// Copyright 2020 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.

// +build !go1.13

package errors

import "reflect"

// Is is a copy of Go 1.13's errors.Is for use with older Go versions.

func Is(err, target error) bool {

	if target == nil {

		return err == target

	}

	isComparable := 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

		}

		if err = unwrap(err); err == nil {

			return false

		}

	}

}

func unwrap(err error) error {

	u, ok := err.(interface {

		Unwrap() error

	})

	if !ok {

		return nil

	}

	return u.Unwrap()

}