fix(fs): log file watcher errors (#3621)

In plugins/fs/src/watcher.rs, notify errors were discarded (TODO), so a
watch that died left no trace. They are now logged with log::error!.
Reporting them to the JS callback would change the event payload and is
deferred to v3.

.changes/fix-fs-watch-errors.md

@@ -0,0 +1,6 @@
+---
+fs: patch
+fs-js: patch
+---
+
+File watcher errors (e.g. the watched directory was removed or the inotify limit was reached) are now logged instead of being silently dropped.

plugins/fs/src/watcher.rs

@@ -69,13 +69,18 @@ pub fn watch<R: Runtime>(
         let mut debouncer = new_debouncer(
             Duration::from_millis(delay),
             None,
-            move |events: Result<Vec<DebouncedEvent>, Vec<notify::Error>>| {
+            move |events: Result<Vec<DebouncedEvent>, Vec<notify::Error>>| match events {
-                if let Ok(events) = events {
+                Ok(events) => {
                     for event in events {
-                        // TODO: Should errors be emitted too?
                         let _ = on_event.send(event.event);
                     }
                 }
+                // TODO(v3): report the errors to the webview
+                Err(errors) => {
+                    for error in errors {
+                        log::error!("file watcher error: {error}");
+                    }
+                }
             },
         )?;
         for path in &resolved_paths {
@@ -84,11 +89,12 @@ pub fn watch<R: Runtime>(
         WatcherKind::Debouncer(debouncer)
     } else {
         let mut watcher = RecommendedWatcher::new(
-            move |event| {
+            move |event: notify::Result<notify::Event>| match event {
-                if let Ok(event) = event {
+                Ok(event) => {
-                    // TODO: Should errors be emitted too?
                     let _ = on_event.send(event);
                 }
+                // TODO(v3): report the errors to the webview
+                Err(error) => log::error!("file watcher error: {error}"),
             },
             Config::default(),
         )?;