Invalid type inferred for call with *args and generic inheritance

[JukkaL]

Invalid types are inferred for f(*expr) below:

from typing import Iterable, Iterator, Tuple, TypeVar

T = TypeVar('T')
S = TypeVar('S')

class C(Iterable[Tuple[T, S]]):
    def __iter__(self) -> Iterator[Tuple[T, S]]: pass

def f(*x: T) -> T: pass

x: C[str, int]
y: C[int, int]
reveal_type(f(*x))  # str, should be Tuple[str, int]
reveal_type(f(*y))  # int, should be Tuple[int, int]

The problem seems to be related to type inference of *args in calls where there is non-trivial generic inheritance from Iterable such as in C above.

Originally reported as python/typeshed#1600.

[ilevkivskyi]

This was actually originally reported in #3943

[erictraut]

This appears to be fixed. It now produces the expected results. (Note: the last line in the code sample above should say "should be Tuple[int, int]".)