Paper/patches/server/0816-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 e1150d36de56466ad9fdd5f2cdb4c30855d4af70..3d36d79a4e7f16f6face3465cdf54656984f3ebc 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftHumanEntity.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftHumanEntity.java
@@ -750,8 +750,15 @@ 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 - Fix HumanEntity#drop not updating the client inv
+        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 - Fix HumanEntity#drop not updating the client inv
     }
 
     @Override