[libcxx-commits] [PATCH] D143914: [libc++] Clean up pair's constructors and assignment operators

[Louis Dionne via Phabricator via libcxx-commits]

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This patch makes std::pair's constructors and assignment operators
closer to conforming in C++23. The only missing bit I am aware of
now is `reference_constructs_from_temporary_v` checks, which we
don't have the tools for yet.

This patch removes a long-standing non-standard extension where we'd
provide constructors for tuple-like types in all standard modes. The
criteria for being a tuple-like type are different from pair-like types
as introduced recently in the standard, leading to a lot of complexity
when trying to implement recent papers that touch the pair constructors.

This is technically a source break. However, we did the same removal
for tuple some years ago and didn't run into any major issues (despite
seeing a couple of breaks). I do expect that will cause a bit of breakage,
but at this point it is necessary to disentangle pair's constructors
and avoid introducing behavior that would be subtly inconsistent between
standard versions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D143914

Files:
  libcxx/docs/ReleaseNotes.rst
  libcxx/include/__tuple_dir/sfinae_helpers.h
  libcxx/include/__utility/pair.h
  libcxx/include/utility
  libcxx/test/std/utilities/utility/pairs/pairs.pair/assign.pair_like_rv.pass.cpp
  libcxx/test/std/utilities/utility/pairs/pairs.pair/assign.pair_like_rv_const.pass.cpp
  libcxx/test/std/utilities/utility/pairs/pairs.pair/ctor.pair_like.pass.cpp

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