[fastapi] Handle parameters with Depends correctly (FAST003)

[InSyncWithFoo]

Summary

Resolves #13657.

Test Plan

cargo nextest run and cargo insta test.

[github-actions]

ruff-ecosystem results

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[MichaReiser]

Nice. A few comments related to how the code is structured and the used terminology

[MichaReiser]

This is great. One small nit and an understand question from my end.

[MichaReiser]

Just for my understanding. Is this an error because fastapi only respects the first Depends? Do you have a reference that documents this behavior or did you find it out by try and error?

[InSyncWithFoo]

The documentation doesn't mention what happens when two Depends are used in a path operation function, only when multiple of them are used in a path operation decorator.

Testing this again, I think I made a mistake. FastAPI seems to respect the last rather than the first. The code in question:

from fastapi import FastAPI, Depends
from typing import Annotated

app = FastAPI()

def foo(a: str) -> str:
    print(f'foo: {a}')
    return 'lorem'
    
def bar(b: str) -> int:
    print(f'bar: {b}')
    return 42
    
def baz(c: str) -> bytes:
    print(f'baz: {c}')
    return b''

@app.get("/things/{c}")  # `a`/`b`
async def read_thing(other: Annotated[str, Depends(baz), Depends(bar), Depends(foo)]):
    return other

$ uv run fastapi run hello.py
      ...
      INFO   1.2.3.4:5 - "GET /things/ipsum HTTP/1.1" 422

{
    "detail": [
        {
            "type": "missing",
            "loc": ["query", "a"],
            "msg": "Field required",
            "input": null
        }
    ]
}

It would be best if we could ask someone with FastAPI expertise to have a look.

[MichaReiser]

Thanks for the detailed investigation.

@charliermarsh do you know someone we could ping on this?

I'd otherwise suggest to bail (ignore the rule) if multiple Depends are seen