Function disambiguated_hunk_id 

pub fn disambiguated_hunk_id(
    file_path: &str,
    lines: &[DiffLine],
    seen: &mut HashMap<HunkId, usize>,
) -> HunkId

hunk_id for one hunk of a file whose other hunks are being assigned ids through the same seen map: each distinct content gets occurrence 0 the first time and counts up from there, so two identical hunks in one file never collide.