build: Add wrap-qt-program.

* guix/build/qt-utils.scm (wrap-qt-program): New file.
* Makefile.am (MODULES): Add it.

Makefile.am

@@ -107,6 +107,7 @@ MODULES =					\
   guix/build/emacs-utils.scm			\
   guix/build/graft.scm				\
   guix/build/bournish.scm			\
+  guix/build/qt-utils.scm			\
   guix/search-paths.scm				\
   guix/packages.scm				\
   guix/import/utils.scm				\

guix/build/qt-utils.scm

@@ -0,0 +1,40 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2016 David Craven <david@craven.ch>
+;;;
+;;; 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 qt-utils)
+  #:use-module (guix build utils)
+  #:export (wrap-qt-program))
+
+(define (wrap-qt-program out program)
+  (define (suffix env-var path)
+    (let ((env-val (getenv env-var)))
+      (if env-val (string-append env-val ":" path) path)))
+
+  (let ((qml-path        (suffix "QML2_IMPORT_PATH"
+                                 (string-append out "/qml")))
+        (plugin-path     (suffix "QT_PLUGIN_PATH"
+                                 (string-append out "/plugins")))
+        (xdg-data-path   (suffix "XDG_DATA_DIRS"
+                                 (string-append out "/share")))
+        (xdg-config-path (suffix "XDG_CONFIG_DIRS"
+                                 (string-append out "/etc/xdg"))))
+    (wrap-program (string-append out "/bin/" program)
+      `("QML2_IMPORT_PATH" = (,qml-path))
+      `("QT_PLUGIN_PATH" = (,plugin-path))
+      `("XDG_DATA_DIRS" = (,xdg-data-path))
+      `("XDG_CONFIG_DIRS" = (,xdg-config-path)))))