[libcxx-commits] [PATCH] D68480: Implementation of C++20's P1135R6 for libcxx

[Martin Storsjö via Phabricator via libcxx-commits]

mstorsjo added a subscriber: mati865.
mstorsjo added a comment.

In D68480#3218277 <https://reviews.llvm.org/D68480#3218277>, @ldionne wrote:

> I will argue that breaking this ABI on Windows is not a big deal since nobody's vending libc++ on Windows. Or at least if they do, they are completely invisible to us ("us" being the people who develop libc++).
>
> Would you be willing to open a patch showing what changes are necessary for each of those? I think we can totally break the ABI on Windows since nobody's shipping it.

I would like to add some nuance to these statements here.

I do ship shared linked libc++ on Windows (as part of the llvm-mingw toolchain distribution), but without any strong ABI guarantees. Ideally ABI wouldn't break between releases, but if it does (especially in a fringe area) it's probably tolerable.

MSYS2 also ships an environment where libc++ is the standard system C++ library, linked shared. That environment is considered somewhat experimental afaik (CC @mati865), so if it breaks some package (which can be fixed by rebuilding), I think they'd consider it tolerable. If none of their packages actually have ended up using and depending on the aspects that may change (I haven't followed closely exactly how widespread it is), the ABI break should be totally transparent though.


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