Extend .TableOfContents from within shortcode

support
3

See https://gohugo.io/content-management/shortcodes/#shortcodes-with-markdown.

Shortcodes using the % as the outer-most delimiter will now be fully rendered when sent to the content renderer. They can be part of the generated table of contents, footnotes, etc.

content/post/test.md

+++
title = "Test"
date = 2021-03-27T04:48:08-07:00
draft = false
introduction = "This is the introduction."
conclusion = "This is the conclusion."
+++

{{% my-shortcode introduction %}}

{{% my-shortcode conclusion %}}

layouts/shortcodes/my-shortcode.html

{{ with $topic := .Get 0 }}
  ## {{ $topic | title }}
  {{ index $.Page.Params $topic }}
{{ else }}
  {{ errorf "The %s shortcode requires a single positional parameter. See %s" .Name .Position }}
{{ end }}

Produces this HTML.

<nav id="TableOfContents">
  <ul>
    <li><a href="#introduction">Introduction</a></li>
    <li><a href="#conclusion">Conclusion</a></li>
  </ul>
</nav>
<h1>Test</h1>
<h2 id="introduction">Introduction</h2>
<p>This is the introduction.</p>
<h2 id="conclusion">Conclusion</h2>
<p>This is the conclusion.</p>