https://gcc.gnu.org/g:151c3837491c9cb6ccf9ff9f87707cb3f8044b38
commit r15-10610-g151c3837491c9cb6ccf9ff9f87707cb3f8044b38 Author: Patrick Palka <[email protected]> Date: Fri Dec 5 13:43:29 2025 -0500 libstdc++: Implement P2655R3 changes to common_reference bullet 1 We implement this paper as a DR against C++20 (as do MSVC and libc++). PR libstdc++/120446 libstdc++-v3/ChangeLog: * include/bits/version.def (common_reference): New. * include/bits/version.h: Regenerate. * include/std/type_traits (__glibcxx_want_common_reference): Define. (__common_reference_impl<T1, T2, 1>): Add pointer convertibility constraints as per P2655R3. * testsuite/20_util/common_reference/p2655r3.cc: New test. Reviewed-by: Tomasz Kamiński <[email protected]> Reviewed-by: Jonathan Wakely <[email protected]> (cherry picked from commit a9fd651fbb54024548158ee605eb13dce77afe26) Diff: --- libstdc++-v3/include/bits/version.def | 8 ++++++++ libstdc++-v3/include/bits/version.h | 10 ++++++++++ libstdc++-v3/include/std/type_traits | 7 +++++++ .../testsuite/20_util/common_reference/p2655r3.cc | 15 +++++++++++++++ 4 files changed, 40 insertions(+) diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def index a08b0b990b2b..d8adeed576a2 100644 --- a/libstdc++-v3/include/bits/version.def +++ b/libstdc++-v3/include/bits/version.def @@ -1693,6 +1693,14 @@ ftms = { }; }; +ftms = { + name = common_reference; + values = { + v = 202302; + cxxmin = 20; // We treat P2655R3 as a DR against C++20. + }; +}; + ftms = { name = formatters; values = { diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h index 3f1562cdc73a..000bde9f9757 100644 --- a/libstdc++-v3/include/bits/version.h +++ b/libstdc++-v3/include/bits/version.h @@ -1890,6 +1890,16 @@ #endif /* !defined(__cpp_lib_flat_set) && defined(__glibcxx_want_flat_set) */ #undef __glibcxx_want_flat_set +#if !defined(__cpp_lib_common_reference) +# if (__cplusplus >= 202002L) +# define __glibcxx_common_reference 202302L +# if defined(__glibcxx_want_all) || defined(__glibcxx_want_common_reference) +# define __cpp_lib_common_reference 202302L +# endif +# endif +#endif /* !defined(__cpp_lib_common_reference) && defined(__glibcxx_want_common_reference) */ +#undef __glibcxx_want_common_reference + #if !defined(__cpp_lib_formatters) # if (__cplusplus >= 202100L) && _GLIBCXX_HOSTED # define __glibcxx_formatters 202302L diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits index 0a402617c52d..5340941c31d5 100644 --- a/libstdc++-v3/include/std/type_traits +++ b/libstdc++-v3/include/std/type_traits @@ -41,6 +41,7 @@ #define __glibcxx_want_bool_constant #define __glibcxx_want_bounded_array_traits +#define __glibcxx_want_common_reference #define __glibcxx_want_has_unique_object_representations #define __glibcxx_want_integral_constant_callable #define __glibcxx_want_is_aggregate @@ -4128,6 +4129,12 @@ template<typename _Ret, typename _Fn, typename... _Args> template<typename _Tp1, typename _Tp2> requires is_reference_v<_Tp1> && is_reference_v<_Tp2> && requires { typename __common_ref<_Tp1, _Tp2>; } +#if __cpp_lib_common_reference // C++ >= 20 + && is_convertible_v<add_pointer_t<_Tp1>, + add_pointer_t<__common_ref<_Tp1, _Tp2>>> + && is_convertible_v<add_pointer_t<_Tp2>, + add_pointer_t<__common_ref<_Tp1, _Tp2>>> +#endif struct __common_reference_impl<_Tp1, _Tp2, 1> { using type = __common_ref<_Tp1, _Tp2>; }; diff --git a/libstdc++-v3/testsuite/20_util/common_reference/p2655r3.cc b/libstdc++-v3/testsuite/20_util/common_reference/p2655r3.cc new file mode 100644 index 000000000000..4188dd2fb29f --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/common_reference/p2655r3.cc @@ -0,0 +1,15 @@ +// P2655R3 - common_reference_t of reference_wrapper Should Be a Reference Type +// Implemented as a DR against C++20 +// { dg-do compile { target c++20 } } + +#include <type_traits> + +#if __cpp_lib_common_reference != 202302L +# error "Feature-test macro __cpp_lib_common_reference has wrong value in <type_traits>" +#endif + +struct A { }; +struct B { operator A&() const; }; + +static_assert( std::is_same_v<std::common_reference_t<A&, const B&>, A&> ); +static_assert( std::is_same_v<std::common_reference_t<const B&, A&>, A&> );
