Add InvRef:is_empty(listname) and make chests/furnaces not diggable if not empty in minimal game

doc/lua_api.txt

@@ -926,6 +926,7 @@ Player-only: (no-op for other objects)
 
 InvRef: Reference to an inventory
 methods:
+- is_empty(listname): return true if list is empty
 - get_size(listname): get size of a list
 - set_size(listname, size): set size of a list
 - get_stack(listname, i): get a copy of stack index i in list

games/minimal/mods/default/init.lua

@@ -1147,6 +1147,11 @@ minetest.register_node("default:chest", {
 		local inv = meta:get_inventory()
 		inv:set_size("main", 8*4)
 	end,
+	can_dig = function(pos,player)
+		local meta = minetest.env:get_meta(pos);
+		local inv = meta:get_inventory()
+		return inv:is_empty("main")
+	end,
     on_metadata_inventory_move = function(pos, from_list, from_index,
 			to_list, to_index, count, player)
 		minetest.log("action", player:get_player_name()..
@@ -1200,6 +1205,11 @@ minetest.register_node("default:chest_locked", {
 		local inv = meta:get_inventory()
 		inv:set_size("main", 8*4)
 	end,
+	can_dig = function(pos,player)
+		local meta = minetest.env:get_meta(pos);
+		local inv = meta:get_inventory()
+		return inv:is_empty("main")
+	end,
     on_metadata_inventory_move = function(pos, from_list, from_index,
 			to_list, to_index, count, player)
 		local meta = minetest.env:get_meta(pos)
@@ -1270,6 +1280,18 @@ minetest.register_node("default:furnace", {
 		inv:set_size("src", 1)
 		inv:set_size("dst", 4)
 	end,
+	can_dig = function(pos,player)
+		local meta = minetest.env:get_meta(pos);
+		local inv = meta:get_inventory()
+		if not inv:is_empty("fuel") then
+			return false
+		elseif not inv:is_empty("dst") then
+			return false
+		elseif not inv:is_empty("src") then
+			return false
+		end
+		return true
+	end,
 })
 
 minetest.register_node("default:furnace_active", {
@@ -1291,6 +1313,18 @@ minetest.register_node("default:furnace_active", {
 		inv:set_size("src", 1)
 		inv:set_size("dst", 4)
 	end,
+	can_dig = function(pos,player)
+		local meta = minetest.env:get_meta(pos);
+		local inv = meta:get_inventory()
+		if not inv:is_empty("fuel") then
+			return false
+		elseif not inv:is_empty("dst") then
+			return false
+		elseif not inv:is_empty("src") then
+			return false
+		end
+		return true
+	end,
 })
 
 function hacky_swap_node(pos,name)

src/scriptapi.cpp

@@ -1718,6 +1718,20 @@ private:
 		return 0;
 	}
 
+	// is_empty(self, listname) -> true/false
+	static int l_is_empty(lua_State *L)
+	{
+		InvRef *ref = checkobject(L, 1);
+		const char *listname = luaL_checkstring(L, 2);
+		InventoryList *list = getlist(L, ref, listname);
+		if(list && list->getUsedSlots() > 0){
+			lua_pushboolean(L, false);
+		} else {
+			lua_pushboolean(L, true);
+		}
+		return 1;
+	}
+
 	// get_size(self, listname)
 	static int l_get_size(lua_State *L)
 	{
@@ -1944,6 +1958,7 @@ public:
 };
 const char InvRef::className[] = "InvRef";
 const luaL_reg InvRef::methods[] = {
+	method(InvRef, is_empty),
 	method(InvRef, get_size),
 	method(InvRef, set_size),
 	method(InvRef, get_stack),