Function diff_index_to_tree 

pub fn diff_index_to_tree(
    odb: &Odb,
    index: &Index,
    tree_oid: Option<&ObjectId>,
) -> Result<Vec<DiffEntry>>

Compare the index against a tree (usually HEAD’s tree).

This shows “staged” changes — what would be committed.

Parameters

• odb — object database.
• index — the current index.
• tree_oid — the tree to compare against (e.g. HEAD’s tree), or None for comparison against an empty tree (initial commit).

Errors

Returns errors from ODB reads.