Parcel 2: Rust transformer

Create the @parcel/transformer-rust package in packages/transforms/rust. This package is a Parcel 2 transform plugin for Rust to WASM. It should be based on the RustAsset from Parcel 1.

The @parcel/transformer-rust package is responsible for the following things:

• Installing the rust toolchain if needed
• Resolving Cargo.toml and running cargo if available.
• Otherwise, running rustc
• Collecting dependencies from the rust compiler and adding them as connected files so Parcel watches them
• Generating WASM

It is possible that the current approach in Parcel 1 is out of date. Additional research on the current Rust/WASM ecosystem is needed here. Some related issues:

• Importing JS from WASM - #647
• ESM integration - #1325
• HMR - #2688

There are also some plugins that have been working on some related stuff:

• https://github.com/mysterycommand/parcel-plugin-wasm-pack
• https://github.com/catsigma/parcel-plugin-wasm.rs
• https://github.com/rustwasm/rust-parcel-template

If someone from the community would like to own this feature in Parcel 2 core, that would be very helpful and appreciated! 😍

cc. @xtuc @linclark @littledan @alexcrichton - what’s the current state of WASM + Rust + ESM? What should we be aiming for in Parcel 2?

[Pauan]

I would just like to point out that in Rust, compilation happens at the crate level, not the file level.

That also means that all extern functions in Rust are exported from the crate, not individual files.

So it doesn’t make any sense to import an individual .rs file, instead you should import the Cargo.toml file (which represents the entire crate).

This is something to keep in mind for the new Rust transformer.

[alexcrichton]

Thanks for the cc @devongovett! The current state of Rust/WASM/ESM is that tooling like wasm-bindgen and wasm-pack have a “bundler” target which is intended to be consumed by Parcel/Webpack/etc. This “bundler” target assumes that the output wasm file is interpreted as an ES module and follows the wasm ESM integration spec.

From our perspective having Parcel act as a polyfill for the wasm ESM integration spec would cover all our use cases!