src/language-html/print-preprocess.js/markTsScript
function markTsScript(ast, options) {
  if (options.parser === "vue") {
    const vueScriptTag = ast.children.find((child) =>
      isVueScriptTag(child, options)
    );
    if (!vueScriptTag) {
      return;
    }
    const { lang } = vueScriptTag.attrMap;
    if (lang === "ts" || lang === "typescript") {
      options.__should_parse_vue_template_with_ts = true;
    }
  }
}