Moveit attempts to execute incomplete trajectories, causing some weird motions to be displayed in RVIZ

[Schteve-Earl]

Description

I have a Moveit config with a manipulator and a gripper motion group. Moveit Task Constructor creates solutions that I segment and then execute separately. I'm running into an issue where I construct an ExecutableMotionPlan from a moveit_msgs::RobotTrajectory and pass it to PlanExecution::executeAndMonitor(). PlanExecution will still attempt to execute the trajectory if the size of the positions vector changes midway through the trajectory points list. This occurs when I try to append a trajectory for the gripper onto a trajectory that contains my motion group that includes both the manipulator and the gripper. The resulting execution looks something like this:

Your environment

• ROS Distro: Melodic
• OS Version: Ubuntu 18.04
• Source build, master branch

Steps to reproduce

Create and execute a plan using a RobotTrajectory that has all the joint names of both motion groups. Fill the first half with a trajectory that includes all joint positions, and then remove the pvae values for one of the motion groups from the last few points.

Expected behaviour

Moveit should never attempt to execute an incomplete trajectory. Instead, an error should be thrown stating that the motion cannot be executed because it is incomplete or changes motion groups midway through the JointTrajectory message.

Actual behaviour

See gif above.

[welcome]

Thanks for reporting an issue. Because we're a volunteer community, providing a pull request with suggested changes is always welcomed.