Move assertion from to_address to __to_address

2017-11-30  Glen Joseph Fernandes  <glenjofe@gmail.com>

	* include/bits/ptr_traits.h (__to_address, to_address): Move static
	assertion.
	* testsuite/20_util/to_address/1_neg.cc: New test.

From-SVN: r255277

libstdc++-v3/ChangeLog

+2017-11-30  Glen Joseph Fernandes  <glenjofe@gmail.com>
+
+	* include/bits/ptr_traits.h (__to_address, to_address): Move static
+	assertion.
+	* testsuite/20_util/to_address/1_neg.cc: New test.
+
 2017-11-30  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/83226

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

@@ -149,7 +149,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     constexpr _Tp*
     __to_address(_Tp* __ptr) noexcept
-    { return __ptr; }
+    {
+      static_assert(!std::is_function<_Tp>::value, "not a function pointer");
+      return __ptr;
+    }
 
 #if __cplusplus <= 201703L
   template<typename _Ptr>
@@ -177,10 +180,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     constexpr _Tp*
     to_address(_Tp* __ptr) noexcept
-    {
-      static_assert(!std::is_function_v<_Tp>, "not a pointer to function");
-      return __ptr;
-    }
+    { return std::__to_address(__ptr); }
 
   /**
    * @brief Obtain address referenced by a pointer to an object

libstdc++-v3/testsuite/20_util/to_address/1_neg.cc

+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+// { dg-error "not a function pointer" "" { target *-*-* } 153 }
+
+#include <memory>
+
+struct P
+{
+  using element_type = void();
+
+  element_type* operator->() const noexcept
+  { return nullptr; }
+};
+
+void test01()
+{
+  P p;
+  std::to_address(p); // { dg-error "required from here" }
+}