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.variant/variant.status/index.pass.cpp

@@ -0,0 +1,55 @@
+// -*- 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 <class ...Types> class variant;
+
+// constexpr size_t index() const noexcept;
+
+#include <cassert>
+#include <string>
+#include <type_traits>
+#include <variant>
+
+#include "archetypes.hpp"
+#include "test_macros.h"
+#include "variant_test_helpers.hpp"
+
+int main() {
+  {
+    using V = std::variant<int, ConstexprTestTypes::NoCtors>;
+    constexpr V v;
+    static_assert(v.index() == 0, "");
+  }
+  {
+    using V = std::variant<int, long>;
+    constexpr V v(std::in_place_index<1>);
+    static_assert(v.index() == 1, "");
+  }
+  {
+    using V = std::variant<int, std::string>;
+    V v("abc");
+    assert(v.index() == 1);
+    v = 42;
+    assert(v.index() == 0);
+  }
+#ifndef TEST_HAS_NO_EXCEPTIONS
+  {
+    using V = std::variant<int, MakeEmptyT>;
+    V v;
+    assert(v.index() == 0);
+    makeEmpty(v);
+    assert(v.index() == std::variant_npos);
+  }
+#endif
+}