[PATCH] D83592: [Parser] Add comment to skipped regions

[Vedant Kumar via Phabricator via cfe-commits]

vsk added a comment.

> ! In D83592#2156758 <https://reviews.llvm.org/D83592#2156758>, @zequanwu wrote:
>  One way I could think is probably when we visit decl in `CounterCoverageMappingBuilder`, check for if there is `SkippedRegion` in the same line and then mark the decl range as `CodeRegion`. For the example, we will have 3 more `CodeRegion` which covers the ranges of `int x = 0`, `int y = 0` and `int z = 0`.

I don't think that will work well, because a decl can span multiple lines (which in turn can include comments).

The key issue seems to be that -- even having SourceRanges for all comments -- we don't know whether a line has non-whitespace, non-comment tokens. If it does, the line should have an execution count (and we don't even need to bother with emitting a skipped region covering the line). It sounds like we need a different hook in the preprocessor that reports SourceRanges for lines with no non-comment, non-whitespace tokens. Practically, I think this can be wired up just like a CommentHandler (maybe it could be called WhitespaceHandler?). One side-benefit of introducing a new hook like this is that coverage will handle whitespace-only lines the same way as comment-only lines.

There's probably more than one way to approach this. One thing to be aware of: llvm's LineCoverageStats class is the one responsible for determining whether a line is "mapped" (i.e. whether it has an execution count). It assumes that when a line begins with a skipped region, the subsequent portion of the line must also be skipped. If we only emit skipped regions for fully whitespace-like lines, that's fine. If not, depending on how C-style comments are handled, that may need updating.


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