import: Add hex.pm importer.

hex.pm is a package repository for Erlang and Elixir.

* guix/scripts/import.scm (importers): Add "hexpm".
* guix/scripts/import/hexpm.scm, guix/import/hexpm.scm,
  guix/hexpm-download.scm: New files.
* guix/import/utils.scm (source-spec->object): Add "hexpm-fetch" to list of
  fetch methods.
* guix/upstream.scm (package-update/hexpm-fetch): New function.
  (%method-updates) Add it.
* Makefile.am: Add them.

guix/scripts/import/hexpm.scm

@@ -0,0 +1,105 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2020, 2022 Hartmut Goebel <h.goebel@crazy-compilers.com>
+;;;
+;;; 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 hexpm)
+  #:use-module (guix ui)
+  #:use-module (guix utils)
+  #:use-module (guix scripts)
+  #:use-module (guix import hexpm)
+  #:use-module (guix scripts import)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-37)
+  #:use-module (srfi srfi-71)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 format)
+  #:export (guix-import-hexpm))
+
+
+;;;
+;;; Command-line options.
+;;;
+
+(define %default-options
+  '())
+
+(define (show-help)
+  (display (G_ "Usage: guix import hexpm PACKAGE-NAME
+Import and convert the hex.pm package for PACKAGE-NAME.\n"))
+  (display (G_ "
+  -h, --help             display this help and exit"))
+  (display (G_ "
+  -V, --version          display version information and exit"))
+  (newline)
+  (display (G_ "
+  -r, --recursive        import packages recursively"))
+  (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 hexpm")))
+         (option '(#\r "recursive") #f #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'recursive #t result)))
+         %standard-import-options))
+
+
+;;;
+;;; Entry point.
+;;;
+
+(define (guix-import-hexpm . args)
+  (define (parse-options)
+    ;; Return the alist of option values.
+    (parse-command-line args %options (list %default-options)
+                        #:build-options? #f))
+
+  (let* ((opts (parse-options))
+         (args (filter-map (match-lambda
+                            (('argument . value)
+                             value)
+                            (_ #f))
+                           (reverse opts))))
+    (match args
+      ((spec)
+       (with-error-handling
+         (let ((name version (package-name->name+version spec)))
+           (if (assoc-ref opts 'recursive)
+               ;; Recursive import
+               (map (match-lambda
+                     ((and ('package ('name name) . rest) pkg)
+                      `(define-public ,(string->symbol name)
+                         ,pkg))
+                     (_ #f))
+                    (hexpm-recursive-import name version))
+               ;; Single import
+               (let ((sexp (hexpm->guix-package name #:version version)))
+                 (unless sexp
+                   (leave (G_ "failed to download meta-data for package '~a'~%")
+                          spec))
+                 sexp)))))
+      (()
+       (leave (G_ "too few arguments~%")))
+      ((many ...)
+       (leave (G_ "too many arguments~%"))))))