Specific case in app crashes Mutter

[aljelly]

I know this is some problem in Mutter and not Gala but I'm not sure what causes the crash or how I'd get more information on it. I hope someone here can find out more information (probably from reproducing it) and report it to the right people. The code from the app is probably doing something wrong but it probably shouldn't be crashing Gala/Mutter.

Steps to reproduce

1. Clone https://github.com/spheras/desktopfolder and switch to the desktopfolder-crashing-mutter branch.
2. Run:

   sudo apt install meson valac libgee-0.8-dev libcairo2-dev libjson-glib-dev libgdk-pixbuf2.0-dev libwnck-3-dev libgtksourceview-3.0-dev libjson-glib-dev
   meson build
   cd build
   meson configure -D prefix=/usr
   sudo ninja install
   com.github.spheras.desktopfolder

3. Right click on the desktop and select New > Panel, if there isn't one already.
4. Right click the desktop again and select "Properties".
5. Go to "General" and turn the "Enable desktop" switch off. Click Close.
6. Now go to the panel you just created (or the one that was already there) and click the gear icon.

Result

The properties dialog will show again and Gala will crash due to an error from Mutter.

I can get it to happen consistently (repeat 2 more times and it appears you get kicked out of your session).

Terminal output

("hgcjfjt" was just keyboard spam to give the panel windows unique names)

Nov 22 02:01:54 aled-eOS gala[30271]: meta_window_set_stack_position_no_sync: assertion 'window->stack_position >= 0' failed
Nov 22 02:01:55 aled-eOS gala[30271]: meta_window_set_stack_position_no_sync: assertion 'window->stack_position >= 0' failed
Nov 22 02:01:56 aled-eOS gala[30271]: meta_window_set_stack_position_no_sync: assertion 'window->stack_position >= 0' failed
Nov 22 02:01:56 aled-eOS gala[30271]: meta_window_set_stack_position_no_sync: assertion 'window->stack_position >= 0' failed
Nov 22 02:01:56 aled-eOS gala[30271]: meta_window_set_stack_position_no_sync: assertion 'window->stack_position >= 0' failed
Nov 22 02:01:56 aled-eOS gala.desktop[30271]: Window manager warning: Attempt to perform window operation 1 on window 0x2200044 (hgcjfjt) when operation 1 on 0x2200044 (hgcjfjt) already in effect
Nov 22 02:01:58 aled-eOS gala[30271]: meta_window_set_stack_position_no_sync: assertion 'window->stack_position >= 0' failed
Nov 22 02:01:58 aled-eOS gala.desktop[30271]: Window manager warning: Attempt to perform window operation 1 on window 0x2200044 (hgcjfjt) when operation 1 on 0x2200044 (hgcjfjt) already in effect
Nov 22 02:01:58 aled-eOS gala.desktop[30271]: **
Nov 22 02:01:58 aled-eOS gala.desktop[30271]: mutter:ERROR:x11/group.c:71:meta_group_new: assertion failed: (g_hash_table_lookup (display->groups_by_leader, &group_leader) == NULL)
Nov 22 02:01:58 aled-eOS gnome-session[1222]: gnome-session-binary[1222]: WARNING: Application 'gala.desktop' killed by signal 6
Nov 22 02:01:58 aled-eOS gnome-session-binary[1222]: WARNING: Application 'gala.desktop' killed by signal 6
Nov 22 02:02:00 aled-eOS gala.desktop[25953]: Window manager warning: Invalid WM_TRANSIENT_FOR window 0x2200003 specified for 0x2200036 (Apps).
Nov 22 02:02:00 aled-eOS gala.desktop[25953]: Window manager warning: Invalid WM_TRANSIENT_FOR window 0x2200003 specified for 0x2200044 (hgcjfjt).