[C++] [Modules] Conform the requirement to the suffix for interface units

[ChuanqiXu9]

Currently, clang requires the filename of interface units ends with .cppm (or .ccm, .cxxm, .c++m). However, MSVC and GCC make different choices. It will be better to make them consistent and SG15 (Tooling subgroup) are working on it.

[llvmbot]

@llvm/issue-subscribers-c-1

[llvmbot]

@llvm/issue-subscribers-clang-modules

[bjornr]

I am not sure it is correct to say these filename extensions are required. It seems cmake experimentL C++20 module support work with named module interface units that all have .cpp filename extensions. Perhaps they create temporary renamed "source" files as work-around, or is this issue solved? I use clang 10.0.2 and instructions here :
https://www.kitware.com/import-cmake-c20-modules/

[ChuanqiXu9]

not sure it is correct to say these filename extensions are required. It seems cmake experimentL C++20 module support work with named module interface units that all have .cpp filename extensions. Perhaps they create temporary renamed "source" files as work-around, or is this issue solved? I use clang 10.0.2 and instructions

This issue is not solved but it doesn't matter so much now since the build system will try to handle them.

The reason why clang want a special suffix for module interfaces is that clang want to know that we're compiling a module interface from the command line. So it is also good to pass -x c++-module explicitly in the command line for module interfaces ends with .cpp. So the build systems are able to control this.

BTW, clang10 doesn't support modules. The minimum version to support modules and clang-scan-deps is clang16.

[bjornr]

Thanks for reply!

BTW, clang10 doesn't support modules. The minimum version to support modules and clang-scan-deps is clang16.

Typo, should have been 16.0.2