class variable of subclass of Unknown type

[pinterior]

I looked at #10847 and noticed different type inference results between class variables and other variables when a base class of variable type is in extension module.
I don't think this is a bug (libraries should provide stub-files in such cases), but is this behavior intended?

from cython_code_without_stub import B

class A(B):
    pass

class T:
    cls_var = A()
    reveal_type(cls_var)

    def f(self):
        reveal_type(T.cls_var)

        self.inst_var = A()
        reveal_type(self.inst_var)

        var = A()
        reveal_type(var)

foo.py
  foo.py:1:6 - error: Import "cython_code_without_stub" could not be resolved (reportMissingImports)
  foo.py:8:17 - information: Type of "cls_var" is "A"
  foo.py:11:21 - information: Type of "T.cls_var" is "Unknown"
  foo.py:14:21 - information: Type of "self.inst_var" is "A"
  foo.py:17:21 - information: Type of "var" is "A"
1 error, 0 warnings, 4 informations

[傅立业（Chris Fu） (Azureblade3808)]

Type of B is Unknown.
-> B could be a descriptor class.
-> A could be a descriptor class.
-> Type of T.cls_var (and also self.cls_var) is Unknown.

[pinterior]

that's right! I never thought about descriptors.
thank you!