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 b3972c0aececb1d7170a47bbe8f1d6ce02d11331..c30f19162e33dbe8f018b7dc66210681b6027389 100644
--- a/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
+++ b/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
@@ -298,6 +298,19 @@ public abstract class AbstractArrow extends Projectile {
         }
     }
 
+    // Paper start - Fix cancelling ProjectileHitEvent for piercing arrows
+    @Override
+    public void preOnHit(HitResult hitResult) {
+        super.preOnHit(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());
+        }
+    }
+    // Paper end - Fix cancelling ProjectileHitEvent for piercing arrows
+
     private boolean shouldFall() {
         return this.inGround && this.level().noCollision((new AABB(this.position(), this.position())).inflate(0.06D));
     }