Re: Detect if the static keyword is supported in array type derivations in function parameters

> This is a C99 feature that helps with static analysis.
>
> >  If the keyword `static` also appears within the `[` and `]` of the arr=
ay type derivation, then for each call to the function, the value of the co=
rresponding actual argument shall provide access to the first element of an=
 array with at least as many elements as specified by the size expression.
>
> See _Array declarators_ and _Function declarators_ from the C standard.
>
> It is not supported by MSVC: [C11: static inside array parameter
> square brackets](https://developercommunity.visualstudio.com/t/C11:-stati=
c-inside-array-parameter-squar/1475168).
>
> Both gcc and clang warn if `NULL` or if an array too small is passed
> to the function. Interestingly gcc also warns in the non-static case
> if an array too small is passed. cppcheck considers in both cases that
> the array has a fixed size and warns for out-of-bounds accesses.
>
> I'm suggesting adding an AC_C_STATIC_ARRAY_DECLARATOR macro, defined
> to static, or empty. I've tentatively written a macro modelled after
> AC_C_FLEXARRAY, attached to this mail.
>
> The name of the macro can, as it should, be bikeshedded. I'm not too
> sure how m4 processes the [ and ] in the description.

Gentle ping; this is useful for a trick from Modern C, 3rd edition,
from Jens Gustedt. See 5.4-2.
https://inria.hal.science/hal-02383654v2/file/modernC.pdf

> 2) We use array notation for pointer parameters.: We do so wherever these=
 assume that the pointer can=E2=80=99t be null. Some examples are as follow=
s:
>
>     /* These emphasize that the arguments cannot be null. */
>     size_t strlen(char const string[static 1]);
>
>     /* Compatible declaration for the same function. */
>     size_t strlen(const char *string);
>
> The first example stresses the fact that strlen must receive a valid (non=
-null) pointer and will access at least one element of string.

Maybe there's not a real need for this in Autoconf, I thought I'd
share the neat trick nonetheless.

-- Antonin