Broken icon data URL prevents loading of external favicon in lab template

[zyzzyxdonta]

Description

The lab template contains a <link rel="icon" ... /> element with a broken data URL (the data URL is probably fine but it doesn't encode an image):

voila/share/jupyter/voila/templates/lab/index.html.j2

Line 60 in 0ffd12a

<link rel="icon" href="data:;base64,=">

This leads to browsers not loading external favicons (/favicon.ico) and trying to display the given one. Since the given icon is not a valid data URL, this does not work.

Firefox struggles with this quite a bit and even sometimes shows the icon of the page previously visited, instead.

Reproduce

1. Create clean venv and install voila
2. Run voila any-notebook.ipynb without any config or setup
3. Inspect the source of the loaded page (after rendering) and look for <link rel="icon" → This shows the broken data URL still
4. Check requests → This shows either an aborted request for favicon.ico (in Firefox) or no request at all (Chromium)

Expected behavior

The HTML should not contain a broken favicon URL. If it contains a favicon it should be minimal (Voilà logo or transparent) and I should be able to replace it easily via a command line parameter. I would prefer for this line to be removed.

Context

• voila version 0.5.7
• Operating System and version: Fedora Linux 40 (KDE Plasma), Ubuntu 22.04.4 LTS
• Browser and version: Firefox 130, Chromium 128

Troubleshoot Output

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Command Line Output

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Browser Output

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If using JupyterLab

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Installed Labextensions

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