CONTRIBUTING.md

Contributing

Contributions are always welcome, no matter how large or small. Before contributing, please read the code of conduct.

Setup local env

To start developing on Babylon you only need to install its dependencies:

npm install

Tests

Running tests locally

To run a build, tests and perform lint/flow checks:

npm test

If you only want to run the tests:

npm run test-only

Note, this does not actually run a build, so you may have to call npm run build after performing any changes.

Checking code coverage locally

To generate code coverage, be sure to set BABEL_ENV=test so that code is instrumented during the rollup build.

BABEL_ENV=test npm run build && npm run test-ci

Writing tests

Writing tests for Babylon is very similar to Babel. Inside the tests/fixtures folder are categories/groupings of test fixtures (es2015, flow, etc.). To add a test, create a folder under one of these groupings (or create a new one) with a descriptive name, and add the following:

• Create an actual.js file that contains the code you want Babylon to parse.

• Add an expected.json file with the expected parser output. For added convenience, if there is no expected.json present, the test runner will generate one for you.

Cross repository changes

If you are making changes to Babylon which make it necessary to also change things in Babel you will want to link both repositories together. This can be done by doing the following (assuming you have both Babel and Babylon already checked out):

cd babylon/
npm link
npm run build
cd ../babel/
make bootstrap
npm link babylon
cd packages/babel-core/
npm link babylon
cd ../../packages/babel-template/
npm link babylon
cd ../../packages/babel-traverse/
npm link babylon
cd ../../packages/babel-generator/
npm link babylon
cd ../..
make build
make test

From now on Babel will use your local checkout of Babylon for its tests.