Don't SFINAE pair's copy assignment operator in C++03 mode.

In C++03 mode evaluating the SFINAE can cause a hard error due to
access control violations. This is a problem because the SFINAE
is evaluated as soon as the class is instantiated, and not later.

llvm-svn: 276594

libcxx/include/utility

@@ -351,9 +351,13 @@ struct _LIBCPP_TYPE_VIS_ONLY pair
     typedef typename remove_reference<_T1>::type _T1Unref;
     typedef typename remove_reference<_T2>::type _T2Unref;
 
+#if !defined(_LIBCPP_CXX03_LANG)
     typedef integral_constant<bool,
            is_copy_assignable<_T1>::value
         && is_copy_assignable<_T2>::value> _CanCopyAssign;
+#else
+    typedef true_type _CanCopyAssign;
+#endif
 
     _LIBCPP_INLINE_VISIBILITY
     pair& operator=(typename conditional<_CanCopyAssign::value, pair, __nat>::type const& __p)

libcxx/test/std/utilities/utility/pairs/pairs.pair/assign_pair_cxx03.pass.cpp

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES-ANY: c++98, c++03
+
+// <utility>
+
+// template <class T1, class T2> struct pair
+
+// pair& operator=(pair const& p);
+
+#include <utility>
+#include <memory>
+#include <cassert>
+
+
+struct NonAssignable {
+  NonAssignable() {}
+private:
+  NonAssignable& operator=(NonAssignable const&);
+};
+
+int main()
+{
+    // Test that we don't constrain the assignment operator in C++03 mode.
+    // Since we don't have access control SFINAE having pair evaluate SFINAE
+    // may cause a hard error.
+    typedef std::pair<int, NonAssignable> P;
+    static_assert(std::is_copy_assignable<P>::value, "");
+}