GCOV parser
The behavior of this parser was informed by the following sources:
the old GcovParser class <https://github.com/gcovr/gcovr/blob/e0b7afef00123b7b6ce4f487a1c4cc9fc60528bc/gcovr/gcov.py#L239>
the Invoking Gcov section in the GCC manual (version 11) <https://gcc.gnu.org/onlinedocs/gcc-11.1.0/gcc/Invoking-Gcov.html>
the
gcov.csource code in GCC (especially for understanding the exact number format) <https://github.com/gcc-mirror/gcc/blob/releases/gcc-11.1.0/gcc/gcov.c>
Error handling
By default the parser raises an exception on unrecognized gcov output.
There are several known issues with the files generated by gcov which can be
handled by --gcov-ignore-parse-errors which are descriped here. If
no value is given to the option the value all is used the whole gcov file
is ignored if the output is not recognized.
Negative hit counts
A bug in gcov can produce negative hit values (see gcov comment) which are not accepted by default.
This behavior can be changed by using the value --gcov-ignore-parse-errors=negative_hits.warn or
--gcov-ignore-parse-errors=negative_hits.warn_once_per_file. The first form warns on every line
with a negative value the second one only once per processed file and adds a summary with the overall
issues in the file.