How to measure code coverage

This guide shows how to enable the project’s built-in coverage targets and how to produce coverage reports manually for a subset of the code using gcovr.

Prerequisites

  • Build tools: CMake (>=3.16), Ninja (or other generator), a working C/C++ toolchain.

  • Coverage tools: gcovr (the CMake coverage helpers check for this).

Enable coverage builds

  1. Create a fresh build directory, configure CMake with the coverage option enabled and build the code:

cmake -B build-Coverage -DCMAKE_BUILD_TYPE=Debug -DMIR_ENABLE_COVERAGE=ON .
cmake --build build-Coverage

  1. Build the coverage targets. The repository defines two coverage targets when coverage is enabled:

  • coverage-html — generates an HTML report (output: build-Coverage/coverage-html/index.html).

  • coverage-xml — generates an XML report (gcovr SonarQube/Cobertura style: build-Coverage/coverage-xml.xml).

Build them with CMake or Ninja:

# build both targets
cmake --build . --target coverage-html -j
cmake --build . --target coverage-xml -j

Measure coverage manually (subset of code)

Sometimes you want to run coverage only for a small portion of the repository or avoid the CMake coverage flow. gcovr can generate HTML reports filtered to a subset of sources.

Example — generate an HTML report for WLCS tests over src/server/frontend_wayland:

# Run tests (this produces .gcda/.gcno files)
cd build-Coverage
ctest --output-on-failure --tests-regex wlcs

# Generate an HTML report for a subtree using gcovr (filter is a regex)
gcovr --html-details ../coverage-wlcs.html --root ../ --filter "../src/server/frontend_wayland"

Tips

  • If gcovr reports no coverage data, verify you built with coverage flags and that tests ran and produced .gcda/.gcno files.

  • Use --exclude to remove third-party/packaging directories from reports (e.g. --exclude '^/usr/' or --exclude '^tests/').

  • Output locations created by the CMake targets are removed by make clean (coverage outputs are marked as GENERATED by the helpers).