Reverts "Reland "Output .js files as ES6 modules. (#52023)" (#53688)" (flutter/engine#53709)

Reverts: flutter/engine#53688
Initiated by: jiahaog
Reason for reverting: canvaskit.js cannot be loaded in an internal end to end test - see b/350885206
Original PR Author: eyebrowsoffire

Reviewed By: {ditman}

This change reverts the following previous change:
This is an attempt to reland https://github.com/flutter/engine/pull/52023. The issue previously is that if it was not specified by the user, the default CanvasKit base URL did not have a leading slash, which does not work when doing dynamic imports.

DEPS

@@ -277,7 +277,7 @@ allowed_hosts = [
 ]
 
 deps = {
-  'src': 'https://github.com/flutter/buildroot.git' + '@' + 'e265c359126b24351f534080fb22edaa159f2215',
+  'src': 'https://github.com/flutter/buildroot.git' + '@' + '8c2d66fa4e6298894425f5bdd0591bc5b1154c53',
 
   'src/flutter/third_party/depot_tools':
   Var('chromium_git') + '/chromium/tools/depot_tools.git' + '@' + '580b4ff3f5cd0dcaa2eacda28cefe0f45320e8f7',

engine/src/flutter/lib/web_ui/flutter_js/src/canvaskit_loader.js

@@ -6,11 +6,11 @@ import { createWasmInstantiator } from "./instantiate_wasm.js";
 import { joinPathSegments } from "./utils.js";
 
 export const loadCanvasKit = (deps, config, browserEnvironment, canvasKitBaseUrl) => {
-  window.flutterCanvasKitLoaded = (async () => {
-    if (window.flutterCanvasKit) {
-      // The user has set this global variable ahead of time, so we just return that.
-      return window.flutterCanvasKit;
-    }
+  if (window.flutterCanvasKit) {
+    // The user has set this global variable ahead of time, so we just return that.
+    return Promise.resolve(window.flutterCanvasKit);
+  }
+  window.flutterCanvasKitLoaded = new Promise((resolve, reject) => {
     const supportsChromiumCanvasKit = browserEnvironment.hasChromiumBreakIterators && browserEnvironment.hasImageCodecs;
     if (!supportsChromiumCanvasKit && config.canvasKitVariant == "chromium") {
       throw "Chromium CanvasKit variant specifically requested, but unsupported in this browser";
@@ -25,11 +25,24 @@ export const loadCanvasKit = (deps, config, browserEnvironment, canvasKitBaseUrl
       canvasKitUrl = deps.flutterTT.policy.createScriptURL(canvasKitUrl);
     }
     const wasmInstantiator = createWasmInstantiator(joinPathSegments(baseUrl, "canvaskit.wasm"));
-    const canvasKitModule = await import(canvasKitUrl);
-    window.flutterCanvasKit = await canvasKitModule.default({
-      instantiateWasm: wasmInstantiator,
+    const script = document.createElement("script");
+    script.src = canvasKitUrl;
+    if (config.nonce) {
+      script.nonce = config.nonce;
+    }
+    script.addEventListener("load", async () => {
+      try {
+        const canvasKit = await CanvasKitInit({
+          instantiateWasm: wasmInstantiator,
+        });
+        window.flutterCanvasKit = canvasKit;
+        resolve(canvasKit);  
+      } catch (e) {
+        reject(e);
+      }
     });
-    return window.flutterCanvasKit;
-  })();
+    script.addEventListener("error", reject);
+    document.head.appendChild(script);
+  });
   return window.flutterCanvasKitLoaded;
 }

engine/src/flutter/lib/web_ui/flutter_js/src/skwasm_loader.js

@@ -5,28 +5,43 @@
 import { createWasmInstantiator } from "./instantiate_wasm.js";
 import { joinPathSegments } from "./utils.js";
 
-export const loadSkwasm = async (deps, config, browserEnvironment, baseUrl) => {
-  let skwasmUrl = joinPathSegments(baseUrl, "skwasm.js");
-  if (deps.flutterTT.policy) {
-    skwasmUrl = deps.flutterTT.policy.createScriptURL(skwasmUrl);
-  }
-  const wasmInstantiator = createWasmInstantiator(joinPathSegments(baseUrl, "skwasm.wasm"));
-  const skwasm = await import(skwasmUrl);
-  return await skwasm.default({
-    instantiateWasm: wasmInstantiator,
-    locateFile: (fileName, scriptDirectory) => {
-      // When hosted via a CDN or some other url that is not the same
-      // origin as the main script of the page, we will fail to create
-      // a web worker with the .worker.js script. This workaround will
-      // make sure that the worker JS can be loaded regardless of where
-      // it is hosted.
-      const url = scriptDirectory + fileName;
-      if (url.endsWith('.worker.js')) {
-        return URL.createObjectURL(new Blob(
-          [`importScripts('${url}');`],
-          { 'type': 'application/javascript' }));
-      }
-      return url;
+export const loadSkwasm = (deps, config, browserEnvironment, baseUrl) => {
+  return new Promise((resolve, reject) => {
+    let skwasmUrl = joinPathSegments(baseUrl, "skwasm.js");
+    if (deps.flutterTT.policy) {
+      skwasmUrl = deps.flutterTT.policy.createScriptURL(skwasmUrl);
     }
+    const wasmInstantiator = createWasmInstantiator(joinPathSegments(baseUrl, "skwasm.wasm"));
+    const script = document.createElement("script");
+    script.src = skwasmUrl;
+    if (config.nonce) {
+      script.nonce = config.nonce;
+    }
+    script.addEventListener("load", async () => {
+      try {
+        const skwasmInstance = await skwasm({
+          instantiateWasm: wasmInstantiator,
+          locateFile: (fileName, scriptDirectory) => {
+            // When hosted via a CDN or some other url that is not the same
+            // origin as the main script of the page, we will fail to create
+            // a web worker with the .worker.js script. This workaround will
+            // make sure that the worker JS can be loaded regardless of where
+            // it is hosted.
+            const url = scriptDirectory + fileName;
+            if (url.endsWith(".worker.js")) {
+              return URL.createObjectURL(new Blob(
+                [`importScripts("${url}");`],
+                { "type": "application/javascript" }));
+            }
+            return url;
+          }
+        });
+        resolve(skwasmInstance);
+      } catch (e) {
+        reject(e);
+      }
+    });
+    script.addEventListener("error", reject);
+    document.head.appendChild(script);
   });
 }

engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/canvaskit_api.dart

@@ -259,13 +259,12 @@ extension CanvasKitExtension on CanvasKit {
   );
 }
 
-@JS()
-@staticInterop
-class CanvasKitModule {}
+@JS('window.CanvasKitInit')
+external JSAny _CanvasKitInit(CanvasKitInitOptions options);
 
-extension CanvasKitModuleExtension on CanvasKitModule {
-  @JS('default')
-  external JSPromise<JSAny> defaultExport(CanvasKitInitOptions options);
+Future<CanvasKit> CanvasKitInit(CanvasKitInitOptions options) {
+  return js_util.promiseToFuture<CanvasKit>(
+          _CanvasKitInit(options).toObjectShallow);
 }
 
 typedef LocateFileCallback = String Function(String file, String unusedBase);
@@ -3662,11 +3661,11 @@ String canvasKitWasmModuleUrl(String file, String canvasKitBase) =>
 /// Downloads the CanvasKit JavaScript, then calls `CanvasKitInit` to download
 /// and intialize the CanvasKit wasm.
 Future<CanvasKit> downloadCanvasKit() async {
-  final CanvasKitModule canvasKitModule = await _downloadOneOf(_canvasKitJsUrls);
+  await _downloadOneOf(_canvasKitJsUrls);
 
-  final CanvasKit canvasKit = (await canvasKitModule.defaultExport(CanvasKitInitOptions(
+  final CanvasKit canvasKit = await CanvasKitInit(CanvasKitInitOptions(
     locateFile: createLocateFileCallback(canvasKitWasmModuleUrl),
-  )).toDart) as CanvasKit;
+  ));
 
   if (canvasKit.ParagraphBuilder.RequiresClientICU() && !browserSupportsCanvaskitChromium) {
     throw Exception(
@@ -3682,12 +3681,10 @@ Future<CanvasKit> downloadCanvasKit() async {
 /// downloads it.
 ///
 /// If none of the URLs can be downloaded, throws an [Exception].
-Future<CanvasKitModule> _downloadOneOf(Iterable<String> urls) async {
+Future<void> _downloadOneOf(Iterable<String> urls) async {
   for (final String url in urls) {
-    try {
-      return await _downloadCanvasKitJs(url);
-    } catch (_) {
-      continue;
+    if (await _downloadCanvasKitJs(url)) {
+      return;
     }
   }
 
@@ -3701,7 +3698,32 @@ Future<CanvasKitModule> _downloadOneOf(Iterable<String> urls) async {
 ///
 /// Returns a [Future] that completes with `true` if the CanvasKit JavaScript
 /// file was successfully downloaded, or `false` if it failed.
-Future<CanvasKitModule> _downloadCanvasKitJs(String url) async {
-  final JSAny scriptUrl = createTrustedScriptUrl(url);
-  return (await importModule(scriptUrl).toDart) as CanvasKitModule;
+Future<bool> _downloadCanvasKitJs(String url) {
+  final DomHTMLScriptElement canvasKitScript =
+      createDomHTMLScriptElement(configuration.nonce);
+  canvasKitScript.src = createTrustedScriptUrl(url);
+
+  final Completer<bool> canvasKitLoadCompleter = Completer<bool>();
+
+  late final DomEventListener loadCallback;
+  late final DomEventListener errorCallback;
+
+  void loadEventHandler(DomEvent _) {
+    canvasKitScript.remove();
+    canvasKitLoadCompleter.complete(true);
+  }
+  void errorEventHandler(DomEvent errorEvent) {
+    canvasKitScript.remove();
+    canvasKitLoadCompleter.complete(false);
+  }
+
+  loadCallback = createDomEventListener(loadEventHandler);
+  errorCallback = createDomEventListener(errorEventHandler);
+
+  canvasKitScript.addEventListener('load', loadCallback);
+  canvasKitScript.addEventListener('error', errorCallback);
+
+  domDocument.head!.appendChild(canvasKitScript);
+
+  return canvasKitLoadCompleter.future;
 }

engine/src/flutter/lib/web_ui/lib/src/engine/configuration.dart

@@ -241,7 +241,7 @@ class FlutterConfiguration {
       _configuration?.canvasKitBaseUrl ?? _defaultCanvasKitBaseUrl;
   static const String _defaultCanvasKitBaseUrl = String.fromEnvironment(
     'FLUTTER_WEB_CANVASKIT_URL',
-    defaultValue: '/canvaskit/',
+    defaultValue: 'canvaskit/',
   );
 
   /// The variant of CanvasKit to download.

engine/src/flutter/lib/web_ui/lib/src/engine/dom.dart

@@ -3383,16 +3383,16 @@ final DomTrustedTypePolicy _ttPolicy = domWindow.trustedTypes!.createPolicy(
 
 /// Converts a String `url` into a [DomTrustedScriptURL] object when the
 /// Trusted Types API is available, else returns the unmodified `url`.
-JSAny createTrustedScriptUrl(String url) {
+Object createTrustedScriptUrl(String url) {
   if (domWindow.trustedTypes != null) {
     // Pass `url` through Flutter Engine's TrustedType policy.
     final DomTrustedScriptURL trustedUrl = _ttPolicy.createScriptURL(url);
 
     assert(trustedUrl.url != '', 'URL: $url rejected by TrustedTypePolicy');
 
-    return trustedUrl as JSAny;
+    return trustedUrl;
   }
-  return url.toJS;
+  return url;
 }
 
 DomMessageChannel createDomMessageChannel() => DomMessageChannel();

engine/src/flutter/lib/web_ui/test/canvaskit/initialization/does_not_mock_module_exports_test.dart

@@ -18,6 +18,13 @@ void testMain() {
       // Initialize CanvasKit...
       await bootstrapAndRunApp();
 
+      // CanvasKitInit should be defined...
+      expect(
+        js_util.hasProperty(domWindow, 'CanvasKitInit'),
+        isTrue,
+        reason: 'CanvasKitInit should be defined on Window',
+      );
+
       // window.exports and window.module should be undefined!
       expect(
         js_util.hasProperty(domWindow, 'exports'),

engine/src/flutter/lib/web_ui/test/engine/configuration_test.dart

@@ -22,16 +22,16 @@ void testMain() {
     test('initializes with null', () async {
       final FlutterConfiguration config = FlutterConfiguration.legacy(null);
 
-      expect(config.canvasKitBaseUrl, '/canvaskit/'); // _defaultCanvasKitBaseUrl
+      expect(config.canvasKitBaseUrl, 'canvaskit/'); // _defaultCanvasKitBaseUrl
     });
 
     test('legacy constructor initializes with a Js Object', () async {
       final FlutterConfiguration config = FlutterConfiguration.legacy(
         js_util.jsify(<String, Object?>{
-          'canvasKitBaseUrl': '/some_other_url/',
+          'canvasKitBaseUrl': 'some_other_url/',
         }) as JsFlutterConfiguration);
 
-      expect(config.canvasKitBaseUrl, '/some_other_url/');
+      expect(config.canvasKitBaseUrl, 'some_other_url/');
     });
   });
 
@@ -39,13 +39,13 @@ void testMain() {
     test('throws assertion error if already initialized from JS', () async {
       final FlutterConfiguration config = FlutterConfiguration.legacy(
         js_util.jsify(<String, Object?>{
-          'canvasKitBaseUrl': '/some_other_url/',
+          'canvasKitBaseUrl': 'some_other_url/',
         }) as JsFlutterConfiguration);
 
       expect(() {
         config.setUserConfiguration(
           js_util.jsify(<String, Object?>{
-            'canvasKitBaseUrl': '/yet_another_url/',
+            'canvasKitBaseUrl': 'yet_another_url/',
           }) as JsFlutterConfiguration);
       }, throwsAssertionError);
     });
@@ -55,10 +55,10 @@ void testMain() {
 
       config.setUserConfiguration(
         js_util.jsify(<String, Object?>{
-          'canvasKitBaseUrl': '/one_more_url/',
+          'canvasKitBaseUrl': 'one_more_url/',
         }) as JsFlutterConfiguration);
 
-      expect(config.canvasKitBaseUrl, '/one_more_url/');
+      expect(config.canvasKitBaseUrl, 'one_more_url/');
     });
 
     test('can receive non-existing properties without crashing', () async {