mypy matching **kwargs positionally instead of by name

[reggied]

I am reporting a bug illustrated by the following code.

from typing import Any


def caller() -> None:
    kwargs = dict(a=object(), b=object(), c=object())
    func(1, **kwargs)
    func(**kwargs)

def func(optional:int = 0, **kwargs:Any) -> None:
    pass

When I run version 0.670 of mypy with Python 3.7.1, I get:

a.py:7: error: Argument 1 to "func" has incompatible type "**Dict[str, object]"; expected "int"

It seems to be trying to match the **kwargs positionally instead of using the names. I would not expect mypy to produce an error on this code. You can see in line 6 that if I specify the optional argument explicitly, there is no error.

This same type of behavior was described in issue #1969, but I'm still getting the behavior with version 0.670, which includes those changes.

[ilevkivskyi]

Mypy is technically right because it doesn't record which keys are present in a dictionary, it is just Dict[str, object]. One could potentially use TypedDict to avoid this, but then this is a duplicate of #5382.