Invalid schema causes "should have required property '$ref'" error

Describe the bug When an OpenAPI v3 Response Object contains a schema which has invalid schemas, an error is thrown saying: should have a required $ref property.

This is probably coming from better-ajv-errors, which is deduping errors which are saying “should be a valid sub schema, or should be a $ref” and its just showing the $ref bit.

To Reproduce

1. Given this OpenAPI document

openapi: 3.0.1
info:
  title: Example $ref error
  version: 1.0.0
paths:
  /user:
    get:
      operationId: getUser
      responses:
        "200":
          description: An Example
          content:
            application/json:
              schema:
                type: object
                properties:
                  user_id: 12345

1. Run this CLI command spectral lint openapi.yml

2. See error

Expected behavior

Show a more appropriate validation error. In this instance, other validators return this error:

Structural error at paths./user.get.responses.200.content.application/json.schema.properties.user_id should be object

Environment:

• Library version: 4.0.1
• OS: Mac OS 10.14.5

[moltar]

This also happens for path params:

  '/modules/{module_id}/sections':
    parameters:
      - type: string
        name: module_id
        in: path
        required: true
        schema:
          type: string
        description: Module ID
    get:

/paths//modules/{module_id}/sections/parameters/0 should have required property '$ref'

[philsturgeon]

We’ve not forgotten about this issue. We are solving problems a few levels down, with supporting multiple JSON Schema and OpenAPI dialects and vocabularies, which will get us to reevaluate some of the dependencies we’ve built features like schema-based validation on top of. If we’re continuing to use schema-based validation it’ll likely be switching to DJV, and we need to work on some functionality there to make it support better errors. Otherwise maybe Sway, but we’ll have to see what happens as this work progresses.

For now invalid schema messages are a bit funky and I’m sorry about that. We’ll get there.