1// Copyright 2022 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package errors
6
7import (
8	"unsafe"
9)
10
11// Join returns an error that wraps the given errors.
12// Any nil error values are discarded.
13// Join returns nil if every value in errs is nil.
14// The error formats as the concatenation of the strings obtained
15// by calling the Error method of each element of errs, with a newline
16// between each string.
17//
18// A non-nil error returned by Join implements the Unwrap() []error method.
19func Join(errs ...error) error {
20	n := 0
21	for _, err := range errs {
22		if err != nil {
23			n++
24		}
25	}
26	if n == 0 {
27		return nil
28	}
29	e := &joinError{
30		errs: make([]error, 0, n),
31	}
32	for _, err := range errs {
33		if err != nil {
34			e.errs = append(e.errs, err)
35		}
36	}
37	return e
38}
39
40type joinError struct {
41	errs []error
42}
43
44func (e *joinError) Error() string {
45	// Since Join returns nil if every value in errs is nil,
46	// e.errs cannot be empty.
47	if len(e.errs) == 1 {
48		return e.errs[0].Error()
49	}
50
51	b := []byte(e.errs[0].Error())
52	for _, err := range e.errs[1:] {
53		b = append(b, '\n')
54		b = append(b, err.Error()...)
55	}
56	// At this point, b has at least one byte '\n'.
57	return unsafe.String(&b[0], len(b))
58}
59
60func (e *joinError) Unwrap() []error {
61	return e.errs
62}
63