RNTester enable concurrent root when using Fabric (facebook#41166)

Summary:
RNTester's `AppDelegate` override `prepareInitialProps` method of super class `RCTAppDelegate` https://github.com/facebook/react-native/blob/70acd3f7d9edae9e40cc4603bede9778da281a85/packages/react-native/Libraries/AppDelegate/RCTAppDelegate.mm#L152, so we missed `concurrentRoot` initial prop.

![image](https://github.com/facebook/react-native/assets/5061845/12af5815-afe6-46f0-8107-54ca443b4962)

cc javache cipolleschi

## Changelog:

[IOS] [FIXED] - RNTester enable concurrent root when using Fabric

Pull Request resolved: facebook#41166

Test Plan: Warning disappear.

Reviewed By: cipolleschi

Differential Revision: D50596693

Pulled By: javache

fbshipit-source-id: d73a17cd137b3088405f86b739cb0ed7b5a9839e

packages/react-native/Libraries/AppDelegate/RCTAppDelegate.h

@@ -101,8 +101,6 @@
  * By default, it assigns the rootView to the view property of the rootViewController
  * If you are not using a simple UIViewController, then there could be other methods to use to setup the rootView.
  * For example: UISplitViewController requires `setViewController(_:for:)`
- *
- * @return: void
  */
 - (void)setRootView:(UIView *)rootView toRootViewController:(UIViewController *)rootViewController;
 

packages/react-native/Libraries/AppDelegate/RCTAppDelegate.mm

@@ -53,6 +53,19 @@ @interface RCTAppDelegate () <
 
 #endif
 
+static NSDictionary *updateInitialProps(NSDictionary *initialProps, BOOL isFabricEnabled)
+{
+#ifdef RCT_NEW_ARCH_ENABLED
+  NSMutableDictionary *mutableProps = [initialProps mutableCopy] ?: [NSMutableDictionary new];
+  // Hardcoding the Concurrent Root as it it not recommended to
+  // have the concurrentRoot turned off when Fabric is enabled.
+  mutableProps[kRNConcurrentRoot] = @(isFabricEnabled);
+  return mutableProps;
+#else
+  return initialProps;
+#endif
+}
+
 @interface RCTAppDelegate () <RCTCxxBridgeDelegate> {
   std::shared_ptr<facebook::react::RuntimeScheduler> _runtimeScheduler;
 }
@@ -80,18 +93,21 @@ - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(
 {
   BOOL enableTM = NO;
   BOOL enableBridgeless = NO;
+  BOOL fabricEnabled = NO;
 #if RCT_NEW_ARCH_ENABLED
   enableTM = self.turboModuleEnabled;
   enableBridgeless = self.bridgelessEnabled;
+  fabricEnabled = [self fabricEnabled];
 #endif
+  NSDictionary *initProps = updateInitialProps([self prepareInitialProps], fabricEnabled);
 
   RCTAppSetupPrepareApp(application, enableTM);
 
   UIView *rootView;
   if (enableBridgeless) {
 #if RCT_NEW_ARCH_ENABLED
     // Enable native view config interop only if both bridgeless mode and Fabric is enabled.
-    RCTSetUseNativeViewConfigsInBridgelessMode([self fabricEnabled]);
+    RCTSetUseNativeViewConfigsInBridgelessMode(fabricEnabled);
 
     // Enable TurboModule interop by default in Bridgeless mode
     RCTEnableTurboModuleInterop(YES);
@@ -100,7 +116,6 @@ - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(
     [self createReactHost];
     [self unstable_registerLegacyComponents];
     [RCTComponentViewFactory currentComponentViewFactory].thirdPartyFabricComponentsProvider = self;
-    NSDictionary *initProps = [self prepareInitialProps];
     RCTFabricSurface *surface = [_reactHost createSurfaceWithModuleName:self.moduleName initialProperties:initProps];
 
     RCTSurfaceHostingProxyRootView *surfaceHostingProxyRootView = [[RCTSurfaceHostingProxyRootView alloc]
@@ -121,7 +136,7 @@ - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(
     [self unstable_registerLegacyComponents];
     [RCTComponentViewFactory currentComponentViewFactory].thirdPartyFabricComponentsProvider = self;
 #endif
-    NSDictionary *initProps = [self prepareInitialProps];
+
     rootView = [self createRootViewWithBridge:self.bridge moduleName:self.moduleName initProps:initProps];
   }
   self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
@@ -143,15 +158,7 @@ - (NSURL *)sourceURLForBridge:(RCTBridge *)bridge
 
 - (NSDictionary *)prepareInitialProps
 {
-  NSMutableDictionary *initProps = self.initialProps ? [self.initialProps mutableCopy] : [NSMutableDictionary new];
-
-#ifdef RCT_NEW_ARCH_ENABLED
-  // Hardcoding the Concurrent Root as it it not recommended to
-  // have the concurrentRoot turned off when Fabric is enabled.
-  initProps[kRNConcurrentRoot] = @([self fabricEnabled]);
-#endif
-
-  return initProps;
+  return self.initialProps;
 }
 
 - (RCTBridge *)createBridgeWithDelegate:(id<RCTBridgeDelegate>)delegate launchOptions:(NSDictionary *)launchOptions