[New Multicolumn] Intrinsic/preferred logical width calculation for spanners.

Source/core/rendering/RenderBlock.cpp

Index: Source/core/rendering/RenderBlock.cpp
diff --git a/Source/core/rendering/RenderBlock.cpp b/Source/core/rendering/RenderBlock.cpp
index cef0c517f6daa44f7db1c7f8a2e2b92dd65fbb52..aef2895bd5757cd85e4ccb23a5548e8bad8f0f2f 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -2956,7 +2956,11 @@ void RenderBlock::computeIntrinsicLogicalWidths(LayoutUnit& minLogicalWidth, Lay
 
     maxLogicalWidth = std::max(minLogicalWidth, maxLogicalWidth);
 
-    adjustIntrinsicLogicalWidthsForColumns(minLogicalWidth, maxLogicalWidth);
+    // The new ("region based") multicol implementation will do this adjustment on the flow thread,
+    // and not here on the multicol container, so that spanners won't incorrectly be treated as
+    // column content (and have spanners' preferred widths multiplied by the number of columns, etc.).
+    if (style()->specifiesColumns() && !document().regionBasedColumnsEnabled())
+        adjustIntrinsicLogicalWidthsForColumns(minLogicalWidth, maxLogicalWidth);
 
     if (isTableCell()) {
         Length tableCellWidth = toLayoutTableCell(this)->styleOrColLogicalWidth();
@@ -3041,8 +3045,9 @@ void RenderBlock::computeBlockPreferredLogicalWidths(LayoutUnit& minLogicalWidth
     RenderBlock* containingBlock = this->containingBlock();
     LayoutUnit floatLeftWidth = 0, floatRightWidth = 0;
     while (child) {
-        // Positioned children don't affect the min/max width
-        if (child->isOutOfFlowPositioned()) {
+        // Positioned children don't affect the min/max width. Spanners only affect the min/max
+        // width of the multicol container, not the flow thread.
+        if (child->isOutOfFlowPositioned() || child->isColumnSpanAll()) {
             child = child->nextSibling();
             continue;
         }
@@ -3083,6 +3088,12 @@ void RenderBlock::computeBlockPreferredLogicalWidths(LayoutUnit& minLogicalWidth
         } else {
             childMinPreferredLogicalWidth = child->minPreferredLogicalWidth();
             childMaxPreferredLogicalWidth = child->maxPreferredLogicalWidth();
+            if (child->isRenderFlowThread()) {

[Julien - ping for review, 2015/01/26 14:50:13]

This looks nasty. Why don't we patch the flow thread's preferred logical widths
computation to do the following? (RenderBlockLineLayout has some similar code so
it's likely broken after this change)

[mstensho (USE GERRIT), 2015/01/26 16:45:15]

I did this because I felt that providing the preferred widths in "multicol
container dimensions" would be bad, since everything in the flow thread is
supposed to have the same size as one column. It's inconsistent if
logicalWidth() is for one column, while minPreferredLogicalWidth() is for the
entire multicol container.
A RenderFlowThread is never inline (aka. a multicol container always has block
children), so that's not an issue.

+                // The preferred intrinsic widths that a flow thread reports pertains to the column
+                // width, but here we want the preferred multicol container width, so we need to
+                // adjust with that in mind.
+                adjustIntrinsicLogicalWidthsForColumns(childMinPreferredLogicalWidth, childMaxPreferredLogicalWidth);
+            }
         }
 
         LayoutUnit w = childMinPreferredLogicalWidth + margin;