[1.19] Fix data-gen output path of custom data-pack registries (#8724)

src/main/java/net/minecraftforge/common/ForgeHooks.java

@@ -1419,4 +1419,29 @@ public class ForgeHooks
 
         return map.buildOrThrow();
     }
+
+    /**
+     * <p>
+     *    This method is used to prefix the path, where elements of the associated registry are stored, with their namespace, if it is not minecraft
+     * </p>
+     * <p>
+     *    This rules conflicts with equal paths out. If for example the mod {@code fancy_cheese} adds a registry named {@code cheeses},
+     *    but the mod {@code awesome_cheese} also adds a registry called {@code cheeses},
+     *    they are going to have the same path {@code cheeses}, just with different namespaces.
+     *    If {@code additional_cheese} wants to add additional cheese to {@code awesome_cheese}, but not {@code fancy_cheese},
+     *    it can not differentiate both. Both paths will look like {@code data/additional_cheese/cheeses}.
+     * </p>
+     * <p>
+     *    The fix, which is applied here prefixes the path of the registry with the namespace,
+     *    so {@code fancy_cheese}'s registry stores its elements in {@code data/<namespace>/fancy_cheese/cheeses}
+     *    and {@code awesome_cheese}'s registry stores its elements in {@code data/namespace/awesome_cheese/cheeses}
+     * </p>
+     *
+     * @param registryKey key of the registry
+     * @return path of the registry key. Prefixed with the namespace if it is not "minecraft"
+     */
+    public static String prefixNamespace(ResourceLocation registryKey)
+    {
+        return registryKey.getNamespace().equals("minecraft") ? registryKey.getPath() : registryKey.getNamespace() +  "/"  + registryKey.getPath();
+    }
 }