[BUG][JAVA|SPRING] Properties duplicated in inheritance chain

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

Properties are duplicated instead of inherited, if inheritance is redeclared.

openapi-generator version

7.7.0

OpenAPI declaration file content

openapi: 3.0.1
info:
  title: "BugSample"
  version: SNAPSHOT-1
paths: {}
components:
  schemas:
    Extensible:
      type: object
      properties:
        '@type':
          type: string
        'baseType':
          type: string
    ErrorMessage:
      allOf:
        - $ref: "#/components/schemas/Extensible"
        - type: object
          properties:
            chuck:
              type: string
      discriminator:
        propertyName: '@type'
        mapping:
          ErrorMessage: '#/components/schemas/ErrorMessage'
          ProductOrderErrorMessage: '#/components/schemas/SpecialErrorMessage'
    SpecialErrorMessage:
      allOf:
        - $ref: "#/components/schemas/Extensible"
        - $ref: "#/components/schemas/ErrorMessage"
        - type: object
          properties:
            norris:
              type: string

Generation Details

docker run --rm -v $PWD:/local openapitools/openapi-generator-cli generate -i /local/bugSample.yaml -g spring -o /local/out

Steps to reproduce

1. Create a sample with at least 3 levels of inheritance A > B > C
2. Declare B as inheritance root via discriminator mapping
3. Declare C as allOf A and B explicitly
4. Generate Java or Spring sources. (I assume this is similar for other typed languages,. not tested)

Expectation

For my example, I expect SpecialErrorMessage to only declare property norris.

Actual

SpecialErrorMessage redeclares atType, atBaseType

Workaround

Don't duplicate composition in allOf. Patch the specs.

On the downside, this is sometimes not obvious in more complicated specs and not ideal, if you're not the owner of the spec. I work with an external party that applies the Design guideline to require re-declaration of Extensible Schema explicitly, because they use it to communicate all Schemas that support further extension.

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/6117 is similar, but only covers flat, simple inheritance.

Suggest a fix

If you point me in the right direction, I'd try to create a PR

Start with the bugSample.yaml declaration shown in the issue and run the provided Docker Spring generator command. Inspect the generated SpecialErrorMessage and its inheritance-related model generation; the work is done when it declares only norris rather than duplicating inherited properties such as @type and baseType.