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

Add -Ddebug.entities=true to your JVM flags to gain more information

1.17: Needs to be reworked for new entity storage system

diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 3e1b2d2cedd44112a6c100ddfffe842d3be8b703..e76241660aaefa1736565515b98f7d33f86e10b3 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -896,6 +896,7 @@ 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) {
@@ -938,7 +939,7 @@ 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 8b28de5755ad4fe50903837700feed32e4530afd..2daa8e2e64829df838bde981a56d6e407b8ee004 100644
--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
+++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
@@ -219,6 +219,9 @@ public class ServerLevel extends Level implements WorldGenLevel {
     public final LevelStorageSource.LevelStorageAccess convertable;
     public final UUID uuid;
     public boolean hasPhysicsEvent = true; // Paper
+    public static Throwable getAddToWorldStackTrace(Entity entity) {
+        return new Throwable(entity + " Added to world at " + new java.util.Date());
+    }
 
     @Override public LevelChunk getChunkIfLoaded(int x, int z) { // Paper - this was added in world too but keeping here for NMS ABI
         return this.chunkSource.getChunk(x, z, false);
@@ -1271,7 +1274,28 @@ 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
+        if (entity.valid) {
+            MinecraftServer.LOGGER.error("Attempted Double World add on " + entity, new Throwable());
+
+            if (DEBUG_ENTITIES) {
+                Throwable thr = entity.addedToWorldStack;
+                if (thr == null) {
+                    MinecraftServer.LOGGER.error("Double add entity has no add stacktrace");
+                } else {
+                    MinecraftServer.LOGGER.error("Double add stacktrace: ", thr);
+                }
+            }
+            return true;
+        }
+        // Paper end
         if (entity.isRemoved()) {
+            // Paper start
+            if (DEBUG_ENTITIES) {
+                new Throwable("Tried to add entity " + entity + " but it was marked as removed already").printStackTrace(); // CraftBukkit
+                getAddToWorldStackTrace(entity).printStackTrace();
+            }
+            // Paper end
             // WorldServer.LOGGER.warn("Tried to add entity {} but it was marked as removed already", EntityTypes.getKey(entity.getType())); // CraftBukkit
             return false;
         } else {
diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
index ac6bd21798192c4c07737a2320c3626caebc7e22..b8257959acd2b38243fd259f367564080aff951e 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -235,6 +235,8 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
     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 @Nullable Throwable addedToWorldStack; // Paper - entity debug
     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/Level.java b/src/main/java/net/minecraft/world/level/Level.java
index 808a025548fd390ef4d657c53eb9bf73e73dbc93..638a77d3ea65b509b9fcdd3c1e3ea0abe5b7566f 100644
--- a/src/main/java/net/minecraft/world/level/Level.java
+++ b/src/main/java/net/minecraft/world/level/Level.java
@@ -147,6 +147,7 @@ public abstract class Level implements LevelAccessor, AutoCloseable {
     public boolean pvpMode;
     public boolean keepSpawnInMemory = true;
     public org.bukkit.generator.ChunkGenerator generator;
+    public static final boolean DEBUG_ENTITIES = Boolean.getBoolean("debug.entities"); // Paper
 
     public boolean preventPoiUpdated = false; // CraftBukkit - SPIGOT-5710
     public boolean captureBlockStates = false;
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..d45d832232be5017dde53816191c2b1830a0da32 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 +34,26 @@ 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 entityCast) {
+                if (net.minecraft.server.level.ServerLevel.DEBUG_ENTITIES) {
+                    entityCast.addedToWorldStack = net.minecraft.server.level.ServerLevel.getAddToWorldStackTrace(entityCast);
+                }
+
+                T old = this.byUuid.get(entity.getUUID());
+                if (old instanceof net.minecraft.world.entity.Entity oldCast && old != null && oldCast.getId() != entity.getId() && oldCast.valid) {
+                    LOGGER.error("Overwrote an existing entity " + oldCast + " with " + entity);
+                    if (net.minecraft.server.level.ServerLevel.DEBUG_ENTITIES) {
+                        if (oldCast.addedToWorldStack != null) {
+                            oldCast.addedToWorldStack.printStackTrace();
+                        } else {
+                            LOGGER.error("Oddly, the old entity was not added to the world in the normal way. Plugins?");
+                        }
+                        entityCast.addedToWorldStack.printStackTrace();
+                    }
+                }
+            }
+            // Paper end
         } else {
             this.byUuid.put(uUID, entity);
             this.byId.put(entity.getId(), entity);
