Consider a "library" that consists of only C++ header files: no C++ source files. I wish to create that as a "library" inside my package, so that other real libraries I am building can find these header files. Additionally, anyone who uses my package will need to pick up these headers on the search path.
I have found that if I gratuitously add a single .cpp file into the directory containing my headers files, then SPM will use the path to this directory by downstream components (i.e. adding the requisite -I flags to the compile line that lead to the header directory) but I cannot figure out what to do when I have no source files at all (i.e. without source files, the -I lines are not generated, presumably because SPM doesn't consider that I've created a library).
Is there something other than a "library" I should be making? Should I be doing this using modulemaps (and if so how)?
Given that so many C++ libraries are header-only (no source) I cannot be the first person to want this, but I've scoured the web and found nothing so far. Help?