Paper/patches/server/0939-Fix-HumanEntity-drop-not-updating-the-client-inv.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jake Potrebic <jake.m.potrebic@gmail.com>
Date: Sun, 10 Oct 2021 18:18:01 -0700
Subject: [PATCH] Fix HumanEntity#drop not updating the client inv

== AT ==
public net.minecraft.server.level.ServerPlayer containerSynchronizer

diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftHumanEntity.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftHumanEntity.java
index 0a35f3510e71bb8c7812eed61bbab3872ea78437..cba6ead3f937f2b3d59c15a864e07e5cb2f2330c 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftHumanEntity.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftHumanEntity.java
@@ -757,8 +757,15 @@ public class CraftHumanEntity extends CraftLivingEntity implements HumanEntity {
     // Paper end
     @Override
     public boolean dropItem(boolean dropAll) {
-        if (!(this.getHandle() instanceof ServerPlayer)) return false;
-        return ((ServerPlayer) this.getHandle()).drop(dropAll);
+        // Paper start - notify client of remote slot change
+        if (!(this.getHandle() instanceof ServerPlayer player)) return false;
+        boolean success = player.drop(dropAll);
+        if (!success) return false;
+        final net.minecraft.world.entity.player.Inventory inv = player.getInventory();
+        final java.util.OptionalInt optionalSlot = player.containerMenu.findSlot(inv, inv.selected);
+        optionalSlot.ifPresent(slot -> player.containerSynchronizer.sendSlotChange(player.containerMenu, slot, inv.getSelected()));
+        return true;
+        // Paper end
     }
 
     @Override