Even in the presence of incorrect position information, the go/printer should always
format //-style comments with a newline at the end. Otherwise, illegal Go programs can
be the result. The following is a test case.

package main

import (
    "bytes"
    "fmt"
    "go/parser"
    "go/printer"
    "go/token"
)

const src =
`// comment 1
// comment 2
// comment 3
package main
`

func newlines(s string) (n int) {
    for _, b := range s {
        if b == '\n' {
            n++
        }
    }
    return
}


func main() {
    fset := token.NewFileSet()
    ast1, err1 := parser.ParseFile(fset, "", src, parser.ParseComments)
    if err1 != nil {
        panic(err1)
    }

    var buf bytes.Buffer
    // Comments are not properly terminated when using a new (empty)
    // file set. Without the assignment below, the code works.
    fset = token.NewFileSet()
    printer.Fprint(&buf, fset, ast1)

    nsrc := newlines(src)
    nbuf := newlines(buf.String())
    if nsrc != nbuf {
        fmt.Printf("got %d, expected %d\n", nbuf, nsrc)
    }
}