[UX/Fix] Respect experimental UMU support disabled

src/backend/game_config.ts

@@ -275,6 +275,10 @@ class GameConfigV0 extends GameConfig {
       // read game's settings
       const settings = JSON.parse(readFileSync(this.path, 'utf-8'))
       gameSettings = settings[this.appName] || ({} as GameSettings)
+    } else {
+      // only set the `disableUMU` default value when getting settings for a new game
+      // we want it to be `undefined` for games that were installed already
+      defaultSettings.disableUMU = false
     }
 
     if (!isWindows) {

src/backend/utils/compatibility_layers.ts

@@ -559,7 +559,22 @@ export async function isUmuSupported(
 ): Promise<boolean> {
   if (!isLinux) return false
   if (gameSettings.wineVersion.type !== 'proton') return false
-  if (gameSettings.disableUMU) return false
+  if (gameSettings.disableUMU === true) return false
+  if (gameSettings.disableUMU === undefined) {
+    // If the disableUMU setting is undefined it means the game was installed and configured
+    // before the introduction of this setting, so the usage of UMU was dictated by the
+    // experimental feature configuration.
+    //
+    // We have to check this to not enable UMU incorrectly even if the setting is not editable
+    // anymore.
+    // If we don't, we would end up enabling UMU for games that are already functional with proton
+    // without UMU to not mess their prefix
+    const experimentalFeatures =
+      GlobalConfig.get().getSettings().experimentalFeatures
+
+    // if UMU was never enabled or was enabled and then disabled
+    if (!experimentalFeatures?.umuSupport) return false
+  }
   if (!checkUmuInstalled) return true
   if (!existsSync(await getUmuPath())) return false
 

src/common/types.ts

@@ -65,6 +65,7 @@ export type ExperimentalFeatures = {
   enableNewDesign: boolean
   enableHelp: boolean
   cometSupport: boolean
+  umuSupport?: boolean
 }
 
 export interface AppSettings extends GameSettings {