`ref` patterns can const-promote a single constant more than once, and can both const-promote and move from the same value.

I'm not sure if this is a bug or not.

I tried this code:

#![allow(dead_code)]

struct NotCopy { data: i32 }

fn main() {
    let ref x @ ref y = NotCopy { data: 1 };
    assert!(std::ptr::eq(x, y));
}

I ran the above code in Miri. The assertion failed.

It seems to me that the NotCopy constant is const-promoted twice, resulting in two implicit NotCopy statics. (I'm guessing that, outside of miri, the consts happen to be deduplicated.)

As a result, it is observable whether const promotion happened or not. In my understanding, promotion is supposed to happen only when it's not observable whether it has happened. Therefore, I think this behavior is incorrect.

See also #145237, where a constant is both moved and promoted.

@rustbot labels +T-lang +A-patterns +A-const-eval

Meta

Reproducible on the playground in version 1.91.0-nightly (2025-08-17 425a9c0a0e365c0b8c6c)

Start with the provided Rust reproducer in Miri and compare its behavior with the related case in #145237. Trace how the ref pattern handles the shared NotCopy value and const promotion. Done means the observable behavior is consistent with the intended promotion rules and the reproducer no longer exposes distinct references unexpectedly.