From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 21 Jul 2018 08:25:40 -0400
Subject: [PATCH] Add Debug Entities option to debug dupe uuid issues


diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 987f867def412552b0d7f6cb2cba50af520f1257..1a80f48a425a81af6acd917f67d33a80746f46c3 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -1425,6 +1425,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
                 } else {
                     ChunkMap.TrackedEntity playerchunkmap_entitytracker = new ChunkMap.TrackedEntity(entity, i, j, entitytypes.trackDeltas());
 
+                    entity.tracker = playerchunkmap_entitytracker; // Paper - Fast access to tracker
                     this.entityMap.put(entity.getId(), playerchunkmap_entitytracker);
                     playerchunkmap_entitytracker.updatePlayers(this.level.players());
                     if (entity instanceof ServerPlayer) {
@@ -1467,7 +1468,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         if (playerchunkmap_entitytracker1 != null) {
             playerchunkmap_entitytracker1.broadcastRemoved();
         }
-
+        entity.tracker = null; // Paper - We're no longer tracked
     }
 
     protected void tick() {
diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
index a6749080a192a591dd4e52f56b691df8d9cfcd98..e1518465e4ffc473a75a57e4d9b3ad399a022589 100644
--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
+++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
@@ -1197,6 +1197,12 @@ public class ServerLevel extends Level implements WorldGenLevel {
     // CraftBukkit start
     private boolean addEntity(Entity entity, CreatureSpawnEvent.SpawnReason spawnReason) {
         org.spigotmc.AsyncCatcher.catchOp("entity add"); // Spigot
+        // Paper start - extra debug info
+        if (entity.valid) {
+            MinecraftServer.LOGGER.error("Attempted Double World add on {}", entity, new Throwable());
+            return true;
+        }
+        // Paper end - extra debug info
         if (entity.isRemoved()) {
             // WorldServer.LOGGER.warn("Tried to add entity {} but it was marked as removed already", EntityTypes.getKey(entity.getType())); // CraftBukkit
             return false;
diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
index 3ff8c6a4aa867e2ceed8c355550c9c20db6e812e..92284eff12eb28034e33563bb3644deeb0fa81ac 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -241,6 +241,7 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource, S
     public com.destroystokyo.paper.loottable.PaperLootableInventoryData lootableData; // Paper
     private CraftEntity bukkitEntity;
 
+    public @org.jetbrains.annotations.Nullable net.minecraft.server.level.ChunkMap.TrackedEntity tracker; // Paper
     public CraftEntity getBukkitEntity() {
         if (this.bukkitEntity == null) {
             this.bukkitEntity = CraftEntity.getEntity(this.level.getCraftServer(), this);
diff --git a/src/main/java/net/minecraft/world/level/entity/EntityLookup.java b/src/main/java/net/minecraft/world/level/entity/EntityLookup.java
index 21a2800db22f287b9c6a8290326fdf3b94ae94b1..2e561ac90a8c91ea13cfc18d09f8e0abbcff9385 100644
--- a/src/main/java/net/minecraft/world/level/entity/EntityLookup.java
+++ b/src/main/java/net/minecraft/world/level/entity/EntityLookup.java
@@ -34,6 +34,14 @@ public class EntityLookup<T extends EntityAccess> {
         UUID uUID = entity.getUUID();
         if (this.byUuid.containsKey(uUID)) {
             LOGGER.warn("Duplicate entity UUID {}: {}", uUID, entity);
+            // Paper start - extra debug info
+            if (entity instanceof net.minecraft.world.entity.Entity) {
+                final T old = this.byUuid.get(entity.getUUID());
+                if (old instanceof net.minecraft.world.entity.Entity oldCast && oldCast.getId() != entity.getId() && oldCast.valid) {
+                    LOGGER.error("Overwrote an existing entity {} with {}", oldCast, entity);
+                }
+            }
+            // Paper end - extra debug info
         } else {
             this.byUuid.put(uUID, entity);
             this.byId.put(entity.getId(), entity);