In the .arcconfig for www, we specify two phutil libraries, facebook-www-arcanist (contained within the www repo) and facebook-phabricator (a dependency of facebook-www-arcanist). It turns out that the facebook-phabricator library has a dependency on phabricator, but the only way that dependency is specified is in the .arcconfig file for the repository containing facebook-phabricator. We should have some way of specifying dependent libraries for a phutil library so that when a library is loaded, its dependencies are loaded first. For example, if repository R contains library A (and lists A in its .arcconfig), but A depends on B (and B depends on C), running arc in R should load A and also automatically load B and C without me having to specify B or C in the .arcconfig for R. (Note that this example doesn't quite match what I described above. If we modify it so A and B are in the .arcconfig for R, then R = www, A = facebook-www-arcanist, B = facebook-phabricator, and C = phabricator).
(In this particular setup, it's stupid that the phabricator library is a dependency of a library we're loading to run arc. My plan is to split facebook-phabricator into two parts: facebook-libphutil and facebook-phabricator (which depends on facebook-libphutil and phabricator), so facebook-www-arcanist only depends on facebook-libphutil. However, there will still be dependencies that need to be loaded.)