Add "guix update" command

[Fabian Harfert <fhmgufs@web.de>]

Hello,

on IRC I already mentioned that, but there wasn't much resonance: I
think for the purposes of non-developers the behavior of the "guix
pull" command is too complicated.

Normal users don't need a development version of the package manager,
when they just want to get the newest package definitions to update
their installed software. So it would be much easier and faster if
there was a separate repository just containing the most recent package
definitions.

I propose to add a new command line option - e.g. "guix update" -
fetching these latest package definitions and not doing anything else.
They could be contained by a package whose definition is downloaded,
for example "guix-packages".

To avoid compatibility issues when there's a new release of Guix itself
this package must be versioned equal to the Guix version numbers. I'm
thinking of the following:

  The user is running Guix 1.2.1 and has installed the package
  guix-packages-1.2.1-4 containing the package definitions. Now he runs
  "guix update" and fetches guix-packages-1.2.1-5 with the new package
  definitions including the new Guix release 1.2.2. He now updates Guix
  to this version which has the new guix-packages-1.2.2-0 as an input.
  When he runs "guix update" again, guix-packages-1.2.2-1 is installed,
  which contains package definitions that make use of some new features.

This would just be for the time between the Guix releases. I think we
don't need support for older versions of Guix except from keeping the
last guix-packages package, but we could also do some security
or minor updates to the older package definitions which would provide
users the possibility to use GuixSD as a stable distribution like
Debian.

Another advantage of the separation between Guix itself and the package
definitions is that it's easy to provide an own or foreign
guix-packages package which would promote the decentralization of Guix.

Initially I thought of doing the same for service definitions except
from the basic ones. But I think that version compatibility problems
would occur more often because service definitions are at a lower level
than the package definitions. In addition the notorious normal users
won't change so much of their service definitions.

Fabian


I don't know why this E-Mail is shown as a reply to the transmission
patch, so I send it again, sorry.