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LibWeb: Extract ancestor hashes from :is() and :where()

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Look through single-argument :is() and :where() pseudo-classes when
collecting ancestor-filter hashes. Reuse hashes from the rightmost
compound of the argument selector, including nested wrappers, because
that compound matches the same ancestor element.

Keep selector lists with multiple alternatives conservative, since no
single hash is mandatory for every branch.
This commit is contained in:
Andreas Kling 2026-06-18 14:49:25 +02:00 committed by Andreas Kling
parent bc201e3257
commit 8d85a17527
1 changed files with 41 additions and 24 deletions
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65
Libraries/LibWeb/CSS/Selector.cpp
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@ -154,39 +154,56 @@ void Selector::collect_ancestor_hashes()
}
size_t next_hash_index = 0;
auto append_unique_hash = [&](u32 hash) -> bool {
if (next_hash_index >= m_ancestor_hashes.size())
return true;
for (size_t i = 0; i < next_hash_index; ++i) {
if (m_ancestor_hashes[i] == hash)
return false;
}
m_ancestor_hashes[next_hash_index++] = hash;
return false;
};
struct AncestorHashCollector {
Array<u32, 8>& ancestor_hashes;
size_t& next_hash_index;
auto append_hashes_from_compound = [&](CompoundSelector const& compound_selector) {
for (auto const& simple_selector : compound_selector.simple_selectors) {
bool append_unique_hash(u32 hash)
{
if (next_hash_index >= ancestor_hashes.size())
return true;
for (size_t i = 0; i < next_hash_index; ++i) {
if (ancestor_hashes[i] == hash)
return false;
}
ancestor_hashes[next_hash_index++] = hash;
return false;
}
bool append_hashes_from_simple_selector(SimpleSelector const& simple_selector)
{
switch (simple_selector.type) {
case SimpleSelector::Type::Id:
case SimpleSelector::Type::Class:
if (append_unique_hash(simple_selector.name().hash()))
return true;
break;
return append_unique_hash(simple_selector.name().hash());
case SimpleSelector::Type::TagName:
if (append_unique_hash(simple_selector.qualified_name().name.lowercase_name.hash()))
return true;
break;
return append_unique_hash(simple_selector.qualified_name().name.lowercase_name.hash());
case SimpleSelector::Type::Attribute:
if (append_unique_hash(simple_selector.attribute().qualified_name.name.lowercase_name.hash()))
return true;
break;
return append_unique_hash(simple_selector.attribute().qualified_name.name.lowercase_name.hash());
case SimpleSelector::Type::PseudoClass: {
auto const& pseudo_class = simple_selector.pseudo_class();
if (pseudo_class.type != PseudoClass::Is && pseudo_class.type != PseudoClass::Where)
return false;
if (pseudo_class.argument_selector_list.size() != 1)
return false;
auto const& argument_selector = *pseudo_class.argument_selector_list.first();
return append_hashes_from_compound(argument_selector.compound_selectors().last());
}
default:
break;
return false;
}
}
return false;
bool append_hashes_from_compound(CompoundSelector const& compound_selector)
{
for (auto const& simple_selector : compound_selector.simple_selectors) {
if (append_hashes_from_simple_selector(simple_selector))
return true;
}
return false;
}
};
AncestorHashCollector ancestor_hash_collector { m_ancestor_hashes, next_hash_index };
// Walk from the compound immediately to the left of the subject toward the left.
// The combinator that connects `i` to `i+1` is stored on `i+1`.
@ -204,7 +221,7 @@ void Selector::collect_ancestor_hashes()
case Combinator::PseudoElement:
// This compound is on the ancestor axis (directly, as the originating element for a pseudo-element,
// or as a shared ancestor past a sibling boundary).
if (append_hashes_from_compound(compound_selector)) {
if (ancestor_hash_collector.append_hashes_from_compound(compound_selector)) {
m_can_use_ancestor_filter = (next_hash_index > 0);
return;
}