4181fb311a
This commit adds experimental support to `wasm-bindgen` to emit and leverage the `anyref` native wasm type. This native type is still in a proposal status (the reference-types proposal). The intention of `anyref` is to be able to directly hold JS values in wasm and pass the to imported functions, namely to empower eventual host bindings (now renamed WebIDL bindings) integration where we can skip JS shims altogether for many imports. This commit doesn't actually affect wasm-bindgen's behavior at all as-is, but rather this support requires an opt-in env var to be configured. Once the support is stable in browsers it's intended that this will add a CLI switch for turning on this support, eventually defaulting it to `true` in the far future. The basic strategy here is to take the `stack` and `slab` globals in the generated JS glue and move them into wasm using a table. This new table in wasm is managed at the fringes via injected shims. At `wasm-bindgen`-time the CLI will rewrite exports and imports with shims that actually use `anyref` if needed, performing loads/stores inside the wasm module instead of externally in the wasm module. This should provide a boost over what we have today, but it's not a fantastic strategy long term. We have a more grand vision for `anyref` being a first-class type in the language, but that's on a much longer horizon and this is currently thought to be the best we can do in terms of integration in the near future. The stack/heap JS tables are combined into one wasm table. The stack starts at the end of the table and grows down with a stack pointer (also injected). The heap starts at the end and grows up (state managed in linear memory). The anyref transformation here will hook up various intrinsics in wasm-bindgen to the runtime functionality if the anyref supoprt is enabled. The main tricky treatment here was applied to closures, where we need JS to use a different function pointer than the one Rust gives it to use a JS function pointer empowered with anyref. This works by switching up a bit how descriptors work, embedding the shims to call inside descriptors rather than communicated at runtime. This means that we're accessing constant values in the generated JS and we can just update the constant value accessed.
wasm-bindgen
Facilitating high-level interactions between wasm modules and JavaScript.
Import JavaScript things into Rust and export Rust things to JavaScript.
extern crate wasm_bindgen;
use wasm_bindgen::prelude::*;
// Import the `window.alert` function from the Web.
#[wasm_bindgen]
extern "C" {
fn alert(s: &str);
}
// Export a `greet` function from Rust to JavaScript, that alerts a
// hello message.
#[wasm_bindgen]
pub fn greet(name: &str) {
alert(&format!("Hello, {}!", name));
}
Use exported Rust things from JavaScript with ECMAScript modules!
import { greet } from "./hello_world";
greet("World!");
Features
-
Lightweight. Only pay for what you use.
wasm-bindgenonly generates bindings and glue for the JavaScript imports you actually use and Rust functionality that you export. For example, importing and using thedocument.querySelectormethod doesn't causeNode.prototype.appendChildorwindow.alertto be included in the bindings as well. -
ECMAScript modules. Just import WebAssembly modules the same way you would import JavaScript modules. Future compatible with WebAssembly modules and ECMAScript modules integration.
-
Designed with the "host bindings" proposal in mind. Eventually, there won't be any JavaScript shims between Rust-generated wasm functions and native DOM methods. Because the wasm functions are statically type checked, some of those native methods' dynamic type checks should become unnecessary, promising to unlock even-faster-than-JavaScript DOM access.
Guide
📚 Read the wasm-bindgen guide here! 📚
API Docs
License
This project is licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.
Contribution
See the "Contributing" section of the guide for information on
hacking on wasm-bindgen!
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this project by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.