Discriminated/narrowed Union type of closure’s upvalues does not carry into closure

[amarshall]

Probably best illustrated with an example:

from typing import TypeVar, Union

_T = TypeVar('_T')
_U = TypeVar('_U')

def f(x: Union[_T, int]) -> None:
    if isinstance(x, int):
        reveal_type(x)  # int
        def g1() -> None:
            reveal_type(x)  # Union[_T, int] (but expect int)
    else:
        reveal_type(x)  # _T
        def g2() -> None:
            reveal_type(x)  # Union[_T, int] (but expect _T)

The same also happens with Optional and if x is None, but I presume the type-checker doesn’t treat this as any different, anyway.

Using:

• Python 3.7.0
• mypy 0.641
• mypy config:

  [mypy]
  check_untyped_defs = True
  disallow_any_decorated = True
  disallow_any_expr = True
  disallow_any_unimported = True
  disallow_incomplete_defs = True
  disallow_subclassing_any = True
  disallow_untyped_calls = True
  disallow_untyped_decorators = True
  disallow_untyped_defs = True
  warn_return_any = True
  warn_unused_ignores = True

[ilevkivskyi]

Duplicate of #2608

[amarshall]

Thanks for finding the duplicate; I searched but couldn’t find it myself :)