chore: upgrade to ESLint v9

.github/workflows/ci.yml

@@ -16,7 +16,8 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu, windows ]
-        node-version: [16.x, 18.x, 20.x]
+        # TODO: We still support Node 16 but can't run ESLint v9 tests with it anymore.
+        node-version: [18.x, 20.x]
 
     steps:
     - uses: actions/checkout@v4

eslint-remote-tester.config.js

@@ -1,7 +1,6 @@
 "use strict";
 
-const fs = require("node:fs");
-const { basename, extname } = require("node:path");
+const eslintPluginQunitRecommended = require("./lib/configs/recommended");
 
 /** @type {import('eslint-remote-tester').Config} */
 module.exports = {
@@ -33,25 +32,7 @@ module.exports = {
     cache: false,
 
     /** ESLint configuration */
-    eslintrc: {
-        plugins: ["qunit"],
-
-        // Enable all of our rules.
-        rules: Object.fromEntries(
-            fs
-                .readdirSync(`${__dirname}/lib/rules`)
-                .map(
-                    (filename) =>
-                        `qunit/${basename(filename, extname(filename))}`,
-                )
-                .map((ruleName) => [ruleName, "error"]),
-        ),
-
-        overrides: [
-            {
-                files: ["*.ts", "*.mts", "*.cts"],
-                parser: "@typescript-eslint/parser",
-            },
-        ],
+    eslintConfig: {
+        ...eslintPluginQunitRecommended,
     },
 };

eslint.config.js

@@ -1,30 +1,28 @@
 "use strict";
 
 const js = require("@eslint/js");
-const { FlatCompat } = require("@eslint/eslintrc");
+const eslintPluginEslintComments = require("@eslint-community/eslint-plugin-eslint-comments/configs");
 const eslintPluginEslintPluginAll = require("eslint-plugin-eslint-plugin/configs/all");
 const eslintPluginMarkdown = require("eslint-plugin-markdown");
+const eslintPluginMocha = require("eslint-plugin-mocha");
+const eslintPluginN = require("eslint-plugin-n");
+const eslintPluginPrettierRecommended = require("eslint-plugin-prettier/recommended");
+const eslintPluginUnicorn = require("eslint-plugin-unicorn");
 const globals = require("globals");
 
-const compat = new FlatCompat({
-    baseDirectory: __dirname,
-    recommendedConfig: js.configs.recommended,
-});
-
 module.exports = [
-    ...compat.extends(
-        "plugin:eslint-comments/recommended",
-        "plugin:node/recommended",
-        "plugin:prettier/recommended",
-        "plugin:unicorn/recommended",
-    ),
+    js.configs.recommended,
 
+    eslintPluginEslintComments.recommended,
     eslintPluginEslintPluginAll,
+    eslintPluginN.configs["flat/recommended"],
+    eslintPluginPrettierRecommended,
+    eslintPluginUnicorn.configs["flat/recommended"],
 
-    // Apply mocha config only to tests.
-    ...compat
-        .extends("plugin:mocha/recommended")
-        .map((config) => ({ ...config, files: ["tests/**/*.js"] })),
+    {
+        ...eslintPluginMocha.configs.flat.recommended,
+        files: ["tests/**/*.js"],
+    },
 
     {
         languageOptions: {
@@ -136,14 +134,6 @@ module.exports = [
             "spaced-comment": ["error", "always", { exceptions: ["-"] }],
             strict: ["error", "global"],
             "use-isnan": "error",
-            "valid-jsdoc": [
-                "error",
-                {
-                    prefer: {
-                        return: "returns",
-                    },
-                },
-            ],
             "valid-typeof": "error",
             yoda: ["error", "never"],
 
@@ -172,8 +162,8 @@ module.exports = [
             ],
             "eslint-plugin/require-meta-schema-description": "off", // TODO: enable this.
 
-            // eslint-plugin-node
-            "node/no-missing-require": [
+            // eslint-plugin-n
+            "n/no-missing-require": [
                 "error",
                 {
                     allowModules: ["@typescript-eslint/parser"],
@@ -207,11 +197,6 @@ module.exports = [
     {
         // Markdown code samples.
         files: ["**/*.md/*.js", "**/*.md/*.javascript"],
-        languageOptions: {
-            parserOptions: {
-                sourceType: "module",
-            },
-        },
         rules: {
             eqeqeq: "off",
             "guard-for-in": "off",

lib/rules/no-compare-relation-boolean.js

@@ -82,6 +82,24 @@ module.exports = {
                     messageId: "redundantComparison",
                     fix(fixer) {
                         const sourceCode = context.getSourceCode();
+                        /* istanbul ignore next */
+                        if (callExprNode.type !== "CallExpression") {
+                            return null;
+                        }
+                        /* istanbul ignore next */
+                        if (callExprNode.callee.type !== "MemberExpression") {
+                            return null;
+                        }
+                        /* istanbul ignore next */
+                        if (callExprNode.callee.object.type !== "Identifier") {
+                            return null;
+                        }
+                        /* istanbul ignore next */
+                        if (
+                            callExprNode.callee.property.type !== "Identifier"
+                        ) {
+                            return null;
+                        }
                         const assertionVariableName =
                             callExprNode.callee.object.name;
 

lib/rules/no-setup-teardown.js

@@ -35,7 +35,12 @@ module.exports = {
         };
 
         function checkModuleHook(propertyNode) {
-            if (replacements.hasOwnProperty(propertyNode.key.name)) {
+            if (
+                Object.prototype.hasOwnProperty.call(
+                    replacements,
+                    propertyNode.key.name,
+                )
+            ) {
                 context.report({
                     node: propertyNode,
                     messageId: "noSetupTeardown",