static assert to prevent remove_vertex with vecS label storage that would invalidate all label-to-vertex mappings after the erased position

Author: Becheler

include/boost/graph/labeled_graph.hpp

@@ -501,6 +501,13 @@ class labeled_graph : protected labeled_graph_types< Graph, Label, Selector >
     /** Remove the vertex with the given label. */
     void remove_vertex(Label const& l)
     {
+        static_assert(
+            !is_same<
+                typename graph_detail::container_traits<map_type>::category,
+                graph_detail::vector_tag
+            >::value,
+            "remove_vertex is not supported with vecS label storage: erasing from the underlying vector invalidates all label-to-vertex mappings after the erased position"
+        );
         return graph_detail::remove_labeled_vertex(_map, _graph, l);
     }
 
@@ -642,6 +649,13 @@ class labeled_graph< Graph*, Label, Selector >
     /** Remove the vertex with the given label. */
     void remove_vertex(Label const& l)
     {
+        static_assert(
+            !is_same<
+                typename graph_detail::container_traits<map_type>::category,
+                graph_detail::vector_tag
+            >::value,
+            "remove_vertex is not supported with vecS label storage: erasing from the underlying vector invalidates all label-to-vertex mappings after the erased position"
+        );
         return boost::remove_vertex(vertex(l), *_graph);
     }
 

test/Jamfile.v2

@@ -31,7 +31,10 @@ alias graph_test_regular :
     # and implementation of graph data structures and adaptors.
     [ run test_graphs.cpp ]
     [ run index_graph.cpp ]     # TODO: Make this part of the test_graphs framework
+
+    [ compile-fail concept_tests/labeled_graph/compile_fail_remove_vertex_vecS.cpp ]
     [ run labeled_graph.cpp ]
+
     [ run finish_edge_bug.cpp ]
 
     [ run transitive_closure_test.cpp /boost/timer//boost_timer ]

test/concept_tests/labeled_graph/compile_fail_remove_vertex_vecS.cpp

@@ -0,0 +1,29 @@
+//=======================================================================
+// Copyright 2026
+// Author: Becheler Arnaud
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//=======================================================================
+
+// This file must FAIL to compile.
+// remove_vertex is not supported when the label map uses vecS storage because 
+// erasing from the underlying vector invalidates all label-to-vertex mappings 
+// after the erased position.
+
+#include <boost/graph/adjacency_list.hpp>
+#include <boost/graph/labeled_graph.hpp>
+
+int main()
+{
+    typedef boost::labeled_graph<
+        boost::adjacency_list<boost::listS, boost::listS, boost::directedS>,
+        unsigned,
+        boost::vecS
+    > Graph;
+
+    Graph g;
+    g.add_vertex(0u);
+    g.remove_vertex(0u);  // should trigger static_assert
+}

test/labeled_graph.cpp

@@ -234,6 +234,8 @@ void test_remove_vertex_suite(Label l1, Label l2, Label l3)
         g.add_vertex(l3);
         BOOST_ASSERT(num_vertices(g) == 3);
 
+        // TODO: this is broken when backed by vecS + unsigned because
+        // erasing middle element invalidates others.
         g.remove_vertex(l2);
         BOOST_ASSERT(num_vertices(g) == 2);
         BOOST_ASSERT(g.vertex(l2) == LabeledGraph::null_vertex());
@@ -384,7 +386,8 @@ void test_remove_vertex_all_types()
     >("a", "b", "c");
 
     // adjacency_list + vecS not supported (unstable removal would require remapping the map)
-    
+    // TODO: fix or not but document
+
     // adjacency_list + listS (stable removal)
     test_remove_vertex_suite<
         labeled_graph<adjacency_list<listS, listS, directedS>, string, mapS>
@@ -394,10 +397,10 @@ void test_remove_vertex_all_types()
         labeled_graph<adjacency_list<listS, listS, undirectedS>, string, mapS>
     >("a", "b", "c");
 
-    // unsigned labels (vecS)
-    test_remove_vertex_suite<
-        labeled_graph<adjacency_list<listS, listS, directedS>, unsigned, vecS>
-    >(0u, 1u, 2u);
+    // unsigned labels (vecS) : should not compile because static assert prevents removing vertices now
+    // test_remove_vertex_suite<
+    //     labeled_graph<adjacency_list<listS, listS, directedS>, unsigned, vecS>
+    // >(0u, 1u, 2u);
 
     // Pointer specialization: 
     // temporarily attach labels to it without copying.
@@ -417,9 +420,9 @@ void test_remove_vertex_all_types()
         labeled_graph<directed_graph<>*, string, hash_mapS>
     >("a", "b", "c");
 
-    // unsigned labels
-    test_remove_vertex_suite_ptr_variant<
-        adjacency_list<listS, listS, directedS>,
-        labeled_graph<adjacency_list<listS, listS, directedS>*, unsigned, vecS>
-    >(0u, 1u, 2u);
+    // unsigned labels (vecS) : should not compile because static assert prevents removing vertices now
+    // test_remove_vertex_suite_ptr_variant<
+    //     adjacency_list<listS, listS, directedS>,
+    //     labeled_graph<adjacency_list<listS, listS, directedS>*, unsigned, vecS>
+    // >(0u, 1u, 2u);
 }