log shortcuts which have the same start/end node

CHANGELOG.md

@@ -103,6 +103,7 @@
    * ADDED: return isotile grid as geotiff  [#4594](https://github.com/valhalla/valhalla/pull/4594)
    * ADDED: `ignore_non_vehicular_restrictions` parameter for truck costing [#4606](https://github.com/valhalla/valhalla/pull/4606)
    * UPDATED: tz database to 2024a [#4643](https://github.com/valhalla/valhalla/pull/4643)
+   * ADDED: log shortcuts which have the same start/end node [4632](https://github.com/valhalla/valhalla/pull/4632)
 
 ## Release Date: 2023-05-11 Valhalla 3.4.0
 * **Removed**

src/mjolnir/shortcutbuilder.cc

@@ -360,6 +360,7 @@
   uint32_t shortcut = 0;
   uint32_t shortcut_count = 0;
   uint32_t total_edge_count = 0;
+  std::unordered_set<uint64_t> end_nodes; // detect shortcuts with same start/end node
   GraphId edge_id(start_node.tileid(), start_node.level(), edge_index);
   for (uint32_t i = 0; i < edge_count; i++, ++edge_id) {
     // Skip transit connection edges.
@@ -547,13 +548,22 @@
       tilebuilder.directededges().emplace_back(std::move(newedge));
       shortcut_count++;
       shortcut++;
+      if (!end_nodes.insert(newedge.endnode()).second) {
+        [[maybe_unused]] PointLL start_ll = tile->get_node_ll(start_node);
+        [[maybe_unused]] PointLL end_ll = tile->get_node_ll(end_node);
+        LOG_WARN("Node " + std::to_string(start_node) +
+                 " has outbound shortcuts with same start/end nodes starting at node at LL = " +
+                 std::to_string(start_ll.lat()) + "," + std::to_string(start_ll.lng()) +
+                 " and ending at node at LL = " + std::to_string(end_ll.lat()) + "," +
+                 std::to_string(end_ll.lng()));
+      }
     }
   }
 
   // Log a warning (with the node lat,lon) if the max number of shortcuts from a node
   // is exceeded. This is not serious (see NOTE above) but good to know where it occurs.
   if (shortcut_count > kMaxShortcutsFromNode) {
-    PointLL ll = tile->get_node_ll(start_node);
+    [[maybe_unused]] PointLL ll = tile->get_node_ll(start_node);
     LOG_WARN("Exceeding max shortcut edges from a node at LL = " + std::to_string(ll.lat()) + "," +
              std::to_string(ll.lng()));
   }