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Fix canHold returning incorrect amount for empty slots #13392

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Fix canHold returning incorrect amount for empty slots #13392

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d8d8f79
Fix canHold returning incorrect amount for empty slots
xSnowyk Dec 14, 2025
fb20780
Add tests for overstacked items in canHold
xSnowyk Dec 14, 2025
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4 changes: 2 additions & 2 deletions paper-server/patches/features/0030-Improve-exact-choice-recipe-ingredients.patch
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Original file line number Diff line number Diff line change
Expand Up @@ -204,10 +204,10 @@ index 6d3e3ec045d5b15a435f7217369968b33e082724..b7a3758af337270737041f84d10eb437
int i = this.inventory.findSlotMatchingCraftingIngredient(item, item1);
if (i == -1) {
diff --git a/net/minecraft/world/entity/player/Inventory.java b/net/minecraft/world/entity/player/Inventory.java
index 76eda3bd8c513c7e42ceedf1aa605fb6df8b7019..41e59f3739945ca7f6ab710c993b5c0f15fcd529 100644
index ae5bce250e5942de8cb08c397efe1b012afdd2a2..e48a80b3b5b6d0098833cd4e0ae3fef75b442ff2 100644
--- a/net/minecraft/world/entity/player/Inventory.java
+++ b/net/minecraft/world/entity/player/Inventory.java
@@ -252,12 +252,12 @@ public class Inventory implements Container, Nameable {
@@ -264,12 +264,12 @@ public class Inventory implements Container, Nameable {
return !stack.isDamaged() && !stack.isEnchanted() && !stack.has(DataComponents.CUSTOM_NAME);
}

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24 changes: 18 additions & 6 deletions paper-server/patches/sources/net/minecraft/world/entity/player/Inventory.java.patch
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Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,7 @@

public Inventory(Player player, EntityEquipment equipment) {
this.player = player;
@@ -93,10 +_,39 @@
@@ -93,10 +_,51 @@

private boolean hasRemainingSpaceForItem(ItemStack destination, ItemStack origin) {
return !destination.isEmpty()
Expand All @@ -96,24 +96,36 @@
+ // CraftBukkit start - Watch method above! :D
+ public int canHold(ItemStack itemStack) {
+ int remains = itemStack.getCount();
+ int maxStackSize = Math.min(this.getMaxStackSize(), itemStack.getMaxStackSize());
+
+ for (int slot = 0; slot < this.items.size(); ++slot) {
+ ItemStack itemInSlot = this.getItem(slot);
+ if (itemInSlot.isEmpty()) {
+ return itemStack.getCount();
+ }
+ remains -= maxStackSize;
+ } else if (this.hasRemainingSpaceForItem(itemInSlot, itemStack)) {
+ int currentItemMaxStack = Math.min(this.getMaxStackSize(), itemInSlot.getMaxStackSize());
+ int space = currentItemMaxStack - itemInSlot.getCount();
+
+ if (this.hasRemainingSpaceForItem(itemInSlot, itemStack)) {
+ remains -= (itemInSlot.getMaxStackSize() < this.getMaxStackSize() ? itemInSlot.getMaxStackSize() : this.getMaxStackSize()) - itemInSlot.getCount();
+ if (space > 0) {
+ remains -= space;
+ }
+ }
+
+ if (remains <= 0) {
+ return itemStack.getCount();
+ }
+ }
+
+ ItemStack itemInOffhand = this.equipment.get(EquipmentSlot.OFFHAND);
+ if (this.hasRemainingSpaceForItem(itemInOffhand, itemStack)) {
+ remains -= (itemInOffhand.getMaxStackSize() < this.getMaxStackSize() ? itemInOffhand.getMaxStackSize() : this.getMaxStackSize()) - itemInOffhand.getCount();
+ int offHandMaxStack = Math.min(this.getMaxStackSize(), itemInOffhand.getMaxStackSize());
+ int space = offHandMaxStack - itemInOffhand.getCount();
+
+ if (space > 0) {
+ remains -= space;
+ }
+ }
+
+ if (remains <= 0) {
+ return itemStack.getCount();
+ }
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12 changes: 12 additions & 0 deletions paper-server/src/test/java/org/bukkit/craftbukkit/inventory/PlayerInventoryTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ public void testCanHold() throws Exception {
ItemStack itemStack32Coal = new ItemStack(Items.COAL, 32);
ItemStack itemStack63Coal = new ItemStack(Items.COAL, 63);
ItemStack itemStack64Coal = new ItemStack(Items.COAL, 64);
ItemStack itemStack80Coal = new ItemStack(Items.COAL, 80); // Overstacked item

// keep one slot empty
Inventory inventory = new Inventory(null, new PlayerEquipment(null));
Expand All @@ -30,13 +31,15 @@ public void testCanHold() throws Exception {
assertEquals(1, inventory.canHold(itemStack1Coal));
assertEquals(32, inventory.canHold(itemStack32Coal));
assertEquals(64, inventory.canHold(itemStack64Coal));
assertEquals(64, inventory.canHold(itemStack80Coal)); // Should only fit 64 items in 1 slot

// no free space with a stack of the item to check in the inventory
inventory.setItem(inventory.getNonEquipmentItems().size() - 1, itemStack64Coal);

assertEquals(0, inventory.canHold(itemStack1Coal));
assertEquals(0, inventory.canHold(itemStack32Coal));
assertEquals(0, inventory.canHold(itemStack64Coal));
assertEquals(0, inventory.canHold(itemStack80Coal));

// no free space without a stack of the item to check in the inventory
inventory.setItem(inventory.getNonEquipmentItems().size() - 1, itemStackApple);
Expand All @@ -51,6 +54,7 @@ public void testCanHold() throws Exception {
assertEquals(1, inventory.canHold(itemStack1Coal));
assertEquals(32, inventory.canHold(itemStack32Coal));
assertEquals(32, inventory.canHold(itemStack64Coal));
assertEquals(32, inventory.canHold(itemStack80Coal));

// free space for 1 item in two slots
inventory.setItem(inventory.getNonEquipmentItems().size() - 1, itemStack63Coal);
Expand All @@ -76,5 +80,13 @@ public void testCanHold() throws Exception {
assertEquals(1, inventory.canHold(itemStack1Coal));
assertEquals(2, inventory.canHold(itemStack32Coal));
assertEquals(2, inventory.canHold(itemStack64Coal));

// two empty slots
inventory.setItem(inventory.getNonEquipmentItems().size() - 1, ItemStack.EMPTY);
inventory.setItem(inventory.getNonEquipmentItems().size() - 2, ItemStack.EMPTY);
inventory.setItem(inventory.getNonEquipmentItems().size() + inventory.getArmorContents().size(), ItemStack.EMPTY);

assertEquals(80, inventory.canHold(itemStack80Coal));
assertEquals(128, inventory.canHold(new ItemStack(Items.COAL, 130)));
}
}
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