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

On Wed, Jul 29, 2026 at 03:41:28PM +0200, Stéphane Marks wrote:
> On Tue, Jul 28, 2026 at 10:30 PM Eli Zaretskii <[email protected]> wrote:
> 
> > > 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?
> >
> 
> Works for me.

Well, I guess I'll make it a proper patch, then.

Al Haji-Ali, are you able to check this fixes the problem for you too?
-- 
Alan Third

From 89e1986ad4fd54c91cdec75125bcb738c31d5174 Mon Sep 17 00:00:00 2001
From: Alan Third <[email protected]>
Date: Wed, 29 Jul 2026 18:43:48 +0100
Subject: [PATCH] Fix crash when clicking on empty tab bar entry (bug#81510)

* src/nsterm.m: ([EmacsView mouseDown:]): Copy order of operations
regarding mouse clicks from the w32 port.
---
 src/nsterm.m | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/nsterm.m b/src/nsterm.m
index a7f3fc292c7..a2ef3f19fe3 100644
--- a/src/nsterm.m
+++ b/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);
-- 
2.54.0