Reports

As @InSync mentioned in the comments we can solve this by adding a third overload.

from __future__ import annotations
from typing import Literal, overload

class WoodData: ...
class ConcreteData: ...

class Foo[T: Literal["wood", "concrete"]]:
    def __init__(self, data_type: T) -> None:
        self.data_type = data_type

    @overload
    def get_data(self: Foo[Literal["wood"]]) -> WoodData: ...

    @overload
    def get_data(self: Foo[Literal["concrete"]]) -> ConcreteData: ...

    @overload
    def get_data(self) -> WooData | ConcreteData: ...


    def get_data(self):
        if self.data_type == "wood":
            return WoodData()
        return ConcreteData()
    
    def bar(self):
        self.get_data()

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