gtk 3 stuck menu bug on Mac

[Christian Schoenebeck <schoenebeck linuxsampler org>]

Hi!

I am currently investigating a menu handling bug of Gtk 3.22.26 on Mac (Quartz 
implementation). It happens quite often that Gtk 3 menus on Mac stop 
processing any mouse events. So when that happens, i.e. menu items are no more 
highlighted when moving the mouse pointer over them, nor do the menu items fire 
when being clicked, nor does i.e. a submenu close when moving the pointer over 
another toplevel menu node. The menu simply remains stuck at this point.

Has somebody looked into this issue before?

What I found out so far is that whenever this problem occurs, both of the 
following two checks in function gtk_menu_motion_notify() (gtkmenu.c) return 
false and the function is thus aborted at this point:

        menu_item = gtk_get_event_widget ((GdkEvent*) event);
        ...
        if (!GTK_IS_MENU_ITEM (menu_item) ||
            !GTK_IS_MENU (parent))
            return false;

So it seems when this misbehavior occurs, a wrong toplevel widget was assigned 
to the gdk event object (exactly: event->any.window->user_data). However so 
far I don't know the root cause yet.

What looks suspicous to me though is that in gdkevents-quartz.c the toplevel 
widget under the pointer coordinates is resolved before the corresponding gdk 
event is pushed into the gdk event queue. I mean if this Quartz implementation 
pushes a bunch of mouse events into the gdk event queue, and one of the events 
i.e. would cause a new menu to popup (which always happens after pulling the 
events from the queue), then the previously resolved toplevel widget (in 
gdkevents-quartz.c) could be wrong since it resolved widgets in the past.

Hints appreciated!

CU
Christian