ref.json "new scope when adjacent to keywords" test

[redmitry]

Hello,

I do not understand this ref.json test. This is related to this discussion.

In the "toggle" example of the specification (section-7.7.1.1), the "default": true is put on the same scope. The other "ref" test is also just extends the referred object. Why the "properties" is different? I may pass the test if I enclose "properties" in "anyOf"... but what is the right way to "merge" referred schema with extended properties?

Kind regards,

D.

[jdesrosiers]

$ref is not a merge. It's like allOf where all assertions apply independently. Therefore, it's possible to have conflicting assertions.

{
  "type": "string",
  "$ref": "#/$defs/foo",

  "$defs": {
    "foo": { "type": "number" }
  }
}

This example says that the JSON instance must be a string and must be a number. That's not possible, so any value you validate against this schema will fail validation. Let's look at another example where the conflicting keyword is an annotation that doesn't effect validation.

{
  "title": "Foo",
  "$ref": "#/$defs/foo",

  "$defs": {
    "foo": { "title": "Bar" }
  }
}

What will be the title of the instance evaluated by this schema, "Foo" or "Bar"? It's really both, but because it doesn't effect validation, Section 7.7.1.1 allows applications (not validators) to choose one or the other. That section doesn't apply in the context of validation, only to how applications use the annotations that are provided after validation.

Hopefully that background helps, so I'll try to answer the question directly.

{
  "properties": {
    "prop1": { "type": "string" }
  },
  "$ref": "#/$defs/A",

  "$defs": {
    "A": { "unevaluatedProperties": false }
  },
}

So, here, properties and $ref are evaluated independently. properties is evaluated without any context from the $ref and the $ref is evaluated without any context from properties. When the $ref is evaluated, it encounters "unevaluatedProperties": false. Since there is nothing else in that scope, the only JSON instance that will validate against this schema is an empty object, {}. The properties keyword is also evaluated independently and will be valid against the test JSON instance. So, properties passes and $ref fails resulting in validation failing.

[redmitry]

Hi Jason,
Thank you for the answer.
So, if I understood correctly,

"schema": {
    "$schema": "https://json-schema.org/draft/2019-09/schema",
        "$defs": {
            "reffed": {
                "type": "array"
            }
        },
        "properties": {
            "foo": {
                "$ref": "#/$defs/reffed",
                "maxItems": 2
            }
      }
},

Here "maxItems": 2 doesn't refer to the "type": "array" so actually we validate
allOf [
{ "maxItems": 2 },
{ "type": "array" }
]

Is this correct?

Thank you very much!

D.

[jdesrosiers]

Yes, it would evaluate similarly to that allOf.

[redmitry]

Great!
Thank you.