That looks like glib. Which is kind of nasty in my opinion. At some point they pushed for Vala, it makes the whole thing a bit more pleasent. But personally I had a feeling it was on life support the entire time. Some bindings were plain broken and impossible to fix, interop had really crappy documentation. At some point I just gave up.

(I'm mixing IDE with language/lib right now, but for Gnome it does go hand in hand IMHO)