ASDF doesn't care about relative locations of .asd files. ASDF systems and their dependencies are completely orthogonal to file/directory structure and oblivious to any source version control.
It just looks in several locations for .asd files. Each such file then may contain definitions for systems. It will generally recurse into the configured folders, so any .asd file in a git submodule would usually also be found.
The definitions, e. g. of components, inside of an .asd file then work relatively from the location of that file.
In your example, if you give a :depends-on ("bar") option to the "foo" system, it would just work, no matter where bar.asd resides (as long as it is somewhere where ASDF finds it).
A bit more awareness would be required if you have several versions of a library. This might happen if you work on "foo" and "bar" at the same time, while a stable version of "bar" is also available, e. g. in a quicklisp dist. Then the lookup order comes into play, but usually your “personal” directories have precedence over “system” directories, so again, it would just work. For more control, you might want to look into qlot.
Thanks for the recommendation. My problem appears to be in getting ASDF to "find it" in the first place. Am I correct that the least hacky way is to invoke
initialize-source-registry? I understand that the old days one might push a value to*central-registry*, but that that way is deprecated now.I think the least hacky way is to use the standard locations. I put my projects under
~/common-lisp/, for example. Take a look at the ASDF manual for other standard locations and the lookup order.Sure, that sounds like best practice, and isn't hacky at all. But when used as a scripting language, Lisp may not ascertain file placement before build-time. Thus, I need to be able to use a function call. I've updated my original post to show a form that seems to work(?).