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LibWeb: Implement :nth-[last-]child(n of foo) syntax

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In Selectors level 4, `:nth-child()` and `:nth-last-child()` can both
optionally take a selector-list argument. This selector-list acts as a
filter, so that only elements matching the list are counted. For
example, this means that the following are equivalent:

```css
:nth-child(2n+1 of p) {}
p:nth-of-type(2n+1) {}
```
This commit is contained in:
Sam Atkins 2022-03-17 19:13:51 +00:00 • committed by Andreas Kling
parent 0e4c35b4b2
commit 5b0187477b
5 changed files with 92 additions and 25 deletions
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37
Userland/Libraries/LibWeb/CSS/Selector.cpp
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@ -42,6 +42,21 @@ u32 Selector::specificity() const
u32 classes = 0;
u32 tag_names = 0;
auto count_specificity_of_most_complex_selector = [&](auto& selector_list) {
u32 max_selector_list_argument_specificity = 0;
for (auto const& complex_selector : selector_list) {
max_selector_list_argument_specificity = max(max_selector_list_argument_specificity, complex_selector.specificity());
}
u32 child_ids = (max_selector_list_argument_specificity & ids_mask) >> ids_shift;
u32 child_classes = (max_selector_list_argument_specificity & classes_mask) >> classes_shift;
u32 child_tag_names = (max_selector_list_argument_specificity & tag_names_mask) >> tag_names_shift;
ids += child_ids;
classes += child_classes;
tag_names += child_tag_names;
};
for (auto& list : m_compound_selectors) {
for (auto& simple_selector : list.simple_selectors) {
switch (simple_selector.type) {
@ -60,18 +75,16 @@ u32 Selector::specificity() const
case SimpleSelector::PseudoClass::Type::Not: {
// The specificity of an :is(), :not(), or :has() pseudo-class is replaced by the
// specificity of the most specific complex selector in its selector list argument.
u32 max_selector_list_argument_specificity = 0;
for (auto const& complex_selector : simple_selector.pseudo_class.argument_selector_list) {
max_selector_list_argument_specificity = max(max_selector_list_argument_specificity, complex_selector.specificity());
}
u32 child_ids = (max_selector_list_argument_specificity & ids_mask) >> ids_shift;
u32 child_classes = (max_selector_list_argument_specificity & classes_mask) >> classes_shift;
u32 child_tag_names = (max_selector_list_argument_specificity & tag_names_mask) >> tag_names_shift;
ids += child_ids;
classes += child_classes;
tag_names += child_tag_names;
count_specificity_of_most_complex_selector(simple_selector.pseudo_class.argument_selector_list);
break;
}
case SimpleSelector::PseudoClass::Type::NthChild:
case SimpleSelector::PseudoClass::Type::NthLastChild: {
// Analogously, the specificity of an :nth-child() or :nth-last-child() selector
// is the specificity of the pseudo class itself (counting as one pseudo-class selector)
// plus the specificity of the most specific complex selector in its selector list argument (if any).
++classes;
count_specificity_of_most_complex_selector(simple_selector.pseudo_class.argument_selector_list);
break;
}
case SimpleSelector::PseudoClass::Type::Where: