Function content_diff_index 

pub fn content_diff_index(
    tree_diff: &TreeDiff,
    index: &WorkspaceIndex,
    workspace: &Path,
    void_dir: &Path,
    staged_key: &SecretKey,
) -> Result<Vec<ContentDiff>>

Content diff for index vs workspace (unstaged changes).

Old content: staged blob (by content hash from index). New content: workspace file on disk.