Jupyter-book: Collapsible TOC entries not displaying correctly

[melaniewalsh]

Describe the bug

I just upgraded to jupyter-book v 0.9 but for some reason the collapsible TOC entries aren't displaying correctly.

To Reproduce

Steps to reproduce the behavior:

1. Go to https://melaniewalsh.github.io/Intro-Cultural-Analytics/Data-Collection/Data-Collection.html
2. See the down arrow next to "Data Collection (Web Scraping, APIs)" not displaying correctly

Here's the HTML for this page: https://github.com/melaniewalsh/Intro-Cultural-Analytics/blob/gh-pages/Data-Collection/Data-Collection.html#L248

1. Go to https://melaniewalsh.github.io/Intro-Cultural-Analytics/
2. See none of the collapsible TOC entries displaying

Environment

• Python Version [e.g. 3.7.1]: 3.7.6
• Package versions or output of jupyter-book --version:

Jupyter Book: 0.9.1
MyST-NB: 0.10.1
Sphinx Book Theme: 0.0.39
MyST-Parser: 0.13.0
Jupyter-Cache: 0.4.1
NbClient: 0.4.0

• Operating System: Mac OS

[chrisjsewell]

Yes the toc collapse icon elements appear malformed:
From https://sphinx-book-theme.readthedocs.io/en/latest/, a chevron looks like:

    <i class="fas fa-chevron-down">
    </i>

But on your site:

    <i attrs="{'class': ['fas', 'fa-chevron-down']}">
    </i>  

what is the sphinx version?

[melaniewalsh]

Sphinx version 3.4.0. Should I try to upgrade it?

[chrisjsewell]

actually also what is your version of beautifulsoup4, perhaps the new_tag implementation has changed here: https://github.com/executablebooks/sphinx-book-theme/blob/1ef9216b50d57d267b57dd96088577b2d342939d/sphinx_book_theme/__init__.py#L175-L176

[melaniewalsh]

beautifulsoup4 Version: 4.6.0

[chrisjsewell]

The sphinx-book-theme documentation was built with version 4.9.3, perhaps try that

[chrisjsewell]

yeh I believe it is due to this change in 4.6.1 https://bazaar.launchpad.net/~leonardr/beautifulsoup/bs4/view/head:/CHANGELOG#L258

[melaniewalsh]

Thank you!! Upgrading beautifulsoup4 fixed the issue and now the collapsible TOC entries are displaying properly.