Update our treatment of repeating headers in tables

third_party/WebKit/Source/core/layout/LayoutTable.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, 2010, 2013 Apple Inc.
  *               All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
@@ skipping 452 matching lines @@
     LayoutUnit logical_left,
     TableHeightChangingValue table_height_changing) {
   section.SetLogicalLocation(LayoutPoint(logical_left, LogicalHeight()));
   if (column_logical_width_changed_)
     layouter.SetChildNeedsLayout(&section);
   if (!section.NeedsLayout())
     MarkChildForPaginationRelayoutIfNeeded(section, layouter);
   bool needed_layout = section.NeedsLayout();
   if (needed_layout)
     section.UpdateLayout();
-  if (needed_layout || table_height_changing == kTableHeightChanging)
+  if (needed_layout || table_height_changing == kTableHeightChanging) {
     section.SetLogicalHeight(LayoutUnit(section.CalcRowLogicalHeight()));
+    section.SetHeaderGroupShouldRepeat();
+  }
 
   if (View()->GetLayoutState()->IsPaginated())
     UpdateFragmentationInfoForChild(section);
   SetLogicalHeight(LogicalHeight() + section.LogicalHeight());
 }
 
 LayoutUnit LayoutTable::LogicalHeightFromStyle() const {
   LayoutUnit computed_logical_height;
   Length logical_height_length = Style()->LogicalHeight();
   if (logical_height_length.IsIntrinsic() ||
@@ skipping 169 matching lines @@
     old_available_logical_height_ = current_available_logical_height;
 
     // Lay out table header group.
     if (LayoutTableSection* section = Header()) {
       LayoutSection(*section, layouter, section_logical_left,
                     table_height_changing);
       if (state.IsPaginated()) {
         // If the repeating header group allows at least one row of content,
         // then store the offset for other sections to offset their rows
         // against.
-        LayoutUnit section_logical_height = section->LogicalHeight();
-        if (section_logical_height <
-                section->PageLogicalHeightForOffset(section->LogicalTop()) &&
-            section->GetPaginationBreakability() != kAllowAnyBreaks) {
+        if (section->IsRepeatingHeaderGroup()) {
+          LayoutUnit offset_for_table_headers =
+              state.HeightOffsetForTableHeaders();
+          offset_for_table_headers += section->LogicalHeight();

[mstensho (USE GERRIT), 2017/05/22 10:40:44]

So here we are re-introducing support for nested repeated headers, while
previously we only repeated the header of the innermost table? Is that really
something we want? I mean, it's fine, but only if the alternative (NOT
re-introducing it) would lead to more complex code. Or is the spec super-clear
on how this is supposed to be handled now? I couldn't find anything.

[rhogan, 2017/05/22 18:06:04]

I think the spec implies it now (by allowing you to repeat a header regardless
of whether one content row fits entirely on the page or not) and I know Francois
the spec editor wants to maintain the majority browser behaviour in most cases,
which is to repeat nested headers. I don't think it makes things simpler to
support it - but I think it will be hard to support repeating headers even where
one content row doesn't fit but not support nested headers.

Relevant discussion re 'one content row':

https://lists.w3.org/Archives/Public/www-style/2016Dec/0070.html

I can raise it but given that FF and Edge currently nest and the spec supports
that implicitly I don't think I'll get a response that supports removing the
nested case.

[mstensho (USE GERRIT), 2017/05/22 19:17:34]

Thanks for the clarification. I agree that support for nested tables is now
implied. I definitely think you did the right thing by bringing it back.

           // Don't include any strut in the header group - we only want the
           // height from its content.
-          LayoutUnit offset_for_table_headers = section_logical_height;
           if (LayoutTableRow* row = section->FirstRow())
             offset_for_table_headers -= row->PaginationStrut();
+          state.SetHeightOffsetForTableHeaders(offset_for_table_headers);
           SetRowOffsetFromRepeatingHeader(offset_for_table_headers);
         }
       }
     }
 
     // Lay out table body groups, and column groups.
     for (LayoutObject* child = FirstChild(); child;
          child = child->NextSibling()) {
       if (child->IsTableSection()) {
         if (child != Header() && child != Footer()) {
@@ skipping 1077 matching lines @@
 }
 
 LayoutUnit LayoutTable::PaddingRight() const {
   if (ShouldCollapseBorders())
     return LayoutUnit();
 
   return LayoutBlock::PaddingRight();
 }
 
 }  // namespace blink