Hi,
 It is a major concern that incremental build of modules may build too many files if the interface units or the included files get changed. To solve/mitigate the issue, I presented two solutions. See https://isocpp.org/files/papers/P3057R0.html <https://isocpp.org/files/papers/P3057R0.html > for details.
The demo tools in the compiler (clang) side are presented. So the build tools are able to do some simple experiments.
 Feedbacks or concerns are highly appreciated.
Thanks,
Chuanqi