Macro thread_local_inner 

#[doc(hidden)] pub macro thread_local_inner {
    (@key $t:ty, $(#[$align_attr:meta])*, const $init:expr) => { ... },
    (@key $t:ty, $(#[$align_attr:meta])*, $init:expr) => { ... },
}

🔬This is a nightly-only experimental API. (thread_local_internals)