PaperMC/nms-patches/DispenseBehaviorProjectile.patch

--- a/net/minecraft/server/DispenseBehaviorProjectile.java
+++ b/net/minecraft/server/DispenseBehaviorProjectile.java
@@ -1,5 +1,10 @@
 package net.minecraft.server;
 
+// CraftBukkit start
+import org.bukkit.craftbukkit.inventory.CraftItemStack;
+import org.bukkit.event.block.BlockDispenseEvent;
+// CraftBukkit end
+
 public abstract class DispenseBehaviorProjectile extends DispenseBehaviorItem {
 
     public DispenseBehaviorProjectile() {}
@@ -11,9 +16,38 @@
         EnumDirection enumdirection = (EnumDirection) isourceblock.e().get(BlockDispenser.FACING);
         IProjectile iprojectile = this.a(world, iposition, itemstack);
 
-        iprojectile.shoot((double) enumdirection.getAdjacentX(), (double) ((float) enumdirection.getAdjacentY() + 0.1F), (double) enumdirection.getAdjacentZ(), this.getPower(), this.a());
+        // iprojectile.shoot((double) enumdirection.getAdjacentX(), (double) ((float) enumdirection.getAdjacentY() + 0.1F), (double) enumdirection.getAdjacentZ(), this.getPower(), this.a());
+        // CraftBukkit start
+        ItemStack itemstack1 = itemstack.cloneAndSubtract(1);
+        org.bukkit.block.Block block = world.getWorld().getBlockAt(isourceblock.getBlockPosition().getX(), isourceblock.getBlockPosition().getY(), isourceblock.getBlockPosition().getZ());
+        CraftItemStack craftItem = CraftItemStack.asCraftMirror(itemstack1);
+
+        BlockDispenseEvent event = new BlockDispenseEvent(block, craftItem.clone(), new org.bukkit.util.Vector((double) enumdirection.getAdjacentX(), (double) ((float) enumdirection.getAdjacentY() + 0.1F), (double) enumdirection.getAdjacentZ()));
+        if (!BlockDispenser.eventFired) {
+            world.getServer().getPluginManager().callEvent(event);
+        }
+
+        if (event.isCancelled()) {
+            itemstack.add(1);
+            return itemstack;
+        }
+
+        if (!event.getItem().equals(craftItem)) {
+            itemstack.add(1);
+            // Chain to handler for new item
+            ItemStack eventStack = CraftItemStack.asNMSCopy(event.getItem());
+            IDispenseBehavior idispensebehavior = (IDispenseBehavior) BlockDispenser.REGISTRY.get(eventStack.getItem());
+            if (idispensebehavior != IDispenseBehavior.NONE && idispensebehavior != this) {
+                idispensebehavior.dispense(isourceblock, eventStack);
+                return itemstack;
+            }
+        }
+
+        iprojectile.shoot(event.getVelocity().getX(), event.getVelocity().getY(), event.getVelocity().getZ(), this.getPower(), this.a());
+        ((Entity) iprojectile).projectileSource = new org.bukkit.craftbukkit.projectiles.CraftBlockProjectileSource((TileEntityDispenser) isourceblock.getTileEntity());
+        // CraftBukkit end
         world.addEntity((Entity) iprojectile);
-        itemstack.subtract(1);
+        // itemstack.subtract(1); // CraftBukkit - Handled during event processing
         return itemstack;
     }