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]}

I was about to create the exact same ticket; I'm nudging this.

It can’t be resolved in fields(): it is still undefined when the fields are created. 

I think the best solution is PEP 649.

I’m deferring any action on this until PEP 649 is ruled on.

Also, when dataclasses was originally written, it deliberately did not import typing, for performance reasons. I don't know if PEP 560 (I think) improved performance enough to make a difference. But adding this dependency needs to be looked at.

But if we are going to import typing, there are other changes that I'd like to make, like improving the ClassVar stuff.

I don't think we should merge this change. get_type_hints() is fragile and full of corner cases around using the right globals and locals dictionaries. dataclasses shouldn't execute it implicitly for you.

I agree with Jelle here: dataclasses shouldn't be calling get_type_hints().