refresh: Add '--load-path' option.

* guix/scripts/refresh.scm (%option): Add '--load-path' option.
* doc/guix.texi: Document it.

doc/guix.texi

@@ -70,7 +70,7 @@ Copyright @copyright{} 2019 Kyle Andrews@*
 Copyright @copyright{} 2019 Alex Griffin@*
 Copyright @copyright{} 2019 Guillaume Le Vaillant@*
 Copyright @copyright{} 2020 Leo Prikler@*
-Copyright @copyright{} 2019 Simon Tournier@*
+Copyright @copyright{} 2019, 2020 Simon Tournier@*
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -9553,6 +9553,13 @@ the user whether to download it or not.  This is the default behavior.
 @item --key-server=@var{host}
 Use @var{host} as the OpenPGP key server when importing a public key.
 
+@item --load-path=@var{directory}
+Add @var{directory} to the front of the package module search path
+(@pxref{Package Modules}).
+
+This allows users to define their own packages and make them visible to
+the command-line tools.
+
 @end table
 
 The @code{github} updater uses the

guix/scripts/refresh.scm

@@ -7,6 +7,7 @@
 ;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
 ;;; Copyright © 2018 Efraim Flashner <efraim@flashner.co.il>
 ;;; Copyright © 2019 Ricardo Wurmus <rekado@elephly.net>
+;;; Copyright © 2020 Simon Tournier <zimon.toutoune@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -27,6 +28,7 @@
   #:use-module (guix ui)
   #:use-module (gcrypt hash)
   #:use-module (guix scripts)
+  #:use-module ((guix scripts build) #:select (%standard-build-options))
   #:use-module (guix store)
   #:use-module (guix utils)
   #:use-module (guix packages)
@@ -116,6 +118,19 @@
                      (leave (G_ "unsupported policy: ~a~%")
                             arg)))))
 
+        ;; The short option -L is already used by --list-updaters, therefore
+        ;; it needs to be removed from %standard-build-options.
+        (let ((%load-path-option (find (lambda (option)
+                                         (member "load-path"
+                                                 (option-names option)))
+                                       %standard-build-options)))
+          (option
+           (filter (lambda (name) (not (equal? #\L name)))
+                   (option-names %load-path-option))
+           (option-required-arg? %load-path-option)
+           (option-optional-arg? %load-path-option)
+           (option-processor     %load-path-option)))
+
         (option '(#\h "help") #f #f
                 (lambda args
                   (show-help)
@@ -165,6 +180,9 @@ specified with `--select'.\n"))
                          'always', 'never', and 'interactive', which is also
                          used when 'key-download' is not specified"))
   (newline)
+  (display (G_ "
+      --load-path=DIR    prepend DIR to the package module search path"))
+  (newline)
   (display (G_ "
   -h, --help             display this help and exit"))
   (display (G_ "