feat(coprocessor): add cargo-llvm-cov code coverage to Rust CI workflows

.github/workflows/coprocessor-cargo-tests.yml

@@ -39,6 +39,7 @@ jobs:
       contents: 'read' # Required to checkout repository code
       checks: 'write' # Required to create GitHub checks for test results
       packages: 'read' # Required to read GitHub packages/container registry
+      pull-requests: 'write' # Required to post coverage comment on PR
     runs-on: large_ubuntu_16
     steps:
     - name: Checkout code
@@ -50,10 +51,16 @@ jobs:
     - name: Checkout LFS objects
       run: git lfs checkout
 
+    - name: Setup Rust toolchain file
+      run: cp coprocessor/fhevm-engine/rust-toolchain.toml .
+
     - name: Setup Rust
-      uses: dtolnay/rust-toolchain@a54c7afa936fefeb4456b2dd8068152669aa8203
+      uses: dsherret/rust-toolchain-file@3551321aa44dd44a0393eb3b6bdfbc5d25ecf621 # v1
+
+    - name: Install cargo-llvm-cov
+      uses: taiki-e/install-action@a37010ded18ff788be4440302bd6830b1ae50d8b # v2.68.25
       with:
-        toolchain: stable
+        tool: cargo-llvm-cov
 
     - name: Install cargo dependencies
       run: |
@@ -71,8 +78,8 @@ jobs:
           ~/.cargo/registry
           ~/.cargo/git
           target
-        key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
-        restore-keys: ${{ runner.os }}-cargo-
+        key: ${{ runner.os }}-cargo-coverage-${{ hashFiles('**/Cargo.lock') }}
+        restore-keys: ${{ runner.os }}-cargo-coverage-
 
     - name: Login to GitHub Container Registry
       uses: docker/login-action@9780b0c442fbb1117ed29e0efdff1e18412f7567 # v3.3.0
@@ -101,7 +108,90 @@ jobs:
       run: |
         docker run --rm -d -p 4566:4566 --name localstack localstack/localstack:latest
 
-    - name: Run tests
+    - name: Clean previous coverage data
+      run: cargo llvm-cov clean --workspace --profile coverage
+      working-directory: coprocessor/fhevm-engine
+
+    - name: Run tests with coverage
       run: |
-        DATABASE_URL=postgresql://postgres:postgres@localhost:5432/coprocessor TEST_GLOBAL_LOCALSTACK=1 cargo test --release -- --test-threads=1
+        DATABASE_URL=postgresql://postgres:postgres@localhost:5432/coprocessor \
+        TEST_GLOBAL_LOCALSTACK=1 \
+        cargo llvm-cov --no-report --workspace --profile coverage -- --test-threads=1
       working-directory: coprocessor/fhevm-engine
+
+    - name: Generate coverage report
+      if: ${{ !cancelled() }}
+      run: |
+        if cargo llvm-cov report --profile coverage > /tmp/cov-report.txt 2>&1; then
+          REPORT=$(cat /tmp/cov-report.txt)
+        else
+          echo "cargo llvm-cov report failed:"
+          cat /tmp/cov-report.txt
+          REPORT=""
+        fi
+        {
+          echo '## Coverage: coprocessor/fhevm-engine'
+          if [ -n "$REPORT" ]; then
+            echo '```'
+            echo "$REPORT"
+            echo '```'
+          else
+            echo '*No coverage data available (tests may have failed before producing profiling data).*'
+          fi
+        } >> "$GITHUB_STEP_SUMMARY"
+        echo "$REPORT"
+      working-directory: coprocessor/fhevm-engine
+
+    - name: Export LCOV coverage data
+      if: ${{ !cancelled() }}
+      run: cargo llvm-cov report --lcov --profile coverage --output-path /tmp/lcov.info || true
+      working-directory: coprocessor/fhevm-engine
+
+    - name: Diff coverage of changed lines
+      if: ${{ !cancelled() }}
+      id: diff-cov
+      env:
+        BASE_REF: ${{ github.base_ref }}
+      run: |
+        if [ ! -f /tmp/lcov.info ]; then
+          echo "diff_pct=N/A" >> "$GITHUB_OUTPUT"
+          exit 0
+        fi
+        pip install --quiet diff-cover
+        git fetch --unshallow origin
+        git fetch origin "${BASE_REF}:refs/remotes/origin/${BASE_REF}"
+        diff-cover /tmp/lcov.info \
+          --compare-branch="origin/${BASE_REF}" \
+          --diff-range-notation='...' \
+          --format "json:/tmp/diff-cover.json,markdown:/tmp/diff-cover-report.md" \
+          --fail-under 0 || true
+        if [ -f /tmp/diff-cover.json ]; then
+          DIFF_PCT=$(python3 -c "import json; d=json.load(open('/tmp/diff-cover.json')); n=d.get('total_num_lines',0); print('N/A') if n==0 else print(f\"{d['total_percent_covered']:.1f}%\")" 2>/dev/null || echo "N/A")
+        else
+          DIFF_PCT="N/A"
+        fi
+        echo "diff_pct=${DIFF_PCT}" >> "$GITHUB_OUTPUT"
+
+    - name: Build diff coverage comment
+      if: ${{ !cancelled() }}
+      env:
+        DIFF_PCT: ${{ steps.diff-cov.outputs.diff_pct }}
+      run: |
+        {
+          echo '### Changed Lines Coverage'
+          echo "Coverage of added/modified lines: **${DIFF_PCT}**"
+          echo ''
+          if [ -f /tmp/diff-cover-report.md ]; then
+            echo '<details><summary>Per-file breakdown</summary>'
+            echo ''
+            cat /tmp/diff-cover-report.md
+            echo ''
+            echo '</details>'
+          fi
+        } | tee -a "$GITHUB_STEP_SUMMARY" > /tmp/coverage-comment.md
+
+    - name: Post coverage comment on PR
+      if: ${{ !cancelled() && github.event.pull_request.head.repo.full_name == github.repository }}
+      uses: marocchino/sticky-pull-request-comment@773744901bac0e8cbb5a0dc842800d45e9b2b405 # v2.9.4
+      with:
+        path: /tmp/coverage-comment.md

coprocessor/fhevm-engine/Cargo.toml

@@ -113,3 +113,10 @@ inherits = "release"
 opt-level = 1
 lto = false
 codegen-units = 16
+
+[profile.coverage]
+inherits = "release"
+opt-level = 1
+lto = false
+debug = 1
+codegen-units = 16

coprocessor/fhevm-engine/rust-toolchain.toml

@@ -1,2 +1,3 @@
 [toolchain]
 channel = "1.91.1"
+components = ["llvm-tools-preview"]