Thanks for the ping, it's been a long time! Sadly, I haven't used lilypond for years. I tried to update my patch, but I cannot spend too much time on it. I see that my change to engraver.cc is no longer needed, as there is a check there that was missing back at the time. The change to engraver-scheme.cc still applies, but I see that the comments here indicate that it's incomplete and doesn't provide much value. I have no recollection what I was doing with ly:engraver-make-grob, so I googled to that symbol and found an implementation of ambitus at http://lilypond.org/doc/v2.19/Documentation/snippets/contexts-and-engravers I replaced "Ambitus" with "Ambituus" and I see the check added in engraver.cc being triggered ("programming error: No grob definition found for `Ambituus’") but the segfault happens not in ly_engraver_make_grob but in Item::spanned_rank_interval. So I think this patch is irrelevant and can be discarded.
https://codereview.appspot.com/5715053/
