extension do not warn for error

main.dart

import 'dart:async';

typedef Nullary<T> = T Function();
typedef NullaryAsync<T> = Nullary<Future<T>>;
typedef NullaryFutureOr<T> = Nullary<FutureOr<T>>;

typedef Unary<T, S> = T Function(S);
typedef UnaryAsync<T, S> = Unary<Future<T>, S>;
typedef UnaryFutureOr<T, S> = Unary<FutureOr<T>, S>;

extension NullaryFutureOrToNullaryAsync<T> on NullaryFutureOr<T> {
  NullaryAsync<T> get future => call();
}

extension UnaryFutureOrToUnaryAsync<T, S> on UnaryFutureOr<T, S> {
  UnaryAsync<T, S> get future => call();
}

FutureOr<void> nullary() {}
FutureOr<void> unary(dynamic _) {}

void main() {
  print(nullary.future.runtimeType);
  print(unary.future.runtimeType);
}