bug#44313: 27.1.50; ns_mouse_position EXC_BAD_ACCESS crash

[Aaron Jensen <aaronjensen@gmail.com>]

On Fri, Oct 30, 2020 at 2:08 PM Eli Zaretskii <eliz@gnu.org> wrote:
> I don't know.  The code in Fmouse_pixel_position uses the
> selected-frame, so it is quite strange, to say the least, that this
> frame could be garbled when you just move the mouse pointer.

I'm in the debugger right now. It happened as soon as I started a
full-screen zoom screenshare (maybe that's a hint?)

The value of f is different than selected_frame and
dpyinfo->ns_focus_frame, which means that it's likely set in this
code:

#ifdef NS_IMPL_COCOA
  /* Find the uppermost Emacs frame under the mouse pointer.

     This doesn't work on GNUstep, although in recent versions there
     is compatibility code that makes it a noop.  */

  NSPoint screen_position = [NSEvent mouseLocation];
  NSInteger window_number = 0;
  do
    {
      NSWindow *w;

      window_number = [NSWindow windowNumberAtPoint:screen_position
                        belowWindowWithWindowNumber:window_number];
      w = [NSApp windowWithWindowNumber:window_number];

      if (w && [[w delegate] isKindOfClass:[EmacsView class]])
        f = ((EmacsView *)[w delegate])->emacsframe;
    }
  while (window_number > 0 && !f);
#endif

I wonder if a check for FRAME_LIVE_P should be added here for safety?