Adam Perry

Nov 2, 2017

WebAssembly is on track to receive a number of features to improve targeting it from languages with large runtimes. What wasm features would you like to see to help Rust be a useful choice for libraries and applications on the web? What work might be done on Rust and in the ecosystem to make it more competitive when targeting the web?

Steve Klabnik

Nov 2, 2017

I personally am most excited about Rust's future with WebAssembly. Wasm is the assembly language of the web. JavaScript is the application language of the web. Rust should be the systems lang of the web. Systems languages succeed because they’re the native language of the platform. For the web platform, that language should be Rust. If you need to do a systems-level task on the web, Rust should be the default choice the same way C is the default choice for systems today.

We have a ways to go to accomplish that goal, and it's going to take a lot of work, but it's one of the areas I'm most excited about for the future.

Your question is about how we get there. On the Rust side, the biggest thing is making it easy to compile to wasm. We're not that difficult, but getting emscripten set up is kind of a pain. I want to make targeting wasm as easy as targeting musl libc; that is

$ rustup target add wasm
$ cargo run --target=wasm

Or whatever the triple ends up being.

The second biggest thing is on the wasm side: right now, wasm can't access the DOM directly, but must "FFI" through JavaScript. It has a pretty huge performance penalty. It's also a similar story with threads.

Community-wise, testing against wasm in CI would be great. Given the aforementioned setup difficulties, I don't think we're ready for that as an ask yet, though.

Aaron Turon

Rust core team

Nov 2, 2017

To add a bit to Steve's answer: on the wasm side, there's work just getting started in exposing the DOM in a way that Rust can easily work with, without requiring full GC integration (which is still years off). That will immediately increase the power of Rust on the web, and we hope to have the Rust side of that story ready in lock-step with it becoming available.

That said, Rust is already usable via wasm for cases that are not DOM-heavy, i.e. if you have pretty compute-heavy components.

Finally, within the Rust ecosystem, I expect we'll have an explosion of libraries for working in wasm (and binding to web platform APIs, as well as ultimately js libs). The cool thing is that this in many ways resembles the no_std/embedded story for Rust, because wasm out of the box doesn't even give you malloc, let alone files etc. Moreover, wasm often has much stronger binary size constraints than even embedded devices. So I think that working on the wasm-centric ecosystem will also help us push Rust for embedded.

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