fix(app): close a project window without blocking the UI thread (#1610)

close_project was a synchronous command, so it ran on the UI thread and dropped the project there: stopping its file watcher and index worker waits for the batch of file events they are applying, many while a build or rust-analyzer writes output. The command now runs off the main thread, and the project is dropped on the project shutdown thread, which a project opened next still waits for (the index database is released first). The window Destroyed path gets the same.

src-tauri/src/commands/app.rs

@@ -129,7 +129,8 @@ pub fn project_rename(window: Window, state: State<'_, AppState>, name: String)
     Ok(project_info(&project))
 }
 
-#[tauri::command]
+// Not on the main thread: closing stops the project's language servers, runs and file watcher.
+#[tauri::command(async)]
 #[specta::specta]
 pub fn close_project(window: Window, state: State<'_, AppState>) {
     crate::windows::close_auxiliary_windows(window.app_handle(), window.label());