Revert "Revert "[web] Move JS content to its own `.js` files (#117691)" (#120275)" (#120363)

This reverts commit 0fb4406c.

packages/flutter_tools/lib/src/artifacts.dart

@@ -9,6 +9,7 @@ import 'base/common.dart';
 import 'base/file_system.dart';
 import 'base/os.dart';
 import 'base/platform.dart';
+import 'base/user_messages.dart';
 import 'base/utils.dart';
 import 'build_info.dart';
 import 'cache.dart';
@@ -62,6 +63,9 @@ enum Artifact {
   /// Tools related to subsetting or icon font files.
   fontSubset,
   constFinder,
+
+  /// The location of file generators.
+  flutterToolsFileGenerators,
 }
 
 /// A subset of [Artifact]s that are platform and build mode independent
@@ -202,6 +206,8 @@ String? _artifactToFileName(Artifact artifact, Platform hostPlatform, [ BuildMod
       return 'font-subset$exe';
     case Artifact.constFinder:
       return 'const_finder.dart.snapshot';
+    case Artifact.flutterToolsFileGenerators:
+      return '';
   }
 }
 
@@ -525,6 +531,8 @@ class CachedArtifacts implements Artifacts {
       case Artifact.windowsCppClientWrapper:
       case Artifact.windowsDesktopPath:
         return _getHostArtifactPath(artifact, platform, mode);
+      case Artifact.flutterToolsFileGenerators:
+        return _getFileGeneratorsPath();
     }
   }
 
@@ -562,6 +570,8 @@ class CachedArtifacts implements Artifacts {
       case Artifact.windowsCppClientWrapper:
       case Artifact.windowsDesktopPath:
         return _getHostArtifactPath(artifact, platform, mode);
+      case Artifact.flutterToolsFileGenerators:
+        return _getFileGeneratorsPath();
     }
   }
 
@@ -611,6 +621,8 @@ class CachedArtifacts implements Artifacts {
       case Artifact.windowsCppClientWrapper:
       case Artifact.windowsDesktopPath:
         return _getHostArtifactPath(artifact, platform, mode);
+      case Artifact.flutterToolsFileGenerators:
+        return _getFileGeneratorsPath();
     }
   }
 
@@ -685,6 +697,8 @@ class CachedArtifacts implements Artifacts {
       case Artifact.fuchsiaFlutterRunner:
       case Artifact.fuchsiaKernelCompiler:
         throw StateError('Artifact $artifact not available for platform $platform.');
+      case Artifact.flutterToolsFileGenerators:
+        return _getFileGeneratorsPath();
     }
   }
 
@@ -952,6 +966,8 @@ class CachedLocalEngineArtifacts implements Artifacts {
       case Artifact.dart2wasmSnapshot:
       case Artifact.frontendServerSnapshotForEngineDartSdk:
         return _fileSystem.path.join(_getDartSdkPath(), 'bin', 'snapshots', artifactFileName);
+      case Artifact.flutterToolsFileGenerators:
+        return _getFileGeneratorsPath();
     }
   }
 
@@ -1099,6 +1115,7 @@ class CachedLocalWebSdkArtifacts implements Artifacts {
         case Artifact.fuchsiaFlutterRunner:
         case Artifact.fontSubset:
         case Artifact.constFinder:
+        case Artifact.flutterToolsFileGenerators:
           break;
       }
     }
@@ -1298,6 +1315,11 @@ class _TestArtifacts implements Artifacts {
     BuildMode? mode,
     EnvironmentType? environmentType,
   }) {
+    // The path to file generators is the same even in the test environment.
+    if (artifact == Artifact.flutterToolsFileGenerators) {
+      return _getFileGeneratorsPath();
+    }
+
     final StringBuffer buffer = StringBuffer();
     buffer.write(artifact);
     if (platform != null) {
@@ -1340,3 +1362,20 @@ class _TestLocalEngine extends _TestArtifacts {
   @override
   final LocalEngineInfo localEngineInfo;
 }
+
+String _getFileGeneratorsPath() {
+  final String flutterRoot = Cache.defaultFlutterRoot(
+    fileSystem: globals.localFileSystem,
+    platform: const LocalPlatform(),
+    userMessages: UserMessages(),
+  );
+  return globals.localFileSystem.path.join(
+    flutterRoot,
+    'packages',
+    'flutter_tools',
+    'lib',
+    'src',
+    'web',
+    'file_generators',
+  );
+}

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -529,7 +529,10 @@ class WebBuiltInAssets extends Target {
 
     // Write the flutter.js file
     final File flutterJsFile = environment.outputDir.childFile('flutter.js');
-    flutterJsFile.writeAsStringSync(flutter_js.generateFlutterJsFile());
+    final String fileGeneratorsPath =
+        globals.artifacts!.getArtifactPath(Artifact.flutterToolsFileGenerators);
+    flutterJsFile.writeAsStringSync(
+        flutter_js.generateFlutterJsFile(fileGeneratorsPath));
   }
 }
 
@@ -598,7 +601,10 @@ class WebServiceWorker extends Target {
     final ServiceWorkerStrategy serviceWorkerStrategy = _serviceWorkerStrategyFromString(
       environment.defines[kServiceWorkerStrategy],
     );
+    final String fileGeneratorsPath =
+        globals.artifacts!.getArtifactPath(Artifact.flutterToolsFileGenerators);
     final String serviceWorker = generateServiceWorker(
+      fileGeneratorsPath,
       urlToHash,
       <String>[
         'main.dart.js',

packages/flutter_tools/lib/src/isolated/devfs_web.dart

@@ -828,7 +828,10 @@ class WebDevFS implements DevFS {
           'stack_trace_mapper.js', stackTraceMapper.readAsBytesSync());
       webAssetServer.writeFile(
           'manifest.json', '{"info":"manifest not generated in run mode."}');
-      webAssetServer.writeFile('flutter.js', flutter_js.generateFlutterJsFile());
+      final String fileGeneratorsPath = globals.artifacts!
+          .getArtifactPath(Artifact.flutterToolsFileGenerators);
+      webAssetServer.writeFile(
+          'flutter.js', flutter_js.generateFlutterJsFile(fileGeneratorsPath));
       webAssetServer.writeFile('flutter_service_worker.js',
           '// Service worker not loaded in run mode.');
       webAssetServer.writeFile(

packages/flutter_tools/lib/src/web/file_generators/flutter_js.dart

@@ -2,388 +2,17 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import '../../globals.dart' as globals;
 
 /// Generates the flutter.js file.
 ///
 /// flutter.js should be completely static, so **do not use any parameter or
 /// environment variable to generate this file**.
-String generateFlutterJsFile() {
-  return r'''
-// Copyright 2014 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-if (!_flutter) {
-  var _flutter = {};
-}
-_flutter.loader = null;
-
-(function () {
-  "use strict";
-
-  const baseUri = ensureTrailingSlash(getBaseURI());
-
-  function getBaseURI() {
-    const base = document.querySelector("base");
-    return (base && base.getAttribute("href")) || "";
-  }
-
-  function ensureTrailingSlash(uri) {
-    if (uri == "") {
-      return uri;
-    }
-    return uri.endsWith("/") ? uri : `${uri}/`;
-  }
-
-  /**
-   * Wraps `promise` in a timeout of the given `duration` in ms.
-   *
-   * Resolves/rejects with whatever the original `promises` does, or rejects
-   * if `promise` takes longer to complete than `duration`. In that case,
-   * `debugName` is used to compose a legible error message.
-   *
-   * If `duration` is < 0, the original `promise` is returned unchanged.
-   * @param {Promise} promise
-   * @param {number} duration
-   * @param {string} debugName
-   * @returns {Promise} a wrapped promise.
-   */
-  async function timeout(promise, duration, debugName) {
-    if (duration < 0) {
-      return promise;
-    }
-    let timeoutId;
-    const _clock = new Promise((_, reject) => {
-      timeoutId = setTimeout(() => {
-        reject(
-          new Error(
-            `${debugName} took more than ${duration}ms to resolve. Moving on.`,
-            {
-              cause: timeout,
-            }
-          )
-        );
-      }, duration);
-    });
-
-    return Promise.race([promise, _clock]).finally(() => {
-      clearTimeout(timeoutId);
-    });
-  }
-
-  /**
-   * Handles the creation of a TrustedTypes `policy` that validates URLs based
-   * on an (optional) incoming array of RegExes.
-   */
-  class FlutterTrustedTypesPolicy {
-    /**
-     * Constructs the policy.
-     * @param {[RegExp]} validPatterns the patterns to test URLs
-     * @param {String} policyName the policy name (optional)
-     */
-    constructor(validPatterns, policyName = "flutter-js") {
-      const patterns = validPatterns || [
-        /\.dart\.js$/,
-        /^flutter_service_worker.js$/
-      ];
-      if (window.trustedTypes) {
-        this.policy = trustedTypes.createPolicy(policyName, {
-          createScriptURL: function(url) {
-            const parsed = new URL(url, window.location);
-            const file = parsed.pathname.split("/").pop();
-            const matches = patterns.some((pattern) => pattern.test(file));
-            if (matches) {
-              return parsed.toString();
-            }
-            console.error(
-              "URL rejected by TrustedTypes policy",
-              policyName, ":", url, "(download prevented)");
-          }
-        });
-      }
-    }
-  }
-
-  /**
-   * Handles loading/reloading Flutter's service worker, if configured.
-   *
-   * @see: https://developers.google.com/web/fundamentals/primers/service-workers
-   */
-  class FlutterServiceWorkerLoader {
-    /**
-     * Injects a TrustedTypesPolicy (or undefined if the feature is not supported).
-     * @param {TrustedTypesPolicy | undefined} policy
-     */
-    setTrustedTypesPolicy(policy) {
-      this._ttPolicy = policy;
-    }
-
-    /**
-     * Returns a Promise that resolves when the latest Flutter service worker,
-     * configured by `settings` has been loaded and activated.
-     *
-     * Otherwise, the promise is rejected with an error message.
-     * @param {*} settings Service worker settings
-     * @returns {Promise} that resolves when the latest serviceWorker is ready.
-     */
-    loadServiceWorker(settings) {
-      if (!("serviceWorker" in navigator) || settings == null) {
-        // In the future, settings = null -> uninstall service worker?
-        return Promise.reject(
-          new Error("Service worker not supported (or configured).")
-        );
-      }
-      const {
-        serviceWorkerVersion,
-        serviceWorkerUrl = `${baseUri}flutter_service_worker.js?v=${serviceWorkerVersion}`,
-        timeoutMillis = 4000,
-      } = settings;
-
-      // Apply the TrustedTypes policy, if present.
-      let url = serviceWorkerUrl;
-      if (this._ttPolicy != null) {
-        url = this._ttPolicy.createScriptURL(url);
-      }
-
-      const serviceWorkerActivation = navigator.serviceWorker
-        .register(url)
-        .then(this._getNewServiceWorker)
-        .then(this._waitForServiceWorkerActivation);
-
-      // Timeout race promise
-      return timeout(
-        serviceWorkerActivation,
-        timeoutMillis,
-        "prepareServiceWorker"
-      );
-    }
-
-    /**
-     * Returns the latest service worker for the given `serviceWorkerRegistrationPromise`.
-     *
-     * This might return the current service worker, if there's no new service worker
-     * awaiting to be installed/updated.
-     *
-     * @param {Promise<ServiceWorkerRegistration>} serviceWorkerRegistrationPromise
-     * @returns {Promise<ServiceWorker>}
-     */
-    async _getNewServiceWorker(serviceWorkerRegistrationPromise) {
-      const reg = await serviceWorkerRegistrationPromise;
-
-      if (!reg.active && (reg.installing || reg.waiting)) {
-        // No active web worker and we have installed or are installing
-        // one for the first time. Simply wait for it to activate.
-        console.debug("Installing/Activating first service worker.");
-        return reg.installing || reg.waiting;
-      } else if (!reg.active.scriptURL.endsWith(serviceWorkerVersion)) {
-        // When the app updates the serviceWorkerVersion changes, so we
-        // need to ask the service worker to update.
-        return reg.update().then((newReg) => {
-          console.debug("Updating service worker.");
-          return newReg.installing || newReg.waiting || newReg.active;
-        });
-      } else {
-        console.debug("Loading from existing service worker.");
-        return reg.active;
-      }
-    }
-
-    /**
-     * Returns a Promise that resolves when the `latestServiceWorker` changes its
-     * state to "activated".
-     *
-     * @param {Promise<ServiceWorker>} latestServiceWorkerPromise
-     * @returns {Promise<void>}
-     */
-    async _waitForServiceWorkerActivation(latestServiceWorkerPromise) {
-      const serviceWorker = await latestServiceWorkerPromise;
-
-      if (!serviceWorker || serviceWorker.state == "activated") {
-        if (!serviceWorker) {
-          return Promise.reject(
-            new Error("Cannot activate a null service worker!")
-          );
-        } else {
-          console.debug("Service worker already active.");
-          return Promise.resolve();
-        }
-      }
-      return new Promise((resolve, _) => {
-        serviceWorker.addEventListener("statechange", () => {
-          if (serviceWorker.state == "activated") {
-            console.debug("Activated new service worker.");
-            resolve();
-          }
-        });
-      });
-    }
-  }
-
-  /**
-   * Handles injecting the main Flutter web entrypoint (main.dart.js), and notifying
-   * the user when Flutter is ready, through `didCreateEngineInitializer`.
-   *
-   * @see https://docs.flutter.dev/development/platform-integration/web/initialization
-   */
-  class FlutterEntrypointLoader {
-    /**
-     * Creates a FlutterEntrypointLoader.
-     */
-    constructor() {
-      // Watchdog to prevent injecting the main entrypoint multiple times.
-      this._scriptLoaded = false;
-    }
-
-    /**
-     * Injects a TrustedTypesPolicy (or undefined if the feature is not supported).
-     * @param {TrustedTypesPolicy | undefined} policy
-     */
-    setTrustedTypesPolicy(policy) {
-      this._ttPolicy = policy;
-    }
-
-    /**
-     * Loads flutter main entrypoint, specified by `entrypointUrl`, and calls a
-     * user-specified `onEntrypointLoaded` callback with an EngineInitializer
-     * object when it's done.
-     *
-     * @param {*} options
-     * @returns {Promise | undefined} that will eventually resolve with an
-     * EngineInitializer, or will be rejected with the error caused by the loader.
-     * Returns undefined when an `onEntrypointLoaded` callback is supplied in `options`.
-     */
-    async loadEntrypoint(options) {
-      const { entrypointUrl = `${baseUri}main.dart.js`, onEntrypointLoaded } =
-        options || {};
-
-      return this._loadEntrypoint(entrypointUrl, onEntrypointLoaded);
-    }
-
-    /**
-     * Resolves the promise created by loadEntrypoint, and calls the `onEntrypointLoaded`
-     * function supplied by the user (if needed).
-     *
-     * Called by Flutter through `_flutter.loader.didCreateEngineInitializer` method,
-     * which is bound to the correct instance of the FlutterEntrypointLoader by
-     * the FlutterLoader object.
-     *
-     * @param {Function} engineInitializer @see https://github.com/flutter/engine/blob/main/lib/web_ui/lib/src/engine/js_interop/js_loader.dart#L42
-     */
-    didCreateEngineInitializer(engineInitializer) {
-      if (typeof this._didCreateEngineInitializerResolve === "function") {
-        this._didCreateEngineInitializerResolve(engineInitializer);
-        // Remove the resolver after the first time, so Flutter Web can hot restart.
-        this._didCreateEngineInitializerResolve = null;
-        // Make the engine revert to "auto" initialization on hot restart.
-        delete _flutter.loader.didCreateEngineInitializer;
-      }
-      if (typeof this._onEntrypointLoaded === "function") {
-        this._onEntrypointLoaded(engineInitializer);
-      }
-    }
-
-    /**
-     * Injects a script tag into the DOM, and configures this loader to be able to
-     * handle the "entrypoint loaded" notifications received from Flutter web.
-     *
-     * @param {string} entrypointUrl the URL of the script that will initialize
-     *                 Flutter.
-     * @param {Function} onEntrypointLoaded a callback that will be called when
-     *                   Flutter web notifies this object that the entrypoint is
-     *                   loaded.
-     * @returns {Promise | undefined} a Promise that resolves when the entrypoint
-     *                                is loaded, or undefined if `onEntrypointLoaded`
-     *                                is a function.
-     */
-    _loadEntrypoint(entrypointUrl, onEntrypointLoaded) {
-      const useCallback = typeof onEntrypointLoaded === "function";
-
-      if (!this._scriptLoaded) {
-        this._scriptLoaded = true;
-        const scriptTag = this._createScriptTag(entrypointUrl);
-        if (useCallback) {
-          // Just inject the script tag, and return nothing; Flutter will call
-          // `didCreateEngineInitializer` when it's done.
-          console.debug("Injecting <script> tag. Using callback.");
-          this._onEntrypointLoaded = onEntrypointLoaded;
-          document.body.append(scriptTag);
-        } else {
-          // Inject the script tag and return a promise that will get resolved
-          // with the EngineInitializer object from Flutter when it calls
-          // `didCreateEngineInitializer` later.
-          return new Promise((resolve, reject) => {
-            console.debug(
-              "Injecting <script> tag. Using Promises. Use the callback approach instead!"
-            );
-            this._didCreateEngineInitializerResolve = resolve;
-            scriptTag.addEventListener("error", reject);
-            document.body.append(scriptTag);
-          });
-        }
-      }
-    }
-
-    /**
-     * Creates a script tag for the given URL.
-     * @param {string} url
-     * @returns {HTMLScriptElement}
-     */
-    _createScriptTag(url) {
-      const scriptTag = document.createElement("script");
-      scriptTag.type = "application/javascript";
-      // Apply TrustedTypes validation, if available.
-      let trustedUrl = url;
-      if (this._ttPolicy != null) {
-        trustedUrl = this._ttPolicy.createScriptURL(url);
-      }
-      scriptTag.src = trustedUrl;
-      return scriptTag;
-    }
-  }
-
-  /**
-   * The public interface of _flutter.loader. Exposes two methods:
-   * * loadEntrypoint (which coordinates the default Flutter web loading procedure)
-   * * didCreateEngineInitializer (which is called by Flutter to notify that its
-   *                              Engine is ready to be initialized)
-   */
-  class FlutterLoader {
-    /**
-     * Initializes the Flutter web app.
-     * @param {*} options
-     * @returns {Promise?} a (Deprecated) Promise that will eventually resolve
-     *                     with an EngineInitializer, or will be rejected with
-     *                     any error caused by the loader. Or Null, if the user
-     *                     supplies an `onEntrypointLoaded` Function as an option.
-     */
-    async loadEntrypoint(options) {
-      const { serviceWorker, ...entrypoint } = options || {};
-
-      // A Trusted Types policy that is going to be used by the loader.
-      const flutterTT = new FlutterTrustedTypesPolicy();
-
-      // The FlutterServiceWorkerLoader instance could be injected as a dependency
-      // (and dynamically imported from a module if not present).
-      const serviceWorkerLoader = new FlutterServiceWorkerLoader();
-      serviceWorkerLoader.setTrustedTypesPolicy(flutterTT.policy);
-      await serviceWorkerLoader.loadServiceWorker(serviceWorker).catch(e => {
-        // Regardless of what happens with the injection of the SW, the show must go on
-        console.warn("Exception while loading service worker:", e);
-      });
-
-      // The FlutterEntrypointLoader instance could be injected as a dependency
-      // (and dynamically imported from a module if not present).
-      const entrypointLoader = new FlutterEntrypointLoader();
-      entrypointLoader.setTrustedTypesPolicy(flutterTT.policy);
-      // Install the `didCreateEngineInitializer` listener where Flutter web expects it to be.
-      this.didCreateEngineInitializer =
-        entrypointLoader.didCreateEngineInitializer.bind(entrypointLoader);
-      return entrypointLoader.loadEntrypoint(entrypoint);
-    }
-  }
-
-  _flutter.loader = new FlutterLoader();
-})();
-
-''';
+String generateFlutterJsFile(String fileGeneratorsPath) {
+  final String flutterJsPath = globals.localFileSystem.path.join(
+    fileGeneratorsPath,
+    'js',
+    'flutter.js',
+  );
+  return globals.localFileSystem.file(flutterJsPath).readAsStringSync();
 }

packages/flutter_tools/lib/src/web/file_generators/flutter_service_worker_js.dart

@@ -2,11 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import '../../globals.dart' as globals;
+
 /// The caching strategy for the generated service worker.
 enum ServiceWorkerStrategy {
   /// Download the app shell eagerly and all other assets lazily.
   /// Prefer the offline cached version.
   offlineFirst,
+
   /// Do not generate a service worker,
   none,
 }
@@ -18,6 +21,7 @@ enum ServiceWorkerStrategy {
 /// invalidation will automatically reactivate workers whenever a new
 /// version is deployed.
 String generateServiceWorker(
+  String fileGeneratorsPath,
   Map<String, String> resources,
   List<String> coreBundle, {
   required ServiceWorkerStrategy serviceWorkerStrategy,
@@ -25,185 +29,21 @@ String generateServiceWorker(
   if (serviceWorkerStrategy == ServiceWorkerStrategy.none) {
     return '';
   }
-  return '''
-'use strict';
-const MANIFEST = 'flutter-app-manifest';
-const TEMP = 'flutter-temp-cache';
-const CACHE_NAME = 'flutter-app-cache';
-const RESOURCES = {
-  ${resources.entries.map((MapEntry<String, String> entry) => '"${entry.key}": "${entry.value}"').join(",\n")}
-};
-
-// The application shell files that are downloaded before a service worker can
-// start.
-const CORE = [
-  ${coreBundle.map((String file) => '"$file"').join(',\n')}];
-// During install, the TEMP cache is populated with the application shell files.
-self.addEventListener("install", (event) => {
-  self.skipWaiting();
-  return event.waitUntil(
-    caches.open(TEMP).then((cache) => {
-      return cache.addAll(
-        CORE.map((value) => new Request(value, {'cache': 'reload'})));
-    })
-  );
-});
-
-// During activate, the cache is populated with the temp files downloaded in
-// install. If this service worker is upgrading from one with a saved
-// MANIFEST, then use this to retain unchanged resource files.
-self.addEventListener("activate", function(event) {
-  return event.waitUntil(async function() {
-    try {
-      var contentCache = await caches.open(CACHE_NAME);
-      var tempCache = await caches.open(TEMP);
-      var manifestCache = await caches.open(MANIFEST);
-      var manifest = await manifestCache.match('manifest');
-      // When there is no prior manifest, clear the entire cache.
-      if (!manifest) {
-        await caches.delete(CACHE_NAME);
-        contentCache = await caches.open(CACHE_NAME);
-        for (var request of await tempCache.keys()) {
-          var response = await tempCache.match(request);
-          await contentCache.put(request, response);
-        }
-        await caches.delete(TEMP);
-        // Save the manifest to make future upgrades efficient.
-        await manifestCache.put('manifest', new Response(JSON.stringify(RESOURCES)));
-        // Claim client to enable caching on first launch
-        self.clients.claim();
-        return;
-      }
-      var oldManifest = await manifest.json();
-      var origin = self.location.origin;
-      for (var request of await contentCache.keys()) {
-        var key = request.url.substring(origin.length + 1);
-        if (key == "") {
-          key = "/";
-        }
-        // If a resource from the old manifest is not in the new cache, or if
-        // the MD5 sum has changed, delete it. Otherwise the resource is left
-        // in the cache and can be reused by the new service worker.
-        if (!RESOURCES[key] || RESOURCES[key] != oldManifest[key]) {
-          await contentCache.delete(request);
-        }
-      }
-      // Populate the cache with the app shell TEMP files, potentially overwriting
-      // cache files preserved above.
-      for (var request of await tempCache.keys()) {
-        var response = await tempCache.match(request);
-        await contentCache.put(request, response);
-      }
-      await caches.delete(TEMP);
-      // Save the manifest to make future upgrades efficient.
-      await manifestCache.put('manifest', new Response(JSON.stringify(RESOURCES)));
-      // Claim client to enable caching on first launch
-      self.clients.claim();
-      return;
-    } catch (err) {
-      // On an unhandled exception the state of the cache cannot be guaranteed.
-      console.error('Failed to upgrade service worker: ' + err);
-      await caches.delete(CACHE_NAME);
-      await caches.delete(TEMP);
-      await caches.delete(MANIFEST);
-    }
-  }());
-});
-
-// The fetch handler redirects requests for RESOURCE files to the service
-// worker cache.
-self.addEventListener("fetch", (event) => {
-  if (event.request.method !== 'GET') {
-    return;
-  }
-  var origin = self.location.origin;
-  var key = event.request.url.substring(origin.length + 1);
-  // Redirect URLs to the index.html
-  if (key.indexOf('?v=') != -1) {
-    key = key.split('?v=')[0];
-  }
-  if (event.request.url == origin || event.request.url.startsWith(origin + '/#') || key == '') {
-    key = '/';
-  }
-  // If the URL is not the RESOURCE list then return to signal that the
-  // browser should take over.
-  if (!RESOURCES[key]) {
-    return;
-  }
-  // If the URL is the index.html, perform an online-first request.
-  if (key == '/') {
-    return onlineFirst(event);
-  }
-  event.respondWith(caches.open(CACHE_NAME)
-    .then((cache) =>  {
-      return cache.match(event.request).then((response) => {
-        // Either respond with the cached resource, or perform a fetch and
-        // lazily populate the cache only if the resource was successfully fetched.
-        return response || fetch(event.request).then((response) => {
-          if (response && Boolean(response.ok)) {
-            cache.put(event.request, response.clone());
-          }
-          return response;
-        });
-      })
-    })
-  );
-});
-
-self.addEventListener('message', (event) => {
-  // SkipWaiting can be used to immediately activate a waiting service worker.
-  // This will also require a page refresh triggered by the main worker.
-  if (event.data === 'skipWaiting') {
-    self.skipWaiting();
-    return;
-  }
-  if (event.data === 'downloadOffline') {
-    downloadOffline();
-    return;
-  }
-});
 
-// Download offline will check the RESOURCES for all files not in the cache
-// and populate them.
-async function downloadOffline() {
-  var resources = [];
-  var contentCache = await caches.open(CACHE_NAME);
-  var currentContent = {};
-  for (var request of await contentCache.keys()) {
-    var key = request.url.substring(origin.length + 1);
-    if (key == "") {
-      key = "/";
-    }
-    currentContent[key] = true;
-  }
-  for (var resourceKey of Object.keys(RESOURCES)) {
-    if (!currentContent[resourceKey]) {
-      resources.push(resourceKey);
-    }
-  }
-  return contentCache.addAll(resources);
-}
-
-// Attempt to download the resource online before falling back to
-// the offline cache.
-function onlineFirst(event) {
-  return event.respondWith(
-    fetch(event.request).then((response) => {
-      return caches.open(CACHE_NAME).then((cache) => {
-        cache.put(event.request, response.clone());
-        return response;
-      });
-    }).catch((error) => {
-      return caches.open(CACHE_NAME).then((cache) => {
-        return cache.match(event.request).then((response) => {
-          if (response != null) {
-            return response;
-          }
-          throw error;
-        });
-      });
-    })
+  final String flutterServiceWorkerJsPath = globals.localFileSystem.path.join(
+    fileGeneratorsPath,
+    'js',
+    'flutter_service_worker.js',
   );
-}
-''';
+  return globals.localFileSystem
+      .file(flutterServiceWorkerJsPath)
+      .readAsStringSync()
+      .replaceAll(
+        r'$$RESOURCES_MAP',
+        '{${resources.entries.map((MapEntry<String, String> entry) => '"${entry.key}": "${entry.value}"').join(",\n")}}',
+      )
+      .replaceAll(
+        r'$$CORE_LIST',
+        '[${coreBundle.map((String file) => '"$file"').join(',\n')}]',
+      );
 }

packages/flutter_tools/lib/src/web/file_generators/js/flutter.js

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+if (!_flutter) {
+  var _flutter = {};
+}
+_flutter.loader = null;
+
+(function () {
+  "use strict";
+
+  const baseUri = ensureTrailingSlash(getBaseURI());
+
+  function getBaseURI() {
+    const base = document.querySelector("base");
+    return (base && base.getAttribute("href")) || "";
+  }
+
+  function ensureTrailingSlash(uri) {
+    if (uri == "") {
+      return uri;
+    }
+    return uri.endsWith("/") ? uri : `${uri}/`;
+  }
+
+  /**
+   * Wraps `promise` in a timeout of the given `duration` in ms.
+   *
+   * Resolves/rejects with whatever the original `promises` does, or rejects
+   * if `promise` takes longer to complete than `duration`. In that case,
+   * `debugName` is used to compose a legible error message.
+   *
+   * If `duration` is < 0, the original `promise` is returned unchanged.
+   * @param {Promise} promise
+   * @param {number} duration
+   * @param {string} debugName
+   * @returns {Promise} a wrapped promise.
+   */
+  async function timeout(promise, duration, debugName) {
+    if (duration < 0) {
+      return promise;
+    }
+    let timeoutId;
+    const _clock = new Promise((_, reject) => {
+      timeoutId = setTimeout(() => {
+        reject(
+          new Error(
+            `${debugName} took more than ${duration}ms to resolve. Moving on.`,
+            {
+              cause: timeout,
+            }
+          )
+        );
+      }, duration);
+    });
+
+    return Promise.race([promise, _clock]).finally(() => {
+      clearTimeout(timeoutId);
+    });
+  }
+
+  /**
+   * Handles the creation of a TrustedTypes `policy` that validates URLs based
+   * on an (optional) incoming array of RegExes.
+   */
+  class FlutterTrustedTypesPolicy {
+    /**
+     * Constructs the policy.
+     * @param {[RegExp]} validPatterns the patterns to test URLs
+     * @param {String} policyName the policy name (optional)
+     */
+    constructor(validPatterns, policyName = "flutter-js") {
+      const patterns = validPatterns || [
+        /\.dart\.js$/,
+        /^flutter_service_worker.js$/
+      ];
+      if (window.trustedTypes) {
+        this.policy = trustedTypes.createPolicy(policyName, {
+          createScriptURL: function(url) {
+            const parsed = new URL(url, window.location);
+            const file = parsed.pathname.split("/").pop();
+            const matches = patterns.some((pattern) => pattern.test(file));
+            if (matches) {
+              return parsed.toString();
+            }
+            console.error(
+              "URL rejected by TrustedTypes policy",
+              policyName, ":", url, "(download prevented)");
+          }
+        });
+      }
+    }
+  }
+
+  /**
+   * Handles loading/reloading Flutter's service worker, if configured.
+   *
+   * @see: https://developers.google.com/web/fundamentals/primers/service-workers
+   */
+  class FlutterServiceWorkerLoader {
+    /**
+     * Injects a TrustedTypesPolicy (or undefined if the feature is not supported).
+     * @param {TrustedTypesPolicy | undefined} policy
+     */
+    setTrustedTypesPolicy(policy) {
+      this._ttPolicy = policy;
+    }
+
+    /**
+     * Returns a Promise that resolves when the latest Flutter service worker,
+     * configured by `settings` has been loaded and activated.
+     *
+     * Otherwise, the promise is rejected with an error message.
+     * @param {*} settings Service worker settings
+     * @returns {Promise} that resolves when the latest serviceWorker is ready.
+     */
+    loadServiceWorker(settings) {
+      if (!("serviceWorker" in navigator) || settings == null) {
+        // In the future, settings = null -> uninstall service worker?
+        return Promise.reject(
+          new Error("Service worker not supported (or configured).")
+        );
+      }
+      const {
+        serviceWorkerVersion,
+        serviceWorkerUrl = `${baseUri}flutter_service_worker.js?v=${serviceWorkerVersion}`,
+        timeoutMillis = 4000,
+      } = settings;
+
+      // Apply the TrustedTypes policy, if present.
+      let url = serviceWorkerUrl;
+      if (this._ttPolicy != null) {
+        url = this._ttPolicy.createScriptURL(url);
+      }
+
+      const serviceWorkerActivation = navigator.serviceWorker
+        .register(url)
+        .then(this._getNewServiceWorker)
+        .then(this._waitForServiceWorkerActivation);
+
+      // Timeout race promise
+      return timeout(
+        serviceWorkerActivation,
+        timeoutMillis,
+        "prepareServiceWorker"
+      );
+    }
+
+    /**
+     * Returns the latest service worker for the given `serviceWorkerRegistrationPromise`.
+     *
+     * This might return the current service worker, if there's no new service worker
+     * awaiting to be installed/updated.
+     *
+     * @param {Promise<ServiceWorkerRegistration>} serviceWorkerRegistrationPromise
+     * @returns {Promise<ServiceWorker>}
+     */
+    async _getNewServiceWorker(serviceWorkerRegistrationPromise) {
+      const reg = await serviceWorkerRegistrationPromise;
+
+      if (!reg.active && (reg.installing || reg.waiting)) {
+        // No active web worker and we have installed or are installing
+        // one for the first time. Simply wait for it to activate.
+        console.debug("Installing/Activating first service worker.");
+        return reg.installing || reg.waiting;
+      } else if (!reg.active.scriptURL.endsWith(serviceWorkerVersion)) {
+        // When the app updates the serviceWorkerVersion changes, so we
+        // need to ask the service worker to update.
+        return reg.update().then((newReg) => {
+          console.debug("Updating service worker.");
+          return newReg.installing || newReg.waiting || newReg.active;
+        });
+      } else {
+        console.debug("Loading from existing service worker.");
+        return reg.active;
+      }
+    }
+
+    /**
+     * Returns a Promise that resolves when the `latestServiceWorker` changes its
+     * state to "activated".
+     *
+     * @param {Promise<ServiceWorker>} latestServiceWorkerPromise
+     * @returns {Promise<void>}
+     */
+    async _waitForServiceWorkerActivation(latestServiceWorkerPromise) {
+      const serviceWorker = await latestServiceWorkerPromise;
+
+      if (!serviceWorker || serviceWorker.state == "activated") {
+        if (!serviceWorker) {
+          return Promise.reject(
+            new Error("Cannot activate a null service worker!")
+          );
+        } else {
+          console.debug("Service worker already active.");
+          return Promise.resolve();
+        }
+      }
+      return new Promise((resolve, _) => {
+        serviceWorker.addEventListener("statechange", () => {
+          if (serviceWorker.state == "activated") {
+            console.debug("Activated new service worker.");
+            resolve();
+          }
+        });
+      });
+    }
+  }
+
+  /**
+   * Handles injecting the main Flutter web entrypoint (main.dart.js), and notifying
+   * the user when Flutter is ready, through `didCreateEngineInitializer`.
+   *
+   * @see https://docs.flutter.dev/development/platform-integration/web/initialization
+   */
+  class FlutterEntrypointLoader {
+    /**
+     * Creates a FlutterEntrypointLoader.
+     */
+    constructor() {
+      // Watchdog to prevent injecting the main entrypoint multiple times.
+      this._scriptLoaded = false;
+    }
+
+    /**
+     * Injects a TrustedTypesPolicy (or undefined if the feature is not supported).
+     * @param {TrustedTypesPolicy | undefined} policy
+     */
+    setTrustedTypesPolicy(policy) {
+      this._ttPolicy = policy;
+    }
+
+    /**
+     * Loads flutter main entrypoint, specified by `entrypointUrl`, and calls a
+     * user-specified `onEntrypointLoaded` callback with an EngineInitializer
+     * object when it's done.
+     *
+     * @param {*} options
+     * @returns {Promise | undefined} that will eventually resolve with an
+     * EngineInitializer, or will be rejected with the error caused by the loader.
+     * Returns undefined when an `onEntrypointLoaded` callback is supplied in `options`.
+     */
+    async loadEntrypoint(options) {
+      const { entrypointUrl = `${baseUri}main.dart.js`, onEntrypointLoaded } =
+        options || {};
+
+      return this._loadEntrypoint(entrypointUrl, onEntrypointLoaded);
+    }
+
+    /**
+     * Resolves the promise created by loadEntrypoint, and calls the `onEntrypointLoaded`
+     * function supplied by the user (if needed).
+     *
+     * Called by Flutter through `_flutter.loader.didCreateEngineInitializer` method,
+     * which is bound to the correct instance of the FlutterEntrypointLoader by
+     * the FlutterLoader object.
+     *
+     * @param {Function} engineInitializer @see https://github.com/flutter/engine/blob/main/lib/web_ui/lib/src/engine/js_interop/js_loader.dart#L42
+     */
+    didCreateEngineInitializer(engineInitializer) {
+      if (typeof this._didCreateEngineInitializerResolve === "function") {
+        this._didCreateEngineInitializerResolve(engineInitializer);
+        // Remove the resolver after the first time, so Flutter Web can hot restart.
+        this._didCreateEngineInitializerResolve = null;
+        // Make the engine revert to "auto" initialization on hot restart.
+        delete _flutter.loader.didCreateEngineInitializer;
+      }
+      if (typeof this._onEntrypointLoaded === "function") {
+        this._onEntrypointLoaded(engineInitializer);
+      }
+    }
+
+    /**
+     * Injects a script tag into the DOM, and configures this loader to be able to
+     * handle the "entrypoint loaded" notifications received from Flutter web.
+     *
+     * @param {string} entrypointUrl the URL of the script that will initialize
+     *                 Flutter.
+     * @param {Function} onEntrypointLoaded a callback that will be called when
+     *                   Flutter web notifies this object that the entrypoint is
+     *                   loaded.
+     * @returns {Promise | undefined} a Promise that resolves when the entrypoint
+     *                                is loaded, or undefined if `onEntrypointLoaded`
+     *                                is a function.
+     */
+    _loadEntrypoint(entrypointUrl, onEntrypointLoaded) {
+      const useCallback = typeof onEntrypointLoaded === "function";
+
+      if (!this._scriptLoaded) {
+        this._scriptLoaded = true;
+        const scriptTag = this._createScriptTag(entrypointUrl);
+        if (useCallback) {
+          // Just inject the script tag, and return nothing; Flutter will call
+          // `didCreateEngineInitializer` when it's done.
+          console.debug("Injecting <script> tag. Using callback.");
+          this._onEntrypointLoaded = onEntrypointLoaded;
+          document.body.append(scriptTag);
+        } else {
+          // Inject the script tag and return a promise that will get resolved
+          // with the EngineInitializer object from Flutter when it calls
+          // `didCreateEngineInitializer` later.
+          return new Promise((resolve, reject) => {
+            console.debug(
+              "Injecting <script> tag. Using Promises. Use the callback approach instead!"
+            );
+            this._didCreateEngineInitializerResolve = resolve;
+            scriptTag.addEventListener("error", reject);
+            document.body.append(scriptTag);
+          });
+        }
+      }
+    }
+
+    /**
+     * Creates a script tag for the given URL.
+     * @param {string} url
+     * @returns {HTMLScriptElement}
+     */
+    _createScriptTag(url) {
+      const scriptTag = document.createElement("script");
+      scriptTag.type = "application/javascript";
+      // Apply TrustedTypes validation, if available.
+      let trustedUrl = url;
+      if (this._ttPolicy != null) {
+        trustedUrl = this._ttPolicy.createScriptURL(url);
+      }
+      scriptTag.src = trustedUrl;
+      return scriptTag;
+    }
+  }
+
+  /**
+   * The public interface of _flutter.loader. Exposes two methods:
+   * * loadEntrypoint (which coordinates the default Flutter web loading procedure)
+   * * didCreateEngineInitializer (which is called by Flutter to notify that its
+   *                              Engine is ready to be initialized)
+   */
+  class FlutterLoader {
+    /**
+     * Initializes the Flutter web app.
+     * @param {*} options
+     * @returns {Promise?} a (Deprecated) Promise that will eventually resolve
+     *                     with an EngineInitializer, or will be rejected with
+     *                     any error caused by the loader. Or Null, if the user
+     *                     supplies an `onEntrypointLoaded` Function as an option.
+     */
+    async loadEntrypoint(options) {
+      const { serviceWorker, ...entrypoint } = options || {};
+
+      // A Trusted Types policy that is going to be used by the loader.
+      const flutterTT = new FlutterTrustedTypesPolicy();
+
+      // The FlutterServiceWorkerLoader instance could be injected as a dependency
+      // (and dynamically imported from a module if not present).
+      const serviceWorkerLoader = new FlutterServiceWorkerLoader();
+      serviceWorkerLoader.setTrustedTypesPolicy(flutterTT.policy);
+      await serviceWorkerLoader.loadServiceWorker(serviceWorker).catch(e => {
+        // Regardless of what happens with the injection of the SW, the show must go on
+        console.warn("Exception while loading service worker:", e);
+      });
+
+      // The FlutterEntrypointLoader instance could be injected as a dependency
+      // (and dynamically imported from a module if not present).
+      const entrypointLoader = new FlutterEntrypointLoader();
+      entrypointLoader.setTrustedTypesPolicy(flutterTT.policy);
+      // Install the `didCreateEngineInitializer` listener where Flutter web expects it to be.
+      this.didCreateEngineInitializer =
+        entrypointLoader.didCreateEngineInitializer.bind(entrypointLoader);
+      return entrypointLoader.loadEntrypoint(entrypoint);
+    }
+  }
+
+  _flutter.loader = new FlutterLoader();
+})();

packages/flutter_tools/lib/src/web/file_generators/js/flutter_service_worker.js

+'use strict';
+const MANIFEST = 'flutter-app-manifest';
+const TEMP = 'flutter-temp-cache';
+const CACHE_NAME = 'flutter-app-cache';
+
+const RESOURCES = $$RESOURCES_MAP;
+// The application shell files that are downloaded before a service worker can
+// start.
+const CORE = $$CORE_LIST;
+
+// During install, the TEMP cache is populated with the application shell files.
+self.addEventListener("install", (event) => {
+  self.skipWaiting();
+  return event.waitUntil(
+    caches.open(TEMP).then((cache) => {
+      return cache.addAll(
+        CORE.map((value) => new Request(value, {'cache': 'reload'})));
+    })
+  );
+});
+// During activate, the cache is populated with the temp files downloaded in
+// install. If this service worker is upgrading from one with a saved
+// MANIFEST, then use this to retain unchanged resource files.
+self.addEventListener("activate", function(event) {
+  return event.waitUntil(async function() {
+    try {
+      var contentCache = await caches.open(CACHE_NAME);
+      var tempCache = await caches.open(TEMP);
+      var manifestCache = await caches.open(MANIFEST);
+      var manifest = await manifestCache.match('manifest');
+      // When there is no prior manifest, clear the entire cache.
+      if (!manifest) {
+        await caches.delete(CACHE_NAME);
+        contentCache = await caches.open(CACHE_NAME);
+        for (var request of await tempCache.keys()) {
+          var response = await tempCache.match(request);
+          await contentCache.put(request, response);
+        }
+        await caches.delete(TEMP);
+        // Save the manifest to make future upgrades efficient.
+        await manifestCache.put('manifest', new Response(JSON.stringify(RESOURCES)));
+        // Claim client to enable caching on first launch
+        self.clients.claim();
+        return;
+      }
+      var oldManifest = await manifest.json();
+      var origin = self.location.origin;
+      for (var request of await contentCache.keys()) {
+        var key = request.url.substring(origin.length + 1);
+        if (key == "") {
+          key = "/";
+        }
+        // If a resource from the old manifest is not in the new cache, or if
+        // the MD5 sum has changed, delete it. Otherwise the resource is left
+        // in the cache and can be reused by the new service worker.
+        if (!RESOURCES[key] || RESOURCES[key] != oldManifest[key]) {
+          await contentCache.delete(request);
+        }
+      }
+      // Populate the cache with the app shell TEMP files, potentially overwriting
+      // cache files preserved above.
+      for (var request of await tempCache.keys()) {
+        var response = await tempCache.match(request);
+        await contentCache.put(request, response);
+      }
+      await caches.delete(TEMP);
+      // Save the manifest to make future upgrades efficient.
+      await manifestCache.put('manifest', new Response(JSON.stringify(RESOURCES)));
+      // Claim client to enable caching on first launch
+      self.clients.claim();
+      return;
+    } catch (err) {
+      // On an unhandled exception the state of the cache cannot be guaranteed.
+      console.error('Failed to upgrade service worker: ' + err);
+      await caches.delete(CACHE_NAME);
+      await caches.delete(TEMP);
+      await caches.delete(MANIFEST);
+    }
+  }());
+});
+// The fetch handler redirects requests for RESOURCE files to the service
+// worker cache.
+self.addEventListener("fetch", (event) => {
+  if (event.request.method !== 'GET') {
+    return;
+  }
+  var origin = self.location.origin;
+  var key = event.request.url.substring(origin.length + 1);
+  // Redirect URLs to the index.html
+  if (key.indexOf('?v=') != -1) {
+    key = key.split('?v=')[0];
+  }
+  if (event.request.url == origin || event.request.url.startsWith(origin + '/#') || key == '') {
+    key = '/';
+  }
+  // If the URL is not the RESOURCE list then return to signal that the
+  // browser should take over.
+  if (!RESOURCES[key]) {
+    return;
+  }
+  // If the URL is the index.html, perform an online-first request.
+  if (key == '/') {
+    return onlineFirst(event);
+  }
+  event.respondWith(caches.open(CACHE_NAME)
+    .then((cache) =>  {
+      return cache.match(event.request).then((response) => {
+        // Either respond with the cached resource, or perform a fetch and
+        // lazily populate the cache only if the resource was successfully fetched.
+        return response || fetch(event.request).then((response) => {
+          if (response && Boolean(response.ok)) {
+            cache.put(event.request, response.clone());
+          }
+          return response;
+        });
+      })
+    })
+  );
+});
+self.addEventListener('message', (event) => {
+  // SkipWaiting can be used to immediately activate a waiting service worker.
+  // This will also require a page refresh triggered by the main worker.
+  if (event.data === 'skipWaiting') {
+    self.skipWaiting();
+    return;
+  }
+  if (event.data === 'downloadOffline') {
+    downloadOffline();
+    return;
+  }
+});
+// Download offline will check the RESOURCES for all files not in the cache
+// and populate them.
+async function downloadOffline() {
+  var resources = [];
+  var contentCache = await caches.open(CACHE_NAME);
+  var currentContent = {};
+  for (var request of await contentCache.keys()) {
+    var key = request.url.substring(origin.length + 1);
+    if (key == "") {
+      key = "/";
+    }
+    currentContent[key] = true;
+  }
+  for (var resourceKey of Object.keys(RESOURCES)) {
+    if (!currentContent[resourceKey]) {
+      resources.push(resourceKey);
+    }
+  }
+  return contentCache.addAll(resources);
+}
+// Attempt to download the resource online before falling back to
+// the offline cache.
+function onlineFirst(event) {
+  return event.respondWith(
+    fetch(event.request).then((response) => {
+      return caches.open(CACHE_NAME).then((cache) => {
+        cache.put(event.request, response.clone());
+        return response;
+      });
+    }).catch((error) => {
+      return caches.open(CACHE_NAME).then((cache) => {
+        return cache.match(event.request).then((response) => {
+          if (response != null) {
+            return response;
+          }
+          throw error;
+        });
+      });
+    })
+  );
+}

packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart

@@ -785,19 +785,40 @@ void main() {
   }));
 
   test('Generated service worker is empty with none-strategy', () {
-    final String result = generateServiceWorker(<String, String>{'/foo': 'abcd'}, <String>[], serviceWorkerStrategy: ServiceWorkerStrategy.none);
+    final String fileGeneratorsPath =
+        environment.artifacts.getArtifactPath(Artifact.flutterToolsFileGenerators);
+    final String result = generateServiceWorker(
+      fileGeneratorsPath,
+      <String, String>{'/foo': 'abcd'},
+      <String>[],
+      serviceWorkerStrategy: ServiceWorkerStrategy.none,
+    );
 
     expect(result, '');
   });
 
   test('Generated service worker correctly inlines file hashes', () {
-    final String result = generateServiceWorker(<String, String>{'/foo': 'abcd'}, <String>[], serviceWorkerStrategy: ServiceWorkerStrategy.offlineFirst);
+    final String fileGeneratorsPath =
+        environment.artifacts.getArtifactPath(Artifact.flutterToolsFileGenerators);
+    final String result = generateServiceWorker(
+      fileGeneratorsPath,
+      <String, String>{'/foo': 'abcd'},
+      <String>[],
+      serviceWorkerStrategy: ServiceWorkerStrategy.offlineFirst,
+    );
 
-    expect(result, contains('{\n  "/foo": "abcd"\n};'));
+    expect(result, contains('{"/foo": "abcd"};'));
   });
 
   test('Generated service worker includes core files', () {
-    final String result = generateServiceWorker(<String, String>{'/foo': 'abcd'}, <String>['foo', 'bar'], serviceWorkerStrategy: ServiceWorkerStrategy.offlineFirst);
+    final String fileGeneratorsPath =
+        environment.artifacts.getArtifactPath(Artifact.flutterToolsFileGenerators);
+    final String result = generateServiceWorker(
+      fileGeneratorsPath,
+      <String, String>{'/foo': 'abcd'},
+      <String>['foo', 'bar'],
+      serviceWorkerStrategy: ServiceWorkerStrategy.offlineFirst,
+    );
 
     expect(result, contains('"foo",\n"bar"'));
   });
@@ -854,7 +875,10 @@ void main() {
   }));
 
   test('flutter.js sanity checks', () {
-    final String flutterJsContents = flutter_js.generateFlutterJsFile();
+    final String fileGeneratorsPath = environment.artifacts
+        .getArtifactPath(Artifact.flutterToolsFileGenerators);
+    final String flutterJsContents =
+        flutter_js.generateFlutterJsFile(fileGeneratorsPath);
     expect(flutterJsContents, contains('"use strict";'));
     expect(flutterJsContents, contains('main.dart.js'));
     expect(flutterJsContents, contains('flutter_service_worker.js?v='));
@@ -873,8 +897,14 @@ void main() {
     await WebBuiltInAssets(globals.fs, globals.cache, false).build(environment);
 
     // No caching of source maps.
-    expect(environment.outputDir.childFile('flutter.js').readAsStringSync(),
-      equals(flutter_js.generateFlutterJsFile()));
+    final String fileGeneratorsPath = environment.artifacts
+        .getArtifactPath(Artifact.flutterToolsFileGenerators);
+    final String flutterJsContents =
+        flutter_js.generateFlutterJsFile(fileGeneratorsPath);
+    expect(
+      environment.outputDir.childFile('flutter.js').readAsStringSync(),
+      equals(flutterJsContents),
+    );
   }));
 
   test('wasm build copies and generates specific files', () => testbed.run(() async {

packages/flutter_tools/test/integration.shard/test_data/project.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:file/file.dart';
+import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/web/file_generators/flutter_js.dart';
 
 import '../test_utils.dart';
@@ -59,9 +60,13 @@ abstract class Project {
     }
     deferredComponents?.setUpIn(dir);
 
+    final String fileGeneratorsPath =
+        Artifacts.test().getArtifactPath(Artifact.flutterToolsFileGenerators);
+    final String flutterJsContents = generateFlutterJsFile(fileGeneratorsPath);
+
     // Setup for different flutter web initializations
     writeFile(fileSystem.path.join(dir.path, 'web', 'index.html'), indexHtml);
-    writeFile(fileSystem.path.join(dir.path, 'web', 'flutter.js'), generateFlutterJsFile());
+    writeFile(fileSystem.path.join(dir.path, 'web', 'flutter.js'), flutterJsContents);
     writeFile(fileSystem.path.join(dir.path, 'web', 'flutter_service_worker.js'), '');
     writePackages(dir.path);
     await getPackages(dir.path);