Paper/Spigot-Server-Patches/0421-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 69060be0daf3fbae2763852209c915be59caac4f..cd04994ed38c7f5d4db6b1ef1796f95ef2c490e1 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -1451,9 +1451,9 @@ public class WorldServer extends World implements GeneratorAccessSeed {
     }
 
     private void removeEntityFromChunk(Entity entity) {
-        IChunkAccess ichunkaccess = chunkProvider.getChunkUnchecked(entity.chunkX, entity.chunkZ); // CraftBukkit - SPIGOT-5228: getChunkAt won't find the entity's chunk if it has already been unloaded (i.e. if it switched to state INACCESSIBLE).
+        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);
         }