Prevent CI OOM Errors: Exclude Mermaid From Shiki

Hey there, fellow developers! If you're building content-heavy websites with Analog.js, especially those involving Markdown, syntax highlighting with Shiki, and the visually appealing Mermaid diagrams, you might have run into a rather frustrating issue: Out-of-Memory (OOM) errors in your Continuous Integration (CI) environments. This isn't just a minor hiccup; it can bring your build process to a screeching halt, particularly on platforms like Cloudflare Pages that have memory constraints. Let's dive deep into why this happens and, more importantly, how we can tackle it.

The Shiki-Mermaid Memory Conundrum in CI

When you're working with Analog.js content routing and want to add some spiffy syntax highlighting using Shiki, things are generally pretty straightforward. You might even decide to jazz up your Markdown content with diagrams generated by Mermaid. The documentation often suggests including mermaid in Shiki's additionalLangs for this very purpose. It sounds like a perfect solution, right? Well, not quite when your build is happening in a memory-limited CI environment. Shiki, while powerful, can be a memory hog, and when it tries to process a language like Mermaid, especially with complex diagrams, it can easily exceed the available heap memory. This leads to those dreaded OOM failures, leaving you scratching your head and wondering what went wrong.

Now, you might think, "Easy fix! Let's just remove Mermaid from Shiki's additionalLangs." But hold on, that doesn't quite solve the problem either. When you remove it, your build pipeline, specifically tools like marked-shiki (which Analog uses under the hood), tries to process all fenced code blocks. If Mermaid is no longer recognized by Shiki, the build will fail with a cryptic message like Language 'mermaid' not found. It's like being stuck in a Catch-22 situation: include Mermaid and risk OOM errors, exclude it and break your build. This leaves developers in a bind, facing unstable builds, the need for undocumented workarounds, or the unfortunate necessity of removing Mermaid diagrams altogether. This isn't just an inconvenience; it's a significant roadblock for content-focused sites, educational platforms, and anyone relying on these tools in common CI setups.

Why This Affects So Many Projects

This memory issue isn't just a niche problem; it has far-reaching implications for a wide array of projects. Content-heavy websites, such as blogs and extensive documentation sites, often rely on both sophisticated syntax highlighting and visual aids like diagrams to engage their audience and convey information effectively. Developers showcasing code snippets or technical processes will find Shiki indispensable. Similarly, DevRel (Developer Relations) and educational use cases frequently leverage Markdown for tutorials, examples, and explanations, where clear code formatting and illustrative diagrams are paramount. These scenarios naturally involve integrating tools like Shiki and Mermaid.

When these projects are deployed or tested using CI environments with limited memory, like Cloudflare Pages (which typically offers around 2GB of heap), the problem becomes acute. The build process, which often involves server-side rendering (SSR) or static site generation (SSG), needs to parse and process all content. Shiki's memory footprint during this process, especially when handling a language like Mermaid, can easily exceed the allocated resources. This leads to build failures, disrupting the development workflow and deployment pipeline. Without a clear solution or API to manage this, users are forced into difficult choices: endure unstable, error-prone builds; resort to potentially brittle, undocumented hacks that might break with future updates; or completely abandon features like Mermaid diagrams, thereby diminishing the richness and clarity of their content. This ultimately impacts the user experience by limiting the expressiveness and utility of the generated websites.

Understanding the Root Cause: API Limitations and Documentation Gaps

At its core, the problem stems from a combination of factors related to how Analog.js, Shiki, and Markdown processors interact, coupled with limitations in the current API and documentation. Analog.js, when configured to use Shiki for Markdown content, doesn't offer a straightforward mechanism to exclude specific languages from the Shiki highlighting pipeline. This is particularly evident when using WithMarkdownRenderer, which, as observed, doesn't natively support extensions or token filters that could allow fine-grained control over which code blocks are processed by Shiki. The intent of including mermaid via shikiOptions.highlighter.additionalLangs is clear: to enable Shiki to parse and highlight Mermaid syntax. However, this approach treats Mermaid as just another code language to be highlighted, failing to account for its unique nature as a diagramming language that often requires a client-side renderer.

Furthermore, the documentation, while helpful in showing how to add languages, lacks crucial warnings about the potential memory implications for constrained environments. It presents additionalLangs: ['mermaid'] as a valid and straightforward configuration without highlighting the risks associated with high memory usage during builds. This creates an expectation that it should just work, leading developers to discover the OOM issue only when they attempt to build in a CI environment. The current setup essentially forces a choice between enabling the feature and facing build failures or disabling it and losing functionality.

What's missing is a more nuanced way to handle different types of fenced code blocks. Ideally, the system should recognize that some blocks, like Mermaid, might not need server-side syntax highlighting by Shiki but rather require a client-side transformation. Analog's API currently doesn't expose hooks or options to:

1. Exclude specific languages from the Shiki pipeline: A skipLanguages: ['mermaid'] or similar option would be invaluable.
2. Mark certain blocks as "raw" or "client-only": This would signal to the build process that Shiki should ignore these blocks, perhaps passing them through directly to be processed by a dedicated client-side library.

Without these capabilities, developers are left trying to find brittle workarounds rather than relying on a stable, documented solution. This lack of flexibility in handling specialized code blocks like Mermaid is the primary driver behind the OOM errors in memory-constrained CI environments.

Potential Solutions: Enhancing Analog.js API for Flexibility

To resolve the Out-of-Memory errors when using Mermaid with Shiki in CI environments, we need to introduce more flexibility into the Analog.js content processing pipeline. The ideal solution would empower developers to control how specific code blocks are handled, particularly those that have distinct client-side rendering requirements. The core of the fix lies in providing a clear, documented way to bypass Shiki for languages like Mermaid. Several approaches could achieve this cleanly:

1. A skipLanguages Configuration Option: This is perhaps the most direct and intuitive solution. By introducing a new option, such as shikiOptions: { skipLanguages: ['mermaid'] }, developers could explicitly tell Shiki to ignore any fenced code blocks tagged with mermaid. This would prevent Shiki from attempting to parse and highlight these blocks during the build, thus significantly reducing memory consumption. The build process could then be configured to pass these mermaid blocks through to a client-side library for rendering.

2. A rawLanguages or clientOnlyLanguages Option: Similar to skipLanguages, this approach would categorize languages based on their processing needs. An option like shikiOptions: { rawLanguages: ['mermaid'] } or shikiOptions: { clientOnlyLanguages: ['mermaid'] } would achieve a similar effect. It signals that these languages are not meant for server-side syntax highlighting by Shiki but should be treated as raw content or specifically designated for client-side processing. This approach could also be extended to handle other types of content that require client-side JavaScript manipulation.

3. Enhanced WithMarkdownRenderer Capabilities: If modifying shikiOptions directly isn't feasible or desirable, extending the capabilities of WithMarkdownRenderer could be another path. This might involve allowing the configuration of marked extensions or token filters. Such an extension could be written to identify mermaid blocks and instruct the Markdown parser to ignore them for Shiki processing, perhaps by wrapping them in a specific marker or simply skipping them before Shiki gets involved. This offers a more programmatic way to customize the pipeline.

4. Clearer Documentation and Best Practices: While not a code change, significantly improving the documentation is a crucial step. Explicitly warning users about the memory usage of certain languages with Shiki in CI environments is essential. Furthermore, providing clear recommendations for handling Mermaid diagrams in SSR/CI setups would be invaluable. This documentation should guide users towards client-side rendering solutions for Mermaid and explain how to configure Analog.js to facilitate this, perhaps by suggesting how to manually extract Mermaid blocks and pass them to a client-side renderer.

Implementing any of these solutions would provide a robust and maintainable way to handle Mermaid diagrams without sacrificing build stability in memory-constrained environments. The goal is to offer a configuration that respects the different processing needs of various code block types, ensuring that developers can leverage powerful features like Mermaid alongside syntax highlighting without facing insurmountable build issues. This not only improves the developer experience but also broadens the applicability of Analog.js for diverse content-driven projects.

The Importance of a Stable Build for Content Developers

For developers building websites with rich content, a stable and predictable build process isn't just a convenience; it's a fundamental requirement. When working with Analog.js, Markdown, Shiki, and Mermaid, any instability in the build pipeline can severely hamper productivity and deployment efficiency. The Out-of-Memory errors encountered in CI environments, particularly those with limited memory like Cloudflare Pages, highlight a critical gap in handling specialized content elements. These errors don't just mean a failed build; they can lead to significant downtime, increased debugging time, and a loss of confidence in the development workflow.

Imagine a scenario where you're constantly pushing updates to a documentation site or a blog. If every few builds result in an OOM error because of a Mermaid diagram being processed by Shiki, your team's momentum is broken. Developers spend valuable time troubleshooting build failures instead of creating new content or features. This is especially detrimental for content-heavy sites where regular updates are key to keeping the audience engaged. Furthermore, for DevRel professionals and educators, who often use these tools to create engaging tutorials and learning materials, a broken build process can disrupt the delivery of crucial information. A smooth deployment pipeline ensures that valuable content reaches its audience promptly and reliably.

Moreover, the current situation forces developers into a difficult position. They must either:

• Accept unstable builds: This is not a sustainable solution for any professional project. Unreliable builds can lead to missed deadlines and unprofessional releases.
• Resort to undocumented hacks: Relying on unofficial workarounds is risky. These hacks might break with minor updates to Analog.js, Shiki, or their dependencies, requiring constant vigilance and re-engineering.
• Remove valuable features: Having to abandon Mermaid diagrams means sacrificing clarity and visual appeal in technical explanations or complex data representations. This can make the content harder to understand and less engaging for the reader.

By providing a supported way to exclude or manage Mermaid blocks (e.g., through a skipLanguages option), Analog.js can offer a significantly better developer experience. It allows developers to seamlessly integrate Mermaid diagrams into their Markdown content without fear of build failures. This flexibility ensures that the tools serve the content creators, rather than becoming an obstacle. Ultimately, ensuring a stable build process empowers developers to focus on what matters most: creating high-quality, engaging content for their users. This not only benefits the developers but also leads to more robust, feature-rich, and reliable websites for end-users.

Current Workarounds and the Path Forward

As it stands, the most reliable method to circumvent the Out-of-Memory errors when integrating Mermaid with Shiki in Analog.js CI builds is, unfortunately, to avoid using Mermaid within the Markdown files that are processed by Shiki. This means either refraining from using Mermaid diagrams altogether in your Markdown content or finding alternative ways to render them that bypass the Shiki highlighting process. This could involve manually extracting Mermaid code blocks from your Markdown files during the build process and then using a client-side JavaScript library (like the official Mermaid.js library) to render these diagrams in the browser. This approach requires custom scripting and a deeper understanding of the build pipeline, which can be complex and time-consuming for many developers.

Another workaround might involve using a different Markdown parser or a more configurable syntax highlighter that allows finer control over language inclusion and exclusion. However, this often means deviating from the recommended Analog.js setup and potentially introducing compatibility issues. The core problem remains: Analog.js, in its current form, doesn't provide a native, straightforward way to tell Shiki to ignore specific languages like Mermaid. This limitation is compounded by the fact that marked-shiki attempts to process all fenced code blocks, leading to the build failure if the language isn't recognized by the highlighter.

The ideal scenario, as discussed, involves enhancing Analog.js's API to offer options like skipLanguages or clientOnlyLanguages. Such additions would allow developers to explicitly mark Mermaid blocks for client-side processing, preventing Shiki from consuming excessive memory during the build. This would not only solve the OOM issue but also provide a cleaner, more maintainable solution than manual workarounds.

The willingness of the community to contribute is a vital part of addressing such issues. If you're encountering this problem and have the technical expertise, consider submitting a Pull Request (PR) to Analog.js. Features like these, driven by real-world use cases, significantly improve the framework for everyone. Even if you're not able to submit a PR, reporting the issue, providing context, and sharing your workarounds can help the maintainers understand the impact and prioritize fixes.

Ultimately, the path forward involves a collaborative effort between the Analog.js team and its users. By identifying these API limitations and documentation gaps, and by working together to implement robust solutions, we can ensure that Analog.js remains a powerful and flexible tool for building modern, content-rich web applications without the frustration of build failures.

For further insights into optimizing build processes and managing JavaScript dependencies, you might find the official documentation for Vite and Cloudflare Pages incredibly useful resources. They offer a wealth of information on build configurations and deployment best practices.