Move Layout Tree Construction code into Element::rebuildLayoutTree()

third_party/WebKit/Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc.
  * All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
@@ skipping 1842 matching lines @@
         data->clearComputedStyle();
 
       if (change >= IndependentInherit) {
         if (ElementAnimations* elementAnimations = data->elementAnimations())
           elementAnimations->setAnimationStyleChange(false);
       }
     }
     if (parentComputedStyle())
       change = recalcOwnStyle(change);
     clearNeedsStyleRecalc();
+    clearNeedsReattachLayoutTree();
   }
 
   // If we reattached we don't need to recalc the style of our descendants
   // anymore.
   if ((change >= UpdatePseudoElements && change < Reattach) ||
       childNeedsStyleRecalc()) {
     SelectorFilterParentScope filterScope(*this);
     StyleSharingDepthScope sharingScope(*this);
 
     updatePseudoElement(PseudoIdBefore, change);
@@ skipping 11 matching lines @@
     updatePseudoElement(PseudoIdBackdrop, change);
 
     // If our children have changed then we need to force the first-letter
     // checks as we don't know if they effected the first letter or not.
     // This can be seen when a child transitions from floating to
     // non-floating we have to take it into account for the first letter.
     updatePseudoElement(PseudoIdFirstLetter,
                         childNeedsStyleRecalc() ? Force : change);
 
     clearChildNeedsStyleRecalc();
+    clearChildNeedsReattachLayoutTree();
   }
 
   if (hasCustomStyleCallbacks())
     didRecalcStyle(change);
-
-  if (change == Reattach)
-    reattachWhitespaceSiblingsIfNeeded(nextTextSibling);
 }
 
 PassRefPtr<ComputedStyle> Element::propagateInheritedProperties(
     StyleRecalcChange change) {
   if (change != IndependentInherit)
     return nullptr;
   if (needsStyleRecalc())
     return nullptr;
   if (hasAnimations())
     return nullptr;
@@ skipping 28 matching lines @@
   StyleRecalcChange localChange =
       ComputedStyle::stylePropagationDiff(oldStyle.get(), newStyle.get());
   if (localChange == NoChange) {
     INCREMENT_STYLE_STATS_COUNTER(document().styleEngine(), stylesUnchanged, 1);
   } else {
     INCREMENT_STYLE_STATS_COUNTER(document().styleEngine(), stylesChanged, 1);
   }
 
   if (localChange == Reattach) {
     document().addNonAttachedStyle(*this, std::move(newStyle));
+    setNeedsReattachLayoutTree();
     return rebuildLayoutTree();
   }
 
   DCHECK(oldStyle);
 
   if (localChange != NoChange)
     updateCallbackSelectors(oldStyle.get(), newStyle.get());
 
   if (LayoutObject* layoutObject = this->layoutObject()) {
     if (localChange != NoChange ||
@@ skipping 26 matching lines @@
       return UpdatePseudoElements;
   }
 
   return localChange;
 }
 
 StyleRecalcChange Element::rebuildLayoutTree() {
   AttachContext reattachContext;
   reattachContext.resolvedStyle = document().getNonAttachedStyle(*this);
   bool layoutObjectWillChange = needsAttach() || layoutObject();
-  reattachLayoutTree(reattachContext);
-  if (layoutObjectWillChange || layoutObject())
+
+  if (needsReattachLayoutTree())

[Bugs Nash, 2016/10/17 00:17:05]

what is the purpose of this check? it doesn't seem necessary at this point

[nainar, 2016/10/17 16:29:12]

Moved to a DCHECK and added an explainer comment here as well. 

+    reattachLayoutTree(reattachContext);
+
+  DCHECK(!childNeedsReattachLayoutTree());

[Bugs Nash, 2016/10/17 00:17:05]

add a comment explaining why we expect this DCHECK to be true (i.e.
reattachLayoutTree handles the children)

[nainar, 2016/10/17 16:29:12]

Done.

+
+  if (layoutObjectWillChange || layoutObject()) {
+    Text* nextTextSibling = nullptr;

[Bugs Nash, 2016/10/17 00:17:04]

the comment about the trade off between storage and calculation was good, I just
meant to remove the part about webkit.

I think this would be better separated into its own method nextTextSibling(),
possibly on Node, which can return null if the next sibling is not an Element or
doesn't have a layout object. In future once Text mirrors Element this could
even be called from within reattachWhitespaceSiblings itself instead of being
passed here.

[nainar, 2016/10/17 16:29:12]

Edited the comment. 

Moved code to function. 

+    for (Node* sibling = this->nextSibling();
+         sibling &&
+         !(sibling->isElementNode() && toElement(sibling)->layoutObject());
+         sibling = sibling->nextSibling()) {
+      if (sibling->isTextNode()) {
+        nextTextSibling = toText(sibling);
+        break;
+      }
+    }
+    reattachWhitespaceSiblingsIfNeeded(nextTextSibling);
     return Reattach;
+  }
   return ReattachNoLayoutObject;
 }
 
 void Element::updateCallbackSelectors(const ComputedStyle* oldStyle,
                                       const ComputedStyle* newStyle) {
   Vector<String> emptyVector;
   const Vector<String>& oldCallbackSelectors =
       oldStyle ? oldStyle->callbackSelectors() : emptyVector;
   const Vector<String>& newCallbackSelectors =
       newStyle ? newStyle->callbackSelectors() : emptyVector;
@@ skipping 2074 matching lines @@
 }
 
 DEFINE_TRACE_WRAPPERS(Element) {
   if (hasRareData()) {
     visitor->traceWrappers(elementRareData());
   }
   ContainerNode::traceWrappers(visitor);
 }
 
 }  // namespace blink