# How to Contribute to SWC: Setting Up the Development Environment and Running Tests > Curious how to contribute to SWC? Learn to set up the development environment, install Rust and pnpm, and run tests with feature flags to validate your contributions. - Repository: [swc/swc](https://github.com/swc-project/swc) - Tags: how-to-guide - Published: 2026-06-15 --- **Contributing to SWC requires forking the repository, installing Rust and pnpm, initializing git submodules, and running the test suite with specific feature flags like `swc_v1` or `swc_v2` to validate your changes.** SWC (Speedy Web Compiler) is a high-performance TypeScript/JavaScript compiler written in Rust and hosted at `swc-project/swc`. Setting up a local development environment involves configuring the Rust toolchain, managing JavaScript dependencies, and understanding the workspace structure defined in the root [`Cargo.toml`](https://github.com/swc-project/swc/blob/main/Cargo.toml). This guide walks you through the exact steps required to build the project, run tests, and validate changes against downstream JavaScript projects. ## Fork and Clone the Repository SWC follows a standard fork-and-pull-request workflow. Start by forking the repository on GitHub, then clone your fork locally and create a feature branch off `main`. ```bash git clone https://github.com/YOUR_USERNAME/swc.git cd swc git checkout -b feature/your-change-name ``` ## Install Required Development Tools The SWC codebase requires both Rust and Node.js ecosystem tools to build and test properly. ### Rust Toolchain You need the **stable Rust** compiler to build the core crates. Install it via rustup: ```bash curl --proto '=https' --tlsv1.2 -sSf https://rustup.rs | sh ``` You must also add the WebAssembly target for running certain tests: ```bash rustup target add wasm32-wasip1 ``` ### System Dependencies - **make**: Required for build helper scripts (pre-installed on most Unix systems; Windows users should install MinGW/MSYS2) - **C/C++ compiler**: `gcc` or `clang` on Linux/macOS, MSVC on Windows, needed for building native crates ### JavaScript Package Manager Install **pnpm** to manage JavaScript dependencies in the `bindings/` directory: ```bash npm install -g pnpm ``` ### Optional Tools - **fd**: A fast file finder used by git hooks, installable via `cargo install fd-find` - **deno**: Required only for running Deno-specific test fixtures ## Initialize the Repository After cloning, you must pull the ECMAScript test suites and install JavaScript dependencies: ```bash git submodule update --init --recursive pnpm install ``` This populates the test fixtures and prepares the `@swc/core` package bindings. ## Configure Environment Variables Set these variables in your shell to ensure full stack traces and proper binary discovery: ```bash export RUST_BACKTRACE=full export PATH="$PATH:$PWD/node_modules/.bin" export RUST_MIN_STACK=16777216 ``` The `RUST_MIN_STACK` variable prevents stack overflow errors during deep recursive parsing, while updating `PATH` makes the locally built `@swc/core` binary discoverable by the test harness. ## Build and Run Tests SWC maintains two parser implementations selectable via feature flags. You must choose which feature set matches your code changes when running tests. ### Running the Full Test Suite For the original parser implementation: ```bash cargo test --all --no-default-features --features swc_v1 --features filesystem_cache ``` For the newer parser implementation: ```bash cargo test --all --no-default-features --features swc_v2 --features filesystem_cache ``` ### Testing Individual Crates If the full suite is too heavy for rapid iteration, run tests for a specific crate. For example, to test only the ECMAScript transforms: ```bash cargo test -p swc_ecma_transforms --all-features ``` The test harness uses helper utilities from [`crates/testing/src/lib.rs`](https://github.com/swc-project/swc/blob/main/crates/testing/src/lib.rs) to compare input and output fixtures. ## Test Changes Against Downstream Projects To validate your Rust changes in a real JavaScript project that consumes `@swc/core`, use the provided patch script at [`scripts/patch-project.sh`](https://github.com/swc-project/swc/blob/main/scripts/patch-project.sh): ```bash ./scripts/patch-project.sh /path/to/your/js/project ``` This script performs three actions: 1. Patches [`bindings/Cargo.toml`](https://github.com/swc-project/swc/blob/main/bindings/Cargo.toml) to point to your local build 2. Rebuilds the Rust bindings 3. Updates the downstream project's [`package.json`](https://github.com/swc-project/swc/blob/main/package.json) to reference the locally built package To revert the changes after testing: ```bash git restore bindings/Cargo.toml bindings/Cargo.lock ``` Then restore the original `@swc/core` entry in your downstream project's [`package.json`](https://github.com/swc-project/swc/blob/main/package.json). ## Submit Your Contribution Push your branch to your fork and open a pull request against `swc-project/swc:main`. The CI system will run the full test suite on your branch before merging. For architectural guidance, consult [`ARCHITECTURE.md`](https://github.com/swc-project/swc/blob/main/ARCHITECTURE.md) in the repository root, which details the module layout and data flow between the parser, transformer, and code generator. ## Contribute to Documentation Documentation fixes for `https://swc.rs` do not belong in the main repository. Each page on the website contains an "Edit this page on GitHub" link that points to the separate **website** repository. Edit the Markdown files there and submit your PR to the documentation repo instead. ## Summary - **Fork** the `swc-project/swc` repository and create a feature branch off `main` - **Install** Rust (stable), pnpm, make, and a C/C++ compiler, plus the `wasm32-wasip1` target - **Initialize** submodules with `git submodule update --init --recursive` and run `pnpm install` - **Export** required environment variables including `RUST_BACKTRACE=full` and `RUST_MIN_STACK=16777216` - **Test** using `cargo test` with `--features swc_v1` or `--features swc_v2` depending on which parser you are modifying - **Validate** locally against JavaScript projects using [`./scripts/patch-project.sh`](https://github.com/swc-project/swc/blob/main/./scripts/patch-project.sh) - **Reference** [`CONTRIBUTING.md`](https://github.com/swc-project/swc/blob/main/CONTRIBUTING.md) and [`ARCHITECTURE.md`](https://github.com/swc-project/swc/blob/main/ARCHITECTURE.md) for detailed contribution guidelines ## Frequently Asked Questions ### Do I need to install Deno to contribute to SWC? No, Deno is only required for running Deno-specific test fixtures. You can contribute to the core Rust compiler and JavaScript bindings without installing Deno, though you should install it if you are modifying code that affects Deno compatibility. ### How do I test my local SWC changes in a JavaScript project? Use the [`scripts/patch-project.sh`](https://github.com/swc-project/swc/blob/main/scripts/patch-project.sh) script to temporarily replace the npm package `@swc/core` in your target project with your local build. The script modifies [`bindings/Cargo.toml`](https://github.com/swc-project/swc/blob/main/bindings/Cargo.toml), rebuilds the native bindings, and updates the downstream [`package.json`](https://github.com/swc-project/swc/blob/main/package.json) to point to your local build artifacts. ### What is the difference between the swc_v1 and swc_v2 test features? `swc_v1` enables the original SWC parser, while `swc_v2` activates the newer parser implementation. You must pass the corresponding feature flag to `cargo test` depending on which parser code your changes affect. Both require the `filesystem_cache` feature for full test suite compatibility. ### Where should I submit documentation fixes? Documentation for the SWC website lives in a separate repository from the main compiler. Click the "Edit this page on GitHub" link on any page at `https://swc.rs` to navigate directly to the source file in the website repository, then submit your pull request there.