Macro generate_sync_commands

macro_rules! generate_sync_commands {
    ($($(#[$attr:meta])* $module:ident),*) => { ... };
    (return_type = $return_type:ty; $($(#[$attr:meta])* $module:ident),*) => { ... };
    (default_command = $default:ident; $($(#[$attr:meta])* $module:ident),*) => { ... };
    (return_type = $return_type:ty, default_command = $default:ident; $($(#[$attr:meta])* $module:ident),*) => { ... };
}