LibWeb: Add debug logging of reasons for layout tree update

Author: https://github.com/awesomekling
Commit: 545ed08519
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4411

Libraries/LibWeb/DOM/Document.cpp

@@ -1446,12 +1446,11 @@ void Document::update_layout(UpdateLayoutReason reason)
         // We mark layout tree for rebuild starting from parent element to correctly invalidate
         // "display" property change to/from "contents" value.
         if (auto parent_element = node.parent_element()) {
-            parent_element->set_needs_layout_tree_update(true);
+            parent_element->set_needs_layout_tree_update(true, SetNeedsLayoutTreeUpdateReason::StyleChange);
         } else {
-            node.set_needs_layout_tree_update(true);
+            node.set_needs_layout_tree_update(true, SetNeedsLayoutTreeUpdateReason::StyleChange);
         }
     }
-    invalidation |= node_invalidation;
     node.set_needs_style_update(false);
     invalidation |= node_invalidation;
 
@@ -6562,6 +6561,18 @@ StringView to_string(SetNeedsLayoutReason reason)
     VERIFY_NOT_REACHED();
 }
 
+StringView to_string(SetNeedsLayoutTreeUpdateReason reason)
+{
+    switch (reason) {
+#define ENUMERATE_SET_NEEDS_LAYOUT_TREE_UPDATE_REASON(e) \
+    case SetNeedsLayoutTreeUpdateReason::e:              \
+        return #e##sv;
+        ENUMERATE_SET_NEEDS_LAYOUT_TREE_UPDATE_REASONS(ENUMERATE_SET_NEEDS_LAYOUT_TREE_UPDATE_REASON)
+#undef ENUMERATE_SET_NEEDS_LAYOUT_TREE_UPDATE_REASON
+    }
+    VERIFY_NOT_REACHED();
+}
+
 StringView to_string(InvalidateLayoutTreeReason reason)
 {
     switch (reason) {

Libraries/LibWeb/DOM/Element.cpp

@@ -883,7 +883,7 @@ WebIDL::ExceptionOr<void> Element::set_inner_html(StringView value)
 
         if (context->is_connected()) {
             // NOTE: Since the DOM has changed, we have to rebuild the layout tree.
-            context->set_needs_layout_tree_update(true);
+            context->set_needs_layout_tree_update(true, DOM::SetNeedsLayoutTreeUpdateReason::ElementSetInnerHTML);
         }
     }
 

Libraries/LibWeb/DOM/Node.cpp

@@ -229,7 +229,7 @@ void Node::set_text_content(Optional<String> const& maybe_content)
 
     if (is_connected()) {
         invalidate_style(StyleInvalidationReason::NodeSetTextContent);
-        set_needs_layout_tree_update(true);
+        set_needs_layout_tree_update(true, SetNeedsLayoutTreeUpdateReason::NodeSetTextContent);
     }
 
     document().bump_dom_tree_version();
@@ -802,9 +802,9 @@ void Node::insert_before(GC::Ref<Node> node, GC::Ptr<Node> child, bool suppress_
 
     if (is_connected()) {
         if (layout_node() && layout_node()->display().is_contents() && parent_element()) {
-            parent_element()->set_needs_layout_tree_update(true);
+            parent_element()->set_needs_layout_tree_update(true, SetNeedsLayoutTreeUpdateReason::NodeInsertBeforeWithDisplayContents);
         }
-        set_needs_layout_tree_update(true);
+        set_needs_layout_tree_update(true, SetNeedsLayoutTreeUpdateReason::NodeInsertBefore);
     }
 
     document().bump_dom_tree_version();
@@ -913,7 +913,7 @@ void Node::remove(bool suppress_observers)
         // NOTE: If we didn't have a layout node before, rebuilding the layout tree isn't gonna give us one
         //       after we've been removed from the DOM.
         if (layout_node())
-            parent->set_needs_layout_tree_update(true);
+            parent->set_needs_layout_tree_update(true, SetNeedsLayoutTreeUpdateReason::NodeRemove);
     }
 
     // 11. Remove node from its parent’s children.
@@ -1399,17 +1399,34 @@ EventTarget* Node::get_parent(Event const&)
     return parent();
 }
 
-void Node::set_needs_layout_tree_update(bool value)
+void Node::set_needs_layout_tree_update(bool value, SetNeedsLayoutTreeUpdateReason reason)
 {
     if (m_needs_layout_tree_update == value)
         return;
     m_needs_layout_tree_update = value;
 
+    if constexpr (UPDATE_LAYOUT_DEBUG) {
+        if (m_needs_layout_tree_update) {
+            // NOTE: We check some conditions here to avoid debug spam in documents that don't do layout.
+            auto navigable = this->navigable();
+            bool any_ancestor_needs_layout_tree_update = false;
+            for (auto* ancestor = parent_or_shadow_host(); ancestor; ancestor = ancestor->parent_or_shadow_host()) {
+                if (ancestor->needs_layout_tree_update()) {
+                    any_ancestor_needs_layout_tree_update = true;
+                    break;
+                }
+            }
+            if (!any_ancestor_needs_layout_tree_update && navigable && navigable->active_document() == &document()) {
+                dbgln("Need tree update ({}): {}", to_string(reason), debug_description());
+            }
+        }
+    }
+
     // NOTE: If this is a shadow root, we need to propagate the layout tree update to the host.
     if (is_shadow_root()) {
         auto& shadow_root = static_cast<ShadowRoot&>(*this);
         if (auto host = shadow_root.host())
-            host->set_needs_layout_tree_update(value);
+            host->set_needs_layout_tree_update(value, reason);
     }
 
     if (m_needs_layout_tree_update) {

Libraries/LibWeb/DOM/Node.h

@@ -108,6 +108,27 @@ enum class SetNeedsLayoutReason {
 
 [[nodiscard]] StringView to_string(SetNeedsLayoutReason);
 
+#define ENUMERATE_SET_NEEDS_LAYOUT_TREE_UPDATE_REASONS(X) \
+    X(ElementSetInnerHTML)                                \
+    X(HTMLInputElementSrcAttribute)                       \
+    X(HTMLObjectElementUpdateLayoutAndChildObjects)       \
+    X(KeyframeEffect)                                     \
+    X(NodeInsertBefore)                                   \
+    X(NodeInsertBeforeWithDisplayContents)                \
+    X(NodeRemove)                                         \
+    X(NodeSetTextContent)                                 \
+    X(None)                                               \
+    X(SVGGraphicsElementTransformChange)                  \
+    X(StyleChange)
+
+enum class SetNeedsLayoutTreeUpdateReason {
+#define ENUMERATE_SET_NEEDS_LAYOUT_TREE_UPDATE_REASON(e) e,
+    ENUMERATE_SET_NEEDS_LAYOUT_TREE_UPDATE_REASONS(ENUMERATE_SET_NEEDS_LAYOUT_TREE_UPDATE_REASON)
+#undef ENUMERATE_SET_NEEDS_LAYOUT_TREE_UPDATE_REASON
+};
+
+[[nodiscard]] StringView to_string(SetNeedsLayoutTreeUpdateReason);
+
 class Node : public EventTarget
     , public TreeNode<Node> {
     WEB_PLATFORM_OBJECT(Node, EventTarget);
@@ -307,7 +328,7 @@ public:
     virtual bool is_child_allowed(Node const&) const { return true; }
 
     [[nodiscard]] bool needs_layout_tree_update() const { return m_needs_layout_tree_update; }
-    void set_needs_layout_tree_update(bool);
+    void set_needs_layout_tree_update(bool, SetNeedsLayoutTreeUpdateReason);
 
     [[nodiscard]] bool child_needs_layout_tree_update() const { return m_child_needs_layout_tree_update; }
     void set_child_needs_layout_tree_update(bool b) { m_child_needs_layout_tree_update = b; }