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//! Tests that errors from both the writer (`Write::write`) and formatter (`Display::fmt`)
//! are correctly propagated: writer errors return `Err`, formatter errors cause panics.
//@ run-pass
//@ needs-unwind
#![feature(io_error_uncategorized)]
use std::fmt;
use std::io::{self, Error, Write};
use std::panic::catch_unwind;
struct ErrorDisplay;
impl fmt::Display for ErrorDisplay {
fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
Err(fmt::Error)
}
}
struct ErrorWriter;
const WRITER_ERROR: io::ErrorKind = io::ErrorKind::NotConnected;
impl Write for ErrorWriter {
fn write(&mut self, _buf: &[u8]) -> io::Result<usize> {
Err(Error::new(WRITER_ERROR, "not connected"))
}
fn flush(&mut self) -> io::Result<()> {
Ok(())
}
}
fn main() {
// Test that an underlying error is propagated
let res = write!(ErrorWriter, "abc");
assert!(res.is_err(), "writer error did not propagate");
// Test that the error from the formatter is detected.
let res = catch_unwind(|| write!(vec![], "{} {} {}", 1, ErrorDisplay, "bar"));
let err = res.expect_err("formatter error did not lead to panic").downcast::<&str>().unwrap();
assert!(
err.contains("formatting trait implementation returned an error"),
"unexpected panic: {}",
err
);
// Writer error when there's some string before the first `{}`
let res = write!(ErrorWriter, "abc {}", ErrorDisplay);
assert!(res.is_err(), "writer error did not propagate");
assert_eq!(res.unwrap_err().kind(), WRITER_ERROR);
// Formatter error when the `{}` comes first
let res = catch_unwind(|| write!(ErrorWriter, "{} abc", ErrorDisplay));
let err = res.expect_err("formatter error did not lead to panic").downcast::<&str>().unwrap();
assert!(
err.contains("formatting trait implementation returned an error"),
"unexpected panic: {}",
err
);
}
|
