Add deduction guides for optional

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@333251 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/optional/optional.object/optional.object.ctor/deduct.fail.cpp

@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// <optional>
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// UNSUPPORTED: libcpp-no-deduction-guides
+
+
+// template<class T>
+//   optional(T) -> optional<T>;
+
+
+#include <optional>
+#include <cassert>
+
+struct A {};
+
+int main()
+{  
+//  Test the explicit deduction guides
+
+//  Test the implicit deduction guides
+    {
+//  optional()
+    std::optional opt;   // expected-error {{no viable constructor or deduction guide for deduction of template arguments of 'optional'}}
+    }
+
+    {
+//  optional(nullopt_t)
+    std::optional opt(std::nullopt);   // expected-error-re@optional:* {{static_assert failed{{.*}} "instantiation of optional with nullopt_t is ill-formed"}}
+    }
+}