feat: support env tag in config (#2577)

* feat: support env tag in config

* chore: add more tests

* chore: add more tests, add stringx.Join

* fix: test fail

* chore: remove print code

* chore: rename variable

core/lang/lang.go

@@ -1,5 +1,11 @@
 package lang
 
+import (
+	"fmt"
+	"reflect"
+	"strconv"
+)
+
 // Placeholder is a placeholder object that can be used globally.
 var Placeholder PlaceholderType
 
@@ -9,3 +15,64 @@ type (
 	// PlaceholderType represents a placeholder type.
 	PlaceholderType = struct{}
 )
+
+// Repr returns the string representation of v.
+func Repr(v interface{}) string {
+	if v == nil {
+		return ""
+	}
+
+	// if func (v *Type) String() string, we can't use Elem()
+	switch vt := v.(type) {
+	case fmt.Stringer:
+		return vt.String()
+	}
+
+	val := reflect.ValueOf(v)
+	if val.Kind() == reflect.Ptr && !val.IsNil() {
+		val = val.Elem()
+	}
+
+	return reprOfValue(val)
+}
+
+func reprOfValue(val reflect.Value) string {
+	switch vt := val.Interface().(type) {
+	case bool:
+		return strconv.FormatBool(vt)
+	case error:
+		return vt.Error()
+	case float32:
+		return strconv.FormatFloat(float64(vt), 'f', -1, 32)
+	case float64:
+		return strconv.FormatFloat(vt, 'f', -1, 64)
+	case fmt.Stringer:
+		return vt.String()
+	case int:
+		return strconv.Itoa(vt)
+	case int8:
+		return strconv.Itoa(int(vt))
+	case int16:
+		return strconv.Itoa(int(vt))
+	case int32:
+		return strconv.Itoa(int(vt))
+	case int64:
+		return strconv.FormatInt(vt, 10)
+	case string:
+		return vt
+	case uint:
+		return strconv.FormatUint(uint64(vt), 10)
+	case uint8:
+		return strconv.FormatUint(uint64(vt), 10)
+	case uint16:
+		return strconv.FormatUint(uint64(vt), 10)
+	case uint32:
+		return strconv.FormatUint(uint64(vt), 10)
+	case uint64:
+		return strconv.FormatUint(vt, 10)
+	case []byte:
+		return string(vt)
+	default:
+		return fmt.Sprint(val.Interface())
+	}
+}