[2.0 regression] `check_call` in a plugin started producing a wrong output

[sobolevn]

I faced this problem in dry-python/returns in a rather complex plugin: https://github.com/dry-python/returns/actions/runs/25487192998/job/74785711812?pr=2396

Here: https://github.com/dry-python/returns/blob/2cab87d042a2df31dcbbe77ffe7d21e0417a1121/returns/contrib/mypy/_typeops/inference.py#L121-L131

The problem is that I pass the correct types / context for checkexpr.check_call method, but the output has changed since 1.20, it started to show an incorrect error.

The same happens for a regular function call:

def convert(first: str, other: int) -> float:
    ...

reveal_type(convert(1))

Produces:

ex.py:4: note: Revealed type is "float"
ex.py:4: error: Missing positional argument "first" in call to "convert"  [call-arg]

However, first was passed, other is missing.

[sobolevn]

Working on it :)

[sobolevn]

Related to ef7e8a6 and #20591 cc @KevinRK29

[sobolevn]

Ok, I see. This is not a "bug", this is a feature. Since 1 matches other: int, mypy helps us to identify that other is provided, but first which is str is missing.

I am a bit confused with the current error message, because in my opinion it should produce two error messages instead:

1. One that first has incorrect type: expected str got int
2. One that other argument is missing

Because this is exactly what happens in the code. And it does not have any confusing parts.

What do others think? CC @JukkaL

[JukkaL]

Yeah, this looks a bit confusing. However, when there is a larger number of arguments, the new message is probably better. One option would be to only use the new logic when there are at least N arguments. Another option would be to add a separate note with something like 'Is positional argument "first" missing?'.