stable_deref_trait VS zorrow

To elaborate, there is a recurring trend of sound C programs turning into unsound Rust programs, because shared mutability is often necessary but Stacked Borrows places strict conditions on constructing &mut T (they invalidate some but not all aliasing *const T), and it's less ergonomic to work solely in raw pointers and avoid creating Box or long-lasting &mut T (or for intrusive collections, any &mut T at all).

For example, matklad (the author of rust-analyzer, one of the preeminent Rust programmers and someone I'd expect to get code right) made a recent blog post on "Caches In Rust" (https://matklad.github.io/2022/06/11/caches-in-rust.html). The cache is built around https://docs.rs/elsa, which is built around https://docs.rs/stable_deref_trait/latest/stable_deref_trait..., which is unsound for Box and violates stacked borrows in its current form (https://github.com/Storyyeller/stable_deref_trait/issues/15). However, the rules may be relaxed or more ergonomic alternatives added (https://github.com/rust-lang/unsafe-code-guidelines/issues/3...), it's uncertain right now.

(Also I go by "they".)

Unsafe Rust is an esoteric language without iron-clad guarantees, and type-level programming and async Rust is an esoteric metalanguage (https://hirrolot.github.io/posts/rust-is-hard-or-the-misery-...). For example, matklad made a recent blog post on "Caches In Rust" (https://matklad.github.io/2022/06/11/caches-in-rust.html). The cache is built around https://docs.rs/elsa, which is built around https://docs.rs/stable_deref_trait/latest/stable_deref_trait..., which is unsound for Box and violates stacked borrows: https://github.com/Storyyeller/stable_deref_trait/issues/15

There is a recurring trend of sound C programs turning into unsound Rust programs, because shared mutability is often necessary but it's difficult to avoid creating &mut, and Stacked Borrows places strict conditions on constructing &mut T (they invalidate some but not all aliasing *const T).

The cache is built around https://docs.rs/elsa, which is built around https://docs.rs/stable_deref_trait/latest/stable_deref_trait/trait.StableDeref.html, which is unsound for Box and violates stacked borrows: https://github.com/Storyyeller/stable_deref_trait/issues/15

StableDeref has multiple issues under the current Stacked Borrows model: https://github.com/Storyyeller/stable_deref_trait/issues/15

Somebody implemented part of it in the past, but it was based on the ability to observe the order of execution of comptime blocks, which is going to be removed from the language (probably already is).

https://github.com/DutchGhost/zorrow

It's not a complete solution, among other things, because it only works if you use it to access variables, as the language has no way of forcing you.