We (ab)use the switch-workspace callback that is supposed to be used for effects for this.

In mutter-plugin-manager.c:mutter_plugin_manager_switch_workspace we do:

---------
      if (!mutter_plugin_disabled (plugin) &&
          (mutter_plugin_features (plugin) & MUTTER_PLUGIN_SWITCH_WORKSPACE) &&
          (actors && *actors))
        {
---------

So when there are no windows (no desktop window and no other open application) the test "(actors && *actors)" fails so we never call klass->switch_workspace which in gnome-shell-plugin.c calls _shell_wm_switch_workspace and than shell-wm.c:_shell_wm_switch_workspace which is supposed to emit the signal.

We should probably use MetaScreen::workspace-switched instead for this purpose.

For the record there is a mutter bug for this issue (which I did not notice):
https://bugzilla.gnome.org/show_bug.cgi?id=621082

(In reply to comment #2)
> For the record there is a mutter bug for this issue (which I did not notice):
> https://bugzilla.gnome.org/show_bug.cgi?id=621082

Seems the bug is already marked as dependency so feel free to ignore both comments; sorry for the noise.

Created attachment 163306 [details] [review]
update GnomeShellPlugin according recent changes in MutterPlugin

Review of attachment 163306 [details] [review]:

Looks good to me. One trivial comment below. Also, in Subject, 'according recent changes' should be 'according to recent changes', and 'update' should have an initial capital u - 'Update'

::: src/shell-wm.c
@@ +20,3 @@
 enum
 {
+  KILL_WINDOW_EFFECTS,

Ordering is rather random here now, I'd move this down together with KILL_SWITCH_WORKSPACE

@@ +56,3 @@
   gobject_class->finalize = shell_wm_finalize;
 
+  shell_wm_signals[KILL_WINDOW_EFFECTS] =

Same ordering here