[libcxx-commits] [PATCH] D125283: reverts "[libc++] Explicitly reject `uniform_int_distribution<bool>` and `<char>`."

[Louis Dionne via Phabricator via libcxx-commits]

ldionne requested changes to this revision.
ldionne added a comment.
This revision now requires changes to proceed.

http://eel.is/c++draft/rand.req.genl#1 says that the effect of instantiating one of these templates with a type that isn't in <list-of-allowed-types> is undefined. That means it's undefined behavior, and we strive to catch cases where users rely on undefined behavior for various reasons, notably to make their code more portable (https://godbolt.org/z/E6oGjfjhP), but also because we can't guarantee what the behavior is for such inputs.

> broken a fair amount of user code.

When I tried this change internally, I did see a few breakages, but all of them were really easy to fix and made the code better. I'm curious to hear about your experience.

If you'd like to pursue this change, what I'd support is adding a escape hatch such that `__libcpp_random_is_valid_inttype<T>::value` is always `true`, and removing that after LLVM 15 has been shipped. This won't really change the fact that user's code needs to be fixed, but it will give them a bit more time to procrastinate on doing it. If that helps, I'm OK with that approach.


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https://reviews.llvm.org/D125283