feature #774 feat: add support for ESLint 7, drop support ESLint 5 (K…

…ocal)

This PR was squashed before being merged into the main branch.

Discussion
----------

feat: add support for ESLint 7, drop support ESLint 5

- bump eslint from `^5.15.2 || ^6.0.0` to `^6.0.0 || ^7.0.0`: https://eslint.org/blog/2020/05/eslint-v7.0.0-released
- bump eslint-loader from `^3.0.0` to `^4.0.0`, which drop support for Node <10.13.0 and set minimum ESLint support to version 6: https://github.com/webpack-contrib/eslint-loader/blob/master/CHANGELOG.md#400-2020-04-03
- had to fix some linting issues

**EDIT:** Ok so ESLint 7 is not compatible with Node 11.
This version is in end of life ([End-of-Life releasese](https://github.com/nodejs/Release#end-of-life-releases), should we drop support for Node 11 too? And maybe add support for Node 13 and Node 14?
WDYT?

**EDIT 2:** PR opened at #775

**EDIT 3:** PR rebased since #775 has been merged

Commits
-------

5a1cfb6 feat: add support for ESLint 7, drop support ESLint 5

.eslintrc.js

@@ -1,3 +1,12 @@
+/*
+ * This file is part of the Symfony Webpack Encore package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
 module.exports = {
     "root": true,
     "plugins": ["node", "header"],
@@ -39,7 +48,7 @@ module.exports = {
             "after": true
         }],
         "no-console": "off",
-        "valid-jsdoc": ["error", {"requireParamDescription": false, "requireReturnDescription": false}],
+        "valid-jsdoc": ["error", { "requireParamDescription": false, "requireReturnDescription": false }],
         "node/no-unsupported-features": ["error", { version: 8 }],
         "node/no-deprecated-api": "error",
         "node/no-missing-import": "error",
@@ -54,6 +63,14 @@ module.exports = {
         "node/no-unpublished-bin": "error",
         "node/no-unpublished-require": "error",
         "node/process-exit-as-throw": "error",
-        "header/header": [2, "block", {"pattern": "This file is part of the Symfony Webpack Encore package"}]
-    }
+        "header/header": [2, "block", { "pattern": "This file is part of the Symfony Webpack Encore package" }]
+    },
+    "overrides": [
+        {
+            "files": [".eslintrc.js"],
+            "rules": {
+                "quotes": ["error", "double"],
+            },
+        }
+    ],
 };

lib/loaders/eslint.js

@@ -12,7 +12,6 @@
 const WebpackConfig = require('../WebpackConfig'); //eslint-disable-line no-unused-vars
 const loaderFeatures = require('../features');
 const applyOptionsCallback = require('../utils/apply-options-callback');
-const logger = require('../logger');
 
 function isMissingConfigError(e) {
     if (!e.message || !e.message.includes('No ESLint configuration found')) {
@@ -36,13 +35,7 @@ module.exports = {
         });
 
         try {
-            if (typeof engine.getConfigForFile === 'function') {
-                logger.debug('Checking ESLint 6+ configuration...');
-                engine.getConfigForFile('webpack.config.js');
-            } else {
-                logger.debug('Checking ESLint 5 configuration...');
-                engine.config.getConfigHierarchy(webpackConfig.runtimeConfig.context);
-            }
+            engine.getConfigForFile('webpack.config.js');
         } catch (e) {
             if (isMissingConfigError(e)) {
                 const chalk = require('chalk');

package.json

@@ -5,7 +5,7 @@
   "main": "index.js",
   "scripts": {
     "test": "mocha --reporter spec test --recursive",
-    "lint": "eslint lib test index.js",
+    "lint": "eslint lib test index.js .eslintrc.js",
     "travis:lint": "npm run lint"
   },
   "bin": {
@@ -72,8 +72,8 @@
     "chai-fs": "^2.0.0",
     "chai-subset": "^1.6.0",
     "core-js": "^3.0.0",
-    "eslint": "^5.15.2 || ^6.0.0",
-    "eslint-loader": "^3.0.0",
+    "eslint": "^6.0.0 || ^7.0.0",
+    "eslint-loader": "^4.0.0",
     "eslint-plugin-header": "^1.0.0",
     "eslint-plugin-import": "^2.8.0",
     "eslint-plugin-node": "^8.0.1",

test/.eslintrc.js

@@ -1,3 +1,12 @@
+/*
+ * This file is part of the Symfony Webpack Encore package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
 module.exports = {
     "env": {
         "node": true,