[waiting for author] Map class type parameters to superclass when checking class method use

[rwbarton]

Fixes #1337.

[JukkaL]

What's the type of cls here?

[JukkaL]

Ah, the above question probably isn't relevant here.

[rwbarton]

It's apparently the full type of A, namely def [T] () -> sm3.A[T1]. That Tis not the same as theTin this method, apparently:a = cls() # type: A[int]` is accepted here. This is maybe a little weird, but not changed by this commit...

[JukkaL]

Hmm I'd like to see a more complete (approximation of) real-world example where this is being used, and I'd like it to type check. Here is a naive try (haven't tried this yet):

from typing import TypeVar, Generic

T = TypeVar('T')

class Maker(Generic[T]):
    @classmethod
    def make(cls) -> T:   
        # this has to be abstract, as T varies totally freely here. but i think that
        # abstract class methods aren't supported. this is close enough.
        raise NotImplementedError

class B(Maker['B']):
    @classmethod
    def make(cls) -> B:
        return B()  # ok

class C(Maker['C']):
    @classmethod
    def make(cls) -> int:   # should be an error
        return 1

def f(o: Maker[T]) -> T:
    return o.make()  # should be okay?

b = f(B())  # type: B  # okay

def g(t: Type[Maker[T]]) -> T:   # should this work?
    return t.make()

bb = g(B)  # type: B  # okay

[gvanrossum]

@rwbarton Do you have time to address Jukka's suggestion above?

[gvanrossum]

Hey @rwbarton,

It looks like this PR is pretty much stuck. I'm trying to clean up stuck PRs so that the list of PRs is not too long. If you feel like working on this some more, just go ahead and reopen it, or open a new PR -- the corresponding issue will remain open with a reference to this (closed) PR in it, so if someone else feels like tackling this problem they still have this PR as a starting point.