Pass exitCode via message

lib/src/embedded/compilation_dispatcher.dart

@@ -3,6 +3,7 @@
 // https://opensource.org/licenses/MIT.
 
 import 'dart:convert';
+import 'dart:io' if (dart.library.js) 'js/io.dart';
 import 'dart:isolate' if (dart.library.js) 'js/isolate.dart';
 import 'dart:typed_data';
 
@@ -366,14 +367,14 @@ final class CompilationDispatcher {
     message.writeToCodedBufferWriter(protobufWriter);
 
     // Add one additional byte to the beginning to indicate whether or not the
-    // compilation has finished (1) or encountered a fatal error (2), so the
+    // compilation has finished (1) or encountered a fatal error (exitCode), so the
     // [IsolateDispatcher] knows whether to treat this isolate as inactive or
     // close out entirely.
     var packet = Uint8List(
         1 + _compilationIdVarint.length + protobufWriter.lengthInBytes);
     packet[0] = switch (message.whichMessage()) {
       OutboundMessage_Message.compileResponse => 1,
-      OutboundMessage_Message.error => 2,
+      OutboundMessage_Message.error => exitCode,
       _ => 0
     };
     packet.setAll(1, _compilationIdVarint);

lib/src/embedded/isolate_dispatcher.dart

@@ -127,11 +127,11 @@ class IsolateDispatcher {
       var fullBuffer = message as Uint8List;
 
       // The first byte of messages from isolates indicates whether the entire
-      // compilation is finished (1) or if it encountered an error (2). Sending
-      // this as part of the message buffer rather than a separate message
-      // avoids a race condition where the host might send a new compilation
-      // request with the same ID as one that just finished before the
-      // [IsolateDispatcher] receives word that the isolate with that ID is
+      // compilation is finished (1) or if it encountered an error (exitCode).
+      // Sending this as part of the message buffer rather than a separate
+      // message avoids a race condition where the host might send a new
+      // compilation request with the same ID as one that just finished before
+      // the [IsolateDispatcher] receives word that the isolate with that ID is
       // done. See sass/dart-sass#2004.
       var category = fullBuffer[0];
       var packet = Uint8List.sublistView(fullBuffer, 1);
@@ -145,8 +145,9 @@ class IsolateDispatcher {
           _inactiveIsolates.add(isolate);
           resource.release();
           _channel.sink.add(packet);
-        case 2:
+        default:
           _channel.sink.add(packet);
+          exitCode = category;
           if (_gracefulShutdown) {
             _channel.sink.close();
           } else {

lib/src/embedded/js/reusable_isolate.dart

@@ -6,7 +6,6 @@ import 'dart:async';
 import 'dart:js_interop';
 import 'dart:typed_data';
 
-import 'io.dart';
 import 'js.dart';
 import 'sync_message_port.dart';
 import 'worker_threads.dart';
@@ -46,14 +45,6 @@ class ReusableIsolate {
             workerData: channel.port2,
             transferList: [channel.port2].toJS,
             argv: argv));
-    worker.once(
-        'exit',
-        (int code) {
-          // Worker exit code 1 means it is killed by worker.terminate()
-          if (code > exitCode && code != 1) {
-            exitCode = code;
-          }
-        }.toJS);
     var controller = StreamController<dynamic>(sync: true);
     var sendPort = SyncMessagePort(channel.port1);
     var receivePort = channel.port1;