puppeteer/docs/contributing.md

# Contributing

First of all, thank you for your interest in Puppeteer! We'd love to accept your
patches and contributions!

## 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.

## Getting started

1. Clone this repository

   ```sh
   git clone https://github.com/puppeteer/puppeteer
   cd puppeteer
   ```

2. Install the dependencies

   ```sh
   npm install # or PUPPETEER_PRODUCT=firefox npm install
   ```

3. Build all packages

   ```sh
   npm run build
   ```

4. Run all tests

   ```sh
   npm test
   ```

### macOS ARM and custom executables.

- To run experimental Chromium macOS ARM tests, firstly ensure you have correct
  Chromium version installed locally (you only need to do this once, not on
  every test run) and then you can run the tests:

  ```bash
  PUPPETEER_EXPERIMENTAL_CHROMIUM_MAC_ARM=1 npm install
  PUPPETEER_EXPERIMENTAL_CHROMIUM_MAC_ARM=1 npm run test
  ```

- To run tests with custom browser executable:

  ```bash
  BINARY=<path-to-chrome/firefox-executable> npm run test:chrome # Or npm run test:firefox
  ```

## Building a single package

To build a single package, you can run

```sh
npm run build --workspace <package> # e.g. puppeteer
```

This will build all dependent packages automatically, so specifying a single
packages is sufficient. This is all possible due to
[wireit](https://github.com/google/wireit) which behaves similar to
[GNU Make](https://www.gnu.org/software/make/).

## Removing stale artifacts

It's possible some generated artifacts (such as
`packages/puppeteer-core/src/types.ts`) can become stale since these artifacts
rely on complex conditions (such as names of distinct files) that cannot be
captured by the build system. To clean artifacts, you can run

```sh
npm run clean # or npm run clean --workspace <package>
```

## Comprehensive testing

Outside of `npm test`, there are several other
[`npm` scripts](https://docs.npmjs.com/cli/v8/using-npm/scripts) that are
usually check through CI:

- `test-install` - Tests whether `puppeteer` and `puppeteer-core` install
  properly and are functional.
- `test-types` - Tests the TypeScript types in `puppeteer` using
  [`tsd`](https://github.com/SamVerschueren/tsd).
- `test:chrome:**` - Tests `puppeteer` on Chromium.
- `test:firefox:**` - Tests `puppeteer` on Firefox.

The default `npm test` runs `test:{chrome,firefox}:headless` which is generally
sufficient.

Puppeteer uses a custom test runner on top of Mocha that consults the
[TestExpectations.json](https://github.com/puppeteer/puppeteer/blob/main/test/TestExpectations.json)
to see if a given test result is expected or not. See more info about the test
runner in
[`tools/mochaRunner`](https://github.com/puppeteer/puppeteer/tree/main/tools/mochaRunner).

## Code reviews

All submissions, including submissions by project members, require review. We
use GitHub pull requests for this purpose. Consult
[GitHub Help](https://help.github.com/articles/about-pull-requests/) for more
information on using pull requests.

## Code Style

Our coding style is fully defined in
[`.eslintrc`](https://github.com/puppeteer/puppeteer/blob/main/.eslintrc.js)
([ESLint](https://eslint.org/)) and
[`.prettierrc.cjs`](https://github.com/puppeteer/puppeteer/blob/main/.prettierrc.cjs)
([Prettier](https://prettier.io)).

Code is checked during `pre-push` using
[Husky](https://typicode.github.io/husky/#/), but you can check your code
manually by running:

```bash
npm run lint
```

If some errors are returned, you can attempt to fix them using:

```bash
npm run format
```

## Project structure

The following is a description of the primary folders in Puppeteer:

- `packages` contains all public source code.
- `test` contains all test source code.
- `test-d` contains type tests using
  [`tsd`](https://github.com/SamVerschueren/tsd).
- `tools` contains miscellaneous scripts that are used in building and etc.
- `tools/mochaRunner` - contains the source code for our test runner.

## API guidelines

When authoring new API methods, consider the following:

- Expose as little information as needed. When in doubt, don’t expose new
  information.
- Methods are used in favor of getters/setters.
  - The only exception is namespaces, e.g. `page.keyboard` and `page.coverage`
- All string literals must be small case. This includes event names and option
  values.
- Avoid adding "sugar" API (API that is trivially implementable in user-space)
  unless they're **extremely** demanded.

## Commit messages

Commit messages should follow
[the Conventional Commits format](https://www.conventionalcommits.org/en/v1.0.0/#summary).
This is enforced via `npm run commitlint`.

In particular, breaking changes should clearly be noted as “BREAKING CHANGE:” in
the commit message footer. Example:

```
fix(page): fix page.pizza method

This patch fixes page.pizza so that it works with iframes.

Issues: #123, #234

BREAKING CHANGE: page.pizza now delivers pizza at home by default.
To deliver to a different location, use the "deliver" option:
  `page.pizza({deliver: 'work'})`.
```

## Writing documentation

Documentation is generated via `npm run docs`. It is automatically published to
our documentation site on merge and gets versioned on release.

## Writing TSDoc comments

Each change to Puppeteer should be thoroughly documented using TSDoc comments.
Refer to the
[API Extractor documentation](https://api-extractor.com/pages/tsdoc/doc_comment_syntax/)
for information on the exact syntax.

- Every new method needs to have either `@public` or `@internal` added as a tag
  depending on if it is part of the public API.
- Keep each line in a comment to no more than 90 characters (ESLint will warn
  you if you go over this). If you're a VSCode user the
  [Rewrap plugin](https://marketplace.visualstudio.com/items?itemName=stkb.rewrap)
  is highly recommended!

## Running the documentation site locally

1. At root, install all dependencies with `npm i --ignore-scripts`.
2. run `npm run docs` which will generate all the `.md` files on
   `puppeteer/docs/api`.
3. run `npm i` in `puppeteer/website`.
4. run `npm start` in `puppeteer/website`.

## Adding new dependencies

For all dependencies (both installation and development):

- **Do not add** a dependency if the desired functionality is easily
  implementable.
- If adding a dependency, it should be well-maintained and trustworthy.

A barrier for introducing new installation dependencies is especially high:

- **Do not add** installation dependency unless it's critical to project
  success.

There are additional considerations for dependencies that are environment
agonistic. See the
[`third_party/README.md`](https://github.com/puppeteer/puppeteer/blob/main/third_party/README.md)
for details.

## Testing tips

- Every feature should be accompanied by a test.
- Every public api event/method should be accompanied by a test.
- Tests should not depend on external services.
- Tests should work on all three platforms: Mac, Linux and Win. This is
  especially important for screenshot tests.

If a test is expected to fail on certain configurations or became flaky, update
[TestExpectations.json](https://github.com/puppeteer/puppeteer/blob/main/test/TestExpectations.json)
to reflect that. See more info about TestExpectations.json in
[`tools/mochaRunner`](https://github.com/puppeteer/puppeteer/tree/main/tools/mochaRunner).

## API Coverage

Every public API method or event should be called at least once in tests. To
ensure this, the main `test` command runs coverage during testing.

## Debugging Puppeteer

See [Debugging Tips](https://pptr.dev/guides/debugging).

# For Project Maintainers

## Rolling new Chromium version

The following steps are needed to update the Chromium version.

1. Find a suitable Chromium revision. Not all revisions have builds for all
   platforms, so we need to find one that does. The easiest way is to run
   `tools/check_availability.js -rd` to find the latest suitable `dev` Chromium
   revision (see `tools/check_availability.js -help` for more options).
2. Update `packages/puppeteer-core/src/revisions.ts` with the found revision
   number.
3. Update `versions.js` with the new Chromium-to-Puppeteer version mapping and
   update `lastMaintainedChromiumVersion` with the latest stable Chrome version.
   You can find the corresponding version by going to [omahaproxy.appspot.com](https://omahaproxy.appspot.com/) then
   searching in `Find Releases` for `r<revision>`.
4. Run `npm run check`. If it fails, update
   `packages/puppeteer-core/package.json` and `packages/puppeteer/package.json`
   with the expected `devtools-protocol` version.
5. Run `npm run clean`, `npm run build` and `npm install`.
6. Run `npm test` and ensure that all tests pass. If a test fails,
   [bisect](#bisecting-upstream-changes) the upstream cause of the failure, and
   either update the test expectations accordingly (if it was an intended
   change) or work around the changes in Puppeteer (if it’s not desirable to
   change Puppeteer’s observable behavior).
7. Commit and push your changes and open a pull request. The commit message must
   contain the version in `Chromium <version> (r<revision>)` format to ensure
   that [pptr.dev](https://pptr.dev/) can parse it correctly, e.g.
   `'feat(chromium): roll to Chromium 90.0.4427.0 (r856583)'`.

### Bisecting upstream changes

Sometimes, performing a Chromium roll causes tests to fail. To figure out the
cause, you need to bisect Chromium revisions to figure out the earliest possible
revision that changed the behavior. The `bisect` script can be helpful here.
Given a pattern for one or more unit tests, it will automatically bisect the
current range:

```sh
npm run bisect -- --good 686378 --bad 706915 script.js
npm run bisect -- --unit-test Response.fromCache
```

By default, it will use the Chromium revision in
`packages/puppeteer-core/src/revisions.ts` from the `main` branch and from the
working tree to determine the range to bisect.

## Releasing to npm

We use [release-please](https://github.com/googleapis/release-please) to
automate releases. When a release should be done, check for the release PR in
our [pull requests](https://github.com/puppeteer/puppeteer/pulls) and merge it.

### In case Release Please fails

<!-- TODO: Remove once release-please is fixed -->

In the event release-please fails, the following needs to be done:

1. Update anything missing in the CHANGELOG of every package that was supposed
   to be published. For example, if the header is missing, you may need to add

   - For puppeteer:

     ```md
     ## [{NEW_VERSION}](https://github.com/puppeteer/puppeteer/compare/v{PREVIOUS_VERSION}...v{NEW_VERSION}) ({CURRENT_DATE})`
     ```

   - For other packages:

     ```md
     ## [{NEW_VERSION}](https://github.com/puppeteer/puppeteer/compare/{PACKAGE_FOLDER_NAME}-v{PREVIOUS_VERSION}...{PACKAGE_FOLDER_NAME}-v{NEW_VERSION}) ({CURRENT_DATE})
     ```

2. Create a GitHub release for each package, following the practice of previous
   releases.

## Bug triage guidelines

[Check incoming bug reports](https://github.com/puppeteer/puppeteer/issues) that do not have a `confirmed` or `needs-feedback` label:

1. Make sure the issue is labeled as either `bug` or `feature`.
2. If the issue does not have a clear repro or you cannot repro, ask for the repro and set the `needs-feedback` label.
3. Follow-up on the issues you previously asked for a feedback on (you should get a notification on GitHub when the user responds).
4. If the user does not provide feedback, the issue will be closed by the stale bot eventually.
5. If you are able to reproduce the issue, add the label `confirmed`.
6. If the bug is on the Chromium side, create a corresponding crbug.com issue, label the GitHub issue with the `upstream` label, and post a link to crbug.com in the comments.
7. If the issue is not related to either Puppeteer or Chromium, close the issue.
8. If the issue is about missing/incorrect documentation, label it as `documentation`.

Issues with PDFs:

1. If the issue reproduces using the regular print dialog and/or headful, [file a crbug.com against the `Blink>Layout` component](https://bugs.chromium.org/p/chromium/issues/entry?components=Blink%3ELayout).
2. If the issue is specific to Headless mode, [file an issue on crbug.com against the `Internals>Headless` component](https://bugs.chromium.org/p/chromium/issues/entry?components=Internals%3EHeadless).