Signature incompatible with supertype when using overload since updating from 1.1.1 to 1.2.0

[erzoe]

Bug Report

Since updating from 1.1.1 to 1.2.0 the following code does not pass anymore.

Reading the change log I am assuming this might be related to #14882.

To Reproduce

#!/usr/bin/env python3

import typing
if typing.TYPE_CHECKING:
	from typing_extensions import Self

T_co = typing.TypeVar('T_co', covariant=True)


class Config(typing.Generic[T_co]):

	def __init__(self, value: T_co) -> None:
		self.value = value

	@typing.overload
	def __get__(self, instance: None, owner: typing.Any = None) -> 'Self':
		pass

	@typing.overload
	def __get__(self, instance: typing.Any, owner: typing.Any = None) -> T_co:
		pass

	def __get__(self, instance: typing.Any, owner: typing.Any = None) -> 'T_co|Self':
		if instance is None:
			return self

		return self.value

class MultiConfig(Config[T_co]):

	def __init__(self, val: T_co) -> None:
		super().__init__(val)
		self.values: 'dict[object, T_co]' = {}

	@typing.overload
	def __get__(self, instance: None, owner: typing.Any = None) -> 'Self':
		pass

	@typing.overload
	def __get__(self, instance: typing.Any, owner: typing.Any = None) -> T_co:
		pass

	def __get__(self, instance: typing.Any, owner: typing.Any = None) -> 'T_co|Self':
		if instance is None:
			return self

		return self.values.get(instance.config_id, self.value)

Expected Behavior

This code should pass, as it did in 1.1.1.

Actual Behavior

$ mypy --strict mwe.py
mwe.py:35: error: Signature of "__get__" incompatible with supertype "Config"  [override]
mwe.py:35: note:      Superclass:
mwe.py:35: note:          @overload
mwe.py:35: note:          def __get__(self, instance: Any, owner: Any = ...) -> T_co
mwe.py:35: note:      Subclass:
mwe.py:35: note:          @overload
mwe.py:35: note:          def __get__(self, instance: None, owner: Any = ...) -> MultiConfig[T_co]
mwe.py:35: note:          @overload
mwe.py:35: note:          def __get__(self, instance: Any, owner: Any = ...) -> T_co
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.2.0
• Mypy command-line flags: --strict (but it does not make a difference)
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: Python 3.10.10

[hauntsaninja]

Thanks for the report! It does look related to the PR you mention.

Slightly smaller repro:

from typing_extensions import Self
from typing import Any, Generic, TypeVar, overload

T_co = TypeVar('T_co', covariant=True)

class Config(Generic[T_co]):
	@overload
	def get(self, instance: None) -> Self: ...
	@overload
	def get(self, instance: Any) -> T_co: ...
	def get(self, *a, **kw): ...

class MultiConfig(Config[T_co]):
	@overload
	def get(self, instance: None) -> Self: ...
	@overload
	def get(self, instance: Any) -> T_co: ...
	def get(self, *a, **kw): ...

Will make a fix