LibWeb: Add a simple StyleInvalidator class

This patch adds a simple, naive & inefficient class for document-wide
style invalidation, e.g. after element attribute updates. During
construction it collects a HashMap of a document's elements and their
matching rules, during destruction it does the same and then compares
the results; dirtying all elements that have a different number or order
of matching rules afterwards.

Much room for improvement, but it solves the problem of stale element
styling after attribute updates for now :^)

Fixes #4404.

1 files changed, 70 insertions, 0 deletions

diff --git a/Libraries/LibWeb/CSS/StyleInvalidator.cpp b/Libraries/LibWeb/CSS/StyleInvalidator.cpp
new file mode 100644
index 0000000000..0dd48840d5
--- /dev/null
+++ b/Libraries/LibWeb/CSS/StyleInvalidator.cpp
@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2020, Linus Groh <mail@linusgroh.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#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)
+{
+    auto& style_resolver = m_document.style_resolver();
+    m_document.for_each_in_subtree_of_type<DOM::Element>([&](auto& element) {
+        m_elements_and_matching_rules_before.set(&element, style_resolver.collect_matching_rules(element));
+        return IterationDecision::Continue;
+    });
+}
+
+StyleInvalidator::~StyleInvalidator()
+{
+    auto& style_resolver = m_document.style_resolver();
+    m_document.for_each_in_subtree_of_type<DOM::Element>([&](auto& element) {
+        auto maybe_matching_rules_before = m_elements_and_matching_rules_before.get(&element);
+        if (!maybe_matching_rules_before.has_value()) {
+            element.set_needs_style_update(true);
+            return IterationDecision::Continue;
+        }
+        auto& matching_rules_before = maybe_matching_rules_before.value();
+        auto matching_rules_after = style_resolver.collect_matching_rules(element);
+        if (matching_rules_before.size() != matching_rules_after.size()) {
+            element.set_needs_style_update(true);
+            return IterationDecision::Continue;
+        }
+        style_resolver.sort_matching_rules(matching_rules_before);
+        style_resolver.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;
+    });
+}
+
+}