Port to Kotlin

build.gradle

@@ -2,6 +2,7 @@ plugins {
     id 'java-library'
     id 'maven-publish'
     id 'net.neoforged.moddev' version '1.0.17'
+    id "org.jetbrains.kotlin.jvm" version ("2.0.10")
 }
 
 tasks.named('wrapper', Wrapper).configure {
@@ -18,6 +19,10 @@ group = mod_group_id
 
 repositories {
     mavenLocal()
+    maven {
+        name = "Kotlin for Forge"
+        setUrl("https://thedarkcolour.github.io/KotlinForForge/")
+    }
 }
 
 base {
@@ -112,6 +117,9 @@ configurations {
 }
 
 dependencies {
+    // Since Kotlin is its own JVM language with its own standard library, a custom language loader needs to be used, i.e. KFF
+    implementation("thedarkcolour:kotlinforforge-neoforge:$kff_version")
+
     // Example optional mod dependency with JEI
     // The JEI API is declared for compile time use, while the full JEI artifact is used at runtime
     // compileOnly "mezz.jei:jei-${mc_version}-common-api:${jei_version}"
@@ -143,6 +151,8 @@ var generateModMetadata = tasks.register("generateModMetadata", ProcessResources
             minecraft_version_range: minecraft_version_range,
             neo_version            : neo_version,
             neo_version_range      : neo_version_range,
+            kff_version            : kff_version,
+            kff_version_range      : kff_version_range,
             loader_version_range   : loader_version_range,
             mod_id                 : mod_id,
             mod_name               : mod_name,

gradle.properties

@@ -24,6 +24,10 @@ neo_version_range=[21.0.0-beta,)
 # The loader version range can only use the major version of FML as bounds
 loader_version_range=[4,)
 
+# KFF
+kff_version=5.3.0
+kff_version_range=[5.3,)
+
 ## Mod Properties
 
 # The unique mod identifier for the mod. Must be lowercase in English locale. Must fit the regex [a-z][a-z0-9_]{1,63}

src/main/java/com/example/examplemod/mixin/ExampleServerMixin.java

@@ -0,0 +1,36 @@
+package com.example.examplemod.mixin;
+
+import com.example.examplemod.ExampleMod;
+import com.mojang.logging.LogUtils;
+import net.minecraft.commands.CommandSource;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.ServerInfo;
+import net.minecraft.server.TickTask;
+import net.minecraft.util.thread.ReentrantBlockableEventLoop;
+import net.minecraft.world.level.chunk.storage.ChunkIOErrorReporter;
+import org.slf4j.Logger;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+// Example Mixin to demonstrate that Mixins should be written in Java.
+// It is _technically_ possible to write them in Kotlin but only if you understand
+// how the Kotlin compiler works internally and what bytecode it produces and are fully
+// aware of that at all times. The general advice is: JUST USE JAVA FOR MIXINS
+
+// Marked as abstract so all the extends and implements clauses don't need to be "followed".
+// Those clauses are added to get easy access to things without needing to @Shadow them.
+@Mixin(MinecraftServer.class)
+public abstract class ExampleServerMixin extends ReentrantBlockableEventLoop<TickTask> implements ServerInfo, ChunkIOErrorReporter, CommandSource, AutoCloseable {
+    // Constructor of a Mixin gets ignored
+    public ExampleServerMixin(String pName) {
+        super(pName);
+    }
+
+    @Inject(method = "loadLevel", at = @At("TAIL"))
+    public void examplemod$loadLevel(CallbackInfo ci) {
+        System.out.println("Example Mixin ran from server startup (modid: " + ExampleMod.MODID + ")");
+    }
+}

src/main/kotlin/com/example/examplemod/Config.kt

@@ -0,0 +1,60 @@
+package com.example.examplemod
+
+import net.minecraft.core.registries.BuiltInRegistries
+import net.minecraft.resources.ResourceLocation
+import net.minecraft.world.item.Item
+import net.neoforged.bus.api.SubscribeEvent
+import net.neoforged.fml.common.EventBusSubscriber
+import net.neoforged.fml.event.config.ModConfigEvent
+import net.neoforged.neoforge.common.ModConfigSpec
+import java.util.stream.Collectors
+
+// An example config class. This is not required, but it's a good idea to have one to keep your config organized.
+// Demonstrates how to use Neo's config APIs
+@EventBusSubscriber(modid = ExampleMod.MODID, bus = EventBusSubscriber.Bus.MOD)
+object Config {
+    private val BUILDER: ModConfigSpec.Builder = ModConfigSpec.Builder()
+
+    private val LOG_DIRT_BLOCK: ModConfigSpec.BooleanValue =
+        BUILDER.comment("Whether to log the dirt block on common setup").define("logDirtBlock", true)
+
+    private val MAGIC_NUMBER: ModConfigSpec.IntValue =
+        BUILDER.comment("A magic number").defineInRange("magicNumber", 42, 0, Int.MAX_VALUE)
+
+    val MAGIC_NUMBER_INTRODUCTION: ModConfigSpec.ConfigValue<String> =
+        BUILDER.comment("What you want the introduction message to be for the magic number")
+            .define("magicNumberIntroduction", "The magic number is... ")
+
+    // a list of strings that are treated as resource locations for items
+    private val ITEM_STRINGS: ModConfigSpec.ConfigValue<List<String>> =
+        BUILDER.comment("A list of items to log on common setup.").defineListAllowEmpty(
+            "items",
+            listOf("minecraft:iron_ingot"),
+            ::validateItemName
+        )
+
+    val SPEC: ModConfigSpec = BUILDER.build()
+
+    var logDirtBlock: Boolean = false
+    var magicNumber: Int = 0
+    lateinit var magicNumberIntroduction: String
+    lateinit var items: Set<Item>
+
+    private fun validateItemName(obj: Any): Boolean {
+        return obj is String && BuiltInRegistries.ITEM.containsKey(ResourceLocation.parse(obj))
+    }
+
+    @SubscribeEvent
+    fun onLoad(event: ModConfigEvent) {
+        logDirtBlock = LOG_DIRT_BLOCK.get()
+        magicNumber = MAGIC_NUMBER.get()
+        magicNumberIntroduction = MAGIC_NUMBER_INTRODUCTION.get()
+
+        // convert the list of strings into a set of items
+        items = ITEM_STRINGS.get().stream().map { itemName: String? ->
+            BuiltInRegistries.ITEM[ResourceLocation.parse(
+                itemName
+            )]
+        }.collect(Collectors.toSet())
+    }
+}