Add <variant> tests but disable them for libc++

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@287728 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/variant/variant.helpers/variant_alternative.pass.cpp

@@ -0,0 +1,77 @@
+// -*- 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, c++11, c++14
+
+// <variant>
+
+// template <size_t I, class T> struct variant_alternative; // undefined
+// template <size_t I, class T> struct variant_alternative<I, const T>;
+// template <size_t I, class T> struct variant_alternative<I, volatile T>;
+// template <size_t I, class T> struct variant_alternative<I, const volatile T>;
+// template <size_t I, class T>
+//   using variant_alternative_t = typename variant_alternative<I, T>::type;
+//
+// template <size_t I, class... Types>
+//    struct variant_alternative<I, variant<Types...>>;
+
+#include <memory>
+#include <type_traits>
+#include <variant>
+
+#include "test_macros.h"
+#include "variant_test_helpers.hpp"
+
+template <class V, size_t I, class E> void test() {
+  static_assert(
+      std::is_same_v<typename std::variant_alternative<I, V>::type, E>, "");
+  static_assert(
+      std::is_same_v<typename std::variant_alternative<I, const V>::type,
+                     const E>,
+      "");
+  static_assert(
+      std::is_same_v<typename std::variant_alternative<I, volatile V>::type,
+                     volatile E>,
+      "");
+  static_assert(
+      std::is_same_v<
+          typename std::variant_alternative<I, const volatile V>::type,
+          const volatile E>,
+      "");
+  static_assert(std::is_same_v<std::variant_alternative_t<I, V>, E>, "");
+  static_assert(std::is_same_v<std::variant_alternative_t<I, const V>, const E>,
+                "");
+  static_assert(
+      std::is_same_v<std::variant_alternative_t<I, volatile V>, volatile E>,
+      "");
+  static_assert(std::is_same_v<std::variant_alternative_t<I, const volatile V>,
+                               const volatile E>,
+                "");
+}
+
+int main() {
+  {
+    using V = std::variant<int, void *, const void *, long double>;
+    test<V, 0, int>();
+    test<V, 1, void *>();
+    test<V, 2, const void *>();
+    test<V, 3, long double>();
+  }
+#if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
+  {
+    using V = std::variant<int, int &, int const &, int &&, long double>;
+    test<V, 0, int>();
+    test<V, 1, int &>();
+    test<V, 2, int const &>();
+    test<V, 3, int &&>();
+    test<V, 4, long double>();
+  }
+#endif
+}