easily include headers from library dependency in cmake
===

I'm experimenting with CMake a bit for a C++ repository, but I'm running into some trouble trying to make it easy to build applications against libraries in the same source tree without a lot of extra CMake code.

The layout of the source tree is basically the following:

    ROOT
        libs/
             lib1/
             lib2/
             lib3/
        apps/
             app1/
             app2/
             app3/

The libraries are independent of one another, and the applications may link against one or more of the libraries.

Currently I have a root CMakeLists.txt that lists out each application and library as a subdirectory so that if the library is changed and the application is rebuilt, so is the library.  This works fine and CMake links it in without me having to specify where the library lives, but I don't see a way to do something similar for include directories.

Is there a common way to handle this?  I'd prefer not to have each application's CMakeLists.txt have to manually list out the path to the libraries it needs.