config: move reflect stuff to util/reflect

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

config/default.go

@@ -5,6 +5,8 @@ import (
 	"reflect"
 	"strconv"
 	"strings"
+
+	rutil "github.com/unistack-org/micro/v3/util/reflect"
 )
 
 type defaultConfig struct {
@@ -45,7 +47,7 @@ func (c *defaultConfig) Load(ctx context.Context) error {
 }
 
 func (c *defaultConfig) fillValue(ctx context.Context, value reflect.Value, val string) error {
-	if !IsEmpty(value) {
+	if !rutil.IsEmpty(value) {
 		return nil
 	}
 	switch value.Kind() {

config/reflect_test.go

@@ -3,7 +3,7 @@ package config_test
 import (
 	"testing"
 
-	"github.com/unistack-org/micro/v3/config"
+	rutil "github.com/unistack-org/micro/v3/util/reflect"
 )
 
 type Config struct {
@@ -18,7 +18,7 @@ type SubConfig struct {
 
 func TestReflect(t *testing.T) {
 	cfg1 := &Config{Value: "cfg1", Config: &Config{Value: "cfg1_1"}, SubConfig: &SubConfig{Value: "cfg1"}}
-	cfg2, err := config.Zero(cfg1)
+	cfg2, err := rutil.Zero(cfg1)
 	if err != nil {
 		t.Fatal(err)
 	}

util/reflect/reflect.go

@@ -1,9 +1,14 @@
-package config
+package reflect
 
 import (
+	"errors"
 	"reflect"
 )
 
+var (
+	ErrInvalidStruct = errors.New("invalid struct specified")
+)
+
 func IsEmpty(v reflect.Value) bool {
 	switch v.Kind() {
 	case reflect.Array, reflect.Map, reflect.Slice, reflect.String: