Widgets: add enum values to QStyleOptionViewItem::ViewItemFeature

Add two new enum values:
IsDecoratedRootColumn: notifies the style that the current cell also
contains place for the tree column branch indicator so it can e.g.
properly draw rounded edges in a cell or complete row.
IsDecorationForRootColumn: the item contains the information to draw
the tree column branch indicator.

Pick-to: 6.9
Task-number: QTBUG-131585
Change-Id: Iee2823fe3a227630f926d0448095a10fad2b0ba7
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/itemviews/qtreeview.cpp

@@ -1786,6 +1786,7 @@ void QTreeView::drawRow(QPainter *painter, const QStyleOptionViewItem &option,
         if (alternate) {
             opt.features.setFlag(QStyleOptionViewItem::Alternate, d->current & 1);
         }
+        opt.features &= ~QStyleOptionViewItem::IsDecoratedRootColumn;
 
         /* Prior to Qt 4.3, the background of the branch (in selected state and
            alternate row color was provided by the view. For backward compatibility,
@@ -1800,7 +1801,6 @@ void QTreeView::drawRow(QPainter *painter, const QStyleOptionViewItem &option,
                 painter->setClipRect(QRect(position, y, width, height));
             }
             // draw background for the branch (selection + alternate row)
-            opt.rect = branches;
 
             // We use showDecorationSelected both to store the style hint, and to indicate
             // that the entire row has to be selected (see overrides of the value if
@@ -1810,10 +1810,15 @@ void QTreeView::drawRow(QPainter *painter, const QStyleOptionViewItem &option,
             const bool oldShowDecorationSelected = opt.showDecorationSelected;
             opt.showDecorationSelected = style()->styleHint(QStyle::SH_ItemView_ShowDecorationSelected,
                                                             &opt, this);
-            opt.features |= QStyleOptionViewItem::HasDecoration;
             opt.rect = branches;
+            if (opt.rect.width() > 0) {
+                // the root item also has a branch decoration
+                opt.features |= QStyleOptionViewItem::IsDecoratedRootColumn;
+                // we now want to draw the branch decoration
+                opt.features |= QStyleOptionViewItem::IsDecorationForRootColumn;
                 style()->drawPrimitive(QStyle::PE_PanelItemViewRow, &opt, painter, this);
-            opt.features &= ~QStyleOptionViewItem::HasDecoration;
+                opt.features &= ~QStyleOptionViewItem::IsDecorationForRootColumn;
+            }
 
             // draw background of the item (only alternate row). rest of the background
             // is provided by the delegate

src/widgets/styles/qstyleoption.cpp

@@ -3093,6 +3093,10 @@ QStyleOptionViewItem::QStyleOptionViewItem(int version)
     \value HasCheckIndicator Indicates that the item has a check state indicator.
     \value HasDisplay        Indicates that the item has a display role.
     \value HasDecoration     Indicates that the item has a decoration role.
+    \value [since 6.9] IsDecoratedRootColumn  Indicates that the item has a tree view branch
+    part for painting.
+    \value [since 6.9] IsDecorationForRootColumn  Indicates that the item contains the
+    information to draw the tree view branch part.
 */
 
 /*!

src/widgets/styles/qstyleoption.h

@@ -403,7 +403,9 @@ public:
         Alternate = 0x02,
         HasCheckIndicator = 0x04,
         HasDisplay = 0x08,
-        HasDecoration = 0x10
+        HasDecoration = 0x10,
+        IsDecoratedRootColumn = 0x20,
+        IsDecorationForRootColumn = 0x40,
     };
     Q_DECLARE_FLAGS(ViewItemFeatures, ViewItemFeature)
 

src/widgets/styles/qstylesheetstyle.cpp

@@ -4875,7 +4875,7 @@ void QStyleSheetStyle::drawPrimitive(PrimitiveElement pe, const QStyleOption *op
                 if (rule.background()->brush.color().alpha() != 1.0)
                     baseStyle()->drawPrimitive(pe, opt, p, w);
                 // Skip border for the branch and draw only the brackground
-                if (vopt->features & QStyleOptionViewItem::HasDecoration &&
+                if (vopt->features & QStyleOptionViewItem::IsDecorationForRootColumn &&
                     (vopt->viewItemPosition == QStyleOptionViewItem::Beginning ||
                      vopt->viewItemPosition == QStyleOptionViewItem::OnlyOne) && rule.hasBorder()) {
                     if (rule.hasDrawable()) {