if prev_hi.line == cur_lo.line {
push_trailing(&mut buf, prev_line.as_ref(), &prev_hi, Some(&cur_lo));
} else {
push_trailing(&mut buf, prev_line.as_ref(), &prev_hi, None);
// push lines between the previous and current span (if any)
for idx in prev_hi.line..(cur_lo.line - 1) {
if prev_hi.line == cur_lo.line {
push_trailing(&mut buf, prev_line.as_ref(), &prev_hi, Some(&cur_lo));
} else {
push_trailing(&mut buf, prev_line.as_ref(), &prev_hi, None);
// push lines between the previous and current span (if any)
for idx in prev_hi.line..(cur_lo.line - 1) {