Paper/patches/unapplied/server/0238-Add-Debug-Entities-option-to-debug-dupe-uuid-issues.patch

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 81eb73e9fde37e3b196bd899ecd4d614897d1a98..4206e1c96cdc7b7e324331681215f735688dd558 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -1353,6 +1353,7 @@ 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) {
@@ -1395,7 +1396,7 @@ 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 1d29f6c12d2c9de7918669ec03da7307a899e9ab..e09638b0ac68a685bf71ae3a84475bde19669b1e 100644
--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
+++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
@@ -209,6 +209,9 @@ 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);
@@ -1099,7 +1102,28 @@ 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 0fe90a47a73266e929022d807d6586e2a76dfb0e..513331442058ee61a08f4ad69b8912fa3e0d6868 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -173,6 +173,8 @@ 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 67566e5f95f7452d31bea485bdb91a4e1a32e5d5..dc2235824853a0d7ccbff51dd26a71e97fe90ba7 100644
--- a/src/main/java/net/minecraft/world/level/Level.java
+++ b/src/main/java/net/minecraft/world/level/Level.java
@@ -142,6 +142,7 @@ 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 e6b9f812e521abd552e0c7dc0429d5a62f2bfc35..f4731d69946871768ecf16149a47d2ef1cb3e910 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);