[PATCH] libstdc++: Deduce function_ref from member object pointers.

[Tomasz Kamiński]

Implement resolution of LWG4425.

libstdc++-v3/ChangeLog:

        * include/bits/funcwrap.h (__polyfunc::__deduce_funcref):
        Adjust signature produced for member object pointers.
        * testsuite/20_util/function_ref/deduction.cc: Update tests.
---
Tested on x86_64-linux locally.

 libstdc++-v3/include/bits/funcwrap.h                     | 6 ++++--
 libstdc++-v3/testsuite/20_util/function_ref/deduction.cc | 8 ++++----
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/include/bits/funcwrap.h 
b/libstdc++-v3/include/bits/funcwrap.h
index 1a81c9a9b46..67fd591e963 100644
--- a/libstdc++-v3/include/bits/funcwrap.h
+++ b/libstdc++-v3/include/bits/funcwrap.h
@@ -546,8 +546,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        if constexpr (is_member_object_pointer_v<_Fn>)
          {
            if constexpr (is_invocable_v<_Fn, _Tr>)
-             // TODO Consider reporting issue to make this noexcept
-             return static_cast<invoke_result_t<_Fn, _Tr>(*)()>(nullptr);
+             // _GLIBCXX_RESOLVE_LIB_DEFECTS
+             // 4425. CTAD function_ref from data member pointer should produce
+             //       noexcept signature
+             return static_cast<invoke_result_t<_Fn, _Tr>(*)() 
noexcept>(nullptr);
          }
        else if constexpr (requires { typename __skip_first_arg<_Fn>::type; })
          return static_cast<__skip_first_arg<_Fn>::type*>(nullptr);
diff --git a/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc 
b/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
index 6ed2b4e5712..b034c7af072 100644
--- a/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
+++ b/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
@@ -89,13 +89,13 @@ S s{};
 const S cs{};
 
 static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, s)),
-                        function_ref<int&()>> );
+                        function_ref<int&() noexcept>> );
 static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, cs)),
-                        function_ref<const int&()>> );
+                        function_ref<const int&() noexcept>> );
 static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, &s)),
-                        function_ref<int&()>> );
+                        function_ref<int&() noexcept>> );
 static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, &cs)),
-                        function_ref<const int&()>> );
+                        function_ref<const int&() noexcept>> );
 static_assert( !deductible<&S::mem, int> );
 
 static_assert( is_same_v<decltype(function_ref(nontype<&S::f>, s)),
-- 
2.51.0