Add extensionSystem

Consumer documentation will live at http://live.gnome.org/GnomeShell/Extensions

In terms of implementation; basically we load extensions from the well-known
directories.  Add a GConf key to disable extensions by uuid.  There is a new
option --create-extension for the gnome-shell script which takes a bit of
interactive input, sets up some sample files, and launches gedit.

No extensions UI in this patch; that will come later.

https://bugzilla.gnome.org/show_bug.cgi?id=599661

src/gnome-shell.in

@@ -212,6 +212,8 @@ parser.add_option("-w", "--wide", action="store_true",
                   help="Use widescreen (1280x800) with Xephyr")
 parser.add_option("", "--eval-file", metavar="EVAL_FILE",
                   help="Evaluate the contents of the given JavaScript file")
+parser.add_option("", "--create-extension", action="store_true",
+                  help="Create a new GNOME Shell extension")
 
 options, args = parser.parse_args()
 
@@ -219,6 +221,87 @@ if args:
     parser.print_usage()
     sys.exit(1)
 
+if options.create_extension:
+    import json
+
+    print
+    print '''Name should be a very short (ideally descriptive) string.
+Examples are: "Click To Focus",  "Adblock", "Shell Window Shrinker".
+'''
+    name = raw_input('Name: ').strip()
+    print
+    print '''Description is a single-sentence explanation of what your extension does.
+Examples are: "Make windows visible on click", "Block advertisement popups"
+              "Animate windows shrinking on minimize"
+'''
+    description = raw_input('Description: ').strip()
+    underifier = re.compile('[^A-Za-z]')
+    sample_uuid = underifier.sub('_', name)
+    # TODO use evolution data server
+    hostname = subprocess.Popen(['hostname'], stdout=subprocess.PIPE).communicate()[0].strip()
+    sample_uuid = sample_uuid + '@' + hostname
+
+    print
+    print '''Uuid is a globally-unique identifier for your extension.
+This should be in the format of an email address (foo.bar@extensions.example.com), but
+need not be an actual email address, though it's a good idea to base the uuid on your
+email address.  For example, if your email address is janedoe@example.com, you might
+use an extension title clicktofocus@janedoe.example.com.'''
+    uuid = raw_input('Uuid [%s]: ' % (sample_uuid, )).strip()
+    if uuid == '':
+        uuid = sample_uuid
+
+    extension_path = os.path.join(os.path.expanduser('~/.config'), 'gnome-shell', 'extensions', uuid)
+    if os.path.exists(extension_path):
+        print "Extension path %r already exists" % (extension_path, )
+        sys.exit(0)
+    os.makedirs(extension_path)
+    meta = { 'name': name,
+             'description': description,
+             'uuid': uuid }
+    f = open(os.path.join(extension_path, 'metadata.json'), 'w')
+    json.dump(meta, f)
+    f.close()
+
+    extensionjs_path = os.path.join(extension_path, 'extension.js')
+    f = open(extensionjs_path, 'w')
+    f.write('''// Sample extension code, makes clicking on the panel show a message
+const St = imports.gi.St;
+const Mainloop = imports.mainloop;
+
+const Main = imports.ui.main;
+
+function _showHello() {
+    let text = new St.Label({ style_class: 'helloworld-label', text: "Hello, world!" });
+    let monitor = global.get_primary_monitor();
+    global.stage.add_actor(text);
+    text.set_position(Math.floor (monitor.width / 2 - text.width / 2), Math.floor(monitor.height / 2 - text.height / 2));
+    Mainloop.timeout_add(3000, function () { text.destroy(); });
+}
+
+// Put your extension initialization code here
+function main() {
+    Main.panel.actor.reactive = true;
+    Main.panel.actor.connect('button-release-event', _showHello);
+}
+''')
+    f.close()
+
+    f = open(os.path.join(extension_path, 'stylesheet.css'), 'w')
+    f.write('''/* Example stylesheet */
+.helloworld-label {
+    font-size: 36px;
+    font-weight: bold;
+    color: #ffffff;
+    background-color: rgba(10,10,10,0.7);
+    border-radius: 5px;
+}
+''')
+    f.close()
+
+    subprocess.Popen(['gedit', extensionjs_path])
+    sys.exit(0)
+
 if options.eval_file:
     import dbus
 

src/shell-global.c

@@ -522,6 +522,73 @@ shell_global_display_is_grabbed (ShellGlobal *global)
   return meta_display_get_grab_op (display) != META_GRAB_OP_NONE;
 }
 
+/* Defining this here for now, see
+ * https://bugzilla.gnome.org/show_bug.cgi?id=604075
+ * for upstreaming status.
+ */
+JSContext * gjs_context_get_context (GjsContext *context);
+
+/**
+ * shell_global_add_extension_importer:
+ * @target_object_script: JavaScript code evaluating to a target object
+ * @target_property: Name of property to use for importer
+ * @directory: Source directory:
+ * @error: A #GError
+ *
+ * This function sets a property named @target_property on the object
+ * resulting from the evaluation of @target_object_script code, which
+ * acts as a GJS importer for directory @directory.
+ *
+ * Returns: %TRUE on success
+ */
+gboolean
+shell_global_add_extension_importer (ShellGlobal *global,
+                                     const char  *target_object_script,
+                                     const char  *target_property,
+                                     const char  *directory,
+                                     GError     **error)
+{
+  jsval target_object;
+  JSObject *importer;
+  JSContext *context = gjs_context_get_context (global->js_context);
+  char *search_path[2] = { 0, 0 };
+
+  // This is a bit of a hack; ideally we'd be able to pass our target
+  // object directly into this function, but introspection doesn't
+  // support that at the moment.  Instead evaluate a string to get it.
+  if (!JS_EvaluateScript(context,
+                         JS_GetGlobalObject(context),
+                         target_object_script,
+                         strlen (target_object_script),
+                         "<target_object_script>",
+                         0,
+                         &target_object))
+    {
+      char *message;
+      gjs_log_exception(context,
+                        &message);
+      g_set_error(error,
+                  G_IO_ERROR,
+                  G_IO_ERROR_FAILED,
+                  "%s", message ? message : "(unknown)");
+      g_free(message);
+      return FALSE;
+    }
+
+  if (!JSVAL_IS_OBJECT (target_object))
+    {
+      g_set_error(error,
+                  G_IO_ERROR,
+                  G_IO_ERROR_FAILED,
+                  "Invalid object");
+      return FALSE;
+    }
+
+  search_path[0] = (char*)directory;
+  importer = gjs_define_importer (context, JSVAL_TO_OBJECT (target_object), target_property, (const char **)search_path, FALSE);
+  return TRUE;
+}
+
 /* Code to close all file descriptors before we exec; copied from gspawn.c in GLib.
  *
  * Authors: Padraig O'Briain, Matthias Clasen, Lennart Poettering

src/shell-global.h

@@ -43,6 +43,12 @@ ShellGlobal *shell_global_get (void);
 
 MetaScreen *shell_global_get_screen (ShellGlobal  *global);
 
+gboolean shell_global_add_extension_importer (ShellGlobal *global,
+                                              const char  *target_object_script,
+                                              const char  *target_property,
+                                              const char  *directory,
+                                              GError     **error);
+
 void shell_global_grab_dbus_service (ShellGlobal *global);
 
 typedef enum {