Complete layout even if a block needs relayout due to widows or column balancing.

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 385 matching lines @@
   ASSERT(isInlineBlockOrInlineTable() || !isInline());
 
   if (!relayoutChildren && simplifiedLayout())
     return;
 
   LayoutAnalyzer::BlockScope analyzer(*this);
   SubtreeLayoutScope layoutScope(*this);
 
   // Multiple passes might be required for column based layout.
   // The number of passes could be as high as the number of columns.
-  bool done = false;
-  while (!done)
-    done = layoutBlockFlow(relayoutChildren, layoutScope);
+  LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread();
+  do {
+    layoutBlockFlow(relayoutChildren, layoutScope);
+
+    if (flowThread && flowThread->columnHeightsChanged()) {
+      setChildNeedsLayout(MarkOnlyThis);
+      continue;
+    }
+
+    if (shouldBreakAtLineToAvoidWidow()) {
+      setEverHadLayout();
+      continue;
+    }
+    break;
+  } while (true);
 
   updateLayerTransformAfterLayout();
 
   updateAfterLayout();
 
   if (isHTMLDialogElement(node()) && isOutOfFlowPositioned())
     positionDialog();
 
   clearNeedsLayout();
   updateIsSelfCollapsing();
@@ skipping 36 matching lines @@
     // exists *between* in-flow siblings (i.e. not before the first child and
     // not after the last child).
     //
     // [1] https://drafts.csswg.org/css-break/#possible-breaks
     setBreakBefore(LayoutBlock::breakBefore());
     setBreakAfter(LayoutBlock::breakAfter());
   }
 }
 
 DISABLE_CFI_PERF
-inline bool LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren,
+inline void LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren,
                                              SubtreeLayoutScope& layoutScope) {
   LayoutUnit oldLeft = logicalLeft();
   bool logicalWidthChanged = updateLogicalWidthAndColumnWidth();
   relayoutChildren |= logicalWidthChanged;
 
   LayoutState state(*this, logicalWidthChanged);
 
   if (m_paginationStateChanged) {
     // We now need a deep layout to clean up struts after pagination, if we
     // just ceased to be paginated, or, if we just became paginated on the
@@ skipping 20 matching lines @@
     layoutBlockChildren(relayoutChildren, layoutScope, beforeEdge, afterEdge);
 
   bool preferredLogicalWidthsBecameDirty =
       !preferredLogicalWidthsWereDirty && preferredLogicalWidthsDirty();
   if (preferredLogicalWidthsBecameDirty) {
     // The only thing that should dirty preferred widths at this point is the
     // addition of overflow:auto scrollbars in a descendant. To avoid a
     // potential infinite loop, run layout again with auto scrollbars frozen in
     // their current state.
     PaintLayerScrollableArea::FreezeScrollbarsScope freezeScrollbars;
-    return layoutBlockFlow(relayoutChildren, layoutScope);
+    layoutBlockFlow(relayoutChildren, layoutScope);

[szager1, 2016/12/01 17:43:24]

Please add:

DCHECK(preferredLogicalWidthsWereDirty || !preferredLogicalWidthsDirty());

[mstensho (USE GERRIT), 2016/12/01 18:11:47]

We can be pretty sure that !preferredLogicalWidthsWereDirty at this point. So I
suppose it's sufficient to DCHECK(!preferredLogicalWidthsDirty()), right?

[mstensho (USE GERRIT), 2016/12/01 19:15:34]

Hmm... scrollbars/overflow-auto-infinite-loop.html crashes then. Maybe deal with
this separately?

[szager1, 2016/12/01 20:30:12]

There's a reason why I added preferredLogicalWidthsWereDirty, rather than just
checking preferredLogicalWidthsDirty() after layoutBlockChildren.  There are
some legitimate cases where this code runs while preferred widths are dirty (I
don't remember exactly why).  So, we only want to flag the case where preferred
widths were clean and became dirty.

[mstensho (USE GERRIT), 2016/12/01 20:36:10]

But we only get here if preferredLogicalWidthsBecameDirty, i.e. if
!preferredLogicalWidthsWereDirty && preferredLogicalWidthsDirty(). So I don't
understand how preferredLogicalWidthsWereDirty can be true here.

(preferred widths are dirty and remain dirty on any object that doesn't need its
min/max widths calculated, but maybe you had something more specific in mind)

+    return;
   }
 
   // Expand our intrinsic height to encompass floats.
   if (lowestFloatLogicalBottom() > (logicalHeight() - afterEdge) &&
       createsNewFormattingContext())
     setLogicalHeight(lowestFloatLogicalBottom() + afterEdge);
 
-  if (LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
-    if (flowThread->columnHeightsChanged()) {
-      setChildNeedsLayout(MarkOnlyThis);
-      return false;
-    }
-  }
-
-  if (shouldBreakAtLineToAvoidWidow()) {
-    setEverHadLayout();
-    return false;
-  }
-
   // Remember the automatic logical height we got from laying out the children.
   LayoutUnit unconstrainedHeight = logicalHeight();
   LayoutUnit unconstrainedClientAfterEdge = clientLogicalBottom();
 
   // Adjust logical height to satisfy whatever computed style requires.
   updateLogicalHeight();
 
   if (!childrenInline())
     addOverhangingFloatsFromChildren(unconstrainedHeight);
 
   if (previousHeight != logicalHeight() || isDocumentElement())
     relayoutChildren = true;
 
   PositionedLayoutBehavior behavior = DefaultLayout;
   if (oldLeft != logicalLeft())
     behavior = ForcedLayoutAfterContainingBlockMoved;
   layoutPositionedObjects(relayoutChildren, behavior);
 
   // Add overflow from children (unless we're multi-column, since in that case
   // all our child overflow is clipped anyway).
   computeOverflow(unconstrainedClientAfterEdge);
 
   m_descendantsWithFloatsMarkedForLayout = false;
-  return true;
 }
 
 void LayoutBlockFlow::addOverhangingFloatsFromChildren(
     LayoutUnit unconstrainedHeight) {
   LayoutBlockFlow* lowestBlock = nullptr;
   bool addedOverhangingFloats = false;
   // One of our children's floats may have become an overhanging float for us.
   for (LayoutObject* child = lastChild(); child;
        child = child->previousSibling()) {
     // TODO(robhogan): We should exclude blocks that create formatting
@@ skipping 3981 matching lines @@
   return LayoutBlock::invalidatePaintIfNeeded(paintInvalidationState);
 }
 
 void LayoutBlockFlow::invalidateDisplayItemClients(
     PaintInvalidationReason invalidationReason) const {
   BlockFlowPaintInvalidator(*this).invalidateDisplayItemClients(
       invalidationReason);
 }
 
 }  // namespace blink