Deprecate EventBusMigrationHelper for removal (#10908)

Migrating away from this should be trivial for mod devs. Refer to the PR for details.

src/main/java/net/minecraftforge/common/EventBusMigrationHelper.java

@@ -14,19 +14,21 @@ import java.lang.invoke.MethodHandles;
 import java.lang.invoke.MethodHandles.Lookup;
 import java.util.Collection;
 
-/**
- * A small helper class to aid Forge modders in migrating from EventBus 6 to the new EventBus 7.
- * <p>
- * Refer to the <a href="https://gist.github.com/PaintNinja/ad82c224aecee25efac1ea3e2cf19b91">migration guide</a>
- * mentioned in the <a href="https://files.minecraftforge.net">Forge 1.21.6 changelog</a> or
- * <a href="https://forums.minecraftforge.net/topic/159525-forge-581-minecraft-1218/">1.21.8 announcement</a> on the
- * forums, or ask in <a href="https://discord.minecraftforge.net">the Forge Discord</a> for help with migrating your mod
- * to the new system.
- * </p>
- * <p>
- * You can also check the updated example code in <a href="https://files.minecraftforge.net">the MDK</a> for the MC
- * version you're using.
- */
+/// A small helper class to aid Forge modders in migrating from EventBus 6 to the new EventBus 7.
+///
+/// Refer to the [migration guide](https://gist.github.com/PaintNinja/ad82c224aecee25efac1ea3e2cf19b91)
+/// mentioned in the [Forge 1.21.6 changelog](https://files.minecraftforge.net) or
+/// [1.21.8 announcement](https://forums.minecraftforge.net/topic/159525-forge-581-minecraft-1218/) on the
+/// forums, or ask in [the Forge Discord](https://discord.minecraftforge.net) for help with migrating your mod
+/// to the new system.
+///
+/// You can also check the updated example code in [the MDK](https://files.minecraftforge.net) for the MC
+/// version you're using.
+///
+/// @deprecated This was intended as a temporary solution to help modders migrate to the new event system. It relies on
+///             JDK internals that may break without notice and will be removed in 26.4.
+///             Replace `MinecraftForge.EVENT_BUS.register(...)` with `BusGroup.DEFAULT.register(MethodHandles.lookup(), ...)`.
+@Deprecated(forRemoval = true, since = "26.4")
 public final class EventBusMigrationHelper {
     public static final EventBusMigrationHelper INSTANCE = new EventBusMigrationHelper(BusGroup.DEFAULT);
 

src/main/java/net/minecraftforge/common/MinecraftForge.java

@@ -39,7 +39,12 @@ public class MinecraftForge {
      * <p>Events marked with {@link IModBusEvent} belong on the
      * {@linkplain FMLJavaModLoadingContext#getModBusGroup() mod BusGroup} and not on the
      * {@linkplain BusGroup#DEFAULT default BusGroup}.</p>
+     *
+     * @deprecated This was intended as a temporary solution to help modders migrate to the new event system.
+     *             It relies on JDK internals that may break without notice and will be removed in 26.4.
+     *             Replace `MinecraftForge.EVENT_BUS.register(...)` with `BusGroup.DEFAULT.register(MethodHandles.lookup(), ...)`.
      */
+    @Deprecated(forRemoval = true, since = "26.4")
     public static final EventBusMigrationHelper EVENT_BUS = EventBusMigrationHelper.INSTANCE;
 
     private static final Logger LOGGER = LogManager.getLogger();

src/main/java/net/minecraftforge/common/extensions/IForgeGameTestHelper.java

@@ -5,6 +5,7 @@
 
 package net.minecraftforge.common.extensions;
 
+import java.lang.invoke.MethodHandles;
 import java.util.Arrays;
 import java.util.Objects;
 import java.util.UUID;
@@ -23,6 +24,8 @@ import net.minecraft.world.entity.item.ItemEntity;
 import net.minecraft.world.item.Item;
 import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.phys.AABB;
+import net.minecraftforge.eventbus.api.bus.BusGroup;
+import net.minecraftforge.unsafe.UnsafeHacks;
 import org.jetbrains.annotations.Nullable;
 
 import com.mojang.authlib.GameProfile;
@@ -205,8 +208,21 @@ public interface IForgeGameTestHelper {
      * Registers an event listener that will be unregistered when the test is finished running.
      */
     default void registerEventListener(Object handler) {
-        var keys = MinecraftForge.EVENT_BUS.register(handler);
-        self().addCleanup(_ -> MinecraftForge.EVENT_BUS.unregister(keys));
+        final class JdkInternalLookup {
+            private JdkInternalLookup() {}
+            private static final MethodHandles.Lookup INSTANCE;
+            static {
+                try {
+                    var lookupField = MethodHandles.Lookup.class.getDeclaredField("IMPL_LOOKUP");
+                    UnsafeHacks.setAccessible(lookupField);
+                    INSTANCE = (MethodHandles.Lookup) lookupField.get(null);
+                } catch (NoSuchFieldException | IllegalAccessException e) {
+                    throw new RuntimeException(e);
+                }
+            }
+        }
+        var keys = BusGroup.DEFAULT.register(JdkInternalLookup.INSTANCE, handler);
+        self().addCleanup(_ -> BusGroup.DEFAULT.unregister(keys));
     }
 
     /**