Anticipate Lane Changes

include/engine/api/route_api.hpp

@@ -149,6 +149,7 @@ class RouteAPI : public BaseAPI
                                                               leg_geometry,
                                                               phantoms.source_phantom,
                                                               phantoms.target_phantom);
+                leg.steps = guidance::anticipateLaneChange(std::move(leg.steps));
                 leg_geometry = guidance::resyncGeometry(std::move(leg_geometry), leg.steps);
             }
 

include/engine/guidance/post_processing.hpp

@@ -43,6 +43,11 @@ std::vector<RouteStep> buildIntersections(std::vector<RouteStep> steps);
 // remove steps invalidated by post-processing
 std::vector<RouteStep> removeNoTurnInstructions(std::vector<RouteStep> steps);
 
+// Constrains lanes for multi-hop situations where lane changes depend on earlier ones.
+// Instead of forcing users to change lanes rapidly in a short amount of time,
+// we anticipate lane changes emitting only matching lanes early on.
+std::vector<RouteStep> anticipateLaneChange(std::vector<RouteStep> steps);
+
 // postProcess will break the connection between the leg geometry
 // for which a segment is supposed to represent exactly the coordinates
 // between routing maneuvers and the route steps itself.