Implement C++17 tuple bits. Including apply and make_from_tuple.

This patch upgrades <tuple> to be C++17 compliant by implementing:

* tuple_size_v: This was forgotten when implementing the other _v traits.
* std::apply: This was added via LFTS v1 in p0220r1.
* std::make_from_tuple: This was added in p0209r2.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@275745 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size.fail.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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... Types>
+//   class tuple_size<tuple<Types...>>
+//     : public integral_constant<size_t, sizeof...(Types)> { };
+
+// Expect failures with a reference type, pointer type, and a non-tuple type.
+
+#include <tuple>
+
+int main()
+{
+    (void)std::tuple_size<std::tuple<> &>::value; // expected-error {{implicit instantiation of undefined template}}
+    (void)std::tuple_size<int>::value; // expected-error {{implicit instantiation of undefined template}}
+    (void)std::tuple_size<std::tuple<>*>::value; // expected-error {{implicit instantiation of undefined template}}
+}

test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_v.fail.cpp

@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <tuple>
+
+// template <class T> constexpr size_t tuple_size_v = tuple_size<T>::value;
+
+// Expect failures with a reference type, pointer type, and a non-tuple type.
+
+#include <tuple>
+
+int main()
+{
+    (void)std::tuple_size_v<std::tuple<> &>; // expected-note {{requested here}}
+    (void)std::tuple_size_v<int>; // expected-note {{requested here}}
+    (void)std::tuple_size_v<std::tuple<>*>; // expected-note {{requested here}}
+    // expected-error@tuple:* 3 {{implicit instantiation of undefined template}}
+}

test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_v.pass.cpp

@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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
+
+// <tuple>
+
+// template <class T> constexpr size_t tuple_size_v = tuple_size<T>::value;
+
+#include <tuple>
+#include <utility>
+#include <array>
+
+template <class Tuple, int Expect>
+void test()
+{
+    static_assert(std::tuple_size_v<Tuple> == Expect, "");
+    static_assert(std::tuple_size_v<Tuple> == std::tuple_size<Tuple>::value, "");
+    static_assert(std::tuple_size_v<Tuple const> == std::tuple_size<Tuple>::value, "");
+    static_assert(std::tuple_size_v<Tuple volatile> == std::tuple_size<Tuple>::value, "");
+    static_assert(std::tuple_size_v<Tuple const volatile> == std::tuple_size<Tuple>::value, "");
+}
+
+int main()
+{
+    test<std::tuple<>, 0>();
+
+    test<std::tuple<int>, 1>();
+    test<std::array<int, 1>, 1>();
+
+    test<std::tuple<int, int>, 2>();
+    test<std::pair<int, int>, 2>();
+    test<std::array<int, 2>, 2>();
+
+    test<std::tuple<int, int, int>, 3>();
+    test<std::array<int, 3>, 3>();
+}