feat: add error_join.go to support join error under go1.19, for internal use.

internal/error_join.go

@@ -0,0 +1,51 @@
+package internal
+
+// Note: this file is copyed from the go standart repo (https://github.com/golang/go/blob/master/src/errors/join.go).
+// just in order to adapt under go1.9
+// do not use it outside lancet lib.
+
+// Join returns an error that wraps the given errors.
+// Any nil error values are discarded.
+// Join returns nil if errs contains no non-nil values.
+// The error formats as the concatenation of the strings obtained
+// by calling the Error method of each element of errs, with a newline
+// between each string.
+func JoinError(errs ...error) error {
+	n := 0
+	for _, err := range errs {
+		if err != nil {
+			n++
+		}
+	}
+	if n == 0 {
+		return nil
+	}
+	e := &joinError{
+		errs: make([]error, 0, n),
+	}
+	for _, err := range errs {
+		if err != nil {
+			e.errs = append(e.errs, err)
+		}
+	}
+	return e
+}
+
+type joinError struct {
+	errs []error
+}
+
+func (e *joinError) Error() string {
+	var b []byte
+	for i, err := range e.errs {
+		if i > 0 {
+			b = append(b, '\n')
+		}
+		b = append(b, err.Error()...)
+	}
+	return string(b)
+}
+
+func (e *joinError) Unwrap() []error {
+	return e.errs
+}