Include project file from library

I currently use lib folder for my custom libraries as means of managing code shared across different stm32cube projects, but i couldn’t figure out how to include source file from library. It would be really handy feature to have.
Is it possible to include for example some standard .h file that is placed in src dir?

simple answer, don’t do it. it is possible with bodges but it is as pointless as pushing brown stuff uphill with a pointy stick.

get your code straight and you won’t need it.