feat: the library's folders are set in Admin › Library, and changing a folder moves its tracks with it, keeping their plays, likes and playlists (#6129)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/library/watcher.go

@@ -67,18 +67,16 @@ type Watcher struct {
 	scanner  *Scanner
 	enricher *coverart.Enricher
 	logger   *slog.Logger
-	roots    []string
 	debounce time.Duration
 }
 
-func NewWatcher(
-	scanner *Scanner, enricher *coverart.Enricher, logger *slog.Logger, roots []string,
-) *Watcher {
+// NewWatcher watches the scanner's folders, and moves to the new ones when
+// they change in Settings (#6129).
+func NewWatcher(scanner *Scanner, enricher *coverart.Enricher, logger *slog.Logger) *Watcher {
 	return &Watcher{
 		scanner:  scanner,
 		enricher: enricher,
 		logger:   logger,
-		roots:    roots,
 		debounce: watcherDebounce,
 	}
 }
@@ -87,8 +85,32 @@ func NewWatcher(
 // fsnotify watcher cannot be created at all; per-path watch failures and
 // fsnotify errors are logged and tolerated.
 func (w *Watcher) Run(ctx context.Context) error {
-	if len(w.roots) == 0 {
-		w.logger.Info("library watcher: no scan paths configured, watcher disabled")
+	for {
+		if err := w.watch(ctx, w.scanner.Roots()); err != nil {
+			return err
+		}
+		if ctx.Err() != nil {
+			return nil
+		}
+	}
+}
+
+// watch watches roots until ctx is cancelled or the folders change.
+func (w *Watcher) watch(ctx context.Context, roots []string) error {
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+	go func() {
+		select {
+		case <-w.scanner.RootsChanged():
+			w.logger.Info("library watcher: folders changed, restarting")
+			cancel()
+		case <-ctx.Done():
+		}
+	}()
+
+	if len(roots) == 0 {
+		w.logger.Info("library watcher: no scan paths configured, watcher idle")
+		<-ctx.Done()
 		return nil
 	}
 	fsw, err := fsnotify.NewWatcher()
@@ -98,10 +120,10 @@ func (w *Watcher) Run(ctx context.Context) error {
 	}
 	defer func() { _ = fsw.Close() }()
 
-	for _, root := range w.roots {
+	for _, root := range roots {
 		w.addRecursive(fsw, root)
 	}
-	w.logger.Info("library watcher: started", "roots", len(w.roots))
+	w.logger.Info("library watcher: started", "roots", len(roots))
 
 	batches := make(chan []string, batchQueueDepth)
 	go w.processLoop(ctx, batches)