src/language-html/print-preprocess.js/addHasHtmComponentClosingTag
function addHasHtmComponentClosingTag(ast, options) {
  ast.walk((node) => {
    if (node.type !== "element") {
      return;
    }

    node.hasHtmComponentClosingTag =
      node.endSourceSpan &&
      /^<\s*\/\s*\/\s*>$/.test(
        options.originalText.slice(
          node.endSourceSpan.start.offset,
          node.endSourceSpan.end.offset
        )
      );
  });
}