PaperMC/patches/server-remapped/0709-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/GiveCommand.java b/src/main/java/net/minecraft/server/commands/GiveCommand.java
index a6259e9160f291cf527a4ea5533a2e5530471874..3b8a7b9bdd2445afa93e4f2dc971a1d252c1463a 100644
--- a/src/main/java/net/minecraft/server/commands/GiveCommand.java
+++ b/src/main/java/net/minecraft/server/commands/GiveCommand.java
@@ -49,7 +49,7 @@ public class GiveCommand {
 
                 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.makeFakeItem();
                     }
diff --git a/src/main/java/net/minecraft/world/entity/player/Player.java b/src/main/java/net/minecraft/world/entity/player/Player.java
index 4817b8ab259d348b48bc325d34ba9351ffe951df..cfb9bd6b9863a0f6f0f50181b7553adce90cfebe 100644
--- a/src/main/java/net/minecraft/world/entity/player/Player.java
+++ b/src/main/java/net/minecraft/world/entity/player/Player.java
@@ -639,7 +639,14 @@ public abstract class Player extends LivingEntity {
 
     @Nullable
     public ItemEntity drop(ItemStack stack, boolean throwRandomly, boolean retainOwnership) {
-        if (stack.isEmpty()) {
+        // Paper start - Fix duplicating /give items on item drop cancel
+        return this.drop(stack, throwRandomly, retainOwnership, false);
+    }
+
+    @Nullable
+    public ItemEntity drop(ItemStack itemstack, boolean flag, boolean flag1, boolean alwaysSucceed) {
+        // Paper end
+        if (itemstack.isEmpty()) {
             return null;
         } else {
             if (this.level.isClientSide) {
@@ -647,17 +654,17 @@ public abstract class Player extends LivingEntity {
             }
 
             double d0 = this.getEyeY() - 0.30000001192092896D;
-            ItemEntity entityitem = new ItemEntity(this.level, this.getX(), d0, this.getZ(), stack);
+            ItemEntity entityitem = new ItemEntity(this.level, this.getX(), d0, this.getZ(), itemstack);
 
             entityitem.setPickUpDelay(40);
-            if (retainOwnership) {
+            if (flag1) {
                 entityitem.setThrower(this.getUUID());
             }
 
             float f;
             float f1;
 
-            if (throwRandomly) {
+            if (flag) {
                 f = this.random.nextFloat() * 0.5F;
                 f1 = this.random.nextFloat() * 6.2831855F;
                 entityitem.setDeltaMovement((double) (-Mth.sin(f1) * f), 0.20000000298023224D, (double) (Mth.cos(f1) * f));
@@ -680,12 +687,12 @@ public abstract class Player extends LivingEntity {
             PlayerDropItemEvent event = new PlayerDropItemEvent(player, drop);
             this.level.getCraftServer().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 (retainOwnership && (cur == null || cur.getAmount() == 0)) {
+                if (flag1 && (cur == null || cur.getAmount() == 0)) {
                     // The complete stack was dropped
                     player.getInventory().setItemInHand(drop.getItemStack());
-                } else if (retainOwnership && cur.isSimilar(drop.getItemStack()) && cur.getAmount() < cur.getMaxStackSize() && drop.getItemStack().getAmount() == 1) {
+                } else if (flag1 && cur.isSimilar(drop.getItemStack()) && cur.getAmount() < cur.getMaxStackSize() && drop.getItemStack().getAmount() == 1) {
                     // Only one item is dropped
                     cur.setAmount(cur.getAmount() + 1);
                     player.getInventory().setItemInHand(cur);
@@ -697,9 +704,9 @@ public abstract class Player extends LivingEntity {
             }
             // CraftBukkit end
             // Paper start - remove player from map on drop
-            if (stack.getItem() == Items.FILLED_MAP) {
-                MapItemSavedData worldmap = MapItem.getOrCreateSavedData(stack, this.level);
-                worldmap.updateSeenPlayers(this, stack);
+            if (itemstack.getItem() == Items.FILLED_MAP) {
+                MapItemSavedData worldmap = MapItem.getOrCreateSavedData(itemstack, this.level);
+                worldmap.updateSeenPlayers(this, itemstack);
             }
             // Paper end