Support for `default` HTTP response

According to the OpenAPI Spec 2.0 the responses section can declare a default response.

      responses:
        '200':
          description: Good things happened
        default:
          description: An error occurred.
          schema:
            $ref: '#/definitions/exception'
...
definitions:
  exception:
    type: object
    required:
      - code
    properties:
      code:
        type: string
      description:
        type: string

When running codegen from sbt the following error is reported:

Unknown HTTP type: default

[dsilvasc]

@blast-hardcheese That seems reasonable. Right now I take the generated swagger and replace all defaults with 200s before feeding it to guardrail.

[kelnos]

What I’d suggest:

For servers, do nothing. Emit a warning when we see a default response. Agreed that catch-alls in a server is a smell.

For clients, it’d be nice if everyone could be explicit, but it appears that’s might be too much to ask. Honestly, it’s not bad how it is now (unknown response codes returning an error containing the raw framework response object), but we could maybe do it a little nicer. Since we’re likely already emitting the definition and decoder for the default response type, we could provide an extra method on the error type in the Left that unmarshals the response to it. At the very least, we need to instead a warning and not bail on generation.