wit-bindgen VS rfcs

The component model is already shipping in Wasmtime, and will be stable for use in Node.js and in browsers via jco (https://github.com/bytecodealliance/jco) soon. WASI Preview 2 will be done in December or January, giving component model users a stable set of interfaces to use for scheduling, streams, and higher level functionality like stdio, filesystem, sockets, and http on an opt-in basis. You should look at wit-bindgen (https://github.com/bytecodealliance/wit-bindgen) to see some of the languages currently supported, and more that will be mature enough to use very soon (https://github.com/bytecodealliance/componentize-py)

Right now jco will automatically generate the JS glue code which implements a Component Model runtime on top of the JS engine's existing WebAssembly implementation. So, yes, Components are a composition of Wasm Modules and JS code is handling passing values from one module/instance to another. You still get the performance benefits of running computation in Wasm.

One day further down the standardization road, we would like to see Web engines ship a native implementation of the Component Model, which might be able to make certain optimizations that the JS implementation cannot. Until then you can consider jco a polyfill for a native implementation, and it still gives you the power to compose isolated programs written in many languages and run them in many different contexts, including the Web.

(Disclosure: I am co-chair of WASI, Wasmtime maintainer, implemented many parts of WASI/CM)

Thank you!

To your point, the primary consideration for choosing the languages is their support for WebAssembly, and WASI in particular.

Due to Spin's heavy use of WASI and the component model, languages that have first party support in the WIT bindings generator (https://github.com/bytecodealliance/wit-bindgen) are the easiest to implement, followed by languages that can be built on top of the support for those with first party support.

For example, the JavaScript support is built by embedding QuickJS (in particular, Shopify's Javy project — https://github.com/fermyon/spin-js-sdk), which then uses the Rust SDK.

There are many options, but what worked best for me is compiling with cargo-wasi and loading the resulting Wasm file with browser_wasi_shim. Using wasm32-wasi instead of wasm32-unknown-unknown requires a bit more work (the communication with JS has to be set up manually), but gives the flexibility of having just a Wasm file that can be dropped in and loaded dynamically. (There's wit-bindgen for generating wrapping code according to an interface definition but I didn't have much success with it.)

I've been playing with creating a go version of the abi for use with wit-bindgen because the current one uses cgo https://github.com/bytecodealliance/wit-bindgen

wit-bindgen - Language Binding Generator for WASM Interface Type

wit-bindgen-rust = { git = "https://github.com/bytecodealliance/wit-bindgen.git", rev = "60e3c5b41e616fee239304d92128e117dd9be0a7" }

Yep, you're right. For this, there are a few options. The ones most relevant to you are fp-bindgen, which targets Wasmer, and wit-bindgen, which targets wasmtime.

Yes, wasm_bindgen is js only. At least for now, in future I would also expect it to migrate to component model. There is also cargo-component which is a way to create modules compatible with component model. You define your module interface in WIT and your dependencies on other wasm modules in the similar way you would define crate dependencies. Alternately there is wit-bindgen that is a codegen tool for multiple languages that also accepts WIT as input.

Are you evaluating if WebAssembly Component Model, its WIT format and related tooling like wit-bindgen could be a good fit for your multiple languages support?

Our plan is to stick with both a Rust host and guest to begin with, and start developing other offerings as required. All of our bindings are implemented on top of wit-bindgen, which acts as our data transfer layer - as long as your guest language is supported by wit-bindgen, you'll be able to use the runtime in some form. (Our bindings make it nicer to use, though 😆)

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