[tool] Add Kotlin autoformatting (#5374)

Updates the tooling to fetch and use `ktfmt` for Kotlin code, the same way it currently does for the Google Java formatter, and applies that formatting (in the default mode; see discussion in the linked issue) to the repository.

In the future we could revisit the formatter or mode, but since this currently seems to be the most consistent with our other languages and to google3 formatting this is likely the option we'll want to stick with.

Fixes https://github.com/flutter/flutter/issues/118756

.ci.yaml

@@ -131,10 +131,11 @@ targets:
       target_file: repo_checks.yaml
       channel: master
       version_file: flutter_master.version
-      # The format check requires clang-format.
+      # The format check requires clang-format, and the current version of ktfmt requires JDK 11+.
       dependencies: >-
         [
-          {"dependency": "clang", "version": "git_revision:5d5aba78dbbee75508f01bcaa69aedb2ab79065a"}
+          {"dependency": "clang", "version": "git_revision:5d5aba78dbbee75508f01bcaa69aedb2ab79065a"},
+          {"dependency": "open_jdk", "version": "version:17"}
         ]
 
   - name: Linux dart_unit_test_shard_1 master

packages/animations/example/android/app/src/main/kotlin/dev/flutter/packages/animations/example/MainActivity.kt

@@ -5,6 +5,4 @@ package dev.flutter.packages.animations.example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-
-}

packages/dynamic_layouts/example/android/app/src/main/kotlin/com/example/example/MainActivity.kt

@@ -5,5 +5,4 @@ package com.example.example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/file_selector/file_selector/example/android/app/src/main/kotlin/dev/flutter/plugins/file_selector_example/MainActivity.kt

@@ -6,5 +6,4 @@ package dev.flutter.plugins.file_selector_example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/flutter_adaptive_scaffold/example/android/app/src/main/kotlin/dev/flutter/example/MainActivity.kt

@@ -6,5 +6,4 @@ package dev.flutter.example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/flutter_image/example/android/app/src/main/kotlin/com/example/example/MainActivity.kt

@@ -6,5 +6,4 @@ package com.example.example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/flutter_markdown/example/android/app/src/main/kotlin/io/flutter/packages/flutter_markdown_example/MainActivity.kt

@@ -5,5 +5,4 @@ package io.flutter.packages.flutter_markdown_example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/go_router/example/android/app/src/main/kotlin/com/example/example/MainActivity.kt

@@ -6,5 +6,4 @@ package com.example.example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/palette_generator/example/android/app/src/main/kotlin/io/flutter/packages/palettegenerator/example/MainActivity.kt

@@ -5,6 +5,4 @@ package io.flutter.packages.palettegenerator.imagecolors
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-
-}

packages/pigeon/example/README.md

@@ -153,7 +153,7 @@ private class PigeonApiImplementation: ExampleHostApi {
 
   override fun add(a: Long, b: Long): Long {
     if (a < 0L || b < 0L) {
-      throw FlutterError("code", "message", "details");
+      throw FlutterError("code", "message", "details")
     }
     return a + b
   }
@@ -258,9 +258,7 @@ private class PigeonFlutterApi {
   }
 
   fun callFlutterMethod(aString: String, callback: (Result<String>) -> Unit) {
-    flutterApi!!.flutterMethod(aString) {
+    flutterApi!!.flutterMethod(aString) { echo -> callback(Result.success(echo)) }
-      echo -> callback(Result.success(echo))
-    }
   }
 }
 ```

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/MainActivity.kt

@@ -5,10 +5,9 @@
 package dev.flutter.pigeon_example_app
 
 import ExampleHostApi
+import FlutterError
 import MessageData
 import MessageFlutterApi
-import FlutterError
-
 import androidx.annotation.NonNull
 import io.flutter.embedding.android.FlutterActivity
 import io.flutter.embedding.engine.FlutterEngine
@@ -22,7 +21,7 @@ private class PigeonApiImplementation: ExampleHostApi {
 
   override fun add(a: Long, b: Long): Long {
     if (a < 0L || b < 0L) {
-      throw FlutterError("code", "message", "details");
+      throw FlutterError("code", "message", "details")
     }
     return a + b
   }
@@ -47,9 +46,7 @@ private class PigeonFlutterApi {
   }
 
   fun callFlutterMethod(aString: String, callback: (Result<String>) -> Unit) {
-    flutterApi!!.flutterMethod(aString) {
+    flutterApi!!.flutterMethod(aString) { echo -> callback(Result.success(echo)) }
-      echo -> callback(Result.success(echo))
-    }
   }
 }
 // #enddocregion kotlin-class-flutter
@@ -59,6 +56,6 @@ class MainActivity: FlutterActivity() {
     super.configureFlutterEngine(flutterEngine)
 
     val api = PigeonApiImplementation()
-    ExampleHostApi.setUp(flutterEngine.dartExecutor.binaryMessenger, api);
+    ExampleHostApi.setUp(flutterEngine.dartExecutor.binaryMessenger, api)
   }
 }

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/Messages.g.kt

@@ -4,7 +4,6 @@
 // Autogenerated from Pigeon, do not edit directly.
 // See also: https://pub.dev/packages/pigeon
 
-
 import android.util.Log
 import io.flutter.plugin.common.BasicMessageChannel
 import io.flutter.plugin.common.BinaryMessenger
@@ -19,25 +18,23 @@ private fun wrapResult(result: Any?): List<Any?> {
 
 private fun wrapError(exception: Throwable): List<Any?> {
   if (exception is FlutterError) {
-    return listOf(
+    return listOf(exception.code, exception.message, exception.details)
-      exception.code,
-      exception.message,
-      exception.details
-    )
   } else {
     return listOf(
         exception.javaClass.simpleName,
         exception.toString(),
-      "Cause: " + exception.cause + ", Stacktrace: " + Log.getStackTraceString(exception)
+        "Cause: " + exception.cause + ", Stacktrace: " + Log.getStackTraceString(exception))
-    )
   }
 }
 
 private fun createConnectionError(channelName: String): FlutterError {
-  return FlutterError("channel-error",  "Unable to establish connection on channel: '$channelName'.", "")}
+  return FlutterError(
+      "channel-error", "Unable to establish connection on channel: '$channelName'.", "")
+}
 
 /**
  * Error class for passing custom error details to Flutter via a thrown PlatformException.
+ *
  * @property code The error code.
  * @property message The error message.
  * @property details The error details. Must be a datatype supported by the api codec.
@@ -65,7 +62,6 @@ data class MessageData (
     val description: String? = null,
     val code: Code,
     val data: Map<String?, String?>
-
 ) {
   companion object {
     @Suppress("UNCHECKED_CAST")
@@ -77,6 +73,7 @@ data class MessageData (
       return MessageData(name, description, code, data)
     }
   }
+
   fun toList(): List<Any?> {
     return listOf<Any?>(
         name,
@@ -92,13 +89,12 @@ private object ExampleHostApiCodec : StandardMessageCodec() {
   override fun readValueOfType(type: Byte, buffer: ByteBuffer): Any? {
     return when (type) {
       128.toByte() -> {
-        return (readValue(buffer) as? List<Any?>)?.let {
+        return (readValue(buffer) as? List<Any?>)?.let { MessageData.fromList(it) }
-          MessageData.fromList(it)
-        }
       }
       else -> super.readValueOfType(type, buffer)
     }
   }
+
   override fun writeValue(stream: ByteArrayOutputStream, value: Any?) {
     when (value) {
       is MessageData -> {
@@ -113,19 +109,23 @@ private object ExampleHostApiCodec : StandardMessageCodec() {
 /** Generated interface from Pigeon that represents a handler of messages from Flutter. */
 interface ExampleHostApi {
   fun getHostLanguage(): String
+
   fun add(a: Long, b: Long): Long
+
   fun sendMessage(message: MessageData, callback: (Result<Boolean>) -> Unit)
 
   companion object {
     /** The codec used by ExampleHostApi. */
-    val codec: MessageCodec<Any?> by lazy {
+    val codec: MessageCodec<Any?> by lazy { ExampleHostApiCodec }
-      ExampleHostApiCodec
-    }
     /** Sets up an instance of `ExampleHostApi` to handle messages through the `binaryMessenger`. */
     @Suppress("UNCHECKED_CAST")
     fun setUp(binaryMessenger: BinaryMessenger, api: ExampleHostApi?) {
       run {
-        val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.getHostLanguage", codec)
+        val channel =
+            BasicMessageChannel<Any?>(
+                binaryMessenger,
+                "dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.getHostLanguage",
+                codec)
         if (api != null) {
           channel.setMessageHandler { _, reply ->
             var wrapped: List<Any?>
@@ -141,7 +141,11 @@ interface ExampleHostApi {
         }
       }
       run {
-        val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.add", codec)
+        val channel =
+            BasicMessageChannel<Any?>(
+                binaryMessenger,
+                "dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.add",
+                codec)
         if (api != null) {
           channel.setMessageHandler { message, reply ->
             val args = message as List<Any?>
@@ -160,7 +164,11 @@ interface ExampleHostApi {
         }
       }
       run {
-        val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.sendMessage", codec)
+        val channel =
+            BasicMessageChannel<Any?>(
+                binaryMessenger,
+                "dev.flutter.pigeon.pigeon_example_package.ExampleHostApi.sendMessage",
+                codec)
         if (api != null) {
           channel.setMessageHandler { message, reply ->
             val args = message as List<Any?>
@@ -187,25 +195,29 @@ interface ExampleHostApi {
 class MessageFlutterApi(private val binaryMessenger: BinaryMessenger) {
   companion object {
     /** The codec used by MessageFlutterApi. */
-    val codec: MessageCodec<Any?> by lazy {
+    val codec: MessageCodec<Any?> by lazy { StandardMessageCodec() }
-      StandardMessageCodec()
-    }
   }
+
   fun flutterMethod(aStringArg: String?, callback: (Result<String>) -> Unit) {
     val channelName = "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod"
     val channel = BasicMessageChannel<Any?>(binaryMessenger, channelName, codec)
     channel.send(listOf(aStringArg)) {
       if (it is List<*>) {
         if (it.size > 1) {
-          callback(Result.failure(FlutterError(it[0] as String, it[1] as String, it[2] as String?)));
+          callback(Result.failure(FlutterError(it[0] as String, it[1] as String, it[2] as String?)))
         } else if (it[0] == null) {
-          callback(Result.failure(FlutterError("null-error", "Flutter api returned null value for non-null return value.", "")));
+          callback(
+              Result.failure(
+                  FlutterError(
+                      "null-error",
+                      "Flutter api returned null value for non-null return value.",
+                      "")))
         } else {
           val output = it[0] as String
-          callback(Result.success(output));
+          callback(Result.success(output))
         }
       } else {
-        callback(Result.failure(createConnectionError(channelName)));
+        callback(Result.failure(createConnectionError(channelName)))
       }
     }
   }

packages/pigeon/platform_tests/test_plugin/android/src/main/kotlin/com/example/test_plugin/TestPlugin.kt

@@ -5,16 +5,9 @@
 package com.example.test_plugin
 
 import androidx.annotation.NonNull
-
 import io.flutter.embedding.engine.plugins.FlutterPlugin
-import io.flutter.plugin.common.MethodCall
-import io.flutter.plugin.common.MethodChannel
-import io.flutter.plugin.common.MethodChannel.MethodCallHandler
 
-/**
+/** This plugin handles the native side of the integration tests in example/integration_test/. */
- * This plugin handles the native side of the integration tests in
- * example/integration_test/.
- */
 class TestPlugin : FlutterPlugin, HostIntegrationCoreApi {
   var flutterApi: FlutterIntegrationCoreApi? = null
 
@@ -23,13 +16,11 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     flutterApi = FlutterIntegrationCoreApi(binding.getBinaryMessenger())
   }
 
-  override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {
+  override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {}
-  }
 
   // HostIntegrationCoreApi
 
-  override fun noop() {
+  override fun noop() {}
-  }
 
   override fun echoAllTypes(everything: AllTypes): AllTypes {
     return everything
@@ -40,15 +31,15 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
   }
 
   override fun throwError(): Any? {
-    throw Exception("An error");
+    throw Exception("An error")
   }
 
   override fun throwErrorFromVoid() {
-    throw Exception("An error");
+    throw Exception("An error")
   }
 
   override fun throwFlutterError(): Any? {
-    throw FlutterError("code", "message", "details");
+    throw FlutterError("code", "message", "details")
   }
 
   override fun echoInt(anInt: Long): Long {
@@ -99,8 +90,15 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     return AllClassesWrapper(AllNullableTypes(aNullableString = nullableString))
   }
 
-  override fun sendMultipleNullableTypes(aNullableBool: Boolean?, aNullableInt: Long?, aNullableString: String?): AllNullableTypes {
+  override fun sendMultipleNullableTypes(
-    return AllNullableTypes(aNullableBool = aNullableBool, aNullableInt = aNullableInt, aNullableString = aNullableString)
+      aNullableBool: Boolean?,
+      aNullableInt: Long?,
+      aNullableString: String?
+  ): AllNullableTypes {
+    return AllNullableTypes(
+        aNullableBool = aNullableBool,
+        aNullableInt = aNullableInt,
+        aNullableString = aNullableString)
   }
 
   override fun echoNullableInt(aNullableInt: Long?): Long? {
@@ -159,7 +157,10 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     callback(Result.success(everything))
   }
 
-  override fun echoAsyncNullableAllNullableTypes(everything: AllNullableTypes?, callback: (Result<AllNullableTypes?>) -> Unit) {
+  override fun echoAsyncNullableAllNullableTypes(
+      everything: AllNullableTypes?,
+      callback: (Result<AllNullableTypes?>) -> Unit
+  ) {
     callback(Result.success(everything))
   }
 
@@ -191,7 +192,10 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     callback(Result.success(aList))
   }
 
-  override fun echoAsyncMap(aMap: Map<String?, Any?>, callback: (Result<Map<String?, Any?>>) -> Unit) {
+  override fun echoAsyncMap(
+      aMap: Map<String?, Any?>,
+      callback: (Result<Map<String?, Any?>>) -> Unit
+  ) {
     callback(Result.success(aMap))
   }
 
@@ -215,7 +219,10 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     callback(Result.success(aString))
   }
 
-  override fun echoAsyncNullableUint8List(aUint8List: ByteArray?, callback: (Result<ByteArray?>) -> Unit) {
+  override fun echoAsyncNullableUint8List(
+      aUint8List: ByteArray?,
+      callback: (Result<ByteArray?>) -> Unit
+  ) {
     callback(Result.success(aUint8List))
   }
 
@@ -227,7 +234,10 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     callback(Result.success(aList))
   }
 
-  override fun echoAsyncNullableMap(aMap: Map<String?, Any?>?, callback: (Result<Map<String?, Any?>?>) -> Unit) {
+  override fun echoAsyncNullableMap(
+      aMap: Map<String?, Any?>?,
+      callback: (Result<Map<String?, Any?>?>) -> Unit
+  ) {
     callback(Result.success(aMap))
   }
 
@@ -242,6 +252,7 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
   override fun callFlutterThrowError(callback: (Result<Any?>) -> Unit) {
     flutterApi!!.throwError() { result -> callback(result) }
   }
+
   override fun callFlutterThrowErrorFromVoid(callback: (Result<Unit>) -> Unit) {
     flutterApi!!.throwErrorFromVoid() { result -> callback(result) }
   }
@@ -256,8 +267,8 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
       aNullableString: String?,
       callback: (Result<AllNullableTypes>) -> Unit
   ) {
-    flutterApi!!.sendMultipleNullableTypes(aNullableBool, aNullableInt, aNullableString) {
+    flutterApi!!.sendMultipleNullableTypes(aNullableBool, aNullableInt, aNullableString) { echo ->
-      echo -> callback(echo)
+      callback(echo)
     }
   }
 
@@ -285,7 +296,10 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     flutterApi!!.echoList(aList) { echo -> callback(echo) }
   }
 
-  override fun callFlutterEchoMap(aMap: Map<String?, Any?>, callback: (Result<Map<String?, Any?>>) -> Unit) {
+  override fun callFlutterEchoMap(
+      aMap: Map<String?, Any?>,
+      callback: (Result<Map<String?, Any?>>) -> Unit
+  ) {
     flutterApi!!.echoMap(aMap) { echo -> callback(echo) }
   }
 
@@ -293,7 +307,10 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     flutterApi!!.echoEnum(anEnum) { echo -> callback(echo) }
   }
 
-  override fun callFlutterEchoAllNullableTypes(everything: AllNullableTypes?, callback: (Result<AllNullableTypes?>) -> Unit) {
+  override fun callFlutterEchoAllNullableTypes(
+      everything: AllNullableTypes?,
+      callback: (Result<AllNullableTypes?>) -> Unit
+  ) {
     flutterApi!!.echoAllNullableTypes(everything) { echo -> callback(echo) }
   }
 
@@ -305,28 +322,42 @@ class TestPlugin: FlutterPlugin, HostIntegrationCoreApi {
     flutterApi!!.echoNullableInt(anInt) { echo -> callback(echo) }
   }
 
-  override fun callFlutterEchoNullableDouble(aDouble: Double?, callback: (Result<Double?>) -> Unit) {
+  override fun callFlutterEchoNullableDouble(
+      aDouble: Double?,
+      callback: (Result<Double?>) -> Unit
+  ) {
     flutterApi!!.echoNullableDouble(aDouble) { echo -> callback(echo) }
   }
 
-  override fun callFlutterEchoNullableString(aString: String?, callback: (Result<String?>) -> Unit) {
+  override fun callFlutterEchoNullableString(
+      aString: String?,
+      callback: (Result<String?>) -> Unit
+  ) {
     flutterApi!!.echoNullableString(aString) { echo -> callback(echo) }
   }
 
-  override fun callFlutterEchoNullableUint8List(aList: ByteArray?, callback: (Result<ByteArray?>) -> Unit) {
+  override fun callFlutterEchoNullableUint8List(
+      aList: ByteArray?,
+      callback: (Result<ByteArray?>) -> Unit
+  ) {
     flutterApi!!.echoNullableUint8List(aList) { echo -> callback(echo) }
   }
 
-  override fun callFlutterEchoNullableList(aList: List<Any?>?, callback: (Result<List<Any?>?>) -> Unit) {
+  override fun callFlutterEchoNullableList(
+      aList: List<Any?>?,
+      callback: (Result<List<Any?>?>) -> Unit
+  ) {
     flutterApi!!.echoNullableList(aList) { echo -> callback(echo) }
   }
 
-  override fun callFlutterEchoNullableMap(aMap: Map<String?, Any?>?, callback: (Result<Map<String?, Any?>?>) -> Unit) {
+  override fun callFlutterEchoNullableMap(
+      aMap: Map<String?, Any?>?,
+      callback: (Result<Map<String?, Any?>?>) -> Unit
+  ) {
     flutterApi!!.echoNullableMap(aMap) { echo -> callback(echo) }
   }
 
   override fun callFlutterEchoNullableEnum(anEnum: AnEnum?, callback: (Result<AnEnum?>) -> Unit) {
     flutterApi!!.echoNullableEnum(anEnum) { echo -> callback(echo) }
   }
-
 }

packages/pigeon/platform_tests/test_plugin/android/src/test/kotlin/com/example/test_plugin/AllDatatypesTest.kt

@@ -7,11 +7,10 @@ package com.example.test_plugin
 import io.flutter.plugin.common.BinaryMessenger
 import io.mockk.every
 import io.mockk.mockk
-import junit.framework.TestCase
-import org.junit.Test
 import java.nio.ByteBuffer
 import java.util.ArrayList
-
+import junit.framework.TestCase
+import org.junit.Test
 
 internal class AllDatatypesTest : TestCase() {
   fun compareAllTypes(firstTypes: AllTypes?, secondTypes: AllTypes?) {
@@ -59,7 +58,8 @@ internal class AllDatatypesTest: TestCase() {
     val binaryMessenger = mockk<BinaryMessenger>()
     val api = FlutterIntegrationCoreApi(binaryMessenger)
 
-        every { binaryMessenger.send(any(), any(), any()) } answers {
+    every { binaryMessenger.send(any(), any(), any()) } answers
+        {
           val codec = FlutterIntegrationCoreApi.codec
           val message = arg<ByteBuffer>(1)
           val reply = arg<BinaryMessenger.BinaryReply>(2)
@@ -73,7 +73,8 @@ internal class AllDatatypesTest: TestCase() {
     var didCall = false
     api.echoAllNullableTypes(everything) {
       didCall = true
-            val output = (it.getOrNull())?.let {
+      val output =
+          (it.getOrNull())?.let {
             assertNull(it.aNullableBool)
             assertNull(it.aNullableInt)
             assertNull(it.aNullableDouble)
@@ -87,7 +88,6 @@ internal class AllDatatypesTest: TestCase() {
             assertNull(it.nullableMapWithObject)
           }
       assertNotNull(output)
-            
     }
 
     assertTrue(didCall)
@@ -95,7 +95,8 @@ internal class AllDatatypesTest: TestCase() {
 
   @Test
   fun testHasValues() {
-        val everything = AllNullableTypes(
+    val everything =
+        AllNullableTypes(
             aNullableBool = false,
             aNullableInt = 1234L,
             aNullableDouble = 2.0,
@@ -112,7 +113,8 @@ internal class AllDatatypesTest: TestCase() {
     val binaryMessenger = mockk<BinaryMessenger>()
     val api = FlutterIntegrationCoreApi(binaryMessenger)
 
-        every { binaryMessenger.send(any(), any(), any()) } answers {
+    every { binaryMessenger.send(any(), any(), any()) } answers
+        {
           val codec = FlutterIntegrationCoreApi.codec
           val message = arg<ByteBuffer>(1)
           val reply = arg<BinaryMessenger.BinaryReply>(2)
@@ -141,7 +143,24 @@ internal class AllDatatypesTest: TestCase() {
     assertNotNull(list[1])
     assertTrue(list[1] == 123L)
 
-        val list2 = listOf(null, 123, null, null, null, null, null, null, null, null, null, null, null, null, null, null)
+    val list2 =
+        listOf(
+            null,
+            123,
+            null,
+            null,
+            null,
+            null,
+            null,
+            null,
+            null,
+            null,
+            null,
+            null,
+            null,
+            null,
+            null,
+            null)
     val everything2 = AllNullableTypes.fromList(list2)
 
     assertEquals(everything.aNullableInt, everything2.aNullableInt)

packages/pigeon/platform_tests/test_plugin/android/src/test/kotlin/com/example/test_plugin/AsyncHandlersTest.kt

@@ -9,10 +9,9 @@ import io.mockk.every
 import io.mockk.mockk
 import io.mockk.slot
 import io.mockk.verify
+import java.nio.ByteBuffer
 import junit.framework.TestCase
 import org.junit.Test
-import java.nio.ByteBuffer
-
 
 internal class AsyncHandlersTest : TestCase() {
   @Test
@@ -22,7 +21,8 @@ internal class AsyncHandlersTest: TestCase() {
 
     val value = "Test"
 
-        every { binaryMessenger.send(any(), any(), any()) } answers {
+    every { binaryMessenger.send(any(), any(), any()) } answers
+        {
           val codec = FlutterIntegrationCoreApi.codec
           val message = arg<ByteBuffer>(1)
           val reply = arg<BinaryMessenger.BinaryReply>(2)
@@ -44,8 +44,7 @@ internal class AsyncHandlersTest: TestCase() {
       binaryMessenger.send(
           "dev.flutter.pigeon.pigeon_integration_tests.FlutterIntegrationCoreApi.echoAsyncString",
           any(),
-                any()
+          any())
-            )
     }
   }
 
@@ -61,10 +60,12 @@ internal class AsyncHandlersTest: TestCase() {
     val channelName = "dev.flutter.pigeon.pigeon_integration_tests.HostSmallApi.echo"
 
     every {
-            binaryMessenger.setMessageHandler("dev.flutter.pigeon.pigeon_integration_tests.HostSmallApi.voidVoid", any())
+      binaryMessenger.setMessageHandler(
+          "dev.flutter.pigeon.pigeon_integration_tests.HostSmallApi.voidVoid", any())
     } returns Unit
     every { binaryMessenger.setMessageHandler(channelName, capture(handlerSlot)) } returns Unit
-        every { api.echo(any(), any()) } answers {
+    every { api.echo(any(), any()) } answers
+        {
           val callback = arg<(Result<String>) -> Unit>(1)
           callback(Result.success(output))
         }
@@ -77,12 +78,9 @@ internal class AsyncHandlersTest: TestCase() {
     handlerSlot.captured.onMessage(message) {
       assertNotNull(it)
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as MutableList<Any>?
-            val wrapped = codec.decodeMessage(it) as MutableList<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(output, wrapped.first()) }
-                assertEquals(output, wrapped.first())
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -100,9 +98,11 @@ internal class AsyncHandlersTest: TestCase() {
 
     every { binaryMessenger.setMessageHandler(channelName, capture(handlerSlot)) } returns Unit
     every {
-            binaryMessenger.setMessageHandler("dev.flutter.pigeon.pigeon_integration_tests.HostSmallApi.echo", any())
+      binaryMessenger.setMessageHandler(
+          "dev.flutter.pigeon.pigeon_integration_tests.HostSmallApi.echo", any())
     } returns Unit
-        every { api.voidVoid(any()) } answers {
+    every { api.voidVoid(any()) } answers
+        {
           val callback = arg<() -> Unit>(0)
           callback()
         }
@@ -113,8 +113,7 @@ internal class AsyncHandlersTest: TestCase() {
     val message = codec.encodeMessage(null)
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as MutableList<Any>?
-            val wrapped = codec.decodeMessage(it) as MutableList<Any>?
       assertNull(wrapped)
     }
 

packages/pigeon/platform_tests/test_plugin/android/src/test/kotlin/com/example/test_plugin/EchoBinaryMessenger.kt

@@ -6,21 +6,15 @@ package com.example.test_plugin
 
 import io.flutter.plugin.common.BinaryMessenger
 import io.flutter.plugin.common.MessageCodec
-import io.flutter.plugin.common.StandardMessageCodec
 import java.nio.ByteBuffer
 import java.util.ArrayList
 
-
 internal class EchoBinaryMessenger(private val codec: MessageCodec<Any?>) : BinaryMessenger {
   override fun send(channel: String, message: ByteBuffer?) {
     // Method not implemented because this messenger is just for echoing.
   }
 
-    override fun send(
+  override fun send(channel: String, message: ByteBuffer?, callback: BinaryMessenger.BinaryReply?) {
-        channel: String,
-        message: ByteBuffer?,
-        callback: BinaryMessenger.BinaryReply?
-    ) {
     message?.rewind()
     val args = codec.decodeMessage(message) as ArrayList<*>
     val replyData = codec.encodeMessage(args)
@@ -28,11 +22,7 @@ internal class EchoBinaryMessenger(private val codec: MessageCodec<Any?>): Binar
     callback?.reply(replyData)
   }
 
-    override fun setMessageHandler(
+  override fun setMessageHandler(channel: String, handler: BinaryMessenger.BinaryMessageHandler?) {
-        channel: String,
-        handler: BinaryMessenger.BinaryMessageHandler?
-    ) {
     // Method not implemented because this messenger is just for echoing.
   }
-
 }

packages/pigeon/platform_tests/test_plugin/android/src/test/kotlin/com/example/test_plugin/EnumTest.kt

@@ -9,10 +9,10 @@ import io.mockk.every
 import io.mockk.mockk
 import io.mockk.slot
 import io.mockk.verify
-import junit.framework.TestCase
-import org.junit.Test
 import java.nio.ByteBuffer
 import java.util.ArrayList
+import junit.framework.TestCase
+import org.junit.Test
 
 internal class EnumTest : TestCase() {
   @Test
@@ -35,8 +35,7 @@ internal class EnumTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
       wrapped?.let {
         assertNotNull(wrapped[0])
@@ -55,7 +54,8 @@ internal class EnumTest: TestCase() {
 
     val input = DataWithEnum(EnumState.SUCCESS)
 
-        every { binaryMessenger.send(any(), any(), any()) } answers {
+    every { binaryMessenger.send(any(), any(), any()) } answers
+        {
           val codec = EnumApi2Flutter.codec
           val message = arg<ByteBuffer>(1)
           val reply = arg<BinaryMessenger.BinaryReply>(2)

packages/pigeon/platform_tests/test_plugin/android/src/test/kotlin/com/example/test_plugin/ListTest.kt

@@ -7,10 +7,10 @@ package com.example.test_plugin
 import io.flutter.plugin.common.BinaryMessenger
 import io.mockk.every
 import io.mockk.mockk
-import junit.framework.TestCase
-import org.junit.Test
 import java.nio.ByteBuffer
 import java.util.ArrayList
+import junit.framework.TestCase
+import org.junit.Test
 
 class ListTest : TestCase() {
   @Test
@@ -21,7 +21,8 @@ class ListTest: TestCase() {
     val inside = TestMessage(listOf(1, 2, 3))
     val input = TestMessage(listOf(inside))
 
-        every { binaryMessenger.send(any(), any(), any()) } answers {
+    every { binaryMessenger.send(any(), any(), any()) } answers
+        {
           val codec = FlutterSmallApi.codec
           val message = arg<ByteBuffer>(1)
           val reply = arg<BinaryMessenger.BinaryReply>(2)

packages/pigeon/platform_tests/test_plugin/android/src/test/kotlin/com/example/test_plugin/MultipleArityTests.kt

@@ -8,10 +8,10 @@ import io.flutter.plugin.common.BinaryMessenger
 import io.mockk.every
 import io.mockk.mockk
 import io.mockk.slot
-import junit.framework.TestCase
-import org.junit.Test
 import java.nio.ByteBuffer
 import java.util.ArrayList
+import junit.framework.TestCase
+import org.junit.Test
 
 class MultipleArityTests : TestCase() {
   @Test
@@ -35,12 +35,9 @@ class MultipleArityTests: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(inputX - inputY, wrapped[0]) }
-                assertEquals(inputX - inputY, wrapped[0])
-            }
     }
   }
 
@@ -52,7 +49,8 @@ class MultipleArityTests: TestCase() {
     val inputX = 10L
     val inputY = 5L
 
-        every { binaryMessenger.send(any(), any(), any()) } answers {
+    every { binaryMessenger.send(any(), any(), any()) } answers
+        {
           val codec = MultipleArityFlutterApi.codec
           val message = arg<ByteBuffer>(1)
           val reply = arg<BinaryMessenger.BinaryReply>(2)

packages/pigeon/platform_tests/test_plugin/android/src/test/kotlin/com/example/test_plugin/NullableReturnsTest.kt

@@ -33,12 +33,9 @@ class NullableReturnsTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(output, wrapped[0]) }
-                assertEquals(output, wrapped[0])
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -52,7 +49,8 @@ class NullableReturnsTest: TestCase() {
 
     val output = 12L
 
-        every { binaryMessenger.send(any(), any(), any()) } answers {
+    every { binaryMessenger.send(any(), any(), any()) } answers
+        {
           val codec = NullableReturnFlutterApi.codec
           val reply = arg<BinaryMessenger.BinaryReply>(2)
           val replyData = codec.encodeMessage(listOf(output))

packages/pigeon/platform_tests/test_plugin/android/src/test/kotlin/com/example/test_plugin/PrimitiveTest.kt

@@ -11,8 +11,6 @@ import io.mockk.slot
 import io.mockk.verify
 import junit.framework.TestCase
 import org.junit.Test
-import java.nio.ByteBuffer
-import java.util.ArrayList
 
 class PrimitiveTest : TestCase() {
   @Test
@@ -35,12 +33,9 @@ class PrimitiveTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(input.toLong(), wrapped[0]) }
-                assertEquals(input.toLong(), wrapped[0])
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -83,12 +78,9 @@ class PrimitiveTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(input, wrapped[0]) }
-                assertEquals(input, wrapped[0])
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -131,12 +123,9 @@ class PrimitiveTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(input, wrapped[0]) }
-                assertEquals(input, wrapped[0])
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -163,12 +152,9 @@ class PrimitiveTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(input, wrapped[0]) }
-                assertEquals(input, wrapped[0])
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -211,12 +197,9 @@ class PrimitiveTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(input, wrapped[0]) }
-                assertEquals(input, wrapped[0])
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -259,12 +242,9 @@ class PrimitiveTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(input, wrapped[0]) }
-                assertEquals(input, wrapped[0])
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -307,12 +287,9 @@ class PrimitiveTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertTrue(input.contentEquals(wrapped[0] as IntArray)) }
-                assertTrue(input.contentEquals(wrapped[0] as IntArray))
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -355,12 +332,9 @@ class PrimitiveTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(input, wrapped[0]) }
-                assertEquals(input, wrapped[0])
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -403,12 +377,9 @@ class PrimitiveTest: TestCase() {
     message?.rewind()
     handlerSlot.captured.onMessage(message) {
       it?.rewind()
-            @Suppress("UNCHECKED_CAST")
+      @Suppress("UNCHECKED_CAST") val wrapped = codec.decodeMessage(it) as List<Any>?
-            val wrapped = codec.decodeMessage(it) as List<Any>?
       assertNotNull(wrapped)
-            wrapped?.let {
+      wrapped?.let { assertEquals(input, wrapped[0]) }
-                assertEquals(input, wrapped[0])
-            }
     }
 
     verify { binaryMessenger.setMessageHandler(channelName, handlerSlot.captured) }
@@ -430,5 +401,4 @@ class PrimitiveTest: TestCase() {
 
     assertTrue(didCall)
   }
-
 }

packages/pigeon/platform_tests/test_plugin/example/android/app/src/main/kotlin/com/example/test_plugin_example/MainActivity.kt

@@ -6,5 +6,4 @@ package com.example.test_plugin_example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/platform/example/android/app/src/main/kotlin/dev/flutter/plaform_example/MainActivity.kt

@@ -6,5 +6,4 @@ package dev.flutter.plaform_example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/rfw/example/hello/android/app/src/main/kotlin/dev/flutter/rfw/examples/hello/MainActivity.kt

@@ -5,5 +5,4 @@ package dev.flutter.rfw.examples.hello
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/rfw/example/local/android/app/src/main/kotlin/dev/flutter/rfw/examples/local/MainActivity.kt

@@ -5,5 +5,4 @@ package dev.flutter.rfw.examples.local
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/rfw/example/remote/android/app/src/main/kotlin/dev/flutter/rfw/examples/remote/MainActivity.kt

@@ -5,5 +5,4 @@ package dev.flutter.rfw.examples.remote
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

packages/two_dimensional_scrollables/example/android/app/src/main/kotlin/com/example/example/MainActivity.kt

@@ -6,5 +6,4 @@ package com.example.example
 
 import io.flutter.embedding.android.FlutterActivity
 
-class MainActivity: FlutterActivity() {
+class MainActivity : FlutterActivity() {}
-}

script/tool/lib/src/format_command.dart

@@ -32,9 +32,12 @@ const int _exitJavaFormatFailed = 5;
 const int _exitGitFailed = 6;
 const int _exitDependencyMissing = 7;
 const int _exitSwiftFormatFailed = 8;
+const int _exitKotlinFormatFailed = 9;
 
-final Uri _googleFormatterUrl = Uri.https('github.com',
+final Uri _javaFormatterUrl = Uri.https('github.com',
     '/google/google-java-format/releases/download/google-java-format-1.3/google-java-format-1.3-all-deps.jar');
+final Uri _kotlinFormatterUrl = Uri.https('maven.org',
+    '/maven2/com/facebook/ktfmt/0.46/ktfmt-0.46-jar-with-dependencies.jar');
 
 /// A command to format all package code.
 class FormatCommand extends PackageCommand {
@@ -62,14 +65,15 @@ class FormatCommand extends PackageCommand {
 
   @override
   final String description =
-      'Formats the code of all packages (Java, Objective-C, C++, Dart, and '
+      'Formats the code of all packages (C++, Dart, Java, Kotlin, Objective-C, '
-      'optionally Swift).\n\n'
+      'and optionally Swift).\n\n'
-      'This command requires "git", "flutter" and "clang-format" v5 to be in '
+      'This command requires "git", "flutter", "java", and "clang-format" v5 '
-      'your path.';
+      'to be in your path.';
 
   @override
   Future<void> run() async {
-    final String googleFormatterPath = await _getGoogleFormatterPath();
+    final String javaFormatterPath = await _getJavaFormatterPath();
+    final String kotlinFormatterPath = await _getKotlinFormatterPath();
 
     // This class is not based on PackageLoopingCommand because running the
     // formatters separately for each package is an order of magnitude slower,
@@ -77,7 +81,8 @@ class FormatCommand extends PackageCommand {
     final Iterable<String> files =
         await _getFilteredFilePaths(getFiles(), relativeTo: packagesDir);
     await _formatDart(files);
-    await _formatJava(files, googleFormatterPath);
+    await _formatJava(files, javaFormatterPath);
+    await _formatKotlin(files, kotlinFormatterPath);
     await _formatCppAndObjectiveC(files);
     final String? swiftFormat = getNullableStringArg(_swiftFormatArg);
     if (swiftFormat != null) {
@@ -187,8 +192,7 @@ class FormatCommand extends PackageCommand {
     throw ToolExit(_exitDependencyMissing);
   }
 
-  Future<void> _formatJava(
+  Future<void> _formatJava(Iterable<String> files, String formatterPath) async {
-      Iterable<String> files, String googleFormatterPath) async {
     final Iterable<String> javaFiles =
         _getPathsWithExtensions(files, <String>{'.java'});
     if (javaFiles.isNotEmpty) {
@@ -202,7 +206,7 @@ class FormatCommand extends PackageCommand {
 
       print('Formatting .java files...');
       final int exitCode = await _runBatched(
-          java, <String>['-jar', googleFormatterPath, '--replace'],
+          java, <String>['-jar', formatterPath, '--replace'],
           files: javaFiles);
       if (exitCode != 0) {
         printError('Failed to format Java files: exit code $exitCode.');
@@ -211,6 +215,30 @@ class FormatCommand extends PackageCommand {
     }
   }
 
+  Future<void> _formatKotlin(
+      Iterable<String> files, String formatterPath) async {
+    final Iterable<String> kotlinFiles =
+        _getPathsWithExtensions(files, <String>{'.kt'});
+    if (kotlinFiles.isNotEmpty) {
+      final String java = getStringArg('java');
+      if (!await _hasDependency(java)) {
+        printError(
+            'Unable to run "java". Make sure that it is in your path, or '
+            'provide a full path with --java.');
+        throw ToolExit(_exitDependencyMissing);
+      }
+
+      print('Formatting .kt files...');
+      final int exitCode = await _runBatched(
+          java, <String>['-jar', formatterPath],
+          files: kotlinFiles);
+      if (exitCode != 0) {
+        printError('Failed to format Kotlin files: exit code $exitCode.');
+        throw ToolExit(_exitKotlinFormatFailed);
+      }
+    }
+  }
+
   Future<void> _formatDart(Iterable<String> files) async {
     final Iterable<String> dartFiles =
         _getPathsWithExtensions(files, <String>{'.dart'});
@@ -283,7 +311,7 @@ class FormatCommand extends PackageCommand {
         (String filePath) => extensions.contains(path.extension(filePath)));
   }
 
-  Future<String> _getGoogleFormatterPath() async {
+  Future<String> _getJavaFormatterPath() async {
     final String javaFormatterPath = path.join(
         path.dirname(path.fromUri(platform.script)),
         'google-java-format-1.3-all-deps.jar');
@@ -292,13 +320,29 @@ class FormatCommand extends PackageCommand {
 
     if (!javaFormatterFile.existsSync()) {
       print('Downloading Google Java Format...');
-      final http.Response response = await http.get(_googleFormatterUrl);
+      final http.Response response = await http.get(_javaFormatterUrl);
       javaFormatterFile.writeAsBytesSync(response.bodyBytes);
     }
 
     return javaFormatterPath;
   }
 
+  Future<String> _getKotlinFormatterPath() async {
+    final String kotlinFormatterPath = path.join(
+        path.dirname(path.fromUri(platform.script)),
+        'ktfmt-0.46-jar-with-dependencies.jar');
+    final File kotlinFormatterFile =
+        packagesDir.fileSystem.file(kotlinFormatterPath);
+
+    if (!kotlinFormatterFile.existsSync()) {
+      print('Downloading ktfmt...');
+      final http.Response response = await http.get(_kotlinFormatterUrl);
+      kotlinFormatterFile.writeAsBytesSync(response.bodyBytes);
+    }
+
+    return kotlinFormatterPath;
+  }
+
   /// Returns true if [command] can be run successfully.
   Future<bool> _hasDependency(String command) async {
     // Some versions of Java accept both -version and --version, but some only

script/tool/test/format_command_test.dart

@@ -22,6 +22,7 @@ void main() {
   late FormatCommand analyzeCommand;
   late CommandRunner<void> runner;
   late String javaFormatPath;
+  late String kotlinFormatPath;
 
   setUp(() {
     fileSystem = MemoryFileSystem();
@@ -34,12 +35,16 @@ void main() {
       platform: mockPlatform,
     );
 
-    // Create the java formatter file that the command checks for, to avoid
+    // Create the Java and Kotlin formatter files that the command checks for,
-    // a download.
+    // to avoid a download.
     final p.Context path = analyzeCommand.path;
     javaFormatPath = path.join(path.dirname(path.fromUri(mockPlatform.script)),
         'google-java-format-1.3-all-deps.jar');
     fileSystem.file(javaFormatPath).createSync(recursive: true);
+    kotlinFormatPath = path.join(
+        path.dirname(path.fromUri(mockPlatform.script)),
+        'ktfmt-0.46-jar-with-dependencies.jar');
+    fileSystem.file(kotlinFormatPath).createSync(recursive: true);
 
     runner = CommandRunner<void>('format_command', 'Test for format_command');
     runner.addCommand(analyzeCommand);
@@ -428,6 +433,62 @@ void main() {
         ]));
   });
 
+  group('kotlin-format', () {
+    test('formats .kt files', () async {
+      const List<String> files = <String>[
+        'android/src/main/kotlin/io/flutter/plugins/a_plugin/a.kt',
+        'android/src/main/kotlin/io/flutter/plugins/a_plugin/b.kt',
+      ];
+      final RepositoryPackage plugin = createFakePlugin(
+        'a_plugin',
+        packagesDir,
+        extraFiles: files,
+      );
+
+      await runCapturingPrint(runner, <String>['format']);
+
+      expect(
+          processRunner.recordedCalls,
+          orderedEquals(<ProcessCall>[
+            const ProcessCall('java', <String>['-version'], null),
+            ProcessCall(
+                'java',
+                <String>[
+                  '-jar',
+                  kotlinFormatPath,
+                  ...getPackagesDirRelativePaths(plugin, files)
+                ],
+                packagesDir.path),
+          ]));
+    });
+
+    test('fails if Kotlin formatter fails', () async {
+      const List<String> files = <String>[
+        'android/src/main/kotlin/io/flutter/plugins/a_plugin/a.kt',
+        'android/src/main/kotlin/io/flutter/plugins/a_plugin/b.kt',
+      ];
+      createFakePlugin('a_plugin', packagesDir, extraFiles: files);
+
+      processRunner.mockProcessesForExecutable['java'] = <FakeProcessInfo>[
+        FakeProcessInfo(
+            MockProcess(), <String>['-version']), // check for working java
+        FakeProcessInfo(MockProcess(exitCode: 1), <String>['-jar']), // format
+      ];
+      Error? commandError;
+      final List<String> output = await runCapturingPrint(
+          runner, <String>['format'], errorHandler: (Error e) {
+        commandError = e;
+      });
+
+      expect(commandError, isA<ToolExit>());
+      expect(
+          output,
+          containsAllInOrder(<Matcher>[
+            contains('Failed to format Kotlin files: exit code 1.'),
+          ]));
+    });
+  });
+
   group('swift-format', () {
     test('formats Swift if --swift-format flag is provided', () async {
       const List<String> files = <String>[