* doc/guix.texi (Invoking guix time-machine): Document limitation.
* guix/inferior.scm (cached-channel-instance): New VALIDATE-CHANNELS
argument. Use it to validate channels when there are no cache hit.
* guix/scripts/time-machine.scm
(%options): Tag the given reference with 'tag-or-commit instead of 'commit.
(%oldest-possible-commit): New variable.
(guix-time-machine) <validate-guix-channel>: New nested procedure. Pass it to
the 'cached-channel-instance' call.
* tests/guix-time-machine.sh: New test.
* Makefile.am (SH_TESTS): Register it.
Suggested-by: Simon Tournier <zimon.toutoune@gmail.com>
Reviewed-by: Ludovic Courtès <ludo@gnu.org>
Reviewed-by: Simon Tournier <zimon.toutoune@gmail.com>
