import: Add Ruby gem importer.

* gnu/scripts/import.scm (importers): Add "gem".
* gnu/import/gem.scm: New file.
* gnu/scripts/import/gem.scm: New file.
* Makefile.am (MODULES): Add them.
* guix.texi ("invoking guix import"): Document it.

5 files changed, 244 insertions, 2 deletions

diff --git a/Makefile.am b/Makefile.am
index c32464921b..85cc7bd50f 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -221,7 +221,8 @@ MODULES +=					\
   guix/import/pypi.scm				\
   guix/scripts/import/pypi.scm			\
   guix/import/cpan.scm				\
-  guix/scripts/import/cpan.scm
+  guix/scripts/import/gem.scm			\
+  guix/import/gem.scm
 
 SCM_TESTS += 					\
   tests/pypi.scm				\
diff --git a/doc/guix.texi b/doc/guix.texi
index 6ea143f37b..88e1ff7f77 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -3894,6 +3894,25 @@ package:
 guix import pypi itsdangerous
 @end example
 
+@item gem
+@cindex gem
+Import meta-data from @uref{https://rubygems.org/,
+RubyGems}@footnote{This functionality requires Guile-JSON to be
+installed.  @xref{Requirements}.}.  Information is taken from the
+JSON-formatted description available at @code{rubygems.org} and includes
+most relevant information, including runtime dependencies.  There are
+some caveats, however.  The meta-data doesn't distinguish between
+synopses and descriptions, so the same string is used for both fields.
+Additionally, the details of non-Ruby dependencies required to build
+native extensions is unavailable and left as an exercise to the
+packager.
+
+The command below imports meta-data for the @code{rails} Ruby package:
+
+@example
+guix import gem rails
+@end example
+
 @item cpan
 @cindex CPAN
 Import meta-data from @uref{https://www.metacpan.org/, MetaCPAN}.
diff --git a/guix/import/gem.scm b/guix/import/gem.scm
new file mode 100644
index 0000000000..3c28d1d9fd
--- /dev/null
+++ b/guix/import/gem.scm
@@ -0,0 +1,131 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2015 David Thompson <davet@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 import gem)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 pretty-print)
+  #:use-module (rnrs bytevectors)
+  #:use-module (json)
+  #:use-module (web uri)
+  #:use-module (guix import utils)
+  #:use-module (guix import json)
+  #:use-module (guix packages)
+  #:use-module (guix licenses)
+  #:use-module (guix base32)
+  #:export (gem->guix-package))
+
+(define (rubygems-fetch name)
+  "Return an alist representation of the RubyGems metadata for the package NAME,
+or #f on failure."
+  (json-fetch
+   (string-append "https://rubygems.org/api/v1/gems/" name ".json")))
+
+(define (ruby-package-name name)
+  "Given the NAME of a package on RubyGems, return a Guix-compliant name for
+the package."
+  (if (string-prefix? "ruby-" name)
+      (snake-case name)
+      (string-append "ruby-" (snake-case name))))
+
+(define (hex-string->bytevector str)
+  "Convert the hexadecimal encoded string STR to a bytevector."
+  (define hex-char->int
+    (match-lambda
+     (#\0 0)
+     (#\1 1)
+     (#\2 2)
+     (#\3 3)
+     (#\4 4)
+     (#\5 5)
+     (#\6 6)
+     (#\7 7)
+     (#\8 8)
+     (#\9 9)
+     (#\a 10)
+     (#\b 11)
+     (#\c 12)
+     (#\d 13)
+     (#\e 14)
+     (#\f 15)))
+
+  (define (read-byte i)
+    (let ((j (* 2 i)))
+      (+ (hex-char->int (string-ref str (1+ j)))
+         (* (hex-char->int (string-ref str j)) 16))))
+
+  (let* ((len (/ (string-length str) 2))
+         (bv  (make-bytevector len)))
+    (let loop ((i 0))
+      (if (= i len)
+          bv
+          (begin
+            (bytevector-u8-set! bv i (read-byte i))
+            (loop (1+ i)))))))
+
+(define (make-gem-sexp name version hash home-page description
+                       dependencies licenses)
+  "Return the `package' s-expression for a Ruby package with the given NAME,
+VERSION, HASH, HOME-PAGE, DESCRIPTION, DEPENDENCIES, and LICENSES."
+  `(package
+     (name ,(ruby-package-name name))
+     (version ,version)
+     (source (origin
+               (method url-fetch)
+               (uri (rubygems-uri ,name version))
+               (sha256
+                (base32
+                 ,(bytevector->nix-base32-string
+                   (hex-string->bytevector hash))))))
+     (build-system ruby-build-system)
+     ,@(if (null? dependencies)
+           '()
+           `((propagated-inputs
+              (,'quasiquote
+               ,(map (lambda (name)
+                       `(,name
+                         (,'unquote
+                          ,(string->symbol name))))
+                     dependencies)))))
+     (synopsis ,description)    ; nothing better to use
+     (description ,description)
+     (home-page ,home-page)
+     (license ,(match licenses
+                 ((license) (license->symbol license))
+                 (_ (map license->symbol licenses))))))
+
+(define* (gem->guix-package package-name #:optional version)
+  "Fetch the metadata for PACKAGE-NAME from rubygems.org, and return the
+`package' s-expression corresponding to that package, or #f on failure."
+  (let ((package (rubygems-fetch package-name)))
+    (and package
+         (let ((name         (assoc-ref package "name"))
+               (version      (assoc-ref package "version"))
+               (hash         (assoc-ref package "sha"))
+               (description  (assoc-ref package "info"))
+               (home-page    (assoc-ref package "homepage_uri"))
+               (dependencies (map (lambda (dep)
+                                    (let ((name (assoc-ref dep "name")))
+                                      (if (string=? name "bundler")
+                                          "bundler" ; special case, no prefix
+                                          (ruby-package-name name))))
+                                  (assoc-ref* package "dependencies"
+                                              "runtime")))
+               (licenses     (map string->license
+                                  (assoc-ref package "licenses"))))
+           (make-gem-sexp name version hash home-page
+                          description dependencies licenses)))))
diff --git a/guix/scripts/import.scm b/guix/scripts/import.scm
index d0bdec133d..6cd762a537 100644
--- a/guix/scripts/import.scm
+++ b/guix/scripts/import.scm
@@ -73,7 +73,7 @@ rather than \\n."
 ;;; Entry point.
 ;;;
 
-(define importers '("gnu" "nix" "pypi" "cpan" "hackage" "elpa"))
+(define importers '("gnu" "nix" "pypi" "cpan" "hackage" "elpa" "gem"))
 
 (define (resolve-importer name)
   (let ((module (resolve-interface
diff --git a/guix/scripts/import/gem.scm b/guix/scripts/import/gem.scm
new file mode 100644
index 0000000000..9f8094feac
--- /dev/null
+++ b/guix/scripts/import/gem.scm
@@ -0,0 +1,91 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2015 David Thompson <davet@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 scripts import gem)
+  #:use-module (guix ui)
+  #:use-module (guix utils)
+  #:use-module (guix import gem)
+  #:use-module (guix scripts import)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-11)
+  #:use-module (srfi srfi-37)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 format)
+  #:export (guix-import-gem))
+
+
+;;;
+;;; Command-line options.
+;;;
+
+(define %default-options
+  '())
+
+(define (show-help)
+  (display (_ "Usage: guix import gem PACKAGE-NAME
+Import and convert the RubyGems package for PACKAGE-NAME.\n"))
+  (display (_ "
+  -h, --help             display this help and exit"))
+  (display (_ "
+  -V, --version          display version information and exit"))
+  (newline)
+  (show-bug-report-information))
+
+(define %options
+  ;; Specification of the command-line options.
+  (cons* (option '(#\h "help") #f #f
+                 (lambda args
+                   (show-help)
+                   (exit 0)))
+         (option '(#\V "version") #f #f
+                 (lambda args
+                   (show-version-and-exit "guix import pypi")))
+         %standard-import-options))
+
+
+;;;
+;;; Entry point.
+;;;
+
+(define (guix-import-gem . args)
+  (define (parse-options)
+    ;; Return the alist of option values.
+    (args-fold* args %options
+                (lambda (opt name arg result)
+                  (leave (_ "~A: unrecognized option~%") name))
+                (lambda (arg result)
+                  (alist-cons 'argument arg result))
+                %default-options))
+
+  (let* ((opts (parse-options))
+         (args (filter-map (match-lambda
+                            (('argument . value)
+                             value)
+                            (_ #f))
+                           (reverse opts))))
+    (match args
+      ((package-name)
+       (let ((sexp (gem->guix-package package-name)))
+         (unless sexp
+           (leave (_ "failed to download meta-data for package '~a'~%")
+                  package-name))
+         sexp))
+      (()
+       (leave (_ "too few arguments~%")))
+      ((many ...)
+       (leave (_ "too many arguments~%"))))))