feat(eslint-plugin): Add new config "eslint-recommended" (#488)

packages/eslint-plugin/src/configs/README.md

@@ -6,6 +6,19 @@ These configs exist for your convenience. They contain configuration intended to
 
 TODO when all config is added.
 
+## eslint-recommended
+
+The `eslint-recommended` ruleset is meant to be used after extending `eslint:recommended`. It disables rules that are already checked by the Typescript compiler and enables rules that promote using more the more modern constructs Typescript allows for.
+
+```cjson
+{
+  "extends": [
+    "eslint:recommended",
+    "plugin:@typescript-eslint/eslint-recommended"
+  ]
+}
+```
+
 ## Recommended
 
 The recommended set is an **_opinionated_** set of rules that we think you should use because:

packages/eslint-plugin/src/configs/eslint-recommended.ts

@@ -0,0 +1,49 @@
+/**
+ * The goal of this ruleset is to update the eslint:recommended config to better
+ * suit Typescript. There are two main reasons to change the configuration:
+ * 1. The Typescript compiler natively checks some things that therefore don't
+ *    need extra rules anymore.
+ * 2. Typescript allows for more modern Javascript code that can thus be
+ *    enabled.
+ */
+export default {
+  overrides: [
+    {
+      files: ['*.ts', '*.tsx'],
+      rules: {
+        /**
+         * 1. Disable things that are checked by Typescript
+         */
+        //Checked by Typescript - ts(2378)
+        'getter-return': false,
+        // Checked by Typescript - ts(2300)
+        'no-dupe-args': false,
+        // Checked by Typescript - ts(1117)
+        'no-dupe-keys': false,
+        // Checked by Typescript - ts(7027)
+        'no-unreachable': false,
+        // Checked by Typescript - ts(2367)
+        'valid-typeof': false,
+        // Checked by Typescript - ts(2588)
+        'no-const-assign': false,
+        // Checked by Typescript - ts(2588)
+        'no-new-symbol': false,
+        // Checked by Typescript - ts(2376)
+        'no-this-before-super': false,
+        // This is checked by Typescript using the option `strictNullChecks`.
+        'no-undef': false,
+        /**
+         * 2. Enable more ideomatic code
+         */
+        // Typescript allows const and let instead of var.
+        'no-var': 'error',
+        'prefer-const': 'error',
+        // The spread operator/rest parameters should be prefered in Typescript.
+        'prefer-rest-params': 'error',
+        'prefer-spread': 'error',
+        // This is already checked by Typescript.
+        'no-dupe-class-members': 'error',
+      },
+    },
+  ],
+};

packages/eslint-plugin/src/index.ts

@@ -2,6 +2,7 @@ import requireIndex from 'requireindex';
 import path from 'path';
 
 import recommended from './configs/recommended.json';
+import eslintRecommended from './configs/eslint-recommended';
 
 const rules = requireIndex(path.join(__dirname, 'rules'));
 // eslint expects the rule to be on rules[name], not rules[name].default
@@ -18,5 +19,6 @@ export = {
   rules: rulesWithoutDefault,
   configs: {
     recommended,
+    eslintRecommended,
   },
 };