refactor: Reuse rule list

es5.js

@@ -1,20 +1,25 @@
 'use strict';
 
-module.exports = {
+const opinions = require('./lib/rules/opinions');
+const conventions = require('./lib/rules/opinions');
+const mistakes = require('./lib/rules/mistakes');
+
+module.exports = Object.assign({
+  env: {
+    es6: false,
+    node: true,
+  },
   parserOptions: {
-    sourceType: 'script',
     ecmaVersion: 5,
+    sourceType: 'script',
   },
-  rules: {
-    'no-param-reassign': 0,
-    'prefer-rest-params': 0,
-    'no-underscore-dangle': [2, { allowAfterThis: true }],
-    strict: [2, 'global'],
-    'comma-dangle': [2, {
-      arrays: 'always-multiline',
-      objects: 'always-multiline',
-      functions: 'never',
-    }],
-    'prefer-spread': 0,
-  }
-};
+  plugins: ['import', 'node', 'prettier'],
+  rules: Object.assign(opinions, conventions, mistakes, {
+    // Additional opinions
+
+    // Additional conventions
+
+    // Additional mistakes
+    'node/no-unsupported-features': [2, { version: 4 }],
+  })
+});

examples/eslint/node4/comma-dangle.js

@@ -1,17 +1,17 @@
 'use strict';
 
-function foo() { }
+function foo() {}
 
 // no comma-dangle for functions
 foo(
-  1,
-  2
+  'some very long argument to force line break',
+  'another very long argument to force line break'
 );
 
 // yes comma-dangle for arrays/objects
 foo([
-  1,
-  2,
+  'some very long argument to force line break',
+  'another very long argument to force line break',
 ]);
 foo({
   x: 1,

examples/eslint/node4/generator.js

@@ -1,4 +1,6 @@
 'use strict';
 
-function* foo() { yield 42; }
+function* foo() {
+  yield 42;
+}
 foo();

examples/eslint/node4/prefer-spread.js

@@ -1,6 +1,6 @@
 'use strict';
 
-function foo() { }
+function foo() {}
 
 const arr = [1, 2, 3];
 

lib/.eslintrc.js

@@ -0,0 +1,3 @@
+'use strict';
+
+module.exports = require('../node8.js');

lib/basics.js

@@ -0,0 +1,16 @@
+'use strict';
+
+/**
+ * Reasonable defaults for most lint settings
+ */
+module.exports = {
+  env: {
+    es6: true,
+    node: true,
+  },
+  parserOptions: {
+    ecmaVersion: 2017,
+    sourceType: 'script',
+  },
+  plugins: ['import', 'node', 'prettier'],
+};

lib/rules/conventions.js

@@ -0,0 +1,15 @@
+'use strict';
+
+/**
+ * Rules in this file have good reasons but don't prevent bugs.
+ *
+ * If any of the rules in here can't be fixed, they should at most warn.
+ * Not following conventions should not break builds, especially since they
+ * might be a moving target.
+ */
+module.exports = {
+  'no-underscore-dangle': ['warn', { allowAfterThis: true }],
+  'no-undef-init': 'off', // pending: Can't be auto-fixed
+  'import/no-dynamic-require': 'off', // pending: Can't be auto-fixed
+  strict: [2, 'global'],
+};

lib/rules/mistakes.js

@@ -0,0 +1,65 @@
+'use strict';
+
+/**
+ * Only things we are pretty sure are mistakes
+ *
+ * There should be a fairly high bar to end up in this list unless the issue
+ * can be fixed automatically. It's expected that each rule comes with a
+ * documented (class of) bug it prevents.
+ */
+module.exports = {
+  'no-debugger': 'error',
+  'no-empty': 'error',
+  'no-func-assign': 'error',
+  'no-template-curly-in-string': 'error',
+  'no-unreachable': 'error',
+  'no-unsafe-finally': 'error',
+  'use-isnan': 'error',
+  'no-unused-vars': [
+    'error',
+    { vars: 'all', args: 'after-used', ignoreRestSiblings: true },
+  ],
+  'no-use-before-define': [
+    'error',
+    { functions: true, classes: true, variables: true },
+  ],
+  'no-undef': 'error',
+  'no-shadow': 'error',
+  'no-label-var': 'error',
+  'no-delete-var': 'error',
+  'no-catch-shadow': 'off',
+
+  'import/no-unresolved': ['error', { commonjs: true, caseSensitive: true }],
+  'import/no-extraneous-dependencies': [
+    'error',
+    {
+      devDependencies: [
+        'test/**', // tape, common npm pattern
+        'tests/**', // also common npm pattern
+        'spec/**', // mocha, rspec-like pattern
+        '**/__tests__/**', // jest pattern
+        '**/*.test.{js,jsx}', // repos with inline test files
+        'test.{js,jsx}', // repos with a single test file
+        'test-*.{js,jsx}', // repos with multiple top-level test files
+        '**/*.{test,spec}.{js,jsx}', // tests where the extension denotes that it is a test
+        '**/jest.config.js', // jest config
+        '**/webpack.config.js', // webpack config
+        '**/webpack.config.*.js', // webpack config
+        '**/rollup.config.js', // rollup config
+        '**/rollup.config.*.js', // rollup config
+        '**/gulpfile.js', // gulp config
+        '**/gulpfile.*.js', // gulp config
+        '**/Gruntfile{,.js}', // grunt config
+        '**/protractor.conf.*.js', // protractor config
+
+        // Allow script & example files
+        'scripts/**',
+        'tasks/**',
+        'examples/**',
+        'example/**',
+      ],
+      optionalDependencies: true, // allow optional deps to be required
+    },
+  ],
+  'import/no-duplicates': 'error',
+};

lib/rules/opinions.js

@@ -0,0 +1,19 @@
+'use strict';
+
+/**
+ * Rules in this file are ultimately random choices.
+ *
+ * No human should have to type on a keyboard to comply.
+ * If it can't be --fix'ed, it doesn't belong in here.
+ */
+module.exports = {
+  'prettier/prettier': [
+    'error',
+    {
+      singleQuote: true,
+      trailingComma: 'es5',
+    },
+  ],
+  'lines-around-directive': ['error', 'always'],
+  'import/newline-after-import': 'error',
+};

node4.js

@@ -1,24 +1,18 @@
 'use strict';
 
-module.exports = {
-  parserOptions: {
-    ecmaVersion: 2017,
-    sourceType: 'script',
-  },
-  plugins: [
-    'node',
-  ],
-  rules: {
+const basics = require('./lib/basics');
+
+const opinions = require('./lib/rules/opinions');
+const conventions = require('./lib/rules/opinions');
+const mistakes = require('./lib/rules/mistakes');
+
+module.exports = Object.assign(basics, {
+  rules: Object.assign(opinions, conventions, mistakes, {
+    // Additional opinions
+
+    // Additional conventions
+
+    // Additional mistakes
     'node/no-unsupported-features': [2, { version: 4 }],
-    'no-param-reassign': 0,
-    'prefer-rest-params': 0,
-    'no-underscore-dangle': [2, { allowAfterThis: true }],
-    strict: [2, 'global'],
-    'comma-dangle': [2, {
-      arrays: 'always-multiline',
-      objects: 'always-multiline',
-      functions: 'never',
-    }],
-    'prefer-spread': 0,
-  }
-};
+  })
+});

node6.js

@@ -1,80 +1,18 @@
 'use strict';
 
-module.exports = {
-  env: {
-    es6: true,
-    node: true
-  },
-  parserOptions: {
-    ecmaVersion: 2017,
-    sourceType: 'script',
-  },
-  plugins: [
-    'import',
-    'node',
-    'prettier',
-  ],
-  rules: {
-    // Random stylistic choices
-    'prettier/prettier': ['error', {
-      singleQuote: true,
-      trailingComma: 'es5',
-    }],
-    'lines-around-directive': ['error', 'always'],
-    'import/newline-after-import': 'error',
+const basics = require('./lib/basics');
 
-    // Code convention
-    'no-underscore-dangle': [2, { allowAfterThis: true }],
-    'no-undef-init': 'off', // pending: Can't be auto-fixed
-    'import/no-dynamic-require': 'off', // pending: Can't be auto-fixed
+const opinions = require('./lib/rules/opinions');
+const conventions = require('./lib/rules/opinions');
+const mistakes = require('./lib/rules/mistakes');
 
-    // Bug prevention
-    strict: [2, 'global'],
-    'node/no-unsupported-features': [2, { version: 6 }],
-    'no-debugger': 'error',
-    'no-empty': 'error',
-    'no-func-assign': 'error',
-    'no-template-curly-in-string': 'error',
-    'no-unreachable': 'error',
-    'no-unsafe-finally': 'error',
-    'use-isnan': 'error',
-    'no-unused-vars': ['error', { vars: 'all', args: 'after-used', ignoreRestSiblings: true }],
-    'no-use-before-define': ['error', { functions: true, classes: true, variables: true }],
-    'no-undef': 'error',
-    'no-shadow': 'error',
-    'no-label-var': 'error',
-    'no-delete-var': 'error',
-    'no-catch-shadow': 'off',
+module.exports = Object.assign(basics, {
+  rules: Object.assign(opinions, conventions, mistakes, {
+    // Additional opinions
 
-    'import/no-unresolved': ['error', { commonjs: true, caseSensitive: true }],
-    'import/no-extraneous-dependencies': ['error', {
-      devDependencies: [
-        'test/**', // tape, common npm pattern
-        'tests/**', // also common npm pattern
-        'spec/**', // mocha, rspec-like pattern
-        '**/__tests__/**', // jest pattern
-        '**/*.test.{js,jsx}', // repos with inline test files
-        'test.{js,jsx}', // repos with a single test file
-        'test-*.{js,jsx}', // repos with multiple top-level test files
-        '**/*.{test,spec}.{js,jsx}', // tests where the extension denotes that it is a test
-        '**/jest.config.js', // jest config
-        '**/webpack.config.js', // webpack config
-        '**/webpack.config.*.js', // webpack config
-        '**/rollup.config.js', // rollup config
-        '**/rollup.config.*.js', // rollup config
-        '**/gulpfile.js', // gulp config
-        '**/gulpfile.*.js', // gulp config
-        '**/Gruntfile{,.js}', // grunt config
-        '**/protractor.conf.*.js', // protractor config
+    // Additional conventions
 
-        // Allow script & example files
-        'scripts/**',
-        'tasks/**',
-        'examples/**',
-        'example/**',
-      ],
-      optionalDependencies: true, // allow optional deps to be required
-    }],
-    'import/no-duplicates': 'error',
-  }
-};
+    // Additional mistakes
+    'node/no-unsupported-features': [2, { version: 6 }],
+  })
+});

node8.js

@@ -0,0 +1,18 @@
+'use strict';
+
+const basics = require('./lib/basics');
+
+const opinions = require('./lib/rules/opinions');
+const conventions = require('./lib/rules/opinions');
+const mistakes = require('./lib/rules/mistakes');
+
+module.exports = Object.assign(basics, {
+  rules: Object.assign(opinions, conventions, mistakes, {
+    // Additional opinions
+
+    // Additional conventions
+
+    // Additional mistakes
+    'node/no-unsupported-features': [2, { version: 8 }],
+  })
+});