Thanks Ryan, that's an interesting catch! Right, there must be red blocks highlighting non-covered regions, even if it's only part of a line.

Looking at how the llvm-cov works, I'm wondering if it's the compound conditionals that contribute to the lack of region coverage, since most of the tests don't exercise the success/failure path for every conditional.

For example, the branches caused by violating the preconditions on lines 189-191 are likely to not be covered. Similarly, in the other compound conditionals (line 277-278, 28-31, 43-52, 63-70, etc), it's likely that the "some of the conditions succeed, others fail" may affect the overall coverage.

At least, based on https://clang.llvm.org/docs/SourceBasedCodeCoverage.html#interpreting-reports

So I also don't know how we'd report this, since the condition itself is covered, just the implicit short-circuits aren't.

I have one idea to try, let me check that.

Didn't work out :( I've tried removing https://cs.chromium.org/chromium/src/build/config/coverage/BUILD.gn?sq=package:chromium&dr&g=0&l=19

Needs more thinking / investigating.

Here's perhaps a simpler example for testing:

https://chromium-coverage.appspot.com/reports/559420/linux/chromium/src/net/der/tag.cc.html

The coverage summary - https://chromium-coverage.appspot.com/reports/559420/linux/chromium/src/net/der/report.html - reports 100% Line and 100% function, but only 11/17 regions covered.

That's a perfect example! Thanks, Ryan!

I'm a bit confused by region coverage. Do we get confused by DCHECKs or UMA macros?
Here's an example:
https://chromium-coverage.appspot.com/reports/561573/linux/chromium/src/components/subresource_filter/content/browser/subframe_navigation_filtering_throttle.cc.html

There are two lines missing, which correspond to two missing regions. That leaves 14 missing regions that I need to search for. Since every other line is covered, I assumed that compound conditionals are what I need to look for. However, there are not really any that I saw from a quick read-through.

Where are those 14 regions?

Sorry, technically there are 4 lines missing if you count {}s, but it should still account for only two regions.

Thanks for the example, csharrison@!

This issue is on my radar, I'll look into that once I can.