From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jake Potrebic <jake.m.potrebic@gmail.com>
Date: Sat, 19 Feb 2022 19:05:59 -0800
Subject: [PATCH] Fix cancelling ProjectileHitEvent for piercing arrows

Piercing arrows search for multiple entities inside a while
loop that is checking the projectile entity's removed state.
If the hit event is cancelled on the first entity, the event will
be called over and over again inside that while loop until the event
is not cancelled. The solution here, is to make use of an
already-existing field on AbstractArrow for tracking entities hit by
piercing arrows to avoid duplicate damage being applied.

== AT ==
protected net.minecraft.world.entity.projectile.Projectile hitCancelled

diff --git a/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java b/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
index a2efc49f2b14c78991a3fa5b3e2cefee0209bcc1..114add343370700a7dbd438432635c76a0cbb871 100644
--- a/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
+++ b/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
@@ -329,6 +329,19 @@ public abstract class AbstractArrow extends Projectile {
         }
     }
 
+    // Paper start - Fix cancelling ProjectileHitEvent for piercing arrows
+    @Override
+    public ProjectileDeflection preHitTargetOrDeflectSelf(HitResult hitResult) {
+        if (hitResult instanceof EntityHitResult entityHitResult && this.hitCancelled && this.getPierceLevel() > 0) {
+            if (this.piercingIgnoreEntityIds == null) {
+                this.piercingIgnoreEntityIds = new IntOpenHashSet(5);
+            }
+            this.piercingIgnoreEntityIds.add(entityHitResult.getEntity().getId());
+        }
+        return super.preHitTargetOrDeflectSelf(hitResult);
+    }
+    // Paper end - Fix cancelling ProjectileHitEvent for piercing arrows
+
     @Override
     protected double getDefaultGravity() {
         return 0.05D;