Flip the newDsl default: drop the opt-out from templates and migrate it away

dev/devicelab/lib/framework/dependency_smoke_test_task_definition.dart

@@ -158,7 +158,10 @@ Future<TaskResult> buildFlutterApkWithSpecifiedDependencyVersions({
       section('Add a dependency on a plugin');
       await flutter(
         'pub',
-        options: <String>['add', 'shared_preferences_android:2.4.7'], // Chosen randomly.
+        options: <String>[
+          'add',
+          'shared_preferences_android:2.4.24',
+        ], // Smallest version jump supporting AGP 9.
         workingDirectory: appPath,
       );
 

dev/integration_tests/android_hardware_smoke_test/android/app/test_result_embedder.gradle.kts

@@ -33,9 +33,23 @@ tasks.register("embedTestResultImages") {
         val packageId = "com.example.android_hardware_smoke_test"
         val discoveredTests = mutableListOf<DiscoveredTest>()
 
-        // Resolve binary safe adb executable from Android Gradle Plugin BaseExtension
-        val android = project.extensions.getByType(com.android.build.gradle.BaseExtension::class.java)
-        val adbPath = android.adbExecutable.absolutePath
+        // Resolve binary-safe adb executable from Android Gradle Plugin (new variant API with BaseExtension fallback)
+        val adbPath =
+            try {
+                val androidComponents =
+                    project.extensions.getByType(
+                        com.android.build.api.variant.ApplicationAndroidComponentsExtension::class.java
+                    )
+                androidComponents.sdkComponents.adb
+                    .get()
+                    .asFile.absolutePath
+            } catch (_: org.gradle.api.UnknownDomainObjectException) {
+                val android = project.extensions.getByType(com.android.build.gradle.BaseExtension::class.java)
+                android.adbExecutable.absolutePath
+            } catch (_: IllegalArgumentException) {
+                val android = project.extensions.getByType(com.android.build.gradle.BaseExtension::class.java)
+                android.adbExecutable.absolutePath
+            }
         println("Resolved binary-safe adb executable from AGP: $adbPath")
 
         // 1. Query the device sandbox to list all files in cache/results/ using ProcessBuilder

docs/platforms/android/Migrating-Flutter-Gradle-Plugin-to-AGP-public-API.md

@@ -97,7 +97,15 @@ projects. That opt-out dies with AGP 10.
      `outputs/flutter-apk` directory, because a shared `@OutputDirectory` would overlap
      between variants by construction. A runtime warning reports produced names outside
      the predicted set.
-6. **P3 pre-spike (afterEvaluate DSL mutation under newDsl).** The planned scratch-app
+6. **Stable-channel add-migrator guard (release management, not in this repo's
+   changes).** The stable channel still carries the old `DisableNewDslMigration`,
+   which ADDS `android.newDsl=false`. Once the P9 removal migrator reaches a
+   channel, switching between that channel and stable would flip-flop
+   gradle.properties. Before P9 is released, cherry-pick a guard onto the
+   stable-side add-migrator (skip adding the opt-out when the project's recorded
+   Flutter/AGP versions indicate the new-DSL-capable plugin) or accept the
+   flip-flop for the overlap window and document it in the release notes.
+7. **P3 pre-spike (afterEvaluate DSL mutation under newDsl).** The planned scratch-app
    spike (AGP 9.1 + `newDsl=true` + custom build type, verifying that build-type
    creation from `pluginProject.afterEvaluate` still works) could not run in the
    implementation sandbox (no AGP artifact access). The `initWith` copy landed on the

docs/platforms/android/website-page-draft.md

@@ -3,7 +3,12 @@
 *Draft breaking-change page for `docs.flutter.dev/release/breaking-changes/`.
 This file is the source of truth until the page is published to
 flutter/website; publishing must complete before the newDsl flip reaches the
-beta channel. Contributor-facing details live in
+beta channel. The page MUST be published at
+`https://docs.flutter.dev/release/breaking-changes/android-agp-new-dsl` —
+that URL is hard-coded as `kNewDslBreakingChangeDocsUrl` in
+`packages/flutter_tools/lib/src/android/gradle_errors.dart` and is printed by
+the legacy-variant-API error handler and the opt-out removal migrator.
+Contributor-facing details live in
 [Migrating-Flutter-Gradle-Plugin-to-AGP-public-API.md](Migrating-Flutter-Gradle-Plugin-to-AGP-public-API.md).*
 
 ## Summary

packages/flutter_tools/lib/src/android/gradle.dart

@@ -42,9 +42,9 @@ import 'java.dart';
 import 'migrations/android_studio_java_gradle_conflict_migration.dart';
 import 'migrations/cmake_android_16k_pages_migration.dart';
 import 'migrations/disable_built_in_kotlin_migration.dart';
-import 'migrations/disable_new_dsl_migration.dart';
 import 'migrations/min_sdk_version_migration.dart';
 import 'migrations/multidex_removal_migration.dart';
+import 'migrations/remove_new_dsl_opt_out_migration.dart';
 import 'migrations/top_level_gradle_build_file_migration.dart';
 
 /// The regex to grab variant names from printBuildVariants gradle task
@@ -518,7 +518,7 @@ To fix this, you can either:
       MultidexRemovalMigration(project.android, _logger),
       CmakeAndroid16kPagesMigration(project.android, _logger),
       DisableBuiltInKotlinMigration(project.android, _logger),
-      DisableNewDslMigration(project.android, _logger),
+      RemoveNewDslOptOutMigration(project.android, _logger),
     ];
 
     final migration = ProjectMigration(migrators);

packages/flutter_tools/lib/src/android/gradle_errors.dart

@@ -85,7 +85,7 @@ final gradleErrors = <GradleHandledError>[
   jlinkErrorWithJava21AndSourceCompatibility,
   missingNdkSourcePropertiesFile,
   applyingKotlinAndroidPluginErrorHandler,
-  useNewAgpDslErrorHandler,
+  legacyVariantApiUsageErrorHandler,
   incompatibleKotlinVersionHandler, // This handler should always be last, as its key log output is sometimes in error messages with other root causes.
 ];
 
@@ -689,9 +689,11 @@ final missingNdkSourcePropertiesFile = GradleHandledError(
 const String kMigrateToBuiltInKotlinDocsUrl =
     'https://docs.flutter.dev/release/breaking-changes/migrate-to-built-in-kotlin';
 
-/// The URL for documentation on opting out of the new AGP DSL.
-const String kOptOutOfNewDslDocsUrl =
-    'https://developer.android.com/build/releases/agp-9-0-0-release-notes';
+/// The URL for the breaking-change page covering the Android Gradle Plugin new-DSL
+/// migration (legacy variant API removal), including before/after recipes and the
+/// temporary `android.newDsl=false` escape hatch.
+const String kNewDslBreakingChangeDocsUrl =
+    'https://docs.flutter.dev/release/breaking-changes/android-agp-new-dsl';
 
 /// Handler when applying the kotlin-android plugin results in a build failure. This failure occurs when
 /// using AGP 9+ because built-in Kotlin has become the default behavior.
@@ -715,29 +717,32 @@ To resolve this, migrate to built-in Kotlin.
   eventLabel: 'applying-kotlin-android-plugin-error',
 );
 
-/// Handler when using the new AGP DSL interfaces. Starting AGP 9+, only the new
-/// DSL interfaces are used. This results in a failure because we still depend
-/// on old DSL types.
+/// Handler for Gradle build scripts that use the removed legacy AGP variant API
+/// (`applicationVariants`, `libraryVariants`, `variantFilter`). Flutter projects build
+/// with the Android Gradle Plugin's new DSL, under which these APIs do not exist.
 @visibleForTesting
-final useNewAgpDslErrorHandler = GradleHandledError(
+final legacyVariantApiUsageErrorHandler = GradleHandledError(
   test: _lineMatcher(const <String>[
-    "> Failed to apply plugin 'dev.flutter.flutter-gradle-plugin'",
-    '> java.lang.NullPointerException (no error message)',
+    "Could not get unknown property 'applicationVariants'",
+    "Could not get unknown property 'libraryVariants'",
+    "Could not get unknown property 'testVariants'",
+    "Could not get unknown property 'variantFilter'",
+    'Could not find method applicationVariants(',
+    'Could not find method libraryVariants(',
+    'Could not find method variantFilter(',
   ]),
   handler:
       ({required String line, required FlutterProject project, required bool usesAndroidX}) async {
-        final File appGradleFile = project.android.appGradleFile;
         globals.printBox(
           '''
-${globals.logger.terminal.warningMark} Starting AGP 9+, only the new DSL interface will be read.
-This results in a build failure when applying the Flutter Gradle plugin at ${appGradleFile.path}.
-\nTo resolve this update flutter or opt out of `android.newDsl`.
-For instructions on how to opt out, see: $kOptOutOfNewDslDocsUrl
-\nIf you are not upgrading to AGP 9+, run `flutter analyze --suggestions` to check for incompatible dependencies.''',
+${globals.logger.terminal.warningMark} A Gradle build script in this project uses the Android Gradle Plugin's legacy variant API (for example `android.applicationVariants`), which does not exist under the new Android Gradle Plugin DSL that Flutter projects now build with.
+\nTo resolve this, migrate the build script to the variant API (`androidComponents.onVariants`).
+For before/after examples of common patterns, see: $kNewDslBreakingChangeDocsUrl
+\nAs a temporary escape hatch, you can add `android.newDsl=false` to android/gradle.properties, but this stops working with Android Gradle Plugin 10, which removes the legacy API entirely.''',
           title: _boxTitle,
         );
 
         return GradleBuildStatus.exit;
       },
-  eventLabel: 'use-new-agp-dsl-error',
+  eventLabel: 'legacy-variant-api-usage',
 );

packages/flutter_tools/lib/src/android/gradle_utils.dart

@@ -50,6 +50,8 @@ const templateAndroidGradlePluginVersionForModule = '9.1.0';
 //  * KGP jvm constant in packages/flutter_tools/gradle/src/test/kotlin/DependencyVersionCheckerTest.kt
 // See https://kotlinlang.org/docs/releases.html#release-details
 const templateKotlinGradlePluginVersion = '2.4.0';
+const templateJunitJupiterEngineVersion = '5.10.2';
+const templateJunitPlatformLauncherVersion = '1.10.2';
 
 // The Flutter Gradle Plugin is only applied to app projects, and modules that
 // are built from source using (`include_flutter.groovy`). The remaining

packages/flutter_tools/lib/src/android/migrations/remove_new_dsl_opt_out_migration.dart

@@ -0,0 +1,77 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import '../../base/file_system.dart';
+import '../../base/project_migrator.dart';
+import '../../project.dart';
+import '../gradle_errors.dart';
+
+/// The marker comment the project templates placed above the opt-out.
+const String _templateMarkerComment = '# This newDsl flag was added by the Flutter template';
+
+/// The marker comment [the former DisableNewDslMigration] placed above the opt-out.
+const String _migratorMarkerComment =
+    '# This newDsl flag was added automatically by Flutter migrator';
+
+/// Matches the opt-out line Flutter wrote (tolerating whitespace and the `:` separator).
+/// Deliberately does NOT match `android.newDsl=true` or other values: if the developer
+/// edited the line, it is theirs now and stays.
+final RegExp _newDslOptOutPattern = RegExp(r'^\s*android\.newDsl\s*[=:]\s*false\s*$');
+
+/// Removes the `android.newDsl=false` opt-out that Flutter previously added to
+/// `gradle.properties` (through the project templates and through the former
+/// `DisableNewDslMigration`), now that the Flutter Gradle Plugin supports the Android
+/// Gradle Plugin's new DSL.
+///
+/// Only line pairs Flutter wrote are removed: one of the two known marker comments
+/// immediately followed by the `android.newDsl=false` property line. The removal is
+/// anchored on the `android.newDsl` property line - never on marker wording alone -
+/// so the adjacent `android.builtInKotlin` marker/flag lines (owned by the separate
+/// built-in Kotlin migration) and hand-added opt-outs are never touched.
+class RemoveNewDslOptOutMigration extends ProjectMigrator {
+  RemoveNewDslOptOutMigration(AndroidProject project, super.logger)
+    : _gradlePropertiesFile = project.hostAppGradleRoot.childFile('gradle.properties');
+
+  final File _gradlePropertiesFile;
+
+  @override
+  Future<void> migrate() async {
+    if (!_gradlePropertiesFile.existsSync()) {
+      // Nothing to remove. (The former DisableNewDslMigration created this file when it
+      // was missing, writing only the marker and the flag; that case is handled by the
+      // pair removal below, leaving an empty file.)
+      return;
+    }
+    processFileLines(_gradlePropertiesFile);
+  }
+
+  @override
+  String migrateFileContents(String fileContents) {
+    final List<String> lines = fileContents.split('\n');
+    final result = <String>[];
+    var removed = false;
+    for (var i = 0; i < lines.length; i++) {
+      final String trimmed = lines[i].trim();
+      final bool isFlutterMarker =
+          trimmed == _templateMarkerComment || trimmed == _migratorMarkerComment;
+      if (isFlutterMarker && i + 1 < lines.length && _newDslOptOutPattern.hasMatch(lines[i + 1])) {
+        // Skip the marker comment and the opt-out line it annotates.
+        i++;
+        removed = true;
+        continue;
+      }
+      result.add(lines[i]);
+    }
+    if (!removed) {
+      return fileContents;
+    }
+    logger.printStatus(
+      'Removed the android.newDsl opt-out that Flutter previously added to '
+      '${_gradlePropertiesFile.path}; Android builds now use the Android Gradle '
+      "Plugin's new DSL. If your Android build fails after this change, see "
+      '$kNewDslBreakingChangeDocsUrl',
+    );
+    return result.join('\n');
+  }
+}

packages/flutter_tools/lib/src/commands/create_base.dart

@@ -393,6 +393,8 @@ mixin CreateBase on FlutterCommand {
       'agpVersion': agpVersion,
       'agpVersionForModule': gradle.templateAndroidGradlePluginVersionForModule,
       'kotlinVersion': kotlinVersion,
+      'junitJupiterEngineVersion': gradle.templateJunitJupiterEngineVersion,
+      'junitPlatformLauncherVersion': gradle.templateJunitPlatformLauncherVersion,
       'gradleVersion': gradleVersion,
       'compileSdkVersion': gradle.compileSdkVersion,
       'minSdkVersion': gradle.minSdkVersion,

packages/flutter_tools/lib/src/project.dart

@@ -990,6 +990,8 @@ See the link below for more information:
       'agpVersion': gradle.templateAndroidGradlePluginVersion,
       'agpVersionForModule': gradle.templateAndroidGradlePluginVersionForModule,
       'kotlinVersion': gradle.templateKotlinGradlePluginVersion,
+      'junitJupiterEngineVersion': gradle.templateJunitJupiterEngineVersion,
+      'junitPlatformLauncherVersion': gradle.templateJunitPlatformLauncherVersion,
       'gradleVersion': gradle.templateDefaultGradleVersion,
       'compileSdkVersion': gradle.compileSdkVersion,
       'minSdkVersion': gradle.minSdkVersion,

packages/flutter_tools/templates/app/android.tmpl/gradle.properties.tmpl

@@ -1,6 +1,4 @@
 org.gradle.jvmargs=-Xmx8G -XX:MaxMetaspaceSize=4G -XX:ReservedCodeCacheSize=512m -XX:+HeapDumpOnOutOfMemoryError
 android.useAndroidX=true
-# This newDsl flag was added by the Flutter template
-android.newDsl=false
 # This builtInKotlin flag was added by the Flutter template
 android.builtInKotlin=false

packages/flutter_tools/templates/module/android/gradle/gradle.properties.tmpl

@@ -1,6 +1,4 @@
 org.gradle.jvmargs=-Xmx8G -XX:MaxMetaspaceSize=4G -XX:ReservedCodeCacheSize=512m -XX:+HeapDumpOnOutOfMemoryError
 android.useAndroidX=true
-# This newDsl flag was added by the Flutter template
-android.newDsl=false
 # This builtInKotlin flag was added by the Flutter template
 android.builtInKotlin=false

packages/flutter_tools/templates/plugin/android-kotlin.tmpl/build.gradle.kts.tmpl

@@ -72,6 +72,9 @@ kotlin {
 }
 
 dependencies {
-    testImplementation("org.jetbrains.kotlin:kotlin-test")
+    testImplementation("org.jetbrains.kotlin:kotlin-test:{{kotlinVersion}}")
+    testImplementation("org.jetbrains.kotlin:kotlin-test-junit5:{{kotlinVersion}}")
+    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:{{junitJupiterEngineVersion}}")
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher:{{junitPlatformLauncherVersion}}")
     testImplementation("org.mockito:mockito-core:5.0.0")
 }