Fix EntityPickupItemEvent getRemaining / PlayerInventory#canHold

Without this change the calculation of fitting items was incorrect, so event.getRemaining() did return 0 when it should not be 0.

By: Brokkonaut <hannos17@gmx.de>

paper-server/nms-patches/PlayerInventory.patch

@@ -66,7 +66,7 @@
      public PlayerInventory(EntityHuman entityhuman) {
          this.items = NonNullList.a(36, ItemStack.a);
          this.armor = NonNullList.a(4, ItemStack.a);
-@@ -42,6 +94,23 @@
+@@ -42,6 +94,22 @@
          return itemstack.getItem() == itemstack1.getItem() && ItemStack.equals(itemstack, itemstack1);
      }
  
@@ -77,8 +77,7 @@
 +            ItemStack itemstack1 = this.getItem(i);
 +            if (itemstack1.isEmpty()) return itemstack.getCount();
 +
-+            // Taken from firstPartial(ItemStack)
++            if (this.a(itemstack1, itemstack)) { // PAIL rename isSimilarAndNotFull
-+            if (!this.a(itemstack, itemstack1)) {
 +                remains -= (itemstack1.getMaxStackSize() < this.getMaxStackSize() ? itemstack1.getMaxStackSize() : this.getMaxStackSize()) - itemstack1.getCount();
 +            }
 +            if (remains <= 0) return itemstack.getCount();
@@ -90,7 +89,7 @@
      public int getFirstEmptySlotIndex() {
          for (int i = 0; i < this.items.size(); ++i) {
              if (((ItemStack) this.items.get(i)).isEmpty()) {
-@@ -502,7 +571,7 @@
+@@ -502,7 +570,7 @@
      }
  
      public int getMaxStackSize() {
@@ -99,7 +98,7 @@
      }
  
      public boolean b(IBlockData iblockdata) {
-@@ -554,6 +623,11 @@
+@@ -554,6 +622,11 @@
      }
  
      public ItemStack getCarried() {

paper-server/src/test/java/org/bukkit/craftbukkit/inventory/PlayerInventoryTest.java

@@ -0,0 +1,60 @@
+package org.bukkit.craftbukkit.inventory;
+
+import net.minecraft.server.ItemStack;
+import net.minecraft.server.Items;
+import net.minecraft.server.PlayerInventory;
+import org.bukkit.support.AbstractTestingBase;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class PlayerInventoryTest extends AbstractTestingBase {
+
+    @Test
+    public void testCanHold() throws Exception {
+        ItemStack itemStackApple = new ItemStack(Items.APPLE);
+        ItemStack itemStack1Coal = new ItemStack(Items.COAL);
+        ItemStack itemStack32Coal = new ItemStack(Items.COAL, 32);
+        ItemStack itemStack63Coal = new ItemStack(Items.COAL, 63);
+        ItemStack itemStack64Coal = new ItemStack(Items.COAL, 64);
+
+        // keep one slot empty
+        PlayerInventory inventory = new PlayerInventory(null);
+        for (int i = 0; i < inventory.items.size() - 1; i++) {
+            inventory.setItem(i, itemStackApple);
+        }
+
+        // one slot empty
+        assertEquals(1, inventory.canHold(itemStack1Coal));
+        assertEquals(32, inventory.canHold(itemStack32Coal));
+        assertEquals(64, inventory.canHold(itemStack64Coal));
+
+        // no free space with a stack of the item to check in the inventory
+        inventory.setItem(inventory.items.size() - 1, itemStack64Coal);
+
+        assertEquals(0, inventory.canHold(itemStack1Coal));
+        assertEquals(0, inventory.canHold(itemStack32Coal));
+        assertEquals(0, inventory.canHold(itemStack64Coal));
+
+        // no free space without a stack of the item to check in the inventory
+        inventory.setItem(inventory.items.size() - 1, itemStackApple);
+
+        assertEquals(0, inventory.canHold(itemStack1Coal));
+        assertEquals(0, inventory.canHold(itemStack32Coal));
+        assertEquals(0, inventory.canHold(itemStack64Coal));
+
+        // free space for 32 items in one slot
+        inventory.setItem(inventory.items.size() - 1, itemStack32Coal);
+
+        assertEquals(1, inventory.canHold(itemStack1Coal));
+        assertEquals(32, inventory.canHold(itemStack32Coal));
+        assertEquals(32, inventory.canHold(itemStack64Coal));
+
+        // free space for 1 item in two slots
+        inventory.setItem(inventory.items.size() - 1, itemStack63Coal);
+        inventory.setItem(inventory.items.size() - 2, itemStack63Coal);
+
+        assertEquals(1, inventory.canHold(itemStack1Coal));
+        assertEquals(2, inventory.canHold(itemStack32Coal));
+        assertEquals(2, inventory.canHold(itemStack64Coal));
+    }
+}