[type/__uci_section] Improve --match support with existing named sections

Use section if named section exists without --match option (e.g. empty section).

cdist/conf/type/__uci_section/explorer/match

@@ -20,62 +20,84 @@
 # This explorer determines the "prefix" of the --type section matching --match
 # if set, or __object_id otherwise.
 
+RS=$(printf '\036')
+NL=$(printf '\n '); NL=${NL% }
+
 squote_values() {
 	sed -e '/=".*"$/{s/="/='\''/;s/"$/'\''/}' \
 	    -e "/='.*'$/"'!{s/=/='\''/;s/$/'\''/}'
 }
+count_lines() (
+	IFS=${NL?}
+	# shellcheck disable=SC2048,SC2086
+	set -f -- $*; echo $#
+)
 
-RS=$(printf '\036')
-
-if ! test -e "${__object:?}/parameter/match"
-then
-	if ! echo "${__object_id:?}" | grep -q -e '^[^.]\{1,\}\.[^.]\{1,\}$'
-	then
+echo "${__object_id:?}" | grep -q -e '^[^.]\{1,\}\.[^.]\{1,\}$' || {
 	echo 'Section identifiers are a package and section name separated by a "." (period).' >&2
 	exit 1
-	fi
+}
 
+test -s "${__object:?}/parameter/match" || {
 	# If no --match is given, we take the __object_id as the section identifier.
 	echo "${__object_id:?}"
 	exit 0
-fi
-
-# shellcheck disable=SC2015
-test -s "${__object:?}/parameter/match" && test -s "${__object:?}/parameter/type" \
-|| {
+}
+test -s "${__object:?}/parameter/type" || {
 	echo 'Parameters --match and --type must be used together.' >&2
 	exit 1
 }
 
-# Find by match
-# NOTE: Apart from section types all values are printed in single quotes by UCI.
-match=$(head -n 1 "${__object:?}/parameter/match" | squote_values)
-
-if ! grep -q -e '^[^.]\{1,\}\.[^.]\{1,\}$' "${__object:?}/parameter/type"
-then
+sect_type_param=$(cat "${__object:?}/parameter/type")
+expr "${sect_type_param}" : '[^.]\{1,\}\.[^.]\{1,\}$' >/dev/null 2>&1 || {
 	echo 'Section types are a package name and section type separated by a "." (period).' >&2
 	exit 1
+}
+package_filter=${sect_type_param%%.*}
+section_filter=${sect_type_param#*.}
+
+# Find by --match
+# NOTE: Apart from section types all values are printed in single quotes by uci show.
+match=$(head -n 1 "${__object:?}/parameter/match" | squote_values)
+
+if uci -s -N get "${__object_id:?}" >/dev/null 2>&1
+then
+	# Named section exists: ensure if --match applies to it
+	# if the "matched" option does not exist (e.g. empty section) we use the
+	# section unconditionally.
+	if match_value_is=$(uci -s -N get "${__object_id:?}.${match%%=*}" 2>/dev/null)
+	then
+		match_value_should=$(expr "${match}" : ".*='\\(.*\\)'$")
+
+		test "${match_value_is}" = "${match_value_should}" || {
+			printf 'Named section "%s" does not match --match "%s"\n' \
+				   "${__object_id:?}" "${match}" >&2
+			exit 1
+		}
+	fi
+
+	echo "${__object_id:?}"
+	exit 0
 fi
 
-sect_type_filter=$(cat "${__object:?}/parameter/type")
-package_filter=${sect_type_filter%%.*}
-section_filter=${sect_type_filter#*.}
-# FIXME: Does not work with named sections
-regex="^${package_filter}\.@${section_filter}\[[0-9]\{1,\}\]\.${match%%=*}="
+# No correctly named section exists already: find one to which --match applies
+regex="^${package_filter}\\.@${section_filter}\\[[0-9]\\{1,\\}\\]\\.${match%%=*}="
 
 matched_sections=$(
 	uci -s -N -d "${RS}" show "${package_filter}" 2>/dev/null \
 	| grep -e "${regex}" \
 	| while read -r _line
 	  do
-		  if test "${_line#*=}" = "${match#*=}"; then echo "${_line}"; fi
+		  if test "${_line#*=}" = "${match#*=}"
+		  then
+			  echo "${_line}"
+		  fi
 	  done \
 	| sed -e 's/\.[^.]*=.*$//')
 
-if test "$(echo "${matched_sections}" | wc -l)" -gt 1
-then
+test "$(count_lines "${matched_sections}")" -le 1 || {
 	printf 'Found multiple matching sections:\n%s\n' "${matched_sections}" >&2
 	exit 1
-fi
+}
 
 echo "${matched_sections}"