[patch] libstdc++/59768 Fix std::invoke support for reference_wrappers

[Jonathan Wakely <jwakely at redhat dot com>]

My attempt to implement LWG 2219 wasn't very good and resulted in
ambiguous overloads for the testcase in PR 59768. This fixes it, and
makes sure that const reference_wrappers can be used too.

Tested powerpc64le-linux, committed to trunk.


commit 9082b4be70fe2e4993ae0c765608fcd8da544bc5
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Dec 11 19:46:49 2015 +0000

    Fix std::invoke support for reference_wrappers
    
    	PR libstdc++/59768
    	* include/std/functional (_Unwrap, __invfwd): Define.
    	(__invoke_impl): Remove reference_wrapper overloads and use __invfwd.
    	* include/std/type_traits (__result_of_memobj, __result_of_memfun):
    	Add partial specializations for const reference_wrappers and simplify.
    	* testsuite/20_util/bind/ref_neg.cc: Use dg-excess-errors.
    	* testsuite/20_util/function_objects/invoke/59768.cc: New.

diff --git a/libstdc++-v3/include/std/functional b/libstdc++-v3/include/std/functional
index f1dc839..19caa96 100644
--- a/libstdc++-v3/include/std/functional
+++ b/libstdc++-v3/include/std/functional
@@ -184,6 +184,33 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : _Weak_result_type_impl<typename remove_cv<_Functor>::type>
     { };
 
+  template<typename _Tp, typename _Up = typename decay<_Tp>::type>
+    struct _Unwrap
+    {
+      using type = _Tp&&;
+
+      // Equivalent to std::forward<_Tp>
+      static constexpr _Tp&&
+      _S_fwd(_Tp& __t) noexcept { return static_cast<_Tp&&>(__t); }
+    };
+
+  template<typename _Tp, typename _Up>
+    struct _Unwrap<_Tp, reference_wrapper<_Up>>
+    {
+      using type = _Up&;
+
+      // Get an lvalue-reference from a reference_wrapper.
+      static _Up&
+      _S_fwd(const _Tp& __t) noexcept { __t.get(); }
+    };
+
+  // Used by __invoke_impl instead of std::forward<_Tp> so that a
+  // reference_wrapper is converted to an lvalue-reference.
+  template<typename _Tp>
+    typename _Unwrap<_Tp>::type
+    __invfwd(typename remove_reference<_Tp>::type& __t) noexcept
+    { return _Unwrap<_Tp>::_S_fwd(__t); }
+
   template<typename _Res, typename _Fn, typename... _Args>
     inline _Res
     __invoke_impl(__invoke_other, _Fn&& __f, _Args&&... __args)
@@ -194,15 +221,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline _Res
     __invoke_impl(__invoke_memfun_ref, _MemFun&& __f, _Tp&& __t,
 		  _Args&&... __args)
-    noexcept(noexcept((forward<_Tp>(__t).*__f)(forward<_Args>(__args)...)))
-    { return (forward<_Tp>(__t).*__f)(forward<_Args>(__args)...); }
-
-  template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
-    inline _Res
-    __invoke_impl(__invoke_memfun_ref, _MemFun&& __f,
-		  reference_wrapper<_Tp> __t, _Args&&... __args)
-    noexcept(noexcept((__t.get().*__f)(forward<_Args>(__args)...)))
-    { return (__t.get().*__f)(forward<_Args>(__args)...); }
+    noexcept(noexcept((__invfwd<_Tp>(__t).*__f)(forward<_Args>(__args)...)))
+    { return (__invfwd<_Tp>(__t).*__f)(forward<_Args>(__args)...); }
 
   template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
     inline _Res
@@ -214,15 +234,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
     inline _Res
     __invoke_impl(__invoke_memobj_ref, _MemFun&& __f, _Tp&& __t)
-    noexcept(noexcept(forward<_Tp>(__t).*__f))
-    { return forward<_Tp>(__t).*__f; }
-
-  template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
-    inline _Res
-    __invoke_impl(__invoke_memobj_ref, _MemFun&& __f,
-		  reference_wrapper<_Tp> __t)
-    noexcept(noexcept(__t.get().*__f))
-    { return __t.get().*__f; }
+    noexcept(noexcept(__invfwd<_Tp>(__t).*__f))
+    { return __invfwd<_Tp>(__t).*__f; }
 
   template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
     inline _Res
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index e5102de..5b4d073 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2391,44 +2391,59 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // 2219.  INVOKE-ing a pointer to member with a reference_wrapper
   //        as the object expression
-  template<typename> struct reference_wrapper;
 
   template<typename _Res, typename _Class, typename _Arg>
     struct __result_of_memobj<_Res _Class::*, reference_wrapper<_Arg>>
-    : __result_of_memobj<_Res _Class::*, _Arg>
-    {
-      typedef typename
-	__result_of_memobj_ref<_Res _Class::*, _Arg&>::type type;
-    };
+    : __result_of_memobj_ref<_Res _Class::*, _Arg&>
+    { };
 
   template<typename _Res, typename _Class, typename _Arg>
     struct __result_of_memobj<_Res _Class::*, reference_wrapper<_Arg>&>
-    : __result_of_memobj<_Res _Class::*, reference_wrapper<_Arg>>
+    : __result_of_memobj_ref<_Res _Class::*, _Arg&>
+    { };
+
+  template<typename _Res, typename _Class, typename _Arg>
+    struct __result_of_memobj<_Res _Class::*, const reference_wrapper<_Arg>&>
+    : __result_of_memobj_ref<_Res _Class::*, _Arg&>
     { };
 
   template<typename _Res, typename _Class, typename _Arg>
     struct __result_of_memobj<_Res _Class::*, reference_wrapper<_Arg>&&>
-    : __result_of_memobj<_Res _Class::*, reference_wrapper<_Arg>>
+    : __result_of_memobj_ref<_Res _Class::*, _Arg&>
+    { };
+
+  template<typename _Res, typename _Class, typename _Arg>
+    struct __result_of_memobj<_Res _Class::*, const reference_wrapper<_Arg>&&>
+    : __result_of_memobj_ref<_Res _Class::*, _Arg&>
     { };
 
   template<typename _Res, typename _Class, typename _Arg, typename... _Args>
     struct __result_of_memfun<_Res _Class::*, reference_wrapper<_Arg>, _Args...>
-    : __result_of_memfun<_Res _Class::*, _Arg&, _Args...>
-    {
-      typedef typename
-	__result_of_memfun_ref<_Res _Class::*, _Arg&, _Args...>::type type;
-    };
+    : __result_of_memfun_ref<_Res _Class::*, _Arg&, _Args...>
+    { };
 
   template<typename _Res, typename _Class, typename _Arg, typename... _Args>
     struct __result_of_memfun<_Res _Class::*, reference_wrapper<_Arg>&,
 			      _Args...>
-    : __result_of_memfun<_Res _Class::*, reference_wrapper<_Arg>, _Args...>
+    : __result_of_memfun_ref<_Res _Class::*, _Arg&, _Args...>
+    { };
+
+  template<typename _Res, typename _Class, typename _Arg, typename... _Args>
+    struct __result_of_memfun<_Res _Class::*, const reference_wrapper<_Arg>&,
+			      _Args...>
+    : __result_of_memfun_ref<_Res _Class::*, _Arg&, _Args...>
     { };
 
   template<typename _Res, typename _Class, typename _Arg, typename... _Args>
     struct __result_of_memfun<_Res _Class::*, reference_wrapper<_Arg>&&,
 			      _Args...>
-    : __result_of_memfun<_Res _Class::*, reference_wrapper<_Arg>, _Args...>
+    : __result_of_memfun_ref<_Res _Class::*, _Arg&, _Args...>
+    { };
+
+  template<typename _Res, typename _Class, typename _Arg, typename... _Args>
+    struct __result_of_memfun<_Res _Class::*, const reference_wrapper<_Arg>&&,
+			      _Args...>
+    : __result_of_memfun_ref<_Res _Class::*, _Arg&, _Args...>
     { };
 
   template<bool, bool, typename _Functor, typename... _ArgTypes>
diff --git a/libstdc++-v3/testsuite/20_util/bind/ref_neg.cc b/libstdc++-v3/testsuite/20_util/bind/ref_neg.cc
index a09788a..d1edfbf 100644
--- a/libstdc++-v3/testsuite/20_util/bind/ref_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/bind/ref_neg.cc
@@ -46,14 +46,9 @@ void test02()
   const int dummy = 0;
   std::bind(Inc(), _1)(dummy);                  // { dg-error  "no match" }
   std::bind(&Inc::f, Inc(), std::ref(dummy))(); // { dg-error  "no match" }
-  // { dg-error "no match" "" { target *-*-* } 594 }
-  // { dg-error "no type" "" { target *-*-* } 237 }
 }
 
-// { dg-error "rvalue|const" "" { target *-*-* } 1024 }
-// { dg-error "rvalue|const" "" { target *-*-* } 1038 }
-// { dg-error "rvalue|const" "" { target *-*-* } 1052 }
-// { dg-error "rvalue|const" "" { target *-*-* } 1066 }
+// { dg-excess-errors "reasons for deduction/substitution failures" }
 
 int main()
 {
diff --git a/libstdc++-v3/testsuite/20_util/function_objects/invoke/59768.cc b/libstdc++-v3/testsuite/20_util/function_objects/invoke/59768.cc
new file mode 100644
index 0000000..44f1418
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/function_objects/invoke/59768.cc
@@ -0,0 +1,43 @@
+// Copyright (C) 2015 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++1z" }
+// { dg-do compile }
+
+#include <functional>
+
+struct A {
+  void foo(int n) { }
+};
+
+void
+test01()
+{
+  A a;
+  auto ref = std::ref(a);
+  std::invoke(&A::foo, ref, 100);		// lvalue
+  std::invoke(&A::foo, std::move(ref), 100);	// rvalue
+  const auto refc = std::ref(a);
+  std::invoke(&A::foo, refc, 100);		// const lvalue
+  std::invoke(&A::foo, std::move(refc), 100);	// const rvalue
+}
+
+int
+main()
+{
+  test01();
+}