swc/crates/swc_common/src/iter.rs

/// Copied from https://users.rust-lang.org/t/iterator-need-to-identify-the-last-element/8836/3
pub trait IdentifyLast: Iterator + Sized {
    fn identify_last(self) -> Iter<Self>;
}

impl<It> IdentifyLast for It
where
    It: Iterator,
{
    fn identify_last(mut self) -> Iter<Self> {
        let e = self.next();
        Iter {
            iter: self,
            buffer: e,
        }
    }
}

pub struct Iter<It>
where
    It: Iterator,
{
    iter: It,
    buffer: Option<It::Item>,
}

impl<It> Iterator for Iter<It>
where
    It: Iterator,
{
    type Item = (bool, It::Item);

    fn next(&mut self) -> Option<Self::Item> {
        match self.buffer.take() {
            None => None,
            Some(e) => match self.iter.next() {
                None => Some((true, e)),
                Some(f) => {
                    self.buffer = Some(f);
                    Some((false, e))
                }
            },
        }
    }
}