[PATCH v1] libstdc++: Fix class mandate for extents.

[Luc Grosheintz]

Without would make sense to me, because whenever I wrote an
identifier with _ I felt like I was presenting the user with
a name that they shouldn't know about.

A pedantic question: Can I also fix the line below, or do
you prefer to be strict about one semantic change per commit?

On 5/15/25 2:40 PM, Tomasz Kaminski wrote:
> No strong preference, but Ville's argument sounds reasonable.
> 
> On Thu, May 15, 2025 at 12:25 PM Ville Voutilainen <
> ville.voutilainen@gmail.com> wrote:
> 
>> Mild preference against; use the names from the standard, not the
>> implementation, in such diagnostics.
>>
>> to 15. toukok. 2025 klo 13.20 Jonathan Wakely <jwakely@redhat.com>
>> kirjoitti:
>>
>>> On Thu, 15 May 2025 at 11:14, Jonathan Wakely <jwakely@redhat.com> wrote:
>>>>
>>>> On Wed, 14 May 2025 at 20:18, Luc Grosheintz <luc.grosheintz@gmail.com>
>>> wrote:
>>>>>
>>>>> The standard states that the IndexType must be a signed or unsigned
>>>>> integer. This mandate was implemented using `std::is_integral_v`.
>>> Which
>>>>> also includes (among others) char and bool, which neither signed nor
>>>>> unsigned integers.
>>>>>
>>>>> libstdc++-v3/ChangeLog:
>>>>>
>>>>>          * include/std/mdspan: Implement the mandate for extents as
>>>>>          signed or unsigned integer and not any interal type.
>>>>>          *
>>> testsuite/23_containers/mdspan/extents/class_mandates_neg.cc: Check
>>>>>          that extents<char,...> and extents<bool,...> are invalid.
>>>>>          * testsuite/23_containers/mdspan/extents/misc.cc: Update
>>>>>          tests to avoid `char` and `bool` as IndexType.
>>>>> ---
>>>>>   libstdc++-v3/include/std/mdspan                        |  3 ++-
>>>>>   .../23_containers/mdspan/extents/class_mandates_neg.cc | 10
>>> +++++++---
>>>>>   .../testsuite/23_containers/mdspan/extents/misc.cc     |  8 ++++----
>>>>>   3 files changed, 13 insertions(+), 8 deletions(-)
>>>>>
>>>>> diff --git a/libstdc++-v3/include/std/mdspan
>>> b/libstdc++-v3/include/std/mdspan
>>>>> index aee96dda7cd..22509d9c8f4 100644
>>>>> --- a/libstdc++-v3/include/std/mdspan
>>>>> +++ b/libstdc++-v3/include/std/mdspan
>>>>> @@ -163,7 +163,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>>     template<typename _IndexType, size_t... _Extents>
>>>>>       class extents
>>>>>       {
>>>>> -      static_assert(is_integral_v<_IndexType>, "_IndexType must be
>>> integral.");
>>>>> +      static_assert(__is_standard_integer<_IndexType>::value,
>>>>> +                   "_IndexType must be a signed or unsigned
>>> integer.");
>>>>
>>>> GCC's diagnostics never end with a full stop (aka period), and we
>>>> follow that convention for our static assertions.
>>>>
>>>> So I'll remove the '.' at the end of the string literal, and then push
>>>> this to trunk.
>>>>
>>>>
>>>>>         static_assert(
>>>>>            (__mdspan::__valid_static_extent<_Extents, _IndexType> &&
>>> ...),
>>>>>            "Extents must either be dynamic or representable as
>>> _IndexType");
>>>
>>> I've just noticed that this static_assert refers to "Extents" without
>>> the leading underscore, but "_IndexType" with a leading underscore.
>>>
>>> I think it's OK to omit the leading underscore, it might be a bit more
>>> user-friendly and I don't think anybody will be confused by the fact
>>> it's not identical to the real template parameter. But we should
>>> either do it consistently for _Extents and _IndexType or for neither
>>> of them.
>>>
>>> Anybody want to argue for or against underscores?
>>>
>>>
>