Re: programming error: note-column has no direction

[Thomas Morley]

Am Sa., 7. Okt. 2023 um 19:23 Uhr schrieb Valentin Petzel <valentin@petzel.at>:
>
> Hello Harm,
>
> The error you are seeing is caused by handling NoteCollisions. This has
> different behavior depending on the direction of the note column. The 
> direction
> is set by the stem engraver, which is removed in this context.
>
> To get rid of this message we can either remove collision handling alltogether
> by doing
>
> \layout {
>   \context {
>     \GregorianTranscriptionStaff
>     \remove Collision_engraver
>   }
> }
>
> or we can let Lilypond properly handle collision by having a Stem grob
> created, but not actually printed:
>
> \layout {
>   \context {
>     \GregorianTranscriptionVoice
>     \consists Stem_engraver
>     \omit Stem
>   }
> }
>
> The second one is most likely the more stable one, as other places might also
> assume that a note column does always have a stem.
>
> Regarding whether this is a valid bug: Basically we are running into UB here.
> This context is explicitely intended for transcribing gregorian chant, so we
> would not expect polyphony in the first place. But I think no syntactically
> correct Lilypond code should trigger an internal error, so I’d say there are
> these two paths to resove this:
>
>  → Remove the very concept of collision from these contexts or
>  → Allow the context to create silent Stem grobs
>
> I do not know if there is any reason for not engraving the stems, but if there
> isn’t I’d say the latter one is the more stable path.
>
> Cheers,
> Valentin
>
> Am Samstag, 7. Oktober 2023, 10:35:20 CEST schrieb Thomas Morley:
> > Hi,
> >
> > this came up in the german forum:
> > https://lilypondforum.de/index.php/topic,1280.msg6613.html
> >
> > A more minimel example:
> >
> > \version "2.24.2"
> >
> > %% \include "gregorian.ly"
> > %%
> > %% \layout {
> > %%   \context {
> > %%     \GregorianTranscriptionVoice
> > %%     \consists Stem_engraver
> > %%     \omit Stem
> > %%   }
> > %% }
> >
> > \new GregorianTranscriptionStaff
> >   <<
> >     \new GregorianTranscriptionVoice
> >     { \voiceOne b' }
> >     \new GregorianTranscriptionVoice
> >     { \voiceTwo g' }
> >
> >
> > Returns:
> > programming error: note-column has no direction
> >     { \voiceOne
> >                 b' }
> >
> > Looks like its triggered by the removed Stem_engraver in 2.24., thus a
> > first fix is to reconsist said engraver and omit Stems.
> >
> > Is this a valid bug?
> >
> >
> > Thanks,
> >   Harm
>

Hi Valentin,

thanks for your hints.
Though, please have a look at https://lsr.di.unimi.it/LSR/Item?id=104
Current 2.24.-output is simply wrong.
I see two possibilities to fix it:
a) tweak Voice-context
b) use GregorianTranscriptionVoice instead
The former will add a bunch of overrides and other settings to an
otherwise simple snippet.
With GregorianTranscriptionVoice one could even delete some of the
present overrides, making for:

\version "2.14.0"

\score {
  <<
    \context GregorianTranscriptionVoice \transpose c c' {
      g4( a) g^\markup { "divisio minima" }
      \divisioMinima
      g4( a) g^\markup { "divisio maior" }
      \divisioMaior
      g4( a) g^\markup { "divisio maxima" }
      \divisioMaxima
      g4( a) g^\markup { "  finalis" }
      \finalis
      \break
      g4( a) g
      ^\markup { "virgula" }
      \virgula
      g4( a) g
      ^\markup { "caesura" }
      \caesura
      g4( a) g
    }
    \new  Lyrics \lyricsto "" {
      Blah blub, blah blam.
      Blah blub, blah blam.
      Blah blub, blah blam.
      Blah blub.
    }
  >>
}

Alas, a plethora of "programming error: no stem for note column" for
this non-polyphonic snippet is returned. Furthermore removing
Collision_engraver takes no effect.One needs to add the already
mentioned:

\layout {
  \context {
    \GregorianTranscriptionVoice
    \consists Stem_engraver
    \omit Stem
  }
}

Thus, I lean toward calling it a bug.
Opinions?

Thanks,
  Harm