fn merge_in_opposite_lines(
matched_lines: &[(Option<LineNumber>, Option<LineNumber>)],
novel_opposite_lines: &[LineNumber],
) -> Vec<(Option<LineNumber>, Option<LineNumber>)>fn merge_in_opposite_lines(
matched_lines: &[(Option<LineNumber>, Option<LineNumber>)],
novel_opposite_lines: &[LineNumber],
) -> Vec<(Option<LineNumber>, Option<LineNumber>)>