fix(util): cross realm IsPlainObject check (#4627)

* fix(util): cross realm IsPlainObject check

* Tweaks and benchmark

* Tweak

* Tweak

---------

Co-authored-by: Colin McDonnell <[email protected]>

Author: gislerro

packages/bench/index.ts

@@ -6,6 +6,7 @@ async function run() {
   const files = process.argv[2].split(",").map((file) => import.meta.resolve(`./${file}`).replace("file://", ""));
 
   for (const file of files) {
+    // await $`pnpm tsx --conditions @zod/source ${file}`;
     await $`pnpm tsx ${file}`;
   }
 }

packages/bench/object-moltar.ts

@@ -1,5 +1,5 @@
 import * as z4 from "zod/v4";
-import * as z4lib from "./node_modules/zod/dist/esm/v4/index.js";
+import * as z4lib from "./node_modules/zod4/dist/esm/v4/classic/index.js";
 import * as z3 from "zod3";
 import { metabench } from "./metabench.js";
 
@@ -24,7 +24,7 @@ const z4LibSchema = z4lib.object({
   string: z4lib.string(),
   longString: z4lib.string(),
   boolean: z4lib.boolean(),
-  deeplyNested: z4lib.strictObject({
+  deeplyNested: z4lib.object({
     foo: z4lib.string(),
     num: z4lib.number(),
     bool: z4lib.boolean(),
@@ -38,40 +38,40 @@ const z4Schema = z4.object({
   string: z4.string(),
   longString: z4.string(),
   boolean: z4.boolean(),
-  deeplyNested: z4.strictObject({
+  deeplyNested: z4.object({
     foo: z4.string(),
     num: z4.number(),
     bool: z4.boolean(),
   }),
 });
 
-const z4SchemaStrict = z4.strictObject({
-  number: z4.number(),
-  negNumber: z4.number(),
-  maxNumber: z4.number(),
-  string: z4.string(),
-  longString: z4.string(),
-  boolean: z4.boolean(),
-  deeplyNested: z4.strictObject({
-    foo: z4.string(),
-    num: z4.number(),
-    bool: z4.boolean(),
-  }),
-});
+// const z4SchemaStrict = z4.strictObject({
+//   number: z4.number(),
+//   negNumber: z4.number(),
+//   maxNumber: z4.number(),
+//   string: z4.string(),
+//   longString: z4.string(),
+//   boolean: z4.boolean(),
+//   deeplyNested: z4.strictObject({
+//     foo: z4.string(),
+//     num: z4.number(),
+//     bool: z4.boolean(),
+//   }),
+// });
 
-const z4SchemaLoose = z4.object({
-  number: z4.number(),
-  negNumber: z4.number(),
-  maxNumber: z4.number(),
-  string: z4.string(),
-  longString: z4.string(),
-  boolean: z4.boolean(),
-  deeplyNested: z4.object({
-    foo: z4.string(),
-    num: z4.number(),
-    bool: z4.boolean(),
-  }),
-});
+// const z4SchemaLoose = z4.object({
+//   number: z4.number(),
+//   negNumber: z4.number(),
+//   maxNumber: z4.number(),
+//   string: z4.string(),
+//   longString: z4.string(),
+//   boolean: z4.boolean(),
+//   deeplyNested: z4.object({
+//     foo: z4.string(),
+//     num: z4.number(),
+//     bool: z4.boolean(),
+//   }),
+// });
 
 const DATA = Array.from({ length: 1000 }, () =>
   Object.freeze({
@@ -97,9 +97,9 @@ const bench = metabench("z.object() safeParse", {
   zod3() {
     for (const _ of DATA) z3Schema.parse(_);
   },
-  // zod4lib() {
-  //   for (const _ of DATA) z4LibSchema.parse(_);
-  // },
+  zod4lib() {
+    for (const _ of DATA) z4LibSchema.parse(_);
+  },
   zod4(){
     for (const _ of DATA) z4Schema.parse(_);
   }

packages/bench/package.json

@@ -6,8 +6,8 @@
     "arktype": "^2.1.19",
     "valibot": "^1.0.0",
     "zod": "workspace:*",
-    "zodnext": "npm:zod@^3.25.0",
-    "zod3": "npm:zod@^3.23.7"
+    "zod3": "npm:zod@~3.24.0",
+    "zod4": "npm:zod@latest"
   },
   "scripts": {
     "bench": "tsx --conditions @zod/source index.ts"

packages/bench/tsconfig.bench.json

@@ -4,7 +4,7 @@
     "noEmit": true,
     "extendedDiagnostics": true,
     "traceResolution": true,
-    "customConditions": [],
+    "customConditions": ["@zod/source"],
     "skipDefaultLibCheck": true,
     "skipLibCheck": true,
   }

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

@@ -328,12 +328,27 @@ export const allowsEval: { value: boolean } = cached(() => {
   }
 });
 
-export function isPlainObject(data: any): data is Record<PropertyKey, unknown> {
-  return (
-    typeof data === "object" &&
-    data !== null &&
-    (Object.getPrototypeOf(data) === Object.prototype || Object.getPrototypeOf(data) === null)
-  );
+function _isObject(o: any) {
+  return Object.prototype.toString.call(o) === "[object Object]";
+}
+
+export function isPlainObject(o: any): o is Record<PropertyKey, unknown> {
+  if (isObject(o) === false) return false;
+
+  // modified constructor
+  const ctor = o.constructor;
+  if (ctor === undefined) return true;
+
+  // modified prototype
+  const prot = ctor.prototype;
+  if (isObject(prot) === false) return false;
+
+  // ctor doesn't have static `isPrototypeOf`
+  if (Object.prototype.hasOwnProperty.call(prot, "isPrototypeOf") === false) {
+    return false;
+  }
+
+  return true;
 }
 
 export function numKeys(data: any): number {