A (Linux compatible) Swift library for server-side syntax highlighting using Prism.js.

Features

• Server-side syntax highlighting for 290+ languages
• Process entire HTML documents
• Support for custom Prism.js bundles and plugins
• Cross-platform: macOS, iOS, and Linux

Installation

Add Moon to your Package.swift:

dependencies: [
  .package(url: "https://github.com/loopwerk/Moon", from: "1.0.0"),
]

Then add it to your target:

.target(
  name: "YourTarget",
  dependencies: ["Moon"]
)

Usage

Basic Usage

import Moon

// Process an entire HTML document
let html = """
<pre><code class="language-python">def hello():
  print("Hello, World!")
</code></pre>
"""

let highlighted = Moon.shared.highlightCodeBlocks(in: html)

Additional Plugins

Moon includes a Prism.js bundle with all standard languages, and it preserves HTML markup within code blocks, like the Keep Markup plugin. For languages not included (like Svelte), you can load additional plugins:

let moon = try Moon(additionalPlugins: ["prism-svelte.js"])

The plugin files must be included in your target's resources:

.target(
  name: "YourTarget",
  dependencies: ["Moon"],
  resources: [
    .copy("Resources/prism-svelte.js"),
  ]
)

Custom Prism.js Bundle

To use a custom Prism.js bundle, create one at prismjs.com/download.html and save it as prism.js in your target's resources:

.target(
  name: "YourTarget",
  dependencies: ["Moon"],
  resources: [
    .copy("Resources/prism.js"),
  ]
)

How It Works

Moon embeds Prism.js and executes it via JavaScriptCore (using JXKit). This provides 100% Prism.js compatibility with all its language definitions.

The highlightCodeBlocks(in:) method finds all <code class="language-xxx"> blocks in HTML and applies syntax highlighting, returning the modified HTML with Prism's token classes applied.

Output Format

Moon outputs HTML with Prism.js CSS classes:

<code class="language-python">
  <span class="token keyword">def</span>
  <span class="token function">hello</span>
  <span class="token punctuation">(</span>
  <span class="token punctuation">)</span>
  <span class="token punctuation">:</span>
  ...
</code>

Use any Prism.js theme to style the output.

Requirements

• Swift 5.5+
• macOS 12+ / iOS 15+ / Linux

On Linux, you need to install WebKit GTK development libraries:

# Ubuntu/Debian
$ sudo apt install libjavascriptcoregtk-4.1-dev

# Fedora
$ sudo dnf install webkit2gtk4.1-devel

License

Moon is available under the MIT license. See the LICENSE file for more info.

Prism.js is available under the MIT license. You can find the LICENSE file here.