sdroege
commented
3 years ago See https://github.com/gtk-rs/gir/pull/604
The "empty" case without virtual methods is easy to automate, the problems come with the virtual methods. Often those are not very bindings friendly and require custom implementations. Those are the bad cases and you can find quite a few in gio, gtk and GStreamer.
Another problem is that it's not clear from the introspection data which virtual methods are optional and which are mandatory, or what the "default" behaviour (and return value) would be. That's a more fundamental problem with gobject-introspection missing information.
And last, the annotations for virtual methods are generally lacking in all the libraries. Which of course should be fixed, but prevents autogeneration too right now.
https://github.com/gtk-rs/gtk/tree/master/src/subclass has a lot of similar code, but still leaves various gtk widgets impossible to subclass from Rust (with safe code anyway).
I'm not sure exactly what difficulties are involved, but that should probably be automated as much as possible (in
gir, a macro, etc.) so as little work as possible is needed to support sub-classing a new type.