[CSS Grid Layout] Support span in auto-placement algorithm

Source/core/rendering/style/GridResolvedPosition.cpp

Index: Source/core/rendering/style/GridResolvedPosition.cpp
diff --git a/Source/core/rendering/style/GridResolvedPosition.cpp b/Source/core/rendering/style/GridResolvedPosition.cpp
index 7249b15e739b0e8d7dac18dabeae7a6dd85219bb..e9712af68b4897378f95c4faae02a66918b5bb34 100644
--- a/Source/core/rendering/style/GridResolvedPosition.cpp
+++ b/Source/core/rendering/style/GridResolvedPosition.cpp
@@ -10,19 +10,49 @@
 
 namespace WebCore {
 
-GridSpan GridResolvedPosition::resolveGridPositionsFromAutoPlacementPosition(const RenderBox&, GridTrackSizingDirection, const GridResolvedPosition& initialPosition)
+void GridResolvedPosition::initialAndFinalPositionsFromStyle(const RenderStyle& gridContainerStyle, const RenderBox& gridItem, GridTrackSizingDirection direction, GridPosition& initialPosition, GridPosition& finalPosition)
 {
-    // FIXME: We don't support spanning with auto positions yet. Once we do, this is wrong. Also we should make
-    // sure the grid can accomodate the new item as we only grow 1 position in a given direction.
-    return GridSpan(initialPosition, initialPosition);
+    initialPosition = (direction == ForColumns) ? gridItem.style()->gridColumnStart() : gridItem.style()->gridRowStart();
+    finalPosition = (direction == ForColumns) ? gridItem.style()->gridColumnEnd() : gridItem.style()->gridRowEnd();
+
+    // We must handle the placement error handling code here instead of in the StyleAdjuster because we don't want to
+    // overwrite the specified values.
+    if (initialPosition.isSpan() && finalPosition.isSpan())
+        finalPosition.setAutoPosition();
+
+    if (initialPosition.isNamedGridArea() && !gridContainerStyle.namedGridArea().contains(initialPosition.namedGridLine()))
+        initialPosition.setAutoPosition();
+
+    if (finalPosition.isNamedGridArea() && !gridContainerStyle.namedGridArea().contains(finalPosition.namedGridLine()))
+        finalPosition.setAutoPosition();
 }
 
-PassOwnPtr<GridSpan> GridResolvedPosition::resolveGridPositionsFromStyle(const RenderStyle& gridContainerStyle, const RenderBox& gridItem, GridTrackSizingDirection direction)
+PassOwnPtr<GridSpan> GridResolvedPosition::resolveGridPositionsFromAutoPlacementPosition(const RenderStyle& gridContainerStyle, const RenderBox& gridItem, GridTrackSizingDirection direction, const GridResolvedPosition& resolvedInitialPosition)
 {
-    GridPosition initialPosition = (direction == ForColumns) ? gridItem.style()->gridColumnStart() : gridItem.style()->gridRowStart();
-    const GridPositionSide initialPositionSide = (direction == ForColumns) ? ColumnStartSide : RowStartSide;
-    GridPosition finalPosition = (direction == ForColumns) ? gridItem.style()->gridColumnEnd() : gridItem.style()->gridRowEnd();
+    GridPosition initialPosition;
+    GridPosition finalPosition;
+    initialAndFinalPositionsFromStyle(gridContainerStyle, gridItem, direction, initialPosition, finalPosition);
+
+    // This method will only be used when both positions need to be resolved against the opposite one.
+    ASSERT(initialPosition.shouldBeResolvedAgainstOppositePosition() && finalPosition.shouldBeResolvedAgainstOppositePosition());
+
     const GridPositionSide finalPositionSide = (direction == ForColumns) ? ColumnEndSide : RowEndSide;
+    GridResolvedPosition resolvedFinalPosition = resolvedInitialPosition;
+
+    if (initialPosition.isSpan()) {
+        resolvedFinalPosition = resolveGridPositionAgainstOppositePosition(gridContainerStyle, resolvedInitialPosition, initialPosition, finalPositionSide)->resolvedFinalPosition;
+    } else if (finalPosition.isSpan()) {
+        resolvedFinalPosition = resolveGridPositionAgainstOppositePosition(gridContainerStyle, resolvedInitialPosition, finalPosition, finalPositionSide)->resolvedFinalPosition;
+    }
+
+    return adoptPtr(new GridSpan(resolvedInitialPosition, resolvedFinalPosition));
+}
+
+PassOwnPtr<GridSpan> GridResolvedPosition::resolveGridPositionsFromStyle(const RenderStyle& gridContainerStyle, const RenderBox& gridItem, GridTrackSizingDirection direction)
+{
+    GridPosition initialPosition;
+    GridPosition finalPosition;
+    initialAndFinalPositionsFromStyle(gridContainerStyle, gridItem, direction, initialPosition, finalPosition);
 
     // We must handle the placement error handling code here instead of in the StyleAdjuster because we don't want to
     // overwrite the specified values.
@@ -43,6 +73,9 @@ PassOwnPtr<GridSpan> GridResolvedPosition::resolveGridPositionsFromStyle(const R
         return nullptr;
     }
 
+    const GridPositionSide initialPositionSide = (direction == ForColumns) ? ColumnStartSide : RowStartSide;
+    const GridPositionSide finalPositionSide = (direction == ForColumns) ? ColumnEndSide : RowEndSide;
+
     if (initialPosition.shouldBeResolvedAgainstOppositePosition()) {
         // Infer the position from the final position ('auto / 1' or 'span 2 / 3' case).
         GridResolvedPosition finalResolvedPosition = resolveGridPositionFromStyle(gridContainerStyle, finalPosition, finalPositionSide);