new type __debian_backports

This new type will setup the backports distribution for the current
Debian release.

cdist/conf/type/__debian_backports/man.rst

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+cdist-type__debian_backports(7)
+===============================
+
+NAME
+----
+cdist-type__debian_backports - Install backports for Debain systems
+
+
+DESCRIPTION
+-----------
+This singleton type installs backports for the current Debian version.
+It aborts if backports are not supported for the specified os or no
+version codename could be fetched (like Debian unstable).
+
+
+REQUIRED PARAMETERS
+-------------------
+None.
+
+
+OPTIONAL PARAMETERS
+-------------------
+state
+    Represents the state of the backports repository. ``present`` or
+    ``absent``, defaults to ``present``.
+
+    Will be directly passed to :strong:`cdist-type__apt_source`\ (7).
+
+mirror
+    The mirror to fetch the backports from. Will defaults to the Debian default
+    `<http://deb.debian.org/debian/>`_.
+
+    Will be directly passed to :strong:`cdist-type__apt_source`\ (7).
+
+
+BOOLEAN PARAMETERS
+------------------
+None.
+
+
+MESSAGES
+--------
+None.
+
+
+EXAMPLES
+--------
+
+.. code-block:: sh
+
+   # setup the backports
+   __debian_backports
+   __debian_backports --state absent
+   __debian_backports --state present --mirror "http://ftp.de.debian.org/debian/"
+
+   # update
+   require="__debian_backports" __apt_update_index
+
+   # install a backports package
+   # currently for the buster release backports
+   require="__apt_update_index" __package_apt wireguard \
+        --target-release buster-backports
+
+
+ABORTS
+------
+Aborts if the detected os is not Debian.
+
+Aborts if no distribuition codename could be detected. This is common for the
+unstable distribution, but there is no backports repository for it already.
+
+
+SEE ALSO
+--------
+`Official Debian Backports site <https://backports.debian.org/>`_
+
+:strong:`cdist-type__apt_source`\ (7)
+
+
+AUTHORS
+-------
+Matthias Stecher <matthiasstecher at gmx.de>
+
+
+COPYING
+-------
+Copyright \(C) 2020 Matthias Stecher. 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.

cdist/conf/type/__debian_backports/manifest

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+#!/bin/sh -e
+# __debian_backports/manifest
+#
+# 2020 Matthias Stecher (matthiasstecher at gmx.de)
+#
+# This file is part of cdist.
+#
+# cdist 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.
+#
+# cdist 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 cdist. If not, see <http://www.gnu.org/licenses/>.
+#
+#
+# Enables/disables backports repository. Utilies __apt_source for it.
+#
+
+
+# detect backport distribution
+os="$(cat "$__global/explorer/os")"
+case "$os" in
+    debian)
+        # distribution codename from /etc/os-release
+        # lsb_release may not be given in all debian installations
+        dist="$(
+            . "$__global/explorer/os-release"
+            printf "%s" "$VERSION_CODENAME"
+        )"
+        ;;
+    *)
+        printf "Backports for %s are not supported!\n" "$os" >&2
+        exit 1
+        ;;
+esac
+
+# error if no codename given (e.g. on Debian unstable)
+if [ -z "$dist" ]; then
+    printf "No backports for unkown version of distribution %s!\n" "$os" >&2
+    exit 1
+fi
+
+
+# parameters
+state="$(cat "$__object/parameter/state")"
+mirror="$(cat "$__object/parameter/mirror")"
+
+# install the given backports repository
+__apt_source "${dist}-backports" \
+    --state "$state" \
+    --distribution "${dist}-backports" \
+    --component main \
+    --uri "$mirror"

cdist/conf/type/__debian_backports/parameter/default/mirror

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+http://deb.debian.org/debian/

cdist/conf/type/__debian_backports/parameter/default/state

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+present

cdist/conf/type/__debian_backports/parameter/optional

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+state
+mirror