Handle circular references

[zmay2030]

Problem statement

When you have a circular reference, the swagger DIFF command goes into an infinite loop. I think this is something to be supported because below is perfectly valid in Go

type A1 struct {
 id int
 name string
 a1 *A1
}

Steps to reproduce

spec_1.json

{
  "swagger": "2.0",
  "info": {
    "title": "Swagger Fixture",
    "version": "1.0"
  },
  "paths": {
    "/a/": {
      "get": {
        "parameters": [
          {
            "name": "",
            "in": "body",
            "schema": { "$ref": "#/definitions/A1" }
          }
        ],
        "responses": {
          "200": {
            "description": "200 response",
            "schema": {
              "type": "array",
              "items": { "$ref": "#/definitions/A1" }
            }
          }
        }
      }
    }
  },
  "definitions": {
    "A1": {
      "type": "object",
      "properties": {
        "id": { "type": "integer" },
        "name": { "type": "string" },
        "a1":{ "$ref": "#/definitions/A1" }
      }
    }
  }
}

spec_2.json
You can just use the same one above

Then Run swagger diff spec_1.json spec_2.json. It will never stop.

Environment

swagger version: 2.0
go version: 1.18
OS: Mac Monterey