From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sun, 24 Mar 2019 01:01:32 -0400
Subject: [PATCH] Only count Natural Spawned mobs towards natural spawn mob
 limit

This resolves the super common complaint about mobs not spawning.

This was ultimately a flaw in the vanilla count algorithim that allows
spawners and other misc mobs to count against the mob limit, which are
not bounded, and can prevent the entire world from spawning new.

I believe Bukkits changes around persistence may of actually made it
worse than vanilla.

This should fully solve all of the issues around it so that only natural
influences natural spawns.

diff --git a/src/main/java/net/minecraft/world/level/NaturalSpawner.java b/src/main/java/net/minecraft/world/level/NaturalSpawner.java
index 2503d4691e47083a9d99a38c4ed3f50a2374821a..23d53f3fd524cc4d827dc95ab95367702a110a05 100644
--- a/src/main/java/net/minecraft/world/level/NaturalSpawner.java
+++ b/src/main/java/net/minecraft/world/level/NaturalSpawner.java
@@ -88,6 +88,13 @@ public final class NaturalSpawner {
             MobCategory enumcreaturetype = entity.getType().getCategory();
 
             if (enumcreaturetype != MobCategory.MISC) {
+                // Paper start - Only count natural spawns
+                if (!entity.level().paperConfig().entities.spawning.countAllMobsForSpawning &&
+                    !(entity.spawnReason == org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.NATURAL ||
+                        entity.spawnReason == org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.CHUNK_GEN)) {
+                    continue;
+                }
+                // Paper end
                 BlockPos blockposition = entity.blockPosition();
 
                 chunkSource.query(ChunkPos.asLong(blockposition), (chunk) -> {