PaperMC/paper-server/nms-patches/net/minecraft/world/level/block/BlockDropper.patch

--- a/net/minecraft/world/level/block/BlockDropper.java
+++ b/net/minecraft/world/level/block/BlockDropper.java
@@ -18,10 +18,16 @@
 import net.minecraft.world.level.block.state.IBlockData;
 import org.slf4j.Logger;
 
+// CraftBukkit start
+import net.minecraft.world.InventoryLargeChest;
+import org.bukkit.craftbukkit.inventory.CraftItemStack;
+import org.bukkit.event.inventory.InventoryMoveItemEvent;
+// CraftBukkit end
+
 public class BlockDropper extends BlockDispenser {
 
     private static final Logger LOGGER = LogUtils.getLogger();
-    private static final IDispenseBehavior DISPENSE_BEHAVIOUR = new DispenseBehaviorItem();
+    private static final IDispenseBehavior DISPENSE_BEHAVIOUR = new DispenseBehaviorItem(true); // CraftBukkit
 
     public BlockDropper(BlockBase.Info blockbase_info) {
         super(blockbase_info);
@@ -39,7 +45,7 @@
 
     @Override
     public void dispenseFrom(WorldServer worldserver, IBlockData iblockdata, BlockPosition blockposition) {
-        TileEntityDispenser tileentitydispenser = (TileEntityDispenser) worldserver.getBlockEntity(blockposition, TileEntityTypes.DROPPER).orElse((Object) null);
+        TileEntityDispenser tileentitydispenser = (TileEntityDispenser) worldserver.getBlockEntity(blockposition, TileEntityTypes.DROPPER).orElse(null); // CraftBukkit - decompile error
 
         if (tileentitydispenser == null) {
             BlockDropper.LOGGER.warn("Ignoring dispensing attempt for Dropper without matching block entity at {}", blockposition);
@@ -60,8 +66,25 @@
                     if (iinventory == null) {
                         itemstack1 = BlockDropper.DISPENSE_BEHAVIOUR.dispense(sourceblock, itemstack);
                     } else {
-                        itemstack1 = TileEntityHopper.addItem(tileentitydispenser, iinventory, itemstack.copy().split(1), enumdirection.getOpposite());
-                        if (itemstack1.isEmpty()) {
+                        // CraftBukkit start - Fire event when pushing items into other inventories
+                        CraftItemStack oitemstack = CraftItemStack.asCraftMirror(itemstack.copy().split(1));
+
+                        org.bukkit.inventory.Inventory destinationInventory;
+                        // Have to special case large chests as they work oddly
+                        if (iinventory instanceof InventoryLargeChest) {
+                            destinationInventory = new org.bukkit.craftbukkit.inventory.CraftInventoryDoubleChest((InventoryLargeChest) iinventory);
+                        } else {
+                            destinationInventory = iinventory.getOwner().getInventory();
+                        }
+
+                        InventoryMoveItemEvent event = new InventoryMoveItemEvent(tileentitydispenser.getOwner().getInventory(), oitemstack.clone(), destinationInventory, true);
+                        worldserver.getCraftServer().getPluginManager().callEvent(event);
+                        if (event.isCancelled()) {
+                            return;
+                        }
+                        itemstack1 = TileEntityHopper.addItem(tileentitydispenser, iinventory, CraftItemStack.asNMSCopy(event.getItem()), enumdirection.getOpposite());
+                        if (event.getItem().equals(oitemstack) && itemstack1.isEmpty()) {
+                            // CraftBukkit end
                             itemstack1 = itemstack.copy();
                             itemstack1.shrink(1);
                         } else {