523b9d9428
Eliminate any redundant, unobservable logic from the their default method implementations. The observable changes are that `Write::write_fmt` for both types now ignores the formatting arguments, so a user fmt impl which has side effects is not invoked, and `Write::write_all_vectored` for both types does not advance the borrowed buffers. Neither behavior is guaranteed by the docs and the latter is documented as unspecified. `Empty` is not marked as vectored, so that `Chain<Empty, _>` and `Chain<_, Empty>` are not forced to be vectored.
55 lines
1.7 KiB
Rust
55 lines
1.7 KiB
Rust
//@ run-pass
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//@ needs-unwind
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#![feature(io_error_uncategorized)]
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use std::fmt;
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use std::io::{self, Error, Write};
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use std::panic::catch_unwind;
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struct ErrorDisplay;
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impl fmt::Display for ErrorDisplay {
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fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
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Err(fmt::Error)
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}
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}
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struct ErrorWriter;
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const WRITER_ERROR: io::ErrorKind = io::ErrorKind::NotConnected;
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impl Write for ErrorWriter {
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fn write(&mut self, _buf: &[u8]) -> io::Result<usize> {
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Err(Error::new(WRITER_ERROR, "not connected"))
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}
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fn flush(&mut self) -> io::Result<()> { Ok(()) }
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}
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fn main() {
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// Test that an underlying error is propagated
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let res = write!(ErrorWriter, "abc");
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assert!(res.is_err(), "writer error did not propagate");
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// Test that the error from the formatter is detected.
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let res = catch_unwind(|| write!(vec![], "{} {} {}", 1, ErrorDisplay, "bar"));
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let err = res.expect_err("formatter error did not lead to panic").downcast::<&str>().unwrap();
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assert!(
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err.contains("formatting trait implementation returned an error"),
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"unexpected panic: {}", err
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);
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// Writer error when there's some string before the first `{}`
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let res = write!(ErrorWriter, "abc {}", ErrorDisplay);
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assert!(res.is_err(), "writer error did not propagate");
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assert_eq!(res.unwrap_err().kind(), WRITER_ERROR);
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// Formatter error when the `{}` comes first
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let res = catch_unwind(|| write!(ErrorWriter, "{} abc", ErrorDisplay));
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let err = res.expect_err("formatter error did not lead to panic").downcast::<&str>().unwrap();
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assert!(
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err.contains("formatting trait implementation returned an error"),
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"unexpected panic: {}", err
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);
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}
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