Use ABM to propagate / remove the beam

mods/ITEMS/mcl_beacons/init.lua

@@ -46,6 +46,9 @@ minetest.register_node("mcl_beacons:beacon_beam",{
 	light_source = 15,
 	walkable = false,
 	pointable = false,
+--	diggable = false,
+	floodable = false,
+	buildable_to = true,
 	groups = {not_in_creative_inventory=1},
 	_mcl_blast_resistance = 1200,
 })
@@ -289,8 +292,28 @@ function register_beaconfuel(itemstring)
 	table.insert(beacon_fuellist, itemstring)
 end
 
-local timer = 0
+minetest.register_abm({
+	label = "Beacon beams propagation",
+	nodenames ={ "mcl_beacons:beacon_beam" },
+	neighbors = { "air" },
+	interval = 3,
+	chance = 1,
+	action = function(pos,node)
+		local p1 = vector.offset(pos,0,-1,0)
+		local p2 = vector.offset(pos,0,1,0)
+		local n1 = minetest.get_node(p1)
+		local n2 = minetest.get_node(p2)
+		if n1.name == "air" then
+			minetest.remove_node(pos)
+			return
+		elseif n2.name == "air" then
+			minetest.set_node(p2,node)
+		end
+	end
+})
 
+
+local timer = 0
 minetest.register_globalstep(function(dtime)
 	timer = timer + dtime
 	if timer >= 3  then