feature(nbt): CompoundBinaryTag#builder(existing)

nbt/src/main/java/net/kyori/adventure/nbt/CompoundBinaryTag.java

@@ -31,6 +31,7 @@
 import java.util.stream.Stream;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.Unmodifiable;
 
 import static java.util.Objects.requireNonNull;
 
@@ -149,6 +150,17 @@ public interface CompoundBinaryTag extends BinaryTag, CompoundTagSetter<Compound
     return new CompoundTagBuilder();
   }
 
+  /**
+   * Creates a builder, pre-filled with the contents of {@code existing}.
+   *
+   * @param existing the compound to pre-fill the builder with
+   * @return a new builder
+   * @since 4.25.0
+   */
+  static @NotNull Builder builder(final @NotNull CompoundBinaryTag existing) {
+    return new CompoundTagBuilder(existing);
+  }
+
   @Override
   default @NotNull BinaryTagType<CompoundBinaryTag> type() {
     return BinaryTagTypes.COMPOUND;
@@ -162,6 +174,14 @@ public interface CompoundBinaryTag extends BinaryTag, CompoundTagSetter<Compound
    */
   @NotNull Set<String> keySet();
 
+  /**
+   * Returns an unmodifiable map representing the contents of this compound.
+   *
+   * @return an unmodifiable map of contents
+   * @since 4.25.0
+   */
+  @Unmodifiable @NotNull Map<String, BinaryTag> asMap();
+
   /**
    * Gets a tag.
    *

nbt/src/main/java/net/kyori/adventure/nbt/CompoundBinaryTagImpl.java

@@ -58,6 +58,11 @@ public boolean contains(final @NotNull String key, final @NotNull BinaryTagType<
     return Collections.unmodifiableSet(this.tags.keySet());
   }
 
+  @Override
+  public @NotNull Map<String, BinaryTag> asMap() {
+    return this.tags;
+  }
+
   @Override
   public @Nullable BinaryTag get(final String key) {
     return this.tags.get(key);

nbt/src/main/java/net/kyori/adventure/nbt/CompoundTagBuilder.java

@@ -32,6 +32,13 @@
 final class CompoundTagBuilder implements CompoundBinaryTag.Builder {
   private @Nullable Map<String, BinaryTag> tags;
 
+  CompoundTagBuilder() {
+  }
+
+  CompoundTagBuilder(final CompoundBinaryTag existing) {
+    this.tags = new HashMap<>(existing.asMap()); // explicitly copy
+  }
+
   private Map<String, BinaryTag> tags() {
     if (this.tags == null) {
       this.tags = new HashMap<>();