Re: Emacs build fails on Windows mingw64

[Paul Eggert]

On 10/24/21 9:58 AM, Eli Zaretskii wrote:
> We could try all that, but not on the release branch.  There, I'd like
> a simple and safe fix.  Is such a thing possible?

Andy suggested a simple fix that I quoted here:

https://lists.gnu.org/r/emacs-devel/2021-10/msg01698.html

We could apply that patch just to ntlib.c and just in emacs-28 (do not 
merge to master) as Andy says that works for him; and we could then 
apply the more-systematic patch of 
<https://lists.gnu.org/r/emacs-devel/2021-10/msg01697.html> to master. 
Andy's patch is definitely safe for GNU and POSIXish hosts. I don't know 
whether it suffices for all MS-Windows platforms and Emacs builds.


> Can you explain why config.h is needed there, and why only for GCC 11?
config.h is needed because it defines macros used by lib/string.h and 
other lib/*.h files that come from Gnulib. I don't know why the problem 
occurs only for GCC 11 on MS-Windows platforms, as I would think it'd 
also occur with earlier GCC versions. Older GCC versions don't do the 
static checking I mentioned, so the macros do not help checking with 
older GCC. The macros can safely be #defined to empty as Andy's patch 
suggested, so long as config.h isn't included (as it would define them 
differently). The downsides of Andy's approach (as compared to the 
more-systematic patch) is that you lose out some static checking with 
recent GCC, and I worry (without really knowing) that similar problems 
may lurk in other MS-Windows-specific .c files on some other MS-Windows 
platforms.