Paper/Spigot-Server-Patches/0449-Fix-unregistering-entities-from-unloading-chunks.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Tue, 31 Mar 2020 03:01:45 -0400
Subject: [PATCH] Fix unregistering entities from unloading chunks

CraftBukkit caused a regression here by making unloading chunks not
have a ticket added and returning unloaded future.

This caused entities who were killed in same tick their chunk is unloading
to not be able to be removed from the chunk.

This then results in dead entities lingering in the Chunk.

Combine that with a buggy detail of the previous implementation of
the Dupe UUID patch, then this was the likely source of the "Ghost entities"

diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
index e635839673b767c630d0d3a2a7c370b05bba7164..255650fc6adcd81df2ee063209d2098745e45e39 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -1497,9 +1497,9 @@ public class WorldServer extends World {
     }
 
     private void removeEntityFromChunk(Entity entity) {
-        IChunkAccess ichunkaccess = this.getChunkAt(entity.chunkX, entity.chunkZ, ChunkStatus.FULL, false);
+        Chunk ichunkaccess = entity.getCurrentChunk(); // Paper - getChunkAt(x,z,full,false) is broken by CraftBukkit as it won't return an unloading chunk. Use our current chunk reference as this points to what chunk they need to be removed from anyways
 
-        if (ichunkaccess instanceof Chunk) {
+        if (ichunkaccess != null) { // Paper
             ((Chunk) ichunkaccess).b(entity);
         }