[Bug] Bug for overriding to sub-structured config

[strx2322]

🐛 Bug

Description

Overriding variable to sub-structured config fails when using CLI

Checklist

• I checked on the latest version of Hydra
• I created a minimal repro (See this for tips).

To reproduce

** Minimal Code/Config snippet to reproduce **

from dataclasses import dataclass
import hydra
from hydra.core.config_store import ConfigStore


@dataclass
class A:
    i: int = 1


@dataclass
class Config:
    a: A = A()


@hydra.main(config_name="config")
def hydra_main(cfg: Config):
    print(cfg)


if __name__ == '__main__':
    cs = ConfigStore.instance()
    cs.store(name='config', node=Config)

    hydra_main()

** Stack trace/error message **

$ python hydra.py +a.j=2
Error merging override +a.j=2
Key 'j' not in 'A'
	full_key: a.j
	reference_type=A
	object_type=A

Set the environment variable HYDRA_FULL_ERROR=1 for a complete stack trace.

Expected Behavior

{'a': {'i': 1, 'j': 2}}

System information

• Hydra Version : 1.0.6, 1.1.0 dev5
• Python version : 3.7.9
• Virtual environment type and version : pyenv, vent
• Operating system : Mac, Ubuntu

[omry]

Thanks for reporting.

You can enable adding keys to a Structured Config by extending Dict:

from dataclasses import dataclass,field
import hydra
from hydra.core.config_store import ConfigStore
from typing import Dict, Any

@dataclass
class A(Dict[str, Any]):
    i: int = 1


@dataclass
class Config:
    a: A = field(default_factory=lambda: A())


@hydra.main(config_name="config")
def hydra_main(cfg: Config):
    print(cfg)


if __name__ == '__main__':
    cs = ConfigStore.instance()
    cs.store(name='config', node=Config)

    hydra_main()

Output:

$ python 1.py  a.x=10
Could not override 'a.x'.
To append to your config use +a.x=10
Key 'x' is not in struct
    full_key: a.x
    reference_type=Dict[str, Any]
    object_type=A

Set the environment variable HYDRA_FULL_ERROR=1 for a complete stack trace.

$ python 1.py  +a.x=10
{'a': {'i': 1, 'x': 10}}

About your PR:
I will want to take a closer look at this. not sure I want it fixed.