Adjust to review findings

include/extractor/guidance/mergable_road_detector.hpp

@@ -2,6 +2,7 @@
 #define OSRM_EXTRACTOR_GUIDANCE_MERGEABLE_ROADS
 
 #include "extractor/compressed_edge_container.hpp"
+#include "extractor/guidance/coordinate_extractor.hpp"
 #include "extractor/guidance/intersection.hpp"
 #include "extractor/guidance/turn_lane_types.hpp"
 #include "extractor/restriction_index.hpp"
@@ -47,7 +48,6 @@ class MergableRoadDetector
                          const RestrictionMap &node_restriction_map,
                          const std::unordered_set<NodeID> &barrier_nodes,
                          const guidance::TurnLanesIndexedArray &turn_lanes_data,
-                         const CoordinateExtractor &coordinate_extractor,
                          const util::NameTable &name_table,
                          const SuffixTable &street_name_suffix_table);
 
@@ -170,12 +170,13 @@ class MergableRoadDetector
     const RestrictionMap &node_restriction_map;
     const std::unordered_set<NodeID> &barrier_nodes;
     const guidance::TurnLanesIndexedArray &turn_lanes_data;
-    const CoordinateExtractor &coordinate_extractor;
 
     // name detection
     const util::NameTable &name_table;
     const SuffixTable &street_name_suffix_table;
 
+    const CoordinateExtractor coordinate_extractor;
+
     // limit for detecting circles / parallel roads
     const static double constexpr distance_to_extract = 150;
 };

include/extractor/intersection/intersection_analysis.hpp

@@ -57,6 +57,9 @@ convertToIntersectionView(const util::NodeBasedDynamicGraph &graph,
                           const IntersectionEdges &outgoing_edges,
                           const std::unordered_set<EdgeID> &merged_edges);
 
+// Check for restrictions/barriers and generate a list of valid and invalid turns present at
+// the node reached from `incoming_edge`. The resulting candidates have to be analyzed
+// for their actual instructions later on.
 guidance::IntersectionView
 getConnectedRoads(const util::NodeBasedDynamicGraph &graph,
                   const EdgeBasedNodeDataContainer &node_data_container,
@@ -67,6 +70,13 @@ getConnectedRoads(const util::NodeBasedDynamicGraph &graph,
                   const guidance::TurnLanesIndexedArray &turn_lanes_data,
                   const IntersectionEdge &incoming_edge);
 
+// Graph Compression cannot compress every setting. For example any barrier/traffic light cannot
+// be compressed. As a result, a simple road of the form `a ----- b` might end up as having an
+// intermediate intersection, if there is a traffic light in between. If we want to look farther
+// down a road, finding the next actual decision requires the look at multiple intersections.
+// Here we follow the road until we either reach a dead end or find the next intersection with
+// more than a single next road. This function skips over degree two nodes to find correct input
+// for getConnectedRoads.
 IntersectionEdge skipDegreeTwoNodes(const util::NodeBasedDynamicGraph &graph,
                                     IntersectionEdge road);
 }