While working with C++ modules, I’ve noticed there’s currently no way to
export macros from a module. Even if you wanted to opt into this, there’s
no mechanism available.

Given that macros are still essential for tasks like conditional
compilation, this feels like a limitation. While macros can be
controversial, they do help avoid repetitive and error-prone boilerplate in
certain cases.

Using headers is still an option, but it somewhat defeats the purpose of
modules since each header needs to be parsed and preprocessed for every
translation unit. PCHs can help, but they’re limited to a single PCH per
project and require additional setup.

I’d like to see a solution to this, but I’m unsure of the best path
forward. Here are a few ideas I’ve considered:
1-) Allow exporting macros from modules (perhaps with a special directive
like "#define_export").
2-) Enhance PCHs to be importable from consumed libraries. (meaning
consumers will have both their own PCH(if there is one) and also consumed
libraries' PCH precompiled)
3-) Introduce a mechanism for exporting macros from modules that are
preprocessed only once.