pub(super) fn edge_ix_to_link(&self, edge_ix: EdgeIndex<PackageIx>) -> PackageLink {
        let (source_ix, target_ix) = self
            .dep_graph
            .edge_endpoints(edge_ix)
            .expect("valid edge ix");
        PackageLink::new(
            self,
            source_ix,
            target_ix,
            edge_ix,
            self.dep_graph.edge_weight(edge_ix),
        )
    }
Maps an edge index to a dependency link.
guppy/src/graph/graph_impl.rs