TreeModel: Add a sibling() implementation

The base implementation uses the parent() index, which
in turn accesses the grand parent level. We can save
a few cycles here.

Change-Id: I3c3696118fe7c3d4563ee3cd28981fca62013828
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/utils/treemodel.cpp

@@ -966,6 +966,18 @@ QModelIndex BaseTreeModel::parent(const QModelIndex &idx) const
     return createIndex(i, 0, static_cast<void*>(parent));
 }
 
+QModelIndex BaseTreeModel::sibling(int row, int column, const QModelIndex &idx) const
+{
+    const TreeItem *item = itemForIndex(idx);
+    QTC_ASSERT(item, return QModelIndex());
+    QModelIndex result;
+    if (TreeItem *parent = item->parent()) {
+        if (TreeItem *sibl = parent->childAt(row))
+            result = createIndex(row, column, static_cast<void*>(sibl));
+    }
+    return result;
+}
+
 int BaseTreeModel::rowCount(const QModelIndex &idx) const
 {
     CHECK_INDEX(idx);

src/libs/utils/treemodel.h

@@ -188,6 +188,7 @@ protected:
     QVariant data(const QModelIndex &idx, int role) const override;
     QModelIndex index(int, int, const QModelIndex &idx = QModelIndex()) const override;
     QModelIndex parent(const QModelIndex &idx) const override;
+    QModelIndex sibling(int row, int column, const QModelIndex &idx) const override;
     Qt::ItemFlags flags(const QModelIndex &idx) const override;
     QVariant headerData(int section, Qt::Orientation orientation, int role) const override;
     bool hasChildren(const QModelIndex &idx) const override;