From 09480f5f29d007a061700da21de8d4af42f509e4 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 6634ef923..2f0b06dc5 100644
--- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
@@ -505,6 +505,16 @@ public class PaperWorldConfig {
         maxAutoSaveChunksPerTick = getInt("max-auto-save-chunks-per-tick", 24);
     }
 
+    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)");
+        }
+    }
+
     public boolean antiXray;
     public boolean asynchronous;
     public EngineMode engineMode;
diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
index 4bfa6ea0e..733f3e10e 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -934,6 +934,13 @@ public class WorldServer extends World {
             EnumCreatureType enumcreaturetype = entity.getEntityType().e();
 
             if (enumcreaturetype != EnumCreatureType.MISC && this.getChunkProvider().b(entity)) {
+                // Paper start - Only count natural spawns
+                if (!this.paperConfig.countAllMobsForSpawning &&
+                    !(entity.spawnReason == CreatureSpawnEvent.SpawnReason.NATURAL ||
+                        entity.spawnReason == CreatureSpawnEvent.SpawnReason.CHUNK_GEN)) {
+                    continue;
+                }
+                // Paper end
                 object2intmap.mergeInt(enumcreaturetype, 1, Integer::sum);
             }
         }
-- 
2.24.1