Fix Registry#getKey implementation

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

@@ -7,7 +7,7 @@ import com.mojang.serialization.JsonOps;
 import net.kyori.adventure.key.Key;
 import net.minecraft.core.Holder;
 import net.minecraft.resources.RegistryOps;
-import org.bukkit.Keyed;
+import org.bukkit.NamespacedKey;
 import org.bukkit.Registry;
 import org.bukkit.craftbukkit.CraftRegistry;
 import org.bukkit.craftbukkit.util.Handleable;
@@ -25,7 +25,7 @@ public interface Holderable<M> extends Handleable<M> {
         return this.getHolder().value();
     }
 
-    static <T extends Keyed, M> @Nullable T fromBukkitSerializationObject(final Object deserialized, final Codec<? extends Holder<M>> codec, final Registry<T> registry) { // TODO remove Keyed
+    static <T extends org.bukkit.Keyed, M> @Nullable T fromBukkitSerializationObject(final Object deserialized, final Codec<? extends Holder<M>> codec, final Registry<T> registry) { // TODO remove Keyed
         return switch (deserialized) {
             case @Subst("key:value") final String string -> {
                 if (!(Key.parseable(string))) {
@@ -75,4 +75,12 @@ public interface Holderable<M> extends Handleable<M> {
     default String implToString() {
         return "%s{holder=%s}".formatted(this.getClass().getSimpleName(), this.getHolder().toString());
     }
+
+    default @Nullable NamespacedKey getKeyOrNull() {
+        return this.getHolder().unwrapKey().map(MCUtil::fromResourceKey).orElse(null);
+    }
+
+    default NamespacedKey getKey() {
+        return MCUtil.fromResourceKey(this.getHolder().unwrapKey().orElseThrow(() -> new IllegalStateException("Cannot get key for this registry item, because it is not registered.")));
+    }
 }

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

@@ -0,0 +1,88 @@
+package io.papermc.paper.util;
+
+import com.google.common.base.Preconditions;
+import java.util.Locale;
+import net.minecraft.core.Holder;
+import org.bukkit.Keyed;
+import org.bukkit.NamespacedKey;
+import org.bukkit.util.OldEnum;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
+
+@SuppressWarnings("removal")
+@Deprecated
+@NullMarked
+public abstract class OldEnumHolderable<A extends OldEnum<A>, M> implements Holderable<M>, OldEnum<A>, Keyed {
+
+    private final Holder<M> holder;
+    private final int ordinal;
+    private final @Nullable String name;
+
+    protected OldEnumHolderable(final Holder<M> holder, final int ordinal) {
+        this.holder = holder;
+        this.ordinal = ordinal;
+        if (holder instanceof final Holder.Reference<M> reference) {
+            // For backwards compatibility, minecraft values will stile return the uppercase name without the namespace,
+            // in case plugins use for example the name as key in a config file to receive registry item specific values.
+            // Custom registry items will return the key with namespace. For a plugin this should look than like a new registry item
+            // (which can always be added in new minecraft versions and the plugin should therefore handle it accordingly).
+            if (NamespacedKey.MINECRAFT.equals(reference.key().location().getNamespace())) {
+                this.name = reference.key().location().getPath().toUpperCase(Locale.ROOT);
+            } else {
+                this.name = reference.key().location().toString();
+            }
+        } else {
+            this.name = null;
+        }
+    }
+
+    @Override
+    public Holder<M> getHolder() {
+        return this.holder;
+    }
+
+    @Override
+    @Deprecated
+    public int compareTo(A other) {
+        this.checkIsReference();
+        return this.ordinal - other.ordinal();
+    }
+
+    @Override
+    @Deprecated
+    public String name() {
+        this.checkIsReference();
+        return this.name;
+    }
+
+    @Override
+    @Deprecated
+    public int ordinal() {
+        this.checkIsReference();
+        return this.ordinal;
+    }
+
+    private void checkIsReference() {
+        Preconditions.checkState(this.holder.kind() == Holder.Kind.REFERENCE, "Cannot call method for this registry item, because it is not registered.");
+    }
+
+    @Override
+    public NamespacedKey getKey() {
+        return MCUtil.fromResourceKey(this.holder.unwrapKey().orElseThrow(() -> new IllegalStateException("Cannot get key for this registry item, because it is not registered.")));
+    }
+
+    @Override
+    public boolean equals(final Object obj) {
+        return this.implEquals(obj);
+    }
+
+    @Override
+    public int hashCode() {
+        return this.implHashCode();
+    }
+
+    @Override
+    public String toString() {
+        return this.implToString();
+    }
+}