I'm experimentally rebuilding rawhide with the not-yet-released GCC 15 to see if anything breaks, and to help write the porting guide.  See https://fedoraproject.org/wiki/User:Dmalcolm/gcc-15

My test build with GCC 15 failed:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3/build/8410923/

whereas my test build with GCC 14 succeeded:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.checker/build/8410982/

The build failure was numerous errors of the form:

menu.c:38:1: error: conflicting types for ‘button’; have ‘void(XButtonEvent *)’
   38 | button(XButtonEvent * e)
      | ^~~~~~
In file included from menu.c:14:
fns.h:58:9: note: previous declaration of ‘button’ with type ‘void(void)’
   58 | void    button();
      |         ^~~~~~
menu.c: In function ‘button’:
menu.c:46:13: error: too many arguments to function ‘getscreen’
   46 |         s = getscreen(e->root);
      |             ^~~~~~~~~
fns.h:14:13: note: declared here
   14 | ScreenInfo *getscreen();
      |             ^~~~~~~~~
menu.c:49:13: error: too many arguments to function ‘getclient’
   49 |         c = getclient(e->window, 0);
      |             ^~~~~~~~~
fns.h:74:10: note: declared here
   74 | Client  *getclient();
      |          ^~~~~~~~~

see the full log for details:
https://download.copr.fedorainfracloud.org/results/dmalcolm/gcc-15-smoketest-3/fedora-rawhide-x86_64/08410923-9wm/builder-live.log.gz

This is probably due to GCC 15 now defaulting to -std=gnu23, whereas GCC 14 defaulted to -std=gnu17, and C23 is stricter about function prototypes than C17.  It's probably fixable by fixing the function prototypes (or by manually adding -std=gnu17 to the C build flags)


Reproducible: Always