@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.

• 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 bindings (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.