Fix prompt for updates on end session dialog

Since PackageKit 1.11.1, the prompt to install updates on the end
session dialog has been (mostly) broken. The problem is that it only
works if PackageKit is running at the time the end session dialog is
opened; otherwise, our GDBusProxy has invalidated all of its properties,
which we read to see if update is possible. We need to autostart
PackageKit before reading its properties to fix this problem. That would
be easy if we were calling a method to see if an update or distro
upgrade were available, but since we're just checking a property, using
cached properties won't suffice. We'll have to manually check the
property value to ensure we autostart PackageKit.

Most of the code is written by Florian. Thanks Florian!

Fixes https://gitlab.gnome.org/GNOME/gnome-shell/issues/2276

js/ui/endSessionDialog.js

@@ -29,6 +29,8 @@ const UserWidget = imports.ui.userWidget;
 
 const { loadInterfaceXML } = imports.misc.fileUtils;
 
+Gio._promisify(Gio.DBusConnection.prototype, 'call', 'call_finish');
+
 const _ITEM_ICON_SIZE = 64;
 
 const EndSessionDialogIface = loadInterfaceXML('org.gnome.SessionManager.EndSessionDialog');
@@ -346,10 +348,8 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
 
         // Use a different description when we are installing a system upgrade
         // if the PackageKit proxy is available (i.e. PackageKit is available).
-        if (this._pkOfflineProxy && dialogContent.upgradeDescription) {
+        if (dialogContent.upgradeDescription) {
-            let name = this._pkOfflineProxy.PreparedUpgrade['name'].deep_unpack();
+            const { name, version } = this._updateInfo.PreparedUpgrade;
-            let version = this._pkOfflineProxy.PreparedUpgrade['version'].deep_unpack();
-
             if (name != null && version != null)
                 description = dialogContent.upgradeDescription(name, version);
         }
@@ -608,16 +608,46 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
         });
     }
 
-    OpenAsync(parameters, invocation) {
+    async _getUpdateInfo() {
+        const connection = this._pkOfflineProxy.get_connection();
+        const reply = await connection.call(
+            this._pkOfflineProxy.g_name,
+            this._pkOfflineProxy.g_object_path,
+            'org.freedesktop.DBus.Properties',
+            'GetAll',
+            new GLib.Variant('(s)', [this._pkOfflineProxy.g_interface_name]),
+            null,
+            Gio.DBusCallFlags.NONE,
+            -1,
+            null);
+        const [info] = reply.recursiveUnpack();
+        return info;
+    }
+
+    async OpenAsync(parameters, invocation) {
         let [type, timestamp, totalSecondsToStayOpen, inhibitorObjectPaths] = parameters;
         this._totalSecondsToStayOpen = totalSecondsToStayOpen;
         this._type = type;
 
+        try {
+            this._updateInfo = await this._getUpdateInfo();
+        } catch (e) {
+            if (this._pkOfflineProxy !== null)
+                log('Failed to get update info from PackageKit: %s'.format(e.message));
+
+            this._updateInfo = {
+                UpdateTriggered: false,
+                UpdatePrepared: false,
+                UpgradeTriggered: false,
+                PreparedUpgrade: {},
+            };
+        }
+
         // Only consider updates and upgrades if PackageKit is available.
         if (this._pkOfflineProxy && this._type == DialogType.RESTART) {
-            if (this._pkOfflineProxy.UpdateTriggered)
+            if (this._updateInfo.UpdateTriggered)
                 this._type = DialogType.UPDATE_RESTART;
-            else if (this._pkOfflineProxy.UpgradeTriggered)
+            else if (this._updateInfo.UpgradeTriggered)
                 this._type = DialogType.UPGRADE_RESTART;
         }
 
@@ -646,9 +676,8 @@ class EndSessionDialog extends ModalDialog.ModalDialog {
         if (dialogContent.showOtherSessions)
             this._loadSessions();
 
-        // Only consider updates and upgrades if PackageKit is available.
+        let updateTriggered = this._updateInfo.UpdateTriggered;
-        let updateTriggered = this._pkOfflineProxy ? this._pkOfflineProxy.UpdateTriggered : false;
+        let updatePrepared = this._updateInfo.UpdatePrepared;
-        let updatePrepared = this._pkOfflineProxy ? this._pkOfflineProxy.UpdatePrepared : false;
         let updatesAllowed = this._updatesPermission && this._updatesPermission.allowed;
 
         _setCheckBoxLabel(this._checkBox, dialogContent.checkBoxText || '');