Function syntax::ext::format::expand_preparsed_format_argsUnstable

pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt, sp: Span, efmt: P<Expr>, args: Vec<P<Expr>>, name_ordering: Vec<String>, names: HashMap<String, P<Expr>>) -> P<Expr>

Take the various parts of format_args!(efmt, args..., name=names...) and construct the appropriate formatting expression.