From 9008debc54aaa4d65444d5cef85df83455d48d7b Mon Sep 17 00:00:00 2001
From: Chris Marusich <cmmarusich@gmail.com>
Date: Tue, 1 Nov 2016 22:48:11 -0700
Subject: profiles: Extract a procedure for getting relative generation
 numbers.
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* guix/profiles.scm (relative-generation-spec->number): New procedure.
* guix/scripts/package.scm (switch-generation-action): Use it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>
---
 guix/profiles.scm        | 19 +++++++++++++++++++
 guix/scripts/package.scm |  8 ++------
 2 files changed, 21 insertions(+), 6 deletions(-)

(limited to 'guix')

diff --git a/guix/profiles.scm b/guix/profiles.scm
index 96f8b65c3e..33a5f50a53 100644
--- a/guix/profiles.scm
+++ b/guix/profiles.scm
@@ -5,6 +5,7 @@
 ;;; Copyright © 2015 Mark H Weaver <mhw@netris.org>
 ;;; Copyright © 2015 Sou Bunnbu <iyzsong@gmail.com>
 ;;; Copyright © 2016 Ricardo Wurmus <rekado@elephly.net>
+;;; Copyright © 2016 Chris Marusich <cmmarusich@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -97,6 +98,7 @@ (define-module (guix profiles)
             generation-number
             generation-numbers
             profile-generations
+            relative-generation-spec->number
             relative-generation
             previous-generation-number
             generation-time
@@ -1039,6 +1041,23 @@ (define (profile-generations profile)
         '()
         generations)))
 
+(define (relative-generation-spec->number profile spec)
+  "Return PROFILE's generation specified by SPEC, which is a string.  The SPEC
+may be a N, -N, or +N, where N is a number.  If the spec is N, then the number
+returned is N.  If it is -N, then the number returned is the profile's current
+generation number minus N.  If it is +N, then the number returned is the
+profile's current generation number plus N.  Return #f if there is no such
+generation."
+  (let ((number (string->number spec)))
+    (and number
+         (case (string-ref spec 0)
+           ((#\+ #\-)
+            (relative-generation profile number))
+           (else (if (memv number (profile-generations profile))
+                     number
+                     #f))))))
+
+
 (define* (relative-generation profile shift #:optional
                               (current (generation-number profile)))
   "Return PROFILE's generation shifted from the CURRENT generation by SHIFT.
diff --git a/guix/scripts/package.scm b/guix/scripts/package.scm
index 70ed0a7ea6..96a22f6fab 100644
--- a/guix/scripts/package.scm
+++ b/guix/scripts/package.scm
@@ -5,6 +5,7 @@
 ;;; Copyright © 2014, 2016 Alex Kost <alezost@gmail.com>
 ;;; Copyright © 2016 Roel Janssen <roel@gnu.org>
 ;;; Copyright © 2016 Benz Schenk <benz.schenk@uzh.ch>
+;;; Copyright © 2016 Chris Marusich <cmmarusich@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -782,12 +783,7 @@ (define* (switch-generation-action store profile spec opts
                                    #:key dry-run?)
   "Switch PROFILE to the generation specified by SPEC."
   (unless dry-run?
-    (let* ((number (string->number spec))
-           (number (and number
-                        (case (string-ref spec 0)
-                          ((#\+ #\-)
-                           (relative-generation profile number))
-                          (else number)))))
+    (let ((number (relative-generation-spec->number profile spec)))
       (if number
           (switch-to-generation* profile number)
           (leave (_ "cannot switch to generation '~a'~%") spec)))))
-- 
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