[clang] [C++20][Modules] Load function body from the module that gives canonical decl (PR #111992)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

@ilya-biryukov I remember last time, the codes you shared to me actually based an open source project. I am wondering if you can open source some use for such projects (even for testing purpose). I think it will be pretty helpful to speedup the overall development process.

https://github.com/llvm/llvm-project/pull/111992