Re: master b99ec5d 3/3: Work around __has_attribute bug in clang 3.4

[Doug Davis]

Paul Eggert <eggert@cs.ucla.edu> writes:

> On 1/23/21 2:11 AM, Mattias Engdegård wrote:
>> 23 jan. 2021 kl. 01.46 skrev Paul Eggert <eggert@cs.ucla.edu>:
>> 
>>> Perhaps someone who can build on macOS directly can provide more info about 
>>> the problem. I had no problem building with clang 11.0 on Ubuntu but 
>>> Apple's clang is special.
>> Apple's clang seems to come with a builtin
>> #define __nonnull _Nonnull
>> which clashes with the the one in lib/cdefs.h. Perhaps we should
>> call it something else.
>
> Thanks for the diagnosis. Although calling it something else would
> obviously work, it would require renaming __nonnull everywhere within
> Gnulib (and eventually Glibc), and that would be entirely contrary to
> the intent of the Apple macro - which was to encourage compatibility
> with GNU code. As I understand things Apple's __nonnull keyword used
> to mean something else but collided with GNU's __nonnull macro, so
> they renamed the keyword and put in a backward-compatibility macro for
> old Applish code, but we don't need that macro and can just use
> __nonnull for our own use.
>
> I attempted to fix the problem by installing the attached patch into
> Gnulib, and then merged Gnulib into Emacs master. Please give it a
> try, as I don't use macOS and so did not check the patch directly.
>

I just gave it a test and successfully built from scratch (latest commit
at b7068be5c4 and on macOS Big Sur with Apple clang 12).