PaperMC/paper-server/nms-patches/net/minecraft/world/entity/projectile/IProjectile.patch

--- a/net/minecraft/world/entity/projectile/IProjectile.java
+++ b/net/minecraft/world/entity/projectile/IProjectile.java
@@ -22,6 +22,10 @@
 import net.minecraft.world.phys.MovingObjectPositionEntity;
 import net.minecraft.world.phys.Vec3D;
 
+// CraftBukkit start
+import org.bukkit.projectiles.ProjectileSource;
+// CraftBukkit end
+
 public abstract class IProjectile extends Entity {
 
     @Nullable
@@ -31,6 +35,10 @@
     private boolean leftOwner;
     private boolean hasBeenShot;
 
+    // CraftBukkit start
+    private boolean hitCancelled = false;
+    // CraftBukkit end
+
     IProjectile(EntityTypes<? extends IProjectile> entitytypes, World world) {
         super(entitytypes, world);
     }
@@ -40,6 +48,7 @@
             this.ownerUUID = entity.getUUID();
             this.cachedOwner = entity;
         }
+        this.projectileSource = (entity != null && entity.getBukkitEntity() instanceof ProjectileSource) ? (ProjectileSource) entity.getBukkitEntity() : null; // CraftBukkit
 
     }
 
@@ -143,6 +152,16 @@
         this.setDeltaMovement(this.getDeltaMovement().add(vec3d.x, entity.isOnGround() ? 0.0D : vec3d.y, vec3d.z));
     }
 
+    // CraftBukkit start - call projectile hit event
+    protected void preOnHit(MovingObjectPosition movingobjectposition) {
+        org.bukkit.event.entity.ProjectileHitEvent event = org.bukkit.craftbukkit.event.CraftEventFactory.callProjectileHitEvent(this, movingobjectposition);
+        this.hitCancelled = event != null && event.isCancelled();
+        if (movingobjectposition.getType() == MovingObjectPosition.EnumMovingObjectType.BLOCK || !this.hitCancelled) {
+            this.onHit(movingobjectposition);
+        }
+    }
+    // CraftBukkit end
+
     protected void onHit(MovingObjectPosition movingobjectposition) {
         MovingObjectPosition.EnumMovingObjectType movingobjectposition_enummovingobjecttype = movingobjectposition.getType();
 
@@ -161,6 +180,11 @@
     protected void onHitEntity(MovingObjectPositionEntity movingobjectpositionentity) {}
 
     protected void onHitBlock(MovingObjectPositionBlock movingobjectpositionblock) {
+        // CraftBukkit start - cancellable hit event
+        if (hitCancelled) {
+            return;
+        }
+        // CraftBukkit end
         IBlockData iblockdata = this.level.getBlockState(movingobjectpositionblock.getBlockPos());
 
         iblockdata.onProjectileHit(this.level, iblockdata, movingobjectpositionblock, this);