Macro rustc_attr

macro_rules! rustc_attr {
    (TEST, $attr:ident, $typ:expr, $tpl:expr, $duplicate:expr, $encode_cross_crate:expr $(,)?) => { ... };
    ($attr:ident, $typ:expr, $tpl:expr, $duplicates:expr, $encode_cross_crate:expr, $msg:expr $(,)?) => { ... };
}