From 7776a06028d95b1840c7008f1545de7bbcd62b0f Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Thu, 3 Nov 2016 20:28:12 -0400
Subject: [PATCH] Don't load Chunks from Hoppers and other things

Hoppers call this to I guess "get the primary side" of a double sided chest.

If the double sided chest crosses chunk lines, it causes the chunk to load.
This will end up causing sync chunk loads, which will unload with Chunk GC,
only to be reloaded again the next tick.

This of course is undesirable, so just return the loaded side as "primary"
and treat it as a single chest if the other sides are unloaded

diff --git a/src/main/java/net/minecraft/server/DoubleBlockFinder.java b/src/main/java/net/minecraft/server/DoubleBlockFinder.java
index 3cb6e6089..7a16a3e0e 100644
--- a/src/main/java/net/minecraft/server/DoubleBlockFinder.java
+++ b/src/main/java/net/minecraft/server/DoubleBlockFinder.java
@@ -21,8 +21,12 @@ public class DoubleBlockFinder {
                 return new DoubleBlockFinder.Result.Single<>(s0);
             } else {
                 BlockPosition blockposition1 = blockposition.shift((EnumDirection) function1.apply(iblockdata));
-                IBlockData iblockdata1 = generatoraccess.getType(blockposition1);
-
+                // Paper start - don't load chunks if the other side of the chest is in unloaded chunk
+                IBlockData iblockdata1 = generatoraccess.getTypeIfLoaded(blockposition1);
+                if (iblockdata1 == null) {
+                    return new DoubleBlockFinder.Result.Single<>(s0);
+                }
+                // Paper end
                 if (iblockdata1.getBlock() == iblockdata.getBlock()) {
                     DoubleBlockFinder.BlockType doubleblockfinder_blocktype1 = (DoubleBlockFinder.BlockType) function.apply(iblockdata1);
 
-- 
2.25.1