For new registry values, allow copying from existing

paper-api/src/main/java/io/papermc/paper/registry/event/WritableRegistry.java

@@ -25,4 +25,17 @@ public interface WritableRegistry<T, B extends RegistryBuilder<T>> {
      * @param value a consumer for the entry's builder
      */
     void register(TypedKey<T> key, Consumer<? super B> value);
+
+    /**
+     * Register a new value with the specified key. This will
+     * fire a {@link RegistryEntryAddEvent} for the new entry. The
+     * builder in the consumer will be pre-filled with the values
+     * from the copyFrom key.
+     *
+     * @param key the entry's key (must be unique from others)
+     * @param copyFrom the key to copy values from (must already be registered)
+     * @param value a consumer for the entry's builder
+     * @throws IllegalArgumentException if copyFrom doesn't exist
+     */
+    void register(TypedKey<T> key, TypedKey<T> copyFrom, Consumer<? super B> value);
 }

paper-server/patches/features/0017-Moonrise-optimisation-patches.patch

@@ -23508,10 +23508,10 @@ index 3d3eec1db91cb47395f40c4f47aa77164ad42175..216f97207dac88cc1dc3df59c6ee8a62
 +    // Paper end - optimise collisions
  }
 diff --git a/net/minecraft/core/MappedRegistry.java b/net/minecraft/core/MappedRegistry.java
-index 47b1fafd91b39e73c4e9134b0b8048000fba108a..76994c1491221c06cca5405ba239e6ff642b19ed 100644
+index 452c358c2cfa0c39e0b09853cd4a9a12c6ced65d..5f752603aa5611ce9d3dd44cc5b70c27ac46a86e 100644
 --- a/net/minecraft/core/MappedRegistry.java
 +++ b/net/minecraft/core/MappedRegistry.java
-@@ -50,6 +50,19 @@ public class MappedRegistry<T> implements WritableRegistry<T> {
+@@ -51,6 +51,19 @@ public class MappedRegistry<T> implements WritableRegistry<T> {
          return this.getTags();
      }
 
@@ -23531,10 +23531,10 @@ index 47b1fafd91b39e73c4e9134b0b8048000fba108a..76994c1491221c06cca5405ba239e6ff
      public MappedRegistry(ResourceKey<? extends Registry<T>> key, Lifecycle registryLifecycle) {
          this(key, registryLifecycle, false);
      }
-@@ -114,6 +127,7 @@ public class MappedRegistry<T> implements WritableRegistry<T> {
-             this.toId.put(value, size);
+@@ -116,6 +129,7 @@ public class MappedRegistry<T> implements WritableRegistry<T> {
              this.registrationInfos.put(key, registrationInfo);
              this.registryLifecycle = this.registryLifecycle.add(registrationInfo.lifecycle());
+             this.temporaryUnfrozenMap.put(key.location(), value); // Paper - support pre-filling in registry mod API
 +            this.injectFluidRegister(key, value); // Paper - fluid method optimisations
              return reference;
          }

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

@@ -1,6 +1,6 @@
 --- a/net/minecraft/core/MappedRegistry.java
 +++ b/net/minecraft/core/MappedRegistry.java
-@@ -33,11 +_,11 @@
+@@ -33,17 +_,18 @@
  public class MappedRegistry<T> implements WritableRegistry<T> {
      private final ResourceKey<? extends Registry<T>> key;
      private final ObjectList<Holder.Reference<T>> byId = new ObjectArrayList<>(256);
@@ -17,6 +17,29 @@
      private Lifecycle registryLifecycle;
      private final Map<TagKey<T>, HolderSet.Named<T>> frozenTags = new IdentityHashMap<>();
      MappedRegistry.TagSet<T> allTags = MappedRegistry.TagSet.unbound();
+     private boolean frozen;
+     @Nullable
+     private Map<T, Holder.Reference<T>> unregisteredIntrusiveHolders;
++    public final Map<ResourceLocation, T> temporaryUnfrozenMap = new HashMap<>(); // Paper - support pre-filling in registry mod API
+
+     @Override
+     public Stream<HolderSet.Named<T>> listTags() {
+@@ -114,6 +_,7 @@
+             this.toId.put(value, size);
+             this.registrationInfos.put(key, registrationInfo);
+             this.registryLifecycle = this.registryLifecycle.add(registrationInfo.lifecycle());
++            this.temporaryUnfrozenMap.put(key.location(), value); // Paper - support pre-filling in registry mod API
+             return reference;
+         }
+     }
+@@ -275,6 +_,7 @@
+             return this;
+         } else {
+             this.frozen = true;
++            this.temporaryUnfrozenMap.clear(); // Paper - support pre-filling in registry mod API
+             this.byValue.forEach((object, reference) -> reference.bindValue((T)object));
+             List<ResourceLocation> list = this.byKey
+                 .entrySet()
 @@ -509,4 +_,13 @@
 
          Stream<HolderSet.Named<T>> getTags();

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

@@ -1,21 +1,19 @@
 package io.papermc.paper.registry;
 
+import com.google.common.base.Preconditions;
 import com.mojang.serialization.Lifecycle;
+import io.papermc.paper.adventure.PaperAdventure;
 import io.papermc.paper.registry.data.util.Conversions;
-import io.papermc.paper.registry.entry.RegistryEntry;
 import io.papermc.paper.registry.entry.RegistryEntryMeta;
-import io.papermc.paper.registry.entry.RegistryTypeMapper;
 import io.papermc.paper.registry.event.WritableRegistry;
 import java.util.Optional;
-import java.util.function.BiFunction;
 import java.util.function.Consumer;
 import net.minecraft.core.MappedRegistry;
 import net.minecraft.core.RegistrationInfo;
 import net.minecraft.resources.ResourceKey;
 import org.bukkit.Keyed;
-import org.bukkit.NamespacedKey;
 import org.bukkit.craftbukkit.CraftRegistry;
-import org.bukkit.craftbukkit.util.ApiVersion;
+import org.jspecify.annotations.Nullable;
 
 public class WritableCraftRegistry<M, T extends Keyed, B extends PaperRegistryBuilder<M, T>> extends CraftRegistry<T, M> {
 
@@ -33,10 +31,17 @@ public WritableCraftRegistry(
         this.meta = meta;
     }
 
-    public void register(final TypedKey<T> key, final Consumer<? super B> value, final Conversions conversions) {
+    public void register(final TypedKey<T> key, final @Nullable TypedKey<T> copyFrom, final Consumer<? super B> value, final Conversions conversions) {
         final ResourceKey<M> resourceKey = PaperRegistries.toNms(key);
         this.registry.validateWrite(resourceKey);
-        final B builder = this.newBuilder(conversions);
+        final B builder;
+        if (copyFrom != null) {
+            final M existing = this.registry.temporaryUnfrozenMap.get(PaperAdventure.asVanilla(copyFrom));
+            Preconditions.checkArgument(existing != null, "Cannot copy from unregistered key: %s", copyFrom);
+            builder = this.meta.builderFiller().fill(conversions, existing);
+        } else {
+            builder = this.meta.builderFiller().create(conversions);
+        }
         value.accept(builder);
         PaperRegistryListenerManager.INSTANCE.registerWithListeners(
             this.registry,
@@ -52,10 +57,6 @@ public WritableRegistry<T, B> createApiWritableRegistry(final Conversions conver
         return new ApiWritableRegistry(conversions);
     }
 
-    protected B newBuilder(final Conversions conversions) {
-        return this.meta.builderFiller().create(conversions);
-    }
-
     public class ApiWritableRegistry implements WritableRegistry<T, B> {
 
         private final Conversions conversions;
@@ -66,7 +67,12 @@ public ApiWritableRegistry(final Conversions conversions) {
 
         @Override
         public void register(final TypedKey<T> key, final Consumer<? super B> value) {
-            WritableCraftRegistry.this.register(key, value, this.conversions);
+            WritableCraftRegistry.this.register(key, null, value, this.conversions);
+        }
+
+        @Override
+        public void register(final TypedKey<T> key, final TypedKey<T> copyFrom, final Consumer<? super B> value) {
+            WritableCraftRegistry.this.register(key, copyFrom, value, this.conversions);
         }
     }
 }