[iOS] Migrate @UIApplicationMain attribute to @main

Author: loic-sharma

packages/flutter_tools/lib/src/ios/migrations/uiapplicationmain_deprecation_migration.dart

@@ -0,0 +1,51 @@
+// 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 '../../xcode_project.dart';
+
+const String _appDelegateFileBefore = r'''
+@UIApplicationMain
+@objc class AppDelegate: FlutterAppDelegate {
+''';
+
+const String _appDelegateFileAfter = r'''
+@main
+@objc class AppDelegate: FlutterAppDelegate {
+''';
+
+/// Replace the deprecated `@UIApplicationMain` attribute with `@main`.
+///
+/// See:
+/// https://github.com/apple/swift-evolution/blob/main/proposals/0383-deprecate-uiapplicationmain-and-nsapplicationmain.md
+class UIApplicationmMainDeprecationMigration extends ProjectMigrator {
+  UIApplicationmMainDeprecationMigration(
+    IosProject project,
+    super.logger,
+  )   : _appDelegateSwift = project.appDelegateSwift;
+
+  final File _appDelegateSwift;
+
+  @override
+  Future<bool> migrate() async {
+    // Skip this migration if the project uses Objective-C.
+    if (!_appDelegateSwift.existsSync()) {
+      return true;
+    }
+
+    // Migrate the ios/Runner/AppDelegate.swift file.
+    final String original = _appDelegateSwift.readAsStringSync();
+    final String migrated = original.replaceFirst(_appDelegateFileBefore, _appDelegateFileAfter);
+    if (original == migrated) {
+      return true;
+    }
+
+    logger.printStatus(
+      'ios/Runner/AppDelegate.swift does not use the @main attribute, updating.',
+    );
+    _appDelegateSwift.writeAsStringSync(migrated);
+    return true;
+  }
+}

packages/flutter_tools/lib/src/xcode_project.dart

@@ -178,15 +178,15 @@ class IosProject extends XcodeBasedProject {
 
   File get appFrameworkInfoPlist => _flutterLibRoot.childDirectory('Flutter').childFile('AppFrameworkInfo.plist');
 
+  /// The 'AppDelegate.swift' file of the host app. This file might not exist if the app project uses Objective-C.
+  File get appDelegateSwift => _editableDirectory.childDirectory('Runner').childFile('AppDelegate.swift');
+
   File get infoPlist => _editableDirectory.childDirectory('Runner').childFile('Info.plist');
 
   Directory get symlinks => _flutterLibRoot.childDirectory('.symlinks');
 
-  /// True, if the app project is using swift.
-  bool get isSwift {
-    final File appDelegateSwift = _editableDirectory.childDirectory('Runner').childFile('AppDelegate.swift');
-    return appDelegateSwift.existsSync();
-  }
+  /// True if the app project uses Swift.
+  bool get isSwift => appDelegateSwift.existsSync();
 
   /// Do all plugins support arm64 simulators to run natively on an ARM Mac?
   Future<bool> pluginsSupportArmSimulator() async {

packages/flutter_tools/templates/app_shared/ios-swift.tmpl/Runner/AppDelegate.swift

@@ -1,7 +1,7 @@
 import Flutter
 import UIKit
 
-@UIApplicationMain
+@main
 @objc class AppDelegate: FlutterAppDelegate {
   override func application(
     _ application: UIApplication,