Add <optional> header.

This patch is largely thanks to Casey Carter @ Microsoft. He did the initial
work of porting our experimental implementation and tests over to namespace
std.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@283977 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/utilities/optional/optional.object/optional.object.assign/move.pass.cpp

@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// XFAIL: libcpp-no-exceptions
+// <optional>
+
+// optional<T>& operator=(optional<T>&& rhs);
+
+#include <optional>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+using std::optional;
+
+struct X {};
+
+struct Y
+{
+    Y() = default;
+    Y& operator=(Y&&) { return *this; }
+};
+
+struct Z1
+{
+    Z1() = default;
+    Z1(Z1&&) = default;
+    Z1& operator=(Z1&&) = delete;
+};
+
+struct Z2
+{
+    Z2() = default;
+    Z2(Z2&&) = delete;
+    Z2& operator=(Z2&&) = default;
+};
+
+#if __cplusplus >= 201402
+template <class T>
+constexpr bool
+test()
+{
+    optional<T> opt;
+    optional<T> opt2;
+    opt = std::move(opt2);
+    return true;
+}
+#endif
+
+int main()
+{
+    {
+        using T = int;
+        static_assert((std::is_trivially_copy_constructible<optional<T>>::value), "");
+#if __cplusplus >= 201402
+        static_assert(test<T>(), "");
+#endif
+    }
+    {
+        using T = X;
+        static_assert((std::is_trivially_copy_constructible<optional<T>>::value), "");
+#if __cplusplus >= 201402
+        static_assert(test<T>(), "");
+#endif
+    }
+    static_assert(!(std::is_trivially_move_assignable<optional<Y>>::value), "");
+    static_assert(!(std::is_trivially_move_assignable<optional<std::string>>::value), "");
+
+    static_assert(!(std::is_move_assignable<optional<Z1>>::value), "");
+    static_assert(!(std::is_move_assignable<optional<Z2>>::value), "");
+}