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Type Error with tagged Unions (working code but mypy/pyright error) #690

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@Gentle

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functionally this code does what I expect it to (asserts go through) but there is a type error in the signature of Converter.structure, it accepts cl: type[T] and UnionType does not match that

from typing import Literal, Union
from dataclasses import dataclass
import cattrs
@dataclass
class Add:
 t: Literal["ADD"]
 v: int
@dataclass
class Sub:
 t: Literal["SUB"]
 v: int
Op = Union[Add, Sub]
Op2 = Add | Sub
assert cattrs.structure(dict(t="ADD", v=10), Op) == Add(t="ADD", v=10)
assert cattrs.structure(dict(t="SUB", v=5), Op2) == Sub(t="SUB", v=5)

if I change this https://github.com/python-attrs/cattrs/blob/main/src/cattrs/converters.py#L587 to

 def structure(self, obj: UnstructuredValue, cl: type[T] | UnionType) -> T:

the type error goes away but I'm not sure if that is the right solution

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