将日志与 Rocket 一起使用时，在此 scope 中找不到宏“日志”

Question

I am getting a compiler error trying to use the log crate in a package in a workspace. The other crates in the workspace are using logging without problem.

Cargo.toml:

[dependencies]
log = "^0"
rocket = "^0"

[dependencies.uuid]
version = "^0"
features = ["v4"]

lib.rs:

#![feature(proc_macro_hygiene, decl_macro)]

use rocket::{
    Request, 
    Data, 
    Response
};

use rocket::request::{
    self, 
    FromRequest,
    Outcome
};

use rocket::fairing::{
    Fairing, 
    Info, 
    Kind
};

use uuid::Uuid;

use std::fmt;

use log;



pub struct LoggerFairing {
    service_name: &'static str
}


impl LoggerFairing {
    pub fn new(service_name: &'static str) -> Self {
        LoggerFairing {
            service_name
        }
    }
}


impl Fairing for LoggerFairing {
    fn info(&self) -> Info {
        Info {
            name: self.service_name,
            kind: Kind::Request | Kind::Response
        }
    }


    fn on_request(&self, req: &mut Request, _: &Data) {
        let ip_addr = req.client_ip().map(|addr| addr.to_string())
            .unwrap_or("IP Address unknown".to_string());

        let method = req.method();

        let url = req.uri();

        let request_id = get_request_id(req);

        log::info!("request {:?} from {}: {} {}", request_id, ip_addr, method, url);
    }


    fn on_response(&self, req: &Request, res: &mut Response) {
        let request_id = get_request_id(req);

        let status = res.status();

        log::info!("request {:?} responded with {}", request_id, status);
    }
}


fn get_request_id<'t, 'r>(req: &'t Request<'r>) -> Option<RequestId<'t>> {
    match req.guard::<RequestId>() {
        Outcome::Success(request_id) => Some(request_id),
        _ => None
    }
}



pub struct RequestId<'t> {
    pub id: &'t Uuid
}    


impl<'t, 'r> FromRequest<'t, 'r> for RequestId<'t> {
    type Error = ();
    
    fn from_request(req: &'t Request<'r>) -> request::Outcome<Self, Self::Error> {
        let id = req.local_cache(|| Uuid::new_v4());
        
        request::Outcome::Success(RequestId {
            id
        })
    }
}


impl<'t> fmt::Display for RequestId<'t> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.id)
    }
}

The error message:

error: cannot find macro `log` in this scope
  --> utils\logging\src\lib.rs:62:9
   |
62 |         log::info!("request {:?} from {}: {} {}", request_id, ip_addr, method, url);
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: cannot find macro `log` in this scope
  --> utils\logging\src\lib.rs:71:9
   |
71 |         log::info!("request {:?} responded with {}", request_id, status);
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 2 previous errors

error: could not compile `logging`.

I've used several variations of the use log statement and how I'm calling the info! macro, but they all cause the same error message. I've tried specifying exact versions in Cargo.toml.

I'm stumped. This is exactly how I'm using log in other crates.

Answer 1

Specifying the exact version of the log crate (0.4.11) in Cargo.toml fixes this problem.

I'm assuming there is something funny happening when Cargo tries to resolve the dependencies.