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How to Contribute

We'd love to accept your patches and contributions to this project. There are just a few small guidelines you need to follow.

Contributor License Agreement

Contributions to this project must be accompanied by a Contributor License Agreement. You (or your employer) retain the copyright to your contribution; this simply gives us permission to use and redistribute your contributions as part of the project. Head over to https://cla.developers.google.com/ to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you've already submitted one (even if it was for a different project), you probably don't need to do it again.

Code reviews

All submissions, including submissions by project members, require review. We use GitHub pull requests for this purpose. Consult GitHub Help for more information on using pull requests.

Community Guidelines

This project follows Google's Open Source Community Guidelines.

Codebase

Before contributing to the code, get an overview of how Lighthouse works in the architecture documentation.

Monorepo

The codebase is organized in a typical monorepo setup using yarn workspaces and lerna. Individual packages are located in packages/* directories each with their own package.json, scripts, and tests. Running yarn at the repository root will create symlinks for all local packages in node_modules/@lhci meaning changes you make in packages/utils will automatically be used by require('@lhci/utils') in packages/cli without further build steps.

Dependencies

npm install -g yarn
yarn install # run in the repo root

Development Flow

When working on the CLI, simply make your changes to packages/cli or packages/utils files and run yarn start <LHCI arguments here>. No build step necessary.

When working on the server, you'll need to build. yarn build in root will build the server and viewer. Also, you can use watch mode.

yarn build:watch
yarn start:server

If you made any changes to the APIs of the server, you will need to restart the yarn start:server command, but UI changes should be picked up on refresh without restarting the server process. Once the server is up and running you can fill it with some test data with yarn start:seed-database.

Problems?

trash node_modules && yarn install
yarn build

Updating the Lighthouse Version

Updating the Lighthouse version used by LHCI involves more than a simple package.json update. When the Lighthouse version changes, it is usually a breaking change for Lighthouse CI (see version policy) and triggers many corresponding updates, including the following (Example PR):

  • Update the package.json version in @lhci/utils and @lhci/cli.
  • Run the new lighthouse version on a sufficiently complex URL (https://www.coursehero.com/ or https://www.theverge.com) and commit the LHR.
    • lighthouse https://www.coursehero.com/ --output=json > ./packages/server/test/fixtures/lh-7-0-0-coursehero-a.json
    • lighthouse https://www.coursehero.com/ --output=json > ./packages/server/test/fixtures/lh-7-0-0-coursehero-b.json
  • Add the new fixture LHRs to the tests.
    • packages/server/test/test-utils.js
    • packages/server/test/api/statistic-definitions.test.js
    • packages/server/src/ui/routes/build-view/lhr-comparison.stories.jsx
    • packages/server/src/ui/routes/build-view/audit-detail/audit-detail-pane.stories.jsx
  • Update the presets with any new or removed audits.
    • packages/utils/src/presets/all.js
  • Update test snapshots with yarn test:unit -u

Server Organization

The server has three primary components: the API, the UI, and cron jobs.

The API is a standard node express server. Code for the API lives in packages/server/src/api/.

The UI is written in preact and bundled with esbuild. Code for the UI lives in packages/server/src/ui/. This is the only part of Lighthouse CI that requires a build step in order to use.

The cron jobs are periodic tasks that run while the server is alive. Code for the cron jobs lives in packages/server/src/cron/.

Tests

Any non-trivial functionality should be accompanied by a test. jest is our test runner for unit and integration tests. Front-end components use storybook examples and/or end-to-end puppeteer tests that get run in the same steps as unit tests.

Typechecking is performed by TypeScript's checkJs option. All new code should leverage JSDoc type annotations and avoid the use of any.

yarn test:typecheck
yarn test:lint
yarn test:unit
yarn test # run all of the above

If working on MySQL or PostgreSQL support in the server, you'll need additional dependencies.

Example for MySQL:

brew install mysql
brew services start mysql
mysql -e "CREATE DATABASE IF NOT EXISTS lighthouse_ci_test;" -u root
mysql -e "GRANT ALL ON lighthouse_ci_test.* TO 'lhci'@'localhost';" -u root
mysql -e ALTER USER 'lhci'@'localhost' IDENTIFIED BY 'password';' -u root
export MYSQL_DB_URL="mysql://lhci:password@localhost/lighthouse_ci_test"
yarn test