Module support about fastbuild HOT 6 CLOSED

Hello

There are no specific plans to support modules at this time, though I'd certainly be interested to see how this space plays out and what potential impacts it might have on build performance.

Looking at the link you sent, it seems that it might be possible to use right now without any changes to FASTBuild, simply by specifying the correct command line options. Depending on how cumbersome that ends up being, in the future, it might be beneficial to have some of the work done automatically by FASTBuild. As the options appear somewhat experimental (and subject to change) it'd be worth waiting for that to stabilize before adding any dedicated functionality.

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Looks like C++20 modules are here, shipped in VS2022.
https://devblogs.microsoft.com/cppblog/using-cpp-modules-in-msvc-from-the-command-line-part-1/

Wondering what could it mean for FASTBuild users. 🤔

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I meanly wonder what it means when it comes to build times. Potentially, this should be a dealbreaker, making the compilation times way faster, but the current implementations are not done properly, as they can be even slower, or faster just in specific scenarios.
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1441r1.pdf

I wonder if they are approaching the order of magnitude compilation time speedup of modules we are expecting to have eventually.

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Some discussion going on on C++ tooling study group mailing list about modules and build systems.

https://lists.isocpp.org/sg15/2022/03/1255.php

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There's now a standard way of specifying source-level dependencies. From my limited understanding of modules the build system needs to do a pre-scan of every source file before the actual build, and this would be the output of that pre-scan: http://wg21.link/P1689
Apparently IDEs can take advantage of that file too, and MSVC already has support for it.
Relevant Reddit discussion: https://www.reddit.com/r/cpp/comments/s99ljm/comment/htmfyxo/?utm_source=share&utm_medium=web2x&context=3

One big expected benefit of modules besides performance is that it should remove the need to put templates in headers. The module you're referencing will just contain a serialized representation of the template that will be used to instantiate it for your specific type.
From a maintenance point of view, being able to transform a method into a templated method without having it forced up into a header sounds like a dream, and will likely make generic code much more palatable to use.

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Update: Cmake shipped official modules support about 3 months ago, so it seems that the necessary support (especially dependency scanning) has shipped in all major compilers: https://gitlab.kitware.com/cmake/cmake/-/issues/18355

And this open-source release by Microsoft seems also quite relevant: https://devblogs.microsoft.com/cppblog/open-sourcing-ifc-sdk-for-cpp-modules/

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