Avoid adding widget to its own layout

Widgets and layouts added or inserted to a layout are checked for:
- Not being NULL
- Not being the parent widget of a layout or the layout itself,
  respectively

Without this commit, adding a widget to its own layout would result in a
CPU-hogging infinite loop. Now, a warning is written to stderr and the
add or insert function call is ignored.

The checks are implemented as public functions of QLayoutPrivate and
thus accessible in QLayout's descendants to be used in various
"addWidget", "insertWidget", etc functions.

Unlike 'classical' layouts like QGridLayout, QFormLayout does indeed
accept widgets that are NULL. To not break this behavior, any call for
the check functions first tests if the widget or layout, respectively,
to test is NULL or not and calls the check only in the latter case.

Automated tests for QBoxLayout, QGridLayout, and QFormLayout were added.
For an unpatched Qt 5.3, each of those automated tests will freeze as
explained in QTBUG-40609. For a fixed version, warning messages about
invalid parameters to addWidget/addLayout/... calls will be read by
QTest::ignoreMessage, resulting in a passed test.

Change-Id: I1522d5727e643da3f7c025755975aca9f482676d
Task-number: QTBUG-40609
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

5 files changed, 67 insertions, 39 deletions

diff --git a/src/widgets/kernel/qboxlayout.cpp b/src/widgets/kernel/qboxlayout.cpp
index 157fa55d2e..a186326551 100644
--- a/src/widgets/kernel/qboxlayout.cpp
+++ b/src/widgets/kernel/qboxlayout.cpp
@@ -51,20 +51,6 @@
 
 QT_BEGIN_NAMESPACE
 
-/*
-    Returns \c true if the \a widget can be added to the \a layout;
-    otherwise returns \c false.
-*/
-static bool checkWidget(QLayout *layout, QWidget *widget)
-{
-    if (!widget) {
-        qWarning("QLayout: Cannot add null widget to %s/%s", layout->metaObject()->className(),
-                  layout->objectName().toLocal8Bit().data());
-        return false;
-    }
-    return true;
-}
-
 struct QBoxLayoutItem
 {
     QBoxLayoutItem(QLayoutItem *it, int stretch_ = 0)
@@ -958,6 +944,8 @@ void QBoxLayout::insertSpacerItem(int index, QSpacerItem *spacerItem)
 void QBoxLayout::insertLayout(int index, QLayout *layout, int stretch)
 {
     Q_D(QBoxLayout);
+    if (!d->checkLayout(layout))
+        return;
     if (!adoptLayout(layout))
         return;
     if (index < 0)                                // append
@@ -991,7 +979,7 @@ void QBoxLayout::insertWidget(int index, QWidget *widget, int stretch,
                               Qt::Alignment alignment)
 {
     Q_D(QBoxLayout);
-    if (!checkWidget(this, widget))
+    if (!d->checkWidget(widget))
          return;
     addChildWidget(widget);
     if (index < 0)                                // append
diff --git a/src/widgets/kernel/qformlayout.cpp b/src/widgets/kernel/qformlayout.cpp
index 239e1ce1e2..9f545b858a 100644
--- a/src/widgets/kernel/qformlayout.cpp
+++ b/src/widgets/kernel/qformlayout.cpp
@@ -1280,6 +1280,8 @@ void QFormLayout::addRow(QLayout *layout)
 void QFormLayout::insertRow(int row, QWidget *label, QWidget *field)
 {
     Q_D(QFormLayout);
+    if ((label && !d->checkWidget(label)) || (field && !d->checkWidget(field)))
+        return;
 
     row = d->insertRow(row);
     if (label)
@@ -1295,6 +1297,8 @@ void QFormLayout::insertRow(int row, QWidget *label, QWidget *field)
 void QFormLayout::insertRow(int row, QWidget *label, QLayout *field)
 {
     Q_D(QFormLayout);
+    if ((label && !d->checkWidget(label)) || (field && !d->checkLayout(field)))
+        return;
 
     row = d->insertRow(row);
     if (label)
@@ -1313,6 +1317,10 @@ void QFormLayout::insertRow(int row, QWidget *label, QLayout *field)
 */
 void QFormLayout::insertRow(int row, const QString &labelText, QWidget *field)
 {
+    Q_D(QFormLayout);
+    if (field && !d->checkWidget(field))
+        return;
+
     QLabel *label = 0;
     if (!labelText.isEmpty()) {
         label = new QLabel(labelText);
@@ -1331,6 +1339,10 @@ void QFormLayout::insertRow(int row, const QString &labelText, QWidget *field)
 */
 void QFormLayout::insertRow(int row, const QString &labelText, QLayout *field)
 {
+    Q_D(QFormLayout);
+    if (field && !d->checkLayout(field))
+        return;
+
     insertRow(row, labelText.isEmpty() ? 0 : new QLabel(labelText), field);
 }
 
@@ -1344,11 +1356,8 @@ void QFormLayout::insertRow(int row, const QString &labelText, QLayout *field)
 void QFormLayout::insertRow(int row, QWidget *widget)
 {
     Q_D(QFormLayout);
-
-    if (!widget) {
-        qWarning("QFormLayout: Cannot add null field to %s", qPrintable(objectName()));
+    if (!d->checkWidget(widget))
         return;
-    }
 
     row = d->insertRow(row);
     d->setWidget(row, SpanningRole, widget);
@@ -1365,11 +1374,8 @@ void QFormLayout::insertRow(int row, QWidget *widget)
 void QFormLayout::insertRow(int row, QLayout *layout)
 {
     Q_D(QFormLayout);
-
-    if (!layout) {
-        qWarning("QFormLayout: Cannot add null field to %s", qPrintable(objectName()));
+    if (!d->checkLayout(layout))
         return;
-    }
 
     row = d->insertRow(row);
     d->setLayout(row, SpanningRole, layout);
diff --git a/src/widgets/kernel/qgridlayout.cpp b/src/widgets/kernel/qgridlayout.cpp
index 5434c40f97..6782e4a9f8 100644
--- a/src/widgets/kernel/qgridlayout.cpp
+++ b/src/widgets/kernel/qgridlayout.cpp
@@ -1430,20 +1430,6 @@ void QGridLayout::addItem(QLayoutItem *item, int row, int column, int rowSpan, i
     invalidate();
 }
 
-/*
-  Returns \c true if the widget \a w can be added to the layout \a l;
-  otherwise returns \c false.
-*/
-static bool checkWidget(QLayout *l, QWidget *w)
-{
-    if (!w) {
-        qWarning("QLayout: Cannot add null widget to %s/%s", l->metaObject()->className(),
-                  l->objectName().toLocal8Bit().data());
-        return false;
-    }
-    return true;
-}
-
 /*!
     Adds the given \a widget to the cell grid at \a row, \a column. The
     top-left position is (0, 0) by default.
@@ -1454,7 +1440,8 @@ static bool checkWidget(QLayout *l, QWidget *w)
 */
 void QGridLayout::addWidget(QWidget *widget, int row, int column, Qt::Alignment alignment)
 {
-    if (!checkWidget(this, widget))
+    Q_D(QGridLayout);
+    if (!d->checkWidget(widget))
         return;
     if (row < 0 || column < 0) {
         qWarning("QGridLayout: Cannot add %s/%s to %s/%s at row %d column %d",
@@ -1483,7 +1470,7 @@ void QGridLayout::addWidget(QWidget *widget, int fromRow, int fromColumn,
                             int rowSpan, int columnSpan, Qt::Alignment alignment)
 {
     Q_D(QGridLayout);
-    if (!checkWidget(this, widget))
+    if (!d->checkWidget(widget))
         return;
     int toRow = (rowSpan < 0) ? -1 : fromRow + rowSpan - 1;
     int toColumn = (columnSpan < 0) ? -1 : fromColumn + columnSpan - 1;
@@ -1518,6 +1505,8 @@ void QGridLayout::addWidget(QWidget *widget, int fromRow, int fromColumn,
 void QGridLayout::addLayout(QLayout *layout, int row, int column, Qt::Alignment alignment)
 {
     Q_D(QGridLayout);
+    if (!d->checkLayout(layout))
+        return;
     if (!adoptLayout(layout))
         return;
     QGridBox *b = new QGridBox(layout);
@@ -1538,6 +1527,8 @@ void QGridLayout::addLayout(QLayout *layout, int row, int column,
                                       int rowSpan, int columnSpan, Qt::Alignment alignment)
 {
     Q_D(QGridLayout);
+    if (!d->checkLayout(layout))
+        return;
     if (!adoptLayout(layout))
         return;
     QGridBox *b = new QGridBox(layout);
diff --git a/src/widgets/kernel/qlayout.cpp b/src/widgets/kernel/qlayout.cpp
index eb21a580b1..778514f47a 100644
--- a/src/widgets/kernel/qlayout.cpp
+++ b/src/widgets/kernel/qlayout.cpp
@@ -858,6 +858,47 @@ void QLayoutPrivate::reparentChildWidgets(QWidget *mw)
 }
 
 /*!
+    Returns \c true if the \a widget can be added to the \a layout;
+    otherwise returns \c false.
+*/
+bool QLayoutPrivate::checkWidget(QWidget *widget) const
+{
+    Q_Q(const QLayout);
+    if (!widget) {
+        qWarning("QLayout: Cannot add a null widget to %s/%s", q->metaObject()->className(),
+                  qPrintable(q->objectName()));
+        return false;
+    }
+    if (widget == q->parentWidget()) {
+        qWarning("QLayout: Cannot add parent widget %s/%s to its child layout %s/%s",
+                  widget->metaObject()->className(), qPrintable(widget->objectName()),
+                  q->metaObject()->className(), qPrintable(q->objectName()));
+        return false;
+    }
+    return true;
+}
+
+/*!
+    Returns \c true if the \a otherLayout can be added to the \a layout;
+    otherwise returns \c false.
+*/
+bool QLayoutPrivate::checkLayout(QLayout *otherLayout) const
+{
+    Q_Q(const QLayout);
+    if (!otherLayout) {
+        qWarning("QLayout: Cannot add a null layout to %s/%s", q->metaObject()->className(),
+                  qPrintable(q->objectName()));
+        return false;
+    }
+    if (otherLayout == q) {
+        qWarning("QLayout: Cannot add layout %s/%s to itself", q->metaObject()->className(),
+                  qPrintable(q->objectName()));
+        return false;
+    }
+    return true;
+}
+
+/*!
     This function is called from \c addWidget() functions in
     subclasses to add \a w as a managed widget of a layout.
 
diff --git a/src/widgets/kernel/qlayout_p.h b/src/widgets/kernel/qlayout_p.h
index 2100d86aba..71e0f9bcd3 100644
--- a/src/widgets/kernel/qlayout_p.h
+++ b/src/widgets/kernel/qlayout_p.h
@@ -76,6 +76,8 @@ public:
     void getMargin(int *result, int userMargin, QStyle::PixelMetric pm) const;
     void doResize(const QSize &);
     void reparentChildWidgets(QWidget *mw);
+    bool checkWidget(QWidget *widget) const;
+    bool checkLayout(QLayout *otherLayout) const;
 
     static QWidgetItem *createWidgetItem(const QLayout *layout, QWidget *widget);
     static QSpacerItem *createSpacerItem(const QLayout *layout, int w, int h, QSizePolicy::Policy hPolicy = QSizePolicy::Minimum, QSizePolicy::Policy vPolicy = QSizePolicy::Minimum);