[flutter_tools] hot reload/restart update for asset manager change (#66742)

Do not upload all assets on initial devFS sync. This should increase the reliability of the initial connection, even in the face of flaky devfs behavior, in addition to a moderate perf improvement.

Updates fast-start to build assets as part of the initial bundle

Requires flutter/engine#21436
Requires flutter/engine#21586
Requires flutter/engine#21611

packages/flutter_tools/gradle/flutter.gradle

@@ -893,11 +893,7 @@ abstract class BaseFlutterTask extends DefaultTask {
         // cache.
         String[] ruleNames;
         if (buildMode == "debug") {
-            if (fastStart) {
-                ruleNames = ["faststart_android_application"]
-            } else {
             ruleNames = ["debug_android_application"]
-            }
         } else {
             ruleNames = targetPlatformValues.collect { "android_aot_bundle_${buildMode}_$it" }
         }

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

@@ -34,11 +34,9 @@ abstract class AndroidAssetBundle extends Target {
 
   @override
   List<String> get depfiles => <String>[
-    if (_copyAssets)
     'flutter_assets.d',
   ];
 
-  bool get _copyAssets => true;
 
   @override
   Future<void> build(Environment environment) async {
@@ -61,7 +59,6 @@ abstract class AndroidAssetBundle extends Target {
       environment.fileSystem.file(isolateSnapshotData)
           .copySync(outputDirectory.childFile('isolate_snapshot_data').path);
     }
-    if (_copyAssets) {
     final Depfile assetDepfile = await copyAssets(
       environment,
       outputDirectory,
@@ -76,7 +73,6 @@ abstract class AndroidAssetBundle extends Target {
       environment.buildDir.childFile('flutter_assets.d'),
     );
   }
-  }
 
   @override
   List<Target> get dependencies => const <Target>[
@@ -108,17 +104,6 @@ class DebugAndroidApplication extends AndroidAssetBundle {
   ];
 }
 
-/// A minimal android application that does not include assets.
-class FastStartAndroidApplication extends DebugAndroidApplication {
-  const FastStartAndroidApplication();
-
-  @override
-  String get name => 'faststart_android_application';
-
-  @override
-  bool get _copyAssets => false;
-}
-
 /// An implementation of [AndroidAssetBundle] that only includes assets.
 class AotAndroidAssetBundle extends AndroidAssetBundle {
   const AotAndroidAssetBundle();

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

@@ -49,7 +49,6 @@ const List<Target> _kDefaultTargets = <Target>[
   CopyFlutterBundle(),
   // Android targets,
   DebugAndroidApplication(),
-  FastStartAndroidApplication(),
   ProfileAndroidApplication(),
   // Android ABI specific AOT rules.
   androidArmProfileBundle,

packages/flutter_tools/lib/src/devfs.dart

@@ -472,7 +472,6 @@ class DevFS {
     String dillOutputPath,
     bool fullRestart = false,
     String projectRootPath,
-    bool skipAssets = false,
   }) async {
     assert(trackWidgetCreation != null);
     assert(generator != null);
@@ -484,25 +483,24 @@ class DevFS {
     final Map<Uri, DevFSContent> dirtyEntries = <Uri, DevFSContent>{};
 
     int syncedBytes = 0;
-    if (bundle != null && !skipAssets) {
+    if (bundle != null) {
       final String assetBuildDirPrefix = _asUriPath(getAssetBuildDirectory());
-      // We write the assets into the AssetBundle working dir so that they
+      // The tool writes the assets into the AssetBundle working dir so that they
       // are in the same location in DevFS and the iOS simulator.
       final String assetDirectory = getAssetBuildDirectory();
       bundle.entries.forEach((String archivePath, DevFSContent content) {
+        if (!content.isModified || bundleFirstUpload) {
+          return;
+        }
         final Uri deviceUri = _fileSystem.path.toUri(_fileSystem.path.join(assetDirectory, archivePath));
         if (deviceUri.path.startsWith(assetBuildDirPrefix)) {
           archivePath = deviceUri.path.substring(assetBuildDirPrefix.length);
         }
-        // Only update assets if they have been modified, or if this is the
-        // first upload of the asset bundle.
-        if (content.isModified || (bundleFirstUpload && archivePath != null)) {
         dirtyEntries[deviceUri] = content;
         syncedBytes += content.size;
         if (archivePath != null && !bundleFirstUpload) {
           assetPathsToEvict.add(archivePath);
         }
-        }
       });
     }
     if (fullRestart) {

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

@@ -818,7 +818,6 @@ class WebDevFS implements DevFS {
     String dillOutputPath,
     bool fullRestart = false,
     String projectRootPath,
-    bool skipAssets = false,
   }) async {
     assert(trackWidgetCreation != null);
     assert(generator != null);

packages/flutter_tools/test/integration.shard/hot_reload_with_asset_test.dart

@@ -0,0 +1,83 @@
+// 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.
+
+import 'dart:async';
+
+import 'package:file/file.dart';
+
+import '../src/common.dart';
+import 'test_data/hot_reload_with_asset.dart';
+import 'test_driver.dart';
+import 'test_utils.dart';
+
+void main() {
+  Directory tempDir;
+  final HotReloadWithAssetProject project = HotReloadWithAssetProject();
+  FlutterRunTestDriver flutter;
+
+  setUp(() async {
+    tempDir = createResolvedTempDirectorySync('hot_reload_test.');
+    await project.setUpIn(tempDir);
+    flutter = FlutterRunTestDriver(tempDir);
+  });
+
+  tearDown(() async {
+    await flutter?.stop();
+    tryToDelete(tempDir);
+  });
+
+  testWithoutContext('hot reload does not need to sync assets on the first reload', () async {
+    final Completer<void> onFirstLoad = Completer<void>();
+    final Completer<void> onSecondLoad = Completer<void>();
+
+    flutter.stdout.listen((String line) {
+      // If the asset fails to load, this message will be printed instead.
+      // this indicates that the devFS was not able to locate the asset
+      // after the hot reload.
+      if (line.contains('FAILED TO LOAD')) {
+        fail('Did not load asset: $line');
+      }
+      if (line.contains('LOADED DATA')) {
+        onFirstLoad.complete();
+      }
+      if (line.contains('SECOND DATA')) {
+        onSecondLoad.complete();
+      }
+    });
+    flutter.stdout.listen(print);
+    await flutter.run();
+    await onFirstLoad.future;
+
+    project.uncommentHotReloadPrint();
+    await flutter.hotReload();
+    await onSecondLoad.future;
+  });
+
+  testWithoutContext('hot restart does not need to sync assets on the first reload', () async {
+    final Completer<void> onFirstLoad = Completer<void>();
+    final Completer<void> onSecondLoad = Completer<void>();
+
+    flutter.stdout.listen((String line) {
+      // If the asset fails to load, this message will be printed instead.
+      // this indicates that the devFS was not able to locate the asset
+      // after the hot reload.
+      if (line.contains('FAILED TO LOAD')) {
+        fail('Did not load asset: $line');
+      }
+      if (line.contains('LOADED DATA')) {
+        onFirstLoad.complete();
+      }
+      if (line.contains('SECOND DATA')) {
+        onSecondLoad.complete();
+      }
+    });
+    flutter.stdout.listen(print);
+    await flutter.run();
+    await onFirstLoad.future;
+
+    project.uncommentHotReloadPrint();
+    await flutter.hotRestart();
+    await onSecondLoad.future;
+  });
+}

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

@@ -0,0 +1,58 @@
+// 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.
+
+import '../test_utils.dart';
+import 'project.dart';
+
+class HotReloadWithAssetProject extends Project {
+  @override
+  final String pubspec = '''
+name: test
+environment:
+  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+
+flutter:
+  assets:
+    - pubspec.yaml
+  ''';
+
+  @override
+  final String main = r'''
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter/widgets.dart';
+
+Future<void> main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+  final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed');
+  await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
+  runApp(MyApp());
+}
+
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    rootBundle.evict('pubspec.yaml');
+    rootBundle.load('pubspec.yaml').then((_) {
+      print('LOADED DATA');
+    }, onError: (dynamic error, StackTrace stackTrace) {
+      print('FAILED TO LOAD');
+    });
+    return Container();
+  }
+}
+''';
+
+  void uncommentHotReloadPrint() {
+    final String newMainContents = main.replaceAll(
+      'LOADED DATA',
+      'SECOND DATA',
+    );
+    writeFile(fileSystem.path.join(dir.path, 'lib', 'main.dart'), newMainContents);
+  }
+}