[BUG] Missing attributes from allOf when target contains oneOf using python-flask

Created by: Holt59

Description

When using the python-flask generator where a component contains a allOf targeting a component with a oneOf, the extra properties of the targeted element are missing from the extending element.

Note: This might be a misunderstanding of the OpenAPI specification on my side. If so, feel free to tell me and close this issue / point me to the specification details.

openapi-generator version

5.3.0

OpenAPI declaration file content or url

---
openapi: 3.0.3

info:
  title: Demo
  version: "1.0.0"

paths:
  /Route:
    post:
      requestBody:
        content:
          application/json:
            schema:
              type: array
              items:
                $ref: "#/components/schemas/ClassB"
        required: true
      responses:
        "200":
          description: Successful operation.
          content: {}
        "500":
          description: Error during operation.
          content: {}


components:
  schemas:

    ClassA:
      type: object
      properties:
        x:
          type: integer
          format: int32
        y:
          type: number


    ClassB:
      type: object
      oneOf:
        - type: object
          properties:
            y:
              type: number
        - type: object
          properties:
            u:
              type: array
              items:
                $ref: '#/components/schemas/ClassA'
      properties:
        z:
          type: string

    ClassC:
      type: object
      properties:
        a:
          type: number

    ClassD:
      type: object
      allOf:
        - $ref: "#/components/schemas/ClassB"
        - properties:
            t:
              $ref: "#/components/schemas/ClassC"

Generation Details / Steps to reproduce

Single command to generate the python server:

java -jar ./openapi-generator-cli-5.3.0.jar generate -i ./openapi.yml -g python-flask -o ./server

The generated ClassD only contains the y, u and t attributes, and is missing the z one. Below is the generated __init__ class of ClassD:

def __init__(self, y=None, u=None, t=None):  # noqa: E501
    """ClassD - a model defined in OpenAPI

    :param y: The y of this ClassD.  # noqa: E501
    :type y: float
    :param u: The u of this ClassD.  # noqa: E501
    :type u: List[ClassA]
    :param t: The t of this ClassD.  # noqa: E501
    :type t: ClassC
    """
    self.openapi_types = {
        'y': float,
        'u': List[ClassA],
        't': ClassC
    }

    self.attribute_map = {
        'y': 'y',
        'u': 'u',
        't': 't'
    }

    self._y = y
    self._u = u
    self._t = t