[google_maps_fluter] Switch to Kotlin Pigeon (#11522)

Replaces the Java Pigeon generator with the Kotlin Pigeon generator, and adjusts the project accordingly:
- Adds Kotlin build setings to Gradle.
- Updates API signatures and number handling for Kotlin/Java generator differences.
- Adds generic Java/Kotlin compat shim to create Result objects from Java, since those haven't been added to the Pigeon generator yet.
- Updates tests to use constructors instead of builders, since the Kotlin generator doesn't create builders.
  - In two cases where replacing the builder pattern would have required major changes, I instead pulled the builders from the old Java generation into the test files.
- Updates tests to use a Java/Kotlin compat shim to read Kotlin Result values, instead of mocking the Java Pigeon response object.

Part of flutter/flutter#158287

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Author: stuartmorgan-g

.ci/legacy_project/README.md

@@ -52,7 +52,7 @@ and then deleting everything but `android/` from it:
   imperative apply (this includes moving where the Android Gradle
   Plugin (AGP) version is set from `build.gradle` to `settings.gradle`).
 - Modifies `settings.gradle` to upgrade the Kotlin Gradle Plugin (KGP)
-  from version 1.9.0 to 2.1.0. If a user runs into an error with the AGP version,
+  from version 1.9.0 to 2.2.20. If a user runs into an error with the AGP version,
   the warning is clear on how to upgrade the version to one that we support.
 - Modifies `gradle.properties` to not set android.enableJetifier=true.
 - Update `app/build.gradle` to enable library desugaring to support

.ci/legacy_project/all_packages/android/settings.gradle

@@ -20,7 +20,7 @@ pluginManagement {
 plugins {
     id "dev.flutter.flutter-plugin-loader" version "1.0.0"
     id "com.android.application" version "8.9.1" apply false
-    id "org.jetbrains.kotlin.android" version "2.1.0" apply false
+    id "org.jetbrains.kotlin.android" version "2.2.20" apply false
 }
 
 include ":app"

packages/google_maps_flutter/google_maps_flutter_android/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.19.8
+
+* Updates internal implementation to use Kotlin Pigeon.
+
 ## 2.19.7
 
 * Fixes warnings in Java code.

packages/google_maps_flutter/google_maps_flutter_android/android/build.gradle.kts

@@ -1,14 +1,18 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 group = "io.flutter.plugins.googlemaps"
 version = "1.0-SNAPSHOT"
 
 buildscript {
+    val kotlinVersion = "2.3.20"
     repositories {
         google()
         mavenCentral()
     }
 
     dependencies {
         classpath("com.android.tools.build:gradle:8.13.1")
+        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion")
     }
 }
 
@@ -21,6 +25,13 @@ allprojects {
 
 plugins {
     id("com.android.library")
+    id("kotlin-android")
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget = JvmTarget.fromTarget(JavaVersion.VERSION_17.toString())
+    }
 }
 
 android {

packages/google_maps_flutter/google_maps_flutter_android/android/src/main/java/io/flutter/plugins/googlemaps/CirclesController.java

@@ -9,10 +9,11 @@
 import com.google.android.gms.maps.GoogleMap;
 import com.google.android.gms.maps.model.Circle;
 import com.google.android.gms.maps.model.CircleOptions;
-import io.flutter.plugins.googlemaps.Messages.MapsCallbackApi;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import kotlin.Result;
+import kotlin.Unit;
 
 class CirclesController {
   @VisibleForTesting final Map<String, CircleController> circleIdToController;
@@ -32,14 +33,14 @@ void setGoogleMap(GoogleMap googleMap) {
     this.googleMap = googleMap;
   }
 
-  void addCircles(@NonNull List<Messages.PlatformCircle> circlesToAdd) {
-    for (Messages.PlatformCircle circleToAdd : circlesToAdd) {
+  void addCircles(@NonNull List<PlatformCircle> circlesToAdd) {
+    for (PlatformCircle circleToAdd : circlesToAdd) {
       addCircle(circleToAdd);
     }
   }
 
-  void changeCircles(@NonNull List<Messages.PlatformCircle> circlesToChange) {
-    for (Messages.PlatformCircle circleToChange : circlesToChange) {
+  void changeCircles(@NonNull List<PlatformCircle> circlesToChange) {
+    for (PlatformCircle circleToChange : circlesToChange) {
       changeCircle(circleToChange);
     }
   }
@@ -59,15 +60,15 @@ boolean onCircleTap(String googleCircleId) {
     if (circleId == null) {
       return false;
     }
-    flutterApi.onCircleTap(circleId, new NoOpVoidResult());
+    flutterApi.onCircleTap(circleId, (Result<Unit> result) -> Unit.INSTANCE);
     CircleController circleController = circleIdToController.get(circleId);
     if (circleController != null) {
       return circleController.consumeTapEvents();
     }
     return false;
   }
 
-  void addCircle(@NonNull Messages.PlatformCircle circle) {
+  void addCircle(@NonNull PlatformCircle circle) {
     CircleBuilder circleBuilder = new CircleBuilder(density);
     String circleId = Convert.interpretCircleOptions(circle, circleBuilder);
     CircleOptions options = circleBuilder.build();
@@ -81,7 +82,7 @@ private void addCircle(String circleId, CircleOptions circleOptions, boolean con
     googleMapsCircleIdToDartCircleId.put(circle.getId(), circleId);
   }
 
-  private void changeCircle(@NonNull Messages.PlatformCircle circle) {
+  private void changeCircle(@NonNull PlatformCircle circle) {
     String circleId = circle.getCircleId();
     CircleController circleController = circleIdToController.get(circleId);
     if (circleController != null) {

packages/google_maps_flutter/google_maps_flutter_android/android/src/main/java/io/flutter/plugins/googlemaps/ClusterManagersController.java

@@ -19,12 +19,12 @@
 import com.google.maps.android.clustering.view.DefaultAdvancedMarkersClusterRenderer;
 import com.google.maps.android.clustering.view.DefaultClusterRenderer;
 import com.google.maps.android.collections.MarkerManager;
-import io.flutter.plugins.googlemaps.Messages.MapsCallbackApi;
-import io.flutter.plugins.googlemaps.Messages.PlatformMarkerType;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import kotlin.Result;
+import kotlin.Unit;
 
 /**
  * Controls cluster managers and exposes interfaces for adding and removing cluster items for
@@ -107,8 +107,8 @@ private void initListenersForClusterManager(
   }
 
   /** Adds new ClusterManagers to the controller. */
-  void addClusterManagers(@NonNull List<Messages.PlatformClusterManager> clusterManagersToAdd) {
-    for (Messages.PlatformClusterManager clusterToAdd : clusterManagersToAdd) {
+  void addClusterManagers(@NonNull List<PlatformClusterManager> clusterManagersToAdd) {
+    for (PlatformClusterManager clusterToAdd : clusterManagersToAdd) {
       addClusterManager(clusterToAdd.getIdentifier());
     }
   }
@@ -216,7 +216,7 @@ void onClusterItemRendered(@NonNull MarkerBuilder item, @NonNull Marker marker)
       String clusterManagerId) {
     ClusterManager<MarkerBuilder> clusterManager = clusterManagerIdToManager.get(clusterManagerId);
     if (clusterManager == null) {
-      throw new Messages.FlutterError(
+      throw new FlutterError(
           "Invalid clusterManagerId",
           "getClusters called with invalid clusterManagerId:" + clusterManagerId,
           null);
@@ -238,7 +238,8 @@ public boolean onClusterClick(Cluster<MarkerBuilder> cluster) {
       MarkerBuilder[] builders = cluster.getItems().toArray(new MarkerBuilder[0]);
       String clusterManagerId = builders[0].clusterManagerId();
       flutterApi.onClusterTap(
-          Convert.clusterToPigeon(clusterManagerId, cluster), new NoOpVoidResult());
+          Convert.clusterToPigeon(clusterManagerId, cluster),
+          (Result<Unit> result) -> Unit.INSTANCE);
     }
 
     // Return false to allow the default behavior of the cluster click event to occur.