Git app that creates libraries from a subset of a project -

is there git application (ui generates editable data configuration or suppose command line working) allows select subset of files publish git project? use case being:

let's have main shared library under src directory. beneficial able manage src directory internally single repository while being able publish sub package/module located in said directory publicly. copying , managing applicable commits subset of available classes huge pain.

is there this?

have looked git submodules? lets collect multiple repositories single directory tree, , used in case managing separate libraries/modules separate project. some people think submodules problematic manage.

the git subtree project alternative take on may meet needs.