Fix snow placement bug due to levelled

Before, when placing snow one node above snow, the lower snow node grew and didn't turn into a snowblock

Also, test for protection

src/nodes.lua

@@ -395,7 +395,8 @@ minetest.override_item("default:snow", {
 			{-0.5, -0.5, -0.5, 0.5, -0.5, 0.5},
 		},
 	},
-	groups = {cracky=3, crumbly=3, choppy=3, oddly_breakable_by_hand=3, falling_node=1, melts=2, float=1},
+	groups = {cracky=3, crumbly=3, choppy=3, oddly_breakable_by_hand=3,
+		falling_node=1, melts=2, float=1},
 	sunlight_propagates = true,
 	walkable = true,
 	node_placement_prediction = "",
@@ -428,43 +429,71 @@ minetest.override_item("default:snow", {
 		end
 	end,
 	--Manage snow levels.
-	on_place = function(itemstack, placer, pointed_thing)
-		local under = pointed_thing.under
-		local oldnode_under = minetest.get_node_or_nil(under)
-		local above = pointed_thing.above
-
-		if not oldnode_under
-		or not above then
-			return
+	on_place = function(itemstack, player, pt)
+		local oldnode_under = minetest.get_node_or_nil(pt.under)
+		if not oldnode_under then
+			return itemstack, false
 		end
 
-		local olddef_under = ItemStack({name=oldnode_under.name}):get_definition()
-		olddef_under = olddef_under or minetest.nodedef_default
+		local olddef_under = minetest.registered_nodes[oldnode_under.name]
+		if not olddef_under then
+			return itemstack, false
+		end
 
-		local place_to
 		-- If node under is buildable_to, place into it instead (eg. snow)
+		local pos, node
 		if olddef_under.buildable_to then
-			place_to = under
+			pos = pt.under
+			node = oldnode_under
 		else
-			-- Place above pointed node
-			place_to = above
+			pos = pt.above
+			node = minetest.get_node(pos)
+			local def = minetest.registered_nodes[node.name]
+			if not def
+			or not def.buildable_to then
+				return itemstack, false
+			end
 		end
 
-		local level = minetest.get_node_level(place_to)
-		if level == 63 then
-			minetest.set_node(place_to, {name="default:snowblock"})
-		else
-			minetest.set_node_level(place_to, level+7)
+		-- nil player can place (for snowballs)
+		if player
+		and minetest.is_protected(pos, player:get_player_name()) then
+			return itemstack, false
 		end
 
-		if minetest.get_node(place_to).name ~= "default:snow" then
-			local itemstack, placed = minetest.item_place_node(itemstack, placer, pointed_thing)
-			return itemstack, placed
+		if node.name ~= "default:snow" then
+			if minetest.get_node{x=pos.x, y=pos.y-1, z=pos.z}.name ==
+					"default:snow" then
+				-- grow the snow below (fixes levelled problem)
+				pos.y = pos.y - 1
+			else
+				-- place a snow
+				return minetest.item_place_node(itemstack, player, pt)
+			end
+		end
+
+		-- grow the snow
+		local level = minetest.get_node_level(pos)
+		level = level + 7
+		if level < 64 then
+			minetest.set_node_level(pos, level)
+		else
+			-- place a snowblock and snow onto it if possible
+			local p = {x=pos.x, y=pos.y+1, z=pos.z}
+			local def = minetest.registered_nodes[minetest.get_node(p).name]
+			if not def
+			or not def.buildable_to then
+				return itemstack, false
+			end
+
+			minetest.set_node(pos, {name="default:snowblock"})
+			minetest.set_node(p, {name="default:snow"})
+			level = math.max(level - 64, 7)
+			minetest.set_node_level(p, level)
 		end
 
 		itemstack:take_item()
-
-		return itemstack
+		return itemstack, true
 	end,
 	on_use = snow.shoot_snowball
 })