Module with a function that prints file name for the top stack frame.
Different versions of this module are identical, but they should return
different file names with -trimpath.
-- .mod --
module example.com/stack

go 1.14
-- .info --
{"Version":"v1.0.1"}
-- stack.go --
package stack

import "runtime"

func TopFile() string {
	_, file, _, _ := runtime.Caller(0)
	return file
}