[LuaMod|Inventory] Fixed a small bug preventing items from being gathered.

docs/lua-api-mod.md

@@ -109,9 +109,11 @@ Give an item stack to a player.
 
 Example:
 ```lua
-mod:give_item_stack(player, item_stack)
+local items_left = mod:give_item_stack(player, item_stack)
 ```
 
+This function returns an `ItemStack` containing the items it couldn't place into player's inventory.
+
 ### `spawn_entity`
 
 Spawn an entity.

source/common/inventory/Inventory.cpp

@@ -35,7 +35,9 @@ void Inventory::setStack(u16 x, u16 y, const std::string &stringID, u16 amount)
 
 ItemStack Inventory::addStack(const std::string &stringID, u16 amount, u16 offset, u16 size, bool mergeOnly) {
 	if (stringID.empty() || stringID == BLOCK_AIR || amount == 0)
-		return {BLOCK_AIR, 0};
+		return ItemStack::Empty;
+
+	bool hasChanged = false;
 
 	ItemStack ret{stringID, amount};
 	for (std::size_t i = offset ; ret.amount() && i < (size ? offset + size : m_items.size()) ; ++i) {
@@ -49,7 +51,8 @@ ItemStack Inventory::addStack(const std::string &stringID, u16 amount, u16 offse
 				m_items[i] = ItemStack(stringID, ret.amount());
 				ret.setAmount(0);
 			}
-			m_hasChanged = true;
+
+			hasChanged = true;
 		}
 		else if (item.stringID() == stringID) {
 			u16 sum = m_items[i].amount() + ret.amount();
@@ -62,12 +65,14 @@ ItemStack Inventory::addStack(const std::string &stringID, u16 amount, u16 offse
 				ret.setAmount(0);
 			}
 
-			m_hasChanged = true;
+			hasChanged = true;
 		}
 	}
 
-	if (!m_hasChanged && mergeOnly && ret.amount())
+	if (!hasChanged && mergeOnly && ret.amount())
 		return addStack(ret.item().stringID(), ret.amount(), offset, size);
+	else if (hasChanged)
+		m_hasChanged = hasChanged;
 
 	return ret;
 }

source/common/inventory/ItemStack.cpp

@@ -27,6 +27,8 @@
 #include "ItemStack.hpp"
 #include "Registry.hpp"
 
+const ItemStack ItemStack::Empty{BLOCK_AIR, 0};
+
 const Item &ItemStack::item() const {
 	return Registry::getInstance().getItemFromStringID(m_stringID);
 }

source/common/inventory/ItemStack.hpp

@@ -46,6 +46,8 @@ class ItemStack {
 
 		static void initUsertype(sol::state &lua);
 
+		static const ItemStack Empty;
+
 	private:
 		std::string m_stringID{BLOCK_AIR};
 

source/server/lua/LuaMod.cpp

@@ -106,16 +106,19 @@ void LuaMod::despawnEntity(EntityWrapper &entity) {
 		gkError() << "In mod '" + m_id + "': Failed to despawn entity: Missing position and network components";
 }
 
-void LuaMod::giveItemStack(ServerPlayer &player, ItemStack *itemStack) {
-	if (itemStack) {
+ItemStack LuaMod::giveItemStack(ServerPlayer &player, ItemStack *itemStack) {
+	if (!itemStack) {
+		gkError() << "In mod '" + m_id + "': Failed to add stack to player";
+		return ItemStack::Empty;
+	}
+
 	// FIXME: This should probably be moved to a mod
 	ItemStack stackRet = player.inventory().addStack(itemStack->item().stringID(), itemStack->amount(), 9, 24, true);
 	if (stackRet.amount() != 0)
-			player.inventory().addStack(stackRet.item().stringID(), stackRet.amount(), 0, 9, true);
+		stackRet = player.inventory().addStack(stackRet.item().stringID(), stackRet.amount(), 0, 9, true);
 
 	m_worldController.server()->sendPlayerInvUpdate(player.clientID(), player.client());
-	}
-	else
-		gkError() << "In mod '" + m_id + "': Failed to add stack to player";
+
+	return stackRet;
 }
 

source/server/lua/LuaMod.hpp

@@ -67,7 +67,7 @@ class LuaMod {
 		void spawnEntity(const std::string &entityID, const sol::table &table);
 		void despawnEntity(EntityWrapper &entity);
 
-		void giveItemStack(ServerPlayer &player, ItemStack *itemStack);
+		ItemStack giveItemStack(ServerPlayer &player, ItemStack *itemStack);
 
 		enum class DefinitionType {
 			Block,