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

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?

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...
-- 
Alan Third