mutter/gnome-shell spews GLib warnings with pointer contraints

Affected version

• Fedora 33
• Mutter from git master
• Wayland

Bug summary

While working on fixing an Xwayland issue with a specific game using a workaround, I noticed that gnome-shell/mutter would log a GLib warning each time the pointer constraints were created/destroyed.

Steps to reproduce

1. Install Xwayland from the WIP branch 581
2. Compile and run the simple reproducer from the Xwayland issue
3. Press the mouse button within the reproducer window

What happened

Dec 21 11:26:52 t480s gnome-shell[572480]: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Dec 21 11:26:52 t480s gnome-shell[572480]: g_object_ref: assertion 'G_IS_OBJECT (object)' failed

What did you expect to happen

No GLib warning

Relevant logs, screenshots, screencasts etc.

Forcing an abort on failure gives the following backtrace in gnome-shell/mutter:

#7  0x00007fe7ef8fbba8 in g_object_ref (_object=0x0) at ../../../../src/gnome/glib/gobject/gobject.c:3389
#8  0x00007fe7eeb798db in meta_seat_impl_set_pointer_constraint (seat=0x225cf20, constraint_impl=0x0)
    at ../../../../src/gnome/mutter/src/backends/native/meta-seat-impl.c:3336
#9  0x00007fe7eeb7ada4 in meta_seat_native_set_pointer_constraint (seat=0x7fe7cc0081d0, constraint_impl=0x0)
    at ../../../../src/gnome/mutter/src/backends/native/meta-seat-native.c:572
#10 0x00007fe7eeb4fee9 in meta_backend_native_set_pointer_constraint (backend=0x1f610e0, constraint=0x0)
    at ../../../../src/gnome/mutter/src/backends/native/meta-backend-native.c:326
#11 0x00007fe7eea33253 in meta_backend_set_client_pointer_constraint (backend=0x1f610e0, constraint=0x0)
    at ../../../../src/gnome/mutter/src/backends/meta-backend.c:1433
#12 0x00007fe7eeb1361f in meta_pointer_confinement_wayland_disable (confinement=0x4003ca0)
    at ../../../../src/gnome/mutter/src/wayland/meta-pointer-confinement-wayland.c:153
#13 0x00007fe7eeb2c57a in meta_wayland_pointer_constraint_disable (constraint=0x24f0f10)
    at ../../../../src/gnome/mutter/src/wayland/meta-wayland-pointer-constraints.c:423
#14 0x00007fe7eeb2c5d1 in meta_wayland_pointer_constraint_destroy (constraint=0x24f0f10)
    at ../../../../src/gnome/mutter/src/wayland/meta-wayland-pointer-constraints.c:435
#15 0x00007fe7eeb2c848 in meta_wayland_pointer_constraint_remove (constraint=0x24f0f10)
    at ../../../../src/gnome/mutter/src/wayland/meta-wayland-pointer-constraints.c:538
#16 0x00007fe7eeb2cb5e in pointer_constraint_resource_destroyed (resource=0x56d6a10)
    at ../../../../src/gnome/mutter/src/wayland/meta-wayland-pointer-constraints.c:657
#17 0x00007fe7ee22fd0f in destroy_resource (element=element@entry=0x56d6a10, data=data@entry=0x0, flags=0)
    at ../../../../src/gnome/wayland/src/wayland-server.c:724
#18 0x00007fe7ee2303e0 in wl_resource_destroy (resource=0x56d6a10) at ../../../../src/gnome/wayland/src/wayland-server.c:741
#19 0x00007fe7eeb2d2a2 in locked_pointer_destroy (client=0x2500bc0, resource=0x56d6a10)
    at ../../../../src/gnome/mutter/src/wayland/meta-wayland-pointer-constraints.c:929
#20 0x00007fe7edcc2b10 in ffi_call_unix64 () at ../src/x86/unix64.S:76
#21 0x00007fe7edcc20a3 in ffi_call (cif=cif@entry=0x7ffcc0a15920, fn=<optimized out>, rvalue=<optimized out>, rvalue@entry=0x0, 
    avalue=avalue@entry=0x7ffcc0a159f0) at ../src/x86/ffi64.c:525
#22 0x00007fe7ee234f92 in wl_closure_invoke (closure=0x53023a0, flags=2, target=<optimized out>, opcode=0, data=<optimized out>)
    at ../../../../src/gnome/wayland/src/connection.c:1018
#23 0x00007fe7ee230972 in wl_client_connection_data (fd=<optimized out>, mask=<optimized out>, data=0x2500bc0)
--Type <RET> for more, q to quit, c to continue without paging--
    at ../../../../src/gnome/wayland/src/wayland-server.c:432
#24 0x00007fe7ee233162 in wl_event_loop_dispatch (loop=0x1f7c960, timeout=<optimized out>) at ../../../../src/gnome/wayland/src/event-loop.c:1027
#25 0x00007fe7eeb16dd6 in wayland_event_source_dispatch (base=0x22c9070, callback=0x0, data=0x0)
    at ../../../../src/gnome/mutter/src/wayland/meta-wayland.c:96
#26 0x00007fe7ef80565b in g_main_dispatch (context=0x1f5dc80) at ../../../../src/gnome/glib/glib/gmain.c:3325
#27 g_main_context_dispatch (context=0x1f5dc80) at ../../../../src/gnome/glib/glib/gmain.c:4043
#28 0x00007fe7ef8058d8 in g_main_context_iterate (context=0x1f5dc80, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>)
    at ../../../../src/gnome/glib/glib/gmain.c:4119
#29 0x00007fe7ef805bbb in g_main_loop_run (loop=0x22cdd70) at ../../../../src/gnome/glib/glib/gmain.c:4317
#30 0x00007fe7eeaad443 in meta_run_main_loop () at ../../../../src/gnome/mutter/src/core/main.c:708
#31 0x00007fe7eeaad454 in meta_run () at ../../../../src/gnome/mutter/src/core/main.c:723
#32 0x0000000000402fce in main (argc=1, argv=0x7ffcc0a15fd8) at ../../../../src/gnome/gnome-shell/src/main.c:507