fix: edge case where allOfs would receive a type when one wasn't present

[erunion]

🧰 What's being changed?

@rafegoldberg stumbled on this in the AWS Workspaces definition while testing out readmeio/api-explorer#1179, but we have an edge case right now where if you're using allOf to dynamically add a description, and only that, to another schema, we'll add type: string to the description object.

For example:

allOf: [
  { 
    type: 'array', 
    items: { 
      type: 'string' 
    }
  }, 
  { description: 'Parameter description' } // This ends up receiving `type: string`.
],

Reason why this ends up failing in the API Explorer is because when @readme/oas-form attempts to merge the schemas in the allOf, array and string collide and json-schema-merge-allof throws an error and instead of merging the schemas together @readme/oas-form instead returns the original schemas sans the allOf -- resulting in a type-less schema.

I continue to be eternally grateful that I took the time to rewrite getParametersAsJsonSchema in December because fixing this kind of thing in the old code would have been a Hot Mess.

🧪 Testing

See attached unit tests, but here's the before and after of this fix in the API Explorer:

Before

After

[erunion]

Since this shapeless case only happens with an allOf where each schema within that block is merged together, we shouldn't apply this logic to oneOf and anyOf polymorphic schemas.

[Dashron]

am I reading this right that we're just leaving this with an empty if block?

Is this preferred over switching the final else to else if not polymporphic? I'm not sure I have an opinion just yet.

[erunion]

Yeah this is just a no-op. Figured it was cleaner and easier to read this way.

[rafegoldberg]

Damn, the turnaround between my comment and this PR was quick af. I haven't run this code, but it code reads well and test cases check out per your screenshots/description of the issue!