Fix ros2 interface show for msg files in subfolders (humble)

[xin700]

Summary

• Fix ros2 interface show for packages that install interface files under nested subdirectories (e.g. msg-common/GenericObject.msg in mrpt_msgs).
• Replace rosidl_runtime_py.get_interface_path() with lookup via the rosidl_interfaces ament index resource, matching the approach in fix non standard interface locations. (#1186) #1205 (kilted backport).

Fixes #1186

Problem

On Humble, ros2 interface show mrpt_msgs/msg/GenericObject fails with InvalidResourceName: // because get_interface_path() cannot resolve interfaces whose .msg files live outside the conventional msg/<Name>.msg layout.

Solution

Use ament_index_python.resources.get_resource('rosidl_interfaces', pkg_name) to find the installed interface file path, then open it from the package share directory.

Test plan

• Reproduced failure on system Humble before fix:

  ros2 interface show mrpt_msgs/msg/GenericObject  # InvalidResourceName: //

• Verified fix with overlay build:

  source install/setup.bash
  ros2 interface show mrpt_msgs/msg/GenericObject  # prints message definition
  ros2 interface show std_msgs/msg/String          # still works

• Updated test_show_not_an_interface expected error message
• colcon build --packages-select ros2interface succeeds
• Full ros2interface CLI test suite (requires ros-humble-test-msgs in CI)

Related

Backport of the fix approach from #1205 to the humble branch.

Made with Cursor

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[fujitatomoya]

1st we need to make sure to merge #1205 to the rolling branch, and then we can backport the fix to the downstream automatically. it looks like backport is straightforward, i do not think we need this backport PR.