Does not support ESLint v9.0.0

[stevepolitodesign]

Environment

yarn: 1.22.17 node: 21.4.0

Steps to reproduce

1. Run yarn add eslint@latest
2. Run yarn add @thoughtbot/eslint-config --dev
3. Add .eslintrc.json with the following:

     {
       "extends": ["@thoughtbot/eslint-config/base"]
     }

4. Add a sample file.

   // index.js
   const foo = 'bar';

5. Run eslint command with ESLINT_USE_FLAT_CONFIG set to false per the latest release's recommendations.

   ESLINT_USE_FLAT_CONFIG=false yarn eslint *.js

Note the following output:

Oops! Something went wrong! :(

ESLint: 9.0.0

Error: Cannot read config file: /Users/polito/Desktop/thoughtbot_eslint_config_example/node_modules/@thoughtbot/eslint-config/base.js
Error: The ESLint patch script has only been tested with ESLint version 6.x, 7.x, and 8.x. (Your version: 9.0.0)
Consider reporting a GitHub issue:
https://github.com/microsoft/rushstack/issues
Referenced from: /Users/polito/Desktop/thoughtbot_eslint_config_example/.eslintrc.json
    at Object.<anonymous> (/Users/polito/Desktop/thoughtbot_eslint_config_example/node_modules/@rushstack/eslint-patch/lib/_patch-base.js:184:11)
    at Module._compile (node:internal/modules/cjs/loader:1376:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1435:10)
    at Module.load (node:internal/modules/cjs/loader:1207:32)
    at Module._load (node:internal/modules/cjs/loader:1023:12)
    at Module.require (node:internal/modules/cjs/loader:1235:19)
    at require (node:internal/modules/helpers:176:18)
    at Object.<anonymous> (/Users/polito/Desktop/thoughtbot_eslint_config_example/node_modules/@rushstack/eslint-patch/lib/modern-module-resolution.js:11:23)
    at Module._compile (node:internal/modules/cjs/loader:1376:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1435:10)
(node:1626) ESLintRCWarning: You are using an eslintrc configuration file, which is deprecated and support will be removed in v10.0.0. Please migrate to an eslint.config.js file. See https://eslint.org/docs/latest/use/configure/migration-guide for details.
(Use `node --trace-warnings ...` to show where the warning was created)
error Command failed with exit code 2.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

[emilford]

These guides were shared while discussing Suspenders and this issue during our Web team sync.

Eslint Migrate to 9.x Guide Configuration Migration Guide Importing Plugins and Custom Parsers

[rakeshpetit]

Based on the guides, I tried to create a eslint.config.js like this:

const globals = require("globals");
const js = require("@eslint/js");
const thoughtbotBase = require("@thoughtbot/eslint-config/base");

module.exports = [
  js.configs.recommended,
  {
    files: ["**/*.js"],
    plugins: {
      "@thoughtbot-eslint": thoughtbotBase,
    },
  },
];

but hit an error in @rushstack/eslint-patch.

Error: Failed to patch ESLint because the calling module was not recognized.
If you are using a newer ESLint version that may be unsupported, please create a GitHub issue:
https://github.com/microsoft/rushstack/issues
    at Object.<anonymous> (.../eslint-config/node_modules/@rushstack/eslint-patch/lib/_patch-base.js:167:19)

This does seem like an issue in @rushstack/eslint-patch with an open https://github.com/microsoft/rushstack/issues/4635 to sort eslint-patch for ESLint 9.

I found in a playground how Flat configs must be specified for ESLint 9.0.0+ and tried that. After installing a few @typescript-eslint dependencies, the config in the playground repo worked well for my example project. So this indicated that we need to add support for Flag configs in our eslint-config based on https://github.com/typescript-eslint/typescript-eslint/pull/7935 where something similar was done.

Based on all this information, I feel like supporting ESLint 9.0.0+ might take longer due to our external dependencies.