From 64d5d633cfdcba5685cdba7c0b7475c306d3e178 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sat, 29 Oct 2022 13:14:15 +0200
Subject: [PATCH] LibWeb: Don't invalidate layout when setting .innerHTML on
 <template>

HTML template elements don't affect rendering, so invalidating the
entire document's layout after poking into a <template> was a huge waste
of work on template-heavy pages.
---
 Userland/Libraries/LibWeb/DOM/Element.cpp          |  6 ------
 Userland/Libraries/LibWeb/DOMParsing/InnerHTML.cpp | 10 ++++++++++
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/Userland/Libraries/LibWeb/DOM/Element.cpp b/Userland/Libraries/LibWeb/DOM/Element.cpp
index dcdd9a2ed5..50457f081d 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Element.cpp
@@ -488,12 +488,6 @@ WebIDL::ExceptionOr<DOM::Element const*> Element::closest(StringView selectors)
 WebIDL::ExceptionOr<void> Element::set_inner_html(String const& markup)
 {
     TRY(DOMParsing::inner_html_setter(*this, markup));
-
-    set_needs_style_update(true);
-
-    // NOTE: Since the DOM has changed, we have to rebuild the layout tree.
-    document().invalidate_layout();
-    document().set_needs_layout();
     return {};
 }
 
diff --git a/Userland/Libraries/LibWeb/DOMParsing/InnerHTML.cpp b/Userland/Libraries/LibWeb/DOMParsing/InnerHTML.cpp
index 1210f241ae..a63c123201 100644
--- a/Userland/Libraries/LibWeb/DOMParsing/InnerHTML.cpp
+++ b/Userland/Libraries/LibWeb/DOMParsing/InnerHTML.cpp
@@ -5,6 +5,7 @@
  */
 
 #include <LibJS/Heap/Heap.h>
+#include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/DocumentFragment.h>
 #include <LibWeb/DOMParsing/InnerHTML.h>
 #include <LibWeb/HTML/Parser/HTMLParser.h>
@@ -47,6 +48,15 @@ WebIDL::ExceptionOr<void> inner_html_setter(JS::NonnullGCPtr<DOM::Node> context_
     // 4. Replace all with fragment within the context object.
     context_object->replace_all(fragment);
 
+    // NOTE: We don't invalidate style & layout for <template> elements since they don't affect rendering.
+    if (!is<HTML::HTMLTemplateElement>(*context_object)) {
+        context_object->set_needs_style_update(true);
+
+        // NOTE: Since the DOM has changed, we have to rebuild the layout tree.
+        context_object->document().invalidate_layout();
+        context_object->document().set_needs_layout();
+    }
+
     return {};
 }