[libcxx] Constrain unique_ptr::operator=(unique_ptr<Tp, Dp>) in C++03 mode

Summary:
This patch properly constrains the converting assignment operator in C++03. It also fixes a bug where std::forward was given the wrong type.
The following two tests begin passing in C++03:

* `unique_ptr.single.asgn/move_convert.pass.cpp`
* `unique_ptr.single.asgn/move_convert13.fail.cpp`

Reviewers: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D12173

llvm-svn: 246272

1 files changed, 9 insertions, 2 deletions

diff --git a/libcxx/include/memory b/libcxx/include/memory
index 9d214beb68f..4ed33084d95 100644
--- a/libcxx/include/memory
+++ b/libcxx/include/memory
@@ -2668,10 +2668,17 @@ public:
         : __ptr_(__u->release(), _VSTD::forward<deleter_type>(__u->get_deleter())) {}
 
     template <class _Up, class _Ep>
-    _LIBCPP_INLINE_VISIBILITY unique_ptr& operator=(unique_ptr<_Up, _Ep> __u)
+    _LIBCPP_INLINE_VISIBILITY
+    typename enable_if<
+        !is_array<_Up>::value &&
+        is_convertible<typename unique_ptr<_Up, _Ep>::pointer, pointer>::value &&
+        is_assignable<deleter_type&, _Ep&>::value,
+        unique_ptr&
+    >::type
+    operator=(unique_ptr<_Up, _Ep> __u)
     {
         reset(__u.release());
-        __ptr_.second() = _VSTD::forward<deleter_type>(__u.get_deleter());
+        __ptr_.second() = _VSTD::forward<_Ep>(__u.get_deleter());
         return *this;
     }