I went to add _lcov_merger as an attribute for iOS tests here bazelbuild/rules_apple#691 and there was some discussion about making this tool a late-bound attribute so we wouldn't incur overhead for this tool always. It doesn't seem like there's an API that currently allows us to do this.

There was also some discussion of if the attribute makes sense to be on every test rule or if it should be more global, maybe with a flag like --lcov_merger with this tool as the default.

I wanted to file this here so we could discuss this and unblock iOS tests supporting coverage.