operations: fix error reporting which was causing mount to overwrite directories.

Before this change, in rclone mount, rclone was not erroring if one
directory was moved over another, instead the contents were combined.

This was caused by this commit

431524445e combine: fix operations.DirMove across upstreams - fixes #7661

The fix is to sharpen the conditions that the fallback code runs.

Fixes #8253

fs/operations/operations.go

@@ -2404,7 +2404,7 @@ func DirMove(ctx context.Context, f fs.Fs, srcRemote, dstRemote string) (err err
 		if err == nil {
 			accounting.Stats(ctx).Renames(1)
 		}
-		if err != fs.ErrorCantDirMove && err != fs.ErrorDirExists {
+		if err != fs.ErrorCantDirMove {
 			return err
 		}
 		fs.Infof(f, "Can't DirMove - falling back to file moves: %v", err)

fs/operations/operations_test.go

@@ -1452,6 +1452,47 @@ func TestDirMove(t *testing.T) {
 	)
 }
 
+func TestDirMoveOverwrite(t *testing.T) {
+	ctx := context.Background()
+	r := fstest.NewRun(t)
+
+	if !r.Fremote.Features().CanHaveEmptyDirectories {
+		t.Skip("Can't test for directory overwrite if can't have empty directories")
+	}
+
+	r.Mkdir(ctx, r.Fremote)
+
+	// Make some files and dirs
+	r.ForceMkdir(ctx, r.Fremote)
+	require.NoError(t, operations.Mkdir(ctx, r.Fremote, "dir1"))
+	require.NoError(t, operations.Mkdir(ctx, r.Fremote, "dir2"))
+
+	fstest.CheckListingWithPrecision(
+		t,
+		r.Fremote,
+		nil,
+		[]string{
+			"dir1",
+			"dir2",
+		},
+		fs.GetModifyWindow(ctx, r.Fremote),
+	)
+
+	// Check we get an error if we try to overwrite an existing directory
+	require.Error(t, operations.DirMove(ctx, r.Fremote, "dir1", "dir2"))
+
+	fstest.CheckListingWithPrecision(
+		t,
+		r.Fremote,
+		nil,
+		[]string{
+			"dir1",
+			"dir2",
+		},
+		fs.GetModifyWindow(ctx, r.Fremote),
+	)
+}
+
 func TestGetFsInfo(t *testing.T) {
 	r := fstest.NewRun(t)