This simple program:

  bool source_func() {
      return true;
  }
  void main() {
      SourceFunc f;
      f = source_func;
      f();
  }

Ends with a segfault when tried to execute it.
This is because vala is currently generating:

void _main (void) {
    	GDestroyNotify f_target_destroy_notify;
    	void* f_target = NULL;
    	GSourceFunc f = NULL;
    	GSourceFunc _tmp0_;
  ...
  ...
    }

The problem is the line:
        GDestroyNotify f_target_destroy_notify;

That is not being initialized to NULL and then should be:
        GDestroyNotify f_target_destroy_notify = NULL;