Paper/patches/server/0412-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 6c06897513ed4d9a2edd5675c71d9966994cecaf..95fcf31b0ea68312f6c3475c1b4a01ca2b269536 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -2143,11 +2143,12 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, i
         } 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
@@ -2900,6 +2901,12 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, i
     @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
@@ -2920,6 +2927,11 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, i
                 // 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) {
@@ -2933,10 +2945,6 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, i
                     // 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
                 }
 
@@ -3057,7 +3065,7 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, i
     }
 
     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 a3a900d10440ed5ebe24370a77ccb6cad911cfc9..0d468631b9c260091e732925da43c177ebda892f 100644
--- a/src/main/java/net/minecraft/world/entity/decoration/ArmorStand.java
+++ b/src/main/java/net/minecraft/world/entity/decoration/ArmorStand.java
@@ -610,7 +610,7 @@ 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);
             }
         }
@@ -618,7 +618,7 @@ 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 bf7c61c767bdfe8ddb63367f1b38dbbeba17ba02..4cdac8044d3a14861dab5b018479c735d094adcf 100644
--- a/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
+++ b/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
@@ -827,7 +827,8 @@ 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;