dataclass class literal subtyping with callables not working

[MatthewMckee4]

Summary

This snippet does not work

@dataclass
class DC:
    x: DC | None

v: Callable[[DC], DC] = DC

The reason is that __init__ for DC is not a FunctionLiteral.

Should we allow other types for these constructor functions too? (other than FunctionLiteral and Callable

astral-sh/ruff#19130 this may also help with allowing any type and converting it to callable

[erictraut]

You may find this section of the typing spec to be useful here. It covers the rules for converting the constructor of a class object into a callable type for purposes of assignability testing.

[MatthewMckee4]

2. If the class defines a __new__ method

Does this mean we should not allow different types of __new__?

And same for __init__

[carljm]

We already implement that section of the spec, it's just that our implementation assumes that __new__/ __init__ will be a FunctionLiteral type, and the synthesized __init__ on a dataclass is not. I think ideally we should support any callable type as __init__ or __new__, using a generalized Type::into_callable_type method. (But practically speaking, just adding support for Type::Callable so we support dataclass synthesized methods would go a long way.)

[MatthewMckee4]

Yeah, I'm trying to generalise it to use the into_callable method we just landed

[MatthewMckee4]

Just going for supporting 'Callable' as using into_callable has proved to be a lot more work