One more bug with union math logic

[ilevkivskyi]

Well, I have found another bug with union math in overloads, this time false negative:

from typing import Union, overload

@overload
def f(x: int, y: int) -> int: ...
@overload
def f(x: object, y: str) -> str: ...
def f(x):
    pass

x: Union[int, str]
y: Union[int, str]
f(x, y) # passes, but should fail because it never matches (str, int)

The problem is that make_simplified_union is used. On one hand this allows us to do unioning in more scenarios, on other hand it is dangerous for union counting in unioned args. I am not sure what to do. @Michael0x2a could you take care of this? (This is however not urgent, since this is a false negative.)

[Michael0x2a]

Will do -- I'll take a look a little later today.

[ilevkivskyi]

Sorry, for overtaking, but I went ahead and now have a possible fix for this in a form of a change to a union math logic, so I am un-assigning you here, but I hope you will review my PR that I will open soon :-)

[Michael0x2a]

No worries :)

I haven't actually started writing any code for this, so this works out perfectly.