Resolving the ESLint Error: "File ignored because of a matching ignore pattern"

In the JavaScript ecosystem, the use of ESLint, lint-staged, and Husky is common practice for maintaining code quality and consistency.

However, these tools, like any other, can present users with occasional challenges.

One such challenge is the error message:

"File ignored because of a matching ignore pattern. Use "--no-ignore" to override".

In this post, we aim to provide a comprehensive understanding of this particular issue, exploring its cause and detailing a method to resolve it effectively.

Our objective is to ensure that encountering this error does not hinder your development workflow, but rather offers an opportunity to deepen your understanding of these critical tools.

Prerequisites

Before we delve into the intricacies of our topic, ensure that you are familiar with the following:

1. Basic understanding of JavaScript.
2. Familiarity with ESLint and its purpose in code quality assurance.
3. Awareness of how lint-staged and Husky work to prevent bad commits.
4. Knowledge of how to read and interpret error messages in JavaScript.

While not strictly necessary, previous experience with encountering and resolving errors in a coding environment would be beneficial.

Objective

Our primary goal in this post is to provide you with a robust solution to the ESLint error File ignored because of a matching ignore pattern. Use "--no-ignore" to override.

This issue arises when lint-staged does not recognize the .eslintignore file in your project repository by default.

By the end of this post, you'll be able to:

1. Understand why lint-staged might disregard your .eslintignore file.
2. Implement a solution that ensures lint-staged acknowledges your .eslintignore file.
3. Distinguish between ES6 modules and CommonJS, and adjust your code accordingly to avoid compatibility issues.

Understanding the Issue and Approach to Fix

Before we delve into our step-by-step guide, it's worth understanding what the error message "File ignored because of a matching ignore pattern. Use "--no-ignore" to override means and why it appears.

This error stems from an issue where lint-staged does not recognize or honor the .eslintignore file in your project repository by default. Essentially, files you've chosen to ignore in ESLint might still be getting picked up during the staging process.

Step-by-Step Guide

In this section, we'll walk you through the process of resolving the ESLint error. We'll start by adding a specific piece of code to your project, then explain how you can modify it if you encounter additional errors related to ES6 modules and CommonJS.

Step 1: Implement the Suggested Fix

The lint-staged team has provided a recommended solution for ESLint version 7.5 and later. Here's the code:

import { ESLint } from 'eslint'

const removeIgnoredFiles = async (files) => {
  const eslint = new ESLint()
  const isIgnored = await Promise.all(
    files.map((file) => {
      return eslint.isPathIgnored(file)
    })
  )
  const filteredFiles = files.filter((_, i) => !isIgnored[i])
  return filteredFiles.join(' ')
}

export default {
  '**/*.{ts,tsx,js,jsx}': async (files) => {
    const filesToLint = await removeIgnoredFiles(files)
    return [`eslint --max-warnings=0 ${filesToLint}`]
  },
}

This code snippet works by creating an instance of ESLint and using it to check whether each file is in the .eslintignore list. If the file is in the list, it gets excluded from the files that ESLint will check.

Side-step 2: Address Compatibility Issues

However, this solution may not work for everyone due to compatibility issues with ESM or ES6 modules.

You'll know you're facing this issue if you receive an error message like Unexpected Token Export or Cannot use import statement outside a module.

In this case, you need to adjust your code to use CommonJS syntax instead:

const { ESLint } = require("eslint");

const removeIgnoredFiles = async (files) => {
  const eslint = new ESLint();
  const isIgnored = await Promise.all(
    files.map((file) => {
      return eslint.isPathIgnored(file);
    })
  );
  const filteredFiles = files.filter((_, i) => !isIgnored[i]);
  return filteredFiles.join(" ");
};

module.exports = {
  "**/*.{ts,tsx,js,jsx}": async (files) => {
    const filesToLint = await removeIgnoredFiles(files);
    return [`eslint --max-warnings=0 ${filesToLint}`];
  },
};

This updated snippet accomplishes the same task, but it uses the CommonJS require statement and module.exports syntax to ensure compatibility with a wider range of JavaScript projects.

In this updated code, we:

• replaced import with require
• replaced default export with module.exports

Wrapping Up

We have now examined the ESLint error File ignored because of a matching ignore pattern. Use "--no-ignore" to override in detail.

We've understood its origins, where lint-staged doesn't recognize the .eslintignore file in your project repository by default.

We've also learned a practical solution to this issue, making use of ESLint's built-in methods and adapting the code to be compatible with both ES6 modules and CommonJS.

Remember, the solution we explored requires ESLint version 7.5 and later, and it involves creating a function to filter out files listed in .eslintignore from the files that ESLint checks.

Finally, be aware of potential compatibility issues with ES6 module syntax, and know how to adjust your code to use CommonJS syntax when needed.

Remember, encountering errors and challenges are a part of the programming journey.

They provide the opportunities to learn and grow, leading to more efficient and effective coding in the long run.

Stay curious and keep making stuff!

Additional Resources

For further insights into ESLint, lint-staged, and Husky, consider checking out the following resources:

1. ESLint User Guide
2. lint-staged GitHub page
3. Husky GitHub page