Add eslint rules to match Firefox

[ianb]

I noticed some eslint failures on import. Because of that, and just for general conformity, we should use the same rules as the Firefox tree.

@Standard8: for you?

[pdehaan]

As close as I can figure, here's the mozilla-central .eslintrc.js config file:

"use strict";

module.exports = {
  // When adding items to this file please check for effects on sub-directories.
  "plugins": [
    "mozilla"
  ],
  "rules": {
    "mozilla/avoid-removeChild": "error",
    "mozilla/import-globals": "warn",
    "mozilla/no-import-into-var-and-global": "error",
    "mozilla/no-useless-parameters": "error",
    "mozilla/no-useless-removeEventListener": "error",
    "mozilla/use-default-preference-values": "error",
    "mozilla/use-ownerGlobal": "error",

    // No (!foo in bar) or (!object instanceof Class)
    "no-unsafe-negation": "error",
  },
  "env": {
    "es6": true
  },
  "parserOptions": {
    "ecmaVersion": 8,
  },
};

And digging further, here's the main source for the eslint-plugin-mozilla plugin:

"use strict";

/**
 * Based on npm coding standards at https://docs.npmjs.com/misc/coding-style.
 *
 * The places we differ from the npm coding style:
 *   - Commas should be at the end of a line.
 *   - Always use semicolons.
 *   - Functions should not have whitespace before params.
 */

module.exports = {
  "env": {
    "node": true
  },

  "rules": {
    "brace-style": ["error", "1tbs"],
    "camelcase": "error",
    "comma-dangle": ["error", "never"],
    "comma-spacing": "error",
    "comma-style": ["error", "last"],
    "curly": ["error", "multi-line"],
    "handle-callback-err": ["error", "er"],
    "indent": ["error", 2, {"SwitchCase": 1}],
    "max-len": ["error", 80, 2],
    "no-multiple-empty-lines": ["error", {"max": 1}],
    "no-undef": "error",
    "no-undef-init": "error",
    "no-unexpected-multiline": "error",
    "object-curly-spacing": "off",
    "one-var": ["error", "never"],
    "operator-linebreak": ["error", "after"],
    "semi": ["error", "always"],
    "space-before-blocks": "error",
    "space-before-function-paren": ["error", "never"],
    "keyword-spacing": "error",
    "strict": ["error", "global"],
  },

  // Globals accessible within node modules.
  "globals": {
    "DTRACE_HTTP_CLIENT_REQUEST": true,
    "DTRACE_HTTP_CLIENT_RESPONSE": true,
    "DTRACE_HTTP_SERVER_REQUEST": true,
    "DTRACE_HTTP_SERVER_RESPONSE": true,
    "DTRACE_NET_SERVER_CONNECTION": true,
    "DTRACE_NET_STREAM_END": true,
    "Intl": true,
  },
};

It's mildly unfortunate that the eslint-plugin-mozilla doesn't export a "recommended" config so we could easily just do something like this, but hey, what can you do...

extends:
  - eslint:recommended
  - plugin:mozilla/recommended

---

UPDATE: Filed plugin:mozilla/recommended request in bugzilla as 1347712.

[Standard8]

@ianb - we have two options:

1. Add a line to .eslintignorerc to ignore pageshot
2. Update pageshot's configuration to match .eslintrc.js and toolkit/.eslintrc.js in m-c (or create a recommended & import it etc).

If we do 1, then I'd say, at a minimum, we want to also add a few more rules to pageshot's configuration, especially no-undef (there's various helpers for this).

[ianb]

I'd like to just integrate the entire of the eslint config. My only concern is it tends to require a big diff that conflicts with other changes, so whoever does it should try to get it done quickly once they start.

[pdehaan]

In other interesting news, I can't get the latest eslint-plugin-mozilla versions to work at all.

I created https://github.com/pdehaan/eslint-mozilla yesterday and tried using latest versions and Node 6/7 and it just fails with some error about not being able to find eslint-plugin-mozilla (even though eslint and eslint-plugin-mozilla are both installed locally -- see below).

Interestingly, eslint-plugin-mozilla works in the mozilla/activity-stream repo, but it's an older version (eslint-plugin-mozilla@0.0.3). As soon as I update to eslint-plugin-mozilla@latest it starts failing with the following odd/vague error:

➜  activity-streams git:(master) ✗ $(npm bin)/eslint . --ext=.js,.jsx

Oops! Something went wrong! :(

ESLint couldn't find the plugin "eslint-plugin-mozilla". This can happen for a couple different reasons:

1. If ESLint is installed globally, then make sure eslint-plugin-mozilla is also installed globally. A globally-installed ESLint cannot find a locally-installed plugin.

2. If ESLint is installed locally, then it's likely that the plugin isn't installed correctly. Try reinstalling by running the following:

   npm i eslint-plugin-mozilla@latest --save-dev

If you still can't figure out the problem, please stop by https://gitter.im/eslint/eslint to chat with the team.

It looks like npm has the following published versions:

$ npm info eslint-plugin-mozilla versions
[ '0.0.3', '0.2.1', '0.2.3', '0.2.5', '0.2.28', '0.2.29' ]

Both eslint-plugin-mozilla@0.2.29 (latest) and eslint-plugin-mozilla@0.2.28 failed for me, but I did manage to get eslint-plugin@0.2.5 working locally in mozilla/activity-stream.

/cc @Standard8

[Standard8]

Ok, I'll bite, we've about 3 projects wanting to use something similar now, so it is time to come up with a better solution.

@pdehaan I thought 0.2.29 should have been working a bit better, but its possible that I missed something. I've got some ideas for how to make this work properly, so I'll start on those.

[pdehaan]

@Standard8: One small question. I seem to be stuck in eslint-plugin-mozilla/lib/environments/places-overlay.js:

var modules = require(path.join(root,
                                "tools", "lint", "eslint", "modules.json"));

This seems to be where my build is failing. I was hacking in my node_modules directly and did some garbage like this:

var root = helpers.getRootDir(module.filename);

var tmp = path.join(root, "tools", "lint", "eslint", "modules.json");

console.log(tmp);
// var modules = require(tmp);

var modules = [];

We're trying to do a dynamic require(), but logging out that tmp variable gives me the following:
/Users/pdehaan/dev/github/mozilla-services/pageshot/tools/lint/eslint/modules.json

I'm guessing that's why this is crashing hard, because I don't have a "tools/lint/eslint/modules.json" file in my Page Shot repo tree (but it looks like it's a path in the m-c repo: http://searchfox.org/mozilla-central/source/tools/lint/eslint/modules.json).

---

UPDATE: Submitted 1347709 in Bugzilla, like a big boy!