LibWeb: Add opt-in tracing of set_needs_layout() calls with reason

Author: https://github.com/awesomekling
Commit: 2abbf99a95
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3852

Libraries/LibWeb/DOM/CharacterData.cpp

@@ -146,7 +146,7 @@ WebIDL::ExceptionOr<void> CharacterData::replace_data(size_t offset, size_t coun
     if (auto* layout_node = this->layout_node(); layout_node && layout_node->is_text_node())
         static_cast<Layout::TextNode&>(*layout_node).invalidate_text_for_rendering();
 
-    document().set_needs_layout();
+    document().set_needs_layout(SetNeedsLayoutReason::CharacterDataReplaceData);
     document().bump_character_data_version();
 
     if (m_grapheme_segmenter)

Libraries/LibWeb/DOM/Document.cpp

@@ -1211,10 +1211,16 @@ Optional<String> Document::encoding_parse_and_serialize_url(StringView url) cons
     return parsed_url->serialize();
 }
 
-void Document::set_needs_layout()
+void Document::set_needs_layout(SetNeedsLayoutReason reason)
 {
     if (m_needs_layout)
         return;
+    if constexpr (UPDATE_LAYOUT_DEBUG) {
+        // NOTE: We check some conditions here to avoid debug spam in documents that don't do layout.
+        auto navigable = this->navigable();
+        if (m_layout_root && navigable && navigable->active_document() == this)
+            dbgln_if(UPDATE_LAYOUT_DEBUG, "NEED LAYOUT {}", to_string(reason));
+    }
     m_needs_layout = true;
     schedule_layout_update();
 }
@@ -1527,7 +1533,7 @@ void Document::update_style()
     if (!invalidation.is_none())
         invalidate_display_list();
     if (invalidation.relayout)
-        set_needs_layout();
+        set_needs_layout(SetNeedsLayoutReason::StyleChange);
     if (invalidation.rebuild_stacking_context_tree)
         invalidate_stacking_context_tree();
     m_needs_full_style_update = false;
@@ -6405,6 +6411,18 @@ void Document::set_onvisibilitychange(WebIDL::CallbackType* value)
     set_event_handler_attribute(HTML::EventNames::visibilitychange, value);
 }
 
+StringView to_string(SetNeedsLayoutReason reason)
+{
+    switch (reason) {
+#define ENUMERATE_SET_NEEDS_LAYOUT_REASON(e) \
+    case SetNeedsLayoutReason::e:            \
+        return #e##sv;
+        ENUMERATE_SET_NEEDS_LAYOUT_REASONS(ENUMERATE_SET_NEEDS_LAYOUT_REASON)
+#undef ENUMERATE_SET_NEEDS_LAYOUT_REASON
+    }
+    VERIFY_NOT_REACHED();
+}
+
 StringView to_string(InvalidateLayoutTreeReason reason)
 {
     switch (reason) {

Libraries/LibWeb/DOM/Document.h

@@ -50,6 +50,26 @@ enum class QuirksMode {
     Yes
 };
 
+#define ENUMERATE_SET_NEEDS_LAYOUT_REASONS(X)         \
+    X(CharacterDataReplaceData)                       \
+    X(FinalizeACrossDocumentNavigation)               \
+    X(HTMLImageElementReactToChangesInTheEnvironment) \
+    X(HTMLImageElementUpdateTheImageData)             \
+    X(HTMLVideoElementSetVideoTrack)                  \
+    X(KeyframeEffect)                                 \
+    X(LayoutTreeUpdate)                               \
+    X(NavigableSetViewportSize)                       \
+    X(SVGImageElementFetchTheDocument)                \
+    X(StyleChange)
+
+enum class SetNeedsLayoutReason {
+#define ENUMERATE_SET_NEEDS_LAYOUT_REASON(e) e,
+    ENUMERATE_SET_NEEDS_LAYOUT_REASONS(ENUMERATE_SET_NEEDS_LAYOUT_REASON)
+#undef ENUMERATE_SET_NEEDS_LAYOUT_REASON
+};
+
+[[nodiscard]] StringView to_string(SetNeedsLayoutReason);
+
 #define ENUMERATE_INVALIDATE_LAYOUT_TREE_REASONS(X)       \
     X(DocumentAddAnElementToTheTopLayer)                  \
     X(DocumentRequestAnElementToBeRemovedFromTheTopLayer) \
@@ -340,7 +360,7 @@ public:
     void update_paint_and_hit_testing_properties_if_needed();
     void update_animated_style_if_needed();
 
-    void set_needs_layout();
+    void set_needs_layout(SetNeedsLayoutReason);
 
     void invalidate_layout_tree(InvalidateLayoutTreeReason);
     void invalidate_stacking_context_tree();

Libraries/LibWeb/DOM/Node.cpp

@@ -1405,7 +1405,7 @@ void Node::set_needs_layout_tree_update(bool value)
                 break;
             ancestor->m_child_needs_layout_tree_update = true;
         }
-        document().set_needs_layout();
+        document().set_needs_layout(SetNeedsLayoutReason::LayoutTreeUpdate);
     }
 }