Font-Display check should consider icon fonts

[Stanzilla]

Feature request summary
A special check to not recommend font-display: swap for icon fonts.

What is the motivation or use case for changing this?

There seems to be no clear recommendation on what is actually best practice for icon fonts, and even if there is, it's not swap but actually block. So I would suggest either adding a special rule to to detect icon fonts or maybe whitelist the most common ones so they don't trigger the lighthouse warning when swap is not set.

Relevant links:

• Lighthouse Issue with Font Performance for font-display FortAwesome/Font-Awesome#14387
• https://www.zachleat.com/web/font-display-icon-fonts/
• https://stackoverflow.com/questions/49461308/correct-font-display-value-for-icon-fonts

How is this beneficial to Lighthouse?

Currently the Lighthouse recommendation is not actual the best practice and might cause people blindly following it to get unintended behaviour.

[patrickhulce]

Thanks for filing @Stanzilla!

so they don't trigger the lighthouse warning when swap is not set.

The Lighthouse audit is not looking for swap it's looking for any valid font-display value that's not the default. If you follow icon font best practices and use block, the audit will pass.

The Learn More docs are misleading on this point, so we'll update those 👍

[craze3]

Here is an example of it currently happening:

[patrickhulce]

@craze3 those font declarations in the stylesheets aren't using the icon font best practice block, that's a valid audit failure.

https://use.fontawesome.com/releases/v5.10.0-11/css/all.css font-display: auto not block
https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css missing font-display completely

[craze3]

Oo, thanks @patrickhulce. What's the quickest fix?

.fa,.fab,.fad,.fal,.far,.fas {
   font-display: block;
}

Think that will work ?

[patrickhulce]

Unfortunately it has to be declared with the font declaration, which if you're using the CDN version is controlled by them and there's no workaround.

It sounds like they plan to address this soon though, see FortAwesome/Font-Awesome#14387 (comment) :)

Also FWIW you don't lose anything on the performance score for this showing up in the audit, and for fonts that are going to change to block it's really just an 'ignore this URL' type of signal anyhow, so feel free to ignore that LH result in the meantime.

[tagliala]

Hi 👋👋

Geremia from Font Awesome here

Sorry for the late feedback, I've missed this.

Unfortunately it has to be declared with the font declaration, which if you're using the CDN version is controlled by them and there's no workaround.

...and unfortunately FA 4.7.0 is in EOL and we do not host it directly. Don't know if bootstrapcdn maintainers are interested in doing the fix and release an unofficial version of 4.7.0, anyone interested in having a fix on the old version maybe can ask.

In any case, since the fix cannot use the same version number for caching reasons, probably some plugins I can see in the screenshot must be updated on their turn