In case you weren't aware there is a 'Modules' directory in OSS that can be used for extension libraries, we use it for our closed source work and we hope to be adding contributions from the community that don't quite fit into OSS through the same channel.
As we are extending the use of the Modules directory we recently hit some snags in how we were writing the modules and the includes to the appropriate module files, we are standardizing access to the module directory and implementing the appropriate changes in the Modules CMake file and our current #include statements
The plan is to make the directories inside the Modules directory the root of the include path, this does mean that the names that the directories have at this level will have to be standardized, but doesn't require another directory under the repository root. All includes in side the modules (especially the ones that should be included from the outside) should refer to that directory) given a module name "SimQuest" and a file "Physics/Physics.h" for example all the includes (internal and external) should look like this
If there are any problems with this approach, please let us know.
Principal Software Engineer
Simquest Solutions Inc.