Jsonschema Forward compatibility fails when deleting an optional field

According to this, deleting an optional field is allowed in Forward compatibility.

Having this schema:

{
  "title": "Person",
  "type": "object",
  "properties": {
    "firstName": {
      "type": "string",
      "description": "The person's first name."
    },
    "lastName": {
      "type": "string",
      "description": "The person's last name."
    },
    "age": {
      "description": "Age in years which must be equal to or greater than zero.",
      "type": "integer",
      "minimum": 0
    }
  }
}

and setting compatibility rule to Forward, and trying to add a new version:

{
  "title": "Person",
  "type": "object",
  "properties": {
    "firstName": {
      "type": "string",
      "description": "The person's first name."
    },
    "age": {
      "description": "Age in years which must be equal to or greater than zero.",
      "type": "integer",
      "minimum": 0
    }
  }
}

the compatibility check is failing with error:

{causes: [{description: "OBJECT_TYPE_PROPERTY_SCHEMAS_NARROWED", context: "/propertySchemasAdded"}],…}
causes: [{description: "OBJECT_TYPE_PROPERTY_SCHEMAS_NARROWED", context: "/propertySchemasAdded"}]
detail: "io.apicurio.registry.rules.RuleViolationException
error_code: 409
message: "Incompatible artifact: person [JSON], num of incompatible diffs: {1}"
name: "RuleViolationException"

[jsenko]

I’m thinking however that my argument may not be valid if there is "additionalProperties":false set. EDIT: I’ve tested our current compatibility checker with "additionalProperties": false and it works as expected.

[jsenko]

Yes, the compatibility checker must be pessimistic because it works based on general rules. There was already some interest from the community to introduce a less strict checking, but I’m not yet sure how it would look like in practice. A straightforward alternative would be to add an option to force an override, on user’s own risk, if they are 100% sure that it’s safe for their application. Registry would then need to take this into account when doing transitive checks.