How to turn makefile into JSON Compilation Database?

Say we have make files (not cmake/premake/ninja etc) for our project that do work for gcc and clang. We want to generate out from them JSON Compilation Database to feed it into clang-modernize tool. How to do such thing? (is there any parser in clang infrastructure or some script with usage like make CC='cc_args.py gcc' CXX='cc_args.py g++' or some other tool)?

I have no personal experience with it but Bear seems to be targeted to your scenario. (It was linked from the clang-modernize site.)

Make has a usually-undesired feature of emitting the compiler command lines to its standard output, but in this case you can use it with a shell (and jq) pipeline. With GNU Make on Bash:

make --always-make --dry-run \
 | grep -wE 'gcc|g\+\+' \
 | grep -w '\-c' \
 | jq -nR '[inputs|{directory:".", command:., file: match(" [^ ]+$").string[1:]}]' \
 > compile_commands.json

On Windows, cmd.exe syntax is similar:

• use ^ instead of \ for line continuation
• use "-delimited strings only
• use """ to escape a " within a "-delimited string
• use ^^ to escape a ^ within a "-delimited string

However, this doesn't handle cases where the makefile recursively invokes itself (or other makefiles) in subdirectories using the -C argument.

Maybe someone is in my same situation. I have a macOS and Bear was generating an empty compile_commands.json file. They acknowledge this problem in the README and suggest to use scan-build as a workaround. Unfortunately, I was still getting an empty file. Two alternative solutions I found are:

• compiledb, which worked in my case.
• a combination of clang++ compiler's -MJ option plus sed, detailed here, that seems simple enough and easy to transform into a make target. This one I have not tested.