Whatever is not async compatible

[bryanlarsen]

Following the instructions on the front page, I have

#[derive(Debug, Snafu)]
pub enum Error {
    #[snafu(whatever, display("{message}"))]
    Whatever {
        message: String,
        #[snafu(source(from(Box<dyn std::error::Error>, Some)))]
        source: Option<Box<dyn std::error::Error>>,
    },

This results in the error:

error: future cannot be sent between threads safely
  --> src/main.rs:45:61
   |
45 |       async fn get(&self, key: &str) -> Result<String, Error> {
   |  _____________________________________________________________^

...  |
   | |_____^ future created by async block is not `Send`
   |
   = help: the trait `Send` is not implemented for `(dyn snafu::Error + 'static)`
note: future is not `Send` as this value is used across an await
  --> src/main.rs:46:12

Removing the Whatever block from my error enum fixes the message. I wasn't using whatever! in my async function but it was annoying stripping it from the rest of my code.

I'm a rust newbie, so problem is likely PBKAC, but in case it might affect others I raised an issue. I've now purged whatever usage, so I'm fine with you closing the issue if that's appropriate.

[shepmaster]

When reporting an issue, it’s useful to produce an MRE.

When next I have time to investigate this issue, I’ll spend it on reproducing the problem. Then the next time i have, I can work on addressing the problem.

[shepmaster]

Should work if you adjust the trait object to be Send / Sync:

use snafu::{prelude::*, whatever};

#[derive(Debug, Snafu)]
pub enum Error {
    #[snafu(whatever, display("{message}"))]
    Whatever {
        message: String,
        #[snafu(source(from(Box<dyn std::error::Error + Send + Sync>, Some)))]
        source: Option<Box<dyn std::error::Error + Send + Sync>>,
    },
}

fn create() -> Result<(), Error> {
    whatever!("Broken")
}

fn main() {
    fn is_send(_: impl Send) {}
    is_send(create());
}

See also Sending trait objects between threads in Rust

[bryanlarsen]

Yes, that works. I don't know if it should be added to the documentation or not.

Thanks.

[hellow554]

I stumbled across this today as well.

It should definitly added to the guide at

snafu/src/lib.rs

Lines 167 to 185 in ba92e75

	//! You can combine the power of the [`whatever!`][] macro with an
	//! enum error type. This is great if you started out with
	//! [`Whatever`][] and are moving to a custom error type:
	//!
	//! ```rust
	//! use snafu::prelude::*;
	//!
	//! #[derive(Debug, Snafu)]
	//! enum Error {
	//! #[snafu(display("ID may not be less than 10, but it was {id}"))]
	//! InvalidId { id: u16 },
	//!
	//! #[snafu(whatever, display("{message}"))]
	//! Whatever {
	//! message: String,
	//! #[snafu(source(from(Box<dyn std::error::Error>, Some)))]
	//! source: Option<Box<dyn std::error::Error>>,
	//! },
	//! }

because that's where I (and everyone else?) copied the code from to use whatever along with other errors.

[shepmaster]

Feedback welcome on #331

[shepmaster]

Published in https://crates.io/crates/snafu/0.7.1