bug#20137: number of generation doesn't always rise monotonically

[ludo@gnu.org (Ludovic Courtès)]

Tomáš Čech <sleep_walker@gnu.org> skribis:

> 1] install some package (you'll have N and N+1)
> 2] install some other package (you'll have N, N+1 and N+2)
> 3] delete generation N+1 (you'll have N and N+2)
> 4] switch to generation N
> 5] install some package - you'll get generation N+1 again
>   (you'll have N, N+1 and N+2 again)

That’s expected, yes.  What makes you think it’s a problem?

When implementing that, there were several possible choices:

  1. Upon rollback to N, remove all generations above N.  Rejected
     because it gratuitously prevents useful use cases.

  2. Upon rollback from P to N, keep all the generations, but use P+1
     for the next generation number.  Doesn’t work, because rolling back
     from P+1 would bring you back to P instead of N.

  3. The current behavior.

See <http://lists.gnu.org/archive/html/bug-guix/2013-01/msg00325.html>
for part of the discussion.

Thanks,
Ludo’.