flat config doesn't work using re-export custom module

[codenoobforreal]

// eslint.config.js
export default tseslint.config(
  { ignores: ["dist"] },
  {
    extends: [js.configs.recommended, ...tseslint.configs.recommended],
    files: ["**/*.{ts,tsx}"],
    languageOptions: {
      ecmaVersion: 2020,
      globals: globals.browser,
    },
    plugins: {
      "react-hooks": reactHooks,
      "react-refresh": reactRefresh,
    },
    rules: {
      ...reactHooks.configs.recommended.rules,
      "react-refresh/only-export-components": [
        "warn",
        { allowConstantExport: true },
      ],
    },
  },
  {
    files: ["**/test/**/*.test.{ts,tsx}"],
    ...testingLibrary.configs["flat/react"],
    ...jestdom.configs["flat/recommended"],
  },
  eslintConfigPrettier,
);

pnpm exec npx eslint --print-config ./src/test/unit/app.test.tsx result:

  "plugins": [
    "@",
    "@typescript-eslint:@typescript-eslint/eslint-plugin@8.18.1",
    "react-hooks",
    "react-refresh",
    "jest-dom:eslint-plugin-jest-dom@5.5.0"
  ],

[Belco90]

What version of the plugin are you using?

[Samielakkad]

I think the issue is the shallow merge here:

{
  files: ["**/test/**/*.test.{ts,tsx}"],
  ...testingLibrary.configs["flat/react"],
  ...jestdom.configs["flat/recommended"],
}

Both flat configs define top-level keys like plugins and rules. Object spread does not deep-merge those objects, so the later jestdom config overwrites the plugins / rules from testing-library. That matches your --print-config output: jest-dom is present, but testing-library is missing.

Use separate config objects instead:

export default tseslint.config(
  { ignores: ["dist"] },
  {
    extends: [js.configs.recommended, ...tseslint.configs.recommended],
    files: ["**/*.{ts,tsx}"],
    languageOptions: {
      ecmaVersion: 2020,
      globals: globals.browser,
    },
    plugins: {
      "react-hooks": reactHooks,
      "react-refresh": reactRefresh,
    },
    rules: {
      ...reactHooks.configs.recommended.rules,
      "react-refresh/only-export-components": [
        "warn",
        { allowConstantExport: true },
      ],
    },
  },
  {
    files: ["**/test/**/*.test.{ts,tsx}"],
    ...testingLibrary.configs["flat/react"],
  },
  {
    files: ["**/test/**/*.test.{ts,tsx}"],
    ...jestdom.configs["flat/recommended"],
  },
  eslintConfigPrettier,
);

If you really want one object, you need to deep-merge plugins and rules manually:

const testingLibraryReact = testingLibrary.configs["flat/react"];
const jestDomRecommended = jestdom.configs["flat/recommended"];

{
  files: ["**/test/**/*.test.{ts,tsx}"],
  plugins: {
    ...testingLibraryReact.plugins,
    ...jestDomRecommended.plugins,
  },
  rules: {
    ...testingLibraryReact.rules,
    ...jestDomRecommended.rules,
  },
}

I would prefer the separate-config-object version because it follows the way flat config composition is intended to work and avoids accidentally dropping nested config keys.