vindex function: error when keyspace not selected (#16534)

Signed-off-by: Harshit Gangal <[email protected]>

go/vt/vtgate/engine/fake_vcursor_test.go

@@ -342,7 +342,7 @@ func (t *noopVCursor) ExceedsMaxMemoryRows(numRows int) bool {
 }
 
 func (t *noopVCursor) GetKeyspace() string {
-	return ""
+	return "test_ks"
 }
 
 func (t *noopVCursor) RecordWarning(warning *querypb.QueryWarning) {

go/vt/vtgate/engine/vindex_func.go

@@ -153,6 +153,9 @@ func (vf *VindexFunc) mapVindex(ctx context.Context, vcursor VCursor, bindVars m
 		case key.DestinationKeyspaceID:
 			if len(d) > 0 {
 				if vcursor != nil {
+					if vcursor.GetKeyspace() == "" {
+						return nil, vterrors.VT09005()
+					}
 					resolvedShards, _, err := vcursor.ResolveDestinations(ctx, vcursor.GetKeyspace(), nil, []key.Destination{d})
 					if err != nil {
 						return nil, err

go/vt/vtgate/executor_select_test.go

@@ -427,6 +427,19 @@ func TestSetSystemVariablesWithReservedConnection(t *testing.T) {
 	sbc1.Queries = nil
 }
 
+func TestSelectVindexFunc(t *testing.T) {
+	executor, _, _, _, _ := createExecutorEnv(t)
+
+	query := "select * from hash_index where id = 1"
+	session := NewAutocommitSession(&vtgatepb.Session{})
+	_, err := executor.Execute(context.Background(), nil, "TestSelectVindexFunc", session, query, nil)
+	require.ErrorContains(t, err, "VT09005: no database selected")
+
+	session.TargetString = KsTestSharded
+	_, err = executor.Execute(context.Background(), nil, "TestSelectVindexFunc", session, query, nil)
+	require.NoError(t, err)
+}
+
 func TestCreateTableValidTimestamp(t *testing.T) {
 	executor, sbc1, _, _, _ := createExecutorEnv(t)
 	executor.normalize = true