Using TypeVar with Annotated Depends

[9en9i]

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Example Code

from typing import Annotated, TypeVar

from fastapi import FastAPI, Depends

app = FastAPI()

T = TypeVar("T")

Inject = Annotated[T, Depends()]


class FirstService:
    pass


class SecondService:
    pass


@app.get("/first")
async def first_service(service: Inject[FirstService]):
    pass


@app.get("/second")
async def second_service(service: Inject[SecondService]):
    pass


if __name__ == "__main__":
    import uvicorn

    uvicorn.run("main:app", host="0.0.0.0", port=8000, reload=True)

Description

When using TypeVar, dependencies are injected incorrectly.
To see this, just run my code in debug mode, put a breakpoint on line 27 (second_service endpoint), and call the /second endpoint in the swagger. Expected Result:
Service variable has type SecondService.
Instead we see type FirstService.

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.95.1

Python Version

Python 3.11.1

Additional Context

No response

[nzig]

Interesting use-case.

This appears to be a bug. I've opened #9479 to fix it.

[tiangolo]

Thanks @nzig! 🚀

This fix is available in FastAPI 0.110.1 🎉