python-format-check.yml

name: Python Format Check

on:
  pull_request:
    types: [opened, reopened]

jobs:
  pre-commit:
    name: Ruff format changed files
    runs-on: ubuntu-latest
    steps:
      - name: Checkout repository
        uses: actions/checkout@v6
        with:
          fetch-depth: 0

      - name: Set up Python
        uses: actions/setup-python@v5
        with:
          python-version: "3.13"

      - name: Install pre-commit
        run: python -m pip install pre-commit==4.6.1

      - name: Check changed files
        env:
          BASE_SHA: ${{ github.event_name == 'pull_request' && github.event.pull_request.base.sha || github.event.before }}
          HEAD_SHA: ${{ github.event_name == 'pull_request' && github.event.pull_request.head.sha || github.sha }}
          DEFAULT_BRANCH: ${{ github.event.repository.default_branch }}
        run: |
          if ! git cat-file -e "${BASE_SHA}^{commit}" 2>/dev/null; then
            if git show-ref --verify --quiet "refs/remotes/origin/${DEFAULT_BRANCH}"; then
              BASE_SHA=$(git merge-base "$HEAD_SHA" "origin/${DEFAULT_BRANCH}")
            elif git cat-file -e "${HEAD_SHA}^" 2>/dev/null; then
              BASE_SHA=$(git rev-parse "${HEAD_SHA}^")
            else
              pre-commit run --all-files
              git diff --cached --exit-code
              exit 0
            fi
          fi

          pre-commit run --from-ref "$BASE_SHA" --to-ref "$HEAD_SHA"

          # The local hook formats and stages files. A clean index proves that
          # every changed Python file was already formatted before CI ran.
          git diff --cached --exit-code