Conflicting dots and rests with partcombine and lyrics

[Pavel Roskin]

Hello!

I'm typesetting a SATB score on two staves.  I want to use partcombine  
so that I can write the parts for each voice the way they supposed to  
be sung.  It's well known that partcombine doesn't work with the  
lyrics, so I tried this workaround by Daniel E. Moctezuma

http://comments.gmane.org/gmane.comp.gnu.lilypond.general/73934

It turns out that the dots are positioned incorrectly, as the  
transparent dots still take place and push the visible dots away.  I  
asked in lilypond-user but got no answer:

http://article.gmane.org/gmane.comp.gnu.lilypond.general/79243

So I implemented an engraver that kills transparent dots.  It's good  
enough for my purpose so far  
(http://gitorious.org/lilypond-music/lilypond-music/blobs/c69aea3ddeecb92227544cf6c83a0fb513657a14/Popular/MyCountry.ly)

#(define-public (Hidden_dots_engraver ctx)
   (make-engraver
    (acknowledgers
     ((dots-interface trans dot source)
      (if (eq? (ly:grob-property dot 'transparent) #t)
          (ly:grob-suicide! dot))))))

\layout {
  \context {
    \Staff
    \consists #Hidden_dots_engraver
  }
}

However, it appears that rests need this treatment as well.

#(define-public (Hidden_voice_engraver ctx)
   (make-engraver
    (acknowledgers
     ((rest-interface trans rest source)
      (if (eq? (ly:grob-property rest 'transparent) #t)
          (ly:grob-suicide! rest)))
     ((dots-interface trans dot source)
      (if (eq? (ly:grob-property dot 'transparent) #t)
          (ly:grob-suicide! dot))))))

If there is a rest with dot, I get an error message:

programming error: unknown grob in dot col support

The result still looks good.  Hopefully I can suppress the error  
message by killing the dots before the rests, but I haven't tried it.

I just want to ask advice from the community whether I'm going in the  
right direction.  I dealt with engravers before, so it was a natural  
choice for me.  But maybe there is a better approach?  Maybe it's  
possible to write a music function that would turn the melody into a  
rhythm that could be suppressed from the output?  Or may it's possible  
to do something to the dots and the rests to make the layout engine  
ignore them completely?

I could make a snippet and post it to LSR.  There is already a snippet  
for the partcombine:

http://lsr.dsi.unimi.it/LSR/Snippet?id=653

But it lacks the comments and seems to deal with some other issues.   
Also, it's not transparent.  Some expressions need to be added to the  
voice parts.  I don't feel good about adding my code to the snippet I  
don't understand.

--
Regards,
Pavel Roskin