asdf:component-pathname

(asdf:component-pathname component)

Returns the component's pathname as a namestring: for a system, the directory it was found in with a trailing /; for a source file (an entry of asdf:component-children), the resolved path of the file itself. component may be the metaobject asdf:find-system answers or a plain name designator (a string, keyword or symbol) — the designator names a system, which must be registered (loaded, or currently loading).

This is how a library locates data files bundled beside its own sources: local-time finds its zoneinfo/ repository with (asdf:component-pathname (asdf:find-system :local-time nil)). asdf:system-relative-pathname composes this with a relative name in one call.

(asdf:load-system "my-lib")
(print (asdf:component-pathname (asdf:find-system "my-lib")))

Backend support

Works on all four backends. The interpreter answers from its system registry at run time; the compile paths fold the call to a literal namestring when the system name is a literal (a literal find-system around it included), which is the shape every library uses — anything else reads the registry the compiled program carries.