Cyclic definition error when defaulting `TypeVar` on base class to subclass

[randolf-scholz]

from typing import Protocol

class SupportsComparison[CompatT, TruthT](Protocol):
 def __gt__(self, other: CompatT, /) -> TruthT: ...
 def __ge__(self, other: CompatT, /) -> TruthT: ...
 def __lt__(self, other: CompatT, /) -> TruthT: ...
 def __le__(self, other: CompatT, /) -> TruthT: ...

class Scalar[CompatT, TruthT = Bool]( # ❌️ Cannot resolve name "Bool"
 SupportsComparison[CompatT, TruthT],
): ...

# Specialized Scalar Types
class Bool(Scalar): ...
class Int(Scalar): ...
class Float(Scalar): ...
class Complex(Scalar): ...

mypy complains with

py:9:30: error: Cannot resolve name "Bool" (possible cyclic definition) [misc]
py:9:30: error: TypeVar "default" must be a type [misc]

pyright, ty and pyrefly report no errors.

tested with mypy 1.19.1 on python 3.14.2

[peacefulotter]

+1 - Having same issue with a similar code.

[peacefulotter]

Could someone look into this ? I am really hitting a wall here..
thanks !

[peacefulotter]

@ilevkivskyi Sorry to bother you, any chance someone can take a look at this issue ?
Thanks !

[ilevkivskyi]

I do want to do some kind of type variable defaults overhaul at some point soon. But probably around June-July.