Add Astro lexer support

[nyaomaru]

The name of the language

Astro

Astro components use the .astro file extension.

The syntax combines a component script section between --- fences with an HTML-like template section.

Official syntax documentation:

• Astro template expressions reference: https://docs.astro.build/en/reference/astro-syntax/
• Astro components overview: https://docs.astro.build/en/basics/astro-components/

Example:

---
const title = "Hello Astro";
const items = ["a", "b", "c"];
---

<h1>{title}</h1>

<ul>
  {items.map((item) => (
    <li>{item}</li>
  ))}
</ul>

---

Implementation in other libraries

Astro syntax highlighting is supported in other syntax highlighting tools/libraries.

• Prism / Astro docs mention that lang="astro" can be used with Astro’s Prism component: https://docs.astro.build/en/guides/syntax-highlighting/
• Shiki is used by Astro for syntax highlighting and supports Astro code highlighting in Astro projects: https://docs.astro.build/en/guides/syntax-highlighting/

I could not find an existing Astro lexer request in Rouge issues or pull requests.

---

Additional context

Supporting Astro in Rouge would help downstream platforms that use Rouge for syntax highlighting, such as Forem / DEV.to.

Currently, Markdown code fences like this are not highlighted as Astro on DEV.to:

---
const title = "Hello Astro";
---

<h1>{title}</h1>

A first implementation could support:

• tag: astro
• filenames: *.astro
• the --- ... --- component script section as JavaScript/TypeScript-like code
• the template section as HTML-like markup
• {...} template expressions as JavaScript-like expressions

I’m opening this as a lexer request because Astro code blocks are becoming common in technical articles and documentation.

I hope this helps anyone interested in adding support for Astro in Rouge.