package dependency

[aremazeilles]

ping @miguelprada

I am bringing this functionality to a ros_comm fork.

The question is related to how properly define the dependency on rospy_message_converter.

In this repo, I have defined it this way:

In package.xml:

  <depend>rospy_message_converter</depend>

In CMakeLists.txt

find_package(catkin REQUIRED COMPONENTS
    rospy
    rospy_message_converter
)

and further on:

catkin_package(
    CATKIN_DEPENDS
        rospy
        rospy_message_converter
)

If I look to the upstream ros_comm config in the rostest package, I find:

• in package.xml, most of the dependencies set as run_depend.
• in CMakeLists.txt, there is very little package dependency placed at the level of find_package and of catkin_package.

Is it because, being a python package, it is sufficient to state the dependency as a run dependency, and so there is no need to place it as dependency in the CMakeLists.txt, as it is not needed for compiling / installing purposes?

I am a bit lost here. Would you have a better understanding of this?

Thanks

[miguelprada]

Is it because, being a python package, it is sufficient to state the dependency as a run dependency, and so there is no need to place it as dependency in the CMakeLists.txt, as it is not needed for compiling / installing purposes?

I think you're right:

• find_package is used to import libraries into your CMake script (e.g. defines variables such as ${some_package_INCLUDE_DIRS}, or exported targets in modern CMake), so you can use them to build your C++ targets. Adding libraries to the find_package(catkin COMPONENTS ...) instead of using separate find_pacakge calls is just a convenience tool, that mainly aggregates everything into the catkin_INCLUDE_DIRS and catkin_LIBRARIES.
• catkin_package is, in turn, used to facilitate exporting the proper flags from your package to dependent C++ targets, so they can build against anything you may export from your package (most commonly headers and binary libraries).

With rospy_message_converter being a pure Python library, there's really no point in find_package-ing it that I'm aware of. Likewise, if everything you export from your package is Python modules/scripts, I think it's safe to issue an empty catkin_package().

I think this the above applies to rospy as well.

TL;DR; I'm pretty sure you only need to add rospy and rospy_message_converter as exec_depend to your package (since you're using manifest format 2), and that you can replace all of this with

find_package(catkin REQUIRED)
catkin_python_setup()
catkin_package()