Add RegistryAccess for managing Registries

RegistryAccess is independant from CraftServer and
doesn't require one to be created allowing the
org.bukkit.Registry class to be loaded earlier.

== AT ==
public net.minecraft.server.RegistryLayer STATIC_ACCESS

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

@@ -1,7 +1,10 @@
 --- a/net/minecraft/core/registries/BuiltInRegistries.java
 +++ b/net/minecraft/core/registries/BuiltInRegistries.java
-@@ -325,12 +325,18 @@
+@@ -323,14 +323,21 @@
+         ResourceKey<? extends Registry<T>> key, R registry, BuiltInRegistries.RegistryBootstrap<T> initializer
+     ) {
          Bootstrap.checkBootstrapCalled(() -> "registry " + key.location());
++        io.papermc.paper.registry.PaperRegistryAccess.instance().registerRegistry(registry.key(), registry); // Paper - initialize API registry
          ResourceLocation resourceLocation = key.location();
          LOADERS.put(resourceLocation, () -> initializer.run(registry));
 -        WRITABLE_REGISTRY.register((ResourceKey<WritableRegistry<?>>)key, registry, RegistrationInfo.BUILT_IN);

paper-server/patches/sources/net/minecraft/resources/RegistryDataLoader.java.patch

@@ -9,3 +9,11 @@
      private static final RegistrationInfo NETWORK_REGISTRATION_INFO = new RegistrationInfo(Optional.empty(), Lifecycle.experimental());
      private static final Function<Optional<KnownPack>, RegistrationInfo> REGISTRATION_INFO_CACHE = Util.memoize(knownPacks -> {
          Lifecycle lifecycle = knownPacks.map(KnownPack::isVanilla).map(vanilla -> Lifecycle.stable()).orElse(Lifecycle.experimental());
+@@ -349,6 +349,7 @@
+ 
+         RegistryDataLoader.Loader<T> create(Lifecycle lifecycle, Map<ResourceKey<?>, Exception> errors) {
+             WritableRegistry<T> writableRegistry = new MappedRegistry<>(this.key, lifecycle);
++            io.papermc.paper.registry.PaperRegistryAccess.instance().registerRegistry(this.key, writableRegistry); // Paper - initialize API registry
+             return new RegistryDataLoader.Loader<>(this, writableRegistry, errors);
+         }
+ 

paper-server/patches/sources/net/minecraft/server/ReloadableServerRegistries.java.patch

@@ -0,0 +1,10 @@
+--- a/net/minecraft/server/ReloadableServerRegistries.java
++++ b/net/minecraft/server/ReloadableServerRegistries.java
+@@ -64,6 +64,7 @@
+     ) {
+         return CompletableFuture.supplyAsync(() -> {
+             WritableRegistry<T> writableRegistry = new MappedRegistry<>(type.registryKey(), Lifecycle.experimental());
++            io.papermc.paper.registry.PaperRegistryAccess.instance().registerReloadableRegistry(type.registryKey(), writableRegistry); // Paper - register reloadable registry
+             Map<ResourceLocation, T> map = new HashMap<>();
+             SimpleJsonResourceReloadListener.scanDirectory(resourceManager, type.registryKey(), ops, type.codec(), map);
+             map.forEach((id, value) -> writableRegistry.register(ResourceKey.create(type.registryKey(), id), (T)value, DEFAULT_REGISTRATION_INFO));

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

@@ -0,0 +1,153 @@
+package io.papermc.paper.registry;
+
+import com.google.common.base.Preconditions;
+import io.papermc.paper.adventure.PaperAdventure;
+import io.papermc.paper.registry.entry.RegistryEntry;
+import java.util.Collections;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import net.minecraft.core.Registry;
+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.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.CraftArt;
+import org.bukkit.craftbukkit.CraftFluid;
+import org.bukkit.craftbukkit.CraftGameEvent;
+import org.bukkit.craftbukkit.CraftJukeboxSong;
+import org.bukkit.craftbukkit.CraftMusicInstrument;
+import org.bukkit.craftbukkit.CraftSound;
+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.CraftNamespacedKey;
+import org.bukkit.damage.DamageType;
+import org.bukkit.enchantments.Enchantment;
+import org.bukkit.entity.Cat;
+import org.bukkit.entity.Frog;
+import org.bukkit.entity.Villager;
+import org.bukkit.entity.Wolf;
+import org.bukkit.entity.memory.MemoryKey;
+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.jspecify.annotations.Nullable;
+
+import static io.papermc.paper.registry.entry.RegistryEntryBuilder.start;
+
+public final class PaperRegistries {
+
+    static final List<RegistryEntry<?, ?>> REGISTRY_ENTRIES;
+    private static final Map<RegistryKey<?>, RegistryEntry<?, ?>> BY_REGISTRY_KEY;
+    private static final Map<ResourceKey<?>, RegistryEntry<?, ?>> BY_RESOURCE_KEY;
+    static {
+        REGISTRY_ENTRIES = List.of(
+            // built-ins
+            start(Registries.GAME_EVENT, RegistryKey.GAME_EVENT).craft(GameEvent.class, CraftGameEvent::new).build(),
+            start(Registries.STRUCTURE_TYPE, RegistryKey.STRUCTURE_TYPE).craft(StructureType.class, CraftStructureType::new).build(),
+            start(Registries.MOB_EFFECT, RegistryKey.MOB_EFFECT).craft(PotionEffectType.class, CraftPotionEffectType::new).build(),
+            start(Registries.BLOCK, RegistryKey.BLOCK).craft(BlockType.class, CraftBlockType::new).build(),
+            start(Registries.ITEM, RegistryKey.ITEM).craft(ItemType.class, CraftItemType::new).build(),
+            start(Registries.CAT_VARIANT, RegistryKey.CAT_VARIANT).craft(Cat.Type.class, CraftCat.CraftType::new).build(),
+            start(Registries.FROG_VARIANT, RegistryKey.FROG_VARIANT).craft(Frog.Variant.class, CraftFrog.CraftVariant::new).build(),
+            start(Registries.VILLAGER_PROFESSION, RegistryKey.VILLAGER_PROFESSION).craft(Villager.Profession.class, CraftVillager.CraftProfession::new).build(),
+            start(Registries.VILLAGER_TYPE, RegistryKey.VILLAGER_TYPE).craft(Villager.Type.class, CraftVillager.CraftType::new).build(),
+            start(Registries.MAP_DECORATION_TYPE, RegistryKey.MAP_DECORATION_TYPE).craft(MapCursor.Type.class, CraftMapCursor.CraftType::new).build(),
+            start(Registries.MENU, RegistryKey.MENU).craft(MenuType.class, CraftMenuType::new).build(),
+            start(Registries.ATTRIBUTE, RegistryKey.ATTRIBUTE).craft(Attribute.class, CraftAttribute::new).build(),
+            start(Registries.FLUID, RegistryKey.FLUID).craft(Fluid.class, CraftFluid::new).build(),
+            start(Registries.SOUND_EVENT, RegistryKey.SOUND_EVENT).craft(Sound.class, CraftSound::new).build(),
+
+            // data-drivens
+            start(Registries.BIOME, RegistryKey.BIOME).craft(Biome.class, CraftBiome::new).build().delayed(),
+            start(Registries.STRUCTURE, RegistryKey.STRUCTURE).craft(Structure.class, CraftStructure::new).build().delayed(),
+            start(Registries.TRIM_MATERIAL, RegistryKey.TRIM_MATERIAL).craft(TrimMaterial.class, CraftTrimMaterial::new).build().delayed(),
+            start(Registries.TRIM_PATTERN, RegistryKey.TRIM_PATTERN).craft(TrimPattern.class, CraftTrimPattern::new).build().delayed(),
+            start(Registries.DAMAGE_TYPE, RegistryKey.DAMAGE_TYPE).craft(DamageType.class, CraftDamageType::new).build().delayed(),
+            start(Registries.WOLF_VARIANT, RegistryKey.WOLF_VARIANT).craft(Wolf.Variant.class, CraftWolf.CraftVariant::new).build().delayed(),
+            start(Registries.ENCHANTMENT, RegistryKey.ENCHANTMENT).craft(Enchantment.class, CraftEnchantment::new).build().withSerializationUpdater(FieldRename.ENCHANTMENT_RENAME).delayed(),
+            start(Registries.JUKEBOX_SONG, RegistryKey.JUKEBOX_SONG).craft(JukeboxSong.class, CraftJukeboxSong::new).build().delayed(),
+            start(Registries.BANNER_PATTERN, RegistryKey.BANNER_PATTERN).craft(PatternType.class, CraftPatternType::new).build().delayed(),
+            start(Registries.PAINTING_VARIANT, RegistryKey.PAINTING_VARIANT).craft(Art.class, CraftArt::new).build().delayed(),
+            start(Registries.INSTRUMENT, RegistryKey.INSTRUMENT).craft(MusicInstrument.class, CraftMusicInstrument::new).build().delayed(),
+
+            // api-only
+            start(Registries.ENTITY_TYPE, RegistryKey.ENTITY_TYPE).apiOnly(PaperSimpleRegistry::entityType),
+            start(Registries.PARTICLE_TYPE, RegistryKey.PARTICLE_TYPE).apiOnly(PaperSimpleRegistry::particleType),
+            start(Registries.POTION, RegistryKey.POTION).apiOnly(PaperSimpleRegistry::potion),
+            start(Registries.MEMORY_MODULE_TYPE, RegistryKey.MEMORY_MODULE_TYPE).apiOnly(() -> (org.bukkit.Registry<MemoryKey<?>>) (org.bukkit.Registry) org.bukkit.Registry.MEMORY_MODULE_TYPE)
+        );
+        final Map<RegistryKey<?>, RegistryEntry<?, ?>> byRegistryKey = new IdentityHashMap<>(REGISTRY_ENTRIES.size());
+        final Map<ResourceKey<?>, RegistryEntry<?, ?>> byResourceKey = new IdentityHashMap<>(REGISTRY_ENTRIES.size());
+        for (final RegistryEntry<?, ?> entry : REGISTRY_ENTRIES) {
+            Preconditions.checkState(byRegistryKey.put(entry.apiKey(), entry) == null, "Duplicate api registry key: %s", entry.apiKey());
+            Preconditions.checkState(byResourceKey.put(entry.mcKey(), entry) == null, "Duplicate mc registry key: %s", entry.mcKey());
+        }
+        BY_REGISTRY_KEY = Collections.unmodifiableMap(byRegistryKey);
+        BY_RESOURCE_KEY = Collections.unmodifiableMap(byResourceKey);
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <M, T extends Keyed> @Nullable RegistryEntry<M, T> getEntry(final ResourceKey<? extends Registry<M>> resourceKey) {
+        return (RegistryEntry<M, T>) BY_RESOURCE_KEY.get(resourceKey);
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <M, T extends Keyed> @Nullable RegistryEntry<M, T> getEntry(final RegistryKey<? super T> registryKey) {
+        return (RegistryEntry<M, T>) BY_REGISTRY_KEY.get(registryKey);
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <M, T> RegistryKey<T> registryFromNms(final ResourceKey<? extends Registry<M>> registryResourceKey) {
+        return (RegistryKey<T>) Objects.requireNonNull(BY_RESOURCE_KEY.get(registryResourceKey), registryResourceKey + " doesn't have an api RegistryKey").apiKey();
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <M, T> ResourceKey<? extends Registry<M>> registryToNms(final RegistryKey<T> registryKey) {
+        return (ResourceKey<? extends Registry<M>>) Objects.requireNonNull(BY_REGISTRY_KEY.get(registryKey), registryKey + " doesn't have an mc registry ResourceKey").mcKey();
+    }
+
+    public static <M, T> TypedKey<T> fromNms(final ResourceKey<M> resourceKey) {
+        return TypedKey.create(registryFromNms(resourceKey.registryKey()), CraftNamespacedKey.fromMinecraft(resourceKey.location()));
+    }
+
+    @SuppressWarnings({"unchecked", "RedundantCast"})
+    public static <M, T> ResourceKey<M> toNms(final TypedKey<T> typedKey) {
+        return ResourceKey.create((ResourceKey<? extends Registry<M>>) PaperRegistries.registryToNms(typedKey.registryKey()), PaperAdventure.asVanilla(typedKey.key()));
+    }
+
+    private PaperRegistries() {
+    }
+}

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

@@ -0,0 +1,122 @@
+package io.papermc.paper.registry;
+
+import io.papermc.paper.registry.entry.ApiRegistryEntry;
+import io.papermc.paper.registry.entry.RegistryEntry;
+import io.papermc.paper.registry.legacy.DelayedRegistry;
+import io.papermc.paper.registry.legacy.DelayedRegistryEntry;
+import io.papermc.paper.registry.legacy.LegacyRegistryIdentifiers;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.stream.Collectors;
+import net.minecraft.resources.ResourceKey;
+import org.bukkit.Keyed;
+import org.bukkit.Registry;
+import org.jetbrains.annotations.VisibleForTesting;
+import org.jspecify.annotations.Nullable;
+
+public class PaperRegistryAccess implements RegistryAccess {
+
+    // We store the API registries in a memoized supplier, so they can be created on-demand.
+    // These suppliers are added to this map right after the instance of nms.Registry is created before it is loaded.
+    // We want to do registration there, so we have access to the nms.Registry instance in order to wrap it in a CraftRegistry instance.
+    // The memoized Supplier is needed because we *can't* instantiate any CraftRegistry class until **all** the BuiltInRegistries have been added
+    // to this map because that would class-load org.bukkit.Registry which would query this map.
+    private final Map<RegistryKey<?>, RegistryHolder<?>> registries = new ConcurrentHashMap<>(); // is "identity" because RegistryKey overrides equals and hashCode
+
+    public static PaperRegistryAccess instance() {
+        return (PaperRegistryAccess) RegistryAccessHolder.INSTANCE.orElseThrow(() -> new IllegalStateException("No RegistryAccess implementation found"));
+    }
+
+    @VisibleForTesting
+    public Set<RegistryKey<?>> getLoadedServerBackedRegistries() {
+        return this.registries.keySet().stream().filter(registryHolder -> !(PaperRegistries.getEntry(registryHolder) instanceof ApiRegistryEntry)).collect(Collectors.toUnmodifiableSet());
+    }
+
+    @SuppressWarnings("unchecked")
+    @Deprecated(forRemoval = true)
+    @Override
+    public <T extends Keyed> @Nullable Registry<T> getRegistry(final Class<T> type) {
+        final RegistryKey<T> registryKey = byType(type);
+        // If our mapping from Class -> RegistryKey did not contain the passed type it was either a completely invalid type or a registry
+        // that merely exists as a SimpleRegistry in the org.bukkit.Registry type. We cannot return a registry for these, return null
+        // as per method contract in Bukkit#getRegistry.
+        if (registryKey == null) return null;
+
+        final RegistryEntry<?, T> entry = PaperRegistries.getEntry(registryKey);
+        final RegistryHolder<T> registry = (RegistryHolder<T>) this.registries.get(registryKey);
+        if (registry != null) {
+            // if the registry exists, return right away. Since this is the "legacy" method, we return DelayedRegistry
+            // for the non-builtin Registry instances stored as fields in Registry.
+            return registry.get();
+        } else if (entry instanceof DelayedRegistryEntry<?, T>) {
+            // if the registry doesn't exist and the entry is marked as "delayed", we create a registry holder that is empty
+            // which will later be filled with the actual registry. This is so the fields on org.bukkit.Registry can be populated with
+            // registries that don't exist at the time org.bukkit.Registry is statically initialized.
+            final RegistryHolder<T> delayedHolder = new RegistryHolder.Delayed<>();
+            this.registries.put(registryKey, delayedHolder);
+            return delayedHolder.get();
+        } else {
+            // if the registry doesn't exist yet or doesn't have a delayed entry, just return null
+            return null;
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    @Override
+    public <T extends Keyed> Registry<T> getRegistry(final RegistryKey<T> key) {
+        if (PaperRegistries.getEntry(key) == null) {
+            throw new NoSuchElementException(key + " is not a valid registry key");
+        }
+        final @Nullable RegistryHolder<T> registryHolder = (RegistryHolder<T>) this.registries.get(key);
+        if (registryHolder == null) {
+            throw new IllegalArgumentException(key + " points to a registry that is not available yet");
+        }
+        // since this is the getRegistry method that uses the modern RegistryKey, we unwrap any DelayedRegistry instances
+        // that might be returned here. I don't think reference equality is required when doing getRegistry(RegistryKey.WOLF_VARIANT) == Registry.WOLF_VARIANT
+        return possiblyUnwrap(registryHolder.get());
+    }
+
+    private static <T extends Keyed> Registry<T> possiblyUnwrap(final Registry<T> registry) {
+        if (registry instanceof final DelayedRegistry<T, ?> delayedRegistry) { // if not coming from legacy, unwrap the delayed registry
+            return delayedRegistry.delegate();
+        }
+        return registry;
+    }
+
+    public <M> void registerReloadableRegistry(final ResourceKey<? extends net.minecraft.core.Registry<M>> resourceKey, final net.minecraft.core.Registry<M> registry) {
+        this.registerRegistry(resourceKey, registry, true);
+    }
+
+    public <M> void registerRegistry(final ResourceKey<? extends net.minecraft.core.Registry<M>> resourceKey, final net.minecraft.core.Registry<M> registry) {
+        this.registerRegistry(resourceKey, registry, false);
+    }
+
+    @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);
+        if (entry == null) { // skip registries that don't have API entries
+            return;
+        }
+        final @Nullable RegistryHolder<B> registryHolder = (RegistryHolder<B>) this.registries.get(entry.apiKey());
+        if (registryHolder == null || replace) {
+            // if the holder doesn't exist yet, or is marked as "replaceable", put it in the map.
+            this.registries.put(entry.apiKey(), entry.createRegistryHolder(registry));
+        } else {
+            if (registryHolder instanceof RegistryHolder.Delayed<?, ?> && entry instanceof final DelayedRegistryEntry<M, B> delayedEntry) {
+                // if the registry holder is delayed, and the entry is marked as "delayed", then load the holder with the CraftRegistry instance that wraps the actual nms Registry.
+                ((RegistryHolder.Delayed<B, R>) registryHolder).loadFrom(delayedEntry, registry);
+            } else {
+                throw new IllegalArgumentException(resourceKey + " has already been created");
+            }
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    @Deprecated
+    @VisibleForTesting
+    public static <T extends Keyed> @Nullable RegistryKey<T> byType(final Class<T> type) {
+        return (RegistryKey<T>) LegacyRegistryIdentifiers.CLASS_TO_KEY_MAP.get(type);
+    }
+}

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

@@ -0,0 +1,38 @@
+package io.papermc.paper.registry;
+
+import java.util.function.Predicate;
+import net.minecraft.core.registries.BuiltInRegistries;
+import org.bukkit.Keyed;
+import org.bukkit.Particle;
+import org.bukkit.Registry;
+import org.bukkit.entity.EntityType;
+import org.bukkit.potion.PotionType;
+import org.jspecify.annotations.NullMarked;
+
+@NullMarked
+public class PaperSimpleRegistry<T extends Enum<T> & Keyed, M> extends Registry.SimpleRegistry<T> {
+
+    static Registry<EntityType> entityType() {
+        return new PaperSimpleRegistry<>(EntityType.class, entity -> entity != EntityType.UNKNOWN, BuiltInRegistries.ENTITY_TYPE);
+    }
+
+    static Registry<Particle> particleType() {
+        return new PaperSimpleRegistry<>(Particle.class, BuiltInRegistries.PARTICLE_TYPE);
+    }
+
+    static Registry<PotionType> potion() {
+        return new PaperSimpleRegistry<>(PotionType.class, BuiltInRegistries.POTION);
+    }
+
+    private final net.minecraft.core.Registry<M> nmsRegistry;
+
+    protected PaperSimpleRegistry(final Class<T> type, final net.minecraft.core.Registry<M> nmsRegistry) {
+        super(type);
+        this.nmsRegistry = nmsRegistry;
+    }
+
+    public PaperSimpleRegistry(final Class<T> type, final Predicate<T> predicate, final net.minecraft.core.Registry<M> nmsRegistry) {
+        super(type, predicate);
+        this.nmsRegistry = nmsRegistry;
+    }
+}

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

@@ -0,0 +1,44 @@
+package io.papermc.paper.registry;
+
+import com.google.common.base.Suppliers;
+import io.papermc.paper.registry.legacy.DelayedRegistry;
+import io.papermc.paper.registry.legacy.DelayedRegistryEntry;
+import java.util.function.Supplier;
+import org.bukkit.Keyed;
+import org.bukkit.Registry;
+
+public interface RegistryHolder<B extends Keyed> {
+
+    Registry<B> get();
+
+    final class Memoized<B extends Keyed, R extends Registry<B>> implements RegistryHolder<B> {
+
+        private final Supplier<R> memoizedSupplier;
+
+        public Memoized(final Supplier<? extends R> supplier) {
+            this.memoizedSupplier = Suppliers.memoize(supplier::get);
+        }
+
+        public Registry<B> get() {
+            return this.memoizedSupplier.get();
+        }
+    }
+
+    final class Delayed<B extends Keyed, R extends Registry<B>> implements RegistryHolder<B> {
+
+        private final DelayedRegistry<B, R> delayedRegistry = new DelayedRegistry<>();
+
+        @Override
+        public DelayedRegistry<B, R> get() {
+            return this.delayedRegistry;
+        }
+
+        <M> void loadFrom(final DelayedRegistryEntry<M, B> delayedEntry, final net.minecraft.core.Registry<M> registry) {
+            final RegistryHolder<B> delegateHolder = delayedEntry.delegate().createRegistryHolder(registry);
+            if (!(delegateHolder instanceof RegistryHolder.Memoized<B, ?>)) {
+                throw new IllegalArgumentException(delegateHolder + " must be a memoized holder");
+            }
+            this.delayedRegistry.load(((Memoized<B, R>) delegateHolder).memoizedSupplier);
+        }
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/entry/ApiRegistryEntry.java

@@ -0,0 +1,27 @@
+package io.papermc.paper.registry.entry;
+
+import io.papermc.paper.registry.RegistryHolder;
+import io.papermc.paper.registry.RegistryKey;
+import java.util.function.Supplier;
+import net.minecraft.core.Registry;
+import net.minecraft.resources.ResourceKey;
+import org.bukkit.Keyed;
+
+public class ApiRegistryEntry<M, B extends Keyed> extends BaseRegistryEntry<M, B> {
+
+    private final Supplier<org.bukkit.Registry<B>> registrySupplier;
+
+    protected ApiRegistryEntry(
+        final ResourceKey<? extends Registry<M>> mcKey,
+        final RegistryKey<B> apiKey,
+        final Supplier<org.bukkit.Registry<B>> registrySupplier
+    ) {
+        super(mcKey, apiKey);
+        this.registrySupplier = registrySupplier;
+    }
+
+    @Override
+    public RegistryHolder<B> createRegistryHolder(final Registry<M> nmsRegistry) {
+        return new RegistryHolder.Memoized<>(this.registrySupplier);
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/entry/BaseRegistryEntry.java

@@ -0,0 +1,27 @@
+package io.papermc.paper.registry.entry;
+
+import io.papermc.paper.registry.RegistryKey;
+import net.minecraft.core.Registry;
+import net.minecraft.resources.ResourceKey;
+import org.bukkit.Keyed;
+
+public abstract class BaseRegistryEntry<M, B extends Keyed> implements RegistryEntry<M, B> { // TODO remove Keyed
+
+    private final ResourceKey<? extends Registry<M>> minecraftRegistryKey;
+    private final RegistryKey<B> apiRegistryKey;
+
+    protected BaseRegistryEntry(final ResourceKey<? extends Registry<M>> minecraftRegistryKey, final RegistryKey<B> apiRegistryKey) {
+        this.minecraftRegistryKey = minecraftRegistryKey;
+        this.apiRegistryKey = apiRegistryKey;
+    }
+
+    @Override
+    public final ResourceKey<? extends Registry<M>> mcKey() {
+        return this.minecraftRegistryKey;
+    }
+
+    @Override
+    public final RegistryKey<B> apiKey() {
+        return this.apiRegistryKey;
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/entry/CraftRegistryEntry.java

@@ -0,0 +1,51 @@
+package io.papermc.paper.registry.entry;
+
+import com.google.common.base.Preconditions;
+import com.mojang.datafixers.util.Either;
+import io.papermc.paper.registry.RegistryHolder;
+import io.papermc.paper.registry.RegistryKey;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import net.minecraft.core.Holder;
+import net.minecraft.core.Registry;
+import net.minecraft.resources.ResourceKey;
+import org.bukkit.Keyed;
+import org.bukkit.NamespacedKey;
+import org.bukkit.craftbukkit.CraftRegistry;
+import org.bukkit.craftbukkit.util.ApiVersion;
+
+public class CraftRegistryEntry<M, B extends Keyed> extends BaseRegistryEntry<M, B> { // TODO remove Keyed
+
+    private static final BiFunction<NamespacedKey, ApiVersion, NamespacedKey> EMPTY = (namespacedKey, apiVersion) -> namespacedKey;
+
+    protected final Class<?> classToPreload;
+    protected final RegistryTypeMapper<M, B> minecraftToBukkit;
+    protected BiFunction<NamespacedKey, ApiVersion, NamespacedKey> updater = EMPTY;
+
+    protected CraftRegistryEntry(
+        final ResourceKey<? extends Registry<M>> mcKey,
+        final RegistryKey<B> apiKey,
+        final Class<?> classToPreload,
+        final RegistryTypeMapper<M, B> minecraftToBukkit
+    ) {
+        super(mcKey, apiKey);
+        Preconditions.checkArgument(!classToPreload.getPackageName().startsWith("net.minecraft"), classToPreload + " should not be in the net.minecraft package as the class-to-preload");
+        this.classToPreload = classToPreload;
+        this.minecraftToBukkit = minecraftToBukkit;
+    }
+
+    @Override
+    public RegistryEntry<M, B> withSerializationUpdater(final BiFunction<NamespacedKey, ApiVersion, NamespacedKey> updater) {
+        this.updater = updater;
+        return this;
+    }
+
+    @Override
+    public RegistryHolder<B> createRegistryHolder(final Registry<M> nmsRegistry) {
+        return new RegistryHolder.Memoized<>(() -> this.createApiRegistry(nmsRegistry));
+    }
+
+    private CraftRegistry<B, M> createApiRegistry(final Registry<M> nmsRegistry) {
+        return new CraftRegistry<>(this.classToPreload, nmsRegistry, this.minecraftToBukkit, this.updater);
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/entry/RegistryEntry.java

@@ -0,0 +1,29 @@
+package io.papermc.paper.registry.entry;
+
+import io.papermc.paper.registry.RegistryHolder;
+import io.papermc.paper.registry.RegistryKey;
+import io.papermc.paper.registry.legacy.DelayedRegistryEntry;
+import java.util.function.BiFunction;
+import net.minecraft.core.Registry;
+import org.bukkit.Keyed;
+import org.bukkit.NamespacedKey;
+import org.bukkit.craftbukkit.util.ApiVersion;
+
+public interface RegistryEntry<M, B extends Keyed> extends RegistryEntryInfo<M, B> { // TODO remove Keyed
+
+    RegistryHolder<B> createRegistryHolder(Registry<M> nmsRegistry);
+
+    default RegistryEntry<M, B> withSerializationUpdater(final BiFunction<NamespacedKey, ApiVersion, NamespacedKey> updater) {
+        return this;
+    }
+
+    /**
+     * This should only be used if the registry instance needs to exist early due to the need
+     * to populate a field in {@link org.bukkit.Registry}. Data-driven registries shouldn't exist
+     * as fields, but instead be obtained via {@link io.papermc.paper.registry.RegistryAccess#getRegistry(RegistryKey)}
+     */
+    @Deprecated
+    default RegistryEntry<M, B> delayed() {
+        return new DelayedRegistryEntry<>(this);
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/entry/RegistryEntryBuilder.java

@@ -0,0 +1,63 @@
+package io.papermc.paper.registry.entry;
+
+import com.mojang.datafixers.util.Either;
+import io.papermc.paper.registry.RegistryKey;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import net.minecraft.core.Holder;
+import net.minecraft.core.Registry;
+import net.minecraft.resources.ResourceKey;
+import org.bukkit.Keyed;
+import org.bukkit.NamespacedKey;
+
+public class RegistryEntryBuilder<M, A extends Keyed> { // TODO remove Keyed
+
+    public static <M, A extends Keyed> RegistryEntryBuilder<M, A> start( // TODO remove Keyed
+        final ResourceKey<? extends Registry<M>> mcKey,
+        final RegistryKey<A> apiKey
+    ) {
+        return new RegistryEntryBuilder<>(mcKey, apiKey);
+    }
+
+    protected final ResourceKey<? extends Registry<M>> mcKey;
+    protected final RegistryKey<A> apiKey;
+
+    private RegistryEntryBuilder(final ResourceKey<? extends Registry<M>> mcKey, RegistryKey<A> apiKey) {
+        this.mcKey = mcKey;
+        this.apiKey = apiKey;
+    }
+
+    public RegistryEntry<M, A> apiOnly(final Supplier<org.bukkit.Registry<A>> apiRegistrySupplier) {
+        return new ApiRegistryEntry<>(this.mcKey, this.apiKey, apiRegistrySupplier);
+    }
+
+    public CraftStage<M, A> craft(final Class<?> classToPreload, final BiFunction<? super NamespacedKey, M, ? extends A> minecraftToBukkit) {
+        return new CraftStage<>(this.mcKey, this.apiKey, classToPreload, new RegistryTypeMapper<>(minecraftToBukkit));
+    }
+
+    public CraftStage<M, A> craft(final Class<?> classToPreload, final Function<Holder<M>, ? extends A> minecraftToBukkit) {
+        return new CraftStage<>(this.mcKey, this.apiKey, classToPreload, new RegistryTypeMapper<>(minecraftToBukkit));
+    }
+
+    public static final class CraftStage<M, A extends Keyed> extends RegistryEntryBuilder<M, A> { // TODO remove Keyed
+
+        private final Class<?> classToPreload;
+        private final RegistryTypeMapper<M, A> minecraftToBukkit;
+
+        private CraftStage(
+            final ResourceKey<? extends Registry<M>> mcKey,
+            final RegistryKey<A> apiKey,
+            final Class<?> classToPreload,
+            final RegistryTypeMapper<M, A> minecraftToBukkit
+        ) {
+            super(mcKey, apiKey);
+            this.classToPreload = classToPreload;
+            this.minecraftToBukkit = minecraftToBukkit;
+        }
+
+        public RegistryEntry<M, A> build() {
+            return new CraftRegistryEntry<>(this.mcKey, this.apiKey, this.classToPreload, this.minecraftToBukkit);
+        }
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/entry/RegistryEntryInfo.java

@@ -0,0 +1,12 @@
+package io.papermc.paper.registry.entry;
+
+import io.papermc.paper.registry.RegistryKey;
+import net.minecraft.core.Registry;
+import net.minecraft.resources.ResourceKey;
+
+public interface RegistryEntryInfo<M, B> {
+
+    ResourceKey<? extends Registry<M>> mcKey();
+
+    RegistryKey<B> apiKey();
+}

paper-server/src/main/java/io/papermc/paper/registry/entry/RegistryTypeMapper.java

@@ -0,0 +1,37 @@
+package io.papermc.paper.registry.entry;
+
+import com.google.common.base.Preconditions;
+import com.mojang.datafixers.util.Either;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import net.minecraft.core.Holder;
+import org.bukkit.NamespacedKey;
+
+public final class RegistryTypeMapper<M, A> {
+
+    final Either<BiFunction<? super NamespacedKey, M, ? extends A>, Function<Holder<M>, ? extends A>> minecraftToBukkit;
+
+    public RegistryTypeMapper(final BiFunction<? super NamespacedKey, M, ? extends A> byValueCreator) {
+        this.minecraftToBukkit = Either.left(byValueCreator);
+    }
+
+    public RegistryTypeMapper(final Function<Holder<M>, ? extends A> byHolderCreator) {
+        this.minecraftToBukkit = Either.right(byHolderCreator);
+    }
+
+    public A createBukkit(final NamespacedKey key, final Holder<M> minecraft) {
+        return this.minecraftToBukkit.map(
+            minecraftToBukkit -> minecraftToBukkit.apply(key, minecraft.value()),
+            minecraftToBukkit -> minecraftToBukkit.apply(minecraft)
+        );
+    }
+
+    public boolean supportsDirectHolders() {
+        return this.minecraftToBukkit.right().isPresent();
+    }
+
+    public A convertDirectHolder(final Holder<M> directHolder) {
+        Preconditions.checkArgument(this.supportsDirectHolders() && directHolder.kind() == Holder.Kind.DIRECT);
+        return this.minecraftToBukkit.right().orElseThrow().apply(directHolder);
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/entry/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.papermc.paper.registry.entry;
+
+import org.jspecify.annotations.NullMarked;

paper-server/src/main/java/io/papermc/paper/registry/legacy/DelayedRegistry.java

@@ -0,0 +1,57 @@
+package io.papermc.paper.registry.legacy;
+
+import java.util.Iterator;
+import java.util.function.Supplier;
+import java.util.stream.Stream;
+import org.bukkit.Keyed;
+import org.bukkit.NamespacedKey;
+import org.bukkit.Registry;
+import org.jspecify.annotations.Nullable;
+
+/**
+ * This is to support the now-deprecated fields in {@link Registry} for
+ * data-driven registries.
+ */
+public final class DelayedRegistry<T extends Keyed, R extends Registry<T>> implements Registry<T> {
+
+    private @Nullable Supplier<? extends R> delegate;
+
+    public void load(final Supplier<? extends R> registry) {
+        if (this.delegate != null) {
+            throw new IllegalStateException("Registry already loaded!");
+        }
+        this.delegate = registry;
+    }
+
+    public Registry<T> delegate() {
+        if (this.delegate == null) {
+            throw new IllegalStateException("You are trying to access this registry too early!");
+        }
+        return this.delegate.get();
+    }
+
+    @Override
+    public @Nullable T get(final NamespacedKey key) {
+        return this.delegate().get(key);
+    }
+
+    @Override
+    public T getOrThrow(final NamespacedKey key) {
+        return this.delegate().getOrThrow(key);
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return this.delegate().iterator();
+    }
+
+    @Override
+    public Stream<T> stream() {
+        return this.delegate().stream();
+    }
+
+    @Override
+    public @Nullable NamespacedKey getKey(final T value) {
+        return this.delegate().getKey(value);
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/legacy/DelayedRegistryEntry.java

@@ -0,0 +1,26 @@
+package io.papermc.paper.registry.legacy;
+
+import io.papermc.paper.registry.RegistryHolder;
+import io.papermc.paper.registry.RegistryKey;
+import io.papermc.paper.registry.entry.RegistryEntry;
+import net.minecraft.core.Registry;
+import net.minecraft.resources.ResourceKey;
+import org.bukkit.Keyed;
+
+public record DelayedRegistryEntry<M, T extends Keyed>(RegistryEntry<M, T> delegate) implements RegistryEntry<M, T> {
+
+    @Override
+    public ResourceKey<? extends Registry<M>> mcKey() {
+        return this.delegate.mcKey();
+    }
+
+    @Override
+    public RegistryKey<T> apiKey() {
+        return this.delegate.apiKey();
+    }
+
+    @Override
+    public RegistryHolder<T> createRegistryHolder(final Registry<M> nmsRegistry) {
+        return this.delegate.createRegistryHolder(nmsRegistry);
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/legacy/LegacyRegistryIdentifiers.java

@@ -0,0 +1,33 @@
+package io.papermc.paper.registry.legacy;
+
+import com.google.common.collect.ImmutableMap;
+import io.leangen.geantyref.GenericTypeReflector;
+import io.papermc.paper.registry.RegistryKey;
+import java.lang.reflect.Field;
+import java.lang.reflect.ParameterizedType;
+import java.util.Map;
+
+@Deprecated
+public final class LegacyRegistryIdentifiers {
+
+    public static final Map<Class<?>, RegistryKey<?>> CLASS_TO_KEY_MAP;
+
+    static {
+        final ImmutableMap.Builder<Class<?>, RegistryKey<?>> builder = ImmutableMap.builder();
+        try {
+            for (final Field field : RegistryKey.class.getFields()) {
+                if (field.getType() == RegistryKey.class) {
+                    // get the legacy type from the RegistryKey generic parameter on the field
+                    final Class<?> legacyType = GenericTypeReflector.erase(((ParameterizedType) field.getGenericType()).getActualTypeArguments()[0]);
+                    builder.put(legacyType, (RegistryKey<?>) field.get(null));
+                }
+            }
+        } catch (final ReflectiveOperationException ex) {
+            throw new RuntimeException(ex);
+        }
+        CLASS_TO_KEY_MAP = builder.build();
+    }
+
+    private LegacyRegistryIdentifiers() {
+    }
+}

paper-server/src/main/java/io/papermc/paper/registry/legacy/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.papermc.paper.registry.legacy;
+
+import org.jspecify.annotations.NullMarked;

paper-server/src/main/java/io/papermc/paper/registry/package-info.java

@@ -0,0 +1,4 @@
+@NullMarked
+package io.papermc.paper.registry;
+
+import org.jspecify.annotations.NullMarked;

paper-server/src/main/java/io/papermc/paper/util/Holderable.java

@@ -0,0 +1,14 @@
+package io.papermc.paper.util;
+
+import net.minecraft.core.Holder;
+import org.bukkit.craftbukkit.util.Handleable;
+
+public interface Holderable<M> extends Handleable<M> {
+
+    Holder<M> getHolder();
+
+    @Override
+    default M getHandle() {
+        return this.getHolder().value();
+    }
+}

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

@@ -216,11 +216,10 @@ public abstract class CraftParticle<D> implements Keyed {
         }
 
         public CraftParticleRegistry(net.minecraft.core.Registry<net.minecraft.core.particles.ParticleType<?>> minecraftRegistry) {
-            super(CraftParticle.class, minecraftRegistry, null, FieldRename.PARTICLE_TYPE_RENAME);
+            super(CraftParticle.class, minecraftRegistry, CraftParticleRegistry::createBukkit, FieldRename.PARTICLE_TYPE_RENAME); // Paper - switch to Holder
         }
 
-        @Override
+        public static CraftParticle<?> createBukkit(NamespacedKey namespacedKey, net.minecraft.core.particles.ParticleType<?> particle) { // Paper - idk why this is a separate implementation, just wrap the function
-        public CraftParticle<?> createBukkit(NamespacedKey namespacedKey, net.minecraft.core.particles.ParticleType<?> particle) {
             if (particle == null) {
                 return null;
             }

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

@@ -93,14 +93,41 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
         Preconditions.checkArgument(minecraft != null);
 
         net.minecraft.core.Registry<M> registry = CraftRegistry.getMinecraftRegistry(registryKey);
-        B bukkit = bukkitRegistry.get(CraftNamespacedKey.fromMinecraft(registry.getResourceKey(minecraft)
+        // Paper start - support direct Holders
-                .orElseThrow(() -> new IllegalStateException(String.format("Cannot convert '%s' to bukkit representation, since it is not registered.", minecraft))).location()));
+        final java.util.Optional<ResourceKey<M>> resourceKey = registry.getResourceKey(minecraft);
+        if (resourceKey.isEmpty() && bukkitRegistry instanceof final CraftRegistry<?, ?> craftRegistry && craftRegistry.supportsDirectHolders()) {
+            return ((CraftRegistry<B, M>) registry).convertDirectHolder(Holder.direct(minecraft));
+        } else if (resourceKey.isEmpty()) {
+            throw new IllegalStateException(String.format("Cannot convert '%s' to bukkit representation, since it is not registered.", minecraft));
+        }
+        final B bukkit = bukkitRegistry.get(CraftNamespacedKey.fromMinecraft(resourceKey.get().location()));
+        // Paper end - support direct Holders
 
         Preconditions.checkArgument(bukkit != null);
 
         return bukkit;
     }
 
+    // Paper start - support direct Holders
+    public static <B extends Keyed, M> B minecraftHolderToBukkit(final Holder<M> minecraft, final Registry<B> bukkitRegistry) {
+        Preconditions.checkArgument(minecraft != null);
+
+        final B bukkit = switch (minecraft) {
+            case final Holder.Direct<M> direct -> {
+                if (!(bukkitRegistry instanceof final CraftRegistry<?, ?> craftRegistry) || !craftRegistry.supportsDirectHolders()) {
+                    throw new IllegalArgumentException("Cannot convert direct holder to bukkit representation");
+                }
+                yield ((CraftRegistry<B, M>) bukkitRegistry).convertDirectHolder(direct);
+            }
+            case final Holder.Reference<M> reference -> bukkitRegistry.get(io.papermc.paper.util.MCUtil.fromResourceKey(reference.key()));
+            default -> throw new IllegalArgumentException("Unknown holder: " + minecraft);
+        };
+        Preconditions.checkArgument(bukkit != null);
+
+        return bukkit;
+    }
+    // Paper end - support direct Holders
+
     /**
      * Usage note: Only use this method to delegate the conversion methods from the individual Craft classes to here.
      * Do not use it in other parts of CraftBukkit, use the methods in the respective Craft classes instead.
@@ -116,6 +143,11 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
 
     public static <B extends Keyed, M> Holder<M> bukkitToMinecraftHolder(B bukkit, ResourceKey<net.minecraft.core.Registry<M>> registryKey) {
         Preconditions.checkArgument(bukkit != null);
+        // Paper start - support direct Holder
+        if (bukkit instanceof io.papermc.paper.util.Holderable<?>) {
+            return ((io.papermc.paper.util.Holderable<M>) bukkit).getHolder();
+        }
+        // Paper end - support direct Holder
 
         net.minecraft.core.Registry<M> registry = CraftRegistry.getMinecraftRegistry(registryKey);
 
@@ -127,96 +159,12 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
                 + ", this can happen if a plugin creates its own registry entry with out properly registering it.");
     }
 
-    /**
+    // Paper - move to PaperRegistries
-     * Note: Newly added registries should also be added to RegistriesArgumentProvider in the test package
-     *
-     * @param bukkitClass the bukkit class of the registry
-     * @param registryHolder the minecraft registry holder
-     * @return the bukkit registry of the provided class
-     */
-    public static <B extends Keyed> Registry<?> createRegistry(Class<? super B> bukkitClass, RegistryAccess registryHolder) {
-        if (bukkitClass == Art.class) {
-            return new CraftRegistry<>(Art.class, registryHolder.lookupOrThrow(Registries.PAINTING_VARIANT), CraftArt::new, FieldRename.NONE);
-        }
-        if (bukkitClass == Attribute.class) {
-            return new CraftRegistry<>(Attribute.class, registryHolder.lookupOrThrow(Registries.ATTRIBUTE), CraftAttribute::new, FieldRename.ATTRIBUTE_RENAME);
-        }
-        if (bukkitClass == Biome.class) {
-            return new CraftRegistry<>(Biome.class, registryHolder.lookupOrThrow(Registries.BIOME), CraftBiome::new, FieldRename.BIOME_RENAME);
-        }
-        if (bukkitClass == Enchantment.class) {
-            return new CraftRegistry<>(Enchantment.class, registryHolder.lookupOrThrow(Registries.ENCHANTMENT), CraftEnchantment::new, FieldRename.ENCHANTMENT_RENAME);
-        }
-        if (bukkitClass == Fluid.class) {
-            return new CraftRegistry<>(Fluid.class, registryHolder.lookupOrThrow(Registries.FLUID), CraftFluid::new, FieldRename.NONE);
-        }
-        if (bukkitClass == GameEvent.class) {
-            return new CraftRegistry<>(GameEvent.class, registryHolder.lookupOrThrow(Registries.GAME_EVENT), CraftGameEvent::new, FieldRename.NONE);
-        }
-        if (bukkitClass == MusicInstrument.class) {
-            return new CraftRegistry<>(MusicInstrument.class, registryHolder.lookupOrThrow(Registries.INSTRUMENT), CraftMusicInstrument::new, FieldRename.NONE);
-        }
-        if (bukkitClass == MenuType.class) {
-            return new CraftRegistry<>(MenuType.class, registryHolder.lookupOrThrow(Registries.MENU), CraftMenuType::new, FieldRename.NONE);
-        }
-        if (bukkitClass == PotionEffectType.class) {
-            return new CraftRegistry<>(PotionEffectType.class, registryHolder.lookupOrThrow(Registries.MOB_EFFECT), CraftPotionEffectType::new, FieldRename.NONE);
-        }
-        if (bukkitClass == Sound.class) {
-            return new CraftRegistry<>(Sound.class, registryHolder.lookupOrThrow(Registries.SOUND_EVENT), CraftSound::new, FieldRename.NONE);
-        }
-        if (bukkitClass == Structure.class) {
-            return new CraftRegistry<>(Structure.class, registryHolder.lookupOrThrow(Registries.STRUCTURE), CraftStructure::new, FieldRename.NONE);
-        }
-        if (bukkitClass == StructureType.class) {
-            return new CraftRegistry<>(StructureType.class, registryHolder.lookupOrThrow(Registries.STRUCTURE_TYPE), CraftStructureType::new, FieldRename.NONE);
-        }
-        if (bukkitClass == Villager.Type.class) {
-            return new CraftRegistry<>(Villager.Type.class, registryHolder.lookupOrThrow(Registries.VILLAGER_TYPE), CraftVillager.CraftType::new, FieldRename.NONE);
-        }
-        if (bukkitClass == Villager.Profession.class) {
-            return new CraftRegistry<>(Villager.Profession.class, registryHolder.lookupOrThrow(Registries.VILLAGER_PROFESSION), CraftVillager.CraftProfession::new, FieldRename.NONE);
-        }
-        if (bukkitClass == TrimMaterial.class) {
-            return new CraftRegistry<>(TrimMaterial.class, registryHolder.lookupOrThrow(Registries.TRIM_MATERIAL), CraftTrimMaterial::new, FieldRename.NONE);
-        }
-        if (bukkitClass == TrimPattern.class) {
-            return new CraftRegistry<>(TrimPattern.class, registryHolder.lookupOrThrow(Registries.TRIM_PATTERN), CraftTrimPattern::new, FieldRename.NONE);
-        }
-        if (bukkitClass == DamageType.class) {
-            return new CraftRegistry<>(DamageType.class, registryHolder.lookupOrThrow(Registries.DAMAGE_TYPE), CraftDamageType::new, FieldRename.NONE);
-        }
-        if (bukkitClass == JukeboxSong.class) {
-            return new CraftRegistry<>(JukeboxSong.class, registryHolder.lookupOrThrow(Registries.JUKEBOX_SONG), CraftJukeboxSong::new, FieldRename.NONE);
-        }
-        if (bukkitClass == Wolf.Variant.class) {
-            return new CraftRegistry<>(Wolf.Variant.class, registryHolder.lookupOrThrow(Registries.WOLF_VARIANT), CraftWolf.CraftVariant::new, FieldRename.NONE);
-        }
-        if (bukkitClass == BlockType.class) {
-            return new CraftRegistry<>(BlockType.class, registryHolder.lookupOrThrow(Registries.BLOCK), CraftBlockType::new, FieldRename.NONE);
-        }
-        if (bukkitClass == ItemType.class) {
-            return new CraftRegistry<>(ItemType.class, registryHolder.lookupOrThrow(Registries.ITEM), CraftItemType::new, FieldRename.NONE);
-        }
-        if (bukkitClass == Frog.Variant.class) {
-            return new CraftRegistry<>(Frog.Variant.class, registryHolder.lookupOrThrow(Registries.FROG_VARIANT), CraftFrog.CraftVariant::new, FieldRename.NONE);
-        }
-        if (bukkitClass == Cat.Type.class) {
-            return new CraftRegistry<>(Cat.Type.class, registryHolder.lookupOrThrow(Registries.CAT_VARIANT), CraftCat.CraftType::new, FieldRename.NONE);
-        }
-        if (bukkitClass == MapCursor.Type.class) {
-            return new CraftRegistry<>(MapCursor.Type.class, registryHolder.lookupOrThrow(Registries.MAP_DECORATION_TYPE), CraftMapCursor.CraftType::new, FieldRename.NONE);
-        }
-        if (bukkitClass == PatternType.class) {
-            return new CraftRegistry<>(PatternType.class, registryHolder.lookupOrThrow(Registries.BANNER_PATTERN), CraftPatternType::new, FieldRename.NONE);
-        }
-
-        return null;
-    }
 
+    // Paper - NOTE: As long as all uses of the method below relate to *serialization* via ConfigurationSerializable, it's fine
     public static <B extends Keyed> B get(Registry<B> bukkit, NamespacedKey namespacedKey, ApiVersion apiVersion) {
         if (bukkit instanceof CraftRegistry<B, ?> craft) {
-            return craft.get(namespacedKey, apiVersion);
+            return craft.get(craft.serializationUpdater.apply(namespacedKey, apiVersion)); // Paper
         }
 
         if (bukkit instanceof Registry.SimpleRegistry<?> simple) {
@@ -234,23 +182,26 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
         return bukkit.get(namespacedKey);
     }
 
-    private final Class<? super B> bukkitClass;
+    private final Class<?> bukkitClass; // Paper - relax preload class
     private final Map<NamespacedKey, B> cache = new HashMap<>();
     private final net.minecraft.core.Registry<M> minecraftRegistry;
-    private final BiFunction<NamespacedKey, M, B> minecraftToBukkit;
+    private final io.papermc.paper.registry.entry.RegistryTypeMapper<M, B> minecraftToBukkit; // Paper - switch to Holder
-    private final BiFunction<NamespacedKey, ApiVersion, NamespacedKey> updater;
+    private final BiFunction<NamespacedKey, ApiVersion, NamespacedKey> serializationUpdater; // Paper - rename to make it *clear* what it is *only* for
     private boolean init;
 
-    public CraftRegistry(Class<? super B> bukkitClass, net.minecraft.core.Registry<M> minecraftRegistry, BiFunction<NamespacedKey, M, B> minecraftToBukkit, BiFunction<NamespacedKey, ApiVersion, NamespacedKey> updater) {
+    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
+        this(bukkitClass, minecraftRegistry, new io.papermc.paper.registry.entry.RegistryTypeMapper<>(minecraftToBukkit), serializationUpdater);
+    }
+    public CraftRegistry(Class<?> bukkitClass, net.minecraft.core.Registry<M> minecraftRegistry, io.papermc.paper.registry.entry.RegistryTypeMapper<M, B> minecraftToBukkit, BiFunction<NamespacedKey, ApiVersion, NamespacedKey> serializationUpdater) { // Paper - relax preload class
+        // Paper end - support Holders
         this.bukkitClass = bukkitClass;
         this.minecraftRegistry = minecraftRegistry;
         this.minecraftToBukkit = minecraftToBukkit;
-        this.updater = updater;
+        this.serializationUpdater = serializationUpdater;
     }
 
-    public B get(NamespacedKey namespacedKey, ApiVersion apiVersion) {
+    // Paper - inline into CraftRegistry#get(Registry, NamespacedKey, ApiVersion) above
-        return this.get(this.updater.apply(namespacedKey, apiVersion));
-    }
 
     @Override
     public B get(NamespacedKey namespacedKey) {
@@ -280,7 +231,7 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
             return this.get(namespacedKey);
         }
 
-        B bukkit = this.createBukkit(namespacedKey, this.minecraftRegistry.getOptional(CraftNamespacedKey.toMinecraft(namespacedKey)).orElse(null));
+        B bukkit = this.createBukkit(namespacedKey, this.minecraftRegistry.get(CraftNamespacedKey.toMinecraft(namespacedKey)).orElse(null)); // Paper - switch to Holder
         if (bukkit == null) {
             return null;
         }
@@ -311,11 +262,21 @@ public class CraftRegistry<B extends Keyed, M> implements Registry<B> {
         return this.stream().iterator();
     }
 
-    public B createBukkit(NamespacedKey namespacedKey, M minecraft) {
+    public B createBukkit(NamespacedKey namespacedKey, Holder<M> minecraft) { // Paper - switch to Holder
         if (minecraft == null) {
             return null;
         }
 
-        return this.minecraftToBukkit.apply(namespacedKey, minecraft);
+        return this.minecraftToBukkit.createBukkit(namespacedKey, minecraft); // Paper - switch to Holder
     }
+
+    // Paper start - support Direct Holders
+    public boolean supportsDirectHolders() {
+        return this.minecraftToBukkit.supportsDirectHolders();
+    }
+
+    public B convertDirectHolder(Holder<M> holder) {
+        return this.minecraftToBukkit.convertDirectHolder(holder);
+    }
+    // Paper end - support Direct Holders
 }

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

@@ -284,7 +284,7 @@ public final class CraftServer implements Server {
     protected final DedicatedServer console;
     protected final DedicatedPlayerList playerList;
     private final Map<String, World> worlds = new LinkedHashMap<String, World>();
-    private final Map<Class<?>, Registry<?>> registries = new HashMap<>();
+    // private final Map<Class<?>, Registry<?>> registries = new HashMap<>(); // Paper - replace with RegistryAccess
     private YamlConfiguration configuration;
     private YamlConfiguration commandsConfiguration;
     private final Yaml yaml = new Yaml(new SafeConstructor(new LoaderOptions()));
@@ -431,6 +431,7 @@ public final class CraftServer implements Server {
     }
 
     private void loadCompatibilities() {
+        if (true) return; // Paper - Big nope
         ConfigurationSection compatibilities = this.configuration.getConfigurationSection("settings.compatibility");
         if (compatibilities == null) {
             this.activeCompatibilities = Collections.emptySet();
@@ -2754,7 +2755,7 @@ public final class CraftServer implements Server {
 
     @Override
     public <T extends Keyed> Registry<T> getRegistry(Class<T> aClass) {
-        return (Registry<T>) this.registries.computeIfAbsent(aClass, key -> CraftRegistry.createRegistry(aClass, this.console.registryAccess()));
+        return io.papermc.paper.registry.RegistryAccess.registryAccess().getRegistry(aClass); // Paper - replace with RegistryAccess
     }
 
     @Deprecated

paper-server/src/main/java/org/bukkit/craftbukkit/legacy/FieldRename.java

@@ -51,11 +51,14 @@ public class FieldRename {
         };
     }
 
-    @RequireCompatibility("allow-old-keys-in-registry")
+    // Paper start - absolutely not, having this as an expectation for plugin developers opens a huge
-    public static <T extends Keyed> T get(Registry<T> registry, NamespacedKey namespacedKey) {
+    // can of worms in the future, especially if mojang comes back and reuses some old key
-        // We don't have version-specific changes, so just use current, and don't inject a version
+    //@RequireCompatibility("allow-old-keys-in-registry")
-        return CraftRegistry.get(registry, namespacedKey, ApiVersion.CURRENT);
+    //public static <T extends Keyed> T get(Registry<T> registry, NamespacedKey namespacedKey) {
-    }
+    //    // We don't have version-specific changes, so just use current, and don't inject a version
+    //    return CraftRegistry.get(registry, namespacedKey, ApiVersion.CURRENT);
+    //}
+    // Paper end
 
     // PatternType
     private static final FieldRenameData PATTERN_TYPE_DATA = FieldRenameData.Builder.newBuilder()

paper-server/src/main/java/org/bukkit/craftbukkit/util/Commodore.java

@@ -220,20 +220,10 @@ public class Commodore {
 
     public byte[] convert(byte[] b, final String pluginName, final ApiVersion pluginVersion, final Set<String> activeCompatibilities) {
         final boolean modern = pluginVersion.isNewerThanOrSameAs(ApiVersion.FLATTENING);
-        final boolean enumCompatibility = pluginVersion.isOlderThanOrSameAs(ApiVersion.getOrCreateVersion("1.20.6")) && activeCompatibilities.contains("enum-compatibility-mode");
         ClassReader cr = new ClassReader(b);
         ClassWriter cw = new ClassWriter(cr, 0);
 
-        List<String> methodEnumSignatures = Commodore.getMethodSignatures(b);
-        Multimap<String, String> enumLessToEnum = HashMultimap.create();
-        for (String method : methodEnumSignatures) {
-            enumLessToEnum.put(method.replace("Ljava/lang/Enum;", "Ljava/lang/Object;"), method);
-        }
-
         ClassVisitor visitor = cw;
-        if (enumCompatibility) {
-            visitor = new LimitedClassRemapper(cw, new SimpleRemapper(Commodore.ENUM_RENAMES));
-        }
 
         visitor = io.papermc.paper.pluginremap.reflect.ReflectionRemapper.visitor(visitor); // Paper
         cr.accept(new ClassRemapper(new ClassVisitor(Opcodes.ASM9, visitor) {
@@ -300,15 +290,6 @@ public class Commodore {
 
             @Override
             public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
-                if (enumCompatibility && (access & Opcodes.ACC_SYNTHETIC) != 0 && (access & Opcodes.ACC_BRIDGE) != 0 && desc.contains("Ljava/lang/Object;")) {
-                    // SPIGOT-7820: Do not use object method if enum method is present
-                    // The object method does only redirect to the enum method
-                    Collection<String> result = enumLessToEnum.get(desc.replace("Ljava/lang/Enum;", "Ljava/lang/Object;") + " " + name);
-                    if (result.size() == 2) {
-                        name = name + "_BUKKIT_UNUSED";
-                    }
-                }
-
                 return new MethodVisitor(this.api, super.visitMethod(access, name, desc, signature, exceptions)) {
                     // Paper start - Plugin rewrites
                     @Override

paper-server/src/main/resources/META-INF/services/io.papermc.paper.registry.RegistryAccess

@@ -0,0 +1 @@
+io.papermc.paper.registry.PaperRegistryAccess

paper-server/src/main/resources/configurations/bukkit.yml

@@ -23,9 +23,6 @@ settings:
     shutdown-message: Server closed
     minimum-api: none
     use-map-color-cache: true
-    compatibility:
-        allow-old-keys-in-registry: false
-        enum-compatibility-mode: false
 spawn-limits:
     monsters: 70
     animals: 10

paper-server/src/test/java/io/papermc/paper/registry/LegacyRegistryIdentifierTest.java

@@ -0,0 +1,21 @@
+package io.papermc.paper.registry;
+
+import org.bukkit.GameEvent;
+import org.bukkit.MusicInstrument;
+import org.bukkit.inventory.meta.trim.TrimPattern;
+import org.bukkit.support.environment.VanillaFeature;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertSame;
+
+@Deprecated
+@VanillaFeature
+class LegacyRegistryIdentifierTest {
+
+    @Test
+    void testSeveralConversions() {
+        assertSame(RegistryKey.GAME_EVENT, PaperRegistryAccess.byType(GameEvent.class));
+        assertSame(RegistryKey.TRIM_PATTERN, PaperRegistryAccess.byType(TrimPattern.class));
+        assertSame(RegistryKey.INSTRUMENT, PaperRegistryAccess.byType(MusicInstrument.class));
+    }
+}

paper-server/src/test/java/io/papermc/paper/registry/RegistryKeyTest.java

@@ -1,15 +1,19 @@
 package io.papermc.paper.registry;
 
+import io.papermc.paper.registry.entry.RegistryEntry;
 import java.util.Optional;
 import java.util.stream.Stream;
 import net.minecraft.core.Registry;
 import net.minecraft.resources.ResourceKey;
 import net.minecraft.resources.ResourceLocation;
-import org.bukkit.support.AbstractTestingBase;
+import org.bukkit.support.RegistryHelper;
+import org.bukkit.support.environment.AllFeatures;
+import org.checkerframework.checker.nullness.qual.Nullable;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 @AllFeatures
@@ -29,6 +33,12 @@ class RegistryKeyTest {
     void testApiRegistryKeysExist(final RegistryKey<?> key) {
         final Optional<Registry<Object>> registry = RegistryHelper.getRegistry().lookup(ResourceKey.createRegistryKey(ResourceLocation.parse(key.key().asString())));
         assertTrue(registry.isPresent(), "Missing vanilla registry for " + key.key().asString());
+    }
 
+    @ParameterizedTest
+    @MethodSource("data")
+    void testRegistryEntryExists(final RegistryKey<?> key) {
+        final @Nullable RegistryEntry<?, ?> entry = PaperRegistries.getEntry(key);
+        assertNotNull(entry, "Missing PaperRegistries entry for " + key);
     }
 }

paper-server/src/test/java/org/bukkit/registry/RegistryArgumentAddedTest.java

@@ -22,14 +22,17 @@ public class RegistryArgumentAddedTest {
         // Make sure every registry is created
         Class.forName(Registry.class.getName());
 
-        Set<Class<?>> loadedRegistries = new HashSet<>(AllFeaturesExtension.getRealRegistries().keySet());
+        // Paper start
-        Set<Class<?>> notFound = new HashSet<>();
+        Set<io.papermc.paper.registry.RegistryKey<?>> loadedRegistries = java.util.Collections.newSetFromMap(new java.util.IdentityHashMap<>());
+        loadedRegistries.addAll(io.papermc.paper.registry.PaperRegistryAccess.instance().getLoadedServerBackedRegistries());
+        // Paper end
+        Set<io.papermc.paper.registry.RegistryKey<?>> notFound = new HashSet<>(); // Paper
 
         RegistriesArgumentProvider
                 .getData()
                 .map(Arguments::get)
                 .map(array -> array[0])
-                .map(clazz -> (Class<?>) clazz)
+                .map(clazz -> (io.papermc.paper.registry.RegistryKey<?>) clazz) // Paper
                 .forEach(clazz -> {
                     if (!loadedRegistries.remove(clazz)) {
                         notFound.add(clazz);

paper-server/src/test/java/org/bukkit/registry/RegistryConversionTest.java

@@ -41,9 +41,9 @@ public class RegistryConversionTest {
 
     @Order(1)
     @RegistriesTest
-    public void testHandleableImplementation(Class<? extends Keyed> clazz) {
+    public void testHandleableImplementation(io.papermc.paper.registry.RegistryKey<? extends Keyed> type, Class<? extends Keyed> clazz) { // Paper
         Set<Class<? extends Keyed>> notImplemented = new HashSet<>();
-        Registry<? extends Keyed> registry = Bukkit.getRegistry(clazz);
+        Registry<? extends Keyed> registry = io.papermc.paper.registry.RegistryAccess.registryAccess().getRegistry(type); // Paper
 
         for (Keyed item : registry) {
             if (!(item instanceof Handleable<?>)) {
@@ -63,7 +63,7 @@ public class RegistryConversionTest {
 
     @Order(2)
     @RegistriesTest
-    public void testMinecraftToBukkitPresent(Class<? extends Keyed> clazz, ResourceKey<net.minecraft.core.Registry<?>> registryKey,
+    public void testMinecraftToBukkitPresent(io.papermc.paper.registry.RegistryKey<? extends Keyed> type, Class<? extends Keyed> clazz, ResourceKey<net.minecraft.core.Registry<?>> registryKey,
                                              Class<? extends Keyed> craftClazz, Class<?> minecraftClazz, boolean newMethod) {
         String methodName = (newMethod) ? RegistryConversionTest.MINECRAFT_TO_BUKKIT_NEW : RegistryConversionTest.MINECRAFT_TO_BUKKIT;
         Method method = null;
@@ -112,7 +112,7 @@ public class RegistryConversionTest {
 
     @Order(2)
     @RegistriesTest
-    public void testBukkitToMinecraftPresent(Class<? extends Keyed> clazz, ResourceKey<net.minecraft.core.Registry<?>> registryKey,
+    public void testBukkitToMinecraftPresent(io.papermc.paper.registry.RegistryKey<? extends Keyed> type, Class<? extends Keyed> clazz, ResourceKey<net.minecraft.core.Registry<?>> registryKey,
                                              Class<? extends Keyed> craftClazz, Class<?> minecraftClazz, boolean newMethod) {
         String methodName = (newMethod) ? RegistryConversionTest.BUKKIT_TO_MINECRAFT_NEW : RegistryConversionTest.BUKKIT_TO_MINECRAFT;
         Method method = null;
@@ -159,9 +159,9 @@ public class RegistryConversionTest {
                 """, minecraftClazz.getName(), methodName, clazz.getSimpleName());
     }
 
-    @Order(2)
+    @Order(3)
     @RegistriesTest
-    public void testMinecraftToBukkitNullValue(Class<? extends Keyed> clazz) throws IllegalAccessException {
+    public void testMinecraftToBukkitNullValue(io.papermc.paper.registry.RegistryKey<? extends Keyed> type, Class<? extends Keyed> clazz) throws IllegalAccessException { // Paper
         this.checkValidMinecraftToBukkit(clazz);
 
         try {
@@ -180,7 +180,7 @@ public class RegistryConversionTest {
 
     @Order(3)
     @RegistriesTest
-    public void testBukkitToMinecraftNullValue(Class<? extends Keyed> clazz) throws IllegalAccessException {
+    public void testBukkitToMinecraftNullValue(io.papermc.paper.registry.RegistryKey<? extends Keyed> type, Class<? extends Keyed> clazz) throws IllegalAccessException { // Paper
         this.checkValidBukkitToMinecraft(clazz);
 
         try {
@@ -199,14 +199,14 @@ public class RegistryConversionTest {
 
     @Order(3)
     @RegistriesTest
-    public void testMinecraftToBukkit(Class<? extends Keyed> clazz) {
+    public void testMinecraftToBukkit(io.papermc.paper.registry.RegistryKey<? extends Keyed> type, Class<? extends Keyed> clazz) { // Paper
         this.checkValidMinecraftToBukkit(clazz);
         this.checkValidHandle(clazz);
 
         Map<Object, Object> notMatching = new HashMap<>();
         Method method = RegistryConversionTest.MINECRAFT_TO_BUKKIT_METHODS.get(clazz);
 
-        RegistryArgumentProvider.getValues(clazz).map(Arguments::get).forEach(arguments -> {
+        RegistryArgumentProvider.getValues(type).map(Arguments::get).forEach(arguments -> { // Paper
             Keyed bukkit = (Keyed) arguments[0];
             Object minecraft = arguments[1];
 
@@ -230,14 +230,14 @@ public class RegistryConversionTest {
 
     @Order(3)
     @RegistriesTest
-    public void testBukkitToMinecraft(Class<? extends Keyed> clazz) {
+    public void testBukkitToMinecraft(io.papermc.paper.registry.RegistryKey<? extends Keyed> type, Class<? extends Keyed> clazz) { // Paper
         this.checkValidBukkitToMinecraft(clazz);
         this.checkValidHandle(clazz);
 
         Map<Object, Object> notMatching = new HashMap<>();
         Method method = RegistryConversionTest.BUKKIT_TO_MINECRAFT_METHODS.get(clazz);
 
-        RegistryArgumentProvider.getValues(clazz).map(Arguments::get).forEach(arguments -> {
+        RegistryArgumentProvider.getValues(type).map(Arguments::get).forEach(arguments -> { // Paper
             Keyed bukkit = (Keyed) arguments[0];
             Object minecraft = arguments[1];
 
@@ -265,7 +265,7 @@ public class RegistryConversionTest {
      */
     @Order(3)
     @RegistriesTest
-    public void testMinecraftToBukkitNoValidMinecraft(Class<? extends Keyed> clazz, ResourceKey<net.minecraft.core.Registry<?>> registryKey,
+    public void testMinecraftToBukkitNoValidMinecraft(io.papermc.paper.registry.RegistryKey<? extends Keyed> type, Class<? extends Keyed> clazz, ResourceKey<net.minecraft.core.Registry<?>> registryKey, // Paper
                                                       Class<? extends Keyed> craftClazz, Class<?> minecraftClazz) throws IllegalAccessException {
         this.checkValidMinecraftToBukkit(clazz);
 

paper-server/src/test/java/org/bukkit/support/extension/AllFeaturesExtension.java

@@ -39,22 +39,7 @@ public class AllFeaturesExtension extends BaseExtension {
 
         Bukkit.setServer(server);
 
-        when(server.getRegistry(any()))
+        // Paper - Add RegistryAccess for managing registries - replaced with registry access
-                .then(invocation -> {
-                    Class<? extends Keyed> keyed = invocation.getArgument(0);
-                    if (spyRegistries.containsKey(keyed)) {
-                        return spyRegistries.get(keyed);
-                    }
-
-                    Registry<?> registry = CraftRegistry.createRegistry(keyed, RegistryHelper.getRegistry());
-                    realRegistries.put(keyed, registry);
-
-                    Registry<?> spy = mock(registry.getClass(), withSettings().stubOnly().spiedInstance(registry).defaultAnswer(CALLS_REAL_METHODS));
-
-                    spyRegistries.put(keyed, spy);
-
-                    return spy;
-                });
 
         CraftRegistry.setMinecraftRegistry(RegistryHelper.getRegistry());
     }

paper-server/src/test/java/org/bukkit/support/extension/LegacyExtension.java

@@ -30,11 +30,7 @@ public class LegacyExtension extends BaseExtension {
 
         Bukkit.setServer(server);
 
-        when(server.getRegistry(any()))
+        // Paper - Add RegistryAccess for managing registries - replaced with registry access
-                .then(invocation -> {
-                    Class<? extends Keyed> keyed = invocation.getArgument(0);
-                    return registries.computeIfAbsent(keyed, k -> CraftRegistry.createRegistry(keyed, RegistryHelper.getRegistry()));
-                });
 
         CraftRegistry.setMinecraftRegistry(RegistryHelper.getRegistry());
     }

paper-server/src/test/java/org/bukkit/support/extension/SlowExtension.java

@@ -30,11 +30,7 @@ public class SlowExtension extends BaseExtension {
 
         Bukkit.setServer(server);
 
-        when(server.getRegistry(any()))
+        // Paper - Add RegistryAccess for managing registries - replaced with registry access
-                .then(invocation -> {
-                    Class<? extends Keyed> keyed = invocation.getArgument(0);
-                    return registries.computeIfAbsent(keyed, k -> CraftRegistry.createRegistry(keyed, RegistryHelper.getRegistry()));
-                });
 
         CraftRegistry.setMinecraftRegistry(RegistryHelper.getRegistry());
     }

paper-server/src/test/java/org/bukkit/support/extension/VanillaFeatureExtension.java

@@ -30,11 +30,7 @@ public class VanillaFeatureExtension extends BaseExtension {
 
         Bukkit.setServer(server);
 
-        when(server.getRegistry(any()))
+        // Paper - Add RegistryAccess for managing registries - replaced with registry access
-                .then(invocation -> {
-                    Class<? extends Keyed> keyed = invocation.getArgument(0);
-                    return registries.computeIfAbsent(keyed, k -> CraftRegistry.createRegistry(keyed, RegistryHelper.getRegistry()));
-                });
 
         CraftRegistry.setMinecraftRegistry(RegistryHelper.getRegistry());
     }

paper-server/src/test/java/org/bukkit/support/provider/RegistriesArgumentProvider.java

@@ -1,6 +1,7 @@
 package org.bukkit.support.provider;
 
 import com.google.common.collect.Lists;
+import io.papermc.paper.registry.RegistryKey;
 import java.util.List;
 import java.util.stream.Stream;
 import net.minecraft.core.registries.Registries;
@@ -73,41 +74,40 @@ public class RegistriesArgumentProvider implements ArgumentsProvider {
     private static final List<Arguments> DATA = Lists.newArrayList();
 
     static {
-        // Order: Bukkit class, Minecraft Registry key, CraftBukkit class, Minecraft class
+        // Order: RegistryKey, Bukkit class, Minecraft Registry key, CraftBukkit class, Minecraft class
-        register(Art.class, Registries.PAINTING_VARIANT, CraftArt.class, PaintingVariant.class);
+        register(RegistryKey.PAINTING_VARIANT, Art.class, Registries.PAINTING_VARIANT, CraftArt.class, PaintingVariant.class);
-        register(Attribute.class, Registries.ATTRIBUTE, CraftAttribute.class, net.minecraft.world.entity.ai.attributes.Attribute.class);
+        register(RegistryKey.ATTRIBUTE, Attribute.class, Registries.ATTRIBUTE, CraftAttribute.class, net.minecraft.world.entity.ai.attributes.Attribute.class);
-        register(Biome.class, Registries.BIOME, CraftBiome.class, net.minecraft.world.level.biome.Biome.class);
+        register(RegistryKey.BIOME, Biome.class, Registries.BIOME, CraftBiome.class, net.minecraft.world.level.biome.Biome.class);
-        register(Enchantment.class, Registries.ENCHANTMENT, CraftEnchantment.class, net.minecraft.world.item.enchantment.Enchantment.class);
+        register(RegistryKey.ENCHANTMENT, Enchantment.class, Registries.ENCHANTMENT, CraftEnchantment.class, net.minecraft.world.item.enchantment.Enchantment.class);
-        register(Fluid.class, Registries.FLUID, CraftFluid.class, net.minecraft.world.level.material.Fluid.class);
+        register(RegistryKey.FLUID, Fluid.class, Registries.FLUID, CraftFluid.class, net.minecraft.world.level.material.Fluid.class);
-        register(GameEvent.class, Registries.GAME_EVENT, CraftGameEvent.class, net.minecraft.world.level.gameevent.GameEvent.class);
+        register(RegistryKey.GAME_EVENT, GameEvent.class, Registries.GAME_EVENT, CraftGameEvent.class, net.minecraft.world.level.gameevent.GameEvent.class);
-        register(MusicInstrument.class, Registries.INSTRUMENT, CraftMusicInstrument.class, Instrument.class);
+        register(RegistryKey.INSTRUMENT, MusicInstrument.class, Registries.INSTRUMENT, CraftMusicInstrument.class, Instrument.class);
-        register(MenuType.class, Registries.MENU, CraftMenuType.class, net.minecraft.world.inventory.MenuType.class);
+        register(RegistryKey.MOB_EFFECT, PotionEffectType.class, Registries.MOB_EFFECT, CraftPotionEffectType.class, MobEffect.class);
-        register(PotionEffectType.class, Registries.MOB_EFFECT, CraftPotionEffectType.class, MobEffect.class);
+        register(RegistryKey.SOUND_EVENT, Sound.class, Registries.SOUND_EVENT, CraftSound.class, SoundEvent.class);
-        register(Sound.class, Registries.SOUND_EVENT, CraftSound.class, SoundEvent.class);
+        register(RegistryKey.STRUCTURE, Structure.class, Registries.STRUCTURE, CraftStructure.class, net.minecraft.world.level.levelgen.structure.Structure.class);
-        register(Structure.class, Registries.STRUCTURE, CraftStructure.class, net.minecraft.world.level.levelgen.structure.Structure.class);
+        register(RegistryKey.STRUCTURE_TYPE, StructureType.class, Registries.STRUCTURE_TYPE, CraftStructureType.class, net.minecraft.world.level.levelgen.structure.StructureType.class);
-        register(StructureType.class, Registries.STRUCTURE_TYPE, CraftStructureType.class, net.minecraft.world.level.levelgen.structure.StructureType.class);
+        register(RegistryKey.VILLAGER_TYPE, Villager.Type.class, Registries.VILLAGER_TYPE, CraftVillager.CraftType.class, VillagerType.class);
-        register(Villager.Type.class, Registries.VILLAGER_TYPE, CraftVillager.CraftType.class, VillagerType.class);
+        register(RegistryKey.VILLAGER_PROFESSION, Villager.Profession.class, Registries.VILLAGER_PROFESSION, CraftVillager.CraftProfession.class, VillagerProfession.class);
-        register(Villager.Profession.class, Registries.VILLAGER_PROFESSION, CraftVillager.CraftProfession.class, VillagerProfession.class);
+        register(RegistryKey.TRIM_MATERIAL, TrimMaterial.class, Registries.TRIM_MATERIAL, CraftTrimMaterial.class, net.minecraft.world.item.equipment.trim.TrimMaterial.class);
-        register(TrimMaterial.class, Registries.TRIM_MATERIAL, CraftTrimMaterial.class, net.minecraft.world.item.equipment.trim.TrimMaterial.class);
+        register(RegistryKey.TRIM_PATTERN, TrimPattern.class, Registries.TRIM_PATTERN, CraftTrimPattern.class, net.minecraft.world.item.equipment.trim.TrimPattern.class);
-        register(TrimPattern.class, Registries.TRIM_PATTERN, CraftTrimPattern.class, net.minecraft.world.item.equipment.trim.TrimPattern.class);
+        register(RegistryKey.DAMAGE_TYPE, DamageType.class, Registries.DAMAGE_TYPE, CraftDamageType.class, net.minecraft.world.damagesource.DamageType.class);
-        register(DamageType.class, Registries.DAMAGE_TYPE, CraftDamageType.class, net.minecraft.world.damagesource.DamageType.class);
+        register(RegistryKey.JUKEBOX_SONG, JukeboxSong.class, Registries.JUKEBOX_SONG, CraftJukeboxSong.class, net.minecraft.world.item.JukeboxSong.class);
-        register(JukeboxSong.class, Registries.JUKEBOX_SONG, CraftJukeboxSong.class, net.minecraft.world.item.JukeboxSong.class);
+        register(RegistryKey.WOLF_VARIANT, Wolf.Variant.class, Registries.WOLF_VARIANT, CraftWolf.CraftVariant.class, WolfVariant.class);
-        register(Wolf.Variant.class, Registries.WOLF_VARIANT, CraftWolf.CraftVariant.class, WolfVariant.class);
+        register(RegistryKey.ITEM, ItemType.class, Registries.ITEM, CraftItemType.class, net.minecraft.world.item.Item.class, true);
-        register(ItemType.class, Registries.ITEM, CraftItemType.class, net.minecraft.world.item.Item.class, true);
+        register(RegistryKey.BLOCK, BlockType.class, Registries.BLOCK, CraftBlockType.class, net.minecraft.world.level.block.Block.class, true);
-        register(BlockType.class, Registries.BLOCK, CraftBlockType.class, net.minecraft.world.level.block.Block.class, true);
+        register(RegistryKey.FROG_VARIANT, Frog.Variant.class, Registries.FROG_VARIANT, CraftFrog.CraftVariant.class, FrogVariant.class);
-        register(Frog.Variant.class, Registries.FROG_VARIANT, CraftFrog.CraftVariant.class, FrogVariant.class);
+        register(RegistryKey.CAT_VARIANT, Cat.Type.class, Registries.CAT_VARIANT, CraftCat.CraftType.class, CatVariant.class);
-        register(Cat.Type.class, Registries.CAT_VARIANT, CraftCat.CraftType.class, CatVariant.class);
+        register(RegistryKey.MAP_DECORATION_TYPE, MapCursor.Type.class, Registries.MAP_DECORATION_TYPE, CraftMapCursor.CraftType.class, MapDecorationType.class);
-        register(MapCursor.Type.class, Registries.MAP_DECORATION_TYPE, CraftMapCursor.CraftType.class, MapDecorationType.class);
+        register(RegistryKey.BANNER_PATTERN, PatternType.class, Registries.BANNER_PATTERN, CraftPatternType.class, BannerPattern.class);
-        register(PatternType.class, Registries.BANNER_PATTERN, CraftPatternType.class, BannerPattern.class);
+        register(RegistryKey.MENU, MenuType.class, Registries.MENU, CraftMenuType.class, net.minecraft.world.inventory.MenuType.class);
-
     }
 
-    private static void register(Class bukkit, ResourceKey registry, Class craft, Class minecraft) {
+    private static void register(RegistryKey registryKey, Class bukkit, ResourceKey registry, Class craft, Class minecraft) { // Paper
-        RegistriesArgumentProvider.register(bukkit, registry, craft, minecraft, false);
+        RegistriesArgumentProvider.register(registryKey, bukkit, registry, craft, minecraft, false);
     }
 
-    private static void register(Class bukkit, ResourceKey registry, Class craft, Class minecraft, boolean newClass) {
+    private static void register(RegistryKey registryKey, Class bukkit, ResourceKey registry, Class craft, Class minecraft, boolean newClass) { // Paper
-        RegistriesArgumentProvider.DATA.add(Arguments.of(bukkit, registry, craft, minecraft, newClass));
+        RegistriesArgumentProvider.DATA.add(Arguments.of(registryKey, bukkit, registry, craft, minecraft, newClass));
     }
 
     @Override

paper-server/src/test/java/org/bukkit/support/provider/RegistryArgumentProvider.java

@@ -22,11 +22,11 @@ public class RegistryArgumentProvider implements ArgumentsProvider, AnnotationCo
 
     @Override
     public Stream<? extends Arguments> provideArguments(ExtensionContext extensionContext) throws Exception {
-        return RegistryArgumentProvider.getValues(this.registryType);
+        return RegistryArgumentProvider.getValues(io.papermc.paper.registry.PaperRegistryAccess.byType(this.registryType)); // Paper
     }
 
-    public static Stream<? extends Arguments> getValues(Class<? extends Keyed> registryType) {
+    public static Stream<? extends Arguments> getValues(io.papermc.paper.registry.RegistryKey<? extends Keyed> registryType) { // Paper
-        Registry<?> registry = Bukkit.getRegistry(registryType);
+        Registry<?> registry = io.papermc.paper.registry.RegistryAccess.registryAccess().getRegistry(registryType); // Paper
         return registry.stream().map(keyed -> (Handleable<?>) keyed)
                 .map(handleAble -> Arguments.of(handleAble, handleAble.getHandle()));
     }