Build correctly for 1.21

src/client/java/xyz/twokilohertz/HotbarReplace.java

@@ -0,0 +1,76 @@
+package xyz.twokilohertz;
+
+import net.fabricmc.api.ClientModInitializer;
+import net.minecraft.client.MinecraftClient;
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraft.entity.player.PlayerInventory;
+import net.minecraft.item.Item;
+import net.minecraft.item.ItemPlacementContext;
+import net.minecraft.screen.slot.SlotActionType;
+import org.lwjgl.glfw.GLFW;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+public class HotbarReplace implements ClientModInitializer {
+    public static final Logger LOGGER = LoggerFactory.getLogger("hotbarreplace");
+    private static final MinecraftClient client = MinecraftClient.getInstance();
+    private static final ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
+
+    @Override
+    public void onInitializeClient() {
+        LOGGER.info("HotbarReplace v0.1.2 initialised");
+    }
+
+    public static void tryReplaceSlot(ItemPlacementContext context, Item item) {
+        // Return immediately if player is a spectator
+        PlayerEntity player = context.getPlayer();
+        if (player.isSpectator())
+            return;
+
+        // Creative inventories don't run out of blocks anyway
+        if (player.getAbilities().creativeMode)
+            return;
+
+        // Get reference to player's current inventory
+        PlayerInventory inventory = player.getInventory();
+        if (inventory == null)
+            return;
+
+        // Return if the inventory is empty
+        if (inventory.isEmpty())
+            return;
+
+        // If current screen handler is null, return
+        if (player.currentScreenHandler == null)
+            return;
+
+        // Attempt to find a stack of matching items in the player's inventory
+        for (int i = 0; i < player.currentScreenHandler.slots.size(); i++) {
+            if (player.currentScreenHandler.slots.get(i).getStack().isOf(item)) {
+                // Simulate moving the stack from one slot to another
+                if (client != null) {
+                    client.interactionManager.clickSlot(player.currentScreenHandler.syncId, i, GLFW.GLFW_MOUSE_BUTTON_1,
+                            SlotActionType.PICKUP, player);
+
+                    /*
+                     * Wait 50 milliseconds (on another thread) before attempting to move the new
+                     * stack
+                     * PlayerInventory.MAIN_SIZE added to the selected slot (hotbar slot) is the
+                     * correct slot ID
+                     */
+                    scheduler.schedule(() -> {
+                        client.interactionManager.clickSlot(player.currentScreenHandler.syncId,
+                                inventory.selectedSlot + PlayerInventory.MAIN_SIZE, GLFW.GLFW_MOUSE_BUTTON_1,
+                                SlotActionType.PICKUP, player);
+                    }, 50, TimeUnit.MILLISECONDS);
+                }
+
+                return;
+            }
+        }
+    }
+}

src/client/java/xyz/twokilohertz/mixin/BlockItemMixin.java

@@ -0,0 +1,35 @@
+package xyz.twokilohertz.mixin;
+
+import net.minecraft.item.BlockItem;
+import net.minecraft.item.Item;
+import net.minecraft.item.ItemPlacementContext;
+import net.minecraft.util.ActionResult;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+import xyz.twokilohertz.HotbarReplace;
+
+@Mixin(BlockItem.class)
+public class BlockItemMixin {
+    private Item lastPlacedItem;
+
+    @Inject(at = @At("HEAD"), method = "Lnet/minecraft/item/BlockItem;place(Lnet/minecraft/item/ItemPlacementContext;)Lnet/minecraft/util/ActionResult;")
+    private void BlockItem_place_head(ItemPlacementContext context, CallbackInfoReturnable<ActionResult> info) {
+        lastPlacedItem = context.getStack().getItem();
+    }
+
+    @Inject(at = @At("TAIL"), method = "Lnet/minecraft/item/BlockItem;place(Lnet/minecraft/item/ItemPlacementContext;)Lnet/minecraft/util/ActionResult;")
+    private void mixin_BlockItem_place_tail(ItemPlacementContext context, CallbackInfoReturnable<ActionResult> info) {
+        // Early return if the block place action would fail
+        if (info.getReturnValue() != ActionResult.SUCCESS)
+            return;
+
+        // Check if the stack is not empty, return if so
+        if (context.getStack().getCount() != 0)
+            return;
+
+        // Try to replace the hotbar slot
+        HotbarReplace.tryReplaceSlot(context, lastPlacedItem);
+    }
+}

src/client/resources/fabric.mod.json

@@ -0,0 +1,35 @@
+{
+  "schemaVersion": 1,
+  "id": "hotbarreplace",
+  "version": "${version}",
+  "name": "HotbarReplace",
+  "description": "Replace blocks in your hotbar when you run out with blocks from your inventory",
+  "authors": [
+    "Adam Macdonald"
+  ],
+  "contact": {
+    "homepage": "https://github.com/twokilohertz/HotbarReplace",
+    "sources": "https://github.com/twokilohertz/HotbarReplace",
+    "issues": "https://github.com/twokilohertz/HotbarReplace/issues"
+  },
+  "license": "MIT",
+  "icon": "assets/hotbarreplace/icon.png",
+  "environment": "client",
+  "entrypoints": {
+    "client": [
+      "xyz.twokilohertz.HotbarReplace"
+    ]
+  },
+  "mixins": [
+    {
+      "config": "hotbarreplace.mixins.json",
+      "environment": "client"
+    }
+  ],
+  "depends": {
+    "fabricloader": ">=0.15.11",
+    "minecraft": "~1.21",
+    "java": ">=21",
+    "fabric-api": "*"
+  }
+}

src/client/resources/hotbarreplace.mixins.json

@@ -0,0 +1,12 @@
+{
+  "required": true,
+  "package": "xyz.twokilohertz.mixin",
+  "compatibilityLevel": "JAVA_21",
+  "mixins": [],
+  "client": [
+    "BlockItemMixin"
+  ],
+  "injectors": {
+    "defaultRequire": 1
+  }
+}