You can get coverage working for almost anything by having each test convert its coverage data to LCOV before stopping, in the same sandbox as the test.

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.