Open

Description
- Are you reporting a bug, or opening a feature request?
Bug
- Please insert below the code you are checking with mypy,
or a mock-up repro if the source is private. We would appreciate
if you try to simplify your case to a minimal repro.
from typing import Optional, Union, TypeVar
MyUnion = Union[int, str]
T = TypeVar("T")
def not_none(x: Optional[T]) -> T:
assert x is not None
return x
# Works
def f(i: Optional[int]) -> int:
return not_none(i)
# Doesn't work
def g(u: Optional[MyUnion]) -> MyUnion:
return not_none(u)
- What is the actual behavior/output?
a.py:19: error: Incompatible return value type (got "object", expected "Union[int, str]")
- What is the behavior/output you expect?
No error.
- What are the versions of mypy and Python you are using?
Do you see the same issue after installing mypy from Git master?
mypy --version
is 0.710+dev.70a4c9858fb3e736dbf4bc6cc9243c5d49bf2e5a
py --version
is Python 3.7.2
Still see the issue after installing from master.
- What are the mypy flags you are using? (For example --strict-optional)
None