Hi.

I will like to showcase my build-system HMake
https://github.com/HassanSajjad-302/HMake. Though this email is about the
HMake build-system, the header-units problem described here applies to the
other build systems as well.

It has C++20 modules and header-units support. It also supports drop-in
header-files to header-units replacement.

With it, with MSVC I compiled an SFML example with C++ 20 header-units.
https://github.com/HassanSajjad-302/SFML

HMake however has a flaw and there is no easy solution for it. To fix this,
I will like to propose a new way to compile source files.
https://github.com/HassanSajjad-302/HMake/wiki/HMake-Flaw-And-Its-Possible-Fixes

I am very confident that the adoption of this will result in flawless
module and header-unit support in HMake which will translate to a very good
user experience while converting their code base to C++20 modules.

Please share your thoughts, especially about solution 5 and the likelihood
of its implementation in the C++ compilers.

Best,
Hassan Sajjad