Add preliminary support for sql_calc_found_rows

Signed-off-by: Andres Taylor <[email protected]>

go/vt/vtgate/planbuilder/select.go

@@ -20,6 +20,9 @@ import (
 	"errors"
 	"fmt"
 
+	"vitess.io/vitess/go/vt/proto/vtrpc"
+	"vitess.io/vitess/go/vt/vterrors"
+
 	"vitess.io/vitess/go/vt/vtgate/evalengine"
 
 	"vitess.io/vitess/go/vt/sqlparser"
@@ -81,6 +84,10 @@ func buildSelectPlan(stmt sqlparser.Statement, vschema ContextVSchema) (engine.P
 // pushed into a route, then a primitive is created on top of any
 // of the above trees to make it discard unwanted rows.
 func (pb *primitiveBuilder) processSelect(sel *sqlparser.Select, outer *symtab) error {
+	if sel.SQLCalcFoundRows && sel.Limit != nil {
+		return vterrors.Errorf(vtrpc.Code_UNIMPLEMENTED, "sql_calc_found_rows not yet fully supported")
+	}
+
 	if err := pb.processTableExprs(sel.From); err != nil {
 		return err
 	}