Recursive $ref crashes generation for OpenAPI and AsyncAPI input

[jonaslagoni]

Summary

A self-referencing $ref in the input document makes generation fail. It affects OpenAPI and AsyncAPI input with different errors, while the same recursive schema through JSON Schema input generates fine.

Version: 0.81.1. Also reproduces on main.

Reproduction

OpenAPI — Converting circular structure to JSON

api.yaml:

openapi: 3.0.3
info:
  title: Recursive
  version: 1.0.0
paths:
  /nodes:
    get:
      operationId: getNode
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Node'
components:
  schemas:
    Node:
      type: object
      required: [label]
      properties:
        label:
          type: string
        children:
          type: array
          items:
            $ref: '#/components/schemas/Node'

codegen.config.js:

export default {
  inputType: 'openapi',
  inputPath: './api.yaml',
  language: 'typescript',
  generators: [{preset: 'payloads', outputPath: './out'}]
};

$ npx @the-codegen-project/cli@0.81.1 generate ./codegen.config.js
Generating code...
✗ Generation failed

Error: Generator 'generate' failed

Details:
Converting circular structure to JSON
    --> starting at object with constructor 'Object'
    |     property 'children' -> object with constructor 'Object'
    |     property 'items' -> object with constructor 'Object'
    --- property 'properties' closes the circle

AsyncAPI — Could not dereference $ref in input

The same recursive schema in an AsyncAPI v3 document fails differently:

asyncapi: 3.0.0
info:
  title: Recursive
  version: 1.0.0
channels:
  nodes:
    address: nodes
    messages:
      Node:
        payload:
          $ref: '#/components/schemas/Node'
operations:
  sendNode:
    action: send
    channel:
      $ref: '#/channels/nodes'
components:
  schemas:
    Node:
      type: object
      required: [label]
      properties:
        label:
          type: string
        children:
          type: array
          items:
            $ref: '#/components/schemas/Node'

Details:
Could not dereference $ref in input, is all the references correct? 1 error occurred while reading '<cwd>'

Deleting only the children property from that same document generates successfully, so the failure is the recursion and not the surrounding document.

JSON Schema input — works

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "Node",
  "type": "object",
  "required": ["label"],
  "properties": {
    "label": {"type": "string"},
    "children": {"type": "array", "items": {"$ref": "#"}}
  }
}

✓ Generated 1 file in 5ms

Modelina handles the recursion; the break is upstream of it, in the OpenAPI/AsyncAPI input processing.

Expected

Recursive $ref should generate a self-referencing model, as it already does for JSON Schema input and as openapi-generator, Kiota and @hey-api/openapi-ts all do for OpenAPI (each emits children?: Node[]).

Notes

Recursive structures are common in real documents — category trees, comment threads, nested rule/filter expressions, JSON-Schema-shaped payloads.

Found while building https://github.com/the-codegen-project/comparisons. documents/openapi/complex.yaml there contains a recursive EvidenceNode, and the listDisputes operation had to be excluded via filter to keep generation working:
https://github.com/the-codegen-project/comparisons/blob/main/comparisons/the-codegen-project/openapi/codegen.complex.config.js

The two different error messages suggest two separate fixes: the OpenAPI path serializes the processed schema with JSON.stringify somewhere it should not, and the AsyncAPI path fails during $ref dereferencing.