From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jake Potrebic <jake.m.potrebic@gmail.com>
Date: Thu, 23 Nov 2023 10:33:25 -0800
Subject: [PATCH] Don't fire EntityPotionEffectEvent during worldgen

Asynchronous chunk generation provides an opportunity for mobs
being added with generation to have effects added to them. The event
does not support asynchronous firing.

diff --git a/src/main/java/net/minecraft/world/entity/LivingEntity.java b/src/main/java/net/minecraft/world/entity/LivingEntity.java
index 1580c3a13a7fd84e709e184ad57e7d70d143abd2..d01ce95110b42000a67e2697eed3da0e050f144b 100644
--- a/src/main/java/net/minecraft/world/entity/LivingEntity.java
+++ b/src/main/java/net/minecraft/world/entity/LivingEntity.java
@@ -1133,6 +1133,11 @@ public abstract class LivingEntity extends Entity implements Attackable {
     }
 
     public boolean addEffect(MobEffectInstance mobeffect, @Nullable Entity entity, EntityPotionEffectEvent.Cause cause) {
+        // Paper start - add boolean param to optionally fire the event
+        return this.addEffect(mobeffect, entity, cause, true);
+    }
+    public boolean addEffect(MobEffectInstance mobeffect, @Nullable Entity entity, EntityPotionEffectEvent.Cause cause, boolean fireEvent) {
+        // Paper end
         // org.spigotmc.AsyncCatcher.catchOp("effect add"); // Spigot // Paper - move to API
         if (this.isTickingEffects) {
             this.effectsToProcess.add(new ProcessableEffect(mobeffect, cause));
@@ -1152,10 +1157,13 @@ public abstract class LivingEntity extends Entity implements Attackable {
                 override = new MobEffectInstance(mobeffect1).update(mobeffect);
             }
 
+            if (fireEvent) { // Paper
             EntityPotionEffectEvent event = CraftEventFactory.callEntityPotionEffectChangeEvent(this, mobeffect1, mobeffect, cause, override);
+            override = event.isOverride(); // Paper
             if (event.isCancelled()) {
                 return false;
             }
+            } // Paper
             // CraftBukkit end
 
             if (mobeffect1 == null) {
@@ -1163,7 +1171,7 @@ public abstract class LivingEntity extends Entity implements Attackable {
                 this.onEffectAdded(mobeffect, entity);
                 flag = true;
                 // CraftBukkit start
-            } else if (event.isOverride()) {
+            } else if (override) { // Paper
                 mobeffect1.update(mobeffect);
                 this.onEffectUpdated(mobeffect1, true, entity);
                 // CraftBukkit end
diff --git a/src/main/java/net/minecraft/world/entity/monster/Spider.java b/src/main/java/net/minecraft/world/entity/monster/Spider.java
index 5a9f4a022c8e7a0804543335bfe91e1328d040e6..9063f66b0497a3eb3893e307e685be692cc5c128 100644
--- a/src/main/java/net/minecraft/world/entity/monster/Spider.java
+++ b/src/main/java/net/minecraft/world/entity/monster/Spider.java
@@ -182,7 +182,7 @@ public class Spider extends Monster {
             MobEffect mobeffectlist = entityspider_groupdataspider.effect;
 
             if (mobeffectlist != null) {
-                this.addEffect(new MobEffectInstance(mobeffectlist, -1), org.bukkit.event.entity.EntityPotionEffectEvent.Cause.SPIDER_SPAWN); // CraftBukkit
+                this.addEffect(new MobEffectInstance(mobeffectlist, -1), null, org.bukkit.event.entity.EntityPotionEffectEvent.Cause.SPIDER_SPAWN, world instanceof net.minecraft.server.level.ServerLevel); // CraftBukkit // Paper - only fire the effect event if this is happening in a ServerLevel
             }
         }