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 8257563afc3fe04c9e821da363b1f3f66de63ad7..5d6d26cfe8f0ab68a3145214b3fc126ca7a71a66 100644
--- a/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
+++ b/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
@@ -290,6 +290,19 @@ public abstract class AbstractArrow extends Projectile {
         }
     }
 
+    // Paper start
+    @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
+
     private boolean shouldFall() {
         return this.inGround && this.level.noCollision((new AABB(this.position(), this.position())).inflate(0.06D));
     }