Dataclass field that contains a descriptor object isn't handled correctly #3245
Description
If a @dataclass field is initialized with a descriptor as a default value, pyright should use the value type of the __set__ method for the descriptor when determining the type of the corresponding parameter within the synthesized __init__ method.
Types are also evaluated incorrectly in this case.
Note that mypy also exhibits these same bugs.
from dataclasses import dataclass
from typing import Any, cast
class MyDescriptor:
def __get__(self, __obj: object | None, __owner: Any) -> "int | MyDescriptor":
if __obj is None:
return self
return cast(Any, __obj)._x
def __set__(self, __obj: object | None, __value: int) -> None:
if __obj is not None:
cast(Any, __obj)._x = __value
@dataclass
class Foo:
y: MyDescriptor = MyDescriptor()
f = Foo(3) # Currently a false positive error in pyright (and mypy)
print(f.y) # 3
f.y = 4
print(f.y) # 4
print(Foo.y) # MyDescriptor object
reveal_type(f.y) # int | MyDescriptor, which is wrong
reveal_type(Foo.y) # int | MyDescriptor, which is wrong