Repeated repeat endings

[Mats Bengtsson]

   Hi,

   I'm typesetting a score with repeats, where only one of the instruments
   has alternative endings, whereas for all the other instruments, the 1st
   and 2nd volta are identical. Reading the manual,
   [1]http://lilypond.org/doc/v2.23/Documentation/notation/long-repeats#al
   ternative-endings, it says about specifications within the alternative
   block that "If they are omitted, alternatives are used once each, but
   the first is repeated as needed to satisfy the repeat count. "

   This gives the impression that it should be possible to only specify
   the alternative once for the instruments where the both endings should
   be identical, and for a single stave score Lilypond does indeed typeset
   something that is semantically correct:

   \version "2.23.5"
   \fixed c' \new Staff {\repeat volta 2 {c1 }\alternative{{c}} d }

   which is typeset with a single volta block marked "1. 2." (in version
   2.22 and earlier, the repeat sign wasn't typeset correctly in this
   example, but that seems to be fixed in 2.23.5).

   However, when you have multiple staves, whereof one has different first
   and second endings, the typeset version is semantically incorrect:

   \version "2.23.5"

   \score{
   \fixed c'
     \new StaffGroup <<
       \new Staff {\repeat volta 2 {c1 }\alternative{{c}} d }
       \new Staff {\repeat volta 2 {e1 }\alternative{{g}{c'}} d' }
     >>
   }

   and the marking of the volta blocks depends on which stave happens to
   be typeset at the top, as the following example illustrates, where the
   two staves have been swapped:

   \version "2.23.5"

   \score{
   \fixed c'
     \new StaffGroup <<
       \new Staff {\repeat volta 2 {e1 }\alternative{{g}{c'}} d' }
       \new Staff {\repeat volta 2 {c1 }\alternative{{c}} d }
     >>
   }

   I know that there's ongoing work on the \repeats and I haven't tried
   the latest version in git, so perhaps this has already improved, but I
   leave it as a feature request that both the two latter examples result
   in a typeset score with two volta blocks marked "1." and "2.", where
   the alternative is repeated for the staves where only a single
   alternative is specified. If that's very hard to implement, please add
   a note in the documentation, along the lines of

   "Note: Specify the same number of alternatives for all staves, to avoid
   unexpected results."

   It's obviously easy to workaround the current limitations, for example
   by defining a substitution function that repeats the alternative ending
   twice, but it would still be very convenient with an implementation
   that actually agrees with the current formulation in the NR.

       /Mats

References

   1. 
http://lilypond.org/doc/v2.23/Documentation/notation/long-repeats#alternative-endings