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simonwuelker merged 2 commits into from
Jul 15, 2026
+323 −109
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script: Populate document.fonts with web fonts from CSS #46509

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244f65b
script: Populate document.fonts with font faces from CSS
simonwuelker Jul 14, 2026
924c2ff
Update wpt expectations
simonwuelker Jul 14, 2026
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1 change: 1 addition & 0 deletions Cargo.lock
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108 changes: 46 additions & 62 deletions components/fonts/font_context.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,8 +12,9 @@ use std::sync::atomic::{AtomicBool, Ordering};
use app_units::Au;
use content_security_policy::Violation;
use fonts_traits::{
CSSFontFaceDescriptors, FontDescriptor, FontIdentifier, FontTemplate, FontTemplateRef,
FontTemplateRefMethods, StylesheetWebFontLoadFinishedCallback,
CSSFontFaceDescriptors, FontDescriptor, FontFaceRuleWithOrigin, FontIdentifier, FontTemplate,
FontTemplateRef, FontTemplateRefMethods, StylesheetWebFontLoadFinishedCallback,
WebFontSetDifference,
};
use log::{debug, trace};
use malloc_size_of::MallocSizeOf;
Expand Down Expand Up @@ -41,8 +42,8 @@ use style::font_face::{
};
use style::properties::generated::font_face::Descriptors as FontFaceRuleDescriptors;
use style::properties::style_structs::Font as FontStyleStruct;
use style::shared_lock::{Locked, StylesheetGuards};
use style::stylesheets::{FontFaceRule, Origin};
use style::shared_lock::StylesheetGuards;
use style::stylesheets::FontFaceRule;
use style::stylist::Stylist;
use style::values::computed::font::{FamilyName, FontFamilyNameSyntax, SingleFontFamily};
use url::Url;
Expand Down Expand Up @@ -644,7 +645,7 @@ pub trait FontContextWebFontMethods {
guards: &StylesheetGuards<'_>,
callback: StylesheetWebFontLoadFinishedCallback,
document_context: &WebFontDocumentContext,
);
) -> WebFontSetDifference;
fn load_single_font_face_rule(
&self,
font_face_rule: &FontFaceRule,
Expand Down Expand Up @@ -697,38 +698,38 @@ impl FontContextWebFontMethods for Arc<FontContext> {
guards: &StylesheetGuards<'_>,
callback: StylesheetWebFontLoadFinishedCallback,
document_context: &WebFontDocumentContext,
) {
let mut removed_any = false;

self.known_font_face_rules
) -> WebFontSetDifference {
let difference = self
.known_font_face_rules
.lock()
.diff_old_and_new_font_face_rules(
stylist,
guards,
|new_rule| {
self.load_single_font_face_rule(
new_rule,
webview_id,
callback.clone(),
document_context,
);
},
|stale_rule| {
self.remove_single_font_face_rule(
&stale_rule.descriptors,
&mut self.web_fonts.write(),
);
removed_any = true;
},
.diff_old_and_new_font_face_rules(stylist, guards);

for added_rule in &difference.added_font_faces {
let added_rule = added_rule.read_with(guards);
self.load_single_font_face_rule(
added_rule,
webview_id,
callback.clone(),
document_context,
);
}
for removed_rule in &difference.removed_font_faces {
let removed_rule = removed_rule.read_with(guards);
self.remove_single_font_face_rule(
&removed_rule.descriptors,
&mut self.web_fonts.write(),
);
}

if removed_any {
if !difference.removed_font_faces.is_empty() {
// We modified the list of available fonts, so invalidate resolved font groups.
self.resolved_font_groups.write().clear();

// Ensure that we clean up any WebRender resources on the next display list update.
self.have_removed_web_fonts.store(true, Ordering::Relaxed);
}

difference
}

fn load_web_font_for_script(
Expand Down Expand Up @@ -1237,47 +1238,24 @@ struct KnownFontFaceRule {
generation: bool,
}

#[derive(MallocSizeOf)]
struct FontFaceRuleWithOrigin {
#[conditional_malloc_size_of]
rule: ServoArc<Locked<FontFaceRule>>,
origin: Origin,
}

impl FontFaceRuleWithOrigin {
fn read_with<'a>(&'a self, guards: &'a StylesheetGuards) -> &'a FontFaceRule {
match self.origin {
Origin::Author => self.rule.read_with(guards.author),
Origin::UserAgent | Origin::User => self.rule.read_with(guards.ua_or_user),
}
}
}

impl KnownFontFaceRules {
/// Computes the difference between the `@font-face `rules that are currently in effect
/// and the ones that the `Stylist` knows about. The caller is notified about new or removed rules
/// with callbacks.
fn diff_old_and_new_font_face_rules<NewRuleCallback, StaleRuleCallback>(
fn diff_old_and_new_font_face_rules(
&mut self,
stylist: &Stylist,
guards: &StylesheetGuards<'_>,
mut new_rule_callback: NewRuleCallback,
mut stale_rule_callback: StaleRuleCallback,
) where
NewRuleCallback: FnMut(&FontFaceRule),
StaleRuleCallback: FnMut(&FontFaceRule),
{
) -> WebFontSetDifference {
let mut difference = WebFontSetDifference::default();
self.generation = !self.generation;

let font_face_rules_in_cascade_order = stylist
.iter_extra_data_origins()
.flat_map(|(extra_data, origin)| {
extra_data.font_faces.iter().rev().zip(iter::repeat(origin))
})
.map(|((rule, _layer), origin)| FontFaceRuleWithOrigin {
rule: rule.clone(),
origin,
});
.map(|((rule, _layer), origin)| FontFaceRuleWithOrigin::new(rule.clone(), origin));

// First, find any *new* font families that were not defined previously
let mut number_of_unchanged_rules = 0;
Expand Down Expand Up @@ -1308,9 +1286,9 @@ impl KnownFontFaceRules {
let mut index_of_existing_entry_for_this_rule = None;
for (index, known_font_face) in known_font_faces_for_family.iter().enumerate() {
// See if this is a entry for this @font-face that existed prior to the current update
if ServoArc::ptr_eq(
&known_font_face.rule_with_origin.rule,
&rule_with_origin.rule,
if FontFaceRuleWithOrigin::ptr_eq(
&known_font_face.rule_with_origin,
&rule_with_origin,
) {
index_of_existing_entry_for_this_rule = Some(index);
}
Expand Down Expand Up @@ -1345,7 +1323,9 @@ impl KnownFontFaceRules {
if conflicting_declaration_with_higher_priority_exists {
let stale_rule =
known_font_faces_for_family.remove(index_of_existing_entry_for_this_rule);
stale_rule_callback(stale_rule.rule_with_origin.read_with(guards));
difference
.removed_font_faces
.push(stale_rule.rule_with_origin);
} else {
number_of_unchanged_rules += 1;
known_font_faces_for_family[index_of_existing_entry_for_this_rule].generation =
Expand All @@ -1357,7 +1337,7 @@ impl KnownFontFaceRules {
continue;
} else {
// This is a new rule that does not conflict with anything that previously existed, so insert it.
new_rule_callback(borrowed_rule);
difference.added_font_faces.push(rule_with_origin.clone());
known_font_faces_for_family.push(KnownFontFaceRule {
rule_with_origin,
generation: self.generation,
Expand All @@ -1369,19 +1349,23 @@ impl KnownFontFaceRules {
// This is the common case, where the new set of known @font-face rules is a superset of
// the old one after applying the cascade. In this case there is nothing more to do,
// because all old @font-face rules are still present.
return;
return difference;
}

// Remove all `@font-face` rules that were not updated - those no longer exist on the stylist.
self.contents.retain(|_, known_font_faces_for_family| {
known_font_faces_for_family
.extract_if(.., |rule| rule.generation != self.generation)
.for_each(|removed_rule| {
stale_rule_callback(removed_rule.rule_with_origin.read_with(guards))
difference
.removed_font_faces
.push(removed_rule.rule_with_origin);
});

!known_font_faces_for_family.is_empty()
});

difference
}
}

Expand Down
66 changes: 45 additions & 21 deletions components/layout/layout_impl.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ use embedder_traits::{
};
use euclid::{Point2D, Rect, Scale, Size2D};
use fonts::{FontContext, FontContextWebFontMethods};
use fonts_traits::StylesheetWebFontLoadFinishedCallback;
use fonts_traits::{StylesheetWebFontLoadFinishedCallback, WebFontSetDifference};
use icu_locid::subtags::Language;
use layout_api::{
AxesOverflow, BoxAreaType, CSSPixelRectVec, DangerousStyleNode, IFrameSizes, Layout,
Expand Down Expand Up @@ -1003,12 +1003,8 @@ impl LayoutThread {
});
let mut reflow_statistics = Default::default();

let (mut reflow_phases_run, iframe_sizes) = self.restyle_and_build_trees(
&mut reflow_request,
document,
root_element,
&image_resolver,
);
let (mut reflow_phases_run, iframe_sizes, changed_web_fonts) = self
.restyle_and_build_trees(&mut reflow_request, document, root_element, &image_resolver);
if self.build_stacking_context_tree_for_reflow(&reflow_request) {
reflow_phases_run.insert(ReflowPhasesRun::BuiltStackingContextTree);
}
Expand Down Expand Up @@ -1042,6 +1038,7 @@ impl LayoutThread {
pending_svg_elements_for_serialization,
iframe_sizes: Some(iframe_sizes),
reflow_statistics,
changed_web_fonts,
})
}

Expand All @@ -1052,7 +1049,7 @@ impl LayoutThread {
document: ServoDangerousStyleDocument<'dom>,
guards: &StylesheetGuards,
ua_stylesheets: &UserAgentStylesheets,
) -> StylesheetInvalidationSet {
) -> StylistStylesheetUpdate {
let need_user_agent_stylesheet_addition = !self.have_added_user_agent_stylesheets;
if need_user_agent_stylesheet_addition {
for stylesheet in &ua_stylesheets.user_agent_stylesheets {
Expand Down Expand Up @@ -1092,17 +1089,23 @@ impl LayoutThread {

// Load new @font-face rules and remove old ones if necessary.
// TODO: Can we make the invalidation set tell us whether any @font-face rules changed?

@TimvdLippe TimvdLippe Jul 15, 2026

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Is this TODO still relevant? I am not intimately familiar with this code, but I think it does now.

@simonwuelker simonwuelker Jul 15, 2026

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Its still relevant. Ideally stylo could tell us whether a stylesheet that was added to the page and then we might not have to call rebuild_font_face_set at all.

if need_user_agent_stylesheet_addition || reflow_request.stylesheets_changed() {
self.font_context.rebuild_font_face_set(
self.webview_id,
&self.stylist,
guards,
self.web_font_finished_loading_callback.clone(),
&reflow_request.document_context,
);
}
let changed_web_fonts =
if need_user_agent_stylesheet_addition || reflow_request.stylesheets_changed() {
self.font_context.rebuild_font_face_set(
self.webview_id,
&self.stylist,
guards,
self.web_font_finished_loading_callback.clone(),
&reflow_request.document_context,
)
} else {
WebFontSetDifference::default()
};

invalidation_set
StylistStylesheetUpdate {
invalidation_set,
changed_web_fonts,
}
}

#[servo_tracing::instrument(skip_all)]
Expand All @@ -1112,7 +1115,7 @@ impl LayoutThread {
document: ServoDangerousStyleDocument<'_>,
root_element: ServoLayoutElement<'_>,
image_resolver: &Arc<ImageResolver>,
) -> (ReflowPhasesRun, IFrameSizes) {
) -> (ReflowPhasesRun, IFrameSizes, WebFontSetDifference) {
let mut snapshot_map = SnapshotMap::new();
let _snapshot_setter = match reflow_request.restyle.as_mut() {
Some(restyle) => SnapshotSetter::new(restyle, &mut snapshot_map),
Expand Down Expand Up @@ -1144,7 +1147,14 @@ impl LayoutThread {
}
}

self.prepare_stylist_for_reflow(reflow_request, document, &guards, &user_agent_stylesheets)
let stylist_update = self.prepare_stylist_for_reflow(
reflow_request,
document,
&guards,
&user_agent_stylesheets,
);
stylist_update
.invalidation_set
.process_style(dangerous_root_element, Some(&snapshot_map));

if self.previously_highlighted_dom_node.get() != reflow_request.highlighted_dom_node {
Expand Down Expand Up @@ -1256,7 +1266,11 @@ impl LayoutThread {

if !damage.contains(LayoutDamage::DescendantCollectedAsLayoutRoot) {
layout_context.style_context.stylist.rule_tree().maybe_gc();
return (ReflowPhasesRun::empty(), IFrameSizes::default());
return (
ReflowPhasesRun::empty(),
IFrameSizes::default(),
stylist_update.changed_web_fonts,
);
}

debug_assert!(!layout_roots.is_empty());
Expand All @@ -1267,6 +1281,7 @@ impl LayoutThread {
return (
ReflowPhasesRun::RanLayout,
std::mem::take(&mut *layout_context.iframe_sizes.lock()),
stylist_update.changed_web_fonts,
);
}

Expand Down Expand Up @@ -1317,6 +1332,7 @@ impl LayoutThread {
(
ReflowPhasesRun::RanLayout,
std::mem::take(&mut *iframe_sizes),
stylist_update.changed_web_fonts,
)
}

Expand Down Expand Up @@ -1891,3 +1907,11 @@ impl ReflowPhases {
}
}
}

/// Summarizes changes after flushing stylesheets on the `Stylist`.
struct StylistStylesheetUpdate {
/// Information about what kind of selectors changed.
invalidation_set: StylesheetInvalidationSet,
/// A list of changes to the set of web fonts.
changed_web_fonts: WebFontSetDifference,
}
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