Add Java-based core mods

Mods must ship a separate Jar-file (for example via jar-in-jar) and mark it as FMLModType: LIBRARY to make it load above the GAME layer. They then must provide an implementation of ICoreMod via the Java ServiceLoader to contribute their transformers.

loader/src/main/java/net/neoforged/fml/loading/FMLLoader.java

@@ -23,7 +23,6 @@
 import net.neoforged.accesstransformer.api.AccessTransformerEngine;
 import net.neoforged.accesstransformer.ml.AccessTransformerService;
 import net.neoforged.api.distmarker.Dist;
-import net.neoforged.coremod.CoreModScriptingEngine;
 import net.neoforged.fml.common.asm.RuntimeDistCleaner;
 import net.neoforged.fml.loading.mixin.DeferredMixinConfigRegistration;
 import net.neoforged.fml.loading.moddiscovery.BackgroundScanHandler;
@@ -38,7 +37,6 @@ public class FMLLoader {
  private static final Logger LOGGER = LogUtils.getLogger();
  private static AccessTransformerEngine accessTransformer;
  private static ModDiscoverer modDiscoverer;
- private static CoreModScriptingEngine coreModEngine;
  private static LanguageLoadingProvider languageLoadingProvider;
  private static Dist dist;
  private static LoadingModList loadingModList;
@@ -89,9 +87,6 @@ static void onInitialLoad(IEnvironment environment, Set<String> otherServices) t
  });
  LOGGER.debug(LogMarkers.CORE, "Found Runtime Dist Cleaner");
 
- coreModEngine = new CoreModScriptingEngine();
- LOGGER.debug(LogMarkers.CORE, "FML found CoreMods version : {}", coreModEngine.getClass().getPackage().getImplementationVersion());
-
  LOGGER.debug(LogMarkers.CORE, "Found ForgeSPI package implementation version {}", Environment.class.getPackage().getImplementationVersion());
  LOGGER.debug(LogMarkers.CORE, "Found ForgeSPI package specification {}", Environment.class.getPackage().getSpecificationVersion());
  if (Integer.parseInt(Environment.class.getPackage().getSpecificationVersion()) < 2) {
@@ -156,10 +151,6 @@ public static List<ITransformationService.Resource> completeScan(IModuleLayerMan
  return List.of(modValidator.getModResources());
  }
 
- static CoreModScriptingEngine getCoreModEngine() {
- return coreModEngine;
- }
-
  public static LanguageLoadingProvider getLanguageLoadingProvider() {
  return languageLoadingProvider;
  }

loader/src/main/java/net/neoforged/fml/loading/FMLServiceProvider.java

@@ -8,22 +8,28 @@
 import static net.neoforged.fml.loading.LogMarkers.CORE;
 
 import com.mojang.logging.LogUtils;
+import cpw.mods.modlauncher.Launcher;
 import cpw.mods.modlauncher.api.IEnvironment;
 import cpw.mods.modlauncher.api.IModuleLayerManager;
 import cpw.mods.modlauncher.api.ITransformationService;
 import cpw.mods.modlauncher.api.ITransformer;
 import cpw.mods.modlauncher.api.IncompatibleEnvironmentException;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.ServiceLoader;
 import java.util.Set;
 import java.util.function.BiFunction;
 import joptsimple.ArgumentAcceptingOptionSpec;
 import joptsimple.OptionSpecBuilder;
+import net.neoforged.coremod.CoreModScriptingEngine;
 import net.neoforged.fml.loading.moddiscovery.ModFile;
 import net.neoforged.neoforgespi.Environment;
+import net.neoforged.neoforgespi.coremod.ICoreMod;
 import org.slf4j.Logger;
 
 public class FMLServiceProvider implements ITransformationService {
@@ -129,6 +135,62 @@ public void argumentValues(OptionResult option) {
  @Override
  public List<? extends ITransformer<?>> transformers() {
  LOGGER.debug(CORE, "Loading coremod transformers");
- return FMLLoader.getCoreModEngine().initializeCoreMods();
+
+ var result = new ArrayList<ITransformer<?>>();
+ addCoreModScripts(result);
+
+ // Find all Java core mods
+ var pluginLayer = Launcher.INSTANCE.findLayerManager()
+ .flatMap(m -> m.getLayer(IModuleLayerManager.Layer.PLUGIN))
+ .orElseThrow();
+ for (var coreMod : ServiceLoader.load(pluginLayer, ICoreMod.class)) {
+ for (var transformer : coreMod.getTransformers()) {
+ if (transformer == null) {
+ throw new IllegalStateException("Core mod " + coreMod + " is trying to add null transformer");
+ }
+ LOGGER.debug(CORE, "Adding {} transformer from core-mod {}", transformer.targets(), coreMod);
+ result.add(transformer);
+ }
+ }
+
+ return result;
+ }
+
+ /**
+ * Enumerate script-based coremods.
+ */
+ private void addCoreModScripts(List<ITransformer<?>> transformers) {
+ var modFiles = LoadingModList.get().getModFiles();
+
+ var modsThatNeedCoreModScripting = new HashSet<>();
+ for (var modFile : modFiles) {
+ if (!modFile.getFile().getCoreMods().isEmpty()) {
+ modsThatNeedCoreModScripting.add(modFile.getFile().getFileName());
+ }
+ }
+
+ if (modsThatNeedCoreModScripting.isEmpty()) {
+ // Don't even bother starting the scripting engine if no mod contains scripting core mods
+ return;
+ }
+
+ CoreModScriptingEngine engine;
+ try {
+ engine = new CoreModScriptingEngine();
+ } catch (NoClassDefFoundError e) {
+ LOGGER.debug(LogMarkers.CORE, "No core mod script engine is installed");
+
+ // Fail for all mods that require a coremod scripting engine to be present
+ throw new IllegalStateException("Could not find a coremod scripting engine, but the following mods require it: " + modsThatNeedCoreModScripting);
+ }
+
+ LOGGER.debug(LogMarkers.CORE, "Loading script-based core mods");
+ for (var modFile : modFiles) {
+ for (var coreMod : modFile.getFile().getCoreMods()) {
+ engine.loadCoreMod(coreMod);
+ }
+ }
+
+ transformers.addAll(engine.initializeCoreMods());
  }
 }

loader/src/main/java/net/neoforged/fml/loading/LoadingModList.java

@@ -66,14 +66,6 @@ public static LoadingModList get() {
  return INSTANCE;
  }
 
- public void addCoreMods() {
- modFiles.stream()
- .map(ModFileInfo::getFile)
- .map(ModFile::getCoreMods)
- .flatMap(List::stream)
- .forEach(FMLLoader.getCoreModEngine()::loadCoreMod);
- }
-
  public void addMixinConfigs() {
  modFiles.stream()
  .map(ModFileInfo::getFile)

loader/src/main/java/net/neoforged/fml/loading/moddiscovery/ModValidator.java

@@ -101,7 +101,6 @@ public BackgroundScanHandler stage2Validation() {
  allErrors.addAll(this.discoveryErrorData);
 
  loadingModList = ModSorter.sort(candidateMods, allErrors);
- loadingModList.addCoreMods();
  loadingModList.addAccessTransformers();
  loadingModList.addMixinConfigs();
  loadingModList.setBrokenFiles(brokenFiles);

spi/src/main/java/net/neoforged/neoforgespi/coremod/ICoreMod.java

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.neoforgespi.coremod;
+
+import cpw.mods.modlauncher.api.ITransformer;
+
+/**
+ * Provide using the Java {@link java.util.ServiceLoader} mechanism.
+ */
+public interface ICoreMod {
+ Iterable<? extends ITransformer<?>> getTransformers();
+}