build: Add minify build system.

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

Makefile.am

@@ -79,6 +79,7 @@ MODULES =					\
   guix/build-system/dub.scm			\
   guix/build-system/emacs.scm			\
   guix/build-system/font.scm			\
+  guix/build-system/minify.scm			\
   guix/build-system/asdf.scm			\
   guix/build-system/glib-or-gtk.scm		\
   guix/build-system/gnu.scm			\
@@ -105,6 +106,7 @@ MODULES =					\
   guix/build/cmake-build-system.scm		\
   guix/build/dub-build-system.scm		\
   guix/build/emacs-build-system.scm		\
+  guix/build/minify-build-system.scm		\
   guix/build/font-build-system.scm		\
   guix/build/asdf-build-system.scm		\
   guix/build/git.scm				\

doc/guix.texi

@@ -3576,6 +3576,21 @@ specified with the @code{#:glib} parameter.
 Both phases are executed after the @code{install} phase.
 @end defvr
 
+@defvr {Scheme Variable} minify-build-system
+This variable is exported by @code{(guix build-system minify)}.  It
+implements a minification procedure for simple JavaScript packages.
+
+It adds @code{uglify-js} to the set of inputs and uses it to compress
+all JavaScript files in the @file{src} directory.  A different minifier
+package can be specified with the @code{#:uglify-js} parameter, but it
+is expected that the package writes the minified code to the standard
+output.
+
+When the input JavaScript files are not all located in the @file{src}
+directory, the parameter @code{#:javascript-files} can be used to
+specify a list of file names to feed to the minifier.
+@end defvr
+
 @defvr {Scheme Variable} ocaml-build-system
 This variable is exported by @code{(guix build-system ocaml)}.  It implements
 a build procedure for @uref{https://ocaml.org, OCaml} packages, which consists

guix/build-system/minify.scm

@@ -0,0 +1,127 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2017 Ricardo Wurmus <rekado@elephly.net>
+;;;
+;;; 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-system minify)
+  #:use-module (guix store)
+  #:use-module (guix utils)
+  #:use-module (guix packages)
+  #:use-module (guix derivations)
+  #:use-module (guix search-paths)
+  #:use-module (guix build-system)
+  #:use-module (guix build-system gnu)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-26)
+  #:export (%minify-build-system-modules
+            minify-build
+            minify-build-system))
+
+;; Commentary:
+;;
+;; Standard minification procedure for JavaScript files.
+;;
+;; Code:
+
+(define %minify-build-system-modules
+  ;; Build-side modules imported by default.
+  `((guix build minify-build-system)
+    (ice-9 popen)
+    ,@%gnu-build-system-modules))
+
+(define (default-uglify-js)
+  "Return the default package to minify JavaScript source files."
+  ;; Lazily resolve the binding to avoid a circular dependency.
+  (let ((lisp-mod (resolve-interface '(gnu packages lisp))))
+    (module-ref lisp-mod 'uglify-js)))
+
+(define* (lower name
+                #:key source inputs native-inputs outputs system
+                (uglify-js (default-uglify-js))
+                #:allow-other-keys
+                #:rest arguments)
+  "Return a bag for NAME."
+  (define private-keywords
+    '(#:source #:target #:inputs #:native-inputs))
+
+  (bag
+    (name name)
+    (system system)
+    (host-inputs `(,@(if source
+                         `(("source" ,source))
+                         '())
+                   ,@inputs
+                   ,@(standard-packages)))
+    (build-inputs `(("uglify-js" ,uglify-js)
+                    ,@native-inputs))
+    (outputs outputs)
+    (build minify-build)
+    (arguments (strip-keyword-arguments private-keywords arguments))))
+
+(define* (minify-build store name inputs
+                       #:key
+                       (javascript-files #f)
+                       (phases '(@ (guix build minify-build-system)
+                                   %standard-phases))
+                       (outputs '("out"))
+                       (system (%current-system))
+                       search-paths
+                       (guile #f)
+                       (imported-modules %minify-build-system-modules)
+                       (modules '((guix build minify-build-system)
+                                  (guix build utils))))
+  "Build SOURCE with INPUTS."
+  (define builder
+    `(begin
+       (use-modules ,@modules)
+       (minify-build #:name ,name
+                     #:source ,(match (assoc-ref inputs "source")
+                                 (((? derivation? source))
+                                  (derivation->output-path source))
+                                 ((source)
+                                  source)
+                                 (source
+                                  source))
+                     #:javascript-files ,javascript-files
+                     #:phases ,phases
+                     #:outputs %outputs
+                     #:search-paths ',(map search-path-specification->sexp
+                                           search-paths)
+                     #:inputs %build-inputs)))
+
+  (define guile-for-build
+    (match guile
+      ((? package?)
+       (package-derivation store guile system #:graft? #f))
+      (#f                               ; the default
+       (let* ((distro (resolve-interface '(gnu packages commencement)))
+              (guile  (module-ref distro 'guile-final)))
+         (package-derivation store guile system #:graft? #f)))))
+
+  (build-expression->derivation store name builder
+                                #:inputs inputs
+                                #:system system
+                                #:modules imported-modules
+                                #:outputs outputs
+                                #:guile-for-build guile-for-build))
+
+(define minify-build-system
+  (build-system
+    (name 'minify)
+    (description "The trivial JavaScript minification build system")
+    (lower lower)))
+
+;;; minify.scm ends here

guix/build/minify-build-system.scm

@@ -0,0 +1,73 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2016 Ricardo Wurmus <rekado@elephly.net>
+;;;
+;;; 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 minify-build-system)
+  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
+  #:use-module ((guix build minify-build-system) #:prefix minify:)
+  #:use-module (guix build utils)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:use-module (ice-9 popen)
+  #:export (%standard-phases
+            minify-build
+            minify))
+
+;; Commentary:
+;;
+;; Builder-side code of the standard minification procedure for JavaScript
+;; files.
+;;
+;; Code:
+
+(define* (minify file #:key target (directory ""))
+  (format #t "minifying ~a\n" file)
+  (let* ((base (basename file ".js"))
+         (installed (or target (string-append directory base ".min.js")))
+         (minified (open-pipe* OPEN_READ "uglify-js" file)))
+    (call-with-output-file installed
+      (cut dump-port minified <>))
+    #t))
+
+(define* (build #:key javascript-files
+                #:allow-other-keys)
+  (let ((files (or javascript-files
+                   (find-files "src" "\\.js$"))))
+    (mkdir-p "guix/build")
+    (every (cut minify <> #:directory "guix/build/") files)))
+
+(define* (install #:key outputs #:allow-other-keys)
+  (let* ((out (assoc-ref outputs "out"))
+         (js  (string-append out "/share/javascript/")))
+    (mkdir-p js)
+    (for-each (cut install-file <> js)
+              (find-files "guix/build" "\\.min\\.js$")))
+  #t)
+
+(define %standard-phases
+  (modify-phases gnu:%standard-phases
+    (delete 'configure)
+    (replace 'build build)
+    (delete 'check)
+    (replace 'install install)))
+
+(define* (minify-build #:key inputs (phases %standard-phases)
+                       #:allow-other-keys #:rest args)
+  "Build the given JavaScript package, applying all of PHASES in order."
+  (apply gnu:gnu-build #:inputs inputs #:phases phases args))
+
+;;; minify-build-system.scm ends here