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.

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 8564ecd20578d907bcfa1b9c149da22e424e254a..bc01e5014e1355a225bdf5c47f2965290b45e2d2 100644
--- a/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
+++ b/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
@@ -300,6 +300,19 @@ public abstract class AbstractArrow extends Projectile {
         }
     }
 
+    // Paper start
+    @Override
+    protected 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));
     }