[BUG][PYTHON] SDK generating on [ allOf, oneOf, anyOf ] not supported for items:

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• 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?

Description

The described issue is not supported for: [ allOf, oneOf, anyOf ] within items:

1. allOf

      allOf:
        - $ref: '#/components/schemas/CreateItemA'
        - $ref: '#/components/schemas/CreateItemB'

2. oneOf

      oneOf:
        - $ref: '#/components/schemas/CreateItemA'
        - $ref: '#/components/schemas/CreateItemB'

3. anyOf

      anyOf:
        - $ref: '#/components/schemas/CreateItemA'
        - $ref: '#/components/schemas/CreateItemB'
      discriminator:
        propertyName: type
        mapping:
          a: '#/components/schemas/CreateItemA'
          b: '#/components/schemas/CreateItemB'

• allOf supported [ not within items: ]

openapi: 3.0.3
...
paths:
  /path:
    post:
      ...
      requestBody:
        required: true
        content:
          application/x-www-form-urlencoded:
            schema:
              $ref: '#/components/schemas/CreateItem'
      responses:
        '200':
          description: OK
components:
  schemas:
    CreateItem:
      allOf:
        - $ref: '#/components/schemas/CreateItemA'
        - $ref: '#/components/schemas/CreateItemB'
...

• [] allOf NOT supported [within items: ]

openapi: 3.0.3
...
paths:
  /path:
    post:
      ...
      requestBody:
        required: true
        content:
          application/x-www-form-urlencoded:
            schema:
              items:
                $ref: '#/components/schemas/CreateItem'
      responses:
        '200':
          description: OK
components:
  schemas:
    CreateItem:
      allOf:
        - $ref: '#/components/schemas/CreateItemA'
        - $ref: '#/components/schemas/CreateItemB'
...

openapi-generator version

v7.16.0

OpenAPI declaration file content

openapi: 3.0.3
info:
  title: Public API
  version: 1.0.0
paths:
  /path:
    post:
      summary: Create
      operationId: createItems
      description: |
        Create items
      requestBody:
        required: true
        content:
          application/x-www-form-urlencoded:
            schema:
              items:
                $ref: '#/components/schemas/CreateItem'
      responses:
        '200':
          description: OK
components:
  schemas:
    CreateItem:
      allOf:
        - $ref: '#/components/schemas/CreateItemA'
        - $ref: '#/components/schemas/CreateItemB'
    CreateItemA:
      type: object
      title: Create Item A
      properties:
        type:
          type: string
          default: a
        a:
          type: string
      required:
        - type
    CreateItemB:
      type: object
      title: Create Item B
      properties:
        type:
          type: string
          default: b
        b:
          type: string
      required:
        - type
        - b

Generation Details

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:v7.16.0 generate -i /local/openapi.yaml -g python -o /local/test_client

Steps to reproduce

The result with the BUG:

...
            schema:
              items:
                $ref: '#/components/schemas/CreateItem'
...

# /local/test_client/api/default_api.py

class DefaultApi:
    """NOTE: This class is auto generated by OpenAPI Generator
    Ref: https://openapi-generator.tech

    Do not edit the class manually.
    """

    def __init__(self, api_client=None) -> None:
        if api_client is None:
            api_client = ApiClient.get_default()
        self.api_client = api_client


    @validate_call
    def create_items(
        self,
        _request_timeout: Union[
            None,
            Annotated[StrictFloat, Field(gt=0)],
            Tuple[
                Annotated[StrictFloat, Field(gt=0)],
                Annotated[StrictFloat, Field(gt=0)]
            ]
        ] = None,
        _request_auth: Optional[Dict[StrictStr, Any]] = None,
        _content_type: Optional[StrictStr] = None,
        _headers: Optional[Dict[StrictStr, Any]] = None,
        _host_index: Annotated[StrictInt, Field(ge=0, le=0)] = 0,
    ) -> None:
        """Create

        Create items 

        :param _request_timeout: timeout setting for this request. If one
                                 number provided, it will be total request
                                 timeout. It can also be a pair (tuple) of
                                 (connection, read) timeouts.
        :type _request_timeout: int, tuple(int, int), optional
        :param _request_auth: set to override the auth_settings for an a single
                              request; this effectively ignores the
                              authentication in the spec for a single request.
        :type _request_auth: dict, optional
        :param _content_type: force content-type for the request.
        :type _content_type: str, Optional
        :param _headers: set to override the headers for a single
                         request; this effectively ignores the headers
                         in the spec for a single request.
        :type _headers: dict, optional
        :param _host_index: set to override the host_index for a single
                            request; this effectively ignores the host_index
                            in the spec for a single request.
        :type _host_index: int, optional
        :return: Returns the result object.
        """ # noqa: E501
...

Against supported allOf [ not within items: ]
Expected result should be similar to:

...
            schema:
              $ref: '#/components/schemas/CreateItem'
...

Result:

# /local/test_client/api/default_api.py

class DefaultApi:
    """NOTE: This class is auto generated by OpenAPI Generator
    Ref: https://openapi-generator.tech

    Do not edit the class manually.
    """

    def __init__(self, api_client=None) -> None:
        if api_client is None:
            api_client = ApiClient.get_default()
        self.api_client = api_client


    @validate_call
    def create_items(
        self,
        type: StrictStr,
        b: StrictStr,
        a: Optional[StrictStr] = None,
        _request_timeout: Union[
            None,
            Annotated[StrictFloat, Field(gt=0)],
            Tuple[
                Annotated[StrictFloat, Field(gt=0)],
                Annotated[StrictFloat, Field(gt=0)]
            ]
        ] = None,
        _request_auth: Optional[Dict[StrictStr, Any]] = None,
        _content_type: Optional[StrictStr] = None,
        _headers: Optional[Dict[StrictStr, Any]] = None,
        _host_index: Annotated[StrictInt, Field(ge=0, le=0)] = 0,
    ) -> None:
        """Create

        Create items 

        :param type: (required)
        :type type: str
        :param b: (required)
        :type b: str
        :param a:
        :type a: str
        :param _request_timeout: timeout setting for this request. If one
                                 number provided, it will be total request
                                 timeout. It can also be a pair (tuple) of
                                 (connection, read) timeouts.
        :type _request_timeout: int, tuple(int, int), optional
        :param _request_auth: set to override the auth_settings for an a single
                              request; this effectively ignores the
                              authentication in the spec for a single request.
        :type _request_auth: dict, optional
        :param _content_type: force content-type for the request.
        :type _content_type: str, Optional
        :param _headers: set to override the headers for a single
                         request; this effectively ignores the headers
                         in the spec for a single request.
        :type _headers: dict, optional
        :param _host_index: set to override the host_index for a single
                            request; this effectively ignores the host_index
                            in the spec for a single request.
        :type _host_index: int, optional
        :return: Returns the result object.
        """ # noqa: E501

        _param = self._create_items_serialize(
            type=type,
            b=b,
            a=a,
            _request_auth=_request_auth,
            _content_type=_content_type,
            _headers=_headers,
            _host_index=_host_index
        )
...

Suggest a fix

Add support for [ allOf, oneOf, anyOf ] on items:

Start with the provided openapi.yaml and reproduce the issue using the Docker generation command for the Python client. Compare the generated default_api.py for schemas using allOf, oneOf, and anyOf under items: with the supported non-items case. Done means the generated method exposes the composed item fields consistently for all three constructs.