[Bug libstdc++/79162] New: [7 Regression] [C++17] ambiguity in string assignment due to string_view overload

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79162

            Bug ID: 79162
           Summary: [7 Regression] [C++17] ambiguity in string assignment
                    due to string_view overload
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

#include <string>

int main() {
 std::string s;
 s = {"abc", 1};
}

This compiled with GCC 6, but with 7 gives:

s.cc: In function ‘int main()’:
s.cc:5:15: error: ambiguous overload for ‘operator=’ (operand types are
‘std::__cxx11::string {aka std::__cxx11::basic_string<char>}’ and
‘<brace-enclosed initializer list>’)
  s = {"abc", 1};
               ^
In file included from /home/jwakely/gcc/7/include/c++/7.0.0/string:52:0,
                 from s.cc:1:
/home/jwakely/gcc/7/include/c++/7.0.0/bits/basic_string.h:627:7: note:
candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(const
std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char;
_Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       operator=(const basic_string& __str)
       ^~~~~~~~
/home/jwakely/gcc/7/include/c++/7.0.0/bits/basic_string.h:680:7: note:
candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&
std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::operator=(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&&) [with
_CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]
       operator=(basic_string&& __str)
       ^~~~~~~~
/home/jwakely/gcc/7/include/c++/7.0.0/bits/basic_string.h:747:7: note:
candidate: std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&
std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::operator=(std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::__sv_type) [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::__sv_type = std::basic_string_view<char>]
       operator=(__sv_type __sv)
       ^~~~~~~~