How to handle cloned packages that have no package.xml or CMake.txt file in ROS workspace.

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You likely need to have CMakeLists.txt and package.xml file to build a package.

src folder only gives you source code. However, a package still needs CMakeLists.txt and package.xml to provide information about things like build or runtime dependencies, required CMake verion, libraries/executables to build, etc... (http://wiki.ros.org/catkin/CMakeLists...).

Since each package is very specific, I think you would need to write them. You may want to start by adding contents from a basic template provided on the ROS tutorial page.

It is unclear what your goal is.

Do you understand the distinction between a "system package" and a "ros package"?

It's common for a ros package/node to depend on a system package/library. A system package is built outside of the ros world, and is typically installed as a library somewhere in /usr. Your ros node then uses this library.

If the library you want to use is available through ubuntu apt or pip, you should simply be declaring this system dependency in the CMakeLists.txt file for your ros package.