From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ricardo Wurmus <rekado@elephly.net>
Subject: Re: rolling back only a single package
Date: Fri, 28 Dec 2018 15:49:05 +0100
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	<20181228143410.283e8d8a@alma-ubu>
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To: =?utf-8?Q?Bj=C3=B6rn_H=C3=B6fling?= <bjoern.hoefling@bjoernhoefling.de>
Cc: cdelia@dc.uba.ar, help-guix@gnu.org

Hi cdelia,

Bj=C3=B6rn wrote:

> There is a nice blog post by Ludivic that describes some aspects of it:
>
> https://www.gnu.org/software/guix/blog/2018/multi-dimensional-transaction=
s-and-rollbacks-oh-my/
>
> It looks like the inferior thing he mentioned is already ready, but I
> haven't yet followed that.

Inferiors work, but you=E2=80=99d use them in manifests.  The idea is to in=
stall
the package with an old version of Guix, but to do it in code instead of
manually.  Here=E2=80=99s an example:

--8<---------------cut here---------------start------------->8---
(use-modules (guix inferior) (guix channels)
             (srfi srfi-1))   ;for 'first'

(define channels
  ;; This is the old revision from which we want to
  ;; extract guile-json.
  (list (channel
         (name 'guix)
         (url "https://git.savannah.gnu.org/git/guix.git")
         (commit
          "65956ad3526ba09e1f7a40722c96c6ef7c0936fe"))))

(define inferior
  ;; An inferior representing the above revision.
  (inferior-for-channels channels))

;; Now create a manifest with the current "guile" package
;; and the old "guile-json" package.
(packages->manifest
 (list (first (lookup-inferior-packages inferior "guile-json"))
       (specification->package "guile")))
--8<---------------cut here---------------end--------------->8---

You can instantiate the manifest the usual way:

    guix package -m /path/to/manifest.scm

--
Ricardo