failpoint doesn't work if the marker function is defined in the main package

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a recipe for reproducing the error.

For example, we have a file named main.go:

package main

import (

    "github.com/pingcap/failpoint"
)

func F1(name string) string {

    failpoint.Inject("failpoint-name", nil)

    return "hello " + name
}

func main() {
    failpoint.Enable("failpoint-name", "panic")
    F1("ttt")
}

After transfrom the code with failpoint-ctl enable, the generated binding__failpoint_binding__.go looks like this:

package main

import "reflect"

type __failpointBindingType struct {pkgpath string}
var __failpointBindingCache = &__failpointBindingType{}

func init() {
    __failpointBindingCache.pkgpath = reflect.TypeOf(__failpointBindingType{}).PkgPath()
}
func _curpkg_(name string) string {
    return  __failpointBindingCache.pkgpath + "/" + name
}

You may notice that binding__failpoint_binding__.go is also in package main, that means binding__failpoint_binding__.go could not be found by main.go.

Run go run main.go then, you will find the following error:

 ./main.go:8:17: undefined: _curpkg_

2. What did you expect to see?

program panics due to failpoint

3. What did you see instead?

 ./main.go:8:17: undefined: _curpkg_

4. Versions of the failpoint

$ ./bin/failpoint-ctl -V
ReleaseVersion bf45ab2
BuildTS 2019-05-15 09:48:44
GitHash bf45ab20bfc48d624b61944a4820768c16d7db99
GitBranch master
GoVersion go version go1.12 darwin/amd64

Start with main.go and the generated binding__failpoint_binding__.go after running failpoint-ctl enable. Reproduce with go run main.go and inspect why the generated curpkg symbol is unavailable. Done means the example compiles and panics when the failpoint is enabled.