Added sample library script for manifest dependency handling

This adds a draft of a library shell script which can be sourced to
utilise all functions. Can be extended with various checks, which are
not implemented yet.

Original, it was done so there is a file in the global library
directory that no errors occur. This should fix the unit tests.

cdist/conf/library/manifest

@@ -0,0 +1,103 @@
+# vi: set filetype=sh:
+# $__library/manifest
+#
+# 2020 Matthias Stecher (matthiasstecher at gmx.de)
+#
+# This file is part of cdist.
+#
+# cdist is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# cdist is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with cdist. If not, see <http://www.gnu.org/licenses/>.
+#
+#
+# This library contains:
+#   common helper functions helping writing the manifest
+
+
+# check if type is a singleton
+#
+# Arguments:
+#  1: name of the type, e.g. `__some_type`
+is_singleton() {
+    if [ -f "$__global/conf/type/$1/singleton" ]; then
+        return 0
+    else
+        return 1
+    fi
+}
+
+# print object id
+#
+# Arguments:
+#  1: type name, e.g. `__some_type`
+#  2: object id; will be ignored if type is a singleton
+get_object_id() {
+    if is_singleton "$1"; then
+        printf "%s" "$1"
+    else
+        printf "%s/%s" "$1" "$2"
+    fi
+}
+
+
+# Helper function to get the correct chain name. It will shorten any
+# invalid character.
+#
+# Arguments:
+#  1: the dependency chain name
+_rec_normalize_chain_name() {
+    # spaces will be underscores
+    # anything other than a-zA-Z0-9 will be removed
+    printf "$1" | sed 's/\([[:space:]]\|-\)/_/g; s/[^a-zA-Z0-9_]//g'
+}
+
+
+# Recording dependencies
+#
+# Arguments:
+#  1: the dependency chain - only chars, numbers and underscores allowed
+#  2..n: the type command; no more nesting possible
+rec_requires() {
+    # make it ready to be passed to eval
+    _rec_chain="$(_rec_normalize_chain_name "$1")"
+    eval "_rec_ch_${_rec_chain}=\"\${_rec_ch_${_rec_chain}:-} $(get_object_id "$2" "$3")\""
+
+    # execute type
+    shift
+    "$@"
+}
+
+
+# Clearing dependency chains
+#
+# Arguments:
+#  1: the dependency chain name
+rec_clear() {
+    _rec_chain="$(printf "$1" | sed 's/\([[:space:]]\|-\)/_/g; s/[^a-zA-Z0-9_]//g')"
+    eval "unset -v _rec_ch_${_rec_chain}"
+}
+
+
+# Export dependencies to current command by appending to the current environment
+#
+# Arguments:
+#  1: the dependency chain
+#  2..n: the type command; no more nesting possible
+depend() {
+    # assemble dependency
+    _rec_chain="$(_rec_normalize_chain_name "$1")"
+    _rec_deps="$(eval "printf \"%s\" \"\${_rec_ch_${_rec_chain}:-}\"")"
+
+    # execute type
+    shift
+    require="$require $_rec_deps" "$@"
+}