Function line_column_to_byte 

pub fn line_column_to_byte(
    source: &str,
    line_starts: &[usize],
    pos: LineColumn,
) -> usize

Converts a LineColumn (1-based line, 0-based character column) to a byte offset in source, using line_starts (from line_start_byte_offsets).

• Precondition: line_starts was built from exactly source, and pos.line - 1 is in range.

• Complexity: O(k) in pos.column.