From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Newwind <support@newwindserver.com>
Date: Sat, 27 Jul 2024 11:09:37 +0200
Subject: [PATCH] Paper PR: Prevent zombie reinforcements loading chunks

Original license: GPLv3
Original project: https://github.com/PaperMC/Paper
Paper pull request: https://github.com/PaperMC/Paper/pull/11175

When a zombie calls reinforcements it tries to spawn them in a random location within a 40 block radius of the zombie,
before spawning, it checks isSpawnPositionOk() for the position which loads the block to check if a mob can spawn on said block.
This patch ensures the chunk at the random location is loaded before trying to spawn the reinforcement zombie in it.

diff --git a/net/minecraft/world/entity/monster/Zombie.java b/net/minecraft/world/entity/monster/Zombie.java
index 447adc3dcfd31a6fb9e673555e9793a82f9e02d4..08cf959a0b96ec765f3405a0b0956932ee0a7d26 100644
--- a/net/minecraft/world/entity/monster/Zombie.java
+++ b/net/minecraft/world/entity/monster/Zombie.java
@@ -401,6 +401,13 @@ public class Zombie extends Monster {
                     int i2 = floor1 + Mth.nextInt(this.random, 7, 40) * Mth.nextInt(this.random, -1, 1);
                     int i3 = floor2 + Mth.nextInt(this.random, 7, 40) * Mth.nextInt(this.random, -1, 1);
                     BlockPos blockPos = new BlockPos(i1, i2, i3);
+
+                    // Paper start - Prevent reinforcement checks from loading chunks
+                    if (this.level().getChunkIfLoadedImmediately(blockPos.getX() >> 4, blockPos.getZ() >> 4) == null) {
+                        continue;
+                    }
+                    // Paper end - Prevent reinforcement checks from loading chunks
+
                     if (SpawnPlacements.isSpawnPositionOk(type, level, blockPos)
                         && SpawnPlacements.checkSpawnRules(type, level, EntitySpawnReason.REINFORCEMENT, blockPos, level.random)) {
                         zombie.setPos(i1, i2, i3);