Type narrowing on object attribute with match statement doesn't apply

[AiroPi]

The bug
It seems that doing a "type checking" with the object UI in pattern matching seems to not work properly.
Attribute match is not considered.

Code

class Test:
    def __init__(self, a: int | str):
        self.a: int | str = a

test = Test(5)

match test:
    case Test(a = int()):
        print(test.a + 3)
    case Test(a = str()):
        print(test.a + "3")

Expected behavior
By doing a match with Test(a = int()), python will check test is of type Test AND test.a is of type int.
But mypy "only assert" that test if of type Test. It keep the type int | str for test.a.

Reproduce :
On mypy-playground :
https://mypy-play.net/?mypy=latest&python=3.11&gist=6f05124abd1ef68032d59651a7d5c6c3

[erictraut]

For reference: microsoft/pyright#4775

[cdce8p]

This should be fixed with #19736.

[tjkuson]

Would it be possible to support narrowing across cases like this as part of this issue, or would it be a separate issue/not possible? I searched the issue tracker and this issue seemed to be the closest to what I'm looking for.

class Test:
    def __init__(self, a: int | str):
        self.a: int | str = a


test = Test(5)

match test:
    case Test(a=int()):
        print(test.a + 3)
    case Test(a=str()):
        print(test.a + "3")
    case Test(a=a):
        assert_never(test.a)

This works if I go back to using isinstance with ordinary if statements, but that would mean being unable to use pattern matching features.

[cdce8p]

Would it be possible to support narrowing across cases like this as part of this issue, or would it be a separate issue/not possible? I searched the issue tracker and this issue seemed to be the closest to what I'm looking for.

@tjkuson With #19736 it would almost work. Just assert_never would still throw an error as I haven't implemented the "else" narrowing. Similarly to how it isn't implemented for just the bound variable yet.

    ...
    case Test(a=a):
        reveal_type(a)  # int | str