Bad \partcombine Output: Example

[Will Oram]

Earlier (see http://lists.gnu.org/archive/html/bug-lilypond/2007-06/ 
msg00046.html), I described very ugly output when using partcombine  
in lilypond .11.21 to the current day. Parts took no heed of each  
other and proceeded to overlap and create a trainwreck.

After a LOT of ripping apart code, I've come up with a reason and an  
example.

REASON: Grace notes! When grace notes occupy the same space, it  
causes a partcombine meltdown.

Try this. In reading the output, note measure two: a quarter and  
dotted half occupy the same beam, and slurring looks plain wrong.

\include "english.ly"

partA = \relative c''' {
        \clef "treble"
        c2 d\trill \bar "" \grace { c16[( d]) } \bar "|"
        
        cflat2.( c4)
        dflat2 r
}
partB = \relative c'' {
        \clef "treble"
        c d2_\trill \bar "" \grace { c16[( d]) } \bar "|"
        
        eflat4( f8 gflat aflat4 gflat)
        f2 r
}


\score {
        \new Staff <<
                \partcombine
                        \partA
                        \partB
        >>

\layout {
}
}

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