Function start_watcher 

pub fn start_watcher(
    project_root: &Path,
    extensions: &[String],
    dirty_files: DirtyFiles,
    diagnostic_store: Option<Arc<DiagnosticStore>>,
) -> Result<Debouncer<RecommendedWatcher, FileIdMap>>

Start watching the project root for file changes.

Returns the debouncer handle (must be kept alive). Dropping it stops the watcher.

Errors

Returns an error if the watcher can’t be created or the project root can’t be watched.