bug#81510: 31.0.90; NS (macOS): clicking a disabled (:enable nil) tab-bar item crases Emacs

> Date: Tue, 28 Jul 2026 20:10:00 +0100
> From: Alan Third <[email protected]>
> Cc: Al Haji-Ali <[email protected]>, [email protected]
> 
> On Tue, Jul 28, 2026 at 09:06:45PM +0300, Eli Zaretskii wrote:
> > > From: Al Haji-Ali <[email protected]>
> > > Date: Tue, 28 Jul 2026 16:25:33 +0100
> > > 
> > > 
> > No, they both assign 'kind' unconditionally.  They then assign the
> > 'arg' member only if tab_bar_arg is non-nil.
> > 
> > > Possible minimal fix: make handle_tab_bar_click's disabled-item
> > > branch return (Fcons (Qtab_bar, Qnil)) instead of bare Qnil, matching
> > > the "click missed" case, which nsterm.m (and presumably the other
> > > ports) already handle correctly as a harmless plain click. I haven't
> > > verified this doesn't have side effects for other callers of
> > > handle_tab_bar_click across the X11/w32 ports.
> > 
> > I prefer that nsterm.m is changed to do the same we do in xterm.c and
> > w32term.c.  There's no need to change xdisp.c, which is a back-end
> > independent part of the display engine.
> > 
> > Alan, WDYT?
> 
> You mean something like this?

Yes.

> modified   src/nsterm.m
> @@ -7955,6 +7955,8 @@ - (void)mouseDown: (NSEvent *)theEvent
>        Lisp_Object tab_bar_arg = Qnil;
>        bool tab_bar_p = false;
>  
> +      emacs_event->kind = MOUSE_CLICK_EVENT;
> +
>        if (WINDOWP (emacsframe->tab_bar_window)
>  	  && WINDOW_TOTAL_LINES (XWINDOW (emacsframe->tab_bar_window)))
>  	{
> @@ -7971,9 +7973,12 @@ - (void)mouseDown: (NSEvent *)theEvent
>  						EV_MODIFIERS (theEvent) | EV_UDMODIFIERS (theEvent));
>  	}
>  
> -      if (!(tab_bar_p && NILP (tab_bar_arg)))
> -	emacs_event->kind = MOUSE_CLICK_EVENT;
> -      emacs_event->arg = tab_bar_arg;
> +      if (tab_bar_p && NILP (tab_bar_arg))
> +	emacs_event->kind = NO_EVENT;
> +
> +      if (!NILP (tab_bar_arg))
> +	emacs_event->arg = tab_bar_arg;
> +
>        emacs_event->code = EV_BUTTON (theEvent);
>        emacs_event->modifiers = EV_MODIFIERS (theEvent)
>                               | EV_UDMODIFIERS (theEvent);
> 
> It looks functionally identical to me, but I don't really understand
> what's going on here...

Does it fix the problem?