Fix merged mod resource pack not returning all resources with the same name when asked. Closes #9194

src/main/java/net/minecraftforge/common/extensions/IForgePackResources.java

@@ -5,7 +5,12 @@
 
 package net.minecraftforge.common.extensions;
 
+import java.util.Collection;
+import org.jetbrains.annotations.Nullable;
+import net.minecraft.server.packs.PackResources;
 import net.minecraft.server.packs.PackType;
+import net.minecraft.server.packs.resources.ResourceManager;
+import net.minecraftforge.resource.DelegatingPackResources;
 
 public interface IForgePackResources
 {
@@ -20,4 +25,14 @@ public interface IForgePackResources
     default void initForNamespace(final String nameSpace) {}
 
     default void init(final PackType packType) {}
+
+    /**
+     * Gets a collection of {@code PackResource} instances nested inside this pack.
+     * Used to merge several packs into one entry in the resource pack selection UI without
+     * losing the ability for each pack to return a resource in
+     * {@link ResourceManager#getResourceStack(ResourceLocation)}
+     * @return Collection of nested {@code PackResource}, or null if this pack has no children
+     * @see DelegatingPackResources
+     */
+    @Nullable default Collection<PackResources> getChildren() { return null; }
 }

src/main/java/net/minecraftforge/resource/DelegatingPackResources.java

@@ -10,6 +10,7 @@ import com.google.common.collect.ImmutableMap;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
@@ -123,6 +124,12 @@ public class DelegatingPackResources extends AbstractPackResources
         return null;
     }
 
+    @Nullable
+    public Collection<PackResources> getChildren()
+    {
+        return delegates;
+    }
+
     private List<PackResources> getCandidatePacks(PackType type, ResourceLocation location)
     {
         Map<String, List<PackResources>> map = type == PackType.CLIENT_RESOURCES ? namespacesAssets : namespacesData;