TypeSpec to Python emitter bug when emitting base/derived models

[dargilco]

I have this base model and two derived models with discriminator decorator in my TypeSpec (comments removed for brevity):

@discriminator("type")
model ChatCompletionsResponseFormat {
  type: string;
}

model ChatCompletionsResponseFormatText extends ChatCompletionsResponseFormat {
  type: "text";
}

model ChatCompletionsResponseFormatJSON extends ChatCompletionsResponseFormat {
  type: "json_object";
}

This is the emitted Python code in _models.py (comments removed for brevity):

class ChatCompletionsResponseFormat(_model_base.Model):

    __mapping__: Dict[str, _model_base.Model] = {}
    type: str = rest_discriminator(name="type")

    @overload
    def __init__(
        self,
        *,
        type: str,
    ): ...

    @overload
    def __init__(self, mapping: Mapping[str, Any]):

    def __init__(self, *args: Any, **kwargs: Any) -> None:
        super().__init__(*args, **kwargs)


class ChatCompletionsResponseFormatJSON(ChatCompletionsResponseFormat, discriminator="json_object"):

    type: Literal["json_object"] = rest_discriminator(name="type")


class ChatCompletionsResponseFormatText(ChatCompletionsResponseFormat, discriminator="text"):

    type: Literal["text"] = rest_discriminator(name="type")

When I run a sample that tries to use one of the two derived classes as input arguments in the operator method, for example response_format=ChatCompletionsResponseFormatJSON(), I get the following error Missing required parameter: 'response_format.type'

To fix it I had to update the two derived classes in the auto generated code in _models.py to implement missing init methods, as following (giving example for only one of the derived classes):

class ChatCompletionsResponseFormatJSON(ChatCompletionsResponseFormat, discriminator="json_object"):

    type: Literal["json_object"] = rest_discriminator(name="type")

    @overload
    def __init__(self): ...

    @overload
    def __init__(self, mapping: Mapping[str, Any]):

    def __init__(self, *args: Any, **kwargs: Any) -> None: 
        super().__init__(*args, type="json_object", **kwargs)

So this seems like an emitter bug to me.