Handle disabled vanilla registry values correctly

paper-server/patches/sources/net/minecraft/core/registries/BuiltInRegistries.java.patch

@@ -41,6 +41,14 @@
          freeze();
          validate(REGISTRY);
      }
+@@ -338,6 +_,7 @@
+             if (supplier.get() == null) {
+                 LOGGER.error("Unable to bootstrap registry '{}'", resourceLocation);
+             }
++            io.papermc.paper.registry.PaperRegistryAccess.instance().lockReferenceHolders(ResourceKey.createRegistryKey(resourceLocation)); // Paper - lock reference holder creation
+         });
+     }
+ 
 @@ -346,6 +_,7 @@
  
          for (Registry<?> registry : REGISTRY) {

paper-server/src/main/java/io/papermc/paper/registry/PaperRegistryAccess.java

@@ -1,5 +1,6 @@
 package io.papermc.paper.registry;
 
+import com.google.common.base.Preconditions;
 import io.papermc.paper.registry.entry.RegistryEntry;
 import io.papermc.paper.registry.entry.RegistryEntryMeta;
 import io.papermc.paper.registry.legacy.DelayedRegistry;
@@ -13,6 +14,7 @@ import java.util.stream.Collectors;
 import net.minecraft.resources.ResourceKey;
 import org.bukkit.Keyed;
 import org.bukkit.Registry;
+import org.bukkit.craftbukkit.CraftRegistry;
 import org.jetbrains.annotations.VisibleForTesting;
 import org.jspecify.annotations.Nullable;
 
@@ -104,6 +106,21 @@ public class PaperRegistryAccess implements RegistryAccess {
         this.registerRegistry(resourceKey, registry, false);
     }
 
+    public <M> void lockReferenceHolders(final ResourceKey<? extends net.minecraft.core.Registry<M>> resourceKey) {
+        final RegistryEntry<M, Keyed> entry = PaperRegistries.getEntry(resourceKey);
+        if (entry == null || !(entry.meta() instanceof final RegistryEntryMeta.ServerSide<M, Keyed> serverSide) || !serverSide.registryTypeMapper().supportsDirectHolders()) {
+            return;
+        }
+        final CraftRegistry<?, M> registry = (CraftRegistry<?, M>) this.getRegistry(entry.apiKey());
+        Preconditions.checkState(registry.isUnloaded(), "Registry %s is already loaded", resourceKey);
+        try {
+            Class.forName(serverSide.classToPreload().getName()); // this should always trigger the initialization of the class
+        } catch (final ClassNotFoundException e) {
+            throw new IllegalStateException("Failed to load class " + serverSide.classToPreload().getName(), e);
+        }
+        registry.lockReferenceHolders();
+    }
+
     @SuppressWarnings("unchecked") // this method should be called right after any new MappedRegistry instances are created to later be used by the server.
     private <M, B extends Keyed, R extends Registry<B>> void registerRegistry(final ResourceKey<? extends net.minecraft.core.Registry<M>> resourceKey, final net.minecraft.core.Registry<M> registry, final boolean replace) {
         final @Nullable RegistryEntry<M, B> entry = PaperRegistries.getEntry(resourceKey);

paper-server/src/main/java/org/bukkit/craftbukkit/CraftRegistry.java

@@ -3,66 +3,26 @@ package org.bukkit.craftbukkit;
 import com.google.common.base.Preconditions;
 import io.papermc.paper.registry.entry.RegistryEntryMeta;
 import io.papermc.paper.util.Holderable;
+import io.papermc.paper.util.MCUtil;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
+import java.util.Optional;
 import java.util.function.BiFunction;
 import java.util.stream.Stream;
 import net.minecraft.core.Holder;
+import net.minecraft.core.HolderOwner;
 import net.minecraft.core.RegistryAccess;
-import net.minecraft.core.registries.Registries;
 import net.minecraft.resources.ResourceKey;
-import org.bukkit.Art;
-import org.bukkit.Fluid;
-import org.bukkit.GameEvent;
-import org.bukkit.JukeboxSong;
 import org.bukkit.Keyed;
-import org.bukkit.MusicInstrument;
 import org.bukkit.NamespacedKey;
 import org.bukkit.Particle;
 import org.bukkit.Registry;
-import org.bukkit.Sound;
-import org.bukkit.attribute.Attribute;
-import org.bukkit.block.Biome;
-import org.bukkit.block.BlockType;
-import org.bukkit.block.banner.PatternType;
-import org.bukkit.craftbukkit.attribute.CraftAttribute;
-import org.bukkit.craftbukkit.block.CraftBiome;
-import org.bukkit.craftbukkit.block.CraftBlockType;
-import org.bukkit.craftbukkit.block.banner.CraftPatternType;
-import org.bukkit.craftbukkit.damage.CraftDamageType;
-import org.bukkit.craftbukkit.enchantments.CraftEnchantment;
-import org.bukkit.craftbukkit.entity.CraftCat;
-import org.bukkit.craftbukkit.entity.CraftFrog;
-import org.bukkit.craftbukkit.entity.CraftVillager;
-import org.bukkit.craftbukkit.entity.CraftWolf;
-import org.bukkit.craftbukkit.generator.structure.CraftStructure;
-import org.bukkit.craftbukkit.generator.structure.CraftStructureType;
-import org.bukkit.craftbukkit.inventory.CraftItemType;
-import org.bukkit.craftbukkit.inventory.CraftMenuType;
-import org.bukkit.craftbukkit.inventory.trim.CraftTrimMaterial;
-import org.bukkit.craftbukkit.inventory.trim.CraftTrimPattern;
 import org.bukkit.craftbukkit.legacy.FieldRename;
-import org.bukkit.craftbukkit.map.CraftMapCursor;
-import org.bukkit.craftbukkit.potion.CraftPotionEffectType;
 import org.bukkit.craftbukkit.util.ApiVersion;
 import org.bukkit.craftbukkit.util.CraftNamespacedKey;
 import org.bukkit.craftbukkit.util.Handleable;
-import org.bukkit.damage.DamageType;
-import org.bukkit.enchantments.Enchantment;
-import org.bukkit.entity.Cat;
 import org.bukkit.entity.EntityType;
-import org.bukkit.entity.Frog;
-import org.bukkit.entity.Villager;
-import org.bukkit.entity.Wolf;
-import org.bukkit.generator.structure.Structure;
-import org.bukkit.generator.structure.StructureType;
-import org.bukkit.inventory.ItemType;
-import org.bukkit.inventory.MenuType;
-import org.bukkit.inventory.meta.trim.TrimMaterial;
-import org.bukkit.inventory.meta.trim.TrimPattern;
-import org.bukkit.map.MapCursor;
-import org.bukkit.potion.PotionEffectType;
 import org.jetbrains.annotations.NotNull;
 
 public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
@@ -202,7 +162,8 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
     private final net.minecraft.core.Registry<M> minecraftRegistry;
     private final io.papermc.paper.registry.entry.RegistryTypeMapper<M, B> minecraftToBukkit; // Paper - switch to Holder
     private final BiFunction<NamespacedKey, ApiVersion, NamespacedKey> serializationUpdater; // Paper - rename to make it *clear* what it is *only* for
-    private boolean init;
+    private final InvalidHolderOwner invalidHolderOwner = new InvalidHolderOwner();
+    private boolean lockReferenceHolders;
 
     public CraftRegistry(Class<?> bukkitClass, net.minecraft.core.Registry<M> minecraftRegistry, BiFunction<? super NamespacedKey, M, B> minecraftToBukkit, BiFunction<NamespacedKey, ApiVersion, NamespacedKey> serializationUpdater) { // Paper - relax preload class
         // Paper start - switch to Holder
@@ -217,6 +178,16 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
         this.minecraftRegistry = minecraftRegistry;
         this.minecraftToBukkit = minecraftToBukkit;
         this.serializationUpdater = serializationUpdater;
+        this.lockReferenceHolders = !this.minecraftToBukkit.supportsDirectHolders();
+    }
+
+    public boolean isUnloaded() {
+        return this.cache.isEmpty();
+    }
+
+    public void lockReferenceHolders() {
+        Preconditions.checkState(!this.lockReferenceHolders, "Reference holders are already locked");
+        this.lockReferenceHolders = true;
     }
 
     // Paper - inline into CraftRegistry#get(Registry, NamespacedKey, ApiVersion) above
@@ -228,28 +199,19 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
             return cached;
         }
 
-        // Make sure that the bukkit class is loaded before creating an instance.
+        final Optional<Holder.Reference<M>> holderOptional = this.minecraftRegistry.get(CraftNamespacedKey.toMinecraft(namespacedKey));
-        // This ensures that only one instance with a given key is created.
+        final Holder.Reference<M> holder;
-        //
+        if (holderOptional.isPresent()) {
-        // Without this code (when bukkit class is not loaded):
+            holder = holderOptional.get();
-        // Registry#get -> #createBukkit -> (load class -> create default) -> put in cache
+        } else if (!this.lockReferenceHolders && this.minecraftToBukkit.supportsDirectHolders()) { // only works if its Holderable
-        // Result: Registry#get != <bukkitClass>.<field> for possible one registry item
+            // we lock the reference holders after the preload class has been initialized
-        //
+            // this is to support the vanilla mechanic of preventing vanilla registry entries being loaded. We need
-        // With this code (when bukkit class is not loaded):
+            // to create something to fill the API constant fields, so we create a dummy reference holder.
-        // Registry#get -> (load class -> create default) -> Registry#get -> get from cache
+            holder = Holder.Reference.createStandAlone(this.invalidHolderOwner, MCUtil.toResourceKey(this.minecraftRegistry.key(), namespacedKey));
-        // Result: Registry#get == <bukkitClass>.<field>
+        } else {
-        if (!this.init) {
+            holder = null;
-            this.init = true;
-            try {
-                Class.forName(this.bukkitClass.getName());
-            } catch (ClassNotFoundException e) {
-                throw new RuntimeException("Could not load registry class " + this.bukkitClass, e);
-            }
-
-            return this.get(namespacedKey);
         }
-
+        final B bukkit = this.createBukkit(namespacedKey, holder);
-        B bukkit = this.createBukkit(namespacedKey, this.minecraftRegistry.get(CraftNamespacedKey.toMinecraft(namespacedKey)).orElse(null)); // Paper - switch to Holder
         if (bukkit == null) {
             return null;
         }
@@ -320,4 +282,7 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
         return new io.papermc.paper.registry.set.NamedRegistryKeySetImpl<>(key, namedHolderSet);
     }
     // Paper end - RegistrySet API
+
+    final class InvalidHolderOwner implements HolderOwner<M> {
+    }
 }

paper-server/src/main/java/org/bukkit/craftbukkit/enchantments/CraftEnchantment.java

@@ -1,11 +1,11 @@
 package org.bukkit.craftbukkit.enchantments;
 
 import com.google.common.base.Preconditions;
+import io.papermc.paper.util.Holderable;
 import java.util.Locale;
 import net.minecraft.Util;
 import net.minecraft.core.Holder;
 import net.minecraft.core.registries.Registries;
-import net.minecraft.network.chat.contents.TranslatableContents;
 import net.minecraft.tags.EnchantmentTags;
 import org.bukkit.NamespacedKey;
 import org.bukkit.Registry;
@@ -13,13 +13,12 @@ import org.bukkit.craftbukkit.CraftRegistry;
 import org.bukkit.craftbukkit.inventory.CraftItemStack;
 import org.bukkit.craftbukkit.legacy.FieldRename;
 import org.bukkit.craftbukkit.util.ApiVersion;
-import org.bukkit.craftbukkit.util.Handleable;
 import org.bukkit.enchantments.Enchantment;
 import org.bukkit.enchantments.EnchantmentTarget;
 import org.bukkit.enchantments.EnchantmentWrapper;
 import org.bukkit.inventory.ItemStack;
 
-public class CraftEnchantment extends Enchantment implements Handleable<net.minecraft.world.item.enchantment.Enchantment> {
+public class CraftEnchantment extends Enchantment implements Holderable<net.minecraft.world.item.enchantment.Enchantment> {
 
     public static Enchantment minecraftToBukkit(net.minecraft.world.item.enchantment.Enchantment minecraft) {
         return CraftRegistry.minecraftToBukkit(minecraft, Registries.ENCHANTMENT, Registry.ENCHANTMENT);
@@ -56,22 +55,20 @@ public class CraftEnchantment extends Enchantment implements Handleable<net.mine
         return CraftRegistry.get(Registry.ENCHANTMENT, key, ApiVersion.CURRENT);
     }
 
-    private final NamespacedKey key;
     private final Holder<net.minecraft.world.item.enchantment.Enchantment> handle;
 
-    public CraftEnchantment(NamespacedKey key, net.minecraft.world.item.enchantment.Enchantment handle) {
+    public CraftEnchantment(Holder<net.minecraft.world.item.enchantment.Enchantment> holder) {
-        this.key = key;
+        this.handle = holder;
-        this.handle = CraftRegistry.getMinecraftRegistry(Registries.ENCHANTMENT).wrapAsHolder(handle);
     }
 
     @Override
-    public net.minecraft.world.item.enchantment.Enchantment getHandle() {
+    public Holder<net.minecraft.world.item.enchantment.Enchantment> getHolder() {
-        return this.handle.value();
+        return this.handle;
     }
 
     @Override
     public NamespacedKey getKey() {
-        return this.key;
+        return Holderable.super.getKey();
     }
 
     @Override
@@ -251,24 +248,16 @@ public class CraftEnchantment extends Enchantment implements Handleable<net.mine
 
     @Override
     public boolean equals(Object other) {
-        if (this == other) {
+        return Holderable.super.implEquals(other);
-            return true;
-        }
-
-        if (!(other instanceof CraftEnchantment)) {
-            return false;
-        }
-
-        return this.getKey().equals(((Enchantment) other).getKey());
     }
 
     @Override
     public int hashCode() {
-        return this.getKey().hashCode();
+        return Holderable.super.implHashCode();
     }
 
     @Override
     public String toString() {
-        return "CraftEnchantment[" + this.getKey() + "]";
+        return Holderable.super.implToString();
     }
 }