PR libstdc++/85183 fix std::variant move-assignment

	PR libstdc++/85183
	* include/std/variant (_Move_assign_base::operator=): Fix incorrect
	value categories.
	* testsuite/20_util/variant/85183.cc: New.

From-SVN: r259059

libstdc++-v3/ChangeLog

+2018-04-03  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/85183
+	* include/std/variant (_Move_assign_base::operator=): Fix incorrect
+	value categories.
+	* testsuite/20_util/variant/85183.cc: New.
+
 2018-03-26  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/std/variant (__get): Qualify calls to avoid ADL.

libstdc++-v3/include/std/variant

@@ -605,13 +605,14 @@ namespace __variant
 	    if (__rhs._M_valid())
 	      {
 		static constexpr void (*_S_vtable[])(void*, void*) =
-		  { &__erased_assign<_Types&, const _Types&>... };
-		_S_vtable[__rhs._M_index](this->_M_storage(), __rhs._M_storage());
+		  { &__erased_assign<_Types&, _Types&&>... };
+		_S_vtable[__rhs._M_index]
+		  (this->_M_storage(), __rhs._M_storage());
 	      }
 	  }
 	else
 	  {
-	    _Move_assign_base __tmp(__rhs);
+	    _Move_assign_base __tmp(std::move(__rhs));
 	    this->~_Move_assign_base();
 	    __try
 	      {

libstdc++-v3/testsuite/20_util/variant/85183.cc

+// Copyright (C) 2018 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++17" }
+// { dg-do compile { target c++17 } }
+
+#include <variant>
+
+struct moveonly {
+  moveonly() noexcept { }
+  moveonly(moveonly&&) noexcept { }
+  moveonly& operator=(moveonly&&) noexcept { return *this; }
+  ~moveonly() { }
+};
+
+void
+test01()
+{
+  std::variant<moveonly> v1, v2;
+  v1 = std::move(v2); // PR libstdc++/85183
+}