From 3413007c69032fcef8ac762e61f743b5c742df67 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sun, 29 Jul 2018 16:56:48 -0400
Subject: [PATCH] Process Chunk.addEntities before chunkLoadEvent

1.13 undesirably changed behavior here that chunk load event fired
before the entities were added to the world.

This means any plugin that spawns entities in chunk load event
causes the entities to be registered to the chunk, and then
added to the world twice.

Moves Entity Add to World to be done anytime a chunk is
registered to the Chunk Map, and ignore other calls.

diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
index 4e32ae7db..f0098e910 100644
--- a/src/main/java/net/minecraft/server/Chunk.java
+++ b/src/main/java/net/minecraft/server/Chunk.java
@@ -897,7 +897,8 @@ public class Chunk implements IChunkAccess {
 
     }
 
-    public void addEntities() {
+    public void addEntities() { } // Paper - do nothing if anything calls this, we call it properly during ChunkMap.put
+    public void addEntitiesToWorld() { // Paper - rename to ensure noone else calls it
         this.j = true;
         this.world.b(this.tileEntities.values());
         List[] aentityslice = this.entitySlices; // Spigot
diff --git a/src/main/java/net/minecraft/server/ChunkMap.java b/src/main/java/net/minecraft/server/ChunkMap.java
index 5757aa80f..c6cedba96 100644
--- a/src/main/java/net/minecraft/server/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/ChunkMap.java
@@ -31,6 +31,7 @@ public class ChunkMap extends Long2ObjectOpenHashMap<Chunk> {
                 }
             }
         }
+        chunk.addEntitiesToWorld(); // Paper - call before ChunkLoadEvent to maintain pre 1.13 order, otherwise CLE can manipulate the chunks entities
 
         org.bukkit.Server server = chunk.world.getServer();
         if (server != null) {
diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
index ece187129..4fc3c2c35 100644
--- a/src/main/java/net/minecraft/server/World.java
+++ b/src/main/java/net/minecraft/server/World.java
@@ -2464,7 +2464,7 @@ public abstract class World implements GeneratorAccess, IIBlockAccess, AutoClose
         while (iterator.hasNext()) {
             Entity entity = (Entity) iterator.next();
 
-            if (entity == null) {
+            if (entity == null || entity.valid) { // Paper - if already added, skip (shouldn't happen, but safety)
                 continue;
             }
             this.entityList.add(entity);
-- 
2.18.0