LibWeb: Support the :first-of-type CSS selector :^)

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/0eb9a9dd133

Base/res/html/misc/first-of-type.html

@@ -0,0 +1,13 @@
+<style>
+article :first-of-type {
+background-color:pink;
+}
+</style>
+<article>
+<div>This `div is first!</div>
+<div>This <span>nested `span` is first</span>!</div>
+<div>This <em> nested `em` is first</em>, but this <em>nested `em` is last</em>!</div>
+<div>This <span>nested `span` gets styled</span>!</div>
+<b>This `b` qualifies!</b>
+<div>This is the final `div`.</div>
+</article>

Base/res/html/misc/welcome.html

@@ -38,6 +38,7 @@ span#loadtime {
     <p>This page loaded in <b><span id="loadtime"></span></b> ms</p>
     <p>Some small test pages:</p>
     <ul>
+        <li><a href="first-of-type.html">CSS :first-of-type selector</a></li>
         <li><a href="background-repeat-test.html">background image with repetition rules</a></li>
         <li><a href="link-over-zindex-block.html">link elements with background box placed with z-index</a></li>
         <li><a href="contenteditable.html">contenteditable</a></li>

Userland/Libraries/LibWeb/CSS/Parser/DeprecatedCSSParser.cpp

@@ -554,6 +554,8 @@ public:
                 simple_selector.pseudo_class = CSS::Selector::SimpleSelector::PseudoClass::Empty;
             } else if (pseudo_name.equals_ignoring_case("root")) {
                 simple_selector.pseudo_class = CSS::Selector::SimpleSelector::PseudoClass::Root;
+            } else if (pseudo_name.equals_ignoring_case("first-of-type")) {
+                simple_selector.pseudo_class = CSS::Selector::SimpleSelector::PseudoClass::FirstOfType;
             } else if (pseudo_name.equals_ignoring_case("before")) {
                 simple_selector.pseudo_element = CSS::Selector::SimpleSelector::PseudoElement::Before;
             } else if (pseudo_name.equals_ignoring_case("after")) {

Userland/Libraries/LibWeb/CSS/Selector.h

@@ -54,6 +54,7 @@ public:
             OnlyChild,
             Empty,
             Root,
+            FirstOfType,
         };
         PseudoClass pseudo_class { PseudoClass::None };
 

Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp

@@ -90,6 +90,12 @@ static bool matches(const CSS::Selector::SimpleSelector& component, const DOM::E
         if (!is<HTML::HTMLElement>(element))
             return false;
         break;
+    case CSS::Selector::SimpleSelector::PseudoClass::FirstOfType:
+        for (auto* sibling = element.previous_element_sibling(); sibling; sibling = sibling->previous_element_sibling()) {
+            if (sibling->tag_name() == element.tag_name())
+                return false;
+        }
+        break;
     }
 
     switch (component.attribute_match_type) {

Userland/Libraries/LibWeb/Dump.cpp

@@ -359,6 +359,9 @@ void dump_selector(StringBuilder& builder, const CSS::Selector& selector)
             case CSS::Selector::SimpleSelector::PseudoClass::Root:
                 pseudo_class_description = "Root";
                 break;
+            case CSS::Selector::SimpleSelector::PseudoClass::FirstOfType:
+                pseudo_class_description = "FirstOfType";
+                break;
             case CSS::Selector::SimpleSelector::PseudoClass::Focus:
                 pseudo_class_description = "Focus";
                 break;