[cfe-dev] ISO C3X proposal: nonnull qualifier

[Alejandro Colomar (man-pages) via cfe-dev]

Hi,

Sorry for Clang people,
when I started this thread,
I wasn't subscribed to your list,
and some messages are not on your list.
You can find the complete thread on the GCC list:
<https://gcc.gnu.org/pipermail/gcc/2021-November/237743.html>

I have a few questions for you.
See below, please.

On 11/16/21 13:34, Alejandro Colomar (man-pages) wrote:
> $ cat _Nonnull.c
> #include <stdlib.h>
> 
> int *_Nonnull f(int *_Nullable p)
> {
>      if (!p)
>          exit(1);
>      return p;
> }
> 
> 
> - I get a warning from f().
>    Ideally,
>    a programmer should not need to cast
>    (casts are dangerous),
>    to convert a nullable pointer to a _Nonnull pointer.
>    For that,
>    appropriate checks should be in the preceeding code.
>    Otherwise, a diagnostic should be issued.
>    To be on the safe side,
>    if a compiler has doubts,
>    it should diagnose.
> 
>    There's some Clang document that talks about something similar.
>    I don't know its validity,
>    or if it was a draft before _Nonnull qualifiers.
>    <https://clang.llvm.org/docs/analyzer/developer-docs/nullability.html>

That document suggests that I shouldn't get a diagnostic from f().
Why did I get a diagnostic?  (I tried clang 11, 13 & 14(experimental))


Is it talking about a different nonnull attribute/qualifier?
Was it about a proposal prior to the current _Nonnull?
Why is it not in use?  Was it too difficult to implement?


Do you think Clang could be improved to not warn on f()?


Thanks,
Alex