Generic constraint inference problem with TypedDict

[JukkaL]

Mypy doesn't seem to infer constraints correctly for TypedDicts. Example:

from typing import TypeVar, Iterable
from mypy_extensions import TypedDict

T = TypeVar('T')

def f(x: Iterable[T]) -> T: pass

A = TypedDict('A', {'x': int})

a: A
reveal_type(f(a)) # Argument 1 to "f" has incompatible type "A"; expected Iterable[<nothing>]

The f(a) call should be okay and the revealed type should be str. This affects iter() at least.