Minimal reproducible example (playground):
def _(
this_is_fine: int = f(), # No error
this_is_not: list[int] = f() # B008: Do not perform function call `f` in argument defaults
): ...
@dataclass
class _:
this_is_not_fine: list[int] = f() # RUF009: Do not perform function call `f` in dataclass defaults
this_is_also_not: int = f() # RUF009: Do not perform function call `f` in dataclass defaults
RUF009 should behave similar to B008 and ignore attributes with immutable types.