Add a test for is_base_of and incomplete types. Because this trait uses a compiler intrinsic which was broken in many clangs, have lots of XFAILs.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@363029 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/std/utilities/meta/meta.rel/is_base_of_union.pass.cpp b/test/std/utilities/meta/meta.rel/is_base_of_union.pass.cpp
new file mode 100644
index 0000000..67cffbd
--- /dev/null
+++ b/test/std/utilities/meta/meta.rel/is_base_of_union.pass.cpp
@@ -0,0 +1,92 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// type_traits
+
+// is_base_of
+
+#include <type_traits>
+
+#include "test_macros.h"
+
+//	Clang before v9 and apple-clang up to and including v10 do not
+//  report that unions are never base classes - nor can they have bases.
+//  See https://reviews.llvm.org/D61858
+// XFAIL: apple-clang-6.0, apple-clang-7.0, apple-clang-8.0, apple-clang-9.0, apple-clang-10.0
+// XFAIL: clang-3.3, clang-3.4, clang-3.5, clang-3.6, clang-3.7, clang-3.8, clang-3.9
+// XFAIL: clang-4.0, clang-5.0, clang-6.0, clang-7.0, clang-8.0
+
+
+template <class T, class U>
+void test_is_base_of()
+{
+    static_assert((std::is_base_of<T, U>::value), "");
+    static_assert((std::is_base_of<const T, U>::value), "");
+    static_assert((std::is_base_of<T, const U>::value), "");
+    static_assert((std::is_base_of<const T, const U>::value), "");
+#if TEST_STD_VER > 14
+    static_assert((std::is_base_of_v<T, U>), "");
+    static_assert((std::is_base_of_v<const T, U>), "");
+    static_assert((std::is_base_of_v<T, const U>), "");
+    static_assert((std::is_base_of_v<const T, const U>), "");
+#endif
+}
+
+template <class T, class U>
+void test_is_not_base_of()
+{
+    static_assert((!std::is_base_of<T, U>::value), "");
+}
+
+struct B {};
+struct B1 : B {};
+struct B2 : B {};
+struct D : private B1, private B2 {};
+union U0;
+union U1 {};
+struct I0;
+struct I1 {};
+
+int main(int, char**)
+{
+//	A union is never the base class of anything (including incomplete types)
+    test_is_not_base_of<U0, B>();
+    test_is_not_base_of<U0, B1>();
+    test_is_not_base_of<U0, B2>();
+    test_is_not_base_of<U0, D>();
+    test_is_not_base_of<U1, B>();
+    test_is_not_base_of<U1, B1>();
+    test_is_not_base_of<U1, B2>();
+    test_is_not_base_of<U1, D>();
+    test_is_not_base_of<U0, I0>();
+    test_is_not_base_of<U1, I1>();
+    test_is_not_base_of<U0, U1>();
+    test_is_not_base_of<U0, int>();
+    test_is_not_base_of<U1, int>();
+    test_is_not_base_of<I0, int>();
+    test_is_not_base_of<I1, int>();
+
+//	A union never has base classes (including incomplete types)
+    test_is_not_base_of<B,  U0>();
+    test_is_not_base_of<B1, U0>();
+    test_is_not_base_of<B2, U0>();
+    test_is_not_base_of<D,  U0>();
+    test_is_not_base_of<B,  U1>();
+    test_is_not_base_of<B1, U1>();
+    test_is_not_base_of<B2, U1>();
+    test_is_not_base_of<D,  U1>();
+    test_is_not_base_of<I0, U0>();
+    test_is_not_base_of<I1, U1>();
+    test_is_not_base_of<U1, U0>();
+    test_is_not_base_of<int, U0>();
+    test_is_not_base_of<int, U1>();
+    test_is_not_base_of<int, I0>();
+    test_is_not_base_of<int, I1>();
+
+  return 0;
+}