[CMake] CMake project building other CMake projects

[Tim Gallagher]

Hi,

I'm working on getting our CMake project to build the other libraries we wrote and I'm not sure how it needs to be done. Our main code is a git repository and inside the repo is a lib/ directory with git submodules for our other libraries. 

What is the best way to get the main project to build these submodules? It seems like I could use ExternalProject to do it, even though I don't need to download/checkout anything, but it also looks like I could just add_subdirectory(lib/myLibrary) also. Which is the "best practice"? 

If I go the add_subdirectory route, do I need to namespace my variables somehow? For instance, all of our projects use CMAKE_INSTALL_PREFIX to indicate the installation directory, but if I were to build them all at once, they need to be installed different places, so will the names clash? Do I need to change all the variables in each library to be myLibrary_*?

If I use ExternalProject, do I have to then manually add the options to my main project's CMakeLists so the user can configure them and then pass them through to the submodule's configure step with -D...? 

Is there something else I'm missing in how to do this? It seems like projects we maintain and can include as git submodules could/should be built differently than projects like Python that we don't include as submodules. But our own projects also provide a *Config.cmake, so maybe they could be treated the same...

Tim

Tim