fix(react-native-host): override feature flags for bridgeless mode

.changeset/plenty-moose-live.md

@@ -0,0 +1,5 @@
+---
+"@rnx-kit/react-native-host": patch
+---
+
+Override feature flags for bridgeless mode

packages/react-native-host/cocoa/RNXBridgelessHeaders.h

@@ -12,6 +12,12 @@
 
 #import <react/config/ReactNativeConfig.h>
 
+#if __has_include(<react/featureflags/ReactNativeFeatureFlags.h>)
+#import <react/featureflags/ReactNativeFeatureFlags.h>
+#import <react/featureflags/ReactNativeFeatureFlagsDefaults.h>
+#define USE_FEATURE_FLAGS
+#endif  // __has_include(<react/featureflags/ReactNativeFeatureFlags.h>)
+
 #if __has_include(<react/runtime/JSEngineInstance.h>)
 using SharedJSRuntimeFactory = std::shared_ptr<facebook::react::JSEngineInstance>;
 #else
@@ -42,6 +48,28 @@ using SharedJSRuntimeFactory = std::shared_ptr<facebook::react::JSRuntimeFactory
 - (RCTSurfacePresenter *)getSurfacePresenter;  // Deprecated in 0.74, and removed in 0.75
 @end
 
+#ifdef USE_FEATURE_FLAGS
+// https://github.com/facebook/react-native/blob/0.74-stable/packages/react-native/Libraries/AppDelegate/RCTAppDelegate.mm#L272-L286
+class RNXBridgelessFeatureFlags : public facebook::react::ReactNativeFeatureFlagsDefaults
+{
+public:
+    bool useModernRuntimeScheduler() override
+    {
+        return true;
+    }
+
+    bool enableMicrotasks() override
+    {
+        return true;
+    }
+
+    bool batchRenderingUpdatesInEventLoop() override
+    {
+        return true;
+    }
+};
+#endif  // USE_FEATURE_FLAGS
+
 #elif USE_FABRIC
 
 #import <React/RCTSurfacePresenterBridgeAdapter.h>

packages/react-native-host/cocoa/ReactNativeHost.mm

@@ -49,6 +49,23 @@ - (instancetype)initWithConfig:(id<RNXHostConfig>)config
 - (instancetype)initWithConfig:(id<RNXHostConfig>)config launchOptions:(NSDictionary *)launchOptions
 {
     if (self = [super init]) {
+        _config = config;
+        _launchOptions = launchOptions;
+        [self enableTurboModule];
+        _isShuttingDown = [[NSLock alloc] init];
+
+        if ([config respondsToSelector:@selector(shouldReleaseBridgeWhenBackgrounded)] &&
+            [config shouldReleaseBridgeWhenBackgrounded]) {
+            _hostReleaser = [[RNXHostReleaser alloc] initWithHost:self];
+        }
+
+#ifdef USE_FEATURE_FLAGS
+        if (self.isBridgelessEnabled) {
+            facebook::react::ReactNativeFeatureFlags::override(
+                std::make_unique<RNXBridgelessFeatureFlags>());
+        }
+#endif  // USE_FEATURE_FLAGS
+
         if ([config respondsToSelector:@selector(isDevLoadingViewEnabled)]) {
             RCTDevLoadingViewSetEnabled([config isDevLoadingViewEnabled]);
         }
@@ -69,16 +86,6 @@ - (instancetype)initWithConfig:(id<RNXHostConfig>)config launchOptions:(NSDictio
             });
         }
 
-        _config = config;
-        _launchOptions = launchOptions;
-        [self enableTurboModule];
-        _isShuttingDown = [[NSLock alloc] init];
-
-        if ([config respondsToSelector:@selector(shouldReleaseBridgeWhenBackgrounded)] &&
-            [config shouldReleaseBridgeWhenBackgrounded]) {
-            _hostReleaser = [[RNXHostReleaser alloc] initWithHost:self];
-        }
-
         [self initializeReactHost];
     }
     return self;