Support GCC C++20+ modules.

[Islam0mar]

This PR does the following:

• Used mapper.txt to expose .gcm location to top/down files, example:
  • mapper.txt content: hello /abs./path/to//modules/example/build/gcm.cache/hello.gcm
  • compile main with: -fmodule-mapper=/abs./path/to/mapper.txt
• Added cmake_parse_arguments as it handle arguments better.

NOTE:

• I haven't tried system modules, maybe some modifications will be needed!
• Tested with gcc-13.1.0 and clang-17.0.0

[vitaut]

Thanks for the PR. GCC C++20 modules are already supported, is there any advantage to using mapper.txt?

[Islam0mar]

You can try to compile module library in path x and use this module inside another source file in parent directory or sub directory of path x i.e different build directories. In this case the error of

error: failed to read compiled module: No such file or directory
note: compiled module file is ‘gcm.cache/~.gcm’
note: imports must be built before being imported
fatal error: returning to the gate for a mechanical issue

is shown.

when gcm.cache/~.gcm isn't in the same directory in build path, gcc can't find the location of .gcm file .

[vitaut]

You can try to compile module library in path x and use this module inside another source file in parent directory or sub directory of path x i.e different build directories

This can be solved by setting the cache path (e.g. https://stackoverflow.com/q/69549286/471164). Is there any advantage to using a mapper file?

[Islam0mar]

GCC doesn't have this option -fmodules-cache-path= this is for clang!

xmake used the same approach here.
I am assuming module file name and module name are the same.

[vitaut]

GCC doesn't have this option -fmodules-cache-path= this is for clang!

I mean that you can set the path for the cache directory with -fmodule-mapper=|@g++-mapper-server -r${MAPPER_DIR}. This seems like an easier option.

[Islam0mar]

Looks nice, but you still have to work out dependencies with foreach and maybe some name conflicts. I haven't tried that, but I may give that another try!

Feel free to close his PR.

[vitaut]

Closing then but thanks for working on this anyway!