[BUG][SCALA] Cannot Output Multiple Response Types

[markgarland]

Bug Report Checklist

• [Y] Have you provided a full/minimal spec to reproduce the issue?
• [N] Have you validated the input using an OpenAPI validator (example)?
• [Y] What's the version of OpenAPI Generator used?
• [Y] Have you search for related issues/PRs?
• [Y] What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

We have an endpoint (see yaml below) which has a body defined for a success, but a different body defined for an error response.
However, ApiInvoker expects a Manifest typed on the success response for all cases. The if statement on this case

openapi-generator/modules/openapi-generator/src/main/resources/scala-akka-client/apiInvoker.mustache

Line 251 in 26830bf

case Some((manifest, state: ResponseState)) if manifest == mf =>

checks for this. If it doesn't match (as in our error case) it then ends up in this case (

openapi-generator/modules/openapi-generator/src/main/resources/scala-akka-client/apiInvoker.mustache

Line 260 in 26830bf

Future.failed(ApiError(response.status.intValue, "Unexpected response code", Some(response.entity.toString)))

) and you get the ConfigServiceError as a string (which isn't what you need).
A workaround is to use asInstanceOf to change the ApiRequest to be typed on the error type, but that isn't practical outside of testing.

openapi-generator version

4.3.0

OpenAPI declaration file content or url

openapi: '3.0.0'
paths:
  /api/v1/config/revision:
    post:
      summary: Add a revision
      description: Add a revision of configuration without applying it
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/RevisionRequest'
      responses:
        '201':
          description: Success
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/RevisionResponse'
        '400':
          description: BadRequest
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ConfigServiceError'
      security:
        - bearerAuth: []
      tags:
        - config
components:
  schemas:
    ConfigServiceError:
      description: A config service error
      type: object
      required:
        - type
      properties:
        type:
          type: string
        errors:
          type: array
          items:
            type: string
          description: The errors

Command line used for generation

Scala, openapi-generator(4.3.0) (but code affected same in master)
sbt clean openapiGenerate

Steps to reproduce

Use an ApiInvoker typed on the success response in an error scenario, and try to unmarshall the error response.

Related issues/PRs

#1096
#316
#3377

Suggest a fix

Have the ApiInvoker and internal map take multiple types? Type the ApiResponse with multiple types (success/failure)? Remove/amend the if from the case statement?