Convert the app template to Kotlin (#36696)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/36696

As the title says, we're converting the new app template to Kotlin.
This will reduce the template size and make it more aligned to market standards.

Changelog:
[Android] [Changed] - Convert the app template to Kotlin

Reviewed By: mdvacca

Differential Revision: D44142081

fbshipit-source-id: 6111360b6580460eba0341e47c55704cc673e444

packages/react-native/template/android/app/build.gradle

@@ -1,4 +1,5 @@
 apply plugin: "com.android.application"
+apply plugin: "org.jetbrains.kotlin.android"
 apply plugin: "com.facebook.react"
 
 /**

packages/react-native/template/android/build.gradle

@@ -9,6 +9,7 @@ buildscript {
 
         // We use NDK 23 which has both M1 support and is the side-by-side NDK version from AGP.
         ndkVersion = "23.1.7779620"
+        kotlinVersion = "1.7.22"
     }
     repositories {
         google()
@@ -17,5 +18,6 @@ buildscript {
     dependencies {
         classpath("com.android.tools.build:gradle")
         classpath("com.facebook.react:react-native-gradle-plugin")
+        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion")
     }
 }

template/android/app/src/debug/java/com/helloworld/ReactNativeFlipper.kt

@@ -0,0 +1,60 @@
+/**
+ * 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.helloworld
+
+import android.content.Context
+import com.facebook.flipper.android.AndroidFlipperClient
+import com.facebook.flipper.android.utils.FlipperUtils
+import com.facebook.flipper.plugins.crashreporter.CrashReporterPlugin
+import com.facebook.flipper.plugins.databases.DatabasesFlipperPlugin
+import com.facebook.flipper.plugins.fresco.FrescoFlipperPlugin
+import com.facebook.flipper.plugins.inspector.DescriptorMapping
+import com.facebook.flipper.plugins.inspector.InspectorFlipperPlugin
+import com.facebook.flipper.plugins.network.FlipperOkhttpInterceptor
+import com.facebook.flipper.plugins.network.NetworkFlipperPlugin
+import com.facebook.flipper.plugins.sharedpreferences.SharedPreferencesFlipperPlugin
+import com.facebook.react.ReactInstanceEventListener
+import com.facebook.react.ReactInstanceManager
+import com.facebook.react.bridge.ReactContext
+import com.facebook.react.modules.network.NetworkingModule
+
+/**
+ * Class responsible of loading Flipper inside your React Native application. This is the debug
+ * flavor of it. Here you can add your own plugins and customize the Flipper setup.
+ */
+object ReactNativeFlipper {
+  fun initializeFlipper(context: Context, reactInstanceManager: ReactInstanceManager) {
+    if (FlipperUtils.shouldEnableFlipper(context)) {
+      val client = AndroidFlipperClient.getInstance(context)
+      client.addPlugin(InspectorFlipperPlugin(context, DescriptorMapping.withDefaults()))
+      client.addPlugin(DatabasesFlipperPlugin(context))
+      client.addPlugin(SharedPreferencesFlipperPlugin(context))
+      client.addPlugin(CrashReporterPlugin.getInstance())
+      val networkFlipperPlugin = NetworkFlipperPlugin()
+      NetworkingModule.setCustomClientBuilder { builder ->
+        builder.addNetworkInterceptor(FlipperOkhttpInterceptor(networkFlipperPlugin))
+      }
+      client.addPlugin(networkFlipperPlugin)
+      client.start()
+
+      // Fresco Plugin needs to ensure that ImagePipelineFactory is initialized
+      // Hence we run if after all native modules have been initialized
+      val currentReactContext = reactInstanceManager.currentReactContext
+      if (currentReactContext == null) {
+        reactInstanceManager.addReactInstanceEventListener(
+            object : ReactInstanceEventListener {
+              override fun onReactContextInitialized(context: ReactContext) {
+                reactInstanceManager.removeReactInstanceEventListener(this)
+                context.runOnNativeModulesQueueThread { client.addPlugin(FrescoFlipperPlugin()) }
+              }
+            })
+      } else {
+        client.addPlugin(FrescoFlipperPlugin())
+      }
+    }
+  }
+}

template/android/app/src/main/java/com/helloworld/MainActivity.kt

@@ -0,0 +1,22 @@
+package com.helloworld
+
+import com.facebook.react.ReactActivity
+import com.facebook.react.ReactActivityDelegate
+import com.facebook.react.defaults.DefaultNewArchitectureEntryPoint.fabricEnabled
+import com.facebook.react.defaults.DefaultReactActivityDelegate
+
+class MainActivity : ReactActivity() {
+
+  /**
+   * Returns the name of the main component registered from JavaScript. This is used to schedule
+   * rendering of the component.
+   */
+  override fun getMainComponentName(): String = "HelloWorld"
+
+  /**
+   * Returns the instance of the [ReactActivityDelegate]. We use [DefaultReactActivityDelegate]
+   * which allows you to enable New Architecture with a single boolean flags [fabricEnabled]
+   */
+  override fun createReactActivityDelegate(): ReactActivityDelegate =
+      DefaultReactActivityDelegate(this, mainComponentName, fabricEnabled)
+}

template/android/app/src/main/java/com/helloworld/MainApplication.kt

@@ -0,0 +1,38 @@
+package com.helloworld
+
+import android.app.Application
+import com.facebook.react.PackageList
+import com.facebook.react.ReactApplication
+import com.facebook.react.ReactNativeHost
+import com.facebook.react.ReactPackage
+import com.facebook.react.defaults.DefaultNewArchitectureEntryPoint.load
+import com.facebook.react.defaults.DefaultReactNativeHost
+import com.facebook.soloader.SoLoader
+
+class MainApplication : Application(), ReactApplication {
+
+  private val reactNativeHost: ReactNativeHost =
+      object : DefaultReactNativeHost(this) {
+        override fun getPackages(): List<ReactPackage> {
+          // Packages that cannot be autolinked yet can be added manually here, for example:
+          // packages.add(new MyReactNativePackage());
+          return PackageList(this).packages
+        }
+        override fun getJSMainModuleName(): String = "index"
+        override fun getUseDeveloperSupport(): Boolean = BuildConfig.DEBUG
+        override val isNewArchEnabled: Boolean = BuildConfig.IS_NEW_ARCHITECTURE_ENABLED
+        override val isHermesEnabled: Boolean = BuildConfig.IS_HERMES_ENABLED
+      }
+
+  override fun getReactNativeHost(): ReactNativeHost = reactNativeHost
+
+  override fun onCreate() {
+    super.onCreate()
+    SoLoader.init(this, false)
+    if (BuildConfig.IS_NEW_ARCHITECTURE_ENABLED) {
+      // If you opted-in for the New Architecture, we load the native entry point for this app.
+      load()
+    }
+    ReactNativeFlipper.initializeFlipper(this, reactNativeHost.reactInstanceManager)
+  }
+}

template/android/app/src/release/java/com/helloworld/ReactNativeFlipper.kt

@@ -0,0 +1,21 @@
+/**
+ * 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.helloworld
+
+import android.content.Context
+import com.facebook.react.ReactInstanceManager
+
+/**
+ * Class responsible of loading Flipper inside your React Native application. This is the release
+ * flavor of it so it's empty as we don't want to load Flipper.
+ */
+object ReactNativeFlipper {
+  @Suppress("UNUSED_PARAMETER")
+  fun initializeFlipper(context: Context, reactInstanceManager: ReactInstanceManager) {
+    // Do nothing as we don't want to initialize Flipper on Release.
+  }
+}