feat(ses,module-source): Add ModuleSource shim

packages/module-source/NEWS.md

@@ -1,5 +1,10 @@
 User-visible changes in `@endo/module-source`:
 
+# Next release
+
+- Adds `@endo/module-source/shim.js` to shim `globalThis.ModuleSource`.
+  The shim currently replaces the native `globalThis.ModuleSource` if present.
+
 # v1.0.0 (2024-07-30)
 
 - Renamed from `@endo/static-module-record` to `@endo/module-source` exporting

packages/module-source/package.json

@@ -23,6 +23,7 @@
   "main": "./index.js",
   "exports": {
     ".": "./index.js",
+    "./shim.js": "./shim.js",
     "./package.json": "./package.json"
   },
   "scripts": {

packages/module-source/shim.js

@@ -0,0 +1,10 @@
+/* global globalThis */
+
+import { ModuleSource } from './index.js';
+
+Object.defineProperty(globalThis, 'ModuleSource', {
+  value: ModuleSource,
+  enumerable: false,
+  writable: true,
+  configurable: true,
+});

packages/module-source/src/module-source.js

@@ -100,3 +100,32 @@ export function ModuleSource(source, opts = {}) {
   this.__needsImportMeta__ = needsImportMeta;
   freeze(this);
 }
+
+// AbstractModuleSource
+// https://github.com/tc39/proposal-source-phase-imports?tab=readme-ov-file#js-module-source
+//
+// We are attempting to ensure that a JavaScript shim (particularly ses) is
+// forward-compatible as the engine evolves beneath it, with or without this
+// ModuleSource shim, and with our without a native AbstractModuleSource which
+// remains undecided.
+// Lockdown does not gracefully handle the presence of an unexpected prototype,
+// but can tolerate the absence of an expected prototype.
+// So, we are providing AbstractModuleSource since we can better tolerate the
+// various uncertain futures.
+//
+// WebAssembly and ModuleSource are both in motion.
+// The Source Phase Imports proposal implies an additional AbstractModuleSource
+// layer above the existing WebAssembly.Module that would be shared by
+// the JavaScript ModuleSource prototype chains.
+// At time of writing, no version of WebAssembly provides the shared base
+// class, and the ModuleSource *shim* gains nothing from sharing one when that
+// prototype when it comes into being.
+// So, we do not attempt to entangle our AbstractModuleSource with
+// WebAssembly.Module.
+
+function AbstractModuleSource() {
+  // no-op, safe to super()
+}
+
+Object.setPrototypeOf(ModuleSource, AbstractModuleSource);
+Object.setPrototypeOf(ModuleSource.prototype, AbstractModuleSource.prototype);

packages/ses/NEWS.md

@@ -13,6 +13,8 @@ User-visible changes in `ses`:
   - Node 18, Node 20, and all browsers have `structuredClone`
   - Node <= 16 have neither, but are also no longer supported by Endo.
 - Now exports separate layer for console shim: `ses/console-shim.js`.
+- Adds permits for `ModuleSource` if present, either the native implementation
+  or from `@endo/module-source/shim.js`.
 
 # v1.8.0 (2024-08-27)
 

packages/ses/src/get-anonymous-intrinsics.js

@@ -161,5 +161,19 @@ export const getAnonymousIntrinsics = () => {
     );
   }
 
+  if (globalThis.ModuleSource) {
+    const AbstractModuleSourcePrototype = getPrototypeOf(
+      globalThis.ModuleSource.prototype,
+    );
+    intrinsics['%AbstractModuleSourcePrototype%'] =
+      AbstractModuleSourcePrototype;
+    intrinsics['%AbstractModuleSource%'] =
+      AbstractModuleSourcePrototype.constructor;
+  }
+
+  if (globalThis.ModuleSource) {
+    intrinsics['%ModuleSourcePrototype%'] = globalThis.ModuleSource.prototype;
+  }
+
   return intrinsics;
 };

packages/ses/src/permits-intrinsics.js

@@ -156,8 +156,10 @@ export default function whitelistIntrinsics(
       return;
     }
 
-    // We can't clean [[prototype]], therefore abort.
-    throw TypeError(`Unexpected intrinsic ${path}.__proto__ at ${protoName}`);
+    // We can't clean [[Prototype]], therefore abort.
+    throw TypeError(
+      `Unexpected [[Prototype]] at ${path}.__proto__ (expected ${protoName || '%ObjectPrototype%'})`,
+    );
   }
 
   /*
@@ -212,7 +214,9 @@ export default function whitelistIntrinsics(
       }
     }
 
-    throw TypeError(`Unexpected whitelist permit ${permit} at ${path}`);
+    throw TypeError(
+      `Unexpected property ${prop} with permit ${permit} at ${path}`,
+    );
   }
 
   /*

packages/ses/src/permits.js

@@ -101,8 +101,12 @@ export const universalPropertyNames = {
 
   // ESNext
 
+  // https://github.com/tc39/proposal-source-phase-imports?tab=readme-ov-file#js-module-source
+  ModuleSource: 'ModuleSource',
+
   lockdown: 'lockdown',
   harden: 'harden',
+
   HandledPromise: 'HandledPromise', // TODO: Until Promise.delegate (see below).
 };
 
@@ -1505,6 +1509,25 @@ export const permitted = {
     resolve: fn,
   },
 
+  // https://github.com/tc39/proposal-source-phase-imports?tab=readme-ov-file#js-module-source
+  '%AbstractModuleSourcePrototype%': {
+    constructor: '%AbstractModuleSource%',
+    '@@toStringTag': getter,
+  },
+  '%AbstractModuleSource%': {
+    '[[Proto]]': '%FunctionPrototype%',
+    prototype: '%AbstractModuleSourcePrototype%',
+  },
+  '%ModuleSourcePrototype%': {
+    '[[Proto]]': '%AbstractModuleSourcePrototype%',
+    constructor: 'ModuleSource',
+    '@@toStringTag': getter,
+  },
+  ModuleSource: {
+    '[[Proto]]': '%AbstractModuleSource%',
+    prototype: '%ModuleSourcePrototype%',
+  },
+
   Promise: {
     // Properties of the Promise Constructor
     '[[Proto]]': '%FunctionPrototype%',

packages/ses/test/module-source.test.js

@@ -1,9 +1,24 @@
+/// <reference types="ses">
+
 import test from 'ava';
 import '../index.js';
-import { ModuleSource } from '@endo/module-source';
+import '@endo/module-source/shim.js';
 
 lockdown();
 
+test('module source property/prototype graph and hardening', t => {
+  const AbstractModuleSource = Object.getPrototypeOf(ModuleSource);
+  t.is(
+    Object.getPrototypeOf(ModuleSource.prototype),
+    AbstractModuleSource.prototype,
+  );
+
+  t.truthy(Object.isFrozen(ModuleSource));
+  t.truthy(Object.isFrozen(AbstractModuleSource));
+  t.truthy(Object.isFrozen(ModuleSource.prototype));
+  t.truthy(Object.isFrozen(AbstractModuleSource.prototype));
+});
+
 test('module source constructor', t => {
   const msr = new ModuleSource(`
     import foo from 'import-default-export-from-me.js';
@@ -42,3 +57,7 @@ test('module source constructor', t => {
     'ModuleSource imports should be frozen',
   );
 });
+
+test('ModuleSource is a shared intrinsic', t => {
+  t.truthy(ModuleSource === new Compartment().globalThis.ModuleSource);
+});