touch: make touch obey --transfers

Before this change, when executed on a directory, rclone would only
touch files sequentially.

This change makes rclone touch --transfers files at once.

Fixes #8402

cmd/touch/touch.go

@@ -51,6 +51,7 @@ unless ` + "`--no-create`" + ` or ` + "`--recursive`" + ` is provided.
 If ` + "`--recursive`" + ` is used then recursively sets the modification
 time on all existing files that is found under the path. Filters are supported,
 and you can test with the ` + "`--dry-run`" + ` or the ` + "`--interactive`/`-i`" + ` flag.
+This will touch ` + "`--transfers`" + ` files concurrently.
 
 If ` + "`--timestamp`" + ` is used then sets the modification time to that
 time instead of the current time. Times may be specified as one of:

fs/operations/operations.go

@@ -2140,20 +2140,28 @@ func SetTierFile(ctx context.Context, o fs.Object, tier string) error {
 
 // TouchDir touches every file in directory with time t
 func TouchDir(ctx context.Context, f fs.Fs, remote string, t time.Time, recursive bool) error {
-	return walk.ListR(ctx, f, remote, false, ConfigMaxDepth(ctx, recursive), walk.ListObjects, func(entries fs.DirEntries) error {
+	ci := fs.GetConfig(ctx)
+	g, gCtx := errgroup.WithContext(ctx)
+	g.SetLimit(ci.Transfers)
+	err := walk.ListR(ctx, f, remote, false, ConfigMaxDepth(ctx, recursive), walk.ListObjects, func(entries fs.DirEntries) error {
 		entries.ForObject(func(o fs.Object) {
 			if !SkipDestructive(ctx, o, "touch") {
-				fs.Debugf(f, "Touching %q", o.Remote())
-				err := o.SetModTime(ctx, t)
-				if err != nil {
-					err = fmt.Errorf("failed to touch: %w", err)
-					err = fs.CountError(ctx, err)
-					fs.Errorf(o, "%v", err)
-				}
+				g.Go(func() error {
+					fs.Debugf(f, "Touching %q", o.Remote())
+					err := o.SetModTime(gCtx, t)
+					if err != nil {
+						err = fmt.Errorf("failed to touch: %w", err)
+						err = fs.CountError(gCtx, err)
+						fs.Errorf(o, "%v", err)
+					}
+					return nil
+				})
 			}
 		})
 		return nil
 	})
+	_ = g.Wait()
+	return err
 }
 
 // ListFormat defines files information print format