extensions: Add new light-style extension

Now that gnome-shell supports a light style, people may want to
use it without forcing all apps to be light.

Add a small extension that switches the default to light, so the
shell follows the regular "dark style" preference.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/256>

extensions/light-style/extension.js

@@ -0,0 +1,45 @@
+/* exported init */
+/*
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+const {St} = imports.gi;
+
+const Main = imports.ui.main;
+
+class Extension {
+    constructor() {
+        this._savedColorScheme = Main.sessionMode.colorScheme;
+    }
+
+    _updateColorScheme(scheme) {
+        Main.sessionMode.colorScheme = scheme;
+        St.Settings.get().notify('color-scheme');
+    }
+
+    enable() {
+        this._updateColorScheme('prefer-light');
+    }
+
+    disable() {
+        this._updateColorScheme(this._savedColorScheme);
+    }
+}
+
+/** */
+function init() {
+    return new Extension();
+}

extensions/light-style/meson.build

@@ -0,0 +1,5 @@
+extension_data += configure_file(
+  input: metadata_name + '.in',
+  output: metadata_name,
+  configuration: metadata_conf
+)

extensions/light-style/metadata.json.in

@@ -0,0 +1,10 @@
+{
+"extension-id": "@extension_id@",
+"uuid": "@uuid@",
+"settings-schema": "@gschemaname@",
+"gettext-domain": "@gettext_domain@",
+"name": "Light Style",
+"description": "Switch default to light style",
+"shell-version": [ "@shell_current@" ],
+"url": "@url@"
+}

meson.build

@@ -37,6 +37,7 @@ classic_extensions = [
 default_extensions = classic_extensions
 default_extensions += [
   'drive-menu',
+  'light-style',
   'screenshot-window-sizer',
   'windowsNavigator',
   'workspace-indicator'