[ Widget Preview ] Add support for dart:ffi imports (#180586)

Adds logic to pass `--include-unsupported-platform-library-stubs` to the
CFE when launched via `flutter widget-preview start`, as well as logic
to ensure the flag can't be passed as an extra frontend option to bypass
compile time errors due to imports of unsupported libraries.

Fixes https://github.com/flutter/flutter/issues/166431

engine/src/flutter/web_sdk/BUILD.gn

@@ -220,6 +220,8 @@ template("_compile_platform") {
     skwasm_library = "dart:_skwasm_stub"
     if (invoker.kernel_target == "dart2wasm") {
       skwasm_library = "dart:_skwasm_impl"
+    } else if (invoker.kernel_target == "ddc") {
+      args += [ "--include-unsupported-platform-library-stubs" ]
     }
 
     args += [

packages/flutter_tools/lib/src/build_info.dart

@@ -53,6 +53,7 @@ class BuildInfo {
     this.assumeInitializeFromDillUpToDate = false,
     this.buildNativeAssets = true,
     this.useLocalCanvasKit = false,
+    this.includeUnsupportedPlatformLibraryStubs = false,
     this.webEnableHotReload = false,
   }) : extraFrontEndOptions = extraFrontEndOptions ?? const <String>[],
        extraGenSnapshotOptions = extraGenSnapshotOptions ?? const <String>[],
@@ -181,6 +182,11 @@ class BuildInfo {
   /// If set, builds native assets with `build.dart` from all packages.
   final bool buildNativeAssets;
 
+  /// If set, unsupported core libraries can be imported without causing a compile time error.
+  ///
+  /// This should only be used by developer tooling as unsupported APIs will throw at runtime.
+  final bool includeUnsupportedPlatformLibraryStubs;
+
   /// If set, web builds will use the locally built CanvasKit instead of using the CDN
   final bool useLocalCanvasKit;
 

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

@@ -481,6 +481,7 @@ final class WidgetPreviewStartCommand extends WidgetPreviewSubCommandBase with C
           // Don't try and download canvaskit from the CDN.
           useLocalCanvasKit: true,
           webEnableHotReload: true,
+          includeUnsupportedPlatformLibraryStubs: true,
         ),
         webEnableExposeUrl: false,
         webEnableExpressionEvaluation: true,

packages/flutter_tools/lib/src/compile.dart

@@ -207,6 +207,16 @@ List<String> buildModeOptions(BuildMode mode, List<String> dartDefines) => switc
   _ => throw Exception('Unknown BuildMode: $mode'),
 };
 
+final _extraFrontEndOptionsFilterSet = <String>{
+  // Don't allow for users to pass --include-unsupported-platform-library-stubs to bypass
+  // unsupported library compile time errors as this flag is only safe for use by developer
+  // tooling.
+  '--include-unsupported-platform-library-stubs',
+};
+
+Iterable<String>? _filterExtraFrontEndOptions(List<String>? options) =>
+    options?.where((e) => !_extraFrontEndOptionsFilterSet.contains(e));
+
 /// A compiler interface for producing single (non-incremental) kernel files.
 class KernelCompiler {
   KernelCompiler({
@@ -371,7 +381,7 @@ class KernelCompiler {
           if (nativeAssets != null) ...<String>['--native-assets', nativeAssets],
           // See: https://github.com/flutter/flutter/issues/103994
           '--verbosity=error',
-          ...?extraFrontEndOptions,
+          ...?_filterExtraFrontEndOptions(extraFrontEndOptions),
           mainUri ?? '--native-assets-only',
         ];
 
@@ -509,6 +519,7 @@ abstract class ResidentCompiler {
     required ShutdownHooks shutdownHooks,
     bool testCompilation,
     bool trackWidgetCreation,
+    bool includeUnsupportedPlatformLibraryStubs,
     String packagesPath,
     List<String> fileSystemRoots,
     String? fileSystemScheme,
@@ -631,6 +642,7 @@ class DefaultResidentCompiler implements ResidentCompiler {
     required ShutdownHooks shutdownHooks,
     this.testCompilation = false,
     this.trackWidgetCreation = true,
+    this.includeUnsupportedPlatformLibraryStubs = false,
     this.packagesPath,
     List<String> fileSystemRoots = const <String>[],
     this.fileSystemScheme,
@@ -653,7 +665,17 @@ class DefaultResidentCompiler implements ResidentCompiler {
        // This is a URI, not a file path, so the forward slash is correct even on Windows.
        sdkRoot = sdkRoot.endsWith('/') ? sdkRoot : '$sdkRoot/',
        // Make a copy, we might need to modify it later.
-       fileSystemRoots = List<String>.from(fileSystemRoots);
+       fileSystemRoots = List<String>.from(fileSystemRoots) {
+    // Currently, the only developer tooling that requires support for importing unsupported
+    // platform libraries at compile time is the widget previewer. Only developer tooling use cases
+    // should support this, so this is restricted to the widget previewer's runtime target for now.
+    if (includeUnsupportedPlatformLibraryStubs && targetModel != TargetModel.dartdevc) {
+      throw StateError(
+        'includeUnsupportedPlatformLibraryStubs should only be used by the widget-preview '
+        'command.',
+      );
+    }
+  }
 
   final Logger _logger;
   final ProcessManager _processManager;
@@ -664,6 +686,7 @@ class DefaultResidentCompiler implements ResidentCompiler {
   final bool testCompilation;
   final BuildMode buildMode;
   final bool trackWidgetCreation;
+  final bool includeUnsupportedPlatformLibraryStubs;
   final String? packagesPath;
   final TargetModel targetModel;
   final List<String> fileSystemRoots;
@@ -867,6 +890,8 @@ class DefaultResidentCompiler implements ResidentCompiler {
           if (packagesPath != null) ...<String>['--packages', packagesPath!],
           ...buildModeOptions(buildMode, dartDefines),
           if (trackWidgetCreation) '--track-widget-creation',
+          if (includeUnsupportedPlatformLibraryStubs)
+            '--include-unsupported-platform-library-stubs',
           for (final String root in fileSystemRoots) ...<String>['--filesystem-root', root],
           if (fileSystemScheme != null) ...<String>['--filesystem-scheme', fileSystemScheme!],
           if (initializeFromDill != null) ...<String>[
@@ -886,7 +911,7 @@ class DefaultResidentCompiler implements ResidentCompiler {
           if (unsafePackageSerialization) '--unsafe-package-serialization',
           // See: https://github.com/flutter/flutter/issues/103994
           '--verbosity=error',
-          ...?extraFrontEndOptions,
+          ...?_filterExtraFrontEndOptions(extraFrontEndOptions),
         ];
     _logger.printTrace(command.join(' '));
     _server = await _processManager.start(command);

packages/flutter_tools/lib/src/resident_runner.dart

@@ -125,6 +125,7 @@ class FlutterDevice {
         globals.artifacts!.getHostArtifact(HostArtifact.flutterWebSdk).path,
         buildMode: buildInfo.mode,
         trackWidgetCreation: buildInfo.trackWidgetCreation,
+        includeUnsupportedPlatformLibraryStubs: buildInfo.includeUnsupportedPlatformLibraryStubs,
         fileSystemRoots: buildInfo.fileSystemRoots,
         // Override the filesystem scheme so that the frontend_server can find
         // the generated entrypoint code.

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

@@ -2,13 +2,21 @@
 // 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 'package:file/memory.dart';
+import 'package:flutter_tools/src/artifacts.dart';
+import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/compile.dart';
+import 'package:package_config/package_config.dart';
 
 import '../src/common.dart';
+import '../src/fake_process_manager.dart';
+import '../src/fakes.dart' hide FakeProcess;
 
 void main() {
   testWithoutContext('StdoutHandler can produce output message', () async {
@@ -147,4 +155,195 @@ void main() {
       );
     },
   );
+
+  testWithoutContext(
+    'includeUnsupportedPlatformLibraryStubs is only valid for Target.dartdevc',
+    () {
+      final unsupportedTargetModels = <TargetModel>{
+        TargetModel.flutter,
+        TargetModel.flutterRunner,
+        TargetModel.vm,
+      };
+
+      // Initializing the compiler with includeUnsupportedPlatformLibraryStubs for targets other
+      // than DDC is not currently supported as it's limited for use with the widget previewer.
+      for (final target in unsupportedTargetModels) {
+        try {
+          ResidentCompiler(
+            'sdkroot',
+            buildMode: BuildMode.debug,
+            logger: BufferLogger.test(),
+            processManager: FakeProcessManager.any(),
+            artifacts: Artifacts.test(),
+            platform: FakePlatform(),
+            fileSystem: MemoryFileSystem.test(),
+            shutdownHooks: FakeShutdownHooks(),
+            targetModel: target,
+            includeUnsupportedPlatformLibraryStubs: true,
+          );
+          fail('Unsupported target did not throw.');
+        } on StateError catch (e) {
+          expect(
+            e.message,
+            'includeUnsupportedPlatformLibraryStubs should only be used by the widget-preview '
+            'command.',
+          );
+        }
+      }
+
+      // Initializing the compiler with includeUnsupportedPlatformLibraryStubs for DDC is
+      // supported.
+      ResidentCompiler(
+        'sdkroot',
+        buildMode: BuildMode.debug,
+        logger: BufferLogger.test(),
+        processManager: FakeProcessManager.any(),
+        artifacts: Artifacts.test(),
+        platform: FakePlatform(),
+        fileSystem: MemoryFileSystem.test(),
+        shutdownHooks: FakeShutdownHooks(),
+        targetModel: TargetModel.dartdevc,
+        includeUnsupportedPlatformLibraryStubs: true,
+      );
+    },
+  );
+
+  testWithoutContext(
+    'Strips --include-unsupported-platform-library-stubs from extraFrontEndOptions',
+    () async {
+      final completer = Completer<void>();
+      final processManager = FakeProcessManager.list([
+        FakeCommand(
+          command: const <String>[
+            'Artifact.engineDartAotRuntime.TargetPlatform.web_javascript',
+            'Artifact.frontendServerSnapshotForEngineDartSdk.TargetPlatform.web_javascript',
+            '--sdk-root',
+            'sdkroot/',
+            '--incremental',
+            '--target=dartdevc',
+            '--experimental-emit-debug-metadata',
+            '--output-dill',
+            'foo.dill',
+            '-Ddart.vm.profile=false',
+            '-Ddart.vm.product=false',
+            '--enable-asserts',
+            '--track-widget-creation',
+            '--verbosity=error',
+            '--extra-flag',
+          ],
+          onRun: (_) => completer.complete(),
+        ),
+      ]);
+      final compiler = DefaultResidentCompiler(
+        'sdkroot',
+        buildMode: BuildMode.debug,
+        logger: BufferLogger.test(),
+        processManager: processManager,
+        artifacts: Artifacts.test(),
+        platform: FakePlatform(),
+        fileSystem: MemoryFileSystem.test(),
+        shutdownHooks: FakeShutdownHooks(),
+        targetModel: TargetModel.dartdevc,
+        // Don't explicitly enable includeUnsupportedPlatformLibraryStubs to ensure it's not
+        // included in the argument list.
+        // ignore: avoid_redundant_argument_values
+        includeUnsupportedPlatformLibraryStubs: false,
+        extraFrontEndOptions: [
+          '--include-unsupported-platform-library-stubs',
+          // Include a random extra flag to ensure not all extra options are stripped.
+          '--extra-flag',
+        ],
+      );
+
+      await runZonedGuarded(
+        () {
+          // This throws ToolExit as the FakeProcess immediately closes stdout and stderr.
+          compiler.recompile(
+            Uri.file('foo.dart'),
+            [],
+            outputPath: 'foo.dill',
+            packageConfig: PackageConfig.empty,
+          );
+        },
+        (e, st) {
+          if (e is! ToolExit) {
+            completer.completeError(e, st);
+          }
+        },
+      );
+
+      // Fail if the command isn't run. This can happen when the commands actual arguments don't
+      // match.
+      await completer.future.timeout(const Duration(seconds: 5));
+    },
+  );
+
+  testWithoutContext(
+    '--include-unsupported-platform-library-stubs when includeUnsupportedPlatformLibraryStubs is set',
+    () async {
+      final completer = Completer<void>();
+      final processManager = FakeProcessManager.list([
+        FakeCommand(
+          command: const <String>[
+            'Artifact.engineDartAotRuntime.TargetPlatform.web_javascript',
+            'Artifact.frontendServerSnapshotForEngineDartSdk.TargetPlatform.web_javascript',
+            '--sdk-root',
+            'sdkroot/',
+            '--incremental',
+            '--target=dartdevc',
+            '--experimental-emit-debug-metadata',
+            '--output-dill',
+            'foo.dill',
+            '-Ddart.vm.profile=false',
+            '-Ddart.vm.product=false',
+            '--enable-asserts',
+            '--track-widget-creation',
+            '--include-unsupported-platform-library-stubs',
+            '--verbosity=error',
+            '--extra-flag',
+          ],
+          onRun: (_) => completer.complete(),
+        ),
+      ]);
+      final compiler = DefaultResidentCompiler(
+        'sdkroot',
+        buildMode: BuildMode.debug,
+        logger: BufferLogger.test(),
+        processManager: processManager,
+        artifacts: Artifacts.test(),
+        platform: FakePlatform(),
+        fileSystem: MemoryFileSystem.test(),
+        shutdownHooks: FakeShutdownHooks(),
+        targetModel: TargetModel.dartdevc,
+        // Explicitly enable includeUnsupportedPlatformLibraryStubs to ensure it's included in the
+        // argument list.
+        includeUnsupportedPlatformLibraryStubs: true,
+        extraFrontEndOptions: [
+          // Include a random extra flag to ensure not all extra options are stripped.
+          '--extra-flag',
+        ],
+      );
+
+      await runZonedGuarded(
+        () {
+          // This throws ToolExit as the FakeProcess immediately closes stdout and stderr.
+          compiler.recompile(
+            Uri.file('foo.dart'),
+            [],
+            outputPath: 'foo.dill',
+            packageConfig: PackageConfig.empty,
+          );
+        },
+        (e, st) {
+          if (e is! ToolExit) {
+            completer.completeError(e, st);
+          }
+        },
+      );
+
+      // Fail if the command isn't run. This can happen when the commands actual arguments don't
+      // match.
+      await completer.future.timeout(const Duration(seconds: 5));
+    },
+  );
 }