A more complex example of the type issue

never_issue_spread.dart

abstract class Stated<T> {
 const Stated._();
  
  factory Stated.idle() => const _Idle<Never>();
  const factory Stated.value(T value) = _Value;
  
  TypeChecker<T> typeChecker() => TypeChecker<T>();
  
  void someMethod(Future<T> future) async {
    print(await future);
  }
  
}

class _Idle<T> extends Stated<T>{
  const _Idle(): super._();
}

class _Value<T> extends Stated<T>{
  final T value;
  const _Value(this.value): super._();
}


class TypeChecker<T> { 
  TypeChecker();
  
  bool checkType(Object another) => another.runtimeType == T;
}

void doSomething<T>(Stated<T> stated, Future<T> future){
  stated.someMethod(future);
}


void main(){
  late Stated<String> stated;
  
  void runTest(){
    print(stated.typeChecker().checkType("Not always true"));
  
    doSomething(stated, Future.value("not always works"));
  }

  stated = Stated.value("value");
  runTest();  
  stated = Stated.idle();  
  runTest();
}