Resolving top-level $ref fails with TypeError: Converting circular structure to JSON

[ahochsteger]

When using $ref on the top-level to reference a defined type in $defs it wrongly results in a TypeError: Converting circular structure to JSON which is not a circular reference.
According to the JSON Schema Core Specification Draft 2020-12 (see 7.5. Applicators) it is valid to use $ref on the top-level.
Here's a example schema:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$ref": "#/$defs/TopLevelType",
  "$defs": {
    "PropType": {
      "title": "Property",
      "type": "string"
    },
    "TopLevelType": {
      "properties": {
        "prop1": {
          "$ref": "#/$defs/PropType"
        }
      },
      "title": "Top Level Type",
      "type": "object"
    }
  }
}

Trying to resolve this issue using the following test program:

import $RefParser from "@apidevtools/json-schema-ref-parser";
import mySchema from "./bundler-demo-non-working.json" with { type: "json" };

try {
  await $RefParser.dereference(mySchema);
  const clonedSchema = await $RefParser.dereference(mySchema, { mutateInputSchema: false });
  console.log(clonedSchema);
} catch (err) {
  console.error(err);
}

Results in the following error:

node test.js 
TypeError: Converting circular structure to JSON
    --> starting at object with constructor 'Object'
    |     property 'TopLevelType' -> object with constructor 'Object'
    |     property 'properties' -> object with constructor 'Object'
    |     property 'prop1' -> object with constructor 'Object'
    --- property '$defs' closes the circle
    at JSON.stringify (<anonymous>)
    at normalizeArgs (node_modules/@apidevtools/json-schema-ref-parser/dist/lib/normalize-args.js:46:34)
    at $RefParser.dereference (node_modules/@apidevtools/json-schema-ref-parser/dist/lib/index.js:193:54)
    at Object.dereference (node_modules/@apidevtools/json-schema-ref-parser/dist/lib/index.js:190:37)
    at file://test.js:6:41

It has been reproduced with version 12.0.1 of @apidevtools/json-schema-ref-parser.

The resolution of this issue is required for skriptfabrik/json-schema-bundler#28.

[github-actions]

🎉 This issue has been resolved in version 12.0.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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