Duplicated xarco "name" argument in the URDFs

[macmacal]

Hello,
In both of the provided URDF files (urdf/ur.urdf.xacro & urdf/ur_mocked.urdf.xacro) there is a requirement for xarco launch argument name. However, in the next line this argument is defined by xacro:arg marker:

<robot xmlns:xacro="http://wiki.ros.org/xacro" name="$(arg name)">
  <!-- robot name parameter -->
  <xacro:arg name="name" default="ur"/>

As far as I understand the authors' intentions, these URDFs should define and contain all parameters to call the xacro:ur_robot macro, without need to pass more information. Even with provided default value with xacro:arg I couldn't parse the file with xacro (on ROS 2 Humble) - the launch argument name:= is required.

I would like to ask to clarify this ambiguity.

[fmauch]

Sorry for the late answer...

That intention is not entirely the case, let me explain:

• The name argument is kind of a hack. Since we use one common xacro for all models and we wanted to achieve having the robot name match the model, we need to set the name field of the robot tag dynamically. It works reading this from a xacro argument, however the default value (when the argument is not provided) is not evaluated at the time when the robot tag is parsed.
• The name argument is not the only required argument, the ur_type argument is also required in a sense that it is used for defining the default values for the model specification. It is set to a default value, however, because it can be omitted if all four robot parametrizations are given.

I hope that explanation helps reasoning the structure as it is. Feel free to comment if you have a suggestion how to handle this differently.