LilyPond - start measure on second volta if first volta measure is not complete

Question

I am trying to transcribe a Bach manuscript from BWV 1004.

Bar 9 of the Sarabande has what looks like a Segno. Then in measure 25 we need to jump back to this segno. I have this for measures 24-26:

\relative c'' {  
    \key f \major
    \time 3/4

    % 24
    \set Score.repeatCommands = #'((volta "1"))
    d8. c!16( bes a g f e d cis d32 e)
    
    % 25
    <<
        {
            e'8. f32( g) -\markup {
                \italic "D.S. "
                \tiny \raise #1
                \musicglyph "scripts.segno"
            }
        }
        \\
        { < cis, a a, >4 }
    >>

    % 26
    % 6th pentagram from Bach's manuscript starts on 2nd beat
    \set Score.repeatCommands = #'((volta "2") end-repeat)
    d16 d, f a g( f e d c bes) c( a)

}

It works like a charm, the only problem is that measure 26 is considering what was written in measure 25 and so it is being cut short by a 4th (just like the end-repeat bar not be there). Is there a way in which I could add hidden rests that do not take up any space? Because if I add ss, it works, bars come back to be written correctly but the hidden rests widen measure 25 in a noticeable/unpleasant way.

Answer 1

The correct way to do this is using a partial measure, specified by \partial duration. So in your case you need \partial 4 like here:

\relative c'' {   
    \time 3/4
    \set Score.repeatCommands = #'((volta "1"))
    d8. c!16( bes a g f e d cis d32 e)
    
    % 25
    \partial 4
    <<
        {
            e'8. f32( g) -\markup {
                \italic "D.S. "
                \tiny \raise #1
                \musicglyph "scripts.segno"
            }
        }
        \\
        { < cis, a a, >4 }
    >>
    \set Score.repeatCommands = #'((volta "2") end-repeat)
    d16 d, f a g( f e d c bes) c( a)
    \set Score.repeatCommands = #'((volta #f))
}

Answer 2

The easiest fix to fool the time-keeping algorithm is usually to make the last note look like one length but count as another. Lilypond calls this "Scaling durations" (see the documentation on this), and the syntax looks like this: d4*2. It renders a quarter note that counts as a half note.