Function diff 

pub fn diff<B: Blockstore + ?Sized>(
    store: &B,
    root_a: &Cid,
    root_b: &Cid,
) -> Result<Vec<DiffEntry>, Error>

Compute the difference between the two Prolly trees a and b.

Returns every added / removed / changed entry, in ascending key order.

Errors

Propagates store and codec errors.