Function compute_diff 

pub fn compute_diff<F>(
    old: &str,
    new: &str,
    options: DiffOptions<'_>,
    formatter: F,
) -> DiffBundle
where
    F: FnOnce(&[DiffHunk], &DiffOptions<'_>) -> String,

Computes a structured diff and passes non-empty hunks to a formatter.

Contract

• Requires: nothing (any &str pair accepted).
• Ensures: identical inputs yield an empty bundle without invoking formatter; otherwise the bundle carries the computed hunks.