fn match_blanks_before(
current: (LineNumber, LineNumber),
lhs_lines: &[&str],
rhs_lines: &[&str],
) -> Vec<(Option<LineNumber>, Option<LineNumber>)>fn match_blanks_before(
current: (LineNumber, LineNumber),
lhs_lines: &[&str],
rhs_lines: &[&str],
) -> Vec<(Option<LineNumber>, Option<LineNumber>)>