Paper/patches/server/0424-Fix-numerous-item-duplication-issues-and-teleport-is.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 25 Apr 2020 06:46:35 -0400
Subject: [PATCH] Fix numerous item duplication issues and teleport issues

This notably fixes the newest "Donkey Dupe", but also fixes a lot
of dupe bugs in general around nether portals and entity world transfer

We also fix item duplication generically by anytime we clone an item
to drop it on the ground, destroy the source item.

This avoid an itemstack ever existing twice in the world state pre
clean up stage.

So even if something NEW comes up, it would be impossible to drop the
same item twice because the source was destroyed.

diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
index f08c8212f7a07fd10da127c65d4cea76921585e4..1307a37848fcf98cfd7ed19a7b746ba57ac88411 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -2146,11 +2146,12 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, n
         } else {
             // CraftBukkit start - Capture drops for death event
             if (this instanceof net.minecraft.world.entity.LivingEntity && !((net.minecraft.world.entity.LivingEntity) this).forceDrops) {
-                ((net.minecraft.world.entity.LivingEntity) this).drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(stack));
+                ((net.minecraft.world.entity.LivingEntity) this).drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asCraftMirror(stack)); // Paper - mirror so we can destroy it later
                 return null;
             }
             // CraftBukkit end
-            ItemEntity entityitem = new ItemEntity(this.level, this.getX(), this.getY() + (double) yOffset, this.getZ(), stack);
+            ItemEntity entityitem = new ItemEntity(this.level, this.getX(), this.getY() + (double) yOffset, this.getZ(), stack.copy()); // Paper - clone so we can destroy original
+            stack.setCount(0); // Paper - destroy this item - if this ever leaks due to game bugs, ensure it doesn't dupe
 
             entityitem.setDefaultPickUpDelay();
             // CraftBukkit start
@@ -2892,6 +2893,12 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, n
     @Nullable
     public Entity teleportTo(ServerLevel worldserver, BlockPos location) {
         // CraftBukkit end
+        // Paper start - fix bad state entities causing dupes
+        if (!isAlive() || !valid) {
+            LOGGER.warn("Illegal Entity Teleport " + this + " to " + worldserver + ":" + location, new Throwable());
+            return null;
+        }
+        // Paper end
         if (this.level instanceof ServerLevel && !this.isRemoved()) {
             this.level.getProfiler().push("changeDimension");
             // CraftBukkit start
@@ -2912,6 +2919,11 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, n
                 // CraftBukkit end
 
                 this.level.getProfiler().popPush("reloading");
+                // Paper start - Change lead drop timing to prevent dupe
+                if (this instanceof Mob) {
+                    ((Mob) this).dropLeash(true, true); // Paper drop lead
+                }
+                // Paper end
                 Entity entity = this.getType().create((Level) worldserver);
 
                 if (entity != null) {
@@ -2925,10 +2937,6 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, n
                     // CraftBukkit start - Forward the CraftEntity to the new entity
                     this.getBukkitEntity().setHandle(entity);
                     entity.bukkitEntity = this.getBukkitEntity();
-
-                    if (this instanceof Mob) {
-                        ((Mob) this).dropLeash(true, false); // Unleash to prevent duping of leads.
-                    }
                     // CraftBukkit end
                 }
 
@@ -3053,7 +3061,7 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, n
     }
 
     public boolean canChangeDimensions() {
-        return true;
+        return isAlive() && valid; // Paper
     }
 
     public float getBlockExplosionResistance(Explosion explosion, BlockGetter world, BlockPos pos, BlockState blockState, FluidState fluidState, float max) {
diff --git a/src/main/java/net/minecraft/world/entity/decoration/ArmorStand.java b/src/main/java/net/minecraft/world/entity/decoration/ArmorStand.java
index bbde9b758643c087733064a126d90689d71830cf..069cdfce085909991a69ebec3004d407526d469d 100644
--- a/src/main/java/net/minecraft/world/entity/decoration/ArmorStand.java
+++ b/src/main/java/net/minecraft/world/entity/decoration/ArmorStand.java
@@ -611,7 +611,7 @@ public class ArmorStand extends LivingEntity {
         for (i = 0; i < this.handItems.size(); ++i) {
             itemstack = (ItemStack) this.handItems.get(i);
             if (!itemstack.isEmpty()) {
-                drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(itemstack)); // CraftBukkit - add to drops
+                drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asCraftMirror(itemstack)); // CraftBukkit - add to drops // Paper - mirror so we can destroy it later - though this call site was safe
                 this.handItems.set(i, ItemStack.EMPTY);
             }
         }
@@ -619,7 +619,7 @@ public class ArmorStand extends LivingEntity {
         for (i = 0; i < this.armorItems.size(); ++i) {
             itemstack = (ItemStack) this.armorItems.get(i);
             if (!itemstack.isEmpty()) {
-                drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asBukkitCopy(itemstack)); // CraftBukkit - add to drops
+                drops.add(org.bukkit.craftbukkit.inventory.CraftItemStack.asCraftMirror(itemstack)); // CraftBukkit - add to drops // Paper - mirror so we can destroy it later - though this call site was safe
                 this.armorItems.set(i, ItemStack.EMPTY);
             }
         }
diff --git a/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java b/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
index 8e4bd4818cf9d50dec7b94e5f1263086b6a6b86a..09c152123d055432266bbb5a1434c21aed64da1f 100644
--- a/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
+++ b/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
@@ -807,7 +807,8 @@ public class CraftEventFactory {
         for (org.bukkit.inventory.ItemStack stack : event.getDrops()) {
             if (stack == null || stack.getType() == Material.AIR || stack.getAmount() == 0) continue;
 
-            world.dropItem(entity.getLocation(), stack);
+            world.dropItem(entity.getLocation(), stack); // Paper - note: dropItem already clones due to this being bukkit -> NMS
+            if (stack instanceof CraftItemStack) stack.setAmount(0); // Paper - destroy this item - if this ever leaks due to game bugs, ensure it doesn't dupe, but don't nuke bukkit stacks of manually added items
         }
 
         return event;