Annoying behaviour of additionalProperties validation when using draft3/extends

[bustbr]

Hi,

there seems to be a problem with validating against the additionalProperties: false constraint when extending a schema using draft 3.

import json, jsonschema

validator = jsonschema.Draft3Validator(json.loads('''{
    "type": "object",
    "extends": {
        "properties": {
            "id": {
                "type": "string"
            }
        }
    },
    "properties": {},
    "additionalProperties": false
}'''))
instance = {'id': 'should be allowed.'}
print([e.message for e in validator.iter_errors(instance)])

=>
["Additional properties are not allowed ('id' was unexpected)"]

I know about the problematic nature of the wording in the draft 3 specs (the behavior of extends can be seen as validating an instance against all constraints in the extending schema as well as the extended schema(s)) and that draft 4 should be preferred, but is there any chance this will be fixed?

In my real world application extends is basically used to emulate mutli level inheritance using $refs, so it's quite a bit more complex than my example here.
In case this won't/can't be fixed in the library, I came up with 3 ways to fix this on the application side so far:

1. Rewrite all schemas for draft 4.
2. Get rid of all the extends and inline everything.
3. Add empty property definitions (i.e. declarations) for all inherited properties, so for my example above that would mean adding "id": {} to the schema's properties.
   1 & 2 being the most time consuming, 3 being kind of an ugly hack. Can you think of yet another, more practical solution?

Thanks.

[Julian]

It's not a wording issue, this is what extends does, and it's the same in draft 4 (it was just "renamed" to allOf).

There's discussion about what to do in draft 5, if there's a desire to support something like this. Personally I'm of the opinion that if you want this then you should have a schema combiner (a function that basically automatically adds empty property definitions for you by walking your schema and its refs). I put sample code for doing that in one of the other related issues here.

[bustbr]

Thanks for the super quick answer!
I'll look into that.