fix collapsing into uturns, that aren't u-turns

features/guidance/collapse-detail.feature

@@ -174,5 +174,5 @@ Feature: Collapse
             | fe    | service   |      |
 
         When I route I should get
-            | waypoints | route  | turns                    |
-            | c,e       | road,, | depart,turn uturn,arrive |
+            | waypoints | route   | turns                               |
+            | c,e       | road,,, | depart,turn right,turn right,arrive |

include/engine/guidance/collapsing_utility.hpp

@@ -4,6 +4,7 @@
 #include "extractor/guidance/turn_instruction.hpp"
 #include "engine/guidance/route_step.hpp"
 #include "util/attributes.hpp"
+#include "util/bearing.hpp"
 #include "util/guidance/name_announcements.hpp"
 
 #include <boost/range/algorithm_ext/erase.hpp>
@@ -189,6 +190,27 @@ inline std::vector<RouteStep> removeNoTurnInstructions(std::vector<RouteStep> st
     return steps;
 }
 
+inline double totalTurnAngle(const RouteStep &entry_step, const RouteStep &exit_step)
+{
+    if (entry_step.geometry_begin > exit_step.geometry_begin)
+        return totalTurnAngle(exit_step, entry_step);
+
+    const auto exit_intersection = exit_step.intersections.front();
+    const auto entry_intersection = entry_step.intersections.front();
+    if ((exit_intersection.out >= exit_intersection.bearings.size()) ||
+        (entry_intersection.in >= entry_intersection.bearings.size()))
+        return entry_intersection.bearings[entry_intersection.out];
+
+    const auto exit_step_exit_bearing = exit_intersection.bearings[exit_intersection.out];
+    const auto entry_step_entry_bearing =
+        util::bearing::reverse(entry_intersection.bearings[entry_intersection.in]);
+
+    const double total_angle =
+        util::bearing::angleBetween(entry_step_entry_bearing, exit_step_exit_bearing);
+
+    return total_angle;
+}
+
 } /* namespace guidance */
 } /* namespace engine */
 } /* namespace osrm */

src/engine/guidance/collapse_scenario_detection.cpp

@@ -306,7 +306,12 @@ bool suppressedStraightBetweenTurns(const RouteStepIterator step_entering_inters
          hasTurnType(*step_leaving_intersection, TurnType::Continue) ||
          hasTurnType(*step_leaving_intersection, TurnType::OnRamp));
 
-    return both_short_enough && similar_length && correct_types;
+    const auto total_angle =
+        totalTurnAngle(*step_entering_intersection, *step_leaving_intersection);
+    const auto total_angle_is_not_uturn =
+        (total_angle > NARROW_TURN_ANGLE) && (total_angle < 360 - NARROW_TURN_ANGLE);
+
+    return both_short_enough && similar_length && correct_types && total_angle_is_not_uturn;
 }
 
 bool maneuverSucceededByNameChange(const RouteStepIterator step_entering_intersection,