Implement validation in lang loaders (#127)

loader/src/main/java/net/neoforged/fml/ModLoader.java

@@ -11,10 +11,12 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.IdentityHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executor;
@@ -37,6 +39,7 @@
 import net.neoforged.fml.loading.moddiscovery.ModInfo;
 import net.neoforged.fml.loading.progress.StartupNotificationManager;
 import net.neoforged.neoforgespi.language.IModInfo;
+import net.neoforged.neoforgespi.language.IModLanguageLoader;
 import net.neoforged.neoforgespi.language.ModFileScanData;
 import net.neoforged.neoforgespi.locating.ForgeFeature;
 import net.neoforged.neoforgespi.locating.IModFile;
@@ -275,12 +278,20 @@ private static void waitForFuture(String name, Runnable periodicTask, Completabl
     }
 
     private static List<ModContainer> buildMods(final IModFile modFile) {
-        return modFile.getModFileInfo()
+        final Map<IModLanguageLoader, Set<ModContainer>> byLoader = new IdentityHashMap<>();
+        var containers = modFile.getModFileInfo()
                 .getMods()
                 .stream()
-                .map(info -> buildModContainerFromTOML(info, modFile.getScanResult()))
+                .map(info -> {
+                    var container = buildModContainerFromTOML(info, modFile.getScanResult());
+                    var cont = byLoader.computeIfAbsent(info.getLoader(), k -> new HashSet<>());
+                    if (container != null) cont.add(container);
+                    return container;
+                })
                 .filter(Objects::nonNull)
                 .toList();
+        byLoader.forEach((loader, loaded) -> loader.validate(modFile, loaded, ModLoader::addLoadingIssue));
+        return containers;
     }
 
     private static ModContainer buildModContainerFromTOML(final IModInfo modInfo, final ModFileScanData scanData) {

loader/src/main/java/net/neoforged/fml/javafmlmod/FMLJavaModLanguageProvider.java

@@ -6,16 +6,21 @@
 package net.neoforged.fml.javafmlmod;
 
 import java.lang.annotation.ElementType;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
 import net.neoforged.fml.ModContainer;
-import net.neoforged.fml.ModLoadingException;
 import net.neoforged.fml.ModLoadingIssue;
 import net.neoforged.fml.common.Mod;
 import net.neoforged.fml.loading.FMLLoader;
+import net.neoforged.neoforgespi.IIssueReporting;
 import net.neoforged.neoforgespi.language.IModInfo;
 import net.neoforged.neoforgespi.language.IModLanguageLoader;
 import net.neoforged.neoforgespi.language.ModFileScanData;
+import net.neoforged.neoforgespi.locating.IModFile;
 
 public class FMLJavaModLanguageProvider implements IModLanguageLoader {
+    @Override
     public String name() {
         return "javafml";
     }
@@ -24,13 +29,28 @@ public String name() {
     public ModContainer loadMod(IModInfo info, ModFileScanData modFileScanResults, ModuleLayer layer) {
         final var modClasses = modFileScanResults.getAnnotatedBy(Mod.class, ElementType.TYPE)
                 .filter(data -> data.annotationData().get("value").equals(info.getModId()))
+                .filter(ad -> AutomaticEventSubscriber.getSides(ad.annotationData().get("dist")).contains(FMLLoader.getDist()))
+                .map(ad -> ad.clazz().getClassName())
                 .toList();
-        if (modClasses.isEmpty()) {
-            throw new ModLoadingException(ModLoadingIssue.error("fml.modloading.javafml.missing_entrypoint").withAffectedMod(info));
+        return new FMLModContainer(info, modClasses, modFileScanResults, layer);
+    }
+
+    @Override
+    public void validate(IModFile file, Collection<ModContainer> loadedContainers, IIssueReporting reporter) {
+        final Set<String> modIds = new HashSet<>();
+        for (IModInfo modInfo : file.getModInfos()) {
+            if (modInfo.getLoader() == this) {
+                modIds.add(modInfo.getModId());
+            }
         }
-        return new FMLModContainer(info, modClasses
-                .stream().filter(ad -> AutomaticEventSubscriber.getSides(ad.annotationData().get("dist")).contains(FMLLoader.getDist()))
-                .map(ad -> ad.clazz().getClassName())
-                .toList(), modFileScanResults, layer);
+
+        file.getScanResult().getAnnotatedBy(Mod.class, ElementType.TYPE)
+                .filter(data -> !modIds.contains((String) data.annotationData().get("value")))
+                .forEach(data -> {
+                    var modId = data.annotationData().get("value");
+                    var entrypointClass = data.clazz().getClassName();
+                    var issue = ModLoadingIssue.error("fml.modloading.javafml.dangling_entrypoint", modId, entrypointClass, file.getFilePath()).withAffectedModFile(file);
+                    reporter.addIssue(issue);
+                });
     }
 }

loader/src/main/java/net/neoforged/neoforgespi/IIssueReporting.java

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.neoforgespi;
+
+import net.neoforged.fml.ModLoadingIssue;
+
+/**
+ * Interface used to report issues to the game.
+ */
+public interface IIssueReporting {
+    /**
+     * Report an issue to the loader.
+     */
+    void addIssue(ModLoadingIssue issue);
+}

loader/src/main/java/net/neoforged/neoforgespi/language/IModLanguageLoader.java

@@ -16,8 +16,10 @@
 
 package net.neoforged.neoforgespi.language;
 
+import java.util.Collection;
 import net.neoforged.fml.ModContainer;
 import net.neoforged.fml.ModLoadingException;
+import net.neoforged.neoforgespi.IIssueReporting;
 import net.neoforged.neoforgespi.locating.IModFile;
 
 /**
@@ -43,4 +45,13 @@ public interface IModLanguageLoader {
      * @throws ModLoadingException if loading encountered an exception
      */
     ModContainer loadMod(IModInfo info, ModFileScanData modFileScanResults, ModuleLayer layer) throws ModLoadingException;
+
+    /**
+     * Validate mod files using this loader, and report any issues (such as entrpoints without medatata).
+     * 
+     * @param file             the file to validate
+     * @param loadedContainers the containers of mods in the file, that have been created using this loader. This list does not contain errored containers
+     * @param reporter         the interface used to report issues to the game
+     */
+    default void validate(IModFile file, Collection<ModContainer> loadedContainers, IIssueReporting reporter) {}
 }

loader/src/main/java/net/neoforged/neoforgespi/locating/IDiscoveryPipeline.java

@@ -9,7 +9,7 @@
 import java.nio.file.Path;
 import java.util.List;
 import java.util.Optional;
-import net.neoforged.fml.ModLoadingIssue;
+import net.neoforged.neoforgespi.IIssueReporting;
 import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.Nullable;
 
@@ -18,7 +18,7 @@
  * discovery pipeline.
  */
 @ApiStatus.NonExtendable
-public interface IDiscoveryPipeline {
+public interface IDiscoveryPipeline extends IIssueReporting {
     /**
      * Adds a single file or folder to the discovery pipeline,
      * to be further processed by registered {@linkplain IModFileReader readers} into a {@linkplain IModFile mod file}.
@@ -62,11 +62,6 @@ default Optional<IModFile> addPath(Path path, ModFileDiscoveryAttributes attribu
      */
     boolean addModFile(IModFile modFile);
 
-    /**
-     * Add an issue to the pipeline that arose during the discovery of mod files (i.e. broken files).
-     */
-    void addIssue(ModLoadingIssue issue);
-
     /**
      * Use the registered {@linkplain IModFileReader readers} to attempt to create a mod-file from the given jar
      * contents.