QFileSystemModel: reimplement sibling for same-row

Since QFSM, like most models, uses QModelIndex::internalPointer() as an
indicator of the row, getting a sibling in the same row is as easy as
copying the internalPointer() of the incoming index and just creating
a new index with the column adjusted.

For rows, the situation is quite a bit more complicated, so we
currently continue to call the generic implementation.

Change-Id: I36921e3f9c01c458a75aa439018f21c4c657e1cf
Reviewed-by: David Faure <david.faure@kdab.com>

src/widgets/dialogs/qfilesystemmodel.cpp

@@ -250,6 +250,21 @@ QModelIndex QFileSystemModel::index(int row, int column, const QModelIndex &pare
     return createIndex(row, column, const_cast<QFileSystemModelPrivate::QFileSystemNode*>(indexNode));
 }
 
+/*!
+    \reimp
+*/
+QModelIndex QFileSystemModel::sibling(int row, int column, const QModelIndex &idx) const
+{
+    if (row == idx.row() && column < QFileSystemModelPrivate::NumColumns) {
+        // cheap sibling operation: just adjust the column:
+        return createIndex(row, column, idx.internalPointer());
+    } else {
+        // for anything else: call the default implementation
+        // (this could probably be optimized, too):
+        return QAbstractItemModel::sibling(row, column, idx);
+    }
+}
+
 /*!
     \overload
 

src/widgets/dialogs/qfilesystemmodel.h

@@ -75,6 +75,7 @@ public:
     QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const Q_DECL_OVERRIDE;
     QModelIndex index(const QString &path, int column = 0) const;
     QModelIndex parent(const QModelIndex &child) const Q_DECL_OVERRIDE;
+    QModelIndex sibling(int row, int column, const QModelIndex &idx) const Q_DECL_OVERRIDE;
     bool hasChildren(const QModelIndex &parent = QModelIndex()) const Q_DECL_OVERRIDE;
     bool canFetchMore(const QModelIndex &parent) const Q_DECL_OVERRIDE;
     void fetchMore(const QModelIndex &parent) Q_DECL_OVERRIDE;