Cannot mutate the value inside a `Mutex` created in a `const` context

[orium]

Hi. I was trying the new Mutex::new() in const a context (new in rust 1.63) and I'm able to mutate it's value:

I tried this code:

use std::sync::Mutex;

const VAR: Mutex<usize> = Mutex::new(0);

fn main() {
    println!("var: {}", *VAR.lock().unwrap());
    *VAR.lock().unwrap() = 3;
    println!("var: {}", *VAR.lock().unwrap());
}

The output is

var: 0
var: 0

Playground link here.

[andjo403]

The problem is that you try to mutate a const this creates a temporary that you mutate, if you change const to static you get the expected result.
cc #40543

[orium]

Closing since this is the expected behavior: https://www.reddit.com/r/rust/comments/wltcf8/comment/ijvx9ym/?context=3

[riking]

Diagnostics part of issue is covered in #40543