Refactor avoidsFloats() to reflect CSS2.1 spec more clearly

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 3742 matching lines @@
 }
 
 static bool isReplacedElement(Node* node)
 {
     // Checkboxes and radioboxes are not isReplaced() nor do they have their own renderer in which to override avoidFloats().
     return node && node->isElementNode() && (toElement(node)->isFormControlElement() || isHTMLImageElement(toElement(node)));
 }
 
 bool RenderBox::avoidsFloats() const
 {
-    return isReplaced() || isReplacedElement(node()) || hasOverflowClip() || isHR() || isLegend() || isWritingModeRoot() || isFlexItemIncludingDeprecated();
+    // CSS2.1: "The border box of a table, a block-level replaced element, or an element in the normal flow that establishes a new block formatting
+    // context .. must not overlap the margin box of any floats in the same block formatting context."
+    // FIXME: The inclusion of horizontal rule and legend elements here isn't covered by any spec.
+    return isReplaced() || isReplacedElement(node()) || isHR() || isLegend() || isTable() || (!isFloatingOrOutOfFlowPositioned() && createsBlockFormattingContext());
 }
 
 PaintInvalidationReason RenderBox::paintInvalidationReason(const RenderLayerModelObject& paintInvalidationContainer,
     const LayoutRect& oldBounds, const LayoutPoint& oldLocation, const LayoutRect& newBounds, const LayoutPoint& newLocation) const
 {
     PaintInvalidationReason invalidationReason = RenderBoxModelObject::paintInvalidationReason(paintInvalidationContainer, oldBounds, oldLocation, newBounds, newLocation);
     if (isFullPaintInvalidationReason(invalidationReason))
         return invalidationReason;
 
     // If the transform is not identity or translation, incremental invalidation is not applicable
@@ skipping 98 matching lines @@
         invalidatePaintUsingContainer(&paintInvalidationContainer, rectClippedByOldBounds, PaintInvalidationIncremental);
         return;
     }
     // Invalidate the bigger one if one contains another. Otherwise invalidate both.
     if (!rectClippedByNewBounds.contains(rectClippedByOldBounds))
         invalidatePaintUsingContainer(&paintInvalidationContainer, rectClippedByOldBounds, PaintInvalidationIncremental);
     if (!rectClippedByOldBounds.contains(rectClippedByNewBounds))
         invalidatePaintUsingContainer(&paintInvalidationContainer, rectClippedByNewBounds, PaintInvalidationIncremental);
 }
 
+bool RenderBox::createsBlockFormattingContext() const
+{
+    return isInlineBlockOrInlineTable() || isFloatingOrOutOfFlowPositioned() || hasOverflowClip() || isFlexItemIncludingDeprecated()
+        || style()->specifiesColumns() || isRenderFlowThread() || isTableCell() || isTableCaption() || isFieldset() || isWritingModeRoot() || isDocumentElement() || style()->columnSpan();
+}
+
 void RenderBox::markForPaginationRelayoutIfNeeded(SubtreeLayoutScope& layoutScope)
 {
     ASSERT(!needsLayout());
     // If fragmentation height has changed, we need to lay out. No need to enter the renderer if it
     // is childless, though.
     if (view()->layoutState()->pageLogicalHeightChanged() && slowFirstChild())
         layoutScope.setChildNeedsLayout(this);
 }
 
 void RenderBox::addVisualEffectOverflow()
@@ skipping 546 matching lines @@
 
     setLogicalTop(oldLogicalTop);
     setLogicalWidth(oldLogicalWidth);
     setMarginLeft(oldMarginLeft);
     setMarginRight(oldMarginRight);
 
     return borderBox;
 }
 
 } // namespace blink