[bug#53818,2/3] import: Add 'repology' updater.

diff --git a/Makefile.am b/Makefile.am
index 7463606d20..6792917b59 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -16,6 +16,7 @@ 
 # Copyright © 2019 Efraim Flashner <efraim@flashner.co.il>
 # Copyright © 2021 Chris Marusich <cmmarusich@gmail.com>
 # Copyright © 2021 Andrew Tropin <andrew@trop.in>
+# Copyright © 2022 Xinglu Chen <public@yoctocell.xyz>
 #
 # This file is part of GNU Guix.
 #
@@ -271,6 +272,7 @@  MODULES =					\
   guix/import/opam.scm				\
   guix/import/print.scm				\
   guix/import/pypi.scm				\
+  guix/import/repology.scm			\
   guix/import/stackage.scm			\
   guix/import/texlive.scm   			\
   guix/import/utils.scm				\
@@ -488,6 +490,7 @@  SCM_TESTS =					\
   tests/home-import.scm				\
   tests/import-git.scm				\
   tests/import-github.scm			\
+  tests/import-repology.scm			\
   tests/import-utils.scm			\
   tests/inferior.scm				\
   tests/lint.scm				\
diff --git a/doc/guix.texi b/doc/guix.texi
index 0cf865a672..15d215dd48 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -12932,6 +12932,13 @@ 
       (release-tag-version-delimiter . ":"))))
 @end lisp
 
+@item repology
+an updater that scans @uref{https://repology.org, Repology}, a website
+that tracks packages on various package repositories, for updates.
+
+The name of a package in Guix is not always that same as the name on
+Repology; users can set the @code{repology-name} package property to
+make the updater use the correct name.
 
 @end table
 
diff --git a/guix/import/repology.scm b/guix/import/repology.scm
new file mode 100644
index 0000000000..1d88022c1d
--- /dev/null
+++ b/guix/import/repology.scm
@@ -0,0 +1,226 @@ 
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2022 Xinglu Chen <public@yoctocell.xyz>
+;;;
+;;; 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 repology)
+  #:use-module (guix diagnostics)
+  #:use-module (guix diagnostics)
+  #:use-module (guix git-download)
+  #:use-module (guix i18n)
+  #:use-module (guix import json)
+  #:use-module (guix import utils)
+  #:use-module (guix memoization)
+  #:use-module (guix packages)
+  #:use-module (guix upstream)
+  #:use-module (guix utils)
+  #:use-module (ice-9 match)
+  #:use-module (json)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-2)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-43)
+  #:export (repology-latest-release
+            %repology-updater))
+
+;;; Commentary:
+;;;
+;;; This module provides an updater which scans Repology, a site that monitors
+;;; several package repolsitories, for updates.  This means that if any other
+;;; package repository has a version of a package that is newer than the
+;;; version in Guix, the package should be able to be updated.  The updater
+;;; should in theory work for all packages in Guix, but the names of some
+;;; packages on Repology don't match the name in Guix.  The 'repology-name'
+;;; package property can be used to fix this.
+;;;
+;;; Guix already has many different updaters for language-specific packages,
+;;; and these typically provide more accurate data, e.g., input changes,
+;;; signature URLs.  The Repology updater should really be treated as a last
+;;; resort for those packages that don't have any other updater to rely on.
+;;;
+;;; See <https://repology.org/api/v1> for the API.
+;;;
+;;; Code:
+
+(define %repology-url
+   "https://repology.org/api/v1/project")
+
+(define* (package-name->repology-name name #:key (attempt 1))
+  "Convert NAME, the name of a Guix package, to the name of the package on
+Repology.  It doesn't always guess the correct name on the first attempt, so
+on the second attempt it will try to guess another name."
+  (match attempt
+    (1 (cond
+        ((string-prefix? "ghc-" name)
+         (string-append "haskell:"
+                        (string-drop name (string-length "ghc-"))))
+        ((string-prefix? "ocaml-" name)
+         (string-append "ocaml:"
+                        (string-drop name (string-length "ocaml-"))))
+        ((string-prefix? "perl-" name)
+         (string-append "perl:"
+                        (string-drop name (string-length "perl-"))))
+        ((string-prefix? "emacs-" name)
+         (string-append "emacs:"
+                        (string-drop name (string-length "emacs-"))))
+        ((string-prefix? "go-" name)
+         (string-append "go:"
+                        (string-drop name (string-length "go-"))))
+        ((string-prefix? "rust-" name)
+         (string-append "rust:"
+                        (string-drop name (string-length "rust-"))))
+        ((string-prefix? "lua-" name)
+         (string-append "lua:"
+                        (string-drop name (string-length "lua-"))))
+        ((string-prefix? "node-" name)
+         (string-append "node:"
+                        (string-drop name (string-length "node-"))))
+        ((string-prefix? "python-" name)
+         (string-append "python:"
+                        (string-drop name (string-length "python-"))))
+        ((string-prefix? "java-" name)
+         (string-append "java:"
+                        (string-drop name (string-length "java-"))))
+        ((string-prefix? "r-" name)
+         (string-append "r:"
+                        (string-drop name (string-length "r-"))))
+        ((string-prefix? "ruby-" name)
+         (string-append "ruby:"
+                        (string-drop name (string-length "ruby-"))))
+        ((string-prefix? "xf86-" name)
+         (string-append "xdrv:"
+                        (string-drop name (string-length "xf86-"))))
+        ((string-prefix? "font-" name)
+         (string-append "fonts:"
+                        (string-drop name (string-length "font-"))))
+        (else name)))
+    (2 (cond
+        ((string-prefix? "xf86-video" name)
+         (string-append "xdrv:"
+                        (string-drop name (string-length "xf86-video-"))))
+        ((string-prefix? "xf86-input" name)
+         (string-append "xdrv:"
+                        (string-drop name (string-length "xf86-input-"))))
+        (else name)))))  
+
+
+;;; JSON mappings.
+
+(define-json-mapping <repology-package> make-repology-package
+  repology-package?
+  json->repology-package
+  (repository repology-package-repository "repo")
+  (src-name repology-package-src-name "srcname")
+  (binary-name repology-package-binary-name "binname")
+  (visible-name repology-package-visible-name "visiblename")
+  (version repology-package-version)
+  (original-version repology-package-original-version "origversion")
+  (status repology-package-status)
+  (summary repology-package-summary)
+  (categories repology-package-categories)
+  (licenses repology-package-licenses)
+  (maintainers repology-package-maintainers))
+
+
+;;; Updater.
+
+(define repology-fetch-info
+  (memoize
+   (lambda (package)
+     "Fetch information about PACKAGE using the Repology API."
+     (define (name->info name )
+       (let ((url (string-append %repology-url "/" name)))
+         (and=> (json-fetch url)
+                (lambda (url)
+                  (vector-map (lambda (a b)
+                                (json->repology-package b))
+                              url)))))
+     
+     (let* ((name (or (assoc-ref (package-properties package)
+                                 'repology-name)
+                      (package-name->repology-name (package-name package))))
+            (info (name->info name)))
+       (if (and info (not (vector-empty? info)))
+           info
+           (let ((info (name->info (package-name->repology-name
+                                    (package-name package)
+                                    #:attempt 2))))
+             (if (and info (not (vector-empty? info)))
+                 info
+                 (begin
+                   (warning (G_ "package not found on Repology: ~a\n")
+                            (package-name package))
+                   #f))))))))
+
+(define (update-url url old-version new-version)
+  "Replace OLD-VERSION in URL with NEW-VERSION."
+  (match (factorize-uri url old-version)
+    ((? string? uri) #f)
+    ((factorized ...)
+     (apply string-append
+            (map (lambda (component)
+                   (match component
+                     ('version new-version)
+                     ((? string?) component)))
+                 factorized)))))
+
+(define (package-source-urls package version)
+  "Return a list of URLs for PACKAGE at VERSION.  If no URL was successfully constructed, return #f."
+  (let ((old-version (package-version package)))
+    ;; XXX: (guix upstream) only supports tarballs and Git repos for now.
+    (match (origin-uri (package-source package))
+      (($ <git-reference> url commit recursive?)
+       (and-let* ((updated-commit (if (string=? old-version commit)
+                                      version
+                                      (update-url commit old-version version))))
+         (list (git-reference
+                (url url)
+                (commit updated-commit)
+                (recursive? recursive?)))))
+      ((? string? url)
+       (list (update-url url old-version version)))
+      ((? list? urls)
+       (map (cut update-url <> old-version version) urls))
+      (_ #f))))
+
+(define (stable-version? repology-package)
+  (and (or (equal? "newest" (repology-package-status repology-package))
+           (equal? "unique" (repology-package-status repology-package)))
+       (repology-package-version repology-package)))
+
+;; XXX: 'package' will clash with the 'package' field of 'upstream-source'.
+(define (repology-latest-release pkg)
+  "Return the latest release of the PKG on Repology named NAME."
+  (and-let* ((packages (repology-fetch-info pkg))
+             (versions (filter-map stable-version?
+                                          (vector->list packages)))
+             (latest-version (if (null? versions)
+                                 #f
+                                 (car versions))))
+    ;; TODO: set 'signature-urls'.
+    (upstream-source
+     (package (package-name pkg))
+     (version latest-version)
+     (urls (package-source-urls pkg latest-version)))))
+
+(define %repology-updater
+(upstream-updater
+ (name 'repology)
+ (description "Updater for packages on Repology")
+ (pred (const #t))
+ (latest repology-latest-release)))
+
+;;; repology.scm ends here
diff --git a/tests/import-repology.scm b/tests/import-repology.scm
new file mode 100644
index 0000000000..f95071ce07
--- /dev/null
+++ b/tests/import-repology.scm
@@ -0,0 +1,145 @@ 
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2022 Xinglu Chen <public@yoctocell.xyz>
+;;;
+;;; 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 (test-import-repology)
+  #:use-module (guix download)
+  #:use-module (guix git-download)
+  #:use-module (guix import repology)
+  #:use-module (guix packages)
+  #:use-module (guix tests)
+  #:use-module (guix upstream)
+  #:use-module (json)
+  #:use-module (srfi srfi-64))
+
+(test-begin "repology")
+
+(define package-using-git-repository
+  (dummy-package
+   "foo"
+   (version "1.0")
+   (source
+    (origin
+      (method git-fetch)
+      (uri (git-reference
+            (url "https://git.example.org/foo")
+            (commit "1.0")))
+      (sha256 #f)))))
+
+(define package-using-tarball
+  (dummy-package
+   "foo"
+   (version "1.0")
+   (source
+    (origin
+      (method git-fetch)
+      (uri (string-append "https://example.org/foo-" version ".tar.gz"))
+      (sha256 #f)))))
+
+(define package-using-tarball-multiple-urls
+  (dummy-package
+   "foo"
+   (version "1.0")
+   (source
+    (origin
+      (method git-fetch)
+      (uri (list (string-append "https://example.org/foo-"
+                                version ".tar.gz")
+                 (string-append "https://mirror.example.org/foo-"
+                                version ".tar.gz")))
+      (sha256 #f)))))
+
+(define %test-json
+"[
+  {
+    \"repo\": \"aur\",
+    \"srcname\": \"foo\",
+    \"binname\": \"foo\",
+    \"visiblename\": \"foo\",
+    \"version\": \"1.0.r25.gb86405a\",
+    \"maintainers\": [
+      \"bob@aur\"
+    ],
+    \"licenses\": [
+      \"LGPL3+\"
+    ],
+    \"summary\": \"foo bar\"
+    \"status\": \"rolling\",
+    \"origversion\": \"1.0.r25.gb86405a-1\"
+  },
+  {
+    \"repo\": \"gnuguix\",
+    \"srcname\": \"foo\",
+    \"binname\": \"foo\",
+    \"visiblename\": \"foo\",
+    \"version\": \"1.0\",
+    \"summary\": \"foo bar\",
+    \"status\": \"outdated\",
+    \"origversion\": null
+  },
+  {
+    \"repo\": \"nix_unstable\",
+    \"name\": \"foo\",
+    \"visiblename\": \"foo\",
+    \"version\": \"2.0\",
+    \"maintainers\": [
+      \"bob@example.org\"
+    ],
+    \"licenses\": [
+      \"LGPL-3.0-or-later\"
+    ],
+    \"summary\": \"foo bar\",
+    \"status\": \"newest\",
+    \"origversion\": null
+  }
+]")
+
+(define (latest-release package)
+  (mock ((guix import json) json-fetch
+         (lambda (url)
+           (json-string->scm %test-json)))
+        (repology-latest-release package)))
+
+(test-equal "package using Git repo: version"
+  "2.0"
+  (upstream-source-version
+   (latest-release package-using-git-repository)))
+
+(test-equal "package using Git repo: git-reference"
+  (list (git-reference
+         (url "https://git.example.org/foo")
+         (commit "2.0")))
+  (upstream-source-urls
+   (latest-release package-using-git-repository)))
+
+(test-equal "package using tarball: version"
+  "2.0"
+  (upstream-source-version
+   (latest-release package-using-tarball)))
+
+(test-equal "package using tarball: URL"
+  (list "https://example.org/foo-2.0.tar.gz")
+  (upstream-source-urls
+   (latest-release package-using-tarball)))
+
+(test-equal "package using tarball: multiple URLs"
+  (list "https://example.org/foo-2.0.tar.gz"
+        "https://mirror.example.org/foo-2.0.tar.gz")
+  (upstream-source-urls
+   (latest-release package-using-tarball-multiple-urls)))
+
+(test-end "repology")