Fix Bellman with visitor

include/graph/algorithm/bellman_ford_shortest_paths.hpp

@@ -164,11 +164,11 @@ requires convertible_to<range_value_t<Sources>, vertex_id_t<G>> &&      //
     }
     distances[static_cast<size_t>(source)] = zero; // mark source as discovered
     if constexpr (has_on_discover_vertex<G, Visitor>) {
-      visitor.on_discover_vertex({source, vertex_value(g, source)});
+      visitor.on_discover_vertex({source, *find_vertex(g, source)});
     }
   }
 
-  // Evalute the shortest paths
+  // Evaluate the shortest paths
   bool at_least_one_edge_relaxed = false;
   for (id_type k = 0; k < N; ++k) {
     at_least_one_edge_relaxed = false;

tests/bellman_shortest_paths_tests.cpp

@@ -714,3 +714,23 @@ TEST_CASE("Bellman-Ford's General Shortest Distances", "[csv][vofl][shortest][di
   optional<vertex_id_t<G>> cycle_vertex_id = bellman_ford_shortest_distances(
         g, frankfurt_id, distance, weight, visitor, std::less<Distance>(), std::plus<Distance>());
 }
+
+class Visitor
+{
+  using G = std::vector<std::vector<int>>;
+  using VD = graph::vertex_info<graph::vertex_id_t<G>, graph::vertex_reference_t<G>, void>;    
+
+public:   
+  void on_discover_vertex(VD const& v) {}
+};
+
+TEST_CASE("Bellman-Ford compiles with a visitor", "[shortest][distances][bellman][general]") {
+  init_console();
+
+  std::vector<std::vector<int>> g = {{1}, {0}};
+  std::vector<double> distances(g.size());
+  std::vector<int> predecessor(g.size());  
+  auto one = [](auto&&) { return 1.0; };
+
+  (void)graph::bellman_ford_shortest_paths(g, 0, distances, predecessor, one, Visitor{});
+}