find: use proper sentinel error to terminate search

cmd/restic/cmd_find.go

@@ -22,6 +22,9 @@ import (
 	"github.com/restic/restic/internal/walker"
 )
 
+// errFindDone is returned from the tree walk when all requested tree IDs were found.
+var errFindDone = errors.New("find: all tree IDs found")
+
 func newFindCommand(globalOptions *global.Options) *cobra.Command {
 	var opts FindOptions
 
@@ -375,7 +378,7 @@ func (f *Finder) findTree(treeID restic.ID, nodepath string) error {
 		// looking for blobs)
 		if f.itemsFound >= len(f.treeIDs) && f.blobIDs == nil {
 			// Return an error to terminate the Walk
-			return errors.New("OK")
+			return errFindDone
 		}
 	}
 	return nil
@@ -688,7 +691,7 @@ func runFind(ctx context.Context, opts FindOptions, gopts global.Options, args [
 
 	for _, sn := range filteredSnapshots {
 		if f.blobIDs != nil || f.treeIDs != nil {
-			if err = f.findIDs(ctx, sn); err != nil && err.Error() != "OK" {
+			if err = f.findIDs(ctx, sn); err != nil && !errors.Is(err, errFindDone) {
 				return err
 			}
 			continue