Bug with grace notes and repeat voltas?

[Joseph Wakeling]

Hello everyone,

I've discovered what I think is a bug in 2.10.25.  Apologies if this has
been fixed in more recent versions but a Google search didn't raise any
awareness of the issue.

Here's the problem.  Suppose I have a repeat volta set up with
alternative end bars:

    \repeat volta 2 {
        % some notes
    }
    \alternative {
        { % alternative 1 }
        { % alternative 2 }
    }

and further, suppose that I have more than one part and that in _one_ of
them---but not the other---one of the alternatives begins with a grace note.

Lilypond generates a warning---"already have a volta spanner, ending
that one prematurely"---and in the resulting score, the grace note and
the rest of the passage occupy _separate_ alternative repeat passages
(but bearing the same number).

Something like this:
                  _____________________________________________
                 |1.    |1.                |2.
  notes notes     grace  notes notes notes  second alternative

A workaround for the bug is to put a grace note in the other part---but
a grace "space" or "skip", as in, \grace { s8 } .

I've attached a little demo file to show where the issue arises and
doesn't arise.  Note that it only occurs if the grace note _begins_ one
of the alternatives.

Is this known about and/or fixed in the latest Lilypond or is it an
ongoing bug?

Thanks,

    -- Joe

\version "2.10.25"

partI = \relative c' {
        \repeat volta 2 {
                c4 d e f g f e d
        }
        \alternative {
                { \grace { c8\glissando } g'4 f e d }
                { g4 f e d }
        }
        
        \repeat volta 2 {
                c4 d e f g f e d
        }
        \alternative {
                { g4 \grace { c,8\glissando } f4 e d }
                { g4 f e d }
        }
        
        \repeat volta 2 {
                c4 d e f g f e d
        }
        \alternative {
                { g4 f e d }
                { \grace { c8\glissando } g'4 f e d }
        }
        
        \repeat volta 2 {
                c4 d e f g f e d
        }
        \alternative {
                { g4 f e d }
                { g4 \grace { c,8\glissando } f4 e d }
        }
        
        \repeat volta 2 {
                c4 d e f g f e d
        }
        \alternative {
                { \grace { c8\glissando } g'4 f e d }
                { g4 f e d }
        }
}

partII = \relative c'' {
        \repeat volta 2 {
                g4 f e d c d e f
        }
        \alternative {
                { c4 d e f }
                { R1 }
        }
        
        \repeat volta 2 {
                g4 f e d c d e f
        }
        \alternative {
                { c4 d e f }
                { R1 }
        }
        
        \repeat volta 2 {
                g4 f e d c d e f
        }
        \alternative {
                { c4 d e f }
                { R1 }
        }
        
        \repeat volta 2 {
                g4 f e d c d e f
        }
        \alternative {
                { c4 d e f }
                { R1 }
        }
        
        \repeat volta 2 {
                g4 f e d c d e f
        }
        \alternative {
                { \grace { s8 } c4 d e f }
                { R1 }
        }
}

\score {
        {
          <<
             \partI
             \partII
          >>
        }
        \layout {}
}

\score {
        {
           \partI
        }
        \layout {}
}