Re: C23 support in Autoconf

On 4/30/24 10:51, Paul Eggert wrote:
> I installed the attached patch into Savannah master to get the ball rolling on 
> Autoconf supporting C23.
> 
> Most C23 compatibility gizmos are now done in Gnulib. However, Autoconf's 
> AC_PROG_CC needs to be changed to tack --std=gnu23 onto $CC. Although this may 
> cause a few backward compatibility hassles with ancient packages that still use 
> K&R C functions, C23 means these packages need to be changed to use function 
> prototypes anyway.

Just FYI, from my experiments building the X.Org packages (a code base that
still has many bits originally written before the C89 standard) with gcc 13.2
and --std=gnu23, the biggest source of problems was not function prototypes,
but the change of "true" and "false" to no longer be acceptable lvalues,
and of "bool" to be a builtin type.

Fortunately in our cases, the patches were small & simple:

https://gitlab.freedesktop.org/xorg/app/xprop/-/commit/0d2837162ef0e54647485eee2ba4b88012fbb1b4
https://gitlab.freedesktop.org/xorg/lib/libxt/-/commit/56875344b2a62845b8a494830bfb0a5f6ed2d3d6
https://gitlab.freedesktop.org/xorg/driver/xf86-video-vbox/-/commit/b66441a27fa85e2a3b63f10a0a5a846344327042

but I know we're not alone here with these changes, even in much newer code:

https://gitlab.freedesktop.org/cairo/cairo/-/issues/825
https://gitlab.freedesktop.org/wlroots/wlroots/-/commit/a0b1329ee6cce22aca0c9b064fe9c136cc05d630

Of course, our experience is somewhat biased by the XORG_COMPILER_FLAGS macro
in our xorg-macros.m4 set of autoconf macros having included
-Wold-style-definition in our default CFLAGS since 2011.

-- 
         -Alan Coopersmith-                 [email protected]
          Oracle Solaris Engineering - https://blogs.oracle.com/solaris