rust-gc VS unsafe-code-guidelines

rust-langdev has a lot of libraries for building compilers in Rust. Perhaps you could use these to make your implementation easier, and revisit it later if you want to build things from scratch. I'd suggest logos for lexing, LALRPOP / chumsky for parsing, and rust-gc for garbage collection.

There's nothing stopping you from doing that in Rust. See rust-gc for an example of a GC implemented in Rust. Another example is mozjs, which is Rust bindings to SpiderMonkey. The GC there is implemented in C++, but it shows how you'd structure wrapper types for GC'd pointers in Rust so that you can use them safely, even with all the "ugliness" of a browser-grade GC.

One can have a GC as a library, https://github.com/Manishearth/rust-gc

The ones I am aware of are gc and broom. None will be as simple to use as the one in old Rust as userland implementations don't have the benefit of first-class integrated compiler support.

Rust has rust-gc, which is an attempt to add opt-in GC over Rust's more traditional automatic memory management. It's a neat project, but I'm not sure where it's actually being used.

Inb4 "already exists": the question is about making it convenient, not just imlementing the behavior.

There is also a library implementation of garbage collection for Rust, made by someone from the Rust core team.

Yep! And I'd actually fully agree those are garbage collection, there's also a crate by Manish which does """real""" garbage collection—https://github.com/Manishearth/rust-gc

I don't know that I'd say it "works" - it's never a technique I've needed to use myself, but it's the approach taken by e.g. https://github.com/Manishearth/rust-gc

Anyway, I found something recent that implements "rc" but in terms of tracing: https://github.com/Manishearth/rust-gc/ . Maybe useful for projects involving graphs of objects.

Useful context on the Rust side is this issue [1]. It sounds like some of the author's concerns are addressed already.

[1]: https://github.com/rust-lang/unsafe-code-guidelines/issues/4...

Is this captured by one of the known soundness conflicts? If not then should consider adding it to the list.

There are some competing proposals for different memory models. Stacked borrows is the current proposal, but there are more work in the approproate WG.

Thank you /u/RalfJung for bringing formal methods to Rust, both through models like Stacked Borrows, by developing miri, and by working on unsafe-code-guidelines which aims to specify exactly what is and isn't allowed in unsafe code (surprisingly, it's an open question as 2023!)

You could imagine some way to make this safe for example automatically convert &'short &'long mut T to &'short &'short T, but it's non-trivial to prove they are safe at all, not to mention ensuring this is correctly implemented in the compiler. If you're interested there's also a discussion on whether the opposite (& & T to & &mut T) is sound here.

Agreed! MIRI is so good, it still feels like magic to me. It also comforts me that the Rust team takes improving unsafe semantics seriously, with the past Unsafe Code Guidelines WG and today's operational semantics team (t-opsem).

I think there are some aspects of this rule that are still undecided. See for example:

- https://github.com/rust-lang/unsafe-code-guidelines/issues/8...

- https://github.com/rust-lang/miri/issues/2732

C is much better specified than unsafe Rust. Some things are just not worked out yet in Rust. This may sometimes even bite very experienced devs, such as this issue with Box's aliasing semantics, which tripped up the author of left-right.