Only lcov is supported, and due to the sandboxing it's impossible to get other tools working since they always spit out extra instrumentation data that's neither cached nor available on the next sandbox.
Does blaze support code coverage properly? Does Google just not care about code coverage? Am I just missing some obvious thing in the documentation?
The most useful leads I've found so far are:
* The design doc for the (abandoned?) coverage framework [1]
* A prototype of GCOVR support [2]
* Comment on getting llvm-profdata working [3]
[1] https://docs.google.com/document/d/1-ZWHF-Q-qCKf19ik-t33ie58...
[2] https://github.com/ulfjack/bazel/commit/e9f21bbf562c1f6006eb...
[3] https://github.com/bazelbuild/bazel/issues/8178#issuecomment...
I forget the exact details but I think you can do this with a custom run_under test wrapper used during coverage. The wrapper runs your test, with whatever custom coverage system you have, then afterwards it converts to LCOV. Sometimes this might require updates to language specific rules because the test runner itself needs to be configured.
The bottom line is that Bazel upstream does not put a lot of attention into this, so it’s under developed outside of Google, because Google internal does not use the OSS rules.
The testing is not all you need to modify. You need to modify every compile and link step, since you get byproducts of the instrumentation on every step.
>Sometimes this might require updates to language specific rules because the test runner itself needs to be configured.
That's what I found, too, however I feel like rewriting the C++ rules is a huge undertaking, since they're not defined in Starlark.
I have to call bullshit on this. With C or C++ you need to build the whole project with specific compiler flags to be able to generate code coverage reports. This is not something you implement by tweaking a setting in unit tests.
Code coverage is pretty well supported in the internal ecosystem but I would not be surprised to hear this is because we designed Bazel around the system Google was already using for coverage.
What you're actually saying is that internally Google managed to get a single and very specific use case to work and forced all projects to either adopt it or have no code coverage.