Allow the shell to run without the screenshield

The screenshield requires gdm 3.5, which can be problematic in
jhbuild configurations, or distributions that don't use GDM as the display
manager. Allow transparent fallback to gnome-screensaver in that case.

https://bugzilla.gnome.org/show_bug.cgi?id=683060

js/ui/main.js

@@ -137,8 +137,10 @@ function start() {
     ctrlAltTabManager = new CtrlAltTab.CtrlAltTabManager();
     overview = new Overview.Overview();
     magnifier = new Magnifier.Magnifier();
-    screenShield = new ScreenShield.ScreenShield();
-    screenSaverDBus = new ShellDBus.ScreenSaverDBus();
+    if (UnlockDialog.isSupported())
+        screenShield = new ScreenShield.ScreenShield();
+    else
+        screenShield = new ScreenShield.ScreenShieldFallback();
     panel = new Panel.Panel();
     wm = new WindowManager.WindowManager();
     messageTray = new MessageTray.MessageTray();

js/ui/screenShield.js

@@ -19,6 +19,7 @@ const Lightbox = imports.ui.lightbox;
 const Main = imports.ui.main;
 const Overview = imports.ui.overview;
 const MessageTray = imports.ui.messageTray;
+const ShellDBus = imports.ui.shellDBus;
 const Tweener = imports.ui.tweener;
 
 const SCREENSAVER_SCHEMA = 'org.gnome.desktop.screensaver';
@@ -415,6 +416,8 @@ const ScreenShield = new Lang.Class({
             this._onStatusChanged(status);
         }));
 
+        this._screenSaverDBus = new ShellDBus.ScreenSaverDBus(this);
+
         this._loginManager = LoginManager.getLoginManager();
         this._loginSession = this._loginManager.getCurrentSessionProxy();
         this._loginSession.connectSignal('Lock', Lang.bind(this, function() { this.lock(false); }));
@@ -827,3 +830,60 @@ const ScreenShield = new Lang.Class({
     },
 });
 Signals.addSignalMethods(ScreenShield.prototype);
+
+/* Fallback code to handle session locking using gnome-screensaver,
+   in case the required GDM dependency is not there
+*/
+const ScreenShieldFallback = new Lang.Class({
+    Name: 'ScreenShieldFallback',
+
+    _init: function() {
+        this._proxy = new Gio.DBusProxy({ g_connection: Gio.DBus.session,
+                                          g_name: 'org.gnome.ScreenSaver',
+                                          g_object_path: '/org/gnome/ScreenSaver',
+                                          g_interface_name: 'org.gnome.ScreenSaver',
+                                          g_flags: (Gio.DBusProxyFlags.DO_NOT_AUTO_START |
+                                                    Gio.DBusProxyFlags.DO_NOT_LOAD_PROPERTIES),
+                                        });
+        this._proxy.init(null);
+
+        this._proxy.connect('g-signal', Lang.bind(this, this._onSignal));
+        this._proxy.connect('notify::g-name-owner', Lang.bind(this, this._onNameOwnerChanged));
+    },
+
+    _onNameOwnerChanged: function(object, pspec) {
+        if (this._proxy.g_name_owner)
+            [this._locked] = this._proxy.call_sync('GetActive', null,
+                                                   Gio.DBusCallFlags.NONE, -1, null).deep_unpack();
+        else
+            this._locked = false;
+
+        this.emit('lock-status-changed', this._locked);
+    },
+
+    _onSignal: function(proxy, senderName, signalName, params) {
+        if (signalName == 'ActiveChanged') {
+            [this._locked] = params.deep_unpack();
+            this.emit('lock-status-changed', this._locked);
+        }
+    },
+
+    get locked() {
+        return this._locked;
+    },
+
+    lock: function() {
+        this._proxy.call('Lock', null, Gio.DBusCallFlags.NONE, -1, null,
+                         Lang.bind(this, function(proxy, result) {
+                             proxy.call_finish(result);
+
+                             this.emit('lock-screen-shown');
+                         }));
+    },
+
+    unlock: function() {
+        this._proxy.call('SetActive', GLib.Variant.new('(b)', false),
+                         Gio.DBusCallFlags.NONE, -1, null, null);
+    },
+});
+Signals.addSignalMethods(ScreenShieldFallback.prototype);

js/ui/shellDBus.js

@@ -340,35 +340,38 @@ const GnomeShellExtensions = new Lang.Class({
 const ScreenSaverDBus = new Lang.Class({
     Name: 'ScreenSaverDBus',
 
-    _init: function() {
+    _init: function(screenShield) {
         this.parent();
 
-        Main.screenShield.connect('lock-status-changed', Lang.bind(this, function(shield) {
+        this._screenShield = screenShield;
+        screenShield.connect('lock-status-changed', Lang.bind(this, function(shield) {
             this._dbusImpl.emit_signal('ActiveChanged', GLib.Variant.new('(b)', [shield.locked]));
         }));
 
         this._dbusImpl = Gio.DBusExportedObject.wrapJSObject(ScreenSaverIface, this);
         this._dbusImpl.export(Gio.DBus.session, '/org/gnome/ScreenSaver');
+
+        Gio.DBus.session.own_name('org.gnome.ScreenSaver', Gio.BusNameOwnerFlags.REPLACE, null, null);
     },
 
     LockAsync: function(parameters, invocation) {
-        let tmpId = Main.screenShield.connect('lock-screen-shown', Lang.bind(this, function() {
-            Main.screenShield.disconnect(tmpId);
+        let tmpId = this._screenShield.connect('lock-screen-shown', Lang.bind(this, function() {
+            this._screenShield.disconnect(tmpId);
 
             invocation.return_value(null);
         }));
 
-        Main.screenShield.lock(true);
+        this._screenShield.lock(true);
     },
 
     SetActive: function(active) {
         if (active)
-            Main.screenShield.lock(true);
+            this._screenShield.lock(true);
         else
-            Main.screenShield.unlock();
+            this._screenShield.unlock();
     },
 
     GetActive: function() {
-        return Main.screenShield.locked;
+        return this._screenShield.locked;
     }
 });

js/ui/unlockDialog.js

@@ -2,7 +2,7 @@
 
 const AccountsService = imports.gi.AccountsService;
 const Clutter = imports.gi.Clutter;
-const Gdm = imports.gi.Gdm;
+const Gdm  = imports.gi.Gdm;
 const Gio = imports.gi.Gio;
 const GLib = imports.gi.GLib;
 const Gtk = imports.gi.Gtk;
@@ -23,6 +23,35 @@ const GdmUtil = imports.gdm.util;
 // The timeout before going back automatically to the lock screen (in seconds)
 const IDLE_TIMEOUT = 2 * 60;
 
+function versionCompare(required, reference) {
+    required = required.split('.');
+    reference = reference.split('.');
+
+    for (let i = 0; i < required.length; i++) {
+        if (required[i] != reference[i])
+            return required[i] < reference[i];
+    }
+
+    return true;
+}
+
+function isSupported() {
+    try {
+        let params = GLib.Variant.new('(ss)', ['org.gnome.DisplayManager.Manager', 'Version']);
+        let result = Gio.DBus.system.call_sync('org.gnome.DisplayManager',
+                                               '/org/gnome/DisplayManager/Manager',
+                                               'org.freedesktop.DBus.Properties',
+                                               'Get', params, null,
+                                               Gio.DBusCallFlags.NONE,
+                                               -1, null);
+
+        let version = result.deep_unpack()[0].deep_unpack();
+        return versionCompare('3.5.91', version);
+    } catch(e) {
+        return false;
+    }
+}
+
 // A widget showing the user avatar and name
 const UserWidget = new Lang.Class({
     Name: 'UserWidget',

src/main.c

@@ -34,7 +34,6 @@ extern GType gnome_shell_plugin_get_type (void);
 
 #define SHELL_DBUS_SERVICE "org.gnome.Shell"
 #define MAGNIFIER_DBUS_SERVICE "org.gnome.Magnifier"
-#define SCREENSAVER_DBUS_SERVICE "org.gnome.ScreenSaver"
 
 #define OVERRIDES_SCHEMA "org.gnome.shell.overrides"
 
@@ -153,8 +152,6 @@ shell_dbus_init (gboolean replace)
                             MAGNIFIER_DBUS_SERVICE, FALSE,
   /* ...and the org.freedesktop.Notifications service. */
                             "org.freedesktop.Notifications", FALSE,
-  /* ...and the org.gnome.ScreenSaver service. */
-                            SCREENSAVER_DBUS_SERVICE, FALSE,
                             NULL);
   /* ...and the on-screen keyboard service */
   shell_dbus_acquire_name (bus,