive, we will see that
+`a.b` is imported somewhere in the file, and therefore assume that the `from...import` statement
+sees the submodule as the value of `b` instead of the integer.
+
+```py
+from a import b
+import a.b
+
+# Python would say `Literal[42]` for `b`
+reveal_type(b)  # revealed: <module 'a.b'>
+reveal_type(a.b)  # revealed: <module 'a.b'>
+```
+
+```py path=a/__init__.py
+b = 42
+```
+
+```py path=a/b.py
+```
+
+[from-import]: https://docs.python.org/3/reference/simple_stmts.html#the-import-statement

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

@@ -7,3 +7,25 @@ from import bar  # error: [invalid-syntax]
 
 reveal_type(bar)  # revealed: Unknown
 ```
+
+## Invalid nested module import
+
+TODO: This is correctly flagged as an error, but we could clean up the diagnostics that we report.
+
+```py
+# TODO: No second diagnostic
+# error: [invalid-syntax] "Expected ',', found '.'"
+# error: [unresolved-import] "Module `a` has no member `c`"
+from a import b.c
+
+# TODO: Should these be inferred as Unknown?
+reveal_type(b)  # revealed: <module 'a.b'>
+reveal_type(b.c)  # revealed: Literal[1]
+```
+
+```py path=a/__init__.py
+```
+
+```py path=a/b.py
+c = 1
+```

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

@@ -121,23 +121,44 @@ X = 42
 ```
 
 ```py path=package/bar.py
-# TODO: support submodule imports
-from . import foo  # error: [unresolved-import]
+from . import foo
 
-y = foo.X
-
-# TODO: should be `Literal[42]`
-reveal_type(y)  # revealed: Unknown
+reveal_type(foo.X)  # revealed: Literal[42]
 ```
 
 ## Non-existent + bare to module
 
+This test verifies that we emit an error when we try to import a symbol that is neither a submodule
+nor an attribute of `package`.
+
 ```py path=package/__init__.py
 ```
 
 ```py path=package/bar.py
-# TODO: support submodule imports
 from . import foo  # error: [unresolved-import]
 
 reveal_type(foo)  # revealed: Unknown
 ```
+
+## Import submodule from self
+
+We don't currently consider `from...import` statements when building up the `imported_modules` set
+in the semantic index. When accessing an attribute of a module, we only consider it a potential
+submodule when that submodule name appears in the `imported_modules` set. That means that submodules
+that are imported via `from...import` are not visible to our type inference if you also access that
+submodule via the attribute on its parent package.
+
+```py path=package/__init__.py
+```
+
+```py path=package/foo.py
+X = 42
+```
+
+```py path=package/bar.py
+from . import foo
+import package
+
+# error: [unresolved-attribute] "Type `<module 'package'>` has no attribute `foo`"
+reveal_type(package.foo.X)  # revealed: Unknown
+```

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

@@ -0,0 +1,100 @@
+# Tracking imported modules
+
+These tests depend on how we track which modules have been imported. There are currently two
+characteristics of our module tracking that can lead to inaccuracies:
+
+- Imports are tracked on a per-file basis. At runtime, importing a submodule in one file makes that
+    submodule globally available via any reference to the containing package. We will flag an error
+    if a file tries to access a submodule without there being an import of that submodule _in that
+    same file_.
+
+    This is a purposeful decision, and not one we plan to change. If a module wants to re-export some
+    other module that it imports, there are ways to do that (tested below) that are blessed by the
+    typing spec and that are visible to our file-scoped import tracking.
+
+- Imports are tracked flow-insensitively: submodule accesses are allowed and resolved if that
+    submodule is imported _anywhere in the file_. This handles the common case where all imports are
+    grouped at the top of the file, and is easiest to implement. We might revisit this decision and
+    track submodule imports flow-sensitively, in which case we will have to update the assertions in
+    some of these tests.
+
+## Import submodule later in file
+
+This test highlights our flow-insensitive analysis, since we access the `a.b` submodule before it
+has been imported.
+
+```py
+import a
+
+# Would be an error with flow-sensitive tracking
+reveal_type(a.b.C)  # revealed: Literal[C]
+
+import a.b
+```
+
+```py path=a/__init__.py
+```
+
+```py path=a/b.py
+class C: ...
+```
+
+## Rename a re-export
+
+This test highlights how import tracking is local to each file, but specifically to the file where a
+containing module is first referenced. This allows the main module to see that `q.a` contains a
+submodule `b`, even though `a.b` is never imported in the main module.
+
+```py
+from q import a, b
+
+reveal_type(b)  # revealed: <module 'a.b'>
+reveal_type(b.C)  # revealed: Literal[C]
+
+reveal_type(a.b)  # revealed: <module 'a.b'>
+reveal_type(a.b.C)  # revealed: Literal[C]
+```
+
+```py path=a/__init__.py
+```
+
+```py path=a/b.py
+class C: ...
+```
+
+```py path=q.py
+import a as a
+import a.b as b
+```
+
+## Attribute overrides submodule
+
+Technically, either a submodule or a non-module attribute could shadow the other, depending on the
+ordering of when the submodule is loaded relative to the parent module's `__init__.py` file being
+evaluated. We have chosen to always have the submodule take priority. (This matches pyright's
+current behavior, and opposite of mypy's current behavior.)
+
+```py
+import sub.b
+import attr.b
+
+# In the Python interpreter, `attr.b` is Literal[1]
+reveal_type(sub.b)  # revealed: <module 'sub.b'>
+reveal_type(attr.b)  # revealed: <module 'attr.b'>
+```
+
+```py path=sub/__init__.py
+b = 1
+```
+
+```py path=sub/b.py
+```
+
+```py path=attr/__init__.py
+from . import b as _
+
+b = 1
+```
+
+```py path=attr/b.py
+```

crates/red_knot_python_semantic/resources/mdtest/known_constants.md

@@ -0,0 +1,52 @@
+# Known constants
+
+## `typing.TYPE_CHECKING`
+
+This constant is `True` when in type-checking mode, `False` otherwise. The symbol is defined to be
+`False` at runtime. In typeshed, it is annotated as `bool`. This test makes sure that we infer
+`Literal[True]` for it anyways.
+
+### Basic
+
+```py
+from typing import TYPE_CHECKING
+import typing
+
+reveal_type(TYPE_CHECKING)  # revealed: Literal[True]
+reveal_type(typing.TYPE_CHECKING)  # revealed: Literal[True]
+```
+
+### Aliased
+
+Make sure that we still infer the correct type if the constant has been given a different name:
+
+```py
+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:
+
+```py path=constants.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`:
+
+```py
+from typing_extensions import TYPE_CHECKING
+
+reveal_type(TYPE_CHECKING)  # revealed: Literal[True]
+```

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

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

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

@@ -1,59 +1,50 @@
 # While loops
 
-## Basic While Loop
+## Basic `while` loop
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1
+    while flag:
+        x = 2
 
-flag = bool_instance()
-x = 1
-while flag:
-    x = 2
-
-reveal_type(x)  # revealed: Literal[1, 2]
-```
-
-## While with else (no break)
-
-```py
-def bool_instance() -> bool:
-    return True
-
-flag = bool_instance()
-x = 1
-while flag:
-    x = 2
-else:
     reveal_type(x)  # revealed: Literal[1, 2]
-    x = 3
-
-reveal_type(x)  # revealed: Literal[3]
 ```
 
-## While with Else (may break)
+## `while` with `else` (no `break`)
 
 ```py
-def bool_instance() -> bool:
-    return True
+def _(flag: bool):
+    x = 1
+    while flag:
+        x = 2
+    else:
+        reveal_type(x)  # revealed: Literal[1, 2]
+        x = 3
 
-flag, flag2 = bool_instance(), bool_instance()
-x = 1
-y = 0
-while flag:
-    x = 2
-    if flag2:
-        y = 4
-        break
-else:
-    y = x
-    x = 3
-
-reveal_type(x)  # revealed: Literal[2, 3]
-reveal_type(y)  # revealed: Literal[1, 2, 4]
+    reveal_type(x)  # revealed: Literal[3]
 ```
 
-## Nested while loops
+## `while` with `else` (may `break`)
+
+```py
+def _(flag: bool, flag2: bool):
+    x = 1
+    y = 0
+    while flag:
+        x = 2
+        if flag2:
+            y = 4
+            break
+    else:
+        y = x
+        x = 3
+
+    reveal_type(x)  # revealed: Literal[2, 3]
+    reveal_type(y)  # revealed: Literal[1, 2, 4]
+```
+
+## Nested `while` loops
 
 ```py
 def flag() -> bool:
@@ -78,3 +69,50 @@ else:
 
 reveal_type(x)  # revealed: Literal[3, 4, 5]
 ```
+
+## Boundness
+
+Make sure that the boundness information is correctly tracked in `while` loop control flow.
+
+### Basic `while` loop
+
+```py
+def _(flag: bool):
+    while flag:
+        x = 1
+
+    # error: [possibly-unresolved-reference]
+    x
+```
+
+### `while` with `else` (no `break`)
+
+```py
+def _(flag: bool):
+    while flag:
+        y = 1
+    else:
+        x = 1
+
+    # no error, `x` is always bound
+    x
+    # error: [possibly-unresolved-reference]
+    y
+```
+
+### `while` with `else` (may `break`)
+
+```py
+def _(flag: bool, flag2: bool):
+    while flag:
+        x = 1
+        if flag2:
+            break
+    else:
+        y = 1
+
+    # error: [possibly-unresolved-reference]
+    x
+    # error: [possibly-unresolved-reference]
+    y
+```

crates/red_knot_python_semantic/resources/mdtest/mdtest_config.md

@@ -5,7 +5,7 @@ The following configuration will be attached to the *root* section (without any
 
 ```toml
 [environment]
-target-version = "3.10"
+python-version = "3.10"
 ```
 
 # Basic
@@ -34,7 +34,7 @@ Here, we make sure that we can overwrite the global configuration in a child sec
 
 ```toml
 [environment]
-target-version = "3.11"
+python-version = "3.11"
 ```
 
 ```py
@@ -55,7 +55,7 @@ Children in this section should all use the section configuration:
 
 ```toml
 [environment]
-target-version = "3.12"
+python-version = "3.12"
 ```
 
 ## Child

crates/red_knot_python_semantic/resources/mdtest/metaclass.md

@@ -68,7 +68,7 @@ class B(metaclass=M2): ...
 # error: [conflicting-metaclass] "The metaclass of a derived class (`C`) must be a subclass of the metaclasses of all its bases, but `M1` (metaclass of base class `A`) and `M2` (metaclass of base class `B`) have no subclass relationship"
 class C(A, B): ...
 
-reveal_type(C.__class__)  # revealed: Unknown
+reveal_type(C.__class__)  # revealed: type[Unknown]
 ```
 
 ## Conflict (2)
@@ -85,7 +85,7 @@ class A(metaclass=M1): ...
 # error: [conflicting-metaclass] "The metaclass of a derived class (`B`) must be a subclass of the metaclasses of all its bases, but `M2` (metaclass of `B`) and `M1` (metaclass of base class `A`) have no subclass relationship"
 class B(A, metaclass=M2): ...
 
-reveal_type(B.__class__)  # revealed: Unknown
+reveal_type(B.__class__)  # revealed: type[Unknown]
 ```
 
 ## Common metaclass
@@ -129,7 +129,7 @@ class C(metaclass=M12): ...
 # error: [conflicting-metaclass] "The metaclass of a derived class (`D`) must be a subclass of the metaclasses of all its bases, but `M1` (metaclass of base class `A`) and `M2` (metaclass of base class `B`) have no subclass relationship"
 class D(A, B, C): ...
 
-reveal_type(D.__class__)  # revealed: Unknown
+reveal_type(D.__class__)  # revealed: type[Unknown]
 ```
 
 ## Unknown
@@ -179,11 +179,11 @@ reveal_type(A.__class__)  # revealed: @Todo(metaclass not a class)
 Retrieving the metaclass of a cyclically defined class should not cause an infinite loop.
 
 ```py path=a.pyi
-class A(B): ...  # error: [cyclic-class-def]
-class B(C): ...  # error: [cyclic-class-def]
-class C(A): ...  # error: [cyclic-class-def]
+class A(B): ...  # error: [cyclic-class-definition]
+class B(C): ...  # error: [cyclic-class-definition]
+class C(A): ...  # error: [cyclic-class-definition]
 
-reveal_type(A.__class__)  # revealed: Unknown
+reveal_type(A.__class__)  # revealed: type[Unknown]
 ```
 
 ## PEP 695 generic
@@ -194,3 +194,26 @@ class A[T: str](metaclass=M): ...
 
 reveal_type(A.__class__)  # revealed: Literal[M]
 ```
+
+## Metaclasses of metaclasses
+
+```py
+class Foo(type): ...
+class Bar(type, metaclass=Foo): ...
+class Baz(type, metaclass=Bar): ...
+class Spam(metaclass=Baz): ...
+
+reveal_type(Spam.__class__)  # revealed: Literal[Baz]
+reveal_type(Spam.__class__.__class__)  # revealed: Literal[Bar]
+reveal_type(Spam.__class__.__class__.__class__)  # revealed: Literal[Foo]
+
+def test(x: Spam):
+    reveal_type(x.__class__)  # revealed: type[Spam]
+    reveal_type(x.__class__.__class__)  # revealed: type[Baz]
+    reveal_type(x.__class__.__class__.__class__)  # revealed: type[Bar]
+    reveal_type(x.__class__.__class__.__class__.__class__)  # revealed: type[Foo]
+    reveal_type(x.__class__.__class__.__class__.__class__.__class__)  # revealed: type[type]
+
+    # revealed: type[type]
+    reveal_type(x.__class__.__class__.__class__.__class__.__class__.__class__.__class__.__class__)
+```

crates/red_knot_python_semantic/resources/mdtest/mro.md

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

@@ -0,0 +1,221 @@
+# Narrowing For Truthiness Checks (`if x` or `if not x`)
+
+## Value Literals
+
+```py
+def foo() -> Literal[0, -1, True, False, "", "foo", b"", b"bar", None] | tuple[()]:
+    return 0
+
+x = foo()
+
+if x:
+    reveal_type(x)  # revealed: Literal[-1] | Literal[True] | Literal["foo"] | Literal[b"bar"]
+else:
+    reveal_type(x)  # revealed: Literal[0] | Literal[False] | Literal[""] | Literal[b""] | None | tuple[()]
+
+if not x:
+    reveal_type(x)  # revealed: Literal[0] | Literal[False] | Literal[""] | Literal[b""] | None | tuple[()]
+else:
+    reveal_type(x)  # revealed: Literal[-1] | Literal[True] | Literal["foo"] | Literal[b"bar"]
+
+if x and not x:
+    reveal_type(x)  # revealed: Never
+else:
+    reveal_type(x)  # revealed: Literal[-1, 0] | bool | Literal["", "foo"] | Literal[b"", b"bar"] | None | tuple[()]
+
+if not (x and not x):
+    reveal_type(x)  # revealed: Literal[-1, 0] | bool | Literal["", "foo"] | Literal[b"", b"bar"] | None | tuple[()]
+else:
+    reveal_type(x)  # revealed: Never
+
+if x or not x:
+    reveal_type(x)  # revealed: Literal[-1, 0] | bool | Literal["foo", ""] | Literal[b"bar", b""] | None | tuple[()]
+else:
+    reveal_type(x)  # revealed: Never
+
+if not (x or not x):
+    reveal_type(x)  # revealed: Never
+else:
+    reveal_type(x)  # revealed: Literal[-1, 0] | bool | Literal["foo", ""] | Literal[b"bar", b""] | None | tuple[()]
+
+if (isinstance(x, int) or isinstance(x, str)) and x:
+    reveal_type(x)  # revealed: Literal[-1] | Literal[True] | Literal["foo"]
+else:
+    reveal_type(x)  # revealed: Literal[b"", b"bar"] | None | tuple[()] | Literal[0] | Literal[False] | Literal[""]
+```
+
+## Function Literals
+
+Basically functions are always truthy.
+
+```py
+def flag() -> bool:
+    return True
+
+def foo(hello: int) -> bytes:
+    return b""
+
+def bar(world: str, *args, **kwargs) -> float:
+    return 0.0
+
+x = foo if flag() else bar
+
+if x:
+    reveal_type(x)  # revealed: Literal[foo, bar]
+else:
+    reveal_type(x)  # revealed: Never
+```
+
+## Mutable Truthiness
+
+### Truthiness of Instances
+
+The boolean value of an instance is not always consistent. For example, `__bool__` can be customized
+to return random values, or in the case of a `list()`, the result depends on the number of elements
+in the list. Therefore, these types should not be narrowed by `if x` or `if not x`.
+
+```py
+class A: ...
+class B: ...
+
+def f(x: A | B):
+    if x:
+        reveal_type(x)  # revealed: A & ~AlwaysFalsy | B & ~AlwaysFalsy
+    else:
+        reveal_type(x)  # revealed: A & ~AlwaysTruthy | B & ~AlwaysTruthy
+
+    if x and not x:
+        reveal_type(x)  # revealed: A & ~AlwaysFalsy & ~AlwaysTruthy | B & ~AlwaysFalsy & ~AlwaysTruthy
+    else:
+        reveal_type(x)  # revealed: A & ~AlwaysTruthy | B & ~AlwaysTruthy | A & ~AlwaysFalsy | B & ~AlwaysFalsy
+
+    if x or not x:
+        reveal_type(x)  # revealed: A & ~AlwaysFalsy | B & ~AlwaysFalsy | A & ~AlwaysTruthy | B & ~AlwaysTruthy
+    else:
+        reveal_type(x)  # revealed: A & ~AlwaysTruthy & ~AlwaysFalsy | B & ~AlwaysTruthy & ~AlwaysFalsy
+```
+
+### Truthiness of Types
+
+Also, types may not be Truthy. This is because `__bool__` can be customized via a metaclass.
+Although this is a very rare case, we may consider metaclass checks in the future to handle this
+more accurately.
+
+```py
+def flag() -> bool:
+    return True
+
+x = int if flag() else str
+reveal_type(x)  # revealed: Literal[int, str]
+
+if x:
+    reveal_type(x)  # revealed: Literal[int] & ~AlwaysFalsy | Literal[str] & ~AlwaysFalsy
+else:
+    reveal_type(x)  # revealed: Literal[int] & ~AlwaysTruthy | Literal[str] & ~AlwaysTruthy
+```
+
+## Determined Truthiness
+
+Some custom classes can have a boolean value that is consistently determined as either `True` or
+`False`, regardless of the instance's state. This is achieved by defining a `__bool__` method that
+always returns a fixed value.
+
+These types can always be fully narrowed in boolean contexts, as shown below:
+
+```py
+class T:
+    def __bool__(self) -> Literal[True]:
+        return True
+
+class F:
+    def __bool__(self) -> Literal[False]:
+        return False
+
+t = T()
+
+if t:
+    reveal_type(t)  # revealed: T
+else:
+    reveal_type(t)  # revealed: Never
+
+f = F()
+
+if f:
+    reveal_type(f)  # revealed: Never
+else:
+    reveal_type(f)  # revealed: F
+```
+
+## Narrowing Complex Intersection and Union
+
+```py
+class A: ...
+class B: ...
+
+def flag() -> bool:
+    return True
+
+def instance() -> A | B:
+    return A()
+
+def literals() -> Literal[0, 42, "", "hello"]:
+    return 42
+
+x = instance()
+y = literals()
+
+if isinstance(x, str) and not isinstance(x, B):
+    reveal_type(x)  # revealed: A & str & ~B
+    reveal_type(y)  # revealed: Literal[0, 42] | Literal["", "hello"]
+
+    z = x if flag() else y
+
+    reveal_type(z)  # revealed: A & str & ~B | Literal[0, 42] | Literal["", "hello"]
+
+    if z:
+        reveal_type(z)  # revealed: A & str & ~B & ~AlwaysFalsy | Literal[42] | Literal["hello"]
+    else:
+        reveal_type(z)  # revealed: A & str & ~B & ~AlwaysTruthy | Literal[0] | Literal[""]
+```
+
+## Narrowing Multiple Variables
+
+```py
+def f(x: Literal[0, 1], y: Literal["", "hello"]):
+    if x and y and not x and not y:
+        reveal_type(x)  # revealed: Never
+        reveal_type(y)  # revealed: Never
+    else:
+        # ~(x or not x) and ~(y or not y)
+        reveal_type(x)  # revealed: Literal[0, 1]
+        reveal_type(y)  # revealed: Literal["", "hello"]
+
+    if (x or not x) and (y and not y):
+        reveal_type(x)  # revealed: Literal[0, 1]
+        reveal_type(y)  # revealed: Never
+    else:
+        # ~(x or not x) or ~(y and not y)
+        reveal_type(x)  # revealed: Literal[0, 1]
+        reveal_type(y)  # revealed: Literal["", "hello"]
+```
+
+## ControlFlow Merging
+
+After merging control flows, when we take the union of all constraints applied in each branch, we
+should return to the original state.
+
+```py
+class A: ...
+
+x = A()
+
+if x and not x:
+    y = x
+    reveal_type(y)  # revealed: A & ~AlwaysFalsy & ~AlwaysTruthy
+else:
+    y = x
+    reveal_type(y)  # revealed: A & ~AlwaysTruthy | A & ~AlwaysFalsy
+
+# TODO: It should be A. We should improve UnionBuilder or IntersectionBuilder. (issue #15023)
+reveal_type(y)  # revealed: A & ~AlwaysTruthy | A & ~AlwaysFalsy
+```

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

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

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

@@ -0,0 +1,58 @@
+# Narrowing in `while` loops
+
+We only make sure that narrowing works for `while` loops in general, we do not exhaustively test all
+narrowing forms here, as they are covered in other tests.
+
+Note how type narrowing works subtly different from `if` ... `else`, because the negated constraint
+is retained after the loop.
+
+## Basic `while` loop
+
+```py
+def next_item() -> int | None: ...
+
+x = next_item()
+
+while x is not None:
+    reveal_type(x)  # revealed: int
+    x = next_item()
+
+reveal_type(x)  # revealed: None
+```
+
+## `while` loop with `else`
+
+```py
+def next_item() -> int | None: ...
+
+x = next_item()
+
+while x is not None:
+    reveal_type(x)  # revealed: int
+    x = next_item()
+else:
+    reveal_type(x)  # revealed: None
+
+reveal_type(x)  # revealed: None
+```
+
+## Nested `while` loops
+
+```py
+from typing import Literal
+
+def next_item() -> Literal[1, 2, 3]: ...
+
+x = next_item()
+
+while x != 1:
+    reveal_type(x)  # revealed: Literal[2, 3]
+
+    while x != 2:
+        # TODO: this should be Literal[1, 3]; Literal[3] is only correct
+        # in the first loop iteration
+        reveal_type(x)  # revealed: Literal[3]
+        x = next_item()
+
+    x = next_item()
+```

crates/red_knot_python_semantic/resources/mdtest/pep695_type_aliases.md

@@ -1,4 +1,11 @@
-# Type aliases
+# PEP 695 type aliases
+
+PEP 695 type aliases are only available in Python 3.12 and later:
+
+```toml
+[environment]
+python-version = "3.12"
+```
 
 ## Basic
 

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

@@ -10,10 +10,10 @@ def returns_bool() -> bool:
     return True
 
 if returns_bool():
-    copyright = 1
+    chr = 1
 
 def f():
-    reveal_type(copyright)  # revealed: Literal[copyright] | Literal[1]
+    reveal_type(chr)  # revealed: Literal[chr] | Literal[1]
 ```
 
 ## Conditionally global or builtin, with annotation
@@ -25,8 +25,8 @@ def returns_bool() -> bool:
     return True
 
 if returns_bool():
-    copyright: int = 1
+    chr: int = 1
 
 def f():
-    reveal_type(copyright)  # revealed: Literal[copyright] | int
+    reveal_type(chr)  # revealed: Literal[chr] | int
 ```

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

@@ -67,9 +67,60 @@ t[:4:0]  # error: [zero-stepsize-in-slice]
 t[0::0]  # error: [zero-stepsize-in-slice]
 t[::0]  # error: [zero-stepsize-in-slice]
 
-def int_instance() -> int: ...
-
-tuple_slice = t[int_instance() : int_instance()]
-# TODO: Support overloads... Should be `tuple[Literal[1, 'a', b"b"] | None, ...]`
-reveal_type(tuple_slice)  # revealed: @Todo(return type)
+def _(m: int, n: int):
+    tuple_slice = t[m:n]
+    # TODO: Support overloads... Should be `tuple[Literal[1, 'a', b"b"] | None, ...]`
+    reveal_type(tuple_slice)  # revealed: @Todo(return type)
+```
+
+## Inheritance
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+```py
+# TODO:
+#  * `tuple.__class_getitem__` is always bound on 3.9 (`sys.version_info`)
+#  * `tuple[int, str]` is a valid base (generics)
+# error: [call-possibly-unbound-method] "Method `__class_getitem__` of type `Literal[tuple]` is possibly unbound"
+# error: [invalid-base] "Invalid class base with type `GenericAlias` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
+class A(tuple[int, str]): ...
+
+# Runtime value: `(A, tuple, object)`
+# TODO: Generics
+reveal_type(A.__mro__)  # revealed: tuple[Literal[A], Unknown, Literal[object]]
+```
+
+## `typing.Tuple`
+
+### Correspondence with `tuple`
+
+`typing.Tuple` can be used interchangeably with `tuple`:
+
+```py
+from typing import Tuple
+
+class A: ...
+
+def _(c: Tuple, d: Tuple[int, A], e: Tuple[Any, ...]):
+    reveal_type(c)  # revealed: tuple
+    reveal_type(d)  # revealed: tuple[int, A]
+    reveal_type(e)  # revealed: @Todo(full tuple[...] support)
+```
+
+### Inheritance
+
+Inheriting from `Tuple` results in a MRO with `builtins.tuple` and `typing.Generic`. `Tuple` itself
+is not a class.
+
+```py
+from typing import Tuple
+
+class C(Tuple): ...
+
+# Runtime value: `(C, tuple, typing.Generic, object)`
+# TODO: Add `Generic` to the MRO
+reveal_type(C.__mro__)  # revealed: tuple[Literal[C], Literal[tuple], Unknown, Literal[object]]
 ```

crates/red_knot_python_semantic/resources/mdtest/suppressions/type-ignore.md

@@ -0,0 +1,128 @@
+# Suppressing errors with `type: ignore`
+
+Type check errors can be suppressed by a `type: ignore` comment on the same line as the violation.
+
+## Simple `type: ignore`
+
+```py
+a = 4 + test  # type: ignore
+```
+
+## Multiline ranges
+
+A diagnostic with a multiline range can be suppressed by a comment on the same line as the
+diagnostic's start or end. This is the same behavior as Mypy's.
+
+```py
+# fmt: off
+y = (
+    4 / 0  # type: ignore
+)
+
+y = (
+    4 /  # type: ignore
+    0
+)
+
+y = (
+    4 /
+    0  # type: ignore
+)
+```
+
+Pyright diverges from this behavior and instead applies a suppression if its range intersects with
+the diagnostic range. This can be problematic for nested expressions because a suppression in a
+child expression now suppresses errors in the outer expression.
+
+For example, the `type: ignore` comment in this example suppresses the error of adding `2` to
+`"test"` and adding `"other"` to the result of the cast.
+
+```py path=nested.py
+# fmt: off
+from typing import cast
+
+y = (
+    cast(int, "test" +
+            2 # type: ignore
+    )
+    + "other"  # TODO: expected-error[invalid-operator]
+)
+```
+
+Mypy flags the second usage.
+
+## Before opening parenthesis
+
+A suppression that applies to all errors before the opening parenthesis.
+
+```py
+a: Test = (  # type: ignore
+  Test()  # error: [unresolved-reference]
+)  # fmt: skip
+```
+
+## Multiline string
+
+```py
+a: int = 4
+a = """
+  This is a multiline string and the suppression is at its end
+"""  # type: ignore
+```
+
+## Line continuations
+
+Suppressions after a line continuation apply to all previous lines.
+
+```py
+# fmt: off
+a = test \
+  + 2  # type: ignore
+
+a = test \
+  + a \
+  + 2  # type: ignore
+```
+
+## Codes
+
+Mypy supports `type: ignore[code]`. Red Knot doesn't understand mypy's rule names. Therefore, ignore
+the codes and suppress all errors.
+
+```py
+a = test  # type: ignore[name-defined]
+```
+
+## Nested comments
+
+TODO: We should support this for better interopability with other suppression comments.
+
+```py
+# fmt: off
+# TODO this error should be suppressed
+# error: [unresolved-reference]
+a = test \
+  + 2  # fmt: skip # type: ignore
+
+a = test \
+  + 2  # type: ignore # fmt: skip
+```
+
+## Misspelled `type: ignore`
+
+```py
+# error: [unresolved-reference]
+a = test + 2  # type: ignoree
+```
+
+## Invalid - ignore on opening parentheses
+
+`type: ignore` comments after an opening parentheses suppress any type errors inside the parentheses
+in Pyright. Neither Ruff, nor mypy support this and neither does Red Knot.
+
+```py
+# fmt: off
+a = (  # type: ignore
+    test + 4  # error: [unresolved-reference]
+)
+```

crates/red_knot_python_semantic/resources/mdtest/sys_version_info.md

@@ -2,7 +2,7 @@
 
 ```toml
 [environment]
-target-version = "3.9"
+python-version = "3.9"
 ```
 
 ## The type of `sys.version_info`

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

@@ -5,10 +5,8 @@
 ```py
 class A: ...
 
-def f() -> type[A]:
-    return A
-
-reveal_type(f())  # revealed: type[A]
+def _(c: type[A]):
+    reveal_type(c)  # revealed: type[A]
 ```
 
 ## Nested class literal
@@ -17,10 +15,8 @@ reveal_type(f())  # revealed: type[A]
 class A:
     class B: ...
 
-def f() -> type[A.B]:
-    return A.B
-
-reveal_type(f())  # revealed: type[B]
+def f(c: type[A.B]):
+    reveal_type(c)  # revealed: type[B]
 ```
 
 ## Deeply nested class literal
@@ -30,10 +26,8 @@ class A:
     class B:
         class C: ...
 
-def f() -> type[A.B.C]:
-    return A.B.C
-
-reveal_type(f())  # revealed: type[C]
+def f(c: type[A.B.C]):
+    reveal_type(c)  # revealed: type[C]
 ```
 
 ## Class literal from another module
@@ -41,10 +35,8 @@ reveal_type(f())  # revealed: type[C]
 ```py
 from a import A
 
-def f() -> type[A]:
-    return A
-
-reveal_type(f())  # revealed: type[A]
+def f(c: type[A]):
+    reveal_type(c)  # revealed: type[A]
 ```
 
 ```py path=a.py
@@ -56,10 +48,8 @@ class A: ...
 ```py
 import a
 
-def f() -> type[a.B]:
-    return a.B
-
-reveal_type(f())  # revealed: type[B]
+def f(c: type[a.B]):
+    reveal_type(c)  # revealed: type[B]
 ```
 
 ```py path=a.py
@@ -71,14 +61,8 @@ class B: ...
 ```py path=a/test.py
 import a.b
 
-# TODO: no diagnostic
-# error: [unresolved-attribute]
-def f() -> type[a.b.C]:
-    # TODO: no diagnostic
-    # error: [unresolved-attribute]
-    return a.b.C
-
-reveal_type(f())  # revealed: @Todo(unsupported type[X] special form)
+def f(c: type[a.b.C]):
+    reveal_type(c)  # revealed: type[C]
 ```
 
 ```py path=a/__init__.py
@@ -88,7 +72,7 @@ reveal_type(f())  # revealed: @Todo(unsupported type[X] special form)
 class C: ...
 ```
 
-## Union of classes
+## New-style union of classes
 
 ```py
 class BasicUser: ...
@@ -98,11 +82,44 @@ class A:
     class B:
         class C: ...
 
-def get_user() -> type[BasicUser | ProUser | A.B.C]:
-    return BasicUser
+def _(u: type[BasicUser | ProUser | A.B.C]):
+    # revealed: type[BasicUser] | type[ProUser] | type[C]
+    reveal_type(u)
+```
 
-# revealed: type[BasicUser] | type[ProUser] | type[C]
-reveal_type(get_user())
+## Old-style union of classes
+
+```py
+from typing import Union
+
+class BasicUser: ...
+class ProUser: ...
+
+class A:
+    class B:
+        class C: ...
+
+def f(a: type[Union[BasicUser, ProUser, A.B.C]], b: type[Union[str]], c: type[Union[BasicUser, Union[ProUser, A.B.C]]]):
+    reveal_type(a)  # revealed: type[BasicUser] | type[ProUser] | type[C]
+    reveal_type(b)  # revealed: type[str]
+    reveal_type(c)  # revealed: type[BasicUser] | type[ProUser] | type[C]
+```
+
+## New-style and old-style unions in combination
+
+```py
+from typing import Union
+
+class BasicUser: ...
+class ProUser: ...
+
+class A:
+    class B:
+        class C: ...
+
+def f(a: type[BasicUser | Union[ProUser, A.B.C]], b: type[Union[BasicUser | Union[ProUser, A.B.C | str]]]):
+    reveal_type(a)  # revealed: type[BasicUser] | type[ProUser] | type[C]
+    reveal_type(b)  # revealed: type[BasicUser] | type[ProUser] | type[C] | type[str]
 ```
 
 ## Illegal parameters
@@ -112,6 +129,16 @@ class A: ...
 class B: ...
 
 # error: [invalid-type-form]
-def get_user() -> type[A, B]:
-    return A
+_: type[A, B]
+```
+
+## As a base class
+
+```py
+# TODO: this is a false positive
+# error: [invalid-base] "Invalid class base with type `GenericAlias` (all bases must be a class, `Any`, `Unknown` or `Todo`)"
+class Foo(type[int]): ...
+
+# TODO: should be `tuple[Literal[Foo], Literal[type], Literal[object]]
+reveal_type(Foo.__mro__)  # revealed: tuple[Literal[Foo], Unknown, Literal[object]]
 ```