From 377b4df13bb7d5bbfa588090f96269ded65351b5 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Thu, 20 Jun 2024 17:56:14 +0200
Subject: [PATCH] [doc] Q(Persistent)ModelIndex: document behavior of data() on
 invalid Q(P)MIs

We return a default-constructed QVariant. What else could we possibly
return? Right: nothing else.

So document it and add a test.

Pick-to: 6.7 6.5 6.2 5.15
Change-Id: If9808703b8ddfd15ceb013996741af8cd4efea12
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit d1a5e602df5978cee6bd263db77745f8047e508e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/itemmodels/qabstractitemmodel.cpp |  6 ++--
 .../tst_qabstractitemmodel.cpp                | 29 +++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/corelib/itemmodels/qabstractitemmodel.cpp b/src/corelib/itemmodels/qabstractitemmodel.cpp
index 216db3b42a5..5b9b215eabe 100644
--- a/src/corelib/itemmodels/qabstractitemmodel.cpp
+++ b/src/corelib/itemmodels/qabstractitemmodel.cpp
@@ -606,7 +606,8 @@ QModelIndex QPersistentModelIndex::sibling(int row, int column) const
 
 /*!
     Returns the data for the given \a role for the item referred to by the
-    index.
+    index, or a default-constructed QVariant if this persistent model index
+    is \l{isValid()}{invalid}.
 
     \sa Qt::ItemDataRole, QAbstractItemModel::setData()
 */
@@ -1315,7 +1316,8 @@ void QAbstractItemModel::resetInternalData()
     \fn QVariant QModelIndex::data(int role) const
 
     Returns the data for the given \a role for the item referred to by the
-    index.
+    index, or a default-constructed QVariant if this model index is
+    \l{isValid()}{invalid}.
 */
 
 /*!
diff --git a/tests/auto/corelib/itemmodels/qabstractitemmodel/tst_qabstractitemmodel.cpp b/tests/auto/corelib/itemmodels/qabstractitemmodel/tst_qabstractitemmodel.cpp
index c48b79b2600..8a2643c0f36 100644
--- a/tests/auto/corelib/itemmodels/qabstractitemmodel/tst_qabstractitemmodel.cpp
+++ b/tests/auto/corelib/itemmodels/qabstractitemmodel/tst_qabstractitemmodel.cpp
@@ -40,6 +40,8 @@ private slots:
     void parent();
     void hasChildren();
     void data();
+    void invalidModelIndexDataReturnsInvalidQVariant();
+    void invalidPersistentModelIndexDataReturnsInvalidQVariant();
     void headerData();
     void itemData();
     void itemFlags();
@@ -390,6 +392,33 @@ void tst_QAbstractItemModel::data()
     QCOMPARE(model.setHeaderData(0, Qt::Horizontal, QVariant(0), 0), false);
 }
 
+void tst_QAbstractItemModel::invalidModelIndexDataReturnsInvalidQVariant()
+{
+    const QModelIndex invalid;
+    QVERIFY(!invalid.isValid());
+    QVERIFY(!invalid.data(Qt::ItemDataRole::DisplayRole).isValid());
+
+    QtTestModel model(1, 1);
+    const QModelIndex mi = model.index(0, 1);
+    QVERIFY(!mi.isValid());
+    QVERIFY(!mi.data(Qt::ItemDataRole::DisplayRole).isValid());
+}
+
+void tst_QAbstractItemModel::invalidPersistentModelIndexDataReturnsInvalidQVariant()
+{
+    const QPersistentModelIndex invalid;
+    QVERIFY(!invalid.isValid());
+    QVERIFY(!invalid.data(Qt::ItemDataRole::DisplayRole).isValid());
+
+    QtTestModel model(1, 1);
+    const QPersistentModelIndex pmi = model.index(0, 0);
+    QVERIFY(pmi.isValid());
+    QVERIFY(pmi.data(Qt::ItemDataRole::DisplayRole).isValid());
+    model.removeRows(0, 1);
+    QVERIFY(!pmi.isValid());
+    QVERIFY(!pmi.data(Qt::ItemDataRole::DisplayRole).isValid());
+}
+
 void tst_QAbstractItemModel::headerData()
 {
     QtTestModel model(1, 1);