build-system: Add 'guile-build-system'.

* guix/build-system/guile.scm, guix/build/guile-build-system.scm: New
files.
* Makefile.am (MODULES): Add them.
* doc/guix.texi (Build Systems): Document 'guile-build-system'.

Makefile.am

@@ -111,6 +111,7 @@ MODULES =					\
   guix/build-system/asdf.scm			\
   guix/build-system/glib-or-gtk.scm		\
   guix/build-system/gnu.scm			\
+  guix/build-system/guile.scm			\
   guix/build-system/haskell.scm			\
   guix/build-system/perl.scm			\
   guix/build-system/python.scm			\
@@ -149,6 +150,7 @@ MODULES =					\
   guix/build/glib-or-gtk-build-system.scm	\
   guix/build/gnu-build-system.scm		\
   guix/build/gnu-dist.scm			\
+  guix/build/guile-build-system.scm		\
   guix/build/perl-build-system.scm		\
   guix/build/python-build-system.scm		\
   guix/build/ocaml-build-system.scm		\

doc/guix.texi

@@ -4045,6 +4045,21 @@ specified with the @code{#:glib} parameter.
 Both phases are executed after the @code{install} phase.
 @end defvr
 
+@defvr {Scheme Variable} guile-build-system
+This build system is for Guile packages that consist exclusively of Scheme
+code and that are so lean that they don't even have a makefile, let alone a
+@file{configure} script.  It compiles Scheme code using @command{guild
+compile} (@pxref{Compilation,,, guile, GNU Guile Reference Manual}) and
+installs the @file{.scm} and @file{.go} files in the right place.  It also
+installs documentation.
+
+This build system supports cross-compilation by using the @code{--target}
+option of @command{guild compile}.
+
+Packages built with @code{guile-build-system} must provide a Guile package in
+their @code{native-inputs} field.
+@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.

guix/build-system/guile.scm

@@ -0,0 +1,202 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 Ludovic Courtès <ludo@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-system guile)
+  #: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 (%guile-build-system-modules
+            guile-build-system))
+
+(define %guile-build-system-modules
+  ;; Build-side modules imported by default.
+  `((guix build guile-build-system)
+    ,@%gnu-build-system-modules))
+
+(define* (lower name
+                #:key source inputs native-inputs outputs system target
+                #:allow-other-keys
+                #:rest arguments)
+  "Return a bag for NAME."
+
+  ;; Note: There's no #:guile argument (unlike, for instance,
+  ;; 'ocaml-build-system' which has #:ocaml.)  This is so we can keep
+  ;; procedures like 'package-for-guile-2.0' unchanged and simple.
+
+  (define private-keywords
+    '(#:target #:inputs #:native-inputs))
+
+  (bag
+    (name name)
+    (system system) (target target)
+    (host-inputs `(
+                   ,@inputs))
+    (build-inputs `(,@(if source
+                          `(("source" ,source))
+                          '())
+                    ,@native-inputs
+                    ,@(map (cute assoc <> (standard-packages))
+                           '("tar" "gzip" "bzip2" "xz" "locales"))))
+    (outputs outputs)
+    (build (if target guile-cross-build guile-build))
+    (arguments (strip-keyword-arguments private-keywords arguments))))
+
+(define %compile-flags
+  ;; Flags passed to 'guild compile' by default.  We choose a common
+  ;; denominator between Guile 2.0 and 2.2.
+  ''("-Wunbound-variable" "-Warity-mismatch" "-Wformat"))
+
+(define* (guile-build store name inputs
+                      #:key source
+                      (guile #f)
+                      (phases '%standard-phases)
+                      (outputs '("out"))
+                      (search-paths '())
+                      (system (%current-system))
+                      (source-directory ".")
+                      (compile-flags %compile-flags)
+                      (imported-modules %guile-build-system-modules)
+                      (modules '((guix build guile-build-system)
+                                 (guix build utils))))
+  "Build SOURCE using Guile taken from the native inputs, and with INPUTS."
+  (define builder
+    `(begin
+       (use-modules ,@modules)
+       (guile-build #:name ,name
+                    #:source ,(match (assoc-ref inputs "source")
+                                (((? derivation? source))
+                                 (derivation->output-path source))
+                                ((source)
+                                 source)
+                                (source
+                                 source))
+                    #:source-directory ,source-directory
+                    #:compile-flags ,compile-flags
+                    #:phases ,phases
+                    #:system ,system
+                    #: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* (guile-cross-build store name
+                            #:key
+                            (system (%current-system)) target
+                            native-drvs target-drvs
+                            (guile #f)
+                            source
+                            (outputs '("out"))
+                            (search-paths '())
+                            (native-search-paths '())
+
+                            (phases '%standard-phases)
+                            (source-directory ".")
+                            (compile-flags %compile-flags)
+                            (imported-modules %guile-build-system-modules)
+                            (modules '((guix build guile-build-system)
+                                       (guix build utils))))
+  (define builder
+    `(begin
+       (use-modules ,@modules)
+
+       (let ()
+         (define %build-host-inputs
+           ',(map (match-lambda
+                    ((name (? derivation? drv) sub ...)
+                     `(,name . ,(apply derivation->output-path drv sub)))
+                    ((name path)
+                     `(,name . ,path)))
+                  native-drvs))
+
+         (define %build-target-inputs
+           ',(map (match-lambda
+                    ((name (? derivation? drv) sub ...)
+                     `(,name . ,(apply derivation->output-path drv sub)))
+                    ((name (? package? pkg) sub ...)
+                     (let ((drv (package-cross-derivation store pkg
+                                                          target system)))
+                       `(,name . ,(apply derivation->output-path drv sub))))
+                    ((name path)
+                     `(,name . ,path)))
+                  target-drvs))
+
+         (guile-build #:source ,(match (assoc-ref native-drvs "source")
+                                  (((? derivation? source))
+                                   (derivation->output-path source))
+                                  ((source)
+                                   source)
+                                  (source
+                                   source))
+                      #:system ,system
+                      #:target ,target
+                      #:outputs %outputs
+                      #:source-directory ,source-directory
+                      #:compile-flags ,compile-flags
+                      #:inputs %build-target-inputs
+                      #:native-inputs %build-host-inputs
+                      #:search-paths ',(map search-path-specification->sexp
+                                            search-paths)
+                      #:native-search-paths ',(map
+                                               search-path-specification->sexp
+                                               native-search-paths)
+                      #:phases ,phases))))
+
+  (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
+                                #:system system
+                                #:inputs (append native-drvs target-drvs)
+                                #:outputs outputs
+                                #:modules imported-modules
+                                #:substitutable? substitutable?
+                                #:guile-for-build guile-for-build))
+
+(define guile-build-system
+  (build-system
+    (name 'guile)
+    (description "The build system for simple Guile packages")
+    (lower lower)))

guix/build/guile-build-system.scm

@@ -0,0 +1,153 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 Ludovic Courtès <ludo@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 guile-build-system)
+  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
+  #:use-module (guix build utils)
+  #:use-module (srfi srfi-26)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 popen)
+  #:use-module (ice-9 rdelim)
+  #:use-module (guix build utils)
+  #:export (target-guile-effective-version
+            %standard-phases
+            guile-build))
+
+(define* (target-guile-effective-version #:optional guile)
+  "Return the effective version of GUILE or whichever 'guile' is in $PATH.
+Return #false if it cannot be determined."
+  (let* ((pipe (open-pipe* OPEN_READ
+                           (if guile
+                               (string-append guile "/bin/guile")
+                               "guile")
+                           "-c" "(display (effective-version))"))
+         (line (read-line pipe)))
+    (and (zero? (close-pipe pipe))
+         (string? line)
+         line)))
+
+(define (file-sans-extension file)                ;TODO: factorize
+  "Return the substring of FILE without its extension, if any."
+  (let ((dot (string-rindex file #\.)))
+    (if dot
+        (substring file 0 dot)
+        file)))
+
+(define %scheme-file-regexp
+  ;; Regexp to match Scheme files.
+  "\\.(scm|sls)$")
+
+(define %documentation-file-regexp
+  ;; Regexp to match README files and the likes.
+  "^(README.*|.*\\.html|.*\\.org|.*\\.md)$")
+
+(define* (set-locale-path #:key inputs native-inputs
+                          #:allow-other-keys)
+  "Set 'GUIX_LOCPATH'."
+  (match (assoc-ref (or native-inputs inputs) "locales")
+    (#f #t)
+    (locales
+     (setenv "GUIX_LOCPATH" (string-append locales "/lib/locale"))
+     #t)))
+
+(define* (build #:key outputs inputs native-inputs
+                (source-directory ".")
+                (compile-flags '())
+                (scheme-file-regexp %scheme-file-regexp)
+                target
+                #:allow-other-keys)
+  "Build files in SOURCE-DIRECTORY that match SCHEME-FILE-REGEXP."
+  (let* ((out        (assoc-ref outputs "out"))
+         (guile      (assoc-ref (or native-inputs inputs) "guile"))
+         (effective  (target-guile-effective-version guile))
+         (module-dir (string-append out "/share/guile/site/"
+                                    effective))
+         (go-dir     (string-append out "/lib/guile/"
+                                    effective "/site-ccache/"))
+         (guild      (string-append guile "/bin/guild"))
+         (flags      (if target
+                         (cons (string-append "--target=" target)
+                               compile-flags)
+                         compile-flags)))
+    (if target
+        (format #t "Cross-compiling for '~a' with Guile ~a...~%"
+                target effective)
+        (format #t "Compiling with Guile ~a...~%" effective))
+    (format #t "compile flags: ~s~%" flags)
+
+    ;; Make installation directories.
+    (mkdir-p module-dir)
+    (mkdir-p go-dir)
+
+    ;; Compile .scm files and install.
+    (setenv "GUILE_AUTO_COMPILE" "0")
+    (setenv "GUILE_LOAD_COMPILED_PATH"
+            (string-append go-dir
+                           (match (getenv "GUILE_LOAD_COMPILED_PATH")
+                             (#f "")
+                             (path (string-append ":" path)))))
+    (for-each (lambda (file)
+                (let* ((go (string-append go-dir
+                                          (file-sans-extension file)
+                                          ".go")))
+                  ;; Install source module.
+                  (install-file (string-append source-directory "/" file)
+                                (string-append module-dir
+                                               "/" (dirname file)))
+
+                  ;; Install and compile module.
+                  (apply invoke guild "compile" "-L" source-directory
+                         "-o" go
+                         (string-append source-directory "/" file)
+                         flags)))
+
+              ;; Arrange to strip SOURCE-DIRECTORY from file names.
+              (with-directory-excursion source-directory
+                (find-files "." scheme-file-regexp)))
+    #t))
+
+(define* (install-documentation #:key outputs
+                                (documentation-file-regexp
+                                 %documentation-file-regexp)
+                                #:allow-other-keys)
+  "Install files that mactch DOCUMENTATION-FILE-REGEXP."
+  (let* ((out (assoc-ref outputs "out"))
+         (doc (string-append out "/share/doc/"
+                             (strip-store-file-name out))))
+    (for-each (cut install-file <> doc)
+              (find-files "." documentation-file-regexp))
+    #t))
+
+(define %standard-phases
+  (modify-phases gnu:%standard-phases
+    (delete 'bootstrap)
+    (delete 'configure)
+    (add-before 'install-locale 'set-locale-path
+      set-locale-path)
+    (replace 'build build)
+    (add-after 'build 'install-documentation
+      install-documentation)
+    (delete 'check)
+    (delete 'strip)
+    (delete 'validate-runpath)
+    (delete 'install)))
+
+(define* (guile-build #:key (phases %standard-phases)
+                      #:allow-other-keys #:rest args)
+  "Build the given Guile package, applying all of PHASES in order."
+  (apply gnu:gnu-build #:phases phases args))