Rspack: Fixing Infinite Build Loop In Dev Mode

Nov 30, 2025 by Alex Johnson 47 views

Experiencing an infinite build loop in Rspack's dev mode can be a frustrating issue, especially when writeToDisk: true is enabled. This article delves into a specific bug report, providing a detailed explanation of the problem, its causes, and potential solutions. We'll break down the issue, the system configurations involved, and the steps to reproduce it, ensuring you have a comprehensive understanding and can effectively troubleshoot similar scenarios.

Understanding the Infinite Build Loop Issue

The core of the problem lies in how Rspack handles file writing in development mode when the writeToDisk option is activated. This feature is designed to write the bundled files directly to the disk, which can be useful for scenarios where other tools or processes need access to these files. However, under certain conditions, this can trigger an infinite loop, where Rspack continuously rebuilds and rewrites files, leading to excessive resource consumption and a non-functional development environment.

When you encounter an infinite build loop, you'll typically notice that Rspack is constantly generating new files with hashed names in your output directory (often dist). These files are usually related to Hot Module Replacement (HMR), a feature that allows you to update modules in the browser without a full refresh. The loop occurs because the changes written to disk trigger another build, which in turn writes more files, perpetuating the cycle. Let’s dive deeper into the specifics of the reported issue to understand the underlying causes and how to address them effectively.

The Bug Report: A Detailed Breakdown

This bug report highlights an infinite build loop occurring in Rspack when running in development mode with writeToDisk: true. The issue manifests as Rspack continuously generating hashed HMR files inside the dist folder, accompanied by an infinite refresh loop in the browser. This behavior makes the development server unusable and consumes significant system resources. To truly understand this issue, it's essential to dissect the system information, the configuration details, and the reproduction steps provided in the report. By thoroughly examining these elements, we can gain insights into the conditions that trigger the bug and develop strategies for resolution.

The bug report provides detailed system information, including the operating system (Windows 11 and macOS), CPU (12th Gen Intel Core i7-1255U), memory, and versions of Node.js, npm, and pnpm. It also specifies the versions of @rspack/cli and @rspack/core being used. This context is crucial because the issue might be specific to certain environments or package versions. The user reported that the problem occurs both on Windows and macOS, suggesting that it is not OS-specific but rather related to Rspack's configuration or internal workings.

Key Observations from the Bug Report

System Agnostic: The issue is present on both Windows and macOS.
Configuration Specific: It occurs when devServer.devMiddleware.writeToDisk: true is set.
HMR Related: The loop involves the generation of hashed HMR files.
Infinite Refresh: The browser enters an infinite refresh loop when running pnpm run serve.

Reproducing the Issue: Step-by-Step Guide

To effectively address a bug, it's crucial to be able to reproduce it consistently. The bug report includes a repository link and a set of steps to reproduce the infinite build loop. By following these steps, developers can confirm the issue, experiment with potential fixes, and ensure that the solution is effective. Reproducing the bug also provides a controlled environment for testing and debugging, making the process of finding the root cause more efficient.

Here are the steps to reproduce the issue, as outlined in the bug report:

Clone the Repository:

git clone <repository_link>
cd <repository_directory>

Install Dependencies:
```
pnpm install
```
Build the Project:
```
pnpm run build
```
(This step is crucial as the bug appears when the dist folder is created with a build.)
Run in Development Mode:
```
pnpm run dev
```

Expected Behavior

After running pnpm run dev, the terminal should enter an infinite build loop, and the dist folder should continuously generate new JavaScript files with new hashes. Additionally, running pnpm run serve should cause the browser to open and enter an infinite refresh loop. These are the key indicators that the bug is successfully reproduced.

Analyzing the Root Cause

Identifying the root cause of an infinite build loop requires a systematic approach. Several factors could be at play, including file system watchers, configuration errors, or internal Rspack logic. One common culprit is the interaction between writeToDisk and the file system watcher. When writeToDisk is enabled, Rspack writes files to the output directory, and the file system watcher may detect these changes as new modifications, triggering another build. This cycle repeats indefinitely, leading to the infinite loop.

Another potential cause could be related to how Rspack handles HMR files. HMR involves updating modules in the browser without a full refresh, which often requires generating small update files. If these files are written to the output directory in a way that triggers the file system watcher, it could also result in a loop.

Potential Causes

File System Watcher Loop: The file system watcher detects changes written by writeToDisk, triggering a new build.
HMR File Generation: Continuous generation of HMR files triggers the watcher.
Configuration Issues: Misconfiguration of output paths or other settings.
Rspack Internal Logic: Bugs within Rspack's build process or file handling.

Potential Solutions and Workarounds

Addressing an infinite build loop often involves tweaking the configuration or adjusting how Rspack interacts with the file system. Several solutions and workarounds can be explored, depending on the specific cause of the issue. These range from modifying the webpack.config.js file to adjusting file system watcher settings.

Configuration Adjustments

Excluding the Output Directory: One common solution is to exclude the output directory (e.g., dist) from the file system watcher. This prevents changes in the output directory from triggering new builds. This can typically be done using the watchOptions configuration in webpack.config.js.
```
module.exports = {
  // ...
  watchOptions: {
    ignored: /dist/,
  },
};
```
This configuration tells Rspack to ignore changes within the dist directory, preventing the loop caused by writeToDisk.
Conditional writeToDisk: Another approach is to conditionally enable writeToDisk based on the environment. For example, you might only enable it in production or staging environments where it is truly needed.
```
module.exports = {
  // ...
  devServer: {
    devMiddleware: {
      writeToDisk: process.env.NODE_ENV === 'production',
    },
  },
};
```
This ensures that writeToDisk is only active when necessary, avoiding potential issues in development.

File System Watcher Tweaks

Using Polling: In some cases, the default file system watcher may not work correctly, especially on network drives or virtual machines. Switching to a polling-based watcher can sometimes resolve these issues.
```
module.exports = {
  // ...
  watchOptions: {
    poll: 1000, // Check for changes every second
  },
};
```
Polling checks for file changes periodically, rather than relying on events, which can be more reliable in certain environments.

Conclusion

Encountering an infinite build loop in Rspack, especially with writeToDisk: true, can be a challenging issue, but understanding the underlying causes and potential solutions can help you resolve it effectively. By systematically analyzing the problem, reproducing the bug, and applying appropriate fixes, you can restore a smooth development workflow. Configuration adjustments, file system watcher tweaks, and staying up-to-date with Rspack releases are key strategies for tackling this issue.

Remember to always test your solutions thoroughly to ensure they resolve the problem without introducing new ones. Debugging build tools can be intricate, but a methodical approach will ultimately lead to a stable and efficient development environment.

For more information on Rspack and related topics, visit the official Webpack documentation.