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This repository was archived by the owner on Dec 1, 2021. It is now read-only.
This repository was archived by the owner on Dec 1, 2021. It is now read-only.

WriteStack() duplicates call stack if err is already a causer #158

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@brianbwong

Description

@brianbwong
package main

import (
    "fmt"
    "github.com/pkg/errors"
)

func GiveError() error {
    return errors.New("this is an error")
}

func Outer() error {
    err := GiveError()
    return errors.WithStack(err)
}

func main() {
    err := Outer()
    fmt.Printf("%+v\n", err)
}

Output:

this is an error
main.GiveError
	/Users/brianwong/go/src/github.com/brianbwong/test.go:9
main.Outer
	/Users/brianwong/go/src/github.com/brianbwong/test.go:13
main.main
	/Users/brianwong/go/src/github.com/brianbwong/test.go:18
runtime.main
	/usr/local/opt/go/libexec/src/runtime/proc.go:198
runtime.goexit
	/usr/local/opt/go/libexec/src/runtime/asm_amd64.s:2361
main.Outer
	/Users/brianwong/go/src/github.com/brianbwong/test.go:14
main.main
	/Users/brianwong/go/src/github.com/brianbwong/test.go:18
runtime.main
	/usr/local/opt/go/libexec/src/runtime/proc.go:198
runtime.goexit
	/usr/local/opt/go/libexec/src/runtime/asm_amd64.s:2361

In this toy example, it's obvious that the output of GiveError() already contains a stack trace, so there's no point in Wrapping it. However, if GiveError() is a function in an external package, it won't be clear whether its output contains a stack trace or not (and hence whether it needs wrapping).

If this isn't intended, here's a rough proposal for a fix:

// WithStack annotates err with a stack trace at the point WithStack was called.
// If err is nil, WithStack returns nil.
func WithStack(err error) error {
	if err == nil {
		return nil
	}

    _, ok := err.(causer)
    if ok {
        return err
    }

	return &withStack{
		err,
		callers(),
	}
}

Though currently it looks like the type fundamental isn't actually a causer.

Happy to submit a PR if desired!

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