allow non-overwriting extends with refinements. 4.3.1

Author: colinhacks

packages/zod/jsr.json

@@ -1,6 +1,6 @@
 {
   "name": "@zod/zod",
-  "version": "4.3.0",
+  "version": "4.3.1",
   "exports": {
     "./package.json": "./package.json",
     ".": "./src/index.ts",

packages/zod/package.json

@@ -1,6 +1,6 @@
 {
   "name": "zod",
-  "version": "4.3.0",
+  "version": "4.3.1",
   "type": "module",
   "license": "MIT",
   "author": "Colin McDonnell <zod@colinhacks.com>",

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

@@ -602,14 +602,31 @@ test("index signature in shape", () => {
   expectTypeOf<schema>().toEqualTypeOf<Record<string, string>>();
 });
 
-test("extent() on object with refinements should throw", () => {
+test("extend() on object with refinements should throw when overwriting properties", () => {
   const schema = z
     .object({
       a: z.string(),
     })
     .refine(() => true);
 
-  expect(() => schema.extend({ b: z.string() })).toThrow();
+  expect(() => schema.extend({ a: z.number() })).toThrow();
+});
+
+test("extend() on object with refinements should not throw when adding new properties", () => {
+  const schema = z
+    .object({
+      a: z.string(),
+    })
+    .refine((data) => data.a.length > 0);
+
+  // Should not throw since 'b' doesn't overlap with 'a'
+  const extended = schema.extend({ b: z.number() });
+
+  // Verify the extended schema works correctly
+  expect(extended.parse({ a: "hello", b: 42 })).toEqual({ a: "hello", b: 42 });
+
+  // Verify the original refinement still applies
+  expect(() => extended.parse({ a: "", b: 42 })).toThrow();
 });
 
 test("safeExtend() on object with refinements should not throw", () => {

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

@@ -656,7 +656,14 @@ export function extend(schema: schemas.$ZodObject, shape: schemas.$ZodShape): an
   const checks = schema._zod.def.checks;
   const hasChecks = checks && checks.length > 0;
   if (hasChecks) {
-    throw new Error("Object schemas containing refinements cannot be extended. Use `.safeExtend()` instead.");
+    // Only throw if new shape overlaps with existing shape
+    // Use getOwnPropertyDescriptor to check key existence without accessing values
+    const existingShape = schema._zod.def.shape;
+    for (const key in shape) {
+      if (Object.getOwnPropertyDescriptor(existingShape, key) !== undefined) {
+        throw new Error("Cannot overwrite keys on object schemas containing refinements. Use `.safeExtend()` instead.");
+      }
+    }
   }
 
   const def = mergeDefs(schema._zod.def, {
@@ -665,7 +672,6 @@ export function extend(schema: schemas.$ZodObject, shape: schemas.$ZodShape): an
       assignProp(this, "shape", _shape); // self-caching
       return _shape;
     },
-    checks: [],
   });
   return clone(schema, def) as any;
 }

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

@@ -1,5 +1,5 @@
 export const version = {
   major: 4,
   minor: 3,
-  patch: 0 as number,
+  patch: 1 as number,
 } as const;

play.ts

@@ -1,7 +1,5 @@
 import * as z from "./packages/zod/src/v4/index.js";
 
-const A = z.object({
-  a: z.string().optional(),
-});
+const Schema = z.record(z.enum(["key1", "key2"]), z.number());
 
-console.log(A.parse({}));
+console.log(z.toJSONSchema(Schema));