import: Add Launchpad updater.

* guix/import/launchpad.scm: New file.
* Makefile.am (MODULES): Register it.
* doc/guix.texi (Invoking guix refresh): Mention the Launchpad updater.

Makefile.am

@@ -202,6 +202,7 @@ MODULES =					\
   guix/import/gnu.scm				\
   guix/import/hackage.scm			\
   guix/import/json.scm				\
+  guix/import/launchpad.scm   			\
   guix/import/opam.scm				\
   guix/import/print.scm				\
   guix/import/pypi.scm				\

doc/guix.texi

@@ -48,7 +48,7 @@ Copyright @copyright{} 2017 Maxim Cournoyer@*
 Copyright @copyright{} 2017, 2018 Tobias Geerinckx-Rice@*
 Copyright @copyright{} 2017 George Clemmer@*
 Copyright @copyright{} 2017 Andy Wingo@*
-Copyright @copyright{} 2017, 2018 Arun Isaac@*
+Copyright @copyright{} 2017, 2018, 2019 Arun Isaac@*
 Copyright @copyright{} 2017 nee@*
 Copyright @copyright{} 2018 Rutger Helling@*
 Copyright @copyright{} 2018 Oleg Pykhalov@*
@@ -8841,6 +8841,8 @@ the updater for @uref{https://hackage.haskell.org, Hackage} packages.
 the updater for @uref{https://www.stackage.org, Stackage} packages.
 @item crate
 the updater for @uref{https://crates.io, Crates} packages.
+@item launchpad
+the updater for @uref{https://launchpad.net, Launchpad} packages.
 @end table
 
 For instance, the following command only checks for updates of Emacs

guix/import/launchpad.scm

@@ -0,0 +1,124 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Arun Isaac <arunisaac@systemreboot.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 import launchpad)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:use-module (web uri)
+  #:use-module ((guix download) #:prefix download:)
+  #:use-module (guix import json)
+  #:use-module (guix packages)
+  #:use-module (guix upstream)
+  #:use-module (guix utils)
+  #:export (%launchpad-updater))
+
+(define (find-extension url)
+  "Return the extension of the archive e.g. '.tar.gz' given a URL, or
+false if none is recognized"
+  (find (lambda (x) (string-suffix? x url))
+        (list ".tar.gz" ".tar.bz2" ".tar.xz"
+              ".zip" ".tar" ".tgz" ".tbz" ".love")))
+
+(define (updated-launchpad-url old-package new-version)
+  ;; Return a url for the OLD-PACKAGE with NEW-VERSION.  If no source url in
+  ;; the OLD-PACKAGE is a Launchpad url, then return false.
+
+  (define (updated-url url)
+    (and (string-prefix? "https://launchpad.net/" url)
+         (let ((ext (or (find-extension url) ""))
+               (name (package-name old-package))
+               (version (package-version old-package))
+               (repo (launchpad-repository url)))
+           (cond
+            ((and
+              (>= (length (string-split version #\.)) 2)
+              (string=? (string-append "https://launchpad.net/"
+                                       repo "/" (version-major+minor version)
+                                       "/" version "/+download/" repo "-" version ext)
+                        url))
+             (string-append "https://launchpad.net/"
+                            repo "/" (version-major+minor new-version)
+                            "/" new-version "/+download/" repo "-" new-version ext))
+            (#t #f))))) ; Some URLs are not recognised.
+
+  (let ((source-uri (and=> (package-source old-package) origin-uri))
+        (fetch-method (and=> (package-source old-package) origin-method)))
+    (cond
+     ((eq? fetch-method download:url-fetch)
+      (match source-uri
+             ((? string?)
+              (updated-url source-uri))
+             ((source-uri ...)
+              (find updated-url source-uri))))
+     (else #f))))
+
+(define (launchpad-package? package)
+  "Return true if PACKAGE is a package from Launchpad, else false."
+  (->bool (updated-launchpad-url package "1.0.0")))
+
+(define (launchpad-repository url)
+  "Return a string e.g. linuxdcpp of the name of the repository, from a string
+URL of the form
+'https://launchpad.net/linuxdcpp/1.1/1.1.0/+download/linuxdcpp-1.1.0.tar.bz2'"
+  (match (string-split (uri-path (string->uri url)) #\/)
+    ((_ repo . rest) repo)))
+
+(define (latest-released-version package-name)
+  "Return a string of the newest released version name given the PACKAGE-NAME,
+for example, 'linuxdcpp'. Return #f if there is no releases."
+  (define (pre-release? x)
+    ;; Versions containing anything other than digit characters and "." (for
+    ;; example, "5.1.0-rc1") are assumed to be pre-releases.
+    (not (string-every (char-set-union (char-set #\.)
+                                       char-set:digit)
+                       (hash-ref x "version"))))
+
+  (hash-ref
+   (last (remove
+          pre-release?
+          (hash-ref (json-fetch
+                     (string-append "https://api.launchpad.net/1.0/"
+                                    package-name "/releases"))
+                    "entries")))
+   "version"))
+
+(define (latest-release pkg)
+  "Return an <upstream-source> for the latest release of PKG."
+  (define (origin-github-uri origin)
+    (match (origin-uri origin)
+      ((? string? url) url) ; surely a Launchpad URL
+      ((urls ...)
+       (find (cut string-contains <> "launchpad.net") urls))))
+
+  (let* ((source-uri (origin-github-uri (package-source pkg)))
+         (name (package-name pkg))
+         (newest-version (latest-released-version name)))
+    (if newest-version
+        (upstream-source
+         (package name)
+         (version newest-version)
+         (urls (list (updated-launchpad-url pkg newest-version))))
+        #f))) ; On Launchpad but no proper releases
+
+(define %launchpad-updater
+  (upstream-updater
+   (name 'launchpad)
+   (description "Updater for Launchpad packages")
+   (pred launchpad-package?)
+   (latest latest-release)))