vm: add support for import.meta to Module

Fixes: https://github.com/nodejs/node/issues/18570

PR-URL: https://github.com/nodejs/node/pull/19277
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>

doc/api/vm.md

@@ -167,9 +167,49 @@ const contextifiedSandbox = vm.createContext({ secret: 42 });
     in stack traces produced by this Module.
   * `columnOffset` {integer} Spcifies the column number offset that is displayed
     in stack traces produced by this Module.
+  * `initalizeImportMeta` {Function} Called during evaluation of this Module to
+    initialize the `import.meta`. This function has the signature `(meta,
+    module)`, where `meta` is the `import.meta` object in the Module, and
+    `module` is this `vm.Module` object.
 
 Creates a new ES `Module` object.
 
+*Note*: Properties assigned to the `import.meta` object that are objects may
+allow the Module to access information outside the specified `context`, if the
+object is created in the top level context. Use `vm.runInContext()` to create
+objects in a specific context.
+
+```js
+const vm = require('vm');
+
+const contextifiedSandbox = vm.createContext({ secret: 42 });
+
+(async () => {
+  const module = new vm.Module(
+    'Object.getPrototypeOf(import.meta.prop).secret = secret;',
+    {
+      initializeImportMeta(meta) {
+        // Note: this object is created in the top context. As such,
+        // Object.getPrototypeOf(import.meta.prop) points to the
+        // Object.prototype in the top context rather than that in
+        // the sandbox.
+        meta.prop = {};
+      }
+    });
+  // Since module has no dependencies, the linker function will never be called.
+  await module.link(() => {});
+  module.initialize();
+  await module.evaluate();
+
+  // Now, Object.prototype.secret will be equal to 42.
+  //
+  // To fix this problem, replace
+  //     meta.prop = {};
+  // above with
+  //     meta.prop = vm.runInContext('{}', contextifiedSandbox);
+})();
+```
+
 ### module.dependencySpecifiers
 
 * {string[]}

lib/internal/bootstrap/node.js

@@ -108,10 +108,13 @@
         'DeprecationWarning', 'DEP0062', startup, true);
     }
 
-    if (process.binding('config').experimentalModules) {
+    if (process.binding('config').experimentalModules ||
-      process.emitWarning(
+        process.binding('config').experimentalVMModules) {
-        'The ESM module loader is experimental.',
+      if (process.binding('config').experimentalModules) {
-        'ExperimentalWarning', undefined);
+        process.emitWarning(
+          'The ESM module loader is experimental.',
+          'ExperimentalWarning', undefined);
+      }
       NativeModule.require('internal/process/esm_loader').setup();
     }
 

lib/internal/process/esm_loader.js

@@ -10,6 +10,10 @@ const { getURLFromFilePath } = require('internal/url');
 const Loader = require('internal/modules/esm/loader');
 const path = require('path');
 const { URL } = require('url');
+const {
+  initImportMetaMap,
+  wrapToModuleMap
+} = require('internal/vm/module');
 
 function normalizeReferrerURL(referrer) {
   if (typeof referrer === 'string' && path.isAbsolute(referrer)) {
@@ -19,7 +23,18 @@ function normalizeReferrerURL(referrer) {
 }
 
 function initializeImportMetaObject(wrap, meta) {
-  meta.url = wrap.url;
+  const vmModule = wrapToModuleMap.get(wrap);
+  if (vmModule === undefined) {
+    // This ModuleWrap belongs to the Loader.
+    meta.url = wrap.url;
+  } else {
+    const initializeImportMeta = initImportMetaMap.get(vmModule);
+    if (initializeImportMeta !== undefined) {
+      // This ModuleWrap belongs to vm.Module, initializer callback was
+      // provided.
+      initializeImportMeta(meta, vmModule);
+    }
+  }
 }
 
 let loaderResolve;

lib/internal/vm/module.js

@@ -43,6 +43,10 @@ const perContextModuleId = new WeakMap();
 const wrapMap = new WeakMap();
 const dependencyCacheMap = new WeakMap();
 const linkingStatusMap = new WeakMap();
+// vm.Module -> function
+const initImportMetaMap = new WeakMap();
+// ModuleWrap -> vm.Module
+const wrapToModuleMap = new WeakMap();
 
 class Module {
   constructor(src, options = {}) {
@@ -80,6 +84,16 @@ class Module {
       perContextModuleId.set(context, 1);
     }
 
+    if (options.initializeImportMeta !== undefined) {
+      if (typeof options.initializeImportMeta === 'function') {
+        initImportMetaMap.set(this, options.initializeImportMeta);
+      } else {
+        throw new ERR_INVALID_ARG_TYPE(
+          'options.initializeImportMeta', 'function',
+          options.initializeImportMeta);
+      }
+    }
+
     const wrap = new ModuleWrap(src, url, {
       [kParsingContext]: context,
       lineOffset: options.lineOffset,
@@ -88,6 +102,7 @@ class Module {
 
     wrapMap.set(this, wrap);
     linkingStatusMap.set(this, 'unlinked');
+    wrapToModuleMap.set(wrap, this);
 
     Object.defineProperties(this, {
       url: { value: url, enumerable: true },
@@ -206,5 +221,7 @@ class Module {
 }
 
 module.exports = {
-  Module
+  Module,
+  initImportMetaMap,
+  wrapToModuleMap
 };

test/parallel/test-vm-module-import-meta.js

@@ -0,0 +1,45 @@
+'use strict';
+
+// Flags: --experimental-vm-modules --harmony-import-meta
+
+const common = require('../common');
+const assert = require('assert');
+const { Module } = require('vm');
+
+common.crashOnUnhandledRejection();
+
+async function testBasic() {
+  const m = new Module('import.meta;', {
+    initializeImportMeta: common.mustCall((meta, module) => {
+      assert.strictEqual(module, m);
+      meta.prop = 42;
+    })
+  });
+  await m.link(common.mustNotCall());
+  m.instantiate();
+  const { result } = await m.evaluate();
+  assert.strictEqual(typeof result, 'object');
+  assert.strictEqual(Object.getPrototypeOf(result), null);
+  assert.strictEqual(result.prop, 42);
+  assert.deepStrictEqual(Reflect.ownKeys(result), ['prop']);
+}
+
+async function testInvalid() {
+  for (const invalidValue of [
+    null, {}, 0, Symbol.iterator, [], 'string', false
+  ]) {
+    common.expectsError(() => {
+      new Module('', {
+        initializeImportMeta: invalidValue
+      });
+    }, {
+      code: 'ERR_INVALID_ARG_TYPE',
+      type: TypeError
+    });
+  }
+}
+
+(async () => {
+  await testBasic();
+  await testInvalid();
+})();