[New Multicolumn] Actual support for layout of column-span:all.

Source/core/rendering/RenderMultiColumnFlowThread.cpp

Index: Source/core/rendering/RenderMultiColumnFlowThread.cpp
diff --git a/Source/core/rendering/RenderMultiColumnFlowThread.cpp b/Source/core/rendering/RenderMultiColumnFlowThread.cpp
index 6eaed6f174181af1b3308840f9bf3bb3b990256a..8e69a72a4677ab8eb94bb69356de38d2b6018288 100644
--- a/Source/core/rendering/RenderMultiColumnFlowThread.cpp
+++ b/Source/core/rendering/RenderMultiColumnFlowThread.cpp
@@ -32,11 +32,13 @@
 namespace blink {
 
 RenderMultiColumnFlowThread::RenderMultiColumnFlowThread()
-    : m_columnCount(1)
+    : m_lastSetWorkedOn(0)
+    , m_columnCount(1)
     , m_columnHeightAvailable(0)
     , m_inBalancingPass(false)
     , m_needsColumnHeightsRecalculation(false)
     , m_progressionIsInline(true)
+    , m_isBeingEvacuated(false)
 {
     setFlowThreadState(InsideInFlowThread);
 }
@@ -102,6 +104,7 @@ void RenderMultiColumnFlowThread::populate()
 void RenderMultiColumnFlowThread::evacuateAndDestroy()
 {
     RenderBlockFlow* multicolContainer = multiColumnBlockFlow();
+    m_isBeingEvacuated = true;
 
     // Remove all sets.
     while (RenderMultiColumnSet* columnSet = firstMultiColumnSet())
@@ -146,6 +149,27 @@ bool RenderMultiColumnFlowThread::needsNewWidth() const
     return newWidth != logicalWidth();
 }
 
+RenderMultiColumnSet* RenderMultiColumnFlowThread::columnSetAtBlockOffset(LayoutUnit offset) const
+{
+    if (m_lastSetWorkedOn) {

[Julien - ping for review, 2014/11/19 17:54:34]

This is the only real use of |m_lastSetWorkedOn|, the other ones could be
replaced by a hash lookup or some parameter.

The fact that we need to lie in this function during layout is a definite bad
smell. Why do we call this function mid-layout as we *know* we can't answer this
truthfully? Can't we avoid doing that altogether?

[mstensho (USE GERRIT), 2014/11/21 15:39:24]

This is called a lot mid-layout (and intentionally so).
RenderBlock::pageRemainingLogicalHeightForOffset(), for example, will take us
here. You want to know how much space is left in a column when laying out some
element. To find out how much space you have left, you need to know the column
height. To find the column height, you need to know which column set you're
currently working on.

So I wouldn't call it lying. But if we for some reason, during layout, use a
flow-tread offset here that's not contained by the current column set, things
will go wrong.

But we've briefly discussed that earlier in this review:
https://codereview.chromium.org/712553003/diff/40001/Source/core/rendering/Re...

+        // Layout in progress. We are calculating the set heights as we speak, so the column set range
+        // information is not up-to-date.
+        return m_lastSetWorkedOn;
+    }
+
+    ASSERT(!m_regionsInvalidated);
+    if (offset <= 0)
+        return m_multiColumnSetList.isEmpty() ? 0 : m_multiColumnSetList.first();
+
+    MultiColumnSetSearchAdapter adapter(offset);
+    m_multiColumnSetIntervalTree.allOverlapsWithAdapter<MultiColumnSetSearchAdapter>(adapter);
+
+    // If no set was found, the offset is in the flow thread overflow.
+    if (!adapter.result() && !m_multiColumnSetList.isEmpty())
+        return m_multiColumnSetList.last();
+    return adapter.result();
+}
+
 void RenderMultiColumnFlowThread::layoutColumns(bool relayoutChildren, SubtreeLayoutScope& layoutScope)
 {
     if (relayoutChildren)
@@ -162,16 +186,19 @@ void RenderMultiColumnFlowThread::layoutColumns(bool relayoutChildren, SubtreeLa
         return;
     }
 
+    bool hasSpannerOrAutoHeightColumnSet = false;
     for (RenderMultiColumnSet* columnSet = firstMultiColumnSet(); columnSet; columnSet = columnSet->nextSiblingMultiColumnSet()) {
         if (!m_inBalancingPass) {
             // This is the initial layout pass. We need to reset the column height, because contents
             // typically have changed.
             columnSet->resetColumnHeight();
         }
+        if (!hasSpannerOrAutoHeightColumnSet)
+            hasSpannerOrAutoHeightColumnSet = columnSet->isRenderMultiColumnSpannerSet() || columnSet->heightIsAuto();
     }
 
     invalidateRegions();
-    m_needsColumnHeightsRecalculation = heightIsAuto();
+    m_needsColumnHeightsRecalculation = hasSpannerOrAutoHeightColumnSet;
     layout();
 }
 
@@ -316,8 +343,74 @@ void RenderMultiColumnFlowThread::willBeRemovedFromTree()
     RenderFlowThread::willBeRemovedFromTree();
 }
 
+bool RenderMultiColumnFlowThread::isColumnSpanner(const RenderObject* descendant) const
+{
+    ASSERT(descendant->isDescendantOf(this));
+    return m_spannerMap.get(descendant);
+}
+
+bool RenderMultiColumnFlowThread::isInsideColumnSpanner(const RenderObject* descendant) const
+{
+    ASSERT(descendant->isDescendantOf(this));
+    return containingColumnSpannerSet(descendant);
+}
+
+LayoutUnit RenderMultiColumnFlowThread::enterColumnSpannerBeforeLayout(RenderBox* renderer, LayoutUnit logicalTop, SubtreeLayoutScope& layoutScope)
+{
+    ASSERT(isColumnSpanner(renderer));
+    RenderMultiColumnSpannerSet* spannerSet = m_spannerMap.get(renderer);
+
+    // FIXME: it's really only necessary to mark the spanner set for layout when the height of
+    // |renderer| changes.
+    spannerSet->setChildNeedsLayout(MarkOnlyThis, &layoutScope);
+
+    RenderMultiColumnSet* previousSet = spannerSet->previousSiblingMultiColumnSet();
+    if (!previousSet) {
+        // The first set is entered at the beginning of flow thread layout. If the first set happens
+        // to be a spanner, we have nothing more to do here.
+        return LayoutUnit();
+    }
+
+    RenderBlock* cb = toRenderBlock(renderer->container());
+    LayoutUnit logicalTopInFlowThread = cb->offsetFromLogicalTopOfFirstPage() + logicalTop;
+    LayoutUnit adjustment;
+    if (!previousSet->isRenderMultiColumnSpannerSet() && previousSet->pageLogicalHeight()) {
+        // Pad flow thread offset to a column boundary, so that contents that's supposed to come
+        // after the spanner (or the spanner itself) don't bleed into the column preceding the
+        // spanner.
+        LayoutUnit columnLogicalTopInFlowThread = previousSet->pageLogicalTopForOffset(logicalTopInFlowThread);
+        if (columnLogicalTopInFlowThread != logicalTopInFlowThread) {
+            adjustment = columnLogicalTopInFlowThread + previousSet->pageLogicalHeight() - logicalTopInFlowThread;
+            logicalTopInFlowThread += adjustment;
+        }
+    }
+
+    if (!previousSet->isRenderMultiColumnSpannerSet())
+        previousSet->endFlow(logicalTopInFlowThread);
+    spannerSet->beginFlow(logicalTopInFlowThread);
+
+    m_lastSetWorkedOn = spannerSet;
+    return adjustment;
+}
+
+void RenderMultiColumnFlowThread::leaveColumnSpannerAfterLayout(RenderBox* renderer, LayoutUnit logicalBottom)
+{
+    ASSERT(m_lastSetWorkedOn == m_spannerMap.get(renderer));
+
+    RenderBlock* cb = toRenderBlock(renderer->container());
+    LayoutUnit logicalBottomInFlowThread = cb->offsetFromLogicalTopOfFirstPage() + logicalBottom;
+    m_lastSetWorkedOn->endFlow(logicalBottomInFlowThread);
+    RenderMultiColumnSet* nextSet = m_lastSetWorkedOn->nextSiblingMultiColumnSet();
+    if (nextSet) {

[Julien - ping for review, 2014/11/19 17:54:34]

This should be a single line:

if (RenderMultiColumnSet* nextSet =
m_lastSetWorkedOn->nextSiblingMultiColumnSet()) {

[mstensho (USE GERRIT), 2014/11/21 15:39:24]

Done.

+        m_lastSetWorkedOn = nextSet;
+        if (!m_lastSetWorkedOn->isRenderMultiColumnSpannerSet())
+            m_lastSetWorkedOn->beginFlow(logicalBottomInFlowThread);
+    }
+}
+
 void RenderMultiColumnFlowThread::flowThreadDescendantWasInserted(RenderObject* descendant)
 {
+    ASSERT(!m_isBeingEvacuated);
     // Go through the subtree that was just inserted and create column sets (needed by regular
     // column content) and spanner sets (one needed by each spanner).
     for (RenderObject* renderer = descendant; renderer; renderer = renderer->nextInPreOrder(descendant)) {
@@ -335,6 +428,34 @@ void RenderMultiColumnFlowThread::flowThreadDescendantWasInserted(RenderObject*
     }
 }
 
+void RenderMultiColumnFlowThread::flowThreadDescendantWillBeRemoved(RenderObject* descendant)
+{
+    if (m_isBeingEvacuated)
+        return;
+    RenderObject* next;
+    // Remove spanner sets that are no longer needed, and merge column sets around them.
+    for (RenderObject* renderer = descendant; renderer; renderer = next) {
+        RenderMultiColumnSpannerSet* spanner = m_spannerMap.get(renderer);
+        if (!spanner) {
+            next = renderer->nextInPreOrder(descendant);
+            continue;
+        }
+        next = renderer->nextInPreOrderAfterChildren(descendant); // It's a spanner. Its children are of no interest to us.
+        if (RenderMultiColumnSet* nextSet = spanner->nextSiblingMultiColumnSet()) {
+            RenderMultiColumnSet* previousSet = spanner->previousSiblingMultiColumnSet();
+            if (nextSet && !nextSet->isRenderMultiColumnSpannerSet()
+                && previousSet && !previousSet->isRenderMultiColumnSpannerSet()) {
+                // Need to merge two column sets.
+                nextSet->destroy();
+                previousSet->setNeedsLayout();
+                invalidateRegions();
+            }
+        }
+        m_spannerMap.remove(renderer);
+        spanner->destroy();
+    }
+}
+
 void RenderMultiColumnFlowThread::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues& computedValues) const
 {
     // We simply remain at our intrinsic height.
@@ -351,9 +472,17 @@ void RenderMultiColumnFlowThread::updateLogicalWidth()
 
 void RenderMultiColumnFlowThread::layout()
 {
+    ASSERT(!m_lastSetWorkedOn);
+    m_lastSetWorkedOn = firstMultiColumnSet();
+    if (m_lastSetWorkedOn)
+        m_lastSetWorkedOn->beginFlow(LayoutUnit());
     RenderFlowThread::layout();
-    if (RenderMultiColumnSet* lastSet = lastMultiColumnSet())
+    if (RenderMultiColumnSet* lastSet = lastMultiColumnSet()) {
+        ASSERT(lastSet == m_lastSetWorkedOn);
+        lastSet->endFlow(logicalHeight());
         lastSet->expandToEncompassFlowThreadContentsIfNeeded();
+    }
+    m_lastSetWorkedOn = 0;
 }
 
 void RenderMultiColumnFlowThread::setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage)
@@ -375,12 +504,6 @@ void RenderMultiColumnFlowThread::updateMinimumPageHeight(LayoutUnit offset, Lay
         multicolSet->updateMinimumColumnHeight(minHeight);
 }
 
-RenderMultiColumnSet* RenderMultiColumnFlowThread::columnSetAtBlockOffset(LayoutUnit /*offset*/) const
-{
-    // For now there's only one column set, so this is easy:
-    return firstMultiColumnSet();
-}
-
 bool RenderMultiColumnFlowThread::addForcedRegionBreak(LayoutUnit offset, RenderObject* /*breakChild*/, bool /*isBefore*/, LayoutUnit* offsetBreakAdjustment)
 {
     if (RenderMultiColumnSet* multicolSet = columnSetAtBlockOffset(offset)) {