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