programmatically decide which property is missing when using 'required' in Draft4Validator

[arianvp]

In the Draft3Validator we could easily determine programatically which required field was missing by looking at ValidationError.

Draft3 set the attribute that was missing in path. That way we could programatically see what property was missing:

def properties_draft3(validator, properties, instance, schema):
    if not validator.is_type(instance, "object"):
        return

    for property, subschema in iteritems(properties):
        if property in instance:
            for error in validator.descend(
                instance[property],
                subschema,
                path=property,
                schema_path=property,
            ):
                yield error
        elif subschema.get("required", False):
            error = ValidationError("%r is a required property" % property)
            error._set(
                validator="required",
                validator_value=subschema["required"],
                instance=instance,
                schema=schema,
            )
            error.path.appendleft(property)
            error.schema_path.extend([property, "required"])
            yield error

In Draft4 however, these attributes aren't set anymore:

def required_draft4(validator, required, instance, schema):
    if not validator.is_type(instance, "object"):
        return
    for property in required:
        if property not in instance:
            yield ValidationError("%r is a required property" % property)

Is there a way to get the old behaviour back?

[Julian]

Hey. At the moment no unfortunately, see #119, would love a patch if you would like. Cheers.