[CP-stable]Roll forward: "Initialize default-app-flavor" (flutter#169298

) (flutter#169623)

This pull request is created by [automatic cherry pick workflow](https://github.com/flutter/flutter/blob/main/docs/releases/Flutter-Cherrypick-Process.md#automatically-creates-a-cherry-pick-request)
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

### Issue Link:
What is the link to the issue this cherry-pick is addressing?

flutter#169602

### Changelog Description:
Explain this cherry pick in one line that is accessible to most Flutter developers. See [best practices](https://github.com/flutter/flutter/blob/main/docs/releases/Hotfix-Documentation-Best-Practices.md) for examples

Fixes a bug where `appFlavor` is `null` when being run with `flutter test` or being hot-restarted.

### Impact Description:
What is the impact (ex. visual jank on Samsung phones, app crash, cannot ship an iOS app)? Does it impact development (ex. flutter doctor crashes when Android Studio is installed), or the shipping production app (the app crashes on launch)

Cannot reliably use `appFlavor` without rebuilding the app from scratch.

### Workaround:
Is there a workaround for this issue?

Do not use hot restart, do not use `flutter test`.

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
What are the steps to validate that this fix works?

Automated test coverage.

packages/flutter_tools/lib/src/build_system/targets/common.dart

@@ -6,16 +6,14 @@ import 'package:package_config/package_config.dart';
 
 import '../../artifacts.dart';
 import '../../base/build.dart';
-import '../../base/common.dart';
 import '../../base/file_system.dart';
 import '../../base/io.dart';
 import '../../build_info.dart';
 import '../../compile.dart';
 import '../../dart/package_map.dart';
 import '../../devfs.dart';
-import '../../globals.dart' as globals show platform, xcode;
+import '../../globals.dart' as globals show xcode;
 import '../../project.dart';
-import '../../runner/flutter_command.dart';
 import '../build_system.dart';
 import '../depfile.dart';
 import '../exceptions.dart';
@@ -310,15 +308,17 @@ class KernelSnapshot extends Target {
     if (flavor == null) {
       return;
     }
-    if (globals.platform.environment[kAppFlavor] != null) {
-      throwToolExit('$kAppFlavor is used by the framework and cannot be set in the environment.');
-    }
-    if (dartDefines.any((String define) => define.startsWith(kAppFlavor))) {
-      throwToolExit(
-        '$kAppFlavor is used by the framework and cannot be '
-        'set using --${FlutterOptions.kDartDefinesOption} or --${FlutterOptions.kDartDefineFromFileOption}',
-      );
-    }
+
+    // It is possible there is a flavor already in dartDefines, from another
+    // part of the build process, but this should take precedence as it happens
+    // last (xcodebuild execution).
+    //
+    // See https://github.com/flutter/flutter/issues/169598.
+
+    // If the flavor is already in the dart defines, remove it.
+    dartDefines.removeWhere((String define) => define.startsWith(kAppFlavor));
+
+    // Then, add it to the end.
     dartDefines.add('$kAppFlavor=$flavor');
   }
 }

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -1438,6 +1438,18 @@ abstract class FlutterCommand extends Command<void> {
     final String? cliFlavor = argParser.options.containsKey('flavor') ? stringArg('flavor') : null;
     final String? flavor = cliFlavor ?? defaultFlavor;
 
+    if (globals.platform.environment[kAppFlavor] != null) {
+      throwToolExit('$kAppFlavor is used by the framework and cannot be set in the environment.');
+    }
+    if (dartDefines.any((String define) => define.startsWith(kAppFlavor))) {
+      throwToolExit(
+        '$kAppFlavor is used by the framework and cannot be '
+        'set using --${FlutterOptions.kDartDefinesOption} or --${FlutterOptions.kDartDefineFromFileOption}',
+      );
+    }
+    if (flavor != null) {
+      dartDefines.add('$kAppFlavor=$flavor');
+    }
     _addFlutterVersionToDartDefines(globals.flutterVersion, dartDefines);
 
     return BuildInfo(

packages/flutter_tools/test/general.shard/build_system/targets/common_test.dart

@@ -13,6 +13,7 @@ import 'package:flutter_tools/src/build_system/exceptions.dart';
 import 'package:flutter_tools/src/build_system/targets/common.dart';
 import 'package:flutter_tools/src/build_system/targets/ios.dart';
 import 'package:flutter_tools/src/compile.dart';
+import 'package:flutter_tools/src/convert.dart';
 import 'package:flutter_tools/src/ios/xcodeproj.dart';
 import 'package:test/fake.dart';
 
@@ -440,69 +441,76 @@ void main() {
   );
 
   testUsingContext(
-    "tool exits when $kAppFlavor is already set in user's environment",
+    'KernelSnapshot sets flavor in dartDefines from Xcode build configuration if ios app',
     () async {
       fileSystem.file('.dart_tool/package_config.json')
         ..createSync(recursive: true)
         ..writeAsStringSync('{"configVersion": 2, "packages":[]}');
-      final Future<void> buildResult = const KernelSnapshot().build(
-        androidEnvironment
-          ..defines[kTargetPlatform] = getNameForTargetPlatform(TargetPlatform.android)
-          ..defines[kBuildMode] = BuildMode.debug.cliName
-          ..defines[kFlavor] = 'strawberry'
-          ..defines[kTrackWidgetCreation] = 'false',
+      final String build = iosEnvironment.buildDir.path;
+      final String flutterPatchedSdkPath = artifacts.getArtifactPath(
+        Artifact.flutterPatchedSdkPath,
+        platform: TargetPlatform.ios,
+        mode: BuildMode.debug,
       );
-
-      expect(
-        buildResult,
-        throwsToolExit(
-          message: '$kAppFlavor is used by the framework and cannot be set in the environment.',
+      fileSystem.directory('/ios/Runner.xcodeproj').createSync(recursive: true);
+      processManager.addCommands(<FakeCommand>[
+        FakeCommand(
+          command: <String>[
+            artifacts.getArtifactPath(Artifact.engineDartAotRuntime),
+            artifacts.getArtifactPath(Artifact.frontendServerSnapshotForEngineDartSdk),
+            '--sdk-root',
+            '$flutterPatchedSdkPath/',
+            '--target=flutter',
+            '--no-print-incremental-dependencies',
+            '-D$kAppFlavor=chocolate',
+            ...buildModeOptions(BuildMode.debug, <String>[]),
+            '--no-link-platform',
+            '--packages',
+            '/.dart_tool/package_config.json',
+            '--output-dill',
+            '$build/app.dill',
+            '--depfile',
+            '$build/kernel_snapshot_program.d',
+            '--incremental',
+            '--initialize-from-dill',
+            '$build/app.dill',
+            '--verbosity=error',
+            'file:///lib/main.dart',
+          ],
+          stdout: 'result $kBoundaryKey\n$kBoundaryKey\n$kBoundaryKey $build/app.dill 0\n',
         ),
-      );
-    },
-    overrides: <Type, Generator>{
-      Platform: () => FakePlatform(environment: <String, String>{kAppFlavor: 'I was already set'}),
-    },
-  );
+      ]);
 
-  testUsingContext(
-    'tool exits when $kAppFlavor is set in --dart-define or --dart-define-from-file',
-    () async {
-      fileSystem.file('.dart_tool/package_config.json')
-        ..createSync(recursive: true)
-        ..writeAsStringSync('{"configVersion": 2, "packages":[]}');
-      final Future<void> buildResult = const KernelSnapshot().build(
-        androidEnvironment
-          ..defines[kTargetPlatform] = getNameForTargetPlatform(TargetPlatform.android)
+      await const KernelSnapshot().build(
+        iosEnvironment
+          ..defines[kTargetPlatform] = getNameForTargetPlatform(TargetPlatform.ios)
           ..defines[kBuildMode] = BuildMode.debug.cliName
           ..defines[kFlavor] = 'strawberry'
-          ..defines[kDartDefines] = encodeDartDefines(<String>[kAppFlavor, 'strawberry'])
+          ..defines[kXcodeConfiguration] = 'Debug-chocolate'
           ..defines[kTrackWidgetCreation] = 'false',
       );
 
-      expect(
-        buildResult,
-        throwsToolExit(
-          message:
-              '$kAppFlavor is used by the framework and cannot be set using --dart-define or --dart-define-from-file',
-        ),
-      );
+      expect(processManager, hasNoRemainingExpectations);
+    },
+    overrides: <Type, Generator>{
+      XcodeProjectInterpreter:
+          () => FakeXcodeProjectInterpreter(schemes: <String>['Runner', 'chocolate']),
     },
   );
 
   testUsingContext(
-    'KernelSnapshot sets flavor in dartDefines from Xcode build configuration if ios app',
+    'KernelSnapshot sets flavor in dartDefines from Xcode build configuration if macos app',
     () async {
       fileSystem.file('.dart_tool/package_config.json')
         ..createSync(recursive: true)
         ..writeAsStringSync('{"configVersion": 2, "packages":[]}');
       final String build = iosEnvironment.buildDir.path;
       final String flutterPatchedSdkPath = artifacts.getArtifactPath(
         Artifact.flutterPatchedSdkPath,
-        platform: TargetPlatform.ios,
+        platform: TargetPlatform.darwin,
         mode: BuildMode.debug,
       );
-      fileSystem.directory('/ios/Runner.xcodeproj').createSync(recursive: true);
+      fileSystem.directory('/macos/Runner.xcodeproj').createSync(recursive: true);
       processManager.addCommands(<FakeCommand>[
         FakeCommand(
           command: <String>[
@@ -514,7 +522,6 @@ void main() {
             '--no-print-incremental-dependencies',
             '-D$kAppFlavor=chocolate',
             ...buildModeOptions(BuildMode.debug, <String>[]),
-            '--no-link-platform',
             '--packages',
             '/.dart_tool/package_config.json',
             '--output-dill',
@@ -533,7 +540,7 @@ void main() {
 
       await const KernelSnapshot().build(
         iosEnvironment
-          ..defines[kTargetPlatform] = getNameForTargetPlatform(TargetPlatform.ios)
+          ..defines[kTargetPlatform] = getNameForTargetPlatform(TargetPlatform.darwin)
           ..defines[kBuildMode] = BuildMode.debug.cliName
           ..defines[kFlavor] = 'strawberry'
           ..defines[kXcodeConfiguration] = 'Debug-chocolate'
@@ -549,7 +556,7 @@ void main() {
   );
 
   testUsingContext(
-    'KernelSnapshot sets flavor in dartDefines from Xcode build configuration if macos app',
+    'KernelSnapshot does not add kAppFlavor twice to Dart defines',
     () async {
       fileSystem.file('.dart_tool/package_config.json')
         ..createSync(recursive: true)
@@ -560,7 +567,6 @@ void main() {
         platform: TargetPlatform.darwin,
         mode: BuildMode.debug,
       );
-      fileSystem.directory('/macos/Runner.xcodeproj').createSync(recursive: true);
       processManager.addCommands(<FakeCommand>[
         FakeCommand(
           command: <String>[
@@ -570,7 +576,7 @@ void main() {
             '$flutterPatchedSdkPath/',
             '--target=flutter',
             '--no-print-incremental-dependencies',
-            '-D$kAppFlavor=chocolate',
+            '-D$kAppFlavor=strawberry',
             ...buildModeOptions(BuildMode.debug, <String>[]),
             '--packages',
             '/.dart_tool/package_config.json',
@@ -592,16 +598,17 @@ void main() {
         iosEnvironment
           ..defines[kTargetPlatform] = getNameForTargetPlatform(TargetPlatform.darwin)
           ..defines[kBuildMode] = BuildMode.debug.cliName
+          ..defines[kDartDefines] = base64Encode(utf8.encode('FLUTTER_APP_FLAVOR=vanilla'))
           ..defines[kFlavor] = 'strawberry'
-          ..defines[kXcodeConfiguration] = 'Debug-chocolate'
           ..defines[kTrackWidgetCreation] = 'false',
       );
 
       expect(processManager, hasNoRemainingExpectations);
     },
     overrides: <Type, Generator>{
-      XcodeProjectInterpreter:
-          () => FakeXcodeProjectInterpreter(schemes: <String>['Runner', 'chocolate']),
+      Platform: () => macPlatform,
+      FileSystem: () => fileSystem,
+      ProcessManager: () => processManager,
     },
   );
 

packages/flutter_tools/test/general.shard/runner/flutter_command_test.dart

@@ -1270,6 +1270,98 @@ flutter:
       );
     });
 
+    testUsingContext(
+      "tool exits when $kAppFlavor is already set in user's environemnt",
+      () async {
+        final CommandRunner<void> runner = createTestCommandRunner(
+          _TestRunCommandThatOnlyValidates(),
+        );
+        expect(
+          runner.run(<String>['run', '--no-pub', '--no-hot']),
+          throwsToolExit(
+            message: '$kAppFlavor is used by the framework and cannot be set in the environment.',
+          ),
+        );
+      },
+      overrides: <Type, Generator>{
+        DeviceManager:
+            () => FakeDeviceManager()..attachedDevices = <Device>[FakeDevice('name', 'id')],
+        FileSystem: () {
+          final MemoryFileSystem fileSystem = MemoryFileSystem.test();
+          fileSystem.file('lib/main.dart').createSync(recursive: true);
+          fileSystem.file('pubspec.yaml').createSync();
+          return fileSystem;
+        },
+        ProcessManager: FakeProcessManager.empty,
+        Platform: () => FakePlatform()..environment = <String, String>{kAppFlavor: 'AlreadySet'},
+      },
+    );
+
+    testUsingContext(
+      'tool exits when $kAppFlavor is set in --dart-define',
+      () async {
+        final CommandRunner<void> runner = createTestCommandRunner(
+          _TestRunCommandThatOnlyValidates(),
+        );
+        expect(
+          runner.run(<String>[
+            'run',
+            '--dart-define=$kAppFlavor=AlreadySet',
+            '--no-pub',
+            '--no-hot',
+          ]),
+          throwsToolExit(
+            message: '$kAppFlavor is used by the framework and cannot be set using --dart-define',
+          ),
+        );
+      },
+      overrides: <Type, Generator>{
+        DeviceManager:
+            () => FakeDeviceManager()..attachedDevices = <Device>[FakeDevice('name', 'id')],
+        FileSystem: () {
+          final MemoryFileSystem fileSystem = MemoryFileSystem.test();
+          fileSystem.file('lib/main.dart').createSync(recursive: true);
+          fileSystem.file('pubspec.yaml').createSync();
+          return fileSystem;
+        },
+        ProcessManager: FakeProcessManager.empty,
+      },
+    );
+
+    testUsingContext(
+      'tool exits when $kAppFlavor is set in --dart-define-from-file',
+      () async {
+        final CommandRunner<void> runner = createTestCommandRunner(
+          _TestRunCommandThatOnlyValidates(),
+        );
+        expect(
+          runner.run(<String>[
+            'run',
+            '--dart-define-from-file=config.json',
+            '--no-pub',
+            '--no-hot',
+          ]),
+          throwsToolExit(
+            message: '$kAppFlavor is used by the framework and cannot be set using --dart-define',
+          ),
+        );
+      },
+      overrides: <Type, Generator>{
+        DeviceManager:
+            () => FakeDeviceManager()..attachedDevices = <Device>[FakeDevice('name', 'id')],
+        FileSystem: () {
+          final MemoryFileSystem fileSystem = MemoryFileSystem.test();
+          fileSystem.file('lib/main.dart').createSync(recursive: true);
+          fileSystem.file('pubspec.yaml').createSync();
+          fileSystem.file('config.json')
+            ..createSync()
+            ..writeAsStringSync('{"$kAppFlavor": "AlreadySet"}');
+          return fileSystem;
+        },
+        ProcessManager: FakeProcessManager.empty,
+      },
+    );
+
     group('Flutter version', () {
       for (final String dartDefine in FlutterCommand.flutterVersionDartDefines) {
         testUsingContext(