Don't stretch margin: auto items in a vertical flexbox

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 2160 matching lines @@
     LayoutUnit logicalWidthResult = fillAvailableMeasure(availableLogicalWidth, marginStart, marginEnd);
 
     if (shrinkToAvoidFloats() && cb->containsFloats())
         logicalWidthResult = min(logicalWidthResult, shrinkLogicalWidthToAvoidFloats(marginStart, marginEnd, cb, region, offsetFromLogicalTopOfFirstPage));        
 
     if (widthType == MainOrPreferredSize && sizesLogicalWidthToFitContent(widthType))
         return max(minPreferredLogicalWidth(), min(maxPreferredLogicalWidth(), logicalWidthResult));
     return logicalWidthResult;
 }
 
-static bool flexItemHasStretchAlignment(const RenderObject* flexitem)
+static bool columnFlexItemHasStretchAlignment(const RenderObject* flexitem)
 {
     RenderObject* parent = flexitem->parent();
+    // auto margins mean we don't stretch. Note that this function will only be used for
+    // widths, so we don't have to check marginBefore/marginAfter.
+    ASSERT(parent->style()->isColumnFlexDirection());
+    if (flexitem->style()->marginStart().isAuto() || flexitem->style()->marginEnd().isAuto())
+        return false;
     return flexitem->style()->alignSelf() == AlignStretch || (flexitem->style()->alignSelf() == AlignAuto && parent->style()->alignItems() == AlignStretch);
 }
 
 static bool isStretchingColumnFlexItem(const RenderObject* flexitem)
 {
     RenderObject* parent = flexitem->parent();
     if (parent->isDeprecatedFlexibleBox() && parent->style()->boxOrient() == VERTICAL && parent->style()->boxAlign() == BSTRETCH)
         return true;
 
     // We don't stretch multiline flexboxes because they need to apply line spacing (align-content) first.
-    if (parent->isFlexibleBox() && parent->style()->flexWrap() == FlexNoWrap && parent->style()->isColumnFlexDirection() && flexItemHasStretchAlignment(flexitem))
+    if (parent->isFlexibleBox() && parent->style()->flexWrap() == FlexNoWrap && parent->style()->isColumnFlexDirection() && columnFlexItemHasStretchAlignment(flexitem))
         return true;
     return false;
 }
 
 bool RenderBox::sizesLogicalWidthToFitContent(SizeType widthType) const
 {
     // Marquees in WinIE are like a mixture of blocks and inline-blocks.  They size as though they're blocks,
     // but they allow text to sit on the same line as the marquee.
     if (isFloating() || (isInlineBlockOrInlineTable() && !isHTMLMarquee()))
         return true;
@@ skipping 15 matching lines @@
             return true;
     }
 
     // Flexible box items should shrink wrap, so we lay them out at their intrinsic widths.
     // In the case of columns that have a stretch alignment, we go ahead and layout at the
     // stretched size to avoid an extra layout when applying alignment.
     if (parent()->isFlexibleBox()) {
         // For multiline columns, we need to apply align-content first, so we can't stretch now.
         if (!parent()->style()->isColumnFlexDirection() || parent()->style()->flexWrap() != FlexNoWrap)
             return true;
-        if (!flexItemHasStretchAlignment(this))
+        if (!columnFlexItemHasStretchAlignment(this))
             return true;
     }
 
     // Flexible horizontal boxes lay out children at their intrinsic widths.  Also vertical boxes
     // that don't stretch their kids lay out their children at their intrinsic widths.
     // FIXME: Think about block-flow here.
     // https://bugs.webkit.org/show_bug.cgi?id=46473
     if (parent()->isDeprecatedFlexibleBox() && (parent()->style()->boxOrient() == HORIZONTAL || parent()->style()->boxAlign() != BSTRETCH))
         return true;
 
@@ skipping 2350 matching lines @@
 
 void RenderBox::reportStaticMembersMemoryUsage(MemoryInstrumentation* memoryInstrumentation)
 {
     memoryInstrumentation->addRootObject(gOverrideHeightMap, WebCoreMemoryTypes::RenderingStructures);
     memoryInstrumentation->addRootObject(gOverrideWidthMap, WebCoreMemoryTypes::RenderingStructures);
     memoryInstrumentation->addRootObject(gOverrideContainingBlockLogicalHeightMap, WebCoreMemoryTypes::RenderingStructures);
     memoryInstrumentation->addRootObject(gOverrideContainingBlockLogicalWidthMap, WebCoreMemoryTypes::RenderingStructures);
 }
 
 } // namespace WebCore