Using colcon test --pytest-with-coverage on a CMake-based package with both Python & C++ source files

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I'm trying to generate code coverage reports. I'm running these commands in a workspace that has all repos from the master ros2.repos :

$ colcon build --packages-up-to ros2trace tracetools tracetools_launch tracetools_read tracetools_test tracetools_trace --cmake-args --no-warn-unused-cli -DCMAKE_BUILD_TYPE=Debug -DINSTALL_EXAMPLES=OFF -DSECURITY=ON --ament-cmake-args -DCMAKE_CXX_FLAGS="${CMAKE_CXX_FLAGS} --coverage" -DCMAKE_C_FLAGS="${CMAKE_C_FLAGS} --coverage"
$ colcon test --packages-select ros2trace tracetools tracetools_launch tracetools_read tracetools_test tracetools_trace --pytest-with-coverage --event-handlers console_direct+ --executor sequential

I based the above commands on the nightly_linux_coverage job's colcon build and colcon test commands (build and test), although I removed the explicit -DBUILD_TESTING=ON because one package failed (it shouldn't change anything for the packages I do want to check).

For pure Python packages (i.e. those with setup.py files), everything works. I get coverage.xml/coverage.html/etc. files in the package's build directory (build/$PACKAGE_NAME/). However, for C++ packages (using CMake) that also have Python files, I get gcov reports, but I do not get any coverage.xml/coverage.html/etc. files.

How can I do this? Maybe I'm missing something. There unfortunately does not seem to be any tutorial that covers everything for generating code coverage reports with colcon.

I'm using colcon-core 0.5.5, which does have the --pytest-with-coverage option so that the package doesn't need to explicitly declare a test dependency on pytest-cov in its setup.py, because, well, it's a CMake package, not a Python package. https://github.com/colcon/colcon-core...