Factor server side move detection

fs/operations.go

@@ -385,6 +385,17 @@ func Move(fdst Fs, dst Object, remote string, src Object) (err error) {
 	return DeleteFile(src)
 }
 
+// CanServerSideMove returns true if fdst support server side moves or
+// server side copies
+//
+// Some remotes simulate rename by server-side copy and delete, so include
+// remotes that implements either Mover or Copier.
+func CanServerSideMove(fdst Fs) bool {
+	_, canMove := fdst.(Mover)
+	_, canCopy := fdst.(Copier)
+	return canMove || canCopy
+}
+
 // DeleteFile deletes a single file respecting --dry-run and accumulating stats and errors.
 func DeleteFile(dst Object) (err error) {
 	if Config.DryRun {

fs/sync.go

@@ -44,6 +44,7 @@ type syncCopyMove struct {
 }
 
 func newSyncCopyMove(fdst, fsrc Fs, Delete bool, DoMove bool) *syncCopyMove {
+	canServerSideMove := CanServerSideMove(fdst)
 	s := &syncCopyMove{
 		fdst:           fdst,
 		fsrc:           fsrc,
@@ -67,12 +68,8 @@ func newSyncCopyMove(fdst, fsrc Fs, Delete bool, DoMove bool) *syncCopyMove {
 		s.noTraverse = false
 	}
 	if s.trackRenames {
-		// Don't track renames for remotes without server-side rename support.
-		// Some remotes simulate rename by server-side copy and delete, so include
-		// remotes that implements either Mover or Copier.
-		switch fdst.(type) {
-		case Mover, Copier:
-		default:
+		// Don't track renames for remotes without server-side move support.
+		if !canServerSideMove {
 			ErrorLog(fdst, "Ignoring --track-renames as the destination does not support server-side move or copy")
 			s.trackRenames = false
 		}

fs/sync_test.go

@@ -617,9 +617,7 @@ func TestSyncWithTrackRenames(t *testing.T) {
 	}()
 
 	haveHash := r.fremote.Hashes().Overlap(r.flocal.Hashes()).GetOne() != fs.HashNone
-	_, canMove := r.fremote.(fs.Mover)
-	_, canCopy := r.fremote.(fs.Copier)
-	canTrackRenames := haveHash && (canMove || canCopy)
+	canTrackRenames := haveHash && fs.CanServerSideMove(r.fremote)
 	t.Logf("Can track renames: %v", canTrackRenames)
 
 	f1 := r.WriteFile("potato", "Potato Content", t1)