[gcc r14-7255] libstdc++: Use variable template to fix -fconcepts-ts error [PR113366]

[gcc r14-7255] libstdc++: Use variable template to fix -fconcepts-ts error [PR113366]

[Jonathan Wakely]

https://gcc.gnu.org/g:6c703b4eb68cbc32de1d62e5b573cb1b9857af29

commit r14-7255-g6c703b4eb68cbc32de1d62e5b573cb1b9857af29
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Sat Jan 13 12:13:33 2024 +0000

    libstdc++: Use variable template to fix -fconcepts-ts error [PR113366]
    
    There's an error for -fconcepts-ts due to using a concept where a bool
    NTTP is required, which is fixed by using the vraiable template that
    already exists in the class scope.
    
    This doesn't fix the problem with -fconcepts-ts as changes to the
    placement of attributes is also needed.
    
    libstdc++-v3/ChangeLog:
    
            PR testsuite/113366
            * include/std/format (basic_format_arg): Use __formattable
            variable template instead of __format::__formattable_with
            concept.

Diff:
---
 libstdc++-v3/include/std/format | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 540f8b805f8..efc4a17ba36 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -3189,8 +3189,7 @@ namespace __format
 	// Format as const if possible, to reduce instantiations.
 	template<typename _Tp>
 	  using __maybe_const_t
-	    = __conditional_t<__format::__formattable_with<_Tp, _Context>,
-			      const _Tp, _Tp>;
+	    = __conditional_t<__formattable<_Tp>, const _Tp, _Tp>;
 
 	template<typename _Tq>
 	  static void
@@ -3208,7 +3207,7 @@ namespace __format
 	  explicit
 	  handle(_Tp& __val) noexcept
 	  {
-	    if constexpr (!__format::__formattable_with<const _Tp, _Context>)
+	    if constexpr (!__formattable<const _Tp>)
 	      static_assert(!is_const_v<_Tp>, "std::format argument must be "
 					      "non-const for this type");