pub(super) fn package_ixs<'g, 'a, B>(
        &'g self,
        package_ids: impl IntoIterator<Item = &'a PackageId>,
    ) -> Result<B, Error>
    where
        B: iter::FromIterator<NodeIndex<PackageIx>>,
    {
        package_ids
            .into_iter()
            .map(|package_id| self.package_ix(package_id))
            .collect()
    }
Maps an iterator of package IDs to their internal graph node indexes.
guppy/src/graph/graph_impl.rs