compile_commands.json is used by LSPs (e.g. `clangd` in VS Code) for
code navigation. `merge-compdb.py`, called by `configure.py`, merges
these files from Scylla, Seastar, and Abseil. The script filters
entries by checking the output attribute against a given prefix. This
is needed because Scylla’s compile_commands.json is generated by Ninja
and includes all build modes, in case the user specified multiple
ones in the call to configure.py. Seastar and Abseil databases,
generated by CMake, used to omit the output attribute, so filtering
did not apply. Starting with `CMake 3.20+`, output attributes are now
included and do not match the expected prefix. For example, they
could be of the form
`absl/synchronization/CMakeFiles/synchronization.dir/internal/futex_waiter.cc.o`.
This causes relevant entries from Seastar and Abseil to be filtered out.
This patch refactors `merge-compdb.py` to allow specifying an
optional prefix per input file, preserving the intent of applying
the output filtering logic only for ninja-generated
Scylla compdb file.
Closesscylladb/scylladb#24211
0443081b0d