[BUG] Generator try to use oneOf* model but does not create it

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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

On oneOf usage in openAPI declaration the generator try to use oneOf* model but does not create it in any language

openapi-generator version

5.0.1

OpenAPI declaration file content or url

{
  "openapi": "3.0.0",
  "info": {
    "title": "service",
    "description": "API",
    "version": "1.0",
    "contact": {}
  },
  "tags": [],
  "servers": [],
  "components": {
    "schemas": {
      "Category": {
        "type": "object",
        "properties": {
          "name": { "type": "string" },
          "parentCategoryId": { "type": "number" }
        },
        "required": ["name", "parentCategoryId"]
      },
      "GetManyCategoryResponseDto": {
        "type": "object",
        "properties": {
          "data": {
            "type": "array",
            "items": { "$ref": "#/components/schemas/Category" }
          },
          "count": { "type": "number" },
          "total": { "type": "number" },
          "page": { "type": "number" },
          "pageCount": { "type": "number" }
        },
        "required": ["data", "count", "total", "page", "pageCount"]
      }
    }
  },
  "paths": {
    "/categories": {
      "get": {
        "operationId": "getManyBaseCategoriesControllerCategory",
        "summary": "Retrieve many Category",
        "parameters": [
          {
            "name": "fields",
            "description": "Selects resource fields",
            "required": false,
            "in": "query",
            "schema": { "type": "array", "items": { "type": "string" } },
            "style": "form",
            "explode": false
          }
        ],
        "responses": {
          "200": {
            "description": "Get many base response",
            "content": {
              "application/json": {
                "schema": {
                  "oneOf": [
                    {
                      "$ref": "#/components/schemas/GetManyCategoryResponseDto"
                    },
                    {
                      "type": "array",
                      "items": { "$ref": "#/components/schemas/Category" }
                    }
                  ]
                }
              }
            }
          }
        },
        "tags": ["Categories"]
      }
    }
  }
}

Generation Details

Steps to reproduce

execute - java -jar openapi-generator-cli.jar generate -i categories.swagger -o out -g (any language)

then at api/categories_api the generated function is:

Future<Response<OneOfGetManyCategoryResponseDtoarray>> getManyBaseCategoriesControllerCategory({ 
  BuiltList<String> fields,
})

the problem is that OneOfGetManyCategoryResponseDtoarray class does not exist in any file.

Related issues/PRs

#3965 - Similar a bit

Suggest a fix

[wing328]

We definitely want to add oneOf, anyof support to all generators. At this stage, we rely on contributions from the community to implement the feature with reference to the generators that support these features or those who need these features with a higher priority can consider sponsoring the tasks to make it a higher priority among the community.

For your case, we welcome contributions from you to add oneOf support to the protobuf-schema generator or you can sponsor the enhancement to have it done by the community.

[nikolasten]

jersey2 and native does not work either