Fix CreateObject after full foreign stack merge

Source/ACE.Server.Tests/StackableMergeMessageTests.cs

@@ -0,0 +1,52 @@
+using System.Collections.Generic;
+
+using ACE.Entity;
+using ACE.Entity.Models;
+using ACE.Server.WorldObjects;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace ACE.Server.Tests
+{
+    [TestClass]
+    public class StackableMergeMessageTests
+    {
+        [TestMethod]
+        public void DoesNotEnqueueCreateObjectForDestroyedForeignSourceStack()
+        {
+            var sourceStack = CreateStack(5);
+            sourceStack.Destroy(false);
+            Assert.IsTrue(sourceStack.IsDestroyed);
+            Assert.AreEqual(5, sourceStack.StackSize ?? -1);
+            var sentObjects = new List<WorldObject>();
+
+            StackableMergeMessageHelper.EnqueueCreateObjectForRemainingSourceStack(
+                sourceStack,
+                sourceIsPlayerOwned: false,
+                sentObjects.Add);
+
+            Assert.AreEqual(0, sentObjects.Count);
+        }
+
+        [TestMethod]
+        public void EnqueuesCreateObjectForRemainingForeignSourceStack()
+        {
+            var sourceStack = CreateStack(3);
+            var sentObjects = new List<WorldObject>();
+
+            StackableMergeMessageHelper.EnqueueCreateObjectForRemainingSourceStack(
+                sourceStack,
+                sourceIsPlayerOwned: false,
+                sentObjects.Add);
+
+            Assert.AreEqual(1, sentObjects.Count);
+            Assert.AreSame(sourceStack, sentObjects[0]);
+        }
+
+        private static Stackable CreateStack(int stackSize)
+        {
+            var stack = new Stackable(new Weenie(), new ObjectGuid(1));
+            stack.StackSize = stackSize;
+            return stack;
+        }
+    }
+}

Source/ACE.Server/ACE.Server.csproj

@@ -242,6 +242,10 @@
     <PackageReference Include="MySqlConnector" Version="2.6.2" />
   </ItemGroup>
 
+  <ItemGroup>
+    <InternalsVisibleTo Include="ACE.Server.Tests" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\ACE.Adapter\ACE.Adapter.csproj" />
     <ProjectReference Include="..\ACE.Common\ACE.Common.csproj" />

Source/ACE.Server/WorldObjects/Player_Inventory.cs

@@ -3051,8 +3051,10 @@ public void HandleActionStackableMerge(uint mergeFromGuid, uint mergeToGuid, int
                         if (DoHandleActionStackableMerge(sourceStack, targetStack, amount))
                         {
                             // If the client used the R key to merge a partial stack from the landscape, it also tries to add the "ghosted" item of the picked up stack to the inventory as well.
-                            if (sourceStackRootOwner != this && sourceStack.StackSize > 0)
-                                Session.Network.EnqueueSend(new GameMessageCreateObject(sourceStack));
+                            StackableMergeMessageHelper.EnqueueCreateObjectForRemainingSourceStack(
+                                sourceStack,
+                                sourceStackRootOwner == this,
+                                stack => Session.Network.EnqueueSend(new GameMessageCreateObject(stack)));
 
                             Session.Network.EnqueueSend(new GameMessagePrivateUpdatePropertyInt(this, PropertyInt.EncumbranceVal, EncumbranceVal ?? 0));
 

Source/ACE.Server/WorldObjects/StackableMergeMessageHelper.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace ACE.Server.WorldObjects
+{
+    internal static class StackableMergeMessageHelper
+    {
+        internal static void EnqueueCreateObjectForRemainingSourceStack(
+            WorldObject sourceStack,
+            bool sourceIsPlayerOwned,
+            Action<WorldObject> enqueueCreateObject)
+        {
+            // A full merge destroys the source but leaves its pre-merge StackSize intact.
+            if (!sourceIsPlayerOwned && !sourceStack.IsDestroyed && sourceStack.StackSize > 0)
+                enqueueCreateObject(sourceStack);
+        }
+    }
+}