Should I use ament_export_dependencies for PRIVATE dependency?

[felixf4xu]

Hi,

I see several examples in ROS2 code that ament_export_dependencies is used for PRIVATE dependencies, like

1. kdl_parser project
   https://github.com/ros/kdl_parser/blob/jazzy/kdl_parser/CMakeLists.txt#L28

target_link_libraries(${PROJECT_NAME} PRIVATE
  rcutils::rcutils
  urdf::urdf)

and it's exported:
https://github.com/ros/kdl_parser/blob/jazzy/kdl_parser/CMakeLists.txt#L59

ament_export_dependencies(rcutils)

2. camera_calibration_parsers project

https://github.com/ros-perception/image_common/blob/jazzy/camera_calibration_parsers/CMakeLists.txt#L33

target_link_libraries(${PROJECT_NAME} PRIVATE
  rclcpp::rclcpp
  yaml-cpp::yaml-cpp)

and it's exported:
https://github.com/ros-perception/image_common/blob/jazzy/camera_calibration_parsers/CMakeLists.txt#L88

ament_export_dependencies(rclcpp sensor_msgs yaml_cpp_vendor)

I can list more if I search more in the ros2 source code. I have to say, those usage really confused me. For PRIVATE dependencies, I don't think it's necessary to export them.

Before I raise an issue for those projects, I'd like to make sure the usage of ament_export_dependencies for PRIVATE dependencies, it's not mentioned here https://docs.ros.org/en/jazzy/How-To-Guides/Ament-CMake-Documentation.html

[clalancette]

I can list more if I search more in the ros2 source code. I have to say, those usage really confused me. For PRIVATE dependencies, I don't think it's necessary to export them.

You are correct. For PRIVATE dependencies, they should not be exported. Those are bugs, so if you'd like to open PRs to fix that, I'd be happy to review them.