[__update_alternatives] rewrite and support --install

cdist/conf/type/__update_alternatives/explorer/alternatives

@@ -0,0 +1,4 @@
+#!/bin/sh -e
+
+update-alternatives --display "$__object_id" 2>/dev/null \
+    | awk -F ' - ' '/priority [0-9]+$/ { print $1 }'

cdist/conf/type/__update_alternatives/explorer/link

@@ -0,0 +1,40 @@
+#!/bin/sh -e
+
+# fedora's (update-)alternatives --display output doesn't have
+# "link <name> is <path>" line, but debian does. so, let's find
+# out how they store this information.
+#
+# debian and friends:
+#   https://salsa.debian.org/dpkg-team/dpkg/-/blob/master/utils/update-alternatives.c
+#   see calls to altdb_print_line function
+#
+# fedora and friends:
+#   https://github.com/fedora-sysv/chkconfig/blob/master/alternatives.c
+#   see calls to parseLine function
+#
+# conclusion: it is safe to assume that (master) link is on second line
+
+for altdir in \
+    /var/lib/dpkg/alternatives \
+    /var/lib/alternatives
+do
+    if [ ! -f "$altdir/$__object_id" ]
+    then
+        continue
+    fi
+
+    link="$( awk 'NR==2' "$altdir/$__object_id" )"
+
+    if [ -n "$link" ]
+    then
+        break
+    fi
+done
+
+if [ -z "$link" ]
+then
+    echo "unable to get link for $__object_id" >&2
+    exit 1
+fi
+
+echo "$link"

cdist/conf/type/__update_alternatives/explorer/path_is

@@ -0,0 +1,12 @@
+#!/bin/sh -e
+
+path_is="$( update-alternatives --display "$__object_id" 2>/dev/null \
+    | awk '/link currently points to/ {print $5}' )"
+
+if [ -z "$path_is" ]
+then
+    echo "unable to get current path for $__object_id" >&2
+    exit 1
+fi
+
+echo "$path_is"

cdist/conf/type/__update_alternatives/explorer/path_should_state

@@ -0,0 +1,8 @@
+#!/bin/sh -e
+
+if [ -f "$( cat "$__object/parameter/path" )" ]
+then
+    echo 'present'
+else
+    echo 'absent'
+fi

cdist/conf/type/__update_alternatives/explorer/state

@@ -1,8 +0,0 @@
-#!/bin/sh -e
-path="$(cat "$__object/parameter/path")"
-name="$__object_id"
-link="$(readlink "/etc/alternatives/$name")"
-if [ "$path" = "$link" ]
-then echo present
-else echo absent
-fi

cdist/conf/type/__update_alternatives/gencode-remote

@@ -1,6 +1,7 @@
 #!/bin/sh -e
 #
 # 2013 Nico Schottelius (nico-cdist at schottelius.org)
+# 2020 Ander Punnar (ander@kvlt.ee)
 #
 # This file is part of cdist.
 #
@@ -16,12 +17,38 @@
 #
 # You should have received a copy of the GNU General Public License
 # along with cdist. If not, see <http://www.gnu.org/licenses/>.
-#
 
-if [ "$(cat "$__object/explorer/state")" = 'present' ]
+path_is="$( cat "$__object/explorer/path_is" )"
-then exit 0
+
+path_should="$( cat "$__object/parameter/path" )"
+
+if [ "$path_is" = "$path_should" ]
+then
+    exit 0
+fi
+
+if [ "$( cat "$__object/explorer/path_should_state" )" = 'absent' ] && [ -z "$__cdist_dry_run" ]
+then
+    echo "$path_should does not exist in target" >&2
+    exit 1
 fi
 
-path="$(cat "$__object/parameter/path")"
 name="$__object_id"
-echo "update-alternatives --quiet --set '$name' '$path'"
+
+alternatives="$( cat "$__object/explorer/alternatives" )"
+
+if ! echo "$alternatives" | grep -Fxq "$path_should"
+then
+    if [ ! -f "$__object/parameter/install" ]
+    then
+        echo "$path_should is not in $name alternatives." >&2
+        echo 'Please install missing packages or use --install to add path to alternatives.' >&2
+        exit 1
+    fi
+
+    link="$( cat "$__object/explorer/link" )"
+
+    echo "update-alternatives --install '$link' '$name' '$path_should' 1000"
+fi
+
+echo "update-alternatives --set '$name' '$path_should'"

cdist/conf/type/__update_alternatives/man.rst

@@ -19,6 +19,12 @@ path
    Use this path for the given alternative
 
 
+BOOLEAN PARAMETERS
+------------------
+install
+   Add (``update-alternatives --install``) missing path to alternatives.
+
+
 EXAMPLES
 --------
 
@@ -36,11 +42,12 @@ SEE ALSO
 AUTHORS
 -------
 Nico Schottelius <nico-cdist--@--schottelius.org>
+Ander Punnar <ander@kvlt.ee>
 
 
 COPYING
 -------
-Copyright \(C) 2013 Nico Schottelius. You can redistribute it
+Copyright \(C) 2013 Nico Schottelius and 2020 Ander Punnar. You can
-and/or modify it under the terms of the GNU General Public License as
+redistribute it and/or modify it under the terms of the GNU General Public
-published by the Free Software Foundation, either version 3 of the
+License as published by the Free Software Foundation, either version 3 of the
 License, or (at your option) any later version.

cdist/conf/type/__update_alternatives/parameter/boolean

@@ -0,0 +1 @@
+install