serial dependency spec and individual `:depends-on` can appear in the same system definition
I just found this in cl-async.asd.
It never occurred to me that this would be possible. I believe that this should be an error condition, since either the explicit :depends-on
specs will be vacuous, or they will contradict the serial specification.
I haven't thoroughly checked, but I don't see that ASDF checks dependency graphs for consistency. If the dependencies don't make an acyclic digraph, then ASDF should probably signal an error.