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

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

doc/guix.texi

@@ -9838,6 +9838,13 @@ the case, @command{guix size} fails as it tries to load it.
 @itemx -s @var{system}
 Consider packages for @var{system}---e.g., @code{x86_64-linux}.
 
+@item --load-path=@var{directory}
+@itemx -L @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
 
 @node Invoking guix graph

guix/scripts/size.scm

@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2015, 2016, 2017, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2019 Simon Tournier <zimon.toutoune@gmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -19,6 +20,7 @@
 (define-module (guix scripts size)
   #:use-module (guix ui)
   #:use-module (guix scripts)
+  #:use-module (guix scripts build)
   #:use-module (guix store)
   #:use-module (guix monads)
   #:use-module (guix combinators)
@@ -242,6 +244,9 @@ Report the size of PACKAGE and its dependencies.\n"))
   -m, --map-file=FILE    write to FILE a graphical map of disk usage"))
   (newline)
   (display (G_ "
+  -L, --load-path=DIR    prepend DIR to the package module search path"))
+  (newline)
+  (display (G_ "
   -h, --help             display this help and exit"))
   (display (G_ "
   -V, --version          display version information and exit"))
@@ -273,6 +278,9 @@ Report the size of PACKAGE and its dependencies.\n"))
         (option '(#\m "map-file") #t #f
                 (lambda (opt name arg result)
                   (alist-cons 'map-file arg result)))
+        (find (lambda (option)
+                (member "load-path" (option-names option)))
+              %standard-build-options)
         (option '(#\h "help") #f #f
                 (lambda args
                   (show-help)