QtWidgets: restore Qt 5 compatibility for save/restore state

Several classes in QWidget use QDataStream internally in order
to save and restore state. These QDataStream usages were not
versioned, meaning that if Qt changes the serialization for some
datatype, then the data saved between different Qt versions becomes
incompatible. Note that the save/restore API in question just produce
opaque blobs as QByteArrays -- the user has no control over the
QDataStream objects and thus versions.

Fix by version the usages.

In QHeaderView this has caused a regression because QBitArray *did*
change version between Qt 5 and 6. In general, using QDataStream without
explicit versioning is a mistake, so deploy the same fix elsewhere as
well.

Fixes: QTBUG-99487
Pick-to: 5.15 6.2 6.3
Change-Id: I82bb5c266f4e5dedc0887cbef855dccab1015e29
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: <doctor.whom@gmail.com>

6 files changed, 42 insertions, 5 deletions

diff --git a/src/widgets/dialogs/qfiledialog.cpp b/src/widgets/dialogs/qfiledialog.cpp
index ae8d0c137a..966d86b089 100644
--- a/src/widgets/dialogs/qfiledialog.cpp
+++ b/src/widgets/dialogs/qfiledialog.cpp
@@ -418,6 +418,7 @@ QByteArray QFileDialog::saveState() const
     int version = 4;
     QByteArray data;
     QDataStream stream(&data, QIODevice::WriteOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
 
     stream << qint32(QFileDialogMagic);
     stream << qint32(version);
@@ -452,6 +453,7 @@ bool QFileDialog::restoreState(const QByteArray &state)
     Q_D(QFileDialog);
     QByteArray sd = state;
     QDataStream stream(&sd, QIODevice::ReadOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     if (stream.atEnd())
         return false;
     QStringList history;
diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index a081a7d0f9..413857bf6c 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -1742,6 +1742,7 @@ QByteArray QHeaderView::saveState() const
     Q_D(const QHeaderView);
     QByteArray data;
     QDataStream stream(&data, QIODevice::WriteOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     stream << QHeaderViewPrivate::VersionMarker;
     stream << 0; // current version is 0
     d->write(stream);
@@ -1763,6 +1764,7 @@ bool QHeaderView::restoreState(const QByteArray &state)
         return false;
     QByteArray data = state;
     QDataStream stream(&data, QIODevice::ReadOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     int marker;
     int ver;
     stream >> marker;
diff --git a/src/widgets/widgets/qmainwindow.cpp b/src/widgets/widgets/qmainwindow.cpp
index 88f710870b..73ca584c7f 100644
--- a/src/widgets/widgets/qmainwindow.cpp
+++ b/src/widgets/widgets/qmainwindow.cpp
@@ -1217,6 +1217,7 @@ QByteArray QMainWindow::saveState(int version) const
 {
     QByteArray data;
     QDataStream stream(&data, QIODevice::WriteOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     stream << QMainWindowLayout::VersionMarker;
     stream << version;
     d_func()->layout->saveState(stream);
@@ -1245,6 +1246,7 @@ bool QMainWindow::restoreState(const QByteArray &state, int version)
         return false;
     QByteArray sd = state;
     QDataStream stream(&sd, QIODevice::ReadOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     int marker, v;
     stream >> marker;
     stream >> v;
diff --git a/src/widgets/widgets/qmainwindowlayout.cpp b/src/widgets/widgets/qmainwindowlayout.cpp
index d1ea0b57da..4a199e0b18 100644
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/src/widgets/widgets/qmainwindowlayout.cpp
@@ -1164,10 +1164,12 @@ bool QMainWindowLayoutState::restoreState(QDataStream &_stream,
     }
 
     QDataStream ds(copy);
+    ds.setVersion(_stream.version());
     if (!checkFormat(ds))
         return false;
 
     QDataStream stream(copy);
+    stream.setVersion(_stream.version());
 
     while (!stream.atEnd()) {
         uchar marker;
diff --git a/src/widgets/widgets/qsplitter.cpp b/src/widgets/widgets/qsplitter.cpp
index 8507ebf356..7dfc2a04fa 100644
--- a/src/widgets/widgets/qsplitter.cpp
+++ b/src/widgets/widgets/qsplitter.cpp
@@ -1650,6 +1650,7 @@ QByteArray QSplitter::saveState() const
     int version = 1;
     QByteArray data;
     QDataStream stream(&data, QIODevice::WriteOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
 
     stream << qint32(SplitterMagic);
     stream << qint32(version);
@@ -1691,6 +1692,7 @@ bool QSplitter::restoreState(const QByteArray &state)
     int version = 1;
     QByteArray sd = state;
     QDataStream stream(&sd, QIODevice::ReadOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     QList<int> list;
     bool b;
     qint32 i;
diff --git a/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp b/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp
index 5e67029cf5..93f991b0fe 100644
--- a/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp
+++ b/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp
@@ -146,6 +146,7 @@ private slots:
     void moveSectionAndReset();
     void moveSectionAndRemove();
     void saveRestore();
+    void QTBUG99487_saveRestoreQt5Compat();
     void restoreToMoreColumns();
     void restoreToMoreColumnsNoMovedColumns();
     void restoreBeforeSetModel();
@@ -1716,16 +1717,24 @@ static QByteArray savedState()
     return h1.saveState();
 }
 
-void tst_QHeaderView::saveRestore()
+// As generated by savedState()
+static const QByteArray qt5SavedSate = QByteArrayLiteral("\x00\x00\x00\xFF\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x01\x00\x00\x00\x02\x01\x00\x00\x00\x04\x00\x00\x00\x02\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x04\x00\x00\x00\x02\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x04\b\x00\x00\x00\x01\x00\x00\x00\x03\x00\x00\x00""d\x00\x00\x00\xD2\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00""d\x00\x00\x00\x00\x00\x00\x00\x84\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00""d\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\n\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00""d\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x03\xE8\x00\x00\x00\x00\x00\x00\x00\x00\x00");
+
+enum class SaveRestoreOption
+{
+    CheckGeneratedState,
+    DoNotCheckGeneratedState,
+};
+
+static void saveRestoreImpl(const QByteArray &state, SaveRestoreOption option)
 {
     QStandardItemModel m(4, 4);
-    const QByteArray s1 = savedState();
 
     QHeaderView h2(Qt::Vertical);
     QSignalSpy spy(&h2, &QHeaderView::sortIndicatorChanged);
 
     h2.setModel(&m);
-    QVERIFY(h2.restoreState(s1));
+    QVERIFY(h2.restoreState(state));
 
     QCOMPARE(spy.count(), 1);
     QCOMPARE(spy.at(0).at(0).toInt(), 2);
@@ -1740,12 +1749,30 @@ void tst_QHeaderView::saveRestore()
     QVERIFY(h2.isSectionHidden(3));
     QCOMPARE(h2.hiddenSectionCount(), 1);
 
-    QByteArray s2 = h2.saveState();
-    QCOMPARE(s1, s2);
+    switch (option) {
+    case SaveRestoreOption::CheckGeneratedState:
+    {
+        QByteArray s2 = h2.saveState();
+        QCOMPARE(state, s2);
+        break;
+    }
+    case SaveRestoreOption::DoNotCheckGeneratedState:
+        break;
+    };
 
     QVERIFY(!h2.restoreState(QByteArrayLiteral("Garbage")));
 }
 
+void tst_QHeaderView::saveRestore()
+{
+    saveRestoreImpl(savedState(), SaveRestoreOption::CheckGeneratedState);
+}
+
+void tst_QHeaderView::QTBUG99487_saveRestoreQt5Compat()
+{
+    saveRestoreImpl(qt5SavedSate, SaveRestoreOption::DoNotCheckGeneratedState);
+}
+
 void tst_QHeaderView::restoreToMoreColumns()
 {
     // Restore state onto a model with more columns