extensionSystem: Create a file to flag that extensions are being loaded

When the extension system is loaded, create the
gnome-shell-disable-extensions file in the users runtime directory. This
file is automatically removed 60s later. The sole purpose of this file
is to be consumed by the systemd units. If the file exists, the systemd
units will disable extensions when the gnome-shell fails.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/858

js/ui/extensionSystem.js

@@ -1,7 +1,7 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 /* exported init connect disconnect */
 
-const { Gio, St } = imports.gi;
+const { GLib, Gio, St } = imports.gi;
 const Signals = imports.signals;
 
 const ExtensionUtils = imports.misc.extensionUtils;
@@ -28,6 +28,23 @@ var ExtensionManager = class {
     }
 
     init() {
+        // The following file should exist for a period of time when extensions
+        // are enabled after start. If it exists, then the systemd unit will
+        // disable extensions should gnome-shell crash.
+        // Should the file already exist from a previous login, then this is OK.
+        let disableFilename = GLib.build_filenamev([GLib.get_user_runtime_dir(), 'gnome-shell-disable-extensions']);
+        let disableFile = Gio.File.new_for_path(disableFilename);
+        try {
+            disableFile.create(Gio.FileCreateFlags.REPLACE_DESTINATION, null);
+        } catch (e) {
+            log(`Failed to create file ${disableFilename}: ${e.message}`);
+        }
+
+        GLib.timeout_add_seconds(GLib.PRIORITY_DEFAULT, 60, () => {
+            FileUtils.deleteGFile(disableFile);
+            return GLib.SOURCE_REMOVE;
+        });
+
         this._sessionUpdated();
     }