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 8e8258333e181491b2d5b61ebdb80de36e8179a9..2df84bc367f650c3d468e0f09ed565e68de43a82 100644
--- a/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
+++ b/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
@@ -305,10 +305,18 @@ public abstract class AbstractArrow extends Projectile {
         }
     }
 
+    // Paper start - Fix cancelling ProjectileHitEvent for piercing arrows
     @Override
-    protected double getDefaultGravity() {
-        return 0.05D;
+    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());
+        }
+        super.preHitTargetOrDeflectSelf(hitResult);
     }
+    // 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));