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

Author: https://github.com/awesomekling
Commit: https://github.com/LadybirdBrowser/ladybird/commit/2abbf99a957
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3852

Libraries/LibWeb/Animations/KeyframeEffect.cpp

@@ -962,7 +962,7 @@ void KeyframeEffect::update_computed_properties()
     }
 
     if (invalidation.relayout)
-        document.set_needs_layout();
+        document.set_needs_layout(DOM::SetNeedsLayoutReason::KeyframeEffect);
     if (invalidation.rebuild_layout_tree)
         document.invalidate_layout_tree(DOM::InvalidateLayoutTreeReason::KeyframeEffect);
     if (invalidation.repaint) {

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);
     }
 }
 

Libraries/LibWeb/HTML/HTMLImageElement.cpp

@@ -762,7 +762,7 @@ void HTMLImageElement::add_callbacks_to_image_request(GC::Ref<ImageRequest> imag
                 document().list_of_available_images().add(key, *image_data, true);
 
                 set_needs_style_update(true);
-                document().set_needs_layout();
+                document().set_needs_layout(DOM::SetNeedsLayoutReason::HTMLImageElementUpdateTheImageData);
 
                 // 4. If maybe omit events is not set or previousURL is not equal to urlString, then fire an event named load at the img element.
                 if (!maybe_omit_events || previous_url != url_string.serialize())
@@ -902,7 +902,7 @@ void HTMLImageElement::react_to_changes_in_the_environment()
             image_request->prepare_for_presentation(*this);
             // FIXME: This is ad-hoc, updating the layout here should probably be handled by prepare_for_presentation().
             set_needs_style_update(true);
-            document().set_needs_layout();
+            document().set_needs_layout(DOM::SetNeedsLayoutReason::HTMLImageElementReactToChangesInTheEnvironment);
 
             // 7. Fire an event named load at the img element.
             dispatch_event(DOM::Event::create(realm(), HTML::EventNames::load));

Libraries/LibWeb/HTML/HTMLVideoElement.cpp

@@ -111,7 +111,7 @@ u32 HTMLVideoElement::video_height() const
 void HTMLVideoElement::set_video_track(GC::Ptr<HTML::VideoTrack> video_track)
 {
     set_needs_style_update(true);
-    document().set_needs_layout();
+    document().set_needs_layout(DOM::SetNeedsLayoutReason::HTMLVideoElementSetVideoTrack);
 
     if (m_video_track)
         m_video_track->pause_video({});

Libraries/LibWeb/HTML/Navigable.cpp

@@ -2100,7 +2100,7 @@ void finalize_a_cross_document_navigation(GC::Ref<Navigable> navigable, HistoryH
     // AD-HOC: If we're inside a navigable container, let's trigger a relayout in the container document.
     //         This allows size negotiation between the containing document and SVG documents to happen.
     if (auto container = navigable->container()) {
-        container->document().set_needs_layout();
+        container->document().set_needs_layout(DOM::SetNeedsLayoutReason::FinalizeACrossDocumentNavigation);
     }
 }
 
@@ -2223,7 +2223,7 @@ void Navigable::set_viewport_size(CSSPixelSize size)
     if (auto document = active_document()) {
         // NOTE: Resizing the viewport changes the reference value for viewport-relative CSS lengths.
         document->invalidate_style(DOM::StyleInvalidationReason::NavigableSetViewportSize);
-        document->set_needs_layout();
+        document->set_needs_layout(DOM::SetNeedsLayoutReason::NavigableSetViewportSize);
     }
 
     if (auto document = active_document()) {

Libraries/LibWeb/SVG/SVGImageElement.cpp

@@ -168,7 +168,7 @@ void SVGImageElement::fetch_the_document(URL::URL const& url)
                 m_animation_timer->start();
             }
             set_needs_style_update(true);
-            document().set_needs_layout();
+            document().set_needs_layout(DOM::SetNeedsLayoutReason::SVGImageElementFetchTheDocument);
 
             dispatch_event(DOM::Event::create(realm(), HTML::EventNames::load));
         },