AppIndicators_IconActor._getIconInfo() returns NULL causing an exception

[delxg]

Hi!

System details:

• Ubuntu 20.04, fully up to date
• gnome-shell on wayland
• appindicators v33

Problem summary

Using syncthing-gtk sometimes causes gnome-shell to crash

Problem analysis

I see this error in the log:

syncthing-gtk[171577]: gtk_widget_get_scale_factor: assertion 'GTK_IS_WIDGET (widget)' failed
syncthing-gtk[171577]: gtk_widget_get_scale_factor: assertion 'GTK_IS_WIDGET (widget)' failed
syncthing-gtk[171577]: gtk_widget_get_scale_factor: assertion 'GTK_IS_WIDGET (widget)' failed
syncthing-gtk[171577]: gtk_widget_get_scale_factor: assertion 'GTK_IS_WIDGET (widget)' failed
syncthing-gtk[171577]: gtk_widget_get_scale_factor: assertion 'GTK_IS_WIDGET (widget)' failed
syncthing-gtk.desktop[171577]: I App           updatecheck: disabled
gnome-shell[171339]: gtk_icon_theme_get_for_screen: assertion 'GDK_IS_SCREEN (screen)' failed
gnome-shell[171339]: JS ERROR: TypeError: src is null
                     connectSmart4A@/usr/share/gnome-shell/extensions/[email protected]/util.js:189:21
                     connectSmart@/usr/share/gnome-shell/extensions/[email protected]/util.js:214:31
                     _init@/usr/share/gnome-shell/extensions/[email protected]/appIndicator.js:325:14
                     _init@/usr/share/gnome-shell/extensions/[email protected]/indicatorStatusIcon.js:42:25
                     _registerItem@/usr/share/gnome-shell/extensions/[email protected]/statusNotifierWatcher.js:95:22
                     _ensureItemRegistered@/usr/share/gnome-shell/extensions/[email protected]/statusNotifierWatcher.js:123:14
                     RegisterStatusNotifierItemAsync@/usr/share/gnome-shell/extensions/[email protected]/statusNotifierWatcher.js:169:14
                     _handleMethodCall@resource:///org/gnome/gjs/modules/core/overrides/Gio.js:371:35
                     _wrapJSObject/<@resource:///org/gnome/gjs/modules/core/overrides/Gio.js:404:34
gnome-shell[171339]: gtk_icon_theme_get_for_screen: assertion 'GDK_IS_SCREEN (screen)' failed
gnome-shell[171339]: JS ERROR: Exception in callback for signal: icon: Error: Argument 'filename' (type filename) may not be null
                     _createIconByName@/usr/share/gnome-shell/extensions/[email protected]/appIndicator.js:406:26
                     _cacheOrCreateIconByName@/usr/share/gnome-shell/extensions/[email protected]/appIndicator.js:368:14
                     _updateIconByType@/usr/share/gnome-shell/extensions/[email protected]/appIndicator.js:574:18
                     _updateIcon@/usr/share/gnome-shell/extensions/[email protected]/appIndicator.js:601:14
                     _emit@resource:///org/gnome/gjs/modules/core/_signals.js:133:47
                     _onPropertiesChanged/<@/usr/share/gnome-shell/extensions/[email protected]/appIndicator.js:220:22
                     _onPropertiesChanged@/usr/share/gnome-shell/extensions/[email protected]/appIndicator.js:214:15

It seems to me like _createIconByName() was called with a path === null, which causes an assertion to fail inside gdk-pixbuf. This ultimately crashes the shell.

There are a couple of ways that _getIconInfo() could return null:

1. It could be called with name === null
2. If lookup_icon_for_scale() returns null then a warning will be logged and _getIconInfo() will return null.
3. If Gtk.IconTheme.get_default() returns null then _getIconInfo() will return null with no logging.

I don't believe (1) is happening because it's called from _cacheOrCreateIconByName() and the check on line 573 guards against this. It's not (2) because I'm not seeing that warning in the log.

By process of elimination I believe it must be (3).

Looking at the docs for gtk_icon_theme_get_default it doesn't say whether it returns null, and I would have assumed it cannot. However checking the implementation in gtkicontheme.c:451 shows this:

GtkIconTheme *
gtk_icon_theme_get_default (void)
{
  return gtk_icon_theme_get_for_screen (gdk_screen_get_default ());
}

GtkIconTheme *
gtk_icon_theme_get_for_screen (GdkScreen *screen)
{
  GtkIconTheme *icon_theme;

  g_return_val_if_fail (GDK_IS_SCREEN (screen), NULL);
  /* snip */
}

Note that gdk_screen_get_default can return null sometimes.

This is supported by the assertion failure in the log I posted:

gtk_icon_theme_get_for_screen: assertion 'GDK_IS_SCREEN (screen)' failed

Conclusion

So in conclusion I think gtk_icon_theme_get_default() is returning null occasionally, causing AppIndicators_IconActor._getIconInfo() to return null, causing GdkPixbuf.Pixbuf.get_file_info_async() to fail an assertion and crash the gnome-shell.

A possible fix is in #243, but it may be nice to look at a few other fixes:

• Could gtk_icon_theme_get_default() be made to never return null?
• Or possibly the docs for gtk_icon_theme_get_default() should be updated to make it clear that it can return null in some cases.
• Are there any other places where gtk_icon_theme_get_default() is assumed to never return null that could be causing other bugs/crashes?

Related bugs

This seems a little related to some other bug reports: #241, #236, #226. In those three _getIconInfo() appears to be returning null due to branch (2) above because it is logging a warning.

Thanks!

I hope this bug report was helpful. Thanks for your time.

Great work on Ubuntu and related gnome-shell extensions! :)

[3v1n0]

Closed as by commit 745c66a