Respect break-inside:avoid on table rows

third_party/WebKit/Source/core/layout/LayoutTableCell.cpp

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple 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 981 matching lines @@
 
 bool LayoutTableCell::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localRect) const
 {
     // If this object has layer, the area of collapsed borders should be transparent
     // to expose the collapsed borders painted on the underlying layer.
     if (hasLayer() && table()->collapseBorders())
         return false;
     return LayoutBlockFlow::backgroundIsKnownToBeOpaqueInRect(localRect);
 }
 
+LayoutUnit LayoutTableCell::calculatePaginationStrutToFitContent(LayoutUnit offset, LayoutUnit strutToNextPage, LayoutUnit contentLogicalHeight) const
+{
+    // If break-inside:avoid/forbid is set on a cell we should avoid setting a strut on lines unless the cell is taller than the page,
+    // in which case we've no choice but to allow it. This special-casing is needed because cells don't propagate struts like normal
+    // layout blocks - the struts are managed directly by the section when it lays out rows and cells.
+    LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(offset);
+    if (toLayoutBox(parent())->getPaginationBreakability() != AllowAnyBreaks && table()->vBorderSpacing() + logicalHeight() + contentLogicalHeight < pageLogicalHeight)

[mstensho (USE GERRIT), 2016/04/04 21:05:39]

I still think this looks strange. We have decided that we need to break here
(e.g. between two lines inside a table cell), but we just nuke the strut, and
brutally slice content across column boundaries. This looks like a hack to me. I
wonder if the problem is in LayoutTableSection::layoutRows(). I prefer if we
just leave the strut as it is here, and instead adjust the row heights correctly
in LayoutTableSection::layoutRows(). When paginationStrutForRow() gives us
something there, we should lay out all affected cells over again, and pay
attention if their heights change. Cell heights will typically shrink, since
there'll typically be fewer pagination struts inside. This height decrease needs
to be propagated to all consecutive rows.

This code here also assumes that logicalHeight() is flush with the bottom for
the piece of content that we're supposed to break after, and it doesn't seem
like that's always the case. Which seems to be the reason why this fails:

<div style="columns:2; column-fill:auto; height:5em; line-height:2em;">
    first column<br>
    <table cellpadding="1" cellspacing="0">
        <tr style="break-inside: avoid;">
            <td>second column<br>second column</td>
        </tr>
    </table>
</div>

I'd also like to point out that fragmentation inside tables is quite broken, in
fact, because we don't always lay out the objects at their correct location; see
crbug.com/534751 - a source of weird and broken layout.

+        return LayoutUnit();
+    return LayoutBlockFlow::calculatePaginationStrutToFitContent(offset, strutToNextPage, contentLogicalHeight);
+}
+
 } // namespace blink