Issue 3692 - Add arrow-parens ESLint rule

eslint-config-eyeo/index.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 /* eslint-env commonjs */
 
 "use strict";
 
 module.exports = {
   extends: "eslint:recommended",
   env: {
     es6: true
   },
   rules: {
     "array-bracket-spacing": "error",
+    "arrow-parens": "error",

[Wladimir Palant, 2017/03/02 10:03:29]

Going through adblockplus and adblockpluscore repositories, the use of
parentheses for single-parameter arrow functions is inconsistent with a tendency
towards no parentheses. I think this might be the result of my personal
preferences changing over time. In adblockpluschrome no parentheses are being
used very consistently.

I don't really see a case for enforcing parentheses from our existing codebase.
I also don't see how it improves readability or prevents bugs. So this is
clearly NOT LGTM to me. My preferred solution would be to leave this rule out
and keep allowing personal preferences here since they don't affect anything. If
we want this to be uniform however, I'd vote for the "as-needed" setting.

Maybe Thomas can help me understand how this is going to improve the quality of
our code.

     "arrow-spacing": "error",
     "block-scoped-var": "error",
     "block-spacing": "error",
     "brace-style": ["error", "allman", {allowSingleLine: true}],
     "camelcase": ["error", {properties: "never"}],
     "comma-dangle": "error",
     "comma-spacing": "error",
     "comma-style": "error",
     "computed-property-spacing": "error",
     "curly": ["error", "multi-or-nest"],
@@ skipping 67 matching lines @@
     "strict": ["error", "global"],
     "valid-jsdoc": ["error", {
       requireParamDescription: false,
       requireReturn: false,
       requireReturnDescription: false
     }],
     "yield-star-spacing": "error",
     "yoda": "error"
   }
 };