sqlparser: parse empty statements as nil

go/vt/sqlparser/ast.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -58,6 +59,9 @@ func Parse(sql string) (Statement, error) {
 		}
 		return nil, vterrors.New(vtrpcpb.Code_INVALID_ARGUMENT, tokenizer.LastError.Error())
 	}
+	if tokenizer.ParseTree == nil {
+		return nil, ErrEmpty
+	}
 	return tokenizer.ParseTree, nil
 }
 
@@ -68,6 +72,9 @@ func ParseStrictDDL(sql string) (Statement, error) {
 	if yyParse(tokenizer) != 0 {
 		return nil, tokenizer.LastError
 	}
+	if tokenizer.ParseTree == nil {
+		return nil, ErrEmpty
+	}
 	return tokenizer.ParseTree, nil
 }
 
@@ -94,9 +101,15 @@ func ParseNext(tokenizer *Tokenizer) (Statement, error) {
 		}
 		return nil, tokenizer.LastError
 	}
+	if tokenizer.ParseTree == nil {
+		return ParseNext(tokenizer)
+	}
 	return tokenizer.ParseTree, nil
 }
 
+// ErrEmpty is a sentinel error returned when parsing empty statements.
+var ErrEmpty = errors.New("empty statement")
+
 // SplitStatement returns the first sql statement up to either a ; or EOF
 // and the remainder from the given buffer
 func SplitStatement(blob string) (string, string, error) {

go/vt/sqlparser/parse_test.go

@@ -1633,6 +1633,9 @@ func TestConvert(t *testing.T) {
 	}, {
 		input:  "select convert('abc', decimal(4+9)) from t",
 		output: "syntax error at position 33",
+	}, {
+		input:  "/* a comment */",
+		output: "empty statement",
 	}}
 
 	for _, tcase := range invalidSQL {