chore(path_optimizer): add warn msg for exceptional behavior (autowarefoundation#9033)

Signed-off-by: Yuki Takagi <yuki.takagi@tier4.jp>

Author: yuki-takagi-66

planning/autoware_path_optimizer/src/mpt_optimizer.cpp

@@ -477,8 +477,13 @@ std::vector<TrajectoryPoint> MPTOptimizer::optimizeTrajectory(const PlannerData
 
   const auto get_prev_optimized_traj_points = [&]() {
     if (prev_optimized_traj_points_ptr_) {
+      RCLCPP_WARN(logger_, "return the previous optimized_trajectory as exceptional behavior.");
       return *prev_optimized_traj_points_ptr_;
     }
+    RCLCPP_WARN(
+      logger_,
+      "Try to return the previous optimized_trajectory as exceptional behavior, "
+      "but this failure also. Then return path_smoother output.");
     return traj_points;
   };
 
@@ -505,8 +510,7 @@ std::vector<TrajectoryPoint> MPTOptimizer::optimizeTrajectory(const PlannerData
   // 6. optimize steer angles
   const auto optimized_variables = calcOptimizedSteerAngles(ref_points, obj_mat, const_mat);
   if (!optimized_variables) {
-    RCLCPP_INFO_EXPRESSION(
-      logger_, enable_debug_info_, "return std::nullopt since could not solve qp");
+    RCLCPP_WARN(logger_, "return std::nullopt since could not solve qp");
     return get_prev_optimized_traj_points();
   }