Add (guix build-system trivial).

* guix/build-system/trivial.scm: New file.
* Makefile.am (MODULES): Add it.
* tests/packages.scm ("trivial"): New test.

* guix/packages.scm (package-derivation): Allow SOURCE to be #f.

Makefile.am

@@ -23,6 +23,7 @@ MODULES =					\
   guix/derivations.scm				\
   guix/build-system.scm				\
   guix/build-system/gnu.scm			\
+  guix/build-system/trivial.scm			\
   guix/http.scm					\
   guix/store.scm				\
   guix/build/gnu-build-system.scm		\

guix/build-system/trivial.scm

@@ -0,0 +1,39 @@
+;;; Guix --- Nix package management from Guile.         -*- coding: utf-8 -*-
+;;; Copyright (C) 2012 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of Guix.
+;;;
+;;; 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.
+;;;
+;;; 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 Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build-system trivial)
+  #:use-module (guix store)
+  #:use-module (guix utils)
+  #:use-module (guix derivations)
+  #:use-module (guix build-system)
+  #:export (trivial-build-system))
+
+(define* (trivial-build store name source inputs
+                        #:key outputs system builder (modules '()))
+  "Run build expression BUILDER, an expression, for SYSTEM.  SOURCE is
+ignored."
+  (build-expression->derivation store name system builder inputs
+                                #:outputs outputs
+                                #:modules modules))
+
+(define trivial-build-system
+  (build-system (name 'trivial)
+                (description
+                 "Trivial build system, to run arbitrary Scheme build expressions")
+                (build trivial-build)
+                (cross-build trivial-build)))

guix/packages.scm

@@ -261,7 +261,7 @@ recursively."
            (cache package system
                   (apply builder
                          store (package-full-name package)
-                         (package-source-derivation store source)
+                         (and source (package-source-derivation store source))
                          inputs
                          #:outputs outputs #:system system
                          (if (procedure? args)

tests/packages.scm

@@ -22,6 +22,7 @@
   #:use-module (guix utils)
   #:use-module (guix derivations)
   #:use-module (guix packages)
+  #:use-module (guix build-system trivial)
   #:use-module (guix build-system gnu)
   #:use-module (distro)
   #:use-module (distro base)
@@ -62,7 +63,24 @@
                    ("d" ,d) ("d/x" "something.drv"))
                  (pk 'x (package-transitive-inputs e))))))
 
-(test-skip (if (not %store) 1 0))
+(test-skip (if (not %store) 2 0))
+
+(test-assert "trivial"
+  (let* ((p (package (inherit (dummy-package "trivial"))
+              (build-system trivial-build-system)
+              (source #f)
+              (arguments
+               '(#:builder
+                 (begin
+                   (mkdir %output)
+                   (call-with-output-file (string-append %output "/test")
+                     (lambda (p)
+                       (display '(hello guix) p))))))))
+         (d (package-derivation %store p)))
+    (and (build-derivations %store (list d))
+         (let ((p (pk 'drv d (derivation-path->output-path d))))
+           (equal? '(hello guix)
+                   (call-with-input-file (string-append p "/test") read))))))
 
 (test-assert "GNU Hello"
   (and (package? hello)