Add test case for PR31384

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@289774 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR31384.pass.cpp

@@ -0,0 +1,38 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <tuple>
+
+// template <class TupleLike> tuple(TupleLike&&); // libc++ extension
+
+// See llvm.org/PR31384
+
+#include <tuple>
+#include <cassert>
+
+
+int count = 0;
+
+template<class T>
+struct derived : std::tuple<T> {
+  using std::tuple<T>::tuple;
+  template<class U>
+  operator std::tuple<U>() && {
+    ++count;
+    return {};
+  }
+};
+
+int main() {
+  std::tuple<int> foo = derived<int&&>{42};
+  assert(count == 1);
+}