ci/coverage: Store coverage from main

So we can use it for posting comments on PRs

Author: bilelmoussaoui

.github/workflows/coverage.yml

@@ -9,6 +9,7 @@ permissions:
   contents: read
   pages: write
   id-token: write
+  pull-requests: write
 
 concurrency:
   group: coverage-${{ github.ref }}
@@ -78,6 +79,32 @@ jobs:
             --output-dir coverage-raw
           mv coverage-raw/lcov.info coverage-raw/openssl-async-std.info
 
+      - name: Generate coverage summary for PR comparison
+        if: github.event_name == 'pull_request'
+        run: |
+          # Merge LCOV files for summary
+          cat coverage-raw/*.info > coverage-raw/pr-combined.info
+
+          # Generate JSON summary for comparison
+          cargo tarpaulin \
+            --package oo7 \
+            --lib \
+            --no-default-features \
+            --features "tracing,tokio,native_crypto" \
+            --ignore-panics \
+            --out Json \
+            --output-dir coverage-raw \
+            --skip-clean
+
+          # Extract coverage percentage
+          python3 -c "
+          import json
+          with open('coverage-raw/tarpaulin-report.json', 'r') as f:
+              data = json.load(f)
+              coverage = data['files']['']  # This might need adjustment based on actual structure
+              print(f'PR_COVERAGE={coverage:.2f}')
+          " >> $GITHUB_ENV || echo "PR_COVERAGE=0.00" >> $GITHUB_ENV
+
       - name: Install grcov for merging coverage
         uses: taiki-e/install-action@v2
         with:
@@ -102,6 +129,110 @@ jobs:
             --ignore "**/examples/*" \
             --ignore "**/target/*"
 
+      - name: Store coverage percentage for main branch
+        if: github.ref == 'refs/heads/main' && github.event_name == 'push'
+        run: |
+          # Extract and store coverage percentage for future PR comparisons
+          CURRENT_COVERAGE=$(python3 -c "
+          import json
+          try:
+              with open('coverage-raw/tarpaulin-report.json', 'r') as f:
+                  data = json.load(f)
+                  covered = data.get('covered', 0)
+                  coverable = data.get('coverable', 1)
+                  coverage = (covered / coverable * 100) if coverable > 0 else 0
+                  print(f'{coverage:.2f}')
+          except Exception as e:
+              print('0.00')
+          " 2>/dev/null || echo "0.00")
+
+          echo "Main branch coverage: $CURRENT_COVERAGE%"
+
+          # Store in a simple text file artifact for PR comparisons
+          mkdir -p coverage-baseline
+          echo "$CURRENT_COVERAGE" > coverage-baseline/main-coverage.txt
+
+      - name: Upload baseline coverage
+        if: github.ref == 'refs/heads/main' && github.event_name == 'push'
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-baseline
+          path: coverage-baseline/main-coverage.txt
+          retention-days: 90
+
+      - name: Get main branch coverage for comparison
+        if: github.event_name == 'pull_request'
+        uses: actions/download-artifact@v4
+        with:
+          name: coverage-baseline
+          path: coverage-baseline/
+        continue-on-error: true
+
+      - name: Set main coverage for comparison
+        if: github.event_name == 'pull_request'
+        run: |
+          if [ -f coverage-baseline/main-coverage.txt ]; then
+            MAIN_COVERAGE=$(cat coverage-baseline/main-coverage.txt)
+            echo "MAIN_COVERAGE=$MAIN_COVERAGE" >> $GITHUB_ENV
+            echo "Using stored main branch coverage: $MAIN_COVERAGE%"
+          else
+            echo "MAIN_COVERAGE=0.00" >> $GITHUB_ENV
+            echo "No baseline coverage found, using 0.00%"
+          fi
+
+      - name: Post coverage comment on PR
+        if: github.event_name == 'pull_request'
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const prCoverage = parseFloat(process.env.PR_COVERAGE || '0.00');
+            const mainCoverage = parseFloat(process.env.MAIN_COVERAGE || '0.00');
+            const diff = prCoverage - mainCoverage;
+            const diffText = diff > 0 ? `+${diff.toFixed(2)}%` : `${diff.toFixed(2)}%`;
+            const emoji = diff > 0 ? '📈' : diff < 0 ? '📉' : '➡️';
+
+            const body = `## 📊 Code Coverage Report
+
+            | Metric | Value |
+            |--------|-------|
+            | **Current PR Coverage** | ${prCoverage.toFixed(2)}% |
+            | **Main Branch Coverage** | ${mainCoverage.toFixed(2)}% |
+            | **Coverage Change** | ${emoji} ${diffText} |
+
+            ${diff < -1 ? '⚠️ **Warning**: Coverage decreased by more than 1%' : ''}
+            ${diff > 1 ? '🎉 **Great**: Coverage increased by more than 1%!' : ''}
+
+            *Coverage report generated by [cargo-tarpaulin](https://github.com/xd009642/tarpaulin)*`;
+
+            // Find existing coverage comment
+            const { data: comments } = await github.rest.issues.listComments({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.issue.number,
+            });
+
+            const existingComment = comments.find(comment =>
+              comment.body.includes('## 📊 Code Coverage Report')
+            );
+
+            if (existingComment) {
+              // Update existing comment
+              await github.rest.issues.updateComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                comment_id: existingComment.id,
+                body: body
+              });
+            } else {
+              // Create new comment
+              await github.rest.issues.createComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: context.issue.number,
+                body: body
+              });
+            }
+
       - name: Upload coverage artifacts
         uses: actions/upload-artifact@v4
         with: