drive: don't list trashed files when removing a directory into the trash - fixes #9681

purgeCheck listed a directory's children with includeAll set, so the Drive API
returned trashed children as well as live ones. The only thing that came of
that was the trashedFiles flag, which is used solely to decide whether to trash
the directory or delete it permanently, and when use_trash is on the directory
gets trashed either way.

That made the common case pay for nothing: after trashing N files in a
directory, removing the now empty directory paged through all N trashed entries,
about one API call and pacer delay per 1000, instead of running a single query
that returns nothing.

Ask the server to filter out trashed children when the directory is going to be
trashed anyway. Hard deletes still enumerate them, since there the distinction
decides whether the directory can be removed permanently (#1040), and
--drive-trashed-only is left alone because it deliberately lists trashed items.

backend/drive/drive.go

@@ -2766,7 +2766,12 @@ func (f *Fs) purgeCheck(ctx context.Context, dir string, check bool) error {
 	}
 	trashedFiles := false
 	if check {
-		found, err := f.list(ctx, []string{directoryID}, "", false, false, f.opt.TrashedOnly, true, func(item *drive.File) bool {
+		// trashedFiles is only consulted to decide between trashing and hard deleting
+		// below, so when the directory is going to be trashed anyway there is no reason
+		// to enumerate trashed children: let the server filter them out instead of
+		// paging through them. Hard deletes still need to see them (#1040).
+		includeAll := !f.opt.UseTrash || f.opt.TrashedOnly
+		found, err := f.list(ctx, []string{directoryID}, "", false, false, f.opt.TrashedOnly, includeAll, func(item *drive.File) bool {
 			if !item.Trashed {
 				fs.Debugf(dir, "Rmdir: contains file: %q", item.Name)
 				return true