ci: Collect code coverage in tests

This adds the necessary infrastructure to collect
code coverage in CI, which could be useful to look
at munually or track consistently via something like
codecov.

Co-authored-by: Jade Lovelace <lix@jade.fyi>

.github/workflows/ci.yml

@@ -29,18 +29,21 @@ jobs:
           - scenario: on ubuntu
             runs-on: ubuntu-24.04
             os: linux
-            sanitizers: false
+            instrumented: false
             primary: true
+            stdenv: stdenv
           - scenario: on macos
             runs-on: macos-14
             os: darwin
-            sanitizers: false
+            instrumented: false
             primary: true
-          - scenario: on ubuntu (with sanitizers)
+            stdenv: stdenv
+          - scenario: on ubuntu (with sanitizers / coverage)
             runs-on: ubuntu-24.04
             os: linux
-            sanitizers: true
+            instrumented: true
             primary: false
+            stdenv: clangStdenv
     name: tests ${{ matrix.scenario }}
     runs-on: ${{ matrix.runs-on }}
     timeout-minutes: 60
@@ -63,13 +66,28 @@ jobs:
       if: matrix.os == 'linux'
     - name: Run component tests
       run: |
-        nix build --file ci/gha/tests componentTests -L \
-          --arg withSanitizers ${{ matrix.sanitizers }}
+        nix build --file ci/gha/tests/wrapper.nix componentTests -L \
+          --arg withInstrumentation ${{ matrix.instrumented }} \
+          --argstr stdenv "${{ matrix.stdenv }}"
     - name: Run flake checks and prepare the installer tarball
       run: |
         ci/gha/tests/build-checks
         ci/gha/tests/prepare-installer-for-github-actions
       if: ${{ matrix.primary }}
+    - name: Collect code coverage
+      run: |
+        nix build --file ci/gha/tests/wrapper.nix codeCoverage.coverageReports -L \
+          --arg withInstrumentation ${{ matrix.instrumented }} \
+          --argstr stdenv "${{ matrix.stdenv }}" \
+          --out-link coverage-reports
+        cat coverage-reports/index.txt >> $GITHUB_STEP_SUMMARY
+      if: ${{ matrix.instrumented }}
+    - name: Upload coverage reports
+      uses: actions/upload-artifact@v4
+      with:
+        name: coverage-reports
+        path: coverage-reports/
+      if: ${{ matrix.instrumented }}
     - name: Upload installer tarball
       uses: actions/upload-artifact@v4
       with: