Is it safe to acquire an `&'static T` from a thread local storage of `T` if `T: !Sync`?

1

In other words, is this function safe?

#![feature(negative_bounds)]

use std::mem;
use std::thread::LocalKey;

pub fn get_thread_local_static_ref<T>(key: &'static LocalKey<T>) -> &'static T
where
    T: !Sync,
{
    key.with(|value| unsafe { mem::transmute(value) })
}

If T is !Sync, &T is !Send, so although &'static T have static lifetime, you can only use it in the current thread.

2

OK, the Drop implementation maybe an issue, because it gains mutable access to the object, while it can also acquire an immutable reference to the object, which breaks the borrow-check rule.

3

It would also allow you to get a &'static _ to any fields, which may be Sync.

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