swc/tests/rust-plugins/swc_internal_plugin

SWC plugin

Multivalue-polyfill

Once plugin completes transform, transformed Program will be re-serialized into array bytes. Host (SWC) will reconstruct & deserialize it via raw pointer to the array bytes plugin's process returns. However since size of serialized array bytes is non-deterministic plugin also should return size of the array as well. In result, signature of raw plugin process fn looks like this:

fn proces(...args) -> (i32, i32)

Rust compiler have target feature (target-feature=+multivalue) to genetare wasm binary with these multivalue support, but there are some known upstream issues like https://github.com/rust-lang/rust/issues/73755 prevents to use it. The other way around is to use bindings like wasm-bindgen.

In this plugin example generated binary polyfills multivalue only instead of relying on whole wasm-bindgen workflow (https://github.com/vmx/wasm-multi-value-reverse-polyfill). This polyfill can be removed once upstream compiler feature works as expected or if we decide to use wasm-bindgen fully.

Since cargo doesn't support workflow like post-build integrating whole process into build is bit unergonomic. build.* is naive substitution to mimic those behaviors. Or otherwise multivalue-polyfill can be excuted manually after main plugin build steps.