[BUG][DefaultCodegen] allOf not respecting readOnly and all

[laDanz]

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?
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Description

I try to use a enum property, but override readOnly attribute (same for description, and all others), but it is not working.
I only noticed, because I'm having my own template script (not related to this problem!) to not generate @NotNull anotation in case of required but readOnly attribut, like here: #9655

This is the proposed way of dealing with readOnly consider by OpenAPI spec / JSON schema, see:

• readOnly listed on object model level in addition to on fields because $ref overwrites  OAI/OpenAPI-Specification#872 (comment)
• readOnly and writeOnly should be at the same level as required in the Schema OAI/OpenAPI-Specification#1671 (comment)

openapi-generator version

latest version, master.

OpenAPI declaration file content or url

File src/test/resources/3_0/allOf-readonly.yaml

openapi: 3.0.1
info:
  version: 1.0.0
  title: Example
  license:
    name: MIT
servers:
  - url: http://api.example.xyz/v1
paths:
  /person/display/{personId}:
    get:
      parameters:
        - name: personId
          in: path
          required: true
          description: The id of the person to retrieve
          schema:
            type: string
      operationId: list
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/clubForCreation"
components:
  schemas:
    ClubType:
      type: string
      enum:
        - serious
        - silly

    clubForCreation:
      properties:
        type:
          $ref: '#/components/schemas/ClubType'

    clubForUpdate:
      properties:
        type:
          allOf:
            - $ref: '#/components/schemas/ClubType'
            - readOnly: true

Generation Details

Steps to reproduce

Test for DefaultCodegenTest

    public void testAllOfReadonly() {
        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/allOf-readonly.yaml");
        DefaultCodegen codegen = new DefaultCodegen();

        // OK
        Schema clubForCreation = openAPI.getComponents().getSchemas().get("clubForCreation");//clubForCreation.getProperties().get("type")).getReadOnly() is null
        CodegenProperty clubForCreationType = codegen.fromProperty("type", clubForCreation);

        Assert.assertEquals(clubForCreationType.isReadOnly, false);

        // NOK
        Schema clubForUpdate = openAPI.getComponents().getSchemas().get("clubForUpdate");// clubForUpdate.getProperties().get("type")).getReadOnly() is null
        CodegenProperty clubForUpdateType = codegen.fromProperty("type", clubForUpdate);

        Assert.assertEquals(clubForUpdateType.isReadOnly, true);
    }

Related issues/PRs

Suggest a fix

When a property is a ComposedSchema (espacially an "allOf") it should sync/merge all readOnly / description / ... values...