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/CoreModScriptLoader.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.fml.loading;
+
+import cpw.mods.modlauncher.api.ITransformer;
+import java.io.IOException;
+import java.io.Reader;
+import java.nio.file.Files;
+import java.util.List;
+import java.util.Objects;
+import net.neoforged.coremod.CoreModScriptingEngine;
+import net.neoforged.coremod.ICoreModScriptSource;
+import net.neoforged.fml.loading.moddiscovery.CoreModFile;
+import net.neoforged.fml.loading.moddiscovery.ModFileInfo;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Uses the coremod scripting engine from https://github.com/neoforged/CoreMods
+ * to load JS-based coremods. Avoids loading any of the classes unless a mod
+ * contains a JS-based coremod.
+ */
+class CoreModScriptLoader {
+ private static final Logger LOGGER = LoggerFactory.getLogger(CoreModScriptLoader.class);
+
+ private CoreModScriptLoader() {}
+
+ /**
+ * Enumerate script-based coremods.
+ */
+ public static List<ITransformer<?>> loadCoreModScripts(List<ModFileInfo> modFileInfos) {
+ CoreModScriptingEngine engine;
+ try {
+ engine = new CoreModScriptingEngine();
+ } catch (NoClassDefFoundError e) {
+ // Fail for all mods that require a coremod scripting engine to be present
+ throw new IllegalStateException("Could not find the coremod script-engine, but the following mods require it: " + modFileInfos, e);
+ }
+
+ LOGGER.debug(LogMarkers.CORE, "Loading coremod scripts");
+ for (var modFile : modFileInfos) {
+ for (var coreMod : modFile.getFile().getCoreMods()) {
+ engine.loadCoreMod(new ScriptSourceAdapter(coreMod));
+ }
+ }
+
+ return engine.initializeCoreMods();
+ }
+
+ private record ScriptSourceAdapter(CoreModFile coreMod) implements ICoreModScriptSource {
+ @Override
+ public Reader readCoreMod() throws IOException {
+ return Files.newBufferedReader(coreMod.path());
+ }
+
+ @Override
+ public String getDebugSource() {
+ return coreMod.path().toString();
+ }
+
+ @Override
+ public Reader getAdditionalFile(final String fileName) throws IOException {
+ return Files.newBufferedReader(coreMod.file().findResource(fileName));
+ }
+
+ @Override
+ public String getOwnerId() {
+ return this.coreMod.file().getModInfos().get(0).getModId();
+ }
+
+ @Override
+ public String toString() {
+ return "{Name: " + coreMod.name() + ", Owner: " + getOwnerId() + " @ " + getDebugSource() + "}";
+ }
+
+ @Override
+ public boolean equals(Object obj) {
+ if (obj == this) return true;
+ if (obj == null || obj.getClass() != this.getClass()) return false;
+ var that = (ScriptSourceAdapter) obj;
+ return Objects.equals(this.coreMod, that.coreMod);
+ }
+ }
+}

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;
@@ -37,7 +36,6 @@ 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;
@@ -88,9 +86,6 @@ 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());
-
  try {
  Class.forName("com.electronwill.nightconfig.core.Config", false, environment.getClass().getClassLoader());
  Class.forName("com.electronwill.nightconfig.toml.TomlFormat", false, environment.getClass().getClassLoader());
@@ -148,10 +143,6 @@ 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 +8,27 @@
 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.Collections;
 import java.util.HashMap;
 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.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 +134,45 @@ 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<>(loadCoreModScripts());
+
+ // 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;
+ }
+
+ private List<ITransformer<?>> loadCoreModScripts() {
+ var filesWithCoreModScripts = LoadingModList.get().getModFiles()
+ .stream()
+ .filter(mf -> !mf.getFile().getCoreMods().isEmpty())
+ .toList();
+
+ if (filesWithCoreModScripts.isEmpty()) {
+ // Don't even bother starting the scripting engine if no mod contains scripting core mods
+ LOGGER.debug(LogMarkers.CORE, "Not loading coremod script-engine since no mod requested it");
+ return Collections.emptyList();
+ }
+
+ LOGGER.info(LogMarkers.CORE, "Loading coremod script-engine for {}", filesWithCoreModScripts);
+ try {
+ return CoreModScriptLoader.loadCoreModScripts(filesWithCoreModScripts);
+ } catch (NoClassDefFoundError e) {
+ var message = "Could not find the coremod script-engine, but the following mods require it: " + filesWithCoreModScripts;
+ ImmediateWindowHandler.crash(message);
+ throw new IllegalStateException(message, e);
+ }
  }
 }

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/CoreModFile.java

@@ -5,45 +5,6 @@
 
 package net.neoforged.fml.loading.moddiscovery;
 
-import java.io.IOException;
-import java.io.Reader;
-import java.nio.file.Files;
 import java.nio.file.Path;
-import net.neoforged.coremod.ICoreModScriptSource;
 
-public class CoreModFile implements ICoreModScriptSource {
- private final Path internalPath;
- private final ModFile file;
- private final String name;
-
- CoreModFile(final String name, final Path path, final ModFile file) {
- this.name = name;
- this.internalPath = path;
- this.file = file;
- }
-
- @Override
- public Reader readCoreMod() throws IOException {
- return Files.newBufferedReader(this.internalPath);
- }
-
- @Override
- public String getDebugSource() {
- return this.internalPath.toString();
- }
-
- @Override
- public Reader getAdditionalFile(final String fileName) throws IOException {
- return Files.newBufferedReader(file.findResource(fileName));
- }
-
- @Override
- public String getOwnerId() {
- return this.file.getModInfos().get(0).getModId();
- }
-
- @Override
- public String toString() {
- return "{Name: " + name + ", Owner: " + getOwnerId() + " @ " + getDebugSource() + "}";
- }
-}
+public record CoreModFile(String name, Path path, ModFile file) {}

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

@@ -105,7 +105,6 @@ public boolean identifyMods() {
  if (this.modFileInfo == null) return this.getType() != Type.MOD;
  LOGGER.debug(LogMarkers.LOADING, "Loading mod file {} with languages {}", this.getFilePath(), this.modFileInfo.requiredLanguageLoaders());
  this.coreMods = ModFileParser.getCoreMods(this);
- this.coreMods.forEach(mi -> LOGGER.debug(LogMarkers.LOADING, "Found coremod {}", mi.getDebugSource()));
  this.mixinConfigs = ModFileParser.getMixinConfigs(this.modFileInfo);
  this.mixinConfigs.forEach(mc -> LOGGER.debug(LogMarkers.LOADING, "Found mixin config {}", mc));
  this.accessTransformers = ModFileParser.getAccessTransformers(this.modFileInfo)

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

@@ -204,4 +204,9 @@ public String versionString() {
  public List<String> usesServices() {
  return usesServices;
  }
+
+ @Override
+ public String toString() {
+ return modFile.toString();
+ }
 }

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);

loader/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();
+}