Since we already have fairly complicated scriptts, I figured it wouldn't
be too hard to use the gcov tools and directly parse their output. Boy
was I wrong.
The gcov intermediary format is a bit of a mess. In version 5.4, a
text-based intermediary format is written to a single .gcov file per
executable. This changed sometime before version 7.5, when it started
writing separate .gcov files per .o files. And in version 9 this
intermediary format has been entirely replaced with an incompatible json
format!
Ironically, this means the internal-only .gcda/.gcno binary format has
actually been more stable than the intermediary format.
Also there's no way to avoid temporary .gcov files generated in the
project root, which risks messing with how test.py runs parallel tests.
Fortunately this looks like it will be fixed in gcov version 9.
---
Ended up switching to lcov, which was the right way to go. lcov handles
all of the gcov parsing, provides an easily parsable output, and even
provides a set of higher-level commands to manage coverage collection
from different runs.
Since this is all provided by lcov, was able to simplify coverage.py
quite a bit. Now it just parses the .info files output by lcov.
Now coverage information can be collected if you provide the --coverage
to test.py. Internally this uses GCC's gcov instrumentation along with a
new script, coverage.py, to parse *.gcov files.
The main use for this is finding coverage info during CI runs. There's a
risk that the instrumentation may make it more difficult to debug, so I
decided to not make coverage collection enabled by default.
