[libc++] Fix PR 31938 - std::basic_string constructors use non-deductible parameter types.

Summary:
This patch fixes http://llvm.org/PR31938. The description below is copy/pasted from the bug:

The standard says:

template<class charT, class traits = char_traits<charT>,
         class Allocator = allocator<charT>>
class basic_string {
  using value_type = typename traits::char_type;
  // ...
  basic_string(const charT* s, const Allocator& a = Allocator());
};

libc++ actually chooses to declare the constructor as

  basic_string(const value_type* s, const Allocator& a = Allocator());

The implicit deduction guides from class template argument deduction make what was previously an implementation detail visible:

std::basic_string s = "foo"; // error, can't deduce charT.

The constructor in question is in the libc++ DSO, but fortunately it looks like fixing this will not result in an ABI break.


@rsmith How does this look? I did more than just the constructors mentioned in the PR, but IDK how far to take it.


Reviewers: mclow.lists, rsmith

Reviewed By: rsmith

Subscribers: cfe-commits, rsmith

Differential Revision: https://reviews.llvm.org/D29863

llvm-svn: 295393

0 files changed, 0 insertions, 0 deletions