Bug with subgroups and config file

[farzadab]

Describe the bug
Subgroups work if parameters are provided as CLI args, but it fails if the same parameter is passed through a config file. See below:

To Reproduce

from typing import Union
import dataclasses
import simple_parsing

@dataclasses.dataclass
class ModelTypeA:
    model_a_param: str

@dataclasses.dataclass
class ModelTypeB:
    model_b_param: str

@dataclasses.dataclass
class TrainConfig:
    model_type: Union[ModelTypeA, ModelTypeB] = simple_parsing.subgroups(
        {"type_a": ModelTypeA, "type_b": ModelTypeB},
        default_factory=ModelTypeA,
        positional=False,
    )


# this works:
simple_parsing.parse(config_class=TrainConfig, args=['--model_a_param', 'test'])

# this doesn't work and throws an error
simple_parsing.parse(config_class=TrainConfig, add_config_path_arg=True, args=['--config_path', 'config.yaml'])

# config.yaml:
# model_a_param: test

Expected behavior
I expect the config file to be allow the same behaviour as the CLI args.

Actual behavior
As described above, the second invocation leads to the following error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/farzad/Library/Caches/pypoetry/virtualenvs/ultravox-o1nHeuex-py3.11/lib/python3.11/site-packages/simple_parsing/parsing.py", line 1030, in parse
    parsed_args = parser.parse_args(args)
                  ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/farzad/.pyenv/versions/3.11.4/lib/python3.11/argparse.py", line 1869, in parse_args
    args, argv = self.parse_known_args(args, namespace)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/farzad/Library/Caches/pypoetry/virtualenvs/ultravox-o1nHeuex-py3.11/lib/python3.11/site-packages/simple_parsing/parsing.py", line 321, in parse_known_args
    self.set_defaults(config_file)
  File "/Users/farzad/Library/Caches/pypoetry/virtualenvs/ultravox-o1nHeuex-py3.11/lib/python3.11/site-packages/simple_parsing/parsing.py", line 405, in set_defaults
    wrapper.set_default(default_for_dataclass)
  File "/Users/farzad/Library/Caches/pypoetry/virtualenvs/ultravox-o1nHeuex-py3.11/lib/python3.11/site-packages/simple_parsing/wrappers/dataclass_wrapper.py", line 313, in set_default
    raise RuntimeError(
RuntimeError: ['model_a_param'] are not fields of <class '__main__.TrainConfig'> at path 'config'!

Desktop (please complete the following information):

• Simple parsing version: 0.1.6
• Python version: 3.11.4
• Machine: M1 Mac

[farzadab]

@lebrice you mentioned on #306 that you are working on a refactor of subgroups. Have you gotten around to that yet?
I know very little about the workings of simple_parsing to propose any fix :)

[lebrice]

Hey @farzadab , thanks for posting!

#284 is the closest I've gotten to it, but no I haven't worked on this problem in a while, unfortunately.