(🐞) False positive error for list of two callables

[KotlinIsland]

This list is perfectly valid. only usages should be an error.

def f1(*, a: int): ...
def f2(*, b: int): ...

[f1, f2]  # error: List item 0 has incompatible type "(NamedArg(int, 'a')) -> None]"; expected "(NamedArg(int, 'b')) -> None"

playground

[ethanhs]

First of all, unions are unordered, and defining some metric for sorting names can become a lot more complex as the names get more complicated.

Secondly, mypy is correct to give an error in your second example (which I'm not sure if it is related to the issue here of ordering names) as the following code:

a = [f1, f2]

for fn in a:
    fn(a = 4)

would error.

[KotlinIsland]

@ethanhs It's not that the error shouldn't be there, it's that the error is complaining about the first element in the list.

I fixed this issue locally and that case is now reporting correctly, so I think they are related.

[erictraut]

The expression [f1, f2] is valid and doesn't violate any type consistency rules, so an error should not be emitted here. The statement fn(a = 4) in the follow-on example is a type violation and should result in an error, but the original expression [f1, f2] is valid. So this does appear to be a bug in mypy.

[JelleZijlstra]

Updated the issue title to reflect the actual bug.

[KotlinIsland]

@JelleZijlstra Do you think the original issue is valid? Should I re raise it

[JelleZijlstra]

Yes it's valid. We can use this issue to track it.

[KotlinIsland]

They seem like completely different issues

[erictraut]

Your original post included two issues. The first was about unions, and that was already answered. Unions are not ordered, so that's not a bug. The second issue is a legitimate bug, and the title of this issue was changed to reflect that.