configure to build from source

Summary: Configure helloworld to build from source, using a combination of our [How to Build from Source](https://reactnative.dev/contributing/how-to-build-from-source#update-your-project-to-build-from-source) guide, as well as using rn-tester's config as a guide.

Differential Revision: D58287748

packages/helloworld/android/app/build.gradle

@@ -23,7 +23,7 @@ react {
     //   The folder where the react-native NPM package is. Default is ../node_modules/react-native
     reactNativeDir = file("../../../react-native")
     //   The folder where the react-native Codegen package is. Default is ../node_modules/@react-native/codegen
-    codegenDir = file("../../../react-native-codegen")
+    codegenDir = file("$rootDir/node_modules/@react-native/codegen")
     //   The cli.js file which is the React Native CLI entrypoint. Default is ../node_modules/react-native/cli.js,
     //   but now points to our simplified bundle wrapper.
     cliFile = file("../../scripts/bundle.js")

packages/helloworld/android/settings.gradle

@@ -6,10 +6,18 @@
  */
 
 // Autolinking has now moved into the React Native Gradle Plugin
-pluginManagement { includeBuild("../node_modules/@react-native/gradle-plugin") }
+pluginManagement { includeBuild("../../react-native-gradle-plugin") }
 plugins { id("com.facebook.react.settings") }
 extensions.configure(com.facebook.react.ReactSettingsExtension){ ex -> ex.autolinkLibrariesFromCommand() }
 
 rootProject.name = 'HelloWorld'
 include ':app'
 includeBuild('../../react-native-gradle-plugin')
+includeBuild('../../react-native') {
+     dependencySubstitution {
+         substitute(module("com.facebook.react:react-android")).using(project(":packages:react-native:ReactAndroid"))
+         substitute(module("com.facebook.react:react-native")).using(project(":packages:react-native:ReactAndroid"))
+         substitute(module("com.facebook.react:hermes-android")).using(project(":packages:react-native:ReactAndroid:hermes-engine"))
+         substitute(module("com.facebook.react:hermes-engine")).using(project(":packages:react-native:ReactAndroid:hermes-engine"))
+     }
+ }

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

@@ -794,7 +794,15 @@ react {
 // module to apply the plugin to, so it's codegenDir and reactNativeDir won't be evaluated.
 if (rootProject.name == "react-native-build-from-source") {
   rootProject.extensions.getByType(PrivateReactExtension::class.java).apply {
-    codegenDir = file("$rootDir/../@react-native/codegen")
+    // We try to guess where codegen lives. Generally is inside
+    // node_modules/@react-native/codegen. If the file is not existing, we
+    // fallback to ../react-native-codegen (used for hello-world app).
+    codegenDir =
+        if (file("$rootDir/../@react-native/codegen").exists()) {
+          file("$rootDir/../@react-native/codegen")
+        } else {
+          file("$rootDir/../react-native-codegen")
+        }
     reactNativeDir = file("$rootDir")
   }
 }