add virtual module loader

Author: Jack-Works

src/devtools/262_worker.mjs

@@ -8,6 +8,13 @@ import {
   Get,
   CreateDataPropertyOrThrow,
   Value,
+  Realm,
+  Throw,
+  Descriptor,
+  CreateBuiltinFunction,
+  JSStringValue,
+  CreateNonEnumerableDataPropertyOrThrow,
+  surroundingAgent,
 } from '../../lib/engine262.mjs';
 import { Inspector, createConsole } from '../../lib/inspector.mjs';
 import { Test262HarnessFiles } from '../shared/harness.mjs';
@@ -44,12 +51,41 @@ function recreateAgent(features, signal) {
   const agent = new Agent({ features });
   setSurroundingAgent(agent);
 
+
   inspector.attachAgent(agent, []);
   signal.addEventListener('abort', () => inspector.detachAgent(agent), { once: true });
 
-  const realm = new ManagedRealm({});
+  const realm = new ManagedRealm({ name: 'playground repl' });
   createConsole(realm, {});
 
+  if (features.includes('virtual-module-loader')) {
+    const virtualModuleCache = new Map();
+    agent.hostDefinedOptions.loadImportedModule = (referrer, specifier, attributes, hostDefined, finish) => {
+      const importerRealm = referrer instanceof Realm ? referrer : referrer.Realm;
+      if (importerRealm instanceof ManagedRealm && virtualModuleCache.has(specifier)) {
+        finish(importerRealm.compileModule(virtualModuleCache.get(specifier), { specifier }));
+        return;
+      }
+      finish(Throw('SyntaxError', 'CouldNotResolveModule', specifier, 'repl'));
+    }
+    realm.scope(() => {
+      const defineModule = CreateBuiltinFunction.from(function* defineModule(specifier, source) {
+        if (!(specifier instanceof JSStringValue)) {
+          return Throw('TypeError', 'NotAString', specifier);
+        }
+        if (!(source instanceof JSStringValue)) {
+          return Throw('TypeError', 'NotAString', source);
+        }
+        if (surroundingAgent.debugger_cannotPreview) {
+          return surroundingAgent.debugger_cannotPreview;
+        }
+        virtualModuleCache.set(specifier.stringValue(), source.stringValue());
+        return Value.undefined;
+      })
+      CreateNonEnumerableDataPropertyOrThrow(realm.GlobalObject, Value('defineModule'), defineModule);
+    });
+  }
+
   if (features.includes('test262-harness')) {
     createTest262Intrinsics(realm, false);
     evalQ((_Q, X) => {

src/devtools/index.mjs

@@ -44,6 +44,7 @@ const L = {
     title: ': A JavaScript engine written in JavaScript for development and exploration',
     featureSwitch: 'Enable {name}',
     includeTest262Env: 'Include test262 environment',
+    includeVirtualModuleLoader: 'Include virtual module loader for the playground',
     evaluateAs: 'Evaluate as ',
     console: 'Console',
     script: 'Script',
@@ -300,6 +301,23 @@ function modifyUI(ConsolePanel) {
       ),
     );
   }
+  {
+    const debugModuleLoader = Common.Settings.Settings.instance().createSetting(
+      'engine262:virtual-module-loader',
+      true,
+    );
+    if (state.features) {
+      debugModuleLoader.set(state.features.includes('virtual-module-loader'));
+    }
+    debugModuleLoader.addChangeListener(updateFeature);
+    featureSettings.push(debugModuleLoader);
+    settingsPane.append(
+      SettingsUI.createSettingCheckbox(
+        S.engine262(L.engine262.includeVirtualModuleLoader),
+        debugModuleLoader,
+      ),
+    );
+  }
   function updateFeature() {
     const features = [];
     for (const setting of featureSettings) {