[flutter_tools] support sound null-safety mode for the web (#60570)

In web debug mode, infer sound null safety by default. When sound null safety is enabled, provide a separate dill and precompiled Dart SDK. Release builds do not need this setting since we run dart2js from source.

Fixes #59873

packages/flutter_tools/lib/src/artifacts.dart

@@ -39,9 +39,22 @@ enum Artifact {
   kernelWorkerSnapshot,
   /// The root of the web implementation of the dart SDK.
   flutterWebSdk,
+  /// The libraries JSON file for web release builds.
   flutterWebLibrariesJson,
   /// The summary dill for the dartdevc target.
   webPlatformKernelDill,
+  /// The summary dill with null safety enabled for the dartdevc target.
+  webPlatformSoundKernelDill,
+  /// The precompiled SDKs and sourcemaps for web debug builds.
+  webPrecompiledSdk,
+  webPrecompiledSdkSourcemaps,
+  webPrecompiledCanvaskitSdk,
+  webPrecompiledCanvaskitSdkSourcemaps,
+  webPrecompiledSoundSdk,
+  webPrecompiledSoundSdkSourcemaps,
+  webPrecompiledCanvaskitSoundSdk,
+  webPrecompiledCanvaskitSoundSdkSourcemaps,
+
   iosDeploy,
   idevicesyslog,
   idevicescreenshot,
@@ -129,6 +142,8 @@ String _artifactToFileName(Artifact artifact, [ TargetPlatform platform, BuildMo
       return 'FlutterMacOS.podspec';
     case Artifact.webPlatformKernelDill:
       return 'flutter_ddc_sdk.dill';
+    case Artifact.webPlatformSoundKernelDill:
+      return 'flutter_ddc_sdk_sound.dill';
     case Artifact.fuchsiaKernelCompiler:
       return 'kernel_compiler.snapshot';
     case Artifact.fuchsiaFlutterRunner:
@@ -141,6 +156,16 @@ String _artifactToFileName(Artifact artifact, [ TargetPlatform platform, BuildMo
       return 'const_finder.dart.snapshot';
     case Artifact.flutterWebLibrariesJson:
       return 'libraries.json';
+    case Artifact.webPrecompiledSdk:
+    case Artifact.webPrecompiledCanvaskitSdk:
+    case Artifact.webPrecompiledSoundSdk:
+    case Artifact.webPrecompiledCanvaskitSoundSdk:
+      return 'dart_sdk.js';
+    case Artifact.webPrecompiledSdkSourcemaps:
+    case Artifact.webPrecompiledCanvaskitSdkSourcemaps:
+    case Artifact.webPrecompiledSoundSdkSourcemaps:
+    case Artifact.webPrecompiledCanvaskitSoundSdkSourcemaps:
+      return 'dart_sdk.js.map';
   }
   assert(false, 'Invalid artifact $artifact.');
   return null;
@@ -348,6 +373,8 @@ class CachedArtifacts implements Artifacts {
         return _fileSystem.path.join(_getFlutterWebSdkPath(), _artifactToFileName(artifact));
       case Artifact.webPlatformKernelDill:
         return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', _artifactToFileName(artifact));
+      case Artifact.webPlatformSoundKernelDill:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', _artifactToFileName(artifact));
       case Artifact.dart2jsSnapshot:
         return _fileSystem.path.join(_dartSdkPath(_fileSystem), 'bin', 'snapshots', _artifactToFileName(artifact));
       case Artifact.dartdevcSnapshot:
@@ -380,6 +407,22 @@ class CachedArtifacts implements Artifacts {
                      .childDirectory(getNameForTargetPlatform(platform))
                      .childFile(_artifactToFileName(artifact, platform, mode))
                      .path;
+      case Artifact.webPrecompiledSdk:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd', _artifactToFileName(artifact, platform, mode));
+      case Artifact.webPrecompiledSdkSourcemaps:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd', _artifactToFileName(artifact, platform, mode));
+      case Artifact.webPrecompiledCanvaskitSdk:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-canvaskit', _artifactToFileName(artifact, platform, mode));
+      case Artifact.webPrecompiledCanvaskitSdkSourcemaps:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-canvaskit', _artifactToFileName(artifact, platform, mode));
+      case Artifact.webPrecompiledSoundSdk:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-sound', _artifactToFileName(artifact, platform, mode));
+      case Artifact.webPrecompiledSoundSdkSourcemaps:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-sound', _artifactToFileName(artifact, platform, mode));
+      case Artifact.webPrecompiledCanvaskitSoundSdk:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-canvaskit-sound', _artifactToFileName(artifact, platform, mode));
+      case Artifact.webPrecompiledCanvaskitSoundSdkSourcemaps:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-canvaskit-sound', _artifactToFileName(artifact, platform, mode));
       default:
         assert(false, 'Artifact $artifact not available for platform $platform.');
         return null;
@@ -542,6 +585,8 @@ class LocalEngineArtifacts implements Artifacts {
         return _fileSystem.path.join(_hostEngineOutPath, _artifactToFileName(artifact));
       case Artifact.webPlatformKernelDill:
         return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', _artifactToFileName(artifact));
+      case Artifact.webPlatformSoundKernelDill:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', _artifactToFileName(artifact));
       case Artifact.fuchsiaKernelCompiler:
         final String hostPlatform = getNameForHostPlatform(getCurrentHostPlatform());
         final String modeName = mode.isRelease ? 'release' : mode.toString();
@@ -557,6 +602,22 @@ class LocalEngineArtifacts implements Artifacts {
         return _fileSystem.path.join(_hostEngineOutPath, 'gen', artifactFileName);
       case Artifact.flutterWebLibrariesJson:
         return _fileSystem.path.join(_getFlutterWebSdkPath(), artifactFileName);
+      case Artifact.webPrecompiledSdk:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd', artifactFileName);
+      case Artifact.webPrecompiledSdkSourcemaps:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd', artifactFileName);
+      case Artifact.webPrecompiledCanvaskitSdk:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-canvaskit', artifactFileName);
+      case Artifact.webPrecompiledCanvaskitSdkSourcemaps:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-canvaskit', artifactFileName);
+      case Artifact.webPrecompiledSoundSdk:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-sound', artifactFileName);
+      case Artifact.webPrecompiledSoundSdkSourcemaps:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-sound', artifactFileName);
+      case Artifact.webPrecompiledCanvaskitSoundSdk:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-canvaskit-sound', artifactFileName);
+      case Artifact.webPrecompiledCanvaskitSoundSdkSourcemaps:
+        return _fileSystem.path.join(_getFlutterWebSdkPath(), 'kernel', 'amd-canvaskit-sound', artifactFileName);
     }
     assert(false, 'Invalid artifact $artifact.');
     return null;

packages/flutter_tools/lib/src/build_info.dart

@@ -30,10 +30,16 @@ class BuildInfo {
     @required this.treeShakeIcons,
     this.performanceMeasurementFile,
     this.packagesPath = '.packages',
+    this.nullSafetyMode = NullSafetyMode.autodetect,
   });
 
   final BuildMode mode;
 
+  /// The null safety mode the application should be run in.
+  ///
+  /// If not provided, defaults to [NullSafetyMode.autodetect].
+  final NullSafetyMode nullSafetyMode;
+
   /// Whether the build should subdset icon fonts.
   final bool treeShakeIcons;
 
@@ -688,3 +694,10 @@ List<String> decodeDartDefines(Map<String, String> environmentDefines, String ke
     .cast<String>()
     .toList();
 }
+
+/// The null safety runtime mode the app should be built in.
+enum NullSafetyMode {
+  sound,
+  unsound,
+  autodetect,
+}

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

@@ -103,6 +103,7 @@ class WebAssetServer implements AssetReader {
     this.internetAddress,
     this._modules,
     this._digests,
+    this._buildInfo,
   );
 
   // Fallback to "application/octet-stream" on null which
@@ -167,6 +168,7 @@ class WebAssetServer implements AssetReader {
         address,
         modules,
         digests,
+        buildInfo,
       );
       if (testMode) {
         return server;
@@ -263,6 +265,7 @@ class WebAssetServer implements AssetReader {
     return null;
   }
 
+  final BuildInfo _buildInfo;
   final HttpServer _httpServer;
   // If holding these in memory is too much overhead, this can be switched to a
   // RandomAccessFile and read on demand.
@@ -458,50 +461,31 @@ class WebAssetServer implements AssetReader {
   /// Whether to use the cavaskit SDK for rendering.
   bool canvasKitRendering = false;
 
-  @visibleForTesting
-  final File dartSdk = globals.fs.file(globals.fs.path.join(
-    globals.artifacts.getArtifactPath(Artifact.flutterWebSdk),
-    'kernel',
-    'amd',
-    'dart_sdk.js',
-  ));
-
-  @visibleForTesting
-  final File canvasKitDartSdk = globals.fs.file(globals.fs.path.join(
-    globals.artifacts.getArtifactPath(Artifact.flutterWebSdk),
-    'kernel',
-    'amd-canvaskit',
-    'dart_sdk.js',
-  ));
-
-  @visibleForTesting
-  final File dartSdkSourcemap = globals.fs.file(globals.fs.path.join(
-    globals.artifacts.getArtifactPath(Artifact.flutterWebSdk),
-    'kernel',
-    'amd',
-    'dart_sdk.js.map',
-  ));
-
-  @visibleForTesting
-  final File canvasKitDartSdkSourcemap = globals.fs.file(globals.fs.path.join(
-    globals.artifacts.getArtifactPath(Artifact.flutterWebSdk),
-    'kernel',
-    'amd-canvaskit',
-    'dart_sdk.js.map',
-  ));
-
   // Attempt to resolve `path` to a dart file.
   File _resolveDartFile(String path) {
     // Return the actual file objects so that local engine changes are automatically picked up.
     switch (path) {
       case 'dart_sdk.js':
-        return canvasKitRendering
-          ? canvasKitDartSdk
-          : dartSdk;
+        if (_buildInfo.nullSafetyMode == NullSafetyMode.unsound) {
+          return globals.fs.file(canvasKitRendering
+            ? globals.artifacts.getArtifactPath(Artifact.webPrecompiledCanvaskitSdk)
+            : globals.artifacts.getArtifactPath(Artifact.webPrecompiledSdk));
+        } else {
+          return globals.fs.file(canvasKitRendering
+            ? globals.artifacts.getArtifactPath(Artifact.webPrecompiledCanvaskitSoundSdk)
+            : globals.artifacts.getArtifactPath(Artifact.webPrecompiledSoundSdk));
+        }
+        break;
       case 'dart_sdk.js.map':
-        return canvasKitRendering
-          ? canvasKitDartSdkSourcemap
-          : dartSdkSourcemap;
+        if (_buildInfo.nullSafetyMode == NullSafetyMode.unsound) {
+          return globals.fs.file(canvasKitRendering
+            ? globals.artifacts.getArtifactPath(Artifact.webPrecompiledCanvaskitSdkSourcemaps)
+            : globals.artifacts.getArtifactPath(Artifact.webPrecompiledSdkSourcemaps));
+        } else {
+          return globals.fs.file(canvasKitRendering
+            ? globals.artifacts.getArtifactPath(Artifact.webPrecompiledCanvaskitSoundSdkSourcemaps)
+            : globals.artifacts.getArtifactPath(Artifact.webPrecompiledSoundSdkSourcemaps));
+        }
     }
     // This is the special generated entrypoint.
     if (path == 'web_entrypoint.dart') {

packages/flutter_tools/lib/src/resident_runner.dart

@@ -92,6 +92,20 @@ class FlutterDevice {
     // a warning message and dump some debug information which can be
     // used to file a bug, but the compiler will still start up correctly.
     if (targetPlatform == TargetPlatform.web_javascript) {
+      Artifact platformDillArtifact;
+      List<String> extraFrontEndOptions;
+      if (buildInfo.nullSafetyMode == NullSafetyMode.unsound) {
+        platformDillArtifact = Artifact.webPlatformKernelDill;
+        extraFrontEndOptions = buildInfo.extraFrontEndOptions;
+      } else {
+        platformDillArtifact = Artifact.webPlatformSoundKernelDill;
+        extraFrontEndOptions = <String>[
+          ...?buildInfo?.extraFrontEndOptions,
+          if (!(buildInfo?.extraFrontEndOptions?.contains('--sound-null-safety') ?? false))
+            '--sound-null-safety'
+        ];
+      }
+
       generator = ResidentCompiler(
         globals.artifacts.getArtifactPath(Artifact.flutterWebSdk, mode: buildInfo.mode),
         buildMode: buildInfo.mode,
@@ -105,9 +119,9 @@ class FlutterDevice {
           dartDefines: buildInfo.dartDefines,
         ),
         targetModel: TargetModel.dartdevc,
-        extraFrontEndOptions: buildInfo.extraFrontEndOptions,
+        extraFrontEndOptions: extraFrontEndOptions,
         platformDill: globals.fs.file(globals.artifacts
-          .getArtifactPath(Artifact.webPlatformKernelDill, mode: buildInfo.mode))
+          .getArtifactPath(platformDillArtifact, mode: buildInfo.mode))
           .absolute.uri.toString(),
         dartDefines: buildInfo.dartDefines,
         librariesSpec: globals.fs.file(globals.artifacts

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -479,8 +479,9 @@ abstract class FlutterCommand extends Command<void> {
       help:
         'Whether to override the inferred null safety mode. This allows null-safe '
         'libraries to depend on un-migrated (non-null safe) libraries. By default, '
-        'Flutter applications will attempt to run at the null safety level of their '
-        'entrypoint library (usually lib/main.dart).',
+        'Flutter mobile & desktop applications will attempt to run at the null safety '
+        'level of their entrypoint library (usually lib/main.dart). Flutter web '
+        'applications will default to sound null-safety, unless specifically configured.',
       defaultsTo: null,
       hide: hide,
     );
@@ -617,15 +618,20 @@ abstract class FlutterCommand extends Command<void> {
       }
     }
 
+    NullSafetyMode nullSafetyMode = NullSafetyMode.unsound;
     if (argParser.options.containsKey(FlutterOptions.kNullSafety)) {
       final bool nullSafety = boolArg(FlutterOptions.kNullSafety);
       // Explicitly check for `true` and `false` so that `null` results in not
       // passing a flag. This will use the automatically detected null-safety
       // value based on the entrypoint
       if (nullSafety == true) {
+        nullSafetyMode = NullSafetyMode.sound;
         extraFrontEndOptions.add('--sound-null-safety');
       } else if (nullSafety == false) {
+        nullSafetyMode = NullSafetyMode.unsound;
         extraFrontEndOptions.add('--no-sound-null-safety');
+      } else if (extraFrontEndOptions.contains('--enable-experiment=non-nullable')) {
+        nullSafetyMode = NullSafetyMode.autodetect;
       }
     }
 
@@ -685,7 +691,8 @@ abstract class FlutterCommand extends Command<void> {
       bundleSkSLPath: bundleSkSLPath,
       dartExperiments: experiments,
       performanceMeasurementFile: performanceMeasurementFile,
-      packagesPath: globalResults['packages'] as String ?? '.packages'
+      packagesPath: globalResults['packages'] as String ?? '.packages',
+      nullSafetyMode: nullSafetyMode,
     );
   }
 

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

@@ -53,7 +53,7 @@ Future<void> buildWeb(
         kCspMode: csp.toString(),
         kIconTreeShakerFlag: buildInfo.treeShakeIcons.toString(),
         if (buildInfo.extraFrontEndOptions?.isNotEmpty ?? false)
-          kExtraFrontEndOptions: buildInfo.extraFrontEndOptions.join(',')
+          kExtraFrontEndOptions: encodeDartDefines(buildInfo.extraFrontEndOptions),
       },
       artifacts: globals.artifacts,
       fileSystem: globals.fs,

packages/flutter_tools/test/general.shard/artifacts_test.dart

@@ -52,6 +52,41 @@ void main() {
       );
     });
 
+    testWithoutContext('precompiled web artifact paths are correct', () {
+      expect(
+        artifacts.getArtifactPath(Artifact.webPrecompiledSdk),
+        'root/bin/cache/flutter_web_sdk/kernel/amd/dart_sdk.js',
+      );
+      expect(
+        artifacts.getArtifactPath(Artifact.webPrecompiledSdkSourcemaps),
+        'root/bin/cache/flutter_web_sdk/kernel/amd/dart_sdk.js.map',
+      );
+      expect(
+        artifacts.getArtifactPath(Artifact.webPrecompiledCanvaskitSdk),
+        'root/bin/cache/flutter_web_sdk/kernel/amd-canvaskit/dart_sdk.js',
+      );
+      expect(
+        artifacts.getArtifactPath(Artifact.webPrecompiledCanvaskitSdkSourcemaps),
+        'root/bin/cache/flutter_web_sdk/kernel/amd-canvaskit/dart_sdk.js.map',
+      );
+      expect(
+        artifacts.getArtifactPath(Artifact.webPrecompiledSoundSdk),
+        'root/bin/cache/flutter_web_sdk/kernel/amd-sound/dart_sdk.js',
+      );
+      expect(
+        artifacts.getArtifactPath(Artifact.webPrecompiledSoundSdkSourcemaps),
+        'root/bin/cache/flutter_web_sdk/kernel/amd-sound/dart_sdk.js.map',
+      );
+      expect(
+        artifacts.getArtifactPath(Artifact.webPrecompiledCanvaskitSoundSdk),
+        'root/bin/cache/flutter_web_sdk/kernel/amd-canvaskit-sound/dart_sdk.js',
+      );
+      expect(
+        artifacts.getArtifactPath(Artifact.webPrecompiledCanvaskitSoundSdkSourcemaps),
+        'root/bin/cache/flutter_web_sdk/kernel/amd-canvaskit-sound/dart_sdk.js.map',
+      );
+    });
+
     testWithoutContext('getEngineType', () {
       expect(
         artifacts.getEngineType(TargetPlatform.android_arm, BuildMode.debug),

packages/flutter_tools/test/general.shard/resident_runner_test.dart

@@ -1540,7 +1540,7 @@ void main() {
     expect(fakeVmServiceHost.hasRemainingExpectations, false);
   }));
 
-  testUsingContext('FlutterDevice uses dartdevc configuration when targeting web', () => testbed.run(() async {
+  testUsingContext('FlutterDevice uses dartdevc configuration when targeting web', () async {
     fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);
     final MockDevice mockDevice = MockDevice();
     when(mockDevice.targetPlatform).thenAnswer((Invocation invocation) async {
@@ -1549,7 +1549,12 @@ void main() {
 
     final DefaultResidentCompiler residentCompiler = (await FlutterDevice.create(
       mockDevice,
-      buildInfo: BuildInfo.debug,
+      buildInfo: const BuildInfo(
+        BuildMode.debug,
+        '',
+        treeShakeIcons: false,
+        nullSafetyMode: NullSafetyMode.unsound,
+      ),
       flutterProject: FlutterProject.current(),
       target: null,
     )).generator as DefaultResidentCompiler;
@@ -1562,12 +1567,46 @@ void main() {
     expect(residentCompiler.targetModel, TargetModel.dartdevc);
     expect(residentCompiler.sdkRoot,
       globals.artifacts.getArtifactPath(Artifact.flutterWebSdk, mode: BuildMode.debug) + '/');
-    expect(
-      residentCompiler.platformDill,
-      globals.fs.file(globals.artifacts.getArtifactPath(Artifact.webPlatformKernelDill, mode: BuildMode.debug))
-        .absolute.uri.toString(),
-    );
-  }));
+    expect(residentCompiler.platformDill, 'file:///Artifact.webPlatformKernelDill.debug');
+  }, overrides: <Type, Generator>{
+    Artifacts: () => Artifacts.test(),
+    FileSystem: () => MemoryFileSystem.test(),
+    ProcessManager: () => FakeProcessManager.any(),
+  });
+
+  testUsingContext('FlutterDevice uses dartdevc configuration when targeting web with null-safety autodetected', () async {
+    fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);
+    final MockDevice mockDevice = MockDevice();
+    when(mockDevice.targetPlatform).thenAnswer((Invocation invocation) async {
+      return TargetPlatform.web_javascript;
+    });
+
+    final DefaultResidentCompiler residentCompiler = (await FlutterDevice.create(
+      mockDevice,
+      buildInfo: const BuildInfo(
+        BuildMode.debug,
+        '',
+        treeShakeIcons: false,
+        extraFrontEndOptions: <String>['--enable-experiment=non-nullable'],
+      ),
+      flutterProject: FlutterProject.current(),
+      target: null,
+    )).generator as DefaultResidentCompiler;
+
+    expect(residentCompiler.initializeFromDill,
+      globals.fs.path.join(getBuildDirectory(), 'cache.dill'));
+    expect(residentCompiler.librariesSpec,
+      globals.fs.file(globals.artifacts.getArtifactPath(Artifact.flutterWebLibrariesJson))
+        .uri.toString());
+    expect(residentCompiler.targetModel, TargetModel.dartdevc);
+    expect(residentCompiler.sdkRoot,
+      globals.artifacts.getArtifactPath(Artifact.flutterWebSdk, mode: BuildMode.debug) + '/');
+    expect(residentCompiler.platformDill, 'file:///Artifact.webPlatformSoundKernelDill.debug');
+  }, overrides: <Type, Generator>{
+    Artifacts: () => Artifacts.test(),
+    FileSystem: () => MemoryFileSystem.test(),
+    ProcessManager: () => FakeProcessManager.any(),
+  });
 
   testUsingContext('connect sets up log reader', () => testbed.run(() async {
     fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);

packages/flutter_tools/test/general.shard/resident_web_runner_test.dart

@@ -764,7 +764,7 @@ void main() {
   testUsingContext('web resident runner can toggle CanvasKit', () async {
     final ResidentRunner residentWebRunner = setUpResidentRunner(mockFlutterDevice);
     fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);
-    final WebAssetServer webAssetServer = WebAssetServer(null, null, null, null, null);
+    final WebAssetServer webAssetServer = WebAssetServer(null, null, null, null, null, null);
     when(mockWebDevFS.webAssetServer).thenReturn(webAssetServer);
 
     expect(residentWebRunner.supportsCanvasKit, true);

packages/flutter_tools/test/general.shard/web/devfs_web_test.dart

@@ -5,6 +5,7 @@
 import 'dart:io';
 
 import 'package:dwds/dwds.dart';
+import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/platform.dart';
@@ -53,6 +54,8 @@ void main() {
         InternetAddress.loopbackIPv4,
         null,
         null,
+        null,
+
       );
     });
   });
@@ -416,7 +419,12 @@ void main() {
       packagesFilePath: '.packages',
       urlTunneller: null,
       useSseForDebugProxy: true,
-      buildInfo: BuildInfo.debug,
+      buildInfo: const BuildInfo(
+        BuildMode.debug,
+        '',
+        treeShakeIcons: false,
+        nullSafetyMode: NullSafetyMode.unsound,
+      ),
       enableDwds: false,
       entrypoint: Uri.base,
       testMode: true,
@@ -428,24 +436,31 @@ void main() {
 
     final Uri uri = await webDevFS.create();
     webDevFS.webAssetServer.entrypointCacheDirectory = globals.fs.currentDirectory;
+    final String webPrecompiledSdk = globals.artifacts
+      .getArtifactPath(Artifact.webPrecompiledSdk);
+    final String webPrecompiledSdkSourcemaps = globals.artifacts
+      .getArtifactPath(Artifact.webPrecompiledSdkSourcemaps);
+    final String webPrecompiledCanvaskitSdk = globals.artifacts
+      .getArtifactPath(Artifact.webPrecompiledCanvaskitSdk);
+    final String webPrecompiledCanvaskitSdkSourcemaps = globals.artifacts
+      .getArtifactPath(Artifact.webPrecompiledCanvaskitSdkSourcemaps);
     globals.fs.currentDirectory
       .childDirectory('lib')
       .childFile('web_entrypoint.dart')
       ..createSync(recursive: true)
       ..writeAsStringSync('GENERATED');
-    webDevFS.webAssetServer.dartSdk
+    globals.fs.file(webPrecompiledSdk)
       ..createSync(recursive: true)
       ..writeAsStringSync('HELLO');
-    webDevFS.webAssetServer.dartSdkSourcemap
+    globals.fs.file(webPrecompiledSdkSourcemaps)
       ..createSync(recursive: true)
       ..writeAsStringSync('THERE');
-    webDevFS.webAssetServer.canvasKitDartSdk
+    globals.fs.file(webPrecompiledCanvaskitSdk)
       ..createSync(recursive: true)
       ..writeAsStringSync('OL');
-    webDevFS.webAssetServer.canvasKitDartSdkSourcemap
+    globals.fs.file(webPrecompiledCanvaskitSdkSourcemaps)
       ..createSync(recursive: true)
       ..writeAsStringSync('CHUM');
-    webDevFS.webAssetServer.dartSdkSourcemap.createSync(recursive: true);
 
     await webDevFS.update(
       mainUri: globals.fs.file(globals.fs.path.join('lib', 'main.dart')).uri,
@@ -465,7 +480,7 @@ void main() {
     expect(await webDevFS.webAssetServer.dartSourceContents('dart_sdk.js.map'), 'THERE');
 
     // Update to the SDK.
-    webDevFS.webAssetServer.dartSdk.writeAsStringSync('BELLOW');
+   globals.fs.file(webPrecompiledSdk).writeAsStringSync('BELLOW');
 
     // New SDK should be visible..
     expect(await webDevFS.webAssetServer.dartSourceContents('dart_sdk.js'), 'BELLOW');
@@ -483,6 +498,116 @@ void main() {
     expect(uri, Uri.http('localhost:0', ''));
 
     await webDevFS.destroy();
+  }, overrides: <Type, Generator>{
+    Artifacts: () => Artifacts.test(),
+  }));
+
+  test('Can start web server with specified assets in sound null safety mode', () => testbed.run(() async {
+    globals.fs.file('.packages').writeAsStringSync('\n');
+    final File outputFile = globals.fs.file(globals.fs.path.join('lib', 'main.dart'))
+      ..createSync(recursive: true);
+    outputFile.parent.childFile('a.sources').writeAsStringSync('');
+    outputFile.parent.childFile('a.json').writeAsStringSync('{}');
+    outputFile.parent.childFile('a.map').writeAsStringSync('{}');
+    outputFile.parent.childFile('.packages').writeAsStringSync('\n');
+
+    final ResidentCompiler residentCompiler = MockResidentCompiler();
+    when(residentCompiler.recompile(
+      any,
+      any,
+      outputPath: anyNamed('outputPath'),
+      packageConfig: anyNamed('packageConfig'),
+    )).thenAnswer((Invocation invocation) async {
+      return const CompilerOutput('a', 0, <Uri>[]);
+    });
+
+    final WebDevFS webDevFS = WebDevFS(
+      hostname: 'localhost',
+      port: 0,
+      packagesFilePath: '.packages',
+      urlTunneller: null,
+      useSseForDebugProxy: true,
+      buildInfo: const BuildInfo(
+        BuildMode.debug,
+        '',
+        treeShakeIcons: false,
+        nullSafetyMode: NullSafetyMode.autodetect,
+      ),
+      enableDwds: false,
+      entrypoint: Uri.base,
+      testMode: true,
+      expressionCompiler: null,
+      chromiumLauncher: null,
+    );
+    webDevFS.requireJS.createSync(recursive: true);
+    webDevFS.stackTraceMapper.createSync(recursive: true);
+
+    final Uri uri = await webDevFS.create();
+    webDevFS.webAssetServer.entrypointCacheDirectory = globals.fs.currentDirectory;
+    globals.fs.currentDirectory
+      .childDirectory('lib')
+      .childFile('web_entrypoint.dart')
+      ..createSync(recursive: true)
+      ..writeAsStringSync('GENERATED');
+    final String webPrecompiledSoundSdk = globals.artifacts
+      .getArtifactPath(Artifact.webPrecompiledSoundSdk);
+    final String webPrecompiledSoundSdkSourcemaps = globals.artifacts
+      .getArtifactPath(Artifact.webPrecompiledSoundSdkSourcemaps);
+    final String webPrecompiledCanvaskitSoundSdk = globals.artifacts
+      .getArtifactPath(Artifact.webPrecompiledCanvaskitSoundSdk);
+    final String webPrecompiledCanvaskitSoundSdkSourcemaps = globals.artifacts
+      .getArtifactPath(Artifact.webPrecompiledCanvaskitSoundSdkSourcemaps);
+    globals.fs.file(webPrecompiledSoundSdk)
+      ..createSync(recursive: true)
+      ..writeAsStringSync('HELLO');
+    globals.fs.file(webPrecompiledSoundSdkSourcemaps)
+      ..createSync(recursive: true)
+      ..writeAsStringSync('THERE');
+    globals.fs.file(webPrecompiledCanvaskitSoundSdk)
+      ..createSync(recursive: true)
+      ..writeAsStringSync('OL');
+    globals.fs.file(webPrecompiledCanvaskitSoundSdkSourcemaps)
+      ..createSync(recursive: true)
+      ..writeAsStringSync('CHUM');
+
+    await webDevFS.update(
+      mainUri: globals.fs.file(globals.fs.path.join('lib', 'main.dart')).uri,
+      generator: residentCompiler,
+      trackWidgetCreation: true,
+      bundleFirstUpload: true,
+      invalidatedFiles: <Uri>[],
+      packageConfig: PackageConfig.empty,
+    );
+
+    expect(webDevFS.webAssetServer.getFile('require.js'), isNotNull);
+    expect(webDevFS.webAssetServer.getFile('stack_trace_mapper.js'), isNotNull);
+    expect(webDevFS.webAssetServer.getFile('main.dart'), isNotNull);
+    expect(webDevFS.webAssetServer.getFile('manifest.json'), isNotNull);
+    expect(webDevFS.webAssetServer.getFile('flutter_service_worker.js'), isNotNull);
+    expect(await webDevFS.webAssetServer.dartSourceContents('dart_sdk.js'), 'HELLO');
+    expect(await webDevFS.webAssetServer.dartSourceContents('dart_sdk.js.map'), 'THERE');
+
+    // Update to the SDK.
+    globals.fs.file(webPrecompiledSoundSdk).writeAsStringSync('BELLOW');
+
+    // New SDK should be visible..
+    expect(await webDevFS.webAssetServer.dartSourceContents('dart_sdk.js'), 'BELLOW');
+
+    // Toggle CanvasKit
+    webDevFS.webAssetServer.canvasKitRendering = true;
+    expect(await webDevFS.webAssetServer.dartSourceContents('dart_sdk.js'), 'OL');
+    expect(await webDevFS.webAssetServer.dartSourceContents('dart_sdk.js.map'), 'CHUM');
+
+    // Generated entrypoint.
+    expect(await webDevFS.webAssetServer.dartSourceContents('web_entrypoint.dart'),
+      contains('GENERATED'));
+
+    // served on localhost
+    expect(uri, Uri.http('localhost:0', ''));
+
+    await webDevFS.destroy();
+  }, overrides: <Type, Generator>{
+    Artifacts: () => Artifacts.test(),
   }));
 
   test('Can start web server with hostname any', () => testbed.run(() async {