Re: State and plans for C++20 module support?

[Paul Smith]

On Tue, 2025-02-18 at 16:32 -0500, Zack Weinberg wrote:
> 2) Besides an "is this feature available" probe, I don't know if any
>    support for C++ 2020 modules is even *necessary*, because I don't
>    know how they work.  If any other changes are necessary, they would
>    probably need to happen in Automake and Libtool, not in Autoconf.

Definitely build systems need to be made module-aware, at some level,
for them to work correctly.

It might be helpful to read about what CMake did to enable C++ modules:

https://cmake.org/cmake/help/latest/manual/cmake-cxxmodules.7.html

You'll note they didn't implement it for makefiles :-/ :-)

There was some very experimental work done alongside GNU Make a number
of years ago, but back then it wasn't clear how we would move forward
with "module descriptions".  There were two ideas: one of them a
"scanner" which was sort of like the old makedepend or gcc -MM or
whatever that generated a description of module dependencies, and the
other an LSP-like client-server solution.

My position so far, from a GNU Make standpoint, is that it's not been
feasible to know how best to proceed, yet.  Maybe that is starting to
change and the compilers are coalescing around a solution that GNU Make
could work with.