Support string compileSdkVersion for preview android SDKs (#104662)

packages/flutter_tools/gradle/flutter.gradle

@@ -458,7 +458,10 @@ class FlutterPlugin implements Plugin<Project> {
     /** Prints error message and fix for any plugin compileSdkVersion or ndkVersion that are higher than the project. */
     private void detectLowCompileSdkVersionOrNdkVersion() {
         project.afterEvaluate {
-            int projectCompileSdkVersion = project.android.compileSdkVersion.substring(8) as int
+            int projectCompileSdkVersion = Integer.MAX_VALUE // Default to int max if using a preview version to skip the sdk check.
+            if (project.android.compileSdkVersion.substring(8).isInteger()) { // Stable versions use ints, legacy preview uses string.
+                projectCompileSdkVersion = project.android.compileSdkVersion.substring(8) as int
+            }
             int maxPluginCompileSdkVersion = projectCompileSdkVersion
             String ndkVersionIfUnspecified = "21.1.6352462" /* The default for AGP 4.1.0 used in old templates. */
             String projectNdkVersion = project.android.ndkVersion ?: ndkVersionIfUnspecified

packages/flutter_tools/test/integration.shard/flutter_build_preview_sdk.dart

+// 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 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/io.dart';
+
+import '../src/common.dart';
+import 'test_utils.dart';
+
+void main() {
+  late Directory tempDir;
+  late String flutterBin;
+  late Directory exampleAppDir;
+
+  setUp(() async {
+    tempDir = createResolvedTempDirectorySync('flutter_plugin_test.');
+    flutterBin = fileSystem.path.join(
+      getFlutterRoot(),
+      'bin',
+      'flutter',
+    );
+    exampleAppDir = tempDir.childDirectory('aaa').childDirectory('example');
+
+    processManager.runSync(<String>[
+      flutterBin,
+      ...getLocalEngineArguments(),
+      'create',
+      '--template=plugin',
+      '--platforms=android',
+      'aaa',
+    ], workingDirectory: tempDir.path);
+  });
+
+  tearDown(() async {
+    tryToDelete(tempDir);
+  });
+
+  test(
+    'build succeeds targeting string compileSdkVersion',
+    () async {
+      final File buildGradleFile = exampleAppDir.childDirectory('android').childDirectory('app').childFile('build.gradle');
+      // write a build.gradle with compileSdkVersion as `android-Tiramisu` which is a string preview version
+      buildGradleFile.writeAsStringSync(
+        buildGradleFile.readAsStringSync().replaceFirst('compileSdkVersion flutter.compileSdkVersion', 'compileSdkVersion "android-Tiramisu"'),
+        flush: true
+      );
+      expect(buildGradleFile.readAsStringSync(), contains('compileSdkVersion "android-Tiramisu"'));
+
+      final ProcessResult result = await processManager.run(<String>[
+        flutterBin,
+        ...getLocalEngineArguments(),
+        'build',
+        'apk',
+        '--debug',
+      ], workingDirectory: exampleAppDir.path);
+      expect(result.stdout, contains('Built build/app/outputs/flutter-apk/app-debug.apk.'));
+      expect(exampleAppDir.childDirectory('build')
+        .childDirectory('app')
+        .childDirectory('outputs')
+        .childDirectory('apk')
+        .childDirectory('debug')
+        .childFile('app-debug.apk').existsSync(), true);
+    },
+  );
+
+  test(
+    'build succeeds targeting string compileSdkPreview',
+    () async {
+      final File buildGradleFile = exampleAppDir.childDirectory('android').childDirectory('app').childFile('build.gradle');
+      // write a build.gradle with compileSdkPreview as `Tiramisu` which is a string preview version
+      buildGradleFile.writeAsStringSync(
+        buildGradleFile.readAsStringSync().replaceFirst('compileSdkVersion flutter.compileSdkVersion', 'compileSdkPreview "Tiramisu"'),
+        flush: true
+      );
+      expect(buildGradleFile.readAsStringSync(), contains('compileSdkPreview "Tiramisu"'));
+
+      final ProcessResult result = await processManager.run(<String>[
+        flutterBin,
+        ...getLocalEngineArguments(),
+        'build',
+        'apk',
+        '--debug',
+      ], workingDirectory: exampleAppDir.path);
+      expect(result.stdout, contains('Built build/app/outputs/flutter-apk/app-debug.apk.'));
+      expect(exampleAppDir.childDirectory('build')
+        .childDirectory('app')
+        .childDirectory('outputs')
+        .childDirectory('apk')
+        .childDirectory('debug')
+        .childFile('app-debug.apk').existsSync(), true);
+    },
+  );
+}