LibWeb/CSS: Prepare pseudo-classes for multiple An+B patterns

The upcoming `:heading()` pseudo-class takes multiple comma-separated
An+Bs. Also rename this field as the `:nth-[last-]child()`
pseudo-classes are only a subset of the users.

Libraries/LibWeb/CSS/Parser/SelectorParsing.cpp

@@ -664,10 +664,10 @@ Parser::ParseErrorOr<Selector::SimpleSelector> Parser::parse_pseudo_simple_selec
     }
 
     if (pseudo_class_token.is_function()) {
-        auto parse_nth_child_selector = [this](auto pseudo_class, Vector<ComponentValue> const& function_values, bool allow_of = false) -> ParseErrorOr<Selector::SimpleSelector> {
+        auto parse_an_plus_b_selector = [this](auto pseudo_class, Vector<ComponentValue> const& function_values, bool allow_of) -> ParseErrorOr<Selector::SimpleSelector> {
             auto tokens = TokenStream<ComponentValue>(function_values);
-            auto nth_child_pattern = parse_a_n_plus_b_pattern(tokens);
+            auto an_plus_b_pattern = parse_a_n_plus_b_pattern(tokens);
-            if (!nth_child_pattern.has_value()) {
+            if (!an_plus_b_pattern.has_value()) {
                 ErrorReporter::the().report(InvalidPseudoClassOrElementError {
                     .name = MUST(String::formatted(":{}", pseudo_class_name(pseudo_class))),
                     .value_string = tokens.dump_string(),
@@ -682,7 +682,7 @@ Parser::ParseErrorOr<Selector::SimpleSelector> Parser::parse_pseudo_simple_selec
                     .type = Selector::SimpleSelector::Type::PseudoClass,
                     .value = Selector::SimpleSelector::PseudoClassSelector {
                         .type = pseudo_class,
-                        .nth_child_pattern = nth_child_pattern.release_value() }
+                        .an_plus_b_patterns = Vector { an_plus_b_pattern.release_value() } }
                 };
             }
 
@@ -705,7 +705,7 @@ Parser::ParseErrorOr<Selector::SimpleSelector> Parser::parse_pseudo_simple_selec
                 .type = Selector::SimpleSelector::Type::PseudoClass,
                 .value = Selector::SimpleSelector::PseudoClassSelector {
                     .type = pseudo_class,
-                    .nth_child_pattern = nth_child_pattern.release_value(),
+                    .an_plus_b_patterns = Vector { an_plus_b_pattern.release_value() },
                     .argument_selector_list = move(selector_list) }
             };
         };
@@ -755,9 +755,9 @@ Parser::ParseErrorOr<Selector::SimpleSelector> Parser::parse_pseudo_simple_selec
 
         switch (metadata.parameter_type) {
         case PseudoClassMetadata::ParameterType::ANPlusB:
-            return parse_nth_child_selector(pseudo_class, pseudo_function.value, false);
+            return parse_an_plus_b_selector(pseudo_class, pseudo_function.value, false);
         case PseudoClassMetadata::ParameterType::ANPlusBOf:
-            return parse_nth_child_selector(pseudo_class, pseudo_function.value, true);
+            return parse_an_plus_b_selector(pseudo_class, pseudo_function.value, true);
         case PseudoClassMetadata::ParameterType::CompoundSelector: {
             auto function_token_stream = TokenStream(pseudo_function.value);
             auto compound_selector_or_error = parse_compound_selector(function_token_stream);

Libraries/LibWeb/CSS/Selector.cpp

@@ -460,7 +460,7 @@ String Selector::SimpleSelector::serialize() const
             case PseudoClassMetadata::ParameterType::ANPlusB:
             case PseudoClassMetadata::ParameterType::ANPlusBOf:
                 // The result of serializing the value using the rules to serialize an <an+b> value.
-                s.append(pseudo_class.nth_child_pattern.serialize());
+                s.append(pseudo_class.an_plus_b_patterns.first().serialize());
                 break;
             case PseudoClassMetadata::ParameterType::CompoundSelector:
             case PseudoClassMetadata::ParameterType::ForgivingSelectorList:

Libraries/LibWeb/CSS/Selector.h

@@ -124,9 +124,8 @@ public:
         struct PseudoClassSelector {
             PseudoClass type;
 
-            // FIXME: We don't need this field on every single SimpleSelector, but it's also annoying to malloc it somewhere.
+            // Used for the :nth-*() pseudo-classes, and :heading()
-            // Only used when "pseudo_class" is "NthChild" or "NthLastChild".
+            Vector<ANPlusBPattern> an_plus_b_patterns {};
-            ANPlusBPattern nth_child_pattern {};
 
             // FIXME: This would make more sense as part of SelectorList but that's currently a `using`
             bool is_forgiving { false };

Libraries/LibWeb/CSS/SelectorEngine.cpp

@@ -670,8 +670,9 @@ static inline bool matches_pseudo_class(CSS::Selector::SimpleSelector::PseudoCla
     case CSS::PseudoClass::NthLastChild:
     case CSS::PseudoClass::NthOfType:
     case CSS::PseudoClass::NthLastOfType: {
-        auto const step_size = pseudo_class.nth_child_pattern.step_size;
+        auto& an_plus_b = pseudo_class.an_plus_b_patterns.first();
-        auto const offset = pseudo_class.nth_child_pattern.offset;
+        auto const step_size = an_plus_b.step_size;
+        auto const offset = an_plus_b.offset;
         if (step_size == 0 && offset == 0)
             return false; // "If both a and b are equal to zero, the pseudo-class represents no element in the document tree."
 

Libraries/LibWeb/Dump.cpp

@@ -563,7 +563,8 @@ void dump_selector(StringBuilder& builder, CSS::Selector const& selector, int in
                     break;
                 case CSS::PseudoClassMetadata::ParameterType::ANPlusB:
                 case CSS::PseudoClassMetadata::ParameterType::ANPlusBOf: {
-                    builder.appendff("(step={}, offset={}", pseudo_class.nth_child_pattern.step_size, pseudo_class.nth_child_pattern.offset);
+                    auto& an_plus_b = pseudo_class.an_plus_b_patterns.first();
+                    builder.appendff("(step={}, offset={}", an_plus_b.step_size, an_plus_b.offset);
                     if (!pseudo_class.argument_selector_list.is_empty()) {
                         builder.append(", selectors=[\n"sv);
                         for (auto const& child_selector : pseudo_class.argument_selector_list)