Improve multi error

common/exceptions/multi.go

@@ -20,6 +20,39 @@ func (e *multiError) UnwrapMulti() []error {
 	return e.errors
 }
 
+func Errors(errors ...error) error {
+	errors = common.FilterNotNil(errors)
+	errors = ExpandAll(errors)
+	errors = common.UniqBy(errors, error.Error)
+	switch len(errors) {
+	case 0:
+		return nil
+	case 1:
+		return errors[0]
+	}
+	return &multiError{
+		errors: errors,
+	}
+}
+
+func Expand(err error) []error {
+	if multiErr, isMultiErr := err.(MultiError); isMultiErr {
+		return ExpandAll(multiErr.UnwrapMulti())
+	}
+	return []error{err}
+}
+
+func ExpandAll(errs []error) []error {
+	return common.FlatMap(errs, Expand)
+}
+
+func Append(err error, other error, block func(error) error) error {
+	if other == nil {
+		return err
+	}
+	return Errors(err, block(err))
+}
+
 func IsMulti(err error, targetList ...error) bool {
 	for _, target := range targetList {
 		if errors.Is(err, target) {