Fixing Children On New Line In ESLint Stylistic Jsx-max-props-per-line Rule

Jul 7, 2025 by Jeany 76 views

Introduction

In the realm of modern web development, maintaining code consistency and readability is paramount. ESLint stands as a powerful tool in this endeavor, helping developers enforce coding standards and identify potential issues. Among ESLint's vast ecosystem of plugins and rules, the @stylistic/eslint-plugin family plays a crucial role in ensuring code style uniformity. Within this family, the jsx-max-props-per-line rule aims to limit the number of props on a single line in JSX elements, enhancing code clarity. However, like any rule, it can sometimes produce unexpected or undesirable outcomes, particularly when combined with ESLint's auto-fix capabilities. This article delves into a specific issue encountered with the jsx-max-props-per-line rule, where the auto-fix feature incorrectly places children elements on the same line as the closing bracket, deviating from the intended code style. We'll explore the problem in detail, provide a reproduction scenario, and discuss potential solutions to rectify this behavior.

Understanding the Issue

The core problem lies in the interaction between the jsx-max-props-per-line rule and ESLint's auto-fix functionality. When the rule is configured to limit the number of props per line, ESLint's auto-fix will attempt to refactor JSX elements to adhere to this constraint. In most cases, this involves breaking props onto new lines, improving readability. However, a specific scenario arises when the element also contains children. Instead of placing the children on a new line after the opening tag, the auto-fix incorrectly places them on the same line as the closing bracket of the opening tag. This outcome is undesirable as it violates the intended code style, which typically dictates that children should reside on a separate line for better clarity.

To illustrate this issue, consider the following JSX code snippet:

<div id='' className='' title=''>Child</div>

With the jsx-max-props-per-line rule configured to allow a maximum of one prop per line in multi-line scenarios, running ESLint's auto-fix transforms the code into:

<div
  id=''
  className=''
  title=''
>Child
</div>

As you can observe, the Child element is placed on the same line as the closing bracket of the div tag, which is not the desired formatting. The expected output should instead be:

<div
  id=''
  className=''
  title=''
>
  Child
</div>

In this corrected version, the Child element is placed on a new line, enhancing readability and adhering to common code style conventions. This discrepancy highlights the bug in the jsx-max-props-per-line rule's auto-fix behavior, which needs to be addressed to ensure accurate and consistent code formatting.

Configuration Details

To reproduce this issue, specific ESLint configuration settings are required. The following configuration snippet demonstrates the necessary setup:

{
  rules: {
    '@stylistic/indent': ['error', 2],
    '@stylistic/jsx-first-prop-new-line': ['error', 'multiline-multiprop'],
    '@stylistic/jsx-max-props-per-line': [
      'error',
      { maximum: { single: 2, multi: 1 } },
    ],
    '@stylistic/jsx-closing-bracket-location': ['error', 'tag-aligned'],
    '@stylistic/jsx-closing-tag-location': 'error',
  },
}

Let's break down these configurations to understand their role in triggering the bug:

@stylistic/indent: This rule enforces consistent indentation throughout the codebase, using two spaces in this case. While not directly related to the bug, it plays a crucial role in the overall code formatting and readability.
@stylistic/jsx-first-prop-new-line: This rule dictates whether the first prop in a JSX element should be placed on a new line. The 'multiline-multiprop' option ensures that the first prop is placed on a new line only when the element has multiple props and spans multiple lines.
@stylistic/jsx-max-props-per-line: This is the core rule responsible for limiting the number of props per line. The configuration specifies a maximum object with two properties:
- single: Sets the maximum number of props allowed on a single line when the element is on a single line (set to 2 in this case).
- multi: Sets the maximum number of props allowed on a single line when the element spans multiple lines (set to 1 in this case). This is the primary setting that triggers the bug when combined with the auto-fix feature.
@stylistic/jsx-closing-bracket-location: This rule controls the placement of the closing bracket in JSX elements. The 'tag-aligned' option aligns the closing bracket with the opening tag, which is a common style preference.
@stylistic/jsx-closing-tag-location: This rule enforces the location of the closing tag in JSX elements. Setting it to 'error' ensures that closing tags are always placed on a new line.

By combining these configurations, particularly the jsx-max-props-per-line rule with its multi-line restriction, the bug becomes apparent when ESLint's auto-fix attempts to refactor JSX elements with multiple props and children. The auto-fix incorrectly places the children on the same line as the closing bracket of the opening tag, violating the intended code style and highlighting the need for a fix.

Reproduction Steps

To effectively address this bug, it's crucial to have a clear and reproducible scenario. The following steps outline how to reproduce the issue using a minimal setup:

Set up a new project: Start by creating a new JavaScript or TypeScript project with the necessary dependencies, including ESLint and the @stylistic/eslint-plugin package.
Configure ESLint: Create an ESLint configuration file (.eslintrc.js or .eslintrc.json) and include the configurations mentioned earlier. Specifically, ensure that the @stylistic/jsx-max-props-per-line rule is configured with a maximum object that restricts the number of props per line in multi-line scenarios (e.g., multi: 1).
Create a JSX component: Create a simple JSX component with multiple props and children. For instance, use the example code snippet provided earlier:
```
<div id='' className='' title=''>Child</div>
```
Run ESLint with auto-fix: Execute ESLint with the --fix flag to trigger the auto-fix functionality. This will instruct ESLint to automatically correct any style violations based on the configured rules.
Observe the output: After running the auto-fix, inspect the modified code. You'll notice that the children element (Child in this example) is incorrectly placed on the same line as the closing bracket of the opening tag, instead of being on a new line.

By following these steps, you can consistently reproduce the bug and verify the issue. This reproducible scenario is essential for debugging and testing potential solutions.

Furthermore, a StackBlitz reproduction is provided in the original issue, offering a convenient way to reproduce the bug in an online environment. StackBlitz allows you to quickly set up and share code examples, making it an invaluable tool for collaboration and issue reporting.

Potential Solutions and Workarounds

Addressing this bug in the jsx-max-props-per-line rule requires careful consideration and a well-defined solution. While a comprehensive fix may involve modifying the rule's auto-fix logic, several potential workarounds can be employed in the interim.

1. Manual Formatting

The most straightforward workaround is to manually format the code after running ESLint's auto-fix. This involves reviewing the output and correcting any instances where the children are incorrectly placed on the same line as the closing bracket. While this approach adds an extra step to the development process, it ensures that the code adheres to the desired style.

2. Disabling Auto-Fix for the Rule

Another option is to disable the auto-fix functionality for the jsx-max-props-per-line rule. This can be achieved by modifying the ESLint configuration to exclude this rule from the auto-fix process. While this prevents the bug from occurring, it also means that the rule will no longer automatically correct violations, requiring manual intervention to address style issues.

3. Custom ESLint Rule

For more advanced users, creating a custom ESLint rule that specifically addresses this issue may be a viable solution. A custom rule can be designed to identify instances where children are incorrectly placed and provide a more accurate auto-fix. This approach requires a deeper understanding of ESLint's API and rule development but offers the most control over the formatting process.

4. Contributing to the Project

The most impactful solution is to contribute directly to the @stylistic/eslint-plugin project by submitting a pull request with a fix for the bug. This involves analyzing the rule's implementation, identifying the root cause of the issue, and developing a solution that correctly handles children elements during auto-fix. Contributing to open-source projects not only benefits the community but also provides valuable learning experiences.

Conclusion

The issue of children being incorrectly placed on the same line as the closing bracket in ESLint's jsx-max-props-per-line rule highlights the challenges of creating robust and accurate code formatting tools. While the auto-fix functionality aims to streamline the development process, bugs like this can lead to unexpected outcomes and require manual intervention. By understanding the problem, reproducing the scenario, and exploring potential solutions, developers can effectively mitigate the impact of this bug. Furthermore, contributing to the open-source project by submitting a fix ensures that the issue is addressed for the entire community, fostering a more consistent and reliable code formatting experience. The willingness to submit a pull request with failing tests and a fix demonstrates a commitment to improving the tool and contributing to the collective knowledge of the development community.

Contributing to the Fix

The user who reported this issue has expressed a willingness to submit a pull request (PR) to fix this issue, including failing tests. This is a significant step towards resolving the problem and ensuring the quality of the fix. Contributing to open-source projects like @stylistic/eslint-plugin is a valuable way to give back to the community and improve the tools that developers rely on. If you're interested in contributing, here's a general outline of the process:

Fork the repository: Start by forking the @stylistic/eslint-plugin repository on GitHub. This creates a copy of the repository under your GitHub account, allowing you to make changes without affecting the original project.
Clone the forked repository: Clone your forked repository to your local machine. This allows you to work on the code locally and test your changes before submitting them.
Create a branch: Create a new branch for your fix. This isolates your changes from the main branch and makes it easier to manage multiple contributions.
Identify the issue: Thoroughly understand the issue and its root cause. Review the existing code, identify the relevant logic, and determine the best approach to fix the bug.
Implement the fix: Implement the necessary changes to correct the auto-fix behavior. Ensure that the fix addresses the specific scenario described in this article and doesn't introduce any new issues.
Write failing tests: Before submitting the fix, write failing tests that specifically target the bug. These tests should fail with the original code and pass after the fix is applied. Failing tests demonstrate that the fix correctly addresses the issue and prevent regressions in the future.
Test the fix: Thoroughly test the fix to ensure that it works as expected and doesn't introduce any new problems. Run the existing tests and add new tests as needed.
Commit your changes: Commit your changes with clear and descriptive commit messages. This makes it easier for reviewers to understand the changes you've made.
Push your branch: Push your branch to your forked repository on GitHub.
Create a pull request: Create a pull request from your branch to the main branch of the @stylistic/eslint-plugin repository. In the pull request description, clearly explain the issue, the fix, and any relevant details.

By following these steps, you can effectively contribute to the @stylistic/eslint-plugin project and help resolve this bug. Your contribution will benefit the entire community and improve the quality of the tool.