Enable position:sticky for <thead> and <tr> elements

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.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 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. 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 15 matching lines @@
 #include "core/layout/LayoutBoxModelObject.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/html/HTMLBodyElement.h"
 #include "core/layout/ImageQualityController.h"
 #include "core/layout/LayoutBlock.h"
 #include "core/layout/LayoutFlexibleBox.h"
 #include "core/layout/LayoutGeometryMap.h"
 #include "core/layout/LayoutInline.h"
+#include "core/layout/LayoutTableCell.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/compositing/CompositedLayerMapping.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/paint/ObjectPaintInvalidator.h"
 #include "core/paint/PaintLayer.h"
 #include "core/style/ShadowList.h"
 #include "platform/LengthFunctions.h"
 #include "platform/geometry/TransformState.h"
 #include "platform/scroll/MainThreadScrollingReason.h"
 #include "wtf/PtrUtil.h"
@@ skipping 928 matching lines @@
   stickyLocation -= containerBorderOffset;
   constraints.setScrollContainerRelativeStickyBoxRect(
       FloatRect(scrollContainerRelativePaddingBoxRect.location() +
                     toFloatSize(stickyLocation),
                 flippedStickyBoxRect.size()));
 
   // To correctly compute the offsets, the constraints need to know about any
   // nested position:sticky elements between themselves and their
   // containingBlock, and between the containingBlock and their scrollAncestor.
   //
-  // The respective search ranges are [container, containingBlock) and
+  // The respective search ranges are [locationContainer, containingBlock) and
   // [containingBlock, scrollAncestor).
+
+  // Table cells are a special case; Blink ignores them for locationContainer()
+  // purposes, but their sticky offset does affect descendant sticky objects.
+  // TODO(smcgruer): Remove cell override once Blink supports the correct
+  // locationContainer for CSS 3.
+  LayoutObject* locationContainerForSticky =

[smcgruer, 2017/03/29 18:02:57]

1. I'm not sure if we also want to do this for its use in
skippedContainersOffset above. Thoughts?

2. I thought we would also want to do this for findFirstStickyBetween, but was
unable to construct a test case. I was thinking of something like the following,
thoughts?

<tr class=".sticky">
  <th><div class=".sticky"></div></th>
</tr>

I think in this case the <div> would fail to notice the <tr> sticky ancestor,
but in my tests this doesn't seem to actually cause any problems which is
strange.

+      isTableCell() ? toLayoutTableCell(this)->row() : locationContainer;
+
   constraints.setNearestStickyBoxShiftingStickyBox(
-      findFirstStickyBetween(locationContainer, containingBlock));
+      findFirstStickyBetween(locationContainerForSticky, containingBlock));
   // We cannot use |scrollAncestor| here as it disregards the root
   // ancestorOverflowLayer(), which we should include.
   constraints.setNearestStickyBoxShiftingContainingBlock(findFirstStickyBetween(
       containingBlock, &layer()->ancestorOverflowLayer()->layoutObject()));
 
   // We skip the right or top sticky offset if there is not enough space to
   // honor both the left/right or top/bottom offsets.
   LayoutUnit horizontalOffsets =
       minimumValueForLength(style()->right(),
                             LayoutUnit(constrainingSize.width())) +
@@ skipping 470 matching lines @@
   if (rootElementStyle->hasBackground())
     return false;
 
   if (node() != document().firstBodyElement())
     return false;
 
   return true;
 }
 
 }  // namespace blink