Hi!

I have been playing with Cuirass and I like it a lot!

Next to replacing Hydra for GuixSD, there is another use case that I'd
like Cuirass to support: tracking an (any) upstream packages' git.

When the target of your continuous integration is not Guix itself but
some specific package, you may well want to allow usage of substitutes
(patch 1).

Assuming you have checked-out guix and cuirass in ~/src/guix and
~/src/cuirass, doing

   ./pre-inst-env cuirass --use-substitutes --specifications=tests/hello-git.scm

will monitor any changes to Cuirass' git repository and rebuild the
latest commit of the Cuirass package using Guix (patch 2 and 3).

Of course, a build a failure should not crash cuirass and also be
noted/stamped, not repeated every heartbeat (patch 4).

I had some trouble with the #:no-compile? option, it's currently
specified twice.  On the Cuirass side I think it should be a property
of the spec, but it seems it gets only passed as part of the
arguments.  Ideas?

Thank you!
Greetings,
Jan