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 0a07a99e67e087db87c493d7c2b8b0c94d5b3771..19218e993052d44a830f825f9a0eb695635861c1 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -2307,11 +2307,12 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
         } 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
@@ -3086,6 +3087,12 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
     @Nullable
     public Entity teleportTo(ServerLevel worldserver, PositionImpl 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
@@ -3112,6 +3119,11 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
                 // 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(worldserver);
 
                 if (entity != null) {
@@ -3125,10 +3137,6 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
                     // 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
                 }
 
@@ -3249,7 +3257,7 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
     }
 
     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/LivingEntity.java b/src/main/java/net/minecraft/world/entity/LivingEntity.java
index 632119d31b2c2821ef4871abf4fd6916668b0de7..b6741c72216378368392e65aad3ff75a3191d0ce 100644
--- a/src/main/java/net/minecraft/world/entity/LivingEntity.java
+++ b/src/main/java/net/minecraft/world/entity/LivingEntity.java
@@ -1647,9 +1647,9 @@ public abstract class LivingEntity extends Entity {
                 // Paper start
                 org.bukkit.event.entity.EntityDeathEvent deathEvent = this.dropAllDeathLoot(damageSource);
                 if (deathEvent == null || !deathEvent.isCancelled()) {
-                    if (this.deathScore >= 0 && entityliving != null) {
-                        entityliving.awardKillScore(this, this.deathScore, damageSource);
-                    }
+                    // if (this.deathScore >= 0 && entityliving != null) { // Paper moved to be run earlier in #dropAllDeathLoot before destroying the drop items in CraftEventFactory#callEntityDeathEvent
+                    //     entityliving.awardKillScore(this, this.deathScore, damageSource);
+                    // }
                     // Paper start - clear equipment if event is not cancelled
                     if (this instanceof Mob) {
                         for (EquipmentSlot slot : this.clearedEquipmentSlots) {
@@ -1747,8 +1747,13 @@ public abstract class LivingEntity extends Entity {
             this.dropCustomDeathLoot(source, i, flag);
             this.clearEquipmentSlots = prev; // Paper
         }
-        // CraftBukkit start - Call death event
-        org.bukkit.event.entity.EntityDeathEvent deathEvent = CraftEventFactory.callEntityDeathEvent(this, this.drops); // Paper
+        // CraftBukkit start - Call death event // Paper start - call advancement triggers with correct entity equipment
+        org.bukkit.event.entity.EntityDeathEvent deathEvent = CraftEventFactory.callEntityDeathEvent(this, this.drops, () -> {
+            final LivingEntity entityliving = this.getKillCredit();
+            if (this.deathScore >= 0 && entityliving != null) {
+                entityliving.awardKillScore(this, this.deathScore, source);
+            }
+        }); // Paper end
         this.postDeathDropItems(deathEvent); // Paper
         this.drops = new ArrayList<>();
         // CraftBukkit end
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 e463ae13ce6f65675c2b6d553ecf91db5a047dbc..7ff1e7e4d493770bfdbc0ad5e8f10387cefc42d2 100644
--- a/src/main/java/net/minecraft/world/entity/decoration/ArmorStand.java
+++ b/src/main/java/net/minecraft/world/entity/decoration/ArmorStand.java
@@ -609,7 +609,7 @@ 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);
             }
         }
@@ -617,7 +617,7 @@ 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 b35dd78b08b15842e87182de9afef6c49c249366..120e21edad328f382b5edc030f546e3b9a80916b 100644
--- a/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
+++ b/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
@@ -809,6 +809,11 @@ public class CraftEventFactory {
     }
 
     public static EntityDeathEvent callEntityDeathEvent(net.minecraft.world.entity.LivingEntity victim, List<org.bukkit.inventory.ItemStack> drops) {
+        // Paper start
+        return CraftEventFactory.callEntityDeathEvent(victim, drops, com.google.common.util.concurrent.Runnables.doNothing());
+    }
+    public static EntityDeathEvent callEntityDeathEvent(net.minecraft.world.entity.LivingEntity victim, List<org.bukkit.inventory.ItemStack> drops, Runnable lootCheck) {
+        // Paper end
         CraftLivingEntity entity = (CraftLivingEntity) victim.getBukkitEntity();
         EntityDeathEvent event = new EntityDeathEvent(entity, drops, victim.getExpReward());
         populateFields(victim, event); // Paper - make cancellable
@@ -822,11 +827,13 @@ public class CraftEventFactory {
         playDeathSound(victim, event);
         // Paper end
         victim.expToDrop = event.getDroppedExp();
+        lootCheck.run(); // Paper - advancement triggers before destroying items
 
         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;
