Issue a warning if the decorated function doesn't use `Provide` arguments

[warvariuc]

When a function is decorated with @inject the wrapped function is inspected for Provide[...] arguments:

python-dependency-injector/src/dependency_injector/wiring.py

Line 564 in cc2304e

signature = inspect.signature(fn)

But if multiple decorators are used like this

@inject
@some_other_decorator
def my_func(...):

and some_other_decorator doesn't use functools.wraps, the Provide arguments are not found.

Here is a reproducible example:

import functools
from dependency_injector import containers, providers
from dependency_injector.wiring import Provide, inject


    
def some_other_decorator(func):
    @functools.wraps(func)
    def wrapped(*args, **kwargs):
        return func(*args, **kwargs)
    return wrapped



class Service:
    ...


class Container(containers.DeclarativeContainer):
    service = providers.Factory(Service)


@inject
@some_other_decorator
def main(service: Service = Provide[Container.service]) -> None:
    print(service)


if __name__ == "__main__":
    container = Container()
    # btw, this doesn't work: container.wire(modules=[__name__])
    # copied from https://github.com/ets-labs/python-dependency-injector/blob/master/examples/wiring/example.py
    container.wire(modules=[__name__])
    main()

If we comment out the @functools.wraps(func) line, we get printed:

<dependency_injector.wiring.Provide object at 0x10ae99fd0>

Issuing a warning inside _fetch_reference_injections if the decorated function doesn't have Provide arguments would help:

1. When such a decorator is used
2. When someone is using @inject and Provide was removed as unnecessary.

[ZipFile]

Since v4.46.0 it is possible to use Annotated to provide injection markers:

@inject
def foo(stuff: Annotated[str, Provide["stuff"]]): ...

This is not a proper fix to your issue, but it works well with @functools.wraps.