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

Source/core/rendering/RenderBlockFlow.cpp

Index: Source/core/rendering/RenderBlockFlow.cpp
diff --git a/Source/core/rendering/RenderBlockFlow.cpp b/Source/core/rendering/RenderBlockFlow.cpp
index afc0212fa770522ad2b8b05610560df1286d5192..6e7ddee59d2e1678777ac80e797ca5ec20b93093 100644
--- a/Source/core/rendering/RenderBlockFlow.cpp
+++ b/Source/core/rendering/RenderBlockFlow.cpp
@@ -546,11 +546,46 @@ void RenderBlockFlow::setLogicalTopForChild(RenderBox* child, LayoutUnit logical
     }
 }
 
+class ColumnSpannerLayoutScope {
+public:
+    ColumnSpannerLayoutScope()
+        : m_spanner(0)
+    {
+    }
+
+    ~ColumnSpannerLayoutScope()
+    {
+        if (!m_spanner)
+            return;
+        m_spanner->flowThreadContainingBlock()->exitColumnSpannerAfterLayout(m_spanner, m_spanner->parentBlock()->logicalHeight());
+    }
+
+    LayoutUnit enterSpanner(RenderBox* spanner, SubtreeLayoutScope& layoutScope)
+    {
+        ASSERT(!m_spanner);
+        m_spanner = spanner;
+        return m_spanner->flowThreadContainingBlock()->enterColumnSpannerBeforeLayout(m_spanner, m_spanner->parentBlock()->logicalHeight(), layoutScope);
+    }
+
+private:
+    RenderBox* m_spanner;
+};
+
 void RenderBlockFlow::layoutBlockChild(RenderBox* child, MarginInfo& marginInfo, LayoutUnit& previousFloatLogicalBottom)
 {
     LayoutUnit oldPosMarginBefore = maxPositiveMarginBefore();
     LayoutUnit oldNegMarginBefore = maxNegativeMarginBefore();
 
+    SubtreeLayoutScope layoutScope(*child);
+
+    ColumnSpannerLayoutScope columnSpannerLayoutScope;
+    if (child->isColumnSpanAll()) {
+        LayoutUnit adjustment = columnSpannerLayoutScope.enterSpanner(child, layoutScope);
+        // A spanner needs to start at an exact column boundary inside the flow thread, so that it
+        // doesn't bleed into a preceding column. That's what the adjustment is about.
+        setLogicalHeight(logicalHeight() + adjustment);
+    }
+
     // The child is a normal flow object. Compute the margins we will use for collapsing now.
     child->computeAndSetBlockDirectionMargins(this);
 
@@ -592,7 +627,6 @@ void RenderBlockFlow::layoutBlockChild(RenderBox* child, MarginInfo& marginInfo,
             previousFloatLogicalBottom = std::max(previousFloatLogicalBottom, oldLogicalTop + childRenderBlockFlow->lowestFloatLogicalBottom());
     }
 
-    SubtreeLayoutScope layoutScope(*child);
     if (!child->needsLayout())
         child->markForPaginationRelayoutIfNeeded(layoutScope);
 
@@ -867,6 +901,8 @@ void RenderBlockFlow::adjustLinePositionForPagination(RootInlineBox* lineBox, La
 
 LayoutUnit RenderBlockFlow::adjustForUnsplittableChild(RenderBox* child, LayoutUnit logicalOffset, bool includeMargins)
 {
+    if (child->isColumnSpanAll())
+        return logicalOffset;
     bool checkColumnBreaks = view()->layoutState()->isPaginatingColumns() || flowThreadContainingBlock();
     bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->pageLogicalHeight();
     bool isUnsplittable = child->isUnsplittableForPagination() || (checkColumnBreaks && child->style()->columnBreakInside() == PBAVOID)
@@ -1297,7 +1333,7 @@ LayoutUnit RenderBlockFlow::collapseMargins(RenderBox* child, MarginInfo& margin
     // If margins would pull us past the top of the next page, then we need to pull back and pretend like the margins
     // collapsed into the page edge.
     LayoutState* layoutState = view()->layoutState();
-    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTop > beforeCollapseLogicalTop) {
+    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTop > beforeCollapseLogicalTop && !child->isColumnSpanAll()) {

[Julien - ping for review, 2014/12/03 23:02:22]

This check feels magical. Why do column-span: all element not have collapsing
margins with the page edge?

[mstensho (USE GERRIT), 2014/12/10 13:48:19]

Calling nextPageLogicalTop() (see a couple of code lines below) is bogus and
nonsensical for spanners. Furthermore, that would take you to
RenderMultiColumnSpannerSet::pageLogicalHeight(), which now has an assertion. It
would never fail in this case, though, since this we're now inside
collapseMargins(), which are called after layout anyway.

I added this when I realized that we needed a similar check in
adjustForUnsplittableChild() (further up in this file). One test would fail
without that check.

         LayoutUnit oldLogicalTop = logicalTop;
         logicalTop = std::min(logicalTop, nextPageLogicalTop(beforeCollapseLogicalTop));
         setLogicalHeight(logicalHeight() + (logicalTop - oldLogicalTop));
@@ -1513,7 +1549,7 @@ LayoutUnit RenderBlockFlow::estimateLogicalTopPosition(RenderBox* child, const M
     // Adjust logicalTopEstimate down to the next page if the margins are so large that we don't fit on the current
     // page.
     LayoutState* layoutState = view()->layoutState();
-    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTopEstimate > logicalHeight())
+    if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTopEstimate > logicalHeight() && !child->isColumnSpanAll())

[Julien - ping for review, 2014/12/03 23:02:22]

Same comment :(

[mstensho (USE GERRIT), 2014/12/10 13:48:19]

Same reply as above, :) only that here we could potentially end up in an
assertion failure. We're now in estimateLogicalTopPosition(), which is called
before layout, so the spanner hasn't been laid out yet, so nextPageLogicalTop()
would take you to a RenderMultiColumnSpannerSet::pageLogicalHeight() whose
assertion would fail.

None of the existing tests trigger this. You'd need a top margin on the spanner,
and we don't support margins on spanners yet (I was saving that for another CL).
Currently, any top margin specified on a spanner would make layout look
miserable, so I don't know if it's worthwhile to add a test for it just yet. Or,
I could of course add a crash test.

         logicalTopEstimate = std::min(logicalTopEstimate, nextPageLogicalTop(logicalHeight()));
 
     logicalTopEstimate += getClearDelta(child, logicalTopEstimate);