Relationship between rospkg and catkin_pkg (& ament_package)

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AFAIUC currently rospkg and catkin_pkg provide Python API for package info handling in ROS1. I'm willing to add an API, which I mainly target catkin pkgs with at the moment but should theoretically be able to handle ament or even rosbuild pkgs as well, and thus can be essentially called manifesto-format agnostic. Then I wonder which package is the right place to add that kind of change.

Current released version of rospkg and catkin_pkg seem to be independent (see below the system output). But a bug fix PR to rospkg introduced a dependency to catkin_pkg, so at the moment dependency tree for Python API pkg is catkin_pkg <- rospkg (excluded ament for now as I'm not yet sure about it). This makes me slightly lean toward opening a PR to catkin_pkg, but I'm not entirely sure (as the portion of the code in rospkg that depends on catkin_pkg is very limited).

Where's the best place would be?

$ apt-cache depends python-rospkg
python-rospkg
  Depends: python
  Depends: python
  Depends: python-yaml
  Depends: python-rospkg-modules
  Conflicts: python3-rospkg
$ apt-cache depends python-catkin-pkg
python-catkin-pkg
  Depends: python
  Depends: python
  Depends: python-docutils
  Depends: python-dateutil
  Depends: python-pyparsing
  Depends: <python-argparse>
    libpython2.7-stdlib
  Depends: python-catkin-pkg-modules
  Conflicts: catkin
  Conflicts: python3-catkin-pkg
$ apt-cache policy python-rospkg
python-rospkg:
  Installed: 1.1.4-100
  Candidate: 1.1.4-100
  Version table:
 *** 1.1.4-100 500
        500 http://packages.ros.org/ros-shadow-fixed/ubuntu xenial/main amd64 Packages
        500 http://packages.ros.org/ros-shadow-fixed/ubuntu xenial/main i386 Packages
        100 /var/lib/dpkg/status
     1.0.38-1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe i386 Packages
$ apt-cache policy python-catkin-pkg
python-catkin-pkg:
  Installed: 0.4.2-100
  Candidate: 0.4.2-100
  Version table:
 *** 0.4.2-100 500
        500 http://packages.ros.org/ros-shadow-fixed/ubuntu xenial/main amd64 Packages
        500 http://packages.ros.org/ros-shadow-fixed/ubuntu xenial/main i386 Packages
        100 /var/lib/dpkg/status
     0.2.10-2 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe i386 Packages