Fix flaky isolate shutdown

lib/src/embedded/compilation_dispatcher.dart

@@ -51,24 +51,18 @@ final class CompilationDispatcher {
   /// This is used in outgoing messages.
   late Uint8List _compilationIdVarint;
 
-  /// Whether we detected a [ProtocolError] while parsing an incoming response.
-  ///
-  /// If we have, we don't want to send the final compilation result because
-  /// it'll just be a wrapper around the error.
-  var _requestError = false;
-
   /// Creates a [CompilationDispatcher] that receives encoded protocol buffers
   /// through [_mailbox] and sends them through [_sendPort].
   CompilationDispatcher(this._mailbox, this._sendPort);
 
   /// Listens for incoming `CompileRequests` and runs their compilations.
   void listen() {
-    do {
+    while (true) {
       Uint8List packet;
       try {
         packet = _mailbox.take();
       } on StateError catch (_) {
-        break;
+        Isolate.exit();
       }
 
       try {
@@ -88,9 +82,7 @@ final class CompilationDispatcher {
           case InboundMessage_Message.compileRequest:
             var request = message.compileRequest;
             var response = _compile(request);
-            if (!_requestError) {
-              _send(OutboundMessage()..compileResponse = response);
-            }
+            _send(OutboundMessage()..compileResponse = response);
 
           case InboundMessage_Message.versionRequest:
             throw paramsError("VersionRequest must have compilation ID 0.");
@@ -113,7 +105,7 @@ final class CompilationDispatcher {
       } catch (error, stackTrace) {
         _handleError(error, stackTrace);
       }
-    } while (!_requestError);
+    }
   }
 
   OutboundMessage_CompileResponse _compile(
@@ -287,20 +279,14 @@ final class CompilationDispatcher {
   void sendLog(OutboundMessage_LogEvent event) =>
       _send(OutboundMessage()..logEvent = event);
 
-  /// Sends [error] to the host.
+  /// Sends [error] to the host and exit.
   ///
   /// This is used during compilation by other classes like host callable.
-  /// Therefore it must set _requestError = true to prevent sending a CompileFailure after
-  /// sending a ProtocolError.
-  void sendError(ProtocolError error) {
-    _sendError(error);
-    _requestError = true;
+  Never sendError(ProtocolError error) {
+    Isolate.exit(
+        _sendPort, _serializePacket((OutboundMessage()..error = error)));
   }
 
-  /// Sends [error] to the host.
-  void _sendError(ProtocolError error) =>
-      _send(OutboundMessage()..error = error);
-
   InboundMessage_CanonicalizeResponse sendCanonicalizeRequest(
           OutboundMessage_CanonicalizeRequest request) =>
       _sendRequest<InboundMessage_CanonicalizeResponse>(
@@ -330,10 +316,7 @@ final class CompilationDispatcher {
     try {
       packet = _mailbox.take();
     } on StateError catch (_) {
-      // Compiler is shutting down, throw without calling `_handleError` as we
-      // don't want to report this as an actual error.
-      _requestError = true;
-      rethrow;
+      Isolate.exit();
     }
 
     try {
@@ -376,21 +359,24 @@ final class CompilationDispatcher {
       return response;
     } catch (error, stackTrace) {
       _handleError(error, stackTrace);
-      _requestError = true;
-      rethrow;
     }
   }
 
   /// Handles an error thrown by the dispatcher or code it dispatches to.
   ///
   /// The [messageId] indicate the IDs of the message being responded to, if
   /// available.
-  void _handleError(Object error, StackTrace stackTrace, {int? messageId}) {
-    _sendError(handleError(error, stackTrace, messageId: messageId));
+  Never _handleError(Object error, StackTrace stackTrace, {int? messageId}) {
+    sendError(handleError(error, stackTrace, messageId: messageId));
   }
 
   /// Sends [message] to the host with the given [wireId].
   void _send(OutboundMessage message) {
+    _sendPort.send(_serializePacket(message));
+  }
+
+  /// Serialize [message] to [Uint8List].
+  Uint8List _serializePacket(OutboundMessage message) {
     var protobufWriter = CodedBufferWriter();
     message.writeToCodedBufferWriter(protobufWriter);
 
@@ -407,6 +393,6 @@ final class CompilationDispatcher {
     };
     packet.setAll(1, _compilationIdVarint);
     protobufWriter.writeTo(packet, 1 + _compilationIdVarint.length);
-    _sendPort.send(packet);
+    return packet;
   }
 }

lib/src/embedded/host_callable.dart

@@ -53,7 +53,6 @@ Callable hostCallable(
       }
     } on ProtocolError catch (error, stackTrace) {
       dispatcher.sendError(handleError(error, stackTrace));
-      throw error.message;
     }
   });
   return callable;

lib/src/embedded/reusable_isolate.dart

@@ -118,12 +118,11 @@ class ReusableIsolate {
 
   /// Shuts down the isolate.
   void kill() {
-    _isolate.kill();
-    _receivePort.close();
-
     // If the isolate is blocking on [Mailbox.take], it won't even process a
     // kill event, so we closed the mailbox to nofity and wake it up.
     _mailbox.close();
+    _isolate.kill(priority: Isolate.immediate);
+    _receivePort.close();
   }
 }