planning: fix stop reason of stopping for head vehicles

modules/planning/tasks/traffic_decider/front_vehicle.cc

@@ -377,7 +377,15 @@ void FrontVehicle::MakeStopDecision(
 
       ObjectDecisionType stop;
       auto stop_decision = stop.mutable_stop();
-      stop_decision->set_reason_code(StopReasonCode::STOP_REASON_OBSTACLE);
+      if (obstacle_type == PerceptionObstacle::UNKNOWN_MOVABLE ||
+          obstacle_type == PerceptionObstacle::BICYCLE ||
+          obstacle_type == PerceptionObstacle::VEHICLE) {
+        stop_decision->set_reason_code(
+            StopReasonCode::STOP_REASON_HEAD_VEHICLE);
+      } else {
+        stop_decision->set_reason_code(
+            StopReasonCode::STOP_REASON_OBSTACLE);
+      }
       stop_decision->set_distance_s(-stop_distance);
       stop_decision->set_stop_heading(stop_heading);
       stop_decision->mutable_stop_point()->set_x(stop_point.x());

modules/planning/testdata/sunnyvale_big_loop_test/result_bypass_parked_bus_0.pb.txt

@@ -849,7 +849,7 @@ trajectory_point {
 decision {
   main_decision {
     stop {
-      reason_code: STOP_REASON_OBSTACLE
+      reason_code: STOP_REASON_HEAD_VEHICLE
       reason: "stop by 6211"
       stop_point {
         x: 586575.19098307879
@@ -865,7 +865,7 @@ decision {
       perception_id: 6211
       object_decision {
         stop {
-          reason_code: STOP_REASON_OBSTACLE
+          reason_code: STOP_REASON_HEAD_VEHICLE
           distance_s: -6
           stop_point {
             x: 586575.19098307879