[libcxx-commits] [PATCH] D114311: [libcxx] Make sequential containers slightly more SFINAE-friendly during CTAD.

[Konstantin Varlamov via Phabricator via libcxx-commits]

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Disable the constructors taking `(size_type, const value_type&,
allocator_type)` if `allocator_type` is not a valid allocator.
Otherwise, these constructors are considered when resolving e.g.
`(int*, int*, NotAnAllocator())`, leading to a hard error during
instantiation. A hard error makes the Standard's requirement to not
consider deduction guides of the form `(Iterator, Iterator,
BadAllocator)` during overload resolution essentially non-functional.

The previous approach was to SFINAE away `allocator_traits`. This patch
SFINAEs away the specific constructors instead, for consistency with
`basic_string` -- see [LWG3076](wg21.link/lwg3076) which describes
a very similar problem for strings (note, however, that unlike LWG3076,
no valid constructor call is affected by the bad instantiation).

Additionally:

- fix SFINAE in `basic_string` to make sure the template parameter is deduced;
- inline the modified constructors.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D114311

Files:
  libcxx/include/__memory/allocator_traits.h
  libcxx/include/deque
  libcxx/include/forward_list
  libcxx/include/list
  libcxx/include/string
  libcxx/include/vector

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