Using gexp for the #:builder arg of build systems

[Maxim Cournoyer]

Hello,

After reading Ludovic's paper about gexps, I was curious to try it in a
package definition. Is this supported yet?

Here's my attempt:

1 file changed, 36 insertions(+)
gnu/packages/android.scm | 36 ++++++++++++++++++++++++++++++++++++

modified   gnu/packages/android.scm
@@ -4,6 +4,7 @@
 ;;; Copyright © 2016 Marius Bakke <address@hidden>
 ;;; Copyright © 2017 Julien Lepiller <address@hidden>
 ;;; Copyright © 2017 Hartmut Goebel <address@hidden>
+;;; Copyright © 2017 Maxim Cournoyer <address@hidden>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -21,10 +22,12 @@
 ;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
 
 (define-module (gnu packages android)
+  #:use-module (guix gexp)
   #:use-module (guix packages)
   #:use-module (guix git-download)
   #:use-module (guix build-system gnu)
   #:use-module (guix build-system python)
+  #:use-module (guix build-system trivial)
   #:use-module ((guix licenses) #:prefix license:)
   #:use-module (gnu packages)
   #:use-module (gnu packages gnupg)
@@ -305,6 +308,39 @@ of device actions, such as installing and debugging apps, 
and it provides access
 to a Unix shell that can run commands on the connected device or emulator.")
     (license license:asl2.0)))
 
+(define-public android-udev-rules
+  (package
+    (name "android-udev-rules")
+    (version "20170910")
+    (source
+     (origin
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/M0Rf30/android-udev-rules";)
+             (commit version)))
+       (file-name (string-append name "-" version "-checkout"))
+       (sha256
+        (base32 "0vic40n3si0dxag3dyc3hi3pn7cjpm5q378x8v2ys19n3iz9fp1g"))))
+    (build-system trivial-build-system)
+    (arguments
+     (list
+      #:builder
+      (with-imported-modules '((guix build utils))
+        #~(begin
+            (use-modules (guix build utils))
+            (install-file "51-android.rules"
+                          (string-append #$output "/lib/udev/rules.d"))))))
+    (home-page "https://github.com/M0Rf30/android-udev-rules";)
+    (synopsis "udev rules for Android devices")
+    (description "Provides a set of udev rules to allow using Android devices
+with tools such as @command{adb} and @command{fastboot} without root
+privileges.  This package is intended to be added as a rule to the
address@hidden in your @code{operating-system}
+configuration. Additionally, an @code{adbusers} group must be defined and your
+user added to it.  @emph{Simply installing this package will @strong{not} have
+an effect.}")
+    (license license:gpl3+)))
+
 (define-public git-repo
   (package
     (name "git-repo")

And here's the error I get when attempting to build it:

--8<---------------cut here---------------start------------->8---
@ build-succeeded 
/gnu/store/6qcm0pxqhi4hd4lldixdlm88zakl4cip-android-udev-rules-20170910-checkout.drv
 -
@ build-started 
/gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv - 
x86_64-linux 
/var/log/guix/drvs/kf//dc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv.bz2
ERROR: In procedure primitive-load:
ERROR: In procedure scm_lreadr: 
/gnu/store/kkrin9p4xd7j4pkiy8rvhq7hlhb5i8kp-android-udev-rules-20170910-guile-builder:1:10:
 Unknown # object: #\<
builder for 
`/gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv' 
failed with exit code 1
@ build-failed 
/gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv - 1 
builder for 
`/gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv' 
failed with exit code 1
guix build: error: build failed: build of 
`/gnu/store/kfdc7a7wnb7wppn0pylhcqq8pqf9gv21-android-udev-rules-20170910.drv' 
failed
--8<---------------cut here---------------end--------------->8---

Possibly, the gexps are not being lowered (compiled) in the generated
builder script. When manually indenting it[1] this builder looks like:

--8<---------------cut here---------------start------------->8---
(begin #<gexp
       (begin (use-modules (guix build utils))
              (install-file "51-android.rules"
                            (string-append #<gexp-output out> 
"/lib/udev/rules.d"))) 286c810>
                            (define %output (getenv "out"))
                            (define %outputs (map (lambda (o) (cons o (getenv 
o))) (quote ("out"))))
                            (define %build-inputs (quote (("source" . 
"/gnu/store/n9prv51xsahbxiz1jypaz6q14gid9r5d-android-udev-rules-20170910-checkout"))))
                            (unsetenv "GUILE_LOAD_COMPILED_PATH")
                            (unsetenv "LD_LIBRARY_PATH"))
(exit (#<gexp
       (begin (use-modules (guix build utils))
              (install-file "51-android.rules"
                            (string-append #<gexp-output out> 
"/lib/udev/rules.d"))) 286c810>))
--8<---------------cut here---------------end--------------->8---

It seems to me that the gexp objects should have been lowered into
absolute file paths at this point, no?

Maxim

[1]  A Guile auto-formatter could be an interesting pet project... :)