bug#23771: Eliminating compiler warnings

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 23771@debbugs.gnu.org, Paul Eggert <eggert@cs.ucla.edu>
> From: Ken Brown <kbrown@cornell.edu>
> Date: Wed, 15 Jun 2016 21:38:19 -0400
> 
> > What warnings does that option produce?  I'm not sure I've seen any
> > warnings about addresses, but maybe I misunderstand the nature of the
> > warning.
> 
> Here's a typical example:
> 
> ../../master/src/menu.c: In function ‘digest_single_submenu’:
> ../../master/src/menu.c:46:30: warning: the address of ‘AppendMenuW’ 
> will always evaluate as ‘true’ [-Waddress]
>   # define unicode_append_menu AppendMenuW
>                                ^
> ../../master/src/menu.c:691:9: note: in expansion of macro 
> ‘unicode_append_menu’
>       if (unicode_append_menu)
>           ^

For this one, I'd suggest to make unicode_append_menu a variable in
the Cygwin build as well, and then do this:

  AppendMenuW_Proc unicode_append_menu = AppendMenuW;

> >> +#else  /* not HAVE_WINDOW_SYSTEM */
> >> +
> >> +_Noreturn void
> >> +decode_window_system_frame (Lisp_Object frame)
> >> +{
> >> +  error ("Window system is not in use");
> >> +}
> >> +
> >> +_Noreturn void
> >> +check_window_system (struct frame *f)
> >> +{
> >> +  error ("Window system is not in use");
> >> +}
> >> +
> >> +#endif	/* not HAVE_WINDOW_SYSTEM */
> >
> > What kind of warnings do you get without these changes?  I don't
> > understand why this is needed.
> 
> A build with no windows system yields these warnings:
> 
> ../../warnings/src/frame.c: In function ‘decode_window_system_frame’:
> ../../warnings/src/frame.c:119:1: warning: function might be candidate 
> for attribute ‘noreturn’ [-Wsuggest-attribute=noreturn]
>   decode_window_system_frame (Lisp_Object frame)
>   ^

How about making check_window_system compile in the no-X builds?

> >> --- a/src/conf_post.h
> >> +++ b/src/conf_post.h
> >> @@ -211,7 +211,7 @@ You lose; /* Emacs for DOS must be compiled with DJGPP */
> >>  extern void _DebPrint (const char *fmt, ...);
> >>  #  define DebPrint(stuff) _DebPrint stuff
> >>  # else
> >> -#  define DebPrint(stuff)
> >> +#  define DebPrint(stuff) {}
> >>  # endif
> >>  #endif
> >
> > Yuck!  Can we simply not use the "empty body" warning option?  When is
> > it important to flag an empty body of a function?
> 
> Here's a typical example:
> 
> Code like this:
> 
>    if (!f->output_data.w32->asked_for_visible)
>      DebPrint (("frame %p (%s) reexposed by WM_PAINT\n", f,
> 	       SDATA (f->name)));
> 
> leads to this warning (if EMACSDEBUG is not defined):
> 
> ../../warnings/src/w32term.c: In function ‘w32_read_socket’:
> ../../warnings/src/w32term.c:4613:28: warning: suggest braces around 
> empty body in an ‘if’ statement [-Wempty-body]
>             SDATA (f->name)));
>                              ^

One way of fixing this is to add those braces.

> But I'd be fine with just disabling this warning, at least for the w32 
> builds.

Right.