Fix a very minor race condition in cargo fix.

src/cargo/util/diagnostic_server.rs

@@ -258,14 +258,23 @@ impl RustfixDiagnosticServer {
 
  fn run(self, on_message: &dyn Fn(Message), done: &AtomicBool) {
  while let Ok((client, _)) = self.listener.accept() {
- let client = BufReader::new(client);
- match serde_json::from_reader(client) {
- Ok(message) => on_message(message),
- Err(e) => warn!("invalid diagnostics message: {}", e),
- }
  if done.load(Ordering::SeqCst) {
  break;
  }
+ let mut client = BufReader::new(client);
+ let mut s = String::new();
+ if let Err(e) = client.read_to_string(&mut s) {
+ warn!("diagnostic server failed to read: {}", e);
+ } else {
+ match serde_json::from_str(&s) {
+ Ok(message) => on_message(message),
+ Err(e) => warn!("invalid diagnostics message: {}", e),
+ }
+ }
+ // The client should be kept alive until after `on_message` is
+ // called to ensure that the client doesn't exit too soon (and
+ // Message::Finish getting posted before Message::FixDiagnostic).
+ drop(client);
  }
  }
 }