subclass registration of generic decorator class fails

[Darkdragon84]

I am using the decorator pattern to create a decorator class Decorated from an abstract base class Base.

from attrs import define

@define
class Base:
    @abstractmethod
    def meth(self): ...

@define
class Decorated(Base):
    base: Base

    def meth(self): pass

Base has many more subclasses in addition and I use it as annotation in many places, so I would like to be able to register all subclasses of it to the converter. This works fine in the above example by e.g.

from cattrs import Converter
from cattrs.strategies import include_subclasses

converter = Converter()
include_subclasses(Base, converter)

However, I would now like to make Decorated generic on subclasses of Base:

from typing import Generic, TypeVar

@define
class Decorated(Base, Generic[T]):
    base: T

    def meth(self): pass

Now, when registering all subclasses of Base I get the error

cattrs.errors.StructureHandlerNotFoundError: Missing type for generic argument T, specify it when structuring.

This happens at registration time, not at (un)structuring time.

Is this expected? Can this be mitigated/circumvented?

[hynek]

dupe of python-attrs/cattrs#595

[Darkdragon84]

oops, I guess I reported in the wrong repo, my bad 🙈