02/06: profiles: Extract a procedure for getting relative generation numbers.

[Ludovic Courtès]

civodul pushed a commit to branch master
in repository guix.

commit 9008debc54aaa4d65444d5cef85df83455d48d7b
Author: Chris Marusich <address@hidden>
Date:   Tue Nov 1 22:48:11 2016 -0700

    profiles: Extract a procedure for getting relative generation numbers.
    
    * guix/profiles.scm (relative-generation-spec->number): New procedure.
    * guix/scripts/package.scm (switch-generation-action): Use it.
    
    Signed-off-by: Ludovic Courtès <address@hidden>
---
 guix/profiles.scm        |   19 +++++++++++++++++++
 guix/scripts/package.scm |    8 ++------
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/guix/profiles.scm b/guix/profiles.scm
index 96f8b65..33a5f50 100644
--- a/guix/profiles.scm
+++ b/guix/profiles.scm
@@ -5,6 +5,7 @@
 ;;; Copyright © 2015 Mark H Weaver <address@hidden>
 ;;; Copyright © 2015 Sou Bunnbu <address@hidden>
 ;;; Copyright © 2016 Ricardo Wurmus <address@hidden>
+;;; Copyright © 2016 Chris Marusich <address@hidden>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -97,6 +98,7 @@
             generation-number
             generation-numbers
             profile-generations
+            relative-generation-spec->number
             relative-generation
             previous-generation-number
             generation-time
@@ -1039,6 +1041,23 @@ former profiles were found."
         '()
         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 70ed0a7..96a22f6 100644
--- a/guix/scripts/package.scm
+++ b/guix/scripts/package.scm
@@ -5,6 +5,7 @@
 ;;; Copyright © 2014, 2016 Alex Kost <address@hidden>
 ;;; Copyright © 2016 Roel Janssen <address@hidden>
 ;;; Copyright © 2016 Benz Schenk <address@hidden>
+;;; Copyright © 2016 Chris Marusich <address@hidden>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -782,12 +783,7 @@ processed, #f otherwise."
                                    #: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)))))