Hi,

As discussed in bug 678597, gnome-shell does not handle boolean objects returned by dbus properly, or alternatively one could argue that the dbus-proxy code returns bad objects.

One example of this (I've not done an extensive audit) is the usage of CanShutdown in js/ui/userMenu.js,
the purpose of this code is to not show "Shutdown" in the user-menu if shutdown is not available.

To reproduce the issue, run:

dbus-send --session --type=method_call --print-reply --dest=org.gnome.SessionManager /org/gnome/SessionManager org.gnome.SessionManager.CanShutdown

Notice how it returns true, click on the usermenu and press/ release alt, The menuitem at the bottom changes from suspend to shutdown and back, this is all good.

Now start dconf-editor, go to gnome.desktop.lockdown and check disable-log-out.

Run:
dbus-send --session --type=method_call --print-reply --dest=org.gnome.SessionManager /org/gnome/SessionManager org.gnome.SessionManager.CanShutdown

Again, notice how it now returns false

Click on the usermenu and press/ release alt, The menuitem at the bottom *still* changes from suspend to shutdown and back, not good!

This can be fixed with the following simple patch:
--- a/js/ui/userMenu.js
+++ b/js/ui/userMenu.js
@@ -572,7 +572,7 @@ const UserMenuButton = new Lang.Class({
         this._session.CanShutdownRemote(Lang.bind(this,
             function(result, error) {
                 if (!error) {
-                    this._haveShutdown = result;
+                    this._haveShutdown = result == 'true';
                     this._updateSuspendOrPowerOff();
                 }
             }));

Change /usr/share/gnome-shell/js/ui/userMenu.js according to this patch, press alt+f2 and enter "r" to reload the shell, and click on the usermenu and press/ release alt again, notice how it now never shows shutdown, as long as the gnome.desktop.lockdown.disable-log-out option is set.

Note this is just an example of the issue which I encountered while working on automount inhibit, this issue very likely impacts more then just CanShutdown. We either need to audit all usages of boolean values returned by dbus proxies and change them to val == 'true', or modify the dbus-proxy code to return a proper js boolean type.

Regards,

Hans