From c1c9d850f16509616e07b8868dfe855d4db98f64 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 21 Jul 2018 10:29:14 -0400
Subject: [PATCH] Add Debug Entities option to debug dupe uuid issues

Add -Ddebug.entities=true to your JVM flags to enable more logging
---
 ...ies-option-to-debug-dupe-uuid-issues.patch | 95 +++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 Spigot-Server-Patches/0336-Add-Debug-Entities-option-to-debug-dupe-uuid-issues.patch

diff --git a/Spigot-Server-Patches/0336-Add-Debug-Entities-option-to-debug-dupe-uuid-issues.patch b/Spigot-Server-Patches/0336-Add-Debug-Entities-option-to-debug-dupe-uuid-issues.patch
new file mode 100644
index 0000000000..c5f5055e2a
--- /dev/null
+++ b/Spigot-Server-Patches/0336-Add-Debug-Entities-option-to-debug-dupe-uuid-issues.patch
@@ -0,0 +1,95 @@
+From b061a231214e88cde43e0c3880f779723828b2b4 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
+
+diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
+index f6b755863..108654d63 100644
+--- a/src/main/java/net/minecraft/server/Entity.java
++++ b/src/main/java/net/minecraft/server/Entity.java
+@@ -73,6 +73,7 @@ public abstract class Entity implements ICommandListener, KeyedObject { // Paper
+         }
+         return bukkitEntity;
+     }
++    Throwable addedToWorldStack; // Paper - entity debug
+     // CraftBukikt end
+ 
+     private static final Logger a = LogManager.getLogger();
+diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
+index b16324e1a..994d4bbb8 100644
+--- a/src/main/java/net/minecraft/server/WorldServer.java
++++ b/src/main/java/net/minecraft/server/WorldServer.java
+@@ -7,6 +7,7 @@ import com.google.common.util.concurrent.ListenableFuture;
+ import java.io.File;
+ import java.util.ArrayList;
+ import java.util.Collection;
++import java.util.Date;
+ import java.util.Iterator;
+ import java.util.List;
+ import java.util.Map;
+@@ -53,6 +54,10 @@ public class WorldServer extends World implements IAsyncTaskHandler {
+     private final List<NextTickListEntry> W = Lists.newArrayList();
+ 
+     // CraftBukkit start
++    private static final boolean DEBUG_ENTITIES = Boolean.getBoolean("debug.entities"); // Paper
++    private static Throwable getAddToWorldStackTrace(Entity entity) {
++        return new Throwable(entity + " Added to world at " + new Date());
++    }
+     public final int dimension;
+ 
+     // Add env and gen to constructor
+@@ -1160,6 +1165,7 @@ public class WorldServer extends World implements IAsyncTaskHandler {
+     private boolean j(Entity entity) {
+         if (entity.dead) {
+             WorldServer.a.warn("Tried to add entity {} but it was marked as removed already", EntityTypes.a(entity)); // CraftBukkit // Paper
++            if (DEBUG_ENTITIES) getAddToWorldStackTrace(entity).printStackTrace();
+             return false;
+         } else {
+             UUID uuid = entity.getUniqueID();
+@@ -1171,8 +1177,14 @@ public class WorldServer extends World implements IAsyncTaskHandler {
+                     this.f.remove(entity1);
+                 } else {
+                     if (!(entity instanceof EntityHuman)) {
+-                        WorldServer.a.error("Keeping entity {} that already exists with UUID {} - " + entity1, EntityTypes.a(entity1), uuid.toString()); // CraftBukkit // Paper
++                        WorldServer.a.error("Keeping entity {} that already exists with UUID {}", entity1, uuid.toString()); // CraftBukkit // Paper
+                         WorldServer.a.error("Deleting duplicate entity {}", entity); // Paper
++                        if (DEBUG_ENTITIES) {
++                            if (entity1.addedToWorldStack != null) {
++                                entity1.addedToWorldStack.printStackTrace();
++                            }
++                            getAddToWorldStackTrace(entity).printStackTrace();
++                        }
+                         return false;
+                     }
+ 
+@@ -1189,7 +1201,24 @@ public class WorldServer extends World implements IAsyncTaskHandler {
+     protected void b(Entity entity) {
+         super.b(entity);
+         this.entitiesById.a(entity.getId(), entity);
+-        this.entitiesByUUID.put(entity.getUniqueID(), entity);
++        // Paper start
++        if (DEBUG_ENTITIES) {
++            entity.addedToWorldStack = getAddToWorldStackTrace(entity);
++        }
++        Entity old = this.entitiesByUUID.put(entity.getUniqueID(), entity);
++        if (old != null && old.getId() != entity.getId() && old.valid) {
++            Logger logger = LogManager.getLogger();
++            logger.error("Overwrote an existing entity " + old + " with " + entity);
++            if (DEBUG_ENTITIES) {
++                if (old.addedToWorldStack != null) {
++                    old.addedToWorldStack.printStackTrace();
++                } else {
++                    logger.error("Oddly, the old entity was not added to the world in the normal way. Plugins?");
++                }
++                entity.addedToWorldStack.printStackTrace();
++            }
++        }
++        // Paper end
+         Entity[] aentity = entity.bb();
+ 
+         if (aentity != null) {
+-- 
+2.18.0
+