Function diff_line_counts 

pub fn diff_line_counts(
    old_bytes: &[u8],
    new_bytes: &[u8],
) -> Option<(usize, usize)>

Added / deleted line counts between two blobs, from the same Myers edit script the unified patch uses. None when either side is binary — matching Git’s heuristic of a NUL byte within the first 8000 bytes (independent of UTF-8 validity), so diff --stat renders Bin … for exactly the blobs Git would.

Used by diff --stat; kept here so the stat counts always agree with the +/- lines text_patch would emit for the same blobs. Lines are split on \n bytes, so the counts hold for any non-binary blob, including non-UTF-8 text.