Erratic coverage reports

[ErikBjare]

As has been the case for some time now, coverage is erratic.

I tried to figure out the cause, but after looking at the Makefile and CI workflow I'm not finding anything that could be the culprit (I thought it could have something to do with the cache, but now I'm not so sure since the cache keys seem to be correctly set).

Do you still not have any lead @johan-bjareholt?

[ErikBjare]

We should probably adopt the recently-announced "source-based coverage": https://blog.rust-lang.org/inside-rust/2020/11/12/source-based-code-coverage.html

Seems like support has landed in grcov.

Edit: apparently source-based coverage has a lot of benefits, like supporting proc macros: mozilla/grcov#494 (comment)

[ErikBjare]

Fixed in #192