Disallow references to static mut

🚧 The 2024 Edition has not yet been released and hence this section is still "under construction".

Summary

• The static_mut_refs lint is now a hard error that cannot be disabled. This prevents taking a shared or mutable reference to a static mut.

Details

Taking a reference to a static mut is no longer allowed:

#![allow(unused)]
fn main() {
static mut X: i32 = 23;
static mut Y: i32 = 24;

unsafe {
    let y = &X;             // ERROR: reference of mutable static
    let ref x = X;          // ERROR: reference of mutable static
    let (x, y) = (&X, &Y);  // ERROR: reference of mutable static
}
}

Shared or mutable references of mutable static are almost always a mistake and can lead to undefined behavior and various other problems in your code. For example, another thread writing to the static mut will cause an aliasing violation and incur Undefined Behavior.

Migration

🚧 The automatic migration for this has not yet been implemented.