Copying by descriptor is in fact necessary

packages/ses/src/compartment-shim.js

@@ -13,7 +13,14 @@ import * as babel from '@agoric/babel-standalone';
 // Both produce:
 //   Error: 'default' is not exported by .../@agoric/babel-standalone/babel.js
 import { makeModuleAnalyzer } from '@agoric/transform-module';
-import { assign, freeze, getOwnPropertyNames, entries } from './commons.js';
+import {
+  assign,
+  create,
+  defineProperties,
+  getOwnPropertyNames,
+  getOwnPropertyDescriptors,
+  entries,
+} from './commons.js';
 import { createGlobalObject } from './global-object.js';
 import { performEval } from './evaluate.js';
 import { getCurrentRealmRec } from './realm-rec.js';
@@ -201,11 +208,9 @@ export class Compartment {
 
     // TODO just pass globalLexicals as globalObject
     // https://github.com/Agoric/SES-shim/issues/365
-    const localObject = freeze({
-      __proto__: null,
-      ...globalLexicals,
-      ...endowments,
-    });
+    const localObject = create(null);
+    defineProperties(localObject, getOwnPropertyDescriptors(globalLexicals));
+    defineProperties(localObject, getOwnPropertyDescriptors(endowments));
 
     return performEval(realmRec, source, globalObject, localObject, {
       globalTransforms,

packages/ses/src/module-instance.js

@@ -1,7 +1,14 @@
 import { performEval } from './evaluate.js';
 import { getCurrentRealmRec } from './realm-rec.js';
 import { getDeferredExports } from './module-proxy.js';
-import { create, entries, keys, freeze, defineProperty } from './commons.js';
+import {
+  create,
+  getOwnPropertyDescriptors,
+  entries,
+  keys,
+  freeze,
+  defineProperty,
+} from './commons.js';
 
 // q, for enquoting strings in error messages.
 const q = JSON.stringify;
@@ -46,9 +53,9 @@ export const makeModuleInstance = (
 
   // {_localName_: accessor} proxy traps for globalThis, globalLexicals, and
   // live bindings.
-  // There must be no accessor properties on globalLexicals so we take a
-  // snapshot of enumerable properties.
-  const localObject = { __proto__: null, ...globalLexicals };
+  // The globalLexicals object is frozen and the corresponding properties of
+  // localObject must be immutable, so we copy the descriptors.
+  const localObject = create(null, getOwnPropertyDescriptors(globalLexicals));
 
   // {_localName_: init(initValue) -> initValue} used by the
   // rewritten code to initialize exported fixed bindings.