extension: Perform runtime-only settings overriding

The extension is overriding the user settings by writing on them, sadly this
implies various issues because even if we reset them on extension unloading,
a shell crash or mis-behavior could always lead to affect user settings.

To prevent this, we can temporary override Settings backend read vfunc so
that the values we want to override won't ever be written to user db and so
there will be no risk of leaving them in a dirty state.

Sadly, this requires fixes to gjs:
  https://gitlab.gnome.org/GNOME/gjs/-/merge_requests/831

Author: 3v1n0

tiling-assistant@leleat-on-github/extension.js

@@ -36,13 +36,73 @@ const { Rect, Util } = Me.imports.src.extension.utility;
  *  => resizeHandler.js (when resizing a window)
  */
 
+class SettingsOverrider {
+    constructor() {
+        this._backend = Gio.SettingsBackend.get_default();
+        this._overriddenValues = new Map();
+
+        this._originalSettingsRead = Util.overrideVFunc(
+            this._backend.constructor.prototype, 'read',
+            (key, expectedType, defaultValue) => {
+                const overridden = this._overriddenValues.get(key);
+                if (overridden !== undefined) {
+                    if (overridden?.is_of_type(expectedType) !== false)
+                        return overridden;
+
+                    logError(new Error(),
+                        'Overriden value is of an invalid type: ' +
+                        `${expectedType} vs ${overridden?.get_type()}`);
+                }
+
+                return this._originalSettingsRead.call(this._backend,
+                    key, expectedType, defaultValue);
+            });
+    }
+
+    _getSettingPath(schema, key) {
+        return `/${schema.replaceAll('.', '/')}/${key}`;
+    }
+
+    add(schema, key, value) {
+        const path = this._getSettingPath(schema, key);
+        this._overriddenValues.set(path, value);
+        this._backend.changed(path, this);
+    }
+
+    remove(schema, key) {
+        const path = this._getSettingPath(schema, key);
+        this._overriddenValues.delete(path);
+        this._backend.changed(path, this);
+
+        if (!this._overriddenValues.size)
+            this._clear();
+    }
+
+    _clear() {
+        if (this._originalSettingsRead) {
+            Util.overrideVFunc(this._backend.constructor.prototype,
+                'read', this._originalSettingsRead);
+            this._originalSettingsRead = null;
+        }
+
+        this._overriddenValues?.forEach((_value, key) =>
+            this._backend.changed(key, this));
+        this._overriddenValues = null;
+    }
+
+    destroy() {
+        this._clear();
+    }
+}
+
 function init() {
     ExtensionUtils.initTranslations(Me.metadata.uuid);
 }
 
 function enable() {
     this._settings = Me.imports.src.common.Settings;
     this._settings.initialize();
+    this._settingsOverrider = new SettingsOverrider();
 
     this._twm = Me.imports.src.extension.tilingWindowManager.TilingWindowManager;
     this._twm.initialize();
@@ -62,45 +122,34 @@ function enable() {
     this._altTabOverride = new AltTabOverride();
 
     // Disable native tiling.
-    this._gnomeMutterSettings = ExtensionUtils.getSettings('org.gnome.mutter');
-    this._gnomeMutterEdgeTilingUserValue = this._gnomeMutterSettings.get_user_value('edge-tiling');
-    this._gnomeMutterSettings.set_boolean('edge-tiling', false);
-
-    if (Gio.SettingsSchemaSource.get_default().lookup('org.gnome.shell.overrides', true)) {
-        this._gnomeShellSettings = ExtensionUtils.getSettings('org.gnome.shell.overrides');
-        this._gnomeShellEdgeTilingUserValue = this._gnomeShellSettings.get_user_value('edge-tiling');
-        this._gnomeShellSettings.set_boolean('edge-tiling', false);
-    }
+    this._settingsOverrider.add('org.gnome.mutter', 'edge-tiling',
+        new GLib.Variant('b', false));
 
     // Disable native keybindings for Super+Up/Down/Left/Right
     this._gnomeMutterKeybindings = ExtensionUtils.getSettings('org.gnome.mutter.keybindings');
     this._gnomeDesktopKeybindings = ExtensionUtils.getSettings('org.gnome.desktop.wm.keybindings');
-    this._nativeKeybindings = [];
     const sc = Me.imports.src.common.Shortcuts;
+    const emptyStrvVariant = new GLib.Variant('as', []);
 
     if (this._gnomeDesktopKeybindings.get_strv('maximize').includes('<Super>Up') &&
             this._settings.getStrv(sc.MAXIMIZE).includes('<Super>Up')) {
-        const userValue = this._gnomeDesktopKeybindings.get_value('maximize');
-        this._gnomeDesktopKeybindings.set_strv('maximize', []);
-        this._nativeKeybindings.push([this._gnomeDesktopKeybindings, 'maximize', userValue]);
+        this._settingsOverrider.add(this._gnomeDesktopKeybindings.schemaId,
+            'maximize', emptyStrvVariant);
     }
     if (this._gnomeDesktopKeybindings.get_strv('unmaximize').includes('<Super>Down') &&
             this._settings.getStrv(sc.RESTORE_WINDOW).includes('<Super>Down')) {
-        const userValue = this._gnomeDesktopKeybindings.get_value('unmaximize');
-        this._gnomeDesktopKeybindings.set_strv('unmaximize', []);
-        this._nativeKeybindings.push([this._gnomeDesktopKeybindings, 'unmaximize', userValue]);
+        this._settingsOverrider.add(this._gnomeDesktopKeybindings.schemaId,
+            'unmaximize', emptyStrvVariant);
     }
     if (this._gnomeMutterKeybindings.get_strv('toggle-tiled-left').includes('<Super>Left') &&
             this._settings.getStrv(sc.LEFT).includes('<Super>Left')) {
-        const userValue = this._gnomeMutterKeybindings.get_value('toggle-tiled-left');
-        this._gnomeMutterKeybindings.set_strv('toggle-tiled-left', []);
-        this._nativeKeybindings.push([this._gnomeMutterKeybindings, 'toggle-tiled-left', userValue]);
+        this._settingsOverrider.add(this._gnomeMutterKeybindings.schemaId,
+            'toggle-tiled-left', emptyStrvVariant);
     }
     if (this._gnomeMutterKeybindings.get_strv('toggle-tiled-right').includes('<Super>Right') &&
             this._settings.getStrv(sc.RIGHT).includes('<Super>Right')) {
-        const userValue = this._gnomeMutterKeybindings.get_value('toggle-tiled-right');
-        this._gnomeMutterKeybindings.set_strv('toggle-tiled-right', []);
-        this._nativeKeybindings.push([this._gnomeMutterKeybindings, 'toggle-tiled-right', userValue]);
+        this._settingsOverrider.add(this._gnomeMutterKeybindings.schemaId,
+            'toggle-tiled-right', emptyStrvVariant);
     }
 
     // Include tiled windows when dragging from the top panel.
@@ -134,6 +183,8 @@ function disable() {
     // them after the session is unlocked again.
     _saveBeforeSessionLock();
 
+    this._settingsOverrider.destroy();
+    this._settingsOverrider = null;
     this._moveHandler.destroy();
     this._moveHandler = null;
     this._resizeHandler.destroy();
@@ -154,30 +205,6 @@ function disable() {
     this._settings.destroy();
     this._settings = null;
 
-    const restoreSetting = (gsettings, key, oldValue) => {
-        if (gsettings) {
-            if (oldValue)
-                gsettings.set_value(key, oldValue);
-            else
-                gsettings.reset(key);
-        }
-    };
-
-    // Re-enable native tiling.
-    restoreSetting(this._gnomeMutterSettings,
-        'edge-tiling', this._gnomeMutterEdgeTilingUserValue);
-    this._gnomeMutterEdgeTilingUserValue = null;
-    this._gnomeMutterSettings = null;
-
-    restoreSetting(this._gnomeShellSettings,
-        'edge-tiling', this._gnomeShellEdgeTilingUserValue);
-    this._gnomeShellEdgeTilingUserValue = null;
-    this._gnomeShellSettings = null;
-
-    // Restore native keybindings for Super+Up/Down/Left/Right
-    this._nativeKeybindings.forEach(([kbSetting, kbName, kbOldValue]) =>
-        restoreSetting(kbSetting, kbName, kbOldValue));
-    this._nativeKeybindings = [];
     this._gnomeMutterKeybindings = null;
     this._gnomeDesktopKeybindings = null;