[eslint-plugin-react-hooks] Missing type declarations

[JstnMcBrd]

all

low

What

When imported in a TypeScript environment, eslint-plugin-react-hooks throws a "missing type declarations" error.

Why

This is because eslint-plugin-react-hooks does not have any type declarations bundled in the package. These would usually be in an index.d.ts file.

Also, eslint-plugin-react-hooks does not have a corresponding @types/... package in the DefinitelyTyped project for users to rely on.

Workaround

Users can follow the instructions in the error message and make a temporary module augmentation to declare their own types for the package.

In my personal project, I've done it this way:

// ./src/@types/eslint-plugin-react-hooks.d.ts
declare module 'eslint-plugin-react-hooks' {
	import type { ESLint } from 'eslint';
	const plugin: Omit<ESLint.Plugin, 'configs'> & {
		// eslint-plugin-react-hooks does not use FlatConfig yet
		configs: Record<string, ESLint.ConfigData>;
	};
	export default plugin;
}

But this will not automatically stay up-to-date with the package and is not guaranteed to be correct. Is it also incomplete and does not contain detailed information about the different configs in the plugin.

How to fix

There are several ways.

1. Usually the preferred solution is just to write everything in TypeScript and let it auto-generate declaration files for you. But I understand if a complete rewrite is not on the table :)

2. You could add a @types/eslint-plugin-react-hooks package in the DefinitelyTyped repo. But then your types would be defined in a completely different place from your actual code, and if you ever decide to migrate to TypeScript in the future, the old @types/... package would need to be deprecated. Sounds messy.

3. Best solution, in my opinion. Just add a index.d.ts file to the package that declare the type exports of the package. Then define it as the type declarations in package.json. Easy peasy.

// package.json
+  "main": "index.js",
+  "types": "index.d.ts",
  "files": [
    "LICENSE",
    "README.md",
    "index.js",
+    "index.d.ts",
    "cjs"
  ],

I would be happy to do this myself. I just wanted to submit an issue first to confirm that the maintainers would approve.

Steps To Reproduce

1. Install typescript, eslint-plugin-react-hooks
2. Create a .ts file
3. Import eslint-plugin-react-hooks

Code example

package.json

{
  "scripts": {
    "build": "tsc"
  },
  "dependencies": {
    "eslint-plugin-react-hooks": "^4.6.2"
  },
  "devDependencies": {
    "typescript": "^5.5.2"
  }
}

index.ts

import reactHooksPlugin from 'eslint-plugin-react-hooks';

(You'll need a tsconfig.json file too, but the settings are irrelevant to this example)

The current behavior

TypeScript build error.

The expected behavior

No errors.

[JstnMcBrd]

After trying to add a index.d.ts declaration file myself, I quickly realized I do not understand the build/bundling system for this monorepo. The declaration files were excluded from the build output.

I found the two different TODO comments explaining how the current build process isn't great for an eslint plugin.

./packages/eslint-plugin-react-hooks/npm/index.js

// TODO: this doesn't make sense for an ESLint rule.
// We need to fix our build process to not create bundles for "raw" packages like this.

./scripts/rollup/bundles.js

// TODO: it's awkward to create a bundle for this but if we don't, the package
// won't get copied. We also can't create just DEV bundle because it contains a
// NODE_ENV check inside. We should probably tweak our build process to allow
// "raw" packages that don't get bundled.

Fixing this would also allow adding declaration files to the published package, instead of being ignored by the bundler.

Makes me wonder if eslint-plugin-react-hooks should be in its own repository like most standalone npm packages, to avoid the awkwardness of a monorepo bundling system that wasn't designed for it. But I'll leave that decision to the maintainers.

[JstnMcBrd]

Figured I'd dump the declaration files I wrote here for anyone who works on this issue in the future:

// index.d.ts
import type { configs, rules } from './src/index';

declare var plugin: {
  configs: typeof configs;
  rules: typeof rules;
};

export default plugin;

// src/index.d.ts
import type { Linter } from "eslint";

import type RulesOfHooks from './RulesOfHooks';
import type ExhaustiveDeps from './ExhaustiveDeps';

export const configs: {
  recommended: Linter.Config;
};

export const rules: {
  'rules-of-hooks': typeof RulesOfHooks;
  'exhaustive-deps': typeof ExhaustiveDeps;
};

// both src/RulesOfHooks.d.ts and src/ExhaustiveDeps.d.ts
import type { Rule } from "eslint";

declare var rule: Rule.RuleModule;

export default rule;