re PR libstdc++/52931 (std::hash shouldn't be defined for unknown types)

2012-04-11  Paolo Carlini  <paolo.carlini@oracle.com>

	PR libstdc++/52931
	* include/bits/functional_hash.h (struct hash): Remove definition.
	* testsuite/20_util/hash/52931.cc: New.

From-SVN: r186310

libstdc++-v3/ChangeLog

+2012-04-11  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR libstdc++/52931
+	* include/bits/functional_hash.h (struct hash): Remove definition.
+	* testsuite/20_util/hash/52931.cc: New.
+
 2012-04-11  Manuel López-Ibáñez  <manu@gcc.gnu.org>
 
 	PR 24985

libstdc++-v3/include/bits/functional_hash.h

 // functional_hash.h header -*- C++ -*-
 
-// Copyright (C) 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
+// Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012
+// 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
@@ -55,12 +56,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// Primary class template hash.
   template<typename _Tp>
-    struct hash : public __hash_base<size_t, _Tp>
-    {
-      static_assert(sizeof(_Tp) < 0,
-		    "std::hash is not specialized for this type");
-      size_t operator()(const _Tp&) const noexcept;
-    };
+    struct hash;
 
   /// Partial specializations for pointer types.
   template<typename _Tp>

libstdc++-v3/testsuite/20_util/hash/52931.cc

+// { dg-options "-std=gnu++11" }
+// { dg-do compile }
+
+// Copyright (C) 2012 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 <type_traits>
+#include <functional>
+
+class S{}; // No hash specialization
+
+template<class T>
+auto f(int) -> decltype(std::hash<T>(), std::true_type());
+
+template<class T>
+auto f(...) -> decltype(std::false_type());
+
+static_assert(!decltype(f<S>(0))::value, "");