Fix cv-qualifiers in std::bind invocation

PR libstdc++/68912
	* include/std/functional (_Bind::operator()): Use lvalue functor to
	deduce return type.
	* testsuite/20_util/bind/68912.cc: New.

From-SVN: r231692

libstdc++-v3/ChangeLog

@@ -1,5 +1,10 @@
 2015-12-16  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/68912
+	* include/std/functional (_Bind::operator()): Use lvalue functor to
+	deduce return type.
+	* testsuite/20_util/bind/68912.cc: New.
+
 	PR libstdc++/68921
 	* src/c++11/futex.cc
 	(__atomic_futex_unsigned_base::_M_futex_wait_until): Use null pointer

libstdc++-v3/include/std/functional

@@ -1122,7 +1122,7 @@ _GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type)
 
       // Call unqualified
       template<typename... _Args, typename _Result
-	= decltype( std::declval<_Functor>()(
+	= decltype( std::declval<_Functor&>()(
 	      _Mu<_Bound_args>()( std::declval<_Bound_args&>(),
 				  std::declval<tuple<_Args...>&>() )... ) )>
 	_Result
@@ -1136,7 +1136,7 @@ _GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type)
       // Call as const
       template<typename... _Args, typename _Result
 	= decltype( std::declval<typename enable_if<(sizeof...(_Args) >= 0),
-		       typename add_const<_Functor>::type>::type>()(
+		       typename add_const<_Functor>::type&>::type>()(
 	      _Mu<_Bound_args>()( std::declval<const _Bound_args&>(),
 				  std::declval<tuple<_Args...>&>() )... ) )>
 	_Result
@@ -1150,7 +1150,7 @@ _GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type)
       // Call as volatile
       template<typename... _Args, typename _Result
 	= decltype( std::declval<typename enable_if<(sizeof...(_Args) >= 0),
-                       typename add_volatile<_Functor>::type>::type>()(
+                       typename add_volatile<_Functor>::type&>::type>()(
 	      _Mu<_Bound_args>()( std::declval<volatile _Bound_args&>(),
 				  std::declval<tuple<_Args...>&>() )... ) )>
 	_Result
@@ -1164,7 +1164,7 @@ _GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type)
       // Call as const volatile
       template<typename... _Args, typename _Result
 	= decltype( std::declval<typename enable_if<(sizeof...(_Args) >= 0),
-                       typename add_cv<_Functor>::type>::type>()(
+                       typename add_cv<_Functor>::type&>::type>()(
 	      _Mu<_Bound_args>()( std::declval<const volatile _Bound_args&>(),
 				  std::declval<tuple<_Args...>&>() )... ) )>
 	_Result

libstdc++-v3/testsuite/20_util/bind/68912.cc

@@ -0,0 +1,53 @@
+// 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++11" }
+// { dg-do compile }
+
+#include<functional>
+
+struct Wrong {};
+struct A {};
+struct B {};
+struct C{};
+struct D{};
+
+struct X {
+  A operator()(int, double) & { return {}; }
+  Wrong operator()(int, double) && {return {}; }
+
+  B operator()(int, double) const & { return {}; }
+  Wrong operator()(int, double) const && {return {}; }
+
+  C operator()(int, double) volatile & { return {}; }
+  Wrong operator()(int, double) volatile && {return {}; }
+
+  D operator()(int, double) const volatile & { return {}; }
+  Wrong operator()(int, double) const volatile && {return {}; }
+};
+
+void test01()
+{
+  auto bound = std::bind(X{}, 5, std::placeholders::_1);
+  A res = bound(1.0);
+  const auto bound_c = bound;
+  B res_c = bound_c(1.0);
+  volatile auto bound_v = bound;
+  C res_v = bound_v(1.0);
+  volatile const auto bound_cv = bound;
+  D res_cv = bound_cv(1.0);
+}