tree 11b8ab20b6cf24f321248179491236b2a8bc5235
parent 0986caac5c7a0506a8cf17a0721bec592b33bca7
author Arthur O'Dwyer <arthur.j.odwyer@gmail.com> 1617648963 -0400
committer Copybara-Service <copybara-worker@google.com> 1618252268 -0700

[libc++] Implement D2351R0 "Mark all library static cast wrappers as [[nodiscard]]"

These [[nodiscard]] annotations are added as a conforming extension;
it's unclear whether the paper will actually be adopted and make them
mandatory, but they do seem like good ideas regardless.

https://isocpp.org/files/papers/D2351R0.pdf

This patch implements the paper's effect on:
- std::to_integer, std::to_underlying
- std::forward, std::move, std::move_if_noexcept
- std::as_const
- std::identity

The paper also affects (but libc++ does not yet have an implementation of):
- std::bit_cast

Differential Revision: https://reviews.llvm.org/D99895

GitOrigin-RevId: 4b7bad9eaea2233521a94f6b096aaa88dc584e23