[gcc r17-499] libstdc++: Use type_identity_t for operator<=> parameter [PR114400]

[Tomasz Kaminski]

https://gcc.gnu.org/g:bbcc9da1f026b202c692e0b47eeacd28e0c69c0d

commit r17-499-gbbcc9da1f026b202c692e0b47eeacd28e0c69c0d
Author: Tomasz Kamiński <tkaminsk@redhat.com>
Date:   Wed May 13 11:51:25 2026 +0200

    libstdc++: Use type_identity_t for operator<=> parameter [PR114400]
    
    This matches change to operator== from r14-9642-gf4605c53ea2eeaf,
    and implements exact resolution of LWG3950, "std::basic_string_view comparison
    operators are overspecified". The difference between __type_identity and
    type_identity is observable as illustrated by PR.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/114400
            * include/std/string_view (operator<=>): Use type_identity_t
            instead of __type_identity_t.
    
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
    Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>

Diff:
---
 libstdc++-v3/include/std/string_view | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/string_view b/libstdc++-v3/include/std/string_view
index 735d46f2de7f..efbf432f1129 100644
--- a/libstdc++-v3/include/std/string_view
+++ b/libstdc++-v3/include/std/string_view
@@ -621,6 +621,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // type (see N3766).
 
 #if __cpp_lib_three_way_comparison
+  // _GLIBCXX_RESOLVE_LIB_DEFECTS
+  // 3950. std::basic_string_view comparison operators are overspecified 
+
   template<typename _CharT, typename _Traits>
     [[nodiscard]]
     constexpr bool
@@ -633,7 +636,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     [[nodiscard]]
     constexpr auto
     operator<=>(basic_string_view<_CharT, _Traits> __x,
-		__type_identity_t<basic_string_view<_CharT, _Traits>> __y)
+		type_identity_t<basic_string_view<_CharT, _Traits>> __y)
     noexcept
     -> decltype(__detail::__char_traits_cmp_cat<_Traits>(0))
     { return __detail::__char_traits_cmp_cat<_Traits>(__x.compare(__y)); }