[flutter_tools] allow disabling pwa from build command, fix run release build caching (#64587)

Fix run release/profile modes generating a full service worker.

packages/flutter_tools/lib/src/build_runner/resident_web_runner.dart

@@ -21,6 +21,7 @@ import '../base/net.dart';
 import '../base/terminal.dart';
 import '../base/utils.dart';
 import '../build_info.dart';
+import '../build_system/targets/web.dart';
 import '../cache.dart';
 import '../dart/language_version.dart';
 import '../dart/pub.dart';
@@ -488,6 +489,7 @@ class _ResidentWebRunner extends ResidentWebRunner {
             debuggingOptions.buildInfo,
             debuggingOptions.initializePlatform,
             false,
+            kNoneWorker,
           );
         }
         await device.device.startApp(
@@ -557,6 +559,7 @@ class _ResidentWebRunner extends ResidentWebRunner {
           debuggingOptions.buildInfo,
           debuggingOptions.initializePlatform,
           false,
+          kNoneWorker,
         );
       } on ToolExit {
         return OperationResult(1, 'Failed to recompile application.');

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

@@ -5,6 +5,7 @@
 import 'dart:math';
 
 import 'package:crypto/crypto.dart';
+import 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 
 import '../../artifacts.dart';
@@ -33,6 +34,32 @@ const String kDart2jsOptimization = 'Dart2jsOptimization';
 /// Whether to disable dynamic generation code to satisfy csp policies.
 const String kCspMode = 'cspMode';
 
+/// The caching strategy to use for service worker generation.
+const String kServiceWorkerStrategy = 'ServiceWorkerStratgey';
+
+/// 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,
+}
+
+const String kOfflineFirst = 'offline-first';
+const String kNoneWorker = 'none';
+
+/// Convert a [value] into a [ServiceWorkerStrategy].
+ServiceWorkerStrategy _serviceWorkerStrategyfromString(String value) {
+  switch (value) {
+    case kNoneWorker:
+      return ServiceWorkerStrategy.none;
+    // offline-first is the default value for any invalid requests.
+    default:
+      return ServiceWorkerStrategy.offlineFirst;
+  }
+}
+
 /// Generates an entry point for a web target.
 // Keep this in sync with build_runner/resident_web_runner.dart
 class WebEntrypointTarget extends Target {
@@ -384,7 +411,12 @@ class WebServiceWorker extends Target {
     final File serviceWorkerFile = environment.outputDir
       .childFile('flutter_service_worker.js');
     final Depfile depfile = Depfile(contents, <File>[serviceWorkerFile]);
-    final String serviceWorker = generateServiceWorker(urlToHash, <String>[
+    final ServiceWorkerStrategy serviceWorkerStrategy = _serviceWorkerStrategyfromString(
+      environment.defines[kServiceWorkerStrategy],
+    );
+    final String serviceWorker = generateServiceWorker(
+      urlToHash,
+      <String>[
         '/',
         'main.dart.js',
         'index.html',
@@ -393,7 +425,9 @@ class WebServiceWorker extends Target {
           'assets/AssetManifest.json',
         if (urlToHash.containsKey('assets/FontManifest.json'))
           'assets/FontManifest.json',
-    ]);
+      ],
+      serviceWorkerStrategy: serviceWorkerStrategy,
+    );
     serviceWorkerFile
       .writeAsStringSync(serviceWorker);
     final DepfileService depfileService = DepfileService(
@@ -413,7 +447,14 @@ class WebServiceWorker extends Target {
 /// The tool embeds file hashes directly into the worker so that the byte for byte
 /// invalidation will automatically reactivate workers whenever a new
 /// version is deployed.
-String generateServiceWorker(Map<String, String> resources, List<String> coreBundle) {
+String generateServiceWorker(
+  Map<String, String> resources,
+  List<String> coreBundle, {
+  @required ServiceWorkerStrategy serviceWorkerStrategy,
+}) {
+  if (serviceWorkerStrategy == ServiceWorkerStrategy.none) {
+    return '';
+  }
   return '''
 'use strict';
 const MANIFEST = 'flutter-app-manifest';
@@ -427,7 +468,6 @@ const RESOURCES = {
 // 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) => {
   return event.waitUntil(
@@ -448,7 +488,6 @@ self.addEventListener("activate", function(event) {
       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);
@@ -462,7 +501,6 @@ self.addEventListener("activate", function(event) {
         await manifestCache.put('manifest', new Response(JSON.stringify(RESOURCES)));
         return;
       }
-
       var oldManifest = await manifest.json();
       var origin = self.location.origin;
       for (var request of await contentCache.keys()) {
@@ -537,7 +575,6 @@ self.addEventListener('message', (event) => {
   if (event.data === 'skipWaiting') {
     return self.skipWaiting();
   }
-
   if (event.message === 'downloadOffline') {
     downloadOffline();
   }

packages/flutter_tools/lib/src/commands/build_web.dart

@@ -8,6 +8,7 @@ import 'package:meta/meta.dart';
 
 import '../base/common.dart';
 import '../build_info.dart';
+import '../build_system/targets/web.dart';
 import '../features.dart';
 import '../project.dart';
 import '../runner/flutter_command.dart'
@@ -38,6 +39,22 @@ class BuildWebCommand extends BuildSubCommand {
       help: 'Disable dynamic generation of code in the generated output. '
         'This is necessary to satisfy CSP restrictions (see http://www.w3.org/TR/CSP/).'
     );
+    argParser.addOption('pwa-strategy',
+      defaultsTo: kOfflineFirst,
+      help:
+        'The caching strategy to be used by the PWA service worker.\n'
+        'offline-first will attempt to cache the app shell eagerly and '
+        'then lazily cache all subsequent assets as they are loaded. When '
+        'making a network request for an asset, the offline cache will be '
+        'preferred.\n'
+        'none will generate a service worker with no body. This is useful for '
+        'local testing or in cases where the service worker caching functionality '
+        'is not desirable',
+      allowed: <String>[
+        kOfflineFirst,
+        kNoneWorker,
+      ]
+    );
   }
 
   @override
@@ -72,6 +89,7 @@ class BuildWebCommand extends BuildSubCommand {
       buildInfo,
       boolArg('web-initialize-platform'),
       boolArg('csp'),
+      stringArg('pwa-strategy'),
     );
     return FlutterCommandResult.success();
   }

packages/flutter_tools/lib/src/web/compile.dart

@@ -28,6 +28,7 @@ Future<void> buildWeb(
   BuildInfo buildInfo,
   bool initializePlatform,
   bool csp,
+  String serviceWorkerStrategy,
 ) async {
   if (!flutterProject.web.existsSync()) {
     throwToolExit('Missing index.html.');
@@ -52,6 +53,8 @@ Future<void> buildWeb(
         kDartDefines: encodeDartDefines(buildInfo.dartDefines),
         kCspMode: csp.toString(),
         kIconTreeShakerFlag: buildInfo.treeShakeIcons.toString(),
+        if (serviceWorkerStrategy != null)
+         kServiceWorkerStrategy: serviceWorkerStrategy,
         if (buildInfo.extraFrontEndOptions?.isNotEmpty ?? false)
           kExtraFrontEndOptions: encodeDartDefines(buildInfo.extraFrontEndOptions),
       },

packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart

@@ -56,6 +56,7 @@ void main() {
       BuildInfo.debug,
       false,
       false,
+      null,
     ), throwsToolExit());
   }, overrides: <Type, Generator>{
     Platform: () => fakePlatform,

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

@@ -475,14 +475,20 @@ void main() {
     ProcessManager: () => processManager,
   }));
 
+  test('Generated service worker is empty with none-strategy', () {
+    final String result = generateServiceWorker(<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>[]);
+    final String result = generateServiceWorker(<String, String>{'/foo': 'abcd'}, <String>[], serviceWorkerStrategy: ServiceWorkerStrategy.offlineFirst);
 
     expect(result, contains('{\n  "/foo": "abcd"\n};'));
   });
 
   test('Generated service worker includes core files', () {
-    final String result = generateServiceWorker(<String, String>{'/foo': 'abcd'}, <String>['foo', 'bar']);
+    final String result = generateServiceWorker(<String, String>{'/foo': 'abcd'}, <String>['foo', 'bar'], serviceWorkerStrategy: ServiceWorkerStrategy.offlineFirst);
 
     expect(result, contains('"foo",\n"bar"'));
   });