Font-Display check should consider icon fonts

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:

• https://github.com/FortAwesome/Font-Awesome/issues/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 👍

[yisibl]

@PatOnTheBack A digression, is there any tool to test and compare the performance of svg and font icons?