Recursive (Circular) model $ref doesn't dereference unless wrapped in anyOf (sibling keys alongside $ref keys)

[iggyfisk]

Pydantic recently released an update changing their JSON schema generator.

Previously the generated schema looked like

{
    "$defs": {
        "RecursiveModel": {
            "additionalProperties": false,
            "properties": {
                "value": {
                    "description": "A string",
                    "type": "string"
                },
                "children": {
                    "description": "Children with strings",
                    "items": {
                        "$ref": "#/$defs/RecursiveModel"
                    },
                    "type": "array"
                }
            },
            "required": [
                "value",
                "children"
            ],
            "title": "RecursiveModel",
            "type": "object"
        }
    },
    "allOf": [
        {
            "$ref": "#/$defs/RecursiveModel"
        }
    ]
}

which dereferences properly with json-schema-ref-parser. However, now the generated schema looks like

{
    "$defs": {
        "RecursiveModel": {
            "additionalProperties": false,
            "properties": {
                "value": {
                    "description": "A string",
                    "type": "string"
                },
                "children": {
                    "description": "Children with strings",
                    "items": {
                        "$ref": "#/$defs/RecursiveModel"
                    },
                    "type": "array"
                }
            },
            "required": [
                "value",
                "children"
            ],
            "title": "RecursiveModel",
            "type": "object"
        }
    },
    "$ref": "#/$defs/RecursiveModel"
}

which results in an unresolved '$ref': '#/%24defs/RecursiveModel/properties/children/items' after $RefParser.dereference(). As far as I can tell the newer schema should be valid.

Here's a full script showing the difference, and unresolved $ref

import $RefParser from "@apidevtools/json-schema-ref-parser";

async function main() {
  console.log("----OLD----");
  const old_dereferenced = await $RefParser.dereference({
    "$defs": {
      "RecursiveModel": {
        "additionalProperties": false,
        "properties": {
          "value": {
            "description": "A string",
            "type": "string",
          },
          "children": {
            "description": "Children with strings",
            "items": {
              "$ref": "#/$defs/RecursiveModel",
            },
            "type": "array",
          },
        },
        "required": ["value", "children"],
        "title": "RecursiveModel",
        "type": "object",
      },
    },
    "allOf": [
      {
        "$ref": "#/$defs/RecursiveModel",
      },
    ],
  });
  console.log(old_dereferenced["$defs"]["RecursiveModel"]["properties"]);

  console.log("----NEW----");
  const new_dereferenced = await $RefParser.dereference({
    "$defs": {
      "RecursiveModel": {
        "additionalProperties": false,
        "properties": {
          "value": {
            "description": "A string",
            "type": "string",
          },
          "children": {
            "description": "Children with strings",
            "items": {
              "$ref": "#/$defs/RecursiveModel",
            },
            "type": "array",
          },
        },
        "required": ["value", "children"],
        "title": "RecursiveModel",
        "type": "object",
      },
    },
    "$ref": "#/$defs/RecursiveModel",
  });
  console.log(new_dereferenced["$defs"]["RecursiveModel"]["properties"]);
}

main();

I get the output

----OLD----
<ref *1> {
  value: { description: 'A string', type: 'string' },
  children: {
    description: 'Children with strings',
    items: {
      additionalProperties: false,
      properties: [Circular *1],
      required: [Array],
      title: 'RecursiveModel',
      type: 'object'
    },
    type: 'array'
  }
}
----NEW----
{
  value: { description: 'A string', type: 'string' },
  children: {
    description: 'Children with strings',
    items: {
      '$defs': [Object],
      '$ref': '#/%24defs/RecursiveModel/properties/children/items'
    },
    type: 'array'
  }
}

Is this expected? Should I be using some different option?