Bug 283538 – font downloaded despite no document characters contained within its unicode-range

• Component: Text
• Status: NEW

[Cameron Beccario]

Created attachment 473325 [details]
screenshot of network tab showing download of myfont.ttf

Webkit is downloading a font even though no characters in the document fall inside its unicode-range.

Steps to Reproduce:
Open the repro described in https://bugs.webkit.org/show_bug.cgi?id=42154, copied here for convenience:

<style>
@font-face {
  font-family:myfont;
  src: url(myfont.ttf);
  unicode-range: U+FFFF;
}
</style>
<span style="font-family:myfont">
No characters here are in the unicode-range.
</span>

Expected:
No attempt to download myfont.ttf

Actual:
myfont.ttf is downloaded

Build Date & Hardware:
- MacBook Pro M1 Max, Sonoma 14.6.1
- Release 207 (Safari 18.2, WebKit 19621.1.4.3)

Both Chrome and FF do not download the font.

Webkit's behavior is non-conformant to the specification of the CSS3 unicode-range descriptor (https://drafts.csswg.org/css-fonts-3/#unicode-range-desc):
"User agents must not download or use the font for codepoints outside this set."

This appears to be a regression of the fix for https://bugs.webkit.org/show_bug.cgi?id=42154

[Radar WebKit Bug Importer]

<rdar://problem/140674753>