pub fn quote<'a>(&self, mut in_bytes: &'a [u8]) -> Result<Cow<'a, [u8]>, QuoteError> {
        if in_bytes.is_empty() {
            // Empty string.  Special case that isn't meaningful as only part of a word.
            return Ok(b"''"[..].into());
        }
        if !self.allow_nul && in_bytes.iter().any(|&b| b == b'\0') {
            return Err(QuoteError::Nul);
        }
        let mut out: Vec<u8> = Vec::new();
        while !in_bytes.is_empty() {
            // Pick a quoting strategy for some prefix of the input.  Normally this will cover the
            // entire input, but in some case we might need to divide the input into multiple chunks
            // that are quoted differently.
            let (cur_len, strategy) = quoting_strategy(in_bytes);
            if cur_len == in_bytes.len() && strategy == QuotingStrategy::Unquoted && out.is_empty() {
                // Entire string can be represented unquoted.  Reuse the allocation.
                return Ok(in_bytes.into());
            }
            let (cur_chunk, rest) = in_bytes.split_at(cur_len);
            assert!(rest.len() < in_bytes.len()); // no infinite loop
            in_bytes = rest;
            append_quoted_chunk(&mut out, cur_chunk, strategy);
        }
        Ok(out.into())
    }

    fn parse_word(&mut self, mut ch: u8) -> Option<Vec<u8>> {
        let mut result: Vec<u8> = Vec::new();
        loop {
            match ch as char {
                '"' => if let Err(()) = self.parse_double(&mut result) {
                    self.had_error = true;
                    return None;
                },
                '\'' => if let Err(()) = self.parse_single(&mut result) {
                    self.had_error = true;
                    return None;
                },
                '\\' => if let Some(ch2) = self.next_char() {
                    if ch2 != '\n' as u8 { result.push(ch2); }
                } else {
                    self.had_error = true;
                    return None;
                },
                ' ' | '\t' | '\n' => { break; },
                _ => { result.push(ch as u8); },
            }
            if let Some(ch2) = self.next_char() { ch = ch2; } else { break; }
        }
        Some(result)
    }

    fn parse_double(&mut self, result: &mut Vec<u8>) -> Result<(), ()> {
        loop {
            if let Some(ch2) = self.next_char() {
                match ch2 as char {
                    '\\' => {
                        if let Some(ch3) = self.next_char() {
                            match ch3 as char {
                                // \$ => $
                                '$' | '`' | '"' | '\\' => { result.push(ch3); },
                                // \<newline> => nothing
                                '\n' => {},
                                // \x => =x
                                _ => { result.push('\\' as u8); result.push(ch3); }
                            }
                        } else {
                            return Err(());
                        }
                    },
                    '"' => { return Ok(()); },
                    _ => { result.push(ch2); },
                }
            } else {
                return Err(());
            }
        }
    }

    fn parse_single(&mut self, result: &mut Vec<u8>) -> Result<(), ()> {
        loop {
            if let Some(ch2) = self.next_char() {
                match ch2 as char {
                    '\'' => { return Ok(()); },
                    _ => { result.push(ch2); },
                }
            } else {
                return Err(());
            }
        }
    }

    fn next_char(&mut self) -> Option<u8> {
        let res = self.in_iter.next().copied();
        if res == Some(b'\n') { self.line_no += 1; }
        res
    }
}

impl<'a> Iterator for Shlex<'a> {
    type Item = Vec<u8>;
    fn next(&mut self) -> Option<Self::Item> {
        if let Some(mut ch) = self.next_char() {
            // skip initial whitespace
            loop {
                match ch as char {
                    ' ' | '\t' | '\n' => {},
                    '#' => {
                        while let Some(ch2) = self.next_char() {
                            if ch2 as char == '\n' { break; }
                        }
                    },
                    _ => { break; }
                }
                if let Some(ch2) = self.next_char() { ch = ch2; } else { return None; }
            }
            self.parse_word(ch)
        } else { // no initial character
            None
        }
    }

}

#![cfg_attr(not(feature = "std"), no_std)]

extern crate alloc;

    type Item = String;
    fn next(&mut self) -> Option<String> {
        self.0.next().map(|byte_word| {
            // Safety: given valid UTF-8, bytes::Shlex will always return valid UTF-8.
            unsafe { String::from_utf8_unchecked(byte_word) }
        })

    pub fn join<'a, I: IntoIterator<Item = &'a str>>(&self, words: I) -> Result<String, QuoteError> {
        // Safety: given valid UTF-8, bytes::join() will always return valid UTF-8.
        self.inner.join(words.into_iter().map(|s| s.as_bytes()))
            .map(|bytes| unsafe { String::from_utf8_unchecked(bytes) })
    }

    /// Given a single word, return a string suitable to encode it as a shell argument.
    pub fn quote<'a>(&self, in_str: &'a str) -> Result<Cow<'a, str>, QuoteError> {
        Ok(match self.inner.quote(in_str.as_bytes())? {
            Cow::Borrowed(out) => {
                // Safety: given valid UTF-8, bytes::quote() will always return valid UTF-8.
                unsafe { core::str::from_utf8_unchecked(out) }.into()
            }
            Cow::Owned(out) => {
                // Safety: given valid UTF-8, bytes::quote() will always return valid UTF-8.
                unsafe { String::from_utf8_unchecked(out) }.into()
            }
        })
    }