Inconsistent add_api_route types

[sidekick-eimantas]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google "How to X in FastAPI" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

Commit to Help

• I commit to help with one of those options 👆

Example Code

### Direct mounting of routes
import pathlib

from fastapi import FastAPI, APIRouter
import uvicorn
import pydantic

class HelloRequest(pydantic.BaseModel):
    id: str


class HelloResponse(pydantic.BaseModel):
    hello: str


class Hello:
    def __init__(self, name: str) -> None:
        self.name = name

    async def handle(self, request: HelloRequest) -> HelloResponse:
        return HelloResponse(hello=self.name)

app = FastAPI()
hello_handler = Hello(name="test")
app.add_api_route("/hello", hello_handler.handle, methods=["POST"])






### Mounting of paths via Router
import pathlib

from fastapi import FastAPI, APIRouter
import uvicorn
import pydantic

class HelloRequest(pydantic.BaseModel):
    id: str


class HelloResponse(pydantic.BaseModel):
    hello: str


class Hello:
    def __init__(self, name: str) -> None:
        self.name = name

    async def handle(self, request: HelloRequest) -> HelloResponse:
        return HelloResponse(hello=self.name)


class RootRouter:
    def __init__(self, name: str):
        self.router = APIRouter()
        hello_handler = Hello(name=name)
        self.router.add_api_route("/hello", hello_handler.handle, methods=["POST"])


app = FastAPI()
root_router = RootRouter(name="test")
app.include_router(root_router.router)

Description

First example produces a mypy error:

error: Argument 2 to "add_api_route" of "FastAPI" has incompatible type "Callable[[HelloRequest], Coroutine[Any, Any, HelloResponse]]"; expected "Callable[..., Coroutine[Any, Any, Response]]"  [arg-type]

Second example does not.

The types of endpoint parameter in FastAPI.add_api_route and APIRouter.add_api_route are inconsistent.

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.103.1

Pydantic Version

2.3.0

Python Version

3.10.7

Additional Context

No response

[Kludex]

As much as simple, and trivial this is to fix, it's a valid thing to fix. 😅

Thanks.

[sidekick-eimantas]

Happy to raise a PR for this - wasn't sure whether this was intended or changing it had wider implications

[Kludex]

I don't know which of those type hints is wanted. 🤷‍♂️

I've created #10236.