Adding a widget to its own layout results in endless loop

Consider the following example (valid both for Qt4 and Qt5):

MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)

{ QWidget *centralWidget = new QWidget(this); QBoxLayout *boxLayout = new QVBoxLayout(centralWidget); boxLayout->addWidget(centralWidget, 1); setCentralWidget(centralWidget); }

Widget "centralWidget" is added to layout "boxLayout" which is layouting just this widget. Obviously, this "addWidget" call does not make sense, but it may happen due to copy&paste errors or auto-complete madness in editors/IDEs.

When compiling and running such a program as shown above, both with Qt 4.8.5 and 5.3.1, the program hogs the CPU and freezes from the user's perspective.

Qt should not accept adding a widget to its own layout. Such a statement should be ignored and/or a warning should be printed to stderr, but silently accepting it and then just freezing is not an option.

A brief look into Qt's source code lets me suggest to enhance static bool checkWidget(..) in qboxlayout.cpp for a "self-insertion" test.

Maybe a more global solution is necessary, as QFormLayout is affected by a similar issue. A modified example using the following code snipplet shows the same behaviour:

QFormLayout *formLayout = new QFormLayout(centralWidget);
formLayout->addRow(centralWidget);

In case you are going to fix this issue, don't forget to add a test to tst_qboxlayout.cpp and friends