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ladybird/Libraries/LibWeb/CSS/StyleScope.cpp
Andreas Kling 66263f142b LibWeb: Add StyleScope to keep style caches per Document/ShadowRoot 
Before this change, we've been maintaining various StyleComputer caches
at the document level.

This made sense for old-school documents without shadow trees, since
all the style information was document-wide anyway. However, documents
with many shadow trees ended up suffering since any time you mutated
a style sheet inside a shadow tree, *all* style caches for the entire
document would get invalidated.

This was particularly expensive on Reddit, which has tons of shadow
trees with their own style elements. Every time we'd create one of their
custom elements, we'd invalidate the document-level "rule cache" and
have to rebuild it, taking about ~60ms each time (ouch).

This commit introduces a new object called StyleScope.

Every Document and ShadowRoot has its own StyleScope. Rule caches etc
are moved from StyleComputer to StyleScope.

Rule cache invalidation now happens at StyleScope level. As an example,
rule cache rebuilds now take ~1ms on Reddit instead of ~60ms.

This is largely a mechanical change, moving things around, but there's
one key detail to be aware of: due to the :host selector, which works
across the shadow DOM boundary and reaches from inside a shadow tree out
into the light tree, there are various places where we have to check
both the shadow tree's StyleScope *and* the document-level StyleScope
in order to get all rules that may apply.
2025-11-14 22:05:33 +01:00

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/*
* Copyright (c) 2018-2025, Andreas Kling <andreas@ladybird.org>
* Copyright (c) 2022-2025, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <LibCore/ReportTime.h>
#include <LibWeb/CSS/CSSKeyframesRule.h>
#include <LibWeb/CSS/CSSLayerBlockRule.h>
#include <LibWeb/CSS/CSSLayerStatementRule.h>
#include <LibWeb/CSS/CSSNestedDeclarations.h>
#include <LibWeb/CSS/CSSStyleRule.h>
#include <LibWeb/CSS/CSSStyleSheet.h>
#include <LibWeb/CSS/Parser/Parser.h>
#include <LibWeb/CSS/PropertyID.h>
#include <LibWeb/CSS/StyleComputer.h>
#include <LibWeb/CSS/StyleScope.h>
#include <LibWeb/DOM/Document.h>
#include <LibWeb/Page/Page.h>
namespace Web::CSS {
void StyleScope::visit_edges(GC::Cell::Visitor& visitor)
{
visitor.visit(m_user_style_sheet);
}
StyleScope::StyleScope(GC::Ref<DOM::Node> node)
: m_node(node)
{
m_qualified_layer_names_in_order.append({});
}
void StyleScope::build_rule_cache()
{
m_author_rule_cache = make<RuleCaches>();
m_user_rule_cache = make<RuleCaches>();
m_user_agent_rule_cache = make<RuleCaches>();
m_selector_insights = make<SelectorInsights>();
m_style_invalidation_data = make<StyleInvalidationData>();
if (auto user_style_source = document().page().user_style(); user_style_source.has_value()) {
m_user_style_sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(document()), user_style_source.value()));
}
build_qualified_layer_names_cache();
m_pseudo_class_rule_cache[to_underlying(PseudoClass::Hover)] = make<RuleCache>();
m_pseudo_class_rule_cache[to_underlying(PseudoClass::Active)] = make<RuleCache>();
m_pseudo_class_rule_cache[to_underlying(PseudoClass::Focus)] = make<RuleCache>();
m_pseudo_class_rule_cache[to_underlying(PseudoClass::FocusWithin)] = make<RuleCache>();
m_pseudo_class_rule_cache[to_underlying(PseudoClass::FocusVisible)] = make<RuleCache>();
m_pseudo_class_rule_cache[to_underlying(PseudoClass::Target)] = make<RuleCache>();
make_rule_cache_for_cascade_origin(CascadeOrigin::Author, *m_selector_insights);
make_rule_cache_for_cascade_origin(CascadeOrigin::User, *m_selector_insights);
make_rule_cache_for_cascade_origin(CascadeOrigin::UserAgent, *m_selector_insights);
}
void StyleScope::invalidate_rule_cache()
{
m_author_rule_cache = nullptr;
// NOTE: We could be smarter about keeping the user rule cache, and style sheet.
// Currently we are re-parsing the user style sheet every time we build the caches,
// as it may have changed.
m_user_rule_cache = nullptr;
m_user_style_sheet = nullptr;
// NOTE: It might not be necessary to throw away the UA rule cache.
// If we are sure that it's safe, we could keep it as an optimization.
m_user_agent_rule_cache = nullptr;
m_pseudo_class_rule_cache = {};
m_style_invalidation_data = nullptr;
}
void StyleScope::build_rule_cache_if_needed() const
{
if (has_valid_rule_cache())
return;
const_cast<StyleScope&>(*this).build_rule_cache();
}
static CSSStyleSheet& default_stylesheet()
{
static GC::Root<CSSStyleSheet> sheet;
if (!sheet.cell()) {
extern String default_stylesheet_source;
sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm()), default_stylesheet_source));
}
return *sheet;
}
static CSSStyleSheet& quirks_mode_stylesheet()
{
static GC::Root<CSSStyleSheet> sheet;
if (!sheet.cell()) {
extern String quirks_mode_stylesheet_source;
sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm()), quirks_mode_stylesheet_source));
}
return *sheet;
}
static CSSStyleSheet& mathml_stylesheet()
{
static GC::Root<CSSStyleSheet> sheet;
if (!sheet.cell()) {
extern String mathml_stylesheet_source;
sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm()), mathml_stylesheet_source));
}
return *sheet;
}
static CSSStyleSheet& svg_stylesheet()
{
static GC::Root<CSSStyleSheet> sheet;
if (!sheet.cell()) {
extern String svg_stylesheet_source;
sheet = GC::make_root(parse_css_stylesheet(CSS::Parser::ParsingParams(internal_css_realm()), svg_stylesheet_source));
}
return *sheet;
}
template<typename Callback>
void StyleScope::for_each_stylesheet(CascadeOrigin cascade_origin, Callback callback) const
{
if (cascade_origin == CascadeOrigin::UserAgent) {
callback(default_stylesheet());
if (document().in_quirks_mode())
callback(quirks_mode_stylesheet());
callback(mathml_stylesheet());
callback(svg_stylesheet());
}
if (cascade_origin == CascadeOrigin::User) {
if (m_user_style_sheet)
callback(*m_user_style_sheet);
}
if (cascade_origin == CascadeOrigin::Author) {
for_each_active_css_style_sheet(move(callback));
}
}
void StyleScope::make_rule_cache_for_cascade_origin(CascadeOrigin cascade_origin, SelectorInsights& insights)
{
GC::Ptr<DOM::ShadowRoot const> scope_shadow_root;
if (m_node->is_shadow_root())
scope_shadow_root = as<DOM::ShadowRoot>(*m_node);
Vector<MatchingRule> matching_rules;
size_t style_sheet_index = 0;
for_each_stylesheet(cascade_origin, [&](auto& sheet) {
auto& rule_caches = [&] -> RuleCaches& {
switch (cascade_origin) {
case CascadeOrigin::Author:
return *m_author_rule_cache;
case CascadeOrigin::User:
return *m_user_rule_cache;
case CascadeOrigin::UserAgent:
return *m_user_agent_rule_cache;
default:
VERIFY_NOT_REACHED();
}
}();
size_t rule_index = 0;
sheet.for_each_effective_style_producing_rule([&](auto const& rule) {
SelectorList const& absolutized_selectors = [&]() {
if (rule.type() == CSSRule::Type::Style)
return static_cast<CSSStyleRule const&>(rule).absolutized_selectors();
if (rule.type() == CSSRule::Type::NestedDeclarations)
return static_cast<CSSNestedDeclarations const&>(rule).parent_style_rule().absolutized_selectors();
VERIFY_NOT_REACHED();
}();
for (auto const& selector : absolutized_selectors) {
m_style_invalidation_data->build_invalidation_sets_for_selector(selector);
}
for (CSS::Selector const& selector : absolutized_selectors) {
MatchingRule matching_rule {
scope_shadow_root,
&rule,
sheet,
sheet.default_namespace(),
selector,
style_sheet_index,
rule_index,
selector.specificity(),
cascade_origin,
false,
};
auto const& qualified_layer_name = matching_rule.qualified_layer_name();
auto& rule_cache = qualified_layer_name.is_empty() ? rule_caches.main : *rule_caches.by_layer.ensure(qualified_layer_name, [] { return make<RuleCache>(); });
bool contains_root_pseudo_class = false;
Optional<CSS::PseudoElement> pseudo_element;
collect_selector_insights(selector, insights);
for (auto const& simple_selector : selector.compound_selectors().last().simple_selectors) {
if (!matching_rule.contains_pseudo_element) {
if (simple_selector.type == CSS::Selector::SimpleSelector::Type::PseudoElement) {
matching_rule.contains_pseudo_element = true;
pseudo_element = simple_selector.pseudo_element().type();
matching_rule.slotted = pseudo_element == PseudoElement::Slotted;
}
}
if (!contains_root_pseudo_class) {
if (simple_selector.type == CSS::Selector::SimpleSelector::Type::PseudoClass
&& simple_selector.pseudo_class().type == CSS::PseudoClass::Root) {
contains_root_pseudo_class = true;
}
}
}
for (size_t i = 0; i < to_underlying(PseudoClass::__Count); ++i) {
auto pseudo_class = static_cast<PseudoClass>(i);
// If we're not building a rule cache for this pseudo class, just ignore it.
if (!m_pseudo_class_rule_cache[i])
continue;
if (selector.contains_pseudo_class(pseudo_class)) {
// For pseudo class rule caches we intentionally pass no pseudo-element, because we don't want to bucket pseudo class rules by pseudo-element type.
m_pseudo_class_rule_cache[i]->add_rule(matching_rule, {}, contains_root_pseudo_class);
}
}
rule_cache.add_rule(matching_rule, pseudo_element, contains_root_pseudo_class);
}
++rule_index;
});
// Loosely based on https://drafts.csswg.org/css-animations-2/#keyframe-processing
sheet.for_each_effective_keyframes_at_rule([&](CSSKeyframesRule const& rule) {
auto keyframe_set = adopt_ref(*new Animations::KeyframeEffect::KeyFrameSet);
HashTable<PropertyID> animated_properties;
// Forwards pass, resolve all the user-specified keyframe properties.
for (auto const& keyframe_rule : *rule.css_rules()) {
auto const& keyframe = as<CSSKeyframeRule>(*keyframe_rule);
Animations::KeyframeEffect::KeyFrameSet::ResolvedKeyFrame resolved_keyframe;
auto key = static_cast<u64>(keyframe.key().value() * Animations::KeyframeEffect::AnimationKeyFrameKeyScaleFactor);
auto const& keyframe_style = *keyframe.style();
for (auto const& it : keyframe_style.properties()) {
if (!is_animatable_property(it.property_id))
continue;
// Unresolved properties will be resolved in collect_animation_into()
StyleComputer::for_each_property_expanding_shorthands(it.property_id, it.value, [&](PropertyID shorthand_id, StyleValue const& shorthand_value) {
animated_properties.set(shorthand_id);
resolved_keyframe.properties.set(shorthand_id, NonnullRefPtr<StyleValue const> { shorthand_value });
});
}
keyframe_set->keyframes_by_key.insert(key, resolved_keyframe);
}
Animations::KeyframeEffect::generate_initial_and_final_frames(keyframe_set, animated_properties);
if constexpr (LIBWEB_CSS_DEBUG) {
dbgln("Resolved keyframe set '{}' into {} keyframes:", rule.name(), keyframe_set->keyframes_by_key.size());
for (auto it = keyframe_set->keyframes_by_key.begin(); it != keyframe_set->keyframes_by_key.end(); ++it)
dbgln(" - keyframe {}: {} properties", it.key(), it->properties.size());
}
rule_caches.main.rules_by_animation_keyframes.set(rule.name(), move(keyframe_set));
});
++style_sheet_index;
});
}
void StyleScope::collect_selector_insights(Selector const& selector, SelectorInsights& insights)
{
for (auto const& compound_selector : selector.compound_selectors()) {
for (auto const& simple_selector : compound_selector.simple_selectors) {
if (simple_selector.type == Selector::SimpleSelector::Type::PseudoClass) {
if (simple_selector.pseudo_class().type == PseudoClass::Has) {
insights.has_has_selectors = true;
}
for (auto const& argument_selector : simple_selector.pseudo_class().argument_selector_list) {
collect_selector_insights(*argument_selector, insights);
}
}
}
}
}
struct LayerNode {
OrderedHashMap<FlyString, LayerNode> children {};
};
static void flatten_layer_names_tree(Vector<FlyString>& layer_names, StringView const& parent_qualified_name, FlyString const& name, LayerNode const& node)
{
FlyString qualified_name = parent_qualified_name.is_empty() ? name : MUST(String::formatted("{}.{}", parent_qualified_name, name));
for (auto const& item : node.children)
flatten_layer_names_tree(layer_names, qualified_name, item.key, item.value);
layer_names.append(qualified_name);
}
void StyleScope::build_qualified_layer_names_cache()
{
LayerNode root;
auto insert_layer_name = [&](FlyString const& internal_qualified_name) {
auto* node = &root;
internal_qualified_name.bytes_as_string_view()
.for_each_split_view('.', SplitBehavior::Nothing, [&](StringView part) {
auto local_name = MUST(FlyString::from_utf8(part));
node = &node->children.ensure(local_name);
});
};
// Walk all style sheets, identifying when we first see a @layer name, and add its qualified name to the list.
// TODO: Separate the light and shadow-dom layers.
for_each_stylesheet(CascadeOrigin::Author, [&](auto& sheet) {
// NOTE: Postorder so that a @layer block is iterated after its children,
// because we want those children to occur before it in the list.
sheet.for_each_effective_rule(TraversalOrder::Postorder, [&](auto& rule) {
switch (rule.type()) {
case CSSRule::Type::Import:
// TODO: Handle `layer(foo)` in import rules once we implement that.
break;
case CSSRule::Type::LayerBlock: {
auto& layer_block = static_cast<CSSLayerBlockRule const&>(rule);
insert_layer_name(layer_block.internal_qualified_name({}));
break;
}
case CSSRule::Type::LayerStatement: {
auto& layer_statement = static_cast<CSSLayerStatementRule const&>(rule);
auto qualified_names = layer_statement.internal_qualified_name_list({});
for (auto& name : qualified_names)
insert_layer_name(name);
break;
}
// Ignore everything else
case CSSRule::Type::Style:
case CSSRule::Type::Media:
case CSSRule::Type::FontFace:
case CSSRule::Type::Keyframes:
case CSSRule::Type::Keyframe:
case CSSRule::Type::Margin:
case CSSRule::Type::Namespace:
case CSSRule::Type::NestedDeclarations:
case CSSRule::Type::Page:
case CSSRule::Type::Property:
case CSSRule::Type::Supports:
break;
}
});
});
// Now, produce a flat list of qualified names to use later
m_qualified_layer_names_in_order.clear();
flatten_layer_names_tree(m_qualified_layer_names_in_order, ""sv, {}, root);
}
bool StyleScope::may_have_has_selectors() const
{
if (!has_valid_rule_cache())
return true;
build_rule_cache_if_needed();
return m_selector_insights->has_has_selectors;
}
bool StyleScope::have_has_selectors() const
{
build_rule_cache_if_needed();
return m_selector_insights->has_has_selectors;
}
DOM::Document& StyleScope::document() const
{
return m_node->document();
}
RuleCache const& StyleScope::get_pseudo_class_rule_cache(PseudoClass pseudo_class) const
{
build_rule_cache_if_needed();
return *m_pseudo_class_rule_cache[to_underlying(pseudo_class)];
}
void StyleScope::for_each_active_css_style_sheet(Function<void(CSS::CSSStyleSheet&)>&& callback) const
{
if (auto* shadow_root = as_if<DOM::ShadowRoot>(*m_node)) {
shadow_root->for_each_active_css_style_sheet(move(callback));
} else {
m_node->document().for_each_active_css_style_sheet(move(callback));
}
}
void StyleScope::invalidate_style_of_elements_affected_by_has()
{
if (m_pending_nodes_for_style_invalidation_due_to_presence_of_has.is_empty()) {
return;
}
ScopeGuard clear_pending_nodes_guard = [&] {
m_pending_nodes_for_style_invalidation_due_to_presence_of_has.clear();
};
// It's ok to call have_has_selectors() instead of may_have_has_selectors() here and force
// rule cache build, because it's going to be built soon anyway, since we could get here
// only from update_style().
if (!have_has_selectors()) {
return;
}
auto nodes = move(m_pending_nodes_for_style_invalidation_due_to_presence_of_has);
for (auto const& node : nodes) {
if (!node)
continue;
for (auto ancestor = node.ptr(); ancestor; ancestor = ancestor->parent_or_shadow_host()) {
if (!ancestor->is_element())
continue;
auto& element = static_cast<DOM::Element&>(*ancestor);
element.invalidate_style_if_affected_by_has();
auto* parent = ancestor->parent_or_shadow_host();
if (!parent)
return;
// If any ancestor's sibling was tested against selectors like ".a:has(+ .b)" or ".a:has(~ .b)"
// its style might be affected by the change in descendant node.
parent->for_each_child_of_type<DOM::Element>([&](auto& ancestor_sibling_element) {
if (ancestor_sibling_element.affected_by_has_pseudo_class_with_relative_selector_that_has_sibling_combinator())
ancestor_sibling_element.invalidate_style_if_affected_by_has();
return IterationDecision::Continue;
});
}
}
}
}
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