only load detached npc inventories when they are really needed - either by the npc dialog or in edit_mode

api/api_inventory.lua

@@ -98,10 +98,54 @@ yl_speak_up.inventory_allow_item = function(player, stack, input_to)
 end
 
 
+-- checks dialog and tries to find out if this dialog needs a detached inventory for the NPC;
+-- returns true if the NPC needs one; else false
+yl_speak_up.dialog_requires_inventory = function(dialog)
+	if(not(dialog)) then
+		return false
+	end
+	for t, t_data in pairs(dialog.trades or {}) do
+		if(t and t ~= "limits") then
+			return true
+		end
+	end
+	for d_id, d_data in pairs(dialog.n_dialogs or {}) do
+		for o_id, o_data in pairs(d_data.d_options or {}) do
+			-- check preconditions:
+			for p_id, p_data in pairs(o_data.o_prerequisites or {}) do
+				local t = p_data.p_type or "?"
+				if(t == "trade" or t == "npc_inv" or t == "player_offered_item") then
+					return true
+				end
+			end
+			-- check actions:
+			for a_id, a_data in pairs(o_data.actions or {}) do
+				local t = a_data.a_type or "?"
+				if(t == "trade" or t == "npc_gives" or t == "npc_wants") then
+					return true
+				end
+			end
+			-- check effects:
+			for r_id, r_data in pairs(o_data.o_results or {}) do
+				local t = r_data.r_type or "?"
+				if(t == "block" or t == "craft" or t == "put_into_block_inv"
+				  or t == "take_from_block_inv" or t == "deal_with_offered_item") then
+					return true
+				end
+			end
+		end
+	end
+	-- nothing found that actually uses the NPC's inventory - so don't load it
+	return false
+end
+
+
 -- create and load the detached inventory in yl_speak_up.after_activate;
 -- direct access to this inventory is only possible for players with the right privs
 -- (this is an inventory for the *NPC*, which is stored to disk sometimes)
-yl_speak_up.load_npc_inventory = function(n_id)
+-- if force_load is true, the inventory will be loaded even if the NPC doesn't usually
+-- 	need one (i.e. in edit_mode, or with "show me your inventory").
+yl_speak_up.load_npc_inventory = function(n_id, force_load, dialog)
 	if(not(n_id)) then
 		return
 	end
@@ -125,9 +169,16 @@ yl_speak_up.load_npc_inventory = function(n_id)
 
 	yl_speak_up.npc_inventory_last_used[ n_id ] = os.time()
 	-- the inventory is already loaded
-	if( yl_speak_up.npc_inventory[ n_id ]) then
+	if(yl_speak_up.npc_inventory[ n_id ]) then
 		return
 	end
+
+	-- check if the NPC actually needs an inventory - else don't load it
+	if(not(force_load) and dialog
+	  and not(yl_speak_up.dialog_requires_inventory(dialog))) then
+		return
+	end
+
 	-- create the detached inventory (it is empty for now)
 	local npc_inv = minetest.create_detached_inventory("yl_speak_up_npc_"..tostring(n_id), {
 		allow_move = function(inv, from_list, from_index, to_list, to_index, count, player)

editor/fs/fs_talkdialog_edit_mode.lua

@@ -49,6 +49,8 @@ yl_speak_up.input_talk = function(player, formname, fields)
 			-- result
 			return
 		end
+		-- make sure the inventory of the NPC is loaded
+		yl_speak_up.load_npc_inventory(n_id, true, nil)
 		-- for older formspec versions: reset scroll counter
 		yl_speak_up.speak_to[pname].counter = 1
 		yl_speak_up.speak_to[pname].option_index = 1

fs/fs_inventory.lua

@@ -45,6 +45,9 @@ yl_speak_up.get_fs_inventory = function(player)
 		                "button_exit[2,1.5;1,0.9;exit;Exit]"
 	end
 
+	-- make sure the inventory of the NPC is loaded
+	yl_speak_up.load_npc_inventory(n_id, true, nil)
+
 	return table.concat({"size[12,11]",
 		"label[2,-0.2;Inventory of ",
 			minetest.formspec_escape(dialog.n_npc),

functions.lua

@@ -589,10 +589,6 @@ function yl_speak_up.talk(self, clicker)
 		self = yl_speak_up.initialize_npc(self)
 	end
 
-	-- TODO: load inventory only when the npc actually uses one?
-        -- create a detached inventory for the npc and load its inventory
-	yl_speak_up.load_npc_inventory(id_prefix.."_"..tostring(self.yl_speak_up.id))
-
 
     local npc_id = self.yl_speak_up.id
     local n_id = id_prefix.."_" .. npc_id
@@ -646,6 +642,10 @@ function yl_speak_up.talk(self, clicker)
        dialog.trades = {}
     end
 
+    -- create a detached inventory for the npc and load its inventory
+    yl_speak_up.load_npc_inventory(id_prefix.."_"..tostring(self.yl_speak_up.id), false, dialog)
+
+
     -- some NPC may have reset the animation; at least set it to the desired
     -- value whenever we talk to the NPC
     if self.yl_speak_up and self.yl_speak_up.animation then