llvm-cov: No way to exclude coverage in a line or part of code

[def-]

Bugzilla Link	34277
Version	trunk
OS	Linux
CC	@Dor1s

Extended Description

Lcov support LCOV_EXCL_LINE and LCOV_EXCL_START / LCOV_EXCL_END in order to exclude a part of the code from coverage. I couldn't find a similar mechanism for llvm-cov. This can be useful when a bug in llvm-cov prevents you from reaching an enforced 100% coverage.

[def-]

assigned to @Dor1s

[Dor1s]

I have a draft CL partially implementing this. I'm adding a new flag allowing to exclude certain files / directories using a regexp:

Also tracked as: https://bugs.chromium.org/p/chromium/issues/detail?id=816635

[Trass3r]

Apparently ignoring whole files has become possible since then: 4220f89
But still no way to exclude only a few lines.

[borrrden]

Is this going to move forward?

[carlosgalvezp]

Any updates on this issue? It seems like given that LLVM coverage is based on Source Code, it would be the best place to support source-code annotations to exclude lines from coverage.

If this is intentionally not supported, it would be great to hear the rationale for it.

[Endilll]

CC @Dor1s

[Dor1s]

I'm not working on LLVM anymore, so frankly I wouldn't be able to make any significant changes right now. That said, excluding certain lines from the report seems to be a fairly specific request. Line numbers are changing regularly, which will make any continuous config hard to maintain. If you have a decent use case for this, preprocessor macro could be used to exclude irrelevant code from the build completely. If that's not possible, I'd split the code into different files and use the -ignore-filename-regex= option.

For the original issue described by @def- , maybe you can overwrite the 100% target number to a smaller value when 100% is not possible to achieve?

[Trass3r]

Line numbers are changing regularly, which will make any continuous config hard to maintain.

That's why we want a simple code-based solution like a pragma or a comment which worked just fine for lcov. Is there anything making such an implementation hard or impossible?

preprocessor macro could be used to exclude irrelevant code from the build completely

You mean there is an llvm-cov specific preprocessor define one could use?
Even then a comment is probably less disruptive for the code reading experience.

[carlosgalvezp]

line numbers are changing regularly

Agreed, that's why the solution should be based on adding a comment next or nearby the problematic line, like it's done for lcov.

I'd be happy to help implementing this given some pointers on where to start :) First of all it would be good to know if this is possible at all in the first place, and if there is some rationale for not having it in the original design.

[Dor1s]

I see. That makes sense. I can't help with the implementation but I agree that it might be useful to have :)

[ion1995]

Any news regarding supporting line exclusions?