[...]

The problem with doing the INTER-system dependencies is that I don't

believe that ASDF currently has the infrastructure to do The Right

Thing.  In order to do the right thing, each system would have to store

with itself information about the state of the dependencies when it was

built.

A timestamp is all you should be needing. What else do you need, really?

Pace Daniel H, I don't believe that timestamps on files is sufficient to

do this.  We have developed an API based on operation-done-p, and I

don't believe that operation-done-p is sufficient for this.  Timestamps

on files is sufficient for make, but I'm not confident it's sufficient

for ASDF.  At any rate, I believe that we need to go through a process

of making proposals about a protocol that will do the right thing, and

then move on.

Maybe the current timestamps in ASDF are somewhat lacking, but

that doesn't mean timestamps can't solve the issue. I think that

one timestamp per pair (op component) should do the trick, stored

as an alist (op timestamp) in a slot of the component.