Problem Cause: modify a package.xml;
This is because a Added:
<exec_depend>rospy</exec_depend>
<ecec_depend>std_msgs</ecec_depend>
<ecec_depend>message_runtime</ecec_depend>
<ecec_depend>tf</ecec_depend>
<ecec_depend>nav_msgs</ecec_depend>
When the exec actually wrote ecec