check empty name string in turn collapsing

include/engine/api/route_api.hpp

@@ -173,7 +173,7 @@ class RouteAPI : public BaseAPI
 
                 guidance::trimShortSegments(steps, leg_geometry);
                 leg.steps = guidance::handleRoundabouts(std::move(steps));
-                leg.steps = guidance::collapseTurnInstructions(std::move(leg.steps));
+                leg.steps = guidance::collapseTurnInstructions(std::move(leg.steps), facade);
                 leg.steps = guidance::anticipateLaneChange(std::move(leg.steps));
                 leg.steps = guidance::buildIntersections(std::move(leg.steps));
                 leg.steps = guidance::suppressShortNameSegments(std::move(leg.steps));

include/engine/guidance/collapse_scenario_detection.hpp

@@ -36,7 +36,10 @@ bool isStaggeredIntersection(const RouteStepIterator step_prior_to_intersection,
 // a - > x
 bool isUTurn(const RouteStepIterator step_prior_to_intersection,
              const RouteStepIterator step_entering_intersection,
-             const RouteStepIterator step_leaving_intersection);
+             const RouteStepIterator step_leaving_intersection,
+             const std::string &step_prior_name,
+             const std::string &step_entering_name,
+             const std::string &step_leaving_name);
 
 // detect oscillating names where a name switch A->B->A occurs. This is often the case due to
 // bridges or tunnels. Any such oszillation is not supposed to show up

include/engine/guidance/collapse_turns.hpp

@@ -1,5 +1,6 @@
 #ifndef OSRM_ENGINE_GUIDANCE_COLLAPSE_HPP
 
+#include "engine/datafacade/datafacade_base.hpp"
 #include "engine/guidance/route_step.hpp"
 #include "util/attributes.hpp"
 
@@ -19,7 +20,8 @@ namespace guidance
 // Collapsing such turns into a single turn instruction, we give a clearer
 // set of instructionst that is not cluttered by unnecessary turns/name changes.
 OSRM_ATTR_WARN_UNUSED
-std::vector<RouteStep> collapseTurnInstructions(std::vector<RouteStep> steps);
+std::vector<RouteStep> collapseTurnInstructions(std::vector<RouteStep> steps,
+                                                const datafacade::BaseDataFacade &facade);
 
 // A combined turn is a set of two instructions that actually form a single turn, as far as we
 // perceive it. A u-turn consisting of two left turns is one such example. But there are also lots