is_dataclass(Any) return type incorrect, differs from is_dataclass(object) #12401
Description
I found this surprising and arguably incorrect. According to mypy:
from typing import Any
from dataclasses import is_dataclass
def example1(arg: Any) -> None:
if is_dataclass(arg):
reveal_type(arg) # ❌ Revealed type is "type[_typeshed.DataclassInstance]"
def example2(arg: object) -> None:
if is_dataclass(arg):
reveal_type(arg) # ✅ Revealed type is "Union[_typeshed.DataclassInstance, type[_typeshed.DataclassInstance]]"This is because Any matches the 1st overload, even if 2nd overload with object argument is more appropriate for Any:
@overload
def is_dataclass(obj: type) -> TypeIs[type[DataclassInstance]]: ...
@overload
def is_dataclass(obj: object) -> TypeIs[DataclassInstance | type[DataclassInstance]]: ...I couldn't think of an elegant fix for this.