How do you export package dependencies to downstream packages?

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First of all, I see that the tutorial for ament_cmake covers this idea. We are supposed to use ament_export_dependencies, however I still can't seem to get it to work. I feel like I'm missing something simple here.

I put together a small reproducible example here.

Things I've tried:

• Changing exported target to ${PROJECT_NAME}Targets in geometry_msgs_arithmetic and vector_arithmetic
• Adding HAS_LIBRARY_TARGET to ament_export_targets in geometry_msgs_arithmetic and vector_arithmetic
• Combination of the two above

Requirements:

• Modern CMake approach

Other details:

• Using docker image from osrf/ros:galactic-desktop