Fixes inventory behaviour with stackable empty shulker boxes. fixes #1048

src/main/java/carpet/mixins/ScreenHandler_stackableSBoxesMixin.java

@@ -0,0 +1,33 @@
+package carpet.mixins;
+
+import carpet.CarpetSettings;
+import carpet.helpers.InventoryHelper;
+import net.minecraft.block.ShulkerBoxBlock;
+import net.minecraft.item.BlockItem;
+import net.minecraft.item.ItemStack;
+import net.minecraft.screen.ScreenHandler;
+import net.minecraft.screen.slot.Slot;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Redirect;
+
+@Mixin(ScreenHandler.class)
+public class ScreenHandler_stackableSBoxesMixin
+{
+    @Redirect(method = "internalOnSlotClick", at = @At(
+            value = "INVOKE",
+            target = "Lnet/minecraft/screen/slot/Slot;getMaxItemCount(Lnet/minecraft/item/ItemStack;)I"
+    ))
+    private int getMaxCountForSboxesInScreenHander(Slot slot, ItemStack stack)
+    {
+        if (CarpetSettings.stackableShulkerBoxes &&
+                stack.getItem() instanceof BlockItem &&
+                ((BlockItem)stack.getItem()).getBlock() instanceof ShulkerBoxBlock &&
+                !InventoryHelper.shulkerBoxHasItems(stack)
+        )
+        {
+            return CarpetSettings.SHULKER_STACK_SIZE;
+        }
+        return slot.getMaxItemCount(stack);
+    }
+}

src/main/java/carpet/mixins/Slot_stackableSBoxesMixin.java

@@ -16,7 +16,7 @@ public class Slot_stackableSBoxesMixin {
             value = "INVOKE",
             target = "Lnet/minecraft/screen/slot/Slot;getMaxItemCount(Lnet/minecraft/item/ItemStack;)I"
     ))
-    private int getMaxCountForSboxes(Slot slot, ItemStack stack)
+    private int getMaxCountForSboxesInSlot(Slot slot, ItemStack stack)
     {
         if (CarpetSettings.stackableShulkerBoxes &&
                 stack.getItem() instanceof BlockItem &&

src/main/resources/carpet.mixins.json

@@ -136,6 +136,7 @@
     "CauldronBlock_stackableSBoxesMixin",
     "AbstractCauldronBlock_stackableSBoxesMixin",
     "Slot_stackableSBoxesMixin",
+    "ScreenHandler_stackableSBoxesMixin",
     "ItemEntityMixin",
     "TntBlockMixin",
     "ExplosionMixin",