1 files changed, 88 insertions, 0 deletions
diff --git a/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR31384.pass.cpp b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR31384.pass.cpp
new file mode 100644
index 000000000000..dd9b832423a6
--- /dev/null
+++ b/test/std/utilities/tuple/tuple.tuple/tuple.cnstr/PR31384.pass.cpp
@@ -0,0 +1,88 @@
+// -*- 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;
+
+struct Explicit {
+  Explicit() = default;
+  explicit Explicit(int) {}
+};
+
+struct Implicit {
+  Implicit() = default;
+  Implicit(int) {}
+};
+
+template<class T>
+struct Derived : std::tuple<T> {
+  using std::tuple<T>::tuple;
+  template<class U>
+  operator std::tuple<U>() && { ++count; return {}; }
+};
+
+
+template<class T>
+struct ExplicitDerived : std::tuple<T> {
+  using std::tuple<T>::tuple;
+  template<class U>
+  explicit operator std::tuple<U>() && { ++count; return {}; }
+};
+
+int main() {
+  {
+    std::tuple<Explicit> foo = Derived<int>{42}; ((void)foo);
+    assert(count == 1);
+    std::tuple<Explicit> bar(Derived<int>{42}); ((void)bar);
+    assert(count == 2);
+  }
+  count = 0;
+  {
+    std::tuple<Implicit> foo = Derived<int>{42}; ((void)foo);
+    assert(count == 1);
+    std::tuple<Implicit> bar(Derived<int>{42}); ((void)bar);
+    assert(count == 2);
+  }
+  count = 0;
+  {
+    static_assert(!std::is_convertible<
+        ExplicitDerived<int>, std::tuple<Explicit>>::value, "");
+    std::tuple<Explicit> bar(ExplicitDerived<int>{42}); ((void)bar);
+    assert(count == 1);
+  }
+  count = 0;
+  {
+    // FIXME: Libc++ incorrectly rejects this code.
+#ifndef _LIBCPP_VERSION
+    std::tuple<Implicit> foo = ExplicitDerived<int>{42}; ((void)foo);
+    static_assert(std::is_convertible<
+        ExplicitDerived<int>, std::tuple<Implicit>>::value,
+        "correct STLs accept this");
+#else
+    static_assert(!std::is_convertible<
+        ExplicitDerived<int>, std::tuple<Implicit>>::value,
+        "libc++ incorrectly rejects this");
+#endif
+    assert(count == 0);
+    std::tuple<Implicit> bar(ExplicitDerived<int>{42}); ((void)bar);
+    assert(count == 1);
+  }
+  count = 0;
+
+}