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// 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 errors
import (
"internal/reflectlite"
)
// Unwrap returns the result of calling the Unwrap method on err, if err's
// type contains an Unwrap method returning error.
// Otherwise, Unwrap returns nil.
//
// Unwrap only calls a method of the form "Unwrap() error".
// In particular Unwrap does not unwrap errors returned by [Join].
func Unwrap(err error) error {
u, ok := err.(interface {
Unwrap() error
})
if !ok {
return nil
}
return u.Unwrap()
}
// Is reports whether any error in err's tree matches target.
//
// The tree consists of err itself, followed by the errors obtained by repeatedly
// calling its Unwrap() error or Unwrap() []error method. When err wraps multiple
// errors, Is examines err followed by a depth-first traversal of its children.
//
// 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.
//
// An error type might provide an Is method so it can be treated as equivalent
// to an existing error. For example, if MyError defines
//
// func (m MyError) Is(target error) bool { return target == fs.ErrExist }
//
// then Is(MyError{}, fs.ErrExist) returns true. See [syscall.Errno.Is] for
// an example in the standard library. An Is method should only shallowly
// compare err and the target and not call [Unwrap] on either.
func Is(err, target error) bool {
if target == nil {
return err == target
}
isComparable := reflectlite.TypeOf(target).Comparable()
return is(err, target, isComparable)
}
func is(err, target error, targetComparable bool) bool {
for {
if targetComparable && err == target {
return true
}
if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(target) {
return true
}
switch x := err.(type) {
case interface{ Unwrap() error }:
err = x.Unwrap()
if err == nil {
return false
}
case interface{ Unwrap() []error }:
for _, err := range x.Unwrap() {
if is(err, target, targetComparable) {
return true
}
}
return false
default:
return false
}
}
}
// As finds the first error in err's tree that matches target, and if one is found, sets
// target to that error value and returns true. Otherwise, it returns false.
//
// The tree consists of err itself, followed by the errors obtained by repeatedly
// calling its Unwrap() error or Unwrap() []error method. When err wraps multiple
// errors, As examines err followed by a depth-first traversal of its children.
//
// An error matches target if the error's concrete value is assignable to the value
// pointed to by target, or if the error has a method As(interface{}) bool such that
// As(target) returns true. In the latter case, the As method is responsible for
// setting target.
//
// An error type might provide an As method so it can be treated as if it were a
// different error type.
//
// As panics if target is not a non-nil pointer to either a type that implements
// error, or to any interface type.
func As(err error, target any) bool {
if err == nil {
return false
}
if target == nil {
panic("errors: target cannot be nil")
}
val := reflectlite.ValueOf(target)
typ := val.Type()
if typ.Kind() != reflectlite.Ptr || val.IsNil() {
panic("errors: target must be a non-nil pointer")
}
targetType := typ.Elem()
if targetType.Kind() != reflectlite.Interface && !targetType.Implements(errorType) {
panic("errors: *target must be interface or implement error")
}
return as(err, target, val, targetType)
}
func as(err error, target any, targetVal reflectlite.Value, targetType reflectlite.Type) bool {
for {
if reflectlite.TypeOf(err).AssignableTo(targetType) {
targetVal.Elem().Set(reflectlite.ValueOf(err))
return true
}
if x, ok := err.(interface{ As(any) bool }); ok && x.As(target) {
return true
}
switch x := err.(type) {
case interface{ Unwrap() error }:
err = x.Unwrap()
if err == nil {
return false
}
case interface{ Unwrap() []error }:
for _, err := range x.Unwrap() {
if err == nil {
continue
}
if as(err, target, targetVal, targetType) {
return true
}
}
return false
default:
return false
}
}
}
var errorType = reflectlite.TypeOf((*error)(nil)).Elem()