Work/better detect code lang

[onigetoc]

Summary

Improve automatic language detection for fenced code blocks in markdown output.

The main goal is to emit better fence labels (for example ```javascript, ```typescript, ```bash) instead of empty or incorrect labels when Defuddle extracts code from documentation pages.

Main implementation

New file added first

• src/elements/detect-code-lang.ts

This file centralizes language guessing logic.

Detection strategy

Language detection now uses ordered heuristics:

1. Strong signature rules first (high confidence)

   • php, html, xml
   • shebang-based detection (bash, python, javascript)
   • dockerfile, cpp, java, go, rust, ruby, python, sql, latex

2. Context/shape-based rules

   • typescript and tsx patterns
   • css and yaml
   • markdown content heuristics (isMarkdown)
   • json

3. Final fallback

   • common CLI patterns => bash
   • JS fallback detection via declarations/import/export patterns

Rule order is intentional to reduce false positives (for example HTML before CSS, markdown before generic fallbacks, JSON after YAML checks).

Other files updated in the original flow

• src/elements/code.ts
  • Uses the new detector in the code normalization/serialization pipeline.
• src/extractors/github.ts
  • Keeps GitHub extraction aligned with improved language labels.

Why this improves output

• More code fences include a reliable language tag.
• Syntax highlighting quality is better in markdown consumers (including Obsidian).
• Less manual cleanup after scraping technical docs.

Backward compatibility

• If no rule matches confidently, behavior still falls back safely.
• The change is additive: existing extraction flow remains intact.

Manual validation

Tested against a mix of docs and code-heavy pages, including:

• https://github.com/kepano/defuddle
• https://kieran.casa/aws-sdk-waiters-ts/
• https://expressjs.com/en/guide/routing/

Also verified on pages containing shell snippets, TypeScript/JavaScript examples, and markdown documentation blocks.

Notes

Branch: work/better-detect-code-lang.