rfcs VS marker

I would add that Equality saturation/E-graphs has become quite a hot topic recently, since their POPL21 paper, with workshops dedicated to applications of e-graphs. They have even recently been added to Cranelift as an IR for optimizations.

I think with Cranelift's investment into an e-graph based optimizer (https://github.com/bytecodealliance/rfcs/blob/main/accepted/cranelift-egraph.md) they are well positioned to have quite competitive performance as a backend.

They're also actively working in this area, for example the recently added equality saturation framework and the pattern matching DSL it builds on.

There's an RFC here: https://github.com/bytecodealliance/rfcs/pull/28 and Saúl Cabrera, the person who is leading this effort and implementing the compiler tier, has a work-in-progress draft PR here: https://github.com/bytecodealliance/wasmtime/pull/4907

We discussed that a bunch in the RFC: https://github.com/bytecodealliance/rfcs/pull/14 . The conclusion was, in short, that the current Wasmtime production users didn't yet require an LTS release process, and the maintenance of an LTS is pretty onerous, so we would come up with one in the future as those requirements become more clear: https://github.com/bytecodealliance/rfcs/pull/14#discussion\_r708638804

Check out this, which aims to implement said stable interface!

Hey, I might be able to give some input how I deal with it in [rust-linting](https://github.com/rust-linting/rust-linting). For some context, the project needs to load several dynamic libraries and provide each of them with an abstract syntax tree. Serializing and deserializing the types for every step would most likely be too expensive. That's why I opted for a Rust <-> Rust FFI. There are two parts of this: 1. The loaded libraries needed to accept data from a driver. For this, I generate functions in the library crates which are marked as `extern "C"` and only use FFI safe types. Passing information to the loaded crates then always calls the generated functions, which intern call access a thread local struct instance in the dynamic crate. It's important that the instance implement a specific trait. For the library creation, it seems like magic. 2. Callbacks. The loaded libraries need to pass information back to the driver. For this, I use a struct with function pointers. These are also marked as `extern "C"` and need to only use FFI safe types. The definition of FFI safe, is a bit difficult. Slices, `str`, `Option<>` and most of the rusts STD types don't have a stable layout to the point, that it can change between compilations with the same compiler. Therefore, it's required that each passed type is `#[repr(C)]`. Options are wrapped in an enum, which has `#[repr(C)]`, slices and strings are dismantled into a data pointer and a length. On the receiving and they're reconstructed again. A small warning. I'm not an expert on FFI interfaces. My implementation would probably have some problems with lifetimes, if I'd use a slightly different memory model. So far, this has worked well (Besides the required boilerplate). The project is currently sadly lacking documentation, as it's still under heavy development. If you want, feel free to lock around the code base. The stable types and most of the interface is inside the `linter_api` crate.