[gatsby-transformer-remark] Add a way to get AST of Table of contents

[iray-tno]

Summary

Adding a way to get AST of Table of contents just like the htmlAst property.

Basic example

{
  allMarkdownRemark {
    edges {
      node {
        html
        htmlAst
        tableOfContents
        tableOfContentsAst // <- add this
      }
    }
  }
}

Motivation

When a user using htmlAst to customize the output DOM, they may want to access the AST of the table of contents too.
In my case, I'm using the htmlAst with rehype-react. When I want to add functionality to the table of contents, like emphasizing the header which a user is reading. It's very convenient if I can get the AST of the table of contents.

[PetroPavlenko]

Hi @freiksenet .
I'm using htmlAst with rehype and can all headers

import rehypeReact from "rehype-react";
const config = {
  createElement: React.createElement,
  Fragment: React.Fragment,
  components: {
    p: P,
    sup: Sup,
    a: StyledLink, 
    ol: Ol,
    ul: Ul,
    li: Li,
    h1: Heading1,
    h2: Heading2,
    h3: Heading3,
    h4: Heading4,
    h5: H5,
    b: Strong,
    i: Em,
    em: Em,
  },
};
const renderAst = new rehypeReact(astConfig).Compiler;

export const AstContent = ({ content, className }: AstContentProps) => (
  <div className={className}>
    {renderAst(content)}
  </div>
);

most tags are custom. And I can add styles how I want.
Not sure that's is answer to your question. But should be helpful )

[iray-tno]

Hi @PetroPavlenko . Maybe wrong mention? XD

Thanks for your comment.

Yeah, I'm doing the same thing with that for article content.
What I meant is I wanted to do that for the table of contents also.

By filtering elements except for headers, I can actually use the htmlAst for rendering the table of contents also.
But the rendering layer (components) looks like the wrong place to filter AST elements.
I think it's more convenient if I'm able to access AST of the table of contents.

[iray-tno]

This looks like the proper use-case of headings. #23546
I'll look into it a bit more tomorrow.

[iray-tno]

I'll look into it a bit more tomorrow.

"tomorrow"... haha

Sorry for the late reply.

I actually could do everything I wanted to do with the headings.
And now it looks enough simple for me. Maybe some functionalities are difficult to implement with my idea (tableOfContentsAst).
headings were better than it.

This issue can be closed.
But since it's already assigned @pieh, I let this open,