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#![cfg(feature="std")]
use snafu::prelude::*;
use std::{
fs, io,
path::{Path, PathBuf},
};
#[derive(Debug, Snafu)]
enum Error {
#[snafu(display("Could not open config file at {}: {}", filename.display(), source))]
OpenConfig {
filename: PathBuf,
source: io::Error,
},
#[snafu(display("Could not open config file at {}", source))]
SaveConfig { source: io::Error },
#[snafu(display("User ID {} is invalid", user_id))]
InvalidUser { user_id: i32 },
#[snafu(display("No user available"))]
MissingUser,
}
type Result<T, E = Error> = std::result::Result<T, E>;
const CONFIG_FILENAME: &str = "/tmp/config";
fn example(root: impl AsRef<Path>, user_id: Option<i32>) -> Result<()> {
let root = root.as_ref();
let filename = &root.join(CONFIG_FILENAME);
let config = fs::read(filename).context(OpenConfigSnafu { filename })?;
let _user_id = match user_id {
None => MissingUserSnafu.fail()?,
Some(user_id) if user_id != 42 => InvalidUserSnafu { user_id }.fail()?,
Some(user_id) => user_id,
};
fs::write(filename, config).context(SaveConfigSnafu)?;
Ok(())
}
#[test]
fn implements_error() {
fn check<T: std::error::Error>() {}
check::<Error>();
example("/some/directory/that/does/not/exist", None).unwrap_err();
}
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