coverage-pr.yml

name: Coverage (PR)

on:
  pull_request:
    types: [opened, synchronize, reopened]

permissions:
  contents: read
  pull-requests: write
  actions: read

jobs:
  cov-head:
    runs-on: ubuntu-latest
    outputs:
      pct: ${{ steps.cov.outputs.coverage }}
    steps:
      - uses: actions/checkout@v4
        with:
          ref: ${{ github.event.pull_request.head.sha }}

      - name: Cache llvm-cov build
        id: cache-llvm-cov
        uses: actions/cache@v4
        continue-on-error: false
        with:
          path: |
            ~/.cargo/bin/
            ~/.cargo/registry/index/
            ~/.cargo/registry/cache/
            ~/.cargo/git/db/
            target/
          key: ${{ runner.os }}-cargo-llvm-cov-${{ hashFiles('**/Cargo.lock') }}
          restore-keys: ${{ runner.os }}-cargo-llvm-cov

      - run: which cargo-llvm-cov || cargo install cargo-llvm-cov
      - run: rustup component add llvm-tools-preview
      - run: cargo llvm-cov --workspace --lcov --output-path lcov.info --ignore-filename-regex '^examples/'

      - name: Upload head coverage artifact (for stacked PRs)
        uses: actions/upload-artifact@v4
        with:
          name: coverage-lcov
          path: lcov.info
          retention-days: 21

      - name: Extract total coverage % (head)
        id: cov
        shell: bash
        run: |
          pct=$(awk -F: '
            /^LH:/ {lh += $2}
            /^LF:/ {lf += $2}
            END { if (lf>0) printf "%.2f", (lh/lf)*100; else print "0.00" }
          ' lcov.info)
          echo "coverage=$pct" >> "$GITHUB_OUTPUT"

  compare-and-comment:
    needs: cov-head
    runs-on: ubuntu-latest
    steps:
      # 1) Try to download base artifact from the base branch
      - name: Download base branch artifact (if present)
        id: dl
        uses: dawidd6/action-download-artifact@ac66b43f0e6a346234dd65d4d0c8fbb31cb316e5
        with:
          name: coverage-lcov
          branch: ${{ github.event.pull_request.base.ref }}
          if_no_artifact_found: ignore  # don't fail if missing

      - name: Check if base artifact was found
        id: base_art
        shell: bash
        run: |
          if [ -f "coverage-lcov/lcov.info" ]; then
            echo "found=true" >> "$GITHUB_OUTPUT"
          else
            echo "found=false" >> "$GITHUB_OUTPUT"
          fi

      # 2) Fallback: if no artifact, checkout base commit and compute base coverage here
      - name: Checkout base
        if: ${{ steps.base_art.outputs.found == 'false' }}
        uses: actions/checkout@v4
        with:
          ref: ${{ github.event.pull_request.base.sha }}

      - name: Cache llvm-cov build
        id: cache-llvm-cov
        if: ${{ steps.base_art.outputs.found == 'false' }}
        uses: actions/cache@v4
        continue-on-error: false
        with:
          path: |
            ~/.cargo/bin/
            ~/.cargo/registry/index/
            ~/.cargo/registry/cache/
            ~/.cargo/git/db/
            target/
          key: ${{ runner.os }}-cargo-llvm-cov-${{ hashFiles('**/Cargo.lock') }}
          restore-keys: ${{ runner.os }}-cargo-llvm-cov

      - name: Install cargo-llvm-cov (fallback path)
        if: ${{ steps.base_art.outputs.found == 'false' }}
        run: which cargo-llvm-cov || cargo install cargo-llvm-cov

      - name: Install llvm-tools (fallback path)
        if: ${{ steps.base_art.outputs.found == 'false' }}
        run: rustup component add llvm-tools-preview

      - name: Run base coverage (fallback path)
        if: ${{ steps.base_art.outputs.found == 'false' }}
        run: cargo llvm-cov --workspace --lcov --output-path base.lcov.info --ignore-filename-regex '^examples/'

      # 3) Extract base coverage (from artifact or from freshly computed fallback)
      - name: Extract total coverage % (base)
        id: basecov
        shell: bash
        run: |
          file="coverage-lcov/lcov.info"
          if [ "${{ steps.base_art.outputs.found }}" != "true" ]; then
            file="base.lcov.info"
          fi
          pct=$(awk -F: '
            /^LH:/ {lh += $2}
            /^LF:/ {lf += $2}
            END { if (lf>0) printf "%.2f", (lh/lf)*100; else print "0.00" }
          ' "$file")
          echo "coverage=$pct" >> "$GITHUB_OUTPUT"

      - name: Find existing coverage comment
        id: find_comment
        uses: peter-evans/find-comment@3eae4d37986fb5a8592848f6a574fdf654e61f9e
        with:
          issue-number: ${{ github.event.pull_request.number }}
          comment-author: 'github-actions[bot]'
          body-includes: '<!-- coverage-bot -->'

      - name: Comment only if head < base
        uses: actions/github-script@v7
        with:
          script: |
            const base = parseFloat(`${{ steps.basecov.outputs.coverage }}`);
            const head = parseFloat(`${{ needs.cov-head.outputs.pct }}`);
            if (!(base >= 0) || !(head >= 0)) {
              core.setFailed(`Bad coverage values. base=${base} head=${head}`);
              return;
            }
            if (head >= base) {
              core.info(`No drop (head ${head}% >= base ${base}%).`);
              return;
            }
            const delta = (head - base).toFixed(2);
            const body = `<!-- coverage-bot -->
            **Coverage (base → head):** \`${base}% → ${head}%\`  ⬇️ ${Math.abs(delta)} pp
            _Only posts when PR coverage is lower than the base branch's latest push (or freshly computed base)._
            `;
            const commentId = `${{ steps.find_comment.outputs.comment-id }}`;
            if (commentId) {
              await github.rest.issues.updateComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                comment_id: parseInt(commentId, 10),
                body
              });
            } else {
              await github.rest.issues.createComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: context.issue.number,
                body
              });
            }