made asc sorting optional and added regression tests

README.md

@@ -29,6 +29,7 @@ Bool does not support the wildcard operator, only the literal strings `true` and
 The sort statement consists of the literal string `sort`, the field name (nesting like above is supported) and the literal strings `asc` or `desc`.
 
 ```
+sort:<struct field> (short version for asc)
 sort:<struct field>:asc
 sort:<struct field>:desc
 sort:<struct field>.<struct field>:desc

filter.go

@@ -115,27 +115,23 @@ func NewQuery(s string) (q *Query, err error) {
 		}
 		if !q.s.enabled {
 			s := strings.SplitN(v, ":", 3)
-			if len(s) == 3 {
-				if s[0] == "sort" {
+			if s[0] == "sort" && len(s) >= 2 {
+				q.s.fields = strings.Split(s[1], ".")
+				if err = checkFields(q.s.fields, v); err != nil {
+					return
+				}
+				if len(s) == 3 {
 					switch s[2] {
-					case asc, desc:
-						q.s.fields = strings.Split(s[1], ".")
-						if err = checkFields(q.s.fields, v); err != nil {
-							return
-						}
-						if len(q.s.fields) > 0 {
-							if s[2] == desc {
-								q.s.desc = true
-							}
-							q.s.enabled = true
-						}
-						continue
+					case desc:
+						q.s.desc = true
+					case asc:
 					default:
 						err = newErr("invalid sort: " + v)
 						return
 					}
-
 				}
+				q.s.enabled = true
+				continue
 			}
 		}
 		m := strings.SplitN(v, ":", 2)

helper.go

@@ -1,7 +1,6 @@
 package filter
 
 import (
-	"errors"
 	"reflect"
 	"strconv"
 	"strings"
@@ -13,9 +12,12 @@ const (
 )
 
 func checkFields(s []string, val string) error {
+	if len(s) == 0 {
+		return newErr("invalid field: " + val)
+	}
 	for _, v := range s {
 		if v == "" {
-			return errors.New("invalid subfield: " + val)
+			return newErr("invalid subfield: " + val)
 		}
 	}
 	return nil

regression_test.go

@@ -0,0 +1,20 @@
+package filter
+
+import "testing"
+
+func TestRegression(t *testing.T) {
+	data := []string{
+		"sort::asc",
+		"Int.:",
+		"String.:",
+		"sort::desc",
+		".:",
+		"sort:.0:asc",
+	}
+	for _, v := range data {
+		_, err := NewQuery(v)
+		if err == nil {
+			t.Errorf("regression: '%s'", v)
+		}
+	}
+}