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

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

Start with src/cattrs/converters.py around the structure signature at line 587, then reproduce the example with mypy and pyright. Check that the annotation accepts both typing.Union and the | form while preserving the shown cattrs.structure assertions; done means the type errors are gone without changing runtime behavior.