There seems to be some parameters that has not been used in the __thread_local_inner macro of the unstabilized standard library.

[3442853561]

When I tried to learn std::thread_local by reading the implementation in the standard library, I found such a piece of code. There seems to be some parameters that has not been used in the __thread_local_inner macro of the unstabilized standard library.

#[doc(hidden)]
#[unstable(feature = "thread_local_internals",
           reason = "should not be necessary",
           issue = "0")]
#[macro_export]
#[allow_internal_unstable(thread_local_internals, cfg_target_thread_local, thread_local)]
#[allow_internal_unsafe]
macro_rules! __thread_local_inner {
    (@key $(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $init:expr) => {
        {
            #[inline]
            fn __init() -> $t { $init }

            unsafe fn __getit() -> $crate::option::Option<&'static $t> {
                #[cfg(all(target_arch = "wasm32", not(target_feature = "atomics")))]
                static __KEY: $crate::thread::__StaticLocalKeyInner<$t> =
                    $crate::thread::__StaticLocalKeyInner::new();

                #[thread_local]
                #[cfg(all(
                    target_thread_local,
                    not(all(target_arch = "wasm32", not(target_feature = "atomics"))),
                ))]
                static __KEY: $crate::thread::__FastLocalKeyInner<$t> =
                    $crate::thread::__FastLocalKeyInner::new();

                #[cfg(all(
                    not(target_thread_local),
                    not(all(target_arch = "wasm32", not(target_feature = "atomics"))),
                ))]
                static __KEY: $crate::thread::__OsLocalKeyInner<$t> =
                    $crate::thread::__OsLocalKeyInner::new();

                __KEY.get(__init)
            }

            unsafe {
                $crate::thread::LocalKey::new(__getit)
            }
        }
    };
    ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $init:expr) => {
        $(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> =
            $crate::__thread_local_inner!(@key $(#[$attr])* $vis $name, $t, $init);
    }
}

$(#[$attr:meta])*, $vis and $name in (@key $(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $init:expr) seems to be useless.

Since this is a macro without stability, why don't we remove these parameters? Like

macro_rules! __thread_local_inner {
    (@key $t:ty, $init:expr) => {
        // blablabla
    };
    ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $init:expr) => {
        $(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> =
            $crate::__thread_local_inner!(@key $t, $init);
    }
}

[3442853561]

There is an example to prove that these parameters are not useful.

#![feature(thread_local_internals)]
use std::cell::RefCell;

pub const FOO: std::thread::LocalKey<RefCell<u32>> = __thread_local_inner!(@key pub BAR, RefCell<u32>, RefCell::new(1));

fn main() {
    FOO.with(|f| {
        assert_eq!(*f.borrow(), 1);
        *f.borrow_mut() = 2;
    });
    
    // BAR.with(|b| {
    //     assert_eq!(*b.borrow(), 1);
    //     *b.borrow_mut() = 2;
    // });
}