async_for_in_wrong_context

The async for-in loop can only be used in an async function.

The analyzer produces this diagnostic when an async for-in loop is found in a function or method whose body isn't marked as being either async or async*.

The following code produces this diagnostic because the body of f isn't marked as being either async or async*, but f contains an async for-in loop:

void f(list) {
  await for (var e in list) {
    print(e);
  }
}

If the function should return a Future, then mark the body with async:

Future<void> f(list) async {
  await for (var e in list) {
    print(e);
  }
}

If the function should return a Stream of values, then mark the body with async*:

Stream<void> f(list) async* {
  await for (var e in list) {
    print(e);
  }
}

If the function should be synchronous, then remove the await before the loop:

void f(list) {
  for (var e in list) {
    print(e);
  }
}