playground.rs

macro_rules! externs {
    ( $name:ident with macros, $($rest:tt)* ) => {
        externs!($x with macros);
        externs!($($rest)*);
    };
    ( $name:ident, $($rest:tt)* ) => {
        externs!($name);
        externs!($($rest)*);
    };
    ( $name:ident with macros ) => {
        #[macro_use] extern crate $name;
    };
    ( $name:ident ) => {
        extern crate $name;
    };
    () => {}
}

externs![rocket, rocket_contrib, serde_json with macros];

// other test cases:
// externs!{ serde_json with macros }
// externs!{ rocket, rocket_contrib, }
// externs!{ rocket }