This program:
  http://play.golang.org/p/f3VrIs2Z70
parses a syntactically well-formed Go program, inserts an additional statement, then
prints it out again.  The result cannot be parsed because a newline was inserted in an
inappropriate place to accommodate a comment.  Here's the output:

package P

func f() {
    print("12"
    /*hi*/)
    g(0, 1)
}

Note that the length of the literal "12" is critical: if a shorter expression
is used, the /*hi*/ comment, which is retains its association with its original byte
offset, will not be inserted at that point.