fix: don't mutate user provided array

packages/builders/__tests__/util.test.ts

@@ -1,5 +1,5 @@
 import { describe, test, expect } from 'vitest';
-import { enableValidators, disableValidators, isValidationEnabled } from '../src/index.js';
+import { enableValidators, disableValidators, isValidationEnabled, normalizeArray } from '../src/index.js';
 
 describe('validation', () => {
 	test('enables validation', () => {
@@ -12,3 +12,19 @@ describe('validation', () => {
 		expect(isValidationEnabled()).toBeFalsy();
 	});
 });
+
+describe('normalizeArray', () => {
+	test('normalizes an array or array (when input is an array)', () => {
+		expect(normalizeArray([[1, 2, 3]])).toEqual([1, 2, 3]);
+	});
+
+	test('normalizes an array (when input is rest parameter)', () => {
+		expect(normalizeArray([1, 2, 3])).toEqual([1, 2, 3]);
+	});
+
+	test('always returns a clone', () => {
+		const arr = [1, 2, 3];
+		expect(normalizeArray([arr])).toEqual(arr);
+		expect(normalizeArray([arr])).not.toBe(arr);
+	});
+});

packages/builders/src/util/normalizeArray.ts

@@ -5,7 +5,7 @@
  * @param arr - The (possibly variadic) data to normalize
  */
 export function normalizeArray<ItemType>(arr: RestOrArray<ItemType>): ItemType[] {
-	if (Array.isArray(arr[0])) return arr[0];
+	if (Array.isArray(arr[0])) return [...arr[0]];
 	return arr as ItemType[];
 }