etc: Add copyright.

* etc/copyright.el: New file.
* doc/contributing.texi (The Perfect Setup): Document this.

doc/contributing.texi

@@ -274,6 +274,33 @@ trigger string @code{origin...}, which can be expanded further.  The
 @code{origin} snippet in turn may insert other trigger strings ending on
 @code{...}, which also can be expanded further.
 
+@cindex insert or update copyright
+@cindex @code{M-x guix-copyright}
+@cindex @code{M-x copyright-update}
+Additionaly we provide insertion and automatic update of a copyright in
+@file{etc/copyright.el}.  You may want to set your full name, mail, and
+load a file.
+
+@lisp
+(setq user-full-name "Alice Doe")
+(setq user-mail-address "alice@@mail.org")
+;; @r{Assuming the Guix checkout is in ~/src/guix.}
+(load-file "~/src/guix/etc/copyright.el")
+@end lisp
+
+To insert a copyright at the current line invoke @code{M-x guix-copyright}.
+
+To update a copyright you need to specify a @code{copyright-names-regexp}.
+
+@lisp
+(setq copyright-names-regexp
+      (format "%s <%s>" user-full-name user-mail-address))
+@end lisp
+
+You can check if your copyright is up to date by evaluating @code{M-x
+copyright-update}.  If you want to do it automatically after each buffer
+save then add @code{(add-hook 'after-save-hook 'copyright-update)} in
+Emacs.
 
 @node Packaging Guidelines
 @section Packaging Guidelines

etc/copyright.el

@@ -0,0 +1,34 @@
+;;; copyright.el --- Insert a Guix copyright.
+
+;; Copyright © 2020 Oleg Pykhalov <go.wigust@gmail.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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This package provides skeleton to insert a copyright with `guix-copyright'.
+
+;;; Code:
+
+(define-skeleton guix-copyright
+  "Insert a copyright by $USER notice at cursor."
+  "FULL_NAME <MAIL_ADDRESS>: "
+  comment-start
+  ";; Copyright © " `(format-time-string "%Y") " "
+  (or (format "%s <%s>" user-full-name user-mail-address) str)
+  comment-end)
+
+;;; copyright.el ends here