The example from GTK4 for Graphical User Interfaces was working fine all the years for me, but after recent upgrade to GTK 4.10 I get a lot messages like
(comboboxtext:14942): Gtk-WARNING **: 14:26:58.897: gtk_widget_size_allocate(): attempt to allocate GtkScrolledWindow scrolledwindow 0x5580fee5a150 with width -12 and height -12
and it does not work any more. The example looks really simple, and I guess it was a plain conversion from C some years ago. I had already trouble with Strange FileChooserDialog behaviour in GTK 4.10 some days ago.
And as expected, that seems not to be a Nim bindings issue. Testing gtk4-demo, the topmost widget of the ComboBox example show the same behaviour for me. So I fear my GTK4 installation is broken.
This is likely issue 5644, which has been fixed in Git and released as 4.10.1; please make sure you’re using that version. If you’re using GTK 4.10.1 and can still reproduce it, please leave a comment on the issue tracker.