[WIP] rustdoc: Add tree-sitter syntax highlighting for non-Rust code blocks #149944
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Integrate arborium (tree-sitter based highlighting) to provide syntax highlighting for non-Rust code blocks in documentation. Previously, code blocks like ```python or ```javascript were rendered as plain text. Supported languages: bash, c, cpp, css, go, html, java, javascript, json, python, ruby, sql, toml, typescript, yaml. The highlighting uses custom HTML elements (a-k for keywords, a-s for strings, etc.) which are styled via CSS to match rustdoc's existing color scheme across all themes (light, dark, ayu).
Gate the arborium-based syntax highlighting behind an unstable flag (-Z unstable-options --highlight-foreign-code) so it can be tested before becoming the default behavior. The flag is threaded through: - RenderOptions in config.rs - SharedContext in context.rs - Markdown/MarkdownWithToc structs in markdown.rs - CodeBlocks iterator for actual highlighting
Test cases: - Highlighting enabled: Python, JavaScript, JSON produce arborium tags - Language aliases work (py -> python, js -> javascript) - Highlighting disabled: no arborium tags produced - Unsupported languages fall back to plain escaped text
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Summary
This PR adds syntax highlighting for non-Rust code blocks in rustdoc using arborium, a tree-sitter based highlighting library.
Currently, code blocks like
```pythonor```javascriptare rendered as plain text. This PR enables proper syntax highlighting for 15 languages: Python, JavaScript, TypeScript, Bash, C, C++, Go, Java, JSON, TOML, YAML, SQL, Ruby, CSS, and HTML.Status
This is not intended to merge as-is, but as a basis for discussion.
There are other approaches being explored, such as post-processing the rustdoc HTML output rather than integrating directly into the rendering pipeline. See bearcove/arborium#36 for context on the different approaches.
Usage
Behind an unstable flag:
Implementation
arboriumas a dependency with 15 language grammarsCodeBlocksiterator inhtml/markdown.rs<a-k>for keywords,<a-s>for strings, etc.)Open questions