Suppose we have a type like this:

@strawberry.type
class Foo:
    some_date: datetime.date

We also have a directive called format_date that formats a date into a human friendly date. We query that type like this:

foo {
  someDateFormatted: someDate @format_date
}

Currently this will raise an error because the Date scalar will call value.isoformat(), expecting a datetime.date as the return value, but the value now is what format_date returns (which in this example, is already a string)