react-native link support for native Android modules developed in Kotlin

Summary:
Currently React Native cli does not support linking native Android modules written in Kotlin. This PR aims to add support to it and closes #14561

- New unit tests added to verify the added functionality, they can be found inside:
`local-cli/core/__tests__/android/findPackageClassName.spec.js`

- Existing unit tests passed.
Closes https://github.com/facebook/react-native/pull/14660

Differential Revision: D5316981

Pulled By: shergin

fbshipit-source-id: 98354ba1e1ce1080a9a4b9958ef39893472038a1

local-cli/core/__fixtures__/android.js

@@ -4,21 +4,27 @@ const path = require('path');
 const manifest = fs.readFileSync(path.join(__dirname, './files/AndroidManifest.xml'));
 const mainJavaClass = fs.readFileSync(path.join(__dirname, './files/Main.java'));
 
-exports.valid = {
-  src: {
-    'AndroidManifest.xml': manifest,
-    main: {
-      com: {
-        some: {
-          example: {
-            'Main.java': mainJavaClass,
-            'ReactPackage.java': fs.readFileSync(path.join(__dirname, './files/ReactPackage.java')),
+function generateValidFileStructure(classFileName) {
+  return {
+    src: {
+      'AndroidManifest.xml': manifest,
+      main: {
+        com: {
+          some: {
+            example: {
+              'Main.java': mainJavaClass,
+              [classFileName]: fs.readFileSync(path.join(__dirname, `./files/${classFileName}`)),
+            },
           },
         },
       },
     },
-  },
-};
+  };
+}
+
+exports.valid = generateValidFileStructure('ReactPackage.java');
+
+exports.validKotlin = generateValidFileStructure('ReactPackage.kt');
 
 exports.userConfigManifest = {
   src: {

local-cli/core/__fixtures__/files/ReactPackage.java

@@ -10,7 +10,7 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 
-public class SomeExamplePackage implements ReactPackage {
+public class SomeExampleJavaPackage implements ReactPackage {
 
   @Override
   public List<NativeModule> createNativeModules(

local-cli/core/__fixtures__/files/ReactPackage.kt

@@ -0,0 +1,19 @@
+package com.some.example;
+
+import android.view.View
+import com.facebook.react.ReactPackage
+import com.facebook.react.bridge.NativeModule
+import com.facebook.react.bridge.ReactApplicationContext
+import com.facebook.react.uimanager.ReactShadowNode
+import com.facebook.react.uimanager.ViewManager
+import java.util.*
+
+class SomeExampleKotlinPackage : ReactPackage {
+
+    override fun createNativeModules(reactContext: ReactApplicationContext): MutableList<NativeModule>
+            = mutableListOf(MaterialPaletteModule(reactContext))
+
+    override fun createViewManagers(reactContext: ReactApplicationContext?):
+            MutableList<ViewManager<View, ReactShadowNode>> = Collections.emptyList()
+
+}

local-cli/core/__tests__/android/findPackageClassName.spec.js

@@ -19,14 +19,25 @@ describe('android::findPackageClassName', () => {
   beforeAll(() => {
     mockFS({
       empty: {},
-      flat: {
+      flatJava: {
         android: mocks.valid,
       },
+      flatKotlin: {
+        android: mocks.validKotlin,
+      },
     });
   });
 
   it('returns manifest content if file exists in the folder', () => {
-    expect(typeof findPackageClassName('flat')).toBe('string');
+    expect(typeof findPackageClassName('flatJava')).toBe('string');
+  });
+
+  it('returns the name of the java class implementing ReactPackage', () => {
+    expect(findPackageClassName('flatJava')).toBe('SomeExampleJavaPackage');
+  });
+
+  it('returns the name of the kotlin class implementing ReactPackage', () => {
+    expect(findPackageClassName('flatKotlin')).toBe('SomeExampleKotlinPackage');
   });
 
   it('returns `null` if there are no matches', () => {

local-cli/core/android/findPackageClassName.js

@@ -14,16 +14,16 @@ const path = require('path');
 
 /**
  * Gets package's class name (class that implements ReactPackage)
- * by searching for its declaration in all Java files present in the folder
+ * by searching for its declaration in all Java/Kotlin files present in the folder
  *
- * @param {String} folder Folder to find java files
+ * @param {String} folder Folder to find java/kt files
  */
 module.exports = function getPackageClassName(folder) {
-  const files = glob.sync('**/*.java', { cwd: folder });
+  const files = glob.sync('**/+(*.java|*.kt)', { cwd: folder });
 
   const packages = files
     .map(filePath => fs.readFileSync(path.join(folder, filePath), 'utf8'))
-    .map(file => file.match(/class (.*) implements ReactPackage/))
+    .map(file => file.match(/class (.*) +(implements|:) ReactPackage/))
     .filter(match => match);
 
   return packages.length ? packages[0][1] : null;