UI package in Turborepo produces TS error intermittently - Could not find a declaration file for module

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04-10-2024

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Turborepo UI Package: Tackling Intermittent "Could not find a declaration file" Errors

Problem:

You're building a UI package in your Turborepo project and, frustratingly, you encounter the "Could not find a declaration file for module..." error in your TypeScript code. This error pops up intermittently, making debugging a nightmare.

Rephrasing:

Imagine you're building a set of UI components for your application using Turborepo. You write your code, but sometimes your TypeScript compiler throws an error saying it can't find the necessary definitions for the UI components you're using. This error doesn't always happen, making it difficult to pinpoint the cause.

Scenario:

Let's say you have a Turborepo setup with a UI package called ui-components. Your ui-components package contains a button component with the following code:

// ui-components/src/Button.tsx
import React from 'react';

const Button: React.FC<ButtonProps> = ({ children, onClick }) => (
  <button onClick={onClick}>{children}</button>
);

export default Button;

interface ButtonProps {
  children: React.ReactNode;
  onClick?: () => void;
}

Now, you're trying to use this button in another package within your Turborepo project. You import the Button component in your app package like this:

// app/src/App.tsx
import Button from '@your-org/ui-components/Button';

const App = () => {
  const handleClick = () => {
    console.log('Button clicked!');
  };

  return (
    <div>
      <Button onClick={handleClick}>Click Me</Button>
    </div>
  );
};

export default App;

Sometimes this code works perfectly, but other times, you encounter the "Could not find a declaration file for module" error, specifically for the Button component.

Analysis:

This error often arises due to inconsistent type information between packages in your Turborepo project. Here's a breakdown of the common causes:

• Missing or Inconsistent Type Declarations: Your UI package might be missing a types folder or index.d.ts file which declares the types for your components. This can lead to TypeScript having difficulty resolving the type definitions when importing your components.
• Incorrect tsconfig.json Configuration: Ensure that your UI package's tsconfig.json is configured correctly. The compiler's types option might be missing entries for necessary dependencies, and declaration should be set to true to generate declaration files.
• Cache Issues: Sometimes, the Turborepo build cache can become corrupted or out of sync, leading to inconsistent type information between packages. This can be fixed by clearing the cache.

Troubleshooting and Solutions:

1. Add a types folder and index.d.ts to your UI package:

   // ui-components/src/types/index.d.ts
   declare module '@your-org/ui-components' {
     export { default as Button } from '../Button'; 
     // Add other component exports here
   }
   

2. Verify tsconfig.json in your UI package:

   // ui-components/tsconfig.json
   {
     "compilerOptions": {
       "outDir": "dist",
       "declaration": true, 
       "moduleResolution": "node",
       "types": ["react"],
       "esModuleInterop": true,
       "jsx": "react" 
     },
     "include": ["src"],
     "exclude": ["node_modules", "dist"]
   }
   

3. Clear the Turborepo Cache: Run turbo clean to clear the build cache and rebuild your project.

4. Use a types option in your tsconfig.json:

   In your app package's tsconfig.json, add the types option to explicitly include the types from your UI package.

   // app/tsconfig.json
   {
     "compilerOptions": {
       // ...
       "types": ["react", "@your-org/ui-components"], // Include the UI package types
       // ...
     }
   }
   

Additional Tips:

• Use turbo run build: When you're working with a Turborepo project, always run turbo run build to build all affected packages to ensure type information is consistent across the project.
• Experiment with tsc --build: Running tsc --build directly in your UI package directory can provide more specific error messages that can help you identify the root cause.
• Consider using a linter: Integrate a linter like ESLint into your project to catch potential type errors early on.

Resources:

• Turborepo Documentation: https://turbo.build/
• TypeScript Documentation: https://www.typescriptlang.org/

By implementing these solutions and understanding the underlying causes, you can effectively address the intermittent "Could not find a declaration file" error and ensure consistent type information across your Turborepo project, leading to a smoother development experience.