shulker stacks can now be moved in 1.17, fixes #976

src/main/java/carpet/CarpetSettings.java

@@ -196,6 +196,7 @@ public class CarpetSettings
             category = {SURVIVAL, FEATURE}
     )
     public static boolean stackableShulkerBoxes = false;
+    public static final int SHULKER_STACK_SIZE = 64;
 
     @Rule( desc = "Explosions won't destroy blocks", category = {CREATIVE, TNT} )
     public static boolean explosionNoBlockDamage = false;

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

@@ -0,0 +1,26 @@
+package carpet.mixins;
+
+import carpet.CarpetSettings;
+import net.minecraft.block.ShulkerBoxBlock;
+import net.minecraft.item.BlockItem;
+import net.minecraft.item.ItemStack;
+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(Slot.class)
+public class Slot_stackableSBoxesMixin {
+    @Redirect(method = "insertStack(Lnet/minecraft/item/ItemStack;I)Lnet/minecraft/item/ItemStack;", at = @At(
+            value = "INVOKE",
+            target = "Lnet/minecraft/screen/slot/Slot;getMaxItemCount(Lnet/minecraft/item/ItemStack;)I"
+    ))
+    private int getMaxCountForSboxes(Slot slot, ItemStack stack)
+    {
+        if (CarpetSettings.stackableShulkerBoxes && stack.getItem() instanceof BlockItem && ((BlockItem)stack.getItem()).getBlock() instanceof ShulkerBoxBlock)
+        {
+            return CarpetSettings.SHULKER_STACK_SIZE;
+        }
+        return slot.getMaxItemCount(stack);
+    }
+}