extensionUtils: Use signals rather than callbacks for finding extensions

This allows us to move to a file-monitor based approach in the future.

Since we need signals, we convert the current set of functions to an
object we attach signals too, leading to the new ExtensionFinder object.

https://bugzilla.gnome.org/show_bug.cgi?id=677586

js/extensionPrefs/main.js

@@ -202,7 +202,12 @@ const Application = new Lang.Class({
     },
 
     _scanExtensions: function() {
-        ExtensionUtils.scanExtensions(Lang.bind(this, function(uuid, dir, type) {
+        let finder = new ExtensionUtils.ExtensionFinder();
+        finder.connect('extension-found', Lang.bind(this, this._extensionFound));
+        finder.scanExtensions();
+    },
+
+    _extensionFound: function(signals, uuid, dir, type) {
         if (ExtensionUtils.extensions[uuid] !== undefined)
             return;
 
@@ -217,9 +222,9 @@ const Application = new Lang.Class({
         let iter = this._model.append();
         this._model.set(iter, [0, 1], [uuid, extension.metadata.name]);
         this._extensionIters[uuid] = iter;
-        }));
     },
 
+
     _onActivate: function() {
         this._window.present();
     },

js/misc/extensionUtils.js

@@ -3,6 +3,9 @@
 // Common utils for the extension system and the extension
 // preferences tool
 
+const Lang = imports.lang;
+const Signals = imports.signals;
+
 const GLib = imports.gi.GLib;
 const Gio = imports.gi.Gio;
 const ShellJS = imports.gi.ShellJS;
@@ -149,7 +152,10 @@ function installImporter(extension) {
     _extension = null;
 }
 
-function scanExtensionsInDirectory(callback, dir, type) {
+const ExtensionFinder = new Lang.Class({
+    Name: 'ExtensionFinder',
+
+    _scanExtensionsInDirectory: function(dir, type) {
         let fileEnum;
         let file, info;
         try {
@@ -165,20 +171,22 @@ function scanExtensionsInDirectory(callback, dir, type) {
                 continue;
             let uuid = info.get_name();
             let extensionDir = dir.get_child(uuid);
-        callback(uuid, extensionDir, type);
+            this.emit('extension-found', uuid, extensionDir, type);
         }
         fileEnum.close(null);
-}
+    },
 
-function scanExtensions(callback) {
+    scanExtensions: function() {
         let userExtensionsDir = Gio.File.new_for_path(GLib.build_filenamev([global.userdatadir, 'extensions']));
-    scanExtensionsInDirectory(callback, userExtensionsDir, ExtensionType.PER_USER);
+        this._scanExtensionsInDirectory(userExtensionsDir, ExtensionType.PER_USER);
 
         let systemDataDirs = GLib.get_system_data_dirs();
         for (let i = 0; i < systemDataDirs.length; i++) {
             let dirPath = GLib.build_filenamev([systemDataDirs[i], 'gnome-shell', 'extensions']);
             let dir = Gio.file_new_for_path(dirPath);
             if (dir.query_exists(null))
-            scanExtensionsInDirectory(callback, dir, ExtensionType.SYSTEM);
+                this._scanExtensionsInDirectory(dir, ExtensionType.SYSTEM);
         }
     }
+});
+Signals.addSignalMethods(ExtensionFinder.prototype);

js/ui/extensionSystem.js

@@ -262,8 +262,10 @@ function init() {
 }
 
 function loadExtensions() {
-    ExtensionUtils.scanExtensions(function(uuid, dir, type) {
+    let finder = new ExtensionUtils.ExtensionFinder();
+    finder.connect('extension-found', function(signals, uuid, dir, type) {
         let enabled = enabledExtensions.indexOf(uuid) != -1;
         loadExtension(dir, type, enabled);
     });
+    finder.scanExtensions();
 }