Implement sass --embedded in pure JS mode

Author: ntkme

bin/sass.dart

@@ -18,8 +18,7 @@ import 'package:sass/src/io.dart';
 import 'package:sass/src/stylesheet_graph.dart';
 import 'package:sass/src/utils.dart';
 import 'package:sass/src/embedded/executable.dart'
-    // Never load the embedded protocol when compiling to JS.
-    if (dart.library.js) 'package:sass/src/embedded/unavailable.dart'
+    if (dart.library.js) 'package:sass/src/embedded/js/executable.dart'
     as embedded;
 
 Future<void> main(List<String> args) async {

lib/src/embedded/compilation_dispatcher.dart

@@ -3,17 +3,16 @@
 // https://opensource.org/licenses/MIT.
 
 import 'dart:convert';
-import 'dart:io';
-import 'dart:isolate';
+import 'dart:isolate' if (dart.library.js) 'js/isolate.dart';
 import 'dart:typed_data';
 
-import 'package:native_synchronization/mailbox.dart';
 import 'package:path/path.dart' as p;
 import 'package:protobuf/protobuf.dart';
 import 'package:pub_semver/pub_semver.dart';
 import 'package:sass/sass.dart' as sass;
 import 'package:sass/src/importer/node_package.dart' as npi;
 
+import '../io.dart' show FileSystemException;
 import '../logger.dart';
 import '../value/function.dart';
 import '../value/mixin.dart';
@@ -23,6 +22,7 @@ import 'host_callable.dart';
 import 'importer/file.dart';
 import 'importer/host.dart';
 import 'logger.dart';
+import 'sync_receive_port.dart';
 import 'util/proto_extensions.dart';
 import 'utils.dart';
 
@@ -35,8 +35,8 @@ final _outboundRequestId = 0;
 /// A class that dispatches messages to and from the host for a single
 /// compilation.
 final class CompilationDispatcher {
-  /// The mailbox for receiving messages from the host.
-  final Mailbox _mailbox;
+  /// The synchronous receive port for receiving messages from the host.
+  final SyncReceivePort _receivePort;
 
   /// The send port for sending messages to the host.
   final SendPort _sendPort;
@@ -52,8 +52,8 @@ final class CompilationDispatcher {
   late Uint8List _compilationIdVarint;
 
   /// Creates a [CompilationDispatcher] that receives encoded protocol buffers
-  /// through [_mailbox] and sends them through [_sendPort].
-  CompilationDispatcher(this._mailbox, this._sendPort);
+  /// through [_receivePort] and sends them through [_sendPort].
+  CompilationDispatcher(this._receivePort, this._sendPort);
 
   /// Listens for incoming `CompileRequests` and runs their compilations.
   void listen() {
@@ -427,9 +427,9 @@ final class CompilationDispatcher {
   /// Receive a packet from the host.
   Uint8List _receive() {
     try {
-      return _mailbox.take();
+      return _receivePort.receive();
     } on StateError catch (_) {
-      // The [_mailbox] has been closed, exit the current isolate immediately
+      // The [SyncReceivePort] has been closed, exit the current isolate immediately
       // to avoid bubble the error up as [SassException] during [_sendRequest].
       Isolate.exit();
     }

lib/src/embedded/concurrency.dart

@@ -0,0 +1,10 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:ffi';
+
+/// More than MaxMutatorThreadCount isolates in the same isolate group
+/// can deadlock the Dart VM.
+/// See https://github.com/sass/dart-sass/pull/2019
+int get concurrencyLimit => sizeOf<IntPtr>() <= 4 ? 7 : 15;

lib/src/embedded/executable.dart

@@ -3,40 +3,19 @@
 // https://opensource.org/licenses/MIT.
 
 import 'dart:io';
-import 'dart:convert';
 
 import 'package:stream_channel/stream_channel.dart';
 
 import 'isolate_dispatcher.dart';
+import 'options.dart';
 import 'util/length_delimited_transformer.dart';
 
 void main(List<String> args) {
-  switch (args) {
-    case ["--version", ...]:
-      var response = IsolateDispatcher.versionResponse();
-      response.id = 0;
-      stdout.writeln(
-        JsonEncoder.withIndent("  ").convert(response.toProto3Json()),
-      );
-      return;
-
-    case [_, ...]:
-      stderr.writeln(
-        "sass --embedded is not intended to be executed with additional "
-        "arguments.\n"
-        "See https://github.com/sass/dart-sass#embedded-dart-sass for "
-        "details.",
-      );
-      // USAGE error from https://bit.ly/2poTt90
-      exitCode = 64;
-      return;
+  if (parseOptions(args)) {
+    IsolateDispatcher(
+            StreamChannel.withGuarantees(stdin, stdout, allowSinkErrors: false)
+                .transform(lengthDelimited),
+            gracefulShutdown: false)
+        .listen();
   }
-
-  IsolateDispatcher(
-    StreamChannel.withGuarantees(
-      stdin,
-      stdout,
-      allowSinkErrors: false,
-    ).transform(lengthDelimited),
-  ).listen();
 }

lib/src/embedded/isolate_dispatcher.dart

@@ -3,19 +3,17 @@
 // https://opensource.org/licenses/MIT.
 
 import 'dart:async';
-import 'dart:ffi';
-import 'dart:io';
-import 'dart:isolate';
+import 'dart:io' if (dart.library.js) 'js/io.dart';
 import 'dart:typed_data';
 
-import 'package:native_synchronization/mailbox.dart';
 import 'package:pool/pool.dart';
 import 'package:protobuf/protobuf.dart';
 import 'package:stream_channel/stream_channel.dart';
 
-import 'compilation_dispatcher.dart';
+import 'concurrency.dart' if (dart.library.js) 'js/concurrency.dart';
 import 'embedded_sass.pb.dart';
-import 'reusable_isolate.dart';
+import 'isolate_main.dart' if (dart.library.js) 'js/isolate_main.dart';
+import 'reusable_isolate.dart' if (dart.library.js) 'js/reusable_isolate.dart';
 import 'util/proto_extensions.dart';
 import 'utils.dart';
 
@@ -25,6 +23,10 @@ class IsolateDispatcher {
   /// The channel of encoded protocol buffers, connected to the host.
   final StreamChannel<Uint8List> _channel;
 
+  /// Whether to wait for all worker isolates to exit before exiting the main
+  /// isolate or not.
+  final bool _gracefulShutdown;
+
   /// All isolates that have been spawned to dispatch to.
   ///
   /// Only used for cleaning up the process when the underlying channel closes.
@@ -38,16 +40,13 @@ class IsolateDispatcher {
 
   /// A pool controlling how many isolates (and thus concurrent compilations)
   /// may be live at once.
-  ///
-  /// More than MaxMutatorThreadCount isolates in the same isolate group
-  /// can deadlock the Dart VM.
-  /// See https://github.com/sass/dart-sass/pull/2019
-  final _isolatePool = Pool(sizeOf<IntPtr>() <= 4 ? 7 : 15);
+  final _isolatePool = Pool(concurrencyLimit);
 
   /// Whether [_channel] has been closed or not.
   var _closed = false;
 
-  IsolateDispatcher(this._channel);
+  IsolateDispatcher(this._channel, {bool gracefulShutdown = true})
+      : _gracefulShutdown = gracefulShutdown;
 
   void listen() {
     _channel.stream.listen(
@@ -107,8 +106,12 @@ class IsolateDispatcher {
         _handleError(error, stackTrace);
       },
       onDone: () {
-        _closed = true;
-        _allIsolates.stream.listen((isolate) => isolate.kill());
+        if (_gracefulShutdown) {
+          _closed = true;
+          _allIsolates.stream.listen((isolate) => isolate.kill());
+        } else {
+          exit(exitCode);
+        }
       },
     );
   }
@@ -125,7 +128,7 @@ class IsolateDispatcher {
       _inactiveIsolates.remove(isolate);
     } else {
       var future = ReusableIsolate.spawn(
-        _isolateMain,
+        isolateMain,
         onError: (Object error, StackTrace stackTrace) {
           _handleError(error, stackTrace);
         },
@@ -158,7 +161,11 @@ class IsolateDispatcher {
           _channel.sink.add(packet);
         case 2:
           _channel.sink.add(packet);
-          exit(exitCode);
+          if (_gracefulShutdown) {
+            _channel.sink.close();
+          } else {
+            exit(exitCode);
+          }
       }
     });
 
@@ -188,7 +195,11 @@ class IsolateDispatcher {
       compilationId ?? errorId,
       handleError(error, stackTrace, messageId: messageId),
     );
-    _channel.sink.close();
+    if (_gracefulShutdown) {
+      _channel.sink.close();
+    } else {
+      exit(exitCode);
+    }
   }
 
   /// Sends [message] to the host.
@@ -199,7 +210,3 @@ class IsolateDispatcher {
   void sendError(int compilationId, ProtocolError error) =>
       _send(compilationId, OutboundMessage()..error = error);
 }
-
-void _isolateMain(Mailbox mailbox, SendPort sendPort) {
-  CompilationDispatcher(mailbox, sendPort).listen();
-}

lib/src/embedded/isolate_main.dart

@@ -0,0 +1,12 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:isolate' show SendPort;
+
+import 'compilation_dispatcher.dart';
+import 'sync_receive_port.dart';
+
+void isolateMain(SyncReceivePort receivePort, SendPort sendPort) {
+  CompilationDispatcher(receivePort, sendPort).listen();
+}

lib/src/embedded/js/concurrency.dart

@@ -0,0 +1,11 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:js_interop';
+
+
+@JS('os.cpus')
+external JSArray _cpus();
+
+int get concurrencyLimit => _cpus().length;

lib/src/embedded/js/executable.dart

@@ -0,0 +1,27 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:stream_channel/stream_channel.dart';
+
+import '../isolate_dispatcher.dart';
+import '../isolate_main.dart';
+import '../options.dart';
+import '../util/length_delimited_transformer.dart';
+import 'io.dart';
+import 'sync_receive_port.dart';
+import 'worker_threads.dart';
+
+void main(List<String> args) {
+  if (parseOptions(args)) {
+    if (isMainThread) {
+      IsolateDispatcher(StreamChannel.withGuarantees(stdin, stdout,
+                  allowSinkErrors: false)
+              .transform(lengthDelimited))
+          .listen();
+    } else {
+      var port = workerData! as MessagePort;
+      isolateMain(JSSyncReceivePort(port), JSSendPort(port));
+    }
+  }
+}

lib/src/embedded/js/io.dart

@@ -0,0 +1,66 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:async';
+import 'dart:js_interop';
+import 'dart:typed_data';
+
+@JS('process.exitCode')
+external int? get _exitCode;
+int get exitCode => _exitCode ?? 0;
+
+@JS('process.exitCode')
+external set exitCode(int code);
+
+@JS('process.exit')
+external void exit([int code]);
+
+@JS()
+extension type _ReadStream(JSObject _) implements JSObject {
+  external void destroy();
+  external void on(String type, JSFunction listener);
+}
+
+@JS('process.stdin')
+external _ReadStream get _stdin;
+
+@JS()
+extension type _WriteStream(JSObject _) implements JSObject {
+  external void write(JSUint8Array chunk);
+}
+
+@JS('process.stdout')
+external _WriteStream get _stdout;
+
+Stream<List<int>> get stdin {
+  var controller = StreamController<Uint8List>(
+      onCancel: () {
+        _stdin.destroy();
+      },
+      sync: true);
+  _stdin.on(
+      'data',
+      (JSUint8Array chunk) {
+        controller.sink.add(chunk.toDart);
+      }.toJS);
+  _stdin.on(
+      'end',
+      () {
+        controller.sink.close();
+      }.toJS);
+  _stdin.on(
+      'error',
+      (JSObject e) {
+        controller.sink.addError(e);
+      }.toJS);
+  return controller.stream;
+}
+
+StreamSink<List<int>> get stdout {
+  var controller = StreamController<Uint8List>(sync: true);
+  controller.stream.listen((buffer) {
+    _stdout.write(buffer.toJS);
+  });
+  return controller.sink;
+}

lib/src/embedded/js/isolate.dart

@@ -0,0 +1,17 @@
+// Copyright 2024 Google LLC. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'dart:isolate' show SendPort;
+export 'dart:isolate' show SendPort;
+
+import 'io.dart' as io;
+
+abstract class Isolate {
+  static Never exit([SendPort? finalMessagePort, Object? message]) {
+    if (message != null) {
+      finalMessagePort?.send(message);
+    }
+    io.exit(io.exitCode) as Never;
+  }
+}