etc: Add 'source-manifest.scm'.

* etc/source-manifest.scm: New file.
* Makefile.am (EXTRA_DIST): Add it.

Makefile.am

@@ -627,6 +627,7 @@ EXTRA_DIST +=						\
   etc/guix-install.sh					\
   etc/news.scm						\
   etc/release-manifest.scm				\
+  etc/source-manifest.scm				\
   etc/system-tests.scm					\
   etc/historical-authorizations				\
   build-aux/build-self.scm				\

etc/source-manifest.scm

@@ -0,0 +1,66 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 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/>.
+
+;;; This file returns a manifest containing origins of all the packages.  The
+;;; main purpose is to allow continuous integration services to keep upstream
+;;; source code around.  It can also be passed to 'guix weather -m'.
+
+(use-modules (srfi srfi-1) (srfi srfi-26)
+             (ice-9 match) (ice-9 vlist)
+             (guix packages) (guix profiles)
+             (gnu packages))
+
+(define (all-packages)
+  "Return the list of all the packages, public or private, omitting only
+superseded packages."
+  (fold-packages (lambda (package lst)
+                   (match (package-replacement package)
+                     (#f (cons package lst))
+                     (replacement
+                      (append (list replacement package) lst))))
+                 '()
+                 #:select? (negate package-superseded)))
+
+(define (upstream-origin source)
+  "Return SOURCE without any patches or snippet."
+  (origin (inherit source)
+          (snippet #f) (patches '())))
+
+(define (all-origins)
+  "Return the list of origins referred to by all the packages."
+  (let loop ((packages (all-packages))
+             (origins  '())
+             (visited   vlist-null))
+    (match packages
+      ((head . tail)
+       (let ((new (remove (cut vhash-assq <> visited)
+                          (package-direct-sources head))))
+         (loop tail (append new origins)
+               (fold (cut vhash-consq <> #t <>)
+                     visited new))))
+      (()
+       origins))))
+
+;; Return a manifest containing all the origins.
+(manifest (map (lambda (origin)
+                 (manifest-entry
+                   (name (or (origin-actual-file-name origin)
+                             "origin"))
+                   (version "0")
+                   (item (upstream-origin origin))))
+               (all-origins)))