Error when using tuple base class not detected #867

Assume m.pyi like this:

from typing import Tuple
a = ... # type: A
class A(Tuple[int, str]): ...

Now this error isn't caught by mypy:

from m import a
a[0]()

This is caused by the class definition being after the type reference in m.pyi. Apparently tuple item types don't get propagated because the class hasn't been semantically analyzed yet when binding the type.