Forward reference is not resolved by `dataclasses.fields()`, but it works with `typing.get_type_hints()`.

E.g. 

from dataclasses import dataclass, fields
from typing import Optional, get_type_hints

@dataclass
class Nestable:
    child: Optional['Nestable']

o = Nestable(None)
print('fields:', fields(o))
print('type hints:', get_type_hints(Nestable))

... outputs the following:
 
fields: (Field(name='child',type=typing.Union[ForwardRef('Nestable'), NoneType] ... )
type hints: {'child': typing.Union[__main__.Nestable, NoneType]}