1 // Copyright 2018 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 5 package xerrors
6 7 import (
8 "reflect"
9 )
10 11 // A Wrapper provides context around another error.
12 type Wrapper interface {
13 // Unwrap returns the next error in the error chain.
14 // If there is no next error, Unwrap returns nil.
15 Unwrap() error
16 }
17 18 // Opaque returns an error with the same error formatting as err
19 // but that does not match err and cannot be unwrapped.
20 func Opaque(err error) error {
21 return noWrapper{err}
22 }
23 24 type noWrapper struct {
25 error
26 }
27 28 func (e noWrapper) FormatError(p Printer) (next error) {
29 if f, ok := e.error.(Formatter); ok {
30 return f.FormatError(p)
31 }
32 p.Print(e.error)
33 return nil
34 }
35 36 // Unwrap returns the result of calling the Unwrap method on err, if err implements
37 // Unwrap. Otherwise, Unwrap returns nil.
38 //
39 // Deprecated: As of Go 1.13, use errors.Unwrap instead.
40 func Unwrap(err error) error {
41 u, ok := err.(Wrapper)
42 if !ok {
43 return nil
44 }
45 return u.Unwrap()
46 }
47 48 // Is reports whether any error in err's chain matches target.
49 //
50 // An error is considered to match a target if it is equal to that target or if
51 // it implements a method Is(error) bool such that Is(target) returns true.
52 //
53 // Deprecated: As of Go 1.13, use errors.Is instead.
54 func Is(err, target error) bool {
55 if target == nil {
56 return err == target
57 }
58 59 isComparable := reflect.TypeOf(target).Comparable()
60 for {
61 if isComparable && err == target {
62 return true
63 }
64 if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(target) {
65 return true
66 }
67 // TODO: consider supporing target.Is(err). This would allow
68 // user-definable predicates, but also may allow for coping with sloppy
69 // APIs, thereby making it easier to get away with them.
70 if err = Unwrap(err); err == nil {
71 return false
72 }
73 }
74 }
75 76 // As finds the first error in err's chain that matches the type to which target
77 // points, and if so, sets the target to its value and returns true. An error
78 // matches a type if it is assignable to the target type, or if it has a method
79 // As(interface{}) bool such that As(target) returns true. As will panic if target
80 // is not a non-nil pointer to a type which implements error or is of interface type.
81 //
82 // The As method should set the target to its value and return true if err
83 // matches the type to which target points.
84 //
85 // Deprecated: As of Go 1.13, use errors.As instead.
86 func As(err error, target interface{}) bool {
87 if target == nil {
88 panic("errors: target cannot be nil")
89 }
90 val := reflect.ValueOf(target)
91 typ := val.Type()
92 if typ.Kind() != reflect.Ptr || val.IsNil() {
93 panic("errors: target must be a non-nil pointer")
94 }
95 if e := typ.Elem(); e.Kind() != reflect.Interface && !e.Implements(errorType) {
96 panic("errors: *target must be interface or implement error")
97 }
98 targetType := typ.Elem()
99 for err != nil {
100 if reflect.TypeOf(err).AssignableTo(targetType) {
101 val.Elem().Set(reflect.ValueOf(err))
102 return true
103 }
104 if x, ok := err.(interface{ As(interface{}) bool }); ok && x.As(target) {
105 return true
106 }
107 err = Unwrap(err)
108 }
109 return false
110 }
111 112 var errorType = reflect.TypeOf((*error)(nil)).Elem()
113