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