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#![no_std]
use thiserror::Error;
#[derive(Error, Debug)]
pub enum Error {
#[error("Error::E")]
E(#[from] SourceError),
}
#[derive(Error, Debug)]
#[error("SourceError {field}")]
pub struct SourceError {
pub field: i32,
}
#[cfg(test)]
mod tests {
use crate::{Error, SourceError};
use core::error::Error as _;
use core::fmt::{self, Write};
use core::mem;
struct Buf<'a>(&'a mut [u8]);
impl Write for Buf<'_> {
fn write_str(&mut self, s: &str) -> fmt::Result {
if s.len() <= self.0.len() {
let (out, rest) = mem::take(&mut self.0).split_at_mut(s.len());
out.copy_from_slice(s.as_bytes());
self.0 = rest;
Ok(())
} else {
Err(fmt::Error)
}
}
}
#[test]
fn test() {
let source = SourceError { field: -1 };
let error = Error::from(source);
let source = error
.source()
.unwrap()
.downcast_ref::<SourceError>()
.unwrap();
let mut msg = [b'~'; 17];
write!(Buf(&mut msg), "{error}").unwrap();
assert_eq!(msg, *b"Error::E~~~~~~~~~");
let mut msg = [b'~'; 17];
write!(Buf(&mut msg), "{source}").unwrap();
assert_eq!(msg, *b"SourceError -1~~~");
}
}
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