[CSS Grid Layout] Add support to place items using named grid lines

Source/core/css/resolver/StyleAdjuster.cpp

Index: Source/core/css/resolver/StyleAdjuster.cpp
diff --git a/Source/core/css/resolver/StyleAdjuster.cpp b/Source/core/css/resolver/StyleAdjuster.cpp
index 7e8b3ee4309acba66f1e09e6ec046b116d58e71b..bfc2e9d4cd16b3e8a024c4f332ac6781fd3a2883 100644
--- a/Source/core/css/resolver/StyleAdjuster.cpp
+++ b/Source/core/css/resolver/StyleAdjuster.cpp
@@ -377,6 +377,83 @@ void StyleAdjuster::adjustRenderStyle(RenderStyle* style, RenderStyle* parentSty
     }
 }
 
+static inline bool gridLineDefinedBeforeGridArea(const String& gridLineName, const String& gridAreaName, const NamedGridAreaMap& gridAreaMap, const NamedGridLinesMap& namedLinesMap, GridPositionSide side)
+{
+    ASSERT(namedLinesMap.contains(gridLineName));
+    // Grid line indexes are inserted in order.
+    size_t namedGridLineFirstDefinition = GridPosition::adjustGridPositionForSide(namedLinesMap.get(gridLineName)[0], side);
+
+    ASSERT(gridAreaMap.contains(gridAreaName));
+    const GridCoordinate& gridAreaCoordinates = gridAreaMap.get(gridAreaName);
+
+    // GridCoordinate refers to tracks while the indexes in namedLinesMap refer to lines, that's why we need to add 1 to
+    // the grid coordinate to get the end line index.
+    switch (side) {
+    case ColumnStartSide:
+        return namedGridLineFirstDefinition < gridAreaCoordinates.columns.initialPositionIndex;
+    case ColumnEndSide:
+        return namedGridLineFirstDefinition < gridAreaCoordinates.columns.finalPositionIndex;
+    case RowStartSide:
+        return namedGridLineFirstDefinition < gridAreaCoordinates.rows.initialPositionIndex;
+    case RowEndSide:
+        return namedGridLineFirstDefinition < gridAreaCoordinates.rows.finalPositionIndex;
+    default:
+        ASSERT_NOT_REACHED();
+        return false;
+    }
+}
+
+PassOwnPtr<GridPosition> StyleAdjuster::adjustNamedGridItemPosition(const NamedGridAreaMap& gridAreaMap, const NamedGridLinesMap& namedLinesMap, const GridPosition& position, GridPositionSide side) const
+{
+    ASSERT(position.isNamedGridArea());
+    // The StyleBuilder always treats <custom-ident> as a named grid area. We must decide here if they are going to be resolved
+    // to either a grid area or a grid line.
+
+    String namedGridAreaOrGridLine = position.namedGridLine();
+    bool hasStartSuffix = namedGridAreaOrGridLine.endsWith("-start");
+    bool hasEndSuffix = namedGridAreaOrGridLine.endsWith("-end");
+    bool isStartSide = side == ColumnStartSide || side == RowStartSide;

[Julien - ping for review, 2014/03/05 01:12:35]

This could probably be an helper function (not really needed for this patch).

+    bool hasStartSuffixForStartSide = hasStartSuffix && isStartSide;
+    bool hasEndSuffixForEndSide = hasEndSuffix && !isStartSide;
+    size_t suffixLength = hasStartSuffix ? strlen("-start") : strlen("-end");
+    String gridAreaName = hasStartSuffixForStartSide || hasEndSuffixForEndSide ? namedGridAreaOrGridLine.substring(0, namedGridAreaOrGridLine.length() - suffixLength) : namedGridAreaOrGridLine;
+
+    if (gridAreaMap.contains(gridAreaName)) {
+        String gridLineName;
+        if (isStartSide && !hasStartSuffix)

[Julien - ping for review, 2014/03/05 01:12:35]

I think I get why we need this now, thanks for the explanation. It's crazy from
my perspective that we need such code though. It makes the implementation
complicated by obfuscating the intent of the code.

It would be cleaner just to generate implicit named lines from the named areas.
That should give us the named line resolution for free.

+            gridLineName = namedGridAreaOrGridLine + "-start";
+        else if (!isStartSide && !hasEndSuffix)
+            gridLineName = namedGridAreaOrGridLine + "-end";
+        else
+            gridLineName = namedGridAreaOrGridLine;
+
+        if (namedLinesMap.contains(gridLineName) && gridLineDefinedBeforeGridArea(gridLineName, gridAreaName, gridAreaMap, namedLinesMap, side)) {
+            // Use the explicitly defined grid line defined before the grid area instead of the grid area.
+            OwnPtr<GridPosition> adjustedPosition = adoptPtr(new GridPosition());
+            adjustedPosition->setExplicitPosition(1, gridLineName);
+            return adjustedPosition.release();
+        }
+
+        if (hasStartSuffixForStartSide || hasEndSuffixForEndSide) {
+            // Renderer expects the grid area name instead of the implicit grid line name.
+            OwnPtr<GridPosition> adjustedPosition = adoptPtr(new GridPosition());
+            adjustedPosition->setNamedGridArea(gridAreaName);
+            return adjustedPosition.release();
+        }
+
+        return nullptr;
+    }
+
+    if (namedLinesMap.contains(namedGridAreaOrGridLine)) {
+        OwnPtr<GridPosition> adjustedPosition = adoptPtr(new GridPosition());
+        adjustedPosition->setExplicitPosition(1, namedGridAreaOrGridLine);
+        return adjustedPosition.release();
+    }
+
+    // We need to clear unknown named grid areas
+    return adoptPtr(new GridPosition());
+}
+
 void StyleAdjuster::adjustGridItemPosition(RenderStyle* style, RenderStyle* parentStyle) const
 {
     const GridPosition& columnStartPosition = style->gridColumnStart();
@@ -395,17 +472,28 @@ void StyleAdjuster::adjustGridItemPosition(RenderStyle* style, RenderStyle* pare
         style->setGridRowEnd(GridPosition());
     }
 
-    // Unknown named grid area compute to 'auto'.
-    const NamedGridAreaMap& map = parentStyle->namedGridArea();
-
-#define CLEAR_UNKNOWN_NAMED_AREA(prop, Prop) \
-    if (prop.isNamedGridArea() && !map.contains(prop.namedGridLine())) \
-        style->setGrid##Prop(GridPosition());
+    // If the grid position is a single <ident> then the spec mandates us to resolve it following this steps:
+    //     * If there is a named grid area called <ident> resolve the position to the area's corresponding edge.
+    //         * If a grid area was found with that name, check that there is no <ident>-start or <ident>-end (depending
+    // on the css property being defined) specified before the grid area. If that's the case resolve to that grid line.
+    //     * Otherwise check if there is a grid line named <ident>.
+    //     * Otherwise treat it as auto.
+
+    const NamedGridLinesMap& namedGridColumnLines = parentStyle->namedGridColumnLines();
+    const NamedGridLinesMap& namedGridRowLines = parentStyle->namedGridRowLines();
+    const NamedGridAreaMap& gridAreaMap = parentStyle->namedGridArea();
+
+#define ADJUST_GRID_POSITION_MAYBE(position, Prop, namedGridLines, side) \
+    if (position.isNamedGridArea()) {                                   \
+        OwnPtr<GridPosition> adjustedPosition = adjustNamedGridItemPosition(gridAreaMap, namedGridLines, position, side); \
+        if (adjustedPosition)                                           \
+            style->setGrid##Prop(*adjustedPosition);                    \
+    }
 
-    CLEAR_UNKNOWN_NAMED_AREA(columnStartPosition, ColumnStart);
-    CLEAR_UNKNOWN_NAMED_AREA(columnEndPosition, ColumnEnd);
-    CLEAR_UNKNOWN_NAMED_AREA(rowStartPosition, RowStart);
-    CLEAR_UNKNOWN_NAMED_AREA(rowEndPosition, RowEnd);
+    ADJUST_GRID_POSITION_MAYBE(columnStartPosition, ColumnStart, namedGridColumnLines, ColumnStartSide);
+    ADJUST_GRID_POSITION_MAYBE(columnEndPosition, ColumnEnd, namedGridColumnLines, ColumnEndSide);
+    ADJUST_GRID_POSITION_MAYBE(rowStartPosition, RowStart, namedGridRowLines, RowStartSide);
+    ADJUST_GRID_POSITION_MAYBE(rowEndPosition, RowEnd, namedGridRowLines, RowEndSide);
 }
 
 }