Prettier Pug Plugin: Bug With CSS Variables?

Nov 29, 2025 by Alex Johnson 45 views

Introduction

In this article, we will discuss a potential issue encountered while using the Prettier plugin for Pug, specifically related to CSS variables. A user reported a false positive error when using CSS variables within their Pug templates. This error, flagged by Prettier, suggests a syntax issue that doesn't actually exist in the rendered output. We'll delve into the details of the problem, examine the code snippet provided by the user, and explore possible causes and solutions.

When working with web development projects, maintaining code consistency and readability is crucial. Tools like Prettier play a significant role in automating code formatting, ensuring that all team members adhere to a unified style guide. Prettier, in particular, is a popular code formatter that supports various languages and templating engines, including Pug. Pug, formerly known as Jade, is a high-performance template engine heavily influenced by HTML and simplifies the process of writing HTML structures. The Prettier plugin for Pug helps format Pug templates automatically, ensuring they adhere to consistent styling and formatting rules.

However, like any software, Prettier and its plugins are not immune to bugs. One such issue arises when dealing with CSS variables within Pug templates. CSS variables, also known as custom properties, are a powerful feature in modern CSS that allow developers to define reusable values within their stylesheets. They enhance maintainability and flexibility, making it easier to manage styles across a project. When these variables are used within Pug templates, Prettier may sometimes misinterpret the syntax, leading to false positive errors. This article aims to shed light on this specific issue and provide insights into how to address it.

The Reported Issue

A user encountered a peculiar issue while using the Prettier plugin for Pug. The plugin incorrectly flagged an error related to CSS syntax within a Pug template, even though the code was valid and rendered correctly in the browser. The error message indicated an "Unknown word css" and pointed to a line where a CSS variable was being used within a <style> tag in the Pug template. This false positive created unnecessary confusion and highlighted a potential compatibility issue between Prettier's Pug plugin and CSS variables.

The user's feedback is invaluable in identifying and addressing software bugs. By reporting their experience, they have brought attention to a specific scenario where Prettier's Pug plugin may not function as expected. This allows developers to investigate the issue further, identify the root cause, and implement a fix to prevent similar errors in the future. The user's detailed description of the problem, including the error message and code snippet, provides a clear starting point for troubleshooting and resolving the issue. This collaborative approach, where users and developers work together to identify and fix bugs, is essential for improving the quality and reliability of software tools.

Code Snippet

The user provided the following code snippet, which demonstrates the issue:

doctype strict
html(lang="und", xmlns="http://www.w3.org/1999/xhtml")
 head
 title #{subject }
 meta(http-equiv="Content-Type", content="text/html; charset=utf-8")
 meta(name="viewport", content="width=device-width,initial-scale=1")
 meta(name="x-apple-disable-message-reformatting")
 link(rel="preconnect", href="https://fonts.googleapis.com")
 link(rel="preconnect", href="https://fonts.gstatic.com", crossorigin)
 link(
 href="https://fonts.googleapis.com/css2?family=Inter:ital,opsz,wght@0,14..32,100..900;1,14..32,100..900&display=swap",
 rel="stylesheet",
 type="text/css"
 )
 style.
 #{css}
 body(dir="ltr")
 block main

In this Pug template, the user is embedding CSS directly within the <style> tag using interpolation (#{css}). The css variable likely holds a string containing CSS code, potentially including CSS variables. The Prettier plugin seems to misinterpret this interpolated CSS, leading to the false positive error. The user confirmed that the code works fine on their website, indicating that the issue lies within Prettier's parsing or formatting of the Pug template, rather than a genuine syntax error in the CSS itself.

Error Message

The error message reported by the user is as follows:

src/server/views/email/layout.pug[PugPrinter:start-pipeless-text]: The following expression could not be formatted correctly. This is likely a syntax error or an issue caused by the missing execution context. If you think this is a bug, please open a bug issue.
code: `#{css}`
You used interpolated code in your pipeless script tag, so you may ignore this warning.
Found css SyntaxError: CssSyntaxError: Unknown word css (1:3)

This error message provides valuable clues about the nature of the problem. It indicates that Prettier's Pug plugin is having trouble formatting the interpolated CSS code (#{css}). The message suggests that this could be due to a syntax error or a missing execution context. The plugin's attempt to parse the CSS code directly within the Pug template seems to be the source of the issue. The "Unknown word css (1:3)" part of the error message suggests that Prettier's CSS parser is encountering an unexpected token, likely because it is not correctly handling the CSS variables or the way the CSS is embedded within the Pug template.

Analysis of the Issue

To understand why this issue occurs, it's essential to consider how Prettier handles different types of code within a template. Prettier typically parses and formats code based on the file type or language specified. In the case of Pug templates, Prettier's Pug plugin is responsible for parsing and formatting the Pug code. However, when it encounters embedded CSS within a <style> tag, it needs to be able to correctly identify and format the CSS as well. This often involves using a separate CSS parser to handle the CSS-specific syntax.

The problem likely arises when Prettier's CSS parser encounters CSS variables within the interpolated CSS code. CSS variables are a relatively recent addition to the CSS specification, and older CSS parsers may not fully support them. If Prettier's CSS parser is not up-to-date or has limitations in handling CSS variables, it may misinterpret the syntax and flag it as an error. This can lead to false positives, where valid CSS code is incorrectly identified as having syntax errors. The fact that the code works correctly in the browser suggests that the issue is specific to Prettier's parsing process, rather than an actual problem with the CSS syntax itself.

Another potential factor could be the way Prettier handles interpolation within Pug templates. Interpolation allows developers to embed dynamic content within their templates, often using variables or expressions. While Prettier is generally good at handling interpolation, complex scenarios, such as embedding entire CSS blocks, can sometimes create parsing challenges. The plugin might struggle to correctly isolate and parse the interpolated CSS code, leading to errors. This is particularly true if the interpolated code contains special characters or syntax elements that the parser doesn't expect.

Possible Solutions and Workarounds

Several solutions and workarounds can be considered to address this issue. These range from updating Prettier and its plugins to restructuring the code to avoid the problematic scenario.

1. Update Prettier and Plugins

The first step in troubleshooting any issue with Prettier is to ensure that you are using the latest versions of Prettier and its relevant plugins, including the Pug plugin. Software updates often include bug fixes and improvements that can resolve compatibility issues. By updating to the latest versions, you can benefit from the most recent enhancements and bug fixes, which may address the CSS variable issue. You can update Prettier and its plugins using your package manager, such as npm or yarn. For example, you can run npm install prettier prettier-plugin-pug --save-dev or yarn add prettier prettier-plugin-pug --dev to update the packages in your project.

2. Use External CSS Files

Instead of embedding CSS directly within the Pug template, consider using external CSS files. This is a common practice in web development and can help to separate concerns, making your code more organized and maintainable. By placing your CSS code in separate .css files, you can avoid the complexities of interpolating CSS within Pug templates. This can also improve the performance of your website, as external CSS files can be cached by the browser. To use external CSS files, you can link them in the <head> section of your Pug template using the <link> tag.

3. Break Up the CSS

If using external CSS files is not feasible, you can try breaking up the CSS code within the Pug template. Instead of interpolating the entire CSS block, you can try interpolating individual CSS properties or values. This can help Prettier to parse the CSS more easily, as it reduces the complexity of the interpolated code. For example, instead of style. #{css}, you can try something like style(color=myColor, font-size=myFontSize), where myColor and myFontSize are variables containing CSS values. This approach can be more verbose, but it may help to avoid the false positive error.

4. Ignore the Error (With Caution)

As the error message suggests, you can choose to ignore the warning if you are confident that the code is correct and the issue is a false positive. However, this should be done with caution. Ignoring errors can mask genuine issues and make it harder to debug your code in the future. Only ignore the error if you have thoroughly verified that the code is working as expected and that the error is indeed a false positive. It's also a good idea to add a comment to the code explaining why the error is being ignored, so that other developers (or your future self) understand the situation.

5. Report the Issue

If you encounter this issue and none of the workarounds are satisfactory, consider reporting the bug to the Prettier or Prettier plugin for Pug developers. Bug reports are valuable for improving software quality. By providing a clear description of the issue, including the code snippet and error message, you can help the developers to identify the root cause and implement a fix. You can typically report bugs through the project's issue tracker on GitHub or other code hosting platforms. Be sure to include as much detail as possible in your bug report, such as the versions of Prettier, the Pug plugin, and any other relevant dependencies.

Conclusion

The issue of Prettier's Pug plugin incorrectly flagging CSS variables as errors highlights the challenges of parsing and formatting complex code structures. While Prettier is a valuable tool for maintaining code consistency, it's important to be aware of its limitations and potential bugs. By understanding the possible causes of these issues and implementing appropriate solutions or workarounds, developers can continue to leverage the benefits of Prettier while minimizing the impact of false positive errors. The collaborative effort of users reporting issues and developers providing fixes is crucial for the ongoing improvement of software tools like Prettier and its plugins.

For more information about Prettier and its Pug plugin, you can visit the official Prettier website: https://prettier.io/