go - 如何在go中显示带有pkg/errors的错误行号？

Question

我可以使用juju/errors打印错误的行号，但不确定如何使用pkg/errors进行操作。

package main

import (
    jerrors "github.com/juju/errors"
    perrors "github.com/pkg/errors"

    "io/ioutil"
    "log"
)

func jerror() error {
    //throw an error....
    _, err := ioutil.ReadDir("r")
    if err != nil {
        return jerrors.Trace(err)
    }
    return nil
}

func perror() error {
    //throw an error....
    _, err := ioutil.ReadDir("r")
    if err != nil {
        return perrors.Cause(err)
    }
    return nil
}

func main() {
    jerr := jerror()
    if jerr != nil {
        log.Println(jerrors.ErrorStack(jerr))
    }

    log.Println("-------------------------")

    perr := perror()
    if perr != nil {
        log.Println(perrors.WithStack(perr))
    }
}

打印输出:

2020/08/26 00:19:48 open r: no such file or directory
go-mock-json-api/main.go:15: 
2020/08/26 00:19:48 -------------------------
2020/08/26 00:19:48 open r: no such file or directory

Answer 1

使用默认的pkg/errors方法时，String()的错误将不会打印堆栈，使用"%+v"而不是来打印堆栈。
在文档的formatted printing of errors部分中对此进行了解释:

All error values returned from this package implement fmt.Formatter and can be formatted by the fmt package. The following verbs are supported:

%s    print the error. If the error has a Cause it will be
      printed recursively.
%v    see %s
%+v   extended format. Each Frame of the error's StackTrace will
      be printed in detail.

WithStack的文档提供了显示不同行为的示例:

cause := errors.New("whoops")
err := errors.WithStack(cause)
fmt.Println(err)

// Output:
// whoops

fmt.Printf("%+v", err)

// Output:
// whoops
// github.com/pkg/errors_test.ExampleWithStack_printf
//         /home/fabstu/go/src/github.com/pkg/errors/example_test.go:55
// testing.runExample
// ...

请注意，如果您直接使用 errors.New，则不需要使用 WithStack， errors.New已经为您做到了，如下面的 playground example所示:

package main

import (
    "fmt"

    "github.com/pkg/errors"
)

func main() {
    err := errors.New("whoops")
    fmt.Printf("String: %s\n", err)
    fmt.Printf("Verbose: %+v\n", err)

}

输出:

String: whoops
Verbose: whoops
main.main
    /tmp/sandbox878560423/prog.go:10
runtime.main
    /usr/local/go-faketime/src/runtime/proc.go:204
runtime.goexit
    /usr/local/go-faketime/src/runtime/asm_amd64.s:1374