handle stronger merge cases as well

include/extractor/guidance/intersection_generator.hpp

@@ -48,11 +48,12 @@ class IntersectionGenerator
     // from `from_node` via `via_eid`
     // The resulting candidates have to be analysed for their actual instructions later on.
     OSRM_ATTR_WARN_UNUSED
-    Intersection getConnectedRoads(const NodeID from_node, const EdgeID via_eid) const;
+    Intersection GetConnectedRoads(const NodeID from_node, const EdgeID via_eid) const;
 
     // check if two indices in an intersection can be seen as a single road in the perceived
     // intersection representation
-    bool canMerge(const Intersection &intersection,
+    bool CanMerge(const NodeID intersection_node,
+                  const Intersection &intersection,
                   std::size_t first_index,
                   std::size_t second_index) const;
 
@@ -68,7 +69,8 @@ class IntersectionGenerator
     // The treatment results in a straight turn angle of 180º rather than a turn angle of approx
     // 160
     OSRM_ATTR_WARN_UNUSED
-    Intersection mergeSegregatedRoads(Intersection intersection) const;
+    Intersection MergeSegregatedRoads(const NodeID intersection_node,
+                                      Intersection intersection) const;
 
     // The counterpiece to mergeSegregatedRoads. While we can adjust roads that split up at the
     // intersection itself, it can also happen that intersections are connected to joining roads.
@@ -81,8 +83,20 @@ class IntersectionGenerator
     //       b
     //
     // for the local view of b at a.
-    Intersection adjustForJoiningRoads(const NodeID node_at_intersection,
+    OSRM_ATTR_WARN_UNUSED
+    Intersection AdjustForJoiningRoads(const NodeID node_at_intersection,
                                        Intersection intersection) const;
+
+    // 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.
+    inline Intersection GetActualNextIntersection(const NodeID starting_node,
+                                                  const EdgeID via_edge,
+                                                  NodeID *resulting_from_node,
+                                                  EdgeID *resulting_via_edge) const;
 };
 
 } // namespace guidance