Support for "C++20" modules

[gdelazzari]

I was wondering if there's someone else interested (or even working) on a first implementation to support the upcoming C++20 modules (not sure if they're actually part of the upcoming C++20, but seems like so). Clang is already supporting some of the syntax and stuff, I can actually compile a module and a program that imports it using such a Makefile:

program: program.cpp stuff.pcm
	clang++ -fmodules-ts -std=c++17 -fmodule-file=stuff.pcm -o program program.cpp stuff.pcm

stuff.pcm: stuff.cppm
	clang++ -fmodules-ts -std=c++17 --precompile -o stuff.pcm stuff.cppm

with import stuff; in program.cpp and export statements in stuff.cppm.

As you can see by the Makefile it's a bit cumbersome to manually handle the compilation. I know this is not yet a final implementation/feature, but I think it's something it would be cool to experiment with for small projects. A build system like Meson handling it would be amazing, build times should also improve (that's one of the promoted reasons for modules in C++).

Is there anyone else interested or someone that wants to share its opinion?

[jpakkane]

We are in the process of writing a paper to the next C++ standardisation meeting about this issue and about the changes we would like to see in the syntax (the current one makes it really hard to implement). Thus it is our hope that the user interface of modules will change so using dev cycles to add support for something that will be changed does not seem like the best use of our limited resources.

[gdelazzari]

Thanks for the information. If I may ask, what's the problem with the current syntax/what syntax would be better? I mean, what are your points?

[jpakkane]

The tl/dr version is that the model as currently defined does the same thing as FORTRAN, which is a nightmare to support in a build system.

[GunpowderGuy]

@jpakkane any updates ? has c++'s module system proposal already been stabilized ?

[GunpowderGuy]

there is an ongoing discussion at
#5024

[dcbaker]

I'm going to go ahead and close this so we can keep all of the modules discussion in the other issue.