I would like to suggest an addition from my experience of working with colleagues at other companies. I'd suggest that we have a way to specify files relative to something akin to *load-truename*.
Here's the use case: you work on a large project with an enormous source code repository, cluttered with binaries and many files in a programming language that begins with "j". You want people to be able to check out the repository and point to an asdf configuration file that is contained in that repository.
Now, the (:add-directory ...) command seems like it might do the job, but it doesn't quite, because it will recurse /everywhere/.
In my not-quite-hypothetical example, the directory tree is way too large for you to blindly recurse looking for .asd files --- it's full of those files in the j-language which, coincidentally, has a compilation and namespacing protocol which causes it to spawn simply /enormous/ directory trees, most of which you will never want to search for a .asd file.
So we'd like to put in this repository a single asdf configuration file that will specify /relative/ paths to search.
I think this would be compatible with the broad outlines of your idea. Indeed, it's possible that this is actually covered by your design, assuming that "." can be used as a DIRECTORY-PATHNAME-DESIGNATOR. Perhaps you could spell out what goes in there?
I'd also like to suggest that we expand the API to
(process-source-registry-configuration-file X)
which seems like a useful convenience.
Best, robert
[a subversive alternative: why don't we provide an alternative to logical pathnames that actually *works*?]