coverage.yml

# if push to PR: checks the coverage vs the coverage in main
# if push to main: generates updated coverage and uploads to artifact
# the unit tests workflow tests a matrix of python versions
# but we can only feasible compare coverage on one version (3.13)

name: Coverage

on:
  workflow_call:

jobs:
  check-coverage:
    runs-on: ubuntu-latest
    steps:
      - name: checkout PR branch
        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10
        with:
          fetch-depth: 2  # https://stackoverflow.com/a/74268200
      - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405
        with:
          python-version: '3.13'
          cache: 'pip'
          cache-dependency-path: |
            pyproject.toml
            .github/workflows/requirements/unit-tests.txt

      - name: Install Python dependencies
        run: |
          pip install .
          pip install -r .github/workflows/requirements/unit-tests.txt

      - name: Download PR coverage artifact
        if: github.event_name == 'pull_request'
        id: download_pr_cov
        continue-on-error: true
        uses: actions/download-artifact@v8.0.1
        with:
          name: pr-coverage-${{ github.sha }}

      - name: Generate coverage
        run: |
          # on push to main, generate base coverage
          if [[ "${GITHUB_REF_NAME}" == "main" && "${GITHUB_EVENT_NAME}" == "push" ]]; then
            coverage run -m pytest
            coverage json -o base_coverage.json
          else
            # for PRs, generate coverage if not already downloaded
            # while the unit-tests workflow should have run before this one,
            # someone may decide to retry this workflow manually after the artifact has expired
            if [ ! -f pr_coverage.json ]; then
              coverage run -m pytest
              coverage json -o pr_coverage.json
            fi
          fi

      - name: Get merge-base of main and PR branch
        # we need this to find the correct base coverage artifact
        if: github.event_name == 'pull_request'
        run: |
          git fetch origin main
          echo "MERGE_BASE_COMMIT=$(git merge-base HEAD origin/main)" >> $GITHUB_ENV

      - name: Download base coverage artifact
        if: github.event_name == 'pull_request'
        id: download_base
        continue-on-error: true
        uses: actions/download-artifact@v8.0.1
        with:
          name: base-coverage-${{ env.MERGE_BASE_COMMIT }}

      - name: Generate fallback base coverage
        if: github.event_name == 'pull_request' && steps.download_base.outcome == 'failure'
        run: |
          git checkout $MERGE_BASE_COMMIT
          coverage run -m pytest
          coverage json -o base_coverage.json
          git checkout $GITHUB_SHA

      - name: Compare coverage and fail if decreased
        if: github.event_name == 'pull_request'
        id: compare
        run: |
          pr_pct=$(jq '.totals.percent_covered | tonumber | (. * 100 | floor) / 100' pr_coverage.json)
          base_pct=$(jq '.totals.percent_covered | tonumber | (. * 100 | floor) / 100' base_coverage.json)

          diff=$(echo "$pr_pct - $base_pct" | bc -l)
          abs_diff=$(echo "$diff" | awk '{print ($1 < 0) ? -$1 : $1}')
          rounded_diff=$(printf "%.2f" "$abs_diff")
          exit_code=0

          # fail if decreased by more than 5%
          if (( $(echo "$pr_pct < ($base_pct - 5)" | bc -l) )); then
            echo "COVERAGE_STATUS=failed" >> $GITHUB_ENV
            echo "🛑 FAIL: coverage decreased by ${rounded_diff}% — add tests 😃 (${base_pct}% -> ${pr_pct}%)" >> $GITHUB_STEP_SUMMARY
            exit_code=1
          # warning if decreased but within 5%
          elif (( $(echo "$pr_pct < $base_pct" | bc -l) )); then
            echo "COVERAGE_STATUS=warning" >> $GITHUB_ENV
            echo "⚠️ WARNING: coverage decreased by ${rounded_diff}% (${base_pct}% -> ${pr_pct}%)" >> $GITHUB_STEP_SUMMARY
          elif (( $(echo "$pr_pct > $base_pct" | bc -l) )); then
            echo "✅ PASS: coverage increased by ${rounded_diff}% (${base_pct}% -> ${pr_pct}%)" >> $GITHUB_STEP_SUMMARY
          else
            echo "✅ PASS: coverage did not change (${pr_pct}%)" >> $GITHUB_STEP_SUMMARY
          fi

          cat $GITHUB_STEP_SUMMARY
          exit $exit_code

        shell: bash

      - name: Upload base coverage artifact
        if: github.ref_name == 'main' && github.event_name == 'push'
        uses: actions/upload-artifact@v7
        with:
          name: base-coverage-${{ github.sha }}
          path: base_coverage.json