Change EventListener to a sealed class (#29)

src/main/java/net/neoforged/bus/ConsumerEventHandler.java

@@ -14,7 +14,7 @@
 /**
  * Wraps a consumer to be used as an event handler, and overrides {@link #toString()} for better debugging.
  */
-public class ConsumerEventHandler extends EventListener {
+public sealed class ConsumerEventHandler extends EventListener {
     protected final Consumer<Event> consumer;
 
     public ConsumerEventHandler(Consumer<Event> consumer) {
@@ -31,7 +31,7 @@ public String toString() {
         return consumer.toString();
     }
 
-    public static class WithPredicate extends ConsumerEventHandler implements IWrapperListener {
+    public static final class WithPredicate extends ConsumerEventHandler implements IWrapperListener {
         private final Predicate<Event> predicate;
         private final EventListener withoutCheck;
 

src/main/java/net/neoforged/bus/EventListenerFactory.java

@@ -27,7 +27,7 @@
 class EventListenerFactory {
     private static final MethodHandles.Lookup LOOKUP = MethodHandles.lookup();
 
-    private static final String HANDLER_DESC = Type.getInternalName(EventListener.class);
+    private static final String HANDLER_DESC = Type.getInternalName(GeneratedEventListener.class);
 
     private static final String HANDLER_FUNC_DESC = Type.getMethodDescriptor(Type.VOID_TYPE, Type.getType(Event.class));
     private static final String INSTANCE_FUNC_DESC = Type.getMethodDescriptor(Type.VOID_TYPE, Type.getType(Object.class), Type.getType(Event.class));

src/main/java/net/neoforged/bus/GeneratedEventListener.java

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.bus;
+
+import net.neoforged.bus.api.EventListener;
+
+/**
+ * Base class for event listeners generated by {@link EventListenerFactory}.
+ */
+public abstract non-sealed class GeneratedEventListener extends EventListener {
+}

src/main/java/net/neoforged/bus/SubscribeEventListener.java

@@ -27,7 +27,7 @@
 /**
  * Wrapper around an event handler generated for a {@link SubscribeEvent} method.
  */
-class SubscribeEventListener extends EventListener implements IWrapperListener {
+public final class SubscribeEventListener extends EventListener implements IWrapperListener {
     private final EventListener handler;
     private final SubscribeEvent subInfo;
     private final boolean isGeneric;

src/main/java/net/neoforged/bus/api/EventListener.java

@@ -19,11 +19,15 @@
 
 package net.neoforged.bus.api;
 
+import net.neoforged.bus.ConsumerEventHandler;
+import net.neoforged.bus.GeneratedEventListener;
+import net.neoforged.bus.SubscribeEventListener;
 
 /**
  * Event listeners are wrapped with implementations of this class.
  */
-public abstract class EventListener
+public abstract sealed class EventListener
+    permits ConsumerEventHandler, GeneratedEventListener, SubscribeEventListener
 {
     public abstract void invoke(Event event);
 }