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    #![allow(dead_code)]

    use crate::fmt::{Formatter, Result, Write};
    use core::str::lossy::{Utf8Lossy, Utf8LossyChunk};

    pub fn debug_fmt_bytestring(slice: &[u8], f: &mut Formatter<'_>) -> Result {
        // Writes out a valid unicode string with the correct escape sequences
        fn write_str_escaped(f: &mut Formatter<'_>, s: &str) -> Result {
            for c in s.chars().flat_map(|c| c.escape_debug()) {
                f.write_char(c)?
            }
            Ok(())
        }

        f.write_str("\"")?;
        for Utf8LossyChunk { valid, broken } in Utf8Lossy::from_bytes(slice).chunks() {
            write_str_escaped(f, valid)?;
            for b in broken {
                write!(f, "\\x{:02X}", b)?;
            }
        }
        f.write_str("\"")
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        use crate::fmt::{Debug, Formatter, Result};

        #[test]
        fn smoke() {
            struct Helper<'a>(&'a [u8]);

            impl Debug for Helper<'_> {
                fn fmt(&self, f: &mut Formatter<'_>) -> Result {
                    debug_fmt_bytestring(self.0, f)
                }
            }

            let input = b"\xF0hello,\tworld";
            let expected = r#""\xF0hello,\tworld""#;
            let output = format!("{:?}", Helper(input));

            assert!(output == expected);
        }
    }