Add event for Copper Golem deciding whether an item belongs in a chest

paper-api/src/main/java/io/papermc/paper/event/entity/ItemTransportingEntitySortEvent.java

@@ -0,0 +1,97 @@
+package io.papermc.paper.event.entity;
+
+import org.bukkit.block.Container;
+import org.bukkit.entity.CopperGolem;
+import org.bukkit.entity.Entity;
+import org.bukkit.event.HandlerList;
+import org.bukkit.event.entity.EntityEvent;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.ItemStack;
+import org.jetbrains.annotations.ApiStatus;
+import org.jspecify.annotations.NullMarked;
+
+/**
+ * Called when an item-transporting entity (typically a {@link CopperGolem},
+ * although other entities may be possible through non-API means)
+ * is inspecting a destination {@link Container} to decide if the item it is holding
+ * belongs in said container. This gives plugin developers an opportunity to
+ * override the {@link CopperGolem}'s sorting behavior.
+ */
+@NullMarked
+public class ItemTransportingEntitySortEvent extends EntityEvent {
+    protected static final HandlerList HANDLER_LIST = new HandlerList();
+
+    private final ItemStack itemStack;
+    private final Inventory containerInventory;
+    private boolean overrideDefaultBehaviour = false;
+    private boolean itemBelongs = true;
+
+    @ApiStatus.Internal
+    public ItemTransportingEntitySortEvent(
+        final Entity entity,
+        final ItemStack itemStack,
+        final Inventory containerInventory
+    ) {
+        super(entity);
+        this.containerInventory = containerInventory;
+        this.itemStack = itemStack;
+    }
+
+    /**
+     * Sets if the item belongs in the container.
+     *
+     * @param belongs Whether the item belongs or not
+     */
+    public void setItemBelongs(boolean belongs) {
+        this.overrideDefaultBehaviour = true;
+        this.itemBelongs = belongs;
+    }
+
+    /**
+     * Gets if the held item stack belongs in the container.
+     *
+     * @return Whether the item stack belongs.
+     */
+    public boolean itemBelongs() {
+        return this.itemBelongs;
+    }
+
+    /**
+     * Whether this event will override the default behavior of the entity.
+     * For example, if {@link ItemTransportingEntitySortEvent#setItemBelongs(boolean)} is not called, the entity
+     * will use the default behavior of adding to empty chests and chests containing a matching item stack.
+     * Once the function is called, the entity will defer to the plugin's decision.
+     *
+     * @return Whether the default behavior is being overridden.
+     */
+    public boolean isOverridingDefaultBehaviour() {
+        return this.overrideDefaultBehaviour;
+    }
+
+    /**
+     * Gets the container the entity is comparing to the held item.
+     *
+     * @return The potential destination container
+     */
+    public Inventory getContainerInventory() {
+        return this.containerInventory;
+    }
+
+    /**
+     * Gets the held item stack being compared against the container.
+     *
+     * @return The held item stack
+     */
+    public ItemStack getHeldItemStack() {
+        return this.itemStack;
+    }
+
+    public static HandlerList getHandlerList() {
+        return HANDLER_LIST;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return HANDLER_LIST;
+    }
+}

paper-server/patches/sources/net/minecraft/world/entity/ai/behavior/TransportItemsBetweenContainers.java.patch

@@ -12,3 +12,20 @@
                  return isValidTarget ? transportItemTarget : null;
              }
          }
+@@ -505,7 +_,15 @@
+     }
+
+     private static boolean matchesLeavingItemsRequirement(final PathfinderMob body, final Container container) {
+-        return container.isEmpty() || hasItemMatchingHandItem(body, container);
++        // Paper start - Add event for container assessment
++        io.papermc.paper.event.entity.ItemTransportingEntitySortEvent sortEvent = org.bukkit.craftbukkit.event.CraftEventFactory.createItemTransportingEntitySortEvent(body, container);
++        sortEvent.callEvent();
++        if (sortEvent.isOverridingDefaultBehaviour()) {
++            return sortEvent.itemBelongs();
++        } else {
++            return container.isEmpty() || hasItemMatchingHandItem(body, container);
++        }
++        // Paper end - Add event for container assessment
+     }
+
+     private static boolean hasItemMatchingHandItem(final PathfinderMob body, final Container container) {

paper-server/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java

@@ -7,11 +7,13 @@
 import com.mojang.authlib.GameProfile;
 import com.mojang.datafixers.util.Either;
 import io.papermc.paper.adventure.PaperAdventure;
+import io.papermc.paper.block.TileStateInventoryHolder;
 import io.papermc.paper.block.bed.BedEnterProblem;
 import io.papermc.paper.connection.HorriblePlayerLoginEventHack;
 import io.papermc.paper.connection.PlayerConnection;
 import io.papermc.paper.event.block.BlockLockCheckEvent;
 import io.papermc.paper.event.connection.PlayerConnectionValidateLoginEvent;
+import io.papermc.paper.event.entity.ItemTransportingEntitySortEvent;
 import io.papermc.paper.event.entity.ItemTransportingEntityValidateTargetEvent;
 import io.papermc.paper.event.player.PlayerBedFailEnterEvent;
 import io.papermc.paper.event.player.PlayerToggleEntityAgeLockEvent;
@@ -104,6 +106,8 @@
 import org.bukkit.craftbukkit.entity.CraftLivingEntity;
 import org.bukkit.craftbukkit.entity.CraftPlayer;
 import org.bukkit.craftbukkit.entity.CraftSpellcaster;
+import org.bukkit.craftbukkit.inventory.CraftContainer;
+import org.bukkit.craftbukkit.inventory.CraftInventory;
 import org.bukkit.craftbukkit.inventory.CraftInventoryCrafting;
 import org.bukkit.craftbukkit.inventory.CraftItemStack;
 import org.bukkit.craftbukkit.inventory.CraftItemType;
@@ -2417,4 +2421,8 @@ public static boolean callPlayerToggleEntityAgeLockEvent(net.minecraft.world.ent
         }
         return true;
     }
+
+    public static ItemTransportingEntitySortEvent createItemTransportingEntitySortEvent(PathfinderMob mob, Container container) {
+        return new ItemTransportingEntitySortEvent(mob.getBukkitEntity(), mob.getMainHandItem().asBukkitCopy(), new CraftInventory(container));
+    }
 }