next.js/packages/next-swc/README.md

@next/swc

This package is responsible for swc compilation customized for next.js

Development

Run tests

cargo test

# Update snapshots and fixtures for tests
UPDATE=1 cargo test

Format code before submitting code

cargo fmt

Build the binary to integrate with next.js

pnpm build-native

Build wasm bindings to integrate with next.js

pnpm build-wasm

napi bindings feature matrix

Due to platform differences napi bindings selectively enables supported features. See below tables for the currently enabled features.

arch\platform	Linux(gnu)	Linux(musl)	Darwin	Windows
x64	a,b,d,e,f	a,b,d,e,f	a,b,d,e,f	a,b,d,e,f
aarch64	a,d,e,f	a,d,e,f	a,b,d,e,f	a,b,c,e

• a: turbo_tasks_malloc
• b: turbo_tasks_malloc_custom_allocator
• c: native-tls (via turbo-tasks-fetch)
• d: rustls-tls (via turbo-tasks-fetch)
• e: image-extended (webp)
• f: plugin

Package hierarchies

@next/swc consist of multiple rust packages to enable features. See below for the high level hierarchies.

flowchart TD
    C(next-custom-transforms) --> A(napi)
    C(next-custom-transforms) --> B(wasm)
    D(next-core) --> A(napi)
    E(next-build) --> A(napi)
    F(next-api) --> A(napi)
    C(next-custom-transforms) --> D
    D(next-core) --> F(next-api)
    D(next-core) --> E(next-build)

• next-custom-transforms: provides next-swc specific SWC transform visitors. Turbopack, and the plain next-swc bidnings (transform) use these transforms. Since this is a bottom package can be imported in any place (turbopack / next-swc / wasm), it is important package do not contain specific dependencies. For example, using Turbopack's VC in this package will cause build failures to wasm bindings.
• next-core: Implements Turbopack features for the next.js core functionality. This is also the place where Turbopack-specific transform providers (implementing CustomTransformer) lives, which wraps swc's transformer in the next-custom-transforms.
• next-api: Binding interface to the next.js provides a proper next.js functionality using next-core.
• napi / wasm: The actual binding interfaces, napi for the node.js and wasm for the wasm. Note wasm bindings cannot import packages using turbopack's feature.

To add new swc transforms

1. Implements a new visitor in next-custom-transforms. It is highly encouraged to use VisitMut instead of Fold for the performance reasons.
2. Implements a new CustomTransformer under crates/next-core/src/next_shared/transforms to make Turbopack's ecma transform plugin, then adjust corresponding rules in crates/next-core/src/(next_client|next_server)/context.rs.