From 60b76b471464505db520bfd096b006c320864b44 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/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
index a70a64070..bfd690ecc 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -598,4 +598,14 @@ public class PaperWorldConfig {
             log("Using vanilla redstone algorithm.");
         }
     }
+
+    public boolean countAllMobsForSpawning = false;
+    private void countAllMobsForSpawning() {
+        countAllMobsForSpawning = getBoolean("count-all-mobs-for-spawning", false);
+        if (countAllMobsForSpawning) {
+            log("Counting all mobs for spawning. Mob farms may reduce natural spawns elsewhere in world.");
+        } else {
+            log("Using improved mob spawn limits (Only Natural Spawns impact spawn limits for more natural spawns)");
+        }
+    }
 }
diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldEntityList.java b/src/main/java/com/destroystokyo/paper/PaperWorldEntityList.java
index a10a5bc13..a5a63f800 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldEntityList.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldEntityList.java
@@ -7,6 +7,7 @@ import net.minecraft.server.IAnimal;
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.server.World;
 import net.minecraft.server.WorldServer;
+import org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -90,7 +91,12 @@ public class PaperWorldEntityList extends ArrayList<Entity> {
     }
 
     public void updateEntityCount(Entity entity, int amt) {
-        if (!(entity instanceof IAnimal)) return;
+        // Only count natural spawns so that mob
+        if (!(entity instanceof IAnimal) || (
+            !world.paperConfig.countAllMobsForSpawning &&
+            entity.spawnReason != SpawnReason.NATURAL &&
+            entity.spawnReason != SpawnReason.CHUNK_GEN
+        )) return;
 
         if (entity instanceof EntityInsentient) {
             EntityInsentient entityinsentient = (EntityInsentient) entity;
-- 
2.21.0