Repository: swc-project/swc
Stars: 33357
CLAUDE.md
AI Agent Rules
When working in a specific directory, apply the rules from that directory and all parent directories up to the root.
While working on .
Source: AGENTS.md
Instructions
General rule
- Read the codebase - the codebase is source of truth, and you should prefer reading lots of source code over searching.
- Do not search web unless explicitly asked to do so. Web search does not help in general for our project.
- Write performant code. Always prefer performance over other things.
- Use gh CLI tool for fetching data from github.com.
Code style
- Write comments and documentations in English.
- Write documentation for your code.
- Commit your work as frequent as possible using git. Do NOT use --no-verify flag.
- Prefer multiple small files over single large file.
---
- When creating Atom instances, it's better to use Cow<str> or &str instead of String. Note that &str is better than Cow<str> here.
Testing
- Write unit tests for your code.
- Prefer fixture tests over inline (#[test]) tests.
- You can do UPDATE=1 cargo test to get test outputs updated for fixture tests.
- When instructed to fix tests, do not remove or modify existing tests.
Fixture Test Common Guide
- Add new coverage by extending existing fixture suites instead of adding ad-hoc inline tests.
- Find the exact fixture harness before adding files with: rg -n "#\(testing::)?fixture\(" tests src --glob "*.rs".
- Keep each suite's naming conventions (for example: input., output., exec.*, .ans).
- For snapshot-style tests, update expected outputs with UPDATE=1 cargo test -p ... using the exact crate command documented in each crate's AGENTS.md.
- Always rerun the same crate tests without UPDATE before finishing.
Verification
- Before finishing a task, always run this baseline locally.
- cargo fmt --all
- cargo clippy --all --all-targets -- -D warnings
- For each touched Rust crate, run crate-level verification locally.
- cargo test -p <crate>
- If wasm binding packages are touched, run:
- (cd bindings/binding_core_wasm && ./scripts/test.sh)
- (cd bindings/binding_minifier_wasm && ./scripts/test.sh)
- (cd bindings/binding_typescript_wasm && ./scripts/test.sh)
- (cd bindings/binding_es_ast_viewer && ./scripts/test.sh)
- If node bindings or integration paths are touched, run:
- (cd packages/core && yarn build:dev && yarn test)
Compatibility rule
- Do not use unstable, nightly only features of rustc.
---
While working on crates/jsdoc
Source: crates/jsdoc/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixtures.
- Update generated fixture outputs with: UPDATE=1 cargo test -p jsdoc.
- Verify without UPDATE before finishing: cargo test -p jsdoc.
---
While working on crates/swc
Source: crates/swc/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/errors, tests/exec, tests/minify, tests/typescript, tests/vercel, tests/stacktrace, tests/babel-exec.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc.
- Verify without UPDATE before finishing: cargo test -p swc.
---
While working on crates/swc_bundler
Source: crates/swc_bundler/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/deno-exec.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_bundler.
- Verify without UPDATE before finishing: cargo test -p swc_bundler.
---
While working on crates/swc_core
Source: crates/swc_core/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_core.
- Verify without UPDATE before finishing: cargo test -p swc_core.
---
While working on crates/swc_css_codegen
Source: crates/swc_css_codegen/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/options, ../swc_css_parser/tests/fixture.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_css_codegen.
- Verify without UPDATE before finishing: cargo test -p swc_css_codegen.
---
While working on crates/swc_css_compat
Source: crates/swc_css_compat/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/nesting, tests/custom-media-query, tests/media-query-ranges, tests/color-hex-alpha, tests/color-legacy, tests/selector-not, tests/color-hwb, tests/all.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_css_compat.
- Verify without UPDATE before finishing: cargo test -p swc_css_compat.
---
While working on crates/swc_css_lints
Source: crates/swc_css_lints/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/rules/pass, tests/rules/fail.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_css_lints.
- Verify without UPDATE before finishing: cargo test -p swc_css_lints.
---
While working on crates/swc_css_minifier
Source: crates/swc_css_minifier/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_css_minifier.
- Verify without UPDATE before finishing: cargo test -p swc_css_minifier.
---
While working on crates/swc_css_modules
Source: crates/swc_css_modules/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/with-compat.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_css_modules.
- Verify without UPDATE before finishing: cargo test -p swc_css_modules.
---
While working on crates/swc_css_parser
Source: crates/swc_css_parser/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/line-comment, tests/recovery, tests/recovery-cssmodules.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_css_parser.
- Verify without UPDATE before finishing: cargo test -p swc_css_parser.
---
While working on crates/swc_css_prefixer
Source: crates/swc_css_prefixer/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_css_prefixer.
- Verify without UPDATE before finishing: cargo test -p swc_css_prefixer.
---
While working on crates/swc_ecma_codegen
Source: crates/swc_ecma_codegen/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/str-lits, ../swc_ecma_parser/tests/test262-parser/pass.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_codegen.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_codegen.
---
While working on crates/swc_ecma_lints
Source: crates/swc_ecma_lints/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/pass.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_lints.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_lints.
---
While working on crates/swc_ecma_minifier
Source: crates/swc_ecma_minifier/AGENTS.md
Instructions
- You can run execution tests by doing ./scripts/exec.sh to see if your changes are working.
- If an execution test fails, you are wrong.
- Always run execution tests after making changes.
- You can run fixture tests by doing ./scripts/test.sh, and you can do UPDATE=1 ./scripts/test.sh to update fixtures.
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/terser, tests/mangle, tests/pass-1, tests/pass-default, tests/full, tests/projects, benches/full.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_minifier.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_minifier.
---
While working on crates/swc_ecma_parser
Source: crates/swc_ecma_parser/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/js, tests/jsx, tests/typescript, tests/typescript-errors, tests/errors, tests/comments, tests/span, tests/shifted.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_parser.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_parser.
---
While working on crates/swc_ecma_preset_env
Source: crates/swc_ecma_preset_env/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixtures.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_preset_env.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_preset_env.
---
While working on crates/swc_ecma_transformer
Source: crates/swc_ecma_transformer/AGENTS.md
Instructions
- The Transformer must implement VisitMut and execute the VisitMutHooks of its subtypes.
- Other types like ES20xx or transforms for specific syntax MUST NOT implement VisitMut.
- Subtypes must implement VisitMutHook<TraverseCtx>.
- Before starting work, read $repositoryRoot/crates/swc_ecma_hooks/src/.
---
While working on crates/swc_ecma_transforms
Source: crates/swc_ecma_transforms/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_transforms.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_transforms.
---
While working on crates/swc_ecma_transforms_base
Source: crates/swc_ecma_transforms_base/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/resolver, tests/ts-resolver, ../swc_ecma_parser/tests.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_transforms_base.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_transforms_base.
---
While working on crates/swc_ecma_transforms_compat
Source: crates/swc_ecma_transforms_compat/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/arrow, tests/async-to-generator, tests/block-scoping, tests/class-properties, tests/class_fields_use_set, tests/classes, tests/destructuring, tests/for-of, tests/new-target, tests/object-rest-spread, tests/optional-chaining, tests/optional-chaining-loose, tests/parameters, tests/private-in-object, tests/shorthand_properties, tests/static-blocks.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_transforms_compat.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_transforms_compat.
---
While working on crates/swc_ecma_transforms_module
Source: crates/swc_ecma_transforms_module/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/paths.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_transforms_module.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_transforms_module.
---
While working on crates/swc_ecma_transforms_optimization
Source: crates/swc_ecma_transforms_optimization/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/const-modules, tests/dce, tests/dce-jsx, tests/expr-simplifier.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_transforms_optimization.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_transforms_optimization.
---
While working on crates/swc_ecma_transforms_proposal
Source: crates/swc_ecma_transforms_proposal/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/decorators, tests/explicit-resource-management.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_transforms_proposal.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_transforms_proposal.
---
While working on crates/swc_ecma_transforms_react
Source: crates/swc_ecma_transforms_react/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/jsx/fixture, tests/integration/fixture, tests/script/jsx/fixture.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_transforms_react.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_transforms_react.
---
While working on crates/swc_ecma_transforms_typescript
Source: crates/swc_ecma_transforms_typescript/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, ../swc_ecma_parser/tests/tsc, ../swc_ecma_parser/tests/typescript.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ecma_transforms_typescript.
- Verify without UPDATE before finishing: cargo test -p swc_ecma_transforms_typescript.
---
While working on crates/swc_error_reporters
Source: crates/swc_error_reporters/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_error_reporters.
- Verify without UPDATE before finishing: cargo test -p swc_error_reporters.
---
While working on crates/swc_estree_compat
Source: crates/swc_estree_compat/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixtures, tests/flavor/acorn/fixtures.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_estree_compat.
- Verify without UPDATE before finishing: cargo test -p swc_estree_compat.
---
While working on crates/swc_html_codegen
Source: crates/swc_html_codegen/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/document_fragment, tests/options, ../swc_html_parser/tests/fixture.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_html_codegen.
- Verify without UPDATE before finishing: cargo test -p swc_html_codegen.
---
While working on crates/swc_html_minifier
Source: crates/swc_html_minifier/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/document_fragment, tests/recovery.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_html_minifier.
- Verify without UPDATE before finishing: cargo test -p swc_html_minifier.
---
While working on crates/swc_html_parser
Source: crates/swc_html_parser/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/recovery, tests/iframe_srcdoc, tests/html5lib-tests-fixture, tests/html5lib-tests.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_html_parser.
- Verify without UPDATE before finishing: cargo test -p swc_html_parser.
---
While working on crates/swc_node_bundler
Source: crates/swc_node_bundler/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/pass.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_node_bundler.
- Verify without UPDATE before finishing: cargo test -p swc_node_bundler.
---
While working on crates/swc_plugin_backend_tests
Source: crates/swc_plugin_backend_tests/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, ../swc_ecma_parser/tests/tsc.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_plugin_backend_tests.
- Verify without UPDATE before finishing: cargo test -p swc_plugin_backend_tests.
---
While working on crates/swc_ts_fast_strip
Source: crates/swc_ts_fast_strip/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/errors, ../swc_ecma_parser/tests/tsc.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_ts_fast_strip.
- Verify without UPDATE before finishing: cargo test -p swc_ts_fast_strip.
---
While working on crates/swc_typescript
Source: crates/swc_typescript/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests//.ts, tests//.tsx.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_typescript.
- Verify without UPDATE before finishing: cargo test -p swc_typescript.
---
While working on crates/swc_xml_codegen
Source: crates/swc_xml_codegen/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/options, ../swc_xml_parser/tests/fixture, ../swc_xml_parser/tests/recovery.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_xml_codegen.
- Verify without UPDATE before finishing: cargo test -p swc_xml_codegen.
---
While working on crates/swc_xml_parser
Source: crates/swc_xml_parser/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/fixture, tests/recovery.
- Update generated fixture outputs with: UPDATE=1 cargo test -p swc_xml_parser.
- Verify without UPDATE before finishing: cargo test -p swc_xml_parser.
---
While working on crates/testing_macros
Source: crates/testing_macros/AGENTS.md
Fixture Test Addition Guide
- Preferred fixture roots in this crate: tests/simple, tests/ignore.
- Update generated fixture outputs with: UPDATE=1 cargo test -p testing_macros.
- Verify without UPDATE before finishing: cargo test -p testing_macros.
README.md
<p align="center">
<a href="https://swc.rs/">
<img alt="swc" src="https://raw.githubusercontent.com/swc-project/logo/master/swc.png" width="546">
</a>
</p>
<p align="center">
Make the web (development) faster.
</p>
<p align="center">
<a href="https://www.npmjs.com/package/@swc/core"><img alt="downloads (@swc/core)" src="https://img.shields.io/npm/dm/@swc/core?label=downloads%20%28%40swc%2Fcore%29"></a>
<a href="https://www.npmjs.com/package/@swc/counter?activeTab=dependents"><img alt="downloads (3rd party)" src="https://img.shields.io/npm/dm/@swc/counter?label=downloads%20%283rd%20party%29"></a>
</p>
<p align="center">
<a href="https://crates.io/crates/swc_ecma_parser"><img alt="undefined" src="https://img.shields.io/crates/d/swc_ecma_parser.svg?label=crates.io%20downloads"></a>
<a href="https://github.com/swc-project/swc/releases/latest"><img alt="GitHub release (latest SemVer)" src="https://img.shields.io/github/v/release/swc-project/swc"></a>
</p>
<p align="center">
<img alt="GitHub code size in bytes" src="https://img.shields.io/github/languages/code-size/swc-project/swc">
<a href="https://github.com/swc-project/swc/blob/main/package.json#L22"><img alt="node-current (scoped)" src="https://img.shields.io/node/v/@swc/core"></a>
</p>
<p align="center">
<a href="https://discord.com/invite/GnHbXTdZz6"><img alt="Discord" src="https://img.shields.io/discord/889779439272075314"></a>
</p>
SWC (stands for Speedy Web Compiler) is a super-fast TypeScript / JavaScript compiler written in Rust. It's a library for Rust and JavaScript at the same time. If you are using SWC from Rust, see [rustdoc and for most users, your entry point for using the library will be parser.
Also, SWC tries to ensure that
If you select the latest version of each crates, it will work
for rust users.
MSRV of crates is currently 1.73.
To update all SWC crates you use, you can run curl https://raw.githubusercontent.com/swc-project/swc/main/scripts/update-all-swc-crates.sh | bash -s. This script will update all dependencies to the latest version and run cargo build to ensure that everything works.
Note that you need
- jq
- cargo upgrade
command to run the script.
Supported Node Versions:
- Node v10+ for usage
- Node v20+ for development
---
If you are using SWC from JavaScript, please refer to docs on the website.
Documentation
Check out the documentation in the website.
Features
Please see comparison with babel.
Performance
Please see benchmark results on the website.
Supporting development
<h2 align="center">Supporting swc</h2>
Star History
Powered by
Sponsors
<p align="center">
<a href="https://opencollective.com/swc">
<img src="https://raw.githubusercontent.com/swc-project/swc-sponsor-images/main/sponsors.svg" alt="Sponsors">
</a>
</p>
SWC is a community-driven project, and is maintained by a group of volunteers. If you'd like to help support the future of the project, please consider:
- Giving developer time on the project. (Message us on Discord (preferred) or Github discussions for guidance!)
- Giving funds by becoming a sponsor (see https://opencollective.com/swc)!
Contributing
See CONTRIBUTING.md. You may also find the architecture
documentation useful (ARCHITECTURE.md).
License
SWC is primarily distributed under the terms of the Apache License (Version 2.0).
See LICENSE for details.