papermc/paper-server/nms-patches/net/minecraft/world/entity/EntityAreaEffectCloud.patch

--- a/net/minecraft/world/entity/EntityAreaEffectCloud.java
+++ b/net/minecraft/world/entity/EntityAreaEffectCloud.java
@@ -31,6 +31,12 @@
 import net.minecraft.world.level.material.EnumPistonReaction;
 import org.slf4j.Logger;
 
+// CraftBukkit start
+import net.minecraft.resources.MinecraftKey;
+import org.bukkit.craftbukkit.entity.CraftLivingEntity;
+import org.bukkit.entity.LivingEntity;
+// CraftBukkit end
+
 public class EntityAreaEffectCloud extends Entity implements TraceableEntity {
 
     private static final Logger LOGGER = LogUtils.getLogger();
@@ -129,6 +135,22 @@
 
     }
 
+    // CraftBukkit start accessor methods
+    public void refreshEffects() {
+        if (!this.fixedColor) {
+            this.getEntityData().set(EntityAreaEffectCloud.DATA_COLOR, PotionUtil.getColor((Collection) PotionUtil.getAllEffects(this.potion, this.effects)));
+        }
+    }
+
+    public String getPotionType() {
+        return ((MinecraftKey) BuiltInRegistries.POTION.getKey(this.potion)).toString();
+    }
+
+    public void setPotionType(String string) {
+        setPotion(BuiltInRegistries.POTION.get(new MinecraftKey(string)));
+    }
+    // CraftBukkit end
+
     public int getColor() {
         return (Integer) this.getEntityData().get(EntityAreaEffectCloud.DATA_COLOR);
     }
@@ -263,6 +285,7 @@
                     if (!list1.isEmpty()) {
                         Iterator iterator1 = list1.iterator();
 
+                        List<LivingEntity> entities = new java.util.ArrayList<LivingEntity>(); // CraftBukkit
                         while (iterator1.hasNext()) {
                             EntityLiving entityliving = (EntityLiving) iterator1.next();
 
@@ -272,6 +295,17 @@
                                 double d8 = d6 * d6 + d7 * d7;
 
                                 if (d8 <= (double) (f * f)) {
+                                    // CraftBukkit start
+                                    entities.add((LivingEntity) entityliving.getBukkitEntity());
+                                }
+                            }
+                        }
+                        org.bukkit.event.entity.AreaEffectCloudApplyEvent event = org.bukkit.craftbukkit.event.CraftEventFactory.callAreaEffectCloudApplyEvent(this, entities);
+                        if (!event.isCancelled()) {
+                            for (LivingEntity entity : event.getAffectedEntities()) {
+                                if (entity instanceof CraftLivingEntity) {
+                                    EntityLiving entityliving = ((CraftLivingEntity) entity).getHandle();
+                                    // CraftBukkit end
                                     this.victims.put(entityliving, this.tickCount + this.reapplicationDelay);
                                     Iterator iterator2 = list.iterator();
 
@@ -281,7 +315,7 @@
                                         if (mobeffect1.getEffect().isInstantenous()) {
                                             mobeffect1.getEffect().applyInstantenousEffect(this, this.getOwner(), entityliving, mobeffect1.getAmplifier(), 0.5D);
                                         } else {
-                                            entityliving.addEffect(new MobEffect(mobeffect1), this);
+                                            entityliving.addEffect(new MobEffect(mobeffect1), this, org.bukkit.event.entity.EntityPotionEffectEvent.Cause.AREA_EFFECT_CLOUD); // CraftBukkit
                                         }
                                     }