Implement sass --embedded in pure JS mode

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';
 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() {
@@ -384,9 +384,9 @@ 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

@@ -3,35 +3,18 @@
 // 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))
+        .listen();
   }
-
-  IsolateDispatcher(
-          StreamChannel.withGuarantees(stdin, stdout, allowSinkErrors: false)
-              .transform(lengthDelimited))
-      .listen();
 }

lib/src/embedded/isolate_dispatcher.dart

@@ -3,19 +3,18 @@
 // 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 '../io.dart';
+import 'concurrency.dart' if (dart.library.js) 'js/concurrency.dart';
 import 'embedded_sass.pb.dart';
-import 'reusable_isolate.dart';
+import 'isolate_main.dart';
+import 'reusable_isolate.dart' if (dart.library.js) 'js/reusable_isolate.dart';
 import 'util/proto_extensions.dart';
 import 'utils.dart';
 
@@ -38,11 +37,7 @@ 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;
@@ -112,7 +107,7 @@ class IsolateDispatcher {
       isolate = _inactiveIsolates.first;
       _inactiveIsolates.remove(isolate);
     } else {
-      var future = ReusableIsolate.spawn(_isolateMain,
+      var future = ReusableIsolate.spawn(isolateMain,
           onError: (Object error, StackTrace stackTrace) {
         _handleError(error, stackTrace);
       });
@@ -179,7 +174,3 @@ 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 +1,10 @@
+// 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:js_interop';
+
+@JS('os.cpus')
+external JSArray _cpus();
+
+int get concurrencyLimit => _cpus().toDart.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 '../compilation_dispatcher.dart';
+import '../isolate_dispatcher.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;
+      CompilationDispatcher(JSSyncReceivePort(port), JSSendPort(port)).listen();
+    }
+  }
+}

lib/src/embedded/js/io.dart

@@ -0,0 +1,60 @@
+// 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:typed_data';
+import 'dart:js_interop';
+
+import '../../io.dart';
+
+/// In Node JS's main thread we need to wait for worker to exit in order
+/// to get exit code set by worker asynchronously. Therefore skip explict
+/// exit on main thread, but close stdin and wait for shutdown.
+void exit([int? code]) {
+  if (code != null) {
+    exitCode = code;
+  }
+  _stdinDestory();
+}
+
+@JS('process.stdin.destroy')
+external void _stdinDestory();
+
+@JS('process.stdin.on')
+external void _stdinOn(String type, JSFunction listener);
+
+@JS('process.stdout.write')
+external void _stdoutWrite(JSUint8Array buffer);
+
+Stream<List<int>> get stdin {
+  var controller = StreamController<Uint8List>(
+      onCancel: () {
+        _stdinDestory();
+      },
+      sync: true);
+  _stdinOn(
+      'data',
+      (JSUint8Array chunk) {
+        controller.sink.add(chunk.toDart);
+      }.toJS);
+  _stdinOn(
+      'end',
+      () {
+        controller.sink.close();
+      }.toJS);
+  _stdinOn(
+      '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) {
+    _stdoutWrite(buffer.toJS);
+  });
+  return controller.sink;
+}

lib/src/embedded/js/isolate.dart

@@ -0,0 +1,22 @@
+// 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 'dart:js_interop';
+
+@JS('process.exit')
+external void _exit();
+
+abstract class Isolate {
+  static Never exit([SendPort? finalMessagePort, Object? message]) {
+    if (message != null) {
+      finalMessagePort?.send(message);
+    }
+    _exit();
+
+    // This is unreachable, but needed for return type [Never]
+    throw Error();
+  }
+}