From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Mon, 23 Jul 2018 22:44:23 -0400
Subject: [PATCH] Add some Debug to Chunk Entity slices

If we detect unexpected state, log and try to recover

This should hopefully avoid duplicate entities ever being created
if the entity was to end up in 2 different chunk slices

diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
index a2cc3e58d59ed3d9f443b77c44d8200cc09b4da9..7847078c54154e28ab066ea8a329f929df1e1a37 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -156,6 +156,7 @@ public abstract class Entity implements Nameable, CommandSource, net.minecraft.s
             }
         }
     };
+    public List<Entity> entitySlice = null;
     // Paper end
 
     public com.destroystokyo.paper.loottable.PaperLootableInventoryData lootableData; // Paper
diff --git a/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java b/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
index bd9b19d988ecf72e099efeff6ec3483a352174ec..09aa608bd303b618ae2c0ebd237bcbdba60a37a8 100644
--- a/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
+++ b/src/main/java/net/minecraft/world/level/chunk/LevelChunk.java
@@ -26,7 +26,9 @@ import net.minecraft.ReportedException;
 import net.minecraft.core.BlockPos;
 import net.minecraft.core.Registry;
 import net.minecraft.nbt.CompoundTag;
+import net.minecraft.server.MinecraftServer;
 import net.minecraft.server.level.ChunkHolder;
+import net.minecraft.server.level.ServerChunkCache;
 import net.minecraft.server.level.ServerLevel;
 import net.minecraft.util.Mth;
 import net.minecraft.world.entity.Entity;
@@ -550,6 +552,25 @@ public class LevelChunk implements ChunkAccess {
         if (k >= this.entitySlices.length) {
             k = this.entitySlices.length - 1;
         }
+        // Paper - remove from any old list if its in one
+        List<Entity> nextSlice = this.entitySlices[k]; // the next list to be added to
+        List<Entity> currentSlice = entity.entitySlice;
+        if (nextSlice == currentSlice) {
+            if (Level.DEBUG_ENTITIES) MinecraftServer.LOGGER.warn("Entity was already in this chunk!" + entity, new Throwable());
+            return; // ??? silly plugins
+        }
+        if (currentSlice != null && currentSlice.contains(entity)) {
+            // Still in an old chunk...
+            if (Level.DEBUG_ENTITIES) MinecraftServer.LOGGER.warn("Entity is still in another chunk!" + entity, new Throwable());
+            LevelChunk chunk = entity.getCurrentChunk();
+            if (chunk != null) {
+                chunk.removeEntity(entity);
+            } else {
+                removeEntity(entity);
+            }
+            currentSlice.remove(entity); // Just incase the above did not remove from the previous slice
+        }
+        // Paper end
 
         if (!entity.inChunk || entity.getCurrentChunk() != this) entityCounts.increment(entity.getMinecraftKeyString()); // Paper
         entity.inChunk = true;
@@ -559,6 +580,7 @@ public class LevelChunk implements ChunkAccess {
         entity.zChunk = this.chunkPos.z;
         this.entities.add(entity); // Paper - per chunk entity list
         this.entitySlices[k].add(entity);
+        entity.entitySlice = this.entitySlices[k]; // Paper
         this.markUnsaved(); // Paper
     }
 
@@ -584,6 +606,10 @@ public class LevelChunk implements ChunkAccess {
 
         // Paper start
         if (entity.currentChunk != null && entity.currentChunk.get() == this) entity.setCurrentChunk(null);
+        if (entitySlices[section] == entity.entitySlice) {
+            entity.entitySlice = null;
+            entity.inChunk = false;
+        }
         if (!this.entitySlices[section].remove(entity)) {
             return;
         }
@@ -742,7 +768,7 @@ public class LevelChunk implements ChunkAccess {
         // Paper start - neighbour cache
         int chunkX = this.chunkPos.x;
         int chunkZ = this.chunkPos.z;
-        ChunkProviderServer chunkProvider = ((ServerLevel)this.world).getChunkSource();
+        ServerChunkCache chunkProvider = ((ServerLevel)this.world).getChunkSource();
         for (int dx = -NEIGHBOUR_CACHE_RADIUS; dx <= NEIGHBOUR_CACHE_RADIUS; ++dx) {
             for (int dz = -NEIGHBOUR_CACHE_RADIUS; dz <= NEIGHBOUR_CACHE_RADIUS; ++dz) {
                 LevelChunk neighbour = chunkProvider.getChunkAtIfLoadedMainThreadNoCache(chunkX + dx, chunkZ + dz);
@@ -802,7 +828,7 @@ public class LevelChunk implements ChunkAccess {
         // Paper start - neighbour cache
         int chunkX = this.chunkPos.x;
         int chunkZ = this.chunkPos.z;
-        ChunkProviderServer chunkProvider = ((ServerLevel)this.world).getChunkSource();
+        ServerChunkCache chunkProvider = ((ServerLevel)this.world).getChunkSource();
         for (int dx = -NEIGHBOUR_CACHE_RADIUS; dx <= NEIGHBOUR_CACHE_RADIUS; ++dx) {
             for (int dz = -NEIGHBOUR_CACHE_RADIUS; dz <= NEIGHBOUR_CACHE_RADIUS; ++dz) {
                 LevelChunk neighbour = chunkProvider.getChunkAtIfLoadedMainThreadNoCache(chunkX + dx, chunkZ + dz);