@shikijs/rehype: keep hast element data and properties

[remcohaszing]

Clear and concise description of the problem

With remark-rehype / MDX, the following markdown:

```js fileName="hello.js"
console.log('hello')
```

generates the following hast:

{
  type: 'element',
  tagName: 'pre',
  properties: {},
  children: [
    {
      type: 'element',
      tagName: 'code',
      properties: {
        className: 'language-js'
      },
      data: {
        meta: 'fileName="hello.js'
      },
      children: [
        {
          type: 'text',
          value: "console.log('hello')",
        }
      ]
    }
  ]
}

Given this has, Shiki replaces the pre element with a newly generated pre element. In this process the node’s data and properties are lost. It would be nice if Shiki keeps this information, so that other rehype plugins, such as rehype-mdx-code-props can use it. Likewise it could even be useful to preserve positional information, which is used for example by React devtools.

Suggested solution

It looks like some logic is needed in https://github.com/shikijs/shiki/blob/main/packages/core/src/code-to-hast.ts to be able to handle an existing pre and code element.

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guide.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

Contributes

• If this feature request is accepted, I am willing to submit a PR to fix this issue

[antfu]

Sure, PR welcome!