QStandardItem: add note about reimplementing data/setData() wrt. flags

Extend the unittests.

Drive-by change: add missing include, otherwise static analyzers
(clangd) complain.

Fixes: QTBUG-105150
Pick-to: 6.5 5.15
Change-Id: I312133d5b35119e2e51002dfefe0e141c0708e3d
Reviewed-by: David Faure <david.faure@kdab.com>
(cherry picked from commit 85eebedb16da67d9f2caeb14ed45c2dae8f82837)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/itemmodels/qstandarditemmodel.cpp

@@ -868,9 +868,15 @@ QStandardItem *QStandardItem::parent() const
     Sets the item's data for the given \a role to the specified \a value.
 
     If you subclass QStandardItem and reimplement this function, your
-    reimplementation should call emitDataChanged() if you do not call
+    reimplementation should:
-    the base implementation of setData(). This will ensure that e.g.
+    \list
-    views using the model are notified of the changes.
+    \li call emitDataChanged() if you do not call the base implementation of
+        setData(). This will ensure that e.g. views using the model are notified
+        of the changes
+    \li call the base implementation for roles you don't handle, otherwise
+        setting flags, e.g. by calling setFlags(), setCheckable(), setEditable()
+        etc., will not work.
+    \endlist
 
     \note The default implementation treats Qt::EditRole and Qt::DisplayRole
     as referring to the same data.
@@ -924,6 +930,11 @@ void QStandardItem::clearData()
     Returns the item's data for the given \a role, or an invalid
     QVariant if there is no data for the role.
 
+    If you reimplement this function, your reimplementation should call
+    the base implementation for roles you don't handle, otherwise getting
+    flags, e.g. by calling flags(), isCheckable(), isEditable() etc.,
+    will not work.
+
     \note The default implementation treats Qt::EditRole and Qt::DisplayRole
     as referring to the same data.
 */

src/gui/itemmodels/qstandarditemmodel_p.h

@@ -15,6 +15,8 @@
 // We mean it.
 //
 
+#include <QtGui/qstandarditemmodel.h>
+
 #include <QtGui/private/qtguiglobal_p.h>
 #include "private/qabstractitemmodel_p.h"
 

tests/auto/gui/itemmodels/qstandarditem/tst_qstandarditem.cpp

@@ -1006,6 +1006,32 @@ public:
 
     using QStandardItem::clone;
     using QStandardItem::emitDataChanged;
+
+    void setData(const QVariant &value, int role) override
+    {
+        switch (role) {
+        case Qt::DisplayRole:
+            QStandardItem::setData(value, role);
+            break;
+        default:
+            // setFlags() uses "UserRole - 1" to store the flags, which is an
+            // implementation detail not exposed in the docs.
+            QStandardItem::setData(value, role);
+            break;
+        }
+    }
+
+    QVariant data(int role) const override
+    {
+        switch (role) {
+        case Qt::DisplayRole:
+            return QStandardItem::data(role);
+        default:
+            // flags() uses "UserRole - 1" to get the flags, which is an implementation
+            // detail not exposed in the docs.
+            return QStandardItem::data(role);
+        }
+    }
 };
 
 Q_DECLARE_METATYPE(QStandardItem*)
@@ -1041,6 +1067,12 @@ void tst_QStandardItem::subclassing()
     QCOMPARE(item->child(0), child2);
     QCOMPARE(item->child(1), child0);
     QCOMPARE(item->child(2), child1);
+
+    item->setFlags(Qt::ItemFlags{0});
+    QCOMPARE(item->flags(), Qt::ItemFlags{0});
+
+    item->setFlags(Qt::ItemFlags{Qt::ItemIsEditable | Qt::ItemIsSelectable});
+    QCOMPARE(item->flags(), Qt::ItemFlags{Qt::ItemIsEditable | Qt::ItemIsSelectable});
 }
 
 void tst_QStandardItem::lessThan()