Crates

The Rust workspace at the root of the repo. Combined with the Turbopack subtree, the framework's Rust code spans 269,139 lines across 948 files in 69 Cargo crates. This page covers the Next.js-specific crates under crates/. The Turbopack crates have their own section: turbopack/.

Crate list

Crate	Page	Role
crates/next-core	next-core	Translates Next.js config into Turbopack module options
crates/next-api	next-api	Public API: build a project, get entries, get manifests
crates/next-build	other-crates	Orchestrates a full build run
crates/next-custom-transforms	next-custom-transforms	SWC visitors for next/font, server actions, dynamic IO
crates/next-napi-bindings	next-napi-bindings	napi-rs glue exposed as @next/swc
crates/wasm	other-crates	wasm-bindgen wrapper
crates/next-build-test	other-crates	Test harness for the build
crates/next-code-frame	other-crates	Source-mapped code-frame error formatter
crates/next-error-code-swc-plugin	other-crates	SWC plugin that rewrites error-code helpers
crates/next-taskless	other-crates	Taskless integration

How they relate

graph TD
    NodeJS[Node.js<br/>packages/next] --> Bindings[next-napi-bindings<br/>napi-rs surface]
    Bindings --> Api[next-api<br/>public crate API]
    Api --> Core[next-core<br/>config + module options]
    Api --> Build[next-build<br/>build orchestration]

    Core --> CustomTransforms[next-custom-transforms<br/>SWC visitors]
    Core --> Tp[turbopack-core<br/>+ siblings]

    Wasm[crates/wasm] --> Api
    BuildTest[next-build-test] --> Build
    BuildTest --> Api

    Bindings --> CustomTransforms

The dependency arrows are deliberate:

• next-napi-bindings is the only crate published as a Node-loadable binary. Everything else exists to support it.
• next-api is the public API crate. It's stable enough that the JavaScript side reads its types and treats it as a contract.
• next-core is where Next.js's opinions live: how to configure Turbopack to produce app-router bundles, edge bundles, server bundles, etc.
• next-custom-transforms is the SWC visitor library. Next.js's compiler quirks (server actions, next/font, 'use server' / 'use client' enforcement) are implemented as SWC passes here.
• next-build orchestrates a full build by composing Turbopack project entries via next-api.

Build outputs

graph LR
    Source[Rust source] --> Cargo[cargo build]
    Cargo --> Native[platform .node binary]
    Cargo --> WasmBuild[wasm-bindgen]
    Native --> Pkg[packages/next-swc/native/]
    WasmBuild --> WasmPkg[wasm package]
    Pkg --> Distro[npm @next/swc-{platform}]

The pnpm swc-build-native script invokes cargo build --release -p next-napi-bindings. The scripts/install-native.mjs postinstall picks the right pre-built binary from npm when local builds aren't required. See packages/next-swc.

Workspace layout

The Cargo workspace is rooted at Cargo.toml and includes:

members = [
  "scripts/send-trace-to-jaeger",
  "crates/next-napi-bindings",
  "crates/wasm",
  "crates/next-api",
  "crates/next-build-test",
  "crates/next-build",
  "crates/next-code-frame",
  "crates/next-core",
  "crates/next-custom-transforms",
  "crates/next-taskless",
  "turbopack/crates/*",
  "turbopack/crates/*/fuzz",
  "turbopack/xtask",
]

exclude = [
  "crates/next-error-code-swc-plugin",
  "rspack/crates/binding"
]

The two excluded directories build standalone:

• crates/next-error-code-swc-plugin — built into a standalone .wasm via crates/next-error-code-swc-plugin/build-and-move.sh. SWC plugins are loaded as wasm modules.
• rspack/crates/binding — built independently for the rspack integration.

Toolchain

• Channel: nightly-2026-04-02 (rust-toolchain.toml)
• Components: rustfmt, clippy, rust-analyzer
• Profile: minimal

The dev profile uses debug = "line-tables-only" for compile-time savings; deps build at opt-level = 1 to keep cold builds fast. The turbo-persistence crate is special-cased to opt-level = 1 even in the workspace because it is performance-sensitive.

How to build everything

# JS only (after bootstrap)
pnpm build

# JS + Rust native binaries
pnpm build-all

# Just the napi binding
pnpm swc-build-native

# Just the wasm
pnpm swc-build-wasm

# Run cargo directly
cargo build --release -p <crate>

After branch switches, prefer pnpm build-all so dependent JS packages pick up Rust changes.

Linting and formatting

cargo fmt           # ASCII-ordered import groups; just run it
cargo clippy        # workspace lints

Workspace lint config (in root Cargo.toml):

[workspace.lints.clippy]
too_many_arguments = "allow"

[workspace.lints.rust]
unexpected_cfgs = { level = "warn", check-cfg = ['cfg(rust_analyzer)', 'cfg(fuzzing)', 'cfg(codspeed)'] }