Allow appending to KVV values (kvv.field[] = val)

pkg/expr/expr.go

@@ -20,7 +20,8 @@ func PathSplit(path string) ([]string, error) {
 	s.Split(pathSplitter)
 
 	for s.Scan() {
-		if len(s.Text()) == 0 {
+		// checks if two consecutive path parts are empty
+		if len(s.Text()) == 0 && len(out) > 0 && len(out[len(out)-1]) == 0 {
 			return nil, invalidPathErr
 		}
 		out = append(out, s.Text())

pkg/expr/expr_test.go

@@ -1,8 +1,9 @@
 package expr
 
 import (
-	"github.com/stretchr/testify/require"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestPathSplit(t *testing.T) {
@@ -16,6 +17,7 @@ func TestPathSplit(t *testing.T) {
 		{p: "a.b[1]", r: []string{"a", "b", "1"}},
 		{p: "a.b[1].baz[0]", r: []string{"a", "b", "1", "baz", "0"}},
 		{p: "a.[]", err: invalidPathErr.Error()},
+		{p: "a[]", r: []string{"a", ""}},
 		{p: "a[1]bzz", err: invalidPathErr.Error()},
 	}
 

pkg/expr/expr_types.go

@@ -540,18 +540,56 @@ func (t *KV) Delete(keys ...string) (out TypedValue, err error) {
 	return kv, nil
 }
 
-func (t *KVV) AssignFieldValue(key string, val TypedValue) error {
+func (t *KVV) AssignFieldValue(key []string, val TypedValue) error {
 	return assignToKVV(t, key, val)
 }
 
-func assignToKVV(t *KVV, key string, val TypedValue) error {
+func assignToKVV(t *KVV, kk []string, val TypedValue) error {
 	if t.value == nil {
 		t.value = make(map[string][]string)
 	}
 
-	str, err := cast.ToStringSliceE(val.Get())
-	t.value[key] = str
-	return err
+	switch len(kk) {
+	case 2:
+		str, err := cast.ToStringE(val.Get())
+		if err != nil {
+			return err
+		}
+
+		key, ind := kk[0], kk[1]
+
+		if len(ind) > 0 {
+			// handles kvv.field[42] = "value"
+			index, err := cast.ToIntE(ind)
+			if err != nil {
+				return err
+			}
+
+			if index >= 0 && index < len(t.value[key]) {
+				// handles positive & in-range indexes
+				t.value[key][index] = str
+				return nil
+			}
+
+			//negative & out-of-range indexes are always appended
+		}
+
+		// handles kvv.field[] = "value"
+		t.value[key] = append(t.value[key], str)
+
+	case 1:
+		str, err := cast.ToStringSliceE(val.Get())
+		if err != nil {
+			return err
+		}
+
+		t.value[kk[0]] = str
+
+	default:
+		return fmt.Errorf("cannot set value on %s with path '%s'", t.Type(), strings.Join(kk, "."))
+	}
+
+	return nil
 }
 
 func CastToKVV(val interface{}) (out map[string][]string, err error) {

pkg/expr/expr_types_test.go

@@ -362,6 +362,17 @@ func TestKVV_Assign(t *testing.T) {
 	req.NoError(kvv.Assign(url.Values{"foo": []string{"bar"}}))
 	req.Contains(kvv.value, "foo")
 	req.Equal([]string{"bar"}, kvv.value["foo"])
+
+	kvv = KVV{}
+	req.NoError(Assign(&kvv, "deep", Must(NewString("bar"))))
+	req.NoError(Assign(&kvv, "deep[0]", Must(NewString("bar"))))
+	req.NoError(Assign(&kvv, "deep[]", Must(NewString("baz"))))
+	req.NoError(Assign(&kvv, "deep[]", Must(NewString("bar"))))
+	req.NoError(Assign(&kvv, "deep[3]", Must(NewString("baz"))))
+	req.NoError(Assign(&kvv, "deep[3]", Must(NewString("b4z"))))
+	req.Contains(kvv.value, "deep")
+	req.Equal([]string{"bar", "baz", "bar", "b4z"}, kvv.value["deep"])
+
 }
 
 func TestKVV_Set(t *testing.T) {