// cache object -> (main class, field name)
static MultiMap<O, Pair<O, S>> cacheVarsOfAllMainClasses() {
  MultiMap<O, Pair<O, S>> mm = identityMultiMap();
  for (O mc : allMainClasses())
    for (S field : allCacheVars(mc))
      mm.put(get(mc, field), pair(mc, field));
  ret mm;
}