following code fails to produce valid C-code

using GLib;

public interface ITest {
	public abstract void foo ();
}

public class Muuh : Main {
	public override void foo () {
		base.foo ();
	}
}

public class Main : ITest {
	public virtual void foo () {
		stdout.printf ("Main.foo ()\n");
	}

	public static int main () {
		var m = new Muuh ();
		m.foo ();
		return 0;
	}
}

GCC output:
In file included from test.c:2:
test.h:26: error: field ‘parent_instance’ has incomplete type
test.c: In function ‘muuh_real_foo’:
test.c:41: error: ‘muuh_itest_parent_iface’ undeclared (first use in this function)
test.c:41: error: (Each undeclared identifier is reported only once
test.c:41: error: for each function it appears in.)
test.c:41: warning: cast to pointer from integer of different size
test.c: In function ‘main_foo’:
test.c:64: error: invalid type argument of ‘->’
error: cc exited with status 256