Support conditional bundling of assets based on `--flavor` (#132985)

Provides support for conditional bundling of assets through the existing `--flavor` option for `flutter build` and `flutter run`. Closes https://github.com/flutter/flutter/issues/21682. Resolves https://github.com/flutter/flutter/issues/136092

## Change
Within the `assets` section pubspec.yaml, the user can now specify one or more `flavors` that an asset belongs to. Consider this example:

```yaml
# pubspec.yaml
flutter:
  assets:
    - assets/normal-asset.png
    - path: assets/vanilla/ice-cream.png
      flavors: 
        - vanilla
    - path: assets/strawberry/ice-cream.png
      flavors:
        - strawberry
```

With this pubspec,
* `flutter run --flavor vanilla` will not include `assets/strawberry/ice-cream.png` in the build output.
* `flutter run --flavor strawberry` will not include `assets/vanilla/ice-cream.png`.
* `flutter run` will only include `assets/normal-asset.png`.

## Open questions

* Should this be supported for all platforms, or should this change be limited to ones with documented `--flavor` support (Android, iOS, and (implicitly) MacOS)? This PR currently only enables this feature for officially supported platforms.

## Design thoughts, what this PR does not do, etc.

### This does not provide an automatic mapping/resolution of asset keys/paths to others based on flavor at runtime.

The implementation in this PR represents a simplest approach. Notably, it does not give Flutter the ability to dynamically choose an asset based on flavor using a single asset key. For example, one can't use `Image.asset('config.json')` to dynamically choose between different "flavors" of `config.json` (such as `dev-flavor/config.json` or `prod-flavor/config.json`). However, a user could always implement such a mechanism in their project or in a library by examining the flavor at runtime.

### When multiple entries affect the same file and 1) at least one of these entries have a `flavors` list provided and 2) these lists are not equivalent, we always consider the manifest to be ambiguous and will throw a `ToolExit`. 

<details>
For example, these manifests would all be considered ambiguous:

```yaml
assets:
  - assets/
  - path: assets/vanilla.png
    flavors: 
      - vanilla

assets:
  - path: assets/vanilla/
    flavors: 
      - vanilla
  - path: assets/vanilla/cherry.png
     flavor:
      - cherry

# Thinking towards the future where we might add glob/regex support and more conditions other than flavor:
assets:
  - path: assets/vanilla/**
    flavors:
      - vanilla
  - path: assets/**/ios/**
    platforms: 
       - ios

# Ambiguous in the case of assets like "assets/vanilla/ios/icon.svg" since we 
# don't know if flavor `vanilla` and platform `ios` should be combined using or-logic or and-logic.
```

See [this review comment thread](https://github.com/flutter/flutter/pull/132985#discussion_r1381909942) for the full story on how I arrived at this decision.
</details>

### This does not support Android's multidimensional flavors feature (in an intuitive way)

<details>

Conder this excerpt from a Flutter project's android/app/build.gradle file:

```groovy
android {
    // ...

    flavorDimensions "mode", "api"

    productFlavors {
        free {
            dimension "mode"
            applicationIdSuffix ".free"
        }

        premium {
            dimension "mode"
            applicationIdSuffix ".premium"
        }

        minApi23 {
            dimension "api"
            versionNameSuffix "-minApi23"
        }

        minApi21 {
            dimension "api"
            versionNameSuffix "-minApi21"
        }
    }
}
```

In this setup, the following values are valid `--flavor` are valid `freeMinApi21`, `freeMinApi23`, `premiumMinApi21`, and `premiumMinApi23`. We call these values "flavor combinations". Consider the following from the Android documentation[^1]:

> In addition to the source set directories you can create for each individual product flavor and build variant, you can also create source set directories for each combination of product flavors. For example, you can create and add Java sources to the src/demoMinApi24/java/ directory, and Gradle uses those sources only when building a variant that combines those two product flavors.
> 
> Source sets you create for product flavor combinations have a higher priority than source sets that belong to each individual product flavor. To learn more about source sets and how Gradle merges resources, read the section about how to [create source sets](https://developer.android.com/build/build-variants#sourcesets).

This feature will not behave in this way. If a user utilizes this feature and also Android's multidimensional flavors feature, they will have to list out all flavor combinations that contain the flavor they want to limit an asset to:

```yaml
assets:
  - assets/free/
    flavors:
      - freeMinApi21
      - freeMinApi23
```

This is mostly due to a technical limitation in the hot-reload feature of `flutter run`. During a hot reload, the tool will try to update the asset bundle on the device, but the tool does not know the flavors contained within the flavor combination (that the user passes to `--flavor`). Gradle is the source of truth of what flavors were involved in the build, and `flutter run` currently does not access to that information since it's an implementation detail of the build process. We could bubble up this information, but it would require a nontrivial amount of engineering work, and it's unclear how desired this functionality is. It might not be worth implementing.

</details>

See https://flutter.dev/go/flavor-specific-assets for the (outdated) design document. 

<summary>Pre-launch Checklist</summary>

</details>

[^1]: https://developer.android.com/build/build-variants#flavor-dimensions

dev/bots/pubspec.yaml

@@ -58,6 +58,7 @@ dependencies:
   source_maps: 0.10.12 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   source_span: 1.10.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   stack_trace: 1.11.1 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
+  standard_message_codec: 0.0.1+4 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   stream_channel: 2.1.2 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   string_scanner: 1.2.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   term_glyph: 1.2.1 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
@@ -74,4 +75,4 @@ dependencies:
 dev_dependencies:
   test_api: 0.6.1
 
-# PUBSPEC CHECKSUM: 29d2
+# PUBSPEC CHECKSUM: b875

dev/devicelab/bin/tasks/flavors_test.dart

@@ -2,12 +2,17 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:io' show File;
+import 'dart:typed_data';
+
+import 'package:collection/collection.dart';
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/task_result.dart';
 import 'package:flutter_devicelab/framework/utils.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
 import 'package:path/path.dart' as path;
+import 'package:standard_message_codec/standard_message_codec.dart';
 
 Future<void> main() async {
   deviceOperatingSystem = DeviceOperatingSystem.android;
@@ -15,31 +20,20 @@ Future<void> main() async {
     await createFlavorsTest().call();
     await createIntegrationTestFlavorsTest().call();
 
+    final String projectPath = '${flutterDirectory.path}/dev/integration_tests/flavors';
     final TaskResult installTestsResult = await inDirectory(
-      '${flutterDirectory.path}/dev/integration_tests/flavors',
+      projectPath,
       () async {
-        await flutter(
-          'install',
-          options: <String>['--debug', '--flavor', 'paid'],
-        );
-        await flutter(
-          'install',
-          options: <String>['--debug', '--flavor', 'paid', '--uninstall-only'],
-        );
-
-        final StringBuffer stderr = StringBuffer();
-        await evalFlutter(
-          'install',
-          canFail: true,
-          stderr: stderr,
-          options: <String>['--flavor', 'bogus'],
-        );
-
-        final String stderrString = stderr.toString();
-        final String expectedApkPath = path.join('build', 'app', 'outputs', 'flutter-apk', 'app-bogus-release.apk');
-        if (!stderrString.contains('"$expectedApkPath" does not exist.')) {
-          print(stderrString);
-          return TaskResult.failure('Should not succeed with bogus flavor');
+        final List<TaskResult> testResults = <TaskResult>[
+          await _testInstallDebugPaidFlavor(projectPath),
+          await _testInstallBogusFlavor(),
+        ];
+
+        final TaskResult? firstInstallFailure = testResults
+          .firstWhereOrNull((TaskResult element) => element.failed);
+
+        if (firstInstallFailure != null) {
+          return firstInstallFailure;
         }
 
         return TaskResult.success(null);
@@ -49,3 +43,49 @@ Future<void> main() async {
     return installTestsResult;
   });
 }
+
+// Ensures installation works. Also tests asset bundling while we are at it.
+Future<TaskResult> _testInstallDebugPaidFlavor(String projectDir) async {
+  await evalFlutter(
+    'install',
+    options: <String>['--debug', '--flavor', 'paid'],
+  );
+
+  final Uint8List assetManifestFileData = File(
+    path.join(projectDir, 'build', 'app', 'intermediates', 'assets', 'paidDebug', 'flutter_assets', 'AssetManifest.bin'),
+  ).readAsBytesSync();
+
+  final Map<Object?, Object?> assetManifest = const StandardMessageCodec()
+    .decodeMessage(ByteData.sublistView(assetManifestFileData)) as Map<Object?, Object?>;
+
+  if (assetManifest.containsKey('assets/free/free.txt')) {
+    return TaskResult.failure('Assets declared with a flavor not equal to the '
+      'argued --flavor value should not be bundled.');
+  }
+
+  await flutter(
+    'install',
+    options: <String>['--debug', '--flavor', 'paid', '--uninstall-only'],
+  );
+
+  return TaskResult.success(null);
+}
+
+Future<TaskResult> _testInstallBogusFlavor() async {
+  final StringBuffer stderr = StringBuffer();
+  await evalFlutter(
+    'install',
+    canFail: true,
+    stderr: stderr,
+    options: <String>['--flavor', 'bogus'],
+  );
+
+  final String stderrString = stderr.toString();
+  final String expectedApkPath = path.join('build', 'app', 'outputs', 'flutter-apk', 'app-bogus-release.apk');
+  if (!stderrString.contains('"$expectedApkPath" does not exist.')) {
+    print(stderrString);
+    return TaskResult.failure('Should not succeed with bogus flavor');
+  }
+
+  return TaskResult.success(null);
+}

dev/devicelab/bin/tasks/flavors_test_ios.dart

@@ -2,11 +2,17 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:collection/collection.dart';
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/task_result.dart';
 import 'package:flutter_devicelab/framework/utils.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
+import 'package:path/path.dart' as path;
+import 'package:standard_message_codec/standard_message_codec.dart';
 
 Future<void> main() async {
   deviceOperatingSystem = DeviceOperatingSystem.ios;
@@ -14,29 +20,20 @@ Future<void> main() async {
     await createFlavorsTest().call();
     await createIntegrationTestFlavorsTest().call();
     // test install and uninstall of flavors app
+    final String projectDir = '${flutterDirectory.path}/dev/integration_tests/flavors';
     final TaskResult installTestsResult = await inDirectory(
-      '${flutterDirectory.path}/dev/integration_tests/flavors',
+      projectDir,
       () async {
-        await flutter(
-          'install',
-          options: <String>['--flavor', 'paid'],
-        );
-        await flutter(
-          'install',
-          options: <String>['--flavor', 'paid', '--uninstall-only'],
-        );
-        final StringBuffer stderr = StringBuffer();
-        await evalFlutter(
-          'install',
-          canFail: true,
-          stderr: stderr,
-          options: <String>['--flavor', 'bogus'],
-        );
-
-        final String stderrString = stderr.toString();
-        if (!stderrString.contains('The Xcode project defines schemes: free, paid')) {
-          print(stderrString);
-          return TaskResult.failure('Should not succeed with bogus flavor');
+        final List<TaskResult> testResults = <TaskResult>[
+            await _testInstallDebugPaidFlavor(projectDir),
+            await _testInstallBogusFlavor(),
+        ];
+
+        final TaskResult? firstInstallFailure = testResults
+          .firstWhereOrNull((TaskResult element) => element.failed);
+
+        if (firstInstallFailure != null) {
+          return firstInstallFailure;
         }
 
         return TaskResult.success(null);
@@ -46,3 +43,47 @@ Future<void> main() async {
     return installTestsResult;
   });
 }
+
+Future<TaskResult> _testInstallDebugPaidFlavor(String projectDir) async {
+  await evalFlutter(
+    'install',
+    options: <String>['--flavor', 'paid'],
+  );
+
+  final Uint8List assetManifestFileData = File(
+    path.join(projectDir, 'build', 'ios', 'Release-iphoneos', 'App.framework', 'flutter_assets', 'AssetManifest.bin'),
+  ).readAsBytesSync();
+
+  final Map<Object?, Object?> assetManifest = const StandardMessageCodec()
+    .decodeMessage(ByteData.sublistView(assetManifestFileData)) as Map<Object?, Object?>;
+
+  if (assetManifest.containsKey('assets/free/free.txt')) {
+    return TaskResult.failure('Assets declared with a flavor not equal to the '
+      'argued --flavor value should not be bundled.');
+  }
+
+  await flutter(
+    'install',
+    options: <String>['--flavor', 'paid', '--uninstall-only'],
+  );
+
+  return TaskResult.success(null);
+}
+
+Future<TaskResult> _testInstallBogusFlavor() async {
+  final StringBuffer stderr = StringBuffer();
+  await evalFlutter(
+    'install',
+    canFail: true,
+    stderr: stderr,
+    options: <String>['--flavor', 'bogus'],
+  );
+
+  final String stderrString = stderr.toString();
+  if (!stderrString.contains('The Xcode project defines schemes: free, paid')) {
+    print(stderrString);
+    return TaskResult.failure('Should not succeed with bogus flavor');
+  }
+
+  return TaskResult.success(null);
+}

dev/devicelab/pubspec.yaml

@@ -24,6 +24,7 @@ dependencies:
   web: 0.4.0
   webkit_inspection_protocol: 1.2.1
   xml: 6.5.0
+  standard_message_codec: 0.0.1+4
 
   _discoveryapis_commons: 1.0.6 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   async: 2.11.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
@@ -72,4 +73,4 @@ dev_dependencies:
   watcher: 1.1.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   web_socket_channel: 2.4.0 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
 
-# PUBSPEC CHECKSUM: 6040
+# PUBSPEC CHECKSUM: 70e2

dev/integration_tests/flavors/assets/common/common.txt

+this is a test asset not meant for any specific flavor
\ No newline at end of file

dev/integration_tests/flavors/assets/free/free.txt

+this is a test asset for --flavor free
\ No newline at end of file

dev/integration_tests/flavors/assets/paid/paid.txt

+this is a test asset for --flavor paid
\ No newline at end of file

dev/integration_tests/flavors/assets/premium/premium.txt

+premium
\ No newline at end of file

dev/integration_tests/flavors/pubspec.yaml

@@ -75,5 +75,13 @@ dev_dependencies:
 
 flutter:
   uses-material-design: true
+  assets:
+    - assets/common/common.txt
+    - path: assets/paid/
+      flavors:
+        - paid
+    - path: assets/free/
+      flavors:
+        - free
 
 # PUBSPEC CHECKSUM: 6bd3

packages/flutter_tools/bin/xcode_backend.dart

@@ -401,6 +401,7 @@ class Context {
       '-dTargetPlatform=ios',
       '-dTargetFile=$targetPath',
       '-dBuildMode=$buildMode',
+      if (environment['FLAVOR'] != null) '-dFlavor=${environment['FLAVOR']}',
       '-dIosArchs=${environment['ARCHS'] ?? ''}',
       '-dSdkRoot=${environment['SDKROOT'] ?? ''}',
       '-dSplitDebugInfo=${environment['SPLIT_DEBUG_INFO'] ?? ''}',

packages/flutter_tools/gradle/src/main/groovy/flutter.groovy

@@ -1042,6 +1042,7 @@ class FlutterPlugin implements Plugin<Project> {
             boolean isAndroidLibraryValue = isBuildingAar || isUsedAsSubproject
 
             String variantBuildMode = buildModeFor(variant.buildType)
+            String flavorValue = variant.getFlavorName()
             String taskName = toCamelCase(["compile", FLUTTER_BUILD_PREFIX, variant.name])
             // Be careful when configuring task below, Groovy has bizarre
             // scoping rules: writing `verbose isVerbose()` means calling
@@ -1079,6 +1080,7 @@ class FlutterPlugin implements Plugin<Project> {
                 deferredComponents deferredComponentsValue
                 validateDeferredComponents validateDeferredComponentsValue
                 isAndroidLibrary isAndroidLibraryValue
+                flavor flavorValue
                 doLast {
                     project.exec {
                         if (Os.isFamily(Os.FAMILY_WINDOWS)) {
@@ -1336,6 +1338,8 @@ abstract class BaseFlutterTask extends DefaultTask {
     Boolean validateDeferredComponents
     @Optional @Input
     Boolean isAndroidLibrary
+    @Optional @Input
+    String flavor
 
     @OutputFiles
     FileCollection getDependenciesFiles() {
@@ -1416,6 +1420,9 @@ abstract class BaseFlutterTask extends DefaultTask {
             if (codeSizeDirectory != null) {
                 args "-dCodeSizeDirectory=${codeSizeDirectory}"
             }
+            if (flavor != null) {
+                args "-dFlavor=${flavor}"
+            }
             if (extraGenSnapshotOptions != null) {
                 args "--ExtraGenSnapshotOptions=${extraGenSnapshotOptions}"
             }

packages/flutter_tools/lib/src/base/deferred_component.dart

@@ -5,6 +5,7 @@
 import '../base/file_system.dart';
 import '../base/logger.dart';
 import '../convert.dart';
+import '../flutter_manifest.dart';
 
 /// Represents a configured deferred component as defined in
 /// the app's pubspec.yaml.
@@ -12,7 +13,7 @@ class DeferredComponent {
   DeferredComponent({
     required this.name,
     this.libraries = const <String>[],
-    this.assets = const <Uri>[],
+    this.assets = const <AssetsEntry>[],
   }) : _assigned = false;
 
   /// The name of the deferred component. There should be a matching
@@ -28,8 +29,8 @@ class DeferredComponent {
   /// libraries that are not listed here.
   final List<String> libraries;
 
-  /// Assets that are part of this component as a Uri relative to the project directory.
-  final List<Uri> assets;
+  /// Assets that are part of this component.
+  final List<AssetsEntry> assets;
 
   /// The minimal set of [LoadingUnit]s needed that contain all of the dart libraries in
   /// [libraries].
@@ -95,8 +96,11 @@ class DeferredComponent {
       }
     }
     out.write('\n  Assets:');
-    for (final Uri asset in assets) {
-      out.write('\n    - ${asset.path}');
+    for (final AssetsEntry asset in assets) {
+      out.write('\n    - ${asset.uri.path}');
+      if (asset.flavors.isNotEmpty) {
+        out.write(' (flavors: ${asset.flavors.join(', ')})');
+      }
     }
     return out.toString();
   }

packages/flutter_tools/lib/src/build_info.dart

@@ -286,6 +286,8 @@ class BuildInfo {
       'PACKAGE_CONFIG': packagesPath,
       if (codeSizeDirectory != null)
         'CODE_SIZE_DIRECTORY': codeSizeDirectory!,
+      if (flavor != null)
+        'FLAVOR': flavor!,
     };
   }
 
@@ -989,6 +991,9 @@ const String kBundleSkSLPath = 'BundleSkSLPath';
 /// The define to pass build name
 const String kBuildName = 'BuildName';
 
+/// The app flavor to build.
+const String kFlavor = 'Flavor';
+
 /// The define to pass build number
 const String kBuildNumber = 'BuildNumber';
 

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

@@ -46,6 +46,7 @@ abstract class AndroidAssetBundle extends Target {
     if (buildModeEnvironment == null) {
       throw MissingDefineException(kBuildMode, name);
     }
+
     final BuildMode buildMode = BuildMode.fromCliName(buildModeEnvironment);
     final Directory outputDirectory = environment.outputDir
       .childDirectory('flutter_assets')
@@ -68,6 +69,7 @@ abstract class AndroidAssetBundle extends Target {
       targetPlatform: TargetPlatform.android,
       buildMode: buildMode,
       shaderTarget: ShaderTarget.impellerAndroid,
+      flavor: environment.defines[kFlavor],
     );
     environment.depFileService.writeToFile(
       assetDepfile,

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

@@ -34,6 +34,7 @@ Future<Depfile> copyAssets(
   BuildMode? buildMode,
   required ShaderTarget shaderTarget,
   List<File> additionalInputs = const <File>[],
+  String? flavor,
 }) async {
   // Check for an SkSL bundle.
   final String? shaderBundlePath = environment.defines[kBundleSkSLPath] ?? environment.inputs[kBundleSkSLPath];
@@ -58,6 +59,7 @@ Future<Depfile> copyAssets(
     packagesPath: environment.projectDir.childFile('.packages').path,
     deferredComponentsEnabled: environment.defines[kDeferredComponents] == 'true',
     targetPlatform: targetPlatform,
+    flavor: flavor,
   );
   if (resultCode != 0) {
     throw Exception('Failed to bundle asset files.');
@@ -323,6 +325,7 @@ class CopyAssets extends Target {
       output,
       targetPlatform: TargetPlatform.android,
       shaderTarget: ShaderTarget.sksl,
+      flavor: environment.defines[kFlavor],
     );
     environment.depFileService.writeToFile(
       depfile,

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

@@ -58,6 +58,8 @@ class CopyFlutterBundle extends Target {
     if (buildModeEnvironment == null) {
       throw MissingDefineException(kBuildMode, 'copy_flutter_bundle');
     }
+    final String? flavor = environment.defines[kFlavor];
+
     final BuildMode buildMode = BuildMode.fromCliName(buildModeEnvironment);
     environment.outputDir.createSync(recursive: true);
 
@@ -78,6 +80,7 @@ class CopyFlutterBundle extends Target {
       targetPlatform: TargetPlatform.android,
       buildMode: buildMode,
       shaderTarget: ShaderTarget.sksl,
+      flavor: flavor,
     );
     environment.depFileService.writeToFile(
       assetDepfile,

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

@@ -533,6 +533,7 @@ abstract class IosAssetBundle extends Target {
         flutterProject.ios.infoPlist,
         flutterProject.ios.appFrameworkInfoPlist,
       ],
+      flavor: environment.defines[kFlavor],
     );
     environment.depFileService.writeToFile(
       assetDepfile,

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

@@ -393,6 +393,7 @@ abstract class MacOSBundleFlutterAssets extends Target {
     if (buildModeEnvironment == null) {
       throw MissingDefineException(kBuildMode, 'compile_macos_framework');
     }
+
     final BuildMode buildMode = BuildMode.fromCliName(buildModeEnvironment);
     final Directory frameworkRootDirectory = environment
         .outputDir
@@ -439,6 +440,7 @@ abstract class MacOSBundleFlutterAssets extends Target {
       assetDirectory,
       targetPlatform: TargetPlatform.darwin,
       shaderTarget: ShaderTarget.sksl,
+      flavor: environment.defines[kFlavor],
     );
     environment.depFileService.writeToFile(
       assetDepfile,

packages/flutter_tools/lib/src/bundle_builder.dart

@@ -114,6 +114,7 @@ Future<AssetBundle?> buildAssets({
   String? assetDirPath,
   String? packagesPath,
   TargetPlatform? targetPlatform,
+  String? flavor,
 }) async {
   assetDirPath ??= getAssetBuildDirectory();
   packagesPath ??= globals.fs.path.absolute('.packages');
@@ -124,6 +125,7 @@ Future<AssetBundle?> buildAssets({
     manifestPath: manifestPath,
     packagesPath: packagesPath,
     targetPlatform: targetPlatform,
+    flavor: flavor,
   );
   if (result != 0) {
     return null;

packages/flutter_tools/lib/src/flutter_manifest.dart

@@ -231,29 +231,12 @@ class FlutterManifest {
         _logger.printError('Expected deferred component manifest to be a map.');
         continue;
       }
-      List<Uri> assetsUri = <Uri>[];
-      final List<Object?>? assets = component['assets'] as List<Object?>?;
-      if (assets == null) {
-        assetsUri = const <Uri>[];
-      } else {
-        for (final Object? asset in assets) {
-          if (asset is! String || asset == '') {
-            _logger.printError('Deferred component asset manifest contains a null or empty uri.');
-            continue;
-          }
-          try {
-            assetsUri.add(Uri.parse(asset));
-          } on FormatException {
-            _logger.printError('Asset manifest contains invalid uri: $asset.');
-          }
-        }
-      }
       components.add(
         DeferredComponent(
           name: component['name'] as String,
           libraries: component['libraries'] == null ?
               <String>[] : (component['libraries'] as List<dynamic>).cast<String>(),
-          assets: assetsUri,
+          assets: _computeAssets(component['assets']),
         )
       );
     }
@@ -311,26 +294,7 @@ class FlutterManifest {
         : fontList.map<Map<String, Object?>?>(castStringKeyedMap).whereType<Map<String, Object?>>().toList();
   }
 
-  late final List<Uri> assets = _computeAssets();
-  List<Uri> _computeAssets() {
-    final List<Object?>? assets = _flutterDescriptor['assets'] as List<Object?>?;
-    if (assets == null) {
-      return const <Uri>[];
-    }
-    final List<Uri> results = <Uri>[];
-    for (final Object? asset in assets) {
-      if (asset is! String || asset == '') {
-        _logger.printError('Asset manifest contains a null or empty uri.');
-        continue;
-      }
-      try {
-        results.add(Uri(pathSegments: asset.split('/')));
-      } on FormatException {
-        _logger.printError('Asset manifest contains invalid uri: $asset.');
-      }
-    }
-    return results;
-  }
+  late final List<AssetsEntry> assets = _computeAssets(_flutterDescriptor['assets']);
 
   late final List<Font> fonts = _extractFonts();
 
@@ -521,15 +485,7 @@ void _validateFlutter(YamlMap? yaml, List<String> errors) {
           errors.add('Expected "$yamlKey" to be a bool, but got $yamlValue (${yamlValue.runtimeType}).');
         }
       case 'assets':
-        if (yamlValue is! YamlList) {
-          errors.add('Expected "$yamlKey" to be a list, but got $yamlValue (${yamlValue.runtimeType}).');
-        } else if (yamlValue.isEmpty) {
-          break;
-        } else if (yamlValue[0] is! String) {
-          errors.add(
-            'Expected "$yamlKey" to be a list of strings, but the first element is $yamlValue (${yamlValue.runtimeType}).',
-          );
-        }
+        errors.addAll(_validateAssets(yamlValue));
       case 'shaders':
         if (yamlValue is! YamlList) {
           errors.add('Expected "$yamlKey" to be a list, but got $yamlValue (${yamlValue.runtimeType}).');
@@ -640,17 +596,52 @@ void _validateDeferredComponents(MapEntry<Object?, Object?> kvp, List<String> er
         }
       }
       if (valueMap.containsKey('assets')) {
-        final Object? assets = valueMap['assets'];
-        if (assets is! YamlList) {
-          errors.add('Expected "assets" to be a list, but got $assets (${assets.runtimeType}).');
-        } else {
-          _validateListType<String>(assets, errors, '"assets" key in the $i element of "${kvp.key}"', 'file paths');
-        }
+        errors.addAll(_validateAssets(valueMap['assets']));
       }
     }
   }
 }
 
+List<String> _validateAssets(Object? yaml) {
+  final (_, List<String> errors) = _computeAssetsSafe(yaml);
+  return errors;
+}
+
+// TODO(andrewkolos): We end up parsing the assets section twice, once during
+// validation and once when the assets getter is called. We should consider
+// refactoring this class to parse and store everything in the constructor.
+// https://github.com/flutter/flutter/issues/139183
+(List<AssetsEntry>, List<String> errors) _computeAssetsSafe(Object? yaml) {
+  if (yaml == null) {
+    return (const <AssetsEntry>[], const <String>[]);
+  }
+  if (yaml is! YamlList) {
+    final String error = 'Expected "assets" to be a list, but got $yaml (${yaml.runtimeType}).';
+    return (const <AssetsEntry>[], <String>[error]);
+  }
+  final List<AssetsEntry> results = <AssetsEntry>[];
+  final List<String> errors = <String>[];
+  for (final Object? rawAssetEntry in yaml) {
+    final (AssetsEntry? parsed, String? error) = AssetsEntry.parseFromYamlSafe(rawAssetEntry);
+    if (parsed != null) {
+      results.add(parsed);
+    }
+    if (error != null) {
+      errors.add(error);
+    }
+  }
+  return (results, errors);
+}
+
+List<AssetsEntry> _computeAssets(Object? assetsSection) {
+  final (List<AssetsEntry> result, List<String> errors) = _computeAssetsSafe(assetsSection);
+  if (errors.isNotEmpty) {
+    throw Exception('Uncaught error(s) in assets section: '
+      '${errors.join('\n')}');
+  }
+  return result;
+}
+
 void _validateFonts(YamlList fonts, List<String> errors) {
   const Set<int> fontWeights = <int>{
     100, 200, 300, 400, 500, 600, 700, 800, 900,
@@ -703,3 +694,103 @@ void _validateFonts(YamlList fonts, List<String> errors) {
     }
   }
 }
+
+/// Represents an entry under the `assets` section of a pubspec.
+@immutable
+class AssetsEntry {
+  const AssetsEntry({
+    required this.uri,
+    this.flavors = const <String>[],
+  });
+
+  final Uri uri;
+  final List<String> flavors;
+
+  static const String _pathKey = 'path';
+  static const String _flavorKey = 'flavors';
+
+  static AssetsEntry? parseFromYaml(Object? yaml) {
+    final (AssetsEntry? value, String? error) = parseFromYamlSafe(yaml);
+    if (error != null) {
+      throw Exception('Unexpected error when parsing assets entry');
+    }
+    return value!;
+  }
+
+  static (AssetsEntry? assetsEntry, String? error) parseFromYamlSafe(Object? yaml) {
+
+    (Uri?, String?) tryParseUri(String uri) {
+      try {
+        return (Uri(pathSegments: uri.split('/')), null);
+      } on FormatException {
+        return (null, 'Asset manifest contains invalid uri: $uri.');
+      }
+    }
+
+    if (yaml == null || yaml == '') {
+      return (null, 'Asset manifest contains a null or empty uri.');
+    }
+
+    if (yaml is String) {
+      final (Uri? uri, String? error) = tryParseUri(yaml);
+      return uri == null ? (null, error) : (AssetsEntry(uri: uri), null);
+    }
+
+    if (yaml is Map) {
+      if (yaml.keys.isEmpty) {
+        return (null, null);
+      }
+
+      final Object? path = yaml[_pathKey];
+      final Object? flavors = yaml[_flavorKey];
+
+      if (path == null || path is! String) {
+        return (null, 'Asset manifest entry is malformed. '
+          'Expected asset entry to be either a string or a map '
+          'containing a "$_pathKey" entry. Got ${path.runtimeType} instead.');
+      }
+
+      final Uri uri = Uri(pathSegments: path.split('/'));
+
+      if (flavors == null) {
+        return (AssetsEntry(uri: uri), null);
+      }
+
+      if (flavors is! YamlList) {
+        return(null, 'Asset manifest entry is malformed. '
+          'Expected "$_flavorKey" entry to be a list of strings. '
+          'Got ${flavors.runtimeType} instead.');
+      }
+
+      final List<String> flavorsListErrors = <String>[];
+      _validateListType<String>(flavors, flavorsListErrors, 'flavors list of entry "$path"', 'String');
+      if (flavorsListErrors.isNotEmpty) {
+        return (null, 'Asset manifest entry is malformed. '
+          'Expected "$_flavorKey" entry to be a list of strings.\n'
+          '${flavorsListErrors.join('\n')}');
+      }
+
+      final AssetsEntry entry = AssetsEntry(
+        uri: Uri(pathSegments: path.split('/')),
+        flavors: List<String>.from(flavors),
+      );
+
+      return (entry, null);
+    }
+
+    return (null, 'Assets entry had unexpected shape. '
+      'Expected a string or an object. Got ${yaml.runtimeType} instead.');
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is! AssetsEntry) {
+      return false;
+    }
+
+    return uri == other.uri && flavors == other.flavors;
+  }
+
+  @override
+  int get hashCode => Object.hash(uri.hashCode, flavors.hashCode);
+}

packages/flutter_tools/lib/src/run_hot.dart

@@ -141,6 +141,8 @@ class HotRunner extends ResidentRunner {
 
   NativeAssetsBuildRunner? _buildRunner;
 
+  String? flavor;
+
   Future<void> _calculateTargetPlatform() async {
     if (_targetPlatform != null) {
       return;
@@ -494,7 +496,10 @@ class HotRunner extends ResidentRunner {
     final bool rebuildBundle = assetBundle.needsBuild();
     if (rebuildBundle) {
       globals.printTrace('Updating assets');
-      final int result = await assetBundle.build(packagesPath: '.packages');
+      final int result = await assetBundle.build(
+        packagesPath: '.packages',
+        flavor: debuggingOptions.buildInfo.flavor,
+      );
       if (result != 0) {
         return UpdateFSReport();
       }

packages/flutter_tools/test/commands.shard/hermetic/run_test.dart

@@ -1567,6 +1567,7 @@ class CapturingAppDomain extends AppDomain {
     bool machine = true,
     String? userIdentifier,
     bool enableDevTools = true,
+    String? flavor,
   }) async {
     this.multidexEnabled = multidexEnabled;
     this.userIdentifier = userIdentifier;

packages/flutter_tools/test/general.shard/asset_bundle_test.dart

@@ -9,11 +9,15 @@ import 'package:file/memory.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/asset.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/platform.dart';
+import 'package:flutter_tools/src/base/user_messages.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/bundle_builder.dart';
+import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/devfs.dart';
 import 'package:flutter_tools/src/globals.dart' as globals;
+import 'package:flutter_tools/src/project.dart';
 import 'package:standard_message_codec/standard_message_codec.dart';
 
 import '../src/common.dart';
@@ -23,7 +27,9 @@ const String shaderLibDir = '/./shader_lib';
 
 void main() {
   group('AssetBundle.build', () {
+    late Logger logger;
     late FileSystem testFileSystem;
+    late Platform platform;
 
     setUp(() async {
       testFileSystem = MemoryFileSystem(
@@ -32,6 +38,8 @@ void main() {
           : FileSystemStyle.posix,
       );
       testFileSystem.currentDirectory = testFileSystem.systemTempDirectory.createTempSync('flutter_asset_bundle_test.');
+      logger = BufferLogger.test();
+      platform = FakePlatform(operatingSystem: globals.platform.operatingSystem);
     });
 
     testUsingContext('nonempty', () async {
@@ -323,6 +331,185 @@ flutter:
       FileSystem: () => testFileSystem,
       ProcessManager: () => FakeProcessManager.any(),
     });
+
+    group('flavors feature', () {
+      Future<ManifestAssetBundle> buildBundleWithFlavor(String? flavor) async {
+        final ManifestAssetBundle bundle = ManifestAssetBundle(
+          logger: logger,
+          fileSystem: testFileSystem,
+          platform: platform,
+          splitDeferredAssets: true,
+        );
+
+        await bundle.build(
+          packagesPath: '.packages',
+          flutterProject: FlutterProject.fromDirectoryTest(testFileSystem.currentDirectory),
+          flavor: flavor,
+        );
+        return bundle;
+      }
+
+      late final String? previousCacheFlutterRootValue;
+
+      setUpAll(() {
+        previousCacheFlutterRootValue = Cache.flutterRoot;
+        Cache.flutterRoot = Cache.defaultFlutterRoot(platform: platform, fileSystem: testFileSystem, userMessages: UserMessages());
+      });
+
+      tearDownAll(() => Cache.flutterRoot = previousCacheFlutterRootValue);
+
+      testWithoutContext('correctly bundles assets given a simple asset manifest with flavors', () async {
+        testFileSystem.file('.packages').createSync();
+        testFileSystem.file(testFileSystem.path.join('assets', 'common', 'image.png')).createSync(recursive: true);
+        testFileSystem.file(testFileSystem.path.join('assets', 'vanilla', 'ice-cream.png')).createSync(recursive: true);
+        testFileSystem.file(testFileSystem.path.join('assets', 'strawberry', 'ice-cream.png')).createSync(recursive: true);
+        testFileSystem.file(testFileSystem.path.join('assets', 'orange', 'ice-cream.png')).createSync(recursive: true);
+        testFileSystem.file('pubspec.yaml')
+          ..createSync()
+          ..writeAsStringSync(r'''
+name: example
+flutter:
+  assets:
+    - assets/common/
+    - path: assets/vanilla/
+      flavors:
+        - vanilla
+    - path: assets/strawberry/
+      flavors:
+        - strawberry
+    - path: assets/orange/ice-cream.png
+      flavors:
+        - orange
+  ''');
+
+        ManifestAssetBundle bundle;
+        bundle = await buildBundleWithFlavor(null);
+        expect(bundle.entries.keys, contains('assets/common/image.png'));
+        expect(bundle.entries.keys, isNot(contains('assets/vanilla/ice-cream.png')));
+        expect(bundle.entries.keys, isNot(contains('assets/strawberry/ice-cream.png')));
+        expect(bundle.entries.keys, isNot(contains('assets/orange/ice-cream.png')));
+
+        bundle = await buildBundleWithFlavor('strawberry');
+        expect(bundle.entries.keys, contains('assets/common/image.png'));
+        expect(bundle.entries.keys, isNot(contains('assets/vanilla/ice-cream.png')));
+        expect(bundle.entries.keys, contains('assets/strawberry/ice-cream.png'));
+        expect(bundle.entries.keys, isNot(contains('assets/orange/ice-cream.png')));
+
+        bundle = await buildBundleWithFlavor('orange');
+        expect(bundle.entries.keys, contains('assets/common/image.png'));
+        expect(bundle.entries.keys, isNot(contains('assets/vanilla/ice-cream.png')));
+        expect(bundle.entries.keys, isNot(contains('assets/strawberry/ice-cream.png')));
+        expect(bundle.entries.keys, contains('assets/orange/ice-cream.png'));
+      });
+
+      testWithoutContext('throws a tool exit when a non-flavored folder contains a flavored asset', () async {
+        testFileSystem.file('.packages').createSync();
+        testFileSystem.file(testFileSystem.path.join('assets', 'unflavored.png')).createSync(recursive: true);
+        testFileSystem.file(testFileSystem.path.join('assets', 'vanillaOrange.png')).createSync(recursive: true);
+
+        testFileSystem.file('pubspec.yaml')
+          ..createSync()
+          ..writeAsStringSync(r'''
+  name: example
+  flutter:
+    assets:
+      - assets/
+      - path: assets/vanillaOrange.png
+        flavors:
+          - vanilla
+          - orange
+  ''');
+
+        expect(
+          buildBundleWithFlavor(null),
+          throwsToolExit(message: 'Multiple assets entries include the file '
+            '"assets/vanillaOrange.png", but they specify different lists of flavors.\n'
+            'An entry with the path "assets/" does not specify any flavors.\n'
+            'An entry with the path "assets/vanillaOrange.png" specifies the flavor(s): "vanilla", "orange".\n\n'
+            'Consider organizing assets with different flavors into different directories.'),
+        );
+      });
+
+      testWithoutContext('throws a tool exit when a flavored folder contains a flavorless asset', () async {
+        testFileSystem.file('.packages').createSync();
+        testFileSystem.file(testFileSystem.path.join('vanilla', 'vanilla.png')).createSync(recursive: true);
+        testFileSystem.file(testFileSystem.path.join('vanilla', 'flavorless.png')).createSync(recursive: true);
+
+        testFileSystem.file('pubspec.yaml')
+          ..createSync()
+          ..writeAsStringSync(r'''
+  name: example
+  flutter:
+    assets:
+      - path: vanilla/
+        flavors:
+          - vanilla
+      - vanilla/flavorless.png
+  ''');
+        expect(
+          buildBundleWithFlavor(null),
+          throwsToolExit(message: 'Multiple assets entries include the file '
+            '"vanilla/flavorless.png", but they specify different lists of flavors.\n'
+            'An entry with the path "vanilla/" specifies the flavor(s): "vanilla".\n'
+            'An entry with the path "vanilla/flavorless.png" does not specify any flavors.\n\n'
+            'Consider organizing assets with different flavors into different directories.'),
+        );
+      });
+
+      testWithoutContext('tool exits when two file-explicit entries give the same asset different flavors', () {
+        testFileSystem.file('.packages').createSync();
+        testFileSystem.file('orange.png').createSync(recursive: true);
+        testFileSystem.file('pubspec.yaml')
+          ..createSync()
+          ..writeAsStringSync(r'''
+  name: example
+  flutter:
+    assets:
+      - path: orange.png
+        flavors:
+          - orange
+      - path: orange.png
+        flavors:
+          - mango
+  ''');
+
+        expect(
+          buildBundleWithFlavor(null),
+          throwsToolExit(message: 'Multiple assets entries include the file '
+            '"orange.png", but they specify different lists of flavors.\n'
+            'An entry with the path "orange.png" specifies the flavor(s): "orange".\n'
+            'An entry with the path "orange.png" specifies the flavor(s): "mango".'),
+        );
+    });
+
+      testWithoutContext('throws ToolExit when flavor from file-level declaration has different flavor from containing folder flavor declaration', () async {
+        testFileSystem.file('.packages').createSync();
+        testFileSystem.file(testFileSystem.path.join('vanilla', 'actually-strawberry.png')).createSync(recursive: true);
+        testFileSystem.file(testFileSystem.path.join('vanilla', 'vanilla.png')).createSync(recursive: true);
+
+        testFileSystem.file('pubspec.yaml')
+          ..createSync()
+          ..writeAsStringSync(r'''
+  name: example
+  flutter:
+    assets:
+      - path: vanilla/
+        flavors:
+          - vanilla
+      - path: vanilla/actually-strawberry.png
+        flavors:
+          - strawberry
+  ''');
+        expect(
+          buildBundleWithFlavor(null),
+          throwsToolExit(message: 'Multiple assets entries include the file '
+            '"vanilla/actually-strawberry.png", but they specify different lists of flavors.\n'
+            'An entry with the path "vanilla/" specifies the flavor(s): "vanilla".\n'
+            'An entry with the path "vanilla/actually-strawberry.png" '
+            'specifies the flavor(s): "strawberry".'),
+        );
+      });
+    });
   });
 
   group('AssetBundle.build (web builds)', () {

packages/flutter_tools/test/general.shard/base/deferred_component_test.dart

@@ -6,6 +6,7 @@ import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/deferred_component.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/flutter_manifest.dart';
 
 import '../../src/common.dart';
 
@@ -15,18 +16,27 @@ void main() {
       final DeferredComponent component = DeferredComponent(
         name: 'bestcomponent',
         libraries: <String>['lib1', 'lib2'],
-        assets: <Uri>[Uri.file('asset1'), Uri.file('asset2')],
+        assets: <AssetsEntry>[
+          AssetsEntry(uri: Uri.file('asset1')),
+          AssetsEntry(uri: Uri.file('asset2')),
+        ],
       );
       expect(component.name, 'bestcomponent');
       expect(component.libraries, <String>['lib1', 'lib2']);
-      expect(component.assets, <Uri>[Uri.file('asset1'), Uri.file('asset2')]);
+      expect(component.assets, <AssetsEntry>[
+          AssetsEntry(uri: Uri.file('asset1')),
+          AssetsEntry(uri: Uri.file('asset2')),
+      ]);
     });
 
     testWithoutContext('assignLoadingUnits selects the needed loading units and sets assigned', () {
       final DeferredComponent component = DeferredComponent(
         name: 'bestcomponent',
         libraries: <String>['lib1', 'lib2'],
-        assets: <Uri>[Uri.file('asset1'), Uri.file('asset2')],
+        assets: <AssetsEntry>[
+          AssetsEntry(uri: Uri.file('asset1')),
+          AssetsEntry(uri: Uri.file('asset2')),
+        ],
       );
       expect(component.libraries, <String>['lib1', 'lib2']);
       expect(component.assigned, false);
@@ -94,7 +104,10 @@ void main() {
       final DeferredComponent component = DeferredComponent(
         name: 'bestcomponent',
         libraries: <String>['lib1', 'lib2'],
-        assets: <Uri>[Uri.file('asset1'), Uri.file('asset2')],
+        assets: <AssetsEntry>[
+          AssetsEntry(uri: Uri.file('asset1')),
+          AssetsEntry(uri: Uri.file('asset2')),
+        ],
       );
       expect(component.toString(), '\nDeferredComponent: bestcomponent\n  Libraries:\n    - lib1\n    - lib2\n  Assets:\n    - asset1\n    - asset2');
     });
@@ -103,7 +116,10 @@ void main() {
       final DeferredComponent component = DeferredComponent(
         name: 'bestcomponent',
         libraries: <String>['lib1', 'lib2'],
-        assets: <Uri>[Uri.file('asset1'), Uri.file('asset2')],
+        assets: <AssetsEntry>[
+          AssetsEntry(uri: Uri.file('asset1')),
+          AssetsEntry(uri: Uri.file('asset2')),
+        ],
       );
       component.assignLoadingUnits(<LoadingUnit>[LoadingUnit(id: 2, libraries: <String>['lib1'])]);
       expect(component.toString(), '\nDeferredComponent: bestcomponent\n  Libraries:\n    - lib1\n    - lib2\n  LoadingUnits:\n    - 2\n  Assets:\n    - asset1\n    - asset2');

packages/flutter_tools/test/general.shard/build_info_test.dart

@@ -207,7 +207,7 @@ void main() {
   });
 
   testWithoutContext('toEnvironmentConfig encoding of standard values', () {
-    const BuildInfo buildInfo = BuildInfo(BuildMode.debug, '',
+    const BuildInfo buildInfo = BuildInfo(BuildMode.debug, 'strawberry',
       treeShakeIcons: true,
       trackWidgetCreation: true,
       dartDefines: <String>['foo=2', 'bar=2'],
@@ -220,7 +220,7 @@ void main() {
       packagesPath: 'foo/.dart_tool/package_config.json',
       codeSizeDirectory: 'foo/code-size',
       // These values are ignored by toEnvironmentConfig
-      androidProjectArgs: <String>['foo=bar', 'fizz=bazz']
+      androidProjectArgs: <String>['foo=bar', 'fizz=bazz'],
     );
 
     expect(buildInfo.toEnvironmentConfig(), <String, String>{
@@ -235,6 +235,7 @@ void main() {
       'BUNDLE_SKSL_PATH': 'foo/bar/baz.sksl.json',
       'PACKAGE_CONFIG': 'foo/.dart_tool/package_config.json',
       'CODE_SIZE_DIRECTORY': 'foo/code-size',
+      'FLAVOR': 'strawberry',
     });
   });
 

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

@@ -32,6 +32,7 @@ void main() {
       fileSystem: fileSystem,
       logger: BufferLogger.test(),
       platform: FakePlatform(),
+      defines: <String, String>{},
     );
     fileSystem.file(environment.buildDir.childFile('app.dill')).createSync(recursive: true);
     fileSystem.file('packages/flutter_tools/lib/src/build_system/targets/assets.dart')
@@ -93,6 +94,69 @@ flutter:
     ProcessManager: () => FakeProcessManager.any(),
   });
 
+  group("Only copies assets with a flavor if the assets' flavor matches the flavor in the environment", () {
+    testUsingContext('When the environment does not have a flavor defined', () async {
+      fileSystem.file('pubspec.yaml')
+        ..createSync()
+        ..writeAsStringSync('''
+  name: example
+  flutter:
+    assets:
+      - assets/common/
+      - path: assets/vanilla/
+        flavors:
+          - vanilla
+      - path: assets/strawberry/
+        flavors:
+          - strawberry
+  ''');
+
+      fileSystem.file('assets/common/image.png').createSync(recursive: true);
+      fileSystem.file('assets/vanilla/ice-cream.png').createSync(recursive: true);
+      fileSystem.file('assets/strawberry/ice-cream.png').createSync(recursive: true);
+
+      await const CopyAssets().build(environment);
+
+      expect(fileSystem.file('${environment.buildDir.path}/flutter_assets/assets/common/image.png'), exists);
+      expect(fileSystem.file('${environment.buildDir.path}/flutter_assets/assets/vanilla/ice-cream.png'), isNot(exists));
+      expect(fileSystem.file('${environment.buildDir.path}/flutter_assets/assets/strawberry/ice-cream.png'), isNot(exists));
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fileSystem,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+
+    testUsingContext('When the environment has a flavor defined', () async {
+      environment.defines[kFlavor] = 'strawberry';
+      fileSystem.file('pubspec.yaml')
+        ..createSync()
+        ..writeAsStringSync('''
+  name: example
+  flutter:
+    assets:
+      - assets/common/
+      - path: assets/vanilla/
+        flavors:
+          - vanilla
+      - path: assets/strawberry/
+        flavors:
+          - strawberry
+  ''');
+
+      fileSystem.file('assets/common/image.png').createSync(recursive: true);
+      fileSystem.file('assets/vanilla/ice-cream.png').createSync(recursive: true);
+      fileSystem.file('assets/strawberry/ice-cream.png').createSync(recursive: true);
+
+      await const CopyAssets().build(environment);
+
+      expect(fileSystem.file('${environment.buildDir.path}/flutter_assets/assets/common/image.png'), exists);
+      expect(fileSystem.file('${environment.buildDir.path}/flutter_assets/assets/vanilla/ice-cream.png'), isNot(exists));
+      expect(fileSystem.file('${environment.buildDir.path}/flutter_assets/assets/strawberry/ice-cream.png'), exists);
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fileSystem,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+  });
+
   testUsingContext('Throws exception if pubspec contains missing files', () async {
     fileSystem.file('pubspec.yaml')
       ..createSync()

packages/flutter_tools/test/general.shard/devfs_test.dart

@@ -733,7 +733,14 @@ class FakeBundle extends AssetBundle {
   List<File> get additionalDependencies => <File>[];
 
   @override
-  Future<int> build({String manifestPath = defaultManifestPath, String? assetDirPath, String? packagesPath, bool deferredComponentsEnabled = false, TargetPlatform? targetPlatform}) async {
+  Future<int> build({
+    String manifestPath = defaultManifestPath,
+    String? assetDirPath,
+    String? packagesPath,
+    bool deferredComponentsEnabled = false,
+    TargetPlatform? targetPlatform,
+    String? flavor,
+  }) async {
     return 0;
   }
 

packages/flutter_tools/test/general.shard/xcode_backend_test.dart

@@ -160,6 +160,7 @@ void main() {
           'FRONTEND_SERVER_STARTER_PATH': frontendServerStarterPath,
           'INFOPLIST_PATH': 'Info.plist',
           'SDKROOT': sdkRoot,
+          'FLAVOR': 'strawberry',
           'SPLIT_DEBUG_INFO': splitDebugInfo,
           'TRACK_WIDGET_CREATION': trackWidgetCreation,
           'TREE_SHAKE_ICONS': treeShake,
@@ -174,6 +175,7 @@ void main() {
               '-dTargetPlatform=ios',
               '-dTargetFile=lib/main.dart',
               '-dBuildMode=${buildMode.toLowerCase()}',
+              '-dFlavor=strawberry',
               '-dIosArchs=$archs',
               '-dSdkRoot=$sdkRoot',
               '-dSplitDebugInfo=$splitDebugInfo',