Function createHighlighter

packages/rehype-shiki/src/highlighter.mjs:44–119

({ coreOptions = {}, highlighterOptions = {} })

 * @returns {SyntaxHighlighter}
 */
const createHighlighter = ({ coreOptions = {}, highlighterOptions = {} }) => {
  const options = {
    themes: [DEFAULT_THEME],
    ...coreOptions,
  };
  const shiki = createHighlighterCoreSync(options);
  const theme = options.themes[0];

  const loadedLanguages = new Set(
    shiki.getLoadedLanguages().map(lang => lang.toLowerCase())
  );

  /**
   * Resolves a language id to one this highlighter can handle.
   * Falls back to plain text for unknown/unloaded languages so
   * highlighting never throws on unrecognized code fences.
   *
   * @param {string} [languageId]
   * @returns {string}
   */
  const resolveLanguage = languageId => {
    const normalized = languageId?.toLowerCase();

    if (
      normalized &&
      (isSpecialLang(normalized) || loadedLanguages.has(normalized))
    ) {
      return languageId;
    }

    return FALLBACK_LANGUAGE;
  };

  /**
   * Highlights code and returns the inner HTML inside the <code> tag
   *
   * @param {string} code - The code to highlight
   * @param {string} lang - The programming language to use for highlighting
   * @param {Record<string, any>} meta - Metadata
   * @returns {string} The inner HTML of the highlighted code
   */
  const highlightToHtml = (code, lang, meta = {}) =>
    shiki
      .codeToHtml(code, {
        lang: resolveLanguage(lang),
        theme,
        meta,
        ...highlighterOptions,
      })
      // Shiki will always return the Highlighted code encapsulated in a <pre> and <code> tag
      // since our own CodeBox component handles the <code> tag, we just want to extract
      // the inner highlighted code to the CodeBox
      .match(/<code>(.+?)<\/code>/s)[1];

  /**
   * Highlights code and returns a HAST tree
   *
   * @param {string} code - The code to highlight