coverage data file is overwritten when kcov run with --report-only option

[nailgo]

on release 38,centos,
As it is written in --help:
first run:
kcov --collect-only /tmp/kcov ./main.sh
the size of coverage.db file is 8208 byte
then run:
kcov --report-only /tmp/kcov ./main.sh
the size of coverage.db file is 16 byte
and the numbers in html report are all 0

[SimonKagstrom]

Sorry for the very late reply!

I can reproduce your problem, but I think it's limited to bash (and probably Python). It works for compiled code still. The collect-only/report-only is sort of a performance optimization, which is relevant for compiled programs, where the program execution is lightning fast compared to kcov. For bash, when running with PS4/debug trap set, the program executes at a nice slow pace anyhow, so the overhead of reporting is less.

I'm not quite sure what causes the problem for bash, but I'm inclined to think that the collect-only option can be forbidden (i.e., a nop) with the bash "engine".