FWIW, Faré provided a couple of new API functions to give ASDF users
this function, notably
SYSTEM-RELATIVE-PATHNAME
and
SYSTEM-SOURCE-DIRECTORY
I insist on the following: in order to achieve purity in ASDF files we
want to keep as far away as possible from using any kind of API in the
compiled code.
The best system build system is one which is
invisible to the code that it builds.
Exposing functions, imposing the dependency of the user code on ASDF API as well as imposing that the library code queries ASDF for its own system is a very
bad design.
We want system definitions to be descriptive, not programatic, and we want the user code to be able to exist in an ASDF-free environment, as standalone systems. The existing situation does not allow this.
One may
1) Use *compile-file/load-truename*
but that leads to very ugly code.
2) Enforce that *default-pathname-defaults* is set to the system root when loading or compiling
3) Provide logical hostnames
For what it's worth, I try to avoid logical-pathnames in portable code,
having been hoist too many times on the petard of ACL/SBCL
incompatibility in handling logical pathnames (SBCL sticks to the spec,
in the name of portability and standardization; ACL accepts sensible,
spec-defying logical pathnames in the name of utility).