Conflict with "from __future__ import annotations"

[ivanovmg]

Hello! Thank you for this useful library!

I found an issue (maybe I am doing something wrong, though) when using Dishka with FastAPI if the code in the module with the routes contains from __future__ import annotations.

Here is a minimal working example, consisting of main.py, use_case.py and entity_router.py.

main.py

from __future__ import annotations

from dishka import (
    Provider,
    Scope,
    make_async_container,
)
from dishka.integrations.fastapi import setup_dishka
from fastapi import FastAPI

from .entity_router import router
from .use_case import RegisterNewEntityUseCase


def create_app():
    app = FastAPI()
    app.include_router(router, prefix='/entities')
    return app


service_provider = Provider(scope=Scope.REQUEST)
service_provider.provide(RegisterNewEntityUseCase)
container = make_async_container(service_provider)

app = create_app()
setup_dishka(container, app)

use_case.py

from __future__ import annotations

from dataclasses import dataclass

@dataclass(frozen=True)
class RegisterNewEntityInputDto:
    title: str
    content: bytes


@dataclass
class RegisterNewEntityUseCase:
    def execute(self, input_dto: RegisterNewEntityInputDto) -> None:
        self.presented_content = {
            'title': input_dto.title,
            'content': input_dto.content.decode(),
        }

entity_router.py

# from __future__ import annotations
# When previous line is uncommented, then the application fails

from typing import Annotated

from dishka.integrations.fastapi import (
    FromDishka,
    inject,
)
from fastapi import (
    APIRouter,
    Form,
    UploadFile,
)
from pydantic import BaseModel

from .use_case import (
    RegisterNewEntityInputDto,
    RegisterNewEntityUseCase,
)

router = APIRouter()

class RegisterNewEntityOutputDto(BaseModel):
    title: str
    content: str


@router.post('/')
@inject
async def register_new_entity(
    title: Annotated[str, Form()],
    file: UploadFile,
    use_case: FromDishka[RegisterNewEntityUseCase],
) -> RegisterNewEntityOutputDto:
    file_bytes = await file.read()
    use_case.execute(
        RegisterNewEntityInputDto(
            title=title,
            content=file_bytes,
        ),
    )
    return RegisterNewEntityOutputDto(**use_case.presented_content)

If entity_router.py contains from __future__ import annotations, then the application fails on startup.

$ fastapi run main.py
...
FastAPIError: Invalid args for response field! Hint: check that ForwardRef('UploadFile') is a valid Pydantic field type. If you are using a return type annotation that is not a valid Pydantic field (e.g. Union[Response, dict, None]) you can disable generating the response model from the type annotation with the path operation decorator parameter response_model=None. Read more: https://fastapi.tiangolo.com/tutorial/response-model/

System info:

└➜ uname -r
5.15.153.1-microsoft-standard-WSL2
└➜ python --version
Python 3.12.3
└➜ pip list
Package           Version
----------------- ---------
annotated-types   0.7.0
anyio             4.8.0
certifi           2025.1.31
click             8.1.8
dishka            1.4.2
dnspython         2.7.0
email_validator   2.2.0
fastapi           0.115.8
fastapi-cli       0.0.7
h11               0.14.0
httpcore          1.0.7
httptools         0.6.4
httpx             0.28.1
idna              3.10
Jinja2            3.1.5
markdown-it-py    3.0.0
MarkupSafe        3.0.2
mdurl             0.1.2
pip               24.0
pydantic          2.10.6
pydantic_core     2.27.2
Pygments          2.19.1
python-dotenv     1.0.1
python-multipart  0.0.20
PyYAML            6.0.2
rich              13.9.4
rich-toolkit      0.13.2
shellingham       1.5.4
sniffio           1.3.1
starlette         0.45.3
typer             0.15.1
typing_extensions 4.12.2
uvicorn           0.34.0
uvloop            0.21.0
watchfiles        1.0.4
websockets        15.0

[Tishka17]

More traceback

  File "/home/tishka17/src/dishka/tmp/q1/entity_router.py", line 29, in <module>
    @router.post('/')
     ^^^^^^^^^^^^^^^^
  File "/home/tishka17/src/dishka/venv/lib/python3.11/site-packages/fastapi/routing.py", line 956, in decorator
    self.add_api_route(
  File "/home/tishka17/src/dishka/venv/lib/python3.11/site-packages/fastapi/routing.py", line 895, in add_api_route
    route = route_class(
            ^^^^^^^^^^^^
  File "/home/tishka17/src/dishka/venv/lib/python3.11/site-packages/fastapi/routing.py", line 525, in __init__
    self.dependant = get_dependant(path=self.path_format, call=self.endpoint)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tishka17/src/dishka/venv/lib/python3.11/site-packages/fastapi/dependencies/utils.py", line 261, in get_dependant
    type_annotation, depends, param_field = analyze_param(
                                            ^^^^^^^^^^^^^^
  File "/home/tishka17/src/dishka/venv/lib/python3.11/site-packages/fastapi/dependencies/utils.py", line 442, in analyze_param
    field = create_response_field(
            ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tishka17/src/dishka/venv/lib/python3.11/site-packages/fastapi/utils.py", line 101, in create_response_field
    raise fastapi.exceptions.FastAPIError(
fastapi.exceptions.FastAPIError: Invalid args for response field! Hint: check that ForwardRef('UploadFile') is a valid Pydantic field type. If you are using a return type annotation that is not a valid Pydantic field (e.g. Union[Response, dict, None]) you can disable generating the response model from the type annotation with the path operation decorator parameter response_model=None. Read more: https://fastapi.tiangolo.com/tutorial/response-model/

[Tishka17]

Looks like a bug in fastapi

Here it should be using typing.get_type_hints() instead of his custom logic
https://github.com/fastapi/fastapi/blob/master/fastapi/dependencies/utils.py#L239