Generate public feature flags entry point (#58742)

Summary:
Pull Request resolved: #58742

Adds a `dangerouslyExposeInPublicCppHeaders` option to the feature flags config. Flags that opt in are generated into `ReactNativePublicFeatureFlags.h`, whose getters forward to `ReactNativeFeatureFlags` from a generated `.cpp`, so exported headers can read them without including the rest of the module. Opts in the flags that exported headers currently read inline.

Changelog: [Internal]

Reviewed By: rubennorte

Differential Revision: D122353811

Author: j-piasecki

packages/react-native/ReactCommon/react/featureflags/ReactNativePublicFeatureFlags.cpp

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @generated SignedSource<<95f86b3476aeff097f532b10cabf067e>>
+ */
+
+/**
+ * IMPORTANT: Do NOT modify this file directly.
+ *
+ * To change the definition of the flags, edit
+ *   packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.config.js.
+ *
+ * To regenerate this code, run the following script from the repo root:
+ *   yarn featureflags --update
+ */
+
+#include "ReactNativeFeatureFlags.h"
+#include "ReactNativePublicFeatureFlags.h"
+
+namespace facebook::react {
+
+bool ReactNativeFeatureFlags_DO_NOT_USE::enableAccumulatedUpdatesInRawPropsAndroid() {
+  return ReactNativeFeatureFlags::enableAccumulatedUpdatesInRawPropsAndroid();
+}
+
+bool ReactNativeFeatureFlags_DO_NOT_USE::enableCppPropsIteratorSetter() {
+  return ReactNativeFeatureFlags::enableCppPropsIteratorSetter();
+}
+
+bool ReactNativeFeatureFlags_DO_NOT_USE::enableExclusivePropsUpdateAndroid() {
+  return ReactNativeFeatureFlags::enableExclusivePropsUpdateAndroid();
+}
+
+bool ReactNativeFeatureFlags_DO_NOT_USE::enableNativeCSSParsing() {
+  return ReactNativeFeatureFlags::enableNativeCSSParsing();
+}
+
+bool ReactNativeFeatureFlags_DO_NOT_USE::enablePropsUpdateReconciliationAndroid() {
+  return ReactNativeFeatureFlags::enablePropsUpdateReconciliationAndroid();
+}
+
+bool ReactNativeFeatureFlags_DO_NOT_USE::useSharedAnimatedBackend() {
+  return ReactNativeFeatureFlags::useSharedAnimatedBackend();
+}
+
+} // namespace facebook::react

packages/react-native/ReactCommon/react/featureflags/ReactNativePublicFeatureFlags.h

@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @generated SignedSource<<39037a69a47b86d0c6643d90f4058002>>
+ */
+
+/**
+ * IMPORTANT: Do NOT modify this file directly.
+ *
+ * To change the definition of the flags, edit
+ *   packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.config.js.
+ *
+ * To regenerate this code, run the following script from the repo root:
+ *   yarn featureflags --update
+ */
+
+#pragma once
+
+#include <string>
+
+#ifndef RN_EXPORT
+#define RN_EXPORT __attribute__((visibility("default")))
+#endif
+
+namespace facebook::react {
+
+/**
+ * This class provides public access to select internal React Native feature flags.
+ */
+class ReactNativeFeatureFlags_DO_NOT_USE {
+ public:
+  /**
+   * When enabled, Android will accumulate updates in rawProps to reduce the number of mounting instructions for cascading re-renders.
+   */
+  RN_EXPORT static bool enableAccumulatedUpdatesInRawPropsAndroid();
+
+  /**
+   * Enable prop iterator setter-style construction of Props in C++ (this flag is not used in Java).
+   */
+  RN_EXPORT static bool enableCppPropsIteratorSetter();
+
+  /**
+   * When enabled, Android will disable Props 1.5 raw value merging when Props 2.0 is available.
+   */
+  RN_EXPORT static bool enableExclusivePropsUpdateAndroid();
+
+  /**
+   * Parse CSS strings using the Fabric CSS parser instead of ViewConfig processing
+   */
+  RN_EXPORT static bool enableNativeCSSParsing();
+
+  /**
+   * When enabled, Android will receive prop updates based on the differences between the last rendered shadow node and the last committed shadow node.
+   */
+  RN_EXPORT static bool enablePropsUpdateReconciliationAndroid();
+
+  /**
+   * Use shared animation backend in C++ Animated
+   */
+  RN_EXPORT static bool useSharedAnimatedBackend();
+};
+
+} // namespace facebook::react

packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.config.js

@@ -181,6 +181,7 @@ const definitions: FeatureFlagDefinitions = {
       ossReleaseStage: 'canary',
     },
     enableAccumulatedUpdatesInRawPropsAndroid: {
+      dangerouslyExposeInPublicCppHeaders: true,
       defaultValue: false,
       metadata: {
         dateAdded: '2024-12-10',
@@ -233,6 +234,7 @@ const definitions: FeatureFlagDefinitions = {
       ossReleaseStage: 'none',
     },
     enableCppPropsIteratorSetter: {
+      dangerouslyExposeInPublicCppHeaders: true,
       defaultValue: false,
       metadata: {
         dateAdded: '2024-09-13',
@@ -287,6 +289,7 @@ const definitions: FeatureFlagDefinitions = {
       ossReleaseStage: 'none',
     },
     enableExclusivePropsUpdateAndroid: {
+      dangerouslyExposeInPublicCppHeaders: true,
       defaultValue: false,
       metadata: {
         dateAdded: '2025-11-11',
@@ -517,6 +520,7 @@ const definitions: FeatureFlagDefinitions = {
       ossReleaseStage: 'none',
     },
     enableNativeCSSParsing: {
+      dangerouslyExposeInPublicCppHeaders: true,
       defaultValue: false,
       metadata: {
         dateAdded: '2025-02-07',
@@ -538,6 +542,7 @@ const definitions: FeatureFlagDefinitions = {
       ossReleaseStage: 'none',
     },
     enablePropsUpdateReconciliationAndroid: {
+      dangerouslyExposeInPublicCppHeaders: true,
       defaultValue: false,
       metadata: {
         dateAdded: '2024-07-12',
@@ -923,6 +928,7 @@ const definitions: FeatureFlagDefinitions = {
       ossReleaseStage: 'none',
     },
     useSharedAnimatedBackend: {
+      dangerouslyExposeInPublicCppHeaders: true,
       defaultValue: false,
       metadata: {
         dateAdded: '2025-08-02',

packages/react-native/scripts/featureflags/generateCommonCxxModules.js

@@ -18,6 +18,8 @@ import ReactNativeFeatureFlagsDefaultsH from './templates/common-cxx/ReactNative
 import ReactNativeFeatureFlagsDynamicProviderH from './templates/common-cxx/ReactNativeFeatureFlagsDynamicProvider.h-template';
 import ReactNativeFeatureFlagsOverrides from './templates/common-cxx/ReactNativeFeatureFlagsOverridesOSS_Stage_.h-template';
 import ReactNativeFeatureFlagsProviderH from './templates/common-cxx/ReactNativeFeatureFlagsProvider.h-template';
+import ReactNativePublicFeatureFlagsCPP from './templates/common-cxx/ReactNativePublicFeatureFlags.cpp-template';
+import ReactNativePublicFeatureFlagsH from './templates/common-cxx/ReactNativePublicFeatureFlags.h-template';
 import path from 'node:path';
 
 export default function generateCommonCxxModules(
@@ -30,6 +32,10 @@ export default function generateCommonCxxModules(
       ReactNativeFeatureFlagsH(featureFlagDefinitions),
     [path.join(commonCxxPath, 'ReactNativeFeatureFlags.cpp')]:
       ReactNativeFeatureFlagsCPP(featureFlagDefinitions),
+    [path.join(commonCxxPath, 'ReactNativePublicFeatureFlags.h')]:
+      ReactNativePublicFeatureFlagsH(featureFlagDefinitions),
+    [path.join(commonCxxPath, 'ReactNativePublicFeatureFlags.cpp')]:
+      ReactNativePublicFeatureFlagsCPP(featureFlagDefinitions),
     [path.join(commonCxxPath, 'ReactNativeFeatureFlagsAccessor.h')]:
       ReactNativeFeatureFlagsAccessorH(featureFlagDefinitions),
     [path.join(commonCxxPath, 'ReactNativeFeatureFlagsAccessor.cpp')]:

packages/react-native/scripts/featureflags/generateFiles.js

@@ -34,7 +34,18 @@ export default function generateFiles(
       ...generatorConfig.featureFlagDefinitions,
       common: Object.fromEntries(
         Object.entries(generatorConfig.featureFlagDefinitions.common).filter(
-          ([_, definition]) => !definition.skipNativeAPI,
+          ([name, definition]) => {
+            if (
+              definition.skipNativeAPI &&
+              definition.dangerouslyExposeInPublicCppHeaders
+            ) {
+              throw new Error(
+                `${name} cannot have both skipNativeAPI and dangerouslyExposeInPublicCppHeaders enabled at the same time.`,
+              );
+            }
+
+            return !definition.skipNativeAPI;
+          },
         ),
       ),
     },

packages/react-native/scripts/featureflags/templates/common-cxx/ReactNativePublicFeatureFlags.cpp-template.js

@@ -0,0 +1,47 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ * @format
+ */
+
+import type {FeatureFlagDefinitions} from '../../types';
+
+import {DO_NOT_MODIFY_COMMENT, getCxxTypeFromDefaultValue} from '../../utils';
+import signedsource from 'signedsource';
+
+export default function (definitions: FeatureFlagDefinitions): string {
+  return signedsource.signFile(`/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * ${signedsource.getSigningToken()}
+ */
+
+${DO_NOT_MODIFY_COMMENT}
+
+#include "ReactNativeFeatureFlags.h"
+#include "ReactNativePublicFeatureFlags.h"
+
+namespace facebook::react {
+
+${Object.entries(definitions.common)
+  .filter(([_, flagConfig]) => flagConfig.dangerouslyExposeInPublicCppHeaders)
+  .map(
+    ([flagName, flagConfig]) =>
+      `${getCxxTypeFromDefaultValue(
+        flagConfig.defaultValue,
+      )} ReactNativeFeatureFlags_DO_NOT_USE::${flagName}() {
+  return ReactNativeFeatureFlags::${flagName}();
+}`,
+  )
+  .join('\n\n')}
+
+} // namespace facebook::react
+`);
+}

packages/react-native/scripts/featureflags/templates/common-cxx/ReactNativePublicFeatureFlags.h-template.js

@@ -0,0 +1,57 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ * @format
+ */
+
+import type {FeatureFlagDefinitions} from '../../types';
+
+import {DO_NOT_MODIFY_COMMENT, getCxxTypeFromDefaultValue} from '../../utils';
+import signedsource from 'signedsource';
+
+export default function (definitions: FeatureFlagDefinitions): string {
+  return signedsource.signFile(`/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * ${signedsource.getSigningToken()}
+ */
+
+${DO_NOT_MODIFY_COMMENT}
+
+#pragma once
+
+#include <string>
+
+#ifndef RN_EXPORT
+#define RN_EXPORT __attribute__((visibility("default")))
+#endif
+
+namespace facebook::react {
+
+/**
+ * This class provides public access to select internal React Native feature flags.
+ */
+class ReactNativeFeatureFlags_DO_NOT_USE {
+ public:
+${Object.entries(definitions.common)
+  .filter(([_, flagConfig]) => flagConfig.dangerouslyExposeInPublicCppHeaders)
+  .map(
+    ([flagName, flagConfig]) =>
+      `  /**
+   * ${flagConfig.metadata.description}
+   */
+  RN_EXPORT static ${getCxxTypeFromDefaultValue(flagConfig.defaultValue)} ${flagName}();`,
+  )
+  .join('\n\n')}
+};
+
+} // namespace facebook::react
+`);
+}

packages/react-native/scripts/featureflags/types.js

@@ -34,6 +34,8 @@ export type CommonFeatureFlagConfig<
   // Indicates if this API should only be defined in JavaScript, only to
   // preserve backwards compatibility with existing native code temporarily.
   skipNativeAPI?: true,
+  // Whether this flag should be exposed by the public feature flags entrypoint.
+  dangerouslyExposeInPublicCppHeaders?: true,
 }>;
 
 export type CommonFeatureFlagList = Readonly<{