[BUG] Request body form parameters do not support complex composed schema use cases

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

Request body form parameters do not support complex composed schema use cases When we handle request body form parameters here: https://github.com/OpenAPITools/openapi-generator/blob/fdb13c3e2e5fa96523102d7c92ae2a6b409c47d4/modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java#L6001 Our code traverses composed schemas and pools all properties inside objects into the returned properties map. This will not work when:

• two schemas define a property with the same name and different types
• we have oneOf or anyOf schemas where some properties should be included and others shouldn’t

This code path is used when request bodies are content-type application/x-www-form-urlencoded, or content-type starts with multipart

openapi-generator version

5.2.1

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  version: '1.0.0'
  title: the title

paths:
  '/users/me':
    post:
      description: Change user password.
      operationId: changeCurrentUserPassword
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              $ref: '#/components/schemas/ChangePasswordRequest'
      responses:
        '200':
          description: Successful operation
          content: {}

components:
  schemas:
    CommonPasswordRequest:
      type: object
      required: [ password, passwordConfirmation ]
      properties:
        password:
          type: string
          format: password
        passwordConfirmation:
          type: string
          format: password

    ChangePasswordRequest:
      type: object
      allOf:
        - $ref: '#/components/schemas/CommonPasswordRequest'
        - type: object
          required: [ oldPassword ]
          properties:
            oldPassword:
              type: string
              format: password

Generation Details

Steps to reproduce

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/10396

Suggest a fix

Update this code to return a single CodegenParameter which represents the composed schema in these cases. Then the generator will require than an instance of the model that this refers to is passed in. This fix should only be done for generators which support full composition. For now our code only handles object schema and pure allOf with no colliding property definitions.

[sebastianblesgen]

Same issue with 5.3.1 of the plugin (java). Models are not generated when ref$ is used. I got message like “Model XXX not generated since it’s marked as unused (due to form parameters) and skipFormModel (global property) set to true (default)” in my console"

Here is my workaround but this should not be the fix as skipFormModel should be true only for OA2 as I understand. The problem I think is related to the fact it’s “marked as unused (due to form parameters)”

                        <goals>
                            <goal>generate</goal>
                        </goals>
                        <configuration>
                        ...
                            <globalProperties>
                                <skipFormModel>false</skipFormModel>
                            </globalProperties>
                        </configuration>

[spacether]

This has been fixed in the new python-experimental generator (added in 5.4.0) which supports Inline schemas anywhere. One can see it working in this PR in 6.0.0.