Allow C/C++ coverage collection for external targets

[fmeum]

Removes hardcoded filters that result in no coverage being reported for cc_* targets in external repositories even when matched by the --instrumentation_filter.

Work towards #16228
Work towards #16208

[fmeum]

@c-mita Would you be available to review this?

The test against coverage tools seems to fail because the coverage output differs from that with the coverage tools at HEAD (the latter has branch coverage). Please let me know if you have an idea how to bridge that gap.

[fmeum]

@kshyanashree I see you assigned awaiting-user-response rather than awaiting-review, is there anything I should clarify?

[sgowroji]

Hello @fmeum, Above buildkite checks are getting failed. Could you please fix them, so that we can change it back to awaiting-review. Even after retrying the checks, they are still getting failed. Thanks!

[fmeum]

@sgowroji Yes, there are conceptual problems with the test that I have asked @c-mita about in #16261 (comment). I think that these are best solved as part of the review.

[sgowroji]

@fmeum Thank you so much for responding.

[lberki]

@c-mita can you take a look? This is coverage collection about which you know more than I do.

[c-mita]

@c-mita Would you be available to review this?

The test against coverage tools seems to fail because the coverage output differs from that with the coverage tools at HEAD (the latter has branch coverage). Please let me know if you have an idea how to bridge that gap.

There seems to be more to the failure than that; the results indicate that no output is being generated at all for the llvm tests in 18.04.

I'm not familiar with the llvm side of coverage; I don't fully understand how the tools come together here and what flags are available to control behaviour. With gcov, branch coverage has to be specifically enabled but it doesn't seem like that's an option here. Perhaps there was a change in behaviour across versions where branch coverage is only emitted for later versions?

If it's controllable with a flag then I would suggest disabling it for now purely for the sake of consistency with gcov.

[celkas]

@fmeum @c-mita Thanks for Your efforts so far. What can be done to make this happen?

[fmeum]

@c-mita I fixed the tests by copying the gcov/llvm-cov setup from other test cases. I'm a bit worried that the tests are skipped instead of running, but if so, that would be the case for basically all other coverage tests.

[c-mita]

I don't really know how to avoid that; different versions of the tools often have their little differences and it's a lot of work to keep track of and support them all.

[fmeum]

@c-mita Friendly ping

[fmeum]

@bazel-io flag

[celkas]

Thank You, @fmeum !!!