Implement LWG3034: P0767R1 breaks previously-standard-layout types

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@328064 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/basic.string/char.bad.fail.cpp

@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// <string>
+//   ... manipulating sequences of any non-array trivial standard-layout types.
+
+#include <string>
+#include "test_traits.h"
+
+struct NotTrivial {
+    NotTrivial() : value(3) {}
+    int value;
+};
+
+struct NotStandardLayout {
+public:
+    NotStandardLayout() : one(1), two(2) {}
+    int sum() const { return one + two; } // silences "unused field 'two' warning"
+    int one;
+private:
+    int two;
+};
+
+int main()
+{
+    {
+//  array
+    typedef char C[3];
+    static_assert(std::is_array<C>::value, "");
+    std::basic_string<C, test_traits<C> > s;
+//  expected-error-re@string:* {{static_assert failed{{.*}} "Character type of basic_string must not be an array"}}
+    }
+
+    {
+//  not trivial
+    static_assert(!std::is_trivial<NotTrivial>::value, "");
+    std::basic_string<NotTrivial, test_traits<NotTrivial> > s;
+//  expected-error-re@string:* {{static_assert failed{{.*}} "Character type of basic_string must be trivial"}}
+    }
+
+    {
+//  not standard layout
+    static_assert(!std::is_standard_layout<NotStandardLayout>::value, "");
+    std::basic_string<NotStandardLayout, test_traits<NotStandardLayout> > s;
+//  expected-error-re@string:* {{static_assert failed{{.*}} "Character type of basic_string must be standard-layout"}}
+    }
+}