allow vendor extensions next to $refs

[BentEngbers]

In the following example, vacuum reports an oas3-no-$ref-siblings error.

openapi: 3.1.0
paths:
  /example:
    get:
      operationId: example
      responses:
        "200":
          content:
            application/json:
              schema:
                x-test: foo
                $ref: "#/components/schemas/response"
components:
  schemas:
    response:
      type: string

The error:

 a `$ref` can only be placed next to `summary` and `description` but got:x-test      | oas3-no-$ref-siblings

[LasneF]

looking on the rules here
https://learn.openapis.org/referencing/overview.html#a-taxonomy-of-references

summary and description has an explicit specification , whereas it has not for extension

the key being if the reference should override the parent or not , this behavior is only specified for description and summary

then to me the rule as it is looks fair ,

2 options for work around :
@BentEngbers disable the rules as it does not suits your need
@daveshanley having a mechanism of rules extension so that the end user can add others key word to the rules (may be simple to say , but complex to specify with dedicated configuration file/ model )

[daveshanley]

I am going to say the same thing I said here: #608

The spec says everything else is ignored, which means they are not supposed to be there. The purpose of vacuum is tell you when you are rolling off the road and deviating from the standard.

The rule as it is, is accurate in my opinion, I won't be changing this. Just disable the rule if you want to use this design.