build: Add ruby build system.

* guix/build-system/ruby.scm: New file.
* guix/build/ruby-build-system: New file.
* Makefile.am (MODULES): Add new files.
* doc/guix.texi (Build Systems): Document ruby-build-system.

guix/build/ruby-build-system.scm

@@ -0,0 +1,75 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2014 David Thompson <davet@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build ruby-build-system)
+  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
+  #:use-module (guix build utils)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 regex)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:export (%standard-phases
+            ruby-build))
+
+;; Commentary:
+;;
+;; Builder-side code of the standard Ruby package build procedure.
+;;
+;; Code:
+
+(define (first-matching-file pattern)
+  "Return the first file name that matches PATTERN in the current working
+directory."
+  (match (find-files "." pattern)
+    ((file-name . _) file-name)
+    (() (error "No files matching pattern: " pattern))))
+
+(define build
+  (lambda _
+    (zero? (system* "gem" "build" (first-matching-file "\\.gemspec$")))))
+
+(define* (check #:key tests? test-target #:allow-other-keys)
+  (if tests?
+      (zero? (system* "rake" test-target))
+      #t))
+
+(define* (install #:key source inputs outputs #:allow-other-keys)
+  (let* ((ruby-version
+          (match:substring (string-match "ruby-(.*)$"
+                                         (assoc-ref inputs "ruby"))
+                           1))
+         (gem-home (string-append (assoc-ref outputs "out")
+                                  "/lib/ruby/gems/"
+                                  ruby-version)))
+    (setenv "GEM_HOME" gem-home)
+    (mkdir-p gem-home)
+    (zero? (system* "gem" "install" "--local"
+                    (first-matching-file "\\.gem$")))))
+
+(define %standard-phases
+  (alist-replace
+   'build build
+   (alist-replace
+    'install install
+    (alist-replace
+     'check check
+     (alist-delete 'configure gnu:%standard-phases)))))
+
+(define* (ruby-build #:key inputs (phases %standard-phases)
+                     #:allow-other-keys #:rest args)
+  (apply gnu:gnu-build #:inputs inputs #:phases phases args))