Duplicate Launch Arguments fail quietly

Bug report

Including 2 python launch descriptions with the same launch arguments declared with different descriptions causes some nodes not to launch and does not specify the cause of failure.

I think the desired functionality would be warning the user and appending the two descriptions together. The latter behaviour would allow for maximum interoperability so that all ROS developers don't need to have the exact same descriptions for common arguments (such as use_sim_time ).

Required Info:

• Operating System:
  • Ubuntu 22.04
• Installation type:
  • Binaries
• Version or commit hash:
  • Humble
• DDS implementation:
  • Fast DDS -- Humble default
• Client library (if applicable):
  • launch

Steps to reproduce issue

Create 2 python launch descriptions with the same launch argument declared with different descriptions. Add some other actions to each description and observe which actions get executed.

Expected behavior

I think the desired functionality would be warning the user and appending the two descriptions together. The latter behaviour would allow for maximum interoperability so that all ROS developers don't need to have the exact same descriptions for common arguments (such as use_sim_time ).

Actual behavior

Some actions do not execute or do not execute correctly, fail quietly.

Start by reproducing the issue with two Python launch descriptions that declare the same argument with different descriptions, using the launch client library. Then trace how duplicate arguments are handled and verify that the result reports the conflict clearly, preserves the intended actions, and avoids silently skipping nodes.