rwlock: require info keys to be present in schema

[ghost]

Previous implementation allowed incomplete info:

SCHEMA({
    "write": {
        "file_1": {"pid": 1, "cmd": "exec"},
        "file_2": {"pid": 2},
        "file_3": {"cmd": "..."},
        "file_4": {},
    },
    "read": {
        "file_1": [{"pid": 1}],
    }
})

[efiop]

So these used to be Optional(default) but now they are Required. Is this intended?

Sure, de-facto we are always setting even empty dicts for these down below, so it won't break anything in dvc itself. But on the other hand, these are not required by our reader and it is not required in terms of format, so I don't really see a point in making them Required now. The problem you've described in the PR description is fully fixed by INFO_SCHEMA adjustment you've done above. If you want to get rid of defaultdict then let's Optional(..., default={}) here instead.

[ghost]

@efiop , I think Required and Optional are the same when a default is provided, is just semantically different.

I'll make the change, since it makes more sense in that regard.

[efiop]

Thanks!