Full bar rest number only if all voices have rests

If you want to display numbers (including the number 1) on full bar rests, but only if all voices have rests simultaneously, here is a "negative" engraver (or "un-engraver").

The un-engraver removes the rest number grob if there is any note head between the bar lines. To avoid problems with cue notes inside a full measure or multi-measure rest, only noteheads with a minimum size trigger the removal of the full-bar rest numbers.

This display method is often preferred if you display only a sub-score of a piece, for example, a choir score.

\version "2.24.0"

%%http://lsr.di.unimi.it/LSR/Item?id=868

%here starts the snippet:

%by: ArnoldTheresius

%incompatible: Version "2.12.3"
%tested: Version "2.21.2"


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% START of my personal include file 'fullbar-restnumber-purger.ly'
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

#(define (Fullbar_restnumber_purger ctx)
  (let ((bar-line-found #f)
        (note-head-found #f)
        (collected-note-head-found #f)
        (multi-measure-count 0)
        (current-multi-measure-numbers '())
        (collected-multi-measure-numbers '()))

    `((acknowledgers
       (bar-line-interface
        . ,(lambda (trans grob source)
             (set! bar-line-found #t)))
       (multi-measure-interface
        . ,(lambda (trans grob source)
             (let ((grob-name (grob::name grob)))
              (if (eq? grob-name 'MultiMeasureRestNumber) (begin
                (set! multi-measure-count (+ 1 multi-measure-count))
                (set! current-multi-measure-numbers
                 (cons grob current-multi-measure-numbers)))))))
       (note-head-interface
        . ,(lambda (trans grob source)
             (let
              ((head-size (ly:grob-property grob 'font-size))
               (minimum-head-size (ly:grob-property grob 'size-threshold-to-remove-mm-rest-rumber -2.5)))
              ; (for-each display (list "\n   Head: font-size = " head-size
              ;  " minimum-head-size = " minimum-head-size " "))
              (if (or (not (number? head-size))
                      (>= head-size minimum-head-size))
               (set! note-head-found #t))))))

      (stop-translation-timestep
       . ,(lambda (trans)
            (if bar-line-found (begin
              (if collected-note-head-found
               (for-each ly:grob-suicide! collected-multi-measure-numbers))
              (set! collected-multi-measure-numbers '())
              (set! collected-note-head-found #f)))
            (if (not (null? current-multi-measure-numbers)) (begin
              (set! collected-multi-measure-numbers
               (append current-multi-measure-numbers collected-multi-measure-numbers))
              (set! current-multi-measure-numbers '())
              (set! multi-measure-count 0)))
            (set! collected-note-head-found
             (or collected-note-head-found note-head-found))
            (set! note-head-found #f)
            (set! bar-line-found #f)
            (set! multi-measure-count 0))))))

% Use this un-engraver by default:
\layout {
  \context {
    \Score
    \consists #Fullbar_restnumber_purger
  }
}

#(define (define-grob-property symbol type? description)
  (if (not (equal? (object-property symbol 'backend-doc) #f))
      (ly:error (_ "symbol ~S redefined") symbol))

  (set-object-property! symbol 'backend-type? type?)
  (set-object-property! symbol 'backend-doc description)
  symbol)

#(for-each
  (lambda (x)
    (apply define-grob-property x))
    `((size-threshold-to-remove-mm-rest-rumber 
      ,number? 
      "The minimum size noteheads need to trigger the removal of multi measure rest numbers.")))

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% END of my personal include file 'fullbar-restnumber-purger.ly'
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\score {
  \new StaffGroup <<
    \new Staff {
      \set Score.restNumberThreshold = #0
      % this way you can tune the size limit, when a notehead is treated as a cue note by this un-engraver:
      \override Score.NoteHead.size-threshold-to-remove-mm-rest-rumber = #-3.0
      \compressEmptyMeasures
      \time 4/4
      R1  c''1  R1*3                 d''1 ~ d''
      << { R1*4 } \new CueVoice { s4*15 a'16 b' c'' d'' } >>
      e''1
      \bar "|."
    }
    \new Staff {
      \set Score.restNumberThreshold = #0
      \compressEmptyMeasures
      \time 4/4
      R1  e'1   R1*2     r4 g'2 g'4  R1*6
      c''1
      \bar "|."
    }
    \new Staff {
      \clef bass
      \set Score.restNumberThreshold = #0
      \compressEmptyMeasures
      \time 4/4
      R1  c1    R1  g,1  R1*2               g1
      R1*4
      g1
      \bar "|."
    }
  >>
}

\paper { tagline = ##f }