Unity-Technologies/UnityCsReference · error · ArgumentException

Creating a variant of an object into the source file of the

Error message

Creating a variant of an object into the source file of the input object is not allowed

What it means

Thrown by CreateVariant when the destination `path` resolves to the same file as the source prefab asset (case-insensitive compare via Paths.AreEqual). Creating a variant of a prefab into its own source file would produce a self-referential/corrupt asset, so Unity blocks it. The check runs only after path is confirmed non-null.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.bindings.cs:241

        extern public static GameObject FindPrefabRoot([NotNull] GameObject source);

        internal static GameObject CreateVariant(GameObject assetRoot, string path)
        {
            if (assetRoot == null)
                throw new ArgumentNullException("The inputObject is null");

            if (!IsPartOfPrefabAsset(assetRoot))
                throw new ArgumentException("Given input object is not a prefab asset");

            if (assetRoot.transform.root.gameObject != assetRoot)
                throw new ArgumentException("Object to create variant from has to be a Prefab root");

            if (path == null)
                throw new ArgumentNullException("The path is null");

            var assetRootObjectPath = AssetDatabase.GetAssetPath(assetRoot);
            if (Paths.AreEqual(path, assetRootObjectPath, true))
                throw new ArgumentException("Creating a variant of an object into the source file of the input object is not allowed");

            if (!Paths.IsValidAssetPath(path, ".prefab"))
                throw new ArgumentException("Given path is not valid: '" + path + "'");

            return CreateVariant_Internal(assetRoot, path);
        }

        [NativeMethod("CreateVariant", IsFreeFunction = true)]
        extern private static GameObject CreateVariant_Internal([NotNull] GameObject original, string path);

        [StaticAccessor("PrefabUtilityBindings", StaticAccessorType.DoubleColon)]
        [NativeMethod(ThrowsException = true)]
        extern private static GameObject SavePrefab_Internal([NotNull] GameObject root, string path, bool connectToInstance, out bool success);

        [StaticAccessor("PrefabUtilityBindings", StaticAccessorType.DoubleColon)]
        extern private static GameObject ApplyPrefabInstance_Internal([NotNull] GameObject root);

        [StaticAccessor("PrefabUtilityBindings", StaticAccessorType.DoubleColon)]

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Choose a distinct output filename, e.g. append "Variant": AssetDatabase.GenerateUniqueAssetPath("Assets/Prefabs/" + root.name + "Variant.prefab").
2. Verify the resolved path differs from AssetDatabase.GetAssetPath(assetRoot) before calling.
3. Prompt the user to pick a different folder/file if they reused the source name.

Example fix

// before
string srcPath = AssetDatabase.GetAssetPath(root);
var v = PrefabUtility.CreateVariant(root, srcPath); // throws

// after
string dir = System.IO.Path.GetDirectoryName(srcPath);
string newPath = AssetDatabase.GenerateUniqueAssetPath(
    dir + "/" + root.name + "Variant.prefab");
var v = PrefabUtility.CreateVariant(root, newPath);

string srcPath = AssetDatabase.GetAssetPath(assetRoot);
if (PathsAreEqual(path, srcPath))
    path = AssetDatabase.GenerateUniqueAssetPath(
        System.IO.Path.GetDirectoryName(srcPath).Replace('\\','/') + "/" + assetRoot.name + "Variant.prefab");

When it happens

Trigger: Calling CreateVariant with a path equal to `AssetDatabase.GetAssetPath(assetRoot)`, or a path differing only by case. Reusing the original prefab's path verbatim, or generating the variant path from the source asset path without changing the filename.

Common situations: Right-click 'Create Variant' workflows where the user picked the same filename, or scripts that derive the output path from the input asset path without appending a suffix. Cross-platform case-insensitive filesystems making two apparently different paths collide.

Related errors

• Given path is not valid: '{path}'
• ApplyPrefabAddedGameObjects requires that GameObjects share
• The path is null
• Prefab Asset path is null or empty
• The Prefab you want to instantiate is null.

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/78953512605fddcf. Report an issue: GitHub.