Fixed QLayout::addChildLayout(QLayout *l) when l had a parent

Previously if l had a parent, addChildLayout would warn and skip the
reparenting, but it would still add the sub layout to the layout.
This caused some inconsistencies in the hierarchy which in worst case
could cause crashes.

Task-number: QTBUG-30758
(cherry-picked from qtbase commit 146658a10f290603470b800d71b778239e764312)
Change-Id: Iee6ace3189620395d7670007a23783823ed616b9
Reviewed-by: Paul Olav Tvete <[email protected]>

Author: Jan Arve Saether

src/gui/kernel/qboxlayout.cpp

@@ -1001,7 +1001,8 @@ void QBoxLayout::insertSpacerItem(int index, QSpacerItem *spacerItem)
 void QBoxLayout::insertLayout(int index, QLayout *layout, int stretch)
 {
     Q_D(QBoxLayout);
-    addChildLayout(layout);
+    if (!adoptLayout(layout))
+        return;
     if (index < 0)                                // append
         index = d->list.count();
     QBoxLayoutItem *it = new QBoxLayoutItem(layout, stretch);

src/gui/kernel/qformlayout.cpp

@@ -976,8 +976,8 @@ void QFormLayoutPrivate::setLayout(int row, QFormLayout::ItemRole role, QLayout
 {
     if (layout) {
         Q_Q(QFormLayout);
-        q->addChildLayout(layout);
-        setItem(row, role, layout);
+        if (q->adoptLayout(layout))
+            setItem(row, role, layout);
     }
 }
 

src/gui/kernel/qgridlayout.cpp

@@ -1609,7 +1609,8 @@ void QGridLayout::addWidget(QWidget *widget, int fromRow, int fromColumn,
 void QGridLayout::addLayout(QLayout *layout, int row, int column, Qt::Alignment alignment)
 {
     Q_D(QGridLayout);
-    addChildLayout(layout);
+    if (!adoptLayout(layout))
+        return;
     QGridBox *b = new QGridBox(layout);
     b->setAlignment(alignment);
     d->add(b, row, column);
@@ -1628,7 +1629,8 @@ void QGridLayout::addLayout(QLayout *layout, int row, int column,
                                       int rowSpan, int columnSpan, Qt::Alignment alignment)
 {
     Q_D(QGridLayout);
-    addChildLayout(layout);
+    if (!adoptLayout(layout))
+        return;
     QGridBox *b = new QGridBox(layout);
     b->setAlignment(alignment);
     d->add(b, row, (rowSpan < 0) ? -1 : row + rowSpan - 1, column, (columnSpan < 0) ? -1 : column + columnSpan - 1);

src/gui/kernel/qlayout.cpp

@@ -935,6 +935,16 @@ void QLayout::addChildLayout(QLayout *l)
 
 }
 
+/*!
+   \internal
+ */
+bool QLayout::adoptLayout(QLayout *layout)
+{
+    const bool ok = !layout->parent();
+    addChildLayout(layout);
+    return ok;
+}
+
 #ifdef QT_DEBUG
 static bool layoutDebug()
 {

src/gui/kernel/qlayout.h

@@ -189,6 +189,7 @@ class Q_GUI_EXPORT QLayout : public QObject, public QLayoutItem
     void childEvent(QChildEvent *e);
     void addChildLayout(QLayout *l);
     void addChildWidget(QWidget *w);
+    bool adoptLayout(QLayout *layout);
 #ifdef QT3_SUPPORT
     QT3_SUPPORT void deleteAllItems();
 #endif

tests/auto/qboxlayout/tst_qboxlayout.cpp

@@ -62,6 +62,7 @@ public slots:
 
 private slots:
     void insertSpacerItem();
+    void insertLayout();
     void sizeHint();
     void sizeConstraints();
     void setGeometry();
@@ -160,6 +161,26 @@ void tst_QBoxLayout::insertSpacerItem()
     window->show();
 }
 
+void tst_QBoxLayout::insertLayout()
+{
+    QWidget *window = new QWidget;
+    QVBoxLayout *vbox = new QVBoxLayout(window);
+    QVBoxLayout *dummyParentLayout = new QVBoxLayout;
+    QHBoxLayout *subLayout = new QHBoxLayout;
+    dummyParentLayout->addLayout(subLayout);
+    QCOMPARE(subLayout->parent(), dummyParentLayout);
+    QCOMPARE(dummyParentLayout->count(), 1);
+
+    // add subLayout to another layout
+    QTest::ignoreMessage(QtWarningMsg, "QLayout::addChildLayout: layout \"\" already has a parent");
+    vbox->addLayout(subLayout);
+    QCOMPARE((subLayout->parent() == vbox), (vbox->count() == 1));
+
+    delete dummyParentLayout;
+    delete window;
+}
+
+
 void tst_QBoxLayout::sizeHint()
 {
     QWidget *window = new QWidget;