False positive for type argument with default value

[alexei]

Bug Report

mypy doesn't seem to like it when a type argument has a default value. I'm not sure how to explain this, so better see below.

To Reproduce

from typing import TypeVar

T = TypeVar("T", bound="Foo")

class Foo:
    pass

class SubFoo(Foo):
    pass

def factory(class_type: type[T]) -> T:
    return class_type()

factory(Foo)
factory(SubFoo)

def alt_factory(class_type: type[T] = Foo) -> T:  # ⚠️ Incompatible default for argument
    return class_type()

alt_factory()
alt_factory(Foo)
alt_factory(SubFoo)

https://mypy-play.net/?mypy=1.8.0&python=3.12&gist=804d71b3f77280d09347b352f535def4

Expected Behavior

I'd expect it to report no issues.

Actual Behavior

Incompatible default for argument "class_type" (default has type "type[Foo]", argument has type "type[T]")

Your Environment

mypy 1.8.0 on Python 3.12

[hauntsaninja]

Duplicate of #3737