[Java] Issue with OneOf types

If we have an API definition like so:

components:
  schemas:
    Foo:
      type: object
      properties:
        foo:
          type: string
    Bar:
      type: object
      properties:
        bar:
          type: string
    Schema:
      oneOf:
        - $ref: '#/components/schemas/Foo'
        - $ref: '#/components/schemas/Bar'

Swagger will generate an interface OneOfSchema , as well as 3 implementors: Schema, Foo, Bar.

The problem is that the APIs (and models) will refer to the empty stub class Schema, e.g.:

public Schema somethingGet(Schema body) throws ApiException {...}

The problem is you when you call this you get issues, e.g.:

var foo = new Foo();
...
api.somethingGet(foo); //doesn't compile because Foo is not a Schema.

The fix is to rename the interface to be Schema and only have 2 implementors: Foo, Bar.

I had a go at doing this myself, seems like a change to subclass SchemaHandler.processComposedSchema() for java so that it's like so:

    @Override
    protected CodegenModel processComposedSchema(CodegenModel codegenModel, ComposedSchema composedSchema, Map<String, CodegenModel> allModels) {
        List<Schema> schemas = composedSchema.getOneOf();
        //Give the composedModel the same name as the parent:
        CodegenModel composedModel = this.createComposedModel(codegenModel.getName(), schemas);
        
        if (composedModel == null) { //returns null if it's not OneOf
            schemas = composedSchema.getAnyOf();
            composedModel = this.createComposedModel(ANY_OF_PREFFIX + codegenModel.getName(), schemas);
            if (composedModel == null) {
                return null;
            }
        }

        this.addInterfaceModel(codegenModel, composedModel);
        this.addInterfaces(schemas, composedModel, allModels);

        //This is a dirty way of saying we don't want to generate the original model
        codegenModel.setClassname("X"+codegenModel.classname);
        codegenModel.setName("X"+codegenModel.name);

        return composedModel;
    }

Start at the Java SchemaHandler.processComposedSchema() entry point and reproduce the supplied oneOf definition to inspect the generated interface, implementors, and API signature. Done means the generated API accepts Foo or Bar directly without the empty Schema stub being used as a separate model.