[CMake] install target added with add_subdirectory(EXCLUDE_FROM_ALL)

[Nick Tasios]

Hello everyone,

I recently started using cmake and I'm having some trouble setting-up my 
project. I've searched quite a lot and couldn't find a clear answer.

The project has a top level CMakeLists.txt which builds the executable. 
In my project, I have included  external libraries which I add using 
add_subdirectory. Most of these already came with a CMakeLists.txt file, 
and some have multiple targets, i.e. to build shared or static 
libraries, etc. In the project, though, I want to be able to choose only 
a specific target to build, i.e. I might only want to build the shared 
libraries. To do this, I add the option EXCLUDE_FROM_ALL when calling 
add_subdirectory, and just add the target to the target link libraries 
of the top-level executable.

This works fine, only in the install step I would like for the built 
libraries to move to where the executable is. From my understanding, the 
install directive of the sub projects is ignored, because install 
depends on all and these sub projects are excluded from it.

So the question is, if there is a clean way to compile only the targets 
(libraries) that are needed by the executable, and be able to install 
these in the directory the executable is being installed. The method 
needs to work cross-platform.

Cheers!