Fails basic typing.List[x] check

[facebook]

Fails basic typing.List[x] check

[compyman]

@Ran4 just a note - strict mode catches this (the comprehension types as List[Any] instead of List[int]

# pyre-strict
from typing import List

def f(s: str) -> List[int]:
    return [ch for ch in s]

assert f("foo") == ["f", "o", "o"]

$ pyre check
 ƛ Found 1 type error!
test.py:6:4 Incompatible return type [7]: Expected `List[int]` but got `List[typing.Any]`.

[shannonzhu]

Working on this! Looks like the problem is due to an edge case in our typeorder join, where we're not instantiating type variables early enough in the case both original types are not parametric.