Re: [r16-7292 Regression] FAIL: g++.dg/concepts/expression.C -std=gnu++17 (test for excess errors) on Linux/x86_64

On Fri, Feb 06, 2026 at 03:30:27AM -0500, Nathan Myers wrote:
> Fixed in 786e316de5c25a3fddeaa2003f6efb64fb5ab4a9  2026-02-06 03:25:21
> 
>     libstdc++: fix C++17 regression in concept __heterogeneous_key
> 
>     The commit 3f7905550483408a2c4c5096a1adc8d7e863eb12 defined a
>     concept using a name not defined in C++17. This is fixed by
>     using an older name.
> 
>     https://gcc.gnu.org/pipermail/gcc-patches/2026-February/707814.html
> 
>     libstdc++-v3/ChangeLog
>     	* include/bits/stl_function.h (__heterogeneous_key): Use
>     	C++17-defined remove_cvref<>::type instead.

Does that really work?

remove_cvref is also C++20 like remove_cvref_t, only __remove_cvref_t
is C++11 and later.

#ifdef __cpp_lib_remove_cvref // C++ >= 20
# if _GLIBCXX_USE_BUILTIN_TRAIT(__remove_cvref)
  template<typename _Tp>
    struct remove_cvref
    { using type = __remove_cvref(_Tp); };
# else
  template<typename _Tp>
    struct remove_cvref
    { using type = typename remove_cv<_Tp>::type; };
             
  template<typename _Tp>
    struct remove_cvref<_Tp&>
    { using type = typename remove_cv<_Tp>::type; };
    
  template<typename _Tp>
    struct remove_cvref<_Tp&&>
    { using type = typename remove_cv<_Tp>::type; };
# endif
    
  template<typename _Tp>
    using remove_cvref_t = typename remove_cvref<_Tp>::type;
  /// @}
#endif // __cpp_lib_remove_cvref

	Jakub