| // Copyright 2018 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package xerrors |
| |
| import ( |
| "reflect" |
| ) |
| |
| // A Wrapper provides context around another error. |
| type Wrapper interface { |
| // Unwrap returns the next error in the error chain. |
| // If there is no next error, Unwrap returns nil. |
| Unwrap() error |
| } |
| |
| // Opaque returns an error with the same error formatting as err |
| // but that does not match err and cannot be unwrapped. |
| func Opaque(err error) error { |
| return noWrapper{err} |
| } |
| |
| type noWrapper struct { |
| error |
| } |
| |
| func (e noWrapper) FormatError(p Printer) (next error) { |
| if f, ok := e.error.(Formatter); ok { |
| return f.FormatError(p) |
| } |
| p.Print(e.error) |
| return nil |
| } |
| |
| // Unwrap returns the result of calling the Unwrap method on err, if err implements |
| // Unwrap. Otherwise, Unwrap returns nil. |
| func Unwrap(err error) error { |
| u, ok := err.(Wrapper) |
| if !ok { |
| return nil |
| } |
| return u.Unwrap() |
| } |
| |
| // Is reports whether any error in err's chain matches target. |
| // |
| // An error is considered to match a target if it is equal to that target or if |
| // it implements a method Is(error) bool such that Is(target) returns true. |
| func Is(err, target error) bool { |
| if target == nil { |
| return err == target |
| } |
| |
| isComparable := target == nil || reflect.TypeOf(target).Comparable() |
| for { |
| if isComparable && err == target { |
| return true |
| } |
| if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(target) { |
| return true |
| } |
| // TODO: consider supporing target.Is(err). This would allow |
| // user-definable predicates, but also may allow for coping with sloppy |
| // APIs, thereby making it easier to get away with them. |
| if err = Unwrap(err); err == nil { |
| return false |
| } |
| } |
| } |
| |
| // As finds the first error in err's chain that matches the type to which target |
| // points, and if so, sets the target to its value and returns true. An error |
| // matches a type if it is assignable to the target type, or if it has a method |
| // As(interface{}) bool such that As(target) returns true. As will panic if target |
| // is not a non-nil pointer to a type which implements error or is of interface type. |
| // |
| // The As method should set the target to its value and return true if err |
| // matches the type to which target points. |
| func As(err error, target interface{}) bool { |
| if target == nil { |
| panic("errors: target cannot be nil") |
| } |
| val := reflect.ValueOf(target) |
| typ := val.Type() |
| if typ.Kind() != reflect.Ptr || val.IsNil() { |
| panic("errors: target must be a non-nil pointer") |
| } |
| if e := typ.Elem(); e.Kind() != reflect.Interface && !e.Implements(errorType) { |
| panic("errors: *target must be interface or implement error") |
| } |
| targetType := typ.Elem() |
| for err != nil { |
| if reflect.TypeOf(err).AssignableTo(targetType) { |
| val.Elem().Set(reflect.ValueOf(err)) |
| return true |
| } |
| if x, ok := err.(interface{ As(interface{}) bool }); ok && x.As(target) { |
| return true |
| } |
| err = Unwrap(err) |
| } |
| return false |
| } |
| |
| var errorType = reflect.TypeOf((*error)(nil)).Elem() |