TypeVars on 'self' on an instance method are not bound to the instance type. #5416

Describe the Bug

When a typevar is applied to 'self' in an instance method, Pyrefly "forgets" that self must be an instance of the class it is defined in. As best I can tell, the same happens for class methods (which is potentially the cause of #5410)

For the below example, pyrefly 1.4.0 reports that it cannot access the attribute baz for class object*. It seems pyrefly is typing self to Self@bin instead of Self@Bar

from typing import TypeVar
Self = TypeVar("Self")
class Bar:
    def baz(self: Self) -> Self:
        return self.__class__.__new__(self.__class__)

    def bin(self: Self) -> Self:
        return self.baz()

This is particularly problematic for python<3.11, since typing.Self did not exist and so TypeVars are the only way to annotate the return types of factory functions that may be inherited by child classes.

Sandbox Link

https://pyrefly.org/sandbox/?project=v2.I6HIhJZWMXmgEg3oGChfI0YJJBCjBAx0SAZzSoQFHighJCVWgfOCFbgkBKcIEAMzoYFzVXw82AygR4DJIbUcmicRwuAEADcamCKINxrkEE3MWFNWCIAIKEADAFheAaM7vRRYKgKjUS8mTxloaqpCRklJQbGVvj5Me35Run5qnn5KfnKxPooOfQVQAk0sS8wEl7Woxinkg1NZMdBYSpKLOiS1qONLLOqgtAJUgTf-AQ

(Only applicable for extension issues) IDE Information

No response