1810709 - Unreliable evaluation of the "first available font" for CSS purposes

Status: RESOLVED FIXED

(Core :: Layout: Text and Fonts, defect)

Description

[Jonathan Kew [:jfkthame]]

The CSS Fonts spec defines the first available font, to be used in computing things like font-relative lengths and 'normal' line-height. This almost corresponds to Gecko's gfxFontGroup::GetFirstValidFont method, but our implementation is not quite correct.

In particular, GetFirstValidFont will return the first font in the fontGroup's list, if it has been instantiated already, even if that font excludes the <space> character. This is incorrect, and results in some WPT test failures.

Comment 1

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1810709 - Make GetFirstValidFont() check whether the required character is supported by the font. r=#layout-reviewers

Except in the case of <space>, which is not required to be present for the font to be used
as the "first available font" in CSS (https://drafts.csswg.org/css-fonts-4/#first-available-font);
for that, only unicode-range coverage is applicable.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/35a64e1c9e32
Make GetFirstValidFont() check whether the required character is supported by the font. r=emilio

Comment 3

[Web Platform Test Sync Bot (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/38033 for changes under testing/web-platform/tests

Comment 4

[Serban Stanca [:SerbanS]]

https://hg.mozilla.org/mozilla-central/rev/35a64e1c9e32

Comment 5

[Web Platform Test Sync Bot (Matrix: #interop:mozilla.org)]

Upstream PR merged by moz-wptsync-bot