For pluginlib to find all plugins based packages in the ROS system, we should export the plugin description file inside package.xml. If we do not include this plugin, the ROS system won't find the plugins inside the package.

Here, we add the export tag to package.xml as follows:

<export> 
  <pluginlib_calculator plugin="${prefix}/calculator_plugins.xml" 
 /> 
</export> 

In order to work this export command properly, we should insert the following lines in package.xml:

 <build_depend>pluginlib_calculator</build_depend> 
 <run_depend>pluginlib_calculator</run_depend> 

The current package should directly depend on itself, both at the time of building and also at runtime.