prettier/CONTRIBUTING.md

# Contributing to Prettier

To get up and running, install the dependencies and run the tests:

```
yarn
yarn lint
yarn test
```

Here's what you need to know about the tests:

* The tests uses [Jest](https://facebook.github.io/jest/) snapshots.
* You can make changes and run `jest -u` (or `yarn test -u`) to update the
  snapshots. Then run `git diff` to take a look at what changed. Always update
  the snapshots when opening a PR.
* You can run `AST_COMPARE=1 jest` for a more robust test run. That formats each
  file, re-parses it, and compares the new AST with the original one and makes
  sure they are semantically equivalent.
* Each test folder has a `jsfmt.spec.js` that runs the tests. Normally you can
  just put `run_spec(__dirname);` there. You can also pass options and
  additional parsers, like this:
  `run_spec(__dirname, { trailingComma: "es5" }, ["babylon"]);`
* `tests/flow/` contains the Flow test suite, and is not supposed to be edited
  by hand. To update it, clone the Flow repo next to the Prettier repo and run:
  `node scripts/sync-flow-tests.js ../flow/tests/`.
* If you would like to debug prettier locally, you can either debug it in node
  or the browser. The easiest way to debug it in the browser is to run the
  interactive `docs` REPL locally. The easiest way to debug it in node, is to
  create a local test file and run it in an editor like VS Code.

Run `yarn lint --fix` to automatically format files.

If you can, take look at [commands.md](commands.md) and check out [Wadler's
paper](http://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf) to
understand how Prettier works.

If you want to know more about Prettier's GitHub labels, see the
[Issue Labels](https://github.com/prettier/prettier/wiki/Issue-Labels)
page on the Wiki.