Thanks for being willing to contribute! 🙏

Working on your first Pull Request (PR)? You can learn how from this free series How to Contribute to an Open Source Project on GitHub.

Please check out the the open issues. Issues labelled Good First Issue are especially good to start with.

Contributing doesn’t have to be in code. Simply answering questions in open issues or providing workarounds is as important as making pull requests.

Pull requests are welcome for this repo!

Bugfixes will always be accepted, though in some cases some small changes may be requested.

However, if adding a feature or breaking change, please open an issue first to discuss. This ensures no time or work is wasted writing code that won’t be accepted to the project (see Project Goals). Undiscussed feature work may be rejected at the discretion of the maintainers.

1. Install pnpm
2. Fork this repo and clone your copy locally
3. Run pnpm i to install dependencies

Create a new branch for your PR with git checkout -b your-branch-name. Add the relevant code as well as docs and tests. When you push everything up (git push), navigate back to your repo in GitHub and you should see a prompt to open a new PR.

While best practices for commit messages are encouraged (e.g. start with an imperative verb, keep it short, use the body if needed), this repo doesn’t follow any specific guidelines. Clarity is favored over strict rules. Changelogs are generated separately from git (see the Changelogs section)

When working locally, run:

pnpm run dev

This will compile the code as you change automatically.

Working with the TypeScript AST can be daunting. Luckily, there’s astexplorer.net which makes it much more accessible. Rather than trying to build an AST from scratch (which is near impossible), instead:

1. Switch to the typescript parser in the top menu
2. Type out code in the left-hand panel
3. Inspect the right-hand panel to see what the desired AST is.

From there, you can refer to existing examples in the codebase. There may even be helper utilities in src/lib/ts.ts to make life easier.

Contributing to this library is hard-bordering-on-impossible without a test-driven development (TDD) strategy. If you’re new to this, the basic workflow is:

1. First, write a test that fully outlines what you’d like the output to be.
2. Next, make sure this test fails when you run npm test (yes, fails!)
3. Then, make changes to src/ until the tests pass.

Reasoning about code generation can be quite difficult until you “invert your thinking” and approach it output-first. Adopting TDD can turn very unclear/abstract problems into concrete ones with clear steps to resolution.

TL;DR: When starting any task, write a failing test first!

To add a schema as a snapshot test, modify the /scripts/download-schemas.ts script with a path to download. There are both single-file schemas as well as multi-file schemas.

It may be surprising to hear, but generating TypeScript types from OpenAPI is opinionated. Even though TypeScript and OpenAPI are close relatives—both JavaScript/JSON-based—they are nonetheless 2 different languages and thus there is room for interpretation. Further, some parts of the OpenAPI specification can be ambiguous on how they’re used, and what the expected type outcomes may be (though this is generally for more advanced use cases, such as specific implementations of anyOf as well as discriminator and complex polymorphism).

All that said, this library should strive to generate the most predictable TypeScript output for a given schema. And to achieve that, it always helps to open an issue or discussion to gather feedback.

When opening a pull request, make sure all of the following is done:

• Tests are added
• Build passes (npm run build)
• Tests pass (npm test)
• Linting passes (npm run lint)

Lastly, be sure to fill out the complete PR template.

The changelog is generated via changesets, and is separate from Git commit messages and pull request titles. To write a human-readable changelog for your changes, run:

npx changeset

This will ask if it’s a patch, minor, or major change (semver), along with a plain description of what you did. Commit this new file along with the rest of your PR, and during the next release this will go into the official changelog!

This library uses Vitest for testing. There’s a great VS Code extension you can optionally use if you’d like in-editor debugging tools.

💡 The tests test the production build in dist/. Be sure to run npm run build before running tests (or keep npm run dev running in the background, which compiles as-you-work)!

To run the entire test suite once, run:

pnpm test

To run an individual test:

pnpm test -- [partial filename]

To start the entire test suite in watch mode:

npx vitest

Linting is handled via Biome, a faster ESLint replacement. It was installed with pnpm i and can be run with:

pnpm run lint

⚠️ This may break tests if schemas have been updated

pnpm run update:examples

This library has both unit tests (tests that test a tiny part of a schema) and snapshot tests (tests that run over an entire, complete schema). When opening a PR, the former are more valuable than the latter, and are always required. However, updating snapshot tests can help with the following:

• Fixing Node.js or OS-related bugs
• Adding a CLI option that changes the entire output

For most PRs, snapshot tests can be avoided. But for scenarios similar to the ones mentioned, they can ensure everything is working as expected.

Some tests import the built package and not the source file. Be sure to run pnpm run build to build the project. You can also run pnpm run dev as you work so changes are always up-to-date.