build: migrate to eslint "flat" config

Author: justinmk

.eslintrc.js

@@ -0,0 +1,143 @@
+import js from '@eslint/js';
+import globals from 'globals';
+import typescriptEslint from '@typescript-eslint/eslint-plugin';
+import typescriptParser from '@typescript-eslint/parser';
+import unicorn from 'eslint-plugin-unicorn';
+import importPlugin from 'eslint-plugin-import';
+import prettierConfig from 'eslint-config-prettier/flat';
+
+export default [
+  js.configs.recommended,
+  typescriptEslint.configs.recommended,
+  unicorn.configs.recommended,
+  prettierConfig,
+  {
+    files: ['**/*.ts', '**/*.js'],
+    ignores: [
+      '.eslintrc.js',
+      'packages/*/lib/',
+      'packages/*/bin/',
+      'packages/neovim/scripts/',
+      'packages/integration-tests/__tests__/',
+      'examples/rplugin/node/',
+      'packages/example-plugin/',
+      'packages/example-plugin-decorators/',
+    ],
+    languageOptions: {
+      parser: typescriptParser,
+      parserOptions: {
+        project: './tsconfig.json',
+        ecmaVersion: 'latest',
+        sourceType: 'module',
+      },
+      globals: {
+        ...globals.node,
+        ...globals.es2020,
+        ...globals.mocha,
+      },
+    },
+    plugins: {
+      import: importPlugin,
+    },
+    settings: {
+      'import/resolver': { node: { extensions: ['.js', '.jsx', '.ts'] } },
+    },
+    reportUnusedDisableDirectives: true,
+    rules: {
+    curly: 'error', // Enforce braces on "if"/"for"/etc.
+    // Avoid accidental use of "==" instead of "===".
+      eqeqeq: 'error',
+      camelcase: ['error', { properties: 'never' }],
+      'class-methods-use-this': 'off',
+      'comma-dangle': [
+        'error',
+        {
+          arrays: 'only-multiline',
+          objects: 'only-multiline',
+          imports: 'only-multiline',
+          exports: 'only-multiline',
+          functions: 'ignore',
+        },
+      ],
+      'no-restricted-syntax': 'off',
+      'no-case-declarations': 'off',
+      'no-prototype-builtins': 'off',
+      'no-underscore-dangle': 'off',
+      'no-mixed-operators': 'off',
+      'func-names': 'off',
+      'max-classes-per-file': 'off',
+      'operator-assignment': ['error', 'never'],
+
+    // For overloading (and typescript throws when dupe members anyway)
+      'no-dupe-class-members': 'off',
+
+    // Causes issues with enums
+      'no-shadow': 'off',
+    'prefer-destructuring': 'off', // Intentionally disabled trash.
+
+      'import/extensions': 'off',
+      'import/prefer-default-export': 'off',
+
+      '@typescript-eslint/no-namespace': 'error',
+    // TODO: '@typescript-eslint/no-floating-promises': 'error', // Promises must catch errors or be awaited.
+    // TODO? '@typescript-eslint/no-unsafe-assignment': 'error',
+    // TODO? '@typescript-eslint/no-unsafe-return': 'error',
+    // TODO? '@typescript-eslint/no-unsafe-call': 'error',
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/explicit-member-accessibility': 'off',
+      '@typescript-eslint/no-unused-vars': 'error',
+      '@typescript-eslint/no-empty-function': 'off',
+      '@typescript-eslint/explicit-function-return-type': 'off',
+      '@typescript-eslint/ban-types': 'off',
+      '@typescript-eslint/explicit-module-boundary-types': 'off',
+
+    // Rules from https://github.com/sindresorhus/eslint-plugin-unicorn
+    // TODO: 'unicorn/no-useless-promise-resolve-reject': 'error',
+    // TODO: 'unicorn/prefer-event-target': 'error',
+    // TODO: 'unicorn/prefer-string-slice': 'error',
+    // TODO? 'unicorn/custom-error-definition': 'error',
+    // TODO? 'unicorn/prefer-json-parse-buffer': 'error',
+    // TODO? ESM modules https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/prefer-module.md
+    // 'unicorn/prefer-module': 'error',
+    // 'unicorn/no-null': 'error',
+      'unicorn/no-abusive-eslint-disable': 'error',
+      'unicorn/prefer-at': 'error',
+      'unicorn/prefer-negative-index': 'error',
+      'unicorn/prefer-regexp-test': 'error',
+      'unicorn/prefer-ternary': 'error',
+      'unicorn/no-unnecessary-polyfills': 'error',
+      'unicorn/no-useless-spread': 'error',
+      'unicorn/prefer-array-some': 'error',
+      'unicorn/prefer-blob-reading-methods': 'error',
+      'unicorn/prefer-code-point': 'error',
+      'unicorn/prefer-date-now': 'error',
+      'unicorn/prefer-dom-node-text-content': 'error',
+      'unicorn/prefer-includes': 'error',
+      'unicorn/prefer-keyboard-event-key': 'error',
+      'unicorn/prefer-modern-dom-apis': 'error',
+      'unicorn/prefer-modern-math-apis': 'error',
+      'unicorn/prefer-native-coercion-functions': 'error',
+      'unicorn/prefer-node-protocol': 'error',
+      'unicorn/prefer-object-from-entries': 'error',
+      'unicorn/prefer-reflect-apply': 'error',
+      'unicorn/prefer-string-trim-start-end': 'error',
+      'unicorn/prefer-type-error': 'error',
+    },
+  },
+  {
+    files: ['**/*.test.ts'],
+    rules: {
+      // This rule requires es2022(?) but the CI node14 job runs the tests
+      // in node14, but the test code is not compiled/polyfilled... so the
+      // test code needs to be compatible with node14.
+      // TODO: can the back-compat CI jobs for older node.js versions run
+      // `jest` against the compiled .js results (would require compiling
+      // the test files as well)?
+      'unicorn/prefer-at': 'off',
+      'import/no-extraneous-dependencies': [
+        'error',
+        { devDependencies: true, optionalDependencies: false, peerDependencies: false },
+      ],
+    },
+  },
+];