fix(restore): allow incrementalFrom to be 1 in restore API (#8988)

This is a minor inconvenience while using the incremental restore API
that when incrementalFrom is set to 1, we throw an error back. The
restore API takes two backup numbers incrementalFrom & backupNum and
restores all the backups including both the ends, i.e. following set
notation all the backups in the set [incrementalFrom, backupNum] are
restored. This should work fine when incrementalFrom is set to 1 which
is a full backup.

systest/integration2/incremental_restore_test.go

@@ -68,9 +68,6 @@ func TestIncrementalRestore(t *testing.T) {
 		t.Logf("restoring backup #%v\n", i)
 
 		incrFrom := i - 1
-		if i == 2 {
-			incrFrom = 0
-		}
 		require.NoError(t, hc.Restore(c, dgraphtest.DefaultBackupDir, "", incrFrom, i))
 		require.NoError(t, dgraphtest.WaitForRestore(c))
 

worker/online_restore.go

@@ -245,8 +245,14 @@ func handleRestoreProposal(ctx context.Context, req *pb.RestoreRequest, pidx uin
 		return errors.Errorf("nil restore request")
 	}
 
+	// This is a minor inconvenience while using the incremental restore API that
+	// when incrementalFrom is set to 1, we throw an error back. The restore API
+	// takes two backup numbers incrementalFrom & backupNum and restores all the
+	// backups including both the ends, i.e. following set notation all the backups
+	// in the set [incrementalFrom, backupNum] are restored. This should work fine
+	// when incrementalFrom is set to 1 which is a full backup.
 	if req.IncrementalFrom == 1 {
-		return errors.Errorf("Incremental restore must not include full backup")
+		req.IncrementalFrom = 0
 	}
 
 	// Clean up the cluster if it is a full backup restore.