Recursive Model Definition is not correctly handled

[laucia]

A simple recursive model definition like this

{
    "swagger": "2.0",
    "info": {
        "version": "1.0.0",
        "title": ""
    },
    "paths": {
        "/recursion": {
            "get": {
                "responses": {
                    "200": {
                        "description": "Recurse",
                        "schema": {
                            "$ref": "#/definitions/Recursion"
                        }
                    }
                },
                "parameters": []
            }
        }
    },
    "host": "localhost",
    "basePath": "/",
    "definitions": {
        "Recursion": {
            "properties": {
                "title": {
                    "description": "user facing localized display string",
                    "type": "string"
                },
                "parent": {
                    "description": "parent recursion",
                    "$ref": "#/definitions/Recursion"
                }
            },
            "required": [
                "title"
            ]
        }
    }
}

Leads to this exception

  File "/usr/local/lib/python2.7/site-packages/bravado_core/spec.py", line 203, in descend
    if is_dict_like(fragment):
  File "/usr/local/lib/python2.7/site-packages/bravado_core/schema.py", line 49, in is_dict_like
    if type(spec) == dict:
RuntimeError: maximum recursion depth exceeded while calling a Python object

As nothing in the swagger spec advise against recursive model definitions and the canonical swagger-codegen handles it, this should also work in bravado.

[analogue]

This is not going to be a simple fix. Just some notes:

• swagger_spec_validator and bravado_core both need this functionality
• jsonschema doesn't support validation of json documents with external refs (local refs are ok) which is a necessary feature
• usage of jsonref will have to be removed entirely since it doesn't support cyclic refs
• all call sites that may encounter a ref need to resolve the ref transparently at runtime
• do some research on how this is handled best in existing libs outside the python ecosystem

[analogue]

Fixed in 4.0.0