fix: global_to_local asserts on edges not in the subgraph, mirroring the vertex overload

Author: Becheler

include/boost/graph/subgraph.hpp

@@ -207,12 +207,14 @@ template < typename Graph > class subgraph
 
     vertex_descriptor global_to_local(vertex_descriptor u_global) const
     {
-        vertex_descriptor u_local;
-        bool in_subgraph;
         if (is_root())
             return u_global;
+        vertex_descriptor u_local;
+        bool in_subgraph;
         boost::tie(u_local, in_subgraph) = this->find_vertex(u_global);
-        BOOST_ASSERT(in_subgraph == true);
+        BOOST_ASSERT_MSG(in_subgraph,
+            "global_to_local: vertex is not in this subgraph. "
+            "Use find_vertex() to check membership first.");
         return u_local;
     }
 
@@ -225,10 +227,15 @@ template < typename Graph > class subgraph
 
     edge_descriptor global_to_local(edge_descriptor e_global) const
     {
-        return is_root() ? e_global
-                         : (*m_local_edge.find(
-                                get(get(edge_index, root().m_graph), e_global)))
-                               .second;
+        if (is_root())
+            return e_global;
+        edge_descriptor e_local;
+        bool in_subgraph;
+        boost::tie(e_local, in_subgraph) = this->find_edge(e_global);
+        BOOST_ASSERT_MSG(in_subgraph,
+            "global_to_local: edge is not in this subgraph. "
+            "Use find_edge() to check membership first.");
+        return e_local;
     }
 
     // Is vertex u (of the root graph) contained in this subgraph?