fix(v4): ensure array defaults are shallow-cloned (#5173)

Author: acburdine

packages/zod/src/v4/classic/tests/default.test.ts

@@ -324,6 +324,14 @@ test("defaulted object schema returns shallow clone", () => {
  expect(result1).toEqual(result2);
 });
 
+test("defaulted array schema returns shallow clone", () => {
+ const schema = z.array(z.string()).default(["x"]);
+ const result1 = schema.parse(undefined);
+ const result2 = schema.parse(undefined);
+ expect(result1).not.toBe(result2);
+ expect(result1).toEqual(result2);
+});
+
 test("direction-aware defaults", () => {
  const schema = z.string().default("hello");
 

packages/zod/src/v4/core/util.ts

@@ -395,6 +395,7 @@ export function isPlainObject(o: any): o is Record<PropertyKey, unknown> {
 
 export function shallowClone(o: any): any {
  if (isPlainObject(o)) return { ...o };
+ if (Array.isArray(o)) return [...o];
  return o;
 }