PaperMC/patches/server-unmapped/0707-Fix-duplicating-give-items-on-item-drop-cancel.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Alphaesia <creepashadowz@gmail.com>
Date: Fri, 23 Apr 2021 09:57:56 +1200
Subject: [PATCH] Fix duplicating /give items on item drop cancel

Fixes SPIGOT-2942 (Give command fires PlayerDropItemEvent, cancelling it causes item duplication).

For every stack of items to give, /give puts the item stack straight
into the player's inventory. However, it also summons a "fake item"
at the player's location. When the PlayerDropItemEvent for this fake
item is cancelled, the server attempts to put the item back into the
player's inventory. The result is that the fake item, which is never
meant to be obtained, is combined with the real items injected directly
into the player's inventory. This means more items than the amount
specified in /give are given to the player - one for every stack of
items given. (e.g. /give @s dirt 1 gives you 2 dirt).

While this isn't a big issue for general building usage, it can affect
e.g. adventure maps where the number of items the player receives is
important (and you want to restrict the player from throwing items).

If there are any overflow items that didn't make it into the inventory
(insufficient space), those items are dropped as a real item instead
of a fake one. While cancelling this drop would also result in the
server attempting to put those items into the inventory, since it is
full this has no effect.

Just ignoring cancellation of the PlayerDropItemEvent seems like the
cleanest and least intrusive way to fix it.

diff --git a/src/main/java/net/minecraft/server/commands/CommandGive.java b/src/main/java/net/minecraft/server/commands/CommandGive.java
index 6685bf1757458d908e32d4069f7a8a22a28c28d7..a10207f7cb9455e29db7e6906cb2138ad5609a1f 100644
--- a/src/main/java/net/minecraft/server/commands/CommandGive.java
+++ b/src/main/java/net/minecraft/server/commands/CommandGive.java
@@ -49,7 +49,7 @@ public class CommandGive {
 
                 if (flag && itemstack.isEmpty()) {
                     itemstack.setCount(1);
-                    entityitem = entityplayer.drop(itemstack, false);
+                    entityitem = entityplayer.drop(itemstack, false, false, true); // Paper - Fix duplicating /give items on item drop cancel
                     if (entityitem != null) {
                         entityitem.s();
                     }
diff --git a/src/main/java/net/minecraft/world/entity/player/EntityHuman.java b/src/main/java/net/minecraft/world/entity/player/EntityHuman.java
index ec0956a98c133bcd3d4f92f696c667eab6ff98f1..3a62bde04d7fbb6c571cfef11d4f6891e11c7ac8 100644
--- a/src/main/java/net/minecraft/world/entity/player/EntityHuman.java
+++ b/src/main/java/net/minecraft/world/entity/player/EntityHuman.java
@@ -642,6 +642,13 @@ public abstract class EntityHuman extends EntityLiving {
 
     @Nullable
     public EntityItem a(ItemStack itemstack, boolean flag, boolean flag1) {
+        // Paper start - Fix duplicating /give items on item drop cancel
+        return this.drop(itemstack, flag, flag1, false);
+    }
+
+    @Nullable
+    public EntityItem drop(ItemStack itemstack, boolean flag, boolean flag1, boolean alwaysSucceed) {
+        // Paper end
         if (itemstack.isEmpty()) {
             return null;
         } else {
@@ -683,7 +690,7 @@ public abstract class EntityHuman extends EntityLiving {
             PlayerDropItemEvent event = new PlayerDropItemEvent(player, drop);
             this.world.getServer().getPluginManager().callEvent(event);
 
-            if (event.isCancelled()) {
+            if (event.isCancelled() && !alwaysSucceed) { // Paper - Fix duplicating /give items on item drop cancel
                 org.bukkit.inventory.ItemStack cur = player.getInventory().getItemInHand();
                 if (flag1 && (cur == null || cur.getAmount() == 0)) {
                     // The complete stack was dropped