PaperMC/patches/server/0771-Fix-cancelling-ProjectileHitEvent-for-piercing-arrow.patch

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 ae4319c2532855315bc45995a39d7eb98961b939..6272b0e1e332789b983a486ee25226e2a1c9fdda 100644
--- a/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
+++ b/src/main/java/net/minecraft/world/entity/projectile/AbstractArrow.java
@@ -297,6 +297,19 @@ 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));
     }