gem-hunter

rollup-plugin-rust

Installation

yarn add --dev @wasm-tool/rollup-plugin-rust binaryen

npm install --save-dev @wasm-tool/rollup-plugin-rust binaryen

Usage

import rust from "@wasm-tool/rollup-plugin-rust";

export default {
    format: "es",
    input: {
        foo: "Cargo.toml",
    },
    plugins: [
        rust(),
    ],
};

Importing Cargo.toml within .js

import { foo, bar } from "./path/to/Cargo.toml";

// Use functions which were exported from Rust...

Extra Tips

Nightly

[toolchain]
channel = "nightly-2025-11-20"
components = [ "rust-std", "rust-src", "rustfmt", "clippy" ]
targets = [ "wasm32-unknown-unknown" ]

Workspaces

[workspace]
members = [
    "src/foo",
    "src/bar",
]

Optimizing for size

[profile.release]
opt-level = "z"

Usage with Vite

async function loadWasm() {
    // This code will only run in the browser
    if (!import.meta.env.SSR) {
        const { foo, bar } = await import("./path/to/Cargo.toml");

        // Use functions which were exported from Rust...
    }
}

Customizing the Wasm loading

import { module, init } from "./path/to/Cargo.toml?custom";

async function loadWasm() {
    const { foo, bar } = await init({
        // The URL or Uint8Array which will be initialized.
        module: module,

        // The WebAssembly.Memory which will be used for the Wasm.
        //
        // If this is undefined then it will automatically create a new memory.
        //
        // This is useful for doing multi-threading with multiple Workers sharing the same SharedArrayBuffer.
        memory: undefined,
    });

    // Use functions which were exported from Rust...
}

Build options

rust({
    // Whether the code will be run in Node.js or not.
    //
    // This is needed because Node.js does not support `fetch`.
    nodejs: false,

    // Whether to inline the `.wasm` file into the `.js` file.
    //
    // This is slower and it increases the file size by ~33%,
    // but it does not require a separate `.wasm` file.
    inlineWasm: false,

    // Whether to display extra compilation information in the console.
    verbose: false,

    extraArgs: {
        // Extra arguments passed to `cargo`.
        cargo: [],

        // Extra arguments passed to `rustc`, this is equivalent to `RUSTFLAGS`.
        rustc: [],

        // Extra arguments passed to `wasm-bindgen`.
        wasmBindgen: [],

        // Extra arguments passed to `wasm-opt`.
        wasmOpt: ["-O", "--enable-threads", "--enable-bulk-memory", "--enable-bulk-memory-opt"],
    },

    optimize: {
        // Whether to build in release mode.
        //
        // In watch mode this defaults to false.
        release: true,

        // Whether to run wasm-opt.
        //
        // In watch mode this defaults to false.
        wasmOpt: true,

        // Whether to use optimized rustc settings.
        //
        // This slows down compilation but significantly reduces the file size.
        //
        // If you use the nightly toolchain, this will reduce the file size even more.
        rustc: true,

        // These options default to false in watch mode.
        strip: {
            // Removes location information, resulting in lower file size but worse stace traces.
            // Currently this only works on nightly.
            location: true,

            // Removes debug formatting from strings, such as `format!("{:?}", ...)`
            // Currently this only works on nightly.
            formatDebug: true,
        },
    },

    // Which files it should watch in watch mode. This is relative to the Cargo.toml file.
    // Supports all of the glob syntax: https://www.npmjs.com/package/glob
    watchPatterns: ["src/**"],

    // These options should not be relied upon, they can change or disappear in future versions.
    experimental: {
        // Compiles with atomics and enables multi-threading.
        // Currently this only works on nightly.
        atomics: false,

        // Whether the Wasm will be initialized synchronously or not.
        //
        // In the browser you can only use synchronous loading inside of Workers.
        //
        // This requires `inlineWasm: true`.
        synchronous: false,

        // Creates a `.d.ts` file for each `Cargo.toml` crate and places them
        // into this directory.
        //
        // This is useful for libraries which want to export TypeScript types.
        typescriptDeclarationDir: null,
    },
})

Environment variables