[libcxx-commits] [libcxx] [libcxx] improves diagnostics for containers with bad value types (PR #106296)

[Christopher Di Bella via libcxx-commits]

================
@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___TYPE_TRAITS_DIAGNOSTIC_UTILITIES_H
+#define _LIBCPP___TYPE_TRAITS_DIAGNOSTIC_UTILITIES_H
+
+#include <__config>
+#include <__type_traits/is_array.h>
+#include <__type_traits/is_const.h>
+#include <__type_traits/is_reference.h>
+#include <__type_traits/is_unbounded_array.h>
+#include <__type_traits/is_void.h>
+#include <__type_traits/is_volatile.h>
+
+#pragma GCC system_header
+
+#if _LIBCPP_STD_VER >= 20
+#  define _LIBCPP_CHECK_CONTAINER_VALUE_TYPE_IS_NOT_ARRAY_BEFORE_CXX20(_Container, _Tp)
+#else
+#  define _LIBCPP_CHECK_CONTAINER_VALUE_TYPE_IS_NOT_ARRAY_BEFORE_CXX20(_Container, _Tp)                                \
+    ;                                                                                                                  \
+    static_assert(!is_array<_Tp>::value, "'std::" _Container "' cannot hold C arrays before C++20")
+#endif
+
+// Per https://eel.is/c++draft/containers#container.reqmts-64, allocator-aware containers must have an
+// allocator that meets the Cpp17Allocator requirements (https://eel.is/c++draft/allocator.requirements).
+// In particular, this means that containers should only accept non-cv-qualified object types, and
+// types that are Cpp17Erasable.
+#define _LIBCPP_CHECK_CONTAINER_VALUE_TYPE_REQUIREMENTS_BASE(_Container, _Tp)                                          \
----------------
cjdb wrote:

I think I was experimenting to identify the bare minimum for all containers, and possibly forgot about that due to the (long) weekend.

https://github.com/llvm/llvm-project/pull/106296