Using either gtk_drag_source_set_icon_name() or gtk_drag_source_set_icon_stock() with an empty string can lead to crashes. While using an empty string probably isn't particularly useful, it would be nice if the API was a bit friendlier by reporting incorrect usage.

This was found because pygobject had a unittest [2] which was calling these methods with empty strings and crashing. The problem may have started after commit [1]. The problem boils down to gtk_image_definition_new_icon_name() returning NULL if its argument is either NULL or an empty string [3]. This NULL return is then stored in the drag source site and attempts to unref the NULL pointer can occur.

I think it would be good to add precondition checks to match the underlying calls to gtk_image_definition_new_icon_name/stock():

    g_return_if_fail (icon_name[0] != '\0');


[1] https://git.gnome.org/browse/gtk+/commit/?id=1c96b703a684
[2] https://git.gnome.org/browse/pygobject/tree/tests/test_overrides_gtk.py?h=3.19.2#n514
[3] https://git.gnome.org/browse/gtk+/tree/gtk/gtkdragsource.c?h=3.19.9#n413