Bug: return_dto not used in openapi spec when Response is returned by handler

[atom-andrew]

Description

When I return a Response[MyDTO], I expect the generated openapi spec to include the full dto but it appears to return an empty schema {} instead. #1631 appears to have implemented support for this, but maybe it broke since then. The code below shows that the DTO is being used (because the camelCase rename strategy is applied) , but just not included in the api spec.

URL to code causing the issue

No response

MCVE

import json

from litestar.contrib.pydantic import PydanticDTO
from litestar.dto import DTOConfig
from litestar import Controller, get, MediaType, Response, Litestar
from litestar.testing import TestClient
from pydantic import BaseModel


class MyResponseSchema(BaseModel):
    my_name: str


class MyResponseDTO(PydanticDTO[MyResponseSchema]):
    config = DTOConfig(rename_strategy="camel")


class MyController(Controller):
    path = "/my-endpoint"

    @get(
        "",
        media_type=MediaType.JSON,
        return_dto=MyResponseDTO,
    )
    async def get_my_data(self) -> Response[MyResponseSchema]:
        data = MyResponseSchema(id=1, my_name="example")
        return Response(data)


if __name__ == "__main__":
    app = Litestar(
        route_handlers=[MyController],
    )
    print(json.dumps(app.openapi_schema.to_schema(), indent=4))
    with TestClient(app=app) as client:
        print(client.get("/my-endpoint").text)

Steps to reproduce

1. Run the script.
2. Look at the printed openapi spec.

Screenshots

This is the output of that script:


{
    "info": {
        "title": "Litestar API",
        "version": "1.0.0"
    },
    "openapi": "3.1.0",
    "servers": [
        {
            "url": "/"
        }
    ],
    "paths": {
        "/my-endpoint": {
            "get": {
                "summary": "GetMyData",
                "operationId": "MyEndpointGetMyData",
                "responses": {
                    "200": {
                        "description": "Request fulfilled, document follows",
                        "headers": {},
                        "content": {
                            "application/json": {
                                "schema": {}
                            }
                        }
                    }
                },
                "deprecated": false
            }
        }
    },
    "components": {
        "schemas": {}
    }
}
{"myName":"example"}

### Logs

_No response_

### Litestar Version

2.12.1

### Platform

- [ ] Linux
- [X] Mac
- [ ] Windows
- [ ] Other (Please specify in the description above)

<!-- POLAR PLEDGE BADGE START -->
---
> [!NOTE]  
> While we are open for sponsoring on [GitHub Sponsors](https://github.com/sponsors/litestar-org/) and 
> [OpenCollective](https://opencollective.com/litestar), we also utilize [Polar.sh](https://polar.sh/) to engage in pledge-based sponsorship.
>
> Check out all issues funded or available for funding [on our Polar.sh dashboard](https://polar.sh/litestar-org)
> * If you would like to see an issue prioritized, make a pledge towards it!
> * We receive the pledge once the issue is completed & verified
> * This, along with engagement in the community, helps us know which features are a priority to our users.

<a href="https://polar.sh/litestar-org/litestar/issues/3760">
<picture>
  <source media="(prefers-color-scheme: dark)" srcset="https://polar.sh/api/github/litestar-org/litestar/issues/3760/pledge.svg?darkmode=1">
  <img alt="Fund with Polar" src="https://polar.sh/api/github/litestar-org/litestar/issues/3760/pledge.svg">
</picture>
</a>
<!-- POLAR PLEDGE BADGE END -->