Getting Maximum call stack size exceeded when having more than one recursive union (anyOf) in the schema

[grreeenn]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

5.2.1

Plugin version

No response

Node.js version

18.20.3, 20.16.0

Operating system

Linux

Operating system version (i.e. 20.04, 11.3, 10)

macOS

Description

When having more than 1 recursive anyOf in the schema, the server fails to start, throwing FastifyError [Error]: Failed building the serialization schema for GET: /, due to error Maximum call stack size exceeded.

The example code throwing the error:

app.get('/', {
  schema: {
    response: {
      200: {
        "$id": "T0",
        "type": "object",
        "properties": {
          "items": {
            "anyOf": [
              {
                "type": "string"
              },
              {
                "$ref": "T0"
              }
            ]
          },
          "additionalProperties": {
            "anyOf": [
              {
                "type": "boolean"
              },
              {
                "$ref": "T0"
              }
            ]
          }
        }
      }
    }
  }
}, async (request, reply) => {
  return {};
})

here's a stackblitz illustrating the issue.

This is a reduction from an attempt to write a validation schema for JSON Schema specification itself.

Link to code that reproduces the bug

https://github.com/grreeenn/fast-json-stringify-max-call-stack-exceeded-bug

Expected Behavior

App starting without an error