refactor: decomposition placement checks.

generalize a repeated node check into a single function.

mods/bg_tree/node_leaves.lua

@@ -63,16 +63,22 @@ reg_leaves("leaves_alive", {
 	},
 })
 
+local function check_decompose (pos)
+	local node = minetest.get_node(pos)
+	return blockgame.item_matches(node.name, {"group:leaves_decomposing"})
+end
+
 -- TODO: generalize stacking node registration and put into API.
 local decomposing_leaves_layers = 4
 
 local function after_place_stack (pos)
-	local node = minetest.get_node(pos)
+	if not check_decompose(pos) then return end
-	if not blockgame.starts_with(node.name, modname .. ":leaves_decomposing") then return end
 
 	local below = pos + blockgame.vector.dirs.down
-	local below_node = minetest.get_node(below)
+	if check_decompose(below) then
-	if blockgame.starts_with(below_node.name, modname .. ":leaves_decomposing") then
+		local node = minetest.get_node(pos)
+		local below_node = minetest.get_node(pos)
+
 		local def = minetest.registered_nodes[node.name]
 		local below_def = minetest.registered_nodes[below_node.name]
 
@@ -90,8 +96,7 @@ local function after_place_stack (pos)
 	end
 
 	local above = pos:offset(0, 1, 0)
-	local above_node = minetest.get_node(above)
+	if check_decompose(above) then
-	if blockgame.starts_with(above_node.name, modname .. ":leaves_decomposing") then
 		after_place_stack(above)
 	end
 end