From 602fe15f55ea6166eeb26b3226d311eed4b55767 Mon Sep 17 00:00:00 2001
From: Eric Fiselier <eric@efcs.ca>
Date: Mon, 25 Jul 2016 02:08:55 +0000
Subject: [PATCH] Make std::is_assignable tolerate references to incomplete
 types.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@276599 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/type_traits                           | 21 +++++--------------
 .../meta.unary.prop/is_assignable.pass.cpp    |  7 +++++--
 2 files changed, 10 insertions(+), 18 deletions(-)

diff --git a/include/type_traits b/include/type_traits
index 14ed698df..0d578bbe0 100644
--- a/include/type_traits
+++ b/include/type_traits
@@ -2036,26 +2036,15 @@ template<typename, typename _Tp> struct __select_2nd { typedef _Tp type; };
 
 template <class _Tp, class _Arg>
 typename __select_2nd<decltype((_VSTD::declval<_Tp>() = _VSTD::declval<_Arg>())), true_type>::type
-#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
-__is_assignable_test(_Tp&&, _Arg&&);
-#else
-__is_assignable_test(_Tp, _Arg&);
-#endif
+__is_assignable_test(int);
+
+template <class, class>
+false_type __is_assignable_test(...);
 
-template <class _Arg>
-false_type
-#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
-__is_assignable_test(__any, _Arg&&);
-#else
-__is_assignable_test(__any, _Arg&);
-#endif
 
 template <class _Tp, class _Arg, bool = is_void<_Tp>::value || is_void<_Arg>::value>
 struct __is_assignable_imp
-    : public common_type
-        <
-            decltype(_VSTD::__is_assignable_test(declval<_Tp>(), declval<_Arg>()))
-        >::type {};
+    : public decltype((_VSTD::__is_assignable_test<_Tp, _Arg>(0))) {};
 
 template <class _Tp, class _Arg>
 struct __is_assignable_imp<_Tp, _Arg, true>
diff --git a/test/std/utilities/meta/meta.unary/meta.unary.prop/is_assignable.pass.cpp b/test/std/utilities/meta/meta.unary/meta.unary.prop/is_assignable.pass.cpp
index b734a1aa6..f4736e713 100644
--- a/test/std/utilities/meta/meta.unary/meta.unary.prop/is_assignable.pass.cpp
+++ b/test/std/utilities/meta/meta.unary/meta.unary.prop/is_assignable.pass.cpp
@@ -43,7 +43,7 @@ void test_is_not_assignable()
 
 struct D;
 
-#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
+#if TEST_STD_VER >= 11
 struct C
 {
     template <class U>
@@ -59,6 +59,8 @@ struct E
 template <typename T>
 struct X { T t; };
 
+struct Incomplete;
+
 int main()
 {
     test_is_assignable<int&, int&> ();
@@ -67,7 +69,7 @@ int main()
     test_is_assignable<B, A> ();
     test_is_assignable<void*&, void*> ();
 
-#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
+#if TEST_STD_VER >= 11
     test_is_assignable<E, int> ();
 
     test_is_not_assignable<int, int&> ();
@@ -80,4 +82,5 @@ int main()
 
 //  pointer to incomplete template type
 	test_is_assignable<X<D>*&, X<D>*> ();
+    test_is_not_assignable<Incomplete&, Incomplete const&>();
 }