syntax::ext::source_util
impl<R> Read for Box<R> where R: Read + ?Sized, impl<W> Write for Box<W> where W: Write + ?Sized, impl<I> Iterator for Box<I> where I: Iterator + ?Sized, type Item = <I as Iterator>::Item;
pub fn expand_include_str( cx: &mut ExtCtxt, sp: Span, tts: &[TokenTree]) -> Box<MacResult + 'static>