[Bug]: (v7) @mdx-js/rollup: Unexpected `FunctionDeclaration` in code: only import/exports are supported. Error for a custom vite server.

[zdunecki]

What version of React Router are you using?

v7

Steps to Reproduce

1. Install react-router (7.0.0-pre.1)
2. Install @mdx-js/rollup (tested with ^3.1.0 and ^3.0.1)
3. Create a custom vite server and add plugins for mdx + react-router
4. Run custom vite server

Demo: https://stackblitz.com/edit/vitejs-vite-xmllxz?file=package.json

Expected Behavior

As a user, I expect the same behaviour for a custom vite server as a react-router one when using a mdx plugin.

Actual Behavior

When I run a react-router via a custom vite server with @mdx-js/rollup plugin I got error:

[plugin:@mdx-js/rollup] Unexpected `FunctionDeclaration` in code: only import/exports are supported
/home/projects/vitejs-vite-xmllxz/Post.mdx:2:1
1  |  import {jsxDEV as _jsxDEV} from "react/jsx-dev-runtime";
2  |  function _createMdxContent(props) {
   |   ^
3  |    const _components = {
4  |      h1: "h1",

Demo: https://stackblitz.com/edit/vitejs-vite-xmllxz?file=package.json