[local_auth] Switch to Kotlin Pigeon (#11482)

Replaces the Java Pigeon generator with the Kotlin Pigeon generator, and adjusts the project accordingly:
- Adds Kotlin build setings to Gradle.
- Updates API signatures for Kotlin/Java 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.
- 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

packages/local_auth/local_auth_android/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.0.8
+
+* Updates internal implementation to use Kotlin Pigeon.
+
 ## 2.0.7
 
 * Updates build files from Groovy to Kotlin.

packages/local_auth/local_auth_android/android/build.gradle.kts

@@ -1,14 +1,18 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 group = "io.flutter.plugins.localauth"
 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 @@ rootProject.allprojects {
 
 plugins {
     id("com.android.library")
+    id("kotlin-android")
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget = JvmTarget.fromTarget(JavaVersion.VERSION_17.toString())
+    }
 }
 
 android {

packages/local_auth/local_auth_android/android/src/main/java/io/flutter/plugins/localauth/AuthenticationHelper.java

@@ -16,8 +16,6 @@
 import androidx.lifecycle.DefaultLifecycleObserver;
 import androidx.lifecycle.Lifecycle;
 import androidx.lifecycle.LifecycleOwner;
-import io.flutter.plugins.localauth.Messages.AuthResult;
-import io.flutter.plugins.localauth.Messages.AuthResultCode;
 import java.util.concurrent.Executor;
 
 /**
@@ -37,7 +35,6 @@ interface AuthCompletionHandler {
   private final Lifecycle lifecycle;
   private final FragmentActivity activity;
   private final AuthCompletionHandler completionHandler;
-  private final Messages.AuthStrings strings;
   private final BiometricPrompt.PromptInfo promptInfo;
   private final boolean isAuthSticky;
   private final UiThreadExecutor uiThreadExecutor;
@@ -47,14 +44,13 @@ interface AuthCompletionHandler {
   AuthenticationHelper(
       Lifecycle lifecycle,
       FragmentActivity activity,
-      @NonNull Messages.AuthOptions options,
-      @NonNull Messages.AuthStrings strings,
+      @NonNull AuthOptions options,
+      @NonNull AuthStrings strings,
       @NonNull AuthCompletionHandler completionHandler,
       boolean allowCredentials) {
     this.lifecycle = lifecycle;
     this.activity = activity;
     this.completionHandler = completionHandler;
-    this.strings = strings;
     this.isAuthSticky = options.getSticky();
     this.uiThreadExecutor = new UiThreadExecutor();
 
@@ -157,14 +153,13 @@ public void onAuthenticationError(int errorCode, @NonNull CharSequence errString
         code = AuthResultCode.UNKNOWN_ERROR;
         break;
     }
-    completionHandler.complete(
-        new AuthResult.Builder().setCode(code).setErrorMessage(errString.toString()).build());
+    completionHandler.complete(new AuthResult(code, errString.toString()));
     stop();
   }
 
   @Override
   public void onAuthenticationSucceeded(@NonNull BiometricPrompt.AuthenticationResult result) {
-    completionHandler.complete(new AuthResult.Builder().setCode(AuthResultCode.SUCCESS).build());
+    completionHandler.complete(new AuthResult(AuthResultCode.SUCCESS, null));
     stop();
   }
 

packages/local_auth/local_auth_android/android/src/main/java/io/flutter/plugins/localauth/LocalAuthPlugin.java

@@ -11,6 +11,7 @@
 import android.content.Context;
 import android.os.Build;
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
 import androidx.biometric.BiometricManager;
 import androidx.fragment.app.FragmentActivity;
@@ -20,16 +21,13 @@
 import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding;
 import io.flutter.embedding.engine.plugins.lifecycle.FlutterLifecycleAdapter;
 import io.flutter.plugins.localauth.AuthenticationHelper.AuthCompletionHandler;
-import io.flutter.plugins.localauth.Messages.AuthClassification;
-import io.flutter.plugins.localauth.Messages.AuthOptions;
-import io.flutter.plugins.localauth.Messages.AuthResult;
-import io.flutter.plugins.localauth.Messages.AuthResultCode;
-import io.flutter.plugins.localauth.Messages.AuthStrings;
-import io.flutter.plugins.localauth.Messages.LocalAuthApi;
-import io.flutter.plugins.localauth.Messages.Result;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicBoolean;
+import kotlin.Result;
+import kotlin.Unit;
+import kotlin.jvm.functions.Function1;
+import org.jetbrains.annotations.NotNull;
 
 /**
  * Flutter plugin providing access to local authentication.
@@ -54,17 +52,17 @@ public class LocalAuthPlugin implements FlutterPlugin, ActivityAware, LocalAuthA
   public LocalAuthPlugin() {}
 
   @Override
-  public @NonNull Boolean isDeviceSupported() {
+  public boolean isDeviceSupported() {
     return isDeviceSecure() || canAuthenticateWithBiometrics();
   }
 
   @Override
-  public @NonNull Boolean deviceCanSupportBiometrics() {
+  public boolean deviceCanSupportBiometrics() {
     return hasBiometricHardware();
   }
 
   @Override
-  public @NonNull List<AuthClassification> getEnrolledBiometrics() {
+  public @Nullable List<AuthClassification> getEnrolledBiometrics() {
     if (biometricManager == null) {
       return null;
     }
@@ -81,7 +79,7 @@ public LocalAuthPlugin() {}
   }
 
   @Override
-  public @NonNull Boolean stopAuthentication() {
+  public boolean stopAuthentication() {
     try {
       if (authHelper != null && authInProgress.get()) {
         authHelper.stopAuthentication();
@@ -98,30 +96,32 @@ public LocalAuthPlugin() {}
   public void authenticate(
       @NonNull AuthOptions options,
       @NonNull AuthStrings strings,
-      @NonNull Result<AuthResult> result) {
+      @NonNull Function1<? super @NotNull Result<@NotNull AuthResult>, @NotNull Unit> callback) {
     if (authInProgress.get()) {
-      result.success(new AuthResult.Builder().setCode(AuthResultCode.ALREADY_IN_PROGRESS).build());
+      ResultUtilsKt.completeWithValue(
+          callback, new AuthResult(AuthResultCode.ALREADY_IN_PROGRESS, null));
       return;
     }
 
     if (activity == null || activity.isFinishing()) {
-      result.success(new AuthResult.Builder().setCode(AuthResultCode.NO_ACTIVITY).build());
+      ResultUtilsKt.completeWithValue(callback, new AuthResult(AuthResultCode.NO_ACTIVITY, null));
       return;
     }
 
     if (!(activity instanceof FragmentActivity)) {
-      result.success(
-          new AuthResult.Builder().setCode(AuthResultCode.NOT_FRAGMENT_ACTIVITY).build());
+      ResultUtilsKt.completeWithValue(
+          callback, new AuthResult(AuthResultCode.NOT_FRAGMENT_ACTIVITY, null));
       return;
     }
 
     if (!isDeviceSupported()) {
-      result.success(new AuthResult.Builder().setCode(AuthResultCode.NO_CREDENTIALS).build());
+      ResultUtilsKt.completeWithValue(
+          callback, new AuthResult(AuthResultCode.NO_CREDENTIALS, null));
       return;
     }
 
     authInProgress.set(true);
-    AuthCompletionHandler completionHandler = createAuthCompletionHandler(result);
+    AuthCompletionHandler completionHandler = createAuthCompletionHandler(callback);
 
     boolean allowCredentials = !options.getBiometricOnly() && canAuthenticateWithDeviceCredential();
 
@@ -130,8 +130,8 @@ public void authenticate(
 
   @VisibleForTesting
   public @NonNull AuthCompletionHandler createAuthCompletionHandler(
-      @NonNull final Result<AuthResult> result) {
-    return authResult -> onAuthenticationCompleted(result, authResult);
+      @NonNull Function1<? super @NotNull Result<@NotNull AuthResult>, @NotNull Unit> callback) {
+    return authResult -> onAuthenticationCompleted(callback, authResult);
   }
 
   @VisibleForTesting
@@ -152,9 +152,11 @@ public void sendAuthenticationRequest(
     authHelper.authenticate();
   }
 
-  void onAuthenticationCompleted(Result<AuthResult> result, AuthResult value) {
+  void onAuthenticationCompleted(
+      @NonNull Function1<? super @NotNull Result<@NotNull AuthResult>, @NotNull Unit> callback,
+      AuthResult value) {
     if (authInProgress.compareAndSet(true, false)) {
-      result.success(value);
+      ResultUtilsKt.completeWithValue(callback, value);
     }
   }
 
@@ -192,12 +194,12 @@ public boolean canAuthenticateWithDeviceCredential() {
 
   @Override
   public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
-    LocalAuthApi.setUp(binding.getBinaryMessenger(), this);
+    LocalAuthApi.Companion.setUp(binding.getBinaryMessenger(), this);
   }
 
   @Override
   public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
-    LocalAuthApi.setUp(binding.getBinaryMessenger(), null);
+    LocalAuthApi.Companion.setUp(binding.getBinaryMessenger(), null);
   }
 
   private void setServicesFromActivity(Activity activity) {