Re: Issue 818 in lilypond: Bus error when adding Instrument_name_engraver to StaffGroup and outputting MIDI.

[lilypond]

Comment #20 on issue 818 by n.puttock: Bus error when adding  
Instrument_name_engraver to StaffGroup and outputting MIDI.
http://code.google.com/p/lilypond/issues/detail?id=818

OK, a few more notes:

Translators of the wrong type (i.e., performers for an Engraver_group,  
engravers for a Performer_group) must be filtered out if they're added to a  
context via \with.  This happens in  
Translator_group::create_child_translator () here:

204   if (dynamic_cast<Engraver_group *> (g))
205     g->simple_trans_list_ = filter_performers (trans_list);
206   else if (dynamic_cast<Performer_group *> (g))
207     g->simple_trans_list_ = filter_engravers (trans_list);

Both filter_engravers () and filter_performers () use dynamic_cast to check  
whether a translator in `trans_list' is of the type which should be  
removed.  In the case of the optimized builds which segfault, the casting  
fails.

Simply adding debug output to display the filtered list of translators at  
the end of filter_engravers () causes the dynamic_cast to work.

Why would optimizing cause RTTI failure?