Unexpected Behavior with Nested Async Generators #44616

import 'dart:async';

void main() async {
  final bloc = Counter()..listen(print);
  bloc.add(CounterEvent.increment);
}

enum CounterEvent { increment }

class Counter extends Bloc<CounterEvent, int> {
  Counter() : super(0);

  @override
  Stream<int> mapEventToState(CounterEvent event) async* {
    // Does not work
    yield* _increment();

    // Works
    // yield state + 1;
    // yield state + 1;
  }

  Stream<int> _increment() async* {
    yield state + 1;
    yield state + 1;
  }
}

abstract class Bloc<E, S> {
  Bloc(this._state) {
    _eventController.stream.asyncExpand(mapEventToState).listen((s) {
      _state = s;
      _stateController.add(_state);
    });
  }

  final _eventController = StreamController<E>();
  final _stateController = StreamController<S>.broadcast();

  S _state;
  S get state => _state;

  StreamSubscription<S> listen(void Function(S) onData) {
    return _stateController.stream.listen(onData);
  }

  Stream<S> mapEventToState(E event);

  void add(E event) => _eventController.add(event);
}

@override
  Stream<int> mapEventToState(CounterEvent event) async* {
    // Does not work
    // yield* _increment();

    // Works
    yield state + 1;
    yield state + 1;
  }