Handle language server termination (helix-editor#4797)

This change handles a language server exiting. This was a UX sore-spot:
if a language server crashed, Helix did not recognize the exit and
continued to send requests to it. All requests would timeout since they
would not receive responses. This would also hold-up Helix closing
itself down since it would try to gracefully shutdown the server which
is implemented in the LSP spec as a request.

We could attempt to automatically restart the language server on crash.
I left this for future work since that change will need to be slightly
complicated: it will need to cover the case of a language server
repeatedly crashing.

helix-lsp/src/lib.rs

@@ -282,6 +282,8 @@ impl MethodCall {
 pub enum Notification {
     // we inject this notification to signal the LSP is ready
     Initialized,
+    // and this notification to signal that the LSP exited
+    Exit,
     PublishDiagnostics(lsp::PublishDiagnosticsParams),
     ShowMessage(lsp::ShowMessageParams),
     LogMessage(lsp::LogMessageParams),
@@ -294,6 +296,7 @@ impl Notification {
 
         let notification = match method {
             lsp::notification::Initialized::METHOD => Self::Initialized,
+            lsp::notification::Exit::METHOD => Self::Exit,
             lsp::notification::PublishDiagnostics::METHOD => {
                 let params: lsp::PublishDiagnosticsParams = params.parse()?;
                 Self::PublishDiagnostics(params)
@@ -350,6 +353,10 @@ impl Registry {
             .map(|(_, client)| client.as_ref())
     }
 
+    pub fn remove_by_id(&mut self, id: usize) {
+        self.inner.retain(|_, (client_id, _)| client_id != &id)
+    }
+
     pub fn restart(
         &mut self,
         language_config: &LanguageConfiguration,

helix-lsp/src/transport.rs

@@ -250,6 +250,26 @@ impl Transport {
                         }
                     };
                 }
+                Err(Error::StreamClosed) => {
+                    // Hack: inject a terminated notification so we trigger code that needs to happen after exit
+                    use lsp_types::notification::Notification as _;
+                    let notification =
+                        ServerMessage::Call(jsonrpc::Call::Notification(jsonrpc::Notification {
+                            jsonrpc: None,
+                            method: lsp_types::notification::Exit::METHOD.to_string(),
+                            params: jsonrpc::Params::None,
+                        }));
+                    match transport
+                        .process_server_message(&client_tx, notification)
+                        .await
+                    {
+                        Ok(_) => {}
+                        Err(err) => {
+                            error!("err: <- {:?}", err);
+                        }
+                    }
+                    break;
+                }
                 Err(err) => {
                     error!("err: <- {:?}", err);
                     break;

helix-term/src/application.rs

@@ -871,6 +871,32 @@ impl Application {
                     Notification::ProgressMessage(_params) => {
                         // do nothing
                     }
+                    Notification::Exit => {
+                        self.editor.set_status("Language server exited");
+
+                        // Clear any diagnostics for documents with this server open.
+                        let urls: Vec<_> = self
+                            .editor
+                            .documents_mut()
+                            .filter_map(|doc| {
+                                if doc.language_server().map(|server| server.id())
+                                    == Some(server_id)
+                                {
+                                    doc.set_diagnostics(Vec::new());
+                                    doc.url()
+                                } else {
+                                    None
+                                }
+                            })
+                            .collect();
+
+                        for url in urls {
+                            self.editor.diagnostics.remove(&url);
+                        }
+
+                        // Remove the language server from the registry.
+                        self.editor.language_servers.remove_by_id(server_id);
+                    }
                 }
             }
             Call::MethodCall(helix_lsp::jsonrpc::MethodCall {