False positive [missing-attribute] when inheriting slotted dataclass

[randolf-scholz]

Describe the Bug

I think the following should type check, it works at runtime and no other type checker complains.

from dataclasses import dataclass

@dataclass(slots=True)
class Foo:
    x: int
    y: int
        
class Bar(Foo):
    def __init__(self, x: int, y: int) -> None:
        super().__init__(x, y)
        self.z = x + y  # ERROR

assert "__slots__" not in Bar.__dict__  # OK
assert Bar(1, 2).__dict__ == {"z": 3}  # OK

ERROR sandbox.py:11:14-15: Object of class `Bar` has no attribute `z` (not declared in `__slots__`) [missing-attribute]

For non-dataclasses, pyrefly reports no error just like all other type checkers: [sandbox]

class Foo:
    __slots__ = "x", "y"

    def __init__(self, x: int, y: int) -> None:
        self.x = x
        self.y = y
        
class Bar(Foo):
    def __init__(self, x: int, y: int) -> None:
        super().__init__(x, y)
        self.z = x + y  # OK

Sandbox Link

https://pyrefly.org/sandbox/?project=v2.pZRBC4JAEIX_ypAHjcKlugldgrp0MDx7kRQLwhVXQ43-e29clSTZS54WeTOOs997xsg02X5qSEc9ZKn2vG7sXvvsJGW_rtrDVZX63Hyd-RnUh6hwUDEAOGNL3WXdd5j1ZZUnhbN0x8Iaaswz8W2LPda0oobIomMQ-IEGlxO24677FQaPcBHMGEZDyxjxDDhR5J9HPU-9WdOWv9kLQO8rXLTglnZvLf9FxaKLfkH91hGSYCytEMVgxw0zCymc0K0sc-UJMZTLIhVJJmJ5VWJSIYhdET2jexfw03YkO7QV2v7DqK0RtU2E2gwoFEboPg

(Only applicable for extension issues) IDE Information

No response

[randolf-scholz]

Weirdly enough, pyrefly accepts a non-slotted subclass if it is also @dataclass decorated.

from dataclasses import dataclass

@dataclass(slots=True)
class Foo:
    x: int
    y: int
        
@dataclass
class Baz(Foo):
    def __init__(self, x: int, y: int) -> None:
        super().__init__(x, y)
        self.z = x + y  # OK

assert "__slots__" not in Baz.__dict__  # OK
assert Baz(1, 2).__dict__ == {"z": 3}  # OK

https://pyrefly.org/sandbox/?project=v2.pZSxDoIwEIZf5SIDGAmNupG4ODj7ACxECJoYSmgxgPHd_a8FYyPpIlNT7q7X6_f_Xsv0yd4VZKTuUqsDjxuztzo7STmNq0_xVNquh681f0uyPuZjhOwZxgWJ2orxVG1Ro11TttE6-ST2iEZvjoZHzLSnDQ2WXTZZg565DbNHeAvGDB2hUgGHxu4cyW1uY9rxIfYXo_vMViOgpf3rl5CAznaDpmHDG4FW1cGBgUyS1QHMt6Sr1o1KhZjTZVuJshaFvCjhZAhiMeSP_GZ83S1H0hCtUPYfNENLZugDM2QuEeFl7Q0