[libcxx-commits] [libcxx] [libc++] Disallow character types being index types of `extents` (PR #105832)

[Nikolas Klauser via libcxx-commits]

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@@ -0,0 +1,49 @@
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// <mdspan>
+
+// template<class IndexType, size_t... Extents>
+//  class extents;
+//
+// Mandates:
+//   - IndexType is a signed or unsigned integer type, and
+//   - each element of Extents is either equal to dynamic_extent, or is representable as a value of type IndexType.
+
+#include <cstddef>
+#include <climits>
+#include <mdspan>
+
+void invalid_index_types() {
+  // expected-error-re@*:* {{static assertion failed {{.*}}extents::index_type must be a signed or unsigned integer type}}
+  [[maybe_unused]] std::extents<char, '*'> ec;
+#ifndef TEST_HAS_NO_CHAR8_T
+  // expected-error-re@*:* {{static assertion failed {{.*}}extents::index_type must be a signed or unsigned integer type}}
+  [[maybe_unused]] std::extents<char8_t, u8'*'> ec8;
+#endif
+  // expected-error-re@*:* {{static assertion failed {{.*}}extents::index_type must be a signed or unsigned integer type}}
+  [[maybe_unused]] std::extents<char16_t, u'*'> ec16;
+  // expected-error-re@*:* {{static assertion failed {{.*}}extents::index_type must be a signed or unsigned integer type}}
+  [[maybe_unused]] std::extents<char32_t, U'*'> ec32;
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  // expected-error-re@*:* {{static assertion failed {{.*}}extents::index_type must be a signed or unsigned integer type}}
+  [[maybe_unused]] std::extents<wchar_t, L'*'> ewc;
+#endif
+}
+
+void invalid_extent_values() {
+  // expected-error-re@*:* {{static assertion failed {{.*}}extents ctor: arguments must be representable as index_type and nonnegative}}
+  [[maybe_unused]] std::extents<signed char, static_cast<std::size_t>(SCHAR_MAX) + 1> esc1;
+  // expected-error-re@*:* {{static assertion failed {{.*}}extents ctor: arguments must be representable as index_type and nonnegative}}
+  [[maybe_unused]] std::extents<signed char, std::dynamic_extent - 1> esc2;
+  // expected-error-re@*:* {{static assertion failed {{.*}}extents ctor: arguments must be representable as index_type and nonnegative}}
+  [[maybe_unused]] std::extents<unsigned char, static_cast<std::size_t>(UCHAR_MAX) + 1> euc1;
+  // expected-error-re@*:* {{static assertion failed {{.*}}extents ctor: arguments must be representable as index_type and nonnegative}}
+  [[maybe_unused]] std::extents<unsigned char, std::dynamic_extent - 1> euc2;
----------------
philnik777 wrote:

```suggestion
  // expected-error-re@*:* 4 {{static assertion failed {{.*}}extents ctor: arguments must be representable as index_type and nonnegative}}
  [[maybe_unused]] std::extents<signed char, static_cast<std::size_t>(SCHAR_MAX) + 1> esc1;
  [[maybe_unused]] std::extents<signed char, std::dynamic_extent - 1> esc2;
  [[maybe_unused]] std::extents<unsigned char, static_cast<std::size_t>(UCHAR_MAX) + 1> euc1;
  [[maybe_unused]] std::extents<unsigned char, std::dynamic_extent - 1> euc2;
```
I don't know whether this is actually better. Just a thought.

https://github.com/llvm/llvm-project/pull/105832