(🐞) `reveal_type` on a lambda parameter from an overloaded higher order function shows two results

[KotlinIsland]

Here the type of value is an non-inferred int, and there is only one usage of reveal_type, yet mypy is outputting two results (one of which is incorrect)

reveal_locals() shows two entries for value, but one being None not Any.

from typing import overload, Callable

@overload
def bar() -> None: ...
@overload
def bar(fn: Callable[[int], object]) -> None: ...

def bar(fn: object=1) -> None: ...
    

bar(lambda value: reveal_type(value))
bar(lambda value: reveal_locals())

main.py:11: note: Revealed type is "Any"
main.py:11: note: Revealed type is "builtins.int"
main.py:12: note: Revealed local types are:
main.py:12: note:     value: None
main.py:12: note:     value: builtins.int
Success: no issues found in 1 source file

Without removing duplicate messages you get this:

test.py:12: note: Revealed local types are:
test.py:12: note:     value: None
test.py:12: note: Revealed local types are:
test.py:12: note:     value: builtings.int

• Cause of Error for lambda containing Any even when type can be inferred #5879

[septatrix]

For some reason reassigning the variable to another name suppresses this behaviour?!

def foobar(data: int | str) -> None:
    reveal_type(data)
    if isinstance(data, int):
        reveal_type(data)
        data2 = data
        filter(lambda element: element == reveal_type(data), [])
        filter(lambda element: element == reveal_type(data2), [])

lambda_confusion.py:2: note: Revealed type is "Union[builtins.int, builtins.str]"
lambda_confusion.py:4: note: Revealed type is "builtins.int"
lambda_confusion.py:6: note: Revealed type is "builtins.int"
lambda_confusion.py:6: note: Revealed type is "Union[builtins.int, builtins.str]"
lambda_confusion.py:7: note: Revealed type is "builtins.int"

PS: And when adding a cast it obviously complaints about a redundant cast so the reassignment actually seems to be the easiest workaround (apart from a strong type: ignore)

[KotlinIsland]

@septatrix Strange, but whats happening here is that data is only locally narrowed (from the isinstance), so when assigning to data2 it's inferring the narrowed type, but when revealing within the lambda, mypy doesn't know that the lambda is executed immediatley, so it has to assume that data could be reassigned back to a str.

I think this is probably a similar but separate issue.

[KotlinIsland]

@AlexWaygood can you add topic-overloads , the reveal type is behaving strange here due to a deeper issue with the overload.

[KotlinIsland]

From what I can tell, this is caused by mypy.checkexpr.ExpressionChecker.check_overload_call which first executes:

arg_types = self.infer_arg_types_in_empty_context(args)

Which is accepting the body of the lambda without knowing the types of anything which causes all the types to be Any.