Being able to get a set of all missing keys

[Ohad31415]

Something I find myself use each time is a function that returns set of all missing keys so that if it's not empty by the end of the configuration setup I raise an error.
This function consists of recursive calls to OmegaConf.is_missing and OmegaConf.is_confg and I think it would be helpful to include it under the library.

The function implementation is something like this -

class OmegaConf:
    # ...
    @staticmethod
    def missing_keys(cfg: Container) -> Set[str]:
        missings = set()

        def gather(_cfg, prefix=""):
            for key in _cfg:
                if OmegaConf.is_missing(_cfg, key):
                    missings.add(f"{prefix}{key}")
                elif OmegaConf.is_config(_cfg[key]):
                    gather(_cfg[key], prefix=f"{prefix}{key}.")

        gather(cfg)
        return missings 

I've set a PR for this here #719

[omry]

Thanks @Ohad31415.
This is something we can consider for OmegaConf 2.2 (which is pretty far away right now).
I am not planning to add any new features to OmegaConf 2.1.

I am going to hold off reviewing the PR until we start working on 2.2.

[Jasha10]

This functionality is similar to the proposed throw_on_missing keyword argument for OmegaConf.to_container (#501).

[Ohad31415]

This functionality is similar to the proposed throw_on_missing keyword argument for OmegaConf.to_container (#501).

It's similar in the sense that they both report missing keys, however throw_on_missing doesn't give a list of the missing keys so that one get prompt that in an error.

[Jasha10]

Yes, that is correct -- the proposed throw_on_missing error message would only report the first missing key that is encountered.