Function diff_workspaces_with 

pub fn diff_workspaces_with(
    old: &[Package],
    old_system: Option<&System>,
    new: &[Package],
    new_system: Option<&System>,
    context: &[Package],
    encodings: &[&str],
) -> DiffReport

diff_workspaces, judged for encodings (diff_refs_with).