Speed up sources.sh even more

by improving slow jq section in sources.sh

sources.sh

@@ -219,6 +219,22 @@ jq <<<"$sources" --argjson pins "$externalPinsJson" '
 		# https://unix.stackexchange.com/a/738744/153467
 		reduce .[] as $a ([]; if IN(.[]; $a) then . else . += [$a] end)
 	;
+	def meld($a; $b):
+		# recursive merge of objects like "*", but also append lists (uniquely) instead of replace
+		# https://stackoverflow.com/a/53666584, but with lists unique-ified
+		if ($a | type) == "object" and ($b | type) == "object" then
+			reduce ([$a, $b] | add | keys_unsorted[]) as $k ({};
+				.[$k] = meld( $a[$k]; $b[$k])
+			)
+		elif ($a | type) == "array" and ($b | type) == "array" then
+			$a + $b
+			| unique_unsorted
+		elif $b == null then
+			$a
+		else
+			$b
+		end
+	;
 	reduce .[] as $in ({};
 		.[$in.sourceId] |=
 			if . == null then
@@ -254,15 +270,26 @@ jq <<<"$sources" --argjson pins "$externalPinsJson" '
 	# TODO a lot of this could be removed/parsed during the above reduce, since it has to parse things in build order anyhow
 	# TODO actually, instead, this bit should be a totally separate script so the use case of "combine sources.json files together" works better 👀
 	| (
-		# TODO make this faster, this reduce takes the longest time now
-		reduce to_entries[] as $e ({};
-			$e.key as $sourceId
-			| .[ $e.value.arches[] | .tags[], .archTags[] ] |= (
-				.[$e.value.arches | keys[]] |= (
-					. + [$sourceId] | unique_unsorted
-				)
+		# creating a lookup of .[tag][arch] to a list of sourceIds
+		[
+			.[] as $e
+			| ( $e.arches[] | .tags[], .archTags[] )
+			| {
+				key: .,
+				value: {
+					($e.arches | keys[]): [$e.sourceId]
+				}
+			}
+		]
+		# do not try to code golf this to one reduce without from_entries or group_by, that is very slow
+		| group_by(.key)
+		| [
+			# many little reduces based on same key (group_by^), instead of one very big and expensive
+			.[] | reduce .[] as $r ({};
+				meld(.; $r)
 			)
-		)
+		]
+		| from_entries
 	) as $tagArches
 	| map_values(
 		.arches |= with_entries(