fix(reducer): make sure $refs are actual pointers

[kanadgupta]

🧰 Changes

@andrew-rdme was seeing the following error when attempting to reduce a file:

$ref.substring is not a function

which is coming from this line:

oas/src/lib/reducer.ts

Line 33 in 6162c84

const $refSchema = jsonPointer.get(schema, $ref.substring(1));

This is happening because of an edge case where a spec file might have an object definition with a property called $ref. In other words, say the object were to look something like this:

{
  "hello": "world",
  "$ref": "example"
}

then its schema definition would look something like:

{
  "type": "object",
  "properties": {
    "hello": {
      "type": "string",
      "description": "A property called `hello`"
    },
    "$ref": {
      "type": "string",
      "description": "A property called $ref to see what happens"
    }
  }
}

The reducer was looking blindly for $ref keys and assuming their values are always strings. This tweaks the logic ever-so-slightly to ensure that the value of the $ref is indeed a string before we attempt to load its $ref.

🧬 QA & Testing

Added a fixture and a test to confirm that the fix works as expected.

[kanadgupta]

This file is mostly just petstore, this is the only chunk that I added.

[erunion]

Ill tag a release tomorrow