Update comments

joint_trajectory_controller/src/joint_trajectory_controller.cpp

@@ -1028,6 +1028,10 @@ controller_interface::CallbackReturn JointTrajectoryController::on_activate(
   // those are not nan
   trajectory_msgs::msg::JointTrajectoryPoint state;
   resize_joint_trajectory_point(state, dof_);
+  // read from cmd joints only if all joints have command interface
+  // otherwise it leaves the entries of joints without command interface NaN.
+  // if no open_loop control, state_current_ is then used for `set_point_before_trajectory_msg` and
+  // future trajectory sampling will always give NaN for these joints
   if (dof_ == num_cmd_joints_ && read_state_from_command_interfaces(state))
   {
     state_current_ = state;

joint_trajectory_controller/test/test_trajectory_controller.cpp

@@ -398,7 +398,6 @@ TEST_P(TrajectoryControllerTestParameterized, correct_initialization_using_param
 /**
  * @brief check if state topic is consistent with parameters
  */
-
 TEST_P(TrajectoryControllerTestParameterized, state_topic_consistency)
 {
   rclcpp::executors::SingleThreadedExecutor executor;
@@ -499,7 +498,6 @@ TEST_P(TrajectoryControllerTestParameterized, state_topic_consistency)
 /**
  * @brief same as state_topic_consistency but with #command-joints < #dof
  */
-
 TEST_P(TrajectoryControllerTestParameterized, state_topic_consistency_command_joints_less_than_dof)
 {
   rclcpp::executors::SingleThreadedExecutor executor;