Patch sqltypes.MakeRowTrusted to lean on field count (#126)

Patch to handle this case while we move towards a permanent fix upstream.
cf. vitessio#4661 vitessio#4669

go/sqltypes/result.go

@@ -159,13 +159,14 @@ func ResultsEqual(r1, r2 []Result) bool {
 // Every place this function is called, a comment is needed that explains
 // why it's justified.
 func MakeRowTrusted(fields []*querypb.Field, row *querypb.Row) []Value {
-	sqlRow := make([]Value, len(row.Lengths))
+	sqlRow := make([]Value, len(fields))
 	var offset int64
-	for i, length := range row.Lengths {
+	for i, fld := range fields {
+		length := row.Lengths[i]
 		if length < 0 {
 			continue
 		}
-		sqlRow[i] = MakeTrusted(fields[i].Type, row.Values[offset:offset+length])
+		sqlRow[i] = MakeTrusted(fld.Type, row.Values[offset:offset+length])
 		offset += length
 	}
 	return sqlRow

go/sqltypes/result_test.go

@@ -23,6 +23,61 @@ import (
 	querypb "vitess.io/vitess/go/vt/proto/query"
 )
 
+func TestMakeRowTrusted(t *testing.T) {
+	fields := MakeTestFields(
+		"some_int|some_text|another_int",
+		"int8|varchar|int8",
+	)
+
+	values := []byte{}
+	hw := []byte("hello, world")
+	values = append(values, hw...)
+	values = append(values, byte(42))
+
+	row := &querypb.Row{
+		Lengths: []int64{-1, int64(len(hw)), 1},
+		Values:  values,
+	}
+
+	want := []Value{
+		MakeTrusted(querypb.Type_NULL_TYPE, nil),
+		MakeTrusted(querypb.Type_VARCHAR, []byte("hello, world")),
+		MakeTrusted(querypb.Type_INT8, []byte{byte(42)}),
+	}
+
+	result := MakeRowTrusted(fields, row)
+	if !reflect.DeepEqual(result, want) {
+		t.Errorf("MakeRowTrusted:\ngot: %#v\nwant: %#v", result, want)
+	}
+}
+
+func TestMakeRowTrustedDoesNotPanicOnNewColumns(t *testing.T) {
+	fields := MakeTestFields(
+		"some_int|some_text",
+		"int8|varchar",
+	)
+
+	values := []byte{byte(123)}
+	hw := []byte("hello, world")
+	values = append(values, hw...)
+	values = append(values, byte(42))
+
+	row := &querypb.Row{
+		Lengths: []int64{1, int64(len(hw)), 1},
+		Values:  values,
+	}
+
+	want := []Value{
+		MakeTrusted(querypb.Type_INT8, []byte{byte(123)}),
+		MakeTrusted(querypb.Type_VARCHAR, []byte("hello, world")),
+	}
+
+	result := MakeRowTrusted(fields, row)
+	if !reflect.DeepEqual(result, want) {
+		t.Errorf("MakeRowTrusted:\ngot: %#v\nwant: %#v", result, want)
+	}
+}
+
 func TestRepair(t *testing.T) {
 	fields := []*querypb.Field{{
 		Type: Int64,