graph: Factorize 'lookup-backend'.

* guix/graph.scm (lookup-backend): New procedure.
* guix/scripts/graph.scm (lookup-backend): Remove.
* guix/scripts/system.scm (lookup-backend): Remove.
* po/guix/POTFILES.in: Add 'guix/graph.scm'.

guix/graph.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2015, 2016, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2015-2016, 2020-2022 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2016 Ricardo Wurmus <rekado@elephly.net>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -22,10 +22,13 @@
   #:use-module (guix monads)
   #:use-module (guix records)
   #:use-module (guix sets)
+  #:autoload   (guix diagnostics) (formatted-message)
+  #:autoload   (guix i18n) (G_)
   #:use-module (rnrs io ports)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-34)
   #:use-module (ice-9 match)
   #:use-module (ice-9 vlist)
   #:export (node-type
@@ -47,6 +50,8 @@
             %graph-backends
             %d3js-backend
             %graphviz-backend
+            lookup-backend
+
             graph-backend?
             graph-backend
             graph-backend-name
@@ -335,6 +340,13 @@ nodeArray.push(nodes[\"~a\"]);~%"
         %d3js-backend
         %cypher-backend))
 
+(define (lookup-backend name)
+  "Return the graph backend called NAME.  Raise an error if it is not found."
+  (or (find (lambda (backend)
+              (string=? (graph-backend-name backend) name))
+            %graph-backends)
+      (raise (formatted-message (G_ "~a: unknown graph backend") name))))
+
 (define* (export-graph sinks port
                        #:key
                        reverse-edges? node-type (max-depth +inf.0)

guix/scripts/graph.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2015-2022 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2019 Simon Tournier <zimon.toutoune@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -429,13 +429,6 @@ package modules, while attempting to retain user package modules."
             %node-types)
       (leave (G_ "~a: unknown node type~%") name)))
 
-(define (lookup-backend name)
-  "Return the graph backend called NAME.  Raise an error if it is not found."
-  (or (find (lambda (backend)
-              (string=? (graph-backend-name backend) name))
-            %graph-backends)
-      (leave (G_ "~a: unknown backend~%") name)))
-
 (define (list-node-types)
   "Print the available node types along with their synopsis."
   (display (G_ "The available node types are:\n"))

guix/scripts/system.scm

@@ -51,7 +51,7 @@
                                        delete-matching-generations)
   #:autoload   (guix scripts pull) (channel-commit-hyperlink)
   #:autoload   (guix graph) (export-graph node-type
-                             graph-backend-name %graph-backends)
+                             graph-backend-name lookup-backend)
   #:use-module (guix scripts graph)
   #:use-module (guix scripts system reconfigure)
   #:use-module (guix build utils)
@@ -887,13 +887,6 @@ Run 'herd status' to view the list of services on your system.\n"))))))
                    (register-root* (list output) gc-root))
                  (return output)))))))))
 
-(define (lookup-backend name)                     ;TODO: factorize
-  "Return the graph backend called NAME.  Raise an error if it is not found."
-  (or (find (lambda (backend)
-              (string=? (graph-backend-name backend) name))
-            %graph-backends)
-      (leave (G_ "~a: unknown backend~%") name)))
-
 (define* (export-extension-graph os port
                                  #:key (backend (lookup-backend "graphviz")))
   "Export the service extension graph of OS to PORT using BACKEND."

po/guix/POTFILES.in

@@ -66,6 +66,7 @@ guix/ci.scm
 guix/cve.scm
 guix/git-authenticate.scm
 guix/gnupg.scm
+guix/graph.scm
 guix/lint.scm
 guix/scripts/download.scm
 guix/scripts/package.scm