Deny static mut declarations entirely

[pitaj]

What it does

The static_mut_refs rustc lint checks for shared or mutable references of mutable statics. This catches most incorrect uses, but doesn't necessarily accomplish the goal of moving the ecosystem away from static mut entirely.

The static_mut clippy lint will check for any declarations of mutable statics, and recommend using an immutable static with a type with interior mutability instead.

Advantage

Move the ecosystem away from static mut. May even catch some unsoundness issues.

Drawbacks

Churn

Example

static mut NUM: usize = 0;
static mut FOO: Thing = Thing::new();

Could be written as:

static NUM: AtomicUsize = AtomicUsize::new(0);
static FOO: Mutex<Thing> = Mutex::new(Thing::new());
// Or RwLock, LazyLock, SyncUnsafeCell, etc

It would be good to point people to the edition guide explanation and the higher level sync objects docs.

[lolbinarycat]

@rustbot claim

[archief2910]

@rustbot claim

[archief2910]

sorry @pitaj it was by mistake that's why i unassigned the issue

[aaron-ang]

@lolbinarycat are you still working on this issue?

[lolbinarycat]

@aaron-ang not really, no.

[aaron-ang]

@pitaj can I confirm that #13770 is not related to this issue?

[pitaj]

Correct, #13770 is unrelated. I was confused earlier

[aaron-ang]

@rustbot claim

[pitaj]

@aaron-ang you might want to read through the discussion on #12914 before putting in any work.

[aaron-ang]

@aaron-ang you might want to read through the discussion on #12914 before putting in any work.

Thanks @pitaj. I'm aware that static mut semantics might change in the future.

[aaron-ang]

• References to static_mut have already been disallowed in rustc: Disallow reference to static mut and adding static_mut_ref lint rust#117556 and Disallow hidden references to mutable static rust#124895
• Waiting for Tracking Issue for SyncUnsafeCell rust#95439 to become stable so we can suggest it in the lint
• Rust community is planning to deprecate static_mut in the future: Deprecate static mut rfcs#3560, pending const_mut_refs to be stabilised: Tracking issue for &mut T in const contexts (const_mut_refs) rust#57349