Function ensureLang

packages/react/src/lib/shiki.ts:174–200

(lang: SupportedLang, onLoaded?: () => void)

const loadingLangs = new Set<string>();

export function ensureLang(lang: SupportedLang, onLoaded?: () => void): boolean {
  const loaded = highlighter.getLoadedLanguages();
  if (loaded.includes(lang)) return true;

  const loader = LAZY_LANG_LOADERS[lang];
  if (!loader) return true; // Not a lazy lang, must be already loaded

  if (!loadingLangs.has(lang)) {
    loadingLangs.add(lang);
    void loader().then((mod: any) => {
      const registration = mod.default ?? mod;
      highlighter.loadLanguageSync(registration);
      loadingLangs.delete(lang);
      onLoaded?.();
    });
  } else if (onLoaded) {
    const l = loader;
    void l().then((mod: any) => {
      const registration = mod.default ?? mod;
      if (!highlighter.getLoadedLanguages().includes(lang)) {
        highlighter.loadLanguageSync(registration);
      }
      onLoaded();
    });
  }
  return false;
}

// ---------------------------------------------------------------------------
// Streamdown code highlighter plugin