Environment

• OS Version: Ubuntu Bionic
• Binaries: SDFormat 9.5.1 , Gazebo 11.5.1

Description

In the test case provided in https://github.com/j-rivero/sdf_bug, Gazebo11 is complaining with:

[Err] [Joint.cc:297] EXCEPTION: Couldn't Find Child Link[sub_door::door]

when using an SDF similar to:

<?xml version="1.0" ?>
<sdf version="1.5">
  <model name='hinged_door_ticket'>
      <static>0</static>
      <link name='frame'>
      </link>
      <model name='sub_door'>
	<static>0</static>
	<link name='door'>
	  <pose frame=''>-0 0 2.04 3.14159 -0 1.58</pose>	   
	</link>
      </model>
      <joint name='hinge' type='revolute'>
        <parent>frame</parent>
        <child>sub_door::door</child>       
      </joint>
    </model>
</sdf>

The great @azeey first impression was: "It looks like the breaking change is that we added a prefix to nested models when flattening (#399). Running gz sdf -p frame.world shows that the joint is looking for sub_door::door. In Gazebo7, there is a model called sub_door. In Gazebo11, that model is now hinged_door_frame::sub_door. For some reason, the flattening logic is not handling that properly

• Expected behavior: the name got resolved correctly
• Actual behavior: failing to resolve the name, error message is emitted

Steps to reproduce

1. Download the example repository in the description
2. Execute GAZEBO_MODEL_PATH=${GAZEBO_MODEL_PATH}:${PWD} gazebo --verbose frame.world