Percussion staff problems

[Gordon Bower]

I am having two issues with a custom unpitched-percussion staff in a score.

Item 1: \RemoveEmptyStaves does not remove the percussion staff even though
it suppresses other staves correctly. (I had the same problem with a
non-customized DrumStaff or RhythmStaff when I tried that earlier.)

This feels like a bug to me.

Looking at the internals PDF, there is probably a one-line fix for this,
where one symbol (the percussion clef maybe?) is in the keepAliveInterfaces
list but should not be.

Can anyone tell me what I need to insert?

Item 2: I can't use a variable to insert the percussion music like I can
everything else.
When I build my score,
<< \drummode {tri4 cymc4 tt4} >> works fine.

But  << \perc >> , after having previously set  perc = {\drummode { tri4
cymc4 tt4  R2.} }, fails with the error "warning: Ignoring non-music
expression {\perc}"
Tried several variations, with and without extra braces, etc.

I assume this one is operator error (<<>> or {} in the wrong place,
\drummode in the wrong place, something...) but it has me confused.

Attached is an example of the problem score.

Thank you!

GRB

%Debugging percussion staff
\version "2.22.0"
\language "deutsch"

globalc = {    \time 3/4
               \tempo 2. = 56
}

%Fill one staff with 3 systems worth of music
cori =  { \unfoldRepeats \repeat volta 12 {c'4 d' e' c' d' e'} }
corii = { \unfoldRepeats \repeat volta 12 {e4 f g e f g} }
%Horns 3-4 correctly appear only in the 1st and 3rd systems
coriii = {R2.*18 g2. R2.*5}
coriv = {R2.*24}
%Timpani correctly appear only in the 1st and 2nd systems
tp =\relative c {\clef bass R2. *12 e,4 h' h h r2 R2.*10}

%Why on earth doesnt this work later??
perc = {\drummode { tri4 cymc4 tt4  R2.} }

\header {
  title = "Any Piece"
  composer = "Any composer"
  copyright =\markup{ \char ##x00A9 "2021 GRB"}
  tagline = ##f
}


assemblescore = {
  <<
    \accidentalStyle Score.modern-voice
  
   
  
      \new StaffGroup \with {instrumentName="Corni (F)"
                             \override InstrumentName.self-alignment-X = #RIGHT
                             shortInstrumentName="Cor."
                             systemStartDelimiter = #'SystemStartBrace }
      <<
        \new Staff = "Horns 1-2"  
        \with { instrumentName="1,2"
        }     <<
          \set Staff.soloText = #"1."
          \set Staff.soloIIText = #"2."
          \set Staff.aDueText = "a 2"
          \transposition f
          \transpose f c' {
            \globalc \partCombine \cori \corii }
        >> 
        \new Staff = "Horns 3-4"  
        \with { instrumentName="3,4"
                \override InstrumentName.self-alignment-X = #RIGHT
        }     <<
          \set Staff.soloText = #"3."
          \set Staff.soloIIText = #"4."
          \set Staff.aDueText = "a 2"
          \transposition f
          \transpose f c' {
            \globalc \partCombine \coriii \coriv }
      >> >>

    \new Staff = "Timpani" \with { instrumentName="Timpani (D, B, E)"
                                   \override InstrumentName.self-alignment-X = #RIGHT
                                   shortInstrumentName = "Tp."
    }
    << \globalc \tp >> 
    %Custom percussion staff:
    #(define perc '(
                     (triangle default #f 2)
                     (cymbals default #f 0)
                     (tamtam default #f -2)
                     ))
    \new DrumStaff = "Percussion" \with { 
      \override InstrumentName.self-alignment-X = #RIGHT
      instrumentName=\markup { \right-column { "Triangolo" "Piatti" "Tamtam" } }
      \override StaffSymbol.line-count=#3
    }    
    <<
      \set DrumStaff.drumStyleTable = #(alist->hash-table perc)
      % This works:
      \globalc \drummode { tri4 cymc4 tt4  R2.*23} 
      % This doesnt, with or without the braces:
      % {\globalc \perc    }    
    >>

  >> % wrapper around whole score
}

\score {

  \assemblescore

  \layout{
    \context { \Staff \RemoveEmptyStaves }
    #(layout-set-staff-size 18)
    indent = 40\mm
  }%end layout
}