Resources for debugging ggplot2 or its extensions?



Whenever I play with ggplot2, I feel there must be some better way of debugging ggplot2 than desperately debug()ing into ggplot_build(). For example, I wonder if it is possible to debug() Geom's or Stat's methods, e.g. compute_group(). I always try debug() or building a package with break points, but none of my attempts have succeeded so far...

Does anyone know how to debug ggplot2 effectively?