What about using typing.get_type_hints to resolve annotations for a class?

It will allow having ClassVar annotated as str:

@runtime_checkable
class P(Protocol):
    x: 'ClassVar[int]' = 1

Good question! I'd considered that too but decided against it for two main reasons:

1. get_type_hints is slow
2. get_type_hints won't work with forward references/ PEP 563 if ClassVar is not defined in the caller's namespace

Consider the following:

# foo.py
from __future__ import annotations
from typing import *

@runtime_checkable
class X(Protocol):
 x: ClassVar[int] = 1
 y: SomeUndeclaredType = None

# bar.py
from .foo import X
class Y: ...

# Error! get_type_hints cannot resolve 'ClassVar' and 'SomeUndeclaredType'
issubclass(X, Y)

Nonetheless, your suggestion has reminded me of a basic workaround for string annotations. Thanks.

Let's also add a case with the same class prop, but different value. Example:

class E:
    x = 2

Because right now all names / values always match. It is not clear whether value is a part of the protocol or not.

One more case that is not covered: same name, different type.

class F:
    x = 'a'

It should not pass, but maybe ClassVar wrapper might break / change that.

Let's also test these classes:

class G:
   x: ClassVar[int] = 1

class H:
   x: 'ClassVar[int]' = 1

What about raw ClassVar annotation with generic argument?