Flutter Web startup and compilation become significantly slower with deep generic mixin inheritance in large projects #190436

Steps to reproduce

Create a large Flutter Web ERP project.
Use approximately 800 feature controllers.
Each feature controller inherits from a common generic Bloc hierarchy.
Each controller mixes in 20+ generic mixins through a shared contract class.
Run:
flutter clean
flutter pub get
flutter run -d chrome
Observe compilation time and application startup behavior.

Expected results

Flutter Web should compile and start the application within a reasonable time.

Expected:

Web compilation time remains stable as the project scales.
Application reaches main() quickly after Chrome launches.
Application successfully loads the first screen.
No startup timeout occurs.

Actual results

After migrating from a composition-based architecture to a generic Bloc + Mixin architecture:

Compilation
Composition Architecture:
3–4 minutes

Bloc + Generic Mixins Architecture:
8–10 minutes
Application Startup

After Chrome launches:

Application initialization is significantly slower.
main() takes a long time to complete.
Initial dependency injection and controller registration become extremely slow.
Application frequently exceeds startup timeout limits.
Browser eventually disconnects and the application closes before the first screen is rendered.

This behavior did not occur before the architectural change.

Code sample

Code Sample

The issue appears when a large number of feature controllers inherit from the same generic Bloc hierarchy and mixin chain.

Base State

abstract class FeatureState {}

class InitialFeatureState extends FeatureState {}

Base Bloc

import 'package:flutter_bloc/flutter_bloc.dart';

abstract class FeatureBlocBase<T extends FeatureState>
    extends Bloc<Object, T> {

  FeatureBlocBase(T initialState) : super(initialState);
}

Interfaces

abstract class IDeleteMixin {
  Future<void> delete();
}

abstract class ISearchMixin {
  Future<void> search();
}

abstract class IPrintMixin {
  Future<void> printDocument();
}

abstract class IUpdateMixin {
  Future<void> update();
}

Main Contract

abstract class IFeatureBloc
    implements
        IDeleteMixin,
        ISearchMixin,
        IPrintMixin,
        IUpdateMixin {}

Generic Mixins

mixin DeleteMixin<T extends FeatureState>
    on FeatureBlocBase<T>
    implements IDeleteMixin {

  @override
  Future<void> delete() async {
    // register events
  }
}

mixin SearchMixin<T extends FeatureState>
    on FeatureBlocBase<T>
    implements ISearchMixin {

  @override
  Future<void> search() async {
    // register events
  }
}

mixin PrintMixin<T extends FeatureState>
    on FeatureBlocBase<T>
    implements IPrintMixin {

  @override
  Future<void> printDocument() async {}
}

mixin UpdateMixin<T extends FeatureState>
    on FeatureBlocBase<T>
    implements IUpdateMixin {

  @override
  Future<void> update() async {}
}

Common Feature Bloc

abstract class FeatureBloc<T extends FeatureState>
    extends FeatureBlocBase<T>
    with
        DeleteMixin<T>,
        SearchMixin<T>,
        PrintMixin<T>,
        UpdateMixin<T>
    implements IFeatureBloc {

  FeatureBloc(super.initialState);
}

Real Feature

class CustomerState extends FeatureState {}

class CustomerBloc extends FeatureBloc<CustomerState> {
  CustomerBloc() : super(CustomerState());
}

Scale In Production

The actual project contains:

• ~800 feature controllers
• ~20+ generic mixins
• ~20+ interface contracts
• 15 business modules
• Shared core package

Every feature controller inherits the same hierarchy:

CustomerBloc
      ↓
FeatureBloc<T>
      ↓
FeatureBlocBase<T>
      ↓
Bloc<Event, State>

+ 20 Generic Mixins
+ 20 Interface Contracts

Observed Results

Composition Architecture:

flutter run -d chrome

3-4 minutes

Generic Bloc + Mixins Architecture:

flutter run -d chrome

8-10 minutes

Additional symptom:

After Chrome launches, application bootstrap becomes very slow and frequently exceeds startup timeout before rendering the first screen.

Screenshots or Video

Logs

PS C:\Users\PR> Flutter --verbose create foo
[ +726 ms] Artifact Instance of 'MaterialFonts' is not required, skipping update.
[ +1 ms] Artifact Instance of 'GradleWrapper' is not required, skipping update.
[ +1 ms] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FlutterWebSdk' is not required, skipping update.
[ +1 ms] Artifact Instance of 'LegacyCanvasKitRemover' is not required, skipping update.
[ ] Artifact Instance of 'FlutterSdk' is not required, skipping update.
[ ] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FontSubsetArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'PubDependencies' is not required, skipping update.
[ +1 ms] executing: [C:\src\PR\Flutter/] git -c log.showSignature=false log HEAD -n 1 --pretty=format:%ad --date=iso
[ +82 ms] Exit code 0 from: git -c log.showSignature=false log HEAD -n 1 --pretty=format:%ad --date=iso
[ ] 2026-07-17 10:20:17 -0700
[ +13 ms] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FlutterWebSdk' is not required, skipping update.
[ ] Artifact Instance of 'FlutterEngineStamp' is not required, skipping update.
[ ] Artifact Instance of 'LegacyCanvasKitRemover' is not required, skipping update.
[ +2 ms] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[ +51 ms] Artifact Instance of 'MaterialFonts' is not required, skipping update.
[ ] Artifact Instance of 'GradleWrapper' is not required, skipping update.
[ ] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FlutterWebSdk' is not required, skipping update.
[ ] Artifact Instance of 'FlutterEngineStamp' is not required, skipping update.
[ ] Artifact Instance of 'LegacyCanvasKitRemover' is not required, skipping update.
[ ] Artifact Instance of 'FlutterSdk' is not required, skipping update.
[ ] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'IosUsbArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'FontSubsetArtifacts' is not required, skipping update.
[ ] Artifact Instance of 'PubDependencies' is not required, skipping update.
[ +60 ms] Unable to get code-sign settings on non-Mac platform.
[ +11 ms] Creating project foo...
[ +773 ms] executing: [C:\Users\PR/] C:\src\PR\Flutter\bin\cache\dart-sdk\bin\dart pub --suppress-analytics --color --directory foo get --example
Resolving dependencies in foo...
Downloading packages...
Got dependencies in foo.
[ +616 ms] Generating C:\Users\PR\foo\android\app\src\main\java\io\flutter\plugins\GeneratedPluginRegistrant.java
[ +120 ms] Wrote 131 files.
[ ]
All done!
[ +4 ms] You can find general documentation for Flutter at: https://docs.flutter.dev/
Detailed API documentation is available at: https://api.flutter.dev/
If you prefer video documentation, consider: https://www.youtube.com/c/flutterdev

       In order to run your application, type:

         $ cd foo
         $ flutter run

       Your application code is in foo\lib\main.dart.

[ +14 ms] executing: C:\Program Files\Android\Android Studio1\jbr\bin\java -version
[ +207 ms] Exit code 0 from: C:\Program Files\Android\Android Studio1\jbr\bin\java -version
[ ] openjdk version "21.0.10" 2026-01-20
OpenJDK Runtime Environment (build 21.0.10+-14961533-b1163.108)
OpenJDK 64-Bit Server VM (build 21.0.10+-14961533-b1163.108, mixed mode)
[ +3 ms] executing: C:\Program Files\Android\Android Studio1\jbr\bin\java --version
[ +192 ms] Exit code 0 from: C:\Program Files\Android\Android Studio1\jbr\bin\java --version
[ ] openjdk 21.0.10 2026-01-20
OpenJDK Runtime Environment (build 21.0.10+-14961533-b1163.108)
OpenJDK 64-Bit Server VM (build 21.0.10+-14961533-b1163.108, mixed mode)
[ +4 ms] "flutter create" took 2,089ms.
[ +90 ms] Running 1 shutdown hook
[ +2 ms] Shutdown hooks complete
[ +170 ms] exiting with code 0

PS C:\Users\PR>

Flutter Doctor output

Changed 7 dependencies!
2 packages have newer versions incompatible with dependency constraints.
Try flutter pub outdated for more information.

🔒 Lock released.
Done with C:\Users\PR\package\onyx_ix_debug_assets

ALL projects processed.

PS C:\Users\PR> flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[v] Flutter (Channel stable, 3.44.7, on Microsoft Windows [Version 10.0.20348.5256], locale en-US)
[v] Windows Version (Server 2022 Standard 64-bit)
[v] Android toolchain - develop for Android devices (Android SDK version 36.0.0)
[v] Chrome - develop for the web
[!] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.14.9 (July 2025))
! Unable to locate a Windows 10 SDK. If building fails, install the Windows 10 SDK in Visual Studio.
[v] Connected device (2 available)
[v] Network resources

! Doctor found issues in 1 category.

PS C:\Users\PR>