Make sure that third party libraries include Fabric code

Summary:
In some previous changes ([a607692](a607692) and [6b53205](6b53205)) we make sure to always include all the pods (including Fabric) and we unify codegen to run in the same way on both architectures.
While doing so, we enabled codegen to run on libraries tat already migrated to Fabric.
These makes those libraries to fail when building as they were not including the Fabric code when the New Architecture is disabled.

This change will make sue that the code is always included, thus the library should always build, and it also make sure that we can control the New/Old Architecture at build time.

## Changelog
[iOS][Changed] - Make sure that libraries always include Fabric code also in the old architecture

Differential Revision: D51617542

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

@@ -81,7 +81,6 @@ - (instancetype)init
 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
 {
   BOOL enableTM = self.turboModuleEnabled;
-  ;
   BOOL enableBridgeless = self.bridgelessEnabled;
   BOOL fabricEnabled = self.fabricEnabled;
 
@@ -112,14 +111,14 @@ - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(
     if (!self.bridge) {
       self.bridge = [self createBridgeWithDelegate:self launchOptions:launchOptions];
     }
-#if RCT_NEW_ARCH_ENABLED
-    self.bridgeAdapter = [[RCTSurfacePresenterBridgeAdapter alloc] initWithBridge:self.bridge
-                                                                 contextContainer:_contextContainer];
-    self.bridge.surfacePresenter = self.bridgeAdapter.surfacePresenter;
-
-    [self unstable_registerLegacyComponents];
-    [RCTComponentViewFactory currentComponentViewFactory].thirdPartyFabricComponentsProvider = self;
-#endif
+    if ([self newArchEnabled]) {
+      self.bridgeAdapter = [[RCTSurfacePresenterBridgeAdapter alloc] initWithBridge:self.bridge
+                                                                   contextContainer:_contextContainer];
+      self.bridge.surfacePresenter = self.bridgeAdapter.surfacePresenter;
+      
+      [self unstable_registerLegacyComponents];
+      [RCTComponentViewFactory currentComponentViewFactory].thirdPartyFabricComponentsProvider = self;
+    }
 
     rootView = [self createRootViewWithBridge:self.bridge moduleName:self.moduleName initProps:initProps];
   }
@@ -190,38 +189,39 @@ - (void)windowScene:(UIWindowScene *)windowScene
 - (std::unique_ptr<facebook::react::JSExecutorFactory>)jsExecutorFactoryForBridge:(RCTBridge *)bridge
 {
   _runtimeScheduler = std::make_shared<facebook::react::RuntimeScheduler>(RCTRuntimeExecutorFromBridge(bridge));
-#if RCT_NEW_ARCH_ENABLED
-  std::shared_ptr<facebook::react::CallInvoker> callInvoker =
-      std::make_shared<facebook::react::RuntimeSchedulerCallInvoker>(_runtimeScheduler);
-  RCTTurboModuleManager *turboModuleManager = [[RCTTurboModuleManager alloc] initWithBridge:bridge
-                                                                                   delegate:self
-                                                                                  jsInvoker:callInvoker];
-  _contextContainer->erase("RuntimeScheduler");
-  _contextContainer->insert("RuntimeScheduler", _runtimeScheduler);
-  return RCTAppSetupDefaultJsExecutorFactory(bridge, turboModuleManager, _runtimeScheduler);
-#else
-  return RCTAppSetupJsExecutorFactoryForOldArch(bridge, _runtimeScheduler);
-#endif
+  if ([self newArchEnabled]) {
+    std::shared_ptr<facebook::react::CallInvoker> callInvoker =
+    std::make_shared<facebook::react::RuntimeSchedulerCallInvoker>(_runtimeScheduler);
+    RCTTurboModuleManager *turboModuleManager = [[RCTTurboModuleManager alloc] initWithBridge:bridge
+                                                                                     delegate:self
+                                                                                    jsInvoker:callInvoker];
+    _contextContainer->erase("RuntimeScheduler");
+    _contextContainer->insert("RuntimeScheduler", _runtimeScheduler);
+    return RCTAppSetupDefaultJsExecutorFactory(bridge, turboModuleManager, _runtimeScheduler);
+  } else {
+    return RCTAppSetupJsExecutorFactoryForOldArch(bridge, _runtimeScheduler);
+  }
 }
 
 #pragma mark - New Arch Enabled settings
 
-- (BOOL)turboModuleEnabled
+- (BOOL)newArchEnabled
 {
-#if RCT_NEW_ARCH_ENABLED
+#if USE_NEW_ARCH
   return YES;
 #else
   return NO;
 #endif
 }
 
+- (BOOL)turboModuleEnabled
+{
+  return [self newArchEnabled];
+}
+
 - (BOOL)fabricEnabled
 {
-#if RCT_NEW_ARCH_ENABLED
-  return YES;
-#else
-  return NO;
-#endif
+  return [self newArchEnabled];
 }
 
 - (BOOL)bridgelessEnabled

packages/react-native/Libraries/AppDelegate/React-RCTAppDelegate.podspec

@@ -19,10 +19,10 @@ end
 folly_flags = ' -DFOLLY_NO_CONFIG -DFOLLY_MOBILE=1 -DFOLLY_USE_LIBCPP=1 -DFOLLY_CFG_NO_COROUTINES=1 -DFOLLY_HAVE_CLOCK_GETTIME=1'
 folly_compiler_flags = folly_flags + ' ' + '-Wno-comma -Wno-shorten-64-to-32'
 
-is_new_arch_enabled = ENV["RCT_NEW_ARCH_ENABLED"] == "1"
+is_new_arch_enabled = ENV["USE_NEW_ARCH"] == "1"
 use_hermes =  ENV['USE_HERMES'] == nil || ENV['USE_HERMES'] == '1'
 
-new_arch_enabled_flag = (is_new_arch_enabled ? " -DRCT_NEW_ARCH_ENABLED" : "")
+new_arch_enabled_flag = (is_new_arch_enabled ? " -DUSE_NEW_ARCH" : "")
 is_fabric_enabled = is_new_arch_enabled || ENV["RCT_FABRIC_ENABLED"]
 hermes_flag = (use_hermes ? " -DUSE_HERMES" : "")
 other_cflags = "$(inherited)" + folly_flags + new_arch_enabled_flag + hermes_flag

packages/react-native/scripts/react_native_pods.rb

@@ -93,9 +93,10 @@ def use_react_native! (
   # Better to rely and enable this environment flag if the new architecture is turned on using flags.
   relative_path_from_current = Pod::Config.instance.installation_root.relative_path_from(Pathname.pwd)
   react_native_version = NewArchitectureHelper.extract_react_native_version(File.join(relative_path_from_current, path))
-  ENV['RCT_NEW_ARCH_ENABLED'] = NewArchitectureHelper.compute_new_arch_enabled(new_arch_enabled, react_native_version)
-
+  ENV['USE_NEW_ARCH'] = NewArchitectureHelper.compute_new_arch_enabled(new_arch_enabled, react_native_version)
   fabric_enabled = fabric_enabled || NewArchitectureHelper.new_arch_enabled
+
+  ENV['RCT_NEW_ARCH_ENABLED'] = "1"
   ENV['RCT_FABRIC_ENABLED'] = fabric_enabled ? "1" : "0"
   ENV['USE_HERMES'] = hermes_enabled ? "1" : "0"