re PR c++/80737 (variant<any> as class member resulting to compile errors)

  PR libstdc++/80737
  * include/std/variant(variant::variant): SFINAE on is_same first.
  * testsuite/20_util/variant/any.cc: test case.

From-SVN: r248548

libstdc++-v3/ChangeLog

+2017-05-20  Tim Shen  <timshen@google.com>
+
+	PR libstdc++/80737
+	* include/std/variant(variant::variant): SFINAE on is_same first.
+	* testsuite/20_util/variant/any.cc: test case.
+
 2017-05-24  Jonathan Wakely  <jwakely@redhat.com>
 
 	* src/c++11/random.cc (random_device::_M_getentropy): Use __CHAR_BIT__

libstdc++-v3/include/std/variant

@@ -936,9 +936,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       noexcept((is_nothrow_move_constructible_v<_Types> && ...)) = default;
 
       template<typename _Tp,
+	       typename = enable_if_t<!is_same_v<decay_t<_Tp>, variant>>,
 	       typename = enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
-			  && is_constructible_v<__accepted_type<_Tp&&>, _Tp&&>
-			  && !is_same_v<decay_t<_Tp>, variant>>>
+			  && is_constructible_v<__accepted_type<_Tp&&>, _Tp&&>>>
 	constexpr
 	variant(_Tp&& __t)
 	noexcept(is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp&&>)

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

+// { dg-options "-std=gnu++17" }
+// { dg-do compile }
+
+// Copyright (C) 2017 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/>.
+
+#include <any>
+#include <variant>
+
+struct A { std::variant<std::any> a; };
+
+void Bar(const A&);
+
+void Foo() {
+  A a;
+  Bar(a);
+}