Had a look are the lcov, my understand is that when I comes to functions/methods, you don't have line details. You only have hits (How many tests passed by) and start line. Maybe I got it wrong.
If I'm right, then, if we would like to have the function/method level of details, we need to define what is expected in the view.
Haven't had the time to check the other coverage formats.

You only have hits (How many test passed by) and start line. Maybe I got it wrong.

I see the same and that would be much better than "nothing". Anything more would need knowledge of "where does the function/method end" and then a look in "how much lines have coverage data passed/missed", then calculate a coverage in %.

That would be even much more useful, but not sure how hard that would be to implement vs. the lcov way (... or add both with a setting/toggle what to show).

Well, it seems that the end line is never there (We could cross match with the lines if we had start and end). Finding the end line is out of scope for this project if not specified in the coverage data.

The "minimal" implementation for showing this for lcov generated data would be:

• gather all functions as presented by lcov, show below each file
• either get the data from lcov or otherwise calculate in the extension
  • for the function: lines covered / lines total
  • for the function coverage in the source: functions with at least one line covered (ideally use the information from above) / functions total