package main

import (
    "fmt"
    "go/format"
)

func main() {
    data := []byte("\ta()\n//line :1")
    data1, err := format.Source(data)
    if err != nil {
        return
    }
    _, err = format.Source(data1)
    if err != nil {
        fmt.Printf("orig: %q\n", data)
        fmt.Printf("new : %q\n", data1)
        panic(err)
    }
}