Allow upgrades to read/write upgrade data from ItemStacks (#1465)

projects/common-api/src/client/java/dan200/computercraft/api/client/turtle/TurtleUpgradeModeller.java

@@ -11,6 +11,7 @@ import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.api.turtle.TurtleSide;
 import dan200.computercraft.api.turtle.TurtleUpgradeSerialiser;
 import net.minecraft.client.resources.model.ModelResourceLocation;
+import net.minecraft.nbt.CompoundTag;
 import net.minecraft.resources.ResourceLocation;
 
 import javax.annotation.Nullable;
@@ -28,12 +29,27 @@ public interface TurtleUpgradeModeller<T extends ITurtleUpgrade> {
      * When the current turtle is {@literal null}, this function should be constant for a given upgrade and side.
      *
      * @param upgrade The upgrade that you're getting the model for.
-     * @param turtle  Access to the turtle that the upgrade resides on. This will be null when getting item models!
+     * @param turtle  Access to the turtle that the upgrade resides on. This will be null when getting item models, unless
+     *                {@link #getModel(ITurtleUpgrade, CompoundTag, TurtleSide)} is overriden.
      * @param side    Which side of the turtle (left or right) the upgrade resides on.
      * @return The model that you wish to be used to render your upgrade.
      */
     TransformedModel getModel(T upgrade, @Nullable ITurtleAccess turtle, TurtleSide side);
 
+    /**
+     * Obtain the model to be used when rendering a turtle peripheral.
+     * <p>
+     * This is used when rendering the turtle's item model, and so no {@link ITurtleAccess} is available.
+     *
+     * @param upgrade The upgrade that you're getting the model for.
+     * @param data    Upgrade data instance for current turtle side.
+     * @param side    Which side of the turtle (left or right) the upgrade resides on.
+     * @return The model that you wish to be used to render your upgrade.
+     */
+    default TransformedModel getModel(T upgrade, CompoundTag data, TurtleSide side) {
+        return getModel(upgrade, (ITurtleAccess) null, side);
+    }
+
     /**
      * A basic {@link TurtleUpgradeModeller} which renders using the upgrade's {@linkplain ITurtleUpgrade#getCraftingItem()
      * crafting item}.

projects/common-api/src/main/java/dan200/computercraft/api/pocket/IPocketAccess.java

@@ -5,9 +5,11 @@
 package dan200.computercraft.api.pocket;
 
 import dan200.computercraft.api.peripheral.IPeripheral;
+import dan200.computercraft.api.upgrades.UpgradeBase;
 import net.minecraft.nbt.CompoundTag;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.entity.Entity;
+import net.minecraft.world.item.ItemStack;
 
 import javax.annotation.Nullable;
 import java.util.Map;
@@ -69,6 +71,8 @@ public interface IPocketAccess {
      *
      * @return The upgrade's NBT.
      * @see #updateUpgradeNBTData()
+     * @see UpgradeBase#getUpgradeItem(CompoundTag)
+     * @see UpgradeBase#getUpgradeData(ItemStack)
      */
     CompoundTag getUpgradeNBTData();
 

projects/common-api/src/main/java/dan200/computercraft/api/turtle/ITurtleAccess.java

@@ -8,10 +8,13 @@ import com.mojang.authlib.GameProfile;
 import dan200.computercraft.api.lua.ILuaCallback;
 import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.peripheral.IPeripheral;
+import dan200.computercraft.api.upgrades.UpgradeBase;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import net.minecraft.core.BlockPos;
 import net.minecraft.core.Direction;
 import net.minecraft.nbt.CompoundTag;
 import net.minecraft.world.Container;
+import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.level.Level;
 import net.minecraft.world.phys.Vec3;
 import org.jetbrains.annotations.ApiStatus;
@@ -245,23 +248,51 @@ public interface ITurtleAccess {
     void playAnimation(TurtleAnimation animation);
 
     /**
-     * Returns the turtle on the specified side of the turtle, if there is one.
+     * Returns the upgrade on the specified side of the turtle, if there is one.
      *
      * @param side The side to get the upgrade from.
      * @return The upgrade on the specified side of the turtle, if there is one.
-     * @see #setUpgrade(TurtleSide, ITurtleUpgrade)
+     * @see #getUpgradeWithData(TurtleSide)
+     * @see #setUpgradeWithData(TurtleSide, UpgradeData)
      */
     @Nullable
     ITurtleUpgrade getUpgrade(TurtleSide side);
 
+    /**
+     * Returns the upgrade on the specified side of the turtle, along with its {@linkplain #getUpgradeNBTData(TurtleSide)
+     * update data}.
+     *
+     * @param side The side to get the upgrade from.
+     * @return The upgrade on the specified side of the turtle, along with its upgrade data, if there is one.
+     * @see #getUpgradeWithData(TurtleSide)
+     * @see #setUpgradeWithData(TurtleSide, UpgradeData)
+     */
+    default @Nullable UpgradeData<ITurtleUpgrade> getUpgradeWithData(TurtleSide side) {
+        var upgrade = getUpgrade(side);
+        return upgrade == null ? null : UpgradeData.of(upgrade, getUpgradeNBTData(side));
+    }
+
     /**
      * Set the upgrade for a given side, resetting peripherals and clearing upgrade specific data.
      *
      * @param side    The side to set the upgrade on.
      * @param upgrade The upgrade to set, may be {@code null} to clear.
      * @see #getUpgrade(TurtleSide)
+     * @deprecated Use {@link #setUpgradeWithData(TurtleSide, UpgradeData)}
      */
-    void setUpgrade(TurtleSide side, @Nullable ITurtleUpgrade upgrade);
+    @Deprecated
+    default void setUpgrade(TurtleSide side, @Nullable ITurtleUpgrade upgrade) {
+        setUpgradeWithData(side, upgrade == null ? null : UpgradeData.ofDefault(upgrade));
+    }
+
+    /**
+     * Set the upgrade for a given side and its upgrade data.
+     *
+     * @param side    The side to set the upgrade on.
+     * @param upgrade The upgrade to set, may be {@code null} to clear.
+     * @see #getUpgradeWithData(TurtleSide)
+     */
+    void setUpgradeWithData(TurtleSide side, @Nullable UpgradeData<ITurtleUpgrade> upgrade);
 
     /**
      * Returns the peripheral created by the upgrade on the specified side of the turtle, if there is one.
@@ -281,6 +312,8 @@ public interface ITurtleAccess {
      * @param side The side to get the upgrade data for.
      * @return The upgrade-specific data.
      * @see #updateUpgradeNBTData(TurtleSide)
+     * @see UpgradeBase#getUpgradeItem(CompoundTag)
+     * @see UpgradeBase#getUpgradeData(ItemStack)
      */
     CompoundTag getUpgradeNBTData(TurtleSide side);
 

projects/common-api/src/main/java/dan200/computercraft/api/turtle/ITurtleUpgrade.java

@@ -7,6 +7,7 @@ package dan200.computercraft.api.turtle;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.api.upgrades.UpgradeBase;
 import net.minecraft.core.Direction;
+import net.minecraft.nbt.CompoundTag;
 
 import javax.annotation.Nullable;
 
@@ -79,4 +80,17 @@ public interface ITurtleUpgrade extends UpgradeBase {
      */
     default void update(ITurtleAccess turtle, TurtleSide side) {
     }
+
+    /**
+     * Get upgrade data that should be persisted when the turtle was broken.
+     * <p>
+     * This method should be overridden when you don't need to store all upgrade data by default. For instance, if you
+     * store peripheral state in the upgrade data, which should be lost when the turtle is broken.
+     *
+     * @param upgradeData Data that currently stored for this upgrade
+     * @return Filtered version of this data.
+     */
+    default CompoundTag getPersistedData(CompoundTag upgradeData) {
+        return upgradeData;
+    }
 }

projects/common-api/src/main/java/dan200/computercraft/api/upgrades/UpgradeBase.java

@@ -4,10 +4,14 @@
 
 package dan200.computercraft.api.upgrades;
 
+import dan200.computercraft.api.pocket.IPocketAccess;
 import dan200.computercraft.api.pocket.IPocketUpgrade;
+import dan200.computercraft.api.turtle.ITurtleAccess;
 import dan200.computercraft.api.turtle.ITurtleUpgrade;
+import dan200.computercraft.api.turtle.TurtleSide;
 import dan200.computercraft.impl.PlatformHelper;
 import net.minecraft.Util;
+import net.minecraft.nbt.CompoundTag;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.item.ItemStack;
 
@@ -50,6 +54,42 @@ public interface UpgradeBase {
      */
     ItemStack getCraftingItem();
 
+    /**
+     * Returns the item stack representing a currently equipped turtle upgrade.
+     * <p>
+     * While upgrades can store upgrade data ({@link ITurtleAccess#getUpgradeNBTData(TurtleSide)} and
+     * {@link IPocketAccess#getUpgradeNBTData()}}, by default this data is discarded when an upgrade is unequipped,
+     * and the original item stack is returned.
+     * <p>
+     * By overriding this method, you can create a new {@link ItemStack} which contains enough data to
+     * {@linkplain #getUpgradeData(ItemStack) re-create the upgrade data} if the item is re-equipped.
+     * <p>
+     * When overriding this, you should override {@link #getUpgradeData(ItemStack)} and {@link #isItemSuitable(ItemStack)}
+     * at the same time,
+     *
+     * @param upgradeData The current upgrade data. This should <strong>NOT</strong> be mutated.
+     * @return The item stack returned when unequipping.
+     */
+    default ItemStack getUpgradeItem(CompoundTag upgradeData) {
+        return getCraftingItem();
+    }
+
+    /**
+     * Extract upgrade data from an {@link ItemStack}.
+     * <p>
+     * This upgrade data will be available with {@link ITurtleAccess#getUpgradeNBTData(TurtleSide)} or
+     * {@link IPocketAccess#getUpgradeNBTData()}.
+     * <p>
+     * This should be an inverse to {@link #getUpgradeItem(CompoundTag)}.
+     *
+     * @param stack The stack that was equipped by the turtle or pocket computer. This will have the same item as
+     *              {@link #getCraftingItem()}.
+     * @return The upgrade data that should be set on the turtle or pocket computer.
+     */
+    default CompoundTag getUpgradeData(ItemStack stack) {
+        return new CompoundTag();
+    }
+
     /**
      * Determine if an item is suitable for being used for this upgrade.
      * <p>

projects/common-api/src/main/java/dan200/computercraft/api/upgrades/UpgradeData.java

@@ -0,0 +1,82 @@
+// SPDX-FileCopyrightText: 2023 The CC: Tweaked Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+package dan200.computercraft.api.upgrades;
+
+import dan200.computercraft.api.pocket.IPocketUpgrade;
+import dan200.computercraft.api.turtle.ITurtleUpgrade;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.world.item.ItemStack;
+import org.jetbrains.annotations.Contract;
+
+import javax.annotation.Nullable;
+
+/**
+ * An upgrade (i.e. a {@link ITurtleUpgrade}) and its current upgrade data.
+ * <p>
+ * <strong>IMPORTANT:</strong> The {@link #data()} in an upgrade data is often a reference to the original upgrade data.
+ * Be careful to take a {@linkplain #copy() defensive copy} if you plan to use the data in this upgrade.
+ *
+ * @param upgrade The current upgrade.
+ * @param data    The upgrade's data.
+ * @param <T>     The type of upgrade, either {@link ITurtleUpgrade} or {@link IPocketUpgrade}.
+ */
+public record UpgradeData<T extends UpgradeBase>(T upgrade, CompoundTag data) {
+    /**
+     * A utility method to construct a new {@link UpgradeData} instance.
+     *
+     * @param upgrade An upgrade.
+     * @param data    The upgrade's data.
+     * @param <T>     The type of upgrade.
+     * @return The new {@link UpgradeData} instance.
+     */
+    public static <T extends UpgradeBase> UpgradeData<T> of(T upgrade, CompoundTag data) {
+        return new UpgradeData<>(upgrade, data);
+    }
+
+    /**
+     * Create an {@link UpgradeData} containing the default {@linkplain #data() data} for an upgrade.
+     *
+     * @param upgrade The upgrade instance.
+     * @param <T>     The type of upgrade.
+     * @return The default upgrade data.
+     */
+    public static <T extends UpgradeBase> UpgradeData<T> ofDefault(T upgrade) {
+        return of(upgrade, upgrade.getUpgradeData(upgrade.getCraftingItem()));
+    }
+
+    /**
+     * Take a copy of a (possibly {@code null}) {@link UpgradeData} instance.
+     *
+     * @param upgrade The copied upgrade data.
+     * @param <T>     The type of upgrade.
+     * @return The newly created upgrade data.
+     */
+    @Contract("!null -> !null; null -> null")
+    public static <T extends UpgradeBase> @Nullable UpgradeData<T> copyOf(@Nullable UpgradeData<T> upgrade) {
+        return upgrade == null ? null : upgrade.copy();
+    }
+
+    /**
+     * Get the {@linkplain UpgradeBase#getUpgradeItem(CompoundTag) upgrade item} for this upgrade.
+     * <p>
+     * This returns a defensive copy of the item, to prevent accidental mutation of the upgrade data or original
+     * {@linkplain UpgradeBase#getCraftingItem() upgrade stack}.
+     *
+     * @return This upgrade's item.
+     */
+    public ItemStack getUpgradeItem() {
+        return upgrade.getUpgradeItem(data).copy();
+    }
+
+    /**
+     * Take a copy of this {@link UpgradeData}. This returns a new instance with the same upgrade and a fresh copy of
+     * the upgrade data.
+     *
+     * @return A copy of the current instance.
+     */
+    public UpgradeData<T> copy() {
+        return new UpgradeData<>(upgrade(), data().copy());
+    }
+}

projects/common/src/client/java/dan200/computercraft/client/model/turtle/TurtleModelParts.java

@@ -4,11 +4,13 @@
 
 package dan200.computercraft.client.model.turtle;
 
+import com.google.common.cache.CacheBuilder;
 import com.mojang.blaze3d.vertex.PoseStack;
 import com.mojang.math.Transformation;
 import dan200.computercraft.api.client.TransformedModel;
 import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.api.turtle.TurtleSide;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.client.platform.ClientPlatformHelper;
 import dan200.computercraft.client.render.TurtleBlockEntityRenderer;
 import dan200.computercraft.client.turtle.TurtleUpgradeModellers;
@@ -21,9 +23,9 @@ import net.minecraft.world.item.ItemStack;
 
 import javax.annotation.Nullable;
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.TimeUnit;
 import java.util.function.Function;
 
 /**
@@ -46,12 +48,19 @@ public final class TurtleModelParts<T> {
 
     private record Combination(
         boolean colour,
-        @Nullable ITurtleUpgrade leftUpgrade,
+        @Nullable UpgradeData<ITurtleUpgrade> leftUpgrade,
-        @Nullable ITurtleUpgrade rightUpgrade,
+        @Nullable UpgradeData<ITurtleUpgrade> rightUpgrade,
         @Nullable ResourceLocation overlay,
         boolean christmas,
         boolean flip
     ) {
+        Combination copy() {
+            if (leftUpgrade == null && rightUpgrade == null) return this;
+            return new Combination(
+                colour, UpgradeData.copyOf(leftUpgrade), UpgradeData.copyOf(rightUpgrade),
+                overlay, christmas, flip
+            );
+        }
     }
 
     private final BakedModel familyModel;
@@ -63,12 +72,20 @@ public final class TurtleModelParts<T> {
      * A cache of {@link TransformedModel} to the transformed {@link BakedModel}. This helps us pool the transformed
      * instances, reducing memory usage and hopefully ensuring their caches are hit more often!
      */
-    private final Map<TransformedModel, BakedModel> transformCache = new HashMap<>();
+    private final Map<TransformedModel, BakedModel> transformCache = CacheBuilder.newBuilder()
+        .concurrencyLevel(1)
+        .expireAfterAccess(30, TimeUnit.SECONDS)
+        .<TransformedModel, BakedModel>build()
+        .asMap();
 
     /**
      * A cache of {@link Combination}s to the combined model.
      */
-    private final Map<Combination, T> modelCache = new HashMap<>();
+    private final Map<Combination, T> modelCache = CacheBuilder.newBuilder()
+        .concurrencyLevel(1)
+        .expireAfterAccess(30, TimeUnit.SECONDS)
+        .<Combination, T>build()
+        .asMap();
 
     public TurtleModelParts(BakedModel familyModel, BakedModel colourModel, ModelTransformer transformer, Function<List<BakedModel>, T> combineModel) {
         this.familyModel = familyModel;
@@ -78,7 +95,15 @@ public final class TurtleModelParts<T> {
     }
 
     public T getModel(ItemStack stack) {
-        return modelCache.computeIfAbsent(getCombination(stack), buildModel);
+        var combination = getCombination(stack);
+        var existing = modelCache.get(combination);
+        if (existing != null) return existing;
+
+        // Take a defensive copy of the upgrade data, and add it to the cache.
+        var newCombination = combination.copy();
+        var newModel = buildModel.apply(newCombination);
+        modelCache.put(newCombination, newModel);
+        return newModel;
     }
 
     private Combination getCombination(ItemStack stack) {
@@ -89,8 +114,8 @@ public final class TurtleModelParts<T> {
         }
 
         var colour = turtle.getColour(stack);
-        var leftUpgrade = turtle.getUpgrade(stack, TurtleSide.LEFT);
+        var leftUpgrade = turtle.getUpgradeWithData(stack, TurtleSide.LEFT);
-        var rightUpgrade = turtle.getUpgrade(stack, TurtleSide.RIGHT);
+        var rightUpgrade = turtle.getUpgradeWithData(stack, TurtleSide.RIGHT);
         var overlay = turtle.getOverlay(stack);
         var label = turtle.getLabel(stack);
         var flip = label != null && (label.equals("Dinnerbone") || label.equals("Grumm"));
@@ -110,18 +135,19 @@ public final class TurtleModelParts<T> {
         if (overlayModelLocation != null) {
             parts.add(transform(ClientPlatformHelper.get().getModel(modelManager, overlayModelLocation), transformation));
         }
-        if (combo.leftUpgrade() != null) {
+
-            var model = TurtleUpgradeModellers.getModel(combo.leftUpgrade(), null, TurtleSide.LEFT);
+        addUpgrade(parts, transformation, TurtleSide.LEFT, combo.leftUpgrade());
-            parts.add(transform(model.getModel(), transformation.compose(model.getMatrix())));
+        addUpgrade(parts, transformation, TurtleSide.RIGHT, combo.rightUpgrade());
-        }
-        if (combo.rightUpgrade() != null) {
-            var model = TurtleUpgradeModellers.getModel(combo.rightUpgrade(), null, TurtleSide.RIGHT);
-            parts.add(transform(model.getModel(), transformation.compose(model.getMatrix())));
-        }
 
         return parts;
     }
 
+    private void addUpgrade(List<BakedModel> parts, Transformation transformation, TurtleSide side, @Nullable UpgradeData<ITurtleUpgrade> upgrade) {
+        if (upgrade == null) return;
+        var model = TurtleUpgradeModellers.getModel(upgrade.upgrade(), upgrade.data(), side);
+        parts.add(transform(model.getModel(), transformation.compose(model.getMatrix())));
+    }
+
     private BakedModel transform(BakedModel model, Transformation transformation) {
         if (transformation.equals(Transformation.identity())) return model;
         return transformCache.computeIfAbsent(new TransformedModel(model, transformation), transformer);

projects/common/src/client/java/dan200/computercraft/client/turtle/TurtleUpgradeModellers.java

@@ -14,8 +14,8 @@ import dan200.computercraft.api.turtle.TurtleUpgradeSerialiser;
 import dan200.computercraft.impl.TurtleUpgrades;
 import dan200.computercraft.impl.UpgradeManager;
 import net.minecraft.client.Minecraft;
+import net.minecraft.nbt.CompoundTag;
 
-import javax.annotation.Nullable;
 import java.util.Map;
 import java.util.WeakHashMap;
 import java.util.concurrent.ConcurrentHashMap;
@@ -52,12 +52,18 @@ public final class TurtleUpgradeModellers {
         }
     }
 
-    public static TransformedModel getModel(ITurtleUpgrade upgrade, @Nullable ITurtleAccess access, TurtleSide side) {
+    public static TransformedModel getModel(ITurtleUpgrade upgrade, ITurtleAccess access, TurtleSide side) {
         @SuppressWarnings("unchecked")
         var modeller = (TurtleUpgradeModeller<ITurtleUpgrade>) modelCache.computeIfAbsent(upgrade, TurtleUpgradeModellers::getModeller);
         return modeller.getModel(upgrade, access, side);
     }
 
+    public static TransformedModel getModel(ITurtleUpgrade upgrade, CompoundTag data, TurtleSide side) {
+        @SuppressWarnings("unchecked")
+        var modeller = (TurtleUpgradeModeller<ITurtleUpgrade>) modelCache.computeIfAbsent(upgrade, TurtleUpgradeModellers::getModeller);
+        return modeller.getModel(upgrade, data, side);
+    }
+
     private static TurtleUpgradeModeller<?> getModeller(ITurtleUpgrade upgradeA) {
         var wrapper = TurtleUpgrades.instance().getWrapper(upgradeA);
         if (wrapper == null) return NULL_TURTLE_MODELLER;

projects/common/src/main/java/dan200/computercraft/data/RecipeProvider.java

@@ -8,6 +8,7 @@ import com.google.gson.JsonObject;
 import dan200.computercraft.api.ComputerCraftAPI;
 import dan200.computercraft.api.pocket.PocketUpgradeDataProvider;
 import dan200.computercraft.api.turtle.TurtleUpgradeDataProvider;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.core.util.Colour;
 import dan200.computercraft.shared.ModRegistry;
 import dan200.computercraft.shared.common.IColouredItem;
@@ -110,7 +111,7 @@ class RecipeProvider extends net.minecraft.data.recipes.RecipeProvider {
             var nameId = turtleItem.getFamily().name().toLowerCase(Locale.ROOT);
 
             for (var upgrade : turtleUpgrades.getGeneratedUpgrades()) {
-                var result = turtleItem.create(-1, null, -1, null, upgrade, -1, null);
+                var result = turtleItem.create(-1, null, -1, null, UpgradeData.ofDefault(upgrade), -1, null);
                 ShapedRecipeBuilder
                     .shaped(RecipeCategory.REDSTONE, result.getItem())
                     .group(String.format("%s:turtle_%s", ComputerCraftAPI.MOD_ID, nameId))
@@ -146,7 +147,7 @@ class RecipeProvider extends net.minecraft.data.recipes.RecipeProvider {
             var nameId = pocket.getFamily().name().toLowerCase(Locale.ROOT);
 
             for (var upgrade : pocketUpgrades.getGeneratedUpgrades()) {
-                var result = pocket.create(-1, null, -1, upgrade);
+                var result = pocket.create(-1, null, -1, UpgradeData.ofDefault(upgrade));
                 ShapedRecipeBuilder
                     .shaped(RecipeCategory.REDSTONE, result.getItem())
                     .group(String.format("%s:pocket_%s", ComputerCraftAPI.MOD_ID, nameId))

projects/common/src/main/java/dan200/computercraft/impl/UpgradeManager.java

@@ -7,6 +7,7 @@ package dan200.computercraft.impl;
 import com.google.gson.*;
 import dan200.computercraft.api.ComputerCraftAPI;
 import dan200.computercraft.api.upgrades.UpgradeBase;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.api.upgrades.UpgradeSerialiser;
 import dan200.computercraft.shared.platform.PlatformHelper;
 import net.minecraft.core.Registry;
@@ -74,13 +75,13 @@ public class UpgradeManager<R extends UpgradeSerialiser<? extends T>, T extends
     }
 
     @Nullable
-    public T get(ItemStack stack) {
+    public UpgradeData<T> get(ItemStack stack) {
         if (stack.isEmpty()) return null;
 
         for (var wrapper : current.values()) {
             var craftingStack = wrapper.upgrade().getCraftingItem();
             if (!craftingStack.isEmpty() && craftingStack.getItem() == stack.getItem() && wrapper.upgrade().isItemSuitable(stack)) {
-                return wrapper.upgrade();
+                return UpgradeData.of(wrapper.upgrade, wrapper.upgrade.getUpgradeData(stack));
             }
         }
 

projects/common/src/main/java/dan200/computercraft/shared/ModRegistry.java

@@ -11,6 +11,7 @@ import dan200.computercraft.api.detail.VanillaDetailRegistries;
 import dan200.computercraft.api.media.IMedia;
 import dan200.computercraft.api.pocket.PocketUpgradeSerialiser;
 import dan200.computercraft.api.turtle.TurtleUpgradeSerialiser;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.core.util.Colour;
 import dan200.computercraft.impl.PocketUpgrades;
 import dan200.computercraft.impl.TurtleUpgrades;
@@ -446,12 +447,12 @@ public final class ModRegistry {
     private static void addTurtle(CreativeModeTab.Output out, TurtleItem turtle) {
         out.accept(turtle.create(-1, null, -1, null, null, 0, null));
         TurtleUpgrades.getVanillaUpgrades()
-            .map(x -> turtle.create(-1, null, -1, null, x, 0, null))
+            .map(x -> turtle.create(-1, null, -1, null, UpgradeData.ofDefault(x), 0, null))
             .forEach(out::accept);
     }
 
     private static void addPocket(CreativeModeTab.Output out, PocketComputerItem pocket) {
         out.accept(pocket.create(-1, null, -1, null));
-        PocketUpgrades.getVanillaUpgrades().map(x -> pocket.create(-1, null, -1, x)).forEach(out::accept);
+        PocketUpgrades.getVanillaUpgrades().map(x -> pocket.create(-1, null, -1, UpgradeData.ofDefault(x))).forEach(out::accept);
     }
 }

projects/common/src/main/java/dan200/computercraft/shared/integration/RecipeModHelpers.java

@@ -5,6 +5,7 @@
 package dan200.computercraft.shared.integration;
 
 import dan200.computercraft.api.ComputerCraftAPI;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.impl.PocketUpgrades;
 import dan200.computercraft.impl.TurtleUpgrades;
 import dan200.computercraft.shared.ModRegistry;
@@ -56,14 +57,14 @@ public final class RecipeModHelpers {
         for (var turtleSupplier : TURTLES) {
             var turtle = turtleSupplier.get();
             for (var upgrade : TurtleUpgrades.instance().getUpgrades()) {
-                upgradeItems.add(turtle.create(-1, null, -1, null, upgrade, 0, null));
+                upgradeItems.add(turtle.create(-1, null, -1, null, UpgradeData.ofDefault(upgrade), 0, null));
             }
         }
 
         for (var pocketSupplier : POCKET_COMPUTERS) {
             var pocket = pocketSupplier.get();
             for (var upgrade : PocketUpgrades.instance().getUpgrades()) {
-                upgradeItems.add(pocket.create(-1, null, -1, upgrade));
+                upgradeItems.add(pocket.create(-1, null, -1, UpgradeData.ofDefault(upgrade)));
             }
         }
 

projects/common/src/main/java/dan200/computercraft/shared/integration/UpgradeRecipeGenerator.java

@@ -9,6 +9,7 @@ import dan200.computercraft.api.pocket.IPocketUpgrade;
 import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.api.turtle.TurtleSide;
 import dan200.computercraft.api.upgrades.UpgradeBase;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.impl.PocketUpgrades;
 import dan200.computercraft.impl.TurtleUpgrades;
 import dan200.computercraft.shared.pocket.items.PocketComputerItem;
@@ -111,20 +112,22 @@ public class UpgradeRecipeGenerator<T> {
 
         if (stack.getItem() instanceof TurtleItem item) {
             // Suggest possible upgrades which can be applied to this turtle
-            var left = item.getUpgrade(stack, TurtleSide.LEFT);
+            var left = item.getUpgradeWithData(stack, TurtleSide.LEFT);
-            var right = item.getUpgrade(stack, TurtleSide.RIGHT);
+            var right = item.getUpgradeWithData(stack, TurtleSide.RIGHT);
             if (left != null && right != null) return Collections.emptyList();
 
             List<T> recipes = new ArrayList<>();
             var ingredient = Ingredient.of(stack);
             for (var upgrade : turtleUpgrades) {
+                if (upgrade.turtle == null) throw new NullPointerException();
+
                 // The turtle is facing towards us, so upgrades on the left are actually crafted on the right.
                 if (left == null) {
-                    recipes.add(turtle(ingredient, upgrade.ingredient, turtleWith(stack, upgrade.turtle, right)));
+                    recipes.add(turtle(ingredient, upgrade.ingredient, turtleWith(stack, UpgradeData.ofDefault(upgrade.turtle), right)));
                 }
 
                 if (right == null) {
-                    recipes.add(turtle(upgrade.ingredient, ingredient, turtleWith(stack, left, upgrade.turtle)));
+                    recipes.add(turtle(upgrade.ingredient, ingredient, turtleWith(stack, left, UpgradeData.ofDefault(upgrade.turtle))));
                 }
             }
 
@@ -137,7 +140,8 @@ public class UpgradeRecipeGenerator<T> {
             List<T> recipes = new ArrayList<>();
             var ingredient = Ingredient.of(stack);
             for (var upgrade : pocketUpgrades) {
-                recipes.add(pocket(upgrade.ingredient, ingredient, pocketWith(stack, upgrade.pocket)));
+                if (upgrade.pocket == null) throw new NullPointerException();
+                recipes.add(pocket(upgrade.ingredient, ingredient, pocketWith(stack, UpgradeData.ofDefault(upgrade.pocket))));
             }
 
             return Collections.unmodifiableList(recipes);
@@ -180,21 +184,21 @@ public class UpgradeRecipeGenerator<T> {
         if (stack.getItem() instanceof TurtleItem item) {
             List<T> recipes = new ArrayList<>(0);
 
-            var left = item.getUpgrade(stack, TurtleSide.LEFT);
+            var left = item.getUpgradeWithData(stack, TurtleSide.LEFT);
-            var right = item.getUpgrade(stack, TurtleSide.RIGHT);
+            var right = item.getUpgradeWithData(stack, TurtleSide.RIGHT);
 
             // The turtle is facing towards us, so upgrades on the left are actually crafted on the right.
             if (left != null) {
                 recipes.add(turtle(
                     Ingredient.of(turtleWith(stack, null, right)),
-                    Ingredient.of(left.getCraftingItem()),
+                    Ingredient.of(left.getUpgradeItem()),
                     stack
                 ));
             }
 
             if (right != null) {
                 recipes.add(turtle(
-                    Ingredient.of(right.getCraftingItem()),
+                    Ingredient.of(right.getUpgradeItem()),
                     Ingredient.of(turtleWith(stack, left, null)),
                     stack
                 ));
@@ -204,9 +208,9 @@ public class UpgradeRecipeGenerator<T> {
         } else if (stack.getItem() instanceof PocketComputerItem) {
             List<T> recipes = new ArrayList<>(0);
 
-            var back = PocketComputerItem.getUpgrade(stack);
+            var back = PocketComputerItem.getUpgradeWithData(stack);
             if (back != null) {
-                recipes.add(pocket(Ingredient.of(back.getCraftingItem()), Ingredient.of(pocketWith(stack, null)), stack));
+                recipes.add(pocket(Ingredient.of(back.getUpgradeItem()), Ingredient.of(pocketWith(stack, null)), stack));
             }
 
             return Collections.unmodifiableList(recipes);
@@ -215,7 +219,7 @@ public class UpgradeRecipeGenerator<T> {
         }
     }
 
-    private static ItemStack turtleWith(ItemStack stack, @Nullable ITurtleUpgrade left, @Nullable ITurtleUpgrade right) {
+    private static ItemStack turtleWith(ItemStack stack, @Nullable UpgradeData<ITurtleUpgrade> left, @Nullable UpgradeData<ITurtleUpgrade> right) {
         var item = (TurtleItem) stack.getItem();
         return item.create(
             item.getComputerID(stack), item.getLabel(stack), item.getColour(stack),
@@ -223,7 +227,7 @@ public class UpgradeRecipeGenerator<T> {
         );
     }
 
-    private static ItemStack pocketWith(ItemStack stack, @Nullable IPocketUpgrade back) {
+    private static ItemStack pocketWith(ItemStack stack, @Nullable UpgradeData<IPocketUpgrade> back) {
         var item = (PocketComputerItem) stack.getItem();
         return item.create(
             item.getComputerID(stack), item.getLabel(stack), item.getColour(stack), back
@@ -272,7 +276,7 @@ public class UpgradeRecipeGenerator<T> {
                     recipes.add(turtle(
                         ingredient, // Right upgrade, recipe on left
                         Ingredient.of(turtleItem.create(-1, null, -1, null, null, 0, null)),
-                        turtleItem.create(-1, null, -1, null, turtle, 0, null)
+                        turtleItem.create(-1, null, -1, null, UpgradeData.ofDefault(turtle), 0, null)
                     ));
                 }
             }
@@ -283,7 +287,7 @@ public class UpgradeRecipeGenerator<T> {
                     recipes.add(pocket(
                         ingredient,
                         Ingredient.of(pocketItem.create(-1, null, -1, null)),
-                        pocketItem.create(-1, null, -1, pocket)
+                        pocketItem.create(-1, null, -1, UpgradeData.ofDefault(pocket))
                     ));
                 }
             }

projects/common/src/main/java/dan200/computercraft/shared/platform/PlatformHelper.java

@@ -68,6 +68,13 @@ public interface PlatformHelper extends dan200.computercraft.impl.PlatformHelper
         return (PlatformHelper) dan200.computercraft.impl.PlatformHelper.get();
     }
 
+    /**
+     * Check if we're running in a development environment.
+     *
+     * @return If we're running in a development environment.
+     */
+    boolean isDevelopmentEnvironment();
+
     /**
      * Create a new config builder.
      *

projects/common/src/main/java/dan200/computercraft/shared/pocket/apis/PocketAPI.java

@@ -7,6 +7,7 @@ package dan200.computercraft.shared.pocket.apis;
 import dan200.computercraft.api.lua.ILuaAPI;
 import dan200.computercraft.api.lua.LuaFunction;
 import dan200.computercraft.api.pocket.IPocketUpgrade;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.impl.PocketUpgrades;
 import dan200.computercraft.shared.pocket.core.PocketServerComputer;
 import net.minecraft.core.NonNullList;
@@ -14,6 +15,7 @@ import net.minecraft.world.entity.player.Player;
 import net.minecraft.world.item.ItemStack;
 
 import javax.annotation.Nullable;
+import java.util.Objects;
 
 /**
  * Control the current pocket computer, adding or removing upgrades.
@@ -68,7 +70,7 @@ public class PocketAPI implements ILuaAPI {
         if (newUpgrade == null) return new Object[]{ false, "Cannot find a valid upgrade" };
 
         // Remove the current upgrade
-        if (previousUpgrade != null) storeItem(player, previousUpgrade.getCraftingItem().copy());
+        if (previousUpgrade != null) storeItem(player, previousUpgrade.getUpgradeItem());
 
         // Set the new upgrade
         computer.setUpgrade(newUpgrade);
@@ -93,7 +95,7 @@ public class PocketAPI implements ILuaAPI {
 
         computer.setUpgrade(null);
 
-        storeItem(player, previousUpgrade.getCraftingItem().copy());
+        storeItem(player, previousUpgrade.getUpgradeItem());
 
         return new Object[]{ true };
     }
@@ -105,13 +107,13 @@ public class PocketAPI implements ILuaAPI {
         }
     }
 
-    private static @Nullable IPocketUpgrade findUpgrade(NonNullList<ItemStack> inv, int start, @Nullable IPocketUpgrade previous) {
+    private static @Nullable UpgradeData<IPocketUpgrade> findUpgrade(NonNullList<ItemStack> inv, int start, @Nullable UpgradeData<IPocketUpgrade> previous) {
         for (var i = 0; i < inv.size(); i++) {
             var invStack = inv.get((i + start) % inv.size());
             if (!invStack.isEmpty()) {
                 var newUpgrade = PocketUpgrades.instance().get(invStack);
 
-                if (newUpgrade != null && newUpgrade != previous) {
+                if (newUpgrade != null && !Objects.equals(newUpgrade, previous)) {
                     // Consume an item from this stack and exit the loop
                     invStack = invStack.copy();
                     invStack.shrink(1);

projects/common/src/main/java/dan200/computercraft/shared/pocket/core/PocketServerComputer.java

@@ -7,6 +7,7 @@ package dan200.computercraft.shared.pocket.core;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.api.pocket.IPocketAccess;
 import dan200.computercraft.api.pocket.IPocketUpgrade;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.core.computer.ComputerSide;
 import dan200.computercraft.shared.common.IColouredItem;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
@@ -109,8 +110,8 @@ public class PocketServerComputer extends ServerComputer implements IPocketAcces
         return upgrade == null ? Collections.emptyMap() : Collections.singletonMap(upgrade.getUpgradeID(), getPeripheral(ComputerSide.BACK));
     }
 
-    public @Nullable IPocketUpgrade getUpgrade() {
+    public @Nullable UpgradeData<IPocketUpgrade> getUpgrade() {
-        return upgrade;
+        return upgrade == null ? null : UpgradeData.of(upgrade, getUpgradeNBTData());
     }
 
     /**
@@ -120,13 +121,11 @@ public class PocketServerComputer extends ServerComputer implements IPocketAcces
      *
      * @param upgrade The new upgrade to set it to, may be {@code null}.
      */
-    public void setUpgrade(@Nullable IPocketUpgrade upgrade) {
+    public void setUpgrade(@Nullable UpgradeData<IPocketUpgrade> upgrade) {
-        if (this.upgrade == upgrade) return;
-
         synchronized (this) {
             PocketComputerItem.setUpgrade(stack, upgrade);
             updateUpgradeNBTData();
-            this.upgrade = upgrade;
+            this.upgrade = upgrade == null ? null : upgrade.upgrade();
             invalidatePeripheral();
         }
     }

projects/common/src/main/java/dan200/computercraft/shared/pocket/items/PocketComputerItem.java

@@ -10,6 +10,7 @@ import dan200.computercraft.api.ComputerCraftAPI;
 import dan200.computercraft.api.filesystem.Mount;
 import dan200.computercraft.api.media.IMedia;
 import dan200.computercraft.api.pocket.IPocketUpgrade;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.core.computer.ComputerSide;
 import dan200.computercraft.impl.PocketUpgrades;
 import dan200.computercraft.shared.ModRegistry;
@@ -23,6 +24,7 @@ import dan200.computercraft.shared.pocket.apis.PocketAPI;
 import dan200.computercraft.shared.pocket.core.PocketServerComputer;
 import dan200.computercraft.shared.pocket.inventory.PocketComputerMenuProvider;
 import dan200.computercraft.shared.util.IDAssigner;
+import dan200.computercraft.shared.util.NBTUtil;
 import net.minecraft.ChatFormatting;
 import net.minecraft.nbt.CompoundTag;
 import net.minecraft.network.chat.Component;
@@ -58,7 +60,7 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
         this.family = family;
     }
 
-    public static ItemStack create(int id, @Nullable String label, int colour, ComputerFamily family, @Nullable IPocketUpgrade upgrade) {
+    public static ItemStack create(int id, @Nullable String label, int colour, ComputerFamily family, @Nullable UpgradeData<IPocketUpgrade> upgrade) {
         return switch (family) {
             case NORMAL -> ModRegistry.Items.POCKET_COMPUTER_NORMAL.get().create(id, label, colour, upgrade);
             case ADVANCED -> ModRegistry.Items.POCKET_COMPUTER_ADVANCED.get().create(id, label, colour, upgrade);
@@ -66,11 +68,14 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
         };
     }
 
-    public ItemStack create(int id, @Nullable String label, int colour, @Nullable IPocketUpgrade upgrade) {
+    public ItemStack create(int id, @Nullable String label, int colour, @Nullable UpgradeData<IPocketUpgrade> upgrade) {
         var result = new ItemStack(this);
         if (id >= 0) result.getOrCreateTag().putInt(NBT_ID, id);
         if (label != null) result.setHoverName(Component.literal(label));
-        if (upgrade != null) result.getOrCreateTag().putString(NBT_UPGRADE, upgrade.getUpgradeID().toString());
+        if (upgrade != null) {
+            result.getOrCreateTag().putString(NBT_UPGRADE, upgrade.upgrade().getUpgradeID().toString());
+            if (!upgrade.data().isEmpty()) result.getOrCreateTag().put(NBT_UPGRADE_INFO, upgrade.data().copy());
+        }
         if (colour != -1) result.getOrCreateTag().putInt(NBT_COLOUR, colour);
         return result;
     }
@@ -207,7 +212,9 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
             setInstanceID(stack, computer.register());
             setSessionID(stack, registry.getSessionID());
 
-            computer.updateValues(entity, stack, getUpgrade(stack));
+            var upgrade = getUpgrade(stack);
+
+            computer.updateValues(entity, stack, upgrade);
             computer.addAPI(new PocketAPI(computer));
 
             // Only turn on when initially creating the computer, rather than each tick.
@@ -244,7 +251,7 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
     public ItemStack withFamily(ItemStack stack, ComputerFamily family) {
         return create(
             getComputerID(stack), getLabel(stack), getColour(stack),
-            family, getUpgrade(stack)
+            family, getUpgradeWithData(stack)
         );
     }
 
@@ -294,20 +301,27 @@ public class PocketComputerItem extends Item implements IComputerItem, IMedia, I
 
     public static @Nullable IPocketUpgrade getUpgrade(ItemStack stack) {
         var compound = stack.getTag();
-        return compound != null && compound.contains(NBT_UPGRADE)
+        if (compound == null || !compound.contains(NBT_UPGRADE)) return null;
-            ? PocketUpgrades.instance().get(compound.getString(NBT_UPGRADE)) : null;
+        return PocketUpgrades.instance().get(compound.getString(NBT_UPGRADE));
     }
 
-    public static void setUpgrade(ItemStack stack, @Nullable IPocketUpgrade upgrade) {
+    public static @Nullable UpgradeData<IPocketUpgrade> getUpgradeWithData(ItemStack stack) {
+        var compound = stack.getTag();
+        if (compound == null || !compound.contains(NBT_UPGRADE)) return null;
+        var upgrade = PocketUpgrades.instance().get(compound.getString(NBT_UPGRADE));
+        return upgrade == null ? null : UpgradeData.of(upgrade, NBTUtil.getCompoundOrEmpty(compound, NBT_UPGRADE_INFO));
+    }
+
+    public static void setUpgrade(ItemStack stack, @Nullable UpgradeData<IPocketUpgrade> upgrade) {
         var compound = stack.getOrCreateTag();
 
         if (upgrade == null) {
             compound.remove(NBT_UPGRADE);
-        } else {
-            compound.putString(NBT_UPGRADE, upgrade.getUpgradeID().toString());
-        }
-
             compound.remove(NBT_UPGRADE_INFO);
+        } else {
+            compound.putString(NBT_UPGRADE, upgrade.upgrade().getUpgradeID().toString());
+            compound.put(NBT_UPGRADE_INFO, upgrade.data().copy());
+        }
     }
 
     public static CompoundTag getUpgradeInfo(ItemStack stack) {

projects/common/src/main/java/dan200/computercraft/shared/pocket/recipes/PocketComputerUpgradeRecipe.java

@@ -5,6 +5,7 @@
 package dan200.computercraft.shared.pocket.recipes;
 
 import dan200.computercraft.api.pocket.IPocketUpgrade;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.impl.PocketUpgrades;
 import dan200.computercraft.shared.ModRegistry;
 import dan200.computercraft.shared.pocket.items.PocketComputerItem;
@@ -62,7 +63,7 @@ public final class PocketComputerUpgradeRecipe extends CustomRecipe {
         if (PocketComputerItem.getUpgrade(computer) != null) return ItemStack.EMPTY;
 
         // Check for upgrades around the item
-        IPocketUpgrade upgrade = null;
+        UpgradeData<IPocketUpgrade> upgrade = null;
         for (var y = 0; y < inventory.getHeight(); y++) {
             for (var x = 0; x < inventory.getWidth(); x++) {
                 var item = inventory.getItem(x + y * inventory.getWidth());

projects/common/src/main/java/dan200/computercraft/shared/turtle/blocks/TurtleBlock.java

@@ -5,7 +5,9 @@
 package dan200.computercraft.shared.turtle.blocks;
 
 import dan200.computercraft.annotations.ForgeOverride;
+import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.api.turtle.TurtleSide;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.shared.computer.blocks.AbstractComputerBlock;
 import dan200.computercraft.shared.computer.blocks.AbstractComputerBlockEntity;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
@@ -128,7 +130,7 @@ public class TurtleBlock extends AbstractComputerBlock<TurtleBlockEntity> implem
             if (stack.getItem() instanceof TurtleItem item) {
                 // Set Upgrades
                 for (var side : TurtleSide.values()) {
-                    turtle.getAccess().setUpgrade(side, item.getUpgrade(stack, side));
+                    turtle.getAccess().setUpgradeWithData(side, item.getUpgradeWithData(stack, side));
                 }
 
                 turtle.getAccess().setFuelLevel(item.getFuelLevel(stack));
@@ -161,11 +163,16 @@ public class TurtleBlock extends AbstractComputerBlock<TurtleBlockEntity> implem
         var access = turtle.getAccess();
         return TurtleItem.create(
             turtle.getComputerID(), turtle.getLabel(), access.getColour(), turtle.getFamily(),
-            access.getUpgrade(TurtleSide.LEFT), access.getUpgrade(TurtleSide.RIGHT),
+            withPersistedData(access.getUpgradeWithData(TurtleSide.LEFT)),
+            withPersistedData(access.getUpgradeWithData(TurtleSide.RIGHT)),
             access.getFuelLevel(), turtle.getOverlay()
         );
     }
 
+    private static @Nullable UpgradeData<ITurtleUpgrade> withPersistedData(@Nullable UpgradeData<ITurtleUpgrade> upgrade) {
+        return upgrade == null ? null : UpgradeData.of(upgrade.upgrade(), upgrade.upgrade().getPersistedData(upgrade.data()));
+    }
+
     @Override
     @Nullable
     public <U extends BlockEntity> BlockEntityTicker<U> getTicker(Level level, BlockState state, BlockEntityType<U> type) {

projects/common/src/main/java/dan200/computercraft/shared/turtle/core/TurtleBrain.java

@@ -13,6 +13,7 @@ import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.api.turtle.TurtleAnimation;
 import dan200.computercraft.api.turtle.TurtleCommand;
 import dan200.computercraft.api.turtle.TurtleSide;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.core.computer.ComputerSide;
 import dan200.computercraft.core.util.Colour;
 import dan200.computercraft.impl.TurtleUpgrades;
@@ -141,17 +142,16 @@ public class TurtleBrain implements TurtleAccessInternal {
         overlay = nbt.contains(NBT_OVERLAY) ? new ResourceLocation(nbt.getString(NBT_OVERLAY)) : null;
 
         // Read upgrades
-        setUpgradeDirect(TurtleSide.LEFT, nbt.contains(NBT_LEFT_UPGRADE) ? TurtleUpgrades.instance().get(nbt.getString(NBT_LEFT_UPGRADE)) : null);
+        setUpgradeDirect(TurtleSide.LEFT, readUpgrade(nbt, NBT_LEFT_UPGRADE, NBT_LEFT_UPGRADE_DATA));
-        setUpgradeDirect(TurtleSide.RIGHT, nbt.contains(NBT_RIGHT_UPGRADE) ? TurtleUpgrades.instance().get(nbt.getString(NBT_RIGHT_UPGRADE)) : null);
+        setUpgradeDirect(TurtleSide.RIGHT, readUpgrade(nbt, NBT_RIGHT_UPGRADE, NBT_RIGHT_UPGRADE_DATA));
+    }
 
-        // NBT
+    private @Nullable UpgradeData<ITurtleUpgrade> readUpgrade(CompoundTag tag, String upgradeKey, String dataKey) {
-        upgradeNBTData.clear();
+        if (!tag.contains(upgradeKey)) return null;
-        if (nbt.contains(NBT_LEFT_UPGRADE_DATA)) {
+        var upgrade = TurtleUpgrades.instance().get(tag.getString(upgradeKey));
-            upgradeNBTData.put(TurtleSide.LEFT, nbt.getCompound(NBT_LEFT_UPGRADE_DATA).copy());
+        if (upgrade == null) return null;
-        }
+
-        if (nbt.contains(NBT_RIGHT_UPGRADE_DATA)) {
+        return UpgradeData.of(upgrade, tag.getCompound(dataKey));
-            upgradeNBTData.put(TurtleSide.RIGHT, nbt.getCompound(NBT_RIGHT_UPGRADE_DATA).copy());
-        }
     }
 
     private void writeCommon(CompoundTag nbt) {
@@ -516,7 +516,7 @@ public class TurtleBrain implements TurtleAccessInternal {
     }
 
     @Override
-    public void setUpgrade(TurtleSide side, @Nullable ITurtleUpgrade upgrade) {
+    public void setUpgradeWithData(TurtleSide side, @Nullable UpgradeData<ITurtleUpgrade> upgrade) {
         if (!setUpgradeDirect(side, upgrade) || owner.getLevel() == null) return;
 
         // This is a separate function to avoid updating the block when reading the NBT. We don't need to do this as
@@ -529,19 +529,18 @@ public class TurtleBrain implements TurtleAccessInternal {
         owner.updateInputsImmediately();
     }
 
-    private boolean setUpgradeDirect(TurtleSide side, @Nullable ITurtleUpgrade upgrade) {
+    private boolean setUpgradeDirect(TurtleSide side, @Nullable UpgradeData<ITurtleUpgrade> upgrade) {
         // Remove old upgrade
-        if (upgrades.containsKey(side)) {
+        var oldUpgrade = upgrades.remove(side);
-            if (upgrades.get(side) == upgrade) return false;
+        if (oldUpgrade == null && upgrade == null) return false;
-            upgrades.remove(side);
-        } else {
-            if (upgrade == null) return false;
-        }
-
-        upgradeNBTData.remove(side);
 
         // Set new upgrade
-        if (upgrade != null) upgrades.put(side, upgrade);
+        if (upgrade == null) {
+            upgradeNBTData.remove(side);
+        } else {
+            upgrades.put(side, upgrade.upgrade());
+            upgradeNBTData.put(side, upgrade.data().copy());
+        }
 
         // Notify clients and create peripherals
         if (owner.getLevel() != null && !owner.getLevel().isClientSide) {

projects/common/src/main/java/dan200/computercraft/shared/turtle/core/TurtleEquipCommand.java

@@ -5,6 +5,7 @@
 package dan200.computercraft.shared.turtle.core;
 
 import dan200.computercraft.api.turtle.*;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.impl.TurtleUpgrades;
 import dan200.computercraft.shared.turtle.TurtleUtil;
 
@@ -18,10 +19,10 @@ public class TurtleEquipCommand implements TurtleCommand {
     @Override
     public TurtleCommandResult execute(ITurtleAccess turtle) {
         // Determine the upgrade to replace
-        var oldUpgrade = turtle.getUpgrade(side);
+        var oldUpgrade = turtle.getUpgradeWithData(side);
 
         // Determine the upgrade to equipLeft
-        ITurtleUpgrade newUpgrade;
+        UpgradeData<ITurtleUpgrade> newUpgrade;
         var selectedStack = turtle.getInventory().getItem(turtle.getSelectedSlot());
         if (!selectedStack.isEmpty()) {
             newUpgrade = TurtleUpgrades.instance().get(selectedStack);
@@ -32,8 +33,8 @@ public class TurtleEquipCommand implements TurtleCommand {
 
         // Do the swapping:
         if (newUpgrade != null) turtle.getInventory().removeItem(turtle.getSelectedSlot(), 1);
-        if (oldUpgrade != null) TurtleUtil.storeItemOrDrop(turtle, oldUpgrade.getCraftingItem().copy());
+        if (oldUpgrade != null) TurtleUtil.storeItemOrDrop(turtle, oldUpgrade.getUpgradeItem());
-        turtle.setUpgrade(side, newUpgrade);
+        turtle.setUpgradeWithData(side, newUpgrade);
 
         // Animate
         if (newUpgrade != null || oldUpgrade != null) {

projects/common/src/main/java/dan200/computercraft/shared/turtle/inventory/UpgradeContainer.java

@@ -7,6 +7,7 @@ package dan200.computercraft.shared.turtle.inventory;
 import dan200.computercraft.api.turtle.ITurtleAccess;
 import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.api.turtle.TurtleSide;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.impl.TurtleUpgrades;
 import net.minecraft.core.NonNullList;
 import net.minecraft.world.Container;
@@ -27,7 +28,7 @@ class UpgradeContainer implements Container {
 
     private final ITurtleAccess turtle;
 
-    private final List<ITurtleUpgrade> lastUpgrade = Arrays.asList(null, null);
+    private final List<UpgradeData<ITurtleUpgrade>> lastUpgrade = Arrays.asList(null, null);
     private final NonNullList<ItemStack> lastStack = NonNullList.withSize(2, ItemStack.EMPTY);
 
     UpgradeContainer(ITurtleAccess turtle) {
@@ -44,22 +45,25 @@ class UpgradeContainer implements Container {
 
     @Override
     public ItemStack getItem(int slot) {
-        var upgrade = turtle.getUpgrade(getSide(slot));
+        var side = getSide(slot);
+        var upgrade = turtle.getUpgrade(side);
+        if (upgrade == null) return ItemStack.EMPTY;
 
         // We don't want to return getCraftingItem directly here, as consumers may mutate the stack (they shouldn't!,
         // but if they do it's a pain to track down). To avoid recreating the stack each tick, we maintain a simple
-        // cache.
+        // cache. We use an inlined getUpgradeData here to avoid the additional defensive copy.
-        if (upgrade == lastUpgrade.get(slot)) return lastStack.get(slot);
+        var upgradeData = UpgradeData.of(upgrade, turtle.getUpgradeNBTData(side));
+        if (upgradeData.equals(lastUpgrade.get(slot))) return lastStack.get(slot);
 
-        var stack = upgrade == null ? ItemStack.EMPTY : upgrade.getCraftingItem().copy();
+        var stack = upgradeData.getUpgradeItem();
-        lastUpgrade.set(slot, upgrade);
+        lastUpgrade.set(slot, upgradeData.copy());
         lastStack.set(slot, stack);
         return stack;
     }
 
     @Override
     public void setItem(int slot, ItemStack itemStack) {
-        turtle.setUpgrade(getSide(slot), TurtleUpgrades.instance().get(itemStack));
+        turtle.setUpgradeWithData(getSide(slot), TurtleUpgrades.instance().get(itemStack));
     }
 
     @Override

projects/common/src/main/java/dan200/computercraft/shared/turtle/items/TurtleItem.java

@@ -8,12 +8,14 @@ import dan200.computercraft.annotations.ForgeOverride;
 import dan200.computercraft.api.ComputerCraftAPI;
 import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.api.turtle.TurtleSide;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.impl.TurtleUpgrades;
 import dan200.computercraft.shared.ModRegistry;
 import dan200.computercraft.shared.common.IColouredItem;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
 import dan200.computercraft.shared.computer.items.AbstractComputerItem;
 import dan200.computercraft.shared.turtle.blocks.TurtleBlock;
+import dan200.computercraft.shared.util.NBTUtil;
 import net.minecraft.core.cauldron.CauldronInteraction;
 import net.minecraft.network.chat.Component;
 import net.minecraft.resources.ResourceLocation;
@@ -32,7 +34,7 @@ public class TurtleItem extends AbstractComputerItem implements IColouredItem {
 
     public static ItemStack create(
         int id, @Nullable String label, int colour, ComputerFamily family,
-        @Nullable ITurtleUpgrade leftUpgrade, @Nullable ITurtleUpgrade rightUpgrade,
+        @Nullable UpgradeData<ITurtleUpgrade> leftUpgrade, @Nullable UpgradeData<ITurtleUpgrade> rightUpgrade,
         int fuelLevel, @Nullable ResourceLocation overlay
     ) {
         return switch (family) {
@@ -46,7 +48,7 @@ public class TurtleItem extends AbstractComputerItem implements IColouredItem {
 
     public ItemStack create(
         int id, @Nullable String label, int colour,
-        @Nullable ITurtleUpgrade leftUpgrade, @Nullable ITurtleUpgrade rightUpgrade,
+        @Nullable UpgradeData<ITurtleUpgrade> leftUpgrade, @Nullable UpgradeData<ITurtleUpgrade> rightUpgrade,
         int fuelLevel, @Nullable ResourceLocation overlay
     ) {
         // Build the stack
@@ -58,11 +60,15 @@ public class TurtleItem extends AbstractComputerItem implements IColouredItem {
         if (overlay != null) stack.getOrCreateTag().putString(NBT_OVERLAY, overlay.toString());
 
         if (leftUpgrade != null) {
-            stack.getOrCreateTag().putString(NBT_LEFT_UPGRADE, leftUpgrade.getUpgradeID().toString());
+            var tag = stack.getOrCreateTag();
+            tag.putString(NBT_LEFT_UPGRADE, leftUpgrade.upgrade().getUpgradeID().toString());
+            if (!leftUpgrade.data().isEmpty()) tag.put(NBT_LEFT_UPGRADE_DATA, leftUpgrade.data().copy());
         }
 
         if (rightUpgrade != null) {
-            stack.getOrCreateTag().putString(NBT_RIGHT_UPGRADE, rightUpgrade.getUpgradeID().toString());
+            var tag = stack.getOrCreateTag();
+            tag.putString(NBT_RIGHT_UPGRADE, rightUpgrade.upgrade().getUpgradeID().toString());
+            if (!rightUpgrade.data().isEmpty()) tag.put(NBT_RIGHT_UPGRADE_DATA, rightUpgrade.data().copy());
         }
 
         return stack;
@@ -117,7 +123,7 @@ public class TurtleItem extends AbstractComputerItem implements IColouredItem {
         return create(
             getComputerID(stack), getLabel(stack),
             getColour(stack), family,
-            getUpgrade(stack, TurtleSide.LEFT), getUpgrade(stack, TurtleSide.RIGHT),
+            getUpgradeWithData(stack, TurtleSide.LEFT), getUpgradeWithData(stack, TurtleSide.RIGHT),
             getFuelLevel(stack), getOverlay(stack)
         );
     }
@@ -127,7 +133,20 @@ public class TurtleItem extends AbstractComputerItem implements IColouredItem {
         if (tag == null) return null;
 
         var key = side == TurtleSide.LEFT ? NBT_LEFT_UPGRADE : NBT_RIGHT_UPGRADE;
-        return tag.contains(key) ? TurtleUpgrades.instance().get(tag.getString(key)) : null;
+        if (!tag.contains(key)) return null;
+        return TurtleUpgrades.instance().get(tag.getString(key));
+    }
+
+    public @Nullable UpgradeData<ITurtleUpgrade> getUpgradeWithData(ItemStack stack, TurtleSide side) {
+        var tag = stack.getTag();
+        if (tag == null) return null;
+
+        var key = side == TurtleSide.LEFT ? NBT_LEFT_UPGRADE : NBT_RIGHT_UPGRADE;
+        if (!tag.contains(key)) return null;
+        var upgrade = TurtleUpgrades.instance().get(tag.getString(key));
+        if (upgrade == null) return null;
+        var dataKey = side == TurtleSide.LEFT ? NBT_LEFT_UPGRADE_DATA : NBT_RIGHT_UPGRADE_DATA;
+        return UpgradeData.of(upgrade, NBTUtil.getCompoundOrEmpty(tag, dataKey));
     }
 
     public @Nullable ResourceLocation getOverlay(ItemStack stack) {

projects/common/src/main/java/dan200/computercraft/shared/turtle/recipes/TurtleOverlayRecipe.java

@@ -38,8 +38,8 @@ public class TurtleOverlayRecipe extends ShapelessRecipe {
             turtle.getComputerID(stack),
             turtle.getLabel(stack),
             turtle.getColour(stack),
-            turtle.getUpgrade(stack, TurtleSide.LEFT),
+            turtle.getUpgradeWithData(stack, TurtleSide.LEFT),
-            turtle.getUpgrade(stack, TurtleSide.RIGHT),
+            turtle.getUpgradeWithData(stack, TurtleSide.RIGHT),
             turtle.getFuelLevel(stack),
             overlay
         );

projects/common/src/main/java/dan200/computercraft/shared/turtle/recipes/TurtleUpgradeRecipe.java

@@ -6,6 +6,7 @@ package dan200.computercraft.shared.turtle.recipes;
 
 import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.api.turtle.TurtleSide;
+import dan200.computercraft.api.upgrades.UpgradeData;
 import dan200.computercraft.impl.TurtleUpgrades;
 import dan200.computercraft.shared.ModRegistry;
 import dan200.computercraft.shared.turtle.items.TurtleItem;
@@ -104,9 +105,10 @@ public final class TurtleUpgradeRecipe extends CustomRecipe {
         // At this point we have a turtle + 1 or 2 items
         // Get the turtle we already have
         var itemTurtle = (TurtleItem) turtle.getItem();
-        var upgrades = new ITurtleUpgrade[]{
+        @SuppressWarnings({ "unchecked", "rawtypes" })
-            itemTurtle.getUpgrade(turtle, TurtleSide.LEFT),
+        UpgradeData<ITurtleUpgrade>[] upgrades = new UpgradeData[]{
-            itemTurtle.getUpgrade(turtle, TurtleSide.RIGHT),
+            itemTurtle.getUpgradeWithData(turtle, TurtleSide.LEFT),
+            itemTurtle.getUpgradeWithData(turtle, TurtleSide.RIGHT),
         };
 
         // Get the upgrades for the new items

projects/common/src/main/java/dan200/computercraft/shared/turtle/upgrades/TurtleModem.java

@@ -9,6 +9,7 @@ import dan200.computercraft.api.turtle.*;
 import dan200.computercraft.shared.peripheral.modem.ModemState;
 import dan200.computercraft.shared.peripheral.modem.wireless.WirelessModemPeripheral;
 import net.minecraft.core.Direction;
+import net.minecraft.nbt.CompoundTag;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.item.ItemStack;
 import net.minecraft.world.level.Level;
@@ -77,4 +78,9 @@ public class TurtleModem extends AbstractTurtleUpgrade {
             }
         }
     }
+
+    @Override
+    public CompoundTag getPersistedData(CompoundTag upgradeData) {
+        return new CompoundTag();
+    }
 }

projects/common/src/main/java/dan200/computercraft/shared/util/NBTUtil.java

@@ -7,6 +7,7 @@ package dan200.computercraft.shared.util;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.io.BaseEncoding;
 import dan200.computercraft.core.util.Nullability;
+import dan200.computercraft.shared.platform.PlatformHelper;
 import net.minecraft.nbt.*;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -19,6 +20,7 @@ import java.io.OutputStream;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -27,9 +29,42 @@ public final class NBTUtil {
     @VisibleForTesting
     static final BaseEncoding ENCODING = BaseEncoding.base16().lowerCase();
 
+    private static final CompoundTag EMPTY_TAG;
+
+    static {
+        // If in a development environment, create a magic immutable compound tag.
+        // We avoid doing this in prod, as I fear it might mess up the JIT inlining things.
+        if (PlatformHelper.get().isDevelopmentEnvironment()) {
+            try {
+                var ctor = CompoundTag.class.getDeclaredConstructor(Map.class);
+                ctor.setAccessible(true);
+                EMPTY_TAG = ctor.newInstance(Collections.emptyMap());
+            } catch (ReflectiveOperationException e) {
+                throw new RuntimeException(e);
+            }
+        } else {
+            EMPTY_TAG = new CompoundTag();
+        }
+    }
+
     private NBTUtil() {
     }
 
+    /**
+     * Get a singleton empty {@link CompoundTag}. This tag should never be modified.
+     *
+     * @return The empty compound tag.
+     */
+    public static CompoundTag emptyTag() {
+        if (EMPTY_TAG.size() != 0) LOG.error("The empty tag has been modified.");
+        return EMPTY_TAG;
+    }
+
+    public static CompoundTag getCompoundOrEmpty(CompoundTag tag, String key) {
+        var childTag = tag.get(key);
+        return childTag != null && childTag.getId() == Tag.TAG_COMPOUND ? (CompoundTag) childTag : emptyTag();
+    }
+
     private static @Nullable Tag toNBTTag(@Nullable Object object) {
         if (object == null) return null;
         if (object instanceof Boolean) return ByteTag.valueOf((byte) ((boolean) (Boolean) object ? 1 : 0));

projects/common/src/test/java/dan200/computercraft/TestPlatformHelper.java

@@ -58,6 +58,11 @@ import java.util.function.Predicate;
 
 @AutoService({ PlatformHelper.class, dan200.computercraft.impl.PlatformHelper.class, ComputerCraftAPIService.class })
 public class TestPlatformHelper extends AbstractComputerCraftAPI implements PlatformHelper {
+    @Override
+    public boolean isDevelopmentEnvironment() {
+        return true;
+    }
+
     @Override
     public ConfigFile.Builder createConfigBuilder() {
         throw new UnsupportedOperationException("Cannot create config file inside tests");

projects/fabric/src/main/java/dan200/computercraft/shared/platform/PlatformHelperImpl.java

@@ -33,6 +33,7 @@ import net.fabricmc.fabric.api.screenhandler.v1.ExtendedScreenHandlerType;
 import net.fabricmc.fabric.api.tag.convention.v1.ConventionalItemTags;
 import net.fabricmc.fabric.api.transfer.v1.item.InventoryStorage;
 import net.fabricmc.fabric.api.transfer.v1.item.ItemStorage;
+import net.fabricmc.loader.api.FabricLoader;
 import net.minecraft.commands.synchronization.ArgumentTypeInfo;
 import net.minecraft.core.BlockPos;
 import net.minecraft.core.Direction;
@@ -81,6 +82,11 @@ import java.util.function.*;
 
 @AutoService(dan200.computercraft.impl.PlatformHelper.class)
 public class PlatformHelperImpl implements PlatformHelper {
+    @Override
+    public boolean isDevelopmentEnvironment() {
+        return FabricLoader.getInstance().isDevelopmentEnvironment();
+    }
+
     @Override
     public ConfigFile.Builder createConfigBuilder() {
         return new FabricConfigFile.Builder();

projects/forge/src/main/java/dan200/computercraft/shared/platform/PlatformHelperImpl.java

@@ -62,6 +62,7 @@ import net.minecraftforge.common.util.NonNullConsumer;
 import net.minecraftforge.event.ForgeEventFactory;
 import net.minecraftforge.eventbus.api.Event;
 import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
+import net.minecraftforge.fml.loading.FMLLoader;
 import net.minecraftforge.items.wrapper.InvWrapper;
 import net.minecraftforge.items.wrapper.SidedInvWrapper;
 import net.minecraftforge.network.NetworkHooks;
@@ -76,6 +77,11 @@ import java.util.function.*;
 
 @AutoService(dan200.computercraft.impl.PlatformHelper.class)
 public class PlatformHelperImpl implements PlatformHelper {
+    @Override
+    public boolean isDevelopmentEnvironment() {
+        return !FMLLoader.isProduction();
+    }
+
     @Override
     public ConfigFile.Builder createConfigBuilder() {
         return new ForgeConfigFile.Builder();