Default/functions: ABM for mossycobble replacing cobble next to water

mods/default/functions.lua

@@ -300,7 +300,7 @@ minetest.register_abm({
 
 
 --
--- Grass growing
+-- Grass growing on well-lit dirt
 --
 
 minetest.register_abm({
@@ -323,6 +323,11 @@ minetest.register_abm({
 	end
 })
 
+
+--
+-- Grass and dry grass removed in darkness
+--
+
 minetest.register_abm({
 	nodenames = {"default:dirt_with_grass", "default:dirt_with_dry_grass"},
 	interval = 2,
@@ -339,3 +344,18 @@ minetest.register_abm({
 	end
 })
 
+
+--
+-- Moss growth on cobble near water
+--
+
+minetest.register_abm({
+	nodenames = {"default:cobble"},
+	neighbors = {"group:water"},
+	interval = 17,
+	chance = 200,
+	catch_up = false,
+	action = function(pos, node)
+		minetest.set_node(pos, {name = "default:mossycobble"})
+	end
+})