LibWeb: Remove CSS::StyleInvalidator in favor of dirtying + lazy update

Style updates are lazy since late last year, so the StyleInvalidator is
actually hurting us more than it's helping by running the entire CSS
selector machine on the whole DOM for every attribute change.

Instead, simply mark the entire DOM dirty and let the lazy style update
mechanism run *once* on next event loop iteration.

4 files changed, 7 insertions, 86 deletions

diff --git a/Userland/Libraries/LibWeb/CMakeLists.txt b/Userland/Libraries/LibWeb/CMakeLists.txt
index f8d7d10cf3..7451212877 100644
--- a/Userland/Libraries/LibWeb/CMakeLists.txt
+++ b/Userland/Libraries/LibWeb/CMakeLists.txt
@@ -46,7 +46,6 @@ set(SOURCES
     CSS/Selector.cpp
     CSS/SelectorEngine.cpp
     CSS/StyleComputer.cpp
-    CSS/StyleInvalidator.cpp
     CSS/StyleProperties.cpp
     CSS/StyleSheet.cpp
     CSS/StyleSheetList.cpp
diff --git a/Userland/Libraries/LibWeb/CSS/StyleInvalidator.cpp b/Userland/Libraries/LibWeb/CSS/StyleInvalidator.cpp
deleted file mode 100644
index 0d0bd93137..0000000000
--- a/Userland/Libraries/LibWeb/CSS/StyleInvalidator.cpp
+++ /dev/null
@@ -1,55 +0,0 @@
-/*
- * Copyright (c) 2020, Linus Groh <linusg@serenityos.org>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#include <LibWeb/CSS/CSSStyleRule.h>
-#include <LibWeb/CSS/StyleInvalidator.h>
-#include <LibWeb/DOM/Document.h>
-#include <LibWeb/DOM/Element.h>
-
-namespace Web::CSS {
-
-StyleInvalidator::StyleInvalidator(DOM::Document& document)
-    : m_document(document)
-{
-    if (!m_document.should_invalidate_styles_on_attribute_changes())
-        return;
-    auto& style_computer = m_document.style_computer();
-    m_document.for_each_in_inclusive_subtree_of_type<DOM::Element>([&](auto& element) {
-        m_elements_and_matching_rules_before.set(&element, style_computer.collect_matching_rules(element));
-        return IterationDecision::Continue;
-    });
-}
-
-StyleInvalidator::~StyleInvalidator()
-{
-    if (!m_document.should_invalidate_styles_on_attribute_changes())
-        return;
-    auto& style_computer = m_document.style_computer();
-    m_document.for_each_in_inclusive_subtree_of_type<DOM::Element>([&](auto& element) {
-        auto matching_rules_before_iter = m_elements_and_matching_rules_before.find(&element);
-        if (matching_rules_before_iter == m_elements_and_matching_rules_before.end()) {
-            element.set_needs_style_update(true);
-            return IterationDecision::Continue;
-        }
-        auto& matching_rules_before = matching_rules_before_iter->value;
-        auto matching_rules_after = style_computer.collect_matching_rules(element);
-        if (matching_rules_before.size() != matching_rules_after.size()) {
-            element.set_needs_style_update(true);
-            return IterationDecision::Continue;
-        }
-        style_computer.sort_matching_rules(matching_rules_before);
-        style_computer.sort_matching_rules(matching_rules_after);
-        for (size_t i = 0; i < matching_rules_before.size(); ++i) {
-            if (matching_rules_before[i].rule != matching_rules_after[i].rule) {
-                element.set_needs_style_update(true);
-                break;
-            }
-        }
-        return IterationDecision::Continue;
-    });
-}
-
-}
diff --git a/Userland/Libraries/LibWeb/CSS/StyleInvalidator.h b/Userland/Libraries/LibWeb/CSS/StyleInvalidator.h
deleted file mode 100644
index c213d39813..0000000000
--- a/Userland/Libraries/LibWeb/CSS/StyleInvalidator.h
+++ /dev/null
@@ -1,26 +0,0 @@
-/*
- * Copyright (c) 2020, Linus Groh <linusg@serenityos.org>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#pragma once
-
-#include <AK/HashMap.h>
-#include <LibWeb/CSS/StyleComputer.h>
-#include <LibWeb/DOM/Document.h>
-#include <LibWeb/DOM/Element.h>
-
-namespace Web::CSS {
-
-class StyleInvalidator {
-public:
-    explicit StyleInvalidator(DOM::Document&);
-    ~StyleInvalidator();
-
-private:
-    DOM::Document& m_document;
-    HashMap<DOM::Element*, Vector<MatchingRule>> m_elements_and_matching_rules_before;
-};
-
-}
diff --git a/Userland/Libraries/LibWeb/DOM/Element.cpp b/Userland/Libraries/LibWeb/DOM/Element.cpp
index 85cb637806..0df7eb3fd0 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Element.cpp
@@ -10,7 +10,6 @@
 #include <LibWeb/CSS/PropertyID.h>
 #include <LibWeb/CSS/ResolvedCSSStyleDeclaration.h>
 #include <LibWeb/CSS/SelectorEngine.h>
-#include <LibWeb/CSS/StyleInvalidator.h>
 #include <LibWeb/DOM/DOMException.h>
 #include <LibWeb/DOM/DOMTokenList.h>
 #include <LibWeb/DOM/Document.h>
@@ -70,8 +69,6 @@ ExceptionOr<void> Element::set_attribute(const FlyString& name, const String& va
     if (name.is_empty())
         return InvalidCharacterError::create("Attribute name must not be empty");
 
-    CSS::StyleInvalidator style_invalidator(document());
-
     // 2. If this is in the HTML namespace and its node document is an HTML document, then set qualifiedName to qualifiedName in ASCII lowercase.
     // FIXME: Handle the second condition, assume it is an HTML document for now.
     bool insert_as_lowercase = namespace_uri() == Namespace::HTML;
@@ -93,14 +90,20 @@ ExceptionOr<void> Element::set_attribute(const FlyString& name, const String& va
     }
 
     parse_attribute(attribute->local_name(), value);
+
+    // FIXME: Invalidate less.
+    document().invalidate_style();
+
     return {};
 }
 
 // https://dom.spec.whatwg.org/#dom-element-removeattribute
 void Element::remove_attribute(const FlyString& name)
 {
-    CSS::StyleInvalidator style_invalidator(document());
     m_attributes->remove_attribute(name);
+
+    // FIXME: Invalidate less.
+    document().invalidate_style();
 }
 
 // https://dom.spec.whatwg.org/#dom-element-hasattribute