chore: upgrade to eslint 9.x (#1267)

Upgrades to eslint 9.x and simplifies the customisation of our config.

bench/memory/sax-parser.js

@@ -1,3 +1,5 @@
+/* eslint-disable no-console */
+
 import { readFile } from 'node:fs/promises';
 import format from 'human-format';
 import memwatch from '@airbnb/node-memwatch';

bench/perf/index.js

@@ -1,3 +1,5 @@
+/* eslint-disable no-console */
+
 import { readFileSync, createReadStream, readdirSync } from 'node:fs';
 import Benchmark from 'benchmark';
 import { loadTreeConstructionTestData } from 'parse5-test-utils/dist/generate-parsing-tests.js';

eslint.config.js

@@ -0,0 +1,89 @@
+import eslintjs from '@eslint/js';
+import eslintConfigPrettier from 'eslint-config-prettier';
+import { configs as tseslintConfigs } from 'typescript-eslint';
+import globals from 'globals';
+import eslintUnicorn from 'eslint-plugin-unicorn';
+
+const { configs: eslintConfigs } = eslintjs;
+
+const sourceFiles = ['bench/**/*.js', 'scripts/**/*.ts', 'packages/*/lib/**/*.ts'];
+const testFiles = ['test/**/*.{ts,js}'];
+const ignoreFiles = [
+    'test/data/html5lib-tests',
+    'test/data/html5lib-tests-fork',
+    'packages/*/dist/',
+    'test/dist/',
+    'docs/build/',
+    'coverage/',
+];
+const allFiles = [...sourceFiles, ...testFiles];
+
+export default [
+    {
+        files: allFiles,
+    },
+    {
+        ignores: ignoreFiles,
+    },
+    {
+        languageOptions: {
+            globals: {
+                ...globals.nodeBuiltin,
+                ...globals.es2019,
+            },
+        },
+    },
+    eslintConfigs.recommended,
+    ...tseslintConfigs.recommended,
+    {
+        rules: {
+            'no-console': 'error',
+            curly: ['error', 'all'],
+            'prefer-arrow-callback': 'error',
+            'one-var': ['error', 'never'],
+            'no-var': 'error',
+            'prefer-const': 'error',
+            'object-shorthand': 'error',
+            'prefer-destructuring': [
+                'error',
+                {
+                    object: true,
+                    array: false,
+                },
+            ],
+            'prefer-template': 'error',
+            'arrow-body-style': ['error', 'as-needed'],
+        },
+    },
+    {
+        files: ['**/*.ts'],
+        rules: {
+            '@typescript-eslint/no-unsafe-declaration-merging': 'off',
+            '@typescript-eslint/no-non-null-assertion': 'warn',
+            '@typescript-eslint/no-explicit-any': 'warn',
+            '@typescript-eslint/explicit-function-return-type': 'error',
+            '@typescript-eslint/consistent-type-imports': 'error',
+
+            '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_' }],
+        },
+    },
+    eslintConfigPrettier,
+    eslintUnicorn.configs['flat/recommended'],
+    {
+        rules: {
+            'unicorn/no-null': 'off',
+            'unicorn/prevent-abbreviations': 'off',
+            'unicorn/prefer-string-slice': 'off',
+            'unicorn/prefer-code-point': 'off',
+            'unicorn/no-array-push-push': 'off',
+            'unicorn/no-for-loop': 'off',
+            'unicorn/consistent-destructuring': 'off',
+            'unicorn/prefer-string-replace-all': 'off',
+            'unicorn/prefer-at': 'off',
+            'unicorn/number-literal-case': 'off',
+            'unicorn/no-nested-ternary': 'off',
+            'unicorn/consistent-function-scoping': 'off',
+            'unicorn/prefer-switch': ['error', { emptyDefaultCase: 'do-nothing-comment' }],
+        },
+    },
+];