System log message: g_object_set: assertion 'G_IS_OBJECT (object)' failed
This issue has been reported previously at Bugzilla #760591 but the bug report has been closed due to insufficient data.
When running a GNOME session (3.28 under Fedora 28), I am seeing many warnings and errors printed to syslog by gnome-shell. This includes one common assertion failure:
g_object_set: assertion 'G_IS_OBJECT (object)' failed
In Bugzilla #760591, the reporter was told to provide more information which I'm giving here.
Truncated backtrace from a gnome-shell instance running as user window manager:
Thread 1 "gnome-shell" hit Breakpoint 1, g_object_set (_object=_object@entry=0x55dfe8940e40, first_property_name=first_property_name@entry=0x7f6ba4a473bc "keep-aspect-ratio") at gobject.c:2464
2464 g_return_if_fail (G_IS_OBJECT (object));
#0 0x00007f6ba72f19e2 in g_object_set (_object=_object@entry=0x55dfe8940e40, first_property_name=first_property_name@entry=0x7f6ba4a473bc "keep-aspect-ratio") at gobject.c:2464
#1 0x00007f6ba4a2deef in create_default_texture () at ../src/st/st-texture-cache.c:71
#2 0x00007f6ba4a2f49a in st_texture_cache_load_gicon (cache=cache@entry=0x55dfe84ba1a0 [StTextureCache], theme_node=theme_node@entry=0x55dff5995960 [StThemeNode], icon=<optimized out>, size=16, scale=1) at ../src/st/st-texture-cache.c:928
#3 0x00007f6ba4a2691e in st_icon_update (icon=0x55dff3b64c60 [Gjs_Icon]) at ../src/st/st-icon.c:361
#4 0x00007f6ba72e8d36 in _g_closure_invoke_va (closure=0x55dfe866a780, return_value=0x0, instance=0x55dff3b64c60, args=0x7ffe71c61120, n_params=0, param_types=0x0) at gclosure.c:867
#5 0x00007f6ba73050c1 in g_signal_emit_valist (instance=0x55dff3b64c60, signal_id=<optimized out>, detail=0, var_args=var_args@entry=0x7ffe71c61120) at gsignal.c:3300
#6 0x00007f6ba7305663 in g_signal_emit (instance=instance@entry=0x55dff3b64c60, signal_id=<optimized out>, detail=detail@entry=0) at gsignal.c:3447
#7 0x00007f6ba4a416d3 in st_widget_recompute_style (widget=widget@entry=0x55dff3b64c60 [Gjs_Icon], old_theme_node=old_theme_node@entry=0x55e00c40f660 [StThemeNode]) at ../src/st/st-widget.c:1659
#8 0x00007f6ba4a4189b in st_widget_style_changed (widget=0x55dff3b64c60 [Gjs_Icon]) at ../src/st/st-widget.c:553
#9 0x00007f6ba4a4271d in st_widget_set_style (actor=0x55dff3b64c60 [Gjs_Icon], style=0x55e000c5afe0 "color: rgb(247,202,23);") at ../src/st/st-widget.c:1453
#10 0x00007f6ba72f0c30 in object_set_property (nqueue=0x7f6b78041520, value=0x7ffe71c61358, pspec=0x55dfe83846b0 [GParamString], object=0x55dff3b64c60 [Gjs_Icon]) at gobject.c:1441
Full backtrace of all threads plus additional information from gdb
Software versions: glib2-2.56.1-4.fc28.x86_64 mutter-3.28.3-3.fc28.x86_64 gnome-shell-3.28.3-1.fc28.x86_64 gjs-1.52.3-1.fc28.x86_64
Additional information: This issue has been present for a long time, at least since the 3.18.x release series.