[BUG][GO] oneOf with enum values is not properly parsed for response body.

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

When schema contains multiple enum string values oneOf with enums. For example:

        actionType:
          type: object 
          oneOf:
            - type: string
              enum:
              - Max
              - Min
              - Top

Parsing response from backend fail as field is represented by number of structures but parser expects string.
I think template would need to be changed to support this use case specifically.

Workaround for that would be to use swagger-core allowedValues - however when we do that and list those inline to the response OpenAPI generator ignores them and sets type as *string.

openapi-generator version

Master/6.2.1

OpenAPI declaration file content or url

If you post the code inline, please wrap it with

        actionType:
          type: object 
          oneOf:
            - type: string
              enum:
              - Max
              - Min
              - Top

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

Marshal function for oneOf should handle this case detecting if type is enum.

Start with the Go generator's response-body parsing and Marshal handling for oneOf schemas, using the inline actionType schema as the reproduction case. Trace how enum members are represented during generation and parsing; done means a response containing the enum values Max, Min, or Top is parsed correctly instead of being treated as a string or multiple structures.