For my custom language plugin, I'd like to define include paths that point to additional source library files, like in C.
First of all, I don't know at all how to define an include path in IDEA. The Project Structure is very Java-centric, and the Settings don't offer additional directories either. You also cannot add extra folders to the project that are located outside the project directory.
Are include paths unique to CLion?
There are Path Variables in Settings -> Appearances & Behavior, and I could even add an include path to my custom language code style settings, but then what? How would I tell IDEA that it should at least process (but not necessarily display) the files in the include directory?