Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)

Affected packages and versions

@mdx-js/mdx@2.1.3

Link to runnable example

No response

Steps to reproduce

My actual use case is that I have an astro site with an mdx file that uses shiki twoslash to highlight code snippets in the mdx. I haven't been able to narrow it down to a smaller reproducible code example, but I do have a fix!

https://github.com/mdx-js/mdx/blob/main/packages/mdx/lib/plugin/recma-jsx-rewrite.js#L390
This line is generating an empty const statement, which is invalid JS. It should not generate a const statement if there are no declarations.

This fix works:

if (declarations.length > 0) {
  statements.push({
    type: 'VariableDeclaration',
    kind: 'const',
    declarations
  })
}

I can send a PR with this change, but I'm not sure how to write a test for this, since I'm not sure how to narrow it down. Would you be able to help with a test, or would you accept a PR without a test?

Expected behavior

Don't emit an empty const declaration

function MDXContent(props = {}) {
  return <MDXLayout {...props}><_createMdxContent {...props} /></MDXLayout>;
}

Actual behavior

It is generating this :(

function MDXContent(props = {}) {
  const ;
  return <MDXLayout {...props}><_createMdxContent {...props} /></MDXLayout>;
}

Runtime

Node v16

Package manager

npm v8

OS

macOS

Build and bundle tools

Astro