Implement new feature flag system (re-land) (#42678)

Summary:
Pull Request resolved: #42678

Changelog: [internal]

This is a re-application of #42430, which had to be reverted because of crashes in optimized builds on Android:

```
Abort Reason: terminating due to uncaught exception of type facebook::jni::JniException: java.lang.ClassNotFoundException: com.facebook.react.internal.featureflags.ReactNativeFeatureFlagsProvider
```

The root cause of that was that that class was removed because it wasn't statically referenced from Kotlin/Java, but it was dynamically referenced from C++ (in `ReactNativeFeatureFlagsProviderHolder.cpp`).

This applies the same changes + adds `DoNotStrip` annotations for the affected class and all its methods.

Reviewed By: huntie

Differential Revision: D53122992

fbshipit-source-id: efc4d5636a3f2d39b86e9c098bff408b6688b80b

Author: rubennorte

package.json

@@ -21,6 +21,8 @@
     "flow": "flow",
     "format-check": "prettier --list-different \"./**/*.{js,md,yml,ts,tsx}\"",
     "format": "npm run prettier && npm run clang-format",
+    "featureflags-check": "cd packages/react-native && yarn featureflags-check",
+    "featureflags-update": "cd packages/react-native && yarn featureflags-update",
     "lint-ci": "./scripts/circleci/analyze_code.sh && yarn shellcheck",
     "lint-java": "node ./scripts/lint-java.js",
     "lint": "eslint .",

packages/react-native/React-Core.podspec

@@ -129,6 +129,7 @@ Pod::Spec.new do |s|
   s.dependency "React-jsi"
   s.dependency "React-jsiexecutor"
   s.dependency "React-utils"
+  s.dependency "React-featureflags"
   s.dependency "SocketRocket", socket_rocket_version
   s.dependency "React-runtimescheduler"
   s.dependency "Yoga"

packages/react-native/ReactAndroid/build.gradle.kts

@@ -526,6 +526,7 @@ android {
             "runtimeexecutor",
             "react_codegen_rncore",
             "react_debug",
+            "react_featureflags",
             "react_utils",
             "react_render_componentregistry",
             "react_newarchdefaults",
@@ -540,6 +541,7 @@ android {
             "jsi",
             "glog",
             "fabricjni",
+            "featureflagsjni",
             "react_render_mapbuffer",
             "yoga",
             "folly_runtime",

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlags.kt

@@ -0,0 +1,78 @@
+/*
+ * 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<<c201b2b577ab4aa4bf6071d6b99b43c9>>
+ */
+
+/**
+ * IMPORTANT: Do NOT modify this file directly.
+ *
+ * To change the definition of the flags, edit
+ *   packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.json.
+ *
+ * To regenerate this code, run the following script from the repo root:
+ *   yarn featureflags-update
+ */
+
+package com.facebook.react.internal.featureflags
+
+/**
+ * This object provides access to internal React Native feature flags.
+ *
+ * All the methods are thread-safe if you handle `override` correctly.
+ */
+object ReactNativeFeatureFlags {
+  private var accessorProvider: () -> ReactNativeFeatureFlagsAccessor = { ReactNativeFeatureFlagsCxxAccessor() }
+  private var accessor: ReactNativeFeatureFlagsAccessor = accessorProvider()
+
+  /**
+   * Common flag for testing. Do NOT modify.
+   */
+  fun commonTestFlag() = accessor.commonTestFlag()
+
+  /**
+   * Overrides the feature flags with the ones provided by the given provider
+   * (generally one that extends `ReactNativeFeatureFlagsDefaults`).
+   *
+   * This method must be called before you initialize the React Native runtime.
+   *
+   * @example
+   *
+   * ```
+   * ReactNativeFeatureFlags.override(object : ReactNativeFeatureFlagsDefaults() {
+   *   override fun someFlag(): Boolean = true // or a dynamic value
+   * })
+   * ```
+   */
+  fun override(provider: ReactNativeFeatureFlagsProvider) = accessor.override(provider)
+
+  /**
+   * Removes the overridden feature flags and makes the API return default
+   * values again.
+   *
+   * This should only be called if you destroy the React Native runtime and
+   * need to create a new one with different overrides. In that case,
+   * call `dangerouslyReset` after destroying the runtime and `override`
+   * again before initializing the new one.
+   */
+  fun dangerouslyReset() {
+    // This is necessary when the accessor interops with C++ and we need to
+    // remove the overrides set there.
+    accessor.dangerouslyReset()
+
+    // This discards the cached values and the overrides set in the JVM.
+    accessor = accessorProvider()
+  }
+
+  /**
+   * This is just used to replace the default ReactNativeFeatureFlagsCxxAccessor
+   * that uses JNI with a version that doesn't, to simplify testing.
+   */
+  internal fun setAccessorProvider(newAccessorProvider: () -> ReactNativeFeatureFlagsAccessor) {
+    accessorProvider = newAccessorProvider
+    accessor = accessorProvider()
+  }
+}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsAccessor.kt

@@ -0,0 +1,14 @@
+/*
+ * 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.
+ */
+
+package com.facebook.react.internal.featureflags
+
+interface ReactNativeFeatureFlagsAccessor : ReactNativeFeatureFlagsProvider {
+  fun override(provider: ReactNativeFeatureFlagsProvider)
+
+  fun dangerouslyReset()
+}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxAccessor.kt

@@ -0,0 +1,38 @@
+/*
+ * 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<<961f1fb0a7ad802a492437f15b1f2dcb>>
+ */
+
+/**
+ * IMPORTANT: Do NOT modify this file directly.
+ *
+ * To change the definition of the flags, edit
+ *   packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.json.
+ *
+ * To regenerate this code, run the following script from the repo root:
+ *   yarn featureflags-update
+ */
+
+package com.facebook.react.internal.featureflags
+
+class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAccessor {
+  private var commonTestFlagCache: Boolean? = null
+
+  override fun commonTestFlag(): Boolean {
+    var cached = commonTestFlagCache
+    if (cached == null) {
+      cached = ReactNativeFeatureFlagsCxxInterop.commonTestFlag()
+      commonTestFlagCache = cached
+    }
+    return cached
+  }
+
+  override fun override(provider: ReactNativeFeatureFlagsProvider) =
+      ReactNativeFeatureFlagsCxxInterop.override(provider as Any)
+
+  override fun dangerouslyReset() = ReactNativeFeatureFlagsCxxInterop.dangerouslyReset()
+}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxInterop.kt

@@ -0,0 +1,36 @@
+/*
+ * 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<<c2e41ac8c3d9471b4cb79f6147cc2bf2>>
+ */
+
+/**
+ * IMPORTANT: Do NOT modify this file directly.
+ *
+ * To change the definition of the flags, edit
+ *   packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.json.
+ *
+ * To regenerate this code, run the following script from the repo root:
+ *   yarn featureflags-update
+ */
+
+package com.facebook.react.internal.featureflags
+
+import com.facebook.proguard.annotations.DoNotStrip
+import com.facebook.soloader.SoLoader
+
+@DoNotStrip
+object ReactNativeFeatureFlagsCxxInterop {
+  init {
+    SoLoader.loadLibrary("reactfeatureflagsjni")
+  }
+
+  @DoNotStrip @JvmStatic external fun commonTestFlag(): Boolean
+
+  @DoNotStrip @JvmStatic external fun override(provider: Any)
+
+  @DoNotStrip @JvmStatic external fun dangerouslyReset()
+}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsDefaults.kt

@@ -0,0 +1,27 @@
+/*
+ * 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<<aa1eaeee7b715e5b1d3cbcf9b7a7062e>>
+ */
+
+/**
+ * IMPORTANT: Do NOT modify this file directly.
+ *
+ * To change the definition of the flags, edit
+ *   packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.json.
+ *
+ * To regenerate this code, run the following script from the repo root:
+ *   yarn featureflags-update
+ */
+
+package com.facebook.react.internal.featureflags
+
+open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvider {
+  // We could use JNI to get the defaults from C++,
+  // but that is more expensive than just duplicating the defaults here.
+
+  override fun commonTestFlag(): Boolean = false
+}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsForTests.kt

@@ -0,0 +1,14 @@
+/*
+ * 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.
+ */
+
+package com.facebook.react.internal.featureflags
+
+object ReactNativeFeatureFlagsForTests {
+  fun setUp() {
+    ReactNativeFeatureFlags.setAccessorProvider({ ReactNativeFeatureFlagsLocalAccessor() })
+  }
+}

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsLocalAccessor.kt

@@ -0,0 +1,52 @@
+/*
+ * 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<<8bbd7e8cc2c50cfbf44ba6671d095f23>>
+ */
+
+/**
+ * IMPORTANT: Do NOT modify this file directly.
+ *
+ * To change the definition of the flags, edit
+ *   packages/react-native/scripts/featureflags/ReactNativeFeatureFlags.json.
+ *
+ * To regenerate this code, run the following script from the repo root:
+ *   yarn featureflags-update
+ */
+
+package com.facebook.react.internal.featureflags
+
+class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAccessor {
+  private var currentProvider: ReactNativeFeatureFlagsProvider = ReactNativeFeatureFlagsDefaults()
+
+  private val accessedFeatureFlags = mutableSetOf<String>()
+
+  private var commonTestFlagCache: Boolean? = null
+
+  override fun commonTestFlag(): Boolean {
+    var cached = commonTestFlagCache
+    if (cached == null) {
+      cached = currentProvider.commonTestFlag()
+      accessedFeatureFlags.add("commonTestFlag")
+      commonTestFlagCache = cached
+    }
+    return cached
+  }
+
+  override fun override(provider: ReactNativeFeatureFlagsProvider) {
+    if (accessedFeatureFlags.isNotEmpty()) {
+      val accessedFeatureFlagsStr = accessedFeatureFlags.joinToString(separator = ", ") { it }
+      throw IllegalStateException(
+          "Feature flags were accessed before being overridden: $accessedFeatureFlagsStr")
+    }
+    currentProvider = provider
+  }
+
+  override fun dangerouslyReset() {
+    // We don't need to do anything here because `ReactNativeFeatureFlags` will
+    // just create a new instance of this class.
+  }
+}