get_attr_data doesn't handle default factory correctly

[ssnl]

If we merge a MISSING field, with an attrs class structured config that uses default factory (e.g., for specifying defaults list in hydra), this expand call

omegaconf/omegaconf/basecontainer.py

Lines 327 to 342 in 6a4fd51

	def expand(node: Container) -> None:
	rt = node._metadata.ref_type
	val: Any
	if rt is not Any:
	if is_dict_annotation(rt):
	val = {}
	elif is_list_annotation(rt) or is_tuple_annotation(rt):
	val = []
	else:
	val = rt
	elif isinstance(node, DictConfig):
	val = {}
	else:
	assert False
	node._set_value(val)

will call node._set_value(attrs_class), which calls get_attr_data(attrs_class).

omegaconf/omegaconf/_utils.py

Lines 313 to 334 in 6a4fd51

	def get_attr_data(obj: Any, allow_objects: Optional[bool] = None) -> Dict[str, Any]:
	from omegaconf.omegaconf import OmegaConf, _maybe_wrap
	flags = {"allow_objects": allow_objects} if allow_objects is not None else {}
	from omegaconf import MISSING
	d = {}
	is_type = isinstance(obj, type)
	obj_type = obj if is_type else type(obj)
	dummy_parent = OmegaConf.create({}, flags=flags)
	dummy_parent._metadata.object_type = obj_type
	for name, attrib in attr.fields_dict(obj_type).items():
	is_optional, type_ = _resolve_optional(attrib.type)
	type_ = _resolve_forward(type_, obj.__module__)
	if not is_type:
	value = getattr(obj, name)
	else:
	value = attrib.default
	if value == attr.NOTHING:
	value = MISSING

and since it is given a class, it will use attrs.Attribute's attribute.default value as the values to set attributes. This normally works, but however, if the attribute uses default factory, the attribute.default is an attrs.Factory object! Then OmegaConf errors out.

To Reproduce

[skipping long stack frames]

[Jasha10]

Thanks for the bug report!

[ssnl]

In a sense this is due to that OmegaConf infers types from values rather than type annotations. I wonder if there can be a way to use type annotations instead (which would also address the structure configs inheritance issue described in facebookresearch/hydra#2227 )

[zoni]

I ran into this bug as well just now. However, I have found it does work correctly with the stdlib dataclasses. This can serve as a possible workaround for others who run into this, and may aid in tracking down the source of the problem.

For reference, here's a minimalistic dataclasses example that works correctly for which the equivalent attrs version throws the exception described in the original report:

from dataclasses import dataclass, field

@dataclass
class Config:
  a_list_of_strings: list[str] = field(default_factory=list)