missing CMake targets on humble

[christian-rauch]

Describe the bug
I am trying to replace ament_target_dependencies with target_link_libraries. In the suggested targets:

target_link_libraries(my_robot_hardware PUBLIC
  hardware_interface::hardware_interface
  hardware_interface::mock_components
  rclcpp::rclcpp
)

none of the targets in the hardware_interface:: namespace are available under humble.

Looking at the bloomed package, I can see that under jazzy, there is a /opt/ros/jazzy/share/hardware_interface/cmake/export_hardware_interfaceExport.cmake with the exported targets hardware_interface::hardware_interface and hardware_interface::mock_components. But there is no such equivalent file that exports these targets in the humble package.

To Reproduce
Steps to reproduce the behavior:

1. find_package(hardware_interface REQUIRED)
2. link a target with target_link_libraries(my_hardware PUBLIC hardware_interface::hardware_interface hardware_interface::mock_components)

You can also manually list the imported targets with:

get_property(my_tgts DIRECTORY "${CMAKE_CURRENT_LIST_DIR}" PROPERTY IMPORTED_TARGETS)
foreach(t ${my_tgts})
    message(WARNING "  ${t}")
endforeach()

and see that those targets are not defined.

Expected behavior
The hardware_interface should export its CMake targets inside the hardware_interface:: namespace.

Screenshots
If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):

• OS: Ubuntu 22.04
• Version Humble

[christophfroehlich]

It seems that
ament_export_targets(export_hardware_interface HAS_LIBRARY_TARGET)
is missing on humble, which was added with #926 but never backported.

Why do you need to change that on humble? ament_target_dependencies is still the preferred way to link against, and only changed from kilted on.

If you can confirm that export_targets solves your issue, we could think about backporting #926, but I'm not sure what we possibly can break there.

[christian-rauch]

Why do you need to change that on humble? ament_target_dependencies is still the preferred way to link against, and only changed from kilted on.

Using the same code for multiple distributions reduces the maintenance costs as I do not have to maintain multiple branches and backport between them. I was asked to apply this change (ament_target_dependencies -> target_link_libraries) on a couple of other repositories and there it worked without issues. So I guess this is an issue with the hardware_interface project.

[christophfroehlich]

Gotcha. I'll trigger a backport of #926, let's see what happens and how many conflicts we have..

[christian-rauch]

Fixed by #2480.