PaperMC/paper-server/nms-patches/net/minecraft/world/entity/item/EntityItem.patch

--- a/net/minecraft/world/entity/item/EntityItem.java
+++ b/net/minecraft/world/entity/item/EntityItem.java
@@ -32,6 +32,12 @@
 import net.minecraft.world.level.gameevent.GameEvent;
 import net.minecraft.world.phys.Vec3D;
 
+// CraftBukkit start
+import net.minecraft.server.MinecraftServer;
+import org.bukkit.event.entity.EntityPickupItemEvent;
+import org.bukkit.event.player.PlayerPickupItemEvent;
+// CraftBukkit end
+
 public class EntityItem extends Entity {
 
     private static final DataWatcherObject<ItemStack> DATA_ITEM = DataWatcher.defineId(EntityItem.class, DataWatcherRegistry.ITEM_STACK);
@@ -46,6 +52,7 @@
     @Nullable
     private UUID owner;
     public final float bobOffs;
+    private int lastTick = MinecraftServer.currentTick - 1; // CraftBukkit
 
     public EntityItem(EntityTypes<? extends EntityItem> entitytypes, World world) {
         super(entitytypes, world);
@@ -95,9 +102,12 @@
             this.discard();
         } else {
             super.tick();
-            if (this.pickupDelay > 0 && this.pickupDelay != 32767) {
-                --this.pickupDelay;
-            }
+            // CraftBukkit start - Use wall time for pickup and despawn timers
+            int elapsedTicks = MinecraftServer.currentTick - this.lastTick;
+            if (this.pickupDelay != 32767) this.pickupDelay -= elapsedTicks;
+            if (this.age != -32768) this.age += elapsedTicks;
+            this.lastTick = MinecraftServer.currentTick;
+            // CraftBukkit end
 
             this.xo = this.getX();
             this.yo = this.getY();
@@ -147,9 +157,11 @@
                 this.mergeWithNeighbours();
             }
 
+            /* CraftBukkit start - moved up
             if (this.age != -32768) {
                 ++this.age;
             }
+            // CraftBukkit end */
 
             this.hasImpulse |= this.updateInWaterStateAndDoFluidPushing();
             if (!this.level.isClientSide) {
@@ -161,6 +173,12 @@
             }
 
             if (!this.level.isClientSide && this.age >= 6000) {
+                // CraftBukkit start - fire ItemDespawnEvent
+                if (org.bukkit.craftbukkit.event.CraftEventFactory.callItemDespawnEvent(this).isCancelled()) {
+                    this.age = 0;
+                    return;
+                }
+                // CraftBukkit end
                 this.discard();
             }
 
@@ -236,10 +254,11 @@
     private static void merge(EntityItem entityitem, ItemStack itemstack, ItemStack itemstack1) {
         ItemStack itemstack2 = merge(itemstack, itemstack1, 64);
 
-        entityitem.setItem(itemstack2);
+        if (!itemstack2.isEmpty()) entityitem.setItem(itemstack2); // CraftBukkit - don't set empty stacks
     }
 
     private static void merge(EntityItem entityitem, ItemStack itemstack, EntityItem entityitem1, ItemStack itemstack1) {
+        if (org.bukkit.craftbukkit.event.CraftEventFactory.callItemMergeEvent(entityitem1, entityitem).isCancelled()) return; // CraftBukkit
         merge(entityitem, itemstack, itemstack1);
         entityitem.pickupDelay = Math.max(entityitem.pickupDelay, entityitem1.pickupDelay);
         entityitem.age = Math.min(entityitem.age, entityitem1.age);
@@ -263,6 +282,11 @@
         } else if (!this.getItem().getItem().canBeHurtBy(damagesource)) {
             return false;
         } else {
+            // CraftBukkit start
+            if (org.bukkit.craftbukkit.event.CraftEventFactory.handleNonLivingEntityDamageEvent(this, damagesource, f)) {
+                return false;
+            }
+            // CraftBukkit end
             this.markHurt();
             this.health = (int) ((float) this.health - f);
             this.gameEvent(GameEvent.ENTITY_DAMAGED, damagesource.getEntity());
@@ -326,6 +350,46 @@
             Item item = itemstack.getItem();
             int i = itemstack.getCount();
 
+            // CraftBukkit start - fire PlayerPickupItemEvent
+            int canHold = entityhuman.getInventory().canHold(itemstack);
+            int remaining = i - canHold;
+
+            if (this.pickupDelay <= 0 && canHold > 0) {
+                itemstack.setCount(canHold);
+                // Call legacy event
+                PlayerPickupItemEvent playerEvent = new PlayerPickupItemEvent((org.bukkit.entity.Player) entityhuman.getBukkitEntity(), (org.bukkit.entity.Item) this.getBukkitEntity(), remaining);
+                playerEvent.setCancelled(!playerEvent.getPlayer().getCanPickupItems());
+                this.level.getCraftServer().getPluginManager().callEvent(playerEvent);
+                if (playerEvent.isCancelled()) {
+                    itemstack.setCount(i); // SPIGOT-5294 - restore count
+                    return;
+                }
+
+                // Call newer event afterwards
+                EntityPickupItemEvent entityEvent = new EntityPickupItemEvent((org.bukkit.entity.Player) entityhuman.getBukkitEntity(), (org.bukkit.entity.Item) this.getBukkitEntity(), remaining);
+                entityEvent.setCancelled(!entityEvent.getEntity().getCanPickupItems());
+                this.level.getCraftServer().getPluginManager().callEvent(entityEvent);
+                if (entityEvent.isCancelled()) {
+                    itemstack.setCount(i); // SPIGOT-5294 - restore count
+                    return;
+                }
+
+                // Update the ItemStack if it was changed in the event
+                ItemStack current = this.getItem();
+                if (!itemstack.equals(current)) {
+                    itemstack = current;
+                } else {
+                    itemstack.setCount(canHold + remaining); // = i
+                }
+
+                // Possibly < 0; fix here so we do not have to modify code below
+                this.pickupDelay = 0;
+            } else if (this.pickupDelay == 0) {
+                // ensure that the code below isn't triggered if canHold says we can't pick the items up
+                this.pickupDelay = -1;
+            }
+            // CraftBukkit end
+
             if (this.pickupDelay == 0 && (this.owner == null || this.owner.equals(entityhuman.getUUID())) && entityhuman.getInventory().add(itemstack)) {
                 entityhuman.take(this, i);
                 if (itemstack.isEmpty()) {
@@ -369,7 +433,9 @@
     }
 
     public void setItem(ItemStack itemstack) {
+        com.google.common.base.Preconditions.checkArgument(!itemstack.isEmpty(), "Cannot drop air"); // CraftBukkit
         this.getEntityData().set(EntityItem.DATA_ITEM, itemstack);
+        this.getEntityData().markDirty(EntityItem.DATA_ITEM); // CraftBukkit - SPIGOT-4591, must mark dirty
     }
 
     @Override